CXCR4-dependent tissue remodeling after experimental stroke

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CXCR4 chemokine receptors are expressed in hematopoietic and neural stem cells. The receptor guides migration of leukocytes and precursor cells that are derived from these stem cells. Consistently, a CXCR4 antagonist (plerixafor, AMD3100) was recently approved for hematopoietic stem cell mobilization. Functions of CXCR4 in neoplastic, inflammatory and regenerative processes are intensively investigated. In this context, it was reported that the CXCR4-mediated signal of the chemokine CXCL12 directs stem cells and inflammatory cells towards lesioned tissues. Accordingly, CXCR4 is thought to be involved in tissue remodeling, neovascularization and tumor formation. However, proper investigation of these processes requires non-ambiguous identification of tissues that develop from Cxcr4-expressing stem cells. In addition, controllable inactivation of CXCR4 is desirable. Since CXCL12- and CXCR4-deficient mice die perinatally, a conditional approach is necessary. The applicant thus generated mice harboring a Cxcr4-knockout/CreER-knockin allele (Cxcr4CreER) and an established Cre-reporter. In these mice, tamoxifen induces permanent expression of the fluorescent protein TdTomato in cells with an active Cxcr4 promoter. When the Cxcr4CreER allele is combined with a Cxcr4LoxP allele, Cxcr4-CreER permits Cxcr4 ablation. Thorough characterization of Cxcr4CreER/WT and Cxcr4CreER/LoxP mice showed that analysis of TdTomato-positive cells permits to trace the lineage of Cxcr4-expressing stem cells in the presence (Cxcr4CreER/WT) and in the absence (Cxcr4CreER/LoxP) of functional CXCR4. The applicant plans to use this model to assess the function of CXCR4 in remodeling processes after experimental stroke (recruitment of monocytes, neutrophils and immature neurons, glial reaction and neovascularization in the lesioned area). In the second focus, stem cells will be in vivo-labeled with Cxcr4-CreER, isolated and characterized during in vitro propagation and reimplantation. The project will shed light on the question if CXCR4 is a suitable drug target in stroke and rigorously test the concept that CXCR4 directs stem cells during remodeling of ischemic lesions.