Role of AE3 and NHE1 in cardiomyocyte homeostasis and remodeling

心肌细胞中Na+/H+交换的刺激是心脏病理的共同特征。值得注意的是，Na+/H+交换剂NHE1的活化并不一定会导致pHi的下降，因为它可以通过诱导阴离子交换剂AE3来平衡。这种同时激活被认为可以提高细胞内Na+浓度，从而抑制Na+/Ca2+交换。伴随的细胞内Ca2+积累可能会促进心脏肥厚。事实上，在多种动物研究中，NHE1抑制剂对心脏重塑有积极作用。由于NHE1和AE3之间的功能相互作用，我们研究了AE3在完整心脏和病变心脏中的作用。我们培育了ae3基因敲除小鼠，结果显示心脏与体重之比显著降低。我们现在建立了一个固定的AE3小鼠，这将使我们能够在心脏中特异性地破坏AE3。这只小鼠的体内特征将包括心电图、血压和超声心动图。体外分析将涵盖心脏重量、组织学、细胞内Na+浓度、心肌细胞收缩力、pHi和Ca2+瞬态的调节。由于AE3的作用，我们随后将评估无AE3时的心脏重构模型。同时，我们将通过38个转基因诱导方法在心肌细胞中过表达AE3和/或NHE1，以验证激活Na+/H+交换和/或阴离子交换可以诱导心脏重构的假设。

Stimulation of Na+/H+-exchange in cardiomyocytes is a common feature in cardiac pathology. Remarkably, activation of the Na+/H+-exchanger NHE1 does not necessarily entail a fall of pHi, because it can be balanced by induction of the anion-exchanger AE3. This simultaneous activation is thought to raise intracellular Na+ concentration and hence inhibit Na+/Ca2+-exchange. The concomitant intracellular Ca2+ accumulation may then promote cardiac hypertrophy. Indeed, NHE1 inhibitors had a positive effect on cardiac remodeling in diverse animal studies. Because of the functional interplay between NHE1 and AE3, we address the role of AE3 in the intact and the diseased heart. We have generated constitutive AE3-knockout mice, which revealed a significant reduction of the heart to body weight ratio. We now established a floxed Ae3-mouse that will allow us to disrupt AE3 specifically in the heart. In vivo characterization of this mouse will include electrocardiograms, blood pressure and echocardiography. In vitro analysis will cover heart weights, histology, intracellular Na+ concentration, cardiomyocyte contractility, regulation of pHi and Ca2+ transients. Because of the suggested role of AE3 we will subsequently assess cardiac remodeling models in the absence of AE3. In parallel, we will overexpress AE3 and/or NHE1 in cardiomyocytes by a 38 transgenic inducible approach to test the hypothesis that activation of Na+/H+-exchange and/or anion-exchange can induce cardiac remodeling.