bims-mitmed 2022-07-03 papers

bims-mitmed

Biomed News

on Mitochondrial medicine

Issue of 2022–07–03
twenty-six papers selected by
Dario Brunetti, Fondazione IRCCS Istituto Neurologico

A novel RRM2B mutation associated with mitochondrial DNA depletion syndrome.
A child with mitochondrial DNA deletion presenting diabetes mellitus as an initial symptom.
Analysis of Organization and Activity of Mitochondrial Respiratory Chain Complexes in Primary Fibroblasts Using Blue Native PAGE.
Combined fibre atrophy and decreased muscle regeneration capacity driven by mitochondrial DNA alterations underlie the development of sarcopenia.
Mitophagy and neuroinflammation: a compelling interplay.
Mitochondrial dysfunction in cell senescence and aging.
Microglial response promotes neurodegeneration in the Ndufs4 KO mouse model of Leigh syndrome.
Rotenone Decreases Ischemia-Induced Injury by Inhibiting Mitochondrial Permeability Transition: A Study in Brain.
Protein misfolding and clearance in the pathogenesis of a new infantile onset ataxia caused by mutations in PRDX3.
Urolithin A improves mitochondrial health, reduces cartilage degeneration, and alleviates pain in osteoarthritis.
Structural basis for defective membrane targeting of mutant enzyme in human VLCAD deficiency.
Examining Mitochondrial Morphology in Mouse Brains.
Mitochondrial dysfunction is associated with lipid metabolism disorder and upregulation of angiotensin-converting enzyme 2.
Evidence for mitochondrial Lonp1 expression in the nucleus.
Quantifying Regulated Mitochondrial Fission in Macrophages.
Neurohormonal Connections with Mitochondria in Cardiomyopathy and Other Diseases.
Impaired oxygen-sensitive regulation of mitochondrial biogenesis within the von Hippel-Lindau syndrome.
Mitohormesis and mitochondrial dynamics in the regulation of stem cell fate.
Dynamics and stabilization mechanism of mitochondrial cristae morphofunction associated with turgor-driven cardiolipin biosynthesis under salt stress conditions.
Mitochondrial protein import stress regulates the LC3 lipidation step of mitophagy through NLRX1 and RRBP1.
Mitochondria-Associated Membrane Scaffolding with Endoplasmic Reticulum: A Dynamic Pathway of Developmental Disease.
Coenzyme A-Dependent Tricarboxylic Acid Cycle Enzymes Are Decreased in Alzheimer's Disease Consistent With Cerebral Pantothenate Deficiency.
Structural basis for mitoguardin-2 mediated lipid transport at ER-mitochondrial membrane contact sites.
Measurements of Mitochondrial Respiration in Intact Cells, Permeabilized Cells, and Isolated Tissue Mitochondria Using the Seahorse XF Analyzer.
Mitochondrial microRNAs are dysregulated in patients with Fabry Disease.
DDX1 vesicles control calcium-dependent mitochondrial activity in mouse embryos.

Mol Genet Metab Rep. 2022 Sep;32 100887

A novel RRM2B mutation associated with mitochondrial DNA depletion syndrome.

Monica Fumagalli, Dario Ronchi, Maria Francesca Bedeschi, Arianna Manini, Gloria Cristofori, Fabio Mosca, Robertino Dilena, Monica Sciacco, Simona Zanotti, Daniela Piga, Gianluigi Ardissino, Fabio Triulzi, Stefania Corti, Giacomo P Comi, Leonardo Salviati.

  Mitochondrial DNA (mtDNA) depletion syndromes are disorders characterized by infantile-onset, severe progression, and the drastic loss of mtDNA content in affected tissues. In a patient who showed severe hypotonia, proximal tubulopathy and sensorineural hearing loss after birth, we observed severe mtDNA depletion and impaired respiratory chain activity in muscle due to heterozygous variants c.686G > T and c.551-2A > G in RRM2B, encoding the p53R2 subunit of the ribonucleotide reductase.

Keywords:  Mitochondrial DNA depletion; Mitochondrial encephalomyopathy; Next generation sequencing; RRM2B; Ribonucleotide reductase

DOI:  https://doi.org/10.1016/j.ymgmr.2022.100887
Radiol Case Rep. 2022 Sep;17(9): 2915-2918

A child with mitochondrial DNA deletion presenting diabetes mellitus as an initial symptom.

Koko Nemoto, Kentaro Sano, Satoko Sato, Yasuhiro Maeda, Kei Murayama, Jun-Ichi Takanashi.

  Children with mitochondrial disease may present with diabetes mellitus (DM) without autoimmune antibodies as an initial manifestation, however, it is difficult to make a precise diagnosis in early stages. We present a 2-year-old male patient with mitochondrial disease who showed insulin-dependent DM without autoimmune antibodies as an initial symptom. He later presented with progressive motor deterioration, hearing disability, ptosis, external ophthalmoplegia, and retinitis pigmentosa at 6 years and 6 months. T2- and diffusion-weighted imaging revealed high signal lesions in the subcortical white matter, anterior thalamus, globus pallidus, and brainstem. MR spectroscopy showed elevated lactate and low N-acetylaspartate in the affected white matter. Genetic analysis revealed a single large-scale mitochondrial DNA deletion at 7117-13994, leading to a diagnosis of mitochondrial DNA deletion syndrome associated with insulin-dependent DM. Although the frequency of DM in pediatric mitochondrial disease is low, mitochondrial disease, especially due to mitochondrial DNA deletion, should be considered as a differential diagnosis in those with insulin-dependent DM without autoimmune antibodies, and MRI and MR spectroscopy are recommended for an early diagnosis.

