Mitochondrial CHCHD-Containing Proteins: Physiologic Functions and Link with Neurodegenerative Diseases

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.

Analgesic targets identified in mouse sensory neuron somata and terminal pain translatomes

The relationship between transcription and protein expression is complex. We identified polysome-associated RNA transcripts in the somata and central terminals of mouse sensory neurons in control, painful (plus nerve growth factor), and pain-free conditions (Nav1.7-null mice). The majority (98%) of translated transcripts are shared between male and female mice in both the somata and terminals. Some transcripts are highly enriched in the somata or terminals. Changes in the translatome in painful and pain-free conditions include novel and known regulators of pain pathways. Antisense knockdown of selected somatic and terminal polysome-associated transcripts that correlate with pain states diminished pain behavior. Terminal-enriched transcripts included those encoding synaptic proteins (e.g., synaptotagmin), non-coding RNAs, transcription factors (e.g., Znf431), proteins associated with transsynaptic trafficking (HoxC9), GABA-generating enzymes (Gad1 and Gad2), and neuropeptides (Penk). Thus, central terminal translation may well be a significant regulatory locus for peripheral input from sensory neurons.

Mutant huntingtin impairs neurodevelopment in human brain organoids through CHCHD2-mediated neurometabolic failure

Expansion of the glutamine tract (poly-Q) in the protein huntingtin (HTT) causes the neurodegenerative disorder Huntington's disease (HD). Emerging evidence suggests that mutant HTT (mHTT) disrupts brain development. To gain mechanistic insights into the neurodevelopmental impact of human mHTT, we engineered male induced pluripotent stem cells to introduce a biallelic or monoallelic mutant 70Q expansion or to remove the poly-Q tract of HTT. The introduction of a 70Q mutation caused aberrant development of cerebral organoids with loss of neural progenitor organization. The early neurodevelopmental signature of mHTT highlighted the dysregulation of the protein coiled-coil-helix-coiled-coil-helix domain containing 2 (CHCHD2), a transcription factor involved in mitochondrial integrated stress response. CHCHD2 repression was associated with abnormal mitochondrial morpho-dynamics that was reverted upon overexpression of CHCHD2. Removing the poly-Q tract from HTT normalized CHCHD2 levels and corrected key mitochondrial defects. Hence, mHTT-mediated disruption of human neurodevelopment is paralleled by aberrant neurometabolic programming mediated by dysregulation of CHCHD2, which could then serve as an early interventional target for HD.

Axonopathy Underlying Amyotrophic Lateral Sclerosis: Unraveling Complex Pathways and Therapeutic Insights

Amyotrophic Lateral Sclerosis (ALS) is a complex neurodegenerative disorder characterized by progressive axonopathy, jointly leading to the dying back of the motor neuron, disrupting both nerve signaling and motor control. In this review, we highlight the roles of axonopathy in ALS progression, driven by the interplay of multiple factors including defective trafficking machinery, protein aggregation, and mitochondrial dysfunction. Dysfunctional intracellular transport, caused by disruptions in microtubules, molecular motors, and adaptors, has been identified as a key contributor to disease progression. Aberrant protein aggregation involving TDP-43, FUS, SOD1, and dipeptide repeat proteins further amplifies neuronal toxicity. Mitochondrial defects lead to ATP depletion, oxidative stress, and Ca2+ imbalance, which are regarded as key factors underlying the loss of neuromuscular junctions and axonopathy. Mitigating these defects through interventions including neurotrophic treatments offers therapeutic potential. Collaborative research efforts aim to unravel ALS complexities, opening avenues for holistic interventions that target diverse pathological mechanisms.

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 (CHCHD10G58R) in aqueous solution. Moreover, we describe the impacts of G58R mutation on the structural ensembles of wild-type CHCHD10 (CHCHD10WT) in aqueous solution. The dynamics properties as well as structural properties of CHCHD10WT 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 CHCHD10WT and CHCHD10G58R proteins possess different structural ensemble characteristics and describe the impacts of G58R mutation on CHCHD10WT. These findings may be helpful for designing new treatments for mitochondrial myopathy.Communicated by Ramaswamy H. Sarma.

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.

The Interaction and Effect of a Small MitoBlock Library as Inhibitor of ALR Protein-Protein Interaction Pathway

MIA40 and ALR of the MIA pathway mediate the import of protein precursors that form disulfides into the mitochondrial intermembrane space. This import pathway is suggested to be a linear pathway in which MIA40 first binds to the precursor via a disulfide linkage and oxidizes it. Subsequently, ALR re-oxidizes MIA40 and then ALR transfers electrons to terminal electron acceptors. However, the precise mechanism by which ALR and MIA40 coordinate translocation is unknown. With a collection of small molecule modulators (MB-5 to MB-9 and MB-13) that inhibit ALR activity, we characterized the import mechanism in mitochondria. NMR studies show that most of the compounds bind to a similar region in ALR. Mechanistic studies with small molecules demonstrate that treatment with compound MB-6 locks the precursor in a state bound to MIA40, blocking re-oxidation of MIA40 by ALR. Thus, small molecules that target a similar region in ALR alter the dynamics of the MIA import pathway differently, resulting in a set of probes that are useful for studying the catalysis of the redox-regulated import pathway in model systems.

