366-OR: 14-3-3-ζ Contributes to Effect of ß-Cell GLP1 Receptor Signaling to Alter a-Cell Proglucagon Processing

Glucagon like peptide 1 (GLP1) , a classically gut derived hormone, potentiates insulin secretion. New evidence suggests that α cells can produce GLP1 under certain conditions, which may offer a novel therapeutic modality for treating diabetes; however, the mechanisms regulating α cell GLP1 production are unknown. We previously found that enhanced β cell GLP1 receptor (GLP1R) signaling activates α cell GLP1 by activating prohormone convertase 1/3 (Pcsk1) expression. We tested the hypothesis that enhanced β cell GLP1R signaling activates α cell GLP1 production through paracrine factors. We studied the impact of conditioned media (CM) generated from β cell GLP1R WT and KO islets of saline (CTRL) and liraglutide (LIRA) treated mice on α cell gene expression and function. CM from LIRA treated islets increased α cell Pcsk1 expression and active GLP-1 secretion only if β cells expressed the GLP1R (Pcsk1 expression (AU) : CTRL WT=1.0±0.1, LIRA WT=2.0±0.3, CTRL KO=1.1±0.2, LIRA KO=1.1±0.2, P<0.01; active GLP-1 (pg/mL) : CTRL WT=124±44, LIRA WT=682±247, CTRL KO=173±101, LIRA KO=116±30, P<0.05) . Subsequent identification of the proteome secreted by mouse and human islets in response to LIRA and CTRL revealed 14-3-3-ζ as a lead candidate in the regulation of α cell Pcsk1 expression. To assess the role of 14-3-3-ζ, islets from LIRA treated mice were treated with and without 14-3-3-ζ, and islets from CTRL treated mice were treated with and without the 14-3-3 inhibitor, R18. Addition of 14-3-3-ζ ablated the effect of CM from LIRA treated islets to increase α cell Pcsk1 expression, while inhibition of 14-3-3 with R18 in CTRL islets resulted in CM that mimicked the effect of CM from LIRA treated islets to stimulate α cell Pcsk1 expression (Pcsk1 expression: CTRL=1.1±0.2, R18=2.0±0.2, LIRA=2.4±0.3, LIRA+14-3-3-ζ=1.3±0.1, P<0.05) . These data refine our understanding of α cell GLP1 regulation and identify 14-3-3-ζ as a potential target with which to enhance α cell GLP1 production for diabetes treatment.