Absence of cannabinoid 1 receptor in beta cells protects against high-fat/high-sugar diet-induced beta cell dysfunction and inflammation in murine islets

Isabel González-Mariscal,Susan M Krzysik-Walker,Elin Lehrmann,Soumita Ghosh,Paritosh Ghosh,Josephine M Egan,Jennifer F O’Connell,Yongqing Zhang,Michael Rouse,Sara Santa-Cruz Calvo,Olga D Carlson,Chee W Chia,Kevin G Becker,Máire E Doyle,Rodrigo A Montoro,Qing-Rong Liu

doi:10.1007/s00125-018-4576-4

Isabel González-Mariscal, Susan M Krzysik-Walker + Show 14 more

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https://doi.org/10.1007/s00125-018-4576-4

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Abstract

Aims/hypothesisThe cannabinoid 1 receptor (CB1R) regulates insulin sensitivity and glucose metabolism in peripheral tissues. CB1R is expressed on pancreatic beta cells and is coupled to the G protein Gαi, suggesting a negative regulation of endogenous signalling in the beta cell. Deciphering the exact function of CB1R in beta cells has been confounded by the expression of this receptor on multiple tissues involved in regulating metabolism. Thus, in models of global genetic or pharmacological CB1R blockade, it is difficult to distinguish the indirect effects of improved insulin sensitivity in peripheral tissues from the direct effects of inhibiting CB1R in beta cells per se. To assess the direct contribution of beta cell CB1R to metabolism, we designed a mouse model that allows us to determine the role of CB1R specifically in beta cells in the context of whole-body metabolism.MethodsWe generated a beta cell specific Cnr1 (CB1R) knockout mouse (β-CB1R−/−) to study the long-term consequences of CB1R ablation on beta cell function in adult mice. We measured beta cell function, proliferation and viability in these mice in response to a high-fat/high-sugar diet and induction of acute insulin resistance with the insulin receptor antagonist S961.Resultsβ-CB1R−/− mice had increased fasting (153 ± 23% increase at 10 weeks of age) and stimulated insulin secretion and increased intra-islet cAMP levels (217 ± 33% increase at 10 weeks of age), resulting in primary hyperinsulinaemia, as well as increased beta cell viability, proliferation and islet area (1.9-fold increase at 10 weeks of age). Hyperinsulinaemia led to insulin resistance, which was aggravated by a high-fat/high-sugar diet and weight gain, although beta cells maintained their insulin secretory capacity in response to glucose. Strikingly, islets from β-CB1R−/− mice were protected from diet-induced inflammation. Mechanistically, we show that this is a consequence of curtailment of oxidative stress and reduced activation of the NLRP3 inflammasome in beta cells.Conclusions/interpretationOur data demonstrate CB1R to be a negative regulator of beta cell function and a mediator of islet inflammation under conditions of metabolic stress. Our findings point to beta cell CB1R as a therapeutic target, and broaden its potential to include anti-inflammatory effects in both major forms of diabetes.Data availabilityMicroarray data have been deposited at GEO (GSE102027).

Highlights

Insulin secretion is tightly controlled as dysregulation has lifethreatening consequences
Results β-cannabinoid 1 receptor (CB1R)−/− mice have increased beta cell proliferation and improved glucose homeostasis Conditional β-CB1R−/− mice were obtained by mating Cnr1flox/flox with MIP-Cre/ERT mice (ESM Fig. 1)
CB1R ablation in beta cells reduced hyperglycaemia during acute insulin resistance We examined whether β-CB1R−/− mice would still respond to acute insulin resistance using S961, a competitive antagonist of the insulin receptor (IR) [28]

Summary

Methods

Please refer to the electronic supplementary material (ESM) Methods. By day 6, S961 had caused a 21-fold increase in beta cell proliferation per islet in β-CB1R+/+ mice compared with baseline, and to a lesser extent (6.5-fold) in β-CB1R−/− mice (Fig. 2d, e, ESM Fig. 3b). HGP-β-CB1R−/− islets had higher intracellular cAMP levels (required for maximal insulin secretion) than control littermates, reflecting increased beta cell functional capacity (Fig. 5j). Intra-islet levels of p-p65 were significantly higher in HFHS-β-CB1R+/+ compared with HFHS-β-CB1R−/− mice (Fig. 7b). Infiltrating cells, such as T cells (CD3+) and macrophages (CD68+), were observed in close proximity to blood vessels, and in and around the islets of HFHS-β-CB1R+/+ mice (yellow arrows, Fig. 7b, c, ESM Fig. 7a). CB1R ablation in beta cells protects islets from metabolic stress and inflammation Obesity-related molecules such as ROS, ceramides, palmitate and elevated circulating glucose activate the NLRP3 (NLR family, pyrin domain containing 3)

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