Myosin ATPase inhibition fails to rescue the metabolically dysregulated proteome of nebulin‐deficient muscle

Abstract Nemaline myopathy (NM) is a genetic muscle disease, primarily caused by mutations in the NEB gene ( NEB‐ NM) and with muscle myosin dysfunction as a major molecular pathogenic mechanism. Recently, we have observed that the myosin biochemical super‐relaxed state was significantly impaired in NEB ‐NM, inducing an aberrant increase in ATP consumption and remodelling of the energy proteome in diseased muscle fibres. Because the small‐molecule Mavacamten is known to promote the myosin super‐relaxed state and reduce the ATP demand, we tested its potency in the context of NEB ‐NM. We first conducted in vitro experiments in isolated single myofibres from patients and found that Mavacamten successfully reversed the myosin ATP overconsumption. Following this, we assessed its short‐term in vivo effects using the conditional nebulin knockout (c Neb KO) mouse model and subsequently performing global proteomics profiling in dissected soleus myofibres. After a 4 week treatment period, we observed a remodelling of a large number of proteins in both c Neb KO mice and their wild‐type siblings. Nevertheless, these changes were not related to the energy proteome, indicating that short‐term Mavacamten treatment is not sufficient to properly counterbalance the metabolically dysregulated proteome of c Neb KO mice. Taken together, our findings emphasize Mavacamten potency in vitro but challenge its short‐term efficacy in vivo . image Key points No cure exists for nemaline myopathy, a type of genetic skeletal muscle disease mainly derived from mutations in genes encoding myofilament proteins. Applying Mavacamten, a small molecule directly targeting the myofilaments, to isolated membrane‐permeabilized muscle fibres from human patients restored myosin energetic disturbances. Treating a mouse model of nemaline myopathy in vivo with Mavacamten for 4 weeks, remodelled the skeletal muscle fibre proteome without any noticeable effects on energetic proteins. Short‐term Mavacamten treatment may not be sufficient to reverse the muscle phenotype in nemaline myopathy.