bims-nenemi 2024-12-29 papers

bims-nenemi

Biomed News

on Neuroinflammation, neurodegeneration and mitochondria

Issue of 2024–12–29
sixteen papers selected by
Marco Tigano, Thomas Jefferson University

Preventing excessive autophagy protects from the pathology of mtDNA mutations in Drosophila melanogaster.
The N-degron pathway mediates the autophagic degradation of cytosolic mitochondrial DNA during sterile innate immune responses.
Functionally conserved inner mitochondrial membrane proteins CCDC51 and Mdm33 demarcate a subset of fission events.
RNA sensing induced by chromosome missegregation augments anti-tumor immunity.
A transcription network underlies the dual genomic coordination of mitochondrial biogenesis.
Targeting mitochondrial RNAs enhances the efficacy of the DNA-demethylating agents.
RNA-binding proteins hnRNPM and ELAVL1 promote type-I interferon induction downstream of the nucleic acid sensors cGAS and RIG-I.
Deafness-associated mitochondrial 12S rRNA mutation reshapes mitochondrial and cellular homeostasis.
Ailanthone blocks mitophagy to promote mtDNA leakage through BAX-BAK1 pores and suppress hepatocellular carcinoma cell proliferation.
The Vsr-like protein FASTKD4 regulates the stability and polyadenylation of the MT-ND3 mRNA.
Nuclear respiratory factor-1 (NRF1) induction as a powerful strategy to deter mitochondrial dysfunction and senescence in mesenchymal stem cells.
SLP2 and MIC13 synergistically coordinate MICOS assembly and crista junction formation.
Melatonin Reduces Mito-Inflammation in Ischaemic Hippocampal HT22 Cells and Modulates the cGAS-STING Cytosolic DNA Sensing Pathway and FGF21 Release.
Pressure to evade cell-autonomous innate sensing reveals interplay between mitophagy, IFN signaling, and SARS-CoV-2 evolution.
OPA3 inhibits the cGAS-STING pathway mediated by mtDNA stress to promote colorectal cancer progression.
Extracellular Mitochondria Exacerbate Retinal Pigment Epithelium Degeneration in Diabetic Retinopathy.

Nat Commun. 2024 Dec 23. 15(1): 10719

Preventing excessive autophagy protects from the pathology of mtDNA mutations in Drosophila melanogaster.

Najla El Fissi, Florian A Rosenberger, Kai Chang, Alissa Wilhalm, Tom Barton-Owen, Fynn M Hansen, Zoe Golder, David Alsina, Anna Wedell, Matthias Mann, Patrick F Chinnery, Christoph Freyer, Anna Wredenberg.

Aberration of mitochondrial function is a shared feature of many human pathologies, characterised by changes in metabolic flux, cellular energetics, morphology, composition, and dynamics of the mitochondrial network. While some of these changes serve as compensatory mechanisms to maintain cellular homeostasis, their chronic activation can permanently affect cellular metabolism and signalling, ultimately impairing cell function. Here, we use a Drosophila melanogaster model expressing a proofreading-deficient mtDNA polymerase (POLγexo-) in a genetic screen to find genes that mitigate the harmful accumulation of mtDNA mutations. We identify critical pathways associated with nutrient sensing, insulin signalling, mitochondrial protein import, and autophagy that can rescue the lethal phenotype of the POLγexo- flies. Rescued flies, hemizygous for dilp1, atg2, tim14 or melted, normalise their autophagic flux and proteasome function and adapt their metabolism. Mutation frequencies remain high with the exception of melted-rescued flies, suggesting that melted may act early in development. Treating POLγexo- larvae with the autophagy activator rapamycin aggravates their lethal phenotype, highlighting that excessive autophagy can significantly contribute to the pathophysiology of mitochondrial diseases. Moreover, we show that the nucleation process of autophagy is a critical target for intervention.

DOI: https://doi.org/10.1038/s41467-024-55559-2
Cell Rep. 2024 Dec 21. pii: S2211-1247(24)01445-1. [Epub ahead of print]44(1): 115094

The N-degron pathway mediates the autophagic degradation of cytosolic mitochondrial DNA during sterile innate immune responses.

