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- Title
Regulation of Adipose Tissue Lipoprotein Lipase by Thyroid Hormone.
- Authors
Ranganathan, Gouri; Resat, Unal; Tripathi, Preeti; Kern, Philip A.
- Abstract
Lipoprotein lipase (LPL) is an important enzyme in lipid metabolism and plays a key role in the transfer of triacylglycerol fatty acids from plasma into adipose tissue. LPL activity is increased in adipocytes of hypothyroid rats and earlier studies by us have indicated that the regulation of LPL by thyroid hormone involves post transcriptional mechanisms and the absence of a translational repressor. LPL regulation by epinephrine in adipocytes also occurs at the level of translation and involves A kinase anchor protein (AKAP121) as a transacting inhibitory protein. Other regulators of LPL activity in adipose include Angiopoietin-like protein 3&4 (ANGPTL), which inhibit LPL during fasting throught posttranscriptional mechanisms. To better understand the mechanism of LPL regulation by thyroid hormone, we studied the expression of AKAP121 or ANGPTL 3&4 mRNA and protein expression in adipose tissue of control, hypothyroid and T3 treated rats. In hypothyroid adipose tissue, AKAP121 protein expression was decreased by 30±5 % with no change in AKAP121 mRNA, and ANGPTL3&4 mRNA expression was inhibited by 50 ± 10 % as compared to control or T3 treated hypothyroid rat adipose. To further understand the effects of thyroid hormone, isolated rat adipocytes were treated with T3 (2nM) for 16h followed by measurement of LPL activity and synthetic rate. Although LPL activity was inhibited through posttranscriptional mechanisms by T3, neither AKAP 121 nor ANGPTL 3&4 mRNA expression were significantly altered. These data suggest a possible role for AKAP121 and ANGPTL 3,4 in the inhibition of LPL, and the relief of this inhibition in the hypothyroid state. However, the changes in AKAP121 and ANGPTL 3,4 do not appear to be a direct result of thyroid hormone, but appear to be secondary to the hypothyroid condition.
- Subjects
LIPOPROTEIN lipase; ADIPOSE tissues; THYROID hormones; GENE expression; LABORATORY rats; MESSENGER RNA
- Publication
Diabetes, 2007, Vol 56, pA666
- ISSN
0012-1797
- Publication type
Article