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

Abstract

Objective Early postnatal life is a critical period for the establishment of the functional β-cell mass that will sustain whole-body glucose homeostasis during the lifetime. β 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 β 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 β-cell development. Methods To study Gs-dependent signaling, we generated conditional knockout mice in which the α subunit of the Gs protein (Gsα) was ablated from β-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. β-cell mass was studied using histomorphometric analysis and optical projection tomography. β-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 β 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 Gsα in β cells led to reduced β-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 β-cell identity and maturation genes in postnatal β-cells. Additionally, loss of Gsα 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 Gsα is required for β-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 β cells, which may have implications for using cAMP-raising agents to promote β-cell regeneration and maturation in diabetes.

Ghrelin deletion and conditional ghrelin cell ablation increase pancreatic islet size in mice

“…Calm1 , Pde10a , and Gnas are of interest because their gene products serve as important intracellular signaling molecules. Genetic deletion of Gnas in β cells reduces both the expression of key β cell identity and maturation genes in postnatal β cells and β cell mass, the latter resulting from decreased β cell proliferation without changes in β cell apoptosis ( 61 ). Although we did not identify increased β cell proliferation following ghrelin cell ablation, we are mindful that the experimental time points used here to detect proliferation changes may have been suboptimal.…”

Glucose-stimulated insulin secretion depends on FFA1 and Gq in neonatal mouse islets

“…Whether Gq solely transmits the effects of FFA1 in neonatal islets is, to our knowledge, not yet known. Nevertheless, Gi and Gs were reported to regulate neonatal beta cell proliferation [ 28 , 48 ].…”

Effects of Arachidonic Acid and Its Metabolites on Functional Beta-Cell Mass

“…↑ function [31] Cyp1a1/2 ↑ function [32] Ptger1 None [33,34] Ptger2 None [33] Ga z ↑ function ↓ death [35,36] Ga s ↓ function ↓ mass [37] 2. Lipoxygenase-Derived Molecules (HETEs)…”

“…EP4 couples to G s , leading to increased cAMP (Figure 2) and activated PKA signaling [25]. Inactivation of Gα s in beta cells of adult mice results in reduced beta-cell mass, decreased insulin secretion, and glucose intolerance [37]. These deficits are apparent as early as postnatal day 28, and are associated with decreases in beta-cell proliferation and expression of beta-cell identity genes, suggesting that signaling through Gα s is required to promote beta-cell maturity and establish functional postnatal beta-cell mass [37].…”

“…Inactivation of Gα s in beta cells of adult mice results in reduced beta-cell mass, decreased insulin secretion, and glucose intolerance [37]. These deficits are apparent as early as postnatal day 28, and are associated with decreases in beta-cell proliferation and expression of beta-cell identity genes, suggesting that signaling through Gα s is required to promote beta-cell maturity and establish functional postnatal beta-cell mass [37]. Signaling through Gα s may be impaired in the context of T2D; Oduori et al recently demonstrated that persistent membrane depolarization of beta cells causes a switch from G s to G q signaling [97].…”