TRPV4 couples with NCX1 to mediate glucose-dependent glucagon-like peptide-1 release and improve glucose homeostasis

Abstract

Although glucose, as a secretagogue of intestinal hormone, can stimulate glucagon-like peptide 1 (GLP-1) release, it has not been fully elucidated how glucose triggers GLP-1 release from enteroendocrine cells (EECs). Here, we investigated the regulatory mechanisms of glucose-induced Ca²⁺-dependent GLP-1 release from EECs. STC-1 cells that possess many features of native intestinal EECs were used. The expression of TRPV4 channels and Na⁺/Ca²⁺ exchanger 1 (NCX1) in STC-1 was analysed by immunocytochemistry. Calcium and sodium imaging, and patch clamp were applied, and GLP-1 was detected using quantitative PCR, western blot and enzyme-linked immunosorbent assays. Glucose markedly induced Na⁺ and Ca²⁺ signalling in STC-1 cells. The glucose-induced Ca²⁺ signalling was significantly attenuated by selective blockers of the voltage-gated Ca²⁺ channels (VGCC), ryanodine receptors and InsP₃ receptors. Most importantly, glucose-induced Ca²⁺ signalling was significantly attenuated by the selective blockers of TRPV4 and NCX1. Moreover, the physical and functional couplings of TRPV4 and NCX1 were demonstrated in STC-1 cells, and they promoted glucose-mediated Ca²⁺ signalling to upregulate expression and release of GLP-1 via Ca²⁺-sensitive PKCα. Finally, the selective TRPV4 activator improved glucose tolerance in an oral glucose tolerance test in mice, but the selective blockers of TRPV4 and NCX1 attenuated glucose-induced intestinal GLP-1 release. We demonstrate a coupling of TRPV4 and NCX1 in EECs to regulate glucose-stimulated intestinal GLP-1 release via a novel TRPV4/NCX1/Ca²⁺/PKCα axis. Targeting this axis may provide new therapeutic potentials for glycometabolic diseases. KEY POINTS: Glucagon-like peptide 1 (GLP-1) secreted primarily from intestinal L cells in response to meals plays a critical role in maintaining glucose homeostasis. Physical and functional couplings of TRPV4 and NCX1 are pivotal in glucose-stimulated GLP-1 release via a novel TRPV4/NCX1/Ca²⁺/PKCα axis. Since this axis is involved in glucose homeostasis, our findings may provide new potential drug targets for prevention/treatment of glycometabolic diseases.

Keywords: EECs; GLP‐1; NCX1; TRPV4; glucose.