蛋白酶体抑制剂MG-132作用下失神经骨骼肌myf-5的表达

背景：MG-132是蛋白酶体抑制剂的一种，有报道显示其对失神经骨骼肌萎缩有延缓作用。 目的：进一步验证蛋白酶体抑制剂MG-132对大鼠骨骼肌成肌调节因子myf-5基因表达的影响。 方法：SD大鼠随机被分成3组，空白对照组不切断坐骨神经，仅做假手术，去神经组和去神经MG-132干预组切断坐骨神经1 cm以上，制作失神经骨骼肌动物模型，去神经MG-132干预组肌肉内注射MG-132。分别于去神经第2，7，28 d处死大鼠。用反转录聚合酶链式反应技术检测myf-5 mRNA表达情况，Western-blot检测myf-5蛋白表达的变化。 结果及结论：在去神经支配后第2，7，28天，与空白对照组比较，去神经组、去神经MG-132干预组myf-5mRNA和蛋白质均表达上调(P < 0.01)；去神经MG-132干预组myf-5mRNA和蛋白表达较去神经组均明显上调(P < 0.01)。结果提示蛋白酶体抑制剂MG-132可以通过抑制泛素-蛋白酶体途径来上调myf-5的表达，从而起到延缓骨骼肌萎缩的作用。     

经皮电刺激大鼠骨骼肌失神经肌萎缩时成肌调节因子基因的表达

背景：在去神经早期大鼠骨骼肌成肌调节因子(MyoD)表达明显上调,有明显延缓骨骼肌肌萎缩的作用。临床实验证实电刺激是治疗失神经肌萎缩的有效方法。尚未有实验证实电刺激对失神经肌萎缩MyoD表达的影响。 目的：验证电刺激对大鼠骨骼肌MyoD基因表达的影响。 设计、时间及地点：随机对照动物实验,于2008-07/11在山西医科大学动物实验中心完成。 材料：健康的SD大鼠36只,雌雄不限。随机分成3组,即空白对照组、去神经组、电刺激组,每组12只。 方法：空白对照组不做任何处理;去神经组和电刺激组大鼠制作右侧坐骨神经离断,腓肠肌失神经支配模型。用电刺激对电刺激组进行刺激,1次/d,30 min/次。分别于去神经第2,7,14,28天,处死大鼠,取小腿的腓肠肌肉标本。 主要观察指标：用反转录聚合酶链式反应技术检测MyoD mRNA的表达变化,免疫组织化学检测MyoD蛋白表达的变化。 结果：在去神经支配后第2,7,14,28天,去神经组和电刺激组标本中MyoDmRNA和蛋白含量表达上调,与空白对照组比较差异有显著性意义(P < 0.05),电刺激组表达高于去神经组(P < 0.05)。 结论：通过电刺激可以上调大鼠腓肠肌失神经模型MyoD的表达,说明电刺激是延缓骨骼失神经肌萎缩的有效方法。     

失神经骨骼肌萎缩与氯沙坦通过核因子κB/MuRF1通路的延缓作用

背景：在失神经骨骼肌萎缩中,核因子κB /MuRF1通路是最关键的分子机制之一,抑制该通路可以提高失神经骨骼肌的力量,保持肌肉数量和促进肌肉再生。 目的：探讨核因子κB、MuRF1在失神经骨骼肌中的表达及氯沙坦对核因子κB/MuRF1通路的影响作用,以期寻找延缓失神经骨骼肌萎缩的新途径。 方法：将Wista大鼠随机分为3组：失神经对照组、氯沙坦治疗组建立右下肢失神经腓肠肌动物模型。氯沙坦治疗组大鼠采用氯沙坦以10 mg/(kg•d)空腹灌胃;失神经对照组大鼠以等剂量生理盐水灌胃,以不做处理的大鼠为正常对照。采用RT-PCR和Western Blotting 检测术后2,14,28 d时大鼠腓肠肌核因子κB和MuRF1的mRNA和蛋白表达水平,并结合肌肉失质量比分析其相关性。 结果与结论：大鼠腓肠肌失神经支配后核因子κB和MuRF1的mRNA和蛋白表达在2,14,28 d持续增加(P < 0.05),而且二因子的表达线性相关有显著性意义(P < 0.05)。失神经支配后14,8 d氯沙坦治疗组腓肠肌湿质量比高于同期失神经对照组(P < 0.05),氯沙坦治疗组两因子mRNA和蛋白的表达在各个时间点低于失神经对照组(P < 0.05)。核因子κB、MuRF1在失神经肌萎缩中表达增高,而且是同一通路。结果提示氯沙坦可以通过干扰核因子κB、MuRF1mRNA和蛋白质的表达来延缓失神经骨骼肌萎缩。     

