CHCHD2 accumulates in distressed mitochondria and facilitates oligomerization of CHCHD10

Abstract

Mutations in paralogous mitochondrial proteins CHCHD2 and CHCHD10 cause autosomal dominant Parkinson Disease (PD) and Amyotrophic Lateral Sclerosis/Frontotemporal Dementia (ALS/FTD), respectively. Using newly generated CHCHD2, CHCHD10 and CHCHD2/10 double knockout cell lines, we find that the proteins are partially functionally redundant, similarly distributed throughout the mitochondrial cristae, and form heterodimers. Unexpectedly, we also find that CHCHD2/CHCHD10 heterodimerization increases in response to mitochondrial stress. This increase is driven by differences in the proteins' stability and mutual affinity: CHCHD2 is preferentially stabilized by loss of mitochondrial membrane potential, and CHCHD10 oligomerization depends on CHCHD2 expression. Exploiting the dependence of CHCHD10 oligomerization on CHCHD2, we developed a heterodimer incorporation assay and demonstrate that CHCHD2 and CHCHD10 with disease-causing mutations readily form heterodimers. As we also find that both proteins are highly expressed in human Substantia nigra and cortical pyramidal neurons, mutant CHCHD2 and CHCHD10 may directly interact with their wild-type paralogs in the context of PD and ALS/FTD pathogenesis. Together, these findings demonstrate that differences in the stability and mutual affinity of CHCHD2 and CHCHD10 regulate their heterodimerization in response to mitochondrial distress, revealing an unanticipated link between PD and ALS/FTD pathogenesis.

Loss of CHCHD2 and CHCHD10 activates OMA1 peptidase to disrupt mitochondrial cristae phenocopying patient mutations in vivo

“…OMA1 levels were likewise decreased, as expected given OMA1 is degraded shortly after its activation (Head et al, 2009). Similar to primary fibroblasts we previously found only a mild oxygen consumption deficit in HEK293 DKO cells compared to wildtype cells (Huang et al, 2018), and TMRE fluorescence was slightly higher for DKO cells compared to wildtype cells (Supplemental Figure 1D). Processing of another substrate of activated OMA1, PGAM5, was unaltered in DKO cells, suggesting that OMA1 activation with C2/C10 DKO may preferentially affect L-OPA1 processing (Supplemental Figure 2A) (Sekine et al, 2012).…”

“…Having identified a functional interaction between C2/C10 and OMA1/OPA1, we next asked whether OMA1 activation is responsible for mitochondrial fragmentation that we and others observed previously following overexpression of the pathogenic C10 mutation G58R in human cells (Ajroud-Driss et al, 2015;Huang et al, 2018). Over-expression of C10 G58R caused severe mitochondrial fragmentation on a wildtype background, as was expected ( Figure 3A and B).…”

“…To assess whether OPA1 processing was altered also in human cells, we evaluated the OMA1/OPA1 axis in HEK293 DKO cells that we described previously (Huang et al, 2018). Similar to DKO mouse fibroblasts, cristae number was significantly reduced in HEK293 DKO cells (Figure 2A and B).…”

“…C2 and C10 are co-expressed in relevant cellular subtypes, such as substantia nigral neurons, pyramidal neurons, and myocytes, where they directly interact within a ~200 kDa complex in the mitochondrial intermembrane space (Straub et al, 2018;Burstein et al, 2018;Huang et al, 2018).…”

“…To explain cristae abnormalities in C2/C10 patients, C10 and later C2 were proposed to be structural components of the mitochondrial contact site and cristae organizing system (MICOS) complex (Bannwarth et al, 2014;Genin et al, 2016;Zhou et al, 2019). However, recent reports have challenged this model, suggesting that C2/C10 mutation or loss may lead to cristae abnormalities by another as of yet unidentified mechanism (Straub et al, 2018;Burstein et al, 2018;Huang et al, 2018).…”