Abstract WP322: Do Mural Cells Differentiate Into Microglia-Like Cells After Ischemic Stroke?
Introduction: Controversial results exist on whether mural cells can differentiate into microglia-like cells after ischemic stroke. This discrepancy can be due to different experimental methods (immunostaining versus lineage tracing) and/or distinct transgenic animals (RGS5 GFP versus Tbx18-CreERT mice). Methods: To determinate whether mural cells are able to differentiate into microglia-like cells after ischemic stroke, we permanently labeled mural cells with tdTomato by crossing PDGFRβ-Cre and PDGFRβ-CreERT with Ai14 reporter mice. The resulting Ai14:PDGFRβ-Cre + and Ai14:PDGFRβ-CreERT + mice were subjected to 45 minutes of middle cerebral artery occlusion (MCAO) followed by reperfusion. At various time points after injury, the proliferation, apoptosis, and differentiation of PDGFRβ + cells were examined. Results: In both Ai14:PDGFRβ-Cre + and Ai14:PDGFRβ-CreERT + mice, we observed a substantial reduction of PDGFRβ + cells at day 2 after ischemic stroke and a subsequent repopulation (mainly due to proliferation) of PDGFRβ + cells at day 7 after ischemic stroke. We also showed that PDGFRβ + cells changed their morphology and differentiated into microglia-like cells at day 7 after injury, suggesting that PDGFRβ + cells can indeed differentiate into microglia-like cells after ischemic stroke. In addition, we noted that PDGFRβ also labeled Col1α1 + fibroblasts in the brain. Interestingly, high numbers of PDGFRβ + Col1α1 + cells were found in both Ai14:PDGFRβ-Cre + and Ai14:PDGFRβ-CreERT + mice at day 7 after ischemic injury. Conclusions: These results suggest that PDGFRβ is not an ideal marker for mural cells in pathological conditions that involve fibroblast activation. It remains unclear whether mural cells or fibroblasts differentiate into microglia-like cells after ischemic stroke. Future research should focus on answering this important question.