Decoding metabolic signatures in Alzheimer's disease: a mitochondrial perspective

Alzheimer's disease (AD) is one of the most prevalent age-related neurodegenerative diseases and accounts for the majority of dementia cases worldwide. Tremendous ongoing efforts of basic and clinical research have expanded our knowledge on AD and its complex multifactorial pathogenesis. For sporadic AD, it is widely assumed that silent and early symptomatic stages initiate decades before the irreversible decline in cognitive abilities that ultimately lead to debilitating conditions. In addition to amyloid plaques and tau-containing neurofibrillary tangles as the most prominent hallmarks of AD lesions within the affected brain areas, we now possess a broader collection of pathological signatures that are associated with AD development and progression. In this regard, there is a substantial body of evidence suggesting that hypometabolism occurs in the brains of individuals at the prodromal stage before dementia is diagnosed, which may reflect an early role of metabolic dysfunction in AD. This perspective surveys the vast literature and critically assesses the current evidence demonstrating a mitochondrial contribution to AD. Additionally, we discuss our interpretations of the reported mitochondrial signatures and consider how altered mitochondrial bioenergetics may be an additional risk factor for AD pathogenesis.

Elevated CHCHD4 orchestrates mitochondrial oxidative phosphorylation to disturb hypoxic pulmonary hypertension

BACKGROUND

Pulmonary arterial hypertension (PAH) is a highly prevalent cardiopulmonary disorder characterized by vascular remodeling and increased resistance in pulmonary artery. Mitochondrial coiled-coil-helix-coiled-coil-helix domain (CHCHD)-containing proteins have various important pathophysiological roles. However, the functional roles of CHCHD proteins in hypoxic PAH is still ambiguous. Here, we aimed to investigate the role of CHCHD4 in hypoxic PAH and provide new insight into the mechanism driving the development of PAH.

METHODS

Serotype 1 adeno-associated viral vector (AAV) carrying Chchd4 was intratracheally injected to overexpress CHCHD4 in Sprague Dawley (SD) rats. The Normoxia groups of animals were housed at 21% O₂. Hypoxia groups were housed at 10% O₂, for 8 h/day for 4 consecutive weeks. Hemodynamic and histological characteristics are investigated in PAH. Primary pulmonary artery smooth muscle cells of rats (PASMCs) are used to assess how CHCHD4 affects proliferation and migration.

RESULTS

We found CHCHD4 was significantly downregulated among CHCHD proteins in hypoxic PASMCs and lung tissues from hypoxic PAH rats. AAV1-induced CHCHD4 elevation conspicuously alleviates vascular remodeling and pulmonary artery resistance, and orchestrates mitochondrial oxidative phosphorylation in PASMCs. Moreover, we found overexpression of CHCHD4 impeded proliferation and migration of PASMCs. Mechanistically, through lung tissues bulk RNA-sequencing (RNA-seq), we further identified CHCHD4 modulated mitochondrial dynamics by directly interacting with SAM50, a barrel protein on mitochondrial outer membrane surface. Furthermore, knockdown of SAM50 reversed the biological effects of CHCHD4 overexpression in isolated PASMCs.

CONCLUSIONS

Collectively, our data demonstrated that CHCHD4 elevation orchestrates mitochondrial oxidative phosphorylation and antagonizes aberrant PASMC cell growth and migration, thereby disturbing hypoxic PAH, which could serve as a promising therapeutic target for PAH treatment.

mtDNA Maintenance and Alterations in the Pathogenesis of Neurodegenerative Diseases

Considerable evidence indicates that the semiautonomous organelles mitochondria play key roles in the progression of many neurodegenerative disorders. Mitochondrial DNA (mtDNA) encodes components of the OXPHOS complex but mutated mtDNA accumulates in cells with aging, which mirrors the increased prevalence of neurodegenerative diseases. This accumulation stems not only from the misreplication of mtDNA and the highly oxidative environment but also from defective mitophagy after fission. In this review, we focus on several pivotal mitochondrial proteins related to mtDNA maintenance (such as ATAD3A and TFAM), mtDNA alterations including mtDNA mutations, mtDNA elimination, and mtDNA release-activated inflammation to understand the crucial role played by mtDNA in the pathogenesis of neurodegenerative diseases such as Alzheimer's disease, Parkinson's disease, amyotrophic lateral sclerosis, and Huntington's disease. Our work outlines novel therapeutic strategies for targeting mtDNA.

