GPRC5B preserves a mature β cell state in obesity by controlling MafA expression
Tianpeng Wang, Remy Bonnavion, Janett Piesker, Stefan Günther, Nina Wettschureck
Tianpeng Wang, Remy Bonnavion, Janett Piesker, Stefan Günther, Nina Wettschureck
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Research Article Endocrinology Metabolism

GPRC5B preserves a mature β cell state in obesity by controlling MafA expression

Abstract

In vitro studies have implicated orphan receptor GPRC5B in β cell survival, proliferation, and insulin secretion, but its relevance for glucose homeostasis in vivo is largely unknown. Using tamoxifen-inducible, β cell–specific GPRC5B-KO mice (Ins-G5b–KOs), we show here that loss of GPRC5B does not affect β cell function in the lean state but results in strongly reduced insulin secretion and disturbed glucose tolerance in mice subjected to high-fat diet for 16 weeks. Flow cytometry and single-cell expression analyses in islets from obese mice show a reduced β cell abundance and a less mature β cell phenotype in Ins-G5b–KOs. Expression of β cell–specific transcription factor MafA is reduced both on the RNA and protein level, as are transcripts of MafA target genes. Mechanistically, we show that phosphorylation of cAMP response element-binding protein (CREB), a major regulator of MafA expression, is reduced in islets of obese Ins-G5b–KOs, and we show that this phenotype precedes the downregulation of MafA and MafA target genes. Taken together, GPRC5B helps to maintain mature β cell function in obesity through cAMP/CREB-dependent regulation of MafA expression.

Authors

Tianpeng Wang, Remy Bonnavion, Janett Piesker, Stefan Günther, Nina Wettschureck

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Figure 2

Metabolic profiling of Ins-G5b–KO mice after 16 weeks of HFD feeding.

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Metabolic profiling of Ins-G5b–KO mice after 16 weeks of HFD feeding. (A...
(A) Body weight gain in control and Ins-G5b–KOs (n = 21/21 mice) during 16 weeks of HFD feeding. (B and C) Blood glucose levels in the fed (B, n = 13/13 mice) and 12-hour–fasted state (C, n = 11/14 mice). (D and E) Blood glucose levels after i.p. (D) or oral (E) administration of glucose (1.5 g/kg body weight) (D, n = 19/21 mice, E, n = 5/5 mice). (F and G) Plasma insulin levels after i.p. (F) or oral (G) administration of glucose (1.5 g/kg body weight) (F, n = 24/24 mice, G, n = 4/5 mice). (H) Insulin secretion from isolated islets of obese control mice and Ins-G5b–KOs in response to 2.8 mM glucose (2.8), 16.7 mM glucose (16.7), or 30 mM KCl (n = 14/13 mice). (I and J) Glucose-induced calcium mobilization in Fluo-8–loaded islets: I, original traces, J, quantification of areas under the curve (AUC) (n = 35/32 islets from 3/4 mice). (K) Blood glucose levels after i.p. application of 0.75 U/kg body weight insulin (insulin tolerance test, n = 12/12 mice). (L) Plasma glucagon levels were determined in the fed and fasted state by ELISA (n = 10/10 mice). (M) Plasma glucagon levels after i.p. application of 1.5 g/kg glucose (n = 10/8 mice). (N and O) Plasma levels of gastrointestinal hormones and mediators implicated in glucose homeostasis in the fasted (N, n = 7/5 mice) and fed state (O, n = 4/4 mice) by MILLIPLEX Assay. Samples below detection limit were set to 0.1 pg/mL for visualization. Data are mean ± SEM; comparisons between control and KO samples were performed using unpaired Student’s t test (B, C, and J), 2-way repeated measures ANOVA with Šidák’s multiple-comparison test (A, D–H, and K–M), and multiple unpaired Student’s t test with 2-stage linear step-up procedure of Benjamini, Krieger ,and Yekutieli (N and O). *P ≤ 0.05, **P ≤ 0.01, ***P ≤ 0.001, ****P ≤ 0.0001.