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RhoA as a signaling hub controlling glucagon secretion from pancreatic α-cells

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posted on 29.07.2022, 16:17 authored by Xue Wen Ng, Yong Hee Chung, Farzad Asadi, Chen Kong, Alessandro Ustione, David W. Piston

Glucagon hypersecretion from pancreatic islet α-cells exacerbates hyperglycemia in type 1 (T1D) and type 2 (T2D) diabetes.  Still, the underlying mechanistic pathways that regulate glucagon secretion remain controversial.  Among the three complementary main mechanisms (intrinsic, paracrine and juxtacrine) proposed to regulate glucagon release from α-cells, juxtacrine interactions are the least studied.  It is known that tonic stimulation of α-cell EphA receptors by ephrinA ligands (EphA forward signaling) inhibits glucagon secretion in mouse and human islets and restores glucose inhibition of glucagon secretion in sorted mouse α-cells, and these effects correlate with increased F-actin density.  Here, we elucidate the downstream target of EphA signaling in α-cells.  We demonstrate that RhoA, a Rho family GTPase, plays a key role in this pathway.  Pharmacological inhibition of RhoA disrupts glucose inhibition of glucagon secretion in islets and decreases cortical F-actin density in dispersed α-cells and α-cells in intact islets.  Quantitative FRET biosensor imaging shows that increased RhoA activity follows directly from EphA stimulation.  In addition to modulating F-actin density, we show that EphA forward signaling and RhoA activity affects α-cell Ca2+ activity in a novel mechanistic pathway.  Finally, we show that stimulating EphA forward signaling restores glucose inhibition of glucagon secretion from human T1D donor islets.  

Funding

This research was supported by the US National Institutes of Health (R01DK123301 and R01DK115972), The Leona M. and Harry B. Helmsley Charitable Trust (grants G-1912-03558 and G-2001-04215), and by the Washington University Center for Cellular Imaging supported in part by the Washington University Diabetes Research Center (NIH grant P30DK020579). T1D donor islet isolation was also supported by The Helmsley Trust (grant G-2018PG-T1D027).

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