Keywords:  Diabetes mellitus; MR spectroscopy; MRI; Mitochondrial DNA deletion syndrome; Mitochondrial disease

DOI:  https://doi.org/10.1016/j.radcr.2022.05.061
Methods Mol Biol. 2022 ;2497 339-348

Analysis of Organization and Activity of Mitochondrial Respiratory Chain Complexes in Primary Fibroblasts Using Blue Native PAGE.

Kritarth Singh, Michael R Duchen.

  Blue Native polyacrylamide gel electrophoresis (BN-PAGE) is a well-established technique for the isolation and separation of mitochondrial membrane protein complexes in a native conformation with high resolution. In combination with histochemical staining methods, BN-PAGE has been successfully used as clinical diagnostic tool for the detection of oxidative phosphorylation (OXPHOS) defects from small tissue biopsies from patients with primary mitochondrial disease. However, its application to patient-derived primary fibroblasts is difficult due to limited proliferation and high background staining. Here, we describe a rapid and convenient method to analyze the organization and activity of OXPHOS complexes from cultured skin fibroblasts.

Keywords:  In-gel activity; Mitochondria; Oxidative phosphorylation; Primary fibroblasts; Supercomplex

DOI:  https://doi.org/10.1007/978-1-0716-2309-1_25
J Cachexia Sarcopenia Muscle. 2022 Jun 28.

Combined fibre atrophy and decreased muscle regeneration capacity driven by mitochondrial DNA alterations underlie the development of sarcopenia.

Sammy Kimoloi, Ayesha Sen, Stefan Guenther, Thomas Braun, Tobias Brügmann, Philipp Sasse, Rudolf J Wiesner, David Pla-Martín, Olivier R Baris.

   BACKGROUND: Mitochondrial dysfunction caused by mitochondrial (mtDNA) deletions have been associated with skeletal muscle atrophy and myofibre loss. However, whether such defects occurring in myofibres cause sarcopenia is unclear. Also, the contribution of mtDNA alterations in muscle stem cells (MuSCs) to sarcopenia remains to be investigated.
METHODS: We expressed a dominant-negative variant of the mitochondrial helicase, which induces mtDNA alterations, specifically in differentiated myofibres (K320Eskm mice) and MuSCs (K320Emsc mice), respectively, and investigated their impact on muscle structure and function by immunohistochemistry, analysis of mtDNA and respiratory chain content, muscle transcriptome and functional tests.
RESULTS: K320Eskm mice at 24 months of age had higher levels of mtDNA deletions compared with controls in soleus (SOL, 0.07673% vs. 0.00015%, P = 0.0167), extensor digitorum longus (EDL, 0.0649 vs. 0.000925, P = 0.0015) and gastrocnemius (GAS, 0.09353 vs. 0.000425, P = 0.0004). K320Eskm mice revealed a progressive increase in the proportion of cytochrome c oxidase deficient (COX- ) fibres in skeletal muscle cross sections, reaching a maximum of 3.03%, 4.36%, 13.58%, and 17.08% in EDL, SOL, tibialis anterior (TA) and GAS, respectively. However, mice did not show accelerated loss of muscle mass, muscle strength or physical performance. Histological analyses revealed ragged red fibres but also stimulated regeneration, indicating activation of MuSCs. RNAseq demonstrated enhanced expression of genes associated with protein synthesis, but also degradation, as well as muscle fibre differentiation and cell proliferation. In contrast, 7 days after destruction by cardiotoxin, regenerating TA of K320Emsc mice showed 30% of COX- fibres. Notably, regenerated muscle showed dystrophic changes, increased fibrosis (2.5% vs. 1.6%, P = 0.0003), increased abundance of fat cells (2.76% vs. 0.23%, P = 0.0144) and reduced muscle mass (regenerated TA: 40.0 mg vs. 60.2 mg, P = 0.0171). In contrast to muscles from K320Eskm mice, freshly isolated MuSCs from aged K320Emsc mice were completely devoid of mtDNA alterations. However, after passaging, mtDNA copy number as well as respiratory chain subunits and p62 levels gradually decreased.
CONCLUSIONS: Taken together, accumulation of large-scale mtDNA alterations in myofibres alone is not sufficient to cause sarcopenia. Expression of K320E-Twinkle is tolerated in quiescent MuSCs, but progressively leads to mtDNA and respiratory chain depletion upon activation, in vivo and in vitro, possibly caused by an increased mitochondrial removal. Altogether, our results suggest that the accumulation of mtDNA alterations in myofibres activates regeneration during aging, which leads to sarcopenia if such alterations have expanded in MuSCs as well.

Keywords:  Mitochondria; Muscle stem cells; Mutations; Myofibres; Satellite cells; mtDNA deletions

DOI:  https://doi.org/10.1002/jcsm.13026
Curr Neuropharmacol. 2022 Jun 28.

Mitophagy and neuroinflammation: a compelling interplay.

Nikolaos Charmpilas, Evandro Fei Fang, Konstantinos Palikaras.

  Mitochondria are the main sites of energy production and a major source of metabolic stress. Not surprisingly, impairment of mitochondrial homeostasis is tightly associated with the development and progression of a broad spectrum of human pathologies, including neurodegenerative disorders. Mitophagy mediates the selective degradation of damaged organelles, thus promoting cellular viability and tissue integrity. Defective mitophagy triggers cellular senescence and prolonged neuroinflammation, leading eventually to cell death and brain homeostasis collapse. Here, we survey the intricate interplay between mitophagy and neuroinflammation, highlighting that mitophagy can be a focal point for therapeutic interventions to tackle neurodegeneration.

