Adenoviral vector mediated ferritin over-expression in mesenchymal stem cells detected by 7T MRI in vitro

OBJECTIVE The aim of the present work was to verify whether adenoviral vector mediated ferritin over-expression in mesenchymal stem cells could be detected by 7T MRI device, and to explore the relationship between ferritin content and MRI signal intensities. METHODS A recombined adenoviral vector (rAdV) encoding ferritin heavy chain (FTH1) subunit was specially designed for the aim of infecting bone marrow mesenchymal stem cells (BMSCs). Ferritin over-expression in BMSCs was determined by cell immunocytochemistry and the ferritin content in cells was determined by ELISA assay. BMSCs were subjected to cell viability, proliferation and multi-differentiation analyses as well as 7T MRI test using fast spin-echo pulse sequence. The R2 value andδR2 were calculated according to T2 mapping images. RESULTS As was confirmed by cell immunocytochemistry and ELISA assay, rAdV mediated ferritin was over-expressed in BMSCs. Ferritin over-expression did not interfere with stem cell viability or pluripotent differentiation but slowed cell proliferation. The R2 value of BMSCs-FTH1 vs control BMSCs from 1-4 weeks was16.65±1.28 s-1 vs 13.99±0.80 s-1, (t = 3.94, p = 0.004), 15.63±1.37 s-1 vs 13.87±0.83 s-1 (t = 2.47, p = 0.039), 15.53±0.88 s-1 vs 14.25±0.53 s-1 (t = 2.80, p = 0.023) and 14.61±1.28 s-1 vs 13.69±1.03 s-1 (t = 1.25, p = 0.24), respectively. δR2 gradually decreased from 1-4 weeks and the difference between the groups had statistical significance (F = 12.45, p<0.01).δR2 was positively correlated with OD value (r = 0.876, p<0.01) and ferritin concentration (r = 0.899, p<0.01) as determined by Pearson correlation. CONCLUSIONS Our study confirms that ferritin could be over-expressed in BMSCs as a result of rAdV mediated infection and could be quantitatively detected by 7T MRI device. The differences in T2 signal intensities and R2 values stem from internal contrast generated by endogenous ferritin over-expression. The correlation between δR2, OD and ferritin concentration suggests that MRI can detect ferritin signal change accurately.