bims-minimp 2021-06-20 papers

bims-minimp

Biomed News

on Mitochondria, innate immunity, proteostasis

Issue of 2021‒06‒20
thirty-four papers selected by
Hanna Salmonowicz
Newcastle University

Stress granules inhibit fatty acid oxidation by modulating mitochondrial permeability.
PGC-1α mediates a metabolic host defense response in human airway epithelium during rhinovirus infections.
The kidnapping of mitochondrial function associated with the SARS-CoV-2 infection.
Mitochondrial Contact Site and Cristae Organization System and F1FO-ATP Synthase Crosstalk Is a Fundamental Property of Mitochondrial Cristae.
Mitochondrial CMPK2 mediates immunomodulatory and antiviral activities through IFN-dependent and IFN-independent pathways.
Dysfunctional mitochondria as critical players in the inflammation of autoimmune diseases: Potential role in Sjögren's syndrome.
VPS13D interacts with VCP/p97 and negatively regulates ER- mitochondrial interactions.
Mitochondrial quality control: Epigenetic signatures and therapeutic strategies.
Novel reporters of mitochondria-associated membranes (MAM), MAMtrackers, demonstrate MAM disruption as a common pathological feature in amyotrophic lateral sclerosis.
Glutamine addiction in virus-infected mammalian cells: A target of the innate immune system?
The extensive and functionally uncharacterized mitochondrial phosphoproteome.
Endothelial Arginase 2 Mediates Retinal Ischemia/Reperfusion Injury by Inducing Mitochondrial Dysfunction.
Hypermethylation of Hepatic Mitochondrial ND6 Provokes Systemic Insulin Resistance.
Diffusive search and trajectories on tubular networks: a propagator approach.
Critical requirement of SOS1 RAS-GEF function for mitochondrial dynamics, metabolism, and redox homeostasis.
Palmitic Acid, but Not Lauric Acid, Induces Metabolic Inflammation, Mitochondrial Fragmentation, and a Drop in Mitochondrial Membrane Potential in Human Primary Myotubes.
Neuronal mitochondrial dysfunction in a cellular model of circadian rhythm disruption is rescued by donepezil.
Hypoxia-induced SETX links replication stress with the unfolded protein response.
Interleukin-6 as potential mediator of long-term neuropsychiatric symptoms of COVID-19.
Superiority of focused ion beam-scanning electron microscope tomography of cardiomyocytes over standard 2D analyses highlighted by unmasking mitochondrial heterogeneity.
Polysulfide inhibits hypoxia-elicited hypoxia-inducible factor activation in a mitochondria-dependent manner.
Parkinson's disease-associated VPS35 mutant reduces mitochondrial membrane potential and impairs PINK1/Parkin-mediated mitophagy.
Inflammation and apoptosis, two key events induced by hyperglycemia mediated reactive nitrogen species in RGC-5 cells.
BTK Promotes Atherosclerosis by Regulating Oxidative Stress, Mitochondrial Injury, and ER Stress of Macrophages.
Protective role of the mitochondrial fusion protein OPA1 in hypertension.
Mitochondrial DNA duplication, recombination, and introgression during interspecific hybridization.
Miro proteins connect mitochondrial function and intercellular transport.
Immunoproteasome impairment via β5i/LMP7-deletion leads to sustained pancreatic injury from experimental pancreatitis.
MicroRNA-17-5p Promotes Cardiac Hypertrophy by Targeting Mfn2 to Inhibit Autophagy.
Post-translational modification control of viral DNA sensors and innate immune signaling.
Physical bioenergetics: Energy fluxes, budgets, and constraints in cells.
Effects of regular exercise on inflammasome activation-related inflammatory cytokine levels in older adults: a systematic review and meta-analysis.
A PGE2-MEF2A axis enables context-dependent control of inflammatory gene expression.
Large-scale Genome sampling reveals unique immunity and metabolic adaptations in Bats.

Cell Rep. 2021 Jun 15. pii: S2211-1247(21)00596-9. [Epub ahead of print]35(11): 109237

Stress granules inhibit fatty acid oxidation by modulating mitochondrial permeability.

Triana Amen, Daniel Kaganovich.

  The formation of stress granules (SGs) is an essential aspect of the cellular response to many kinds of stress, but its adaptive role is far from clear. SG dysfunction is implicated in aging-onset neurodegenerative diseases, prompting interest in their physiological function. Here, we report that during starvation stress, SGs interact with mitochondria and regulate metabolic remodeling. We show that SG formation leads to a downregulation of fatty acid β-oxidation (FAO) through the modulation of mitochondrial voltage-dependent anion channels (VDACs), which import fatty acids (FAs) into mitochondria. The subsequent decrease in FAO during long-term starvation reduces oxidative damage and rations FAs for longer use. Failure to form SGs, whether caused by the genetic deletion of SG components or an amyotrophic lateral sclerosis (ALS)-associated mutation, translates into an inability to downregulate FAO. Because metabolic dysfunction is a common pathological element of neurodegenerative diseases, including ALS, our findings provide a direction for studying the clinical relevance of SGs.

Keywords:  ALS; VDAC; fatty acid oxidation; lipid droplet; lipid metabolism; metabolic adaptation; mitochondria; porin; starvation; stress granule

DOI:  https://doi.org/10.1016/j.celrep.2021.109237
Nat Commun. 2021 06 16. 12(1): 3669

PGC-1α mediates a metabolic host defense response in human airway epithelium during rhinovirus infections.

Aubrey N Michi, Bryan G Yipp, Antoine Dufour, Fernando Lopes, David Proud.

Human rhinoviruses (HRV) are common cold viruses associated with exacerbations of lower airways diseases. Although viral induced epithelial damage mediates inflammation, the molecular mechanisms responsible for airway epithelial damage and dysfunction remain undefined. Using experimental HRV infection studies in highly differentiated human bronchial epithelial cells grown at air-liquid interface (ALI), we examine the links between viral host defense, cellular metabolism, and epithelial barrier function. We observe that early HRV-C15 infection induces a transitory barrier-protective metabolic state characterized by glycolysis that ultimately becomes exhausted as the infection progresses and leads to cellular damage. Pharmacological promotion of glycolysis induces ROS-dependent upregulation of the mitochondrial metabolic regulator, peroxisome proliferator-activated receptor-γ coactivator 1α (PGC-1α), thereby restoring epithelial barrier function, improving viral defense, and attenuating disease pathology. Therefore, PGC-1α regulates a metabolic pathway essential to host defense that can be therapeutically targeted to rescue airway epithelial barrier dysfunction and potentially prevent severe respiratory complications or secondary bacterial infections.

DOI: https://doi.org/10.1038/s41467-021-23925-z
Histol Histopathol. 2021 Jun 16. 18354

The kidnapping of mitochondrial function associated with the SARS-CoV-2 infection.

Elizabeth Soria-Castro, María Elena Soto, Verónica Guarner-Lans, Gustavo Rojas, Mario Perezpeña-Diazconti, Sergio A Críales-Vera, Linaloe Manzano Pech, Israel Pérez-Torres.

Infection by the Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) leads to multi-organ failure associated with a cytokine storm and septic shock. The virus evades the mitochondrial production of interferons through its N protein and, from that moment on, it hijacks the functions of these organelles. The aim of this study was to show how the virus kidnaps the mitochondrial machinery for its benefit and survival, leading to alterations of serum parameters and to nitrosative stress (NSS). In a prospective cohort of 15 postmortem patients who died from COVID-19, six markers of mitochondrial function (COX II, COX IV, MnSOD, nitrotyrosine, Bcl-2 and caspase-9) were analyzed by the immune colloidal gold technique in samples from the lung, heart, and liver. Biometric laboratory results from these patients showed alterations in hemoglobin, platelets, creatinine, urea nitrogen, glucose, C-reactive protein, albumin, D-dimer, ferritin, fibrinogen, Ca²⁺, K⁺, lactate and troponin. These changes were associated with alterations in the mitochondrial structure and function. The multi-organ dysfunction present in COVID-19 patients may be caused, in part, by damage to the mitochondria that results in an inflammatory state that contributes to NSS, which activates the sepsis cascade and results in increased mortality in COVID-19 patients.

DOI: https://doi.org/10.14670/HH-18-354
mSphere. 2021 Jun 16. e0032721

Mitochondrial Contact Site and Cristae Organization System and F1FO-ATP Synthase Crosstalk Is a Fundamental Property of Mitochondrial Cristae.

