SD COBRE: MYOCYTE POLARITY AND SIGNAL TRANSDUCTION IN MYOCARDIAL INFARCTION

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This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Cardiac myocytes size increases through either longitudinal growth by series addition of sarcomeres or cross-sectional growth by parallel addition of sarcomeres. How cardiac myocytes incorporate sarcomeres is dependent on loading condition and resultant cytoskeletal changes. The activation of longitudinally-oriented cadherin-beta-catenin signaling pathways may recruit signal molecules to the polar plasma membrane and lead to series addition of sarcomeres, progressive cell lengthening and eventually pump failure. Glycogen synthase kinase-3beta (GSK-3beta)phosphorylates beta-catenin on serine and threonine, regulating cytoplasmic beta-catenin level and controlling gene expression. We hypothesize that activation of the beta-catenin signaling pathway by GSK-3beta inhibition triggers myocyte lengthening and eccentric hypertrophy. During the first year, we have focused on specific aims 1 and 3. These two aims are critical to the study of specific aim 2 and 4. In specific aim 1, we have conducted further studies on beta-catenin signaling during myocardial infarction. Our preliminary results have demonstrated that cytoplasmic free beta-catenin levels increase during acute myocardial ischemia. To further prove that beta-catenin signaling regulates gene regulation in cardiac myocytes, we have used a reporter mouse expressing lacZ under the control of a c-Fos minimal promoter and three Tcf binding sites. During beta-catenin signaling, free beta-catenin translocates to the nucleus and binds to TCF/LEF transcription factors resulting in increased LacZ expression. We continue to investigate myocyte polarity changes in a hypertensive rat model. Our data have showed that myocyte polarity changes during myocyte lengthening. The established protocols and techniques for myocyte polarity are ready to use in this proposal once mice with myocardial infarction are created. In specific aim 3, we have acquired transgenic mice conditionally overexpressing beta-catenin under the control of TA transactivator. These mice are currently bred with mice expressing TA transactivator under the control of either MHC or CMV promoter. We will induce gene expression with doxycycline and analyze phenotype once mice are available. These studies will further our understanding of myocyte shape and polarity regulation in cardiac hypertrophy and failure and identify key molecules involved in myocyte shape and polarity regulation for future genetic manipulation and gene therapy.