We hypothesized that lubabegron fumarate (LUB) (Experior, Elanco Animal Health, Greenfield, IN) would act as an antagonist to β-adrenergic receptor (β-AR) subtypes in primary bovine subcutaneous (s.c.) and intramuscular (i.m.) adipocytes differentiated in culture. This study employed LUB, dobutamine (DOB, a selective β1-agonist), salbutamol (SAL, a selective β2-agonist), and propranolol (PRO, a non-selective β-AR antagonist). Preadipocytes were isolated by standard techniques from bovine longissimus muscle and overlying s.c. adipose tissue and differentiated to adipocytes for 14 d. The adipocyte source x stage of differentiation interaction was significant for β-adrenergic receptors-1 (ADRB1) (P = 0.001) and ADRB2 (P = 0.01) in that expression of ADRB1 and ADRB2 was greater in s.c. adipocytes than in s.c. preadipocytes; expression of the ADRB1-3 did not change after differentiation of i.m. adipocytes. CCATT/enhancer-binding protein alpha (CEBPA) expression increased upon differentiation in both s.c. and i.m. adipocytes (P = 0.006). The source x stage of differentiation interaction was significant for peroxisome proliferator-activated receptor gamma (PPARG) (P ≤ 0.001) and fatty acid binding protein-4 (FABP4) (P = 0.004). Expression of PPARG increased after differentiation of s.c. preadipocytes to adipocytes, but PPARG expression did not change with differentiation of i.m. preadipocytes to adipocytes. FABP4 expression increased after differentiation of both s.c. and i.m. adipocytes, but FABP4 expression increased to a greater extent in s.c. adipocytes. In s.c. adipocytes, DOB elevated cAMP and glycerol production and protein kinase A (PKA) activity, and SAL increased PKA activity; these effects were abolished by LUB and PRO (P < 0.001). Incubation of i.m. adipocytes with SAL increased cAMP production and PKA activity, which was attenuated by LUB and PRO (P ≤ 0.006). In s.c. adipocytes, SAL, LUB + SAL, and LUB + DOB upregulated hormone sensitive lipase (HSL) (P < 0.001) and perilipin (P = 0.002) gene expression. In i.m. adipocytes, DOB and LUB + DOB increased HSL gene expression (P = 0.001) and LUB + SAL depressed adipose triglyceride lipase expression below control levels (P = 0.001). These results demonstrate that LUB is a β-AR antagonist at the β1-AR and β2-AR subtypes in s.c. adipocytes, and that s.c. and i.m. exhibit different responses to β-AA and LUB.
Keywords: bovine adipocytes; cAMP; gene expression; β-adrenergic agonist; β-adrenergic antagonist; β-adrenergic receptor.
We hypothesized that lubabegron fumarate (Experior, Elanco, Greenfield, IN) would act as an antagonist to β-adrenergic receptor subtypes in primary bovine backfat (subcutaneous) and marbling (intramuscular) adipocytes differentiated in culture. Fat cells were isolated from marbling of longissimus muscle and overlying backfat. In backfat cells, lubabegron fumarate downregulated genes associated with turnover of stored lipid, and lubabegron fumarate reversed the increase in cyclic AMP and protein kinase A caused by the β1-adrenergic receptor agonist, dobutamine, and the β2-adrenergic agonist, salbutamol. Increasing cyclic AMP amount and protein kinase A activity would lead to a decrease in backfat lipid stores (reducing backfat thickness), and this would be effectively blocked by lubabegron fumarate. Salbutamol but not dobutamine increased cyclic AMP amount and protein kinase A activity in marbling fat cells, and this effect was blocked by lubabegron fumarate. Taken together, the results of this study indicate that lubabegron fumarate antagonizes the effects of hormones that promote lipid loss from backfat and marbling. However, marbling fat cells are not as responsive as backfat fat cells to β-adrenergic agonists, so β-adrenergic agonists such as Zilmax and OptiFlex should have less effect on marbling scores than on backfat thickness.
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