Chan Hoon Jung, Yoon Jee Lee, Eun Hye Cho, Gee Eun Lee, Sung Tae Kim, Ki Sa Sung, Daeho Kim, Dong Hyun Kim, Yeon Sung Son, Jin-Hyun Ahn, Dohyun Han, Yong Tae Kwon.

  The human body reacts to tissue damage by generating damage-associated molecular patterns (DAMPs) that activate sterile immune responses. To date, little is known about how DAMPs are removed to avoid excessive immune responses. Here, we show that proteasomal dysfunction induces the release of mitochondrial DNA (mtDNA) as a DAMP that activates the cyclic GMP-AMP synthase (cGAS)-stimulator of interferon gene (STING) pathway and is subsequently degraded through the N-degron pathway. In the resolution phase of sterile immune responses, DNA-dependent protein kinase (DNA-PK) senses cytosolic mtDNA and activates N-terminal (Nt-) arginylation by ATE1 R-transferases. The substrates of Nt-arginylation include the molecular chaperone BiP/GRP78 retrotranslocated from the endoplasmic reticulum (ER). R-BiP, the Nt-arginylated species of BiP, is associated with cytosolic mtDNA to accelerate its targeting to autophagic membranes for lysosomal degradation. Thus, cytosolic mtDNA activates the N-degron pathway to facilitate its own degradation and form a negative feedback loop, by which the cell can turn off sterile immune responses at the right time.

Keywords:  ATE1; CP: Immunology; DNA-PK; KU70; R-BiP; autophagy; mitochondrial DNA; proteasomal dysfunction; sterile immune response; the N-degron pathway; type I interferon

DOI:  https://doi.org/10.1016/j.celrep.2024.115094
J Cell Biol. 2025 Mar 03. pii: e202403140. [Epub ahead of print]224(3):

Functionally conserved inner mitochondrial membrane proteins CCDC51 and Mdm33 demarcate a subset of fission events.

Alia R Edington, Olivia M Connor, Abigail C Love, Madeleine Marlar-Pavey, Jonathan R Friedman.

While extensive work has examined the mechanisms of mitochondrial fission, it remains unclear whether internal mitochondrial proteins in metazoans play a direct role in the process. Previously, the yeast inner membrane protein Mdm33 was shown to be required for normal mitochondrial morphology and has been hypothesized to be involved in mitochondrial fission. However, it is unknown whether Mdm33 plays a direct role, and it is not thought to have a mammalian homolog. Here, we use a bioinformatic approach to identify a structural ortholog of Mdm33 in humans, CCDC51 (also called MITOK), whose depletion phenocopies loss of Mdm33. We find that knockdown of CCDC51 also leads to reduced rates of mitochondrial fission. Further, we spatially and temporally resolve Mdm33 and CCDC51 to a subset of mitochondrial fission events. Finally, we show that CCDC51 overexpression promotes its spatial association with Drp1 and induces mitochondrial fragmentation, suggesting it is a positive effector of mitochondrial fission. Together, our data reveal that Mdm33 and CCDC51 are functionally conserved and suggest that internal mitochondrial proteins are directly involved in at least a subset of mitochondrial fission events in human cells.

DOI: https://doi.org/10.1083/jcb.202403140
Mol Cell. 2024 Dec 10. pii: S1097-2765(24)00950-X. [Epub ahead of print]

RNA sensing induced by chromosome missegregation augments anti-tumor immunity.

Nobunari Sasaki, Mizuki Homme, Takahiko Murayama, Tatsuya Osaki, Toshiyuki Tenma, Tadaichi An, Yujiro Takegami, Tetsuo Tani, Patrick C Gedeon, Yoshihisa Kobayashi, Israel Cañadas, David A Barbie, Ryoji Yao, Shunsuke Kitajima.

