The current findings also reflect elements of the apparent paradox previously noted in the lipid JQ1 mw profiles of hepatocytes and HSCs and the pathogenesis and progression of steatohepatitis.11 On the one hand, NAFLD is characterized by the accumulation of LDs in hepatocytes, an observation that drives the rationale for reversing hepatic steatosis as a therapeutic goal.1 On the other hand, the activation of HSCs is coupled with LD depletion,8 with reduced expression of prolipogenic genes.8, 10 This process of HSC activation has been referred to as an “antiadipogenic” phenomenon,9 similar to that described during adipocyte dedifferentiation. Based on

these findings, potential strategies to attenuate HSC activation and decrease fibrogenesis include augmenting HSC lipid content with restoration of lipogenesis.10 Stated differently, the regulated accumulation of LDs within HSCs appears beneficial compared to LD accumulation in hepatocytes, specifically in terms of HSC activation and the development and progression of hepatic fibrosis.29 Other examples

exist for the apparently paradoxical cell-specific regulation of LDs and HSC activation. Specifically, adipose differentiation-related protein (Adrp/Plin2) is up-regulated in association with drug- and diet-induced hepatic steatosis.30, 31 Adrp−/− mice and mice treated with an antisense oligonucleotide (ASO) against Adrp both exhibit decreased hepatic steatosis when fed a high-fat diet32, 33 and Adrp−/− mice demonstrate improved insulin resistance and decreased hepatic steatosis when crossed into the Lepob/ob background.34 These observations Selleck Inhibitor Library together imply that hepatocyte Adrp/Plin2 might augment hepatic steatosis and potentially promote liver injury. Conversely, up-regulation of Adrp was demonstrated in HSCs upon retinol and palmitate supplementation, which in turn inhibited HSC activation with down-regulation of fibrogenic genes.35 Those findings are of particular interest in view of the current demonstration that palmitate abundance was attenuated in freshly isolated HSCs from L-Fabp−/− mice. While the source of free palmitate in HSCs

is yet to be completely understood, our findings raise the possibility that the attenuated LD abundance in HSCs from L-Fabp−/− mice may reflect a corresponding decrease in retinyl palmitate. We were unable to detect ADP ribosylation factor HSC retinyl esters directly using our lipidomic assays, likely reflecting the detection limit with the available material, although other investigators have successfully quantitated retinyl esters in murine HSCs.36 Another example of the divergence in cell-specific modulation of lipid metabolism and HSC activation is found in Pparγ. Basal expression of PPARγ in the liver is relatively low,37 yet PPARγ is highly expressed in steatotic liver in obese mice38 and in human subjects.39 Although some studies suggest an antisteatotic role for Pparγ,40, 41 others have indicated that hepatic Pparγ is prosteatotic.