低频电刺激对坐骨神经损伤大鼠不同类型骨骼肌萎缩及内源性胰岛素样生长因子1表达的影响

背景：低频电刺激可以缓解骨骼肌的萎缩,但对肌纤维类型的影响尚不清楚,同时内源性胰岛素样生长因子1在萎缩后的肌纤维中的表达与电刺激的关系尚无公识。 目的：观察低频电刺激对坐骨神经损伤大鼠不同类型骨骼肌纤维萎缩情况及内源性胰岛素样生长因子1表达的影响。 方法：将健康雄性SD大鼠随机分为3组,切断模型组和电刺激组大鼠左侧坐骨神经制备失神经支配模型,适应5 d后,对电刺激组大鼠损伤侧腓肠肌施以2 Hz的电刺激,2次/d,每次持续20 min,正常组和模型组常规饲养。30 d后,取大鼠腓肠肌腹部,检测其肌纤维直径和数量;免疫组织化学法检测肌组织中胰岛素样生长因子1的水平。 结果与结论：失神经支配后,大鼠腓肠肌Ⅰ、Ⅱ型肌纤维直径减小,Ⅰ型肌纤维数比例增大。与模型组比较,电刺激组大鼠腓肠肌Ⅰ、Ⅱ型肌纤维直径有所增大,尤以Ⅰ型肌纤维直径增大更明显(P < 0.05)。同时,电刺激组大鼠腓肠肌中胰岛素样生长因子1的表达也明显高于模型组(P < 0.05)。提示,2 Hz的电刺激可促进胰岛素样生长因子1的表达,减轻Ⅰ型肌纤维的萎缩。     

失神经骨骼肌萎缩中泛素蛋白连接酶Murf1和核转录因子NF-κB表达与被动运动干预

背景：蛋白质分解是延缓肌萎缩发生的关键环节,在慢性病性、制动性肌萎缩中泛素蛋白连接酶Murf1和核转录因子NF-κB的表达增加,被动运动已被证实可以有效抑制肌萎缩的发生。 目的：探讨泛素蛋白连接酶Murf1和核转录因子NF-κB在大鼠失神经肌萎缩中不同时段的表达,以及被动运动对失神经骨骼肌Murf1和NF-κB表达的影响。 方法：假手术组大鼠不切断右下肢坐骨神经,失神经组、失神经被动运动组大鼠切断右下肢坐骨神经。术后1 d起,将失神经被动运动组大鼠置于自制的网夹内,拉出右后肢,抓住趾部,与脊柱呈45°向后外方牵拉,至右后肢完全伸直,再将右后肢推向身体,使之完全屈曲紧贴身体,每天训练2次,每次屈伸运动300下,3 min/次,直至切取标本之日。干预2,14,28 d后,采用RT-PCR与Western Blot技术分别检测Murf1,NF-κB mRNA和蛋白质的表达。 结果与结论：与假手术组比较,各时间点失神经组Murf1,NF-κB mRNA及蛋白的表达均明显增加(P < 0.05);与失神经组比较,各时间点失神经被动运动组Murf1及NF-κB mRNA的表达均显著降低(P < 0.01)。失神经支配后肌湿质量比明显下降,被动运动14 d时肌湿质量比明显高于失神经组(P < 0.05)。失神经腓肠肌中Murf1,NF-κB mRNA和蛋白的表达与肌湿质量呈负相关(r= -0.795,P < 0.01;r=-0.834,P < 0.01),提示被动运动可能通过降低Murf1和NF-κB的表达发挥肌萎缩防治作用。     

