4A). Importantly, this Adeno-PLA2GXIIB virus but not the control virus elevated the rate of hepatic VLDL secretion in PLA2GXIIB−/− mice close to that of the wild-type level (Fig. 6A,B) and restored the decrease in serum TG level in PLA2GXIIB−/−
mice (Fig. 6C), strongly indicating that PLA2GXIIB functions to regulate lipid metabolism. Finally, to confirm that PLA2GXIIB functions down-stream of HNF-4α to control lipid metabolism, we injected into wild-type and PLA2GXIIB−/− mice the control Adeno-ΔE1E3 or Adeno-HNF-4α and measured the selleck chemical changes in serum TG levels. We established that Adeno-HNF-4α was effective in overexpressing HNF-4α and inducing PEPCK, MTP, and PLA2GXIIB mRNA expressions in HepG2 cells (Supporting Information Fig. 4B,C). Although Adeno-HNF-4α elevated the serum TG level in wild-type mice compared to the control adenovirus (Fig. 6D), it failed to elevate serum TG level in PLA2GXIIB−/− mice (Fig. 6D). In all, our analysis strongly suggested that PLA2GXIIB is an important target of HNF-4α necessary for controlling lipid metabolism. We demonstrated Selleckchem YAP-TEAD Inhibitor 1 in this study that PLA2GXIIB is an HNF-4α target gene. First, close
to its transcriptional start site at positions −68 to −86, PLA2GXIIB promoter contains an HNF-4α response element composed of 5′-AGAGGACAAAGGTGAAAC-3′, representing a direct repeat with a 1 base pair spacer (DR1) of an imperfect nuclear hormone receptor consensus binding
sequence AGGTCA. Second, HNF-4α bound to this response element by EMSA analysis and that an anti-HNF-4α antibody immunoprecipitated a chromatin fragment spanning this response element from mouse liver. Third, HNF-4α modulators regulated PLA2GXIIB expression in HepG2 cells and fasting induces hepatic PLA2GXIIB expression similar to other HNF-4α target genes. Noticeably, HNF-4α overexpression by adenovirus or knockdown by small interfering RNA also regulated PLA2GXIIB expression.9 Moreover, PLA2GXIIB expression is strongly reduced in HNF4αLivKO mice.6 Importantly, Non-specific serine/threonine protein kinase PLA2GXIIB-null mice accumulated TG, cholesterol, and fatty acids in the liver and developed severe hepatosteatosis despite reduced serum TG and cholesterol levels, closely resembling some of the phenotypes of HNF4αLivKO mice.6 Because cholesterols, TGs, and phospholipids are first exported from the liver via VLDL-TG particles which then serve as key precursors for LDL and HDL cholesterol,13 we found that PLA2GXIIB-null mice are defective in hepatic VLDL-TG secretion, which is likely responsible for the hepatosteatosis and reduced serum total TG, cholesterol, and phospholipids levels observed. Critically, an adenovirus encoding HNF-4α failed to elevate serum TG levels in PLA2GXIIB-null mice.
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