Keywords:  Ageing; energy homeostasis; immunity; inflammation; metabolism; mitochondria; mitophagy; neurodegeneration

DOI:  https://doi.org/10.2174/1570159X20666220628153632
J Clin Invest. 2022 Jul 01. pii: e158447. [Epub ahead of print]132(13):

Mitochondrial dysfunction in cell senescence and aging.

Satomi Miwa, Sonu Kashyap, Eduardo Chini, Thomas von Zglinicki.

Mitochondrial dysfunction and cell senescence are hallmarks of aging and are closely interconnected. Mitochondrial dysfunction, operationally defined as a decreased respiratory capacity per mitochondrion together with a decreased mitochondrial membrane potential, typically accompanied by increased production of oxygen free radicals, is a cause and a consequence of cellular senescence and figures prominently in multiple feedback loops that induce and maintain the senescent phenotype. Here, we summarize pathways that cause mitochondrial dysfunction in senescence and aging and discuss the major consequences of mitochondrial dysfunction and how these consequences contribute to senescence and aging. We also highlight the potential of senescence-associated mitochondrial dysfunction as an antiaging and antisenescence intervention target, proposing the combination of multiple interventions converging onto mitochondrial dysfunction as novel, potent senolytics.

DOI: https://doi.org/10.1172/JCI158447
Glia. 2022 Jun 30.

Microglial response promotes neurodegeneration in the Ndufs4 KO mouse model of Leigh syndrome.

Kevin Aguilar, Gemma Comes, Carla Canal, Albert Quintana, Elisenda Sanz, Juan Hidalgo.

  Leigh syndrome is a mitochondrial disease characterized by neurodegeneration, neuroinflammation, and early death. Mice lacking NDUFS4, a mitochondrial complex I subunit (Ndufs4 KO mice), have been established as a good animal model for studying human pathology associated with Leigh syndrome. As the disease progresses, there is an increase in neurodegeneration and neuroinflammation, thereby leading to deteriorating neurological symptoms, including motor deficits, breathing alterations, and eventually, death of the animal. However, despite the magnitude of neuroinflammation associated with brain lesions, the role of neuroinflammatory pathways and their main cellular components have not been addressed directly as relevant players in the disease pathology. Here, we investigate the role of microglial cells, the main immune cells of the CNS, in Leigh-like syndrome pathology, by pharmacologically depleting them using the colony-stimulating factor 1 receptor antagonist PLX3397. Microglial depletion extended lifespan and delayed motor symptoms in Ndufs4 KO mice, likely by preventing neuronal loss. Next, we investigated the role of the major cytokine interleukin-6 (IL-6) in the disease progression. IL-6 deficiency partially rescued breathing abnormalities and modulated gliosis but did not extend the lifespan or rescue motor decline in Ndufs4 KO mice. The present results show that microglial accumulation is pathogenic, in a process independent of IL-6, and hints toward a contributing role of neuroinflammation in the disease of Ndufs4 KO mice and potentially in patients with Leigh syndrome.

Keywords:  IL-6; Leigh syndrome; Ndufs4 KO; microglia; neuroinflammation

DOI:  https://doi.org/10.1002/glia.24234
Methods Mol Biol. 2022 ;2497 63-72

Rotenone Decreases Ischemia-Induced Injury by Inhibiting Mitochondrial Permeability Transition: A Study in Brain.

Ramune Morkuniene, Evelina Rekuviene, Dalia M Kopustinskiene.

  Mitochondria participate in many physiological and pathological processes in the cells, including cellular energy supply, regulation of calcium homeostasis, apoptosis, and ROS generation. Alterations of mitochondrial functions, especially the opening of mitochondrial permeability transition pore (mPTP) are the main mechanisms responsible for the ischemic brain damage. Recently, the inhibitors of the Complex I of mitochondrial respiratory chain emerged as promising suppressors of mitochondrial ROS generation and mPTP opening. Here we describe the assay that can be implemented easily to evaluate the protective effects of rotenone or other potential inhibitors of the Complex I of mitochondrial respiratory chain against acute ischemia-induced injuries in brain.

Keywords:  Brain ischemia; Calcium retention capacity; Complex I; Complex II; Isolated brain mitochondria; Mitochondrial permeability transition pore; Mitochondrial respiration; ROS generation; Rotenone

DOI:  https://doi.org/10.1007/978-1-0716-2309-1_3
Hum Mol Genet. 2022 Jun 29. pii: ddac146. [Epub ahead of print]

Protein misfolding and clearance in the pathogenesis of a new infantile onset ataxia caused by mutations in PRDX3.

Dolores Martínez-Rubio, Ángela Rodríguez-Prieto, Paula Sancho, Carmen Navarro-González, Nerea Gorría-Redondo, Javier Miquel-Leal, Clara Marco-Marín, Alison Jenkins, Mario Soriano-Navarro, Alberto Hernández, Belén Pérez-Dueñas, Pietro Fazzari, Sergio AƗguilera-Albesa, Carmen Espinós.