  Viral mimicry driven by endogenous double-stranded RNA (dsRNA) stimulates innate and adaptive immune responses. However, the mechanisms that regulate dsRNA-forming transcripts during cancer therapy remain unclear. Here, we demonstrate that dsRNA is significantly accumulated in cancer cells following pharmacologic induction of micronuclei, stimulating mitochondrial antiviral signaling (MAVS)-mediated dsRNA sensing in conjunction with the cyclic GMP-AMP synthase (cGAS)/stimulator of interferon genes (STING) pathway. Activation of cytosolic dsRNA sensing cooperates with double-stranded DNA (dsDNA) sensing to upregulate immune cell migration and antigen-presenting machinery. Tracing of dsRNA-sequences reveals that dsRNA-forming transcripts are predominantly generated from non-exonic regions, particularly in locations proximal to genes exhibiting high chromatin accessibility. Activation of this pathway by pulsed monopolar spindle 1 (MPS1) inhibitor treatment, which potently induces micronuclei formation, upregulates cytoplasmic dsRNA sensing and thus promotes anti-tumor immunity mediated by cytotoxic lymphocyte activation in vivo. Collectively, our findings uncover a mechanism in which dsRNA sensing cooperates with dsDNA sensing to boost immune responses, offering an approach to enhance the efficacy of cancer therapies targeting genomic instability.

Keywords:  MAVS; Mps1; STING; cGAS; chromosome missegregation; dsRNA; micronuclei; tumor immunity; type I interferon

DOI:  https://doi.org/10.1016/j.molcel.2024.11.025
Elife. 2024 Dec 27. pii: RP96536. [Epub ahead of print]13

A transcription network underlies the dual genomic coordination of mitochondrial biogenesis.

Fan Zhang, Annie Lee, Anna V Freitas, Jake T Herb, Zong-Heng Wang, Snigdha Gupta, Zhe Chen, Hong Xu.

  Mitochondrial biogenesis requires the expression of genes encoded by both the nuclear and mitochondrial genomes. However, aside from a handful transcription factors regulating specific subsets of mitochondrial genes, the overall architecture of the transcriptional control of mitochondrial biogenesis remains to be elucidated. The mechanisms coordinating these two genomes are largely unknown. We performed a targeted RNAi screen in developing eyes with reduced mitochondrial DNA content, anticipating a synergistic disruption of tissue development due to impaired mitochondrial biogenesis and mitochondrial DNA (mtDNA) deficiency. Among 638 transcription factors annotated in the Drosophila genome, 77 were identified as potential regulators of mitochondrial biogenesis. Utilizing published ChIP-seq data of positive hits, we constructed a regulatory network revealing the logic of the transcription regulation of mitochondrial biogenesis. Multiple transcription factors in core layers had extensive connections, collectively governing the expression of nearly all mitochondrial genes, whereas factors sitting on the top layer may respond to cellular cues to modulate mitochondrial biogenesis through the underlying network. CG1603, a core component of the network, was found to be indispensable for the expression of most nuclear mitochondrial genes, including those required for mtDNA maintenance and gene expression, thus coordinating nuclear genome and mtDNA activities in mitochondrial biogenesis. Additional genetic analyses validated YL-1, a transcription factor upstream of CG1603 in the network, as a regulator controlling CG1603 expression and mitochondrial biogenesis.

Keywords:  ChIP-seq; D. melanogaster; RNA-seq; SDHA; TFAM; genetics; genomics; mitochondrial biogenesis; transcription factors

DOI:  https://doi.org/10.7554/eLife.96536
Sci Rep. 2024 Dec 28. 14(1): 30767

Targeting mitochondrial RNAs enhances the efficacy of the DNA-demethylating agents.

Stephanie Tan, Sujin Kim, Yoosik Kim.

  Hypomethylating agents (HMAs) such as azacytidine and decitabine are FDA-approved chemotherapy drugs for hematologic malignancy. By inhibiting DNA methyltransferases, HMAs reactivate tumor suppressor genes (TSGs) and endogenous double-stranded RNAs (dsRNAs) that limit tumor growth and trigger apoptosis via viral mimicry. Yet, HMAs show limited effects in many solid tumors despite the strong induction of TSGs and dsRNAs. Here we show that targeting mitochondrial RNAs (mtRNAs) can enhance the HMA-mediated cell death in lung adenocarcinoma cells. We find that HMA treatment accompanies increased mtRNA levels and subsequent enhancement of metabolic activity, resulting in higher ATP production. Compromising the mitochondrial function by downregulating mature mtRNA expression increased cell death by HMAs. We further perform a CRISPR screening on mtRNA processing factors and find that mtRNA polymerase (POLRMT) and ElaC Ribonuclease Z 2 (ELAC2) depleted cells show increased sensitivity to HMAs by suppressing decitabine-triggered enhancement of ATP production. Moreover, we show that a small molecular inhibitor of POLRMT compromises the metabolic activity and synergistically enhances the cytotoxicity of HMAs. Our study unveils the insensitivity to HMAs through the elevation of mtRNAs and suggests mtRNA regulatory factors as potential synergistic targets to improve the therapeutic benefit of HMAs.

