Experimental study of monitoring stem cells with reporter gene in rat middle cerebral artery occlusion model

Objectives To investigate the feasibility of imaging mesenchymal stem cells (MSC) in rat middle cerebral artery occlusion (MCAO) models with reporter gene/probe system, HSV1-tk/131I-FIAU, and to get the optimal way of injecting stem cells and the time for acquiring image.

Methods The adenovirus recombinant, carrying HSV1-tk (as reporter gene)-internal ribosome entry site (IRES, as linker)-brain derived neurophic factor(BDNF, as therapeutic gene)-EGFP (Ad5-TIBE), was prepared. After transfected with Ad5-TIBE, MSC were injected to MCAO models via local injection to brain, lateral ventricle, carotid artery and tail vein, respectively. Normal rats were used as control group. 24 hours after 131I-FIAU injected, rats were killed to do biodistribution study. The expression of TK was evaluated by RQ-PCR and western-blot. Autoradiography (ARG) was done for ex vivo imaging.

Results The %ID/g of infarcted brain tissue in the local injection group was 0.12±0.01, which was significantly higher than that in ventricular (0.05±0.004), carotid (0.06±0.002), vein injection (0.06±0.005) and control group (0.005±0.001), but no difference could be seen among the other cell-transplanted groups. The %ID/g of infarcted brain tissue was higher than that of the contralateral brain tissue in all experimental groups, but not in control group. The expression of TK in local injection group was superior to all the other groups. TK mRNA and protein expression showed positive correlation with %ID/g in brain tissue. From ARG, higher radioactivity was seen on the injection site in all experimental groups than the surrounding and contralateral brain tissue. The ratio of gray values of bilateral brain tissue reached to the peak (6.63) at 24 hours.

Conclusions The reporter gene system HSV1-tk/131I-FIAU could be used to monitor MSC in MCAO rat. Local injection stem cells may be an optimal way for cell transplanted. 24 hours after injected with 131I-FIAU may be suitable time to get image for its highest target to non-target ratio.

Research Support Supported by NSFC 3077060