c-Kit signaling determines neointimal hyperplasia in arteriovenous fistulae

Elevated c-kit expression in failed autologous arteriovenous fistulas in end-stage renal disease patients

BACKGROUND

Serum stem cell factor is elevated in end-stage renal disease (ESRD) patients. This study aimed to investigate the expression of the c-kit receptor, which is the specific membrane receptor of stem cell factor, in failed autologous arteriovenous fistulas (AVFs) in end-stage renal disease patients.

METHODS

A total of 14 ESRD patients with initial AVFs creation and 16 ESRD patients with reconstruction were enrolled in this study. Hematoxylin and eosin (H&E) and elastic Verhoeff-Van Gieson (EVG) staining were used for histomorphometric analyses. Immunohistochemistry was used to examine the expression of c-kit in the intima, and a correlation analysis was performed with the intimal area and the percentage of area stenosis. A double-label immunofluorescence method was used to explore the colocalization of c-kit with α-smooth muscle actin (α-SMA) and CD31. The expression of c-kit and the related PI3K/Akt signaling axis, including PI3K, P-PI3K, Akt, P-Akt473, P-Akt308, and mTOR, was measured by western blotting.

RESULTS

Internal elastic lamina (IEL) area, intimal area, percentage of area stenosis, and average optical density (AOD) of c-kit in the intima were significantly higher in the failed group than in the preoperative group (p ⩽ 0.001). The AOD of c-kit in the intima was positively correlated with the intimal area and the percentage of stenosis (intimal area: R = 0.744, p < 0.001; the percentage of stenosis: R = 0.923, p < 0.001). C-kit colocalized with α-SMA but not with CD31 in studies of c-kit target cells. Moreover, the levels of c-kit and P-PI3K, P-Akt473 and mTOR in the PI3K/Akt axis were also higher in the failed group than in the initial group (p < 0.05).

CONCLUSIONS

C-kit and related proteins associated with the PI3K/Akt pathway were elevated in failed AVFs among ESRD patients and that the expression level of c-kit in the intima correlates with the degree of AVF stenosis.

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.

Treatment with imatinib was useful to delay the neointimal hyperplasia of aortocaval fistula in adenine-induced renal failure rats

PURPOSE

The study was conducted to investigate the effect of the treatment with imatinib, a c-kit specific inhibitor, on the neointimal hyperplasia (NIH) of aortocaval fistula (ACF) in adenine-induced renal failure rats.

MATERIALS AND METHODS

All rats were randomly assigned to 4 groups: rats were fed on a normal diet (normal group); rats were fed on a 0.75% adenine-rich diet (renal failure group). The remaining rats underwent ACF after receiving a 0.75% adenine-rich diet and received daily saline gavage (model group) or imatinib gavage (imatinib group) for 7 days after surgery. Immunohistochemical method was used to detect c-kit expression, and Elastomeric Verhoeff-Van Gieson (EVG) staining was used to observe morphological changes of the ACF. The Pearson correlation analysis was used to evaluate the correlations of c-kit expression with intimal thickness and the percentage of stenosis, respectively.

RESULTS

The renal failure group showed positive c-kit expression on the intima of the inferior vena cava (IVC), whereas the normal group did not. Compared to the model group, intimal thickness (P = 0.001), the percentage of stenosis (P = 0.006) and c-kit expression (P = 0.04) were decreased in the imatinib group at 8 weeks postoperatively. C-kit expression was positively correlated with both intimal thickness and percentage of stenosis (intimal thickness: R = 0.650, P = 0.003; the percentage of stenosis: R = 0.581, P = 0.011) in both the model and imatinib groups.

CONCLUSION

Treatment with imatinib, a c-kit specific inhibitor, was useful to delay the NIH of ACF in adenine-induced renal failure rats.

