LOW-PROTEIN DIETS POSTTRANSCRIPTIONALLY REPRESS APOLIPOPROTEIN-B EXPRESSION IN RAT-LIVER

In an attempt to elucidate molecular mechanisms related to low protein diet-induced fatty fivers, apolipoprotein (ape) mRNA and its expressi on in the fiver were studied in rats. Rats were fed for 14 days a diet containing 5% and 20% casein, and whey protein equivalent in protein to these caseins. In the protein-deficient groups, fiver triacylglycer ols elevated to 1.5-2 fold higher than did the diet sufficient groups. The mRNAs for apo A-IV, apo B and apo E were 20 to 50% lower in the d eficient groups than in the sufficient groups, but apo A-I mRNA was no t reduced The rate of transcription transcription of apo apo A-IV, B, and E genes in hepatic nuclei isolated from those animals was not alte red with different levels of dietary protein. Apo B concentration in t he serum was lowered and correlated positively with apo B mRNA abundan ce but the concentrations of apo IV and apo E were elevated in the def icient groups. It thus appears that a low protein diet decreases apo B synthesis through a posttranscriptional mechanism and thereby depress es secretion of triacylglycerol-rich lipoproteins fi om the liver.