UC San Diego

αB-crystallin (CryAB) is a ~20-kD small heat shock protein commonly expressed in heart tissue. However, the CryAB R120G missense mutation causes misfolding of the protein, leading to the formation of insoluble CryAB aggregates in cardiomyocytes linked to the development of desmin-related cardiomyopathy. Typically, cells utilize mechanisms such as the ubiquitin-proteasome system (UPS) and autophagic-lysosome pathway to maintain proteostasis, while growing evidence shows that secretion of extracellular vesicles (EVs) may also play a role in protein quality control. Here, we analyze how these mechanisms function in the context of CryAB R120G. After confirming presence of insoluble CryAB protein in mouse hearts from a CryAB R120G KI mutant line, we observed that UPS activity seemed to decrease in mice aged 3-4 months. We identified CryAB in secreted extracellular vesicles from R120G KI heart tissue and observed the presence of autophagic markers, indicating a relationship between EV secretion and autophagy mechanisms. We also found that inhibition of the UPS decreases EV secretion. Further, secreted EVs carrying R120G CryAB do not appear to cause a pro-inflammatory response in macrophages. Our findings suggest insoluble CryAB R120G aggregates impact quality control in cardiomyocytes, and that EVs assist in clearing misfolded CryAB from the cell.