Cell Death & Differentiation

Amyotrophic lateral sclerosis (ALS) is characterized by progressive motor neuron degeneration associated with genomic instability and mitochondrial dysfunction, although the mechanistic relationship between these hallmarks remains unclear. To determine whether nuclear DNA damage alone induces mitochondrial dysfunction, we exploited the AID-DIvA system, selectively generating DNA double-strand breaks (DSBs) in nuclear DNA. DSB induction caused early impairment of mitochondrial bioenergetics, including reduced basal respiration, ATP-linked respiration, and maximal respiratory capacity, preceding more pronounced mitochondrial alterations, after prolonged damage. Resolution of DSBs restored mitochondrial function, demonstrating a direct and reversible link between nuclear genome instability and mitochondrial dysfunction. Mechanistically, persistent activation of the DNA damage response (DDR) triggered PARP1-dependent NAD{square} depletion, while PARP1 inhibition rescued mitochondrial respiration and ATP synthesis. We next investigated the consequences of DDR activation triggered by the expression of 102 (G4C2) repeats in an inducible cell model of C9ORF72-linked ALS. In these cells, DDR activation preceded mitochondrial dysfunction, recapitulating the sequence observed in AID-DIvA cells. Mitochondrial defects included impaired oxidative phosphorylation and reduced ATP production without increased mitochondrial ROS, suggesting that DNA damage signalling acts upstream of mitochondrial dysfunction. In support of this hypothesis, inhibition of ATM as well as nicotinamide riboside-mediated replenishment of cellular NAD+significantly restored mitochondrial functions. Collectively, our findings identify nuclear DNA damage as a trigger of mitochondrial dysfunction and uncover a pathogenic DDR-mitochondria crosstalk mediated by persistent DNA damage signalling. These results support a bidirectional relationship between genome instability and mitochondrial dysfunction and highlight mitochondrial and DNA damage response modulators as potential therapeutic targets for ALS and related neurodegenerative disorders.

Recent evidence indicates that mitochondria, through the activity of the E3 Ub ligase MARCH5, are critical for de novo peroxisome biogenesis. Here we report that peroxisome biogenesis factor Pex26 is a MARCH5 client protein. In peroxisome-containing cells, MARCH5 interacts with Pex26 and facilitates the transfer of newly synthesized Pex26 from the OMM to peroxisomes. MARCH5 also controls peroxisomal delivery of other candidate peroxins in peroxisome-containing cells. On the other hand, in peroxisome-deficient cells, the turnover rate of Pex26 is dramatically increased, and MARCH5 targets this protein for p97-dependent proteasomal degradation. Both activities are mediated by MARCH5-dependent Pex26 ubiquitination. Knockout of Pex26 induces the accumulation of cells containing Tom20-positive, Catalase-deficient pre-peroxisomes. Further supporting the critical role of MARCH5 in peroxisome biogenesis, these structures are absent in Pex26/MARCH5 double knockout cells. The data support the model, where in peroxisome-containing cells, MARCH5 acts as a peroxisome biogenesis factor, while with defective peroxisome biogenesis, as in Zellweger syndrome cells, it protects mitochondria from potentially toxic accumulation of peroxins on the OMM.

