Farnesoid X receptor (FXR) is a nuclear receptor that plays a critical role in controlling cell apoptosis in diverse diseases. Previous studies have shown that knocking out FXR improved cardiac function by reducing cardiomyocyte apoptosis in myocardial ischemic mice. However, the role of FXR after cerebral ischemia remains unknown. In this study, we explored the effects and mechanisms of FXR knockout (KO) on the functional recovery of mice post cerebral ischemia-reperfusion. Adult male C57BL/6 wild type and FXR KO mice were subjected to 90-min transient middle cerebral artery occlusion (tMCAO). The mice were divided into five groups: sham, wild-type tMCAO, FXR KO tMCAO, wild-type tMCAO treated with calcium agonist Bayk8644, and FXR KO tMCAO treated with Bayk8644. FXR expression was examined using immunohistochemistry and Western blot. Brain infarct and brain atrophy volume were examined at 3 and 14 days after stroke respectively. Neurobehavioral tests were conducted up to 14 days after stroke. The protein levels of apoptotic factors (Bcl-2, Bax, and Cleaved caspase-3) and mRNA levels of pro-inflammatory factors (TNF-α, IL-6, IL-1β, IL-17, and IL-18) were examined using Western blot and RT-PCR. TUNEL staining and calcium imaging were obtained using confocal and two-photon microscopy. The expression of FXR was upregulated after ischemic stroke, which is located in the nucleus of the neurons. FXR KO was found to reduce infarct volume and promote neurobehavioral recovery following tMCAO compared to the vehicle. The expression of apoptotic and pro-inflammatory factors decreased in FXR KO mice compared to the control. The number of NeuN+/TUNEL+ cells declined in the peri-infarct area of FXR KO mice compared to the vehicle. We further demonstrated that inhibition of FXR reduced calcium overload and addition of ionomycin could reverse this neuroprotective effect in vitro. What is more, in vivo results showed that enhancement of intracellular calcium concentrations could aggravate ischemic injury and reverse the neuroprotective effect of FXR KO in mice. FXR KO can promote neurobehavioral recovery and attenuate ischemic brain injury, inflammatory release, and neuronal apoptosis via reducing calcium influx, suggesting its role as a therapeutic target for stroke treatments.

中文翻译：

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Farnesoid X受体敲除可通过减少小鼠神经元凋亡来保护大脑免受缺血性损伤。

法尼醇X受体（FXR）是一种核受体，在控制多种疾病的细胞凋亡中起着关键作用。先前的研究表明，敲除FXR可以通过减少心肌缺血小鼠的心肌细胞凋亡来改善心脏功能。但是，FXR在脑缺血后的作用仍然未知。在这项研究中，我们探讨了FXR敲除（KO）对脑缺血再灌注后小鼠功能恢复的影响及其机制。对成年雄性C57BL / 6野生型和FXR KO小鼠进行90分钟的短暂脑中动脉闭塞（tMCAO）。将小鼠分为五组：假手术，野生型tMCAO，FXR KO tMCAO，用钙激动剂Bayk8644处理的野生型tMCAO和用Bayk8644处理的FXR KO tMCAO。使用免疫组织化学和蛋白质印迹检查FXR表达。脑卒中后第3天和第14天分别检查脑梗塞和脑萎缩量。中风后长达14天进行神经行为测试。凋亡因子的蛋白质水平（Bcl-2，Bax和Cleaved caspase-3）和促炎因子的mRNA水平（TNF-α，IL-6，IL-1β，IL-17和IL-18）为使用Western印迹和RT-PCR检测。使用共聚焦和双光子显微镜获得TUNEL染色和钙成像。缺血性中风后FXR的表达上调，其位于神经元的核内。与媒介物相比，发现tMCAO后FXR KO可以减少梗死体积并促进神经行为恢复。与对照组相比，FXR KO小鼠的凋亡和促炎因子表达降低。与媒介物相比，FXR KO小鼠的梗死周围区域的NeuN + / TUNEL +细胞数量下降。我们进一步证明，抑制FXR可以减少钙超载，而加入离子霉素可以逆转这种神经保护作用。此外，体内结果显示，细胞内钙浓度的增加可加重缺血性损伤并逆转FXR KO对小鼠的神经保护作用。FXR KO可以通过减少钙流入来促进神经行为恢复，并减轻缺血性脑损伤，炎症释放和神经元凋亡，表明其作为中风治疗的治疗靶标发挥了作用。此外，体内结果显示，细胞内钙浓度的增加可加重缺血性损伤并逆转FXR KO对小鼠的神经保护作用。FXR KO可以通过减少钙流入来促进神经行为恢复，并减轻缺血性脑损伤，炎症释放和神经元凋亡，表明其作为中风治疗的治疗靶标发挥了作用。此外，体内结果显示，细胞内钙浓度的增加可加重缺血性损伤并逆转FXR KO对小鼠的神经保护作用。FXR KO可以通过减少钙流入来促进神经行为恢复，并减轻缺血性脑损伤，炎症释放和神经元凋亡，表明其作为中风治疗的治疗靶标发挥了作用。