In vivo imaging of labelled neural stem cells in a mouse model of spinal cord injury

Introduction: Recent discoveries describe the possibility to use neural stem cells (NSC) in cell-mediated therapeutic protocols, for the regeneration of damaged tissues. Treatment efficacy evaluation is generally based on functional recovery end points, skipping the evaluation of the distribution of injected cells, localization at the target organ, cell survival and differentiation. Here we tested a multiple labelling approach for in vivo visualization by MRI and Bioluminescence Imaging (BLI) of murine NSC in a mouse model of traumatic spinal cord injury [1]. Methods: NSC, isolated from the subventricular zone of the adult mouse brain, were labelled for 24 h with 200 g Fe/ml of Endorem®, in presence of Protamine Sulphate and analyzed for iron content, viability, morphology and differentiation capability. Labelled cells were injected either locally, at the site of the injury, or systemically into the tail vein and followed by MRI (Bruker Pharmascan 7.0 T) for more than a month to visualize NSC localization at the lesion site. Cells distribution and viability were also analyzed in vivo by BLI (Xenogen IVIS 100) after injection of NSC infected with a viral vector expressing luciferase. After imaging, mice were perfused with PFA and spinal cords extracted to perform ex vivo MRI and histopathological analysis. Results: Iron oxide labelling procedure did not significantly perturb viability and proliferation rate of NSC. The percentage of iron positive cells increased with the PS content in the medium, reaching 210 pg Fe/cell. NSC, infected with the viral vector, were detected by BLI at the site of the injury after intramedullary injection, and at the same site one week after i.v. injection. MRI showed on both RARE T2-W and FLASH images an hypointense signal due to Fe+ labelled cells at the injury site three weeks after i.v. injection. Iron presence was confirmed on ex vivo MR images and on histological sections of perfused spinal cords. Conclusions: Adult NSC can be efficiently labelled without significantly perturbing physiological features and self-renewal capability. Labelled NSC were visualized in vivo by MRI and BLI providing information on their localization at the spinal cord injury site and survival.