Differentiation of bovine intramuscular and subcutaneous preadipocytes

Intramuscular (i.m.) and subcutaneous (s.c. ) adipose tissue substantially influence beef carcass value, and are of economic importance to the beef industry. Adipose development is at least partially controlled by the differentiation of preadipocytes into mature adipocytes. We hypothesized that bovine i.m. and s.c. preadipocyte differentiation would be enhanced by a peroxisome proliferator-activated receptor ( PPAR)-gamma agonist, troglitazone (TRO), and a glucocorticoid, dexamethasone (DEX), with the relative response being greater in i.m. than s.c. cells.; In the first set of experiments, preadipocytes from i.m. and s.c. stromal-vascular (S-V) cells of an Angus steer were cloned and used to optimize culture conditions supporting adipose differentiation, as well as compare the adipogenic responses of i.m. and s.c. preadipocytes to TRO. A higher percentage of isolated s.c. clones (47%) were identified as adipogenic than i.m. (12.5%) (P < 0.001). A s.c. preadipocyte clone was used to optimize differentiation culture conditions. Addition of 10 and 20 muL/mL serum lipid (SL) to serum-free media containing 280 nM insulin increased glycerol-3-phosphate dehydrogenase (GPDH) activity. Inclusion of 1.25 to 10 muM TRO to media containing insulin and SL also increased GPDH activity (P < 0.001). No GPDH activity was detected when medium included insulin, octanoate, and acetic acid, following 48 h exposure to DEX. However, insulin, SL, TRO, and DEX stimulated GPDH activity ( P < 0.001). Omission of TRO or insulin from this media lowered GPDH activity (P < 0.001), while removal of DEX tended to reduce activity (P = 0.06). When i.m. (n = 3) and s.c. (n = 2) clones were compared, all clones responded to addition of 20 to 60 muM TRO (P < 0.02), with no depot differences (P = 0.47).; In the second set of experiments, i.m. and s.c. S-V cells isolated from three Angus steers were used to determine the adipogenic effects of DEX and TRO. Forty and 60 pM TRO increased GPDH activity 2.9- and 3.4-fold compared to non-treated cells (P < 0.03), with no depot differences (P = 0.32). When DEX and TRO were tested in combination, DEX stimulated a 1.8-fold increase in GPDH activity (P = 0.006), while TRO induced a 2.5-fold increase in GPDH activity (P = 0.02). No DEX x TRO interaction (P = 0.53) or depot effects (P = 0.41) were found. In clonal analysis experiments, DEX increased the percentage of adipogenic colonies by 1.2-fold ( P = 0.02), while TRO increased the proportion of differentiated colonies by 2.3-fold (P = 0.01). No DEX x TRO interaction ( P = 0.65) or depot differences (P = 0.10) were found. However, the percentage of differentiated cells within adipogenic colonies was 6.4-fold greater in s.c. isolates than i.m. (P < 0.001). Dexamethasone had no significant effect (P = 0.10) while TRO increased the proportion of differentiated cells by 10-fold (P < 0.001). In summary, differentiation of bovine i.m. and s.c. preadipocytes was enhanced in response to SL, DEX, and TRO. Under identical media conditions, s.c. preadipocytes have a greater capacity to differentiate compared to i.m.