The regulation of hepatic very-low-density lipoprotein (VLDL) secretion plays an important role in the pathogenesis of dyslipidemia and fatty liver diseases. VLDL is controlled by hepatic microsomal triglyceride transfer protein (MTTP). Mttp is regulated by carbohydrate response element binding protein (ChREBP) and small heterodimer partner (SHP). However, it is unclear whether both coordinately regulate Mttp expression and VLDL secretion. Here, adenoviral overexpression of ChREBP and SHP in rat primary hepatocytes induced and suppressed Mttp mRNA, respectively. However, Mttp induction by ChREBP was much more potent than suppression by SHP. Promoter assays of Mttp and the liver type pyruvate kinase gene revealed that SHP and ChREBP did not affect the transcriptional activity of each other. Mttp mRNA and protein levels of Shp-/- mice were similar to those of wild-types; however, those of Chrebp-/-Shp-/- and Chrebp-/- mice were significantly much lower. Consistent with this, the VLDL particle number and VLDL secretion rates in Shp-/- mice were similar to wild-types but were much lower in Chrebp-/- and Chrebp-/-Shp-/- mice. These findings suggest that ChREBP, rather than SHP, regulates VLDL secretion under normal conditions and that ChREBP and SHP do not affect the transcriptional activities of each other.
Keywords: carbohydrate response element binding protein; microsomal triglyceride transfer protein; small heterodimer partner; very-low-density lipoprotein.