低密度脂蛋白受体相关蛋白6在机械应力引起心肌细胞损伤中的作用和分子机制研究

Mechanical stresses produced by increases in cardiac afterload induce adaptive cardiomyocytes hypertrophy, and may subsequently result in mitochondrial dysfunction and cardiomyocytes injury or death when the stimulus persist, however, the molecular mechanisms still remain elucidative. LDL receptor-related protein 6 (LRP6), a co-receptor of WNTs, has been reported to be involved in the differentiation and proliferation of stem cells. But whether it would be involved in cardiomyocytes dysfunction is unclear. Recently, we observed in our preliminary studies that mechanical stresses induced downregulation of LRP6 both in cultured cardiomyocytes and hearts of mice. We further generated cardiac specific and conditional LRP6-knockout mice, and found an enlarged heart with the lowered cardiac function, injured mitochondria and increased mitophagy in the mice, suggesting that LRP6 might play a critical role in protection of mitochondria and cardiomyocytes. Moreover, we also observed that knockdown of LRP6 in cardiomyocytes induced a decreased AMPK activation and an enhanced BNIP3, a mitochondrial protein expression. We therefore plan to investigate whether LRP6 knockdown leads to mitochondrial injury through AMPK pathway and/or BNIP3 signaling in cardiomyocytes and whether overexpression of LRP6 in cardiomyocytes could improve mitochondrial injury and cardiomyocytes dysfunction induced by mechanical stresses. Our study will expand the understanding of the functions of LRP6 and provide evidence for LRP6 to regulate cardiomyocytes function through regulation of mitochondria.

心脏后负荷增加产生的机械应力在早期引起代偿性心肌细胞肥大，后期因线粒体产生能量不足导致细胞受损进而死亡，其分子机制有待进一步阐明。我们在前期研究中发现持续机械应力引起心肌细胞低密度脂蛋白受体相关蛋白6（LRP6）明显下调；心脏特异性LRP6敲除导致小鼠心脏扩大、心肌细胞功能损害、线粒体自噬增加及功能障碍、AMPK磷酸化下调及线粒体外膜蛋白BNIP3上调，提示LRP6是维持线粒体稳态进而维持心肌细胞功能的重要分子。本项目拟研究机械应力下LRP6下调通过AMPK和/或BNIP3通路介导线粒体损伤、导致心肌细胞功能障碍继而死亡的分子机制，并进一步确定心肌特异性过表达LRP6能否改善持续机械应力导致的线粒体功能障碍，修复心肌细胞损伤。该研究将拓展以往对LRP6功能和机制的认识，阐明 LRP6调控心肌细胞能量代谢、维持心肌细胞功能的机制，为高血压等机械应力导致的心肌细胞损伤的有效干预提供新的靶点。

心脏后负荷增加产生的机械应力在早期引起代偿性心肌细胞肥大，后期细胞受损失代偿进而死亡，其分子机制有待进一步阐明。我们在本项目的研究中观察到持续压力负荷介导心肌细胞低密度脂蛋白受体相关蛋白6（LRP6）先升高后明显下调；他莫昔芬诱导型心脏特异性LRP6敲除导致小鼠心衰表型，观察到心脏扩大、心肌肥大、线粒体自噬降解障碍以及功能障碍和脂肪酸代谢障碍等。后发现其机制AMPK和/或BNIP3通路关系不大，主要是激活Drp1信号有关。杂合子LRP6敲低的小鼠基态下正常，但压力负荷情况下容易心衰，心肌特异性LRP6过表达小鼠可明显抑制压力负荷小鼠心肌肥大和纤维化，延缓心衰的发展。进一步发现溶酶体标志蛋白LAMP2表达上调，溶酶体抑制剂可弱化LRP6的心脏保护作用。此外还发现LRP6敲除后心房纤维化与β2微球蛋白水平上调有关。进一步发现压力负荷可促进心肌β2微球蛋白分泌激活成纤维细胞EGFR介导心脏纤维化。本研究阐明LRP6调控心肌细胞自噬、脂肪酸代谢，溶酶体功能等维持心肌细胞功能的机制，为压力负荷等机械应力导致的心肌细胞损伤以及成纤维细胞活化的有效干预提供新的靶点。

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