Altered hemodynamics during arteriovenous fistula remodeling leads to reduced fistula patency in female mice

A mouse model of deep vein thrombosis by inferior vena cava hypoperfusion using ameroid constrictors

Traditional mouse models for deep vein thrombosis (DVT), frequently utilized in research focused on cancer-associated thrombosis (CAT), reliably induce thrombus formation by obstructing blood flow (BF) in the inferior vena cava (IVC), which does not occur in humans. Therefore, to develop a new DVT model for CAT studies, we implanted an ameroid constrictor (AC), a hygroscopic casein C-shape device, around the IVC and aorta of immunocompromised mice. We evaluated the thrombus 3 and 8 days post-AC implantation and compared it with the traditional model 2 days post-vena cava ligation. The size of each thrombus was measured, and the composition was assessed using histological staining; BF through the IVC was confirmed using ultrasound imaging. The thrombus size variability in the AC and ligation models was equivalent. Compared with thrombi on day 3 post-AC implantation, those on day 8 showed characteristics of human thrombi in the subacute to chronic stage. The BF in the IVC was maintained even on day 8. In summary, the AC model showed reproducibility with no significant difference in thrombus size variability from the traditional ligation model while maintaining the BF of the IVC.

Circulating miRNA profiles as predictive biomarkers for aneurysm healing following endovascular treatment: a prospective study

BACKGROUND

Aneurysm treatments are crucial to minimize the rupture risk. The underlying molecular processes mediating cellular remodeling, endothelialization, and aneurysm healing following endovascular treatment are poorly understood. The current study aims to explore circulating miRNA as a treatment and outcome-associated biomarkers in patients undergoing endovascular treatment.

METHODS

Patients undergoing endovascular interventions for unruptured intracranial aneurysms, using either flow diverter placement or coil embolization, were enrolled. Blood samples were collected before the intervention and during a follow-up period between 6 and 18 months. Total mRNA/miRNA was isolated from plasma, followed by RNA-seq analysis. Gene Ontology analysis was used to identify pathways linked to altered miRNA expression.

RESULTS

Twenty-three patients participated, with 13 (56.5%) undergoing flow diversion and 10 (43.5%) coil embolization. The median follow-up sample collection time was 10.70 months (SEM ± 1.32). No significant differences in angiographic occlusion were noted between intervention groups. Differentially expressed miRNAs were not identified between groups at baseline. However, at follow-up, 39 miRNAs were upregulated and 41 were downregulated, independent of intervention. Notably, three miRNAs (miR-4746-5p, miR-4685-3p, and miR-490-3p) were downregulated in the flow diversion group compared to the coil embolization group. Bioinformatics analysis revealed associations with upregulated fluid shear stress, p53, adherens junction pathways, along with downregulated apoptosis pathways.

CONCLUSIONS

This study suggests that fluid shear stress and apoptosis may influence aneurysm healing or thromboembolic events in flow diverter-treated patients. Further research is warranted to elucidate the functional significance of these findings in treatment outcomes, providing valuable insights for improved patient care in intracranial aneurysm management.

Rebuilding vascular access: from the viewpoint of mechanics and materials

This review presents a comprehensive analysis of vascular access in hemodialysis, focusing on the current modalities, their associated challenges, and recent technological advancements. It closely examines the status of three primary types of vascular access: arteriovenous fistulas, arteriovenous grafts, and central venous catheters. The review delves into the complications and pathologies associated with these access types, emphasizing the mechanobiology-related pathogenesis of arteriovenous access. Furthermore, it explores recent clinical trials, biomaterials, and device innovations, highlighting novel pharmaceutical approaches, advanced materials, device designs, and cutting-edge technologies aimed at enhancing the efficacy, safety, and longevity of vascular access in hemodialysis. This synthesis of current knowledge and emerging trends underscores the dynamic evolution of vascular access strategies and their critical role in improving patient care in hemodialysis.