Keywords:  Decitabine; Drug response; Hypomethylating agents; Mitochondrial RNA; RNA processing

DOI:  https://doi.org/10.1038/s41598-024-80834-z
EMBO J. 2024 Dec 20.

RNA-binding proteins hnRNPM and ELAVL1 promote type-I interferon induction downstream of the nucleic acid sensors cGAS and RIG-I.

Alexander Kirchhoff, Anna-Maria Herzner, Christian Urban, Antonio Piras, Robert Düster, Julia Mahlberg, Agathe Grünewald, Thais M Schlee-Guimarães, Katrin Ciupka, Petro Leka, Robert J Bootz, Christina Wallerath, Charlotte Hunkler, Ann Kristin de Regt, Beate M Kümmerer, Maria Hønholt Christensen, Florian I Schmidt, Min Ae Lee-Kirsch, Claudia Günther, Hiroki Kato, Eva Bartok, Gunther Hartmann, Matthias Geyer, Andreas Pichlmair, Martin Schlee.

  The cytosolic nucleic acid sensors RIG-I and cGAS induce type-I interferon (IFN)-mediated immune responses to RNA and DNA viruses, respectively. So far no connection between the two cytosolic pathways upstream of IKK-like kinase activation has been investigated. Here, we identify heterogeneous nuclear ribonucleoprotein M (hnRNPM) as a positive regulator of IRF3 phosphorylation and type-I IFN induction downstream of both cGAS and RIG-I. Combining interactome analysis with genome editing, we further uncover the RNA-binding protein ELAV-like protein 1 (ELAVL1; also known as human antigen R, HuR) as an hnRNPM interactor. Depletion of hnRNPM or ELAVL1 impairs type-I IFN induction by herpes simplex virus 1 or Sendai virus. In addition, we show that hnRNPM and ELAVL1 interact with TANK-binding kinase 1, IκB kinase ε, IκB kinase β, and NF-κB p65. Our confocal microscopy experiments demonstrate cytosolic and perinuclear interactions between hnRNPM, ELAVL1, and TBK1. Furthermore, pharmacological inhibition of ELAVL1 strongly reduces cytokine release from type-I interferonopathy patient fibroblasts. The RNA-binding proteins hnRNPM and ELAVL1 are the first non-redundant regulators to bridge the cGAS/STING and RIG-I/MAVS pathways. Overall, our study characterizes the hnRNPM-ELAVL1 complex as a novel system promoting antiviral defense, pointing to a potential therapeutic target to reduce auto-inflammation in patients with type-I interferonopathies.

Keywords:  ELAVL1; IRF3; RIG-I Signaling; cGAS Signaling; hnRNPM

DOI:  https://doi.org/10.1038/s44318-024-00331-x
J Biol Chem. 2024 Dec 21. pii: S0021-9258(24)02626-7. [Epub ahead of print] 108124

Deafness-associated mitochondrial 12S rRNA mutation reshapes mitochondrial and cellular homeostasis.

Yunfan He, Zhining Tang, Gao Zhu, Luhang Cai, Chao Chen, Min-Xin Guan.

