Alpha-Melanocyte Stimulating Hormone Preserves Islet Graft Survival Through Down-Regulation of Toll-Like Receptors

Abstract The induction of Toll-like receptors (TLRs) in β cells is involved in β-cell death and graft rejection after transplantation. This study investigated the ability of alpha-melanocyte stimulating hormone (α-MSH) to protect pancreatic islets and improve graft survival through regulation of TLRs. To test the effect of α-MSH on TLR regulation, we first isolated pancreatic islets from rats pretreated with/without α-MSH and assayed inflammatory cytokines and insulin release, and measured the expression of TLRs. Pancreatic islets were transplanted into the kidney capsule of a diabetes mellitus (DM) mouse with and without prior injection of α-MSH. The blood glucose levels were measured and TLR4 expression in transplanted kidney tissue was assessed. Islet morphology, including size and total mass, was improved in the α-MSH group compared to the control group. The expression of TLRs as well as nitric oxide and monocyte chemoattractant protein 1 production were decreased in islets isolated from α-MSH–treated rats. In DM mice, the normoglycemic ratio was higher in the α-MSH–treated group than in the sham group. Moreover, the high levels of TLR4 expression observed in DM kidney tissue were significantly decreased in islet-transplanted tissue with α-MSH. This study showed that α-MSH protects pancreatic islets from cell death and dysfunction through downregulation of TLRs. In conclusion, α-MSH could contribute to improved islet graft survival and function in pancreatic islet transplantation.