Dysregulation of cardiomyocyte active relaxation in heart failure with preserved ejection fraction -a mechanistic study

射血分数保留性心力衰竭（HFpEF）是一种常见的临床综合征，随着发病率的增高，目前尚无改善预后的治疗方法。HFpEF由临床因素（如动脉高血压、年龄、糖尿病、肾脏疾病）触发，其特征为心肌重塑伴舒张功能障碍。细胞机制还不清楚。我们和其他人可以表明，减缓主动（Ca 2+依赖）松弛有助于HFpEF。心肌细胞舒张期Ca ~（2+）浓度受心肌细胞膜Na/Ca交换器（NCX）的影响，NCX在心动周期中主要以正向模式（Ca ~（2+）输出）工作，也以反向模式（Ca ~（2+）输入）工作。NCX连接Ca到Na稳态。我们可以在HFPEF的动物模型中显示，NCX的慢性特异性抑制改善心肌细胞松弛和心脏功能。这可能是高度控制的细胞内Na和Ca稳态的复杂适应的结果，但机制还不清楚。在计划中的项目中，我们结合联合收割机全面的实验表征心肌细胞功能和（亚）细胞结构（Heinzel）与多尺度建模的离子信号的基础上，适应的数学模型（Falcke），允许量化的相互依赖的钙和钠处理蛋白质。我们使用已建立的HFpEF模型（肾次全切除+盐大鼠）进行细胞调节的电生理学定量，无和有特异性NCX抑制。此外，我们进行蛋白质组和磷酸化蛋白质组分析和亚细胞结构的定量（共聚焦，STORM），以深入表征兴奋收缩耦合的适应。根据实验数据改编的数学模拟使用反应扩散偏微分方程和有限元方法，考虑到细胞内微区（例如二分体）中Ca 2+稳态的局部控制。在另一种方法中，在从计划进行择期心脏手术的HFpEF患者的过量心肌样品获得的人心室心肌细胞中验证了实验和机制结果和概念。这种组合方法的结果预计将评估在无NCX抑制和有NCX抑制的HFpEF中心肌细胞Na+和Ca 2+稳态适应不良的相关步骤和靶点，并确定潜在的新靶点以改善Ca 2+依赖性收缩功能。

Heart failure with preserved ejection fraction (HFpEF) is a common syndrome with increasing prevalene and without therapeutic approach to improve prognosis. HFpEF is triggered by clinical factors (e.g. arterial hypertension, age, diabetes, kidney disease) and characterized by myocardial remodeling with diastolic dysfunction. The cellular mechanisms are not well understood. We and others could show that slowed active (Ca2+-depdendent) relaxation contributes to HFpEF. The diastolic Ca concentration in cardiomyocytes is influenced by the sarcolemmal Na/Ca exchanger (NCX) which during the cardiac cycle mainly works in forward mode (Ca out) but also in reverse mode (Ca in). The NCX connects Ca to Na homeostasis. We could show in an animal model of HFPEF that chronic specific inhibition of the NCX improves cardiomyocyte relaxation and cardiac function. This is likely a result of a complex adaptation of the highly controlled intracellular Na and Ca homeostasis, but the mechanims are not well understood. In the planned project we combine comprehensive experimental characterization of cardiomyocyte function and (sub)cellular structures (Heinzel) with multi-scale modeling of ion signaling based on an adapted mathematical model (Falcke), to allow quantification of the interdependence of the Ca- and Na-handling proteins. We use an established HFpEF model (subtotal nephrectomy + salt rat) for electrophysiological quantification of cellular regulation without and with specific NCX inhibition. In addition, we perform proteome and phosphoproteome analyses and quantification of subcellular structures (confocal, STORM) to characterize in depth the adaptation of excitation contraction coupling. The mathematical simulations adapted based on the experimental data use reaction diffusion parital differential equations and finite elements methods taking into account the local control of Ca2+ homeostasis in intracellular microdomains (e.g. dyads). In an additional approach the experimental and mechanistic results and concepts are validated in human ventricular cardiomyocytes obtained from excess myocardial samples from HFpEF patients scheduled for elective heart surgery. The results from this combined approach are expected to assess the relevant steps and targets involved in the maladaptation of cardiomyocyte Na+ and Ca2+ homeostasis in HFpEF without and with NCX inhibition and to identify potential new targets to improve Ca2+dependent contractile function.