环氧化酶2下游通路通过Akt/FOXO3a介导尿毒症肌肉萎缩机制研究

Protein-energy wasting is one of the strongest predictors of mortality in patients with chronic kidney disease(CKD), which is described as a state of muscular atrophy, decreased body stores of protein and energy fuels. In patients with CKD, there is evidence for activation of the ubiquitin-proteasome pathway(UPP) in skeletal muscle. However, the precise mechanisms by which UPP influences muscular atrophy are unclear. Cyclooxygenase 2(COX-2), officially known as prostaglandin-endoperoxide synthase 2 activation plays an important role in muscle atrophy induced by sepsis and cancer and COX-2 inhibitors are able to improve muscular atrophy by acting on the UPP. Our group recently confirmed that COX-2 was upregulated in the muscle of uremic rats and inhibition of COX-2 increased the body weight of uremic rats. It is demonstrated that Cyclooxygenase 2 and PGE2 expression was associated with tumor angiogenesis and metastasis by modulating the activity of PI3K/Akt signaling pathway. PI3K/Akt can inhibit FOXO3a nuclear translocation and plays a regulatory role in its target gene E3 ubiquitin ligase MAFbx promoter. Thereby, we hypothesized that: Cyclooxygenase 2 downstream promotes muscle atrophy in uremia by Akt/FOXO3a pathway. The aim of this study was to assess the effect of COX-2 downstream pathway mPGES-1-PGE2-EP and Akt/FOXO3a in muscle wasting of uremia in vivo and vitro, by using C2C12 cell culture and muscle atrophy model of uremia mice. We also assessed the multi-target therapeutic effect of COX-2 pathway inhibition and tried to find new directions for clinical prevention and treatment of uremic muscle atrophy.

蛋白能量消耗是导致尿毒症患者死亡的最强预测因素之一，表现为肌肉萎缩和体重下降。尿毒症肌肉萎缩存在泛素-蛋白酶途径(UPP)活化，但机制未明。在脓毒症中研究发现，环氧化酶2(COX-2)介导UPP活化导致肌肉萎缩。前期工作证实，尿毒症大鼠萎缩肌肉中存在COX-2上调，应用COX-2抑制剂可以使其体重增加。而COX-2调控PI3K/Akt参与肿瘤转移，PI3K/Akt抑制FOXO3a核转位发挥对其靶基因泛素连接酶MAFbx启动子的调控作用。故推测：尿毒症时，COX-2及其下游通路(mPGES-1-PGE2-EP)通过调控Akt/FOXO3a，使FOXO3a磷酸化降低，移位于细胞核，启动MAFbx基因转录，导致肌肉萎缩。本研究将通过构建动物模型、细胞培养及质粒转染等方法，系统论证COX-2下游通路及Akt/FOXO3a在尿毒症肌肉萎缩中的确切机制，明确多靶点阻断治疗效果，为临床治疗提供新方向。

蛋白能量消耗是导致尿毒症患者死亡的独立预测因素之一，表现为肌肉萎缩和体重下降。研究发现，尿毒症肌肉萎缩存在泛素-蛋白酶途径(UPP)活化，但机制不明。本研究首先通过尿毒症患者肌肉组织以及构建动物模型发现，COX-2及其下游通路(mPGES-1-PGE2-EP2)异常活化。进一步体外通过细胞培养发现，尿毒症慢性炎症状态下，COX-2及其下游通路(mPGES-1-PGE2-EP2)活化，FOXO3a磷酸化降低，MAFbx基因转录增加，发生肌肉萎缩。下调COX-2及其下游通路，则可以改善肌肉萎缩相关指标。活性维生素D是尿毒症患者常用的药物之一。活性维生素D位于COX-2上游，通过抑制COX-2活性发挥抑制炎症的作用。本研究发现，应用活性维生素D后，维生素D受体激动剂骨化三醇刺激肌管细胞VDR表达，对肌肉萎缩相关指标无影响，成肌调节因子MyoD以及Myogenin无明显变化，但肌肉抑制素Myostatin较对照组有所降低、肌管增粗。反之，下调VDR加剧炎症导致的肌管萎缩。同时，在尿毒症患者中检测肌力、肌肉量等指标，明确尿毒症患者肌肉萎缩的各种危险因素。结果显示，肱二头肌肌力是影响MHD患者生存的独立危险因素。影响<65岁MHD患者上肢肱二头肌肌力的主要因素包括性别、改良SGA评分、肌肉量、25(OH)D以及IL-6水平。影响≥65岁MHD患者上肢肱二头肌肌力的主要因素包括年龄、肌肉量、25(OH)D以及NT-proBNP水平。随着25(OH)D水平升高，肱二头肌肌力上升，提示维生素D系统可能和肌肉功能密切相关。本研究系统论证COX-2 以及下游通路、COX-2上游活性维生素D在尿毒症肌肉萎缩中的确切机制，并且将基础研究与临床研究有机结合，为临床治疗PEW这一棘手的问题提供新方向。