Chronic inhibition of the mitochondrial ATP synthase in skeletal muscle triggers sarcoplasmic reticulum distress and tubular aggregates

An ETFDH-driven metabolon supports OXPHOS efficiency in skeletal muscle by regulating coenzyme Q homeostasis

Coenzyme Q (Q) is a key lipid electron transporter, but several aspects of its biosynthesis and redox homeostasis remain undefined. Various flavoproteins reduce ubiquinone (oxidized form of Q) to ubiquinol (QH2); however, in eukaryotes, only oxidative phosphorylation (OXPHOS) complex III (CIII) oxidizes QH2 to Q. The mechanism of action of CIII is still debated. Herein, we show that the Q reductase electron-transfer flavoprotein dehydrogenase (ETFDH) is essential for CIII activity in skeletal muscle. We identify a complex (comprising ETFDH, CIII and the Q-biosynthesis regulator COQ2) that directs electrons from lipid substrates to the respiratory chain, thereby reducing electron leaks and reactive oxygen species production. This metabolon maintains total Q levels, minimizes QH2-reductive stress and improves OXPHOS efficiency. Muscle-specific Etfdh-/- mice develop myopathy due to CIII dysfunction, indicating that ETFDH is a required OXPHOS component and a potential therapeutic target for mitochondrial redox medicine.

Interactions of mitochondrial and skeletal muscle biology in mitochondrial myopathy

Mitochondrial dysfunction in skeletal muscle fibres occurs with both healthy aging and a range of neuromuscular diseases. The impact of mitochondrial dysfunction in skeletal muscle and the way muscle fibres adapt to this dysfunction is important to understand disease mechanisms and to develop therapeutic interventions. Furthermore, interactions between mitochondrial dysfunction and skeletal muscle biology, in mitochondrial myopathy, likely have important implications for normal muscle function and physiology. In this review, we will try to give an overview of what is known to date about these interactions including metabolic remodelling, mitochondrial morphology, mitochondrial turnover, cellular processes and muscle cell structure and function. Each of these topics is at a different stage of understanding, with some being well researched and understood, and others in their infancy. Furthermore, some of what we know comes from disease models. Whilst some findings are confirmed in humans, where this is not yet the case, we must be cautious in interpreting findings in the context of human muscle and disease. Here, our goal is to discuss what is known, highlight what is unknown and give a perspective on the future direction of research in this area.

Antioxidants restore store-operated Ca2+ entry in patient-iPSC-derived myotubes with tubular aggregate myopathy-associated Ile484ArgfsX21 STIM1 mutation via upregulation of binding immunoglobulin protein

Store-operated Ca2+ entry (SOCE) is indispensable for intracellular Ca2+ homeostasis in skeletal muscle, and constitutive activation of SOCE causes tubular aggregate myopathy (TAM). To understand the pathogenesis of TAM, we induced pluripotent stem cells (iPSCs) from a TAM patient with a rare mutation (c.1450_1451insGA; p. Ile484ArgfsX21) in the STIM1 gene. This frameshift mutation produces a truncated STIM1 with a disrupted C-terminal inhibitory domain (CTID) and was reported to diminish SOCE. Myotubes induced from the patient's-iPSCs (TAM myotubes) showed severely impaired SOCE, but antioxidants greatly restored SOCE partly via upregulation of an endoplasmic reticulum (ER) chaperone, BiP (GRP78), in the TAM myotubes. Our observation suggests that antioxidants are promising tools for treatment of TAM caused by reduced SOCE.

IF1 promotes oligomeric assemblies of sluggish ATP synthase and outlines the heterogeneity of the mitochondrial membrane potential

The coexistence of two pools of ATP synthase in mitochondria has been largely neglected despite in vitro indications for the existence of reversible active/inactive state transitions in the F1-domain of the enzyme. Herein, using cells and mitochondria from mouse tissues, we demonstrate the existence in vivo of two pools of ATP synthase: one active, the other IF1-bound inactive. IF1 is required for oligomerization and inactivation of ATP synthase and for proper cristae formation. Immunoelectron microscopy shows the co-distribution of IF1 and ATP synthase, placing the inactive "sluggish" ATP synthase preferentially at cristae tips. The intramitochondrial distribution of IF1 correlates with cristae microdomains of high membrane potential, partially explaining its heterogeneous distribution. These findings support that IF1 is the in vivo regulator of the active/inactive state transitions of the ATP synthase and suggest that local regulation of IF1-ATP synthase interactions is essential to activate the sluggish ATP synthase.

Polymorphisms of CRELD1 and DNAJC30 and their relationship with chicken carcass traits

Carcass traits play important roles in the broiler industry and single nucleotide polymorphism (SNP) can be efficient molecular markers for marker-assisted breeding of chicken carcass traits. Based on our previous RNA-seq data (accession number GSE58755), cysteine rich with epidermal growth factor like domains 1 (CRELD1) and DnaJ heat shock protein family member C30 (DNAJC30) are differentially expressed in breast muscle between white recessive rock chicken (WRR) and Xinghua chicken (XH). In this study, we further characterize the potential function and SNP mutation of CRELD1 and DNAJC30 in chicken for the first time. According to protein interaction network and enrichment analysis, CRELD1 and DNAJC30 may play some roles in chicken muscle development and fat deposition. In WRR and XH, the results of the relative tissue expression pattern demonstrated that CRELD1 and DNAJC30 are not only differentially expressed in breast muscle but also leg muscle and abdominal fat. Therefore, we identified 5 SNP sites of CRELD1 and 7 SNP sites of DNAJC30 and genotyped them in an F₂ chicken population. There are 4 sites of CRELD1 and 3 sites of DNAJC30 are associated with chicken carcass traits like breast muscle weight, body weight, dressed weight, leg weight percentage, eviscerated weight with giblet percentage, intermuscular adipose width, shank length, and girth. These results suggest that the SNP sites of CRELD1 and DNAJC30 can be potential molecular markers to improve the chicken carcass traits and lay the foundation for marker-assisted selection.