Shavlakadze T, Boswell J M, Burt D W, Asante E A, Tomas F M, Davies M J, White J D, Grounds M D, Goddard C
School of Anatomy and Human Biology, The University of Western Australia, Crawley, Perth.
Growth Horm IGF Res. 2006 Jun;16(3):157-73. doi: 10.1016/j.ghir.2005.11.003. Epub 2006 May 22.
Human IGF-I was over-expressed in skeletal muscles of C57/BL6xCBA mice under the control of the rat skeletal alpha-actin gene promoter. RT-PCR verified expression of the transgene in skeletal muscle but not in the liver of 1- and 21-day old heterozygote transgenic mice. The concentration of endogenous mouse IGF-I, measured by an immunoassay which does not detect human IGF-I, was not significantly different between transgenic mice and wild-type littermates (9.5 +/- 0.8 and 13.3 +/- 1.9 ng/g in muscle; 158.3 +/- 18.6 and 132.9 +/- 33.1 ng/ml in plasma, respectively). In contrast, quantitation with antibodies to human IGF-I showed an increase in IGF-I of about 100 ng/ml in plasma and 150 ng/g in muscle of transgenic mice at 6 months of age. Transgenic males, compared to their age matched wild-type littermates, had a significantly higher body weight (38.6 +/- 0.53 g vs. 35.8 +/- 0.64 g at 6 months of age; P < 0.001), dry fat-free carcass mass (5.51 +/- 0.085 vs. 5.08 +/- 0.092 g; P < 0.001) and myofibrillar protein mass (1.62 +/- 0.045 vs. 1.49 +/- 0.048 g; P < 0.05), although the fractional content of fat in the carcass was lower (167 +/- 7.0 vs. 197 +/- 7.7 g/kg wet weight) in transgenic animals. There was no evidence of muscle hypertrophy and no change in the proportion of slow type I myofibres in the limb muscles of Rskalpha-actin/hIGF-I transgenic mice at 3 or 6 months of age. Phenotypic changes in Rskalpha-actin/hIGF-I mice are likely to be due to systemic as well as autocrine/paracrine effects of overproduction of IGF-I due to expression of the human IGF-I transgene. The effect of muscle specific over-expression of Rskalpha-actin/hIGF-I transgene was tested on: (i) muscle regeneration in auto-transplanted whole muscle grafts; (ii) myofibre atrophy following sciatic nerve transection; and (iii) sarolemmal damage and myofibre necrosis in dystrophic mdx muscle. No beneficial effect of muscle specific over-expression of Rskalpha-actin/hIGF-I transgene was seen in these three experimental models.
在大鼠骨骼肌α-肌动蛋白基因启动子的控制下，人胰岛素样生长因子I（IGF-I）在C57/BL6xCBA小鼠的骨骼肌中过表达。逆转录聚合酶链反应（RT-PCR）证实了转基因在1日龄和21日龄杂合子转基因小鼠的骨骼肌中表达，但在肝脏中未表达。通过一种无法检测人IGF-I的免疫测定法测量，转基因小鼠和野生型同窝仔鼠的内源性小鼠IGF-I浓度无显著差异（肌肉中分别为9.5±0.8和13.3±1.9 ng/g；血浆中分别为158.3±18.6和132.9±33.1 ng/ml）。相比之下，用抗人IGF-I抗体定量显示，6月龄转基因小鼠的血浆中IGF-I增加约100 ng/ml，肌肉中增加150 ng/g。与年龄匹配的野生型同窝仔鼠相比，转基因雄性小鼠体重显著更高（6月龄时为38.6±0.53 g对35.8±0.64 g；P<0.001），无脂干胴体质量更高（5.51±0.085对5.08±0.092 g；P<0.001），肌原纤维蛋白质量更高（1.62±0.045对1.49±0.048 g；P<0.05），尽管转基因动物胴体中的脂肪含量较低（湿重为167±7.0对197±7.7 g/kg）。在3或6月龄的Rskα-肌动蛋白/hIGF-I转基因小鼠的肢体肌肉中，没有肌肉肥大的证据，I型慢肌纤维比例也没有变化。Rskα-肌动蛋白/hIGF-I小鼠的表型变化可能是由于人IGF-I转基因表达导致IGF-I过量产生的全身以及自分泌/旁分泌效应。测试了Rskα-肌动蛋白/hIGF-I转基因肌肉特异性过表达对以下方面的影响：（i）自体移植全肌移植物中的肌肉再生；（ii）坐骨神经横断后的肌纤维萎缩；以及（iii）营养不良性mdx肌肉中的肌膜损伤和肌纤维坏死。在这三个实验模型中未观察到Rskα-肌动蛋白/hIGF-I转基因肌肉特异性过表达的有益作用。
