X-linked myopathy with excessive autophagy: characterization and therapy testing in a zebrafish model.

X-linked myopathy with excessive autophagy (XMEA), a rare childhood-onset autophagic vacuolar myopathy caused by mutations in VMA21, is characterized by proximal muscle weakness and progressive vacuolation. VMA21 encodes a protein chaperone of the vacuolar hydrogen ion ATPase, the loss of which leads to lysosomal neutralization and impaired function. At present, there is an incomplete understanding of XMEA, its mechanisms, consequences on other systems, and therapeutic strategies. A significant barrier to advancing knowledge and treatments is the lack of XMEA animal models. Therefore, we used CRISPR-Cas9 editing to engineer a loss-of-function mutation in zebrafish vma21. The vma21 mutant zebrafish phenocopy the human disease with impaired motor function and survival, liver dysfunction, and dysregulated autophagy indicated by lysosomal de-acidification, the presence of characteristic autophagic vacuoles in muscle fibers, altered autophagic flux, and reduced lysosomal marker staining. As proof-of-concept, we found that two drugs, edaravone and LY294002, improve swim behavior and survival. In total, we generated and characterized a novel preclinical zebrafish XMEA model and demonstrated its suitability for studying disease pathomechanisms and identifying potential therapeutic targets.