Factors affecting suboptimal maturation of autogenous arteriovenous fistula in elderly patients with diabetes:A narrative review

Autogenous arteriovenous fistula (AVF) is considered the preferred vascular access choice for individuals undergoing maintenance hemodialysis (MHD) and is widely utilized in China, as reported by the Dialysis Outcomes and Practice Patterns Study. Despite its popularity, the significant incidence of poor AVF maturation often leads to the need for central venous catheter insertion, increasing the risk of complications like superior vena cava stenosis and catheter-related infections, which in turn raises the overall mortality risk. With the prevalence of diabetes rising globally among the elderly and diabetic kidney disease being a leading cause of end-stage renal disease necessitating renal replacement therapy, our retrospective review aims to explore the various factors affecting AVF maturation in this specific patient population. While there have been numerous studies examining AVF complications in MHD patients, including issues like failure, patency loss, stenosis, thrombosis, poor maturation, and other influencing factors, there remains a gap in large-scale clinical studies focusing on the incidence and risk factors for immature AVF specifically in elderly diabetic patients. This paper delves into the pathophysiological mechanisms, diagnostic criteria, and unique considerations surrounding AVF maturation in elderly diabetic patients, distinguishing them from the general population. Our literature review reveals that elderly diabetic patients exhibit a higher risk of AVF immaturity compared to the general population. Additionally, there exists a continuing discourse regarding several aspects related to this group, including the choice of dialysis access, timing of AVF surgery, and surgical site selection. Furthermore, we delve into the management strategies for vascular access within this specific group with the goal of providing evidence-based guidance for the establishment and maintenance of functional vascular access in elderly diabetic patients.

Heterogeneous gene expression during early arteriovenous fistula remodeling suggests that downregulation of metabolism predicts adaptive venous remodeling

Clinical outcomes of arteriovenous fistulae (AVF) for hemodialysis remain inadequate since biological mechanisms of AVF maturation and failure are still poorly understood. Aortocaval fistula creation (AVF group) or a sham operation (sham group) was performed in C57BL/6 mice. Venous limbs were collected on postoperative day 7 and total RNA was extracted for high throughput RNA sequencing and bioinformatic analysis. Genes in metabolic pathways were significantly downregulated in the AVF, whereas significant sex differences were not detected. Since gene expression patterns among the AVF group were heterogenous, the AVF group was divided into a 'normal' AVF (nAVF) group and an 'outliers' (OUT) group. The gene expression patterns of the nAVF and OUT groups were consistent with previously published data showing venous adaptive remodeling, whereas enrichment analyses showed significant upregulation of metabolism, inflammation and coagulation in the OUT group compared to the nAVF group, suggesting the heterogeneity during venous remodeling reflects early gene expression changes that may correlate with AVF maturation or failure. Early detection of these processes may be a translational strategy to predict fistula failure and reduce patient morbidity.

Disturbed flow in the juxta-anastomotic area of an arteriovenous fistula correlates with endothelial loss, acute thrombus formation, and neointimal hyperplasia

