CHCHD10S59L/+ mouse model: Behavioral and neuropathological features of frontotemporal dementia

CHCHD10-related disease causes a spectrum of clinical presentations including mitochondrial myopathy, cardiomyopathy, amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD). We generated a knock-in mouse model bearing the p.Ser59Leu (S59L) CHCHD10 variant. Chchd10S59L/+ mice have been shown to phenotypically replicate the disorders observed in patients: myopathy with mtDNA instability, cardiomyopathy and typical ALS features (protein aggregation, neuromuscular junction degeneration and spinal motor neuron loss). Here, we conducted a comprehensive behavioral, electrophysiological and neuropathological assessment of Chchd10S59L/+ mice. These animals show impaired learning and memory capacities with reduced long-term potentiation (LTP) measured at the Perforant Pathway-Dentate Gyrus (PP-DG) synapses. In the hippocampus of Chchd10S59L/+ mice, neuropathological studies show the involvement of protein aggregates, activation of the integrated stress response (ISR) and neuroinflammation in the degenerative process. These findings contribute to decipher mechanisms associated with CHCHD10 variants linking mitochondrial dysfunction and neuronal death. They also validate the Chchd10S59L/+ mice as a relevant model for FTD, which can be used for preclinical studies to test new therapeutic strategies for this devastating disease.

Loss of CHCHD2 Stability Coordinates with C1QBP/CHCHD2/CHCHD10 Complex Impairment to Mediate PD-Linked Mitochondrial Dysfunction

Novel CHCHD2 mutations causing C-terminal truncation and interrupted CHCHD2 protein stability in Parkinson's disease (PD) patients were previously found. However, there is limited understanding of the underlying mechanism and impact of subsequent CHCHD2 loss-of-function on PD pathogenesis. The current study further identified the crucial motif (aa125-133) responsible for diminished CHCHD2 expression and the molecular interplay within the C1QBP/CHCHD2/CHCHD10 complex to regulate mitochondrial functions. Specifically, CHCHD2 deficiency led to decreased neural cell viability and mitochondrial structural and functional impairments, paralleling the upregulation of autophagy under cellular stresses. Meanwhile, as a binding partner of CHCHD2, C1QBP was found to regulate the stability of CHCHD2 and CHCHD10 proteins to maintain the integrity of the C1QBP/CHCHD2/CHCHD10 complex. Moreover, C1QBP-silenced neural cells displayed severe cell death phenotype along with mitochondrial damage that initiated a significant mitophagy process. Taken together, the evidence obtained from our in vitro and in vivo studies emphasized the critical role of CHCHD2 in regulating mitochondria functions via coordination among CHCHD2, CHCHD10, and C1QBP, suggesting the potential mechanism by which CHCHD2 function loss takes part in the progression of neurodegenerative diseases.

Mitochondrial protein CHCHD10 inhibits NDV replication and reduces pathological changes

Newcastle disease (ND) is a disease that threatens the world's poultry industry, which is caused by virulent Newcastle disease virus (NDV). As its pathogenic mechanism remains not fully clear, the proteomics of NDV-infected cells were analyzed. The results revealed that coiled-coil-helix-coiled-coil-helix domain containing 10 (CHCHD10) protein displayed a significant decrease at the late stage of NDV infection. To investigate the function of CHCHD10 in NDV infection, its expression after NDV infection was detected both in vivo and in vitro. Besides, the tissue viral loads and pathological damage of C57BL/6 mice with CHCHD10 differently expressed were also investigated. The results showed that the CHCHD10 expression was significantly decreased both in vivo and in vitro at the late stage of NDV infection. The viral loads were significantly higher in CHCHD10 silenced C57BL/6 mice, along with more severe pathological damage and vice versa.

NDV inhibited IFN-β secretion through impeding CHCHD10-mediated mitochondrial fusion to promote viral proliferation

Newcastle disease virus (NDV) is an RNA virus that can promote its own replication through the inhibition of cellular mitochondrial fusion. The proteins involved in mitochondrial fusion, namely mitofusin 1 (Mfn1) and optic atrophy 1 (OPA1) are associated with interferon-beta (IFN-β) secretion during NDV infection. However, the precise mechanism by which NDV modulates the Mfn1-mediated or OPA1-mediated fusion of mitochondria, thereby impacting IFN-β, remains elusive. This study revealed that the downregulation of the mitochondrial protein known as coiled-coil-helix-coiled-coil-helix domain containing 10 (CHCHD10) exerts a negative regulatory effect on OPA1 and Mfn1 in human lung adenocarcinoma (A549) cells during the late stage of NDV infection. This reduction in CHCHD10 expression impeded cellular mitochondrial fusion, subsequently leading to a decline in the activation of interferon regulatory factor 3 (IRF3) and nuclear factor kappa B (NF-κB), ultimately resulting in diminished secretion of IFN-β. In contrast, the overexpression of CHCHD10 alleviated infection-induced detrimental effect in mitochondrial fusion, thereby impeding viral proliferation. In summary, NDV enhances its replication by inhibiting the CHCHD10 protein, which impedes mitochondrial fusion and suppresses IFN-β production through the activation of IRF3 and NF-κB.

CHCHD10 mutations induce tissue-specific mitochondrial DNA deletions with a distinct signature

Mutations affecting the mitochondrial intermembrane space protein CHCHD10 cause human disease, but it is not known why different amino acid substitutions cause markedly different clinical phenotypes, including amyotrophic lateral sclerosis-frontotemporal dementia, spinal muscular atrophy Jokela-type, isolated autosomal dominant mitochondrial myopathy and cardiomyopathy. CHCHD10 mutations have been associated with deletions of mitochondrial DNA (mtDNA deletions), raising the possibility that these explain the clinical variability. Here, we sequenced mtDNA obtained from hearts, skeletal muscle, livers and spinal cords of WT and Chchd10 G58R or S59L knockin mice to characterise the mtDNA deletion signatures of the two mutant lines. We found that the deletion levels were higher in G58R and S59L mice than in WT mice in some tissues depending on the Chchd10 genotype, and the deletion burden increased with age. Furthermore, we observed that the spinal cord was less prone to the development of mtDNA deletions than the other tissues examined. Finally, in addition to accelerating the rate of naturally occurring deletions, Chchd10 mutations also led to the accumulation of a novel set of deletions characterised by shorter direct repeats flanking the deletion breakpoints. Our results indicate that Chchd10 mutations in mice induce tissue-specific deletions which may also contribute to the clinical phenotype associated with these mutations in humans.

