Abstract 13.55 HOW DO ARTERIOVENOUS LOOPS INDUCE ANGIOGENESIS? FLOW-DEPENDENT ALTERATIONS OF MIRNA- AND GENE EXPRESSION PROFILES IN A RAT AV LOOP MODEL

Abstract

PURPOSE: Arteriovenous (AV) loops are able to induce neoangiogenesis and, if placed into isolation chambers with a carrier matrix, lead to the development of a functional microcirculation, thereby enabling the creation of axially vascularized, transplantable soft-tissue units. The molecular driving forces behind the rapid neovascularization are elusive so far. To test the hypothesis that the increased blood flow in the AV loop mechanically induces proangiogenic regulatory pathways, we analyzed microRNA (miRNA) and gene expression profiles in a rat AV loop model in comparison with sham-operated rats. METHODS: AV loops were created in 21 rats by anastomosing a saphenous vein graft between the contralateral saphenous artery and vein. The AV loops were placed into isolation chambers filled with acellular dermal matrix and explanted 5, 10, and 15 days after exposure to enhanced blood flow (n=7 per group). Sham samples from 8 end-to-end anastomosed veins without enhanced blood flow served as controls. The expression profiles of 758 miRNAs and 30,584 mRNAs were determined by microarray analysis and quantitative real-time polymerase chain reaction. RESULTS: Marked alterations of miRNA and gene expression profiles were present in AV shunts compared to controls. A strong overexpression of proangiogenic cytokines, oxygenation-associated genes and angiopoetic growth factors was observed in AV shunts compared to controls. Moreover, significant inverse correlations of the expression levels of miR-223-3p, miR-130b-3p, miR-19b-3p, miR-449a-5p, and miR-511-3p which are up-regulated in AV shunts, and miR-27b-3p, miR-10b-5p, let-7b-5p, and let-7c-5p, which are down-regulated in AV shunts, with their predicted interacting targets C-X-C chemokine ligand 2 (CXCL2), IL1A, ephrin receptor kinase 2 (EPHA2), synaptojanin-2 binding protein (SYNJ2BP), forkhead box C1 (FOXC1) were present. CONCLUSION: Elevated vascular shear stress due to enhanced blood flow within AV loops induces rapid and strong changes of angiogenesis-related miRNA and gene expression profiles. Our in vivo data provide evidence that flow-stimulated angiogenesis is driven by miRNA-regulated induction of cytokines, oxygenation associated genes, the embryonic transcription factor FOXC1, EPHA2, and SYNJ2BP. Synthetic proangiogenic miRNAs (miRNA mimics) may serve as specific tools to therapeutically enhance the vascularization of tissue-engineered soft-tissue free flaps in the future.