Role of Abcg2/Bcrp1 in Cardiac Side Population Cells

描述（由申请人提供）：慢性心力衰竭是美国住院的主要原因，影响超过500万患者，每年有超过50万新诊断病例。目前的治疗方法并没有解决心衰发展的核心病理生理学，即功能心肌细胞的丧失。因此，心脏祖细胞在治疗性心脏修复和再生方面具有巨大的潜力。我们和其他人最近证实了在成年小鼠心肌中存在这样一个祖细胞群。这些所谓的心脏侧细胞群（CSP）通过其独特的Hoechst 33342染料挤压特性在成人心脏中被鉴定出来，代表了一个独特的祖细胞群。虽然体外这些CSP细胞具有生化分化和更重要的功能性心肌分化的能力，但在体内这种分化发生的速度非常有限，并且受到细胞存活、增殖和分化的调节机制的限制。CSP细胞表达一组独特的ATP结合盒（ABC）转运蛋白，包括乳腺癌耐药蛋白（Abcg2/Bcrp1）。虽然这些ABC转运蛋白赋予SP细胞特有的Hoechst染料外溢特性，但新出现的证据也表明，ABC转运蛋白家族的成员可能作为干细胞与其局部环境相互作用的管道，从而介导祖细胞命运和功能的复杂调节，以响应外部和内部刺激。事实上，我们的初步数据表明，Abcg2/Bcrp1的表达在出生后发育的最初几周内逐渐下调，并在心脏损伤后再次急剧上调，与CSP增殖能力密切相关。此外，通过功能得失实验，我们的数据也证明了Abcg2/Bcrp1的动态表达在正常心肌和损伤后CSP细胞的保护和功能调节中起着关键作用。目前对Abcg2/Bcrp1动态表达的调控及其对CSP增殖和功能的调控知之甚少。因此，利用体外和体内方法的多学科方法，在这里，我们建议确定(a)控制Abcg2/Bcrp1表达的分子机制和(b) Abcg2/Bcrp1在出生后发育和损伤后调节心脏SP细胞生物学功能中的作用。从该应用中获得的数据将首次深入了解ABCG2/Bcrp1在心脏祖细胞中的作用，并为增强治疗性心脏再生提供新的分子靶点。在西化的世界里，心血管疾病仍然是最大的死亡原因，在美国，心血管疾病夺去的生命比紧随其后的四个主要原因加起来还要多。在心血管疾病中，心力衰竭的发病率继续以惊人的速度上升。最近发现的心脏干细胞/祖细胞的存在突出了这些细胞在心脏修复和再生中的治疗潜力。然而，我们对这些心脏祖细胞的生物学及其增殖和分化的调节的了解有限，使我们无法实现这种干预的全部潜力。从我们的建议中获得的结果将填补这一空白，并有助于我们了解这些心脏祖细胞的分子调控。

DESCRIPTION (provided by applicant): Chronic heart failure is the leading cause for hospitalization in the US, affecting over five million patients, with over a half million newly diagnosed cases each year. Current therapies do not address the central pathophysiology underlying the development of heart failure, namely, the loss of functional cardiomyocytes. Therefore, cardiac progenitor cells hold enormous potential for therapeutic cardiac repair and regeneration. We and others have recently confirmed the existence of one such progenitor cell population in adult murine myocardium. These so-termed cardiac side population (CSP) cells are identified in adult hearts by their distinct Hoechst 33342 dye extrusion properties, and represent a distinct progenitor cell population. While in-vitro these CSP cells are capable of both biochemical and more importantly, functional cardiomyogenic differentiation, in- vivo such differentiation occurs at an exceedingly limited rate, and is limited by the mechanisms regulating cellular survival, proliferation and differentiation. CSP cells express a unique set of ATP binding cassette (ABC) transporters, including the breast cancer resistant protein (Abcg2/Bcrp1). While these ABC transporters confer the Hoechst dye efflux properties characteristic of SP cells, emerging evidence has also suggested that members of the ABC transporter family may serve as a conduit for the interaction of stem cells with their local environment, thereby mediating the intricate regulation of progenitor cell fate and function in response to external and internal stimuli. Indeed, our preliminary data demonstrate that Abcg2/Bcrp1 expression is gradually down- regulated during the first few weeks of post-natal development and is sharply up-regulated again in response to cardiac injury, in close correlation with CSP proliferation capacity. Furthermore, through gain and loss of function experiments, our data also demonstrate that the dynamic expression of Abcg2/Bcrp1 plays a critical role in the protection and functional regulation of CSP cells in both normal myocardium and following injury. Little is known about the control of dynamic Abcg2/Bcrp1 expression and its subsequent regulation of CSP proliferation and function. Thus, utilizing a multidisciplinary approach of in-vitro and in-vivo methodologies, here, we propose to determine (a) the molecular mechanism(s) controlling Abcg2/Bcrp1 expression and (b) the role of Abcg2/Bcrp1 in regulating the biological function of cardiac SP cells during post-natal development and following injury. Data obtained from this application will provide the first insight into the role of ABCG2/Bcrp1 in cardiac progenitor cells as well as provide novel molecular targets for enhancing therapeutic cardiac regeneration. PUBLIC HEALTH RELEVANCE Cardiovascular disease remains the single greatest cause of death in the Westernized world, claiming more lives in the US than the four next leading causes, combined. Among cardiovascular disease, the incidence of heart failure continues to rise at a staggering rate. Recent identification of the existence of cardiac stem/progenitor cells highlights the therapeutic potential of using these cells in cardiac repair and regeneration. However, our limited understanding of the biology of these cardiac progenitor cells and the regulation of their proliferation and differentiation prevents us from realizing the full potential of such intervention. The results obtained from our proposal will fill this gap and contribute to our understanding of molecular regulation of these cardiac progenitor cells.