Nrf2在调节心肌细胞自噬功能中的作用与分子机制

Heart failure, a complex clinical syndrome with high morbidity and mortality, is increasing in prevalence without a cure. A rapidly increasing evidence has revealed that nuclear factor-erythroid 2-related factor 2 （Nrf2）, a key transcription factor antioxidant defense, is a neagtive regulator of maladaptive cardiac remodeling and dysfunction. While we have demonstrated that knockout of Nrf2 enhances pressure overload-induced cardiac oxidative stress, hypertrophy, fibrosis, apoptosis and dysfunction in mice, we found that Nrf2 cardiomyocyte specific transgenic (Nrf2ctg) mice were resistant to myocardial oxidative stress and heart failture in a setting of pressure overload. Of note, the sustained Nrf2 activation increased a net level of myocardial autophagosomes, decreased the levels of myocardial ubiquitinated proteins and protein aggregates with an upregulation of p62, a critical adaptor for autophagic clearance. Importantly, Nrf2 activation suppressed necroptosis rather than apoptosis in cardiomyocytes, these Nrf2-mediated autophagic activities seem to be independent of reactive oxygen species (ROS) formation. These exciting results led us to test a working hypothesis that Nrf2 drives p62-mediated autophagic clearance of toxic protein aggregates independent of ROS formation to inhibit cardiomyocyte necroptosis thereby protecting against cardiac dysfunction. The outcome will provide novel insights into a better understanding of how pharmacological intervention on Nrf2 pathway might be prudent, facilitating the development of a new class of Nrf2 activators for the treatment of cardiovascular disease.

心力衰竭是一个复杂的临床症状，发病率和死亡率高，难以治愈。大量证据表明激活转录因子Nrf2能启动内源性抗氧化应激反应防御体系，抑制心肌的氧化应激损伤，从而防止心衰的发生和发展。我们前期的研究结果显示：①Nrf2缺失能增加心肌的氧化应激、肥大、纤维化、凋亡、以及心功能紊乱；②心肌特异性过表达Nrf2能显著抑制心衰的发生和发展。在细胞水平，心肌特异性过表达Nrf2抑制心肌的氧化应激、肥大，但是并不影响心脏的纤维化和心肌细胞的凋亡！③进一步的研究揭示激活Nrf2促进心肌的自噬小体的形成，降低心肌的泛素化蛋白和蛋白聚集体的水平，上调p62（自噬清除的关键因子）的表达，并抑制心肌细胞的坏死；而这些作用与Nrf2的抗氧化应激功能无关！在这些新颖而独特的观察基础上，本研究将首次揭示一条抗氧化应激以外的Nrf2-p62信号通路在心肌细胞中如何通过自噬清除蛋白聚合体，抑制心肌细胞的坏死，而保护心脏功能。

心力衰竭是一个复杂的临床症状，发病率和死亡率高，难以治愈。在我们前期的研究结果显示基础上，本研究首次聚焦于揭示一条抗氧化应激以外的Nrf2-p62信号通路在心肌细胞中如何通过自噬清除蛋白聚合体，抑制心肌细胞的坏死，而保护心脏功能；探索以Nrf2作为治疗心血管疾病靶点可能性。利用心肌特异性的过表达和沉默技术，我们证实激活Nrf2可以促进自噬清除功能，并抑制由蛋白聚集体蓄积而导致的心肌细胞坏死。但是，Nrf2的心肌保护作用依赖于心肌自嗜功能。如果心肌自嗜功能受到损伤，Nrf2的心肌保护作用大大减弱，甚至走向反面，反而促进心肌损伤。同时，我们发现去泛素化酶CYLD可以下调Nrf2的表达和转录活性，而促进心肌损伤。另外，我们还发现两条信号通路调控Nrf2病理性转录活性，即Jak2-Fyn和ERK通路；也证明了p62参与Nrf2介导的双向作用。