Peroxiredoxin 3 (PRDX3) encodes a mitochondrial antioxidant protein which is essential for the control of reactive oxidative species (ROS) homeostasis. So far, PRDX3 mutations are involved in mild-to-moderate progressive juvenile onset cerebellar ataxia. We aimed to unravel the molecular bases underlying the disease in an infant suffering from cerebellar ataxia that started at 19 months old and presented severe cerebellar atrophy and peripheral neuropathy early in the course of disease. By whole exome sequencing, we identified a novel homozygous mutation, PRDX3 p.D163E, which impaired the mitochondrial ROS defense system. In mouse primary cortical neurons, the exogenous expression of PRDX3 p.D163E was reduced and triggered alterations in neurite morphology and in mitochondria. Mitochondrial computational parameters showed that p.D163E led to serious mitochondrial alterations. In transfected HeLa cells expressing the mutation, mitochondria accumulation was detected by correlative light electron microscopy (CLEM). Mitochondrial morphology showed severe changes, including extremely damaged outer and inner membranes with a notable cristae disorganization. Moreover, spherical structures compatible with lipid droplets were identified, which can be associated with a generalized response to stress and can be involved in the removal of unfolded proteins. In the patient's fibroblasts, PRDX3 expression was nearly absent. The biochemical analysis suggested that the mutation p.D163E would result in an unstable structure tending to form aggregates that trigger unfolded protein responses via mitochondria and endoplasmic reticulum. Altogether, our findings broaden the clinical spectrum of the recently described PRDX3-associated neurodegeneration and provide new insight into the pathological mechanisms underlying this new form of cerebellar ataxia.

DOI: https://doi.org/10.1093/hmg/ddac146
Aging Cell. 2022 Jul 01. e13662

Urolithin A improves mitochondrial health, reduces cartilage degeneration, and alleviates pain in osteoarthritis.

Davide D'Amico, Merissa Olmer, Andréane M Fouassier, Pamela Valdés, Pénélope A Andreux, Chris Rinsch, Martin Lotz.

  Osteoarthritis (OA) is the most common age-related joint disorder with no effective therapy. According to the World Health Organization, OA affects over 500 million people and is characterized by degradation of cartilage and other joint tissues, severe pain, and impaired mobility. Mitochondrial dysfunction contributes to OA pathology. However, interventions to rescue mitochondrial defects in human OA are not available. Urolithin A (Mitopure) is a natural postbiotic compound that promotes mitophagy and mitochondrial function and beneficially impacts muscle health in preclinical models of aging and in elderly and middle-aged humans. Here, we showed that Urolithin A improved mitophagy and mitochondrial respiration in primary chondrocytes from joints of both healthy donors and OA patients. Furthermore, Urolithin A reduced disease progression in a mouse model of OA, decreasing cartilage degeneration, synovial inflammation, and pain. These improvements were associated with increased mitophagy and mitochondrial content, in joints of OA mice. These findings indicate that UA promotes joint mitochondrial health, alleviates OA pathology, and supports Urolithin A's potential to improve mobility with beneficial effects on structural damage in joints.

Keywords:  Mitopure; chondrocytes; mitochondria; mitophagy; osteoarthritis; urolithin

DOI:  https://doi.org/10.1111/acel.13662
Nat Commun. 2022 Jun 27. 13(1): 3669

Structural basis for defective membrane targeting of mutant enzyme in human VLCAD deficiency.

Michelle S Prew, Christina M Camara, Thomas Botzanowski, Jamie A Moroco, Noah B Bloch, Hannah R Levy, Hyuk-Soo Seo, Sirano Dhe-Paganon, Gregory H Bird, Henry D Herce, Micah A Gygi, Silvia Escudero, Thomas E Wales, John R Engen, Loren D Walensky.

Very long-chain acyl-CoA dehydrogenase (VLCAD) is an inner mitochondrial membrane enzyme that catalyzes the first and rate-limiting step of long-chain fatty acid oxidation. Point mutations in human VLCAD can produce an inborn error of metabolism called VLCAD deficiency that can lead to severe pathophysiologic consequences, including cardiomyopathy, hypoglycemia, and rhabdomyolysis. Discrete mutations in a structurally-uncharacterized C-terminal domain region of VLCAD cause enzymatic deficiency by an incompletely defined mechanism. Here, we conducted a structure-function study, incorporating X-ray crystallography, hydrogen-deuterium exchange mass spectrometry, computational modeling, and biochemical analyses, to characterize a specific membrane interaction defect of full-length, human VLCAD bearing the clinically-observed mutations, A450P or L462P. By disrupting a predicted α-helical hairpin, these mutations either partially or completely impair direct interaction with the membrane itself. Thus, our data support a structural basis for VLCAD deficiency in patients with discrete mutations in an α-helical membrane-binding motif, resulting in pathologic enzyme mislocalization.

DOI: https://doi.org/10.1038/s41467-022-31466-2
Methods Mol Biol. 2022 ;2515 17-28

Examining Mitochondrial Morphology in Mouse Brains.

Jessika Royea, Mireille Khacho.

  Mitochondria are dynamic organelles that rely on a balance of opposing fission and fusion events to sustain mitochondrial function and efficiently meet the energy demands of a cell. As high-energy demanding cells, neurons rely heavily on optimally functional mitochondria with balanced mitochondrial dynamics, to ensure a sufficient energy supply required to maintain cell survival, establish membrane excitability and partake in processes of neurotransmission and plasticity. As such, many neurodegenerative diseases (e.g., Alzheimer's disease, Parkinson's disease) and stress conditions (e.g., stroke) leading to neuronal dysfunction or death are often associated with impaired mitochondrial function and dynamics, characterized by excessive mitochondrial fragmentation. For this reason, the assessment of mitochondrial morphology in neurons and within the brain can provide valuable information. The dynamic nature of mitochondria is not only observed in shape changes, but also changes in mitochondrial network connectivity and in cristae architecture. In this chapter, we will describe how mitochondrial morphology can be examined in vitro using hippocampal neuronal cultures and in vivo using mouse brain sections by immunocytochemistry, immunohistochemistry, and electron microscopy techniques.

