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

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. As the small-molecule Mavacamten is known to promote the myosin super-relaxed state and reduce the ATP demand, here, 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 over-consumption. Following this, we assessed its short-term in vivo effects by using the conditional nebulin knock-out (c Neb KO) mouse model and by subsequently performing global proteomics profiling in dissected soleus myofibres. After a four-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 . Key points summary 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 myofilament, 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 four weeks, remodeled 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.