Clusterin Protects Lipotoxicity-Induced Apoptosis via Upregulation of Autophagy in Insulin-Secreting Cells

BACKGROUND: There is a great need to discover factors that could protect pancreatic β-cells from apoptosis and thus prevent diabetes mellitus. Clusterin (CLU), a chaperone protein, plays an important role in cell protection in numerous cells and is involved in various cellular mechanisms, including autophagy. In the present study, we investigated the protective role of CLU through autophagy regulation in pancreatic β-cells. METHODS: To identify the protective role of CLU, mouse insulinoma 6 (MIN6) cells were incubated with CLU and/or free fatty acid (FFA) palmitate, and cellular apoptosis and autophagy were examined. RESULTS: Treatment with CLU remarkably upregulated microtubule-associated protein 1-light chain 3 (LC3)-II conversion in a dose- and time-dependent manner with a significant increase in the autophagy-related 3 (Atg3) gene expression level, which is a mediator of LC3-II conversion. Moreover, co-immunoprecipitation and fluorescence microscopy experiments showed that the molecular interaction of LC3 with Atg3 and p62 was markedly increased by CLU. Stimulation of LC3-II conversion by CLU persisted in lipotoxic conditions, and FFA-induced apoptosis and dysfunction were simultaneously improved by CLU treatment. Finally, inhibition of LC3-II conversion by Atg3 gene knockdown markedly attenuated the cytoprotective effect of CLU. CONCLUSION: Taken together, these findings suggest that CLU protects pancreatic β-cells against lipotoxicity-induced apoptosis via autophagy stimulation mediated by facilitating LC3-II conversion. Thus, CLU has therapeutic effects on FFA-induced pancreatic β-cell dysfunction.