CNTF protects MIN6 cells against apoptosis induced by Alloxan and IL-1β through downregulation of the AMPK pathway

Abstract

Our group previously demonstrated that CNTF protects pancreatic islets against apoptosis induced by IL1β. In addition, it is known that AMPK knockout protects beta cells from IL1β-mediated apoptosis, however how AMPK activation leads to apoptosis remains unknown. The present study was designed to investigate the possible role of AMPK pathway modulation in CNTF protective effects against apoptosis induced by IL1β or Alloxan and how AMPK activation leads to beta cells apoptosis. First, we observed that apoptosis of MIN6 cells, induced by Alloxan as well as IL-1β, requires activation of the AMPK pathway, and also that CNTF protective effects are dependent on downregulation of AMPK. In addition, we found that Alloxan induces AMPK differently from IL1β, as Alloxan acts mainly through CaMKII while IL1β acts through LKB1 phosphorylation. Meanwhile, CNTF by itself inhibited the AMPK pathway and protected against AMPK activation induced by Alloxan or IL1β via downregulation of CaMKII. Finally, AMPK-dependent MIN6 cell apoptosis, induced by IL1β or Alloxan, required increased iNOS expression, an effect that was reversed by CNTF downregulation of AMPK pathway and iNOS expression. In conclusion, IL1β upregulates the LKB1-AMPK-INOS pathway, while Alloxan acts through CaMKII-AMPK-INOS, both ultimately leading to beta cell death. In this context, CNTF protects beta cells against apoptosis, induced by either IL1β or Alloxan, through downregulation of the CaMKII-AMPK-INOS pathway.