Insulin-like growth factor-I gene transfer by electroporation prevents skeletal muscle atrophy in glucocorticoid-treated rats.

Schakman, Olivier [UCL] Gilson, Hélène [UCL] de Coninck, Virginie [UCL] Lause, Pascale [UCL] Verniers, Josiane [UCL] Havaux, Xavier [UCL] Ketelslegers, Jean-Marie [UCL] Thissen, Jean-Paul [UCL]

Hypercatabolic states caused by injury are characterized by a loss of skeletal muscle which is associated with an increased morbidity and mortality. The anabolic action of Insulin-like Growth Factor (IGF)-I on muscle and the reduction of its muscle content in response to injury suggest that IGF-I overexpression might prevent skeletal muscle loss caused by injury. To test this hypothesis, we investigated whether local overexpression of IGF-I gene by gene transfer could prevent skeletal muscle atrophy induced by dexamethasone. Localized overexpression of IGF-I in tibialis anterior (TA) muscle was performed by injection of DNA followed by electroporation 3 days before starting dexamethasone injections (0.1 mg/kg/d SC). A total of 100 μg of hIGF-I DNA inserted in the plasmid pM1 under control of the CMV promoter was injected in 10 injections of 10 μg each, followed by 10 pulses of 200 V/cm applied in 20 ms square wave at 1Hz. A control plasmid was electroporated in the contralateral TA muscle. Ten days after electroporation, animals were sacrificed by decapitation and tibialis anterior muscles were collected. As expected, dexamethasone induced atrophy of the muscle injected with the control plasmid. Indeed, TA muscle mass (40311, n=5 vs. 46119 mg, n=6; P <0.05), muscle area (31.71.7 vs. 35.80.8 mm2, P <0.05) and fiber cross-sectional area (1759131 vs. 251793 μm2, P <0.05) were decreased in dexamethasone-treated animals compared to control animals. This muscle atrophy was parallel with a decrease in the IGF-I muscle content (7.20.9 vs. 15.71.4 ng/g of muscle, P <0.001, n=6). However, in the TA muscle electroporated with IGF-I DNA, the muscle mass (4378 vs. 40311 mg, P <0.01, n=5), the muscle area (35.51.2 vs. 31.71.7 mm2, P <0.05) and the fiber cross-sectional area (2269129 vs. 1759131 μm2, P <0.05) were increased compared to the contralateral muscle electroporated with a control plasmid. As the result of IGF-I gene transfer, the IGF-I muscle content was about 2-fold higher in the IGF-I-treated muscle than in the contralateral muscle of the dexamethasone-treated rats (15.81.2 vs. 7.20.9 ng/g of muscle, P <0.001, n=6). In conclusion, our results show that IGF-I gene transfer by electroporation prevents muscle atrophy in dexamethasone-treated rats. In further investigations, we plan to test whether preventing loss of muscle mass by IGF-I overexpression in dexamethasone-treated animals is associated with improved functional muscle parameters.