Disruption of Mitophagy Flux through the PARL-PINK1 Pathway by CHCHD10 Mutations or CHCHD10 Depletion

Coiled-coil-helix-coiled-coil-helix domain-containing 10 (CHCHD10) is a nuclear-encoded mitochondrial protein which is primarily mutated in the spectrum of familial and sporadic amyotrophic lateral sclerosis (ALS)-frontotemporal dementia (FTD). Endogenous CHCHD10 levels decline in the brains of ALS-FTD patients, and the CHCHD10S59L mutation in Drosophila induces dominant toxicity together with PTEN-induced kinase 1 (PINK1), a protein critical for the induction of mitophagy. However, whether and how CHCHD10 variants regulate mitophagy flux in the mammalian brain is unknown. Here, we demonstrate through in vivo and in vitro models, as well as human FTD brain tissue, that ALS/FTD-linked CHCHD10 mutations (R15L and S59L) impair mitophagy flux and mitochondrial Parkin recruitment, whereas wild-type CHCHD10 (CHCHD10WT) normally enhances these measures. Specifically, we show that CHCHD10R15L and CHCHD10S59L mutations reduce PINK1 levels by increasing PARL activity, whereas CHCHD10WT produces the opposite results through its stronger interaction with PARL, suppressing its activity. Importantly, we also demonstrate that FTD brains with TAR DNA-binding protein-43 (TDP-43) pathology demonstrate disruption of the PARL-PINK1 pathway and that experimentally impairing mitophagy promotes TDP-43 aggregation. Thus, we provide herein new insights into the regulation of mitophagy and TDP-43 aggregation in the mammalian brain through the CHCHD10-PARL-PINK1 pathway.

Mitochondria, a Key Target in Amyotrophic Lateral Sclerosis Pathogenesis

Mitochondrial dysfunction occurs in numerous neurodegenerative diseases, particularly amyotrophic lateral sclerosis (ALS), where it contributes to motor neuron (MN) death. Of all the factors involved in ALS, mitochondria have been considered as a major player, as secondary mitochondrial dysfunction has been found in various models and patients. Abnormal mitochondrial morphology, defects in mitochondrial dynamics, altered activities of respiratory chain enzymes and increased production of reactive oxygen species have been described. Moreover, the identification of CHCHD10 variants in ALS patients was the first genetic evidence that a mitochondrial defect may be a primary cause of MN damage and directly links mitochondrial dysfunction to the pathogenesis of ALS. In this review, we focus on the role of mitochondria in ALS and highlight the pathogenic variants of ALS genes associated with impaired mitochondrial functions. The multiple pathways demonstrated in ALS pathogenesis suggest that all converge to a common endpoint leading to MN loss. This may explain the disappointing results obtained with treatments targeting a single pathological process. Fighting against mitochondrial dysfunction appears to be a promising avenue for developing combined therapies in the future.

The identification of high-performing antibodies for Coiled-coil-helix-coiled-coil-helix domain containing protein 10 (CHCHD10) for use in Western Blot, immunoprecipitation and immunofluorescence

CHCHD10 is a mitochondrial protein, implicated in the regulation of mitochondrial morphology and cristae structure, as well as the maintenance of mitochondrial DNA integrity. Recently discovered to be associated with amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD) in its mutant form, the scientific community would benefit from the availability of validated anti-CHCHD10 antibodies. In this study, we characterized four CHCHD10 commercial antibodies for Western Blot, immunoprecipitation, and immunofluorescence using a standardized experimental protocol based on comparing read-outs in knockout cell lines and isogenic parental controls. As this study highlights high-performing antibodies for CHCHD10, we encourage readers to use it as a guide to select the most appropriate antibody for their specific needs.

The impacts of the mitochondrial myopathy-associated G58R mutation on the dynamic structural properties of CHCHD10

The mitochondria are responsible for producing energy within the cell, and in mitochondrial myopathy, there is a defect in the energy production process. The CHCHD10 gene codes for a protein called coiled-coil-helix-coiled-coil-helix domain-containing protein 10 (CHCHD10), which is found in the mitochondria and is involved in the regulation of mitochondrial function. G58R mutation has been shown to disrupt the normal function of CHCHD10, leading to mitochondrial dysfunction and ultimately to the development of mitochondrial myopathy. The structures of G58R mutant CHCHD10 and how G58R mutation impacts the wild-type CHCHD10 protein at the monomeric level are unknown. To address this problem, we conducted homology modeling, multiple run molecular dynamics simulations and bioinformatics calculations. We represent herein the structural ensemble properties of the G58R mutant CHCHD10 (CHCHD10^G58R) in aqueous solution. Moreover, we describe the impacts of G58R mutation on the structural ensembles of wild-type CHCHD10 (CHCHD10^WT) in aqueous solution. The dynamics properties as well as structural properties of CHCHD10^WT are impacted by the mitochondrial myopathy-related G58R mutation. Specifically, the secondary and tertiary structure properties, root mean square fluctuations, Ramachandran diagrams and results from principal component analysis demonstrate that the CHCHD10^WT and CHCHD10^G58R proteins possess different structural ensemble characteristics and describe the impacts of G58R mutation on CHCHD10^WT. These findings may be helpful for designing new treatments for mitochondrial myopathy.Communicated by Ramaswamy H. Sarma.

Frontotemporal Dementia-Related V57E Mutation Impairs Mitochondrial Function and Alters the Structural Properties of CHCHD10

The V57E pathological variant of the mitochondrial coiled-coil-helix-coiled-coil-helix domain-containing protein 10 (CHCHD10) plays a role in frontotemporal dementia. The wild-type and V57E mutant CHCHD10 proteins contain intrinsically disordered regions, and therefore, these regions hampered structural characterization of these proteins using conventional experimental tools. For the first time in the literature, we represent that the V57E mutation is pathogenic to mitochondria as it increases mitochondrial superoxide and impairs mitochondrial respiration. In addition, we represent here the structural ensemble properties of the V57E mutant CHCHD10 and describe the impacts of V57E mutation on the structural ensembles of wild-type CHCHD10 in aqueous solution. We conducted experimental and computational studies for this research. Namely, MitoSOX Red staining and Seahorse Mito Stress experiments, atomic force microscopy measurements, bioinformatics, homology modeling, and multiple-run molecular dynamics simulation computational studies were conducted. Our experiments show that the V57E mutation results in mitochondrial dysfunction, and our computational studies present that the structural ensemble properties of wild-type CHCHD10 are impacted by the frontotemporal dementia-associated V57E genetic mutation.

