Role of Wnts in Cardiac Repair

描述(由申请人提供)： 项目摘要心脏病是美国死亡率和死亡率的主要案例，并正在迅速成为发展中国家的一个主要公共卫生问题。成人心脏具有有限的再生能力，不能用新的心肌细胞取代心肌损伤后受损的心肌。因此，纤维化和疤痕形成是成人心脏常见的典型“损伤反应”。无功能的瘢痕组织对心脏的泵血能力没有贡献，随着时间的推移，纤维组织对心脏施加的血液动力学负担增加，导致不利的心脏重构、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保护心肌梗死后的心功能大有可为。在这项建议中，我们证明，心肌损伤后48小时，心脏内注射分泌相关卷曲蛋白2(SFRP2)，一种细胞外Wnt拮抗剂，显著减少心脏瘢痕形成。虽然这表明WNTS作为促纤维化分子的作用，但WNTS在梗塞心脏中的表达和功能是完全未知的。WNTs是一个由19个亲脂蛋白组成的家族，在器官发生包括心脏发育过程中起着至关重要的作用，但在未受损伤的成年心脏中，WNTs的表达水平最低。我们提供的证据表明，一些WNTT在损伤后重新表达，WNT1的表达在心脏损伤后显著升高，并诱导心脏成纤维细胞的增殖和激活。梗死区的心脏成纤维细胞是Wnt反应的，并上调Wnt1信号的下游介质。我们进一步证明，在成纤维细胞产生部位的胚胎心脏也是WNT反应的。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现依赖Wnt1的发育程序，以促进心脏纤维化和修复；(Ii)阻断心脏成纤维细胞中的Wnt信号将减少心脏纤维化，保护损伤后的心功能。我们的具体目标是：A)确定受损心脏是否概括了WNT1表达和反应的发育程序；B)确定介导心脏成纤维细胞激活的WNT1下游靶点；最后C)确定在成纤维细胞特异性阻断WNT/2连环蛋白信号后，梗死心脏心功能的变化。综上所述，我们提出的使用分子、遗传学和生理学方法的研究将剖析WNT1在调节受损心脏心肌纤维化中的作用和机制。识别分泌Wnts的细胞成分、对Wnts有反应的靶细胞以及阻断Wnt1信号的生理益处可能会导致心肌梗死的新疗法。

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.