Mechanisms of mitochondrial respiratory adaptation

Mitochondrial energetic adaptations encompass a plethora of conserved processes that maintain cell and organismal fitness and survival in the changing environment by adjusting the respiratory capacity of mitochondria. These mitochondrial responses are governed by general principles of regulatory biology exemplified by changes in gene expression, protein translation, protein complex formation, transmembrane transport, enzymatic activities and metabolite levels. These changes can promote mitochondrial biogenesis and membrane dynamics that in turn support mitochondrial respiration. The main regulatory components of mitochondrial energetic adaptation include: the transcription coactivator peroxisome proliferator-activated receptor-γ (PPARγ) coactivator 1α (PGC1α) and associated transcription factors; mTOR and endoplasmic reticulum stress signalling; TOM70-dependent mitochondrial protein import; the cristae remodelling factors, including mitochondrial contact site and cristae organizing system (MICOS) and OPA1; lipid remodelling; and the assembly and metabolite-dependent regulation of respiratory complexes. These adaptive molecular and structural mechanisms increase respiration to maintain basic processes specific to cell types and tissues. Failure to execute these regulatory responses causes cell damage and inflammation or senescence, compromising cell survival and the ability to adapt to energetically demanding conditions. Thus, mitochondrial adaptive cellular processes are important for physiological responses, including to nutrient availability, temperature and physical activity, and their failure leads to diseases associated with mitochondrial dysfunction such as metabolic and age-associated diseases and cancer.

Relevance of the TRIAP1/p53 axis in colon cancer cell proliferation and adaptation to glutamine deprivation

Human TRIAP1 (TP53-regulated inhibitor of apoptosis 1; also known as p53CSV for p53-inducible cell survival factor) is the homolog of yeast Mdm35, a well-known chaperone that interacts with the Ups/PRELI family proteins and participates in the intramitochondrial transfer of lipids for the synthesis of cardiolipin (CL) and phosphatidylethanolamine. Although recent reports indicate that TRIAP1 is a prosurvival factor abnormally overexpressed in various types of cancer, knowledge about its molecular and metabolic function in human cells is still elusive. It is therefore critical to understand the metabolic and proliferative advantages that TRIAP1 expression provides to cancer cells. Here, in a colorectal cancer cell model, we report that the expression of TRIAP1 supports cancer cell proliferation and tumorigenesis. Depletion of TRIAP1 perturbed the mitochondrial ultrastructure, without a major impact on CL levels and mitochondrial activity. TRIAP1 depletion caused extramitochondrial perturbations resulting in changes in the endoplasmic reticulum-dependent lipid homeostasis and induction of a p53-mediated stress response. Furthermore, we observed that TRIAP1 depletion conferred a robust p53-mediated resistance to the metabolic stress caused by glutamine deprivation. These findings highlight the importance of TRIAP1 in tumorigenesis and indicate that the loss of TRIAP1 has extramitochondrial consequences that could impact on the metabolic plasticity of cancer cells and their response to conditions of nutrient deprivation.

AIFM1 beyond cell death: An overview of this OXPHOS-inducing factor in mitochondrial diseases

Apoptosis-inducing factor (AIF) is a mitochondrial intermembrane space flavoprotein with diverse functions in cellular physiology. In this regard, a large number of studies have elucidated AIF's participation to chromatin condensation during cell death in development, cancer, cardiovascular and brain disorders. However, the discovery of rare AIFM1 mutations in patients has shifted the interest of biomedical researchers towards AIF's contribution to pathogenic mechanisms underlying inherited AIFM1-linked metabolic diseases. The functional characterization of AIF binding partners has rapidly advanced our understanding of AIF biology within the mitochondria and beyond its widely reported role in cell death. At the present time, it is reasonable to assume that AIF contributes to cell survival by promoting biogenesis and maintenance of the mitochondrial oxidative phosphorylation (OXPHOS) system. With this review, we aim to outline the current knowledge around the vital role of AIF by primarily focusing on currently reported human diseases that have been linked to AIFM1 deficiency.

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.

Potential proteomic alteration in the brain of Tg(SOD1*G93A)1Gur mice: A new pathogenesis insight of amyotrophic lateral sclerosis

The pathogenesis of amyotrophic lateral sclerosis (ALS) remains unclear. The recent studies have suggested that the protein abnormalities could play some important roles in ALS because several protein mutations were found in individuals with this disease. However, proteins that are currently known to be associated with ALS only explain the pathogenesis of this disease in a minority of cases, thus, further screening is needed to identify other ALS-related proteins. In this study, we systematically analyzed and compared the brain proteomic alterations between a mouse model of ALS, the Tg(SOD1*G93A)1Gur model, and wild-type mice using isobaric tags for relative and absolute quantitation (iTRAQ) as well as bioinformatics methods. The results revealed some significant up- and downregulated proteins at the different developmental stages in the ALS-like mice as well as the possibly related cellular components, molecular functions, biological processes, and pathways in the development of ALS. Our results identified some possible proteins that participate in the pathogenesis of ALS as well as the cellular components that are damaged by these proteins, we additionally identified the molecular functions, the biological processes, and the pathways of these proteins as well as the molecules that are associated with these pathways. This study represents an important preliminary investigation of the role of proteomic abnormalities in the pathogenesis of ALS, both in human patients and other animal models. We present some novel findings that may serve as a basis for further investigation of abnormal proteins that are involved in the pathogenesis of ALS.