Clinical failure of arteriovenous neointimal hyperplasia (NIH) fistulae (AVF) is frequently due to juxta-anastomotic NIH (JANIH). Although the mouse AVF model recapitulates human AVF maturation, previous studies focused on the outflow vein distal to the anastomosis. We hypothesized that the juxta-anastomotic area (JAA) has increased NIH compared with the outflow vein. AVF was created in C57BL/6 mice without or with chronic kidney disease (CKD). Temporal and spatial changes of the JAA were examined using histology and immunofluorescence. Computational techniques were used to model the AVF. RNA-seq and bioinformatic analyses were performed to compare the JAA with the outflow vein. The jugular vein to carotid artery AVF model was created in Wistar rats. The neointima in the JAA shows increased volume compared with the outflow vein. Computational modeling shows an increased volume of disturbed flow at the JAA compared with the outflow vein. Endothelial cells are immediately lost from the wall contralateral to the fistula exit, followed by thrombus formation and JANIH. Gene Ontology (GO) enrichment analysis of the 1,862 differentially expressed genes (DEG) between the JANIH and the outflow vein identified 525 overexpressed genes. The rat jugular vein to carotid artery AVF showed changes similar to the mouse AVF. Disturbed flow through the JAA correlates with rapid endothelial cell loss, thrombus formation, and JANIH; late endothelialization of the JAA channel correlates with late AVF patency. Early thrombus formation in the JAA may influence the later development of JANIH.NEW & NOTEWORTHY Disturbed flow and focal endothelial cell loss in the juxta-anastomotic area of the mouse AVF colocalizes with acute thrombus formation followed by late neointimal hyperplasia. Differential flow patterns between the juxta-anastomotic area and the outflow vein correlate with differential expression of genes regulating coagulation, proliferation, collagen metabolism, and the immune response. The rat jugular vein to carotid artery AVF model shows changes similar to the mouse AVF model.

Ruminant model for hemodialysis cannulation

BACKGROUND

Preventative strategies that minimize hemodialysis access complications remain limited.

OBJECTIVE

This study aimed to address this gap by developing a Caprine cannulation model to investigate the impact of repeated cannulations on vascular access patency rates.

RESEARCH DESIGN AND MEASURES

In this pilot study, a meta-analysis was conducted using experimental control data from four trials to explore the impact of Caprine breed (independent variable) on the dependent variables that affect hemodialysis cannulation, including AVF growth, AVF depth, and flow rate.

SUBJECTS

Arteriovenous Fistulas (AVFs) were created using the carotid artery and jugular vein in the necks of seven goats from the French alpine, dwarf, and pygmy breeds. All seven AVFs exhibited vessel remodeling patterns similar to that observed in humans and remained patent, enabling hemodialysis access over the 6 month study.

RESULTS

Over the course of 18 weeks, a total of 291 cannulations were completed using standard 15 g dialysis needles without complications demonstrating the feasibility of using the Caprine species as a cannulation model. The ease of access coupled with the animals' cooperative behavior further contributes to the suitability of the Caprine species for hemodialysis investigations. Notably, no infections or clinically significant incidents were observed throughout the study.

CONCLUSIONS

The stability of AVF patency and flow underscores the viability and potential of the Caprine species animal model as a valuable research platform for exploring interventions aimed at improving vascular access survival in hemodialysis patients.

A central arteriovenous fistula reduces systemic hypertension in a mouse model

Objective

A central arteriovenous fistula (AVF) has been proposed as a potential novel solution to treat patients with refractory hypertension. We hypothesized that venous remodeling after AVF creation in the hypertensive environment reduces systemic blood pressure but results in increased AVF wall thickness compared with remodeling in the normotensive environment.

Methods

A central AVF was performed in C57BL6/J mice previously made hypertensive with angiotensin II (Ang II); mice were sacrificed on postoperative day 7 or 21.

Results

In mice treated with Ang II alone, the mean systolic blood pressure increased from 90 ± 5 mmHg to 160 ± 5 mmHg at day 21; however, in mice treated with both Ang II and an AVF, the blood pressure decreased with creation of an AVF. There were significantly more PCNA-positive cells, SM22α/PCNA-positive cells, collagen I deposition, and increased Krüppel-like Factor 2 immunoreactivity in hypertensive mice with an AVF compared with normotensive mice with an AVF.

Conclusions

These data show that a central AVF decreases systemic hypertension as well as induces local alterations in venous remodeling.

