Reversal of diet-induced hepatic steatosis by peripheral CB1 receptor blockade in mice is p53/miRNA-22/SIRT1/PPARα dependent

Abstract

Objective The endocannabinoid (eCB) system is increasingly recognized as being crucially important in obesity-related hepatic steatosis. By activating the hepatic cannabinoid-1 receptor (CB 1 R), eCBs modulate lipogenesis and fatty acid oxidation. However, the underlying molecular mechanisms are largely unknown. Methods We combined unbiased bioinformatics techniques, mouse genetic manipulations, multiple pharmacological, molecular, and cellular biology approaches, and genomic sequencing to systematically decipher the role of the hepatic CB 1 R in modulating fat utilization in the liver and explored the downstream molecular mechanisms. Results Using an unbiased normalized phylogenetic profiling analysis, we found that the CB 1 R evolutionarily coevolves with peroxisome proliferator-activated receptor-alpha (PPARα), a key regulator of hepatic lipid metabolism. In diet-induced obese (DIO) mice, peripheral CB 1 R blockade (using AM6545) induced the reversal of hepatic steatosis and improved liver injury in WT, but not in PPARα −/− mice. The antisteatotic effect mediated by AM6545 in WT DIO mice was accompanied by increased hepatic expression and activity of PPARα as well as elevated hepatic levels of the PPARα-activating eCB-like molecules oleoylethanolamide and palmitoylethanolamide. Moreover, AM6545 was unable to rescue hepatic steatosis in DIO mice lacking liver sirtuin 1 (SIRT1), an upstream regulator of PPARα. Both of these signaling molecules were modulated by the CB 1 R as measured in hepatocytes exposed to lipotoxic conditions or treated with CB 1 R agonists in the absence/presence of AM6545. Furthermore, using microRNA transcriptomic profiling, we found that the CB 1 R regulated the hepatic expression, acetylation, and transcriptional activity of p53, resulting in the enhanced expression of miR-22, which was found to specifically target SIRT1 and PPARα. Conclusions We provide strong evidence for a functional role of the p53/miR-22/SIRT1/PPARα signaling pathway in potentially mediating the antisteatotic effect of peripherally restricted CB 1 R blockade.

The Endocannabinoid System and PPARs: Focus on Their Signalling Crosstalk, Action and Transcriptional Regulation

“…Azar et al in a recent paper disclosed the existence of a molecular link between CB1R and p53/miR-22/SIRT1/PPARα signaling in hepatocytes [ 124 ]. Using unbiased bioinformatics techniques and combined in vitro and in vivo experiments, they found that PPARα is evolutionarily coevolved with CB1R and is negatively modulated by CB1R in hepatocytes since ACEA can downregulate both mRNA and protein levels of PPARα as well as its targeted genes.…”

CB1 Cannabinoid Receptor Signaling and Biased Signaling

“…In addition to regulating feeding behavior in the CNS [ 56 ], peripheral CB1 enhances lipogenesis [ 57 , 58 , 59 ], inhibits lipolysis [ 59 , 60 , 61 ], and promotes leptin resistance [ 62 , 63 , 64 ]. Peripheral CB1 also promotes the development of nonalcoholic fatty liver disease [ 65 , 66 , 67 ], pancreatic β-cell death, and peripheral insulin resistance [ 68 , 69 , 70 ]. Therefore, therapies aiming at CB1 agonism may not be suitable for patients that already suffer from cardiovascular and metabolic diseases.…”

Relevance of Peroxisome Proliferator Activated Receptors in Multitarget Paradigm Associated with the Endocannabinoid System

“…Another therapeutic strategy involving both targets was developed upon the peripheral blockade of CB 1 R in a diet-induced obese (DIO) mouse model [53]. The peripherally restricted antagonist AM6545 was able to reduce hepatic steatosis and improved liver injury through PPARα as shown by its lack of activity in PPARα knockout DIO mice.…”