Blaauw Bert, Mammucari Cristina, Toniolo Luana, Agatea Lisa, Abraham Reimar, Sandri Marco, Reggiani Carlo, Schiaffino Stefano
Department of Biomedical Sciences, CNR Institute of Neurosciences, University of Padova, Padova, Italy.
Hum Mol Genet. 2008 Dec 1;17(23):3686-96. doi: 10.1093/hmg/ddn264. Epub 2008 Aug 27.
Skeletal muscles of the mdx mouse, a model of Duchenne Muscular Dystrophy, show an excessive reduction in the maximal tetanic force following eccentric contractions. This specific sign of the susceptibility of dystrophin-deficient muscles to mechanical stress can be used as a quantitative test to measure the efficacy of therapeutic interventions. Using inducible transgenesis in mice, we show that when Akt activity is increased the force drop induced by eccentric contractions in mdx mice becomes similar to that of wild-type mice. This effect is not correlated with muscle hypertrophy and is not blocked by rapamycin treatment. The force drop induced by eccentric contractions is similar in skinned muscle fibers from mdx and Akt-mdx mice when stretch is applied directly to skinned fibers. However, skinned fibers isolated from mdx muscles exposed to eccentric contractions in vivo develop less isometric force than wild-type fibers and this force depression is completely prevented by Akt activation. These experiments indicate that the myofibrillar-cytoskeletal system of dystrophin-deficient muscle is highly susceptible to a damage caused by eccentric contraction when elongation is applied in vivo, and this damage can be prevented by Akt activation. Microarray and PCR analyses indicate that Akt activation induces up-regulation of genes coding for proteins associated with Z-disks and costameres, and for proteins with anti-oxidant or chaperone function. The protein levels of utrophin and dysferlin are also increased by Akt activation.
mdx小鼠是杜兴氏肌营养不良症的模型，其骨骼肌在离心收缩后最大强直力过度降低。肌营养不良蛋白缺陷型肌肉对机械应力敏感性的这一特定迹象可作为一种定量测试，用于衡量治疗干预的效果。利用小鼠中的诱导转基因技术，我们发现当Akt活性增加时，mdx小鼠离心收缩诱导的力下降变得与野生型小鼠相似。这种效应与肌肉肥大无关，且不受雷帕霉素治疗的阻断。当直接对去表皮肌纤维施加拉伸时，mdx和Akt-mdx小鼠的去表皮肌纤维中离心收缩诱导的力下降相似。然而，从体内经历过离心收缩的mdx肌肉中分离出的去表皮纤维产生的等长力比野生型纤维小，而Akt激活可完全防止这种力的降低。这些实验表明，当在体内施加伸长时，肌营养不良蛋白缺陷型肌肉的肌原纤维 - 细胞骨架系统对离心收缩引起的损伤高度敏感，而这种损伤可通过Akt激活来预防。微阵列和PCR分析表明，Akt激活诱导编码与Z盘和肌膜小体相关蛋白质以及具有抗氧化或伴侣功能蛋白质的基因上调。Akt激活还会增加抗肌萎缩蛋白和dysferlin的蛋白质水平。
