Cannabinoid Receptor Type 1 (CB1R) Signaling Regulates Hepatic Gluconeogenesis via Induction of Endoplasmic Reticulum-bound Transcription Factor cAMP-responsive Element-binding Protein H (CREBH) in Primary Hepatocytes

Seung-Hoi Koo,Don-Kyu Kim,John Y.L. Chiang,Tiangang Li,Yong-Hoon Kim,Chul-Ho Lee,Hueng-Sik Choi,Dipanjan Chanda

doi:10.1074/jbc.m111.224352

Abstract

Activated cannabinoid 1 receptor (CB1R) signaling has been implicated in the development of phenotypes associated with fatty liver, insulin resistance, and impaired suppression of hepatic glucose output. Endoplasmic reticulum stress-associated liver-specific transcription factor CREBH is emerging as a critical player in various hepatic metabolic pathways and regulates hepatic gluconeogenesis in diet-induced obese settings. In this study, we elucidated the critical role of CREBH in mediating CB1R signaling to regulate glucose homeostasis in primary rat and human hepatocytes. mRNA and protein levels and glucose production were analyzed in primary rat and human hepatocytes. ChIP assays were performed together with various transcriptional analyses using standard techniques. CB1R activation by 2-arachidonoylglycerol (2-AG) specifically induced CREBH gene expression via phosphorylation of the JNK signaling pathway and c-Jun binding to the AP-1 binding site in the CREBH gene promoter. 2-AG treatment significantly induced hepatic gluconeogenic gene expression and glucose production in primary hepatocytes, and we demonstrated that the CREBH binding site mutant significantly attenuated 2-AG-mediated activation of the gluconeogenic gene promoter. Endogenous knockdown of CREBH led to ablation of 2-AG-induced gluconeogenic gene expression and glucose production, and the CB1R antagonist AM251 or insulin exhibited repression of CREBH gene induction and subsequently inhibited gluconeogenesis in both rat and human primary hepatocytes. These results demonstrate a novel mechanism of action of activated CB1R signaling to induce hepatic gluconeogenesis via direct activation of CREBH, thereby contributing to a better understanding of the endocannabinoid signaling mechanism involved in regulating the hepatic glucose metabolism.

Highlights

Endogenous cannabinoids are lipid mediators that interact with cannabinoid receptors, the two main endocannabinoids being arachidonoyl ethanolamide (AEA,2 anandamide) and 2-arachidonoylglycerol (2-AG)
Treatment of rat primary hepatocytes with the cannabinoid 1 receptor (CB1R) agonist 2-AG demonstrated a significant increase of Cyclic AMP response element-binding protein H (CREBH) gene expression in a time-dependent manner, along with the CB1R mRNA level (Fig. 1A, left panel)
Real-time PCR analysis of gene expression showed that 2-AG treatment induces CREBH but has no significant effect on activating transcription factor 6 (Atf6) gene expression (Fig. 1A, center panel), an endoplasmic reticulum (ER) stress-activated transcription factor belonging to the CREB/ ATF family [13, 18]

Summary

Introduction

Endogenous cannabinoids (endocannabinoids) are lipid mediators that interact with cannabinoid receptors, the two main endocannabinoids being arachidonoyl ethanolamide (AEA,2 anandamide) and 2-arachidonoylglycerol (2-AG). Treatment of rat primary hepatocytes with the CB1R agonist 2-AG demonstrated a significant increase of CREBH gene expression in a time-dependent manner, along with the CB1R mRNA level (Fig. 1A, left panel).

Results

Conclusion