Lawrence Rudy Cadena, Ondřej Gahura, Brian Panicucci, Alena Zíková, Hassan Hashimi.

  Mitochondrial cristae are polymorphic invaginations of the inner membrane that are the fabric of cellular respiration. Both the mitochondrial contact site and cristae organization system (MICOS) and the F1FO-ATP synthase are vital for sculpting cristae by opposing membrane-bending forces. While MICOS promotes negative curvature at crista junctions, dimeric F1FO-ATP synthase is crucial for positive curvature at crista rims. Crosstalk between these two complexes has been observed in baker's yeast, the model organism of the Opisthokonta supergroup. Here, we report that this property is conserved in Trypanosoma brucei, a member of the Discoba clade that separated from the Opisthokonta ∼2 billion years ago. Specifically, one of the paralogs of the core MICOS subunit Mic10 interacts with dimeric F1FO-ATP synthase, whereas the other core Mic60 subunit has a counteractive effect on F1FO-ATP synthase oligomerization. This is evocative of the nature of MICOS-F1FO-ATP synthase crosstalk in yeast, which is remarkable given the diversification that these two complexes have undergone during almost 2 eons of independent evolution. Furthermore, we identified a highly diverged, putative homolog of subunit e, which is essential for the stability of F1FO-ATP synthase dimers in yeast. Just like subunit e, it is preferentially associated with dimers and interacts with Mic10, and its silencing results in severe defects to cristae and the disintegration of F1FO-ATP synthase dimers. Our findings indicate that crosstalk between MICOS and dimeric F1FO-ATP synthase is a fundamental property impacting crista shape throughout eukaryotes. IMPORTANCE Mitochondria have undergone profound diversification in separate lineages that have radiated since the last common ancestor of eukaryotes some eons ago. Most eukaryotes are unicellular protists, including etiological agents of infectious diseases, like Trypanosoma brucei. Thus, the study of a broad range of protists can reveal fundamental features shared by all eukaryotes and lineage-specific innovations. Here, we report that two different protein complexes, MICOS and F1FO-ATP synthase, known to affect mitochondrial architecture, undergo crosstalk in T. brucei, just as in baker's yeast. This is remarkable considering that these complexes have otherwise undergone many changes during their almost 2 billion years of independent evolution. Thus, this crosstalk is a fundamental property needed to maintain proper mitochondrial structure even if the constituent players considerably diverged.

Keywords:  ATP synthase; MICOS; Trypanosoma; evolution; mitochondria

DOI:  https://doi.org/10.1128/mSphere.00327-21
iScience. 2021 Jun 25. 24(6): 102498

Mitochondrial CMPK2 mediates immunomodulatory and antiviral activities through IFN-dependent and IFN-independent pathways.

Jenn-Haung Lai, De-Wei Wu, Chien-Hsiang Wu, Li-Feng Hung, Chuan-Yueh Huang, Shuk-Man Ka, Ann Chen, Zee-Fen Chang, Ling-Jun Ho.

  Mitochondria regulate the immune response after dengue virus (DENV) infection. Microarray analysis of genes identified the upregulation of mitochondrial cytidine/uridine monophosphate kinase 2 (CMPK2) by DENV infection. We used small interfering RNA-mediated knockdown (KD) and CRISPR-Cas9 knockout (KO) approaches, to investigate the role of CMPK2 in mouse and human cells. The results showed that CMPK2 was critical in DENV-induced antiviral cytokine release and mitochondrial oxidative stress and mitochondrial DNA release to the cytosol. The DENV-induced activation of Toll-like receptor (TLR)-9, inflammasome pathway, and cell migration was suppressed by CMPK2 depletion; however, viral production increased under CMPK2 deficiency. Examining mouse bone marrow-derived dendritic cells from interferon-alpha (IFN-α) receptor-KO mice and signal transducer and activator of transcription 1 (STAT1)-KO mice, we confirmed that CMPK2-mediated antiviral activity occurred in IFN-dependent and IFN-independent manners. In sum, CMPK2 is a critical factor in DENV-induced immune responses to determine innate immunity.

Keywords:  Immunology; Molecular biology; Virology

DOI:  https://doi.org/10.1016/j.isci.2021.102498
Autoimmun Rev. 2021 Jun 09. pii: S1568-9972(21)00139-7. [Epub ahead of print]20(8): 102867

Dysfunctional mitochondria as critical players in the inflammation of autoimmune diseases: Potential role in Sjögren's syndrome.

María-José Barrera, Sergio Aguilera, Isabel Castro, Patricia Carvajal, Daniela Jara, Claudio Molina, Sergio González, María-Julieta González.

  Relevant reviews highlight the association between dysfunctional mitochondria and inflammation, but few studies address the contribution of mitochondria and mitochondria-endoplasmic reticulum (ER) contact sites (MERCs) to cellular homeostasis and inflammatory signaling. The present review outlines the important role of mitochondria in cellular homeostasis and how dysfunctional mitochondrion can release and misplace mitochondrial components (cardiolipin, mitochondrial DNA (mtDNA), and mitochondrial formylated peptides) through multiple mechanisms. These components can act as damage-associated molecular patterns (DAMPs) and induce an inflammatory response via pattern recognition receptors (PRRs). Accumulation of damaged ROS-generating mitochondria, accompanied by the release of mitochondrial DAMPs, can activate PRRs such as the NLRP3 inflammasome, TLR9, cGAS/STING, and ZBP1. This process would explain the chronic inflammation that is observed in autoimmune diseases such as systemic lupus erythematosus (SLE), rheumatoid arthritis (RA), type I diabetes (T1D), and Sjögren's syndrome. This review also provides a comprehensive overview of the importance of MERCs to mitochondrial function and morphology, cellular homeostasis, and the inflammatory response. MERCs play an important role in calcium homeostasis by mediating the transfer of calcium from the ER to the mitochondria and thereby facilitating the production of ATP. They also contribute to the synthesis and transfer of phospholipids, protein folding in the ER, mitochondrial fission, mitochondrial fusion, initiation of autophagosome formation, regulation of cell death/survival signaling, and regulation of immune responses. Therefore, alterations within MERCs could increase inflammatory signaling, modulate ER stress responses, cell homeostasis, and ultimately, the cell fate. This study shows severe ultrastructural alterations of mitochondria in salivary gland cells from Sjögren's syndrome patients for the first time, which could trigger alterations in cellular bioenergetics. This finding could explain symptoms such as fatigue and malfunction of the salivary glands in Sjögren's syndrome patients, which would contribute to the chronic inflammatory pathology of the disease. However, this is only a first step in solving this complex puzzle, and several other important factors such as changes in mitochondrial morphology, functionality, and their important contacts with other organelles require further in-depth study. Future work should focus on detecting the key milestones that are related to inflammation in patients with autoimmune diseases, such as Sjögren´s syndrome.

Keywords:  DAMPs (mitochondrial damage-associated molecular patterns); Inflammation (chronic inflammation); MERCs (mitochondria-endoplasmic reticulum contact sites); Mitochondria (dysfunctional mitochondria); PRRs (pattern recognition receptors); ROS (reactive oxygen species)

DOI:  https://doi.org/10.1016/j.autrev.2021.102867
Mol Biol Cell. 2021 Jun 16. mbcE21030097

VPS13D interacts with VCP/p97 and negatively regulates ER- mitochondrial interactions.

Yuanjiao Du, Jingru Wang, Juan Xiong, Na Fang, Wei-Ke Ji.

Membrane contact sites (MCSs) between the endoplasmic reticulum (ER) and mitochondria are emerging as critical hubs for diverse cellular events, and alterations in the extent of these contacts are linked to neurodegenerative diseases. However, the mechanisms that control ER-mitochondrial interactions are so far elusive. Here, we demonstrate a key role of vacuolar protein sorting-associated protein 13D (VPS13D) in the negative regulation of ER-mitochondrial MCSs. VPS13D suppression results in extensive ER-mitochondrial tethering, a phenotype that can be substantially rescued by suppression of the tethering proteins VAPB and PTPIP51. VPS13D interacts with valosin-containing protein (VCP/p97) to control the level of ER-resident VAPB at contacts. VPS13D is required for the stability of p97. Functionally, VPS13D suppression leads to severe defects in the mitochondrial morphology, mitochondrial cellular distribution and mitochondrial DNA synthesis. Together our results suggest that VPS13D negatively regulates the ER-mitochondrial MCSs partially through its interactions with VCP/p97. [Media: see text].