Defects of Nutrient Signaling and Autophagy in Neurodegeneration

Neurons are post-mitotic cells that allocate huge amounts of energy to the synthesis of new organelles and molecules, neurotransmission and to the maintenance of redox homeostasis. In neurons, autophagy is not only crucial to ensure organelle renewal but it is also essential to balance nutritional needs through the mobilization of internal energy stores. A delicate crosstalk between the pathways that sense nutritional status of the cell and the autophagic processes to recycle organelles and macronutrients is fundamental to guarantee the proper functioning of the neuron in times of energy scarcity. This review provides a detailed overview of the pathways and processes involved in the balance of cellular energy mediated by autophagy, which when defective, precipitate the neurodegenerative cascade of Parkinson's disease, frontotemporal dementia, amyotrophic lateral sclerosis or Alzheimer's disease.

Mechanistic Insights of Mitochondrial Dysfunction in Amyotrophic Lateral Sclerosis: An Update on a Lasting Relationship

Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disease characterized by progressive loss of the upper and lower motor neurons. Despite the increasing effort in understanding the etiopathology of ALS, it still remains an obscure disease, and no therapies are currently available to halt its progression. Following the discovery of the first gene associated with familial forms of ALS, Cu–Zn superoxide dismutase, it appeared evident that mitochondria were key elements in the onset of the pathology. However, as more and more ALS-related genes were discovered, the attention shifted from mitochondria impairment to other biological functions such as protein aggregation and RNA metabolism. In recent years, mitochondria have again earned central, mechanistic roles in the pathology, due to accumulating evidence of their derangement in ALS animal models and patients, often resulting in the dysregulation of the energetic metabolism. In this review, we first provide an update of the last lustrum on the molecular mechanisms by which the most well-known ALS-related proteins affect mitochondrial functions and cellular bioenergetics. Next, we focus on evidence gathered from human specimens and advance the concept of a cellular-specific mitochondrial “metabolic threshold”, which may appear pivotal in ALS pathogenesis.

Mitochondrial DNA Depletion Syndrome and Its Associated Cardiac Disease

Mitochondria is a ubiquitous, energy-supplying (ATP-based) organelle found in nearly all eukaryotes. It acts as a “power plant” by producing ATP through oxidative phosphorylation, providing energy for the cell. The bioenergetic functions of mitochondria are regulated by nuclear genes (nDNA). Mitochondrial DNA (mtDNA) and respiratory enzymes lose normal structure and function when nuclear genes encoding the related mitochondrial factors are impaired, resulting in deficiency in energy production. Massive generation of reactive oxygen species and calcium overload are common causes of mitochondrial diseases. The mitochondrial depletion syndrome (MDS) is associated with the mutations of mitochondrial genes in the nucleus. It is a heterogeneous group of progressive disorders characterized by the low mtDNA copy number. TK2, FBXL4, TYPM, and AGK are genes known to be related to MDS. More recent studies identified new mutation loci associated with this disease. Herein, we first summarize the structure and function of mitochondria, and then discuss the characteristics of various types of MDS and its association with cardiac diseases.

Genetic architecture of motor neuron diseases

Motor neuron diseases (MNDs) are rare and frequently fatal neurological disorders in which motor neurons within the brainstem and spinal cord regions slowly die. MNDs are primarily caused by genetic mutations, and > 100 different mutant genes in humans have been discovered thus far. Given the fact that many more MND-related genes have yet to be discovered, the growing body of genetic evidence has offered new insights into the diverse cellular and molecular mechanisms involved in the aetiology and pathogenesis of MNDs. This search may aid in the selection of potential candidate genes for future investigation and, eventually, may open the door to novel interventions to slow down disease progression. In this review paper, we have summarized detailed existing research findings of different MNDs, such as amyotrophic lateral sclerosis (ALS), spinal muscular atrophy (SMA), spinal bulbar muscle atrophy (SBMA) and hereditary spastic paraplegia (HSP) in relation to their complex genetic architecture.

