Cre/lox-assisted non-invasive in vivo tracking of specific cell populations by positron emission tomography

Martin Thunemann,Barbara F Schörg,Michael Schäfers,Jakob Voelkl,Manfred Kneilling,Christoph M Griessinger,Gerald Reischl,Matthias Golla,Marcus Olbrich,Florian Läng ,Susanne Feil,Meinrad Gawaz,Harald F Langer,Leticia Quintanilla-Martı́nez ,Angelos Vachaviolos,Yuan Lin ,Bernd J Pichler,Ursula Kohlhofer,Walter Ehrlichmann,Robert Feil

doi:10.1038/s41467-017-00482-y

Abstract

Many pathophysiological processes are associated with proliferation, migration or death of distinct cell populations. Monitoring specific cell types and their progeny in a non-invasive, longitudinal and quantitative manner is still challenging. Here we show a novel cell-tracking system that combines Cre/lox-assisted cell fate mapping with a thymidine kinase (sr39tk) reporter gene for cell detection by positron emission tomography (PET). We generate Rosa26-mT/sr39tk PET reporter mice and induce sr39tk expression in platelets, T lymphocytes or cardiomyocytes. As proof of concept, we demonstrate that our mouse model permits longitudinal PET imaging and quantification of T-cell homing during inflammation and cardiomyocyte viability after myocardial infarction. Moreover, Rosa26-mT/sr39tk mice are useful for whole-body characterization of transgenic Cre mice and to detect previously unknown Cre activity. We anticipate that the Cre-switchable PET reporter mice will be broadly applicable for non-invasive long-term tracking of selected cell populations in vivo.

Highlights

Many pathophysiological processes are associated with proliferation, migration or death of distinct cell populations
One such positron emission tomography (PET) reporter gene is the herpes simplex virus type 1 thymidine kinase (HSV1-tk). It is used in combination with 18F- or 124I-labeled nucleoside analogues, which are phosphorylated by HSV1-tk, but not by mammalian thymidine kinases
A cell population of interest is labeled by Cre-dependent activation of sr39tk expression and the fate of these cells is followed by non-invasive PET imaging with [18F]FHBG

Summary

Introduction

Many pathophysiological processes are associated with proliferation, migration or death of distinct cell populations. Transgenic mice with a chromosomally integrated Cre-responsive PET reporter gene have not been described to date In such a mouse line, Cre-expressing cell populations will be labeled for PET imaging through Cre-mediated activation of reporter gene expression at the genomic level. Once reporter gene expression is activated, cells and their progeny are stably labeled, even if the cells proliferate or change their phenotype, which may lead to a loss of Cre expression This approach would permit non-invasive long-term visualization of any given cell population for which a respective cell type-specific Cre mouse line is available. As these mice express membrane-targeted tandem-dimer tomato red fluorescent protein (mT) before Cre recombination and sr39tk after Cre recombination, we named them “R26-mT/sr39tk” mice In these mice, a cell population of interest is labeled by Cre-dependent activation of sr39tk expression and the fate of these cells is followed by non-invasive PET imaging with [18F]FHBG. The Cre-responsive PET reporter allele permits non-invasive whole-body characterization of transgenic Cre mouse lines

Methods

Results

Conclusion