Cannabinoid receptor 1 signaling in hepatocytes and stellate cells does not contribute to NAFLD
Simeng Wang, … , Philipp E. Scherer, Jay D. Horton
Simeng Wang, … , Philipp E. Scherer, Jay D. Horton
Published September 9, 2021
Citation Information: J Clin Invest. 2021;131(22):e152242. https://doi.org/10.1172/JCI152242.
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Research Article Hepatology Metabolism

Cannabinoid receptor 1 signaling in hepatocytes and stellate cells does not contribute to NAFLD

Abstract

The endocannabinoid system regulates appetite and energy expenditure and inhibitors of cannabinoid receptor 1 (CB-1) induce weight loss with improvement in components of the metabolic syndrome. While CB-1 blockage in brain is responsible for weight loss, many of the metabolic benefits associated with CB-1 blockade have been attributed to inhibition of CB-1 signaling in the periphery. As a result, there has been interest in developing a peripherally restricted CB-1 inhibitor for the treatment of nonalcoholic fatty liver disease (NAFLD) that would lack the unwanted centrally mediated side effects. Here, we produced mice that lacked CB-1 in hepatocytes or stellate cells to determine if CB-1 signaling contributes to the development of NAFLD or liver fibrosis. Deletion of CB-1 in hepatocytes did not alter the development of NAFLD in mice fed a high-sucrose diet (HSD) or a high-fat diet (HFD). Similarly, deletion of CB-1 specifically in stellate cells also did not prevent the development of NAFLD in mice fed the HFD, nor did it protect mice from carbon tetrachloride–induced fibrosis. Combined, these studies do not support a direct role for hepatocyte or stellate cell CB-1 signaling in the development of NAFLD or liver fibrosis.

Authors

Simeng Wang, Qingzhang Zhu, Guosheng Liang, Tania Franks, Magalie Boucher, Kendra K. Bence, Mingjian Lu, Carlos M. Castorena, Shangang Zhao, Joel K. Elmquist, Philipp E. Scherer, Jay D. Horton

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Figure 5

Cnr1 expression is low in cultured HSCs and Cnr1 deletion in HSCs does not alter CCl4-induced fibrosis.

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Cnr1 expression is low in cultured HSCs and Cnr1 deletion in HSCs does ...
(A) Representative images of freshly isolated HSCs (upper panels) from chow-fed wild-type mice and from isolated HSCs cultured for 6 days (lower panels). Confocal microscopy was performed for detection of retinoid fluorescence (blue). Endogenous retinoid expression was visualized in cytoplasmic lipid droplets of HSCs (left panels). The merged right panels show that the retinoid signal overlaps with lipid droplets in activated HSCs. Scale bar: 50 μm. (B) Total RNA from freshly isolated HSCs and HSCs cultured for 6 days was extracted for qPCR quantification of Col1a1, Lrat, Acta2 (αSMA), and Cnr1. Actb (β-actin) was used as an invariant control. Values were expressed relative to that of freshly isolated HSCs, which was arbitrarily set to 1. Corresponding mean Ct values are denoted above. (C) Plasma ALT and AST levels in chow-fed doxycycline-treated Hsc-Cnr1–/– and Cnr1fl/fl mice injected with either CCl4 or corn oil (5–11/group). (D) Mice described in C were euthanized at 16 weeks of age. Total RNA was extracted from HSCs of each mouse, and the relative mRNA levels of Col1a1, Lrat, Acta2 (αSMA), and Cnr1 were quantified by qPCR. Actb was used as an invariant control. Values were expressed relative to that of chow-fed doxycycline-treated Cnr1fl/fl mice injected with corn oil, which was arbitrarily set to 1. Corresponding mean Ct values are denoted above. Results shown as mean ± SEM. **P < 0.01, ***P < 0.001 by ANOVA. (E) Gross appearance of representative livers of chow-fed, doxycycline-treated Cnr1fl/fl (top) and Hsc-Cnr1–/– (bottom) mice injected with CCl4 for 10 weeks. (F) H&E and trichrome staining of liver from mice described in E. Scale bar: 200 μm. All experiments (A–F) were repeated with a separate cohort of mice and the results were similar.