Effects of the Jokela type of spinal muscular atrophy-related G66V mutation on the structural ensemble characteristics of CHCHD10

The G66V pathological variant of the coiled-coil-helix-coiled-coil-helix domain-containing protein 10 (CHCHD10), mitochondrial, plays a role in Jokela type spinal muscular atrophy. The wild-type and G66V mutant-type CHCHD10 proteins contain intrinsically disordered regions, and therefore, their structural ensemble studies have been experiencing difficulties using conventional tools. Here, we show our results regarding the first characterization of the structural ensemble characteristics of the G66V mutant form of CHCHD10 and the first comparison of these characteristics with the structural ensemble properties of wild-type CHCHD10. We find that the structural properties, potential of mean force surfaces, and principal component analysis show stark differences between these two proteins. These results are important for a better pathology, biochemistry and structural biology understanding of CHCHD10 and its G66V genetic variant and it is likely that these reported structural properties are important for designing more efficient treatments for the Jokela type of spinal muscular atrophy disease.

Loss of mitochondrial Chchd10 or Chchd2 in zebrafish leads to an ALS-like phenotype and Complex I deficiency independent of the mitochondrial integrated stress response

Mutations in CHCHD10 and CHCHD2, encoding two paralogous mitochondrial proteins, have been identified in cases of amyotrophic lateral sclerosis, frontotemporal lobar degeneration, and Parkinson's disease. Their role in disease is unclear, though both have been linked to mitochondrial respiration and mitochondrial stress responses. Here, we investigated the biological roles of these proteins during vertebrate development using knockout (KO) models in zebrafish. We demonstrate that loss of either or both proteins leads to motor impairment, reduced survival and compromised neuromuscular junction integrity in larval zebrafish. Compensation by Chchd10 was observed in the chchd2^-/- model, but not by Chchd2 in the chchd10^-/- model. The assembly of mitochondrial respiratory chain Complex I was impaired in chchd10^-/- and chchd2^-/- zebrafish larvae, but unexpectedly not in a double chchd10^-/- and chchd2^-/- model, suggesting that reduced mitochondrial Complex I cannot be solely responsible for the observed phenotypes, which are generally more severe in the double KO. We observed transcriptional activation markers of the mitochondrial integrated stress response (mt-ISR) in the double chchd10^-/- and chchd2^-/- KO model, suggesting that this pathway is involved in the restoration of Complex I assembly in our double KO model. The data presented here demonstrates that the Complex I assembly defect in our single KO models arises independently of the mt-ISR. Furthermore, this study provides evidence that both proteins are required for normal vertebrate development.

CHCHD2 and CHCHD10: Future therapeutic targets in cognitive disorder and motor neuron disorder

CHCHD2 and CHCHD10 are homolog mitochondrial proteins that play key roles in the neurological, cardiovascular, and reproductive systems. They are also involved in the mitochondrial metabolic process. Although previous research has concentrated on their functions within mitochondria, their functions within apoptosis, synaptic plasticity, cell migration as well as lipid metabolism remain to be concluded. The review highlights the different roles played by CHCHD2 and/or CHCHD10 binding to various target proteins (such as OPA-1, OMA-1, PINK, and TDP43) and reveals their non-negligible effects in cognitive impairments and motor neuron diseases. This review focuses on the functions of CHCHD2 and/or CHCHD10. This review reveals protective effects and mechanisms of CHCHD2 and CHCHD10 in neurodegenerative diseases characterized by cognitive and motor deficits, such as frontotemporal dementia (FTD), Lewy body dementia (LBD), Parkinson's disease (PD) and amyotrophic lateral sclerosis (ALS). However, there are numerous specific mechanisms that have yet to be elucidated, and additional research into these mechanisms is required.

Modulation of synaptic plasticity, motor unit physiology, and TDP-43 pathology by CHCHD10

Mutations in CHCHD10, a gene coding for a mitochondrial intermembrane space protein, are associated with Frontotemporal dementia (FTD)-Amyotrophic lateral sclerosis (ALS) spectrum disorders, which are pathologically characterized by cytoplasmic inclusions containing TDP-43. FTD/ALS-linked CHCHD10 mutations and TDP-43 inclusions similarly induce mitochondrial defects in respiration, fusion/fission, mtDNA stability, and cristae structure, while sizeable amounts of cytoplasmic TDP-43 aggregates are found in mitochondria. However, the mechanistic link between CHCHD10 and TDP-43 pathogenesis remains unclear. In this study, we present immunohistochemical and biochemical evidence demonstrating that insoluble CHCHD10 aggregates accumulate and colocalize with phospho-TDP-43 inclusions in brains of FTLD-TDP and AD patients, and that insoluble CHCHD10 levels tightly correlate with insoluble TDP-43 levels in control and FTLD-TDP brains. In an experimental exploration of this pathological phenotype, transgenic mice neuronally expressing FTD/ALS-linked CHCHD10R15L or CHCHDS59L mutations but not CHCHD10WT transgenic mice exhibit significantly increased CHCHD10 aggregation and phospho-TDP-43 pathology, which often colocalize within the same inclusions. Such pathologies are reflected in poor functional outcomes in long-term synaptic plasticity, motor unit physiology, and behavior in CHCHD10R15L and CHCHDS59L transgenic mice. In contrast, expression of CHCHD10WT in hTDP-43 transgenic mice (TAR4;CHCHD10WT) significantly mitigates phospho-TDP-43 pathology and rescues TDP-43-induced impairments in synaptic integrity and long-term synaptic plasticity. In isolated mitochondria, the S59L mutation induces the aggregation of resident CHCHD10S59L protein as well as the aggregation and slower turnover of recombinant TDP-43 imported into mitochondria. Likewise, in an in vitro cell-free system, the S59L mutation induces the aggregation of CHCHD10S59L protein while simultaneously enhancing the aggregation of recombinant TDP-43, as evidenced by filter trap assays and atomic force microscopy. In contrast, recombinant CHCHD10WT inhibits the growth of TDP-43 aggregates. These results in human brains, transgenic mice, and in vitro systems substantiate the role of wild type and mutant CHCHD10 in modulating mitochondrial CHCHD10 and TDP-43 pathogenesis together with associated phenotypes in long-term synaptic plasticity and motor unit physiology in mice and humans.

