From the Medical Faculty, Department of Cardiovascular Physiology, Heinrich-Heine-University, Düsseldorf, Germany (A.-E.H., C.A., S.K., M.I., S.S., S.B., M.K.).
Department of Systems Physiology, Ruhr-University Bochum, Germany (K.U., N.H.).
Circ Res. 2018 Jul 20;123(3):342-355. doi: 10.1161/CIRCRESAHA.117.312166. Epub 2018 May 14.
Increased titin-dependent cardiomyocyte tension is a hallmark of heart failure with preserved ejection fraction associated with type-2 diabetes mellitus. However, the insulin-related signaling pathways that modify titin-based cardiomyocyte tension, thereby contributing to modulation of diastolic function, are largely unknown.
We aimed to determine how impaired insulin signaling affects titin expression and phosphorylation and thus increases passive cardiomyocyte tension, and whether metformin or neuregulin-1 (NRG-1) can correct disturbed titin modifications and increased titin-based stiffness.
We used cardiac biopsies from human diabetic (n=23) and nondiabetic patients (n=19), cultured rat cardiomyocytes, left ventricular tissue from apolipoprotein E-deficient mice with streptozotocin-induced diabetes mellitus (n=12-22), and ZSF1 (obese diabetic Zucker fatty/spontaneously hypertensive heart failure F1 hybrid) rats (n=5-6) and analyzed insulin-dependent signaling pathways that modulate titin phosphorylation. Titin-based passive tension was measured using permeabilized cardiomyocytes. In human diabetic hearts, we detected titin hypophosphorylation at S4099 and hyperphosphorylation at S11878, suggesting altered activity of protein kinases; cardiomyocyte passive tension was significantly increased. When applied to cultured cardiomyocytes, insulin and metformin increased titin phosphorylation at S4010, S4099, and S11878 via enhanced ERK1/2 (extracellular signal regulated kinase 1/2) and PKCα (protein kinase Cα) activity; NRG-1 application enhanced ERK1/2 activity but reduced PKCα activity. In apolipoprotein E-deficient mice, chronic treatment of streptozotocin-induced diabetes mellitus with NRG-1 corrected titin phosphorylation via increased PKG (protein kinase G) and ERK1/2 activity and reduced PKCα activity, which reversed the diabetes mellitus-associated changes in titin-based passive tension. Acute application of NRG-1 to obese ZSF1 rats with type-2 diabetes mellitus reduced end-diastolic pressure.
Mechanistically, we found that impaired cGMP-PKG signaling and elevated PKCα activity are key modulators of titin-based cardiomyocyte stiffening in diabetic hearts. We conclude that by restoring normal kinase activities of PKG, ERK1/2, and PKCα, and by reducing cardiomyocyte passive tension, chronic NRG-1 application is a promising approach to modulate titin properties in heart failure with preserved ejection fraction associated with type-2 diabetes mellitus.
肌联蛋白依赖的心肌细胞张力增加是射血分数保留型心力衰竭伴 2 型糖尿病的一个标志。然而，调节基于肌联蛋白的心肌细胞张力从而调节舒张功能的胰岛素相关信号通路在很大程度上尚不清楚。
我们旨在确定受损的胰岛素信号如何影响肌联蛋白的表达和磷酸化，从而增加心肌细胞的被动张力，以及二甲双胍或神经调节蛋白 1（NRG-1）是否可以纠正肌联蛋白修饰的紊乱和增加的基于肌联蛋白的僵硬。
我们使用了来自人类糖尿病（n=23）和非糖尿病患者（n=19）的心脏活检，培养的大鼠心肌细胞，载脂蛋白 E 缺陷型小鼠的左心室组织，该组织用链脲佐菌素诱导糖尿病（n=12-22），以及 ZSF1（肥胖型糖尿病 Zucker 肥胖/自发性高血压心力衰竭 F1 杂种）大鼠（n=5-6），并分析了调节肌联蛋白磷酸化的胰岛素依赖性信号通路。使用透化的心肌细胞测量基于肌联蛋白的被动张力。在人类糖尿病心脏中，我们检测到肌联蛋白在 S4099 处的低磷酸化和 S11878 处的高磷酸化，表明蛋白激酶的活性改变；心肌细胞的被动张力显著增加。当应用于培养的心肌细胞时，胰岛素和二甲双胍通过增强 ERK1/2（细胞外信号调节激酶 1/2）和 PKCα（蛋白激酶 Cα）活性增加肌联蛋白在 S4010、S4099 和 S11878 处的磷酸化；NRG-1 的应用增强了 ERK1/2 活性，但降低了 PKCα 活性。在载脂蛋白 E 缺陷型小鼠中，NRG-1 对链脲佐菌素诱导的糖尿病的慢性治疗通过增加 PKG（蛋白激酶 G）和 ERK1/2 活性以及降低 PKCα 活性来纠正肌联蛋白磷酸化，从而逆转了与糖尿病相关的基于肌联蛋白的被动张力变化。急性应用 NRG-1 于患有 2 型糖尿病的肥胖 ZSF1 大鼠可降低舒张末期压力。
从机制上讲，我们发现受损的 cGMP-PKG 信号和升高的 PKCα 活性是糖尿病心脏中基于肌联蛋白的心肌细胞僵硬的关键调节剂。我们得出的结论是，通过恢复 PKG、ERK1/2 和 PKCα 的正常激酶活性，以及降低心肌细胞的被动张力，慢性 NRG-1 应用是调节射血分数保留型心力衰竭伴 2 型糖尿病中肌联蛋白特性的一种有前途的方法。