Keywords:  Confocal and electron microscopy; Cristae; Hippocampus; Mitochondrial dynamics; Mitochondrial dysfunction; Mitochondrial fission; Mitochondrial fusion; Mitochondrial morphology; Neurodegenerative diseases; Neuronal cultures

DOI:  https://doi.org/10.1007/978-1-0716-2409-8_2
PLoS One. 2022 ;17(6): e0270418

Mitochondrial dysfunction is associated with lipid metabolism disorder and upregulation of angiotensin-converting enzyme 2.

Qian Zhao, Xiaoshan Zhou, Raoul Kuiper, Sophie Curbo, Anna Karlsson.

Thymidine kinase 2 (TK2) deficiency in humans leads to a myopathic form of mitochondrial DNA (mtDNA) deficiency. Here we present a skeletal and cardiac muscle specific TK2 knockout mouse (mTk2 KO). The mice showed dilated hearts and markedly reduced adipose tissue during week 12 to 16. A severe decrease of mtDNA was found only in skeletal muscle and heart tissue in mTk2 KO mice. Expression analysis of key metabolic genes of 16 weeks knockout mice showed significant changes of genes involved in lipid metabolism, with different patterns in heart and skeletal muscle. Our study further suggests that lipoprotein lipase (LPL) from liver supports the metabolism when heart and skeletal muscle were impaired due to mitochondrial dysfunction. The angiotensin-converting enzyme 2 (ACE2), which is involved in glucose homeostasis, was also affected by mtDNA deficiency in our study. Interestingly, both the gene and protein expression of ACE2 were increased in cardiac tissue of mTk2 KO mice. Since ACE2 is a receptor for the SARS-CoV-2 virus, its regulation in relation to mitochondrial function may have important clinical implications.

DOI: https://doi.org/10.1371/journal.pone.0270418
Sci Rep. 2022 Jun 27. 12(1): 10877

Evidence for mitochondrial Lonp1 expression in the nucleus.

Lara Gibellini, Rebecca Borella, Anna De Gaetano, Giada Zanini, Domenico Lo Tartaro, Gianluca Carnevale, Francesca Beretti, Lorena Losi, Sara De Biasi, Milena Nasi, Mattia Forcato, Andrea Cossarizza, Marcello Pinti.

The coordinated communication between the mitochondria and nucleus is essential for cellular activities. Nonetheless, the pathways involved in this crosstalk are scarcely understood. The protease Lonp1 was previously believed to be exclusively located in the mitochondria, with an important role in mitochondrial morphology, mtDNA maintenance, and cellular metabolism, in both normal and neoplastic cells. However, we recently detected Lonp1 in the nuclear, where as much as 22% of all cellular Lonp1 can be found. Nuclear localization is detectable under all conditions, but the amount is dependent on a response to heat shock (HS). Lonp1 in the nucleus interacts with heat shock factor 1 (HSF1) and modulates the HS response. These findings reveal a novel extramitochondrial function for Lonp1 in response to stress.

DOI: https://doi.org/10.1038/s41598-022-14860-0
Methods Mol Biol. 2022 ;2523 281-301

Quantifying Regulated Mitochondrial Fission in Macrophages.

Syeda Farhana Afroz, Nicholas D Condon, Matthew J Sweet, Ronan Kapetanovic.

  Mitochondria have co-evolved with eukaryotic cells for more than a billion years, becoming an important cog in their machinery. They are best known for being tasked with energy generation through the production of adenosine triphosphate, but they also have roles in several other cellular processes, for example, immune and inflammatory responses. Mitochondria have important functions in macrophages, key innate immune cells that detect pathogens and drive inflammation. Mitochondrial activity is influenced by the highly dynamic nature of the mitochondrial network, which alternates between interconnected tubular and fragmented forms. The dynamic balance between this interconnected fused network and fission-mediated mitochondrial fragmentation modulates inflammatory responses such as production of cytokines and mitochondrial reactive oxygen species. Here we describe methods to differentiate mouse bone marrow cells into macrophages and the use of light microscopy, electron microscopy, flow cytometry, and Western blotting to quantify regulated mitochondrial dynamics in these differentiated macrophages.

Keywords:  Drp1; Fission; Fusion; Inflammation; Macrophages; Microscopy; Mitochondria; Mitochondrial dynamics

DOI:  https://doi.org/10.1007/978-1-0716-2449-4_18
Am J Physiol Cell Physiol. 2022 Jun 27.

Neurohormonal Connections with Mitochondria in Cardiomyopathy and Other Diseases.

Gerald W Dorn Ii.

  Neurohormonal signaling and mitochondrial dynamism are seemingly distinct processes that are almost ubiquitous among multicellular organisms. Both of these processes are regulated by GTPases, and disturbances in either can provoke disease. Here, inconspicuous pathophysiological connectivity between neurohormonal signaling and mitochondrial dynamism is reviewed in the context of cardiac and neurological syndromes. For both processes, greater understanding of basic mechanisms has evoked a reversal of conventional pathophysiological concepts. Thus, neurohormonal systems induced in, and previously thought to be critical for, cardiac functioning in heart failure are now pharmaceutically interrupted as modern standard of care. And, mitochondrial abnormalities in neuropathies that were originally attributed to an imbalance between mitochondrial fusion and fission are increasingly recognized as an interruption of axonal mitochondrial transport. The data are presented in a historical context to provided insight into how scientific thought has evolved and to foster an appreciation for how seemingly different areas of investigation can converge. Finally, some theoretical notions are presented to explain how different molecular and functional defects can evoke tissue-specific disease.

