Frontiers in Microbiology (Feb 2014)

Biophysical features of MagA expression in mammalian cells: implications for MRI contrast

  • Anindita eSengupta,
  • Anindita eSengupta,
  • Anindita eSengupta,
  • Karina eQuiaoit,
  • Karina eQuiaoit,
  • Karina eQuiaoit,
  • R Terry Thompson,
  • R Terry Thompson,
  • Frank S Prato,
  • Frank S Prato,
  • Neil eGelman,
  • Neil eGelman,
  • Donna E Goldhawk,
  • Donna E Goldhawk,
  • Donna E Goldhawk

DOI
https://doi.org/10.3389/fmicb.2014.00029
Journal volume & issue
Vol. 5

Abstract

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We compared overexpression of the magnetotactic bacterial gene MagA with the modified mammalian ferritin genes HF+LF, in which both heavy and light subunits lack iron response elements. Whereas both expression systems have been proposed for use in non-invasive, magnetic resonance (MR) reporter gene expression, limited information is available regarding their relative potential for providing gene-based contrast. Measurements of MR relaxation rates in these expression systems are important for optimizing cell detection and specificity, for developing quantification methods, and for refinement of gene-based iron contrast using magnetosome associated genes. We measured the total transverse relaxation rate (R2*), its irreversible and reversible components (R2 and R2′, respectively) and the longitudinal relaxation rate (R1) in MDA-MB-435 tumor cells. Clonal lines overexpressing MagA and HF+LF were cultured in the presence and absence of iron supplementation, and mounted in a spherical phantom for relaxation mapping at 3 Tesla. In addition to MR measures, cellular changes in iron and zinc were evaluated by inductively-coupled plasma mass spectrometry, in ATP by luciferase bioluminescence and in transferrin receptor by Western blot. Only transverse relaxation rates were significantly higher in iron-supplemented, MagA- and HF+LF-expressing cells compared to non-supplemented cells and the parental control. R2* provided the greatest absolute difference and R2′ showed the greatest relative difference, consistent with the notion that R2′ may be a more specific indicator of iron-based contrast than R2, as observed in brain tissue. Iron supplementation of MagA- and HF+LF-expressing cells increased the iron/zinc ratio approximately 20-fold, while transferrin receptor expression decreased approx. 10-fold. Level of ATP was similar across all cell types and culture conditions. These results highlight the potential of magnetotactic bacterial gene expression for improving MR contrast.

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