1895-P: The Role of Endocannabinoid Receptor 1 (CB1R) in the Insulin Signaling Pathway

Abstract

Cannabinoid 1 receptors (CB1Rs) are G protein-coupled receptors that are present in peripheral organs such as liver, pancreas, adipose tissue and skeletal muscle where they are involved in fine-tuning many metabolic functions. It was previously reported that liver-specific genetic deletion of CB1R (hCNR1-/-) mice fed high fat diets (HFD) had similar body weight to HFD-fed hCNR1+/+ mice, but they retained insulin sensitivity comparable to normal chow-fed (NCD) hCNR1+/+ mice. Therefore, this study was undertaken to uncover how hCB1Rs impact the insulin signaling pathway. Male hCNR1-/- and hCNR1+/+ mice were fed with a high fat high sugar diet (HFSD: N = 8-12) for 15 weeks. In contrast with the previous study of HFD only, HFSD-fed hCNR1-/- mice had less body weight gain than HFSD-fed hCNR1+/+ mice (25.1±2.7 vs. 19.8±1.7g), less fat accumulation in the liver, 1.3-fold increase in glucose disposal and 1.7-fold increase in insulin sensitivity compared to HFSD-fed hCNR1+/+ mice. Further study demonstrated that the lack of hepatic CB1R resulted in upregulated phosphorylation in liver of protein kinase B (AKT), causing activation of downstream target molecules, such as proline-rich AKT substrate 40 (PRAS40) in the mammalian target of rapamycin complex 1 (mTORC1). Similarly, primary hepatocytes isolated from hCNR1-/- mice had increased amounts of phosphorylated AKT and PRAS40 in comparison to hepatocytes from hCNR1+/+ mice. The co-immunoprecipitation studies clearly revealed hepatic CB1R modulates insulin signaling by the association or dissociation of the components of mTORC1. In support of these data, the deficiency of hepatic CB1R leads to upregulation of phosphoinositide 3-kinase (PI3K) class IB, p110γ, resulting in increased association between p110γ and G-protein beta. These findings indicate that genetic deletion of hepatic CB1R contributes to improved glucose homeostasis. Therefore, modulation of CB1R activity in liver may be a useful therapeutic in obese and diabetic individuals. Disclosure Y. Kim: None. J.M. Egan: None.