Structures of the Wild-Type and S59L Mutant CHCHD10 Proteins Important in Amyotrophic Lateral Sclerosis-Frontotemporal Dementia

The S59L genetic mutation of the mitochondrial coiled-coil-helix-coiled-coil-helix domain-containing protein 10 (CHCHD10) is involved in the pathogenesis of amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD). The wild-type and mutant forms of this protein contain intrinsically disordered regions, and their structural characterization has been facing challenges. Here, for the first time in the literature, we present the structural ensemble properties of the wild-type and S59L mutant form of CHCHD10 in an aqueous solution environment at the atomic level with dynamics. Even though available experiments suggested that the S59L mutation may not change the structure of the CHCHD10 protein, our structural analysis clearly shows that the structure of this protein is significantly affected by the S59L mutation. We present here the secondary structure components with their abundances per residue, the tertiary structure properties, the free energy surfaces based on the radius of gyration and end-to-end distance values, the Ramachandran plots, the quantity of intramolecular hydrogen bonds, and the principal component analysis results. These results may be crucial in designing more efficient treatment for ALS and FTD diseases.

Mutant CHCHD10 causes an extensive metabolic rewiring that precedes OXPHOS dysfunction in a murine model of mitochondrial cardiomyopathy

Mitochondrial cardiomyopathies are fatal diseases, with no effective treatment. Alterations of heart mitochondrial function activate the mitochondrial integrated stress response (ISR^mt), a transcriptional program affecting cell metabolism, mitochondrial biogenesis, and proteostasis. In humans, mutations in CHCHD10, a mitochondrial protein with unknown function, were recently associated with dominant multi-system mitochondrial diseases, whose pathogenic mechanisms remain to be elucidated. Here, in CHCHD10 knockin mutant mice, we identify an extensive cardiac metabolic rewiring triggered by proteotoxic ISR^mt. The stress response arises early on, before the onset of bioenergetic impairments, triggering a switch from oxidative to glycolytic metabolism, enhancement of transsulfuration and one carbon (1C) metabolism, and widespread metabolic imbalance. In parallel, increased NADPH oxidases elicit antioxidant responses, leading to heme depletion. As the disease progresses, the adaptive metabolic stress response fails, resulting in fatal cardiomyopathy. Our findings suggest that early interventions to counteract metabolic imbalance could ameliorate mitochondrial cardiomyopathy associated with proteotoxic ISR^mt.

Sayles et al. report that mutant CHCHD10 proteotoxicity activates the mitochondrial integrated stress response (ISR^mt) in a mouse model of mitochondrial cardiomyopathy. Chronic ISR^mt causes profound metabolic imbalances, culminating in oxidative stress and iron dysregulation, ultimately resulting in mitochondrial dysfunction and contributing to disease pathogenesis.

Mitochondrial CHCHD2: Disease-Associated Mutations, Physiological Functions, and Current Animal Models

Rare mutations in the mitochondrial protein coiled-coil-helix-coiled-coil-helix domain containing 2 (CHCHD2) are associated with Parkinson's disease (PD) and other Lewy body disorders. CHCHD2 is a bi-organellar mediator of oxidative phosphorylation, playing crucial roles in regulating electron flow in the mitochondrial electron transport chain and acting as a nuclear transcription factor for a cytochrome c oxidase subunit (COX4I2) and itself in response to hypoxic stress. CHCHD2 also regulates cell migration and differentiation, mitochondrial cristae structure, and apoptosis. In this review, we summarize the known disease-associated mutations of CHCHD2 in Asian and Caucasian populations, the physiological functions of CHCHD2, how CHCHD2 mutations contribute to α-synuclein pathology, and current animal models of CHCHD2. Further, we discuss the necessity of continued investigation into the divergent functions of CHCHD2 and CHCHD10 to determine how mutations in these similar mitochondrial proteins contribute to different neurodegenerative diseases.

Meta-analysis of the association between CHCHD10 Pro34Ser variant and the risk of amyotrophic lateral sclerosis

BACKGROUND

Amyotrophic lateral sclerosis (ALS), one of the motor neuron diseases, appears to be caused by genetic and environmental risk factors. However, the influence of Pro34Ser variant of CHCHD10 gene in increasing risk of ALS remains indeterminate. This study conducted a meta-analysis to establish the association between Pro34Ser variant of CHCHD10 gene and risk of ALS.

METHODS

PubMed, Web of Science, and Embase databases were systematically searched for genome-wide association studies or case-control studies published up to March 28, 2020, on the association between Pro34Ser variant and risk of ALS. Data from eligible studies were extracted and analyzed.

RESULTS

Twelve case-control studies involving 7442 patients with sporadic ALS and 75,371 controls were analyzed. The Pro34Ser variant was not associated with increased risk of ALS disease based on fixed-effects meta-analysis (Pro34Ser-positive vs Pro34Ser-negative: OR 1.23, 95% CI 0.90 to 1.69, P = 0.201).

CONCLUSION

Existing evidence suggests that Pro34Ser variant in CHCHD10 is not associated with risk of ALS, particularly in Caucasian participants. However, our results ought to be validated using large, well-designed studies, especially in Asian and African populations.

CHCHD10-regulated OPA1-mitofilin complex mediates TDP-43-induced mitochondrial phenotypes associated with frontotemporal dementia

Mutations in CHCHD10, a gene coding for a mitochondrial protein, are implicated in ALS-FTD spectrum disorders, which are pathologically characterized by transactive response DNA binding protein 43 kDa (TDP-43) accumulation. While both TDP-43 and CHCHD10 mutations drive mitochondrial pathogenesis, mechanisms underlying such phenotypes are unclear. Moreover, despite the disruption of the mitochondrial mitofilin protein complex at cristae junctions in patient fibroblasts bearing the CHCHD10S59L mutation, the role of CHCHD10 variants in mitofilin-associated protein complexes in brain has not been examined. Here, we utilized novel CHCHD10 transgenic mouse variants (WT, R15L, & S59L), TDP-43 transgenic mice, FTLD-TDP patient brains, and transfected cells to assess the interplay between CHCHD10 and TDP-43 on mitochondrial phenotypes. We show that CHCHD10 mutations disrupt mitochondrial OPA1-mitofilin complexes in brain, associated with impaired mitochondrial fusion and respiration. Likewise, CHCHD10 levels and OPA1-mitofilin complexes are significantly reduced in brains of FTLD-TDP patients and TDP-43 transgenic mice. In cultured cells, CHCHD10 knockdown results in OPA1-mitofilin complex disassembly, while TDP-43 overexpression also reduces CHCHD10, promotes OPA1-mitofilin complex disassembly via CHCHD10, and impairs mitochondrial fusion and respiration, phenotypes that are rescued by wild type (WT) CHCHD10. These results indicate that disruption of CHCHD10-regulated OPA1-mitofilin complex contributes to mitochondrial abnormalities in FTLD-TDP and suggest that CHCHD10 restoration could ameliorate mitochondrial dysfunction in FTLD-TDP.