TDP-43 and PINK1 mediate CHCHD10S59L mutation-induced defects in Drosophila and in vitro

Mutations in coiled-coil-helix-coiled-coil-helix domain containing 10 (CHCHD10) can cause amyotrophic lateral sclerosis and frontotemporal dementia (ALS-FTD). However, the underlying mechanisms are unclear. Here, we generate CHCH10^S59L-mutant Drosophila melanogaster and HeLa cell lines to model CHCHD10-associated ALS-FTD. The CHCHD10^S59L mutation results in cell toxicity in several tissues and mitochondrial defects. CHCHD10^S59L independently affects the TDP-43 and PINK1 pathways. CHCHD10^S59L expression increases TDP-43 insolubility and mitochondrial translocation. Blocking TDP-43 mitochondrial translocation with a peptide inhibitor reduced CHCHD10^S59L-mediated toxicity. While genetic and pharmacological modulation of PINK1 expression and activity of its substrates rescues and mitigates the CHCHD10^S59L-induced phenotypes and mitochondrial defects, respectively, in both Drosophila and HeLa cells. Our findings suggest that CHCHD10^S59L-induced TDP-43 mitochondrial translocation and chronic activation of PINK1-mediated pathways result in dominant toxicity, providing a mechanistic insight into the CHCHD10 mutations associated with ALS-FTD.

Amyotrophic Lateral Sclerosis and Frontotemporal Lobar Degenerations: Similarities in Genetic Background

Amyotrophic lateral sclerosis (ALS) is a devastating, uniformly lethal progressive degenerative disorder of motor neurons that overlaps with frontotemporal lobar degeneration (FTLD) clinically, morphologically, and genetically. Although many distinct mutations in various genes are known to cause amyotrophic lateral sclerosis, it remains poorly understood how they selectively impact motor neuron biology and whether they converge on common pathways to cause neuronal degeneration. Many of the gene mutations are in proteins that share similar functions. They can be grouped into those associated with cell axon dynamics and those associated with cellular phagocytic machinery, namely protein aggregation and metabolism, apoptosis, and intracellular nucleic acid transport. Analysis of pathways implicated by mutant ALS genes has provided new insights into the pathogenesis of both familial forms of ALS (fALS) and sporadic forms (sALS), although, regrettably, this has not yet yielded definitive treatments. Many genes play an important role, with TARDBP, SQSTM1, VCP, FUS, TBK1, CHCHD10, and most importantly, C9orf72 being critical genetic players in these neurological disorders. In this mini-review, we will focus on the molecular mechanisms of these two diseases.

Assessment of genetic risk of type 2 diabetes among Pakistanis based on GWAS-implicated loci

Genome-wide association studies (GWAS) have identified multiple type 2 diabetes (T2D) loci, mostly among populations of European descent. There is a high prevalence of T2D among Pakistanis. Both genetic and environmental factors may be responsible for this high prevalence. In order to understand the shared genetic basis of T2D among Pakistanis and Europeans, we examined 77 genome-wide significant variants previously implicated among European populations. We genotyped 77 single-nucleotide polymorphisms (SNPs) by iPLEX® Gold or TaqMan® assays in a case-control sample of 1,683 individuals. Association analysis was performed using logistic regression. A total of 16 SNPs (TCF7L2/rs7903146, GLIS3/rs7041847, CHCHD9/rs13292136, PLEKHA1/rs2292626, FTO/rs9936385, CDKAL1/rs7756992, KCNJ11/rs5215, LOC105372155/rs12970134, KCNQ1/rs163182, CTRB1/rs7202877, ST6GAL1/rs16861329, ADAMTS9-AS2/rs6795735, LOC105370275/rs1359790, C5orf67/rs459193, ZBED3-AS1/rs6878122 and UBE2E2/rs7612463) showed statistically significant associations after controlling for the false discovery rate. While KCNQ1/rs163182 and ZBED3-AS1/rs6878122 showed opposite allelic effects, the remaining significant SNPs had the same allelic effects as reported previously. Our data indicate that a selected number of T2D loci previously identified among populations of European descent also affect the risk of T2D in the Pakistani population.

Reduced erythrocytic CHCHD2 mRNA is associated with brain pathology of Parkinson's disease

Peripheral biomarkers indicative of brain pathology are critically needed for early detection of Parkinson’s disease (PD). In this study, using NanoString and digital PCR technologies, we began by screening for alterations in genes associated with PD or atypical Parkinsonism in erythrocytes of PD patients, in which PD-related changes have been reported, and which contain ~ 99% of blood α-synuclein. Erythrocytic CHCHD2 mRNA was significantly reduced even at the early stages of the disease. A significant reduction in protein and/or mRNA expression of CHCHD2 was confirmed in PD brains collected at autopsy as well as in the brains of a PD animal model overexpressing α-synuclein, in addition to seeing a reduction of CHCHD2 in erythrocytes of the same animals. Overexpression of α-synuclein in cellular models of PD also resulted in reduced CHCHD2, via mechanisms likely involving altered subcellular localization of p300 histone acetyltransferase. Finally, the utility of reduced CHCHD2 mRNA as a biomarker for detecting PD, including early-stage PD, was validated in a larger cohort of 205 PD patients and 135 normal controls, with a receiver operating characteristic analysis demonstrating > 80% sensitivity and specificity.

