Postnatal development of stearoyl coenzyme A desaturase gene expression and adiposity in bovine subcutaneous adipose tissue.

Abstract

This investigation addressed the hypothesis that stearoyl coenzyme A desaturase (SCD) gene expression would serve as a postnatal marker of adipocyte differentiation in bovine s.c. adipose tissue. Samples of tailhead s.c. adipose tissue were obtained by biopsy from preweaning steer calves 2.5 wk, 5 mo, and 7.5 mo of age and from yearling steers 12 mo of age. Samples also were obtained at slaughter when the steers were 18 mo of age. The steers sampled as yearlings were fed native pasture from weaning until 12 mo of age, and the steers sampled at slaughter were fed a high-concentrate diet from 12 to 18 mo of age. Major peak adipocyte volumes for the 2.5-wk-, 5-mo-, and 7.5-mo-old steers were 14, 270, and 700 pL, respectively (P < .001). The steers did not gain weight during pasture feeding, and at 12 mo of age peak adipocyte volume had decreased (P = .009) to 270 pL. At this time, a second, smaller population of adipocytes had appeared with a peak volume of 115 pL. At slaughter, adjusted fat thickness of the steers was 1.60 +/- .13 cm, the USDA yield grade of the carcasses was 3.51 +/- .31, and peak adipocyte volume had increased (P = .01) to over 2,500 pL. The number of adipocytes per 100 mg of adipose tissue doubled (P = .006) between 2.5 wk and 5 mo of age, concurrent with the nearly 20-fold increase in peak adipocyte volume, indicating that this was a period of apparent adipocyte hyperplasia. Uncoupling protein mRNA was undetectable at all stages of postnatal growth, indicating that differentiating tailhead s.c. adipocytes do not acquire brown adipocyte characteristics postnatally. Lipogenesis expressed on a cellular basis was low in all preweaning samples and increased significantly above preweaning values only in the 18-mo-old steers. Stearoyl coenzyme A desaturase mRNA concentration also was low in all preweaning samples, but it peaked (P = .07) at 12 mo of age. Because the peak in SCD mRNA concentration preceded a significant rise in lipogenesis and lipid filling, we conclude that the level SCD gene expression may be indicative of the extent of terminal differentiation in bovine tailhead s.c. adipose tissue.

Adiposity, fatty acid composition, and delta‐9 desaturase activity during growth in beef cattle

“…Similarly, Lee et al (2005) observed peak SCD mRNA at 12 months of age in muscle from Hanwoo steers. The rate of de novo fatty acid biosynthesis increased gradually in the adipose tissue of Angus steers, but lagged behind the elevation in desaturase gene expression (Martin et al 1999). These data suggest that desaturase activity is essential for the subsequent development of lipogenic capacity of subcutaneous adipose tissue in growing steers.…”

“…Expression of the ∆ 9 desaturase gene increased profoundly between weaning and 12 months of age in subcutaneous adipose tissue of Angus steers (Martin et al 1999;Fig. 6).…”

“…During this time, there was no significant change in ∆ 9 desaturase gene expression. Between the period of 7.5 and 12 months of age, the calves of Martin et al (1999) were moved to native pasture. As a result of this postweaning reduction in energy intake, there was a depression in the adipocyte volume, but desaturase gene expression increased markedly.…”

“…It was concluded from these studies that American Wagyu steers perform as well on a high roughage (hay/corn) diet as they do on a low roughage, corn-based diet; Angus steers do not. The study of Martin et al (1999) measured desaturase gene expression only up to 18 months of age. The data in Figure 7 indicate that desaturase activity continued to increase up to 24 months of age in corn-fed steers, and up to 28 months of age in hay-fed Wagyu steers.…”

In vitro metabolism of rumenic acid in bovine liver slices

“…The incorporation of CLA into lipids in ruminant tissues or in milk results, for a low part, from bacterial biohydrogenation and trans isomerisation of dietary polyunsaturated fatty acids (PUFA) (mainly linoleic acid from forages, cereals or oleaginous seeds) in the rumen [7] and, for a large part, from endogenous synthesis [8]. Synthesis of CLA can take place in the tissues of ruminants where the ∆9 desaturase enzyme is expressed i.e., the mammary gland in lactating ruminants and adipose tissues in growing ruminants [9,10]. Likewise, it has been demonstrated that vaccenic acid (another intermediate of bacterial biohydrogenation of PUFA, trans-11 C18:1) is desaturated to CLA in the mammary gland of lactating cows, and has been estimated to represent about 60 to 90% of CLA deposited in milk fat [8,11,12], whereas no desaturation of VA into CLA occurred in the liver of ruminants [13].…”