DOI: https://doi.org/10.1091/mbc.E21-03-0097
Neurochem Int. 2021 Jun 08. pii: S0197-0186(21)00141-8. [Epub ahead of print]148 105095

Mitochondrial quality control: Epigenetic signatures and therapeutic strategies.

Tanuja Ambekar, Jyoti Pawar, Ramdev Rathod, Monica Patel, Valencia Fernandes, Rahul Kumar, Shashi Bala Singh, Dharmendra Kumar Khatri.

  Mitochondria are semi-autonomous organelle staging a crucial role in cellular stress response, energy metabolism and cell survival. Maintaining mitochondrial quality control is very important for its homeostasis. Pathological conditions such as oxidative stress and neurodegeneration, disrupt this quality control, and involvement of genetic and epigenetic materials in this disruption have been reported. These regulatory factors trigger mitochondrial imbalance, as seen in many neurodegenerative diseases like Alzheimer's disease, Parkinson's disease, Amyotrophic lateral sclerosis, and Huntington's disease. The dynamic regulatory pathways i.e. mitophagy, biogenesis, permeability pore transitioning, fusion-fission are affected as a consequence and have been reviewed in this article. Moreover, several epigenetic mechanisms such as DNA methylation and histone modulation participating in such neurological disorders have also been discussed. Apart from it, therapeutic approaches targeting mitochondrial quality control have been tremendously explored showing ameliorative effects for these diseases, and have been discussed here with a novel perspective.

Keywords:  Biogenesis; DNA methylation; Histone acetylation; Mitochondrial quality control; Mitophagy; Neurodegeneration

DOI:  https://doi.org/10.1016/j.neuint.2021.105095
FASEB J. 2021 Jul;35(7): e21688

Novel reporters of mitochondria-associated membranes (MAM), MAMtrackers, demonstrate MAM disruption as a common pathological feature in amyotrophic lateral sclerosis.

Shohei Sakai, Seiji Watanabe, Okiru Komine, Akira Sobue, Koji Yamanaka.

  The mitochondria-associated membrane (MAM) is a functional subdomain of the endoplasmic reticulum membrane that tethers to the mitochondrial outer membrane and is essential for cellular homeostasis. A defect in MAM is involved in various neurological diseases, including amyotrophic lateral sclerosis (ALS). Recently, we and others reported that MAM was disrupted in the models expressing several ALS-linked genes, including SOD1, SIGMAR1, VAPB, TARDBP, and FUS, suggesting that MAM disruption is deeply involved in the pathomechanism of ALS. However, it is still uncertain whether MAM disruption is a common pathology in ALS, mainly due to the absence of a simple, quantitative tool for monitoring the status of MAM. In this study, to examine the effects of various ALS-causative genes on MAM, we created the following two novel MAM reporters: MAMtracker-Luc and MAMtracker-Green. The MAMtrackers could detect MAM disruption caused by suppression of SIGMAR1 or the overexpression of ALS-linked mutant SOD1 in living cells. Moreover, the MAMtrackers have an advantage in their ability to monitor reversible changes in the MAM status induced by nutritional conditions. We used the MAMtrackers with an expression plasmid library of ALS-causative genes and noted that 76% (16/21) of the genes altered MAM integrity. Our results suggest that MAM disruption is a common pathological feature in ALS. Furthermore, we anticipate our MAMtrackers, which are suitable for high-throughput assays, to be valuable tools to understand MAM dynamics.

Keywords:  ER-mitochondria contact; amyotrophic lateral sclerosis (ALS); mitochondria-associated membrane (MAM); organelle; sigma-1 receptor (Sig1R)

DOI:  https://doi.org/10.1096/fj.202100137R
Med Hypotheses. 2021 Jun 02. pii: S0306-9877(21)00139-0. [Epub ahead of print]153 110620

Glutamine addiction in virus-infected mammalian cells: A target of the innate immune system?

C Koufaris, V Nicolaidou.

  Control of core cell metabolism is a key aspect of the evolutionary conflict between viruses and the host's defence mechanisms. From their side, the invading viruses press the accelerator on their host cell's glycolysis, fatty acid, and glutaminolytic metabolic processes among others. It is also well established that activation of innate immune system responses modulates facets of metabolism such as that of polyamine, cholesterol, tryptophan and many more. But what about glutamine, a proteogenic amino acid that is a crucial nutrient for multiple cellular biosynthetic processes? Although mammalian cells can normally synthesize glutamine de novo, it has been noted that infections with genetically and phylogenetically diverse viruses are followed by the acquisition of a dependency on supplies of exogenous glutamine i.e. "glutamine addiction". Here we present our novel hypothesis that glutamine metabolism is also a target of the innate immune system, possibly through the action of interferons, as part of the evolutionary conserved antiviral metabolic reprogramming.

Keywords:  Cellular metabolism; Glutamine; Immune response; Viral infection

DOI:  https://doi.org/10.1016/j.mehy.2021.110620
J Biol Chem. 2021 Jun 15. pii: S0021-9258(21)00680-3. [Epub ahead of print] 100880

The extensive and functionally uncharacterized mitochondrial phosphoproteome.

Natalie M Niemi, David J Pagliarini.

  More than half a century ago, reversible protein phosphorylation was first linked to mitochondrial metabolism through the regulation of pyruvate dehydrogenase. Since this discovery, the number of identified mitochondrial protein phosphorylation sites has increased by orders of magnitude, driven largely by technological advances in mass spectrometry-based phosphoproteomics. However, the majority of these modifications remain uncharacterized, rendering their function and relevance unclear. Nonetheless, recent studies have shown that disruption of resident mitochondrial protein phosphatases causes substantial metabolic dysfunction across organisms, suggesting that proper management of mitochondrial phosphorylation is vital for organellar and organismal homeostasis. While these data suggest that phosphorylation within mitochondria is of critical importance, significant gaps remain in our knowledge of how these modifications influence organellar function. Here, we curate publicly available datasets to map the extent of protein phosphorylation within mammalian mitochondria and to highlight the known functions of mitochondrial-resident phosphatases. We further propose models by which phosphorylation may affect mitochondrial enzyme activities, protein import and processing, and overall organellar homeostasis.

Keywords:  mitochondria; phosphoproteomics; protein kinase; protein phosphatase; protein phosphorylation

DOI:  https://doi.org/10.1016/j.jbc.2021.100880
Mol Metab. 2021 Jun 14. pii: S2212-8778(21)00118-6. [Epub ahead of print] 101273

Endothelial Arginase 2 Mediates Retinal Ischemia/Reperfusion Injury by Inducing Mitochondrial Dysfunction.

Esraa Shosha, Abdelrahman Y Fouda, Tahira Lemtalsi, Stephen Haigh, David Fulton, Ahmed Ibrahim, Mohamed Al-Shabrawey, R William Caldwell, Ruth B Caldwell.

  OBJECTIVE: Retinal ischemic disease is a major cause of vision loss. Current treatment options are limited to late stage disease and the molecular mechanisms of the initial insult are not fully understood. We have previously shown that deletion of the mitochondrial arginase isoform, arginase 2 (A2), limits neurovascular injury in models of ischemic retinopathy. Here, we investigated the involvement of A2-mediated alterations in mitochondrial dynamics and function in the pathology.METHODS: We used wild type (WT), global A2 knockout (A2KO-) mice, cell-specific A2 knockout mice subjected to retinal ischemia/reperfusion (I/R) and bovine retinal endothelial cells (BRECs) subjected to oxygen glucose deprivation/reperfusion (OGD/R) insult. We used western blotting to measure levels of cell stress and death markers and the mitochondrial fragmentation protein, dynamin related protein 1(Drp1) along with live cell mitochondrial labelling and Seahorse XF analysis to evaluate mitochondrial fragmentation and function, respectively.
RESULTS: We found that the global deletion of A2 limited I/R-induced disruption of retinal layers, fundus abnormalities and albumin extravasation. The specific deletion of A2 in endothelial cells was protective against I/R-induced neurodegeneration. The OGD/R insult in BRECs increased A2 expression and induced cell stress and cell death along with decreased mitochondrial respiration, increased Drp1 expression and mitochondrial fragmentation. The overexpression of A2 in BREC also decreased mitochondrial respiration, promoted increases in expression of Drp1, mitochondrial fragmentation, cell stress, and resulted in decreased cell survival. In contrast, overexpression of the cytosolic isoform, arginase 1 (A1), had no effect on these parameters.
CONCLUSION: This study is the first to show that A2 in endothelial cells mediates retinal ischemic injury through a mechanism involving alterations in mitochondrial dynamics and function.