Human mitochondrial 12S ribosomal RNA (rRNA) 1555A>G mutation has been associated with aminoglycoside-induced and nonsyndromic deafness in many families worldwide. Our previous investigation revealed that the m.1555A>G mutation impaired mitochondrial translation and oxidative phosphorylation (OXPHOS). However, the mechanisms by which mitochondrial dysfunctions induced by m.1555A>G mutation regulate intracellular signaling for mitochondrial and cellular integrity remain poorly understood. Here, we demonstrated that the m.1555A>G mutation downregulated the expression of nuclear-encoded subunits of complexes I and IV but upregulated the expression of assemble factors for OXPHOS complexes, using cybrids derived from one hearing-impaired Chinese subject bearing the m.1555A>G mutation and from one hearing normal control lacking the mutation. These alterations resulted in the aberrant assembly, instability and reduced activities of respiratory chain enzyme complexes I, IV and V, rate of oxygen consumption, and diminished ATP production. Furthermore, the mutant cell lines carrying the m.1555A>G mutation exhibited decreased membrane potential and increased the production of reactive oxygen species. The aberrant assembly and biogenesis of OXPHOS impacted mitochondrial quality controls, including the imbalance of mitochondrial dynamics via increasing fission with abnormal mitochondrial morphology and impaired mitophagy. Strikingly, the cells bearing the m.1555A>G mutation revealed the upregulation of both ubiquitin-dependent and independent mitophagy pathways, evidenced by increasing the levels of Parkin, Pink, BNIP3L and NIX. The m.1555A>G mutation-induced deficiencies ameliorate the cell homeostasis via elevating the autophagy process and upregulating apoptotic pathways. Our findings provide new insights into pathophysiology of mitochondrial deafness arising from reshaping mitochondrial and cellular homeostasis due to 12S rRNA 1555A>G mutation.

DOI: https://doi.org/10.1016/j.jbc.2024.108124
Front Pharmacol. 2024 ;15 1509482

Ailanthone blocks mitophagy to promote mtDNA leakage through BAX-BAK1 pores and suppress hepatocellular carcinoma cell proliferation.

Yan Qin, Ying Gao, Dan Wu, Qing-Qing Liu, Chang Su, Guan Liu, Le Yang, Ming-Gao Zhao, Jing-Yue Yao.

   Introduction: Hepatocellular carcinoma (HCC), the third leading cancer mortality worldwide, shows rising incidence. The mitochondria in HCC cells are prone to damage from metabolic stress and oxidative stress, necessitating heightened mitophagy for mitochondrial homeostasis and cell survival. Thus, mitophagy inhibition is a promising HCC therapy. The traditional Chinese medicinal herb ailanthone have proved promote mitochondrial dysfunction and inhibits HCC. However, the underlying mechanism remains unclear.
Methods: CCK8 assay was applied to detect the proliferation. JC-1, MitoTracker Red/Green and MitoSOX staining were applied to detect the mitochondrial homeostasis. Inflammatory factors were analysed via ELISA and WB assay. Mitochondria and cytoplasm separation, genome extraction and qPCR were used to detect mitochondrial DNA (mtDNA) leakage. Mitochondria ultrastructure was detected by transmission electron microscopy. WB and IHC experiments were applied to detect protein expression. Protein-protein interactions detected by immunoprecipitation and immunofluorescence imaging. The in vivo antitumor effect was validated by the xenograft mouse model.
Results: In this study, we demonstrated the potent anti-HCC properties of ailanthone and revealed its molecular mechanism. In vitro studies demonstrated that ailanthone effectively inhibited PINK1-PRKN mediated mitophagy and promoted BAX-BAK1 mitochondrial pores formation through PRKN inhibition. This process led to the mitochondrial mtDNA leakage into the cytoplasm, which subsequently triggered the induction of inflammatory factors. The inhibition of mitophagy and the activation of inflammatory response ultimately led to HCC proliferation inhibition. In vivo studies demonstrated that ailanthone exhibited stronger anti-HCC activity than 5-Fluorouracil (5-FU), with no significant adverse effects on animal body weight or the physiological functions of vital organs.
Conclusion: This study highlighted the efficacy of ailanthone against HCC and elucidated its underlying molecular mechanisms, suggesting the promising therapeutic potential of ailanthone for HCC.

Keywords:  BAX-BAK1; PINK1-PRKN; ailanthone; hepatocellular carcinoma; inflammation; mtDNA

DOI:  https://doi.org/10.3389/fphar.2024.1509482
Nucleic Acids Res. 2024 Dec 27. pii: gkae1261. [Epub ahead of print]

The Vsr-like protein FASTKD4 regulates the stability and polyadenylation of the MT-ND3 mRNA.

Xuan Yang, Maike Stentenbach, Laetitia A Hughes, Stefan J Siira, Kelvin Lau, Michael Hothorn, Jean-Claude Martinou, Oliver Rackham, Aleksandra Filipovska.

