A. The mouse aortocaval fistula recapitulates human arteriovenous fistula maturation. Am J Physiol Heart Circ Physiol 305: H1718 -H1725, 2013. First published October 4, 2013 doi:10.1152/ajpheart.00590.2013.-Several models of arteriovenous fistula (AVF) have excellent patency and help in understanding the mechanisms of venous adaptation to the arterial environment. However, these models fail to exhibit either maturation failure or fail to develop stenoses, both of which are critical modes of AVF failure in human patients. We used high-resolution Doppler ultrasound to serially follow mice with AVFs created by direct 25-gauge needle puncture. By day 21, 75% of AVFs dilate, thicken, and increase flow, i.e., mature, and 25% fail due to immediate thrombosis or maturation failure. Mature AVF thicken due to increased amounts of smooth muscle cells. By day 42, 67% of mature AVFs remain patent, but 33% of AVFs fail due to perianastomotic thickening. These results show that the mouse aortocaval model has an easily detectable maturation phase in the first 21 days followed by a potential failure phase in the subsequent 21 days. This model is the first animal model of AVF to show a course that recapitulates aspects of human AVF maturation. aortocaval fistula; arteriovenous fistula; maturation; mouse; model THE ARTERIOVENOUS FISTULA (AVF) is the most common access chosen for hemodialysis as the first-line therapy before renal replacement. Despite the superiority of AVF access compared with its alternatives, AVFs are still far from perfect. AVFs fail to "mature," e.g., dilate, thicken, and increase flow, before the beginning of dialysis in ϳ20 -50% of cases, with the majority of AVFs requiring some additional therapeutic intervention to mature successfully (9,14,20,21). In addition, 1-yr primary AVF patency rates are typically only 60 -65%, with many mature AVFs subsequently failing secondarily due to neointimal hyperplasia, generally perianastomotic (2,4,7,19,21,22). The poor patency of AVFs clearly reflects our imperfect understanding of the biology of venous remodeling to the arterial environment.The AVF has been studied using several models, including the surgical anastomosis model as well as the puncture model (1, 5, 6, 8, 10 -12, 15-17). All of these models have strengths and weakness, including technical difficulty due to surgery as well as the use of animals larger than mice (1,5,8,12,15,16). A common feature of all these models is that they are good models of surgical access, with good patency; unfortunately, they fail to exhibit a percentage of animals that either fail to mature or fail to develop stenoses in long-term followup, both of which are both important aspects of understanding modes of failure of human AVF.Recent advances in ultrasound technology have allowed increasingly accurate analysis of blood flow within small vessels, such as in a mouse, as well as allowing the ability to serially examine the same mouse over time. We used this technology to observe the time course of venous remodeling in the mouse ao...

Derivation of functional vascular smooth muscle cells (VSMCs) from human induced pluripotent stem cells (hiPSCs) to generate tissue-engineered blood vessels (TEBVs) holds great potential in treating patients with vascular diseases. Herein, hiPSCs were differentiated into alpha-smooth muscle actin (α-SMA) and calponin-positive VSMCs, which were seeded onto polymer scaffolds in bioreactors for vascular tissue growth. A functional TEBV with abundant collagenous matrix and sound mechanics resulted, which contained cells largely positive for α-SMA and smooth muscle myosin heavy chain (SM-MHC). Moreover, when hiPSC-derived TEBV segments were implanted into nude rats as abdominal aorta interposition grafts, they remained unruptured and patent with active vascular remodeling, and showed no evidence of teratoma formation during a 2-week proof-of-principle study. Our studies represent the development of the first implantable TEBVs based on hiPSCs, and pave the way for developing autologous or allogeneic grafts for clinical use in patients with vascular disease.

Veins are exposed to the arterial environment during two common surgical procedures, creation of vein grafts and arteriovenous fistulae (AVF). In both cases veins adapt to the arterial environment that is characterized by different hemodynamic conditions and increased oxygen tension compared to the venous environment. Successful venous adaptation to the arterial environment is critical for long term success of the vein graft or AVF, and in both cases is generally characterized by venous dilation and wall thickening. However, AVF are exposed to a high flow, high shear stress, low pressure arterial environment, and adapt mainly via outward dilation with less intimal thickening. Vein grafts are exposed to a moderate flow, moderate shear stress, high pressure arterial environment, and adapt mainly via increased wall thickening with less outward dilation. We review the data that describe these differences, as well as the underlying molecular mechanisms that mediate these processes. Despite extensive research, there are few differences in the molecular pathways that regulate cell proliferation and migration or matrix synthesis, secretion, or degradation currently identified between vein graft adaptation and AVF maturation that account for the different types of venous adaptation to arterial environments.

Early occurrence of anastomotic false aneurysm is characteristic of BD. Further investigation is necessary to establish effective postoperative treatment.