ALS and Parkinson's disease genes CHCHD10 and CHCHD2 modify synaptic transcriptomes in human iPSC-derived motor neurons

Mitochondrial intermembrane space proteins CHCHD2 and CHCHD10 have roles in motor neuron diseases such as amyotrophic lateral sclerosis, spinal muscular atrophy and axonal neuropathy and in Parkinson's disease. They form a complex of unknown function. Here we address the importance of these two proteins in human motor neurons. We show that gene edited human induced pluripotent stem cells (iPSC) lacking either CHCHD2 or CHCHD10 are viable and can be differentiated into functional motor neurons that fire spontaneous and evoked action potentials. Mitochondria in knockout iPSC and motor neurons sustain ultrastructure but show increased proton leakage and respiration, and reciprocal compensatory increases in CHCHD2 or CHCHD10. Knockout motor neurons have largely overlapping transcriptome profiles compared to isogenic control line, in particular for synaptic gene expression. Our results show that the absence of either CHCHD2 or CHCHD10 alters mitochondrial respiration in human motor neurons, inducing similar compensatory responses. Thus, pathogenic mechanisms may involve loss of synaptic function resulting from defective energy metabolism.

Mitochondrial defect in muscle precedes neuromuscular junction degeneration and motor neuron death in CHCHD10S59L/+ mouse

Recently, we provided genetic basis showing that mitochondrial dysfunction can trigger motor neuron degeneration, through identification of CHCHD10 encoding a mitochondrial protein. We reported patients, carrying the p.Ser59Leu heterozygous mutation in CHCHD10, from a large family with a mitochondrial myopathy associated with motor neuron disease (MND). Rapidly, our group and others reported CHCHD10 mutations in amyotrophic lateral sclerosis (ALS), frontotemporal dementia-ALS and other neurodegenerative diseases. Here, we generated knock-in (KI) mice, carrying the p.Ser59Leu mutation, that mimic the mitochondrial myopathy with mtDNA instability displayed by the patients from our original family. Before 14 months of age, all KI mice developed a fatal mitochondrial cardiomyopathy associated with enhanced mitophagy. CHCHD10^S59L/+ mice also displayed neuromuscular junction (NMJ) and motor neuron degeneration with hyper-fragmentation of the motor end plate and moderate but significant motor neuron loss in lumbar spinal cord at the end stage of the disease. At this stage, we observed TDP-43 cytoplasmic aggregates in spinal neurons. We also showed that motor neurons differentiated from human iPSC carrying the p.Ser59Leu mutation were much more sensitive to Staurosporine or glutamate-induced caspase activation than control cells. These data confirm that mitochondrial deficiency associated with CHCHD10 mutations can be at the origin of MND. CHCHD10 is highly expressed in the NMJ post-synaptic part. Importantly, the fragmentation of the motor end plate was associated with abnormal CHCHD10 expression that was also observed closed to NMJs which were morphologically normal. Furthermore, we found OXPHOS deficiency in muscle of CHCHD10^S59L/+ mice at 3 months of age in the absence of neuron loss in spinal cord. Our data show that the pathological effects of the p.Ser59Leu mutation target muscle prior to NMJ and motor neurons. They likely lead to OXPHOS deficiency, loss of cristae junctions and destabilization of internal membrane structure within mitochondria at motor end plate of NMJ, impairing neurotransmission. These data are in favor with a key role for muscle in MND associated with CHCHD10 mutations.

ALS/FTD mutant CHCHD10 mice reveal a tissue-specific toxic gain-of-function and mitochondrial stress response

Mutations in coiled-coil-helix-coiled-coil-helix domain containing 10 (CHCHD10), a mitochondrial protein of unknown function, cause a disease spectrum with clinical features of motor neuron disease, dementia, myopathy and cardiomyopathy. To investigate the pathogenic mechanisms of CHCHD10, we generated mutant knock-in mice harboring the mouse-equivalent of a disease-associated human S59L mutation, S55L in the endogenous mouse gene. CHCHD10^S55L mice develop progressive motor deficits, myopathy, cardiomyopathy and accelerated mortality. Critically, CHCHD10 accumulates in aggregates with its paralog CHCHD2 specifically in affected tissues of CHCHD10^S55L mice, leading to aberrant organelle morphology and function. Aggregates induce a potent mitochondrial integrated stress response (mtISR) through mTORC1 activation, with elevation of stress-induced transcription factors, secretion of myokines, upregulated serine and one-carbon metabolism, and downregulation of respiratory chain enzymes. Conversely, CHCHD10 ablation does not induce disease pathology or activate the mtISR, indicating that CHCHD10^S55L-dependent disease pathology is not caused by loss-of-function. Overall, CHCHD10^S55L mice recapitulate crucial aspects of human disease and reveal a novel toxic gain-of-function mechanism through maladaptive mtISR and metabolic dysregulation.

CHCHD10 is involved in the development of Parkinson's disease caused by CHCHD2 loss-of-function mutation p.T61I

Previously we identified the p.Thr61Ile mutation in coiled-coil-helix-coiled-coil-helix domain containing 2 (CHCHD2) in a Chinese family with autosomal dominant Parkinson's disease. But the mechanism is still unclear. In this study, we explored the effects of CHCHD2 p.Thr61Ile mutation in cells and its association with coiled-coil-helix-coiled-coil-helix domain containing 10 (CHCHD10). We found that overexpression of Parkinson's disease-associated T61I mutant CHCHD2 did not produce mitochondrial dysfunction. Rather, its protective effect from stress was abrogated. And, the level of the CHCHD2 protein and mRNA in patient fibroblasts was not significantly different from control. In addition, CHCHD2 T61I mutation caused increased interaction with CHCHD10 and reduced CHCHD10 level. The mitochondrial ultrastructural alterations in CHCHD2 T61I mutant patient fibroblasts are similar to that of CHCHD10 mutations. We therefore propose that CHCHD10 is involved in the development of Parkinson's disease caused by CHCHD2 loss-of-function mutation p.T61I.

