Hepatic expression of genes regulating lipid metabolism in rabbits

The liver plays a central role in lipid metabolism and plasma lipoprotein homeostasis. This dynamic process is regulated by a variety of liver-derived proteins. However, the specific liver cells that express these proteins are largely unknown. In the current study we measured mRNA levels for 13 genes encoding proteins involved in lipid metabolism in isolated rabbit hepatic parenchymal and nonparenchymal cells. For these analyses we cloned partial rabbit cDNAs for apolipoprotein A-I (apoA-I), apolipoprotein B (apoB), apolipoprotein E (apoE), cholesteryl ester transfer protein (CETP), hepatic lipase (HL), lipoprotein lipase (LPL), HMG-CoA reductase, LDL-receptor, 7 alpha-hydroxylase, albumin, bile salt-dependent cholesteryl ester hydrolase (CEH), lecithin:cholesterol acyl transferase (LCAT), and plasminogen activator inhibitor protein-1 (PAI-1). The cDNAs provided the basis for developing quantitative RNAse protection assays for each mRNA. These assays were used to determine whether differential patterns of mRNA expression existed between liver and other tissues and between hepatic parenchymal and nonparenchymal cells. The data demonstrate a diverse range in tissue distribution and mRNA abundance. Liver expressed all mRNAs except for LPL and CEH. Messenger RNA levels in isolated liver cell populations normalized to total RNA revealed a cell segregation pattern for hepatic gene expression: parenchymal cells showed higher levels of apoA-I, apoB, apoE, albumin, LCAT, HL, and 7 alpha-hydroxylase mRNAs compared to nonparenchymal cells while nonparenchymal cells showed higher levels of CETP, LDL-receptor, HMG-CoA reductase, and PAI-1 mRNAs compared to parenchymal cells. These data demonstrate the existence of differential mRNA expression patterns in rabbit liver cell populations for genes encoding proteins affecting lipid metabolism.