Department of Pharmacology and Cell Biophysics, University of Cincinnati College of Medicine, 231 Albert Sabin Way, Cincinnati, OH 45267-0575, USA.
Circ Res. 2011 Jun 10;108(12):1429-38. doi: 10.1161/CIRCRESAHA.110.237644. Epub 2011 Apr 14.
Heat shock proteins (Hsp) are known to enhance cell survival under various stress conditions. In the heart, the small Hsp20 has emerged as a key mediator of protection against apoptosis, remodeling, and ischemia/reperfusion injury. Moreover, Hsp20 has been implicated in modulation of cardiac contractility ex vivo. The objective of this study was to determine the in vivo role of Hsp20 in the heart and the mechanisms underlying its regulatory effects in calcium (Ca) cycling.
Hsp20 overexpression in intact animals resulted in significant enhancement of cardiac function, coupled with augmented Ca cycling and sarcoplasmic reticulum Ca load in isolated cardiomyocytes. This was associated with specific increases in phosphorylation of phospholamban (PLN) at both Ser16 and Thr17, relieving its inhibition of the apparent Ca affinity of SERCA2a. Accordingly, the inotropic effects of Hsp20 were abrogated in cardiomyocytes expressing nonphosphorylatable PLN (S16A/T17A). Interestingly, the activity of type 1 protein phosphatase (PP1), a known regulator of PLN signaling, was significantly reduced by Hsp20 overexpression, suggesting that the Hsp20 stimulatory effects are partially mediated through the PP1-PLN axis. This hypothesis was supported by cell fractionation, coimmunoprecipitation, and coimmunolocalization studies, which revealed an association between Hsp20, PP1, and PLN. Furthermore, recombinant protein studies confirmed a physical interaction between AA 73 to 160 in Hsp20 and AA 163 to 330 in PP1.
Hsp20 is a novel regulator of sarcoplasmic reticulum Ca cycling by targeting the PP1-PLN axis. These findings, coupled with the well-recognized cardioprotective role of Hsp20, suggest a dual benefit of targeting Hsp20 in heart disease.
热休克蛋白（Hsp）已知可增强各种应激条件下细胞的存活率。在心脏中，小分子 Hsp20 已成为对抗细胞凋亡、重塑和缺血/再灌注损伤的关键介质。此外，Hsp20 已被牵涉到心肌收缩力的体外调节中。本研究的目的是确定 Hsp20 在心脏中的体内作用及其对钙（Ca）循环调节作用的机制。
在完整动物中过表达 Hsp20 可显著增强心脏功能，同时伴有分离的心肌细胞中 Ca 循环和肌浆网 Ca 负荷增加。这与磷酸化肌浆网钙转运蛋白（PLN）在 Ser16 和 Thr17 上的特异性增加相关，从而减轻其对 SERCA2a 表观 Ca 亲和力的抑制作用。因此，在表达不可磷酸化 PLN（S16A/T17A）的心肌细胞中，Hsp20 的变力作用被阻断。有趣的是，Hsp20 过表达显著降低了 1 型蛋白磷酸酶（PP1）的活性，这是 PLN 信号的已知调节剂，这表明 Hsp20 的刺激作用部分通过 PP1-PLN 轴介导。这一假设得到了细胞分级分离、共免疫沉淀和共免疫定位研究的支持，这些研究揭示了 Hsp20、PP1 和 PLN 之间的关联。此外，重组蛋白研究证实了 Hsp20 的 AA 73 至 160 与 PP1 的 AA 163 至 330 之间的物理相互作用。
Hsp20 是通过靶向 PP1-PLN 轴来调节肌浆网 Ca 循环的新型调节剂。这些发现，加上 Hsp20 已被公认的心脏保护作用，表明在心脏病中靶向 Hsp20 具有双重益处。
