23. Endothelial Specific CXCL12 Regulates Neovascularization Through Fibroblast VEGF Signaling During Tissue Repair and Regeneration

PURPOSE: The formation of new blood vessels into microvascular networks, known as neovascularization, is critical in tissue repair and regeneration. C-X-C motif chemokine ligand 12 (CXCL12; Stromal cell-derived factor 1 [SDF-1]), a chemokine protein ubiquitously expressed by various cell and tissue types, has primarily been characterized for its role in embryogenesis and hematopoiesis. Our lab’s previous work demonstrated that CXCL12 expression is inducible secondary to the stabilization of Hypoxia-Inducible Factor (HIF)-1 following hypoxic tissue injury. Our findings demonstrated that CXCL12 has an essential role in the complex molecular underpinnings regulating neovascularization and tissue repair, but questions remain regarding its molecular and cellular interactions. To further characterize the nature of CXCL12 expression and regulatory control during neovascularization, we engineered a conditional CXCL12 knockout mouse specifically ablating vascular endothelial CXCL12. METHODS: We utilized transgenic C57BL/6 mice strains aged 14±2 weeks with endothelial-cell-specific (Tie2-Cre) CXCL12 knockout (eKO). Littermates negative for Cre expression were used as the controls (WT). To investigate the role of CXCL12 in neovascularization, we performed excisional wounding to eKO, and WT mice (n=6) followed by immunohistochemical analysis. RESULTS: Floxed control mice subjected to the excisional cutaneous wounding healed by day 10 on average, compared to day 16 in the eKO mouse model. Immunostaining for CD31 and vWF demonstrated a significant decrease in the vascular density of healed tissue in eKO mice compared to controls. Colocalization immunostaining for PDGFRA/VEGF demonstrated diminished expression of angiogenesis (VEGF) co-localized with fibroblasts in eKO mice compared to WT mice, demonstrating that endothelial-specific knockout of CXCL12 had a direct effect on fibroblast cytokine expression. CONCLUSION: Our work demonstrates that endothelial expressed CXCL12 specifically influences wound healing through fibroblast specific VEGF expression, leading to downstream neovascularization and angiogenesis. These findings demonstrate that global CXCL12 (SDF1) modulation may be less efficient than cell specific targeting, and that endothelial specific expression of SDF1 may provide therapeutic benefits during tissue repair and regeneration.