ORF14-03 - Endocrine-Vascular Coupling in the Pancreatic Islet and Its Effects on Blood Flow

Although endocrine and exocrine pancreatic tissues share their vascular networks, a selective increase in islet blood flow is observed upon increases in glycemia. We have previously shown that pericytes participate in this vascular response, known as functional hyperemia, and that these acute changes in blood flow are needed for proper hormonal responses to a glucose challenge. However, the cellular and molecular mechanisms that orchestrate these vascular responses have not been fully characterized. In this study, we investigated whether beta cells can control islet blood flow by releasing different vasoactive molecules which act on pericytes.

To acutely manipulate beta cell activity, we injected adeno-associated viruses encoding excitatory (M3) and inhibitory (M4) designer receptors exclusively activated by designer drugs (DREADD) under the insulin promoter into mice that express GCaMP3 in pericytes. We activated beta cells in living pancreas slices from non-diabetic organ donors by stimulating them with high glucose. We monitored pericyte activity ex vivo in living pancreas slices from mice and humans and islet blood flow in the exteriorized mouse pancreas.

We found that acute stimulation with the DREADD agonist clozapine (CNO) decreased [Ca2+]i in islet pericytes ex vivo, and increased islet blood flow in the exteriorized pancreas of M3-DREADD mice. In contrast, inhibiting beta cells with CNO in living slices from M4-DREADD mice, increased [Ca2+]i in a subset of islet pericytes. Manipulating endogenous levels and receptor signaling of vasoactive molecules released by beta cells (e.g. adenosine (ADO)) altered pericyte [Ca2+]i responses to beta cell activation with CNO. To examine the potential role of ADO as a mediator of beta cell-pericyte crosstalk also in human islets, we incubated ADO biosensor cells (Ready-to-Assay A2A Adenosine Receptor Cells; loaded with [Ca2+]i indicator Fluo-4) with islets isolated from non-diabetic donors. High glucose stimulation led to an increase in ADO released from islets, as well as decreased [Ca2+]i in islet pericytes ex vivo in living pancreas slices. Importantly, antagonizing ADO receptor 2A using ZM241385 blunted pericyte calcium responses to high glucose, indicating that ADO may also mediate endo-vascular coupling in human islet.

In summary, our data show that beta cells participate in the regulation of their own blood flow. By releasing vasoactive molecules, such as purinergic signals, beta cell activation reduces islet pericyte activity, resulting in capillary dilation and increasing local blood supply to islets. Such an increase in blood supply to islets upon beta cell activation would enable sustained delivery of nutrients and oxygen to endocrine cells in during states of enhanced activity and hormone release into the circulation.