Regulation of apolipoprotein gene expression and plasma high-density lipoprotein composition in experimental nephrosis.

Hepatic and intestinal RNA levels were measured in rats made nephrotic by injection of puromycin aminonucleoside (PAN). The following increases in hepatic RNA levels, relative to controls, were measured: poly A+ (1.2), ribosomal (1.2), mRNA levels for transferrin (1.8), albumin (3.8) apolipoprotein (apo)E (2.3), apoB (2.5), apoA-II (1.9) and apoA-I (6.1). Increases of 1.5- to 2.2-fold in hepatic mRNA levels for albumin, apoA-II, apoB and apoE were measured in pre-nephrotic animals killed before the onset of proteinuria. Intestinal RNA levels in pre-nephrotic and nephrotic animals were not significantly different from control values. Transcription of the hepatic apoA-I gene increased 1.8-fold in nephrotic animals compared to controls. Immunological detection of apolipoproteins in high-density lipoproteins (HDL) separated by gradient gel electrophoresis indicated an increase in apoA-I and a decrease in apoA-IV and apoE containing HDL particles in nephrosis. To simulate the effects of increased apoA-I gene expression, human apoA-I was added to rat plasma in vivo and in vitro. ApoE was displaced from HDL by increased concentration of apoA-I. The results indicate that relatively small changes in apoA-I levels in the serum lead to significant changes in the apolipoprotein composition of HDL.