We conducted 3 independent experiments to demonstrate functional G-coupled protein receptor 43 (GPR43) and GPR120 in bovine intramuscular (i.m.) and subcutaneous (s.c.) adipose tissues. We hypothesized that media volatile fatty acids and long-chain fatty acids would affect cAMP-activated protein kinase-alpha (AMPKα) protein expression and cAMP concentrations differently in i.m. and s.c. adipose tissue. Experiment 1: oleic acid (18:1n-9) decreased phosphorylated AMPKα protein (p-AMPKα) and the p-AMPKα/AMPKα protein ratio in i.m. preadipocytes, increased the p-AMPKα/AMPKα protein ratio in bovine satellite cells, and had no effect in s.c. preadipocytes. Experment 2: ex vivo explants from the 5th to 8th longissimus thoracic rib muscle section of Angus crossbred steers were cultured 48 hr in media containing 0.25 µM ciglitizone, 5 mM glucose, and 5 mM acetate, in the absence or the presence of 100 µM oleic acid. Oleic acid increased acetate incorporation into fatty acids and GPR43 gene expression in i.m. adipose tissue (P < 0.05), but oleic acid had no effect on fatty acid synthesis or GPR43 expression in s.c. adipose tissue. Experiment 3: fresh s.c. and i.m. adipose tissue from the 5th to 8th longissimus thoracic rib muscle section of Angus crossbred steers was transferred immediately to 6-well culture plates containing 3 mL of KHB/Hepes/5 mM glucose. Samples were preincubated with 0.5 mM theophylline plus 10 μM forskolin for 30 min, after which increasing concentrations of acetate or propionate (0, 10−3, 10−2.3, and 10−3 M) in the absence or the presence of 100 μM oleic acid or 100 µM palmitic acid (16:0) were added to the incubation media. Acetate had no effect on forskolin-stimulated cAMP production in s.c. adipose tissue but decreased cAMP in i.m. adipose tissue (P < 0.05); this indicates a functional GPR43 receptor in i.m. adipose tissue. The combination of 10−2 M acetate and oleic acid decrease cAMP production in s.c. adipose tissue, consistent with GPR120 receptor activity, but oleic acid and palmitic acid attenuated the depression of cAMP production caused by acetate in i.m. adipose tissue. Palmitic acid depressed cAMP production in s.c. adipose tissue, and increased cAMP production in i.m. adipose tissue (P < 0.05). Propionate had no effect on cAMP production in s.c. or i.m. adipose tissue. These results provide evidence for functional GPR43 receptors in i.m. adipose tissue and GPR120 receptors in s.c. adipose tissue, both of which would suppress lipolysis.

中文翻译：

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安格斯杂交阉牛皮下和肌肉内脂肪组织中功能性 G 偶联蛋白受体 43 和 120 的证据

我们进行了 3 次独立实验，以证明牛肌肉内 (im) 和皮下 (sc) 脂肪组织中的功能性 G 偶联蛋白受体 43 (GPR43) 和 GPR120。我们假设中等挥发性脂肪酸和长链脂肪酸会影响 im 和 sc 脂肪组织中不同的 cAMP 活化蛋白激酶-α (AMPKα) 蛋白表达和 cAMP 浓度。实验一：油酸（18:1n-9）降低前脂肪细胞磷酸化AMPKα蛋白（p-AMPKα）和p-AMPKα/AMPKα蛋白比例，增加牛卫星细胞中p-AMPKα/AMPKα蛋白比例，并具有对 sc 前脂肪细胞没有影响。实验 2：在含有 0.25 µM 西格列酮、5 mM 葡萄糖、和 5 mM 醋酸盐，在不存在或存在 100 µM 油酸的情况下。油酸增加乙酸盐掺入脂肪酸和脂肪组织中 GPR43 基因的表达（P < 0.05），但油酸对脂肪组织中的脂肪酸合成或 GPR43 表达没有影响。实验3：将来自安格斯杂交肉牛第5至第8胸最长肋肌切片的新鲜皮下和脂肪组织立即转移到含有3mL KHB/Hepes/5mM葡萄糖的6孔培养板中。将样品与 0.5 mM 茶碱加 10 μM 毛喉素预孵育 30 分钟，然后在不存在或存在 100 μM 油酸的情况下增加乙酸盐或丙酸盐（0、10-3、10-2.3 和 10-3 M）的浓度将酸或 100 µM 棕榈酸 (16:0) 添加到培养介质中。醋酸盐对毛喉素刺激的 sc 脂肪组织中 cAMP 的产生没有影响，但降低了脂肪组织中的 cAMP（P < 0.05）；这表明在脂肪组织中存在功能性 GPR43 受体。10-2 M 乙酸盐和油酸的组合降低了 sc 脂肪组织中 cAMP 的产生，这与 GPR120 受体活性一致，但油酸和棕榈酸减弱了脂肪组织中乙酸盐引起的 cAMP 产生的抑制。棕榈酸抑制 sc 脂肪组织中 cAMP 的产生，并增加脂肪组织中 cAMP 的产生 (P < 0.05)。丙酸盐对 sc 或脂肪组织中 cAMP 的产生没有影响。这些结果为脂肪组织中的功能性 GPR43 受体和 sc 脂肪组织中的 GPR120 受体提供了证据，这两者都会抑制脂肪分解。