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.

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.