The Mechanistic Basis of Cyclin A2-Mediated Cardiac Repair

刺激心肌细胞有丝分裂的概念对心脏再生和心血管疾病具有重大意义。我们先前首次证明，在转基因小鼠模型中，如果细胞周期蛋白A2在心肌细胞中有成分地表达，哺乳动物心肌细胞有丝分裂可以在出生后发生。我们最近的研究结果表明，与非转基因对照相比，细胞周期蛋白A2介导了心肌梗死后转基因心脏的有丝分裂，从而修复了心脏，并显著恢复了心功能。为了探索这些结果的潜在临床翻译，我们通过灭活的腺病毒给脑梗塞大鼠注射了编码细胞周期蛋白A2的cDNA，并注意到与接受空腺病毒的对照组相比，接受腺周期蛋白A2的大鼠在注射部位进行了细胞再生，并保存了心输出量。我们假设，在我们观察到的再生过程中，有两种潜在的机制。首先，在我们的小鼠脑梗塞模型中，侧群(SP)干细胞似乎分化为心肌细胞，但这些未成熟的心肌细胞中的有丝分裂只在转基因小鼠中被发现，因此可能揭示了一种新的诱导过度增殖的祖细胞的机制。其次，我们注意到，与非转基因对照相比，转基因小鼠梗死周围区磷组蛋白H3的表达和BrdU的摄取显著增加，这意味着成年心肌细胞的去分化和分裂。利用转基因和非转基因小鼠的SP细胞，我们建议通过SP细胞来源的祖细胞的体外增殖研究和SP细胞移植到小鼠脑梗塞模型的体内研究来探索第一种机制。此外，我们将使用新型的工程化心肌组织，通过测试转基因和非转基因小鼠的SP细胞来源的祖细胞和成年心肌细胞对损伤的反应来评估这两种机制。第二种机制还将通过病毒将细胞周期蛋白A2基因转移到体外培养的成人心肌细胞中，并利用视频显微镜来监测这些细胞的有丝分裂和胞质分裂。这些研究的提出是为了阐明一条更直接的临床治疗途径。

The concept of stimulating cardiomyocyte mitotic divisions has dramatic implications for cardiac regeneration and hence, cardiovascular disease. We previously demonstrated for the first time that mammalian cardiomyocyte mitoses can occur postnatally if cyclin A2 is constitutively expressed in cardiomyocytes in a transgenic mouse model. Our more recent results demonstrate that cyclin A2 mediates cardiomyocyte mitoses in the transgenic hearts after myocardial infarction (Ml) is induced, thus repairing the heart with significant recovery of cardiac function when compared with nontransgenic littermate controls. To explore potential clinical translation of these results, we administered cDNA encoding cyclin A2 via de-activated adenovirus to infarcted rats and noted that the rats receiving adeno-cyclin A2 undergo cellular regeneration at the sites of injection and have preserved cardiac output when compared to controls which received empty adenovirus. We hypothesize that there are two potential mechanisms mediating the regeneration we have observed. First, side population (SP) stem cells appear to differentiate into cardiomyocytes in our mouse infarction model, but mitoses in these immature cardiomyocytes are only noted in the transgenic mice, thus possibly uncovering a novel mechanism to induce hyperproliferative progenitor cells. Second, we note a significant increase in expression of phosphohistone H3 and uptake of BrdU in the peri-infarct zone of transgenic mice compared to nontransgenic controls, implicating dedifferentiation and division of adult cardiomyocytes. Utilizing SP cells from transgenic and nontransgenic mice, we propose to explore the first mechanism via in vitro studies of proliferation of SP cell-derived progenitor cells and in vivo studies of SP cell transplantation into a mouse infarction model. Additionally, we will use novel engineered cardiac tissues to evaluate both mechanisms by testing the response to injury of both SP cell-derived progenitors and adult cardiomyocytes from transgenic and nontransgenic mice. The second mechanism will also be examined using viral transfer of cyclin A2 cDNA into adult cardiomyocytes in vitro and the utilization of video microscopy to monitor mitosis and cytokinesis of these cells. These studies are proposed in order to elucidate a more directed path to clinical therapy.