Keywords:  angiotensin; cardiomyopathy; epinephrine; mitofusin; neuropathy

DOI:  https://doi.org/10.1152/ajpcell.00167.2022
Nat Metab. 2022 Jun;4(6): 739-758

Impaired oxygen-sensitive regulation of mitochondrial biogenesis within the von Hippel-Lindau syndrome.

Shuijie Li, Wenyu Li, Juan Yuan, Petra Bullova, Jieyu Wu, Xuepei Zhang, Yong Liu, Monika Plescher, Javier Rodriguez, Oscar C Bedoya-Reina, Paulo R Jannig, Paula Valente-Silva, Meng Yu, Marie Arsenian Henriksson, Roman A Zubarev, Anna Smed-Sörensen, Carolyn K Suzuki, Jorge L Ruas, Johan Holmberg, Catharina Larsson, C Christofer Juhlin, Alex von Kriegsheim, Yihai Cao, Susanne Schlisio.

Mitochondria are the main consumers of oxygen within the cell. How mitochondria sense oxygen levels remains unknown. Here we show an oxygen-sensitive regulation of TFAM, an activator of mitochondrial transcription and replication, whose alteration is linked to tumours arising in the von Hippel-Lindau syndrome. TFAM is hydroxylated by EGLN3 and subsequently bound by the von Hippel-Lindau tumour-suppressor protein, which stabilizes TFAM by preventing mitochondrial proteolysis. Cells lacking wild-type VHL or in which EGLN3 is inactivated have reduced mitochondrial mass. Tumorigenic VHL variants leading to different clinical manifestations fail to bind hydroxylated TFAM. In contrast, cells harbouring the Chuvash polycythaemia VHLR200W mutation, involved in hypoxia-sensing disorders without tumour development, are capable of binding hydroxylated TFAM. Accordingly, VHL-related tumours, such as pheochromocytoma and renal cell carcinoma cells, display low mitochondrial content, suggesting that impaired mitochondrial biogenesis is linked to VHL tumorigenesis. Finally, inhibiting proteolysis by targeting LONP1 increases mitochondrial content in VHL-deficient cells and sensitizes therapy-resistant tumours to sorafenib treatment. Our results offer pharmacological avenues to sensitize therapy-resistant VHL tumours by focusing on the mitochondria.

DOI: https://doi.org/10.1038/s42255-022-00593-x
J Cell Physiol. 2022 Jul 01.

Mitohormesis and mitochondrial dynamics in the regulation of stem cell fate.

Abolfazl Barzegari, Sobhan Aaboulhassanzadeh, Rebecca Landon, Virginie Gueguen, Anne Meddahi-Pellé, Sepideh Parvizpour, Fani Anagnostou, Graciela Pavon-Djavid.

  The ability of stem cells for self-renewing, differentiation, and regeneration of injured tissues is believed to occur via the hormetic modulation of nuclear/mitochondrial signal transductions. The evidence now indicates that in damaged tissues, the mitochondria set off the alarm under oxidative stress conditions, hence they are the central regulators of stem cell fate decisions. This review aimed to provide an update to a broader concept of stem cell fate in stress conditions of damaged tissues, and insights for the mitochondrial hormesis (mitohormesis), including the integrated stress response (ISR), mitochondrial dynamics, mitochondria uncoupling, unfolded protein response, and mitokines, with implications for the control of stem cells programing in a successful clinical cell therapy.

Keywords:  hypoxia; integrated stress response; mitohormesis; mitokines; oxidative stress; stem cell

DOI:  https://doi.org/10.1002/jcp.30820
Sci Rep. 2022 Jul 01. 12(1): 9727

Dynamics and stabilization mechanism of mitochondrial cristae morphofunction associated with turgor-driven cardiolipin biosynthesis under salt stress conditions.

Keisuke Nakata, Yuto Hatakeyama, Rosa Erra-Balsells, Hiroshi Nonami, Hiroshi Wada.

Maintaining energy production efficiency is of vital importance to plants growing under changing environments. Cardiolipin localized in the inner mitochondrial membrane plays various important roles in mitochondrial function and its activity, although the regulation of mitochondrial morphology to various stress conditions remains obscure, particularly in the context of changes in cellular water relations and metabolisms. By combining single-cell metabolomics with transmission electron microscopy, we have investigated the adaptation mechanism in tomato trichome stalk cells at moderate salt stress to determine the kinetics of cellular parameters and metabolisms. We have found that turgor loss occurred just after the stress conditions, followed by the contrasting volumetric changes in mitochondria and cells, the accumulation of TCA cycle-related metabolites at osmotic adjustment, and a temporal increase in cardiolipin concentration, resulting in a reversible topological modification in the tubulo-vesicular cristae. Because all of these cellular events were dynamically observed in the same single-cells without causing any disturbance for redox states and cytoplasmic streaming, we conclude that turgor pressure might play a regulatory role in the mitochondrial morphological switch throughout the temporal activation of cardiolipin biosynthesis, which sustains mitochondrial respiration and energy conversion even under the salt stress conditions.

DOI: https://doi.org/10.1038/s41598-022-14164-3
Mol Cell. 2022 Jun 16. pii: S1097-2765(22)00540-8. [Epub ahead of print]

Mitochondrial protein import stress regulates the LC3 lipidation step of mitophagy through NLRX1 and RRBP1.

Samuel A Killackey, Yuntian Bi, Fraser Soares, Ikram Hammi, Nathaniel J Winsor, Ali A Abdul-Sater, Dana J Philpott, Damien Arnoult, Stephen E Girardin.