Keywords:  Retina; arginase; endothelial cells; ischemia; mitochondria

DOI:  https://doi.org/10.1016/j.molmet.2021.101273
Adv Sci (Weinh). 2021 Jun;8(11): 2004507

Hypermethylation of Hepatic Mitochondrial ND6 Provokes Systemic Insulin Resistance.

Ke Cao, Weiqiang Lv, Xueqiang Wang, Shanshan Dong, Xuyun Liu, Tielin Yang, Jie Xu, Mengqi Zeng, Xuan Zou, Daina Zhao, Qingqing Ma, Mu Lin, Jiangang Long, Weijin Zang, Feng Gao, Zhihui Feng, Jiankang Liu.

  Mitochondrial epigenetics is rising as intriguing notion for its potential involvement in aging and diseases, while the details remain largely unexplored. Here it is shown that among the 13 mitochondrial DNA (mtDNA) encoded genes, NADH-dehydrogenase 6 (ND6) transcript is primarily decreased in obese and type 2 diabetes populations, which negatively correlates with its distinctive hypermethylation. Hepatic mtDNA sequencing in mice unveils that ND6 presents the highest methylation level, which dramatically increases under diabetic condition due to enhanced mitochondrial translocation of DNA methyltransferase 1 (DNMT1) promoted by free fatty acid through adenosine 5'-monophosphate (AMP)-activated protein kinase (AMPK) activation. Hepatic knockdown of ND6 or overexpression of Dnmt1 similarly impairs mitochondrial function and induces systemic insulin resistance both in vivo and in vitro. Genetic or chemical targeting hepatic DNMT1 shows significant benefits against insulin resistance associated metabolic disorders. These findings highlight the pivotal role of ND6 epigenetic network in regulating mitochondrial function and onset of insulin resistance, shedding light on potential preventive and therapeutic strategies of insulin resistance and related metabolic disorders from a perspective of mitochondrial epigenetics.

Keywords:  DNA methyltransferase 1 (DNMT1); insulin resistance; mitochondrial NADH‐dehydrogenase 6 (ND6); mitochondrial dysfunction; obesity and type 2 diabetes mellitus (T2DM)

DOI:  https://doi.org/10.1002/advs.202004507
Eur Phys J E Soft Matter. 2021 Jun 18. 44(6): 80

Diffusive search and trajectories on tubular networks: a propagator approach.

Zubenelgenubi C Scott, Aidan I Brown, Saurabh S Mogre, Laura M Westrate, Elena F Koslover.

Several organelles in eukaryotic cells, including mitochondria and the endoplasmic reticulum, form interconnected tubule networks extending throughout the cell. These tubular networks host many biochemical pathways that rely on proteins diffusively searching through the network to encounter binding partners or localized target regions. Predicting the behavior of such pathways requires a quantitative understanding of how confinement to a reticulated structure modulates reaction kinetics. In this work, we develop both exact analytical methods to compute mean first passage times and efficient kinetic Monte Carlo algorithms to simulate trajectories of particles diffusing in a tubular network. Our approach leverages exact propagator functions for the distribution of transition times between network nodes and allows large simulation time steps determined by the network structure. The methodology is applied to both synthetic planar networks and organelle network structures, demonstrating key general features such as the heterogeneity of search times in different network regions and the functional advantage of broadly distributing target sites throughout the network. The proposed algorithms pave the way for future exploration of the interrelationship between tubular network structure and biomolecular reaction kinetics.

DOI: https://doi.org/10.1140/epje/s10189-021-00083-0
Oncogene. 2021 Jun 12.

Critical requirement of SOS1 RAS-GEF function for mitochondrial dynamics, metabolism, and redox homeostasis.

Rósula García-Navas, Pilar Liceras-Boillos, Carmela Gómez, Fernando C Baltanás, Nuria Calzada, Cristina Nuevo-Tapioles, José M Cuezva, Eugenio Santos.

SOS1 ablation causes specific defective phenotypes in MEFs including increased levels of intracellular ROS. We showed that the mitochondria-targeted antioxidant MitoTEMPO restores normal endogenous ROS levels, suggesting predominant involvement of mitochondria in generation of this defective SOS1-dependent phenotype. The absence of SOS1 caused specific alterations of mitochondrial shape, mass, and dynamics accompanied by higher percentage of dysfunctional mitochondria and lower rates of electron transport in comparison to WT or SOS2-KO counterparts. SOS1-deficient MEFs also exhibited specific alterations of respiratory complexes and their assembly into mitochondrial supercomplexes and consistently reduced rates of respiration, glycolysis, and ATP production, together with distinctive patterns of substrate preference for oxidative energy metabolism and dependence on glucose for survival. RASless cells showed defective respiratory/metabolic phenotypes reminiscent of those of SOS1-deficient MEFs, suggesting that the mitochondrial defects of these cells are mechanistically linked to the absence of SOS1-GEF activity on cellular RAS targets. Our observations provide a direct mechanistic link between SOS1 and control of cellular oxidative stress and suggest that SOS1-mediated RAS activation is required for correct mitochondrial dynamics and function.

DOI: https://doi.org/10.1038/s41388-021-01886-3
Front Nutr. 2021 ;8 663838

Palmitic Acid, but Not Lauric Acid, Induces Metabolic Inflammation, Mitochondrial Fragmentation, and a Drop in Mitochondrial Membrane Potential in Human Primary Myotubes.

Domenico Sergi, Natalie Luscombe-Marsh, Nenad Naumovski, Mahinda Abeywardena, Nathan O'Callaghan.

  The chain length of saturated fatty acids may dictate their impact on inflammation and mitochondrial dysfunction, two pivotal players in the pathogenesis of insulin resistance. However, these paradigms have only been investigated in animal models and cell lines so far. Thus, the aim of this study was to compare the effect of palmitic (PA) (16:0) and lauric (LA) (12:0) acid on human primary myotubes mitochondrial health and metabolic inflammation. Human primary myotubes were challenged with either PA or LA (500 μM). After 24 h, the expression of interleukin 6 (IL-6) was assessed by quantitative polymerase chain reaction (PCR), whereas Western blot was used to quantify the abundance of the inhibitor of nuclear factor κB (IκBα), electron transport chain complex proteins and mitofusin-2 (MFN-2). Mitochondrial membrane potential and dynamics were evaluated using tetraethylbenzimidazolylcarbocyanine iodide (JC-1) and immunocytochemistry, respectively. PA, contrarily to LA, triggered an inflammatory response marked by the upregulation of IL-6 mRNA (11-fold; P < 0.01) and a decrease in IκBα (32%; P < 0.05). Furthermore, whereas PA and LA did not differently modulate the levels of mitochondrial electron transport chain complex proteins, PA induced mitochondrial fragmentation (37%; P < 0.001), decreased MFN-2 (38%; P < 0.05), and caused a drop in mitochondrial membrane potential (11%; P < 0.01) compared to control, with this effect being absent in LA-treated cells. Thus, LA, as opposed to PA, did not trigger pathogenetic mechanisms proposed to be linked with insulin resistance and therefore represents a healthier saturated fatty acid choice to potentially preserve skeletal muscle metabolic health.

Keywords:  fatty acids; lauric acid; metabolic inflammation; mitochondria; palmitic acid; skeletal muscle

DOI:  https://doi.org/10.3389/fnut.2021.663838
Biochem Biophys Res Commun. 2021 Jun 15. pii: S0006-291X(21)00950-5. [Epub ahead of print]567 56-62

Neuronal mitochondrial dysfunction in a cellular model of circadian rhythm disruption is rescued by donepezil.

Harshavardhan Kenche, Meharvan Singh, Jacquez Smith, Kai Shen.

