Linkage analysis of neointimal hyperplasia and vascular wall transformation after balloon angioplasty

Long-term outcomes following thrombolysis of arteriovenous grafts

BACKGROUND

Thrombolysis for arteriovenous grafts (AVG) yields high technical success rates, however, long-term outcomes are unclear. We conducted a multicenter retrospective cohort study to analyze 5-year patency rates following AVG thrombolysis.

METHODS

All patients who underwent AVG thrombolysis between 2005 and 2015 at three academic hospitals were included. Prospectively maintained institutional nephrology and radiology databases were used to record demographic, clinical, and AVG characteristics. The primary outcome was primary patency, defined as AVG access survival without re-intervention including angioplasty ± stent with/without re-thrombolysis. Secondary outcomes were assisted primary patency and cumulative patency, defined as AVG access survival until re-thrombosis requiring re-thrombolysis or abandonment, respectively. Technical success was defined as restoration of flow with <30% residual stenosis. Patients were followed until 2017. Patency rates were assessed using Kaplan-Meier survival analysis and Cox proportional hazards were calculated to determine associations between covariates and patency loss.

RESULTS

Seventy-four patients underwent AVG thrombolysis during the study period with a median follow-up period of 21.4 (IQR 8.3-42.8) months. The average age was 58.6 years with a high rate of comorbidities, including hypertension (82.4%) and diabetes (54.1%). Thrombolysis technical success was 96%. There were 147 re-interventions in 46 patients, of which 98 were re-thrombolysis (mean re-intervention rate of 1.27/patient/year). Primary patency at 1, 3, and 5 years were 43.2%, 20.2%, and 7.7%. Assisted primary patency at 1, 3, and 5 years were 47.5%, 20.2%, and 7.7%. Cumulative patency at 1, 3, and 5 years were 75.0%, 38.8%, and 22.6%. Cox proportional hazards analysis demonstrated no associations between demographic, clinical, and procedural characteristics and patency rates.

CONCLUSIONS

Despite a high technical success rate, thrombolysis for AVG dysfunction is associated with poor long-term patency. Future studies are needed to determine risk factors for re-thrombosis to identify patients who will benefit from AVG thrombolysis in the long-term.

RNO3 QTL Regulates Vascular Structure and Arterial Stiffness in the Spontaneously Hypertensive Rat

Increased arterial stiffness is an independent risk factor for hypertension, stroke, and cardiovascular morbidity. Thus, understanding the factors contributing to vascular stiffness is of critical importance. Here, we used a rat model containing a known quantitative trait locus (QTL) on chromosome 3 (RNO3) for vasoreactivity to assess potential genetic elements contributing to blood pressure, arterial stiffness, and their downstream effects on cardiac structure and function. Although no differences were found in blood pressure at any time point between parental spontaneously hypertensive rats (SHRs) and congenic SHR.BN3 rats, the SHRs showed a significant increase in arterial stiffness measured by pulse wave velocity. The degree of arterial stiffness increased with age in the SHRs and was associated with compensatory cardiac changes at 16 wk of age, and decompensatory changes at 32 wk, with no change in cardiac structure or function in the SHR.BN3 hearts at these time points. To evaluate the arterial wall structure, we used multiphoton microscopy to quantify cells and collagen content within the adventitia and media of SHR and SHR.BN3 arteries. No difference in cell numbers or proliferation rates was found, although phenotypic diversity was characterized in vascular smooth muscle cells. Herein, significant anatomical and physiological differences related to arterial structure and cardiovascular tone including collagen, pulse wave velocity (PWV), left ventricular (LV) geometry and function, and vascular smooth muscle cell (VSMC) contractile apparatus proteins were associated with the RNO3 QTL, thus providing a novel platform for studying arterial stiffness. Future studies delimiting the RNO3 QTL could aid in identifying genetic elements responsible for arterial structure and function.

Natriuretic Peptide Receptor 2 Locus Contributes to Carotid Remodeling

Background Carotid artery intima/media thickness (IMT) is a hallmark trait associated with future cardiovascular events. The goal of this study was to map new genes that regulate carotid IMT by genome-wide association. Methods and Results We induced IMT by ligation procedure of the left carotid artery in 30 inbred mouse strains. Histologic reconstruction revealed significant variation in left carotid artery intima, media, adventitia, external elastic lamina volumes, intima-to-media ratio, and (intima+media)/external elastic lamina percent ratio in inbred mice. The carotid remodeling trait was regulated by distinct genomic signatures with a dozen common single-nucleotide polymorphisms associated with left carotid artery intima volume, intima-to-media ratio, and (intima+media)/external elastic lamina percent ratio. Among genetic loci on mouse chromosomes 1, 4, and 12, there was natriuretic peptide receptor 2 (Npr2), a strong candidate gene. We observed that only male, not female, mice heterozygous for a targeted Npr2 deletion (Npr2^+/-) exhibited defective carotid artery remodeling compared with Npr2 wild-type (Npr2^+/+) littermates. Fibrosis in carotid IMT was significantly increased in Npr2^+/- males compared with Npr2^+/- females or Npr2^+/+ mice. We also detected decreased Npr2 expression in human atherosclerotic plaques, similar to that seen in studies in Npr2^+/- mice. Conclusions We found that components of carotid IMT were regulated by distinct genetic factors. We also showed a critical role for Npr2 in genetic regulation of vascular fibrosis associated with defective carotid remodeling.

