Hepatic CB1 receptor signaling triggers G_i/oα-mediated lipolysis in lean mice but G_sα-mediated lipogenesis in obese mice

Objectives: Obesity-induced steatotic liver disease (SLD) is driven by the uptake of adipocyte-derived fatty acids (FAs) into hepatocytes via the FA translocase CD36, which also prevents their consumption by inhibiting AMP kinase (AMPK)-mediated FA oxidation (FAO). We explored the role of hepatocyte CB1 receptors (hCB1R) in controlling hepatic triglyceride (TG) content by regulating CD36 and its downstream targets. Methods: hCB1R knockout (hCB1Rko) mice and their control littermates kept on standard or high-fat diet were used to analyze hCB1R-mediated hepatic gene expression profile and lipid metabolism in intact mice and in cultured hepatocytes. Results: Multi-omics data indicate that hCB1R target a distinct set of genes associated with SLD, including Cd36. In mice with diet-induced obesity, hCB1R signaling via CD36-AMPK-FAO pathway contributes to both the development of SLD and its reversal by CB1R blockade. But, in lean mice hCB1R signaling inhibits CD36 expression and activates AMPK-mediated FAO. These opposite effects were replicated in AML12 mouse hepatocytes incubated with or without oleic acid (OA). OA, an endogenous ligand of GPR3, induced a switch in hCB1R signaling from a G_i/oα-mediated reduction in cAMP to a G_sα-mediated increase in cAMP in a GPR3/G_sα -dependent manner, facilitated by increasing the ratio of G_sα:G_i/oα proteins in the steatotic compared to lean liver. Conclusions: In the lean state, endocannabinoid activation of hCB1R increases FAO, which mitigates SLD, as reported for chronic marihuana smokers, whereas in obese mice hCB1R tonically inhibit FAO, which promotes SLD and underlies the anti-steatotic effect of peripheral CB1R blockade.