Hubas, A. | Search bioRxiv

bioRxiv2023

Epigenetic control of myogenic identity of human muscle stem cells in Duchenne Muscular Dystrophy

In Duchenne Muscular Dystrophy (DMD), the absence of the subsarcolemmal dystrophin protein leads to repeated myofiber damages inducing cycles of muscle regeneration that is driven by muscle stem cells (MuSCs). With time, MuSC regenerative capacities are overwhelmed, leading to fibrosis and muscle atrophy. Whether MuSCs from DMD muscle have intrinsic defects that limit regenerative potential or are disrupted by their degenerative/regenerative environment is unclear. We investigated cell behavior and gene expression in human using MuSCs derived from DMD or healthy muscles. We found that proliferation, differentiation and fusion were not altered in DMD-MuSCs, but with time, they lost their myogenic identity twice as fast as healthy MuSCs. The rapid drift towards a fibroblast-like cell identity was observed at the clonal level, and resulted from the altered expression of epigenetic enzymes required to maintain the myogenic cell fate. Indeed, the re-expression of CBX3, SMC3, H2AFV and H3F3B prevented the MuSC identity drift. Amongst the epigenetic changes, a closing of chromatin at the gene encoding the transcription factor MEF2B caused a down-regulation of its expression and a loss of the myogenic fate. Thus, MEF2B is a key mediator of the myogenic identity in human MuSCs, that is altered in DMD pathology.

genomics↗

bioRxiv2023

Abnormal autophagy is a critical mechanism in TANGO2-related rhabdomyolysis

Patients with pathogenic variants in the TANGO2 gene suffer from severe and recurrent rhabdomyolysis (RM) episodes precipitated by fasting. Since starvation promotes autophagy induction, we wondered whether TANGO2-related muscle symptoms result from autophagy insufficiency to meet cellular demands in stress conditions. Autophagy functioning was analyzed in vitro, in primary skeletal muscle cells from TANGO2 patients in basal and fasting conditions. In addition, we developed a tango2 morphant zebrafish model to assess the effect of tango2 knockdown (KD) on locomotor function and autophagy efficiency in vivo. We report that TANGO2 mutations are associated with decreased LC3-II levels upon starvation in primary muscle cells, but not in fibroblasts. In zebrafish larvae, tango2 knockdown induces locomotor defects characterized by reduced evoked movements which are exacerbated by exposure to atorvastatin, a compound known to cause RM. Importantly, RM features of tango2 KD are also associated with autophagy and mitophagy defects in zebrafish. Calpeptin treatment, a known activator of autophagy, is sufficient to rescue the locomotor properties, thanks to its beneficial effect on autophagy functioning in zebrafish and independently to its effect on calpain activity. LC3-II levels of primary muscle cells of TANGO2 patients are also improved by calpeptin treatment. Overall, we demonstrate that TANGO2 plays an important role in autophagy, and that autophagy efficiency is critical to prevent RM, thus giving rise to new therapeutic perspectives in the prevention of these life-threatening episodes in TANGO2 pathology.

cell biology↗