J. J. Hanisch1,2, G. Kuwahara1, K. Yamamoto1, T. Hashimoto1, C. D. Protack1,2, T. Foster1,2, H. Bai1, S. M. Jay3, A. Dardik1,2 1Yale University School Of Medicine,Department Of Surgery,New Haven, CT, USA 2VA Connecticut Healthcare System,Department Of Surgery,West Haven, CT, USA 3University Of Maryland,Department Of Bioengineering,College Park, MD, USA
Introduction:
Arteriovenous fistulae (AVF) remain the optimal conduit for hemodialysis access but continue to demonstrate poor patency and with poor rates of primary maturation. We have previously shown that there is a distinct temporal regulation of extracellular matrix (ECM) components during AVF maturation. CD44 is a widely expressed cellular adhesion molecule that serves as a major receptor for ECM components such as hyaluronic acid as well as promoting adhesion of leukocytes to endothelial cells and stimulating smooth muscle cell proliferation and migration. We hypothesized that CD44 promotes wall thickening and ECM deposition during AVF maturation by promoting inflammation in the maturing vein.
Methods:
Aortocaval fistulae were performed by needle puncture in wild-type (WT) C57BL/6J and CD44 knockout (KO) mice. AVF diameter was serially assessed weekly by duplex ultrasound. AVF were harvested at days 7 or 21 and histology analyzed using computerized morphometry, as well as qRT-PCR and Western blot. In both WT and CD44 KO mice, after AVF formation, microspheres containing MCP-1 were placed over the adventitia using a pluronic gel.
Results:
CD44 expression was increased 2.1-fold in AVF (day 7). CD44 KO mice showed reduced AVF wall thickness (8.9 μm vs. 26.8 μm; p = 0.0114, ANOVA), collagen density (1.7 fold; p = 0.0186, ANOVA), and hyaluronic acid density (2.6 fold; p = 0.0004, ANOVA), but similar elastin density (p = 0.9315) when compared to control AVF (day 21). CD44 KO mice also showed reduced VCAM-1 expression (12.0 fold; p = 0.0092, ANOVA), ICAM-1 expression (30.5 fold; p = 0.0002, ANOVA ), and MCP-1 expression (11.4 fold; p = 0.0006, ANOVA) in the AVF compared to control AVF; there were also reduced M2 macrophage markers (TGM2: 81.5 fold; p = 0.0001, ANOVA and IL-10: 7.6 fold; p = 0.0228, ANOVA) in CD44 KO mice. Delivery of MCP-1 to the AVF in WT mice resulted in thicker AVF walls (32.0 μm vs. 24.5 μm; p = 0.0383, t-test), increased collagen density (1.6 fold; p = 0.0184, t-test), and increased number of M2 macrophages (1.5 fold; p = 0.0241, t-test).
Conclusion:
CD44 promotes accumulation of M2 macrophages, ECM deposition and inflammation, enhancing AVF maturation. These data suggest that promoting CD44 activity may be a strategy to enhance AVF maturation, and also show the importance of inflammation to enable wall thickening during AVF maturation.