Using the tyrosinase gene as a tri-modality reporter gene for monitoring transplanted stem cells in acute myocardial infarction

Objectives: Bone marrow mesenchymal stem cells (MSCs) have been proved to own therapeutic potential for limiting infarct size and improve cardiac function after acute myocardial infarction (AMI). The study aimed to investigate the feasibility of noninvasive monitoring of MSCs transfected with the tyrosinase (TYR) reporter gene for AMI with photoacoustic imaging (PAI), magnetic resonance imaging (MRI), and positron emission tomography (PET) in vitro and in vivo.

Methods: MSCs harvested from Sprague-Dawley rats were transduced with a lentivirus carrying a TYR reporter gene and selected by puromycin. TYR protein expression in transduced MSCs (TYR-MSCs) was evaluated by Masson-Fontana silver staining, a tyrosinase kinase activity assay, and western blot. After transduction, the rate of ¹⁸F-5-fluoro-N-(2-[diethylamino]ethyl)picolinamide (¹⁸F-5-FPN) uptake was measured. PAI and MRI of the TYR-MSCs were performed in vitro. AMI model was induced in a group of rats and verified in vitro by 2,3,5-triphenyltetrazolium chloride (TTC) and hematoxylin and eosin (H&E) staining, and in vivo with ¹⁸F-FDG myocardial metabolic imaging. To perform in vivo experiments, TYR-MSCs were injected into the margins of the infarcted areas, and MSCs without TYR transfection were served as control. PAI, MRI, and PET images were acquired 1, 7, 14, 21, and 28 days after cell injection.

Results: Uptake of ¹⁸F-5-FPN by TYR-MSCs were noticeably higher than that by non-transduced MSCs at 60, 90, and 120 min (P<0.05). In vitro cell imaging studies revealed that TYR-MSCs showed stronger signals in T1-weighted MRI and PAI in comparison to non-transduced MSCs. In vivo studies revealed prominent signals in the injected area of the infarcted myocardium on PAI/MRI/PET images, while no signal could be seen in rats injected with non-transduced MSCs. Uptake values of ¹⁸F-5-FPN in vivo showed a slight decrease over 28 days (Fig. 1), while MRI and PAI signal intensity decreased dramatically (Fig. 1).

Conclusion: MSCs stable transfected with the TYR gene cells could be monitored in vivo in myocardial infarction models by PET, MRI and PAI, which provides a feasible and reliable method for checking viability, location, and dwell time of transplanted stem cells. Research Support: This work was supported by the National Natural Science Foundation of China (No. 81371626).

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