Loss of MICOS complex integrity and mitochondrial damage, but not TDP-43 mitochondrial localisation, are likely associated with severity of CHCHD10-related diseases

Following the involvement of CHCHD10 in FrontoTemporal-Dementia-Amyotrophic Lateral Sclerosis (FTD-ALS) clinical spectrum, a founder mutation (p.Gly66Val) in the same gene was identified in Finnish families with late-onset spinal motor neuronopathy (SMAJ). SMAJ is a slowly progressive form of spinal muscular atrophy with a life expectancy within normal range. In order to understand why the p.Ser59Leu mutation, responsible for severe FTD-ALS, and the p.Gly66Val mutation could lead to different levels of severity, we compared their effects in patient cells. Unlike affected individuals bearing the p.Ser59Leu mutation, patients presenting with SMAJ phenotype have neither mitochondrial myopathy nor mtDNA instability. The expression of CHCHD10^S59L mutant allele leads to disassembly of mitochondrial contact site and cristae organizing system (MICOS) with mitochondrial dysfunction and loss of cristae in patient fibroblasts. We also show that G66V fibroblasts do not display the loss of MICOS complex integrity and mitochondrial damage found in S59L cells. However, S59L and G66V fibroblasts show comparable accumulation of phosphorylated mitochondrial TDP-43 suggesting that the severity of phenotype and mitochondrial damage do not depend on mitochondrial TDP-43 localization. The expression of the CHCHD10^G66V allele is responsible for mitochondrial network fragmentation and decreased sensitivity towards apoptotic stimuli, but with a less severe effect than that found in cells expressing the CHCHD10^S59L allele. Taken together, our data show that cellular phenotypes associated with p.Ser59Leu and p.Gly66Val mutations in CHCHD10 are different; loss of MICOS complex integrity and mitochondrial dysfunction, but not TDP-43 mitochondrial localization, being likely essential to develop a severe motor neuron disease.

A novel CHCHD10 mutation implicates a Mia40-dependent mitochondrial import deficit in ALS

CHCHD10 mutations are linked to amyotrophic lateral sclerosis, but their mode of action is unclear. In a 29-year-old patient with rapid disease progression, we discovered a novel mutation (Q108P) in a conserved residue within the coiled-coil-helix-coiled-coil-helix (CHCH) domain. The aggressive clinical phenotype prompted us to probe its pathogenicity. Unlike the wild-type protein, mitochondrial import of CHCHD10 Q108P was blocked nearly completely resulting in diffuse cytoplasmic localization and reduced stability. Other CHCHD10 variants reported in patients showed impaired mitochondrial import (C122R) or clustering within mitochondria (especially G66V and E127K) often associated with reduced expression. Truncation experiments suggest mitochondrial import of CHCHD10 is mediated by the CHCH domain rather than the proposed N-terminal mitochondrial targeting signal. Knockdown of Mia40, which introduces disulfide bonds into CHCH domain proteins, blocked mitochondrial import of CHCHD10. Overexpression of Mia40 rescued mitochondrial import of CHCHD10 Q108P by enhancing disulfide-bond formation. Since reduction in CHCHD10 inhibits respiration, mutations in its CHCH domain may cause aggressive disease by impairing mitochondrial import. Our data suggest Mia40 upregulation as a potential therapeutic salvage pathway.

Genetic Features of MAPT, GRN, C9orf72 and CHCHD10 Gene Mutations in Chinese Patients with Frontotemporal Dementia

BACKGROUND

Mutations in microtubule associated protein tau (MAPT), progranulin (GRN), chromosome 9 open-reading frame 72 (C9orf72) and CHCHD10 genes have been reported causing frontotemporal dementia (FTD) in different populations. However, collective analysis of mutations in these four genes in Chinese FTD patients has not been reported yet.

METHODS

The aim of this study was to investigate the genetic features of Chinese patients with MAPT, GRN, C9orf72 or CHCHD10 gene mutations in an FTD cohort recruited from multi clinical centers in Shanghai metropolitan areas, China. MAPT, GRN and CHCHD10 genes were analysed by direct sequencing, and C9orf72 hexanucleotide repeat expansion was analysed by repeat-primed PCR in 82 patients with sporadic FTD. The identified gene variants were screened in 400 age matched controls.

RESULTS

We found one known pathogenic variant (rs63750959) and one novel mutation (NG_007398.1: g.120962C>T; H299Y) of MAPT gene, one novel variant (c.750C>A; D250E) of GRN gene and two novel mutations in CHCHD10 gene (c.63C>T, no AA change; c.71G>A, P24L). No abnormal C9orf72 gene hexanucleotide repeat expansion was identified in this cohort. Collectively, genetic testing could discover 4.9% sporadic FTD patients with genetic causes. In addition, MAPT and CHCHD10 might be more important genes affecting Chinese with FTD.

Mutation analysis of CHCHD2 and CHCHD10 in Italian patients with mitochondrial myopathy

Mutations in CHCHD2 and CHCHD10 were recently reported in a broad spectrum of neurodegenerative diseases, for example, Parkinson's disease, amyotrophic lateral sclerosis, frontotemporal dementia, or mitochondrial myopathy (MM). The aim of the study was to evaluate the prevalence of CHCHD2 and CHCHD10 mutations in Italian MM patients without mitochondrial DNA mutations. The coding regions of CHCHD2 and CHCHD10 were sequenced in 62 MM patients. None of the patients showed CHCHD2 mutations, whereas 1 sporadic MM patient carried a homozygous Pro96Thr substitution in CHCHD10. Muscle biopsy of this patient showed intracellular glycogen accumulation with cytochrome c oxidase negative and ragged red fibers. Our study suggests that the homozygous Pro96Thr mutation in CHCHD10 might be pathogenic but does not support a major role for CHCHD2 in MM pathogenesis.

Investigating the role of ALS genes CHCHD10 and TUBA4A in Belgian FTD-ALS spectrum patients

Mutation screening and phenotypic profiling of 2 amyotrophic lateral sclerosis-(ALS) and frontotemporal dementia-(FTD) associated genes, CHCHD10 and TUBA4A, were performed in a Belgian cohort of 459 FTD, 28 FTD-ALS, and 429 ALS patients. In CHCHD10, we identified a novel nonsense mutation (p.Gln108*) in a patient with atypical clinical FTD and pathology-confirmed Parkinson's disease (1/459, 0.22%) leading to loss of transcript. We further observed 3 previously described missense variants (p.Pro34Ser, p.Pro80Leu, and p.Pro96Thr) that were also present in the matched control series. In TUBA4A, we detected a novel frameshift mutation (p.Arg64Glyfs*90) leading to a truncated protein in 1 FTD patient (1/459 of 0.22%) with family history of Parkinson's disease and cognitive impairment, and a novel missense mutation (p.Thr381Met) in 2 sibs with familial ALS and memory problems (1 index patient/429, 0.23%) in whom we previously identified a pathogenic Chromosome 9 open reading frame 72 repeat expansion mutation. The present study confirms the role of CHCHD10 and TUBA4A in the FTD-ALS spectrum, although genetic variations in these 2 genes are extremely rare in the Belgian population and often associated with symptomatology of related neurodegenerative diseases including Parkinson's disease and Alzheimer's disease.

