Non-invasive imaging using reporter genes altering cellular water permeability
Non-invasive imaging of gene expression in live, optically opaque animals is important for multiple applications, including monitoring of genetic circuits and tracking of cell-based therapeutics. Magnetic resonance imaging (MRI) could enable such monitoring with high spatiotemporal resolution. However, existing MRI reporter genes based on metalloproteins or chemical exchange probes are limited by their reliance on metals or relatively low sensitivity. Here we introduce a new class of MRI reporters based on the human water channel aquaporin 1. We show that aquaporin overexpression produces contrast in diffusion-weighted MRI by increasing tissue water diffusivity without affecting viability. Low aquaporin levels or mixed populations comprising as few as 10% aquaporin-expressing cells are sufficient to produce MRI contrast. We characterize this new contrast mechanism through experiments and simulations, and demonstrate its utility in vivo by imaging gene expression in tumours. Our results establish an alternative class of sensitive, metal-free reporter genes for non-invasive imaging.
© 2016 Macmillan Publishers Limited. This work is licensed under a Creative Commons Attribution 4.0 International License. The images or other third party material in this article are included in the article's Creative Commons license, unless indicated otherwise in the credit line; if the material is not included under the Creative Commons license, users will need to obtain permission from the license holder to reproduce the material. To view a copy of this license, visit http://creativecommons.org/licenses/by/4.0/ Received: 12 May 2016. Accepted: 10 November 2016. Published online: 23 December 2016. We acknowledge George Lu, Pradeep Ramesh, Russell Jacobs, Xiaowei Zhang and Michael Tyszka for helpful discussions, and Philip Petersen for experimental contributions. A.M. was supported by the James G. Boswell Fellowship in Molecular Engineering and MRI. D.W. was supported by a Medical Engineering Amgen Fellowship. This research was supported by the Dana Foundation, the Burroughs Wellcome Career Award at the Scientific Interface and the National Institutes of Health (U54CA199090A). Work in the Shapiro laboratory is also supported by the Heritage Medical Research Institute, the Pew Scholarship in the Biomedical Sciences and the Packard Fellowship for Science and Engineering. These authors contributed equally to this work: Arnab Mukherjee & Di Wu. Author Contributions: A.M. and M.G.S. conceived the study. A.M. designed, performed and analysed data from in vitro experiments. A.M. and D.W. designed, performed and analysed data from in vivo experiments. H.C.D. designed and performed the simulations with input from co-authors. All authors contributed to the study design. A.M., M.G.S., D.W. and H.C.D. wrote the manuscript. Data availability: All data presented in support of the findings in this study and plasmids are available from the authors upon request. Code availability: Python and MATLAB scripts for Monte Carlo simulations are available at http://shapirolab.caltech.edu/?page_id=525. The authors declare no competing financial interests. Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.
Submitted - 037515.full.pdf
Supplemental Material - ncomms13891-s1.pdf
Published - ncomms13891.pdf