TY - JOUR
T1 - Regulation of adipose tissue lipoprotein lipase gene expression by thyroid hormone in rats
AU - Saffari, B.
AU - Ong, J. M.
AU - Kern, P. A.
N1 - Copyright:
Copyright 2004 Elsevier B.V., All rights reserved.
PY - 1992
Y1 - 1992
N2 - Lipoprotein lipase (LPL) is an important enzyme in lipid metabolism, and adipose LPL activity is increased in rats that are deficient in thyroid hormone. To examine the mechanism of thyroid hormone's effect on LPL, LPL gene expression was assessed in the epididymal fat pads of hypothyroid rats. When compared to control rats, LPL activity, mass, and synthetic rate in hypothyroid rats were increased; heparin-releasable LPL activity and mass were increased to 448% and 300% of control, respectively, and [35S]methionine incorporation into LPL was increased to 250% of control. The increases in LPL activity and mass were reversed by treatment of hypothyroid rats with triiodothyronine (T3). However, there was no change in the level of LPL mRNA when compared to the level of gamma-actin mRNA and no effect on LPL transcription using run-off assays. Isolated adipocytes were prepared from normal rats and exposed to 2 nM T3 in vitro for 24 h. The addition of T3 to cultures of adipocytes resulted in a decrease in LPL activity, mass, and [35S]methionine incorporation, but still no change in LPL mRNA level. To determine whether thyroid hormone regulated catecholamine responsiveness, adipocytes were prepared from hypothyroid and control rats, and the responses to epinephrine were compared. Although epinephrine inhibited [35S]methionine incorporation into LPL in control rat adipocytes, there was essentially no effect in hypothyroid rat cells. In addition, T3 treatment of the hypothyroid rats restored the responsiveness to epinephrine. Thus, thyroid hormone regulates LPL in rat adipose tissue posttranscriptionally, resulting in parallel changes in LPL synthetic rate, immunoreactive mass, and activity. Although thyroid hormone had direct effects on adipose LPL, it also altered the responsiveness of adipocytes to epinephrine.
AB - Lipoprotein lipase (LPL) is an important enzyme in lipid metabolism, and adipose LPL activity is increased in rats that are deficient in thyroid hormone. To examine the mechanism of thyroid hormone's effect on LPL, LPL gene expression was assessed in the epididymal fat pads of hypothyroid rats. When compared to control rats, LPL activity, mass, and synthetic rate in hypothyroid rats were increased; heparin-releasable LPL activity and mass were increased to 448% and 300% of control, respectively, and [35S]methionine incorporation into LPL was increased to 250% of control. The increases in LPL activity and mass were reversed by treatment of hypothyroid rats with triiodothyronine (T3). However, there was no change in the level of LPL mRNA when compared to the level of gamma-actin mRNA and no effect on LPL transcription using run-off assays. Isolated adipocytes were prepared from normal rats and exposed to 2 nM T3 in vitro for 24 h. The addition of T3 to cultures of adipocytes resulted in a decrease in LPL activity, mass, and [35S]methionine incorporation, but still no change in LPL mRNA level. To determine whether thyroid hormone regulated catecholamine responsiveness, adipocytes were prepared from hypothyroid and control rats, and the responses to epinephrine were compared. Although epinephrine inhibited [35S]methionine incorporation into LPL in control rat adipocytes, there was essentially no effect in hypothyroid rat cells. In addition, T3 treatment of the hypothyroid rats restored the responsiveness to epinephrine. Thus, thyroid hormone regulates LPL in rat adipose tissue posttranscriptionally, resulting in parallel changes in LPL synthetic rate, immunoreactive mass, and activity. Although thyroid hormone had direct effects on adipose LPL, it also altered the responsiveness of adipocytes to epinephrine.
KW - hypothyroidism
KW - lipid metabolism
KW - translation regulation
KW - triiodothyronine
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M3 - Article
C2 - 1569376
AN - SCOPUS:0026510623
SN - 0022-2275
VL - 33
SP - 241
EP - 249
JO - Journal of Lipid Research
JF - Journal of Lipid Research
IS - 2
ER -