Biallelic mutations in the sorbitol dehydrogenase (SORD) gene have been identified as one of the most common causes of autosomal-recessive Charcot-Marie-Tooth disease type 2 (CMT2) and distal hereditary neuropathy, collectively referred to as SORD deficiency. These mutations result in loss of sorbitol dehydrogenase activity, a key enzyme in the polyol pathway that metabolizes glucose, leading to marked accumulation of sorbitol in patient-derived fibroblasts. However, the mechanisms by which SORD dysfunction drives axonal degeneration remain poorly understood, and robust in vitro models of human SORD-deficient motor neurons (MNs) are still lacking. To address this gap, we established a human in vitro model of SORD deficiency by generating induced pluripotent stem cells (iPSCs) from fibroblasts affected individual carrying biallelic SORD mutations (SORDc.757delG/c.316_425+165del), and unaffected heterozygous carriers (SORDc.757delG/wt and SORDwt/c.316_425+165del). These iPSCs were subsequently differentiated into motor neuron progenitors (MNPs) and MNs. Comprehensive analysis of SORD-deficient human cells--including fibroblasts, MNPs, and MNs--revealed pronounced structural and functional abnormalities in the mitochondrial compartment, characterized by mitochondrial fragmentation and increased proton leak. Importantly, fibroblasts derived from two additional unrelated patients carrying the SORD mutation (SORDc.757delG/ c.757delG) further confirmed that SORD deficiency is associated with a mitochondrial phenotype. At the molecular level, SORD deficiency led to upregulation of aldose reductase (AR), another key enzyme of the polyol pathway, resulting in disruption of cellular redox homeostasis and increased oxidative stress. Consistent with these alterations, MNs derived from CMT2/SORD patients exhibited clear neurodegenerative features, including severe defects in neurite branching and synaptic architecture, ultimately impairing neuronal connectivity. Notably, pharmacological inhibition of AR effectively rescued both mitochondrial dysfunction and neuronal structural defects, supporting the targeting of AR as a promising therapeutic strategy for polyol pathway-associated neuropathies as CMT2/SORD and diabetic neuropathy.

The mitochondrial membrane protein phosphoglycerate mutase 5 (PGAM5) is a protein of interest in the complex transition from hepatic steatosis to hepatocellular carcinoma. PGAM5 is a serine/threonine/histidine phosphatase that plays a role in mitochondrial biogenesis, mitophagy, and multiple cell death pathways. Increased expression of PGAM5 in hepatocellular carcinoma is correlated with reduced patient survival. In this study, we demonstrate that loss of PGAM5 alters the bioenergetic landscape of liver cancer by promoting mitochondrial oxidant injury and suppressing the glycerophospholipid and lysophospholipid pathways, leading to accumulation of the bioactive phospholipid lysophosphatidylcholine. Additionally, PGAM5 deletion downregulates fatty acid biosynthesis, resulting in reduced cellular diacylglycerol concentrations through two probable mechanisms: attenuated long chain fatty acid uptake and suppressed de novo synthesis. These findings underscore the broad impact of a single phosphatase on mitochondrial function and provide a rationale for therapeutically targeting PGAM5 to disrupt lipid metabolism in hepatocellular carcinoma.

Epithelial-mesenchymal transition (EMT) and glycolytic metabolism are well-characterized drivers of cancer progression and metastasis. However, most primary breast tumors and metastases express E-cadherin and the epithelial phenotype is associated with mitochondrial oxidative metabolism, yet the causality and relevance of these relationships and their underlying mechanisms remain poorly understood. Using a 3D culture model with mechano-stimulation, we found that E-cadherin promotes mitochondrial oxidative phosphorylation (OXPHOS) while reducing oxidative stress. Through pharmacological and genetic manipulations of inflammatory breast cancer (IBC) and/or triple negative breast cancer (TNBC) cell lines, we identified pyruvate carboxylase (PC) as an E-cadherin effector. Critically, restoring PC in E-cadherin-silenced cells rescued mitochondrial oxygen consumption and protection from oxidative stress. Co-expression of E-cadherin and PC was confirmed in breast cancer tissues and experimental lung metastases. Mechanistically, E-cadherin induced PC expression and OXPHOS via AKT-mediated activation of YAP/ /TEAD transcription factors, which are better known as supporting EMT. Clinically relevant AKT and TEAD inhibitors reduced both PC expression and oxidative respiration. Importantly, PC inhibition as monotherapy attenuated established experimental lung metastases and primary tumor burden in mice. Taken together, these findings reveal that E-cadherin-mediated cell-cell adhesions directly support mitochondrial metabolism through AKT-YAP/TEAD-PC signaling, identifying a therapeutic vulnerability in metastatic epithelial TNBC.

