31 Our results identify CB2 receptors as a novel regulator of Kupffer-cell polarization. Indeed, in vivo and in vitro experiments demonstrate GSK3235025 cell line that genetic deletion of CB2 receptors is associated with a marked hepatic induction of the M1 signature in response to chronic alcohol feeding and a parallel loss of the M2 alternative response. These findings, therefore, suggest that endogenous

CB2 receptors are responsible for M2 response to alcohol feeding. Interestingly, the CB2 agonist, JWH-133, blunts the induction of the M1 classical signature without affecting M2 response to alcohol. Whether the lack of enhancement of M2 markers in animals treated with the CB2 agonist may be the result of partial agonist properties of the compound or to constitutive activity of CB2 receptors remains to be determined.36, 37 Nevertheless, these data demonstrate that, during chronic alcohol exposure, CB2 receptors shift the M1/M2 balance toward a predominant alternative M2 response. Besides their anti-inflammatory properties click here on Kupffer cells, CB2 receptors also prevent the development of

alcohol-induced fatty liver. Recent studies have demonstrated that cross-talk between Kupffer cells and hepatocytes is determinant in the control of hepatic steatosis. In rodents exposed to an alcohol diet or a high-fat diet, depletion of Kupffer cells blunts the development of fatty liver.9, 38-40 Furthermore, cocultures of M1-polarized Kupffer cells with hepatocytes promote lipid accumulation into parenchymal cells.5, 6, 38, 39 In keeping with these data, we show that CM obtained

from JWH-133- and LPS-stimulated macrophages reduces lipid accumulation in hepatocytes, compared to CM prepared from macrophages exposed to LPS alone. These data indicate that Kupffer-cell CB2 receptors decrease hepatocyte steatosis after inhibition of M1 polarization. Of note, recent studies have shown that IL-1β and TNF-α, two proinflammatory Kupffer-cell–derived cytokines, promote steatosis.38-40 We show that liver Sclareol expression of IL-1β and TNF-α decreases in alcohol-fed mice concurrently treated with JWH-133 and increases in CB2-deficient counterparts. A similar pattern of regulation was also found in our in vitro experiments, therefore suggesting that the reduction in Kupffer-cell production of IL-1β and TNF-α may contribute to the protective effects of CB2 receptors on hepatocyte lipid accumulation. HO-1 is the rate-limiting enzyme in the catabolism of heme into biliverdin, free iron, and carbon monoxide. HO-1 is a stress-inducible protein with potent-protective effects against hepatocyte damage,41 liver inflammation,31, 33 and fibrogenesis.42, 43 Recent studies have shown that up-regulating HO-1 in Kupffer cells by means of overexpression or by pharmacological activators prevents alcohol-induced release of inflammatory mediators by Kupffer cells.31, 41 However, characterization of HO-1 inducers in Kupffer cells remains poorly documented.