Loss of heat shock protein HSPA4 aggravates pressure overload-induced myocardial damage

Failure of molecular chaperones to direct the correct folding of newly synthesized proteins leads to the accumulation of misfolded proteins in cells. HSPA4 is a member of the heat shock protein 110 family (HSP110) that acts as a nucleotide exchange factor of HSP70 chaperones. We found that the expression of HSPA4 is upregulated in murine hearts subjected to pressure overload and in failing human hearts. To investigate the cardiac function of HSPA4, Hspa4 knockout (KO) mice were generated and exhibited cardiac hypertrophy and fibrosis. Hspa4 KO hearts were characterized by a significant increase in heart weight/body weight ratio, elevated expression of hypertrophic and fibrotic gene markers, and concentric hypertrophy with preserved contractile functions. Cardiac hypertrophy in Hspa4 KO hearts was associated with enhanced activation of gp130-STAT3, CaMKII, and calcineurin-NFAT signaling. Further analyses revealed a significant increase in cross sectional area of cardiomyocytes, and in expression levels of hypertrophic markers in cultured neonatal Hspa4 KO cardiomyocytes suggesting that the hypertrophy of mutant mice was a result of primary defects in cardiomyocytes. Gene expression profile in hearts of 3.5-week-old mice revealed a differentially expressed gene sets related to ion channels and stress response. Taken together, these results reveal that HSPA4 is implicated in protection against pressure overload-induced heart failure. Total RNA was extracted from heart ventricles of 3.5-week-old Hspa4+/+ and Hspa4-/- males (n = 3 mice for each genotype).分子伴侣（molecular chaperones）无法指导新合成蛋白质进行正确折叠，会导致细胞内错误折叠蛋白质的积累。HSPA4属于热休克蛋白110家族（heat shock protein 110 family，HSP110），可作为HSP70分子伴侣的核苷酸交换因子。本研究发现，在经受压力超负荷的小鼠心脏以及衰竭的人类心脏中，HSPA4的表达均会上调。为探究HSPA4的心脏功能，我们构建了Hspa4基因敲除（knockout，KO）小鼠，该小鼠表现出心脏肥大与心肌纤维化特征。Hspa4 KO小鼠的心脏表现为心脏重量/体重比显著升高、肥大与纤维化相关基因标志物的表达水平上升，同时伴有收缩功能保留的向心性肥大。Hspa4 KO小鼠的心脏肥大与gp130-STAT3、CaMKII以及calcineurin-NFAT信号通路的激活增强密切相关。进一步分析显示，体外培养的新生Hspa4 KO心肌细胞的横截面积显著增大，肥大标志物的表达水平升高，提示该突变小鼠的心肌肥大源于心肌细胞的原发性缺陷。对3.5周龄小鼠心脏的基因表达谱分析发现，存在与离子通道及应激反应相关的差异表达基因集。综上，本研究结果表明HSPA4在抵御压力超负荷诱导的心力衰竭过程中发挥保护作用。本研究从3.5周龄的Hspa4+/+与Hspa4-/-雄性小鼠（每种基因型各3只）的心室中提取总RNA。