Protective effects of heme oxygenase-1 gene transfer mediated by adeno-associated virus on spinal cord injury in rats

Objective To investigate the effect of heme oxygenase-1 (HO-1) overexpression on motor function recovery after spinal cord injury (SCI), and its mechanism in rats. Methods Ninety-six adult male Sprague-Dawley rats were randomly assigned to 4 groups, including Sham, SCI, AAV-enhanced green fluorescent protein (EGFP) and AAV-HO-1 groups in completely randomized method. SCl was induced by epidural compression. Motor function of hind limbs was evaluated by Basso-Beattie-Bresnahan (BBB) score. The expression levels of green fluorescence in injured spinal cord tissue were evaluated by fluorescence microscope. The expression levels of NeuN positive cells in spinal cord tissue were detected by immunofluorescence. Western blotting and TdT-mediated dUTP nick end labeling (TUNEL) were also performed. Results The expressions of green fluorescence in injured spinal cord tissue were observed in the AAV-EGFP and AAV-HO-1 groups one day after SCI. In addition, compared with SCI group and AAV-EGFP group, the level of B cell lymphoma/leukemia-2 associated X protein (bax) proteinin AAV-HO-1 group (1.96±0.24, 1.77±0.30 and 1.15±0.19, respectively)and the number of TUNEL-positive cells in AAV-HO-1 group [(49.83±13.60)%, (44.83±11.74)% and (21.50±8.02)%], respectively)were significantly decreased (F=29.900, P=0.000 and F=30.630, P=0.000) but the level of HO-1 (1.48±0.23, 1.54±0.16 and 1.96±0.28, respectively) and B-cell lymphoma/leukemia-2 (bcl-2) (0.35±0.11, 0.29±0.10 and 0.69±0.13, respectively) protein was significantly increased(F=23.900, P=0.000 and F=68.140, P=0.000) one day after SCI. The BBB score of AAV-HO-1 group (8.00±1.79, 11.67±2.16 and 13.83±2.22, respectively)at 7 d, 14 d and 21 d after SCI was significantly lower than that of SCI group (5.17±1.94, 6.17±1.72 and 7.50±1.97, respectively) and AAV-EGFP group (4.67±1.51, 5.67±1.86 and 7.17±2.14, respectively; F=152.900, P=0.000, F=109.700, P=0.000 and F=75.880, P=0.000, respectively). AAV-HO-1 group (108.5±27.74)compared with SCI group (50.00±20.93) and AAV-EGFP group (55.83±13.57), NeuN positive cells increased significantly(F=40.740, P=0.000). Conclusion Overexpression of HO-1 can promote the survival of spinal cord neurons and the recovery of limb motor function in SCI rats, and has a protective effect on SCI. Key words: Spinal cord injury; Adeno-associated virus; Heme oxygenase-1; Gene therapy