Dataset Information

Inhibition of the Akt1-mTORC1 Axis Alters Venous Remodeling to Improve Arteriovenous Fistula Patency.

ABSTRACT: Arteriovenous fistulae (AVF) are the most common access created for hemodialysis, but up to 60% do not sustain dialysis within a year, suggesting a need to improve AVF maturation and patency. In a mouse AVF model, Akt1 regulates fistula wall thickness and diameter. We hypothesized that inhibition of the Akt1-mTORC1 axis alters venous remodeling to improve AVF patency. Daily intraperitoneal injections of rapamycin reduced AVF wall thickness with no change in diameter. Rapamycin decreased smooth muscle cell (SMC) and macrophage proliferation; rapamycin also reduced both M1 and M2 type macrophages. AVF in mice treated with rapamycin had reduced Akt1 and mTORC1 but not mTORC2 phosphorylation. Depletion of macrophages with clodronate-containing liposomes was also associated with reduced AVF wall thickness and both M1- and M2-type macrophages; however, AVF patency was reduced. Rapamycin was associated with improved long-term patency, enhanced early AVF remodeling and sustained reduction of SMC proliferation. These results suggest that rapamycin improves AVF patency by reducing early inflammation and wall thickening while attenuating the Akt1-mTORC1 signaling pathway in SMC and macrophages. Macrophages are associated with AVF wall thickening and M2-type macrophages may play a mechanistic role in AVF maturation. Rapamycin is a potential translational strategy to improve AVF patency.

SUBMITTER: Guo X

PROVIDER: S-EPMC6667481 | biostudies-literature | 2019 Jul

REPOSITORIES: biostudies-literature

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Inhibition of the Akt1-mTORC1 Axis Alters Venous Remodeling to Improve Arteriovenous Fistula Patency.

Guo Xiangjiang X Fereydooni Arash A Isaji Toshihiko T Gorecka Jolanta J Liu Shirley S Hu Haidi H Ono Shun S Alozie Michelle M Lee Shin Rong SR Taniguchi Ryosuke R Yatsula Bogdan B Nassiri Naiem N Zhang Lan L Dardik Alan A

Scientific reports 20190730 1

Arteriovenous fistulae (AVF) are the most common access created for hemodialysis, but up to 60% do not sustain dialysis within a year, suggesting a need to improve AVF maturation and patency. In a mouse AVF model, Akt1 regulates fistula wall thickness and diameter. We hypothesized that inhibition of the Akt1-mTORC1 axis alters venous remodeling to improve AVF patency. Daily intraperitoneal injections of rapamycin reduced AVF wall thickness with no change in diameter. Rapamycin decreased smooth m ...[more]

PMID: 31363142

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Project description:Objective:The arteriovenous fistula (AVF) is the preferred method of dialysis access because of its proven superior long-term outcomes.However, women havelower rates of AVF patency andutilizationthan men.We used a novel mouseAVF model that recapitulates human AVF maturation to determine whether there are differences in AVF patency in female and male mice. Methods:Aortocaval fistulas were created in female and male C57BL/6 mice (9-10 weeks). At days 0, 3, 7, and 21, infrarenal inferior vena cava (IVC) and aortic diameters and flow velocity were monitored by Doppler ultrasound and used to calculate the vessel diameter, blood flow, and shear stress. AVF were harvested, and expression of proteins was examined by proteomic analysis and immunofluorescence and of messenger RNA by quantitative polymerase chain reaction analysis. Results:At baseline, female mice weighed less and had lower IVC velocity and smaller magnitudes of shear stress, but there was no significant difference in IVC diameter and thickness. After AVF creation, both female and male mice had similar IVC dilation and thickening with no significant differences in IVC wall thickness at day 21. However, female mice had diminished AVF patency by day 42 (25.7% vs 64.3%; P = .039). During fistula remodeling, female mice had lower IVC mean velocity and shear stress magnitude and increased spectral broadening (days 0-21). Messenger RNA and protein expression of Krüppel-like factor 2, endothelial nitric oxide synthase, and vascular cell adhesion molecule 1 was similar at baseline in female and male mice but increased in the AVF only in male mice but not in female mice (day 21). Proteomic analysis of female and male mice detected 56 proteins expressed at significantly higher levels in the IVC of female mice and 67 proteins expressed at significantly higher levels in the IVC of male mice (day 7); function-specific analysis showed that the IVC of male mice overexpressed proteins that belong to pathways implicated in the regulation of vascular function, thrombosis, response to flow, and vascular remodeling. Conclusions:AVF in female mice have diminished patency, preceded by lower velocity, reduced magnitudes of shear stress, and less laminar flow during remodeling. There is also sex-specific differential expression of proteins involved in thrombosis, response to laminar flow, inflammation, and proliferation. These findings suggest that hemodynamic changes during fistula maturation may play an important role underlying the diminished rates of AVF utilization in women. Clinical Relevance:Women have lower rates of arteriovenous fistula (AVF) utilization than men. Using a mouse AVF model that recapitulates human AVF maturation, we show that female mice have similar AVF remodeling but diminished patency. AVF remodeling in female mice is associated with reduced shear stress and laminar flow; lack of increased transcription and translation of several anti-inflammatory, antiproliferative, and laminar flow response proteins (endothelial nitric oxide synthase, Krüppel-like factor 2, and vascular cell adhesion molecule 1); and different patterns of expression of pathways that regulate thrombosis and venous remodeling. Identifying downstream targets involved in these mechanisms may improve AVF outcomes in female patients.

