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

心力衰竭伴保留射血分数（HFpEF）是一种常见的综合征，其患病率不断增加，且没有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、肾病）引发，以心肌重构伴舒张功能障碍为特征。细胞机制尚不清楚。我们和其他人可以证明，活性（Ca2+依赖性）松弛减慢有助于HFpEF。心肌细胞舒张期Ca浓度受肌层Na/Ca交换器（NCX）的影响，NCX在心脏周期中主要以正向模式（Ca out）工作，但也以反向模式（Ca in）工作。NCX连接钙和钠的稳态。我们可以在HFPEF动物模型中证明慢性特异性抑制NCX可改善心肌细胞松弛和心功能。这可能是细胞内高度控制的Na和Ca稳态的复杂适应的结果，但其机制尚不清楚。在计划中的项目中，我们将心肌细胞功能和（亚）细胞结构的综合实验表征（Heinzel）与基于适应性数学模型的离子信号多尺度建模（Falcke）相结合，以量化Ca-和na处理蛋白的相互依赖性。我们使用已建立的HFpEF模型（次全肾切除+盐大鼠）对细胞调节进行电生理量化，并对NCX特异性抑制进行电生理量化。此外，我们还进行了蛋白质组学和磷酸化蛋白质组学分析，并对亚细胞结构（共聚焦，STORM）进行了量化，以深入表征兴奋收缩耦合的适应性。基于实验数据的数学模拟采用反应扩散偏微分方程和有限元方法，考虑到细胞内微域（如双元体）Ca2+稳态的局部控制。在另一种方法中，实验和机械结果和概念在从计划进行择期心脏手术的HFpEF患者的多余心肌样本中获得的人类心室心肌细胞中得到验证。这种联合方法的结果有望评估在没有NCX抑制和有NCX抑制的HFpEF中心肌细胞Na+和Ca2+稳态失调的相关步骤和目标，并确定改善Ca2+依赖性收缩功能的潜在新靶点。

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.