Gunteski-Hamblin A M, Song G, Walsh R A, Frenzke M, Boivin G P, Dorn G W, Kaetzel M A, Horseman N D, Dedman J R
Department of Molecular and Cellular Physiology, University of Cincinnati College of Medicine, Ohio 45267-0576, USA.
Am J Physiol. 1996 Mar;270(3 Pt 2):H1091-100. doi: 10.1152/ajpheart.1996.270.3.H1091.
Annexin VI is a member of a family of Ca(2+)-dependent phospholipid-binding proteins that is expressed in many tissues, including the heart. It is a regulator of membrane-associated events, including the skeletal muscle ryanodine-sensitive Ca2+ release channel and the cardiac Na+/Ca2+ exchanger. The potential roles of annexin VI in Ca2+ signaling in cardiac myocytes were evaluated by targeting its overexpression to the hearts of transgenic mice. Expression of full-length human annexin VI cDNA was targeted to the heart using the alpha-myosin heavy chain gene promoter (Subramaniam, A., W. K. Jones, J. Gulick, S. Wert, J. Neumann, and J. Robbins. J. Biol. Chem. 266: 24613-24620, 1991). Five transgenic lines exhibited at least 10-fold overexpression of annexin VI protein in both atria and ventricles. Pathological evaluation indicated mice overexpressing annexin VI had enlarged dilated hearts, acute diffuse myocarditis, lymphocytic infiltration, moderate to severe fibrosis throughout the heart, and mild fibrosis around the pulmonary veins of the lungs. Contractile mechanics of cardiomyocytes isolated from hearts of transgenic animals showed frequency-dependent reduced percent shortening and decreased rates of contraction and relaxation compared with control animals. Cardiomyocytes isolated from transgenic animals had lower basal levels of intracellular free Ca2+ and a reduced rise in free Ca2+ following depolarization. After stimulation, intracellular free Ca2+ returned to basal levels faster in transgenic cells than in cells from control animals. These data demonstrate that the overexpression of annexin VI in the heart disrupts normal Ca2+ homeostasis and suggests that this dysfunction may be due to annexin VI regulation of pumps and/or exchangers in the membranes of cardiomyocytes.
膜联蛋白VI是一类Ca(2+)依赖性磷脂结合蛋白家族的成员，在包括心脏在内的许多组织中都有表达。它是膜相关事件的调节因子，包括骨骼肌兰尼碱敏感的Ca2+释放通道和心脏Na+/Ca2+交换器。通过将膜联蛋白VI的过表达靶向转基因小鼠的心脏，评估了其在心肌细胞Ca2+信号传导中的潜在作用。使用α-肌球蛋白重链基因启动子将全长人膜联蛋白VI cDNA的表达靶向心脏（Subramaniam, A., W. K. Jones, J. Gulick, S. Wert, J. Neumann, and J. Robbins. J. Biol. Chem. 266: 24613 - 24620, 1991）。五个转基因品系在心房和心室中均表现出膜联蛋白VI蛋白至少10倍的过表达。病理评估表明，过表达膜联蛋白VI的小鼠心脏扩大、扩张，有急性弥漫性心肌炎、淋巴细胞浸润、整个心脏中度至重度纤维化以及肺静脉周围轻度纤维化。与对照动物相比，从转基因动物心脏分离的心肌细胞的收缩力学显示频率依赖性缩短百分比降低以及收缩和舒张速率降低。从转基因动物分离的心肌细胞的细胞内游离Ca2+基础水平较低，去极化后游离Ca2+的升高减少。刺激后，转基因细胞内的游离Ca2+比对照动物细胞更快地恢复到基础水平。这些数据表明，心脏中膜联蛋白VI的过表达破坏了正常的Ca2+稳态，并表明这种功能障碍可能是由于膜联蛋白VI对心肌细胞膜上的泵和/或交换器的调节所致。