The tight regulation of iron homeostasis is of great importance for cellular health. An increase in intracellular iron levels results in the formation of free radicals, which damages macromolecules and membranes, eventually resulting in cell death by Ferroptosis. Recently, we showed that patients with mutations in VPS41 display a severe neurodegenerative phenotype with iron deposition in the brain. VPS41 is well known as subunit of the HOPS complex required for fusion of late endosomes and autophagosomes with lysosomes. However, VPS41 has also been identified as inhibitor of Ferroptosis and regulator of redox homeostasis. How VPS41 exerts these functions and if these are dependent on the HOPS complex is unknown. Here we show that depletion of VPS41 results in increased intracellular iron levels, ROS formation and mitochondrial fission. Our findings indicate an important role for VPS41 in the regulation of iron homeostasis and mitochondrial fission and suggest Ferroptosis as a possible cause for neurodegeneration in VPS41 patients.

Hepatocellular carcinoma (HCC) remains a lethal malignancy with limited therapeutic options. While Poly (ADP-ribose) polymerase inhibitors (PARPi) exploit synthetic lethality in tumors with DNA repair defects, their clinical utility in HCC is hindered by the low prevalence of canonical repair gene mutations and the enhancing DNA repair capacity. Through proteomic analysis of two independent cohorts (n=260), we identified the THO complex component THOC2 as a master regulator of DNA damage response (DDR) via mRNA nuclear export control. Clinically, THOC2 overexpression predicted poor survival (HR=2.68-6.84, P<0.001) and correlated with enhanced DDR gene expression. Mechanistically, THOC2 chaperones mRNA nuclear export of DDR effectors (MDC1, PRKDC, MSH6) and proliferation drivers (TOP2A), thereby establishing a dual pro-repair/pro-growth program. Targeting this vulnerability, THOC2 knockdown induced synthetic lethality with PARPi, reducing Olaparib IC50 by up to 61% and suppressing tumor growth by 76% (P<0.001). Our study illuminates mRNA transport as a druggable DDR modulator and establishes THOC2 as both a prognostic biomarker and a therapeutic target to overcome PARPi resistance in HCC. This work pioneers a strategy to expand synthetic lethality beyond genetic defects by targeting post-transcriptional regulation.

Basal keratinocytes in the skin are essential for epidermal homeostasis and repair; however, how intrinsic alterations in these cells contribute to inflammatory skin pathology remains poorly understood. In this study, we employed a tamoxifen-inducible mouse model to express the human RUNX1-ETO fusion gene, a well-established oncogenic driver of acute myeloid leukemia, in epidermal basal keratinocytes. RUNX1-ETO induction in keratinocytes resulted in progressive skin inflammation in vivo, accompanied by splenomegaly, epidermal hyperplasia, increased cytokine production, and alterations in epidermal stem cell composition. Inflammatory lesions were prominent in the tail, ear, and plantar epidermis, whereas hair-bearing dorsal skin remained largely unaffected. RNA-seq analysis of FACS-isolated RUNX1-ETO+ basal keratinocytes revealed global changes in gene expression, characterized by the suppression of epidermal homeostatic and metabolic programs and the activation of inflammatory signaling pathways. In particular, RUNX1-ETO expression was associated with increased TNF/NF-{kappa}B and IL-6-STAT signaling, as well as interferon-associated inflammatory pathways, together with the induction of neutrophil-attracting chemokines and epithelial inflammatory mediators. Together, these findings indicate that RUNX1-ETO-mediated transcriptional dysregulation in basal keratinocytes promotes a pro-inflammatory cellular state that drives progressive skin inflammation.

