Reg3α Overexpression Protects Pancreatic Beta-Cells From Cytokine-Induced Damage and Improves Islet Transplant Outcome.

The process of islet transplantation for treating type 1 diabetes has been limited by the high level of graft failure that may be overcome by locally delivering trophic factors to enhance engraftment. Regenerating islet-derived protein 3 alpha (Reg3α) is a pancreatic secretory protein, which functions as an antimicrobial peptide in control of inflammation and cell proliferation. In this study, to investigate whether Reg3α could improve islet engraftment, a marginal mass of syngeneic islets pretransduced with adenoviruses expressing Reg3α or control EGFP were transplanted under the renal capsule of streptozotocin-induced diabetic mice. Mice receiving islets with elevated Reg3α production exhibited significantly lower blood glucose levels (9.057 ± 0.59 mmol/l vs 13.48 ± 0.35 mmol/l, P < 0.05) and improved glucose-stimulated insulin secretion (1.80 ± 0.17 ng/ml vs 1.16 ± 0.16 ng/ml, P < 0.05) compared with control group. The decline of apoptotic events (0.57% ± 0.15% vs 1.06% ± 0.07%, P < 0.05) and increased beta-cell proliferation (0.70% ± 0.10% vs 0.36% ± 0.14%, P < 0.05) were confirmed in islet grafts overexpressing Reg3α by morphometric analysis. Further experiments showed that Reg3α production dramatically protected cultured islets and pancreatic beta-cells from cytokine-induced apoptosis and the impairment of glucose-stimulated insulin secretion. Moreover, exposure to cytokines led to the activation of MAPKs in pancreatic beta-cells, which was reversed by Reg3α overexpression in contrast to control group. These results strongly suggest that Reg3α could enhance islet engraftments through its cytoprotective effect and advance the therapeutic efficacy of islet transplantation.