Receptor interacting protein kinase 3 (RIPK3) can activate and be activated by ER stress. Islet inflammation associated with underlying activation of RIPK3 is conserved from zebrafish to humans. However, the role of RIPK3 in mammalian beta cells and the mechanism by which ER stress activates RIPK3 are not well defined. To investigate the role of RIPK3 in beta cell function, we generated beta cell specific Ripk3 knockout mice (Ripk3ßKO) in C57BL/6J background with or without the Akita mutation (Ins2C96Y/+, which causes ER stress induced beta cell apoptosis and early onset diabetes) (Ripk3ßKOAkita) . We found that the glucose tolerance was worsened in Ripk3ßKO mice than wildtype controls after 16 weeks of high fat diet. Similarly, Ripk3ßKOAkita mice had higher random blood glucose, lower circulating insulin, and worse glucose tolerance than Akita C57BL/6J mice as early as 4 weeks of age. Unexpectedly, isolated islets from Ripk3ßKO and Ripk3ßKOAkita mice have comparable glucose stimulated insulin secretion (GSIS) and are more resilient to palmitate-induced lipotoxicity than their control counterparts. Similarly, pharmacological inhibition of RIPK3 protected human islets from palmitate-induced impairment of GSIS ex vivo. We are currently investigating the role of specific islet inflammation stages in the divergent GSIS phenotypes between in vivo and ex vivo. To investigate how ER stress activates RIPK3 in beta cells, we tested the effect of inhibiting classic UPR branches on RIPK3 activation in MIN6 cells, a mouse beta cell line. We found that IRE1a activation appears to play an essential role in RIPK3 activation. Interestingly, Ripk3 knockdown in MIN6 cells also decreased IRE1a levels. We next seek to define the mechanism underlying the crosstalk between RIPK3 and IRE1a signaling pathways.
L.Yang: None. B.Yang: None. X.Tong: None. C.Dai: None. Z.Tang: None. W.Chen: None.
National Institutes of Health (DK117147)