CHCHD10 mutations p.R15L and p.G66V cause motoneuron disease by haploinsufficiency

Abstract

Mutations in the mitochondrially located protein CHCHD10 cause motoneuron disease by an unknown mechanism. In this study, we investigate the mutations p.R15L and p.G66V in comparison to wild-type CHCHD10 and the non-pathogenic variant p.P34S in vitro, in patient cells as well as in the vertebrate in vivo model zebrafish. We demonstrate a reduction of CHCHD10 protein levels in p.R15L and p.G66V mutant patient cells to approximately 50%. Quantitative real-time PCR revealed that expression of CHCHD10 p.R15L, but not of CHCHD10 p.G66V, is already abrogated at the mRNA level. Altered secondary structure and rapid protein degradation are observed with regard to the CHCHD10 p.G66V mutant. In contrast, no significant differences in expression, degradation rate or secondary structure of non-pathogenic CHCHD10 p.P34S are detected when compared with wild-type protein. Knockdown of CHCHD10 expression in zebrafish to about 50% causes motoneuron pathology, abnormal myofibrillar structure and motility deficits in vivo. Thus, our data show that the CHCHD10 mutations p.R15L and p.G66V cause motoneuron disease primarily based on haploinsufficiency of CHCHD10.

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

“…We therefore cannot exclude that the reduced expression of R15L is due to slightly less efficient mitochondrial import. Indeed, consistent with other recent reports, CHCHD10 R15L has a shorter half‐life time than wild‐type (Brockmann et al , ). The N‐terminal arginine‐rich sequence may enhance mitochondrial import although it is neither necessary nor sufficient for mitochondrial import by itself.…”

“…Several previous reports of conflicting findings of respiratory function in CHCHD10 cellular models (mutant, knockdown, and overexpression) and the recent finding of impaired respiration in muscle but not in whole brain of homozygous CHCHD10 knockout mice suggest cell type‐specific effects are at play (Burstein et al , ; Straub et al , ). Interestingly, CHCHD10 knockdown in zebrafish also causes muscle pathology (Brockmann et al , ). Altered metabolism in muscle may promote to ALS pathogenesis (Loeffler et al , ).…”

“…The reported inhibition of apoptosis by CHCHD10 S59L (Genin et al, 2016) has not been replicated by others (Woo et al, 2017) and is difficult to reconcile with a neurodegenerative process. The neuropathological features of CHCHD10 cases have not been comprehensively characterized, but CHCHD10 was recently linked to synaptic integrity and nuclear retention of TDP-43 (Woo et al, 2017), although the latter has not been replicated (Brockmann et al, 2018).…”

A CHCHD10 variant causing ALS elicits an unfolded protein response through the IRE1/XBP1 pathway

“…For instance, the p.S59L variant reported in patients with ALS-FTD (frontotemporal dementia) is associated with a fragmented mitochondrial network, protein aggregates in mitochondria, and the activation of the integrated stress response (ISR), ascribed to a toxic gain of function (Anderson, Bredvik et al, 2019, Genin, Bannwarth et al, 2018, Genin, Madji Hounoum et al, 2019. On the other hand, the p.R15L and p.G66V variants, in which reduced levels of CHCHD10 protein are associated with mitochondrial respiratory chain dysfunction, appear to be haploinsufficient (Brockmann, Freischmidt et al, 2018, Penttila, Jokela et al, 2015, Straub et al, 2018.…”

Chchd10 or Chchd2 are not Required for Human Motor Neuron Differentiation In Vitro but Modify Synaptic Transcriptomes

“…Dominant CHCHD10 mutations underlie motor neuron phenotypes such as amyotrophic lateral sclerosis (ALS), spinal muscular atrophy of Jokela type (SMAJ) and axonal Charcot Marie Tooth disease (CMT2) (Bannwarth et al, 2014;Müller et al, 2014;Auranen et al, 2015;Penttilä et al, 2015) whereas dominant CHCHD2 mutations cause Parkinson's disease (Funayama et al, 2015). Evidence for whether the mutations cause disease through loss-of-function or toxic gain-of-function has been provided by different studies depending on the model system used (Genin et al, 2016;Meng et al, 2017;Brockmann et al, 2018;Burstein et al, 2018;Anderson et al, 2019).…”