Circadian regulation of proteostasis, a key determinant of muscle health, remains poorly understood. Here, we identified DNAJB6, an Hsp40 (DnaJ) co-chaperone, as a substrate of the circadian E3 ligase FBXL21. FBXL21 mediated the ubiquitination-dependent proteasomal degradation of both DNAJB6 and its client proteins including Desmin; causative mutations of DNAJB6 in myopathies, however, rendered resistance to FBXL21-directed degradation. Fbxl21 KO C2C12 cells displayed aberrant accumulation of Desmin, and showed aggravated cytoplasmic accumulation of TDP-43, another DNAJB6 client protein, in heat shock response. Under timed exercise as a physiological stressor, WT mice displayed robust diurnal rhythms in the levels of stress granule markers (G3BP1 and FUS) and TDP-43 as a function of exercise timing. In contrast, the Fbxl21 hypomorph Psttm mutant mice showed elevated expression of these proteins without exercise, which was exacerbated under exercise-induced stress conditions; importantly, these abnormalities were rescued by skeletal muscle-specific FBXL21 expression. Our study elucidates a novel diurnal regulatory mechanism of skeletal muscle proteostasis via FBXL21 as a chaperone-linked E3 ligase, highlighting the FBXL21-DNAJB6 axis as a potential therapeutic target for myopathies.

Oncogenic KRAS mutations drive tumorigenesis by promoting pro-survival signaling and metabolic reprogramming, including the maintenance of redox balance to evade oxidative stress. A key mechanism involves the upregulation of the xCT cystine/glutamate antiporter, which sustains glutathione (GSH) synthesis and protects cells from oxidative damage and ferroptosis. While it is known that the ETS1-ATF4 complex mediates transcriptional upregulation of xCT, the upstream regulators linking KRAS signaling to this axis remain to be fully defined. Here, we demonstrate that oncogenic KRAS signaling induces the GSK3{beta}-mediated proteasomal degradation of the tumor suppressor CCDC6. We show that CCDC6 acts as a negative regulator of the xCT-promoting transcription factor ATF4 by directly interacting with it and preventing its recruitment to the xCT promoter. Consequently, KRAS-driven CCDC6 degradation disinhibits ATF4, leading to increased xCT expression, elevated intracellular GSH, and enhanced resistance to ferroptosis. Crucially, pharmacological inhibition of CCDC6 turnover using proteasome, GSK3{beta}, or specific KRAS mutant inhibitors (Sotorasib, Adagrasib, HRS4642) restored CCDC6 protein levels and robustly sensitized KRAS-mutated cells to ferroptosis-inducing agents like Sulfasalazine. Furthermore, validation in preclinical models and human colorectal cancer samples revealed that CCDC6 protein levels are predominantly downregulated in KRAS-mutant cases This work uncovers a novel KRAS/CCDC6/xCT signaling axis that mediates ferroptosis resistance in KRAS-mutated cancers. Moreover, it identifies CCDC6 turnover as a critical vulnerability and a promising therapeutic target to enhance the efficacy of ferroptosis-inducing agents.

Mitochondrial dysfunction is a central driver of neonatal hypoxic-ischaemic encephalopathy (HIE), yet the specific vulnerabilities of mitochondrial fusion machinery in the neonatal brain remain poorly defined. Here, we investigate Optic Atrophy (OPA)1 as a critical determinant of mitochondrial resilience during hypoxia-ischaemia (HI). Human developmental transcriptomics showed stable perinatal expression of mitochondrial dynamics genes, supporting their potential utility as therapeutic targets at birth. In a neonatal mouse model, HI induced rapid proteolytic processing of OPA1 in whole brain. In vitro, exposure of primary astrocytes to oxygen-glucose deprivation (OGD) mimicked the OPA1 sensitivity observed in whole brain, with aberrant processing and loss of expression. We genetically replicated this observation by knocking down OPA1 expression in primary astrocytes. The predicted mitochondrial fragmentation and impaired bioenergetics was also accompanied by increased vulnerability to hypoxia, revealing an OPA1dependent susceptibility under moderate metabolic stress. Transcriptomics analyses of these cells highlighted an OPA1-mediated depletion of mitochondrial DNA. This mtDNA depletion was also evident in OGD-treated astrocytes and ex vivo brain samples at 24h after HI in our rodent model. In contrast, mild OPA1 overexpression enhanced astrocyte survival following OGD and OPA1 overexpression in vivo markedly reduced tissue damage after neonatal HI. MtDNA levels in OPA1-overexpressing mice before and at 7 days after HI were significantly higher than in wild-type mice. These findings position OPA1 as a key mediator of mitochondrial impairment after HI and to our knowledge, is the first study showing that loss of mtDNA is a consequence of neonatal HI. Our data highlight that maintaining OPA1 expression is a promising therapeutic strategy for protecting the neonatal brain following birth asphyxia.

