Paracrine actions of fibroblasts promote pathologic cardiac myocyte remodeling in Duchenne muscular dystrophy

项目总结：我们研究的长期目标是提高我们对病理学的理解。 Duchenne肌营养不良症(DMD)的机制，并利用这一知识来推动治疗。 治疗呼吸功能不全和肌肉恶化的其他并发症的进展导致心脏 疾病成为DMD发病和死亡的主要原因。因此，迫切需要 确定促进DMD相关心脏疾病的特定致病机制，以便有针对性地 治疗学可以被开发出来。复杂的病理始于机械性受损的心肌细胞，但 与继发性缺陷交织在一起，这些缺陷对疾病的发展起到了重要作用。纤维化是一种 DMD心脏受累的最早临床表现发生在心功能不全之前 在病理发展的早期，激活的成纤维细胞的存在。成纤维细胞产生细胞外 由纤维性瘢痕组成的基质，但尚不清楚它们是否具有其他适应不良功能 影响疾病进展。我们的初步研究结果表明，成纤维细胞生长因子23在很大程度上 在DMD的遗传性小鼠模型MDX小鼠的心脏成纤维细胞中增加。FGF23升高显著 肾脏病患者发生与心血管疾病和死亡率相关的重要临床事件 在疾病和普通人群中。FGF23是一种主要与其辅助受体协同工作的激素 Klotho，但也可以刺激非典型细胞靶点的病理信号。FGF23发挥病理作用 通过与成纤维细胞生长因子受体(FGFR)4结合，而不依赖于Klotho，该受体在心肌细胞中不表达 心。我们的中心假设是营养不良的心脏成纤维细胞对心肌细胞起旁分泌作用。 通过FGF23，从而激活FGFR4，从而促进DMD的心脏疾病。我们的初步调查结果显示 Klotho在MDX小鼠中具有心脏保护作用，有力地支持了我们的假设，即FGF23信号参与了 对心脏重塑很重要。核心假设将通过追求两个全面的具体 目标。在目标1中，我们将测试FGF23是否是由心脏成纤维细胞产生的旁分泌因子，它促进 结合条件遗传学方法研究Dystrophin缺陷型心脏病理和功能缺陷 进行体外细胞培养实验。在目标2中，我们将确定FGFR4在心肌细胞中的激活 通过补充性功能丧失和功能获得影响dystrophin缺乏性心脏重塑和功能 功能遗传学方法。这项拟议的研究具有创新性，因为它预计将表明成纤维细胞 对心肌细胞发挥调节作用并建立FGF23/FGFR4信号通路作为新的致病因子 DMD的发病机制。这一贡献意义重大，因为预计它将提供强大的机械性 有理由将FGF23/FGFR4作为治疗DMD的靶点。

PROJECT SUMMARY: The long-term goal of our research is to improve our understanding of the pathologic mechanisms of Duchenne muscular dystrophy (DMD) and to leverage that knowledge to advance therapeutics. Progress in treating respiratory insufficiency and other complications of muscle deterioration has led to cardiac disease emerging as a principal cause of morbidity and mortality in DMD. Consequently, there is a critical need to identify the specific pathogenic mechanisms that promote DMD-related cardiac disease so that targeted therapeutics can be developed. The complex pathology initiates with mechanically compromised myocytes but is intertwined with secondary defects that contribute importantly to disease progression. Fibrosis is one of the earliest clinical manifestations of cardiac involvement in DMD occurring prior to ventricular dysfunction indicating the presence of activated fibroblasts early in the progression of pathology. Fibroblasts produce extracellular matrix that comprises fibrotic scar, but it is not known whether they possess other maladaptive functions that affect disease progression. Our preliminary findings now show that fibroblast growth factor (FGF) 23 is greatly increased in cardiac fibroblasts of mdx mice, a genetic mouse model of DMD. Elevated FGF23 is remarkably associated with important clinical events related to cardiovascular disease and mortality in patients with renal disease and in the general population. FGF23 is a hormone that mostly works in cooperation with its co-receptor Klotho, but can also stimulate pathological signaling in atypical cellular targets. FGF23 exerts pathologic effects on cardiac myocytes by binding to FGF receptor (FGFR) 4 independent of Klotho, which is not expressed in the heart. Our central hypothesis is that dystrophic cardiac fibroblasts exert paracrine effects on cardiac myocytes via FGF23, thereby activating FGFR4 to promote cardiac disease in DMD. Our preliminary findings showing that Klotho is cardioprotective in mdx mice strongly supports our hypothesis that FGF23 signaling contributes importantly to cardiac remodeling. The central hypothesis will be tested by pursuing two comprehensive specific aims. In Aim 1 we will test whether FGF23 is a paracrine factor produced by cardiac fibroblasts that promotes dystrophin-deficient cardiac pathology and functional defects using a conditional genetic approach combined with ex vivo cell culture experiments. In Aim 2 we will determine whether FGFR4 activation in cardiac myocytes affects dystrophin-deficient cardiac remodeling and function using complementary loss-of-function and gain-of- function genetic approaches. The proposed research is innovative because it is predicted to show that fibroblasts exert regulatory effects on cardiac myocytes and establish FGF23/FGFR4 signaling as a novel pathogenic mechanism of DMD. This contribution is significant because it is expected to provide strong mechanistic justification for modulating FGF23/FGFR4 as a therapeutic target to treat DMD.