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

项目概述：我们研究的长期目标是提高我们对病理性 杜氏肌营养不良症（DMD）的发病机制，并利用这些知识来推进治疗。 在治疗呼吸功能不全和肌肉退化的其他并发症方面的进展导致了心脏 是DMD发病和死亡的主要原因。因此， 确定促进DMD相关心脏病的特定致病机制， 可以开发治疗方法。复杂的病理始于机械性受损的肌细胞， 与继发性缺陷交织在一起，这些继发性缺陷对疾病进展有重要作用。纤维化是一种 DMD心脏受累的最早临床表现发生在心室功能障碍之前，表明 在病理学进展的早期存在活化的成纤维细胞。成纤维细胞产生细胞外 基质，包括纤维化瘢痕，但不知道它们是否具有其他适应不良的功能， 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（FGF）23是非常重要的。 在mdx小鼠（DMD的遗传小鼠模型）的心脏成纤维细胞中增加。升高的FGF 23显著地 与肾衰竭患者的心血管疾病和死亡率相关的重要临床事件 疾病和一般人群。FGF 23是一种激素，主要与其辅助受体合作 Klotho，但也可以刺激非典型细胞靶点的病理信号传导。FGF 23发挥病理作用 通过与不依赖于Klotho的FGF受体（FGFR）4结合，在心肌细胞上表达， 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产生旁分泌作用 通过FGF 23，从而激活FGFR 4以促进DMD中的心脏疾病。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，这有力地支持了我们的假设，即FGF 23信号通路有助于 对心脏重塑很重要中心假设将通过追求两个全面的具体测试 目标。在目标1中，我们将测试FGF 23是否是由心脏成纤维细胞产生的旁分泌因子，其促进心脏成纤维细胞增殖。 使用条件遗传学方法结合抗肌萎缩蛋白缺陷的心脏病理学和功能缺陷 离体细胞培养实验。在目标2中，我们将确定心肌细胞中FGFR 4的激活是否 影响肌营养不良蛋白缺乏的心脏重塑和功能，使用互补的功能丧失和功能获得， 功能遗传学方法。这项研究具有创新性，因为据预测， 对心肌细胞发挥调节作用，并将FGF 23/FGFR 4信号转导作为一种新的致病因子， DMD机制这一贡献是重要的，因为它有望提供强有力的机制， 这是调节FGF 23/FGFR 4作为治疗DMD的治疗靶标的理由。

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.