A cold-stress-inducible PERK/OGT axis controls TOM70-assisted mitochondrial protein import and cristae formation

The architecture of cristae provides a spatial mitochondrial organization that contains functional respiratory complexes. Several protein components including OPA1 and MICOS complex subunits organize cristae structure, but upstream regulatory mechanisms are largely unknown. Here, in vivo and in vitro reconstitution experiments show that the endoplasmic reticulum (ER) kinase PERK promotes cristae formation by increasing TOM70-assisted mitochondrial import of MIC19, a critical subunit of the MICOS complex. Cold stress or β-adrenergic stimulation activates PERK that phosphorylates O-linked N-acetylglucosamine transferase (OGT). Phosphorylated OGT glycosylates TOM70 on Ser94, enhancing MIC19 protein import into mitochondria and promoting cristae formation and respiration. In addition, PERK-activated OGT O-GlcNAcylates and attenuates CK2α activity, which mediates TOM70 Ser94 phosphorylation and decreases MIC19 mitochondrial protein import. We have identified a cold-stress inter-organelle PERK-OGT-TOM70 axis that increases cell respiration through mitochondrial protein import and subsequent cristae formation. These studies have significant implications in cellular bioenergetics and adaptations to stress conditions.

The mitochondrial intermembrane space: the most constricted mitochondrial sub-compartment with the largest variety of protein import pathways

The mitochondrial intermembrane space (IMS) is the most constricted sub-mitochondrial compartment, housing only about 5% of the mitochondrial proteome, and yet is endowed with the largest variability of protein import mechanisms. In this review, we summarize our current knowledge of the major IMS import pathway based on the oxidative protein folding pathway and discuss the stunning variability of other IMS protein import pathways. As IMS-localized proteins only have to cross the outer mitochondrial membrane, they do not require energy sources like ATP hydrolysis in the mitochondrial matrix or the inner membrane electrochemical potential which are critical for import into the matrix or insertion into the inner membrane. We also explore several atypical IMS import pathways that are still not very well understood and are guided by poorly defined or completely unknown targeting peptides. Importantly, many of the IMS proteins are linked to several human diseases, and it is therefore crucial to understand how they reach their normal site of function in the IMS. In the final part of this review, we discuss current understanding of how such IMS protein underpin a large spectrum of human disorders.

Genetic architecture of common non-Alzheimer's disease dementias

Frontotemporal dementia (FTD), dementia with Lewy bodies (DLB) and vascular dementia (VaD) are the most common forms of dementia after Alzheimer's disease (AD). The heterogeneity of these disorders and/or the clinical overlap with other diseases hinder the study of their genetic components. Even though Mendelian dementias are rare, the study of these forms of disease can have a significant impact in the lives of patients and families and have successfully brought to the fore many of the genes currently known to be involved in FTD and VaD, starting to give us a glimpse of the molecular mechanisms underlying these phenotypes. More recently, genome-wide association studies have also pointed to disease risk-associated loci. This has been particularly important for DLB where familial forms of disease are very rarely described. In this review we systematically describe the Mendelian and risk genes involved in these non-AD dementias in an effort to contribute to a better understanding of their genetic architecture, find differences and commonalities between different dementia phenotypes, and uncover areas that would benefit from more intense research endeavors.

Understanding and managing metabolic dysfunction in Amyotrophic Lateral Sclerosis

INTRODUCTION

Amyotrophic Lateral Sclerosis (ALS) is a fatal motor neuron disease that leads to death after a median survival of 36 months. The development of an effective treatment has proven to be extremely difficult due to the inadequate understanding of the pathogenesis of ALS. Energy metabolism is thoroughly involved in the disease based on the discoveries of hypermetabolism, lipid/glucose metabolism, the tricarboxylic acid (TCA) cycle, and mitochondrial impairment.

AREA COVERED

Many perturbed metabolites within these processes have been identified as promising therapeutic targets. However, the therapeutic strategies targeting these pathways have failed to produce clinically significant results. The authors present in this review the metabolic disturbances observed in ALS and the derived-therapeutics.

EXPERT OPINION

The authors suggest that this is due to the insufficient knowledge of the relationship between the metabolic targets and the type of ALS of the patient, depending on genetic and environmental factors. We must improve our understanding of the pathological mechanisms and pay attention to the subtle hidden effects of changing diet, for example, and to use this strategy in addition to other drugs or to use metabolism status to determine subgroups of patients.

The Overlapping Genetics of Amyotrophic Lateral Sclerosis and Frontotemporal Dementia

Amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD) are two diseases that form a broad neurodegenerative continuum. Considerable effort has been made to unravel the genetics of these disorders, and, based on this work, it is now clear that ALS and FTD have a significant genetic overlap. TARDBP, SQSTM1, VCP, FUS, TBK1, CHCHD10, and most importantly C9orf72, are the critical genetic players in these neurological disorders. Discoveries of these genes have implicated autophagy, RNA regulation, and vesicle and inclusion formation as the central pathways involved in neurodegeneration. Here we provide a summary of the significant genes identified in these two intrinsically linked neurodegenerative diseases and highlight the genetic and pathological overlaps.