Delayed Diagnosis of Spinal Dural Arteriovenous Fistula: A Case Report and Scoping Review

Spinal dural arteriovenous fistula (SDAVF) is among the most common arterial shunt diseases typically found in middle aged or older men. Herein, we aimed to clarify the reasons for misdiagnoses and delayed diagnoses of SDAVF, determine how these affect prognoses, and establish how they can be prevented. We conducted a PubMed/MEDLINE literature search using "spinal dural arteriovenous fistula", "delayed diagnosis", "late diagnosis", and "misdiagnosis" terms. We identified 18 articles, including 965 SDAVF cases. Patients were predominantly males (71.8-100.0%) (mean age: 53.5-71.0 years). Misdiagnoses rates varied (17.5-100.0%) and encompassed many conditions. The mean time between early manifestations and confirmed diagnosis was approximately 10-15 months and from the first radiologic image revealing dural arteriovenous fistula (DAVF) features to diagnosis was 9.2-20.7 months. Posttreatment outcomes showed a significant improvement in motor functions, gait, and micturition, particularly in patients exhibiting preoperative symptoms over a short period. SDAVF is frequently misdiagnosed or subject to delayed diagnosis, causing poor clinical outcomes. SDAVF symptoms including progressive lower-limb weakness, paresthesia, and vesicorectal dysfunction are indications for spinal magnetic resonance imaging with subsequent spinal angiography, wherein DAVF is evidenced by extensive T2 hyperintensity and flow-void abnormalities. We reported a representative case with delayed diagnosis.

The rodent models of arteriovenous fistula

Arteriovenous fistulas (AVFs) have long been used as dialysis access in patients with end-stage renal disease; however, their maturation and long-term patency still fall short of clinical needs. Rodent models are irreplaceable to facilitate the study of mechanisms and provide reliable insights into clinical problems. The ideal rodent AVF model recapitulates the major features and pathology of human disease as closely as possible, and pre-induction of the uremic milieu is an important addition to AVF failure studies. Herein, we review different surgical methods used so far to create AVF in rodents, including surgical suturing, needle puncture, and the cuff technique. We also summarize commonly used evaluations after AVF placement. The aim was to provide recent advances and ideas for better selection and induction of rodent AVF models. At the same time, further improvements in the models and a deeper understanding of AVF failure mechanisms are expected.

Bioinformatics identifies predictors of arteriovenous fistula maturation

BACKGROUND

Arteriovenous fistulae (AVF) are the preferred access for hemodialysis but still have poor rates of maturation and patency limiting their clinical use. The underlying mechanisms of venous remodeling remain poorly understood, and only limited numbers of unbiased approaches have been reported.

METHODS

Biological Gene Ontology (GO) term enrichment analysis and differentially expressed genes (DEG) analysis were performed for three AVF datasets. A microRNA enrichment analysis and L1000CDS2 query were performed to identify factors predicting AVF patency.

RESULTS

The inflammatory and immune responses were activated during both early and late phases of AVF maturation, with upregulation of neutrophil and leukocyte regulation, cytokine production, and cytokine-mediated signaling. In men with failed AVF, negative regulation of myeloid-leukocyte differentiation and regulation of macrophage activation were significantly upregulated. Compared to non-diabetic patients, diabetic patients had significantly reduced immune response-related enrichment such as cell activation in immune response, regulation of immune-effector process, and positive regulation of defense response; in addition, diabetic patients showed no enrichment of the immune response-regulating signaling pathway.

CONCLUSIONS

These data show coordinated, and differential regulation of genes associated with AVF maturation, and different patterns of several pathways are associated with sex differences in AVF failure. Inflammatory and immune responses are activated during AVF maturation and diabetes may impair AVF maturation by altering these responses. These findings suggest several novel molecular targets to improve sex specific AVF maturation.

