The overall goal of this proposal is to determine the molecular basis for the decline in the hormonal and dietary induction of lipogenic enzymes in the livers of mice as the animals mature and age. ATP citrate nase (ACL) and malic enzyme (ME) will be studied. In young animals liver lipogenic enzymes are de-duced during starvation and induced (typically 20- to 40-fold) to levels well above those observed in control animals when the starved animals are subsequently refed with a high carbohydrate/low fat diet. In addition insulin and thyroid hormone (T3) are also necessary for the induction of lipogenic enzymes. Hormones that raise intracellular cAMP levels suppress the accumulation of lipogenic enzymes. In older animals the induction and deinduction of lipogenic enzymes by dietary manipulation and hormones is dramatically diminished. To determine how age-dependent processes affect the control of gene expression by hormones and nutrients we shall: 1. Employ cDNA probes for ACL and ME mRNA sequences to establish that lipogenic enzyme biosynthesis is controlled at a pretraslational level in young and ageing mice. 2. Determine whether the diminished hormonal and nutritional regulation of ACL and Me genes in older animals can be attributed to alterations in the rates of specific mRNA transcription or processing, or to a change in mRNA stability. 3. Determine whether diminished hormonal regulation of ACL and ME genes is correleted with alterations in the number, affinity and functionality of T3 and insulin receptors. 4. Determine whether alterations in gene or chromatin structure may account for diminished nutritional and hormonal regulation of lipogenic enzyme genes in older animals. Gene mythylation sites will be examined and we shall determine whether DNAse hypersensitive regions of chromatin associated with ME and ACL genes are modified during aging.
