Vitamin A deficiency increases hepatic apolipoprotein A-I mRNA expression in both euthyroid and hypothyroid rats

Abstract

We have examined the effects of chronic thyroid hormone deficiency, vitamin A deficiency, and subsequent acute repletion with thyroid hormone (T 3) and/or retinoic acid (RA) on the expression of hepatic apolipoprotein (apo) A-I mRNA. Chronically hypothyroid and/or retinoid-deficient male Lewis rats were treated once or three times with T 3, all- trans-RA, or both hormones. The hypothyroid state significantly reduced ( P < 0.001) and the vitamin A-deficient state significantly elevated ( P < 0.0001) the expression of apo A-I mRNA. A single injection of T 3 (10 μg/100 gm body weight) significantly elevated apo A-I mRNA in hypothyroid rats ( P < 0.001). A single injection of RA (20 μg/rat) reduced apo A-I mRNA by about 20 to 25% and daily injection of RA for three days reduced apo A-I mRNA abundance further in hypothyroid ( P < 0.05), but not euthyroid, rats. There was a significant interaction between T 3 hormone treatment and vitamin A status of the rats, as well as between RA and T 3 treatment and the thyroid status of the rats. These in vivo results may indicate that nuclear retinoid receptors and thyroid hormone receptors interact in the regulation of the apo A-I gene in liver.