  Human circadian rhythm refers to the intrinsic ∼24-h oscillation that regulates biological processes to adapt to environments. Disruption of rhythmicity causes mitochondrial dysfunction, changes metabolism, and is associated with neurodegenerative diseases and mental disorders. By employing cellular respiration analyses and mitochondrial membrane potential characterization, we confirmed that donepezil, a sigma-1 receptor agonist, restored mitochondrial function in neuronal cells with induced-circadian rhythm disruption (CRD). This protective effect was elicited by boosting oxidative respiration and increasing mitochondrial membrane potentials. Furthermore, donepezil treatment reinstated rhythmicity of core clock genes. Our findings suggest a novel countermeasure for treating CRD-related neurodegeneration and mental disorders.

Keywords:  Circadian rhythm disruption; Clock genes; Mitochondrial dysfunction; Sigma-1 receptor

DOI:  https://doi.org/10.1016/j.bbrc.2021.06.029
Nat Commun. 2021 06 17. 12(1): 3686

Hypoxia-induced SETX links replication stress with the unfolded protein response.

Shaliny Ramachandran, Tiffany S Ma, Jon Griffin, Natalie Ng, Iosifina P Foskolou, Ming-Shih Hwang, Pedro Victori, Wei-Chen Cheng, Francesca M Buffa, Katarzyna B Leszczynska, Sherif F El-Khamisy, Natalia Gromak, Ester M Hammond.

Tumour hypoxia is associated with poor patient prognosis and therapy resistance. A unique transcriptional response is initiated by hypoxia which includes the rapid activation of numerous transcription factors in a background of reduced global transcription. Here, we show that the biological response to hypoxia includes the accumulation of R-loops and the induction of the RNA/DNA helicase SETX. In the absence of hypoxia-induced SETX, R-loop levels increase, DNA damage accumulates, and DNA replication rates decrease. Therefore, suggesting that, SETX plays a role in protecting cells from DNA damage induced during transcription in hypoxia. Importantly, we propose that the mechanism of SETX induction in hypoxia is reliant on the PERK/ATF4 arm of the unfolded protein response. These data not only highlight the unique cellular response to hypoxia, which includes both a replication stress-dependent DNA damage response and an unfolded protein response but uncover a novel link between these two distinct pathways.

DOI: https://doi.org/10.1038/s41467-021-24066-z
Psychoneuroendocrinology. 2021 Jun 03. pii: S0306-4530(21)00169-4. [Epub ahead of print]131 105295

Interleukin-6 as potential mediator of long-term neuropsychiatric symptoms of COVID-19.

Nils Kappelmann, Robert Dantzer, Golam M Khandaker.

  The majority of COVID-19 survivors experience long-term neuropsychiatric symptoms such as fatigue, sleeping difficulties, depression and anxiety. We propose that neuroimmune cross-talk via inflammatory cytokines such as interleukin-6 (IL-6) could underpin these long-term COVID-19 symptoms. This hypothesis is supported by several lines of research, including population-based cohort and genetic Mendelian Randomisation studies suggesting that inflammation is associated with fatigue and sleeping difficulties, and that IL-6 could represent a possible causal driver for these symptoms. Immune activation following COVID-19 can disrupt T helper 17 (TH17) and regulatory T (Treg) cell responses, affect central learning and emotional processes, and lead to a vicious cycle of inflammation and mitochondrial dysfunction that amplifies the inflammatory process and results in immuno-metabolic constraints on neuronal energy metabolism, with fatigue being the ultimate result. Increased cytokine activity drives this process and could be targeted to interrupt it. Therefore, whether persistent IL-6 dysregulation contributes to COVID-19-related long-term fatigue, sleeping difficulties, depression, and anxiety, and whether targeting IL-6 pathways could be helpful for treatment and prevention of long COVID are important questions that require investigation. This line of research could inform new approaches for treatment and prevention of long-term neuropsychiatric symptoms of COVID-19. Effective treatment and prevention of this condition could also help to stem the anticipated rise in depression and other mental illnesses ensuing this pandemic.

Keywords:  COVID-19; Depression; Fatigue; Interleukin-6; Long COVID; Sleep

DOI:  https://doi.org/10.1016/j.psyneuen.2021.105295
J Cachexia Sarcopenia Muscle. 2021 Jun 13.

Superiority of focused ion beam-scanning electron microscope tomography of cardiomyocytes over standard 2D analyses highlighted by unmasking mitochondrial heterogeneity.

Jacqueline Heinen-Weiler, Mike Hasenberg, Martin Heisler, Stephan Settelmeier, Anna-Lena Beerlage, Hannah Doepper, Bernd Walkenfort, Andrea Odersky, Peter Luedike, Elke Winterhager, Tienush Rassaf, Ulrike B Hendgen-Cotta.

  BACKGROUND: Cardioprotection by preventing or repairing mitochondrial damage is an unmet therapeutic need. To understand the role of cardiomyocyte mitochondria in physiopathology, the reliable characterization of the mitochondrial morphology and compartment is pivotal. Previous studies mostly relied on two-dimensional (2D) routine transmission electron microscopy (TEM), thereby neglecting the real three-dimensional (3D) mitochondrial organization. This study aimed to determine whether classical 2D TEM analysis of the cardiomyocyte ultrastructure is sufficient to comprehensively describe the mitochondrial compartment and to reflect mitochondrial number, size, dispersion, distribution, and morphology.METHODS: Spatial distribution of the complex mitochondrial network and morphology, number, and size heterogeneity of cardiac mitochondria in isolated adult mouse cardiomyocytes and adult wild-type left ventricular tissues (C57BL/6) were assessed using a comparative 3D imaging system based on focused ion beam-scanning electron microscopy (FIB-SEM) nanotomography. For comparison of 2D vs. 3D data sets, analytical strategies and mathematical comparative approaches were performed. To confirm the value of 3D data for mitochondrial changes, we compared the obtained values for number, coverage area, size heterogeneity, and complexity of wild-type cardiomyocyte mitochondria with data sets from mice lacking the cytosolic and mitochondrial protein BNIP3 (BCL-2/adenovirus E1B 19-kDa interacting protein 3; Bnip3-/- ) using FIB-SEM. Mitochondrial respiration was assessed on isolated mitochondria using the Seahorse XF analyser. A cardiac biopsy was obtained from a male patient (48 years) suffering from myocarditis.
RESULTS: The FIB-SEM nanotomographic analysis revealed that no linear relationship exists for mitochondrial number (r = 0.02; P = 0.9511), dispersion (r = -0.03; P = 0.9188), and shape (roundness: r = 0.15, P = 0.6397; elongation: r = -0.09, P = 0.7804) between 3D and 2D results. Cumulative frequency distribution analysis showed a diverse abundance of mitochondria with different sizes in 3D and 2D. Qualitatively, 2D data could not reflect mitochondrial distribution and dynamics existing in 3D tissue. 3D analyses enabled the discovery that BNIP3 deletion resulted in more smaller, less complex cardiomyocyte mitochondria (number: P < 0.01; heterogeneity: C.V. wild-type 89% vs. Bnip3-/- 68%; complexity: P < 0.001) forming large myofibril-distorting clusters, as seen in human myocarditis with disturbed mitochondrial dynamics. Bnip3-/- mice also show a higher respiration rate (P < 0.01).
CONCLUSIONS: Here, we demonstrate the need of 3D analyses for the characterization of mitochondrial features in cardiac tissue samples. Hence, we observed that BNIP3 deletion physiologically acts as a molecular brake on mitochondrial number, suggesting a role in mitochondrial fusion/fission processes and thereby regulating the homeostasis of cardiac bioenergetics.

Keywords:  3D morphometry; BNIP3; Cardiac mitochondria; Focused ion beam-scanning electron microscopy; Mitochondrial dynamics; Mitochondrial energetics

DOI:  https://doi.org/10.1002/jcsm.12742
Mitochondrion. 2021 Jun 13. pii: S1567-7249(21)00080-5. [Epub ahead of print]

Polysulfide inhibits hypoxia-elicited hypoxia-inducible factor activation in a mitochondria-dependent manner.

Takeo Uba, Yoshiyuki Matsuo, Chisato Sumi, Tomohiro Shoji, Kenichiro Nishi, Munenori Kusunoki, Hiroshi Harada, Hideo Kimura, Hidemasa Bono, Kiichi Hirota.