Expression of the compact mitochondrial genome is regulated by nuclear encoded, mitochondrially localized RNA-binding proteins (RBPs). RBPs regulate the lifecycles of mitochondrial RNAs from transcription to degradation by mediating RNA processing, maturation, stability and translation. The Fas-activated serine/threonine kinase (FASTK) family of RBPs has been shown to regulate and fine-tune discrete aspects of mitochondrial gene expression. Although the roles of specific targets of FASTK proteins have been elucidated, the molecular mechanisms of FASTK proteins in mitochondrial RNA metabolism remain unclear. Therefore, we resolved the structure of FASTKD4 at atomic level that includes the RAP domain and the two FAST motifs, creating a positively charged cavity resembling that of the very short patch repair endonuclease. Our biochemical studies show that FASTKD4 binds the canonical poly(A) tail of MT-ND3 enabling its maturation and translation. The in vitro role of FASTKD4 is consistent with its loss in cells that results in decreased MT-ND3 polyadenylation, which destabilizes this messenger RNA in mitochondria.

DOI: https://doi.org/10.1093/nar/gkae1261
Aging Cell. 2024 Dec 25. e14446

Nuclear respiratory factor-1 (NRF1) induction as a powerful strategy to deter mitochondrial dysfunction and senescence in mesenchymal stem cells.

Hyunho Lee, Matteo Massaro, Nourhan Abdelfattah, Gherardo Baudo, Haoran Liu, Kyuson Yun, Elvin Blanco.

  Mesenchymal stem cells (MSCs) are promising candidates for regenerative therapies due to their self-renewal and differentiation capabilities. Pathological microenvironments expose MSCs to senescence-inducing factors such as reactive oxygen species (ROS), resulting in MSC functional decline and loss of stemness. Oxidative stress leads to mitochondrial dysfunction, a hallmark of senescence, and is prevalent in aging tissues characterized by elevated ROS levels. We hypothesized that overexpression of nuclear respiratory factor-1 (NRF1), a driver of mitochondrial biogenesis, could metabolically potentiate MSCs and prevent MSC senescence. Single-cell RNA sequencing (scRNA-Seq) revealed that MSCs transfected with NRF1 messenger RNA (mRNA) exhibited upregulated expression of genes associated with oxidative phosphorylation (OXPHOS), decreased glycolytic markers, and suppression of senescence-related pathways. To test whether NRF1 induction could mitigate stress-induced premature senescence, we exposed MSCs to hydrogen peroxide (H2O2) and validated our findings in a replicative senescence model. NRF1 mRNA transfection significantly increased mitochondrial mass and improved aberrant mitochondrial processes associated with senescence, including reduced mitochondrial and intracellular total ROS production. Mitochondrial health and dynamics were preserved, and respiratory function was restored, as evidenced by enhanced OXPHOS, reduced glycolysis, and increased ATP production. Notably, NRF1 overexpression led to decreased senescence-associated β-galactosidase (SA-β-gal) activity and reduced expression of senescence markers p53, p21, and p16. Our findings demonstrate that NRF1 induction attenuates MSC senescence by enhancing mitochondrial function, suggesting potential translational applications for MSC-based therapies and senescence-targeted interventions.

Keywords:  mesenchymal stem cells; mitochondrial biogenesis; mitochondrial dysfunction; nuclear respiratory factor‐1 (NRF1); oxidative stress; senescence

DOI:  https://doi.org/10.1111/acel.14446
iScience. 2024 Dec 20. 27(12): 111467

SLP2 and MIC13 synergistically coordinate MICOS assembly and crista junction formation.

Ritam Naha, Rebecca Strohm, Yulia Schaumkessel, Jennifer Urbach, Ilka Wittig, Andreas S Reichert, Arun Kumar Kondadi, Ruchika Anand.