Strain survey and genetic analysis of vasoreactivity in mouse aorta

Understanding the genetic influence on vascular reactivity is important for identifying genes underlying impaired vascular function. The purpose of this study was to characterize the genetic contribution to intrinsic vascular function and to identify loci associated with phenotypic variation in vascular reactivity in mice. Concentration response curves to phenylephrine (PE), potassium chloride (KCl), acetylcholine (ACh), and sodium nitroprusside (SNP) were generated in aortic rings from male mice (12 wk old) from 27 inbred mouse strains. Significant strain-dependent differences were found for both maximal responses and sensitivity for each agent, except for SNP Max (%). Strain differences for maximal responses to ACh, PE, and KCl varied by two- to fivefold. On the basis of these large strain differences, we performed genome-wide association mapping (GWAS) to identify loci associated with variation in responses to these agents. GWAS for responses to ACh identified four significant and 19 suggestive loci. Several suggestive loci for responses to SNP, PE, and KCl (including one significant locus for KCl EC₅₀) were also identified. These results demonstrate that intrinsic endothelial function, and more generally vascular function, is genetically determined and associated with multiple genomic loci. Furthermore, these results are supported by the finding that several genes residing in significant and suggestive loci for responses to ACh were previously identified in rat and/or human quantitative trait loci/GWAS for cardiovascular disease. This study represents the first step toward the unbiased comprehensive discovery of genetic determinants that regulate intrinsic vascular function, particularly endothelial function.

Genetic analysis of ligation-induced neointima formation in an F2 intercross of C57BL/6 and FVB/N inbred mouse strains

Objective

Proliferation and migration of vascular smooth muscle cells (SMCs) are central for arterial diseases including atherosclerosis and restenosis. We hypothesized that the underlying mechanisms may be modeled by carotid ligation in mice. In FVB/N inbred mice, ligation leads to abundant neointima formation with proliferating media-derived SMCs, whereas in C57BL/6 mice hardly any neointima is formed. In the present study, we aimed to identify the chromosomal location of the causative gene variants in an F2 intercross between these two mouse strains.

Methods and Results

The neointimal cross-sectional area was significantly different between FVB/N, C57BL/6 and F1 female mice 4 weeks after ligation. Carotid artery ligation and a genome scan using 800 informative SNP markers were then performed in 157 female F2 mice. Using quantitative trait loci (QTL) analysis, we identified suggestive, but no genome-wide significant, QTLs on chromosomes 7 and 12 for neointimal cross-sectional area and on chromosome 14 for media area. Further analysis of the cross revealed 4 QTLs for plasma cholesterol, which combined explained 69% of the variation among F2 mice.

Conclusions

We identified suggestive QTLs for neointima and media area after carotid ligation in an intercross of FVB/N and C57BL/6 mice, but none that reached genome-wide significance indicating a complex genetic architecture of the traits. Genome-wide significant QTLs for total cholesterol levels were identified on chromosomes 1, 3, 9, and 12.

Targeted disruption of Adamts16 gene in a rat genetic model of hypertension

A disintegrin-like metalloproteinase with thrombospondin motifs-16 (Adamts16) is an important candidate gene for hypertension. The goal of the present study was to further assess the candidacy of Adamts16 by targeted disruption of this gene in a rat genetic model of hypertension. A rat model was generated by manipulating the genome of the Dahl Salt-sensitive (S) rat using zinc-finger nucleases, wherein the mutant rat had a 17 bp deletion in the first exon of Adamts16, introducing a stop codon in the transcript. Systolic blood pressure (BP) of the homozygous Adamts16(mutant) rats was lower by 36 mmHg compared with the BP of the S rats. The Adamts16(mutant) rats exhibited significantly lower aortic pulse wave velocity and vascular media thickness compared with S rats. Scanning electron and fluorescence microscopic studies indicated that the mechanosensory cilia of vascular endothelial cells from the Adamts16(mutant) rats were longer than that of the S rats. Furthermore, Adamts16(mutant) rats showed splitting and thickening of glomerular capillaries and had a longer survival rate, compared with the S rats. Taken together, these physiological observations functionally link Adamts16 to BP regulation and suggest the vasculature as the potential site of action of Adamts16 to lower BP.

