Abstract
Insulin secretion by pancreatic islet β-cells is regulated by glucose levels and is accompanied by proton generation. The voltage-gated proton channel Hv1 is present in pancreatic β-cells and extremely selective for protons. However, whether Hv1 is involved in insulin secretion is unclear. Here we demonstrate that Hv1 promotes insulin secretion of pancreatic β-cells and glucose homeostasis. Hv1-deficient mice displayed hyperglycemia and glucose intolerance because of reduced insulin secretion but retained normal peripheral insulin sensitivity. Moreover, Hv1 loss contributed much more to severe glucose intolerance as the mice got older. Islets of Hv1-deficient and heterozygous mice were markedly deficient in glucose- and K+-induced insulin secretion. In perifusion assays, Hv1 deletion dramatically reduced the first and second phase of glucose-stimulated insulin secretion. Islet insulin and proinsulin content was reduced, and histological analysis of pancreas slices revealed an accompanying modest reduction of β-cell mass in Hv1 knockout mice. EM observations also indicated a reduction in insulin granule size, but not granule number or granule docking, in Hv1-deficient mice. Mechanistically, Hv1 loss limited the capacity for glucose-induced membrane depolarization, accompanied by a reduced ability of glucose to raise Ca2+ levels in islets, as evidenced by decreased durations of individual calcium oscillations. Moreover, Hv1 expression was significantly reduced in pancreatic β-cells from streptozotocin-induced diabetic mice, indicating that Hv1 deficiency is associated with β-cell dysfunction and diabetes. We conclude that Hv1 regulates insulin secretion and glucose homeostasis through a mechanism that depends on intracellular Ca2+ levels and membrane depolarization.
Highlights
Insulin secretion by pancreatic islet -cells is regulated by glucose levels and is accompanied by proton generation
The voltage-gated proton channel Hv1 is extremely selective for protons and has no detectable permeability to other cations [13, 14]
We show in vivo that Hv1 KO and heterozygous mice display hyperglycemia and glucose intolerance because of markedly decreased insulin secretion
Summary
T2D, type 2 diabetes; GSIS, glucose-stimulated insulin secretion; IPGTT, i.p. glucose tolerance test; IPITT, i.p. insulin tolerance test; AUC, area under the curve; TEM, transmission EM; GSCa, glucosestimulated calcium; PMA, phorbol 12-myristate 13-acetate; KRBH, Krebs–Ringer bicarbonate HEPES; pHc, cytosolic pH; STZ, streptozotocin; HOMA-IR, homeostasis model assessment insulin resistance; VSOP, voltage sensor domain-only protein; Hv1, hydrogen voltage-gated channel 1. Ever, the regulatory mechanism of Hv1 for insulin secretion of pancreatic islet -cells is not known. We discovered a regulatory mechanism for Hv1 in the modulation of -cell insulin secretory function. Our in vivo and in vitro studies demonstrated that Hv1-deficient mice exhibit hyperglycemia and glucose intolerance because of abnormally decreased insulin secretion. These data provide direct genetic evidence that Hv1 regulates biphasic insulin secretion and glucose homeostasis in mice, implying a potential link between Hv1 and the pathogenesis of diabetes mellitus
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