Amyotrophic lateral sclerosis (ALS) is a progressive neurodegenerative disease of poor prognosis, for which age is the strongest risk factor. Despite significant progress in the discovery of ALS-associated mutations, no model explains how such a diversity of mutations converges in a common pathology. In addition, most ALS cases are sporadic and lack known genetic drivers. We recently reported that arginine-rich peptides arising from the C9ORF72 mutation trigger a widespread accumulation of orphan ribosomal proteins (oRP). Here, we show that oRP accumulation is also observed upon expression of other RNA-related ALS mutations, such as hnRNPA2D290V and TDP-43A315T, as well as upon exposure to the ALS-related neurotoxin {beta}-N-methylamino-L-alanine (BMAA). Furthermore, the transcriptional signature of patients with sporadic ALS resembles that of Diamond-Blackfan anemia (DBA), a known ribosomopathy. Supporting the usefulness of our in vitro data, a transcriptional signature defined from these models provides diagnostic and prognostic value in ALS patients. We propose that the accumulation of oRPs due to dysfunctional ribosome biogenesis is a molecular hallmark of ALS that can contribute to the progressive loss of motor neurons in the disease.

Collagen VI-related myopathies, including Bethlem myopathy (BM), are progressive muscle disorders, but the mechanisms driving age-dependent disease progression remain poorly understood. Here, we used a zebrafish BM model carrying an exon-skipping mutation that generates a shorter collagen VI 1 chain and disrupts supramolecular assembly, recapitulating key features of the human disease. We further demonstrated that this model reproduces disease progression, with worsening muscle wasting, increased myofiber size variability, and age-associated skeletal deformities consistent with secondary consequences of muscle dysfunction rather than intrinsic bone defects. Single-nucleus RNA sequencing of trunk skeletal muscle revealed an early shift in cellular composition, with reduced myonuclei and increased fibroblast abundance, indicative of disease-associated aging. Myonuclei activated stress and quality control pathways, including autophagy and mitophagy, along with metabolic rewiring. In contrast, fibroblasts displayed early translational activation followed by progressive proteostatic and endoplasmic reticulum stress. At later stages, fibroblasts adopted a pro-fibrotic state, driving extracellular matrix remodeling and enhanced muscle-fibroblast communication. Consistently, analyses at the protein level confirmed early intracellular retention of the mutant protein, along with increased extracellular matrix deposition and fibrotic tissue formation in BM muscle. Among the three tested drugs targeting ER-stress and protein degradation, only TUDCA significantly ameliorated collagen VI deposition in the extracellular space in larvae. These findings identify fibroblasts as key drivers of disease progression and potential therapeutic targets.