Correlation between stem cell molecular phenotype and atherosclerotic plaque neointima formation and analysis of stem cell signal pathways

Vascular stem cells exist in the three-layer structure of blood vessel walls and play an indispensable role in angiogenesis under physiological conditions and vascular remodeling under pathological conditions. Vascular stem cells are mostly quiescent, but can be activated in response to injury and participate in endothelial repair and neointima formation. Extensive studies have demonstrated the differentiation potential of stem/progenitor cells to repair endothelium and participate in neointima formation during vascular remodeling. The stem cell population has markers on the surface of the cells that can be used to identify this cell population. The main positive markers include Stem cell antigen-1 (Sca1), Sry-box transcription factor 10 (SOX10). Stromal cell antigen 1 (Stro-1) and Stem cell growth factor receptor kit (c-kit) are still controversial. Different parts of the vessel have different stem cell populations and multiple markers. In this review, we trace the role of vascular stem/progenitor cells in the progression of atherosclerosis and neointima formation, focusing on the expression of stem cell molecular markers that occur during neointima formation and vascular repair, as well as the molecular phenotypic changes that occur during differentiation of different stem cell types. To explore the correlation between stem cell molecular markers and atherosclerotic diseases and neointima formation, summarize the differential changes of molecular phenotype during the differentiation of stem cells into smooth muscle cells and endothelial cells, and further analyze the signaling pathways and molecular mechanisms of stem cells expressing different positive markers participating in intima formation and vascular repair. Summarizing the limitations of stem cells in the prevention and treatment of atherosclerotic diseases and the pressing issues that need to be addressed, we provide a feasible scheme for studying the signaling pathways of vascular stem cells involved in vascular diseases.

Sex Differences in Arteriovenous Fistula Failure: Insights from Bioinformatics Analysis

(1) Background: Arteriovenous fistulas (AVFs) are the preferred access for hemodialysis. Unfortunately, about 60% of patients, especially female patients, fail to receive normal dialysis within one year after surgery because of AVF failure. However, the underlying mechanisms caused by sex differences in AVF failure remain unclear. (2) Methods: We performed analysis of DEGs and functional analysis with the dataset GSE119296 to reveal the biology underlying AVF failure. Immune responses were calculated using CIBERSORT. A protein-protein interaction network and hub gene were constructed using STRING and stepwise identification of potential drugs was performed online. (3) Results: Functional analysis showed that extracellular matrix reprogramming and PI3K-AKT pathway enrichment were significant in both male and female patients. COL1A1 was the hub gene in male patients, whereas CDK1 was the hub gene in female patients. Immune responses including γδ-T cells and mast cells are activated in female patients while no significant differences were noted in the male group. (4) Conclusions: In this study, we used a series of mature and recognized bioinformatic strategies to determine the following items: (1) Reveal the pathogenesis of AVF failure through HUB genes and signaling pathways between the different sexes. (2) Determine the relationship between sex differences in AVF failure and immune abnormalities. (3) Search for relevant sex-specific drugs targeting AVF failure.

The anatomical sources of neointimal cells in the arteriovenous fistula

Neointimal cells are an elusive population with ambiguous origins, functions, and states of differentiation. Expansion of the venous intima in arteriovenous fistula (AVF) is one of the most prominent remodeling processes in the wall after access creation. However, most of the current knowledge about neointimal cells in AVFs comes from extrapolations from the arterial neointima in non-AVF systems. Understanding the origin of neointimal cells in fistulas may have important implications for the design and effective delivery of therapies aimed to decrease intimal hyperplasia (IH). In addition, a broader knowledge of cellular dynamics during postoperative remodeling of the AVF may help clarify other transformation processes in the wall that combined with IH determine the successful remodeling or failure of the access. In this review, we discuss the possible anatomical sources of neointimal cells in AVFs and their relative contribution to intimal expansion.

Interleukin-9 mediates chronic kidney disease-dependent vein graft disease: a role for mast cells

Aims

Chronic kidney disease (CKD) is a powerful independent risk factor for cardiovascular events, including vein graft failure. Because CKD impairs the clearance of small proteins, we tested the hypothesis that CKD exacerbates vein graft disease by elevating serum levels of critical cytokines that promote vein graft neointimal hyperplasia.

Methods and results

We modelled CKD in C57BL/6 mice with 5/6ths nephrectomy, which reduced glomerular filtration rate by 60%, and we modelled vein grafting with inferior-vena-cava-to-carotid interposition grafting. CKD increased vein graft neointimal hyperplasia four-fold, decreased vein graft re-endothelialization two-fold, and increased serum levels of interleukin-9 (IL-9) five-fold. By quantitative immunofluorescence and histochemical staining, vein grafts from CKD mice demonstrated a ∼two-fold higher prevalence of mast cells, and a six-fold higher prevalence of activated mast cells. Concordantly, vein grafts from CKD mice showed higher levels of TNF and NFκB activation, as judged by phosphorylation of NFκB p65 on Ser536 and by expression of VCAM-1. Arteriovenous fistula veins from humans with CKD also showed up-regulation of mast cells and IL-9. Treating CKD mice with IL-9-neutralizing IgG reduced vein graft neointimal area four-fold, increased vein graft re-endothelialization ∼two-fold, and reduced vein graft total and activated mast cell levels two- and four-fold, respectively. Treating CKD mice with the mast cell stabilizer cromolyn reduced neointimal hyperplasia and increased re-endothelialization in vein grafts. In vitro, IL-9 promoted endothelial cell apoptosis but had no effect on smooth muscle cell proliferation.

