Danos Maria, Taylor William A, Hatch Grant M
Department of Pharmacology and Therapeutics, University of Manitoba,753 McDermot Avenue, Winnipeg, Manitoba, Canada.
Biochem Cell Biol. 2008 Feb;86(1):11-20. doi: 10.1139/o07-156.
Cardiolipin (CL) is a major mitochondrial membrane phospholipid in the mammalian heart and the remodeling of CL is essential to maintain its unique unsaturated fatty acyl composition. We examined CL de novo biosynthesis and remodeling in the surviving population of H9c2 cardiac myoblast cells exposed to 2-deoxyglucose (2-DG). H9c2 cells were incubated in the absence or presence of 2-DG for 16 h with [1,3-3H]glycerol or [1-14C]linoleic acid (bound to albumin in a 1:1 molar ratio). Dead cells were removed and radioactivity was incorporated into CL. Its pool size, fatty acid composition, and the activities of the CL biosynthesis and remodeling enzymes were determined. The CL pool size, its fatty acid composition, and [1,3-3H]glycerol or [1-14C]linoleic acid incorporated into CL were unaltered in the surviving population of 2-DG-treated cells compared with controls. In addition, the activities of the CL de novo biosynthetic enzymes were unaltered. Cleaved caspase-3 and poly(ADP-ribose) polymerase were slightly elevated in the surviving population of 2-DG-treated cells compared with controls, indicating that apoptosis induction was occurring in these cells. Mitochondrial phospholipase A2 and monolysocardiolipin acyltransferase (MLCL AT) activities increased 33% (p < 0.05) and 63% (p < 0.05), respectively, in 2-deoxyglucose-treated cells compared with controls. In contrast, the activity of ALCAT1, an endoplasmic reticulum MLCL AT, decreased 77% (p < 0.05), but this was not due to a reduction in ALCAT1 mRNA expression. The mRNA expression of the Barth syndrome gene TAZ, encoding a mitochondrial CL transacylase, was unaltered in 2-DG treated cells. The increase in mitochondrial MLCL AT activity was due to an elevated expression in MLCL AT protein. Thus, an increase in MLCL AT activity and expression occurs to maintain the CL pool in the surviving population of H9c2 cells as a compensatory mechanism for the elevated phospholipase A2 activity seen in 2-DG-induced apoptosis. We hypothesize that increased mitochondrial MLCL AT activity and its expression, and hence, elevated CL resynthesis, may be a protective mechanism against monolysocardiolipin-mediated apoptosis.
心磷脂（CL）是哺乳动物心脏中的一种主要线粒体膜磷脂，CL的重塑对于维持其独特的不饱和脂肪酰基组成至关重要。我们研究了暴露于2-脱氧葡萄糖（2-DG）的H9c2心肌成肌细胞存活群体中的CL从头生物合成和重塑。将H9c2细胞在不存在或存在2-DG的情况下与[1,3-³H]甘油或[1-¹⁴C]亚油酸（以1:1摩尔比与白蛋白结合）一起孵育16小时。去除死细胞，并将放射性掺入CL中。测定其池大小、脂肪酸组成以及CL生物合成和重塑酶的活性。与对照相比，2-DG处理细胞的存活群体中CL池大小、其脂肪酸组成以及掺入CL中的[1,3-³H]甘油或[1-¹⁴C]亚油酸均未改变。此外，CL从头生物合成酶的活性也未改变。与对照相比，2-DG处理细胞的存活群体中裂解的半胱天冬酶-3和聚（ADP-核糖）聚合酶略有升高，表明这些细胞中正在发生凋亡诱导。与对照相比，2-脱氧葡萄糖处理细胞中的线粒体磷脂酶A2和单溶血心磷脂酰基转移酶（MLCL AT）活性分别增加了33%（p < 0.05）和63%（p < 0.05）。相反，内质网MLCL AT即ALCAT1的活性降低了77%（p < 0.05），但这并不是由于ALCAT1 mRNA表达的降低。编码线粒体CL转酰基酶的Barth综合征基因TAZ的mRNA表达在2-DG处理的细胞中未改变。线粒体MLCL AT活性的增加是由于MLCL AT蛋白表达的升高。因此，MLCL AT活性和表达的增加会在H9c2细胞的存活群体中维持CL池，作为对2-DG诱导凋亡中磷脂酶A2活性升高的一种补偿机制。我们推测线粒体MLCL AT活性及其表达的增加，以及因此CL再合成的升高，可能是一种针对单溶血心磷脂介导的凋亡的保护机制。
