Reduction of circulating PCSK9 and LDL-C levels by liver-specific knockdown of HNF1α in normolipidemic mice.
Journal of lipid research
PPARδ activation induces hepatic long-chain acyl-CoA synthetase 4 expression in vivo and in vitro.
Biochimica et biophysica acta
The transcription factors HNF1α and HNF1β can bind to the HNF1 site on PCSK9 promoter to activate transcription in HepG2 cells. However, it is unknown whether one or both HNF1 factors are obligatory for transactivating hepatic PCSK9 gene expression in vivo. We developed shRNA adenoviral constructs (Ad-shHNF1α and Ad-shHNF1β) to examine the effects of knockdown of HNF1α or HNF1β on PCSK9 expression and its consequent impact on LDL receptor (LDLR) protein levels in cultured hepatic cells and liver tissue. We demonstrated that infection with Ad-shHNF1α but not Ad-shHNF1β markedly reduced PCSK9 mRNA expression in HepG2 cells with concomitant increase in LDLR protein abundance. Injecting Ad-shHNF1α in mice fed a normal diet significantly (~50%) reduced liver mRNA expression and serum concentration of PCSK9 with a concomitant increase (~1.9-fold) in hepatic LDLR protein abundance. Furthermore, we observed a modest but significant reduction in circulating LDL-C after knockdown of HNF1α in these normolipidemic mice. Consistent with the observation that knockdown of HNF1β did not affect PCSK9 mRNA or protein expression in cultured hepatic cells, Ad-shHNF1β infection in mice resulted in no change in the hepatic mRNA expression or serum content of PCSK9. Altogether, our study demonstrates that HNF1α but not HNF1β is the primary positive regulator of PCSK9 transcription in mouse liver.
View details for DOI 10.1194/jlr.M052969
View details for PubMedID 25652089
A novel posttranscriptional mechanism for dietary cholesterol-mediated suppression of liver LDL receptor expression
JOURNAL OF LIPID RESEARCH
2014; 55 (7): 1397-1407
The arachidonic acid preferred long-chain acyl-CoA synthetase 4 (ACSL4) is a key enzyme for fatty acid metabolism in various metabolic tissues. In this study, we utilized hamsters fed a normal chow diet, a high-fat diet or a high cholesterol and high fat diet (HCHFD) as animal models to explore novel transcriptional regulatory mechanisms for ACSL4 expression under hyperlipidemic conditions. Through cloning hamster ACSL4 homolog and tissue profiling ACSL4 mRNA and protein expressions we observed a selective upregulation of ACSL4 in testis and liver of HCHFD fed animals. Examination of transcriptional activators of the ACSL family revealed an increased hepatic expression of PPARδ but not PPARα in HCHFD fed hamsters. To explore a role of PPARδ in dietary cholesterol-mediated upregulation of ACSL4, we administered a PPARδ specific agonist L165041 to normolipidemic and dyslipidemic hamsters. We observed significant increases of hepatic ACSL4 mRNA and protein levels in all L165041-treated hamsters as compared to control animals. The induction of ACSL4 expression by L165041 in liver tissue in vivo was recapitulated in human primary hepatocytes and hepatocytes isolated from hamster and mouse. Moreover, employing the approach of adenovirus-mediated gene knockdown, we showed that depletion of PPARδ in hamster hepatocytes specifically reduced ACSL4 expression. Finally, utilizing HepG2 as a model system, we demonstrate that PPARδ activation leads to increased ACSL4 promoter activity, mRNA and protein expression, and consequently higher arachidonoyl-CoA synthetase activity. Taken together, we have discovered a novel PPARδ-mediated regulatory mechanism for ACSL4 expression in liver tissue and cultured hepatic cells.
View details for DOI 10.1016/j.bbalip.2015.01.008
View details for PubMedID 25645621