CHCHD10 mutations promote loss of mitochondrial cristae junctions with impaired mitochondrial genome maintenance and inhibition of apoptosis

CHCHD10-related diseases include mitochondrial DNA instability disorder, frontotemporal dementia-amyotrophic lateral sclerosis (FTD-ALS) clinical spectrum, late-onset spinal motor neuropathy (SMAJ), and Charcot-Marie-Tooth disease type 2 (CMT2). Here, we show that CHCHD10 resides with mitofilin, CHCHD3 and CHCHD6 within the "mitochondrial contact site and cristae organizing system" (MICOS) complex. CHCHD10 mutations lead to MICOS complex disassembly and loss of mitochondrial cristae with a decrease in nucleoid number and nucleoid disorganization. Repair of the mitochondrial genome after oxidative stress is impaired in CHCHD10 mutant fibroblasts and this likely explains the accumulation of deleted mtDNA molecules in patient muscle. CHCHD10 mutant fibroblasts are not defective in the delivery of mitochondria to lysosomes suggesting that impaired mitophagy does not contribute to mtDNA instability. Interestingly, the expression of CHCHD10 mutant alleles inhibits apoptosis by preventing cytochrome c release.

Identification of CHCHD10 Mutation in Chinese Patients with Alzheimer Disease

CHCHD10 gene has been identified to be associated with frontotemporal dementia (FTD) and amyotrophic lateral sclerosis (ALS). Considering the clinical phenotype and pathology characterization were overlapped between FTD and Alzheimer disease (AD), and so far, no systematic analysis of CHCHD10 mutation was conducted in patients with AD in Asian population. Therefore, we screened of all exons in CHCHD10 in a cohort of 484 AD patients (60 with family history) from Mainland China. A heterozygous variant p.A35D (c.104C>A), previously reported in a patient with FTD in Italian population, was identified in a female patient with sporadic LOAD. The age at onset of mutation carrier was 86, presented as typical amnestic dementia. The mutation was found to be deleterious according to in silico predictions and excluded in 500 ethnically and geographically matched controls. Our finding revealed the clinical manifestations of variant p.A35D (c.104C>A) in a LOAD case and indicated that CHCHD10 mutation was presented in different types of dementia.

Intrafamilial clinical variability in individuals carrying the CHCHD10 mutation Gly66Val

OBJECTIVES

Mutations in the CHCHD10 gene, which encodes a mitochondrially targeted protein, have emerged as an important cause of motor neuron disease and frontotemporal lobar degeneration. The aim of this study was to assess the clinical variability in a large family carrying the p.Gly66Val mutation of the CHCHD10 gene. This mutation has recently been reported to cause late-onset spinal muscular atrophy (SMAJ) or sensorimotor axonal Charcot-Marie-Tooth neuropathy (CMT2) in the Finnish population.

MATERIALS AND METHODS

Nine affected members of an extended Finnish pedigree were included in the study. Detailed clinical and neurophysiological examinations were performed. The CHCHD10 p.Gly66Val mutation was examined by Sanger sequencing.

RESULTS

The heterozygous p.Gly66Val mutation was present in all affected individuals from whom a DNA sample was available. The clinical phenotype varied from proximal sensorimotor neuropathy to spinal muscular atrophy and in one case resembled motor neuron disease ALS at its early stages. The age of onset varied from 30 to 73 years.

CONCLUSIONS

Our data demonstrate that even within the same family, the p.Gly66Val variant can cause variable phenotypes ranging from CMT2-type axonal neuropathy to spinal muscular atrophy, which may also present as an ALS-like disease. The spectrum of CHCHD10-related neuromuscular disease has widened rapidly, and we recommend keeping the threshold for genetic testing low particularly when dominant inheritance or mitochondrial pathology is present.

CHCHD10 is not a frequent causative gene in Chinese ALS patients

Amyotrophic lateral sclerosis (ALS) is a devastating neurodegenerative disorder characterized by the death of motor neurons. Recently, mutations in CHCHD10 have been reported to cause ALS in Western populations. In the present study, direct DNA sequencing has been performed on CHCHD10 in a cohort of 294 ALS patients of Chinese Han origin. No mutations were identified in CHCHD10 in ALS cases of Chinese ancestry. We propose CHCHD10 might not be a frequent causal gene among Chinese with ALS.

Mutation Screening of the CHCHD10 Gene in Chinese Patients with Amyotrophic Lateral Sclerosis

Mutations in the coiled-coil-helix-coiled-coil-helix domain-containing protein 10 gene (CHCHD10), involved in mitochondrial function, have recently been reported as a causative gene of amyotrophic lateral sclerosis (ALS). The aim of this study was to obtain the mutation prevalence of CHCHD10 and the phenotypes with mutations in Chinese ALS patients. A cohort of 499 ALS patients including 487 sporadic ALS (SALS) and 12 familial ALS (FALS), from the Department of Neurology, West China Hospital of Sichuan University, were screened for mutations of all exons of the CHCHD10 gene by Sanger sequencing. Novel candidate mutations or variants were confirmed by polymerase chain reaction-restriction fragment length polymorphism in 466 healthy individuals. All patients identified with mutations of CHCHD10 gene were screened for mutations of the common ALS causative genes including C9orf72, SOD1, TARDBP, FUS, PFN1, and SQSTM1. Three heterozygous variants, including two missense mutations (c.275A > G (p.Y92C) and c.306G > C (p.Q102H)) and a synonymous change c.306G > A (p.Q102Q), were found in exon 3 of CHCHD10 in three alive SALS individuals (with the longest disease duration of 8.6 years), all of which were not detected in healthy controls. No mutation in CHCHD10 was identified in FALS patients. No mutation was found in the aforementioned common ALS causative genes in the patients who carried CHCHD10 mutations. The mutation frequency of CHCHD10 (0.4 %, 2/487) in a Chinese SALS population suggests CHCHD10 gene mutation appears to be an uncommon cause of ALS in Chinese populations. CHCHD10 mutations are associated with a slow progression and long disease duration.

