Chinese PLA General Hospital, Medical School of Chinese PLA, Beijing, 100853, China.
Center for Cardiovascular Research and Alternative Medicine, University of Wyoming College of Health Sciences, Laramie, WY, 82071, USA.
Angiogenesis. 2018 Aug;21(3):599-615. doi: 10.1007/s10456-018-9611-z. Epub 2018 Apr 6.
Mitochondrial fission has been identified as the pathogenesis underlying the development of cardiac microvascular ischemia reperfusion (IR) injury, although the regulatory signaling upstream from fission is far from clear. Bax inhibitor is a novel anti-apoptotic factor, and, however, its role of cardiac microvascular IR injury and mitochondrial homeostasis remains unclear.
The cardiac microvascular IR injury was performed in WT mice and BI1 transgenic (BI) mice. The alterations of microvascular structure and function were detected via electron microscope, immunohistochemistry and immunofluorescence in vivo. Cardiac microvascular endothelial cells were isolated form WT and BI mice and underwent hypoxia/reoxygenation injury in vitro. Cellular viability and apoptosis were analyzed via MTT assay and caspase-3 activity. Mitochondrial function, morphology and apoptosis were detected. Signaling pathways were analyzed via inhibitor, siRNA and mutant plasmid.
Herein, we demonstrated that Bax inhibitor 1 (BI1) was downregulated following cardiac microvascular IR injury, and its expression correlated negatively with microvascular collapse, endothelial cell apoptosis and mitochondrial damage. However, compared to wild-type mice, BI1 transgenic mice were actually protected from the acute microvascular injury and mitochondrial dysfunction. Functional studies illustrated that reintroduced BI1 directly interacted with and inhibited the Syk pathway, leading to the inactivation of Nox2. Subsequently, less Nox2 was associated with ROS downregulation, inhibiting Drp1 phosphorylated activation. Through repression of the Syk-Nox2-Drp1 signaling axis, BI1 strongly disrupted mitochondrial fission, abolishing mitochondrial apoptosis and thus sustaining endothelial cell viability.
In summary, our report illustrates that BI1 functions as a novel microvascular guardian in cardiac IR injury that operates via inhibition of the Syk-Nox2-Drp1-mitochondrial fission signaling axis. Thus, novel therapeutic strategies to regulate the balance between BI1 and mitochondrial fission could provide a survival advantage to microvasculature following IR stress.
线粒体裂变已被确定为心脏微血管缺血再灌注（IR）损伤发展的发病机制，尽管裂变上游的调节信号远未明确。Bax 抑制剂是一种新型的抗凋亡因子，然而，其在心脏微血管 IR 损伤和线粒体动态平衡中的作用尚不清楚。
在 WT 小鼠和 BI1 转基因（BI）小鼠中进行心脏微血管 IR 损伤。通过电子显微镜、免疫组织化学和免疫荧光在体内检测微血管结构和功能的变化。从 WT 和 BI 小鼠中分离心脏微血管内皮细胞，并在体外进行缺氧/复氧损伤。通过 MTT 测定和 caspase-3 活性分析细胞活力和细胞凋亡。检测线粒体功能、形态和凋亡。通过抑制剂、siRNA 和突变质粒分析信号通路。
本文证明，心脏微血管 IR 损伤后 Bax 抑制剂 1（BI1）下调，其表达与微血管塌陷、内皮细胞凋亡和线粒体损伤呈负相关。然而，与野生型小鼠相比，BI1 转基因小鼠实际上可以免受急性微血管损伤和线粒体功能障碍的影响。功能研究表明，重新引入的 BI1 直接与 Syk 通路相互作用并抑制其活性，导致 Nox2 失活。随后，ROS 下调，抑制 Drp1 磷酸化激活，Nox2 减少。通过抑制 Syk-Nox2-Drp1 信号轴，BI1 强烈破坏线粒体裂变，阻止线粒体凋亡，从而维持内皮细胞活力。
总之，本研究表明，BI1 作为心脏 IR 损伤中的一种新型微血管保护因子，通过抑制 Syk-Nox2-Drp1-线粒体裂变信号轴发挥作用。因此，调节 BI1 和线粒体裂变之间平衡的新治疗策略可能为 IR 应激后微血管提供生存优势。
