Xu Huifen, Luo Jun, Ma Gongzhen, Zhang Xueying, Yao Dawei, Li Ming, Loor Juan J
Shaanxi Key Laboratory of Molecular Biology for Agriculture, College of Animal Science and Technology, Northwest A&F University, Yangling, Shaanxi, P. R. China.
College of Animal Science and Veterinary Medicine, Henan Agricultural University, Zhengzhou, Henan, P. R. China.
J Cell Physiol. 2018 Feb;233(2):1005-1016. doi: 10.1002/jcp.25954. Epub 2017 May 24.
Sterol regulatory element binding protein 1 (SREBP-1) is well-known as the master regulator of lipogenesis in rodents. Acyl-CoA synthetase short-chain family member 2 (ACSS2) plays a key role in lipogenesis by synthesizing acetyl-CoA from acetate for lipogenesis. ATP citrate lyase (ACLY) catalyzes the conversion of citrate and coenzyme A to acetyl-CoA, hence, it is also important for lipogenesis. Although ACSS2 function in cancer cells has been elucidated, its essentiality in ruminant mammary lipogenesis is unknown. Furthermore, ACSS2 gene promoter and its regulatory mechanisms have not known. Expression of ACSS2 was high in lipid synthesizing tissues, and its expression increased during lactation compared with non-lactating period. Simultaneous knockdown of both ACSS2 and ACLY by siRNA in primary goat mammary epithelial cells decreased (p < 0.05) the mRNA abundance of genes associated with de novo fatty acid synthesis (FASN, ACACA, SCD1) and triacylglycerol (TAG) synthesis (DGAT1, DGAT2, GPAM, and AGPAT6). Genes responsible for lipid droplet formation and secretion (PLIN2 and PLIN3) and fatty acid oxidation (ATGL, HSL, ACOX, and CPT1A) all decreased (p < 0.05) after ACSS2 and ACLY knockdown. Total cellular TAG content and lipid droplet formation also decreased. Use of a luciferase reporter assay revealed a direct regulation of ACSS2 by SREBP-1. Furthermore, SREBP-1 interacted with an SRE (SREBP response element) spanning at -475 to -483 bp on the ACSS2 promoter. Taken together, our results revealed a novel pathway that SREBP-1 may regulate fatty acid and TAG synthesis by regulating the expression of ACSS2.
甾醇调节元件结合蛋白1（SREBP-1）是啮齿动物中众所周知的脂肪生成主要调节因子。酰基辅酶A合成酶短链家族成员2（ACSS2）通过将乙酸盐合成用于脂肪生成的乙酰辅酶A在脂肪生成中起关键作用。ATP柠檬酸裂解酶（ACLY）催化柠檬酸和辅酶A转化为乙酰辅酶A，因此，它对脂肪生成也很重要。虽然ACSS2在癌细胞中的功能已得到阐明，但其在反刍动物乳腺脂肪生成中的必要性尚不清楚。此外，ACSS2基因启动子及其调控机制也不清楚。ACSS2在脂质合成组织中的表达较高，与非泌乳期相比，其表达在泌乳期增加。在原代山羊乳腺上皮细胞中通过siRNA同时敲低ACSS2和ACLY会降低（p < 0.05）与从头脂肪酸合成（FASN、ACACA、SCD1）和三酰甘油（TAG）合成（DGAT1、DGAT2、GPAM和AGPAT6）相关基因的mRNA丰度。负责脂滴形成和分泌（PLIN2和PLIN3）以及脂肪酸氧化（ATGL、HSL、ACOX和CPT1A）的基因在ACSS2和ACLY敲低后均降低（p < 0.05）。总细胞TAG含量和脂滴形成也减少。荧光素酶报告基因检测显示SREBP-1对ACSS2有直接调控作用。此外，SREBP-1与ACSS2启动子上-475至-483 bp的SRE（SREBP反应元件）相互作用。综上所述，我们的结果揭示了一条新的途径，即SREBP-1可能通过调节ACSS2的表达来调节脂肪酸和TAG合成。
