Pancreatic Alpha-Cell Function and Identity in Human T2D

Glucagon is synthesized and released by pancreatic α-cells and, along with insulin, maintains blood glucose levels within the physiological range. We seek to understand the impact of glucose on the biophysical properties of α-cells in T2D. We studied α-cells from human donors (34 nondiabetic, and 14 T2D) and from mice fed a high fat diet (HFD) by whole-cell patch-clamp electrophysiology, with and without combined single-cell RNA sequencing (patch-seq). We found that, opposite to what is observed in β-cells, depolarization-induced exocytosis and Ca²⁺-channel function is enhanced at low glucose (LG, 1 mM G) and suppressed at high glucose (HG, 5-20 mM G) in nondiabetic (ND) α-cells. This is reversed in α-cells from T2D donors, which display a β-cell-like phenotype where HG amplifies exocytosis and LG inhibits it. Using pharmacological antagonists of Ca²⁺ channels, we found that LG increases P/Q-type Ca²⁺ currents in human α-cells, which are specifically linked to glucagon exocytosis. Similar results were obtained from α-cells of HFD mice for 10-14 weeks, where α-cell exocytosis and glucagon secretion were both enhanced, while exocytosis shifted from a dependency on P/Q-type (α-cell-like) to L-type (β-cell-like) Ca²⁺ channels. Finally, given that the Ca²⁺ responsiveness of α-cells is variable (suggesting cell- to-cell heterogeneity) and the function of α-cells is dysregulated in diabetes, we applied combined computational approaches and single-cell RNA sequencing with patch-clamp analysis (patch-seq) to link single human α-cell function with transcriptomic profiles. We found distinct α-cell sub-populations in human islets that are either resistant to, or sensitive to, dysfunction in the form of a shift towards a more ’β-cell like’ functional phenotype in T2D. In all, we provide new information to understand normal function of α-cells and important determinants of glucagon secretion in health and diabetes.