Role of myocyte Na+ dysregulation in diabetic heart disease

摘要 2 型糖尿病 (T2D) 会增加心力衰竭、心律失常和心源性猝死的风险，即使在 没有血管并发症。然而，人们对潜在机制知之甚少。我们建议 糖尿病性心脏病的一个关键因素涉及肌细胞 Na 失调。心脏保养 Na 稳态对于维持心脏功能至关重要。肌细胞 Na 浓度 ([Na ]i) 升高导致 氧化应激并增加肌浆网 (SR) Ca2 泄漏，从而增加以下风险： 心律失常并促进心脏功能障碍。使用迟发性 T2D 大鼠模型（HIP 大鼠）显示 心肌功能障碍和心律失常，我们最近发现 T2D 心脏中 [Na ]i 增加。 出乎意料的是，较高的 [Na ]i 似乎是由通过 Na-葡萄糖协同转运蛋白的 Na 进入增强引起的 同工型 1 (SGLT1)，以前被忽视的细胞 Na 稳态参与者。此外，我们发现更高 与瘦、非糖尿病个体和心脏相比，2型糖尿病患者心脏中 SGLT1 的表达 糖尿病 HIP 大鼠与对照大鼠的比较。最近显示心脏特异性 SGLT1 过度表达会导致 肥厚和左心室功能障碍，而 SGLT1 激活与心肌病有关 由编码 AMP 激活蛋白激酶 γ2 亚基的基因突变引起。因此，证据 SGLT1 活性增强会损害心脏的说法越来越多，但对其潜在机制知之甚少 机制及其在糖尿病心肌病中的作用。基于这些发现，我们假设 SGLT1 上调通过扰动促进 T2D 心脏重塑的多因素机制 肌细胞Na稳态失调。为了检验这一总体假设，我们将 i) 评估 SGLT1 激活在 肌细胞 [Na ]i 升高，随之而来的氧化应激、更大的 SR Ca2 泄漏和自发性 T2D 中的后除极，ii) 测试 SGLT1 上调是否是心肌的适应不良 胰岛素依赖性葡萄糖摄取受损，以及 iii) 评估心脏中 SGLT1 和 [Na ]i 是否升高 来自患有 T2D 的人类。实验将结合荧光成像、电生理学、生物化学， 心脏功能、药理学工具、T2D 和转基因动物模型以及人类的体内评估 研究。通过整合大鼠和人类心脏的生理和药理学分析，该项目将 确定 SGLT1 激活和 Na 超载是否是糖尿病心脏病病理学中的关键事件 并将确定 SGLT1 作为 T2D 患者心脏并发症的新治疗靶点。

ABSTRACT Type-2 diabetes (T2D) heightens the risk of heart failure, arrhythmias and sudden cardiac death, even in the absence of vascular complications. However, the underlying mechanisms are poorly understood. We propose that a critical contributor to diabetic heart disease involves myocyte Na+ dysregulation. Maintenance of cardiac Na+ homeostasis is vital for preserving heart function. Elevated myocyte Na+ concentration ([Na+]i) causes oxidative stress and augments the sarcoplasmic reticulum (SR) Ca2+ leak, thus amplifying the risk for arrhythmias and promoting heart dysfunction. Using a rat model of late-onset T2D (the HIP rat) that displays myocardial dysfunction and arrhythmias, we recently found that [Na+]i is increased in T2D hearts. Unexpectedly, higher [Na+]i seems to be caused by enhanced Na+ entry through the Na+-glucose cotransporter isoform 1 (SGLT1), a previously ignored player in cellular Na+ homeostasis. Furthermore, we found higher SGLT1 expression in hearts from patients with T2D compared to lean, non-diabetic individuals and in hearts from diabetic HIP rats vs. control rats. Cardiac-specific SGLT1 overexpression was recently shown to cause hypertrophy and left-ventricular dysfunction, while SGLT1 activation has been linked to the cardiomyopathy caused by mutations in the gene encoding the γ2 subunit of AMP-activated protein kinase. Thus, the evidence that enhanced SGLT1 activity damages the heart is mounting, but little is known about the underlying mechanisms and its role in diabetic cardiomyopathy. Based on these findings, we hypothesize that SGLT1 upregulation contributes to the multifactorial mechanism driving cardiac remodeling in T2D by perturbing myocyte Na+ dyshomeostasis. To test this overall hypothesis, we will i) assess the role of SGLT1 activation in the myocyte [Na+]i rise and consequent oxidative stress, larger SR Ca2+ leak and spontaneous afterdepolarizations in T2D, ii) test whether SGLT1 upregulation is a maladaptation of the myocardium to impaired insulin-dependent glucose uptake, and iii) assess whether SGLT1 and [Na+]i are elevated in hearts from humans with T2D. Experiments will combine fluorescence imaging, electrophysiology, biochemistry, in vivo assessment of heart function, pharmacological tools, T2D and transgenic animal models and human studies. By integrating physiological and pharmacological analyses in rat and human hearts, this project will establish whether SGLT1 activation and Na+ overload are key events in the pathology of diabetic heart disease and will identify SGLT1 as a new therapeutic target for cardiac complications in T2D patients.