  Protein import into mitochondria is a highly regulated process, yet how cells clear mitochondria undergoing dysfunctional protein import remains poorly characterized. Here we showed that mitochondrial protein import stress (MPIS) triggers localized LC3 lipidation. This arm of the mitophagy pathway occurs through the Nod-like receptor (NLR) protein NLRX1 while, surprisingly, without the engagement of the canonical mitophagy protein PINK1. Mitochondrial depolarization, which itself induces MPIS, also required NLRX1 for LC3 lipidation. While normally targeted to the mitochondrial matrix, cytosol-retained NLRX1 recruited RRBP1, a ribosome-binding transmembrane protein of the endoplasmic reticulum, which relocated to the mitochondrial vicinity during MPIS, and the NLRX1/RRBP1 complex in turn controlled the recruitment and lipidation of LC3. Furthermore, NLRX1 controlled skeletal muscle mitophagy in vivo and regulated endurance capacity during exercise. Thus, localization and lipidation of LC3 at the site of mitophagosome formation is a regulated step of mitophagy controlled by NLRX1/RRBP1 in response to MPIS.

Keywords:  NLRX1; Nod-like receptors; mitochondria; mitochondrial protein import; mitophagy

DOI:  https://doi.org/10.1016/j.molcel.2022.06.004
Front Mol Biosci. 2022 ;9 908721

Mitochondria-Associated Membrane Scaffolding with Endoplasmic Reticulum: A Dynamic Pathway of Developmental Disease.

Russell P Saneto, Francisco A Perez.

  Communication between intracellular organelles is essential for overall cellular function. How this communication occurs and under what circumstances alterations transpire are only the beginning to be elucidated. The pathways of calcium homeostasis, lipid transfer, mitochondrial dynamics, and mitophagy/apoptosis have been linked to the endoplasmic reticulum and tethering sites on the outer and/or inner mitochondrial membrane called mitochondria-associated endoplasmic reticulum membranes (MAM). Sensitive visualization by high-powered microscopy coupled with the advent of massive parallel sequencing has elaborated the structure, while patient's diseases have uncovered the physiological function of these networks. Using specific patient examples from our pediatric mitochondrial center, we expand how specific genetic pathological variants in certain MAM structures induce disease. Genetic variants in MICU1, PASC-2, CYP2U1, SERAC1, and TANGO2 can induce early development abnormalities in the areas of cognition, motor, and central nervous system structures across multiple MAM pathways and implicate mitochondrial dysregulation.

Keywords:  autophagy; calcium; fatty acid metabolism; gene products; metabolism; mitochondria-associated endoplasmic reticulum membrane; phospholipids

DOI:  https://doi.org/10.3389/fmolb.2022.908721
Front Aging Neurosci. 2022 ;14 893159

Coenzyme A-Dependent Tricarboxylic Acid Cycle Enzymes Are Decreased in Alzheimer's Disease Consistent With Cerebral Pantothenate Deficiency.

Crystal Sang, Sasha A Philbert, Danielle Hartland, Richard D Unwin, Andrew W Dowsey, Jingshu Xu, Garth J S Cooper.

  Sporadic Alzheimer's disease (sAD) is the commonest cause of age-related neurodegeneration and dementia globally, and a leading cause of premature disability and death. To date, the quest for a disease-modifying therapy for sAD has failed, probably reflecting our incomplete understanding of aetiology and pathogenesis. Drugs that target aggregated Aβ/tau are ineffective, and metabolic defects are now considered to play substantive roles in sAD pathobiology. We tested the hypothesis that the recently identified, pervasive cerebral deficiency of pantothenate (vitamin B5) in sAD, might undermine brain energy metabolism by impairing levels of tricarboxylic acid (TCA)-cycle enzymes and enzyme complexes, some of which require the pantothenate-derived cofactor, coenzyme A (CoA) for their normal functioning. We applied proteomics to measure levels of the multi-subunit TCA-cycle enzymes and their cytoplasmic homologues. We analysed six functionally distinct brain regions from nine sAD cases and nine controls, measuring 33 cerebral proteins that comprise the nine enzymes of the mitochondrial-TCA cycle. Remarkably, we found widespread perturbations affecting only two multi-subunit enzymes and two enzyme complexes, whose function is modulated, directly or indirectly by CoA: pyruvate dehydrogenase complex, isocitrate dehydrogenase, 2-oxoglutarate dehydrogenase complex, and succinyl-CoA synthetase. The sAD cases we studied here displayed widespread deficiency of pantothenate, the obligatory precursor of CoA. Therefore, deficient cerebral pantothenate can damage brain-energy metabolism in sAD, at least in part through impairing levels of these four mitochondrial-TCA-cycle enzymes.

Keywords:  coenzyme A (CoA); human brain; pantothenic acid/vitamin B5; pyruvate dehydrogenase complex; sporadic Alzheimer’s disease; tricarboxylic acid cycle (TCA cycle)

DOI:  https://doi.org/10.3389/fnagi.2022.893159
Nat Commun. 2022 Jun 28. 13(1): 3702

Structural basis for mitoguardin-2 mediated lipid transport at ER-mitochondrial membrane contact sites.

Hyunwoo Kim, Seowhang Lee, Youngsoo Jun, Changwook Lee.

