The role of GLP-1 and CCK in the pancreatic islet to promote beta-cell survival

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Reduced β-cell mass and increased β-cell apoptosis are key to the pathophysiology of both type 1 and type 2 diabetes. Therefore, identifying factors that can protect from β-cell apoptosis will meet a critical therapeutic need in the prevention and treatment of diabetes. Glucagon-like peptide-1 (GLP-1) and cholecystokinin (CCK) are peptide hormones normally produced in the intestine with beneficial effects on β-cell mass and function. Both GLP-1 and CCK are produced within the pancreatic islet under conditions of islet stress. GLP-1 based therapies are in widespread use for the treatment of type 2 diabetes, and there is substantial evidence in cell lines and rodent models that GLP-1 can protect from β-cell apoptosis. Similarly, we have shown that CCK is necessary and sufficient to protect from β-cell apoptosis in mouse models. While CCK has been widely studied in exocrine pancreatic cells, there is limited information about the role of CCK in the β-cell. We propose that the production of these hormones in the islet represents a compensatory physiologic mechanism to promote β-cell survival. The long-term goal is to identify novel pathways critical in the preservation of β-cell mass. The overall objective of this application is to determine the regulation of locally produced GLP-1 and CCK and their role in protection from β-cell apoptosis. The central hypothesis is that an intra-islet signaling network exists, whereby GLP-1 produced in the α-cell and CCK produced in the β-cell are co-regulated and work together to promote β-cell survival. To achieve the objective, three Specific Aims are proposed. In Aim 1, we will determine how GLP-1 and CCK production are regulated in the pancreatic islet. Preliminary evidence support the hypothesis that CCK and GLP-1 signal in a paracrine manner within the islet to co-regulate one another. We will use transgenic overexpression of β-cell CCK and receptor knockout mouse models to clarify how these hormones regulate one another in the islet. In Aim 2, we will identify the mechanism of CCK-mediated protection from cytokine-induced apoptosis. We will use receptor antagonists and knockouts to determine which CCK receptor regulates β-cell survival and we will determine the intracellular signaling pathways activated by CCK in the β-cell. In Aim 3, we will determine if GLP-1 and CCK can synergistically and interdependently protect human islets from apoptosis. We have intriguing evidence that the role of GLP-1 in β-cell survival is dependent on CCK receptor signaling in a cell line. This suggests the innovative concept that the impact of GLP-1 on the β-cell relies on its ability to stimulate CCK. As human islets have very different characteristics than mouse islet, examining the role of GLP-1 and CCK specifically in human islets is of critical importance to translation of our findings to diabetes therapies. These studies will contribute to our fundamental understanding of this novel intra-islet hormonal regulatory pathway and the mechanisms whereby GLP-1 and CCK promote β-cell survival. This contribution is significant as it will advance knowledge of both adaptive and therapeutic mechanisms of β- cell survival, allowing development of targeted therapies with maximal efficacy and minimal side effects.