Evaluating the effectiveness of transferrin receptor‐1 (TfR1) as a magnetic resonance reporter gene

Abstract

Magnetic resonance (MR) reporter genes have the potential for tracking the biodistribution and fate of cells in vivo, thus allowing the safety, efficacy and mechanisms of action of cell‐based therapies to be comprehensively assessed. In this study, we evaluate the effectiveness of the iron importer transferrin receptor‐1 (TfR1) as an MR reporter gene in the model cell line CHO‐K1. Overexpression of the TfR1 transgene led to a reduction in the levels of endogenous TfR1 mRNA, but to a 60‐fold increase in total TfR1 protein levels. Although the mRNA levels of ferritin heavy chain‐1 (Fth1) did not change, Fth1 protein levels increased 13‐fold. The concentration of intracellular iron increased significantly, even when cells were cultured in medium that was not supplemented with iron and the amount of iron in the extracellular environment was thus at physiological levels. However, we found that, by supplementing the cell culture medium with ferric citrate, a comparable degree of iron uptake and MR contrast could be achieved in control cells that did not express the TfR1 transgene. Sufficient MR contrast to enable the cells to be detected in vivo following their administration into the midbrain of chick embryos was obtained irrespective of the reporter gene. We conclude that TfR1 is not an effective reporter and that, to track the biodistribution of cells with MR imaging in the short term, it is sufficient to simply culture cells in the presence of ferric citrate. Copyright © 2016 The Authors Contrast Media & Molecular Imaging Published by John Wiley & Sons Ltd.

MS-1magA

“…30 We have previously shown that overexpression of iron transporters such as TFR1 can lead to a decrease in the expression of endogenous transferrin receptors and an upregulation of ferritin expression. 31 In contrast to TFR1 overexpression, magA did not affect the expression of endogenous TFR1 , although we have seen a modest increase in FTH1 protein. Although it is tempting to suggest that this could be related to magA ’s function as an iron transporter, leading to more iron uptake and consequently an increase in FTH1 translation, recent evidence suggests that magA is not only unnecessary for magnetosome formation in MTBs but also unlikely to work as an iron transporter.…”

Genetically Controlled Lysosomal Entrapment of Superparamagnetic Ferritin for Multimodal and Multiscale Imaging and Actuation with Low Tissue Attenuation

“…Due to surface effects and cation vacancies in its antiferromagnetic iron core, ferritin generates detectable T 2 ‐derived MR‐contrast . However, despite all efforts to further improve its relaxivity,[1c,2] ferritin still does not qualify as a robust gene reporter for MRI, mainly because of the limits imposed by its weakly magnetized ferrihydrite core. [1b]…”

Optical fluorescence imaging with shortwave infrared light emitter nanomaterials for in vivo cell tracking in regenerative medicine

“…Thus, approximately 10% of these nanoparticles can be seen in the macrophages and finally lead to misinterpretation of results related to the location and survival of therapeutic administered cells . Indirect labelling of the transplanted cells is implemented by the genetic manipulation via MRI reporter gene, but this method lacks sufficient sensitivity for the cell detection . MRI offers the best anatomical position of the cell graft but lacks adequate information about function, viability and behaviour of the transplanted cells …”

“…68 Longitudinal relaxation time agents (paramagnetic-based agents, implemented by the genetic manipulation via MRI reporter gene, but this method lacks sufficient sensitivity for the cell detection. 68,89 MRI offers the best anatomical position of the cell graft but lacks adequate information about function, viability and behaviour of the transplanted cells. 90…”