A peripheral endocannabinoid mechanism contributes to glucocorticoid-mediated metabolic syndrome

Abstract

Glucocorticoids are known to promote the development of metabolic syndrome through the modulation of both feeding pathways and metabolic processes; however, the precise mechanisms of these effects are not well-understood. Recent evidence shows that glucocorticoids possess the ability to increase endocannabinoid signaling, which is known to regulate appetite, energy balance, and metabolic processes through both central and peripheral pathways. The aim of this study was to determine the role of endocannabinoid signaling in glucocorticoid-mediated obesity and metabolic syndrome. Using a mouse model of excess corticosterone exposure, we found that the ability of glucocorticoids to increase adiposity, weight gain, hormonal dysregulation, hepatic steatosis, and dyslipidemia was reduced or reversed in mice lacking the cannabinoid CB1 receptor as well as mice treated with the global CB1 receptor antagonist AM251. Similarly, a neutral, peripherally restricted CB1 receptor antagonist (AM6545) was able to attenuate the metabolic phenotype caused by chronic corticosterone, suggesting a peripheral mechanism for these effects. Biochemical analyses showed that chronic excess glucocorticoid exposure produced a significant increase in hepatic and circulating levels of the endocannabinoid anandamide, whereas no effect was observed in the hypothalamus. To test the role of the liver, specific and exclusive deletion of hepatic CB1 receptor resulted in a rescue of the dyslipidemic effects of glucocorticoid exposure, while not affecting the obesity phenotype or the elevations in insulin and leptin. Together, these data indicate that glucocorticoids recruit peripheral endocannabinoid signaling to promote metabolic dysregulation, with hepatic endocannabinoid signaling being especially important for changes in lipid metabolism.

Keywords: 2-AG; anandamide; corticosterone; liver; obesity.

Fig. 1.

CB₁R signaling is required for GC-mediated metabolic abnormalities. Graphs show that CORT-treated CB₁R^−/− mice have reduced (A) weight, (B) adiposity, and (C) adipocyte size. Similarly, (D) plasma insulin and (E) plasma leptin as measured by ELISA show a blunted CORT-induced increase compared with WT. (F) The CORT-induced increase in food consumption is reduced in CB₁R^−/− mice as shown in week 4 of food intake; however, pair-feeding studies show that this hyperphagia does not mediate the development of obesity (Fig. S2). CB₁R^−/− mice are also protected against the CORT-induced increase in (G) liver weight, (H) plasma cholesterol, (I) alanine aminotransferase (ALT), (J) triglycerides, and (K) hepatic triglycerides. (L) CB₁R^−/− mice are also protected against the development of hepatic steatosis as noted by the decreased accumulation of lipid droplets in the liver as measured by Oil Red O staining as well as decreased macrovesicular steatosis as measured by H&E staining (Fig. S1B). Data are expressed as means ± SEMs (n = 4–5 per group). Asterisks indicate the significant effects of CORT treatment relative to vehicle treatment in mice. Pound signs indicate statistically significant differences between CORT-treated WT and CB₁R^−/− mice. VEH, vehicle. *P < 0.05; **P < 0.01; ***P < 0.001; ^#P < 0.05; ^##P < 0.01; ^###P < 0.001. (Scale bar, 100 µm.)

Fig. 2.

Blockade of the CB₁R modulates the effect of chronic CORT. Concurrent treatment of CORT in the water for 28 d with either the global CB₁R antagonist AM251 or the peripheral specific CB₁R antagonist AM6545 results in decreased (A) weight, (B) adiposity, (C) circulating plasma leptin, and (D) insulin compared with WT controls. (E) Triglycerides were significantly decreased in AM6545-treated mice but remained unaltered in AM251-treated mice. (F) However, both AM251 and AM6545 treatments prevent development of hepatic steatosis as indicated by Oil Red O staining. Data are expressed as means ± SEMs (n = 4–9 per group). Asterisks indicate the significant effects of CORT treatment relative to vehicle treatment in mice. Pound signs indicate the effect of AM251 or AM6545 compared with saline in CORT-treated mice. VEH, vehicle. *P < 0.05; **P < 0.01; ***P < 0.001; ^#P < 0.05; ^##P < 0.01; ^###P < 0.001. (Scale bar, 100 µm.)

Fig. 3.

Liver-specific CB₁R^−/− reveals a unique role of hepatic signaling in CORT-treated mice. LCB₁R^−/− does not prevent the CORT-induced (A) weight gain, (B) increased adiposity, or increased (C) plasma leptin and (D) insulin. In contrast, LCB₁R^−/− does attenuate CORT-induced increases in (E) plasma triglycerides, (F) plasma alanine aminotransferase (ALT), and (G) hepatic triglycerides. (H) Furthermore, liver-specific KO of CB₁R prevents development of hepatic steatosis as indicated by Oil Red O staining. Data are expressed as means ± SEMs (n = 6–8 per group). Asterisks indicate the significant effects of CORT treatment relative to vehicle treatment in mice. Pound signs indicate statistically significant differences between CORT-treated WT and LCB₁R^−/− mice. VEH, vehicle. *P < 0.05; **P < 0.01; ***P < 0.001; ^#P < 0.05; ^##P < 0.01. (Scale bar, 100 µm.)