Abstract W MP43: Fetal and Maternal Microchimeric Responses to Ischemic Stroke

Abstract

Background and Purpose: Ischemic stroke is a sexually dimorphic disease. Events that occur during pregnancy can have lasting implications on both the mother and fetus for decades after parturition. In particular, fetomaternal microchimerism, the bidirectional exchange and persistence of cells between a pregnant female and her fetus, has been shown to play a role in various disease pathologies but has not been well studied in the brain. We hypothesized that microchimeric cells (MCs) home to sites of injury as part of the immune response to stroke and display a stem cell phenotype with potential to aid in repair. Methods: C57Bl/6 mice were bred with GFP transgenic mice using specific mating paradigms to generate fetal and maternal microchimeras. Young 10-12 week old maternal-microchimeric mice and 12-14 week old parous fetal-microchimeric mice were subject to a 90 min MCAO or sham surgery and sacrificed at 72hr or 30 day post-reperfusion (n=10). Blood, bone marrow (BM), and brain tissue were analyzed by co-labeling with anti-GFP antibody using immunohistochemistry, flow cytometry, and cytospin preparations. RNA was extracted from GFP+ cells in situ by laser capture microdissection to further characterize MCs. Results: At 72hrs after stroke, clusters of MCs were present in the ischemic area. Flow cytometry of maternal blood and BM identified a rare cell population (0.01-0.001%) of GFP+CD45+CD34+, indicative of umbilical cord stem cells. Engrafted MCs with stem-like phenotypes were also found in cytospin preparations of blood and BM. At 30 day after stroke, MCs in the brain displayed mature endothelial morphology in 60% of animals. This was validated by RT-qPCR, confirming the presence of MCs in the ischemic brain. Conclusions: We have shown that MCs display stem cell phenotypes, are actively recruited to the ischemic brain, and selectively aggregate at sites of injury. Our data show that MCs are mobilized in BM and blood early after stroke and later give rise to endothelial cells, indicating a potential angiogenic role in promoting revascularization. Further characterization of the functional contribution and mechanisms that underlie these responses may prove useful in assessing female responses to brain injury.