Increased expression of direct gene transfer into skeletal muscles observed after acute ischemic injury in rats

The direct injection of plasmid DNA into skeletal muscles represents a novel strategy that is potentially applicable to lower limb ischemic diseases. Most previous studies that involved skeletal muscle gene transfer have used only normal animals, however, and the efficiency of gene transfer into the ischemic muscles has not yet been well characterized. Accordingly, we sought to determine the extent to which gene expression is altered by performing skeletal muscle transfection under ischemic conditions. The femoral artery was ligated in one limb to induce limb ischemia in rats. The rectus femoris muscle of the ipsilateral limb was transfected 0 to 14 days later with the plasmid pRSVLUC, which contains the firefly luciferase coding sequence. Muscles of the contralateral nonischemic limb also were transfected in an identical fashion to serve as controls. At the end of the study, the rectus femoris muscle of the ischemic limb showed a significant reduction in weight compared with the controls (0.99 +/- 0.02 mg vs 1.07 +/- 0.03 mg, p < 0.0001), which demonstrates that the ligation of the femoral artery created significant limb ischemia in this animal model. Luciferase expression was readily detected in all 98 transfected limb muscles from 49 rats but not in nontransfected muscles or other organs. The relative luciferase activity (ischemic limb to nonischemic limb) calculated for each rat was 1.64 +/- 0.49 at Day 0. It significantly increased after Day 4 (3.76 +/- 1.33), reached its peak at Day 7 (9.00 +/- 3.38, p < 0.05), and declined to the base-line levels by Day 14 (1.44 +/- 0.43). These in vivo results indicate that gene expression after skeletal muscle transfection is significantly augmented by transfecting genes under ischemic conditions, which may have potential implications to increase the efficacy of gene therapy for lower limb vascular occlusive disease.