Quercetin protects against palmitate-induced pancreatic ß-cell apoptosis by restoring lysosomal function and autophagic flux.

Quercetin, a natural flavonoid, has been reported to prevent pancreatic ß-cell apoptosis in animal models of diabetes. However, the underlying mechanism remains unclear. We investigated the mechanisms through which quercetin protects ß cells from palmitate-induced apoptosis and determined whether autophagy is involved in this process. We found that quercetin treatment partially reduced palmitate-induced ß-cell apoptosis. This protective effect was abolished by pharmacologic inhibition of autophagy and by silencing a key autophagy gene. Further analysis revealed that palmitate treatment promoted the expression of LC3 II, a marker of autophagosomes, but resulted in the blockade of autophagic flux due to lysosome dysfunction. Defective lysosome accumulation can cause lysosomal membrane permeabilization and the release of cathepsins from lysosome into the cytosol that triggers apoptosis. Treatment with quercetin reversed lysosomal dysfunction and promoted autophagosome-lysosome fusion, which restored defective autophagic flux and provoked autophagy. Overall, our results indicate that lysosomal dysfunction is a major factor that contributes to ß-cell apoptosis and demonstrates that quercetin improves cell survival by restoring lysosomal function and autophagic flux. This study provides new evidence regarding the anti-apoptotic mechanism of quercetin in the treatment of type 2 diabetes.