1724-P: Caspase 3/7 Activation and RIPK3 Are Dispensable for Synthetic hIAPP-Induced ß-Cell Death

Islet amyloid is a hallmark of type 2 diabetes that is associated with β-cell loss. Aggregation of the β-cell secretory product human islet amyloid polypeptide (hIAPP) to form islet amyloid promotes β-cell death 1) via direct effects on the β cell and 2) by stimulating islet immune cell cytokine production. We recently showed that β cells are susceptible to TNFα-induced necroptosis, a form of caspase-independent, receptor interacting protein kinase 3 (RIPK3)-mediated cell death. We hypothesized that RIPK3 also promotes β-cell death in response to islet amyloid formation. To test this hypothesis, we evaluated INS-1, NIT-1 and isolated mouse islet cells treated with synthetic hIAPP (20 μM) +/− the pan-caspase inhibitor zVAD (40 μM). We found synthetic hIAPP increased cell death and caspase activity in INS-1, NIT-1 and mouse islet cells over 48 h. Remarkably, inhibition of caspases with zVAD (as measured by caspase 3/7 activity) failed to reduce synthetic hIAPP-mediated cell death in INS-1 (n=3, p=0.99), NIT-1 (n=3, p=0.99) or mouse islet cells (n=4, p=0.98). To evaluate RIPK3 in hIAPP-induced β-cell death, we examined a small molecule RIPK3 inhibitor (GSK’872, 5 μM), gene-edited NIT-1 Ripk3Δ cells (gRNA targeting exon 6), and intact isolated Ripk3^−/− mouse islets. We found GSK’872 failed to protect INS-1 (n=3, p=0.32) or NIT-1 (n=3, p=0.30) cells from hIAPP-induced cell death over 48 h. Similarly, neither NIT-1 Ripk3Δ cells (n=2, hIAPP: p=0.82, hIAPP+zVAD: p=0.97) nor Ripk3^−/− islets (n=4, hIAPP: p=0.63, hIAPP+zVAD: p=0.86) were protected from synthetic hIAPP-induced cell death either when caspases were active or inhibited. Our data indicate that caspase 3/7 activity and RIPK3 are dispensable for synthetic hIAPP-induced β-cell death in vitro. However, we found that RIPK3 is upregulated in response to endogenous islet amyloid formation in vitro. Future studies will determine whether RIPK3 promotes β-cell loss in part via effects on endogenous amyloid-induced cytokine signaling.