Project Summary The training strategy demonstrated in this document will help me advance my career to be an independent research scientist in the field of diabetes. I propose to assess the role of arginine transport in the regulation of pancreatic islet cell proliferation and hormone secretion. Disease progression of diabetes is attributed to the inability of pancreatic β-cells to sufficiently secrete insulin and the combined failure to suppress pancreatic α-cell secretion of glucagon. Inhibition of glucagon signaling reduces hyperglycemia for individuals with diabetes.3 However, impairment of glucagon signaling leads to hyperglucagonemia, hyperaminoacidemia, and α-cell proliferation.4,5 Our lab has identified a liver-α-cell axis that contributes to α-cell proliferation through the accumulation of amino acids in the blood.4 We have identified two major amino acids that contribute to α-cell proliferation, glutamine4 and arginine (unpublished data). However, the mechanisms underlying arginine transport in the α-cell specifically and its contribution to α-cell proliferation and secretion are not well defined. The cationic amino acid transporter SLC7A2 is highly expressed in mouse and human pancreatic α-cells. Therefore, we hypothesize that hyperaminoacidemia that results from interrupted glucagon signaling contributes to increased arginine transport promoting α-cell proliferation and dysfunction. Our preliminary studies show that SLC7A2 is required for α-cell proliferation and glucagon secretion even when challenged with strong membrane depolarizing agents challenging current cation-centric models of arginine stimulated secretion (Figure 2 and 4). Using a new α-cell specific Slc7a2 knockout mouse model, we will unravel the molecular mechanisms that lead to arginine-stimulated α-cell proliferation and glucagon secretion. To assess whether SLC7A2 in α-cells is necessary for amino acid-dependent α-cell proliferation, Slc7a2 knockout in immortalized mouse αTC1-6 cells and an inducible α-cell specific Slc7a2 knockout mouse model will be used to assess changes in α-cell proliferation and mass. Additionally, the mechanism of arginine-induced mTORC1 activation will be targeted to determine if arginine activates mTORC1 through the inactivation of the CASTOR1- GATOR2 pathway (Aim 1). Furthermore, to test the ability for arginine transport via SLC7A2 to modulate glucagon secretion we will combine tools used in Aim 1 with chemical and genetically encoded Ca2+ sensors to observe changes in α-cell glucagon secretion. We will also measure nitric oxide levels, and test the affect of nitric oxide on glucagon secretion to understand the mechanism behind arginine-induced glucagon secretion (Aim 2). Successfully accomplishing this study will enhance our current understanding of amino acid-induced α- cell proliferation and function, as well as broaden the possibilities of therapeutic treatments for diabetes. My training will be achieved through the execution of this st...