Early glucagon-positive cells restrict pancreatic branching through VMAT2-noradrenaline-mediated ROS signaling.

Vesicular monoamine transporter 2 (VMAT2) transports monoamines into storage vesicles. We have previously reported that VMAT2 negatively regulates pancreatic progenitor differentiation into endocrine beta cells; however, the underlying mechanism remains unknown. Using a pancreatic bud explant culture, we show here that inhibiting VMAT2-mediated catecholamine uptake promotes pancreatic epithelial branching and increases the number of insulin-expressing cells. The increase in pancreatic branching was mimicked by inhibition of tyrosine hydroxylase, monoamine oxidase A, dopamine beta-hydroxylase or norepinephrine transporter. RNA sequencing analysis of the pancreatic buds revealed that reactive oxygen species (ROS) play a role in branch formation. We found that these early glucagon (GCG) and insulin (INS) co-expressing cells express VMAT2 and monoamine signaling components. Lineage-specific VMAT2 deletion in Gcg-expressing cells resulted in increased pancreatic branching and islet areas, and decreased ROS accumulation. We conclude that early GCG and INS co-expressing cells regulate pancreatic branching morphogenesis via VMAT2-noradrenaline-mediated ROS signaling.