Purpose The venous limb of arteriovenous fistulae (AVF) adapts to the arterial environment by dilation and wall thickening; however the temporal regulation of the expression of extracellular matrix (ECM) components in the venous limb of the maturing AVF has not been well characterized. We used a murine model of AVF maturation that recapitulates human AVF maturation to determine the temporal pattern of expression of these ECM components. Methods Aortocaval fistulae were created in C57BL/6J mice and the venous limb was analyzed on post-operative days 1, 3, 7, 21, and 42. A gene microarray analysis was performed on day 7; results were confirmed by qPCR, histology, and immunohistochemistry. Proteases, protease-inhibitors, collagens, glycoproteins and other non-collagenous proteins were characterized. Results The maturing AVF has increased expression of many ECM components, including increased collagen and elastin. Matrix metalloproteinases (MMP) and tissue inhibitor of metalloproteinase 1 (TIMP1) showed increased mRNA and protein expression during the first 7 days of maturation. Increased collagen and elastin expression was also significant at day 7. Expression of structural proteins was increased later during AVF maturation. Osteopontin (OPN) expression was increased at day 1 and sustained during AVF maturation. Conclusion During AVF maturation there is significantly increased expression of ECM components, each of which shows distinct temporal patterns during AVF maturation. Increased expression of regulatory proteins such as MMP and TIMP precedes increased expression of structural proteins such as collagen and elastin, potentially mediating a controlled pattern of ECM degradation and vessel remodeling without structural failure.

Objective Arteriovenous fistulae (AVF) remain the optimal conduit for hemodialysis access but continue to demonstrate poor patency and poor rates of maturation. We hypothesized that CD44, a widely expressed cellular adhesion molecule that serves as a major receptor for extracellular matrix (ECM) components, promotes wall thickening and ECM deposition during AVF maturation. Approach and Results AVF were created via needle puncture in wild-type (WT) C57BL/6J and CD44 knockout (KO) mice. CD44 mRNA and protein expression was increased in WT AVF. CD44 KO mice showed no increase in AVF wall thickness (8.9 μm vs. 26.8 μm; P = 0.0114), collagen density, and hyaluronic acid density, but similar elastin density when compared to control AVF. CD44 KO mice also showed no increase in VCAM-1 expression, ICAM-1 expression and MCP-1 expression in the AVF compared to controls; there were also no increased M2 macrophage markers (TGM2: 81.5 fold, P = 0.0015; IL-10: 7.6 fold, P = 0.0450) in CD44 KO mice. Delivery of MCP-1 to CD44 KO mice rescued the phenotype with thicker AVF walls (27.2 μm vs. 14.7 μm; P = 0.0306), increased collagen density (2.4 fold; P = 0.0432), and increased number of M2 macrophages (2.1 fold; P = 0.0335). Conclusions CD44 promotes accumulation of M2 macrophages, ECM deposition and wall thickening during AVF maturation. These data show the association of M2 macrophages with wall thickening during AVF maturation and suggest that enhancing CD44 activity may be a strategy to increase AVF maturation.

Low rates of arteriovenous fistula (AVF) maturation prevent optimal fistula use for hemodialysis; however, the mechanism of venous remodeling in the fistula environment is not well understood. We hypothesized that the embryonic venous determinant Eph-B4 mediates AVF maturation. In human AVF and a mouse aortocaval fistula model, Eph-B4 protein expression increased in the fistula vein; expression of the arterial determinant Ephrin-B2 also increased. Stimulation of Eph-B-mediated signaling with Ephrin-B2/Fc showed improved fistula patency with less wall thickness. Mutagenesis studies showed that tyrosine-774 is critical for Eph-B4 signaling and administration of inactive Eph-B4-Y774F increased fistula wall thickness. Akt1 expression also increased in AVF; Akt1 knockout mice showed reduced fistula diameter and wall thickness. In Akt1 knockout mice, stimulation of Eph-B signaling with Ephrin-B2/Fc showed no effect on remodeling. These results show that AVF maturation is associated with acquisition of dual arteriovenous identity; increased Eph-B activity improves AVF patency. Inhibition of Akt1 function abolishes Eph-B-mediated venous remodeling suggesting that Eph-B4 regulates AVF venous adaptation through an Akt1-mediated mechanism.

Background The poor clinical results that are frequently reported for arteriovenous fistulae (AVF) for hemodialysis are typically due to failure of AVF maturation. We hypothesized that early AVF maturation is associated with generation of reactive oxygen species and activation of the HIF-1 pathway, potentially promoting neointimal hyperplasia. We tested this hypothesis using a previously reported mouse AVF model that recapitulates human AVF maturation. Methods Aortocaval fistulae were created in C57Bl/6 mice, and compared to sham-operated mice. AVFs or inferior vena cavas were analysed using a microarray, Amplex Red for extracellular H2O2, qPCR, immunohistochemistry, and immunoblotting for HIF-1α, and immunofluorescence for NOX-2, nitrotyrosine, HO-1 and VEGF-A. Results Oxidative stress was higher in AVF compared to control veins, with more H2O2 (p=0.007) and enhanced nitrotyrosine immunostaining (p=0.005). Immunohistochemistry and immunoblot showed increased HIF-1α immunoreactivity in the AVF endothelium; HIF-1 targets NOX-2, HO-1 and VEGF-A were overexpressed in the AVF (p<0.01). AVF expressed increased numbers of HIF-1α (p<0.0001) and HO-1 (p<0.0001) mRNA transcripts. Conclusions Oxidative stress increases in mouse AVF during early maturation, with increased expression of HIF-1α and its target genes NOX-2, HO-1 and VEGF-A. These results suggest that clinical strategies to improve AVF maturation could target the HIF-1 pathway.