两种肌少症小鼠模型的功能表型、肌肉质量及力量特点比较

Comparison of phenotypes and mechanistic characteristics in two mouse models of sarcopenia

背景:地塞米松和后肢悬吊是常用的动物肌少症造模方法,具有造模时间短、操作简便、成本低等特点。目的:比较地塞米松和后肢悬吊诱导小鼠肌少症模型在肌肉质量、力量及功能表型以及分子机制表型方面的差异。方法:采用随机抽样法将30只C57BL/6小鼠随机分成3组,每组10只:正常对照组不进行任何干预;地塞米松组小鼠腹腔注射地塞米松磷酸钠溶液1 mg/(kg•d),连续注射6周,建立肌少症模型;后肢悬吊组采用鼠尾套悬吊小鼠后肢16 h,1次/d,连续悬吊6周,建立肌少症模型。造模6周内,监测小鼠体质量变化;造模6周后,检测小鼠四肢抓力、活动能力(游泳实验)、骨骼肌湿质量、骨骼肌病理形态,采用RT-PCR与Western blot检测骨骼肌蛋白质合成与分解代谢指标、AMPK/FoXO3α信号通路的表达。结果与结论:①从造模后第2周开始,地塞米松组、后肢悬吊组小鼠体质量均低于正常对照组(P<0.05)。②造模6周后,与正常对照组相比,造模两组小鼠四肢抓力均下降(P<0.05),腓肠肌湿质量、趾长伸肌湿质量、腓肠肌与比目鱼肌横截面积均下降(P<0.05);地塞米松组小鼠腓肠肌横截面积明显小于后肢悬吊组(P<0.05),比目鱼肌横截面积大于后肢悬吊组(P<0.05);与正常对照组、后肢悬吊组相比,地塞米松组小鼠活动能力降低(P<0.05)。③与正常对照组相比,造模两组PI3K、mTOR、AMPK、PGC-1αmRNA表达与p-AMPK/AMPK蛋白均降低(P<0.05),FoXO3αmRNA表达与PGC-1α、FoXO3蛋白表达均升高(P<0.05);地塞米松组Akt1 mRNA表达降低(P<0.05),Atrogin-1、MuRF-1 mRNA表达升高(P<0.05);后肢悬吊组Akt1 mRNA表达升高(P<0.05)。④与地塞米松组相比,后肢悬吊组mTOR、Akt1、FoXO3αmRNA表达升高(P<0.05),Atrogin-1、MuRF-1 mRNA表达降低(P<0.05)。⑤结果表明,两种造模方法均会导致骨骼肌线粒体能量代谢水平下降,地塞米松组通过泛素蛋白酶体和能量代谢途径的双重作用介导骨骼肌发生萎缩,后肢悬吊组通过AMPK/FoXO3α信号通路介导能量代谢途径引起骨骼肌发生萎缩,从而引起骨骼肌的质量、力量及功能下降。

BACKGROUND:Dexamethasone and hindlimb suspension are commonly used methods for modeling sarcopenia in animal experiments due to their short modeling time,ease of operation,and low cost.OBJECTIVE:To compare the differences in muscle mass,strength and functional phenotypes and molecular mechanisms between two mouse sarcopenia models induced by dexamethasone and hindlimb suspension.METHODS:Thirty male C57BL/6 mice were randomly divided into three groups(n=10 per group).The normal control group received no intervention.The dexamethasone group received daily intraperitoneal injections of 1 mg/kg/d dexamethasone sodium phosphate solution for 6 continuous days to establish sarcopenia models in mice,while mice in the hindlimb suspension group were suspended by tail harness for 16 hours,once per day,to establish sarcopenia models.Within 6 weeks after modeling,changes in body mass were monitored.After 6 weeks of modeling,mice were tested for limb grip strength,mobility(swimming test),skeletal muscle wet mass,and skeletal muscle pathological morphology.Expressions of skeletal muscle protein synthesis and catabolism indexes as well as the AMPK/FoXO3αsignaling pathway were detected by RT-PCR and western blot.RESULTS AND CONCLUSION:(1)Two weeks after modeling,both dexamethasone and hindlimb suspension groups showed a significant decrease in body mass compared with the normal control group(P<0.001).After 6 weeks of modeling,grip strength of mice in both dexamethasone and hindlimb suspension groups was lower than that in the normal control group(P<0.001).The wet mass of gastrocnemius and extensor digitorum longus muscles and the crosssectional area of gastrocnemius and soleus muscles in the dexamethasone group were lower than those in the normal control group(P<0.05).Compared with the hindlimb suspension group,the cross-sectional area of gastrocnemius muscle was significantly smaller in the dexamethasone group(P<0.05),while the cross-sectional area of soleus muscle was larger in the dexamethasone group(P<0.05).Mice in the dexamethasone group had reduced mobility when compared with those in the normal control group and the hindlimb suspension group(P<0.05).(3)Compared with the normal control group,PI3K,mTOR,AMPK,and PGC-1αmRNA expression and P-AMPK/AMPK protein were decreased in the two modeling groups(P<0.05),and FoXO3αmRNA expression and PGC-1αand FoXO3 protein expression were elevated(P<0.05);in the dexamethasone group,Akt1 mRNA expression was decreased(P<0.05),while Atrogin-1 and MuRF-1 mRNA expression was elevated(P<0.05);in the hindlimb suspension group,Akt1 mRNA expression was elevated(P<0.05).(4)Compared with the dexamethasone group,mTOR,Akt1,and FoXO3αmRNA expression was elevated in the hindlimb suspension group(P<0.05),while Atrogin-1 and MuRF-1 mRNA expression was decreased(P<0.05).To conclude,both modeling methods could decrease the levels of mitochondrial energy metabolism in skeletal muscle,with the dexamethasone group mediating atrophy of skeletal muscle through the dual action of ubiquitin proteasome and energy metabolism pathways,and the hindlimb suspension group inducing atrophy of skeletal muscle by mediating the energy metabolism pathway through the AMPK/FoXO3αsignaling pathway,subsequently causing a reduction in mass,strength,and function of skeletal muscle.