Objective: The endogenous glucocorticoids ( GC) is required for activation of muscle protein degradation in chronic kidney disease (CKD) related protein energy wasting. We studied the muscle wasting in a muscle specific glucocorticoids receptor knockout mouse ( MGRKO) with CKD model. We hypothesis the MGRKO could suppress muscle atrophy. Methodology: MGRKO and lox/lox mice CKD model was made by 5/6 nephroctomy, and the sham was regarded as control (CTL). The serum corticosteroid hormone was measured by ELISA. The bodyweight and Tibia Anterior (TA) muscle weight were measured. The TA muscle size of was observed under microscope and calculated with software. The expression of Atrogin-1 ( Muscle Atrophy Fbox-1) and MuRF-1 ( Muscle RING finger 1) was measured by Q-PCR and western blot. We also analyzed the signaling pathway of Akt/FoxOl. Results: The levels of serum BUN and corticosteroids were increased dramatically in lox/lox-CKD and MGRKO-CKD, but no differences between two groups. The bodyweight and TA muscle weight in the lox/lox-CKD was lower than that in the lox/lox- CTL L; but no difference between the MGKO-CTL and MGKO-CKD. The cross-sectional area of muscle fibers in the MGRKO-CKD was smaller, and the shrinkages of fibers sizes caused leftward shift in fiber size distribution was obvious in lox/lox-CKD, but only mild change in ' MGRKO + CKD mice's muscle. The level of Atrogin-1 and MuRF-1 was increased dramatically, and the Akt/FoxOlsignaling pathway was abnormal which showed the level of phosphorylated Akt/FoxOl repressive simultaneously in lox/lox-CKD (P< 0.001). Whereas, the Atrogin-1 mRNA showed a mild higher ( P < 0. 05 ), the MuRF-1 mRNA 'showed no difference, and the Akt/FoxOl signaling abnormal was unconspicuous in the MGKO-CKD, which showed suppresses insulin/ IGF-1 stimulation of Akt/FoxOl activities. The MGRKO could resist to this abnormal, hence, ameliorate CKD induced muscle wasting. Conclusion: Endogenous Glucocorticoids ( GC) may play an important role in CKD induced muscle wasting, muscle specific GC receptor knockout (MGRKO) can be resistant to muscle atrophy and loss of bodyweight induced by CKD. The mechanism might be MGRKO arrest the GC suppressing insulin/IGF-1 stimulation of Akt/FoxOl activities, then,stop the active of Atrogin-1 and MuFR-1.%目的:内源性糖皮质激素水平异常升高可引起和加重慢性肾脏病(CKD)引起的骨骼肌消耗.本研究观察肌肉特异性糖皮质激素受体基因敲除(MGRKO)对CKD状态下小鼠骨骼肌消耗的影响. 方法:采用5/6肾切除制作CKD小鼠模型,以假手术组(CTL组)为对照组.组织病理学检测胫骨前肌横截面积并计算肌纤维面积分布图；荧光定量PCR检测肌肉萎缩蛋白Fbox-1(Atrogin-1)和肌环指蛋白1(MuRF-1)mRNA水平；Western Blot检测其蛋白表达及Akt/FoxO1信号通路；ELISA方法检测血清皮质酮水平. 结果:造模1月后,lox/lox-CKD和MGRKO-CKD小鼠的血尿素氮和皮质酮水平均明显升高；lox/lox-CKD的体重明显下降胫骨前肌湿重明显降低.而MGRKO-CTL和MGRKO-CKD两组间体重无明显差异,胫骨前肌湿重仅轻微降低.组织学观察到lox/lox-CKD胫骨前肌肌纤维明显萎缩,横截面积减少,肌纤维面积分布图明显左移.而MGRKO-CKD组的体重下降不明显,胫骨前肌仍较饱满,肌肉湿重略降低,横截面积略降低,与MGRKO-CTL组比较,肌纤维面积分布图仅轻度左移.荧光定量PCR和Western Blot结果显示lox/lox-CKD组的腓肠肌Atrogin-1和MuRF-1的mRNA和蛋白表达水平显著升高,同时其Akt磷酸化水平(pAkt/Akt)较lox/lox-CTL组显著降低3.1倍,FoxO1磷酸化水平(pFoxO1/FoxO1)较lox/lox-CTL组降低2.3倍；而MGRKO-CKD组的Atrogin-1表达仅轻微上调,MuRF-1则无明显变化；MGRKO-CKD组Atrogin-1蛋白表达水平仅比MGRKO-CTL组升高,同时pAkt/Akt、pFoxO1/FoxO1水平较对照组仅轻微降低. 结论:内源性糖皮质激素水平升高在CKD肌肉消耗中发挥重要作用；MGRKO可减轻/阻止CKD状态下的体重下降和肌肉萎缩,下调肌萎缩关键基因Atrogin-1和MuRF-1表达水平；该效应与阻断糖皮质激素影响Akt/FoxO1信号途径有关,抑制糖皮质激素信号通路可能改善CKD肌肉消耗.
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