Therefore, Cidea appears to be a VX-770 solubility dmso specific mediator of dietary saturated FA-induced hepatic steatosis. We also demonstrated that saturated FA-induced Cidea expression is likely mediated by SREBP1c, based on the following evidences. First, Cidea and SREBP1c expression is highly correlated in livers of HFD-treated mice and in isolated primary hepatocytes treated with FAs. Second, overexpressing SREBP1c induced Cidea expression, and this induction was further boosted by saturated FAs. Most important, knocking down

of SREBP1c led to a marked abrogation of saturated FA-induced Cidea expression. In contrast, expression levels of Fsp27 and Cideb in hepatocytes were not affected by the overexpression or knockdown of SREBP1c. The mechanism of the up-regulation of SREBP1c by saturated FAs is not clear. Saturated

FAs have been KPT-330 datasheet shown to induce ER stress,12 which may result in enhanced SREBP1c cleavage and increased nuclear activity.13 Consistent with this, the increased levels of the mature nuclear form of SREBP1c were observed in HFD- or saturated FA-treated hepatocytes. Interestingly, we only observed a slightly reduced basal expression of Cidea in SREBP1c knock-down hepatocytes in the absence of FA treatment. It is possible that SREBP1c may play a minor role in mediating basal Cidea expression in hepatocytes. Hepatic Cidea expression is also reported to be induced by PPARα/γ agonists.21 However, this induction was not easily recapitulated in isolated primary MCE hepatocytes.22 It is possible that the induction of hepatic Cidea

expression by a PPARα/γ agonist is dependent on the presence of both PPARα/γ and other specific cofactors, such as mediator 1, which bridges PPARγ and RNA polymerase II.34 Another interesting observation that explains the high levels of Cidea and Fsp27 in livers of HFD-fed and ob/ob mice is the drastically increased stability of these proteins in the presence of FFAs. This phenomenon is likely the result of an increased incorporation of FAs into TAG and to the formation of large LDs, because the knockdown of DGAT1/2, the enzymes responsible for TAG synthesis, abrogates the FFA-induced stabilization of Cidea and Fsp27. Levels of intermediate lipids in the TAG-synthesis pathway, including DAG, may also affect Cidea and Fsp27 stability. Increased Fsp27 stability in the presence FFA has also been observed in white adipocytes and led to an increase in lipid storage capacity.33 Therefore, enhanced Cidea stability in hepatocytes may provide a positive feedback to promote hepatic lipid storage and the development of hepatic steatosis. Overall, our current data demonstrate that the gene expression and protein stability of CIDE family proteins are differentially regulated in the liver in response to various stimuli (Fig. 8).