Zhang Chongben, Hwarng Gwen, Cooper Daniel E, Grevengoed Trisha J, Eaton James M, Natarajan Viswanathan, Harris Thurl E, Coleman Rosalind A
From the Department of Nutrition, University of North Carolina, Chapel Hill, North Carolina 27599.
the Department of Pharmacology, University of Virginia Health System, Charlottesville, Virginia 22908, and.
J Biol Chem. 2015 Feb 6;290(6):3519-28. doi: 10.1074/jbc.M114.602789. Epub 2014 Dec 15.
Although an elevated triacylglycerol content in non-adipose tissues is often associated with insulin resistance, the mechanistic relationship remains unclear. The data support roles for intermediates in the glycerol-3-phosphate pathway of triacylglycerol synthesis: diacylglycerol (DAG), which may cause insulin resistance in liver by activating PKCϵ, and phosphatidic acid (PA), which inhibits insulin action in hepatocytes by disrupting the assembly of mTOR and rictor. To determine whether increases in DAG and PA impair insulin signaling when produced by pathways other than that of de novo synthesis, we examined primary mouse hepatocytes after enzymatically manipulating the cellular content of DAG or PA. Overexpressing phospholipase D1 or phospholipase D2 inhibited insulin signaling and was accompanied by an elevated cellular content of total PA, without a change in total DAG. Overexpression of diacylglycerol kinase-θ inhibited insulin signaling and was accompanied by an elevated cellular content of total PA and a decreased cellular content of total DAG. Overexpressing glycerol-3-phosphate acyltransferase-1 or -4 inhibited insulin signaling and increased the cellular content of both PA and DAG. Insulin signaling impairment caused by overexpression of phospholipase D1/D2 or diacylglycerol kinase-θ was always accompanied by disassociation of mTOR/rictor and reduction of mTORC2 kinase activity. However, although the protein ratio of membrane to cytosolic PKCϵ increased, PKC activity itself was unaltered. These data suggest that PA, but not DAG, is associated with impaired insulin action in mouse hepatocytes.
尽管非脂肪组织中三酰甘油含量升高常与胰岛素抵抗相关，但其机制关系仍不清楚。数据支持甘油-3-磷酸途径中三酰甘油合成的中间产物发挥作用：二酰甘油（DAG），其可通过激活PKCε在肝脏中导致胰岛素抵抗；磷脂酸（PA），其通过破坏mTOR和rictor的组装来抑制肝细胞中的胰岛素作用。为了确定由从头合成以外的途径产生的DAG和PA增加是否会损害胰岛素信号传导，我们在酶促操纵DAG或PA的细胞含量后检查了原代小鼠肝细胞。过表达磷脂酶D1或磷脂酶D2会抑制胰岛素信号传导，并伴有总PA细胞含量升高，而总DAG无变化。二酰甘油激酶-θ的过表达抑制胰岛素信号传导，并伴有总PA细胞含量升高和总DAG细胞含量降低。过表达甘油-3-磷酸酰基转移酶-1或-4会抑制胰岛素信号传导，并增加PA和DAG的细胞含量。磷脂酶D1/D2或二酰甘油激酶-θ过表达引起的胰岛素信号传导损伤总是伴随着mTOR/rictor的解离和mTORC2激酶活性的降低。然而，尽管膜与胞质PKCε的蛋白比率增加，但PKC活性本身未改变。这些数据表明，在小鼠肝细胞中，与胰岛素作用受损相关的是PA，而非DAG。
