Reduction of circulating PCSK9 and LDL-C levels by liver-specific knockdown of HNF1a in normolipidemic mice

The transcription factors HNF1a and HNF1ß 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-shHNF1a and Ad-shHNF1ß) to examine the effects of knockdown of HNF1a or HNF1ß 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-shHNF1a but not Ad-shHNF1ß markedly reduced PCSK9 mRNA expression in HepG2 cells with concomitant increase in LDLR protein abundance. Injecting Ad-shHNF1a 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 HNF1a in these normolipidemic mice. Consistent with the observation that knockdown of HNF1ß did not affect PCSK9 mRNA or protein expression in cultured hepatic cells, Ad-shHNF1ß infection in mice resulted in no change in the hepatic mRNA expression or serum content of PCSK9. Altogether, our study demonstrates that HNF1a but not HNF1ß is the primary positive regulator of PCSK9 transcription in mouse liver.