Bovine intramuscular, subcutaneous, and perirenal stromal-vascular cells express similar glucocorticoid receptor isoforms, but exhibit different adipogenic capacity

Abstract

Understanding preadipocyte differentiation in economically important adipose depots will facilitate efforts to selectively increase intramuscular (i.m.) lipid accretion in cattle. The objectives of this study were to determine if glucocorticoid receptor (GR) expression differs among bovine stromal-vascular (S-V) cells derived from i.m., subcutaneous (s.c.), and peri-renal (p.r.) adipose tissue, and to evaluate the effects of dexamethasone (DEX) on adipogenesis of these cell populations. Stromal-vascular cells isolated from i.m., s.c., and p.r. adipose tissues of 2 steers were propagated in culture and exposed to 0 or 250 nM DEX for 48 h. Cell lysates were subjected to GR immunoblot analysis, and immunoreactive protein bands of approximately 97, approximately 62, and approximately 48 kDa were detected and expressed relative to beta-actin immunoreactivity. The abundance of each GR immunoreactive protein was similar among S-V cell populations (P > 0.50). Dexamethasone exposure decreased the abundance of the approximately 97 and approximately 62 kDa GR immunoreactive bands in S-V cells from the 3 depots (P < 0.001), but did not affect the expression of the approximately 48 kDa band (P = 0.96). Stromal-vascular cells isolated from 3 steers were grown in culture, and upon confluence, were exposed to 0, 25, or 2,500 nM DEX for 48 h. After an additional 10 d in differentiation media, differentiation was determined by glycerol-3-phosphate dehydrogenase (GPDH) specific activity and oil red O staining. The extent of differentiation differed by depot (p.r. > s.c. > i.m.; P < 0.05). Compared with control, 2,500 nM DEX increased GPDH activity in S-V cells from all depots (P < 0.05), and no interaction between depot and DEX concentration was observed (P = 0.99). We observed an adipose tissue depot by DEX concentration interaction (P = 0.03) for S-V cells with large (> or = 10 microm-diameter) lipid droplets. The percentage of p.r. S-V cells with large lipid droplets increased in response to DEX in a linear manner (P < 0.02), but only increased greater than control in s.c. cells exposed to 2,500 nM DEX (P = 0.002). Dexamethasone did not significantly increase the percentage of i.m. S-V cells with large lipid droplets (P > 0.27). Collectively, these data demonstrate differences in adipogenic activity among bovine i.m., s.c., and p.r. S-V cells, but indicate no relationship between adipogenic activity and glucocorticoid receptor abundance or function.