Introduction Autophagy protects against muscle disease, with autophagy gene mutations causing muscular dystrophies and myopathies. While these disorders can be fatal early in life, their pathomechanisms remain enigmatic and genetic therapies, while promising, are not yet the ‘treatment panacea’. Autophagy-targeting therapies including dietary modification, offer new hope for fast-tracked treatments, but depend on improved mechanistic understanding of autophagy defects. We focus on the importance of lysosome repopulation as an essential process for continued autophagy function. Autophagic lysosome reformation (ALR) is an unusual membrane recycling process that we showed is crucial for muscle health. We now address the knowledge gap of how ALR defects contribute to inherited muscle disease.
Methods We have developed a novel pipeline to screen for ALR defects using iPSC-derived patient myoblasts, matched patient muscle biopsies, and with CRISPR-mediated knockout myoblast models for detailed mechanistic analysis. Advanced microscopy is used to examine effects on reformation tubules, specialized structures involved in ALR, and made possible by our new preservation techniques that preserve these unique membranous structures. Combined with the use of phosphoinositide-specific biosensors, we map the underlying molecular basis of ALR defects for specific muscle diseases.
Results and conclusion We identified novel ALR defects that unexpectedly link genetically distinct subtypes through shared effects on phosphoinositide-driven ALR. In patient muscle, this ALR defect was associated with autophagy inhibition and severe disease. Our discoveries further reveal unexpected complexity in the diverse array of phosphoinositides required to complete the ALR process, together with unique functional specificity for each phosphoinositide species. These new links between ALR defects and severe muscle disease, bring us one step closer to developing effective autophagy-targeted therapies. This is particularly important for ALR disorders, given they are affected by both autophagy and lysosome defects, making them a unique clinical challenge.