Sex hormones impact early maturation and immune response in the arteriovenous fistula mouse model

Arteriovenous fistulae (AVF) fail to mature more frequently in female patients compared with male patients, leading to inferior outcomes and decreased utilization. Since our mouse AVF model recapitulates sex differences in human AVF maturation, we hypothesized that sex hormones mediate these differences during AVF maturation. C57BL/6 mice (9-11 wk) were treated with aortocaval AVF surgery and/or gonadectomy. AVF hemodynamics were measured via ultrasound (days 0-21). Blood was collected for FACS and tissue for immunofluorescence and ELISA (days 3 and 7); wall thickness was assessed by histology (day 21). Inferior vena cava shear stress was higher in male mice (P = 0.0028) after gonadectomy, and they had increased wall thickness (22.0 ± 1.8 vs. 12.7 ± 1.2 µm; P < 0.0001). Conversely, female mice had decreased wall thickness (6.8 ± 0.6 vs. 15.3 ± 0.9 µm; P = 0.0002). Intact female mice had higher proportions of circulating CD3+ T cells on day 3 (P = 0.0043), CD4+ (P = 0.0003) and CD8+ T cells (P = 0.005) on day 7, and CD11b+ monocytes on day 3 (P = 0.0046). After gonadectomy, these differences disappeared. In intact female mice, CD3+ T cells (P = 0.025), CD4+ T cells (P = 0.0178), CD8+ T cells (P = 0.0571), and CD68+ macrophages (P = 0.0078) increased in the fistula wall on days 3 and 7. This disappeared after gonadectomy. Furthermore, female mice had higher IL-10 (P = 0.0217) and TNF-α (P = 0.0417) levels in their AVF walls than male mice. Sex hormones mediate AVF maturation, suggesting that hormone receptor signaling may be a target to improve AVF maturation.NEW & NOTEWORTHY After arteriovenous fistula creation, females have lower rates of maturation and higher rates of failure than males. In a mouse model of venous adaptation that recapitulates human fistula maturation, sex hormones may be mechanisms of the sexual dimorphism: testosterone is associated with reduced shear stress, whereas estrogen is associated with increased immune cell recruitment. Modulating sex hormones or downstream effectors suggests sex-specific therapies and could address disparities in sex differences in clinical outcomes.

Choroidal arteriovenous anastomoses: a hypothesis for the pathogenesis of central serous chorioretinopathy and other pachychoroid disease spectrum abnormalities

The pachychoroid disease spectrum (PDS) includes several chorioretinal diseases that share specific choroidal abnormalities. Although their pathophysiological basis is poorly understood, diseases that are part of the PDS have been hypothesized to be the result of venous congestion. Within the PDS, central serous chorioretinopathy is the most common condition associated with vision loss, due to an accumulation of subretinal fluid in the macula. Central serous chorioretinopathy is characterized by distinct risk factors, most notably a high prevalence in males and exposure to corticosteroids. Interestingly, sex differences and corticosteroids are also strongly associated with specific types of arteriovenous anastomoses in the human body, including dural arteriovenous fistula and surgically created arteriovenous shunts. In this manuscript, we assess the potential of such arteriovenous anastomoses in the choroid as a causal mechanism of the PDS. We propose how this may provide a novel unifying concept on the pathophysiological basis of the PDS, and present cases in which this mechanism may play a role.

Endothelial Cell TGF-β (Transforming Growth Factor-Beta) Signaling Regulates Venous Adaptive Remodeling to Improve Arteriovenous Fistula Patency

BACKGROUND

Arteriovenous fistulae (AVF) are the gold standard for vascular access for hemodialysis. Although the vein must thicken and dilate for successful hemodialysis, excessive wall thickness leads to stenosis causing AVF failure. Since TGF-β (transforming growth factor-beta) regulates ECM (extracellular matrix) deposition and smooth muscle cell (SMC) proliferation-critical components of wall thickness-we hypothesized that disruption of TGF-β signaling prevents excessive wall thickening during venous remodeling.

METHODS

A mouse aortocaval fistula model was used. SB431542-an inhibitor of TGF-β receptor I-was encapsulated in nanoparticles and applied to the AVF adventitia in C57BL/6J mice. Alternatively, AVFs were created in mice with conditional disruption of TGF-β receptors in either SMCs or endothelial cells. Doppler ultrasound was performed serially to confirm patency and to measure vessel diameters. AVFs were harvested at predetermined time points for histological and immunofluorescence analyses.

