Abstract 160: Non Invasive Detection of Vascular Pericytes in Living Brains After Forebrain Ischemia
Introduction: Endogenous neural progenitor cells (NPC) during tissue regeneration are detected in post mortem samples which often limit clinical applications. We aimed to detect pericytes, one type of NPC, as a biomarker for cerebral angiogenesis in live C57black6 mouse brains using magnetic resonance imaging (MRI). We attached short DNA to superparamagnetic iron oxide nanoparticles (SPION, a T2 contrast agent). Our SPION has no charge and does not enter cells by itself with sufficient efficiencies. By attaching DNA to SPION, we increase the uptake efficiencies of SPION-DNA and the resident time of SPION-DNA in the cell by binding to intracellular mRNA. The mechanism of rapid exclusion of unbound MR-visible probes in vivo can be applied in targeting MRI. Success lies in finding the optimal window after probe delivery to avoid imaging unbound probe. Because Nestin-and Actin-expressing pericytes are associated with new endothelia, we described here a novel strategy for imaging pericytes in newly formed cerebral vessels in living mouse brains using DNA-based MR-visible probes targeting these two mRNA transcripts.
Methods: We induced cerebral ischemia by occluding both carotid arteries for 30, 45 or 60 minutes (n ≥ 3 each, as determined by power analysis) in C57black6 mice. SPION were attached to short DNA targeting Actin and Nestin mRNA [40 ± 10 nm diameters, targeting capacity of 2.02 ± 1.23 × 10−15 mole per R2* elevation over the baseline] and delivered by minimally invasive intraperitoneal injection (4 mg Fe per kg). In vivo cell typing was analyzed 24 hours later by MR imaging.
Results: The lower limit of NPC detection with targeted MRI was 0.03 mm2 or 4 pixels in a 9.4T MR system. Bound SPION-sODN was validated afterwards by inductively coupled plasma-mass spectrometry, reverse transcription polymerase chain reaction, RNaseH protection assay, in vivo hybridization in knock-in mice producing Actin driven red fluorescence protein and immunohistochemistry.
Conclusions: Non-invasive targeted MRI offers important, but previously unmeasurable aspects of neural progenitor activity. Supported by grants from NIH (NS057556; DA024235, DA026108; DA029889, and RR14075), from AHA (09GRNT2060416); from the Stanley Center for Mental Health Res of the Broad Institute.
- © 2010 by American Heart Association, Inc.