Neointimal hyperplasia and vasoreactivity are controlled by genetic elements on rat chromosome 3

Neointimal hyperplasia (NIH) can lead to restenosis after clinical vascular interventions. NIH results from complex and poorly understood interactions between signaling cascades in the extracellular matrix and the disrupted endothelium, which lead to vessel occlusion. Quantitative trait loci (QTLs) were reported previously on rat chromosomes 3 and 6 through linkage analysis of postinjury NIH in midiliac arterial sections. In the current study, substitution mapping validated the RNO3 NIH QTL but not the RNO6 NIH QTL. The SHR.BN3 congenic strain had a 3-fold increase in the percentage of NIH compared with the parental spontaneously hypertensive rat strain. A double congenic study of RNO3+RNO6 NIH QTL segments suggested less than additive effects of these 2 genomic regions. To test the hypothesis that changes in vessel dynamics account for the differences in NIH formation, we performed vascular reactivity studies in the Brown Norway (BN), spontaneously hypertensive rat (SHR), SHR.BN3, and SHR.BN6 strains. De-endothelialized left common carotid artery rings of the SHR.BN3 showed an increased vascular responsiveness when treated with serotonin or prostaglandin F2(alpha), with significant differences in EC(50) and maximum effect (P<0.01) values compared with the spontaneously hypertensive rat parental strain. Because both vascular reactivity and percentage of NIH formation in the SHR.BN3 strain are significantly higher than the SHR strain, we postulate that these traits may be associated and are controlled by genetic elements on RNO3. In summary, these results confirm that the RNO3 NIH QTL carries the gene(s) contributing to postinjury NIH formation.

Development of transplant vasculopathy in aortic allografts correlates with neointimal smooth muscle cell proliferative capacity and fibrocyte frequency

OBJECTIVE

Transplant vasculopathy consists of neointima formation in graft vasculature resulting from vascular smooth muscle cell recruitment and proliferation. Variation in the severity of vasculopathy has been demonstrated. Genetic predisposition is suggested as a putative cause of this variation, although cellular mechanisms are still unknown. Using a rat aorta transplant model we tested the hypothesis that kinetics of development of transplant vasculopathy are related to neointimal smooth muscle cell proliferative capacity and fibrocyte frequency, the latter being putative neointimal smooth muscle ancestral cells.

METHODS

Aortic allografts were transplanted in Lewis and Brown Norway, as well as MHC-congenic Lewis.1N and Brown Norway.1L recipients. Severity of transplant vasculopathy was quantified 4, 8, 12 and 24 weeks after transplantation. Host-endothelial chimerism, as a reflection of vascular injury, was determined by specific immunofluorescence. Neointimal smooth muscle cell proliferative capacity was determined in vitro and in situ. Fibrocyte frequency and phenotype were determined after in vitro culture by cell counting, immunofluorescence and in situ zymography.

RESULTS

Compared to Lewis, Brown Norway recipients developed accelerated transplant vasculopathy which is dependent on the presence of Brown Norway non-MHC-encoded determinants. Accelerated transplant vasculopathy was associated with increased levels of host-endothelial chimerism and increased neointimal smooth muscle cell proliferation, the latter being accompanied by increased endothelial and smooth muscle cell-derived neuropilin-like protein mRNA expression. Moreover, accelerated transplant vasculopathy was associated with increased frequency of circulating gelatinase-expressing CD45(+)vimentin(+) fibrocytes.

CONCLUSION

Susceptibility for transplant vasculopathy appears to be genetically controlled and correlates with neointimal smooth muscle cell proliferative capacity and circulating fibrocyte frequency.

Genetic modifier loci linked to intima formation induced by low flow in the mouse carotid

OBJECTIVE

Previously we found dramatic strain-dependent differences in a low flow model of vascular remodeling. Specifically, intima formation in the left common carotid artery was approximately 30-fold greater in SJL compared to C3HeB/Fe (C3H/F) mice. We hypothesized that a few genes control intima formation in response to low flow. A C3H/F and SJL backcross resulted in broad range of N2 intima phenotypes.

METHODS AND RESULTS

Using genome-wide scan we identified two highly significant quantitative trait loci (QTLs) for intima, Im1 (intima modifier 1 locus) on chromosome 2 (Chr2; 77.6 cM, LOD=6.4), and Im2 on Chr11 (17 cM, LOD=5.3). One significant QTL Im3 was found on Chr18 (6 cM, LOD=3.0), and two suggestive QTLs (LOD=1.5 and 1.8) were identified on Chr7 and Chr17, respectively. Interestingly, the intima/media ratio trait mapped to the same QTLs as the intima trait. Haplotype mapping predicted 40 candidate genes. Six of these genes contained SNPs that differed between C3H/F and SJL.

CONCLUSIONS

We have successfully mapped 3 QTLs (Im1, Im2, and Im3) that are associated with carotid intima formation in response to low blood flow. These results may be important in identifying genes that influence carotid intima-media thickening and predict cardiovascular disease in humans.