失神经支配的骨骼肌萎缩与防治

背景：随着当今医学的发展,失神经支配骨骼肌萎缩的防治已取得了显著的进步,但临床疗效仍不十分满意。 目的：对失神经支配骨骼肌萎缩防治方法的研究现状作一总结,试图寻找更为有效的失神经支配骨骼肌萎缩防治方法。 方法：以denervation,muscle atrophy,treatment为检索词,检索Medline数据库(1998-01/2008-01)。以失神经,肌萎缩,治疗为检索词,检索中国期刊全文数据库(1998-01/2008-01)、万方数据库(1998-01/2008-01)和《中国临床康复》杂志(1998-01/2008-01)。文献检索语种限制为英文和中文。以肌肉的耐力及收缩力、失神经的肌湿重和骨骼肌的修复情况为评价指标。纳入研究失神经支配骨骼肌萎缩的显微外科手术方法、物理疗法、生物和化学疗法、基因疗法。排除上述方法之外失神经支配骨骼肌萎缩的其他疗法。 结果与结论：周围神经损伤后,骨骼肌失神经支配将不可避免的发生萎缩。因此,探索失神经支配骨骼肌萎缩的防治方法,吸引了国内外许多学者的兴趣,必将成为21世纪周围神经领域内的重要任务和研究热点。显微外科手术、物理疗法、生物和化学疗法、基因疗法等都是失神经支配骨骼肌萎缩有效的防治手段。目前,该领域的研究已经呈现多角度、多方面的趋势。失神经肌萎缩的防治方面已经有了针对性的措施,但在改善微循环、防止细胞凋亡、抑制胶原过度生长以及如何应用基因治疗的方法在基因水平改变生肌调节因子的表达等方面,还有大量工作需要进行。随着组织工程学、细胞培养学、分子生物学、基因工程等方面的不断发展,防治失神经肌萎缩必定会有新的突破。     

双侧坐骨神经及股神经离断并固定大鼠神经肽Y水平对骨密度的影响

背景：以往研究认为,刺激坐骨神经及中枢神经受伤可使神经肽Y含量发生改变,神经肽Y对破骨细胞产生作用,影响骨代谢。 目的：验证双侧坐骨神经、股神经失神经及固定后神经肽物质对大鼠双侧胫骨骨密度的影响,并进行相关性分析。 设计、时间及地点：随机对照动物实验,于2006-09/11在湘南学院附属医院完成。 材料：10周龄SD雄性大鼠96只,体质量220~250 g,用于制备失神经支配模型。 方法：96只SD大鼠按数字表法随机分为3组,每组32只。①失神经支配组：切断大鼠两侧后肢坐骨神经和两侧股神经,远端游离5 mm,缝合切口。②固定组：大鼠切断神经,程序同前,继之采用管型石膏固定。③对照组：行假手术,仅暴露神经,然后缝合伤口。 主要观察指标：实验期间大鼠的一般情况。造模后1,10,30,60 d每组分别处死大鼠8只,观察双侧胫骨骨密度和神经肽Y的变化及神经肽Y水平与骨密度水平的相关性。 结果：96只SD大鼠均进入结果分析。①失神经后神经肽Y含量先降低,后升高,随着失神经支配时间的延长,神经肽Y持续升高,超过正常水平。②固定组神经肽Y含量先升高,后下降,但随着固定时间的延长,逐步升高并超过正常水平。③随着神经肽Y含量变化,大鼠双侧胫骨骨量也相应发生改变,大鼠失神经、固定30 d后双侧胫骨骨密度明显下降。失神经及固定后神经肽Y与骨密度含量变化高度相关(P < 0.01)。 结论：失神经支配及固定后大鼠神经肽Y含量变化均与骨密度改变具有高度相关,故可认为神经肽Y可作为骨质疏松形成的关键指标之一。     

