Date of Award
Doctor of Philosophy (PhD)
Animal and Veterinary Sciences
Duckett, Susan K.
Burg , Karen J. L.
Jenkins , Thomas C.
Pratt , Scott L.
Obsesity, the excess deposition of white adipose tissue, is a growing problem in the U.S. and other developed countries. Formerly thought to be inert, adipose tissue is now recognized as a dynamic endocrine organ with its secretion of adipokines and a newly proposed class hormone class 'lipokine'. Adipocytes are the functional unit of adipose tissue and can influence the tissue through hyperplasic and hypertrophic growth. In order to investigate the mechanisms involved in adipogenesis and lipogenesis of adipose tissue, stromal vascular cultures were isolated from adipose tissue of finishing cattle for use in experiments.
There is a positive relationship between lipogenic gene expression and increased energy in steer diets. The objectives of the studies presented in Chapter 2 were to determine if differences in fatty acid profiles or gene expression exist when adipocytes are exposed to different, simulated energy sources: linoleic acid, insulin, or both following differentiation. With limited information in the literature about the timing of lipid uptake and fatty acid composition in differentiating bovine adipocytes, a secondary objective of these studies was to evaluate fatty acid composition over time. Overall, results from these studies indicate that fatty acid composition changes over time post-differentiation and is modulated by linoleic acid supplementation. Expression of SCD1 mRNA was up-regulated prior to changes in fatty acid desaturation profiles. In addition, linoleic acid treatment was incorporated into cells and its supplementation decreased production of de novo fatty acids synthesis or increased beta-oxidation of fatty acids or both.
Recent evidence links palmitoleic acid to decreased lipogenesis in murine hepatocytes. Since adipocytes are the primary site of lipogenesis in ruminants, the objectives of the experiment in Chapter 3 was to determine if a similar effect could be seen in bovine adipocytes and titrate an effective dose of palmitoleic acid supplementation. Concurrent with palmitoleic acid, cis-vaccenic (C18:1 cis-11) and eicosenoic (C20:1 cis-13) acids increased linearly with palmitoleic acid supplementation in bovine adipocytes. In addition, activity and mRNA expression of several lipogenic genes were down-regulated and beta-oxidation was increased in response to palmitoleic acid supplementation. Therefore, palmitoleic acid was having an anti-lipogenic effect on the bovine adipocyte cultures.
The elevated presence of suspected elongation products of palmtioleic acid, cis-vaccenic and eicosenoic acids, in cultures supplemented with palmitoleic acid left doubt as to which fatty acid contributes to anti-lipogenic effects. The objectives of the studies performed in Chapter 4 were to confirm cis-vaccenic and eicosenoic acids as elongation products of palmtioleic acid using a stable isotope tracer and test lipogenic effects of cis-vaccenic acid. Cis-vaccenic and eicosenoic acids are, indeed, direct elongation products of palmtioleic acid. In addition, cis-vaccenic acid decreased lipogenesis rates, but did not affect desaturation. Therefore, palmitoleic acid differentially affects aspects of lipogenesis relative to its elongation products. Overall, the results of this work advance our understanding of the biological mechanisms underlying lipogenesis.
Burns, Taber, "FATTY ACIDS AND LIPOGENESIS IN RUMINANT ADIPOCYTES" (2011). All Dissertations. 840.