Multiple acyl-CoA dehydrogenase deficiency (MADD) is a mitochondrial lipid storage myopathy characterized by impaired fatty acid {beta}-oxidation, mitochondrial dysfunction, and progressive neuromuscular and cardiac disease. MADD is most commonly caused by pathogenic variants in electron transfer flavoprotein dehydrogenase (ETFDH), which encodes electron transfer flavoprotein-ubiquinone oxidoreductase (Etf-QO), a critical redox enzyme that transfers electrons from acyl-CoA dehydrogenases to the mitochondrial electron transport chain. Defective Etf-QO activity disrupts electron flow, promotes reactive oxygen species (ROS) production, and impairs cellular energy metabolism, linking abnormal lipid oxidation to oxidative stress-mediated tissue damage. To investigate the role of redox imbalance in MADD pathogenesis, we generated CRISPR/Cas9 knock-in Drosophila melanogaster models carrying patient-relevant Etf-QO missense mutations (L127R, S296C, and L399F; corresponding to human L138R, S307C, and L409F) within conserved FAD- and ubiquinone-binding domains. Mutant flies developed progressive locomotor impairment, reduced muscle performance, and marked lipid droplet accumulation in skeletal muscle, cardiac tissue, and fat bodies, indicating systemic defects in mitochondrial lipid utilization. Cardiac analyses demonstrated reduced fractional shortening, prolonged heart period, and increased arrhythmia index, consistent with metabolic cardiomyopathy associated with mitochondrial oxidative stress. In vivo respirometry revealed significantly decreased oxygen consumption, reflecting impaired oxidative phosphorylation. At the molecular level, mutant flies exhibited elevated ROS levels and ATP depletion, accompanied by increased expression of AMPK, PGC-1, and Tfam, suggesting activation of energy stress signaling and compensatory mitochondrial biogenesis. Importantly, endurance exercise significantly improved locomotor and cardiac function while reducing lipid accumulation and oxidative stress. Together, these findings establish a redox-centered in vivo model of MADD and identify oxidative stress as a major driver of disease pathology and a potential therapeutic target.

NRF1 is a key mediator of the proteasome recovery pathway, yet its regulation by ER-resident factors is not fully elucidated. Here, we demonstrate that selenoproteins SELS and SELK are critical regulators for NRF1 protein dynamics. SELS stabilizes NRF1, while SELK induces its insolubilization. Their deficiency leads to a hyper-accumulation and increased nuclear localization of NRF1 under proteasome inhibition condition. This results in an augmented transcriptional response of proteasome subunits. These results indicate that SELS and SELK cooperatively gate NRF1 activity by controlling its retrotranslocation and solubility, highlighting a novel layer of selenoprotein-mediated quality control in the proteostasis network.

Cellular senescence, a hallmark of aging, leads to the accumulation of apoptosis-resistant cells that compromise tissue homeostasis. While senescent cells are known to influence neighboring cells through the senescence-associated secretory phenotype (SASP), the precise nature of the interactions between senescent and normal cells remains elusive. Here we show that progerin-induced senescent cells undergo apoptosis when co-cultured with normal cells. This elimination requires direct cell-cell contact and is mediated by the JNK and p38-MAPK pathways, leading to p53 upregulation and p21 downregulation in progerin-expressing cells. Furthermore, neighboring normal cells exert persistent mechanical compression on progerin-expressing cells prior to their elimination, consistent with mechanical cell competition. In contrast, p16-induced senescent cells resist elimination under the same co-culture conditions, maintaining high p21 levels. Our findings reveal a non-cell-autonomous mechanism for senescent cell clearance, providing new insights into the maintenance of tissue homeostasis during aging.

Hepatocellular carcinoma (HCC), a leading cause of cancer death, has a dynamic and heterogeneous tumor microenvironment (TME) that drives progression and therapeutic resistance. We previously elucidated that apoptosis antagonizing transcription factor (AATF) drives angiogenesis in HCC. However, its role in TME remains unexplored. We employed an orthotopic xenograft mouse model, implanting human HCC cells into the liver, and achieved liver-specific silencing via tail vein injection of AAV8 carrying mouse-specific siAATF or siControl. Histological, biochemical, and molecular analyses, combined with whole-genome transcriptomics mapped to mouse and human genomes, were used to study TME and tumor compartments separately. Silencing of AATF in the TME significantly reduced tumor growth compared with controls. Furthermore, AATF loss disrupted key processes in TME, including inflammation, immune response, angiogenesis, and extracellular matrix remodeling. Mechanistically, TGF-{beta} signaling was significantly suppressed in the TME, thereby affecting tumor cell cycle and metabolic activity, ultimately leading to tumor regression. The long noncoding RNA (lncRNA) analysis identified MIR100HG as a key downstream regulator of AATF in the TGF-{beta} signaling pathway. These findings expand the oncogenic role of AATF to include regulation of the TME via the AATF-MIR100HG-TGF-{beta} axis, highlighting its potential as a therapeutic target in HCC.

