ABSTRACT
Objective To evaluate the feasibility of monitoring the gene expression of VEGF165 via the diglycylcysteine (GGC) reporter gene system by reporter probe of 99Tcm-GH. Methods DNA fragments encoding GGC binding motifs were prepared by PCR and positioned at the C end of VEGF165 gene after the linearization of pcDNA3-VEGF165 plasmid. A replication-defective adenovirus vector Ad5-VEGF165GGC motif-internal ribosomal entry site(IRES) -enhanced green fluorescent protein (EGFP) (Ad5-VIE)was constructed, with a cytomegalovirus (CMV) early promoter driving the expression of VEGF165 gene,GGC motif and EGFP, under the aid of an IRFS. A replication-defective adenovirus carrying the Ad5-EGFP was used as the control. Mensenchymal stem cells (MSC) were infected with the recombinant adenovirus at a multiplicity of infection (MOI) from 0 to 100 infectious units (0,10,25,50,100). The cellular uptake of 99Tcm-GH in infected MSC were then studied at 30, 60, 90 and 120 min. VEGF165 was detected by quantitative reverse transcriptase real-time PCR (RT-PCR), Western-blot, and immunohistochemisty. EGFP was observed by RT-PCR and fluorescence microscopy. The correlation analysis was studied between the cellular uptake of 99Tcm-GH and the expression of VEGF165. SPSS 13.0 was applied for statistical analysis. Independent samples t-test, q-test and Pearson correlation coefficient were used. Results After infected with different viral titer of Ad-VIE, the cellular uptake of 99Tcm-GH increased with the increasing virus titer(r2 =0.86, P ＜0.05), with the peak rate (7.94 ±0.75) % at MOI = 100. In time-dependent uptake study, the cellular uptake rates increased rapidly with the time extension, and the highest uptake occurred at 120 min with the peak uptake rate (7.72 ±0.22)%. The uptake rates of 99Tcm-GH in Ad5-VIE-infected cells were significantly higher than those of Ad5 -EGFP-transfected cells at all time points (t = 15.10- 54.92, all P ＜0.05). The VEGF165 and EGFP mRNA levels increased with increasing virus titer, and the VEGF165 mRNA correlated well with the EGFP mRNA(r2 = 0. 99, P ＜ 0.05). After infected with different MOI of Ad5-VIE, good relationship was found between the cellular uptake of 99Tcm-GH and the expression of VEGF165protein in MSC(r2 =0.90, P ＜0.05). Inmunohistochemisty showed VEGF165 protein expressed obviously at Ad5-VIE-infected MSC, and the EGFP was observed by fluorescence microscopy. Conclusions The cellular uptake of 99Tcm-GH in Ad5-VIE-infected MSC are well correlated with the expression of VEGF165 in vitro. The expression of therapeutic gene VEGF165 can be monitored by the GGC peptide expression.