Identification of Key Pro-Survival Proteins in Isolated Colonic Goblet Cells of Winnie, a Murine Model of Spontaneous Colitis

BACKGROUND

Accumulating evidence suggests that the goblet cell-derived mucin-2 (Muc2) is a major component of the immune system and that perturbations in Muc2 lead to an ulcerative colitis-like phenotype. The animal model Winnie carries a missense mutation in Muc2 that causes Muc2 misfolding, accumulation in goblet cells, and ER stress. Excessive ER stress is a hallmark of many diseases, including ulcerative colitis, cancer, diabetes and Parkinson's disease. However, rather than committing to cell death, which is the typical outcome of unresolved ER stress, Winnie goblet cells are characterized by hyperproliferation, suggesting additional regulation of this cellular stress response.

METHODS

To elucidate the molecular mechanisms underlying ulcerative colitis in the Winnie model, we isolated goblet cells from Winnie and wild-type mice and used label-free quantitative proteomics and bioinformatics to understand the functional consequences of Muc2 misfolding and accumulation.

RESULTS

A large number of changes were identified that highlight a dramatic reprogramming of energy production, including enhanced utilization of butyrate, a key energy source of colonic cells. A major finding was the marked upregulation of the coiled-coil-helix-coiled-coil-helix domain proteins Chchd2, Chchd3, and Chchd6. In particular, we identified and confirmed the upregulation and nuclear translocation of Chchd2, a protein known to inhibit oxidative stress induced apoptosis.

CONCLUSIONS

This study is the first to apply proteome-level analysis to the preclinical Winnie model of ulcerative colitis. Identification of proteins and pathways affected in isolated Winnie goblet cells provides evidence for novel adaptive mechanisms underlying cell survival under conditions of chronic ER stress.

CHCHD2 promotes hepatocellular carcinoma and indicates poor prognosis of hepatocellular carcinoma patients

The coiled-coil-helix-coiled-coil-helix domain containing 2 (CHCHD2) is overexpressed in several types of cancer. This study aimed to investigate the role of CHCHD2 in hepatocellular carcinoma (HCC). The expression of CHCHD2 in HCC and non-tumorous tissues was detected by immunohistochemistry and Western blot analysis, and the correlation between CHCHD2 expression and clinicopathological features of HCC was analyzed. Furthermore, the proliferation, apoptosis and migration of HepG2 cells with CHCHD2 knockdown were examined. We found that CHCHD2 was upregulated in HCC tissues, and high CHCHD2 expression was associated with poor differentiation, lymph node metastasis, local tissue invasion, high TNM grade of HCC and poor patient survival. Depletion of CHCHD2 led to significantly reduced cell proliferation, increased apoptosis and diminished migratory capacity in HepG2 cells. In addition, HCC tissues had high expression of CD105, a microvessel marker, and HepG2 cells depleted of CHCHD2 had low CD105 expression. In conclusion, CHCHD2 may play an oncogenic role in HCC via promoting tumor cell growth and migration while preventing apoptosis. CHCHD2 is a potential biomarker for poor outcome of HCC patients.

Loss of mitochondrial protein CHCHD10 in skeletal muscle causes neuromuscular junction impairment

The neuromuscular junction (NMJ) is a synapse between motoneurons and skeletal muscles to control motor behavior. Acetylcholine receptors (AChRs) are restricted at the synaptic region for proper neurotransmission. Mutations in the mitochondrial CHCHD10 protein have been identified in multiple neuromuscular disorders; however, the physiological roles of CHCHD10 at NMJs remain elusive. Here, we report that CHCHD10 is highly expressed at the postsynapse of NMJs in skeletal muscles. Muscle conditional knockout CHCHD10 mice showed motor defects, abnormal neuromuscular transmission and NMJ structure. Mechanistically, we found that mitochondrial CHCHD10 is required for ATP production, which facilitates AChR expression and promotes agrin-induced AChR clustering. Importantly, ATP could effectively rescue the reduction of AChR clusters in the CHCHD10-ablated muscles. Our study elucidates a novel physiological role of CHCHD10 at the peripheral synapse. It suggests that mitochondria dysfunction contributes to neuromuscular pathogenesis.

