GLP1R Regualtion of Gap Junction Coupling in the Islet of Langerhans

Abstract

Pancreatic islets regulate glucose homeostasis through insulin secretion. β‐cells are connected by gap junctions, which regulate depolarization, calcium signaling and insulin secretion. In diabetes, pro‐inflammatory cytokines contribute to β‐cell mass depletion and dysfunction. Low levels decrease Gap Junction Coupling (GJC) in the islet, disrupting calcium signaling and insulin secretion dynamics. Cyclic adenosine monophosphate (cAMP), elevated by a Type 2 Diabetes treatment called Exendin‐4, has been shown to increase GJC. Increased cAMP acts via protein kinase A (PKA) and exchange protein activated by cAMP 2 (Epac2) to regulate GJC in other systems; however, this has not been shown in pancreatic islets. We hypothesized Exendin‐4 can overcome cytokine induced decreases in GJC through PKA and Epac2 dependent mechanisms.To test this, isolated mouse islets were cultured overnight with a cocktail of pro‐inflammatory cytokines, 10nM Exendin‐4 and activators and inhibitors of PKA and EPAC2. Changes in GJC were quantified with Fluorescent Recovery After Photo‐bleaching, and calcium signaling was measured with calcium imaging of Fluo‐4.Cytokine+Exendin‐4 increased GJC compared to the cytokine treatment alone. PKA inhibitor decreased the Exendin‐4 recovery and had higher GJC than the cytokine treatment. PKA activator also recovered cytokine induced GJC decreases. Epac2 had little effect on recovery.These results suggest that Exendin‐4 is acting through PKA to overcome cytokine induced decreases in GJC while EPAC2 has minimal effect. Future work is needed to determine how PKA increases GJC via Cx36 in this system. This work will be important for targeting decreased GJC in pre‐diabetic patients.