The endoplasmic reticulum (ER)-mitochondria contact site (ERMCS) is crucial for exchanging biological molecules such as phospholipids and Ca2+ ions between these organelles. Mitoguardin-2 (MIGA2), a mitochondrial outer membrane protein, forms the ERMCS in higher eukaryotic cells. Here, we report the crystal structures of the MIGA2 Lipid Droplet (LD) targeting domain and the ER membrane protein VAPB bound to the phosphorylated FFAT motif of MIGA2. These structures reveal that the MIGA2 LD targeting domain has a large internal hydrophobic pocket that accommodates phospholipids and that two phosphorylations of the FFAT motif are required for tight interaction of MIGA2 with VAPB, which enhances the rate of lipid transport. Further biochemical studies show that MIGA2 transports phospholipids between membranes with a strong preference for binding and trafficking phosphatidylserine (PS). These results provide a structural and molecular basis for understanding how MIGA2 mediates the formation of ERMCS and facilitates lipid trafficking at the ERMCS.

DOI: https://doi.org/10.1038/s41467-022-31462-6
Methods Mol Biol. 2022 ;2497 185-206

Measurements of Mitochondrial Respiration in Intact Cells, Permeabilized Cells, and Isolated Tissue Mitochondria Using the Seahorse XF Analyzer.

Jessica Pfleger.

  Energy homeostasis is critical for cellular function. Significant increases in energy demand or reduced energy supply, however, often result in cellular dysfunction and death. Since mitochondria are the primary cellular energy source, their impairment is often pathogenic. Accordingly, quantitative measurements of cellular and mitochondrial energy utilization and production are crucial for understanding disease development and progression. In the final step of cellular respiration, specifically, oxidative phosphorylation within the mitochondria, oxygen is consumed and drives ATP production. Herein, we provide the complete protocols for measuring oxygen consumption rates and their coupling to ATP production in intact and permeabilized cells, as well as in mitochondria isolated from tissue using the Seahorse XF Extracellular Flux Analyzer (Agilent Technologies).

Keywords:  Bioenergetics; Cellular respiration; Mitochondrial respiration; Permeabilized cells; Seahorse XF Extracellular Flux Analyzer

DOI:  https://doi.org/10.1007/978-1-0716-2309-1_12
J Pharmacol Exp Ther. 2022 Jun 28. pii: JPET-AR-2022-001250. [Epub ahead of print]

Mitochondrial microRNAs are dysregulated in patients with Fabry Disease.

Jessica Gambardella, Antonella Fiordelisi, Daniela Sorriento, Federica Cerasuolo, Antonietta Buonaiuto, Roberta Avvisato, Antonio Pisani, Fahimeh Varzideh, Eleonora Riccio, Gaetano Santulli, Guido Iaccarino.

  Fabry disease (FD) is a lysosomal storage disorder caused by mutations in the gene for alpha- galactosidase A (GAL) inducing a progressive accumulation of globotriaosylceramide (Gb3) and its metabolites in different organs and tissues. GB3 deposition does not fully explain the clinical manifestations of FD, and other pathogenetic mechanisms have been proposed requiring the identification of new biomarkers for monitoring FD patients. Previous evidence suggests the involvement of mitochondrial alterations in FD. Here, we propose mitochondrial related microRNA (miRNAs, miRs) as potential biomarkers of mitochondrial involvement in FD. We observed that miRNAs regulating different aspects of mitochondrial homeostasis including expression and assembly of respiratory chain, mitogenesis, antioxidant capacity, and apoptosis are consistently dysregulated in FD patients. Our data unveil a novel non-coding RNA signature of FD patients, indicating mitochondrial related miRNAs (mitomiRs) as new potential pathogenic players and biomarkers in FD. Significance StatementWe demonstrate for the first time that a specific signature of circulating mitochondrial microRNAs (mitomiRs) are dysregulated in Fabry disease (FD). In our study, we observed that mitomiRs regulating fundamental aspects of mitochondrial homeostasis, including expression and assembly of the respiratory chain, mitogenesis, antioxidant capacity, and apoptosis are significantly dysregulated in FD patients. Taken together, our new findings introduce mitomiRs as unprecedented biomarkers of FD and point at mitochondrial dysfunction as a novel potential mechanistic target for therapeutic approaches.

Keywords:  cardiovascular disease; miRNA; mitochondria

DOI:  https://doi.org/10.1124/jpet.122.001250
Nat Commun. 2022 Jul 01. 13(1): 3794

DDX1 vesicles control calcium-dependent mitochondrial activity in mouse embryos.

Yixiong Wang, Lubna Yasmin, Lei Li, Pinzhang Gao, Xia Xu, Xuejun Sun, Roseline Godbout.

The DEAD box protein DDX1, previously associated with 3'-end RNA processing and DNA repair, forms large aggregates in the cytoplasm of early mouse embryos. Ddx1 knockout causes stalling of embryos at the 2-4 cell stages. Here, we identify a DDX1-containing membrane-bound calcium-containing organelle with a nucleic acid core. We show that aggregates of these organelles form ring-like structures in early-stage embryos which we have named Membrane Associated RNA-containing Vesicles. We present evidence that DDX1 is required for the formation of Membrane Associated RNA-containing Vesicles which in turn regulate the spatial distribution of calcium in embryos. We find that Ddx1 knockout in early embryos disrupts calcium distribution, and increases mitochondria membrane potential, mitochondrial activity, and reactive oxygen species. Sequencing analysis of embryos from Ddx1 heterozygote crosses reveals downregulation of a subset of RNAs involved in developmental and mitochondrial processes in the embryos with low Ddx1 RNA. We propose a role for Membrane Associated RNA-containing Vesicles in calcium-controlled mitochondrial functions that are essential for embryonic development.

DOI: https://doi.org/10.1038/s41467-022-31497-9