Tissue-specific regulation of lipogenic mRNAs by thyroid hormone.

We have previously shown that triiodothyronine (T3) regulates rat fatty acid synthesis in a tissue specific manner. Here, we determined the effects of thyroid state on mRNAs encoding the lipogenic enzymes, acetyl CoA carboxylase (ACC) and fatty acid synthase (FAS). S14 mRNA, a sequence tightly associated with lipogenesis, was also measured. Levels of the three mRNA were 9-13-fold higher in hyper- than hypothyroid liver. Limited expression in kidney and heart was also increased by thyroid hormone. In brown adipose tissue, highest levels were recorded in hypothyroid animals. Thyroid state did not affect expression in lung and brain. All these changes are consistent with those previously measured in fatty acid synthesis. In white adipose tissue, mRNA expression was increased by hyperthyroidism. This increase may not be reflected in fatty acid synthesis, since we recently showed lipogenesis to be reduced under these circumstances. All three mRNAs responded rapidly to T3 in liver, but more slowly in kidney and fat. Thus, T3 regulates lipogenesis by altering levels of ACC and FAS mRNAs. S14 mRNA changes in parallel.