失神经固定制动不同时间大鼠降钙素基因相关肽水平变化对骨密度的影响*

背景：大量研究认为降钙素基因相关肽具有刺激成骨、增加骨量,促进神经再生等诸多功能,然而不同制动后降钙素基因相关肽的变化规律及对骨质疏松形成过程中的作用和机制至今仍不十分清楚。 目的：观察失神经固定后神经肽物质对大鼠骨密度的影响及其可能机制。 设计、时间及地点：随机对照动物实验,于2006-09/11在湘南学院附属医院完成。 材料：10周龄SD雄性大鼠96只,体质量220~250 g,用于制备失神经支配模型。 方法：96只SD大鼠按数字表法随机分为3批,每批4组,每组8只。失神经支配组：大鼠麻醉后,先于俯卧位行两侧后肢股外侧切口,于股骨转子水平切断双侧坐骨神经;再置大鼠于仰卧位,行两侧股正中纵切口,于腹股沟韧带水平切断大鼠两侧股神经,远端游离5 mm,缝合切口。固定组：大鼠固定与失神经支配手术同时进行,麻醉后应用管型石膏分别固定1,10,30,60 d。对照组行假手术,即在造模过程中仅暴露神经,然后缝合伤口。 主要观察指标：实验期间大鼠的一般情况;造模后1,10,30,60 d各组大鼠胫骨骨密度和降钙素基因相关肽的变化及降钙素基因相关肽水平与骨密度水平相关性。 结果：96只SD大鼠均进入结果分析。①大鼠失神经造模后两后肢无主动屈伸功能,前进时以臀部肌群帮助行走,后退时靠腰腹部肌群收缩代偿,活动量显著减少。固定组大鼠精神好,活动时后肢拖地。对照组大鼠无明显异常。②造模后10,30,60 d失神经支配组大鼠胫骨降钙素基因相关肽的表达低于对照组(P < 0.05~0.01);而固定组仅造模后30 d时与对照组之间存在显著性差异(P < 0.05)。造模后10,60 d固定组高于失神经支配组(P < 0.05~0.01)。③与对照组相比,失神经支配组、固定组造模后30,60 d骨密度降低(P < 0.05~0.01);失神经支配组和固定组造模30 d时骨密度开始下降,60 d后下降明显,组内比较差异有显著性意义(P < 0.05~0.01)。④失神经后降钙素基因相关肽与骨密度水平变化高度相关(P < 0.05);而固定后降钙素基因相关肽与骨密度水平变化相关程度不高。 结论：神经的完整性是降钙素基因相关肽水平维持正常的关键,动态观察降钙素基因相关肽水平变化,可在一定程度上预测失神经性骨质疏松形成、发展。     

带神经血管肌束分点植入后失神经肌肉形态学改变

背景：失神经支配的肌萎缩一直是临床治疗的难点,目前仍没有突破性的研究成果。 目的：观察带神经血管的肌束分点植入后对失神经支配肌肉形态学影响，探求一种失神经支配肌萎缩研究的新思路。 设计、时间及地点：同体对照动物实验，于2006-07/2007-12在南京鼓楼医院手外科完成。 材料：清洁级健康Wistar大白鼠30只，雌雄不限，体质量250 g左右。 方法：建立大鼠双下肢腓肠肌外侧头失神经支配模型。其中右侧在腓肠肌外侧头肌腹中远1/3处做两切口，用比目鱼肌作成带神经血管肌束，分点植入失神经支配肌肉内，作为实验组。左侧只切断腓肠肌外侧头肌支作为对照组。分别于术后4，8，12周取材。 主要观察指标：观察肌肉外观、超微结构变化，测定肌纤维周径及截面积、胶原纤维含量。 结果：①实验侧的腓肠肌饱满、有弹性、色泽好、切之出血多。对照组肌肉萎缩变细、色泽灰白、切之出血少。②各时间点实验组肌细胞周长和肌肉纤维横截面积测量值大于对照组（P均< 0.01）；胶原纤维含量低于对照组（P < 0.01）。③实验组细胞核基本正常，肌膜光滑，肌纤维间距小，线粒体数量多、嵴完整。对照组肌肉细胞核变形、空泡化，肌膜呈乳突样改变，肌纤维明显变细，间距增大，线粒体数量少、出现空泡化及絮状化，脂滴增多。 结论：带神经血管肌束分点植入法是一种延缓失神经支配肌肉萎缩的有效方法。     