RESULTS

Inhibition of TGF-β signaling with SB431542-containing nanoparticles significantly reduced p-Smad2-positive cells in the AVF wall during the early maturation phase (days 7-21) and was associated with decreased AVF wall thickness that showed both decreased collagen density and decreased SMC proliferation. SMC-specific TGF-β signaling disruption decreased collagen density but not SMC proliferation or wall thickness. Endothelial cell-specific TGF-β signaling disruption decreased both collagen density and SMC proliferation in the AVF wall and was associated with reduced wall thickness, increased outward remodeling, and improved AVF patency.

CONCLUSIONS

Endothelial cell-targeted TGF-β inhibition may be a translational strategy to improve AVF patency.

Inhibition of β-catenin signaling attenuates arteriovenous fistula thickening in mice by suppressing myofibroblasts

Background

Arteriovenous fistula (AVF) is the most important vascular access for hemodialysis; however, preventive treatment to maintain the patency of AVFs has not been developed. In endothelium, β-catenin functions in both the intercellular adherens complex and signaling pathways that induce the transition of endothelial cells to myofibroblasts in response to mechanical stimuli. We hypothesize that mechanical disturbances in the AVF activate β-catenin signaling leading to the transition of endothelial cells to myofibroblasts, which cause AVF thickening. The present study aimed to test this hypothesis.

Methods

Chronic kidney disease in mice was induced by a 0.2% adenine diet. AVFs were created by aortocaval puncture. Human umbilical vein endothelial cells (HUVECs) were used in the cell experiments. A pressure-culture system was used to simulate mechanical disturbances of the AVF.

Results

Co-expression of CD31 and smooth muscle alpha-actin (αSMA), loss of cell–cell adhesions, and the expression of the myofibroblast marker, integrin subunit β6 (ITGB6), indicated transition to myofibroblasts in mouse AVF. Nuclear translocation of β-catenin, decreased axin2, and increased c-myc expression were also observed in the AVF, indicating activated β-catenin signaling. To confirm that β-catenin signaling contributes to AVF lesions, β-catenin signaling was inhibited with pyrvinium pamoate; β-catenin inhibition significantly attenuated AVF thickening and decreased myofibroblasts. In HUVECs, barometric pressure-induced nuclear localization of β-catenin and increased expression of the myofibroblast markers, αSMA and ITGB6. These changes were attenuated via pretreatment with β-catenin inhibition.

Conclusions

The results of this study indicate that mechanical disturbance in AVF activates β-catenin signaling to induce the transition of endothelial cells to myofibroblasts. This signaling cascade can be targeted to maintain AVF patency.

Supplementary Information

The online version contains supplementary material available at 10.1186/s10020-022-00436-1.

Creating patient-specific vein models to characterize wall shear stress in hemodialysis population

End-Stage Renal Disease (ESRD) patients require arteriovenous fistulas (AVF) that allow a mature vein to withstand hemodialysis. Unfortunately, venous thrombosis and stenosis in the cephalic vein arch after AVF placement is common and heavily influenced by hemodynamics. To better assess forces and flow behavior in the cephalic arch, we have built patient-specific millifluidic models that allow us to explore the complex interplay between patient-specific vein geometry and fluctuating hemodynamics. These 3D models were created from patient-specific intravascular ultrasound and venogram images obtained three- and twelve-months post AVF creation and fabricated into soft elastomer-based millifluidic devices. Geometric validation of fabricated phantom millifluidic device shows successful replication of original computational 3D model. Millifluidic devices were perfused with a blood-mimicking fluid containing fluorescent tracer beads under steady-state physiologic cephalic vein flow conditions (20 mL/min). Particle image velocimetry was employed to calculate wall shear stress (WSS) across the cephalic arches. Experimental WSS profile evaluation reveals that the physiologic cephalic arch model yields WSS values within physiologic range [76–760 mPa]. Moreover, upon comparing WSS profiles across all models, it is noticeable that WSS values increase as vein diameter decreases, which further supports employed experimental and analysis strategy. The presented millifluidic devices show promise for experimental WSS characterization under pathologic flow conditions to contrast from calculated physiologic hemodynamics and better understand WSS influence on thrombosis and stenosis in hemodialysis patients.

