Adipogenic gene expression and fatty acid composition in subcutaneous adipose tissue depots of Angus steers between 9 and 16 months of age.
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abstract
We have demonstrated that among carcass adipose tissue depots, brisket subcutaneous adipose tissue contains the greatest concentration of MUFA and lowest concentration of SFA. Therefore, we hypothesized that brisket subcutaneous adipose tissue depots would exhibit greater adipogenic gene expression over time than other major subcutaneous adipose tissue depots. Four Angus steers, each at 9, 12, 14, and 16 mo of age, were harvested and fresh subcutaneous adipose tissue samples were collected from over the brisket, chuck, rib, loin, sirloin, round, flank, and plate. Relative gene expression for C/EBP, PPAR, carnitine palmitoyltransferase-1 beta (CPT-1), stearoyl-coenzyme A desaturase (SCD), AMP-activated protein kinase alpha (AMPK), and G-coupled protein receptor 43 (GPR43) was analyzed by quantitative real-time PCR. Expression of C/EBP, PPAR, and CPT-1 was greatest at 12 to 14 mo of age (all P < 0.0001) and declined to very low abundance by 16 mo of age in all depots. Expression of PPAR and CPT-1 was greater (P < 0.03) in flank, rib, and sirloin subcutaneous adipose tissues than in brisket and round adipose tissues. The expression of the SCD gene did not differ among the 4 age groups (P = 0.95). The palmitoleic:stearic acid ratio (an estimate of SCD activity) was greater (P < 0.001) in the subcutaneous adipose tissues from brisket, plate, and round than in the loin, rib, and sirloin. Conversely, subcutaneous adipose tissue from the loin, rib, and sirloin had greater (P < 0.001) SCD gene expression than the brisket, plate, and round. In general, subcutaneous adipose tissues with the highest concentration of MUFA and least SFA consistently exhibited the least SCD gene expression and adipogenic gene expression. We conclude that MUFA in the brisket and other depots with large SCD indices were deposited before 9 mo of age, during a time when the subcutaneous adipocytes were highly differentiated.