富含酸性成纤维细胞生长因子纤维蛋白凝胶预防失神经支配运动终板

背景：作者前期研究证实酸性成纤维细胞生长因子纤维蛋白凝胶植入大鼠失神经支配肌肉可以明显减轻运动终板退行性改变及肌萎缩。 目的：采用免疫组织化学研究方法进一步探索酸性成纤维细胞生长因子纤维蛋白凝胶预防失神经支配运动终板退行性改变的作用。 设计、时间及地点：随机对照动物实验,于2006-06/12在南方医科大学珠江医院完成。 材料：选取清洁级SD大鼠24只,随机分为3组：酸性成纤维细胞生长因子+纤维蛋白凝胶组、单纯植入纤维蛋白凝胶组、空白对照组,每组8只。 方法：各组大鼠全麻状态下切断右侧腓总神经(距神经入肌点约1 cm处)。酸性成纤维细胞生长因子+纤维蛋白凝胶组缝合神经外膜,失神经支配胫前肌神经区周围肌间隙植入酸性成纤维细胞生长因子纤维蛋白凝胶;单纯植入纤维蛋白凝胶组修复神经肌肉植入纤维蛋白凝胶;空白对照组修复神经肌肉不给药。 主要观察指标：6周后分离切取腓总神经胫前肌分支神经肌肉接头及其附近肌肉,采用SP法免疫组织化学进行酸性成纤维细胞生长因子受体染色,观察酸性成纤维细胞生长因子受体表达部位;酸性成纤维细胞生长因子受体阳性毛细血管计数,采用图像分析测定毛细血管壁酸性成纤维细胞生长因子受体灰度值。 结果：①光镜下见酸性成纤维细胞生长因子受体主要定位在毛细血管壁;酸性成纤维细胞生长因子+纤维蛋白凝胶组毛细血管酸性成纤维细胞生长因子受体表达数量多,血管壁内酸性成纤维细胞生长因子受体表达广泛、密度高,毛细血管密集;单纯植入纤维蛋白凝胶组及空白对照组毛细血管酸性成纤维细胞生长因子受体表达数量少,血管壁内酸性成纤维细胞生长因子受体表达范围少、密度低,毛细血管稀少;酸性成纤维细胞生长因子+纤维蛋白凝胶组毛细血管酸性成纤维细胞生长因子受体表达阳性率高于单纯植入纤维蛋白凝胶组及空白对照组。③酸性成纤维细胞生长因子+纤维蛋白凝胶组酸性成纤维细胞生长因子受体表达量高于单纯植入纤维蛋白凝胶组及空白对照组。 结论：酸性成纤维细胞生长因子作用于毛细血管,通过改善运动终板附近微循环而保护运动终板。     

Electrical stimulation based on chronaxie reduces atrogin-1 and myoD gene expressions in denervated rat muscle

Denervation induces muscle fiber atrophy and changes in the gene expression rates of skeletal muscle. Electrical stimulation (ES) is a procedure generally used to treat denervated muscles in humans. This study evaluated the effect of ES based on chronaxie and rheobase on the expression of the myoD and atrogin-1 genes in denervated tibialis anterior (TA) muscle of Wistar rats. Five groups were examined: (1) denervated (D); (2) D+ES; (3) sham denervation; (4) normal (N); and (5) N+ES. Twenty muscle contractions were stimulated every 48 h using surface electrodes. After 28 days, ES significantly decreased the expression of myoD and atrogin-1 in D+ES compared to the D group. However, ES did not prevent muscle-fiber atrophy after denervation. Thus, ES based on chronaxie values and applied to denervated muscles using surface electrodes, as normally used in human rehabilitation, was able to reduce the myoD and atrogin-1 gene expressions, which are related to muscular growth and atrophy, respectively. The results of this study provide new information for the treatment of denervated skeletal muscle using surface ES.     

Electrical stimulation increases matrix metalloproteinase-2 gene expression but does not change its activity in denervated rat muscle

