Magnetic Resonance Imaging of Cells Overexpressing MagA, an Endogenous Contrast Agent for Live Cell Imaging

Abstract

Molecular imaging with magnetic resonance imaging (MRI) may benefit from the ferrimagnetic properties of magnetosomes, membrane-enclosed iron biominerals whose formation in magnetotactic bacteria is encoded by multiple genes. One such gene is MagA, a putative iron transporter. We have examined expression of MagA in mouse neuroblastoma N2A cells and characterized their response to iron loading and cellular imaging by MRI. MagA expression augmented both Prussian blue staining and the elemental iron content of N2A cells, without altering cell proliferation, in cultures grown in the presence of iron supplements. Despite evidence for iron incorporation in both MagA and a variant, MagAE137V, only MagA expression produced intracellular contrast detectable by MRI at 11 Tesla. We used this stable expression system to model a new sequence for cellular imaging with MRI, using the difference between gradient and spin echo images to distinguish cells from artifacts in the field of view. Our results show that MagA activity in mammalian cells responds to iron supplementation and functions as a contrast agent that can be deactivated by a single point mutation. We conclude that MagA is a candidate MRI reporter gene that can exploit more fully the superior resolution of MRI in noninvasive medical imaging.

The MagA Protein of Magnetospirilla Is Not Involved in Bacterial Magnetite Biomineralization

“…Although beyond the scope of our study, it can be speculated that MagA has a function in the homeostasis of monovalent cations, such as sodium or potassium, under certain, still-unexplored growth conditions. In apparent contrast to its lack of function in bacterial magnetite biomineralization, the heterologous expression of magA in mammalian cell lines reportedly caused rather drastic effects, resulting in a 7-fold increased intracellular iron content or the formation of small magnetite particles (9,46). However, the disparity of these observations argues against effects associated with the genuine function of MagA and could be explained by pathological consequences of gene expression or artificially high iron levels used in these studies.…”

“…Goldhawk et al (9) described that the expression of magA in N2A mouse neuroblastoma cell lines resulted in elevated intracellular MRI contrast due to the increased iron load of the cells. Even more intriguingly, Zurkiya et al (46) reported that the expression of magA in human 293FT cell lines was sufficient to cause the biomineralization of small magnetite particles.…”

Longitudinal Monitoring of Stem Cell Grafts In Vivo Using Magnetic Resonance Imaging with Inducible Maga as a Genetic Reporter

“…To date, several genetic MRI reporting systems have been investigated, including creatine kinase 24, divalent metal transporter (DMT1) 25, ferritin 26-34, β-galactosidase 35, MagA 23, 32, 36, and tyrosinase 37. Most of these genetic reporters were developed for monitoring metastatic cancer cells 23, 26, 27, 31, 32, 36, and only ferritin has been reported for monitoring stem cell grafts in mice 33. Until now, there were no reports on the longitudinal monitoring of stem cell grafts using a genetic MRI reporter, particularly in an inducible manner, which is important to minimize the potential toxicity from the constitutive expression of the imaging reporter.…”

The Role of Nanotechnology in Induced Pluripotent and Embryonic Stem Cells Research

“…170 Other methods for long-term tracking of distribution and engraftment of stem cells in infarct myocardium include, magnetic resonance reporter genes and a combination of magnetic nanoparticles and reporter genes. [171][172][173][174][175] …”