Role of Wnts in Cardiac Repair

描述（由申请人提供）： 心脏病是美国死亡率和死亡率的主要病例，并迅速成为发展中国家的主要公共卫生问题。成人心脏具有有限的再生能力，并且不能用新的心肌细胞替换心脏损伤后受损的心肌。因此，纤维化和瘢痕形成是在成人心脏中看到的典型的“损伤反应”。无功能的瘢痕组织对心脏的泵送能力没有贡献，并且随着时间的推移，由纤维组织施加在心脏上的增加的血液动力学负担导致不利的心脏重塑、心脏扩张和心力衰竭。因此，抑制心肌梗死后心脏纤维化的策略对心肌梗死后心脏功能的保护具有很大的希望。我们在这个建议中证明，心脏内注射分泌相关卷曲蛋白2（Sfrp 2），细胞外Wnt拮抗剂，心肌损伤后48小时，显着减少心脏瘢痕形成。尽管这表明Wnt作为促纤维化分子的作用，但Wnt在梗塞心脏中的表达和功能是完全未知的。Wnts是一个由19种亲脂性蛋白组成的家族，在器官发生（包括心脏发育）过程中起着至关重要的作用，但成年未受伤的心脏最低限度地表达Wnts。我们提供的证据表明，一些Wnt在损伤后重新表达，Wnt 1的表达在心脏损伤后显著升高，并诱导心脏成纤维细胞增殖和活化。梗死部位的心脏成纤维细胞是Wnt反应性的，并上调Wnt 1信号传导的下游介质。我们进一步证明，胚胎心脏在网站的成纤维细胞生成也Wnt响应。考虑到这些观察结果，我们假设（i）成人心脏在心脏损伤后重演了Wnt 1依赖性发育程序，以促进心脏纤维化和修复;（ii）心脏成纤维细胞中Wnt信号传导的中断将减少心脏纤维化并保护损伤后的心脏功能。我们的具体目标是：A）确定受损心脏是否重现Wnt 1表达和反应的发育程序; B）确定介导心脏成纤维细胞活化的Wnt 1下游靶点;以及最后C）确定梗死心脏中成纤维细胞特异性中断Wnt/2连环蛋白信号传导后心脏功能的变化。总之，我们提出的研究使用分子，遗传和生理学的方法将剖析Wnt 1在调节损伤心脏的心脏纤维化中的作用和机制。鉴定分泌Wnt的细胞成分、对Wnt应答的靶细胞以及中断梗死心脏中Wnt 1信号传导的生理益处可能会导致心肌梗死的新疗法。 公共卫生相关性： 心脏病发作后的成人心脏不会再生受损的肌肉，而是在受伤部位形成无功能的疤痕。我们已经确定了一种发育上重要的分子，称为Wnt 1，有助于受伤心脏的瘢痕形成。在这项提案中，我们将确定Wnt 1如何调节受损心脏中的瘢痕形成，并旨在通过操纵Wnt信号来最大限度地减少瘢痕形成并改善心脏功能。

DESCRIPTION (provided by applicant): PROJECT SUMMARY Heart disease is a leading case of mortality and mortality in the United States and is rapidly emerging as a major public health problem in the developing world. The adult heart possesses a limited ability to regenerate and is unable to replace damaged heart muscle after cardiac injury with new cardiac muscle cells. Consequently, fibrosis and scarring are the typical "response to injury" seen in the adult heart. Nonfunctioning scar tissue does not contribute towards the pumping ability of the heart and over time the increased hemodynamic burden imposed on the heart by the fibrous tissue leads to adverse cardiac remodeling, cardiac dilatation and heart failure. Consequently strategies to inhibit cardiac fibrosis after myocardial infarction hold great promise for preserving cardiac function after myocardial infarction. We demonstrate in this proposal that, intra-cardiac injection of Secreted related frizzled protein 2 (Sfrp2), an extracellular Wnt antagonist, 48 hours after myocardial injury, dramatically decreases cardiac scarring. Although this suggests a role of Wnts as pro- fibrotic molecules, the expression and function of Wnts in the infarcted heart are completely unknown. Wnts are a family of 19 lipophilic proteins that play a crucial role during organogenesis including heart development but the adult uninjured heart minimally expresses Wnts. We provide evidence that several Wnts are re- expressed following injury and expression of Wnt1 is dramatically elevated following cardiac injury and induces cardiac fibroblast proliferation and activation. Cardiac fibroblasts at the infarct site are Wnt responsive and up-regulate downstream mediators of Wnt1 signaling. We further demonstrate that the embryonic heart at sites of fibroblast generation is also Wnt responsive. Considering these observations, we have hypothesized (i) that the adult heart recapitulates a Wnt1 dependent developmental program after cardiac injury to promote cardiac fibrosis and repair and (ii) interruption of Wnt signaling in the cardiac fibroblast will decrease cardiac fibrosis and preserve cardiac function after injury. Our specific aims are to A) To determine whether the injured heart recapitulates a developmental program of Wnt1 expression and response B) To determine downstream targets of Wnt1 that mediate cardiac fibroblast activation and finally C) To determine changes in cardiac function following fibroblast specific interruption of Wnt/2 catenin signaling in the infarcted heart. In summary, our proposed studies using molecular, genetic and physiologic approaches will dissect the role and mechanisms of Wnt1 in regulating cardiac fibrosis in the injured heart. Identification of cell components secreting Wnts, target cells responding to Wnts, and physiological benefits of interrupting Wnt1 signaling in the infarcted heart can potentially lead to novel therapies for myocardial infarction. PUBLIC HEALTH RELEVANCE: PROJECT NARRATIVE The adult heart following a heart attack does not regenerate damaged muscle but forms a non-functioning scar in the injured region. We have identified that a developmentally important molecule known as Wnt1 contributes to scar formation in the injured heart. In this proposal, we will determine how Wnt1 regulates scar formation in the injured heart and aim to minimize scar formation and improve cardiac function through manipulation of Wnt signaling.