  The MICOS complex, essential for cristae organization, comprises MIC10 and MIC60 subcomplexes, with MIC13 as a crucial subunit. MIC13 mutations cause severe mitochondrial hepato-encephalopathy, cristae defects, and MIC10-subcomplex loss. We demonstrate that depletion of the mitochondrial protease YME1L in MIC13 KO stabilizes MIC10-subcomplex, restoring MIC60-MIC10 interaction and crista junction (CJ) defects, indicating MIC13 is crucial for MIC10-subcomplex stabilization rather than MIC60-MIC10 bridging. We identified stomatin-like protein 2 (SLP2) as a key MIC13 interaction partner, essential for cristae morphology and CJ formation. SLP2 serves as an interaction hub for MICOS subunits and stabilizes MIC26 by protecting it from YME1L-mediated degradation. Deleting both SLP2 and MIC13 impairs MIC60-subcomplex assembly and its nanoscale organization. Restoring the MIC10-subcomplex in MIC13-SLP2 double KO cells through YME1L depletion reinstates MIC60-subcomplex assembly and cristae morphology. Overall, we propose SLP2 and the MIC10-subcomplex act as a proteolytically controlled 'seeder' complex, facilitating MICOS-MIB complex assembly and maintaining mitochondrial integrity.

Keywords:  Cell biology; Molecular biology

DOI:  https://doi.org/10.1016/j.isci.2024.111467
J Cell Mol Med. 2024 Dec;28(24): e70285

Melatonin Reduces Mito-Inflammation in Ischaemic Hippocampal HT22 Cells and Modulates the cGAS-STING Cytosolic DNA Sensing Pathway and FGF21 Release.

Silvia Carloni, Maria Gemma Nasoni, Anna Casabianca, Chiara Orlandi, Loredana Capobianco, Giorgia Natalia Iaconisi, Liana Cerioni, Sabrina Burattini, Serena Benedetti, Russel J Reiter, Walter Balduini, Francesca Luchetti.

  Mitochondrial dysfunction is a key event in many pathological conditions, including neurodegenerative processes. When mitochondria are damaged, they release damage-associated molecular patterns (DAMPs) that activate mito-inflammation. The present study assessed mito-inflammation after in vitro oxygen-glucose deprivation as a representation of ischaemia, followed by reoxygenation (OGD/R) of HT22 cells and modulation of the inflammatory response by melatonin. We observed that melatonin prevented mitochondrial structural damage and dysfunction caused by OGD/R. Melatonin reduced oxidative damage and preserved the enzymatic activity for complexes I, III and IV, encoded by mitochondrial DNA, which were reduced by OGD/R. No effect was observed on complex II activity encoded by nuclear DNA. The release of mtDNA into the cytosol was also prevented with a consequent reduction of the cGAS-STING pathway and IFNβ and IL-6 production. Interestingly, melatonin also increased the early release of the fibroblast growth factor-21 (FGF-21), a mitokine secreted in response to mitochondrial stress. These data indicate that melatonin reduces mito-inflammation and modulates FGF-21 release, further highlighting the key role of this molecule in preserving mitochondrial integrity in OGD/R deprivation-type ischaemic brain injury.

Keywords:  FGF‐21; HT22; melatonin; mito‐inflammation; mtDNA; oxygen–glucose deprivation

DOI:  https://doi.org/10.1111/jcmm.70285
Cell Rep. 2024 Dec 20. pii: S2211-1247(24)01466-9. [Epub ahead of print]44(1): 115115

Pressure to evade cell-autonomous innate sensing reveals interplay between mitophagy, IFN signaling, and SARS-CoV-2 evolution.

Jae Seung Lee, Mark Dittmar, Jesse Miller, Minghua Li, Kasirajan Ayyanathan, Max Ferretti, Jesse Hulahan, Kanupriya Whig, Zienab Etwebi, Trevor Griesman, David C Schultz, Sara Cherry.

  SARS-CoV-2 emerged, and continues to evolve, to efficiently infect humans worldwide. SARS-CoV-2 evades early innate recognition, interferon signaling occurring only in bystander cells. How the virus continues to evolve in the face of innate responses has important consequences, but the pathways involved are incompletely understood. Here, we find that autophagy genes regulate innate immune signaling, impacting the basal set point of interferons and, thus, permissivity to infection. Mechanistically, autophagy (mitophagy) genes negatively regulate MAVS, and this low basal level of MAVS is efficiently antagonized by SARS-CoV-2 ORF9b, blocking interferon activation in infected cells. However, loss of autophagy increased MAVS and overcomes ORF9b-mediated antagonism. This has driven the evolution of SARS-CoV-2 to express more ORF9b, allowing SARS-CoV-2 to replicate under conditions of increased MAVS signaling. Altogether, we find a critical role of mitophagy in the regulation of innate immunity and uncover an evolutionary trajectory of SARS-CoV-2 ORF9b to overcome host defenses.