  In cellular signaling, the diverse physiological actions of biological gases, including O2, CO, NO, and H2S, have attracted much interest. Hypoxia-inducible factors (HIFs), including HIF-1 and HIF-2, are transcription factors that respond to reduced intracellular O2 availability. Polysulfides are substances containing varying numbers of sulfur atoms (H2Sn) that are generated endogenously from H2S by 3-mercaptopyruvate sulfurtransferase in the presence of O2, and regulate ion channels, specific tumor suppressors, and protein kinases. However, the effect of polysulfides on HIF activation in hypoxic mammalian cells is largely unknown. Here, we have investigated the effect of polysulfide on cells in vitro. In established cell lines, polysulfide donors reversibly reduced cellular O2 consumption and inhibited hypoxia-induced HIF-1α protein accumulation and the expression of genes downstream of HIFs; however, these effects were not observed in anoxia. In Von Hippel-Lindau tumor suppressor (VHL)- and mitochondria-deficient cells, polysulfides did not affect HIF-1α protein synthesis but destabilized it in a VHL- and mitochondria-dependent manner. For the first time, we show that polysulfides modulate intracellular O2 homeostasis and regulate HIF activation and subsequent hypoxia-induced gene expression in a VHL- and mitochondria-dependent manner.

Keywords:  Electron Transport Chain; RNA-Seq; VHL; hydrogen sulfide; hypoxia-inducible factor; mitochondria; oxygen consumption; polysulfide; sulfane sulfur; ρ0 cell

DOI:  https://doi.org/10.1016/j.mito.2021.06.007
Transl Neurodegener. 2021 Jun 15. 10(1): 19

Parkinson's disease-associated VPS35 mutant reduces mitochondrial membrane potential and impairs PINK1/Parkin-mediated mitophagy.

Kai Yu Ma, Michiel R Fokkens, Fulvio Reggiori, Muriel Mari, Dineke S Verbeek.

  BACKGROUND: Mitochondrial dysfunction plays a prominent role in the pathogenesis of Parkinson's disease (PD), and several genes linked to familial PD, including PINK1 (encoding PTEN-induced putative kinase 1 [PINK1]) and PARK2 (encoding the E3 ubiquitin ligase Parkin), are directly involved in processes such as mitophagy that maintain mitochondrial health. The dominant p.D620N variant of vacuolar protein sorting 35 ortholog (VPS35) gene is also associated with familial PD but has not been functionally connected to PINK1 and PARK2.METHODS: To better mimic and study the patient situation, we used CRISPR-Cas9 to generate heterozygous human SH-SY5Y cells carrying the PD-associated D620N variant of VPS35. These cells were treated with a protonophore carbonyl cyanide m-chlorophenylhydrazone (CCCP) to induce the PINK1/Parkin-mediated mitophagy, which was assessed using biochemical and microscopy approaches.
RESULTS: Mitochondria in the VPS35-D620N cells exhibited reduced mitochondrial membrane potential and appeared to already be damaged at steady state. As a result, the mitochondria of these cells were desensitized to the CCCP-induced collapse in mitochondrial potential, as they displayed altered fragmentation and were unable to accumulate PINK1 at their surface upon this insult. Consequently, Parkin recruitment to the cell surface was inhibited and initiation of the PINK1/Parkin-dependent mitophagy was impaired.
CONCLUSION: Our findings extend the pool of evidence that the p.D620N mutation of VPS35 causes mitochondrial dysfunction and suggest a converging pathogenic mechanism among VPS35, PINK1 and Parkin in PD.

Keywords:  Mitochondrial membrane potential; Mitophagy; PINK1; Parkin; Parkinson’s disease; VPS35

DOI:  https://doi.org/10.1186/s40035-021-00243-4
Life Sci. 2021 Jun 07. pii: S0024-3205(21)00679-2. [Epub ahead of print]279 119693

Inflammation and apoptosis, two key events induced by hyperglycemia mediated reactive nitrogen species in RGC-5 cells.

Sweta Pal, G Nageswar Rao, Arttatrana Pal.

  Nitrosative stress plays a critical role in retinal injury in high glucose (HG) environment of eye, but the mechanisms remain poorly understood. Here we tested the hypothesis that HG induced reactive nitrogen species (RNS) production acts as a key functional mediator of antioxidant depletion, mitochondrial dysfunction, biomolecule damage, inflammation and apoptosis. Our findings illustrated that exposure of cultured RGC-5 cells to HG significantly disrupts the antioxidant defense mechanism and mitochondrial machineries by increasing the loss of mitochondrial membrane potential (ΔѰM) and elevating mitochondrial mass. Furthermore, we used biochemical tools to analyze the changes in metabolites, sulfur amino acids (SAAs) such as L-glutathione (GSH) and L-cysteine (Cys), in the presence of HG environment. These metabolic changes were followed by an increase in glycolytic flux that is phosphofructokinase-2 (PFK-2) activity. Moreover, HG exposure results in a significant disruption of protein carbonylation (PC) and lipid peroxidation (LPO), downregulation of OGG1 and increase in 8-OHdG accumulations in RGC-5 cells. In addition, our results demonstrated that HG environment coinciding with increased expression of inflammatory mediators, cell cycle deregulation, decreased in cell viability and expression of FoxOs, increased lysosomal content leading to apoptosis. Pre-treatment of selective inhibitors of RNS significantly reduced the HG-induced cell cycle deregulation and apoptosis in RGC-5 cells. Collectively, these results illustrated that accumulated RNS exacerbates the antioxidant depletion, mitochondrial dysfunction, biomolecule damage, inflammation and apoptosis induced by HG exposure in RGC-5 cells. Treatment of pharmacological inhibitors attenuated the HG induced in retinal cells.

Keywords:  Apoptosis; High glucose; Inflammation; Metabolites; Reactive nitrogen species (RNS)

DOI:  https://doi.org/10.1016/j.lfs.2021.119693
Oxid Med Cell Longev. 2021 ;2021 9972413

BTK Promotes Atherosclerosis by Regulating Oxidative Stress, Mitochondrial Injury, and ER Stress of Macrophages.

Junxiong Qiu, Yuan Fu, Zhiteng Chen, Lisui Zhang, Ling Li, Diefei Liang, Feng Wei, Zhuzhi Wen, Yajing Wang, Shi Liang.

Atherosclerosis (AS) is a chronic metabolic disease in arterial walls, characterized by lipid deposition and persistent aseptic inflammation. AS is regarded as the basis of a variety of cardiovascular and cerebrovascular diseases. It is widely acknowledged that macrophages would become foam cells after internalizing lipoprotein particles, which is an initial factor in atherogenesis. Here, we showed the influences of Bruton's tyrosine kinase (BTK) in macrophage-mediated AS and how BTK regulates the inflammatory responses of macrophages in AS. Our bioinformatic results suggested that BTK was a potential hub gene, which is closely related to oxidative stress, ER stress, and inflammation in macrophage-induced AS. Moreover, we found that BTK knockdown could restrain ox-LDL-induced NK-κB signaling activation in macrophages and repressed M1 polarization. The mechanistic studies revealed that oxidative stress, mitochondrial injury, and ER stress in macrophages were also suppressed by BTK knockdown. Furthermore, we found that sh-BTK adenovirus injection could alleviate the severity of AS in ApoE-/- mice induced by a high-fat diet in vivo. Our study suggested that BTK promoted ox-LDL-induced ER stress, oxidative stress, and inflammatory responses in macrophages, and it may be a potential therapeutic target in AS.

DOI: https://doi.org/10.1155/2021/9972413
FASEB J. 2021 Jul;35(7): e21678

Protective role of the mitochondrial fusion protein OPA1 in hypertension.

Pauline Robert, Phuc Minh Chau Nguyen, Alexis Richard, Céline Grenier, Arnaud Chevrollier, Mathilde Munier, Linda Grimaud, Coralyne Proux, Tristan Champin, Eric Lelièvre, Emmanuelle Sarzi, Emilie Vessières, Samir Henni, Delphine Prunier, Pascal Reynier, Guys Lenaers, Céline Fassot, Daniel Henrion, Laurent Loufrani.

