CryAB-driven amyloidogenesis in Drosophila muscle engages extracellular vesicle pathways for cellular release.

Mutations in the small heat shock protein α-crystallin B (CryAB) result in cataracts, cardiomyopathies, and myofibrillar myopathies (MFMs), all of which are marked by protein aggregation. To investigate pathological mechanisms, we expressed four human CryAB disease alleles in Drosophila skeletal muscle. All variants resulted in the accumulation of protein aggregates. Mutations within the conserved α-crystallin domain (ACD) caused CryAB-positive structures that colocalized with an amyloidogenic form of human Desmin. The amyloid-like nature of these CryAB variants was further supported by thioflavin T spectroscopy and Congo red staining, the latter of which was also evident in other MFM-causing genes in zebrafish muscles and human biopsies. Muscle-enriched CryAB amyloid-like structures co-localized with extracellular vesicle (EV) markers and were detected in the hemolymph, suggesting an EV-mediated export mechanism. This is the first report of CryAB amyloid formation in skeletal muscle and broadens amyloid dynamics beyond the nervous system.