Zhou Jibin, Qu Jiaxiang, Yi Xian Ping, Graber Kelly, Huber Lu, Wang Xuejun, Gerdes A Martin, Li Faqian
Cardiovascular Research Institute, South Dakota Health Research Foundation, 1100 East 21st St., Suite 700, Sioux Falls, SD 57105, USA.
Am J Physiol Heart Circ Physiol. 2007 Jan;292(1):H270-6. doi: 10.1152/ajpheart.00576.2006. Epub 2006 Aug 25.
Recent progresses in signal transduction have revealed that beta-catenin signaling controls embryonic development, tumorigenesis, cell shape, and polarity. The role of this pathway in myocyte shape regulation during cardiac hypertrophy and failure is, however, not clearly defined. Since homozygous knockout of beta-catenin is embryonically lethal, we have deleted beta-catenin genes specifically in the heart of adult mice by crossing loxP-flanked beta-catenin mice with transgenic mice expressing tamoxifen-activated MerCreMer protein (MCM) driven by the alpha-myosin heavy chain promoter. Administration of tamoxifen to homozygous loxP-flanked beta-catenin mice positive for MCM induces the deletion of beta-catenin only in cardiomyocytes. Immunolabeling with beta-catenin antibody demonstrates that 90% of cardiomyocytes completely lose their beta-catenin expression but maintain normal rod-shaped morphology. The intercalated disk of cardiomyocytes lacking beta-catenin is morphologically unremarkable with normal distribution of vinculin, N-cadherin, desmoplakin, ZO-1, connexin43, and alpha-, gamma-, and p120 catenins. The expression level of these proteins, except that of gamma-catenin, is also similar in tamoxifen-treated and control mice with both homozygous loxP-flanked beta-catenin genes and the MCM transgene. Western blot analyses reveal that gamma-catenin increases in the heart of beta-catenin knockout mice compared with controls. Confocal microscopy also demonstrates that gamma-catenin has significantly increased in the intercalated disk of cardiomyocytes lacking beta-catenin. Echocardiographic data indicate that the knockout mice maintain normal ventricular geometry and cardiac function. The results suggest that upregulation of gamma-catenin can compensate for the loss of beta-catenin in cardiomyocytes to maintain normal cardiac structure and function.
信号转导领域的最新进展表明，β-连环蛋白信号通路控制着胚胎发育、肿瘤发生、细胞形状和极性。然而，该通路在心肌肥厚和心力衰竭过程中对心肌细胞形状调节的作用尚不清楚。由于β-连环蛋白的纯合敲除在胚胎期是致死性的，我们通过将loxP侧翼的β-连环蛋白小鼠与表达由α-肌球蛋白重链启动子驱动的他莫昔芬激活的MerCreMer蛋白（MCM）的转基因小鼠杂交，特异性地删除了成年小鼠心脏中的β-连环蛋白基因。给纯合的loxP侧翼β-连环蛋白且MCM阳性的小鼠注射他莫昔芬，仅在心肌细胞中诱导β-连环蛋白的缺失。用β-连环蛋白抗体进行免疫标记显示，90%的心肌细胞完全失去β-连环蛋白表达，但保持正常的杆状形态。缺乏β-连环蛋白的心肌细胞闰盘在形态上无明显异常，纽蛋白、N-钙黏着蛋白、桥粒斑蛋白、ZO-1、连接蛋白43以及α-、γ-和p120连环蛋白分布正常。在同时具有纯合loxP侧翼β-连环蛋白基因和MCM转基因的他莫昔芬处理小鼠和对照小鼠中，除γ-连环蛋白外，这些蛋白的表达水平也相似。蛋白质印迹分析显示，与对照相比，β-连环蛋白敲除小鼠心脏中的γ-连环蛋白增加。共聚焦显微镜检查也表明，在缺乏β-连环蛋白的心肌细胞闰盘中，γ-连环蛋白显著增加。超声心动图数据表明，敲除小鼠维持正常的心室几何形状和心脏功能。结果表明，γ-连环蛋白的上调可以补偿心肌细胞中β-连环蛋白的缺失，以维持正常的心脏结构和功能。
