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

本子项目是利用由NIH/NCRR资助的中心赠款提供的资源的众多研究子项目之一。子项目和研究者（PI）可能已经从另一个NIH来源获得了主要资金，因此可以在其他CRISP条目中表示。列出的机构是中心的，不一定是研究者的机构。出生后不久，心肌细胞的生长模式从增生转变为肥大。导致这一转变的分子机制尚不清楚。许多细胞内信号转导通路被认为对心脏生长的调节很重要，包括磷酸肌肽3激酶(PI3K)/p70 S6激酶（p70S6K）途径和细胞外信号调节激酶1和2 （ERK1,2）。我们证明了b-肾上腺素能受体（bAR）阻断后新生儿心肌细胞增殖的显著减少。这种效应与p70S6K活性的降低有关，但与ERK1,2活性无关。这些提示bAR在有丝分裂信号传导和胎儿及新生儿早期发育过程中心脏生长调控中具有重要作用。我们进一步证明p70S6K和PI3K在心脏中的个体发育似乎是同步的，并且在心脏发育的整个过程中受到高度调节。在妊娠晚期胎儿和新生儿中，心脏p70S6K和PI3K活性的基础水平较高，而在成人中则没有。这两种激酶的高活性发生在心肌细胞增生生长时。因此，p70S6K/PI3K活性与心肌细胞生长之间存在相关性。遗传技术的最新进展为回答基本的生物学问题提供了有价值的实验工具。可以开发条件表达系统，在发育过程中的选定时间点允许心脏特异性过表达PI3K。我们将使用这种方法来检查这些途径在不同发育阶段的作用，并确定增殖后心肌细胞是否可以在PI3K的控制下“重新启动”进行细胞分裂。本提案的具体目标是：1)表征b1AR在bAR和PI3K信号基因改变的小鼠模型中对p70S6K/PI3K活性的调节作用；2)创建心脏中PI3K条件过表达的小鼠系，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过渡期和成年期病理状态下心脏生长的调节。

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 (bAR) 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 b1AR regulation of p70S6K/PI3K activity in mouse models with genetically altered bAR 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.