Project description:Background: Although clinical outcome of arteriovenous fistula (AVF) as a preferred vascular access for hemodialysis has been inadequate, biological mechanisms of AVF maturation and failure is still poorly understood. Since our mouse AVF model recapitulates human AVF maturation and partial failure, we hypothesized that high throughput RNA sequencing (RNA-seq) analysis would identify early changes in gene expression that might predict AVF maturation and failure. Method: Aortocaval fistula creation (AVF group) or sham operation (sham group) was performed with C57BL/6 mice (10 wk). Ultrasound was performed to confirm the AVF patency and to measure hemodynamics. Venous limbs were collected on postoperative day 7 and total RNA was extracted. After Poly-A mRNA libraries were constructed, RNA-seq was performed. Differentially expressed genes (DEG) were identified, and subsequent enrichment analyses of gene ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways were performed with bioinformatics techniques. Results: 1057 DEG were identified between the AVF and sham groups. Genes in metabolic pathways were significantly downregulated in the AVF. Since gene expression patterns among the AVF group were significantly heterogenous, the AVF group was divided into 2 groups (‘normal’ AVF group; nAVF and ‘outliers’ group; OUT), and subgroup analyses were performed. Although physiological data of body weight change and hemodynamics were not different between the nAVF and OUT groups, 413 DEG were identified between them. Enrichment analyses showed significant overrepresentation of metabolism, immunity, and coagulation in the OUT group. Comparing the nAVF group with the sham group, 403 DEG were identified. Enrichment analyses showed increase of gene expression related to cell cycle, extracellular matrix, and immunity. Comparing these results with previously published data, the gene expression patterns of the nAVF group was consistent with AVF maturation and adaptive remodeling, whereas the OUT group showed attenuated difference, suggesting the heterogeneity of the AVF group reflects early gene expression changes in the process of AVF maturation and failure. Significant sex differences were not observed in the AVF group. Conclusions: A small subset of AVF undergoes aberrant biological processes in the early phase including diminished ECM remodeling, activated coagulation and upregulated metabolism, that could lead to fistula failure. Detection of these processes might be a viable translational strategy to predict fistula failure and reduce patient morbidity.

Project description:Rationale & objectiveThe current clinical guidelines for vascular access do not have specific recommendations for older hemodialysis patients. Our study aimed to determine the association of age with arteriovenous fistula (AVF) placement, maturation, and primary and secondary patency loss among older hemodialysis recipients.Study designRetrospective cohort study.Setting & participantsA US national cohort of incident hemodialysis patients 67 years or older (N = 43,851) assembled from the US Renal Data System.ExposureAge at dialysis initiation.OutcomesAVF placement, maturation, primary patency loss, and abandonment.Analytical approachCause-specific and subdistribution proportional hazards models were used to examine the association of age and AVF outcomes, with kidney transplantation, peritoneal dialysis, and death treated as competing events. Age cutoff was identified by restricted cubic splines. We compared crude and inverse probability-weighted cumulative incidence functions using Gray's test.ResultsAs compared with those aged 67-<77 years, patients 77 years or older had significantly lower probabilities of AVF placement (adjusted cause-specific HR [cHR], 0.96 [95% CI, 0.92-0.99]; adjusted subdistribution HR [sHR], 0.92 [95% CI, 0.89-0.95]; Gray's test P < 0.001) and maturation (adjusted cHR, 0.95 [95% CI, 0.91-0.99]; adjusted sHR, 0.93 [95% CI, 0.90-0.97]; P < 0.001). However, age was not associated with AVF primary (adjusted cHR, 1.05 [95% CI, 1.00-1.11]; adjusted sHR, 1.04 [95% CI, 0.99-1.09]; P = 0.09) or secondary (adjusted cHR, 1.06 [95% CI, 0.94-1.20]; adjusted sHR, 1.05 [95% CI, 0.93-1.18]; P = 0.4) patency loss.LimitationsReliance on administrative claims to ascertain AVF outcomes.ConclusionsThe likelihood of AVF maturation is an important consideration for vascular access planning. Age alone should not be the basis for excluding older dialysis patients from AVF creation because maintenance of fistula patency was not reduced with older age despite a modest reduction in fistula maturation.

Dataset Information

Inhibition of the Akt1-mTORC1 Axis Alters Venous Remodeling to Improve Arteriovenous Fistula Patency.

Publications

Inhibition of the Akt1-mTORC1 Axis Alters Venous Remodeling to Improve Arteriovenous Fistula Patency.

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