Muscle-fiber atrophy occurs concomitantly with intramuscular connective tissue proliferation following denervation. These events contribute to the impairment of mechanical and functional properties of denervated muscles and compromise their recovery. Electrical stimulation (ES) is used in human rehabilitation to treat denervated muscles. However, the effects of this therapy on the intramuscular extracellular matrix (ECM) remain uncertain. Metalloproteinases (MMPs) are responsible by remodeling ECM in many neuromuscular disorders. This study evaluates the effect of ES on the activity of two important MMPs, MMP-2 and MMP-9, both involved in ECM remodeling of rat denervated muscles. Thirty-four Wistar rats (3 months old, 356 +/- 38.7 g) were divided into five groups: denervated (D); D+ES; sham denervation; normal (N); and N+ES. Twenty maximal muscle contractions were stimulated every 48 h using surface electrodes, as generally used in the rehabilitation of human denervated muscle. Both zymographic analysis and real-time polymerase chain reaction (PCR) of MMPs were used to evaluate muscle after denervation for 28 days. Both the D and D+ES groups showed increased MMP-2 activity compared with the N group (P < 0.05). Furthermore, only the D+ES had increased MMP-2 gene expression compared with the N group (P < 0.05). MMP-9 activity was not detected in any of the groups. The results of this study indicate that denervation increases MMP-2 activity, and ES regulates MMP-2 gene expression in rat denervated skeletal muscle. These findings clarify the effects of ES on the ECM of denervated muscle and may be helpful in designing new therapeutic strategies for rehabilitation in patients with denervation of muscle.     

Effect of nerve extract on atrophy of denervated or immobilized muscles

Changes in denervated muscles are due to disuse caused by paralysis of the muscle and the loss of special neurotrophic substances. We determined the relative roles of these two factors in the production of atrophy in denervated rats' extensor digitorum longus (EDL) muscles. Muscles were denervated and/or immobilized (by fixation of the ankle) for 7 days. Some rats also received daily intramuscular injections of a saline extract of rats' sciatic nerves (2.0 mg protein/ml). Atrophy was assessed by measurement of wet weight, total protein, and cross-sectional areas of types IIA and IIB fibers (in sections stained for ATPase). Both denervation and immobilization produced significant decreases in weight, protein, and areas of fiber. The group of rats with denervated EDL muscles had significantly greater atrophy than the group with immobilized muscles. In another group, denervated EDL muscles had significantly greater atrophy than contralateral muscles which were immobilized. However, when denervated muscles were injected with nerve extract, they did not differ significantly from contralateral, noninjected, immobilized muscles. Comparisons of the group of rats in which one EDL was denervated with groups in which one muscle was immobilized or was denervated and injected with nerve extract, indicated that loss of trophic influence was responsible for about 40% of the decreases in wet weight, total protein, and cross-sectional area of type IIB fibers, and the remaining 60% was due to disuse. Loss of trophic influence was responsible for only about 5% of the atrophy of denervated type IIA fibers. Therefore, inactivity and loss of neurotrophic influence were responsible for the atrophy which occurred in denervated skeletal muscles, and these two factors influenced the two types of fiber differently. The component of denervation atrophy due to loss of trophic influence could be completely prevented by injection of substances extracted from peripheral nerves.     

Changes in intramuscular collagen and fibronectin in denervation atrophy

The distribution of collagen types I, III, and V and fibronectin was investigated by means of immunofluorescent techniques in denervated and normal rat skeletal muscle. During a period of 28 days, a distinct atrophy developed in the denervated gastrocnemius muscle and was accompanied by an increase in types I and III collagen in the endomysium and perimysium. The amount of type V collagen showed little change, whereas fibronectin increase closely parallelled types I and III collagen. The results indicate that denervation atrophy in muscles is accompanied by striking fibrotic changes due to mesenchymal types I and III collagen.     

Insulin-like growth factor I slows the rate of denervation induced skeletal muscle atrophy

Loss of the nerve supply to skeletal muscle results in a relentless loss of muscle mass (atrophy) over time. The ability of insulin-like growth factor-1 to reduce atrophy resulting from denervation was examined after transection of the sciatic nerve in transgenic MLC/mIGF-1 mice that over-express mIGF-1 specifically in differentiated myofibres. The cross sectional area (CSA) of all types of myofibres and specifically type IIB myofibres was measured in tibialis anterior muscles from transgenic and wild-type mice at 28 days after denervation. There was a marked myofibre atrophy ( approximately 60%) in the muscles of wild-type mice over this time with increased numbers of myofibres with small CSA. In the muscles of MLC/mIGF-1 mice, over-expression of mIGF-1 reduced the rate of denervation induced myofibre atrophy by approximately 30% and preserved myofibres with larger CSA, compared to wild-type muscles. It is proposed that the protective effect of mIGF-1 on denervated myofibres might be due to reduced protein breakdown.     

