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

Vesicular monoamine transporter 2 (VMAT2) transports monoamines into storage vesicles. We previously reported that VMAT2 negatively regulates pancreatic progenitor differentiation into endocrine beta cells (Sakano et al., 2014). However, the underlying mechanism remains unknown. Using a pancreatic bud explant culture, here we show 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 GCG- and 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.