  Hypertension is associated with excessive reactive oxygen species (ROS) production in vascular cells. Mitochondria undergo fusion and fission, a process playing a role in mitochondrial function. OPA1 is essential for mitochondrial fusion. Loss of OPA1 is associated with ROS production and cell dysfunction. We hypothesized that mitochondria fusion could reduce oxidative stress that defect in fusion would exacerbate hypertension. Using (a) Opa1 haploinsufficiency in isolated resistance arteries from Opa1+/- mice, (b) primary vascular cells from Opa1+/- mice, and (c) RNA interference experiments with siRNA against Opa1 in vascular cells, we investigated the role of mitochondria fusion in hypertension. In hypertension, Opa1 haploinsufficiency induced altered mitochondrial cristae structure both in vascular smooth muscle and endothelial cells but did not modify protein level of long and short forms of OPA1. In addition, we demonstrated an increase of mitochondrial ROS production, associated with a decrease of superoxide dismutase 1 protein expression. We also observed an increase of apoptosis in vascular cells and a decreased VSMCs proliferation. Blood pressure, vascular contractility, as well as endothelium-dependent and -independent relaxation were similar in Opa1+/- , WT, L-NAME-treated Opa1+/- and WT mice. Nevertheless, chronic NO-synthase inhibition with L-NAME induced a greater hypertension in Opa1+/- than in WT mice without compensatory arterial wall hypertrophy. This was associated with a stronger reduction in endothelium-dependent relaxation due to excessive ROS production. Our results highlight the protective role of mitochondria fusion in the vasculature during hypertension by limiting mitochondria ROS production.

Keywords:  Opa1; hypertension; mitochondria; oxidative stress; vascular function

DOI:  https://doi.org/10.1096/fj.202000238RRR
Sci Rep. 2021 Jun 16. 11(1): 12726

Mitochondrial DNA duplication, recombination, and introgression during interspecific hybridization.

Silvia Bágeľová Poláková, Žaneta Lichtner, Tomáš Szemes, Martina Smolejová, Pavol Sulo.

mtDNA recombination events in yeasts are known, but altered mitochondrial genomes were not completed. Therefore, we analyzed recombined mtDNAs in six Saccharomyces cerevisiae × Saccharomyces paradoxus hybrids in detail. Assembled molecules contain mostly segments with variable length introgressed to other mtDNA. All recombination sites are in the vicinity of the mobile elements, introns in cox1, cob genes and free standing ORF1, ORF4. The transplaced regions involve co-converted proximal exon regions. Thus, these selfish elements are beneficial to the host if the mother molecule is challenged with another molecule for transmission to the progeny. They trigger mtDNA recombination ensuring the transfer of adjacent regions, into the progeny of recombinant molecules. The recombination of the large segments may result in mitotically stable duplication of several genes.

DOI: https://doi.org/10.1038/s41598-021-92125-y
Crit Rev Biochem Mol Biol. 2021 Jun 17. 1-25

Miro proteins connect mitochondrial function and intercellular transport.

Zuzana Nahacka, Renata Zobalova, Maria Dubsiova, Jakub Rohlena, Jiri Neuzil.

  Mitochondria are organelles present in most eukaryotic cells, where they play major and multifaceted roles. The classical notion of the main mitochondrial function as the powerhouse of the cell per se has been complemented by recent discoveries pointing to mitochondria as organelles affecting a number of other auxiliary processes. They go beyond the classical energy provision via acting as a relay point of many catabolic and anabolic processes, to signaling pathways critically affecting cell growth by their implication in de novo pyrimidine synthesis. These additional roles further underscore the importance of mitochondrial homeostasis in various tissues, where its deregulation promotes a number of pathologies. While it has long been known that mitochondria can move within a cell to sites where they are needed, recent research has uncovered that mitochondria can also move between cells. While this intriguing field of research is only emerging, it is clear that mobilization of mitochondria requires a complex apparatus that critically involves mitochondrial proteins of the Miro family, whose role goes beyond the mitochondrial transfer, as will be covered in this review.

Keywords:  Miro proteins; Mitochondria; endoplasmic reticulum; intercellular transfer; mitophagy; motor proteins; respiration

DOI:  https://doi.org/10.1080/10409238.2021.1925216
J Cell Mol Med. 2021 Jun 15.

Immunoproteasome impairment via β5i/LMP7-deletion leads to sustained pancreatic injury from experimental pancreatitis.

Laura L de Freitas Chama, Frédéric Ebstein, Birthe Wiesrecker, Preshit R Wagh, Elke Hammer, Frank U Weiss, Heike Junker, Maja Studencka-Turski, Markus M Lerch, Elke Krüger, Matthias Sendler.

  Uncovering potential new targets involved in pancreatitis may permit the development of new therapies and improvement of patient's outcome. Acute pancreatitis is a primarily sterile disease characterized by a severe systemic inflammatory response associated with extensive necrosis and a mortality rate of up to 24%. Considering that one of the reported disease mechanisms comprises the endoplasmic reticulum (ER) stress response and that the immunoproteasome is a key regulator to prevent proteotoxic stress in an inflammatory context, we investigated its role in acute pancreatitis. In this study, we demonstrate that immunoproteasome deficiency by deletion of the β5i/LMP7-subunit leads to persistent pancreatic damage. Interestingly, immunoproteasome-deficient mice unveil increased activity of pancreatic enzymes in the acute disease phase as well as higher secretion of Interleukin-6 and transcript expression of the Interleukin IL-1β, IFN-β cytokines and the CXCL-10 chemokine. Cell death was increased in immunoproteasome-deficient mice, which appears to be due to the increased accumulation of ubiquitin-protein conjugates and prolonged unfolded protein response. Accordingly, our findings suggest that the immunoproteasome plays a protective role in acute pancreatitis via its role in the clearance of damaged proteins and the balance of ER stress responses in pancreatic acini and in macrophages cytokine production.

Keywords:  ER stress; PSMB8; cell death; cytokines; pancreatitis

DOI:  https://doi.org/10.1111/jcmm.16682
Cardiovasc Toxicol. 2021 Jun 12.

MicroRNA-17-5p Promotes Cardiac Hypertrophy by Targeting Mfn2 to Inhibit Autophagy.

Xuan Xu, Yi-Ling Su, Jia-Yu Shi, Qi Lu, Chu Chen.

  Pathological cardiac hypertrophy is the leading cause of heart failure, and miRNAs have been recognized as key factors in cardiac hypertrophy. This study aimed to elucidate whether miR-17-5p affects cardiac hypertrophy by targeting the mitochondrial fusion protein mitofusin 2 (Mfn2)-mediated phosphatidylinositol-3-kinase (PI3K)/AKT/mammalian target of rapamycin (mTOR) pathway and regulating autophagy. miR-17-5p expression was shown to be upregulated both in vivo and in vitro. In addition, a miR-17-5p inhibitor significantly reversed AngII-induced cell hypertrophy in neonatal rat left ventricle myocytes (NRVMs). In contrast to miR-17-5p expression, Mfn2 expression was inhibited in rat hearts at 4 weeks after transverse aortic constriction (TAC) and in an Ang II-induced cell hypertrophy model. We examined miR-17-5p targeting of Mfn2 by dual luciferase reporter and Western blot assays. In addition, we also verified the relationship between Mfn2 and the PI3K/AKT/mTOR pathway. Mfn2 overexpression attenuated miR-17-5p-induced cell hypertrophy, and in rat myocardial tissue, miR-17-5p induced autophagy inhibition. In summary, the results of the present study demonstrated that miR-17-5p inhibits Mfn2 expression, activates the PI3K/AKT/mTOR pathway and suppresses autophagy to promote cardiac hypertrophy.

Keywords:  Autophagy; Cardiac hypertrophy; Mfn2; MicroRNA-17-5p; PI3K/AKT/mTOR pathway

DOI:  https://doi.org/10.1007/s12012-021-09667-w
Adv Virus Res. 2021 ;pii: S0065-3527(21)00002-6. [Epub ahead of print]109 163-199

Post-translational modification control of viral DNA sensors and innate immune signaling.

Bokai Song, Dawei Liu, Todd M Greco, Ileana M Cristea.