Mutation Screening of the CHCHD2 Gene for Alzheimer's Disease and Frontotemporal Dementia in Chinese Mainland Population

As an important multifunctional protein involved in regulation of mitochondrial metabolism, CHCHD2 was identified as a causative gene for Parkinson's disease (PD), yet the relationship between CHCHD2 and neurodegenerative dementia is not well understood. We directly sequenced the entire coding region of CHCHD2 gene in 150 AD patients, 84 FTD patients, and 417 controls. Four rare putative pathogenic variants of CHCHD2, including rs142444896 (c.5C>T, p.P2L), rs752705344 (c.15C>G, p.S5R), rs145190179 (c.94G>A, p.A32T), and rs182992574 (c.255T>A, p.S85R) were identified from a cohort composed of 150 AD and 84 FTD patients. These results suggest that CH CHD2 gene play an important role in other neurodegenerative disorders from our dementia study in China.

Loss of CHCHD10-CHCHD2 complexes required for respiration underlies the pathogenicity of a CHCHD10 mutation in ALS

Coiled-helix coiled-helix domain containing protein 10 (CHCHD10) and its paralogue CHCHD2 belong to a family of twin CX9C motif proteins, most of which localize to the intermembrane space of mitochondria. Dominant mutations in CHCHD10 cause amyotrophic lateral sclerosis (ALS)/frontotemporal dementia, and mutations in CHCHD2 have been associated with Parkinson's disease, but the function of these proteins remains unknown. Here we show that the p.R15L CHCHD10 variant in ALS patient fibroblasts destabilizes the protein, leading to a defect in the assembly of Complex I, impaired cellular respiration, mitochondrial hyperfusion, an increase in the steady-state level of CHCHD2, and a severe proliferation defect on galactose, a substrate that forces cells to synthesize virtually all of their ATP aerobically. CHCHD10 and CHCHD2 appeared together in distinct foci by immunofluorescence analysis and could be quantitatively immunoprecipitated with antibodies against either protein. Blue native polyacrylamide gel electrophoresis analyses showed that both proteins migrated in a high molecular weight complex (220 kDa) in control cells, which was, however, absent in patient cells. CHCHD10 and CHCHD2 levels increased markedly in control cells in galactose medium, a response that was dampened in patient cells, and a new complex (40 kDa) appeared in both control and patient cells cultured in galactose. Re-entry of patient cells into the cell cycle, which occurred after prolonged culture in galactose, was associated with a marked increase in Complex I, and restoration of the oxygen consumption defect. Our results indicate that CHCHD10-CHCHD2 complexes are necessary for efficient mitochondrial respiration, and support a role for mitochondrial dysfunction in some patients with ALS.

Identification and characterization of protein N-myristoylation occurring on four human mitochondrial proteins, SAMM50, TOMM40, MIC19, and MIC25

Previously, we showed that SAMM50, a mitochondrial outer membrane protein, is N-myristoylated, and this lipid modification is required for the proper targeting of SAMM50 to mitochondria. In this study, we characterized protein N-myristoylation occurring on four human mitochondrial proteins, SAMM50, TOMM40, MIC19, and MIC25, three of which are components of the mitochondrial intermembrane space bridging (MIB) complex, which plays a critical role in the structure and function of mitochondria. In vitro and in vivo metabolic labeling experiments revealed that all four of these proteins were N-myristoylated. Analysis of intracellular localization of wild-type and non-myristoylated G2A mutants of these proteins by immunofluorescence microscopic analysis and subcellular fractionation analysis indicated that protein N-myristoylation plays a critical role in mitochondrial targeting and membrane binding of two MIB components, SAMM50 and MIC19, but not those of TOMM40 and MIC25. Immunoprecipitation experiments using specific antibodies revealed that MIC19, but not MIC25, was a major N-myristoylated binding partner of SAMM50. Immunoprecipitation experiments using a stable transformant of MIC19 confirmed that protein N-myristoylation of MIC19 is required for the interaction between MIC19 and SAMM50, as reported previously. Thus, protein N-myristoylation occurring on two mitochondrial MIB components, SAMM50 and MIC19, plays a critical role in the mitochondrial targeting and protein-protein interaction between these two MIB components.

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.

Reversal of Phenotypic Abnormalities by CRISPR/Cas9-Mediated Gene Correction in Huntington Disease Patient-Derived Induced Pluripotent Stem Cells

Huntington disease (HD) is a dominant neurodegenerative disorder caused by a CAG repeat expansion in HTT. Here we report correction of HD human induced pluripotent stem cells (hiPSCs) using a CRISPR-Cas9 and piggyBac transposon-based approach. We show that both HD and corrected isogenic hiPSCs can be differentiated into excitable, synaptically active forebrain neurons. We further demonstrate that phenotypic abnormalities in HD hiPSC-derived neural cells, including impaired neural rosette formation, increased susceptibility to growth factor withdrawal, and deficits in mitochondrial respiration, are rescued in isogenic controls. Importantly, using genome-wide expression analysis, we show that a number of apparent gene expression differences detected between HD and non-related healthy control lines are absent between HD and corrected lines, suggesting that these differences are likely related to genetic background rather than HD-specific effects. Our study demonstrates correction of HD hiPSCs and associated phenotypic abnormalities, and the importance of isogenic controls for disease modeling using hiPSCs.