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PPAR-alpha dependent regulation of vanin-1 mediates hepatic lipid metabolism.

ABSTRACT: Peroxisome proliferator-activated receptor alpha (PPARα) is a key regulator of hepatic fat oxidation that serves as an energy source during starvation. Vanin-1 has been described as a putative PPARα target gene in liver, but its function in hepatic lipid metabolism is unknown. We investigated the regulation of vanin-1, and total vanin activity, by PPARα in mice and humans. Furthermore, the function of vanin-1 in the development of hepatic steatosis in response to starvation was examined in Vnn1 deficient mice, and in rats treated with an inhibitor of vanin activity. Liver microarray analyses reveals that Vnn1 is the most prominently regulated gene after modulation of PPARα activity. In addition, activation of mouse PPARα regulates hepatic- and plasma vanin activity. In humans, consistent with regulation by PPARα, plasma vanin activity increases in all subjects after prolonged fasting, as well as after treatment with the PPARα agonist fenofibrate. In mice, absence of vanin-1 exacerbates the fasting-induced increase in hepatic triglyceride levels. Similarly, inhibition of vanin activity in rats induces accumulation of hepatic triglycerides upon fasting. Microarray analysis reveal that the absence of vanin-1 associates with gene sets involved in liver steatosis, and reduces pathways involved in oxidative stress and inflammation. We show that hepatic vanin-1 is under extremely sensitive regulation by PPARα and that plasma vanin activity could serve as a readout of changes in PPARα activity in human subjects. In addition, our data propose a role for vanin-1 in regulation of hepatic TG levels during fasting.

ORGANISM(S): Mus musculus

PROVIDER: GSE51712 | GEO | 2014/04/24

SECONDARY ACCESSION(S): PRJNA224687

REPOSITORIES: GEO

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Project description:The role of PPARα in gene regulation in mouse liver is well characterized. However, less is known about the effect of PPARα activation in human liver. The aim of the present study was to better characterize the impact of PPARα activation on gene regulation in human liver by combining transcriptomics with the use of hepatocyte humanized livers. To that end, chimeric mice containing hepatocyte humanized livers were given an oral dose of 300 mg/kg fenofibrate daily for 4 days. Livers were collected and analysed by hematoxilin and eosin staining, qPCR, and transcriptomics. Transcriptomics data were compared with existing datasets on fenofibrate treatment in normal mice. The human hepatocytes exhibited excessive lipid accumulation. Fenofibrate increased the size of the mouse but not human hepatocytes, and tended to reduce steatosis in the human hepatocytes. Quantitative PCR indicated that induction of PPARα targets by fenofibrate was less pronounced in the human hepatocytes than in the residual mouse hepatocytes. Transcriptomics analysis indicated that, after filtering, a total of 282 genes was significantly different between fenofibrate- and control-treated mice (P<0.01). 123 genes were significantly lower and 159 genes significantly higher in the fenofibrate-treated mice, including many established PPARα targets such as FABP1, HADHB, HADHA, VNN1, PLIN2, ACADVL and HMGCS2. According to gene set enrichment analysis, fenofibrate upregulated interferon/cytokine signaling-related pathways in hepatocyte humanized liver, but downregulated these pathways in normal mouse liver. Also, fenofibrate downregulated pathways related to DNA synthesis in hepatocyte humanized liver but not in normal mouse liver. The results support the major role of PPARα in regulating hepatic lipid metabolism, and underscore the more modest effect of PPARα activation on gene regulation in human liver compared to mouse liver. The data suggest that PPARα may have a suppressive effect on DNA synthesis in human liver, and a stimulatory effect on interferon/cytokine signalling.

Project description:The role and molecular mechanisms of intermittent fasting (IF) in non-alcoholic steatohepatitis (NASH) and its transition to hepatocellular carcinoma (HCC) are unknown. Here, we identified that an IF 5:2 regimen (two non-consecutive days of food deprivation per week), initiated in the active phase of mice, prevents NASH development as well as ameliorates established NASH and fibrosis without affecting total calorie intake. Furthermore, the IF 5:2 regimen also blunted NASH-HCC transition when applied therapeutically in two independent models of diet-induced NASH and NASH-HCC. The timing (7pm-7pm > 7am-7am), length (24h > 12h) and number (5:2 > 6:1) of fasting cycles as well as the type (WD / CDHFD) of NASH diet were all critical parameters determining the effectiveness of the fasting benefits. Combined proteome, transcriptome and metabolome analyses identified that PPARα and glucocorticoid signalling-induced phosphoenolpyruvate carboxykinase 1 (PCK1) act co-operatively as hepatic executors of the fasting response by promoting fatty acid catabolism and gluconeogenesis while suppressing anabolic lipogenesis. In line, PPARα targets and PCK1 were reduced in human NASH. Notably, only fasting during the active phase (7pm-7pm) of mice robustly induced glucocorticoid signalling in hepatocytes including PCK1 expression; while both active and inactive phase (7am-7am) fasting induced free fatty acid-induced PPARα signalling, highlighting the increased efficacy of fasting during the active phase. However, hepatocyte-specific glucocorticoid receptor (GR) deletion only partially abrogated the hepatic fasting response, illustrating the need for both glucocorticoid-induced PCK1 expression and free fatty acid-induced PPARα activation for mediating the benefits of fasting. In support, the combined knockdown of Ppara and Pck1 in vivo abolished the beneficial outcomes of fasting against inflammation and fibrosis, confirming their causal relationship in integrating systemic signalling in hepatocytes. Moreover, overexpression of Pck1 alone or together with Ppara in vivo lowered hepatic triglycerides and steatosis upon Western-diet feeding. Altogether, our data support that the IF 5:2 regimen could be a promising and viable intervention against NASH and subsequent liver cancer.

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PPAR-alpha dependent regulation of vanin-1 mediates hepatic lipid metabolism.

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