γ‐aminobutyric acid stimulates β‐cell proliferation through the mTORC1/p70S6K pathway, an effect amplified by Ly49, a novel γ‐aminobutyric acid type A receptor positive allosteric modulator

Aim To examine the mechanism of action of γ‐aminobutyric acid (GABA) on β‐cell proliferation and investigate if co‐treatment with Ly49, a novel GABA type A receptor positive allosteric modulator (GABAA‐R PAM), amplifies this effect. Methods Human or mouse islets were co‐treated for 4‐5 days with GABA and selected receptor or cell signalling pathway modulators. Immunofluorescence was used to determine protein co‐localization, cell number or proliferation, and islet size. Osmotic minipumps were surgically implanted in mice to assess Ly49 effects on pancreatic β‐cells. Results Amplification of GABAA‐R signalling enhanced GABA‐stimulated β‐cell proliferation in cultured mouse islets. Co‐treatment of GABA with an inhibitor specific for PI3K, mTORC1/2, or p70S6K, abolished GABA‐stimulated β‐cell proliferation in mouse and human islets. Nuclear p‐AktSer473 and p‐p70S6KThr421/Ser424 expression in pancreatic β‐cells was increased in GABA‐treated mice compared with vehicle‐treated mice, an effect augmented with GABA and Ly49 co‐treatment. Mice co‐treated with GABA and Ly49 exhibited enhanced β‐cell area and proliferation compared with GABA‐treated mice. Furthermore, S961 injection (an insulin receptor antagonist) resulted in enhanced plasma insulin in GABA and Ly49 co‐treated mice compared with GABA‐treated mice. Importantly, GABA co‐treated with Ly49 increased β‐cell proliferation in human islets providing a potential application for human subjects. Conclusions We show that GABA stimulates β‐cell proliferation via the PI3K/mTORC1/p70S6K pathway in both mouse and human islets. Furthermore, we show that Ly49 enhances the β‐cell regenerative effects of GABA, showing potential in the intervention of diabetes.