PD-L1 (Programmed Death Ligand 1) Regulates T-Cell Differentiation to Control Adaptive Venous Remodeling

OBJECTIVE

Patients with end-stage renal disease depend on hemodialysis for survival. Although arteriovenous fistulae (AVF) are the preferred vascular access for hemodialysis, the primary success rate of AVF is only 30% to 50% within 6 months, showing an urgent need for improvement. PD-L1 (programmed death ligand 1) is a ligand that regulates T-cell activity. Since T cells have an important role during AVF maturation, we hypothesized that PD-L1 regulates T cells to control venous remodeling that occurs during AVF maturation. Approach and results: In the mouse aortocaval fistula model, anti-PD-L1 antibody (200 mg, 3×/wk intraperitoneal) was given to inhibit PD-L1 activity during AVF maturation. Inhibition of PD-L1 increased T-helper type 1 cells and T-helper type 2 cells but reduced regulatory T cells to increase M1-type macrophages and reduce M2-type macrophages; these changes were associated with reduced vascular wall thickening and reduced AVF patency. Inhibition of PD-L1 also inhibited smooth muscle cell proliferation and increased endothelial dysfunction. The effects of anti-PD-L1 antibody on adaptive venous remodeling were diminished in nude mice; however, they were restored after T-cell transfer into nude mice, indicating the effects of anti-PD-L1 antibody on venous remodeling were dependent on T cells.

CONCLUSIONS

Regulation of PD-L1 activity may be a potential therapeutic target for clinical translation to improve AVF maturation.

Sex Differences in Inflammation During Venous Remodeling of Arteriovenous Fistulae

Vascular disorders frequently have differing clinical presentations among women and men. Sex differences exist in vascular access for hemodialysis; women have reduced rates of arteriovenous fistula (AVF) maturation as well as fistula utilization compared with men. Inflammation is increasingly implicated in both clinical studies and animal models as a potent mechanism driving AVF maturation, especially in vessel dilation and wall thickening, that allows venous remodeling to the fistula environment to support hemodialysis. Sex differences have long been recognized in arterial remodeling and diseases, with men having increased cardiovascular events compared with pre-menopausal women. Many of these arterial diseases are driven by inflammation that is similar to the inflammation during AVF maturation. Improved understanding of sex differences in inflammation during vascular remodeling may suggest sex-specific vascular therapies to improve AVF success.

Inhibition of T-Cells by Cyclosporine A Reduces Macrophage Accumulation to Regulate Venous Adaptive Remodeling and Increase Arteriovenous Fistula Maturation

OBJECTIVE

Arteriovenous fistulae (AVF) are the preferred vascular access for hemodialysis, but the primary success rate of AVF remains poor. Successful AVF maturation requires vascular wall thickening and outward remodeling. A key factor determining successful AVF maturation is inflammation that is characterized by accumulation of both T-cells and macrophages. We have previously shown that anti-inflammatory (M2) macrophages are critically important for vascular wall thickening during venous remodeling; therefore, regulation of macrophage accumulation may be an important mechanism promoting AVF maturation. Since CD4+ T-cells such as T-helper type 1 cells, T-helper type 2 cells, and regulatory T-cells can induce macrophage migration, proliferation, and polarization, we hypothesized that CD4+ T-cells regulate macrophage accumulation to promote AVF maturation. Approach and Results: In a mouse aortocaval fistula model, T-cells temporally precede macrophages in the remodeling AVF wall. CsA (cyclosporine A; 5 mg/kg, sq, daily) or vehicle (5% dimethyl sulfoxide) was administered to inhibit T-cell function during venous remodeling. CsA reduced the numbers of T-helper type 1 cells, T-helper type 2, and regulatory T-cells, as well as M1- and M2-macrophage accumulation in the wall of the remodeling fistula; these effects were associated with reduced vascular wall thickening and increased outward remodeling in wild-type mice. However, these effects were eliminated in nude mice, showing that the effects of CsA on macrophage accumulation and adaptive venous remodeling are T-cell-dependent.

