Gsα-dependent signaling is required for postnatal establishment of a functional β-cell mass

Objective: Early postnatal life is a critical period for the establishment of the functional beta-cell mass that will sustain whole-body glucose homeostasis during the lifetime. beta cells are formed from progenitors during embryonic development but undergo significant expansion in quantity and attain functional maturity after birth. The signals and pathways involved in these processes are not fully elucidated. Cyclic adenosine monophosphate (cAMP) is an intracellular signaling molecule that is known to regulate insulin secretion, gene expression, proliferation, and survival of adult beta cells. The heterotrimeric G protein Gs stimulates the cAMP-dependent pathway by activating adenylyl cyclase. In this study, we sought to explore the role of Gs-dependent signaling in postnatal beta-cell development. Methods: To study Gs-dependent signaling, we generated conditional knockout mice in which the alpha subunit of the Gs protein (Gs alpha) was ablated from beta-cells using the Cre deleter line Ins1(Cre). Mice were characterized in terms of glucose homeostasis, including in vivo glucose tolerance, glucose-induced insulin secretion, and insulin sensitivity. beta-cell mass was studied using histomorphometric analysis and optical projection tomography. beta-cell proliferation was studied by ki67 and phospho-histone H3 immunostatining, and apoptosis was assessed by TUNEL assay. Gene expression was determined in isolated islets and sorted beta cells by qPCR. Intracellular cAMP was studied in isolated islets using HTRF-based technology. The activation status of the cAMP and insulin-signaling pathways was determined by immunoblot analysis of the relevant components of these pathways in isolated islets. In vitro proliferation of dissociated islet cells was assessed by BrdU incorporation. Results: Elimination of Gs alpha in beta cells led to reduced beta-cell mass, deficient insulin secretion, and severe glucose intolerance. These defects were evident by weaning and were associated with decreased proliferation and inadequate expression of key beta-cell identity and maturation genes in postnatal beta-cells. Additionally, loss of Gs alpha caused a broad multilevel disruption of the insulin transduction pathway that resulted in the specific abrogation of the islet proliferative response to insulin. Conclusion: We conclude that Gs alpha is required for beta-cell growth and maturation in the early postnatal stage and propose that this is partly mediated via its crosstalk with insulin signaling. Our findings disclose a tight connection between these two pathways in postnatal beta cells, which may have implications for using cAMP-raising agents to promote beta-cell regeneration and maturation in diabetes. (C) 2021 The Author(s). Published by Elsevier GmbH.

Automated summary

This study reveals the essential role of Gs protein in early postnatal beta-cell growth and maturation, partly mediated through its crosstalk with insulin signaling pathways. The findings suggest a close connection between these two pathways in postnatal beta cells, potentially implicating the use of cAMP-raising agents for promoting beta-cell regeneration and maturation in diabetes.