Colorectal cancer (CRC) poses a severe global health threat with high incidence, mortality, and poor 5-year survival rates for advanced cases despite existing treatments. This study aims to explore the role of STRIP2 in CRC progression and its underlying mechanisms. Impact of STRIP2 on CRC in vitro was investigated via CRC cell proliferation, migration, invasion, and apoptosis. The in vivo impact was investigated via nude mice models. The role of STRIP2 in CRC was investigated via transcriptomic analysis, Western blot, Co-immunoprecipitation assays and ferroptosis validations. STRIP2 is overexpressed in CRC, driving malignant phenotypes in vitro and in vivo. Mechanically, STRIP2 stabilizes the IL17 downstream effector LCN2 by blocking its K48-linked ubiquitination and degradation, enhances anti-ferroptosis of CRC cells. Oe-STRIP2 suppresses ferroptosis, boosting proliferation and reducing oxidative stress; while si-STRIP2 induces the opposite effect. This study suggests STRIP2-mediated stabilization of LCN2 and enhances CRC cells ferroptosis resistance, thus promoting CRC cell survival and mediates malignant progression in CRC, which provides a novel link between STRIP2 and ferroptosis regulation in CRC. HighlightO_LISTRIP2 is overexpressed in CRC tissues and cells C_LIO_LISTRIP2 blocks LCN2 Ubiquitination and stabilizes LCN2 C_LIO_LISTRIP2 suppresses CRC ferroptosis C_LIO_LISTRIP2 drives CRC malignant phenotypes both in vitro & in vivo C_LI Graphical Abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=113 SRC="FIGDIR/small/725308v1_ufig1.gif" ALT="Figure 1"> View larger version (52K): org.highwire.dtl.DTLVardef@1baf7baorg.highwire.dtl.DTLVardef@1de15d9org.highwire.dtl.DTLVardef@16c8078org.highwire.dtl.DTLVardef@667840_HPS_FORMAT_FIGEXP M_FIG C_FIG

Mitochondrial poly-A polymerase (MTPAP) is essential for mitochondrial mRNA (mt-mRNA) polyadenylation, a critical step in mt-mRNA maturation. Mutations in MTPAP have been reported to cause a mitochondrial cytopathy. Here, we provide evidence of enhanced type I interferon (IFN) signalling in the blood of patients carrying mutations in MTPAP. Further, deletion of MTPAP in a fibroblast cell model led to abnormalities in mitochondrial respiration and mtRNA processing, and an upregulation of type I IFN signalling. Notably, both in patients fibroblast and in MTPAP-deleted cells, we observed the accumulation of non-coding mtRNA and mitochondrial double-stranded RNA (mt-dsRNA) within enlarged mitochondrial RNA granules. Cytosolic release of mt-dsRNA led to type I IFN induction mediated primarily by the RNA sensor MDA5 and its adaptor MAVS. Our findings reveal a novel consequence of MTPAP dysfunction, highlighting how impaired mtRNA maturation can drive innate immune system activation.

Microglial activation has been closely associated with accelerated ALS disease progression. However, specific microglial pathways that regulate microglial activation and ALS disease progression remain limitedly understood. Here, we determined the role of Clec7a (or Dectin-1), a core signature gene of disease-associated microglia (DAM) in ALS, in regulating microglial activation and ALS disease progression. Our spinal cord scRNA-Seq results found that Clec7a deficiency specifically attenuated microglial neuroimmune gene expression in SOD1G93A mice and human ALS. In addition, in vivo two-photon imaging of human (h) TDP43 phagocytosis by microglia in the cortex showed that Clec7a deficiency promotes microglial phagocytosis of pathological hTDP43 by enhancing microglial process dynamics. Subsequent survival analysis further showed that selective deletion of Clec7a in microglia mitigates motor neuron degeneration and delays disease progression in SOD1G93A ALS mice. Together, our results establish that Clec7a is a key regulator in shaping disease microglial functions and promotes disease progression in ALS.