The CHCHD10 P34S variant is not associated with ALS in a UK cohort of familial and sporadic patients

Mutations in CHCHD10 have recently been reported as a cause of amyotrophic lateral sclerosis (ALS) and frontotemporal dementia. To address the genetic contribution of CHCHD10 to ALS, we have screened a cohort of 425 UK ALS ± frontotemporal dementia patients and 576 local controls in all coding exons of CHCHD10 by Sanger sequencing. We identified a previously reported p.P34S variant that is also present in neurologically healthy controls (p = 0.58). Our results suggest that CHCHD10 is not a primary cause of ALS in UK cases.

Spontaneous activity in electromyography may differentiate certain benign lower motor neuron disease forms from amyotrophic lateral sclerosis

There is limited data on electromyography (EMG) findings in other motor neuron disorders than amyotrophic lateral sclerosis (ALS). We assessed whether the distribution of active denervation detected by EMG, i.e. fibrillations and fasciculations, differs between ALS and slowly progressive motor neuron disorders. We compared the initial EMG findings of 43 clinically confirmed, consecutive ALS patients with those of 41 genetically confirmed Late-onset Spinal Motor Neuronopathy and 14 Spinal and Bulbar Muscular Atrophy patients. Spontaneous activity was more frequently detected in the first dorsal interosseus and deltoid muscles of ALS patients than in patients with the slowly progressive motor neuron diseases. The most important observation was that absent fibrillations in the first dorsal interosseus muscle identified the benign forms with sensitivities of 66%-77% and a specificity of 93%. The distribution of active denervation may help to separate ALS from mimicking disorders at an early stage.

Mitochondrial dynamism and the pathogenesis of Amyotrophic Lateral Sclerosis

Research on mitochondria in the last years has been characterized by the fundamental finding that the morphology of mitochondria is deeply connected to the regulation of a vast number of different processes, including oxidative phosphorylation and ATP production, calcium buffering, and apoptosis. This has immediately focused the attention of the neuroscience community to the possible involvement of mitochondrial dynamism, the process underlying morphological features of mitochondria, in neurodegeneration, where mitochondrial dysfunction is believed to represent an important contributing event, or even a primary causative factor. Amyotrophic Lateral Sclerosis (ALS), a disease of motor neurons and their neighboring cells, has long been considered as a neurodegenerative disease with an important mitochondrial issue. Yet, whether mitochondria have a causative, primary role in the pathogenic process has always been debated, and the specific defects which account for this role are elusive. Here we discuss recent genetic advances suggesting that defective mitochondrial dynamism is primarily involved in the pathogenic mechanisms of ALS, and that foster the longstanding concept that disruption of mitochondrial function is a vulnerable factor for motor neurons.

CHCH10 mutations in an Italian cohort of familial and sporadic amyotrophic lateral sclerosis patients

Mutations in CHCHD10 have recently been described as a cause of frontotemporal dementia (FTD) comorbid with amyotrophic lateral sclerosis (ALS). The aim of this study was to assess the frequency and clinical characteristics of CHCHD10 mutations in Italian patients diagnosed with familial (n = 64) and apparently sporadic ALS (n = 224). Three apparently sporadic patients were found to carry c.100C>T (p.Pro34Ser) heterozygous variant in the exon 2 of CHCHD10. This mutation had been previously described in 2 unrelated French patients with FTD-ALS. However, our patients had a typical ALS, without evidence of FTD, cerebellar or extrapyramidal signs, or sensorineural deficits. We confirm that CHCHD10 mutations account for ∼ 1% of Italian ALS patients and are a cause of disease in subjects without dementia or other atypical clinical signs.

Screening of CHCHD10 in a French cohort confirms the involvement of this gene in frontotemporal dementia with amyotrophic lateral sclerosis patients

Mutations in the CHCHD10 gene have been recently identified in a large family with a complex phenotype variably associating frontotemporal dementia (FTD) with amyotrophic lateral sclerosis (ALS), cerebellar ataxia, myopathy, and hearing impairment. CHCHD10 encodes a protein located in the mitochondrial intermembrane space and is likely involved in mitochondrial genome stability and maintenance of cristae junctions. However, the exact contribution of CHCHD10 in FTD and ALS diseases spectrum remains unknown. In this study, we evaluated the frequency of CHCHD10 mutations in 115 patients with FTD and FTD-ALS phenotypes. We identified 2 heterozygous variants in 3 unrelated probands presenting FTD and ALS, characterized by early and predominant bulbar symptoms. This study demonstrates the implication of CHCHD10 in FTD and ALS spectrum. Although the frequency of mutations is low in this series (2.6%), our work suggests that CHCHD10 mutations should be searched particularly when bulbar symptoms are present at onset.

A mitochondrial origin for frontotemporal dementia and amyotrophic lateral sclerosis through CHCHD10 involvement

Mitochondrial DNA instability disorders are responsible for a large clinical spectrum, among which amyotrophic lateral sclerosis-like symptoms and frontotemporal dementia are extremely rare. We report a large family with a late-onset phenotype including motor neuron disease, cognitive decline resembling frontotemporal dementia, cerebellar ataxia and myopathy. In all patients, muscle biopsy showed ragged-red and cytochrome c oxidase-negative fibres with combined respiratory chain deficiency and abnormal assembly of complex V. The multiple mitochondrial DNA deletions found in skeletal muscle revealed a mitochondrial DNA instability disorder. Patient fibroblasts present with respiratory chain deficiency, mitochondrial ultrastructural alterations and fragmentation of the mitochondrial network. Interestingly, expression of matrix-targeted photoactivatable GFP showed that mitochondrial fusion was not inhibited in patient fibroblasts. Using whole-exome sequencing we identified a missense mutation (c.176C>T; p.Ser59Leu) in the CHCHD10 gene that encodes a coiled-coil helix coiled-coil helix protein, whose function is unknown. We show that CHCHD10 is a mitochondrial protein located in the intermembrane space and enriched at cristae junctions. Overexpression of a CHCHD10 mutant allele in HeLa cells led to fragmentation of the mitochondrial network and ultrastructural major abnormalities including loss, disorganization and dilatation of cristae. The observation of a frontotemporal dementia-amyotrophic lateral sclerosis phenotype in a mitochondrial disease led us to analyse CHCHD10 in a cohort of 21 families with pathologically proven frontotemporal dementia-amyotrophic lateral sclerosis. We identified the same missense p.Ser59Leu mutation in one of these families. This work opens a novel field to explore the pathogenesis of the frontotemporal dementia-amyotrophic lateral sclerosis clinical spectrum by showing that mitochondrial disease may be at the origin of some of these phenotypes.