Keywords:  CP: Immunology; CP: Microbiology; ORF9b; SARS-CoV-2; autophagy; cell-autonomous interferon response; coronavirus; innate immune signaling; mitophagy; viral evolution

DOI:  https://doi.org/10.1016/j.celrep.2024.115115
In Vitro Cell Dev Biol Anim. 2024 Dec 26.

OPA3 inhibits the cGAS-STING pathway mediated by mtDNA stress to promote colorectal cancer progression.

Yuqiang Yin, Zhenxin Ma, Siwen Yuan, Kangfeng Xu, Xiaofeng Wang.

  Colorectal cancer (CRC) is an extremely harmful malignant tumor. Optic atrophy 3 (OPA3) is highly expressed in multiple tumors, but its action in CRC is still unknown. This research aims to explore the role of OPA3 and its related molecular mechanisms for CRC. Firstly, we overexpressed and knocked down OPA3 to examine its effect on CRC cell (HT29 cell) growth. CRC cell viability, migration, invasion, and levels of proliferation markers and cell cycle-associated proteins were measured. Then, we treated cells with carbonyl cyanide m-chlorophenyl hydrazone (CCCP) to explore mitochondrial dysfunction and mtDNA stress in HT29 cells. Next, we overexpressed cGAS and STING to examine their correlation with OPA3. The results showed that OPA3 overexpression enhanced CRC cell viability, migration, invasion, and the levels of PCNA, Cyclin A2, and Cyclin B1. Knockdown of OPA3 had the opposite effects. Moreover, OPA3 knockdown facilitated mitochondrial dysfunction and mtDNA stress in CRC cells. OPA3 overexpression also inhibited CCCP-induced mitochondrial stress disorder. Additionally, OPA3 knockdown elevated the protein levels of p-STING and cGAS and the mRNA level of STING target genes. Furthermore, overexpression of either cGAS or STING partially alleviated the enhancement of HT29 cell proliferation, migration, and invasion mediated by OPA3 overexpression. In conclusion, OPA3 promotes CRC progression via inhibiting the cGAS-STING pathway, which is mediated by mtDNA stress. OPA3 may be a new potential target for CRC.

Keywords:  CGAS-STING pathway; Colorectal cancer; MtDNA stress; OPA3

DOI:  https://doi.org/10.1007/s11626-024-01000-3
Diabetes. 2024 Dec 23. pii: db240040. [Epub ahead of print]

Extracellular Mitochondria Exacerbate Retinal Pigment Epithelium Degeneration in Diabetic Retinopathy.

Keiichi Nishikawa, Tomoaki Murakami, Miyo Yoshida, Noriko Terada, Kenji Ishihara, Yuki Mori, Shinji Ito, Akitaka Tsujikawa.

Advances in fundus imaging are revealing disruptions in the neurovascular unit in diabetic retinopathy (DR). In the era of anti-VEGF treatment, a thorough characterization of neurodegeneration is imperative until DR patients are sufficiently cured. Here we demonstrate that extracellular mitochondria exacerbate retinal pigment epithelium (RPE) degeneration and inflammation in DR. Extracellular mitochondria increased in the vitreous of DR patients and were associated with visual impairment but not with proliferative diabetic retinopathy or diabetic macular edema. Animal experiments demonstrated detrimental effects of extracellular mitochondria on RPE and photoreceptors. Lysosomal cell death induced by extracellular mitochondria in RPE cells required mitochondrial DNA but not its pattern recognition receptors. Furthermore, biochemical screening identified candidates for DNA receptors. Among them, DNA-dependent protein kinase was necessary for extracellular mitochondria-induced cell death in both in vitro and in vivo experiments. Extracellular mitochondria further induced IL-1β and TNF-α expression in RPE cells in a Toll-like receptor 9 dependent manner. RNA sequencing suggested that extracellular mitochondria exacerbate inflammation by promoting the proliferation and migration of macrophages, at least in part. In summary, extracellular mitochondria are designated as a novel exacerbating factor of RPE degeneration in DR.

DOI: https://doi.org/10.2337/db24-0040