Mutations in TIMM50 cause severe mitochondrial dysfunction by targeting key aspects of mitochondrial physiology

Abstract

3‐Methylglutaconic aciduria (3‐MGA‐uria) syndromes comprise a heterogeneous group of diseases associated with mitochondrial membrane defects. Whole‐exome sequencing identified compound heterozygous mutations in TIMM50 (c.[341 G>A];[805 G>A]) in a boy with West syndrome, optic atrophy, neutropenia, cardiomyopathy, Leigh syndrome, and persistent 3‐MGA‐uria. A comprehensive analysis of the mitochondrial function was performed in fibroblasts of the patient to elucidate the molecular basis of the disease. TIMM50 protein was severely reduced in the patient fibroblasts, regardless of the normal mRNA levels, suggesting that the mutated residues might be important for TIMM50 protein stability. Severe morphological defects and ultrastructural abnormalities with aberrant mitochondrial cristae organization in muscle and fibroblasts were found. The levels of fully assembled OXPHOS complexes and supercomplexes were strongly reduced in fibroblasts from this patient. High‐resolution respirometry demonstrated a significant reduction of the maximum respiratory capacity. A TIMM50‐deficient HEK293T cell line that we generated using CRISPR/Cas9 mimicked the respiratory defect observed in the patient fibroblasts; notably, this defect was rescued by transfection with a plasmid encoding the TIMM50 wild‐type protein. In summary, we demonstrated that TIMM50 deficiency causes a severe mitochondrial dysfunction by targeting key aspects of mitochondrial physiology, such as the maintenance of proper mitochondrial morphology, OXPHOS assembly, and mitochondrial respiratory capacity.

Mitochondrial protein import dysfunction: mitochondrial disease, neurodegenerative disease and cancer

“…Similar results were found in patients with heterozygous mutations in Tim50 R114Q and G269S who present with 3-MGA-uria, a generalised reduction in the activity and assembly of the Accepted Article respiratory chain complexes, reduced respiration and aberrant cristae [99]. Patients with heterozygous Tim50 mutations (S112* and G190A; R114Q and G269S) also had reduced Tim50 protein levels, potentially contributing to the observed heterozygous patient phenotypes [97,99]. The variable effects on protein import, respiration and severity of disease progression may be a consequence of the specific mutation and how that mutation affects protein structure and function.…”

“…3-Methylglutaconic aciduria (3-MGA-uria) syndromes comprise a group of diseases with elevated 3-MGA-uria in urinary secretions and mitochondrial membrane defects ( Table 1). A variety of mutations (missense and nonsense) in Tim50 result in the autosomal recessive disorder 3-MGA-uria type IX (MGCA9), which is characterised by early onset seizures, 3-MGA-uria, intellectual disability and delayed development, and hypotonia or spasticity [97][98][99]. Reyes et al, (2018) identified a patient with heterozygous mutations in Tim50 (S112* and G190A), levels of Complex I, II and IV respiratory components were reduced, decreased respiration and increased reactive oxygen species (ROS) [97].…”

PGC1/PPAR drive cardiomyocyte maturation at single cell level via YAP1 and SF3B2

“…7a). We found that the ability of PPARα signaling to shorten CTD is significantly impaired when targeting genes encoding SF3B2/SAP18 (RNA splicing factors) 39,40 , and TIMM50 (a mitochondrial translocase) 41 (Fig. 7b-c, Fig.…”

PGC1/PPAR Drive Cardiomyocyte Maturation through Regulation of Yap1 and SF3B2

“…This analysis identified 148 genes directly regulated by PGC1/PPARα ( Figure 4G and Table S1). They included several novel targets of PGC1/PPARα with unknown roles in CM maturation, including genes encoding Yap1, a transcriptional effector of Hippo signaling with crucial roles in cardiac regeneration (Xin et al, 2013), SF3B2/SAP18, RNA splicing factors (Golas et al, 2003;Singh et al, 2010), TIMM50, a mitochondrial translocase regulating mitochondrial function (Tort et al, 2019), and STRIP1, a core component of the striatin-interacting phosphatases and kinase complex regulating cell contractility (Suryavanshi et al, 2018).…”