摘要
目的：近年来研究发现多种核受体家族成员包括肝X受体在抑制机体炎症反应中起到不同程度的作用,但在心肌细胞炎症反应以及心肌肥厚方面却无研究。本文通过体内及体外实验,研究肝X受体是否对病理性刺激后小鼠心脏细胞炎症反应以及病理性心肌肥厚反应具有调节作用,并探讨其可能的作用机制。
方法：(1)通过TAC手术建立小鼠心肌肥厚模型,检测小鼠模型心肌细胞LXR表达情况；(2)分别对野生型和LXRα基因敲除小鼠进行TAC手术,诱导心肌炎症反应以及病理性心肌肥厚,通过观察其心肌肥厚反应程度以分析LXR心肌炎症反应的关系；(3)通过体外细胞实验,观察LXR人工合成配体T1317对AngⅡ或LPS诱导心肌肥厚反应作用,并通过质粒转染及荧光素酶实验进一步分析其作用机制。
结果：在TAC诱导的小鼠心肌肥厚模型中,LXRα表达明显增加,而LXRβ表达没有改变。LXRα基因敲除后,小鼠在TAC手术的诱导下,出现更为显著的心肌肥厚变化。细胞实验进一步证实T1317激活LXR的表达后,能够抑制由AngⅡ或LPS诱导的心肌细胞炎症反应以及心肌肥厚。同时,LXR激活对心肌肥厚反应的抑制作用是通过阻断NF-κB信号传导通路而实现。通过腺病毒分别激活两种LXR亚型,发现虽然两者都有抑制心肌肥厚的作用,LXRα在两者中起主要的作用。
结论：(1) LXRα是心肌适应病理性心肌肥厚的重要调控元素,在病理性刺激的情况下,其缺失将导致小鼠心脏出现更加严重的心肌肥厚现象；(2)LXR人工合成配体T1317激活LXR后,可抑制NF-κB信号传导通路,从而减轻病理性刺激诱导的心肌肥厚现象。(3)LXRα与LXRβ均能通过抑制NF-κB信号传导通路从而负调节心肌细胞肥厚性生长,而且LXRα作用更为明显。
目的：LXR不但作为全身胆固醇调节元件,同时在脂肪酸代谢方面也有着重要的调节作用。尽管LXR已被证明在成年心脏内表达,但是LXR在成年心脏能量代谢方面的具体作用却仍然不清楚。本部分实验我们通过对条件性心肌特异LXRα基因敲除小鼠进行相关研究,分析成年小鼠心肌LXRα基因缺失后心肌代谢改变,并观察其对心脏形态及功能的影响。
方法：(1)培育条件性心肌特异LXRα基因敲除小鼠,在LXRα基因敲除后检测心肌代谢相关基因的变化。(2)通过离体工作心实验以及体外细胞实验对LXRα基因敲除小鼠心脏及心肌细胞的糖脂代谢进行研究。(3)对转基因小鼠心脏进行组织形态学观察,并通过超声心动图和离体心实验对小鼠心脏功能分别进行研究。
结果：成年小鼠心肌特异敲除LXRα基因后,导致部分调节脂肪酸与葡萄糖代谢靶基因的下调。心肌脂肪酸与葡萄糖氧化率以及葡萄糖摄取率下降,ATP生成减少,并引起了小鼠心脏出现以心肌纤维化、心肌肥厚为特征的心肌重构,心脏功能下降。
结论：本研究表明LXRα是心肌脂肪酸与葡萄糖代谢的重要调节因子,成年小鼠LXRα心肌特异性敲除可使得脂肪酸及葡萄糖代谢的靶基因表达下调,引起心脏代谢紊乱,心功能降低以及心肌重构。
Several members of nuclear receptor superfamily, including liver X receptors (LXRa and LXRP), have been shown to suppress inflammatory responses, but little is known about their effects in cardiomyocytes. We investigated LXR expression patterns in pressure overload-induced hypertrophic hearts and the hypertrophic growth of the LXRa-deficient hearts from mice (C57/B6) in response to pressure overload. The underlying mechanisms were also explored using cultured myocytes. We found that cardiac expression of LXRa was upregulated in pressure overload-induced left ventricular hypertrophy in mice. Transverse aorta coarctation-induced left ventricular hypertrophy was exacerbated in LXRa-null mice relative to control mice. A synthetic LXR ligand, T1317, suppressed cardiomyocyte hypertrophy in response to angiotensinⅡand lipopolysaccharide treatments. In addition, LXR activation suppressed NF-κB signalling and the expression of associated inflammatory factors. Overexpression of constitutively active LXRa and b in cultured myocytes suppressed NF-κB activity. LXRs are negative regulators of cardiac growth and inflammation via suppressing NF-κB signaling in cardiomyocytes. This should provide new insights into novel therapeutic targets for treating cardiac hypertrophy and heart failure.
In addition to its important role in maintaining cholesterol homeostasis, LXRs is also essential in regulating lipid metabolism. Expression of LXRa has long been identified in adult heart, however, the role of LXRa in the transcriptional regulation of myocardial metabolism and cardiac pathophysiology remains obscure. To test the hypothesis that LXRa plays an important role in regulating lipid and glucose metabolism in the heart, Cardiomyocyte-restricted LXRa knockout were induced in mice treated with tamoxifen. After confirmation of LXRa knockout, LXRs target genes that were crucial in lipid and glucose metabolism were downregulated. Lipid and glucose metabolism were examined in ex vivo heart and in vitro cardiomyocytes. And in vivo and in vitro cardiac function was evaluated with echocardiography and isolated heart working system. Morphological and histological examinations of heart were also performed in transgenic mice. Fatty acid and glucose oxidation, as well as glucose uptake were both decreased in cardiomyocytes, followed by repressed cardiac function, cardiac hypertrophy and remodeling. Therefore, the present study demonstrated LXRa is essential in myocardial lipid and glucose metabolism, inducible cardiomyocyte-restricted LXRa knockout in adults leads to downregulation of related gene expression which regulates lipid and glucose metabolism, depressed ATP production, as well as cardiac dysfunction and remodeling.
引文
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