Conclusion

CKD aggravates vein graft disease through mechanisms involving IL-9 and mast cell activation.

c-Kit modifies the inflammatory status of smooth muscle cells

BACKGROUND

c-Kit is a receptor tyrosine kinase present in multiple cell types, including vascular smooth muscle cells (SMC). However, little is known about how c-Kit influences SMC biology and vascular pathogenesis.

METHODS

High-throughput microarray assays and in silico pathway analysis were used to identify differentially expressed genes between primary c-Kit deficient (Kit^W/W-v) and control (Kit^+/+) SMC. Quantitative real-time RT-PCR and functional assays further confirmed the differences in gene expression and pro-inflammatory pathway regulation between both SMC populations.

RESULTS

The microarray analysis revealed elevated NF-κB gene expression secondary to the loss of c-Kit that affects both the canonical and alternative NF-κB pathways. Upon stimulation with an oxidized phospholipid as pro-inflammatory agent, c-Kit deficient SMC displayed enhanced NF-κB transcriptional activity, higher phosphorylated/total p65 ratio, and increased protein expression of NF-κB regulated pro-inflammatory mediators with respect to cells from control mice. The pro-inflammatory phenotype of mutant cells was ameliorated after restoring c-Kit activity using lentiviral transduction. Functional assays further demonstrated that c-Kit suppresses NF-κB activity in SMC in a TGFβ-activated kinase 1 (TAK1) and Nemo-like kinase (NLK) dependent manner.

DISCUSSION

Our study suggests a novel mechanism by which c-Kit suppresses NF-κB regulated pathways in SMC to prevent their pro-inflammatory transformation.

Responses of adventitial CD34+ vascular wall-resident stem/progenitor cells and medial smooth muscle cells to carotid injury in rats

Cell culture and carotid injury studies with SD rats were performed to investigate the roles of CD34⁺ vascular wall-resident stem/progenitor cells (VRS/Pcs) and vascular smooth muscle cells (SMCs) in neointimal formation. In vitro, the media-isolated SM MHC⁺ SMCs occupied 93.92±8.62% of total BrdU⁺ cells, whereas the CD34⁺ cells, only 2.61±0.82%, indicating that the cell expansion in SMC culture was attributed to SM MHC⁺ SMCs. The adventitia-isolated CD34⁺ VRS/Pcs responded to PDGF-BB by differentiating into SMC-like cells which expressed SM22α (an early stage SMC marker), but seldom SM MHC (a late stage SMC marker). In carotid injury model, the CD34⁺ VRS/Pcs differentiated SMC-like cells migrated in very few numbers into only the outer layer of the media, and this was further confirmed by a cell tracking analysis. While the neointimal cells were consistently SM MHC⁺ and CD34^- SMCs during whole course of the post-injury remodeling. Thus it is speculated that the adventitial CD34⁺ VRS/Pcs, at least in rat model, do not directly participate in neointimal formation, but function to maintain homeostasis of the media during injury-induced vascular wall remodeling.

New Insights into Dialysis Vascular Access: Molecular Targets in Arteriovenous Fistula and Arteriovenous Graft Failure and Their Potential to Improve Vascular Access Outcomes

Vascular access dysfunction remains a major cause of morbidity and mortality in hemodialysis patients. At present there are few effective therapies for this clinical problem. The poor understanding of the pathobiology that leads to arteriovenous fistula (AVF) and graft (AVG) dysfunction remains a critical barrier to development of novel and effective therapies. However, in recent years we have made substantial progress in our understanding of the mechanisms of vascular access dysfunction. This article presents recent advances and new insights into the pathobiology of AVF and AVG dysfunction and highlights potential therapeutic targets to improve vascular access outcomes.