CONCLUSIONS

T-cells regulate macrophage accumulation in the maturing venous wall to control adaptive remodeling. Regulation of T-cells during AVF maturation may be a strategy that can improve AVF maturation. Graphic Abstract: A graphic abstract is available for this article.

A mouse model of stenosis distal to an arteriovenous fistula recapitulates human central venous stenosis

Objective

Central venous stenosis (CVS) is a major cause of arteriovenous fistula (AVF) failure. However, central veins are relatively inaccessible to study with conventional Doppler ultrasound methods. To understand mechanisms underlying AVF failure owing to CVS, an animal model was established that creates a stenosis distal to an AVF. We hypothesized that this mouse model will show comparable morphology and physiology to human CVS.

Methods

An aortocaval fistula was created between the distal aorta and inferior vena cava (IVC); a stenosis was then created distal to the fistula by partial IVC ligation. Sham-operated animals, AVF without venous stenosis, and venous stenosis without AVF were used as controls. Physiologic properties of the IVC, both upstream and downstream of the stenosis, or the corresponding sites in models without stenosis, were assessed with ultrasound examination on days 0 to 21. The spectral broadening index was measured to assess the degree of disturbed shear stress. The IVC was harvested at day 21 and specimens were analyzed with immunofluorescence.

Results

The IVC diameter of mice with an AVF and stenosis showed increased upstream (P = .013), but decreased downstream diameter (P = .001) compared with mice with an AVF but without a stenosis, at all postoperative times (days 3-21). IVC wall thickness increased in mice with an AVF, compared with IVC without an AVF (upstream of stenosis: 13.9 μm vs 11.0 μm vs 4.5 μm vs 3.9 μm; P = .020; downstream of stenosis: 6.0 μm vs 6.6 μm vs μm 4.5 μm vs 3.8 μm; P = .002; AVF with stenosis, AVF, stenosis, sham, respectively). AVF patency significantly decreased in mice with an AVF and stenosis by day 21 (50% vs 90%; P = .048). The IVC of mice with AVF and stenosis showed a venous waveform with pulsatility as well as enhanced velocity at and downstream of the stenosis; similar waveforms were observed in a human case of CVS. Downstream to the stenosis, the spectral broadening index was significantly higher compared with mice with AVF alone (1.06 vs 0.78; P = .011; day 21), and there was a trend towards less immunoreactivity of both Krüppel-like factor 2 and phosphorylated-endothelial nitric oxide synthase compared with mice with an AVF alone.

Conclusions

Partial IVC ligation distal to a mouse aortocaval fistula alters the fistula diameter and wall thickness, decreases patency, and increases distal disturbed flow compared with fistulae without a distal stenosis. Our mouse model of stenosis distal to an AVF may be a faithful representation of human CVS that shows similar morphology and physiology, including disturbed shear stress.

A mouse model of venous stenosis distal to an arteriovenous fistula shows similar Doppler waveforms as those observed in a human case of central venous stenosis. These mice retain disturbed shear stress in the vein distal to the fistula, characterized by a sustained increase of the spectral broadening index and diminished expression of proteins upregulated by laminar shear stress. This novel mouse model will enable investigation of the physiology and downstream molecular pathways involved in central venous stenosis in humans.