Age-associated changes in the serum level of apolipoproteins A-I and A-IV and the gene expression as revealed by fasting and refeeding in mice.

Alterations of serum apolipoproteins A-I (apo A-I) and A-IV and their mRNAs in young and old mice by fasting and refeeding were investigated by polyacrylamide gel elecrophoresis and Northern blot, respectively. After fasting for three days, serum apo A-I concentration in young mice (6-9 month-old) was increased about 1.5 fold while that of old animals (25-34 month-old) did not change significantly. Apo A-I mRNA was increased about 3-fold and 1.7-fold in the liver and small intestine of the young mice, respectively. The increase in old animals was not more than 1.5-fold in both tissues. The serum apo A-IV was elevated 2-fold and its mRNA was markedly (ca. 50-fold) induced in the liver of fasted young mice, whereas the increase of the mRNA was less than 2-fold in the small intestine. In contrast, induced levels of the protein in serum and its mRNA in both tissues were much less in old mice. In view of the roles of apo A-I and A-IV in triglyceride mobilization and reverse cholesterol transport, the present findings suggest that the reduced induction of the mRNAs for these apolipoproteins in the liver by prolonged fasting and possibly under normal feeding conditions can be an important factor in the impaired immobilization of lipid in old animals, and may, in turn, have implication in age-related diseases such as coronary, cerebral and other vascular disorders.