  The vertebrate innate immune system confers host cells with mechanisms to protect against both evolutionarily ancient pathogens and newly emerging pathogenic strains. Innate immunity relies on the host cell's ability to distinguish between self and pathogen-derived molecules. To achieve this, the innate immune system uses germline encoded receptors called pattern recognition receptors (PRRs), which recognize various molecular signatures, including nucleic acids, proteins, lipids, glycans and glycolipids. Among these molecules, the recognition of pathogenic, mislocalized, or damaged DNA by cellular protein receptors, commonly called DNA sensors, represents a major surveillance pathway for initiating immune signaling. The ability of cells to temporally regulate DNA sensor activation and subsequent signal termination is critical for effective immune signaling. These same mechanisms are also co-opted by pathogens to promote their replication. Therefore, there is significant interest in understanding DNA sensor regulatory networks during microbial infections and autoimmune disease. One emerging aspect of DNA sensor regulation is through post-translational modifications (PTMs), including phosphorylation, acetylation, ubiquitination, ADP-ribosylation, SUMOylation, methylation, deamidation, glutamylation. In this chapter, we discuss how PTMs have been shown to positively or negatively impact DNA sensor functions via diverse mechanisms, including direct regulation of enzymatic activity, protein-protein and protein-DNA interactions, protein translocations and protein turnover. In addition, we highlight the ability of virus-induced PTMs to promote immune evasion. We also discuss the recent evidence linking PTMs on DNA sensors with human diseases and more broadly, highlight promising directions for future research on PTM-mediated regulation of DNA sensor-dependent immune signaling.

Keywords:  DNA sensing; IFI16; Immunoaffinity purification; Innate immunity; Mass spectrometry; PTM; Post-translational modification; Proteomics; Targeted mass spectrometry; Virus; cGAS

DOI:  https://doi.org/10.1016/bs.aivir.2021.03.001
Proc Natl Acad Sci U S A. 2021 Jun 29. pii: e2026786118. [Epub ahead of print]118(26):

Physical bioenergetics: Energy fluxes, budgets, and constraints in cells.

Xingbo Yang, Matthias Heinemann, Jonathon Howard, Greg Huber, Srividya Iyer-Biswas, Guillaume Le Treut, Michael Lynch, Kristi L Montooth, Daniel J Needleman, Simone Pigolotti, Jonathan Rodenfels, Pierre Ronceray, Sadasivan Shankar, Iman Tavassoly, Shashi Thutupalli, Denis V Titov, Jin Wang, Peter J Foster.

  Cells are the basic units of all living matter which harness the flow of energy to drive the processes of life. While the biochemical networks involved in energy transduction are well-characterized, the energetic costs and constraints for specific cellular processes remain largely unknown. In particular, what are the energy budgets of cells? What are the constraints and limits energy flows impose on cellular processes? Do cells operate near these limits, and if so how do energetic constraints impact cellular functions? Physics has provided many tools to study nonequilibrium systems and to define physical limits, but applying these tools to cell biology remains a challenge. Physical bioenergetics, which resides at the interface of nonequilibrium physics, energy metabolism, and cell biology, seeks to understand how much energy cells are using, how they partition this energy between different cellular processes, and the associated energetic constraints. Here we review recent advances and discuss open questions and challenges in physical bioenergetics.

Keywords:  energetic constraints; energetic costs; energy fluxes; physical bioenergetics

DOI:  https://doi.org/10.1073/pnas.2026786118
J Sports Sci. 2021 Jun 12. 1-15

Effects of regular exercise on inflammasome activation-related inflammatory cytokine levels in older adults: a systematic review and meta-analysis.

Yijian Ding, Xi Xu.

  Exercise has been found to play important roles in regulating inflammation, although the mechanisms are unclear. The present systematic review and meta-analysis aimed to investigate whether regular exercise could regulate inflammation through inflammasome activation signalling in older adults. Five databases were searched, and 19 randomised controlled trials (RCTs) studying effects of regular exercise on inflammasome activation-related inflammatory cytokines interleukin (IL)-1β and IL-18 and other key molecules involved in inflammasome activation signalling such as NOD-like receptor family pyrin domain containing 3 (NLRP3), apoptosis-associated speck-like protein containing a caspase recruitment domain (ASC), caspase-1 in older adults aged 50 years or older were included. The results showed that regular exercise could significantly decrease the levels of IL-1β and IL-18, important end-products of inflammasome activation in older adults. Subgroup analyses showed that aerobic exercise is the most effective training modality, and low-to-moderate intensity and mixed intensity are better compared with high intensity to decrease IL-1β and IL-18. The effect of regular exercise on key molecules involved in inflammasome activation signalling including NLRP3, ASC and caspase-1 is understudied and needs to be further investigated. These findings demonstrate that regular exercise could effectively decrease inflammasome activation-related inflammatory cytokine levels in older adults.

Keywords:  Ageing; Exercise; Inflammasome; Meta-Analysis; Systematic review

DOI:  https://doi.org/10.1080/02640414.2021.1932279
Immunity. 2021 Jun 09. pii: S1074-7613(21)00222-3. [Epub ahead of print]

A PGE2-MEF2A axis enables context-dependent control of inflammatory gene expression.

Francesco Cilenti, Giulia Barbiera, Nicoletta Caronni, Dario Iodice, Elisa Montaldo, Simona Barresi, Eleonora Lusito, Vincenzo Cuzzola, Francesco Maria Vittoria, Luca Mezzanzanica, Paolo Miotto, Pietro Di Lucia, Dejan Lazarevic, Daniela Maria Cirillo, Matteo Iannacone, Marco Genua, Renato Ostuni.

  Tight control of inflammatory gene expression by antagonistic environmental cues is key to ensure immune protection while preventing tissue damage. Prostaglandin E2 (PGE2) modulates macrophage activation during homeostasis and disease, but the underlying mechanisms remain incompletely characterized. Here we dissected the genomic properties of lipopolysaccharide (LPS)-induced genes whose expression is antagonized by PGE2. The latter molecule targeted a set of inflammatory gene enhancers that, already in unstimulated macrophages, displayed poorly permissive chromatin organization and were marked by the transcription factor myocyte enhancer factor 2A (MEF2A). Deletion of MEF2A phenocopied PGE2 treatment and abolished type I interferon (IFN I) induction upon exposure to innate immune stimuli. Mechanistically, PGE2 interfered with LPS-mediated activation of ERK5, a known transcriptional partner of MEF2. This study highlights principles of plasticity and adaptation in cells exposed to a complex environment and uncovers a transcriptional circuit for IFN I induction with relevance for infectious diseases or cancer.

Keywords:  LPS; MEF2; PGE2; chromatin; cytokines; inflammation; innate immunity; interferons; macrophages; transcription

DOI:  https://doi.org/10.1016/j.immuni.2021.05.016
Mol Ecol. 2021 Jun 19.

Large-scale Genome sampling reveals unique immunity and metabolic adaptations in Bats.

Diana D Moreno Santillán, Tanya M Lama, Yocelyn T Gutierrez Guerrero, Alexis M Brown, Paul Donat, Huabin Zhao, Stephen J Rossiter, Laurel R Yohe, Joshua H Potter, Emma C Teeling, Sonja C Vernes, Kalina T J Davies, Eugene Myers, Graham M Hughes, Zixia Huang, Federico Hoffmann, Angelique P Corthals, David A Ray, Liliana M Dávalos.

  Comprising more than 1,400 species, bats possess adaptations unique among mammals including powered flight, unexpected longevity, and extraordinary immunity. Some of the molecular mechanisms underlying these unique adaptations includes DNA repair, metabolism and immunity. However, analyses have been limited to a few divergent lineages, reducing the scope of inferences on gene family evolution across the Order Chiroptera. We conducted an exhaustive comparative genomic study of 37 bat species, one generated in this study, encompassing a large number of lineages, with a particular emphasis on multi-gene family evolution across immune and metabolic genes. In agreement with previous analyses, we found lineage-specific expansions of the APOBEC3 and MHC-I gene families, and loss of the proinflammatory PYHIN gene family. We inferred more than 1,000 gene losses unique to bats, including genes involved in the regulation of inflammasome pathways such as epithelial defense receptors, the natural killer gene complex and the interferon-gamma induced pathway. Gene set enrichment analyses revealed genes lost in bats are involved in defense response against pathogen-associated molecular patterns and damage-associated molecular patterns. Gene family evolution and selection analyses indicate bats have evolved fundamental functional differences compared to other mammals in both innate and adaptive immune system, with the potential to enhance anti-viral immune response while dampening inflammatory signaling. In addition, metabolic genes have experienced repeated expansions related to convergent shifts to plant-based diets. Our analyses support the hypothesis that, in tandem with flight, ancestral bats had evolved a unique set of immune adaptations whose functional implications remain to be explored.

Keywords:  adaptive immunity; gene family evolution; inflammatory pathway; innate immunity; metabolism; viral tolerance

DOI:  https://doi.org/10.1111/mec.16027