COBRE: W & I HOSP OF RI: SIGNALING PATHWAYS IN CARDIOMYOCYTE PROLIFERATION

这个子项目是许多研究子项目中利用 资源由NIH/NCRR资助的中心拨款提供。子项目和 调查员(PI)可能从NIH的另一个来源获得了主要资金， 并因此可以在其他清晰的条目中表示。列出的机构是 该中心不一定是调查人员的机构。 心肌细胞的生长模式在出生后不久就从增殖转变为肥大。导致这种转换的分子机制还不是很清楚。许多细胞内信号转导通路在调节心脏生长中起重要作用，包括磷脂酰肌醇3-激酶(PI3K)/p70S6K(P70S6K)通路和细胞外信号调节激酶1和2(ERK1，2)。我们证实，在b-肾上腺素能受体阻断后，新生儿心肌细胞的增殖显著减少。这种作用与p70S6K活性降低有关，但与ERK1，2活性无关。这些结果表明，在胎儿和新生儿早期发育过程中，BAR在有丝分裂信号和心脏生长调节中起着重要作用。我们进一步证明了p70S6K和PI3K在心脏中的个体发育似乎是同步的，并在心脏的整个发育过程中受到高度调控。心脏P70S6K和PI3K活性在妊娠晚期胎儿和新生儿基础水平较高，而成人则不明显。当心肌细胞经历增生性生长时，这两种酶的高活性都会发生。因此，p70S6K/PI3K活性与心肌细胞生长密切相关。基因技术的最新进展为回答基本的生物学问题提供了宝贵的实验工具。可以开发条件表达系统，允许在发育过程中的选定时间点过表达心脏特异性的PI3K。我们将使用这种方法来研究这些通路在不同发育阶段的作用，并确定后增殖的心肌细胞是否可以在PI3K的控制下“重新启动”进行细胞分裂。这项提案的具体目标将1)表征β-1AR对p70S6K/PI3K活性的调节在带有遗传改变的β-AR和PI3K信号的小鼠模型中的作用；2)创造一只小鼠 与心脏中有条件地过表达心脏PI3K一致，并表征其在不同发育阶段对心肌细胞增殖的影响。这些研究将有助于我们理解围产期心脏发育的调节以及成人生活中的病理状态。

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. The growth mode of cardiomyocytes switches from hyperplasia to hypertrophy shortly after birth. The molecular mechanisms responsible for the switch are not well understood. A number of intracellular signal transduction pathways have been suggested to be important in regulation of cardiac growth including the phosphoinositide 3-kinase (PI3K)/p70 S6 kinase (p70S6K) pathway and extracellular signal-regulated kinase 1 & 2 (ERK1,2). We demonstrated a profound reduction in neonatal cardiomyocyte proliferation following b-adrenergic receptor blockade. This effect is associated with reduction in p70S6K activity but not in ERK1,2 activity. These suggest that bAR have an important role in mitogenic signaling and regulation of cardiac growth during fetal and early newborn development. We further demonstrated the ontogeny of p70S6K and PI3K in the heart appears to be synchronized and highly regulated throughout development in the heart. There are high basal levels of cardiac p70S6K and PI3K activity in the late gestation fetus and newborn but not in the adult. The high activities of both kinases occur when cardiomyocytes are undergoing hyperplastic growth. Hence, there is a correlation between p70S6K/PI3K activities and cardiomyocyte growth. Recent advances in genetic techniques have provided valuable experimental tools to answer fundamental biological questions. Conditional expression systems can be developed which allows cardiac-specific overexpression of PI3K at selected time points during development. We will us this approach to examine the role of these pathways at different developmental stages and to determine if post-proliferative cardiomyocytes can be "re-initiated" to undergo cell division under the control of the PI3K. The specific aims in this proposal will 1) characterize the role of beta-1AR regulation of p70S6K/PI3K activity in mouse models with genetically altered beta-AR and PI3K signaling and 2) create a mouse line with conditional overexpression of cardiac PI3K in the heart and characterize its effects on cardiomyocyte proliferation at different stages of development. These studies will contribute to our understanding of the regulation of cardiac growth during the perinatal transition and in pathological conditions during adult life.