The role of G protein-dependent and -independent EP3 signaling in beta-cell compensation and diabetes - SUMMARY/ABSTRACT: Diabetes is a costly and complex chronic illness and a serious public health problem. The number of individuals with diabetes, particularly obesity-linked type 2 diabetes (T2D), is certain to increase over the next decades. Shockingly, the children of today have an estimated overall lifetime risk of developing diabetes of nearly 50%. Therefore, developing new methods to prevent T2D and properly treat T2D patients is exceptionally timely and of great significance. The progression to T2D is increasingly being linked with changes in cellular and molecular signaling pathways in the insulin-secreting pancreatic β-cell, preventing adequate insulin secretion to stimulate the body’s cells to take up glucose from the blood. Yet, few T2D drugs specifically target the β-cell, and those that do are not effective in all individuals and are controversially linked with β-cell failure long-term. Two molecules that are cornerstones of our research program are prostaglandin EP3 receptor (EP3), a G protein-coupled receptor (GPCR) for the arachidonic acid metabolite, prostaglandin E2 (PGE2), and its associated G protein alpha subunit, Gαz. Work from our group and others has definitively shown EP3 expression and signaling is increased in β-cells of T2D mice and human organ donors and blocking EP3 signaling can stimulate β-cell insulin secretion and proliferation. These exciting results suggest targeting EP3 and/or Gαz might increase the number of functional β-cells in T2D; yet, much more work is necessary to achieve this. Our long-term goal is to fully characterize the EP3 and Gαz activation and signaling pathways during the progression to T2D at the whole body, tissue, cellular, and molecular levels, providing us key information on how to target this β-cell pathway in T2D. The overall objective of this work, which is the next logical step in pursuit of our goal, is to define the molecular signaling pathways responsible for the impact of EP3 signaling, both Gɑz-dependent and -independent, on mouse and human β-cell compensation and β-cell failure. Our central hypothesis is EP3 and Gαz, when active, modulate intracellular signaling pathways critical for β-cell compensation in obesity but, when chronically active, contribute to β-cell dysfunction and loss in T2D. We will test our central hypothesis with a combination of innovative cellular imaging, metabolomics, and proteomics assays, correlating changes in EP3 and Gɑz signaling pathways with measurements of β-cell function in response to glucose and glucagon-like peptide 1: a well-accepted class of T2D drugs. We will accomplish this goal by pursuing the following three Specific Aims: 1. Determine effects of EP3 on discrete cellular pools of β-cell Ca2+ and cAMP and downstream β-cell function and mass; 2. Quantify Gɑz-dependent Rap1GAP translocation, Rap1GAP phosphorylation, and their effects on β-cell function and mass; and 3. Quantify changes in the human islet arachidonic acid metabolome, and the functional consequence of these changes, during the progression to T2D. This work, when completed, will provide a much more complete understanding of the role of the β-cell and its signaling molecules in the progression to and pathophysiology of T2D.
