The Role of Sca-1+ and ABCG2+ Cardiac Progenitor Cells in Endogenous Heart Regeneration

 描述（由申请人提供）：心力衰竭（HF）是多种心血管疾病的终末期形式，仍然是美国和全球发病率和死亡率的主要来源。进展为HF通常是由于心肌梗死（MI）后心脏的不良结构和功能重塑。其特征在于由于缺血性损伤而导致存活心肌细胞的进行性丧失，并被不能支持心脏收缩需求的纤维化瘢痕替代，导致功能性失代偿、病理性肥大和衰竭。从历史上看，成年哺乳动物的心脏被认为缺乏在出生后生长或损伤后产生新的心肌细胞的能力，完全依赖于组织纤维化和瘢痕形成作为唯一的愈合手段。然而，在过去的二十年中，越来越多的证据表明，成年哺乳动物（包括人类）具有适度的心脏再生潜力，这表明缺失心肌组织的再生是限制HF进展的潜在治疗途径。然而，心脏的内源性再生能力似乎不足以解决MI后发生的大规模损伤。更重要的是，内源性心脏再生的潜在分子机制仍然没有得到解决。使用抗原标记物（c-Kit、Sca-1和侧群[SP]细胞标记物ABCG 2）分离和表征成人心脏中的几种类型的心脏驻留祖细胞（CPC）已经引起了对驻留心脏干/祖细胞的相当大的关注（和几项临床试验），驻留心脏干/祖细胞是成人心脏中心肌细胞更新和替换的潜在重要贡献者。然而，到目前为止，还没有共识的程度，CPC贡献新的心肌细胞的成年心脏在生理或病理条件下。这部分是因为该领域主要采用CPC的离体分离、扩增和移植，但尚未进行明确的遗传学研究来确定这些细胞在其内源性小生境内的体内生物学作用。该提案旨在解决这一问题，并确定两类CPC- Sca-1+细胞和ABCG 2 + SP细胞-在正常生理生长期间或MI后向成人心脏贡献新肌细胞的程度。先前的研究已经证明Sca 1+和ABCG 2 + CPC在体外具有一定程度的心肌形成潜力。使用申办方实验室生成的转基因小鼠模型，我们将采用遗传谱系追踪方法定量评估这些CPC在1）正常生理生长和衰老期间或2）MI损伤后对体内新心肌细胞形成的贡献和功能意义。申办者的实验室最近采用这种遗传方法来确定c-Kit+ CPC的贡献（货车Berlo et.自然。2014），并且发现c-Kit+细胞主要贡献脉管系统，但随着衰老和损伤，对心脏贡献最小程度的心肌细胞。结合这些数据，我们提出的研究将解决心脏再生中一个长期存在的中心问题：在多大程度上常驻心脏祖细胞（CPC）有助于成年心脏在衰老期间或损伤后再生的内源性能力？这些研究将有助于阐明成人心脏内在再生能力的分子机制，并提供关于CPC在恢复MI后受损心肌、缓解HF进展方面的潜在治疗应用的见解。

 DESCRIPTION (provided by applicant): Heart failure (HF), which is the end-stage form of multiple cardiovascular diseases, remains a leading source of morbidity and mortality in the United States and worldwide. Progression to HF often results from adverse structural and functional remodeling of the heart following myocardial infarction (MI). This is characterized by the progressive loss of viable cardiomyocytes due to ischemic injury and replacement with a fibrotic scar that is unable to support the contractile needs of the heart, leading to functional decompensation, pathological hypertrophy, and failure. Historically, the adult mammalian heart was thought to lack the capacity to generate new cardiomyocytes following postnatal growth or after injury, relying exclusively on tissue fibrosis and scarring as the only means of healing. However, growing evidence over the past two decades has now demonstrated a modest degree of cardiac regenerative potential in adult mammals including humans, suggesting that regeneration of lost myocardial tissue is a potential therapeutic avenue for limiting HF progression. However, the endogenous regenerative capacity of the heart appears insufficient to resolve the massive injury that occurs post-MI. More importantly, the underlying molecular mechanisms of endogenous cardiac regeneration remain unresolved. The isolation and characterization of several types of cardiac-resident progenitor cells (CPCs) in the adult heart using antigenic markers (c-Kit, Sca-1 and the side population [SP] cell marker ABCG2) has led to considerable attention (and several clinical trials) on resident cardiac stem/progenitor cells a potential significant contributors to cardiomyocyte turnover and replacement in the adult heart. However, as-yet there is no consensus as to the extent that CPCs contribute new cardiomyocytes to the adult heart under physiological or pathological conditions. This is in part because the field has largely employed ex vivo isolation, expansion, and transplantation of CPCs, but no definitive genetic studies have been performed to determine the biological role of these cells in vivo, within their endogenous niches. This proposal seeks to address this issue and define the extent that two classes of CPCs - Sca-1+ cells and ABCG2+ SP cells - contribute new myocytes to the adult heart during normal physiological growth or post-MI. Previous studies have demonstrated that Sca1+ and ABCG2+ CPCs possess some degree of cardiomyogenic potential in vitro. Using transgenic mouse models generated in the Sponsor's lab, we will employ a genetic lineage tracing approach to quantitatively assess the contribution and functional significance of these CPCs to new cardiomyocyte formation in vivo, during 1) normal physiological growth and aging or 2) after MI injury. The Sponsor's lab has recently employed this genetic approach to define the contribution of c-Kit+ CPCs (van Berlo et. al. Nature. 2014), and found that c-Kit+ cells contribute primarily vasculature but a minimal degree of cardiomyocytes to the heart with aging and injury. Taken together with these data, our proposed studies will address a long-standing central question in cardiac regeneration: to what extent do resident cardiac progenitor cells (CPCs) contribute to the endogenous capacity of the adult heart to regenerate during aging or after injury? These studies will serve to both elucidate the molecular mechanisms underlying the intrinsic regenerative capacity of the adult heart, and provide insight as to potential therapeutic application of CPCs in restoring damaged myocardium post-MI, mitigating the progression to HF.