Rat hepatic mRNA-S14 and lipogenic enzymes during weaning: role of S14 in lipogenesis
Perez-Castillo, A.; Schwartz, H.L.; Oppenheimer, J.H.
American Journal of Physiology 253(5 Pt 1): E536-E542
1987
ISSN/ISBN: 0002-9513 PMID: 3688223 Document Number: 299005
The rapid and marked response of hepatic mRNA-S14 sequence to triiodothyronine and carbohydrate intake has made this sequence an attractive model for studying the action of hormonal and dietary factors. Because it is highly expressed and regulated only in lipogenic tissues, it is suggested that it plays a role in some aspects of lipid synthesis, transport or metabolism. To provide more precise information regarding the function of S14, lipogenesis, lipogenic enzymes, beta -oxidation and mRNA-S14 values were estimated in spontaneously weaning neonatal rats and in rats prematurely weaned to a laboratory diet on day 17 after birth. After birth, values of lipogenesis, mRNA-S14 and the lipogenic enzymes malic enzyme (ME) and fatty acid synthase (FAS) were almost undetectable but increased with the onset of spontaneous weaning. Coincident with these changes, beta -oxidation decreased. Premature weaning beginning on day 17 resulted in an earlier and even more marked increase in lipogenesis, ME, FAS and mRNA-S14. On day 19, ME and FAS activity were 6- to 19-fold more than activities in control sucking young, whereas mRNA-S14 had risen to more than 100 times the control value. Thus directional shifts in mRNA-S14 corresponded with indices of lipogenesis and were opposite to indices reflecting beta -oxidation. The response of mRNA-S14 therefore suggests that it may be related to the synthesis of fatty acids. The level of lipogenesis in the foetus was high despite the fact that the values of mRNA-S14 and ME were low. This dissociation raises the possibility that the S14 protein participates in lipogenesis in the neonate and adult but not in the foetus.