Wang A, Gu Z, Heid B, Akers R M, Jiang H
Department of Animal and Poultry Sciences, Virginia Polytechnic Institute and State University, Blacksburg 24061, USA.
J Dairy Sci. 2009 Jun;92(6):2696-705. doi: 10.3168/jds.2009-2037.
Volatile fatty acids (VFA), including acetate, propionate, and butyrate, are not only a primary source of energy, but also regulate rumen development, insulin and glucagon secretion, and other physiological processes in cattle and sheep. The mechanism underlying the regulatory effects of VFA is unknown. Recent "reverse pharmacology" studies identified human G protein-coupled receptors GPR41 and GPR43 as receptors for short-chain fatty acids. It is possible that proteins similar to human GPR41 and GPR43 mediate the regulatory effects of VFA in cattle. In this study, we determined first, whether the bovine genome contains genes similar to the human GPR41 and GPR43 genes; second, whether and where these genes are expressed in cattle; and third, if the proteins encoded by these genes can be activated by acetate, propionate, and butyrate. A search of GenBank revealed bovine genomic sequences and expressed sequence tags highly similar to the human GPR41 and GPR43 DNA and cDNA sequences. The protein-coding and 5' untranslated regions of the bovine GPR41 and GPR43 mRNA were cloned and sequenced from spleen tissue. Based on these sequences, the bovine GPR41 gene contains 3 exons and its transcription is initiated at 2 leader exons, generating 2 GPR41 mRNA variants differing in the 5' untranslated region. The bovine GPR43 gene contains 2 exons and transcription of this gene is initiated from a single start site. The amino acid sequences deduced from the bovine GPR41 and GPR43 mRNA sequences are more than 75% identical to those of the human GPR41 and GPR43 and are predicted to encode 7 transmembrane domains, typical of G protein-coupled receptors. Both bovine GPR41 and GPR43 mRNA were detected in a variety of tissues including rumen and pancreas. In a cell system, interaction of the overexpressed bovine GPR41 or GPR43 protein with acetate, propionate, or butyrate inhibited luciferase reporter expression from a cyclic AMP-responsive promoter, suggesting that the bovine GPR41 and GPR43 proteins couple to Galpha(i/11). In total, these results demonstrate that the bovine genome encodes functional GPR41 and GPR43 genes and suggest that GPR41 and GPR43 may play a role in the regulatory effects of VFA in cattle.
挥发性脂肪酸（VFA），包括乙酸、丙酸和丁酸，不仅是能量的主要来源，还能调节牛羊的瘤胃发育、胰岛素和胰高血糖素分泌以及其他生理过程。VFA发挥调节作用的潜在机制尚不清楚。最近的“反向药理学”研究确定人类G蛋白偶联受体GPR41和GPR43是短链脂肪酸的受体。有可能与人类GPR41和GPR43相似的蛋白质介导了VFA在牛体内的调节作用。在本研究中，我们首先确定牛基因组是否包含与人类GPR41和GPR43基因相似的基因；其次，这些基因在牛体内是否表达以及在何处表达；第三，这些基因编码的蛋白质是否能被乙酸、丙酸和丁酸激活。对GenBank的搜索揭示了与人类GPR41和GPR43的DNA及cDNA序列高度相似的牛基因组序列和表达序列标签。从脾脏组织中克隆并测序了牛GPR41和GPR43 mRNA的蛋白质编码区和5'非翻译区。基于这些序列，牛GPR41基因包含3个外显子，其转录起始于2个前导外显子，产生2种在5'非翻译区不同的GPR41 mRNA变体。牛GPR43基因包含2个外显子，该基因的转录从单个起始位点开始。从牛GPR41和GPR43 mRNA序列推导的氨基酸序列与人类GPR41和GPR43的氨基酸序列有超过75%的同一性，并预计编码7个跨膜结构域，这是G蛋白偶联受体的典型特征。在包括瘤胃和胰腺在内的多种组织中都检测到了牛GPR41和GPR43 mRNA。在细胞系统中，过表达的牛GPR41或GPR43蛋白与乙酸、丙酸或丁酸的相互作用抑制了来自环磷酸腺苷反应性启动子的荧光素酶报告基因表达，这表明牛GPR41和GPR43蛋白与Gα(i/11)偶联。总体而言，这些结果表明牛基因组编码功能性的GPR41和GPR43基因，并提示GPR41和GPR43可能在VFA对牛的调节作用中发挥作用。