Transferrin receptor 1 plays an important role in muscle development and denervation-induced muscular atrophy

Previous studies demonstrate an accumulation of transferrin and transferrin receptor 1(TfR1) in regenerating peripheral nerves.However, the expression and function of transferrin and TfR1 in the denervated skeletal muscle remain poorly understood.In this study, a mouse model of denervation was produced by complete tear of the left brachial plexus nerve.RNA-sequencing revealed that transferrin expression in the denervated skeletal muscle was upregulated, while TfR1 expression was downregulated.We also investigated the function of TfR1 during development and in adult skeletal muscles in mice with inducible deletion or loss of TfR1.The ablation of TfR1 in skeletal muscle in early development caused severe muscular atrophy and early death.In comparison, deletion of TfR1 in adult skeletal muscles did not affect survival or glucose metabolism, but caused skeletal muscle atrophy and motor functional impairment, similar to the muscular atrophy phenotype observed after denervation.These findings suggest that TfR1 plays an important role in muscle development and denervation-induced muscular atrophy.This study was approved by the Institutional Animal Care and Use Committee of Beijing Institute of Basic Medical Sciences, China(approval No.SYXK 2017-C023) on June 1, 2018.     

Mechano-sensitivity of normal and long term denervated soleus muscle of the rat

INTRODUCTION AND OBJECTIVES: Evidence showed that physical forces, as passive stretching or active contraction, may counteract various kinds of skeletal muscle atrophy due, for instance, to muscle immobilization, pathophysiology or denervation. Accordingly, active muscle contraction induced by functional electric stimulation is helpful to reduce the muscle atrophic state in denervated man. Moreover, there is evidence that also passive mechanical stimulation of the sarcolemnic membrane may reduce the atrophic muscle state. As to the mechanisms by which mechanical stimulation modulates muscle physiology and pathophysiology, there is a growing list of facts that signaling pathway to the nucleus involves stretch activated channels (SACs) of the sarcolemma and the cytoskeleton. SACs activation allowed a Ca(2+) inflow that activates Ca(2+)-dependent molecular signals. Cytoskeleton may be activated by Ca(2+)-dependent and -independent paths and its contraction and elongation represent not only a mechanical signal to the nucleus but also a stimulus for many molecular signals. The aim of this work was to evaluate in soleus muscle of the rat, the mechano-sensitivity of SACs before and after medium and long term denervation. METHODS: Electrophysiologic experiments were made in normal and denervated Soleus muscle of Wistar rats. Currents were recorded in voltage clamp by intracellular microelectrodes inserted in a single fiber. RESULTS: Our findings demonstrated that SACs were expressed in normal soleus muscle and that SAC currents were potentiated by muscle stretching. Another important result was that the sensitivity to stretching increased after denervation and was particularly evident in long term denervated muscles. DISCUSSION: The reported effects are in agreement with the effects of exercise on inducing muscle hypertrophy or with the positive effects on repairing the atrophic state of skeletal muscles by mechanical stimulation or, in denervated humans, by the functional electrical stimulation (FES).     

Effect of ketoleucine treatment on atrophy of skeletal muscle

There is a net loss of skeletal muscle protein in muscle-wasting disorders including the muscular dystrophies and denervation atrophy. Regardless of the nature of the underlying defect, a treatment that could reduce the rate of muscle protein degradation may be of therapeutic value in these conditions. Ketoleucine (alpha-ketoisocaproic acid) has been reported to reduce the rate of protein degradation in skeletal muscle. To evaluate ketoleucine's therapeutic potential, we studied its effect on the muscle protein loss that follows denervation in rats. Maximum tolerated doses of ketoleucine were administered twice daily to rats after surgical denervation of one leg. Wet weights and noncollagen proteins of the soleus and extensor digitorum longus muscles were measured. The ketoleucine-treated animals failed to show significant decrease in muscle wasting, compared with nontreated denervated controls. Further, urinary 3-methylhistidine excretion, a putative measure of muscle breakdown, was not reduced in ketoleucine-treated animals. Our findings do not support the suggested therapeutic role for ketoleucine in muscle-wasting disease.