Biliverdin Reductase B Is a Plasma Biomarker for Intraplaque Hemorrhage and a Predictor of Ischemic Stroke in Patients with Symptomatic Carotid Atherosclerosis

BACKGROUND

Intraplaque hemorrhage (IPH) is a hallmark of atherosclerotic plaque instability. Biliverdin reductase B (BLVRB) is enriched in plasma and plaques from patients with symptomatic carotid atherosclerosis and functionally associated with IPH.

OBJECTIVE

We explored the biomarker potential of plasma BLVRB through (1) its correlation with IPH in carotid plaques assessed by magnetic resonance imaging (MRI), and with recurrent ischemic stroke, and (2) its use for monitoring pharmacotherapy targeting IPH in a preclinical setting.

METHODS

Plasma BLVRB levels were measured in patients with symptomatic carotid atherosclerosis from the PARISK study (n = 177, 5 year follow-up) with and without IPH as indicated by MRI. Plasma BLVRB levels were also measured in a mouse vein graft model of IPH at baseline and following antiangiogenic therapy targeting vascular endothelial growth factor receptor 2 (VEGFR-2).

RESULTS

Plasma BLVRB levels were significantly higher in patients with IPH (737.32 ± 693.21 vs. 520.94 ± 499.43 mean fluorescent intensity (MFI), p = 0.033), but had no association with baseline clinical and biological parameters. Plasma BLVRB levels were also significantly higher in patients who developed recurrent ischemic stroke (1099.34 ± 928.49 vs. 582.07 ± 545.34 MFI, HR = 1.600, CI [1.092-2.344]; p = 0.016). Plasma BLVRB levels were significantly reduced following prevention of IPH by anti-VEGFR-2 therapy in mouse vein grafts (1189 ± 258.73 vs. 1752 ± 366.84 MFI; p = 0.004).

CONCLUSIONS

Plasma BLVRB was associated with IPH and increased risk of recurrent ischemic stroke in patients with symptomatic low- to moderate-grade carotid stenosis, indicating the capacity to monitor the efficacy of IPH-preventive pharmacotherapy in an animal model. Together, these results suggest the utility of plasma BLVRB as a biomarker for atherosclerotic plaque instability.

Transcriptomic and physiological analyses reveal temporal changes contributing to the delayed healing response to arterial injury in diabetic rats

Objective

Atherosclerosis is a leading cause of mortality in the rapidly growing population with diabetes mellitus. Vascular interventions in patients with diabetes can lead to complications attributed to defective vascular remodeling and impaired healing response in the vessel wall. In this study, we aim to elucidate the molecular differences in the vascular healing response over time using a rat model of arterial injury applied to healthy and diabetic conditions.

Methods

Wistar (healthy) and Goto-Kakizaki (GK, diabetic) rats (n = 40 per strain) were subjected to left common carotid artery (CCA) balloon injury and euthanized at different timepoints: 0 and 20 hours, 5 days, and 2, 4, and 6 weeks. Noninvasive morphological and physiological assessment of the CCA was performed with ultrasound biomicroscopy (Vevo 2100) and corroborated with histology. Total RNA was isolated from the injured CCA at each timepoint, and microarray profiling was performed (n = 3 rats per timepoint; RaGene-1_0-st-v1 platform). Bioinformatic analyses were conducted using R software, DAVID bioinformatic tool, online STRING database, and Cytoscape software.

Results

Significant increase in the neointimal thickness (P < .01; two-way analysis of variance) as well as exaggerated negative remodeling was observed after 2 weeks of injury in GK rats compared with heathy rats, which was confirmed by histological analyses. Bioinformatic analyses showed defective expression patterns for smooth muscle cells and immune cell markers, along with reduced expression of key extracellular matrix-related genes and increased expression of pro-thrombotic genes, indicating potential faults on cell regulation level. Transcription factor-protein-protein interaction analysis provided mechanistic evidence with an array of transcription factors dysregulated in diabetic rats.

Conclusions

In this study, we have demonstrated that diabetic rats exhibit impaired arterial remodeling characterized by a delayed healing response. We show that increased contractile smooth muscle cell marker expression coincided with decreased matrix metalloproteinase expression, indicating a potential mechanism for a lack of extracellular matrix reorganization in the impaired vascular healing in GK rats. These results further corroborate the higher prevalence of restenosis in patients with diabetes and provide vital molecular insights into the mechanisms contributing to the impaired arterial healing response in diabetes. Moreover, the presented study provides the research community with the valuable longitudinal gene expression data bank for further exploration of diabetic vasculopathy.

Interleukin-6 trans-signaling induced laminin switch contributes to reduced trans-endothelial migration of granulocytic cells

BACKGROUND AND AIMS

Laminins are essential components of the endothelial basement membrane, which predominantly contains LN421 and LN521 isoforms. Regulation of laminin expression under pathophysiological conditions is largely unknown. In this study, we aimed to investigate the role of IL-6 in regulating endothelial laminin profile and characterize the impact of altered laminin composition on the phenotype, inflammatory response, and function of endothelial cells (ECs).

METHODS

HUVECs and HAECs were used for in vitro experiments. Trans-well migration experiments were performed using leukocytes isolated from peripheral blood of healthy donors. The BiKE cohort was used to assess expression of laminins in atherosclerotic plaques and healthy vessels. Gene and protein expression was analyzed using Microarray/qPCR and proximity extension assay, ELISA, immunostaining or immunoblotting techniques, respectively.

RESULTS

Stimulation of ECs with IL-6+sIL-6R, but not IL-6 alone, reduces expression of laminin α4 (LAMA4) and increases laminin α5 (LAMA5) expression at the mRNA and protein levels. In addition, IL-6+sIL-6R stimulation of ECs differentially regulates the release of several proteins including CXCL8 and CXCL10, which collectively were predicted to inhibit granulocyte transmigration. Experimentally, we demonstrated that granulocyte migration is inhibited across ECs pre-treated with IL-6+sIL-6R. In addition, granulocyte migration across ECs cultured on LN521 was significantly lower compared to LN421. In human atherosclerotic plaques, expression of endothelial LAMA4 and LAMA5 is significantly lower compared to control vessels. Moreover, LAMA5-to-LAMA4 expression ratio was negatively correlated with granulocytic cell markers (CD177 and myeloperoxidase (MPO)) and positively correlated with T-lymphocyte marker CD3.

CONCLUSIONS

We showed that expression of endothelial laminin alpha chains is regulated by IL-6 trans-signaling and contributes to inhibition of trans-endothelial migration of granulocytic cells. Further, expression of laminin alpha chains is altered in human atherosclerotic plaques and is related to intra-plaque abundance of leukocyte subpopulations.

Mast cells participate in smooth muscle cell reprogramming and atherosclerotic plaque calcification

BACKGROUND

Calcification, a key feature of advanced human atherosclerosis, is positively associated with vascular disease burden and adverse events. We showed that macrocalcification can be a stabilizing factor for carotid plaque molecular biology, due to inverse association with immune processes. Mast cells (MCs) are important contributors to plaque instability, but their relationship with macrocalcification is unexplored. With a hypothesis that MC activation negatively associates with carotid plaque macrocalcification, we aimed to investigate the link between MCs and carotid plaque vulnerability, and study MC role in plaque calcification via smooth muscle cells (SMCs).

METHODS

Pre-operative computed tomography angiographies of patients (n = 40) undergoing surgery for carotid stenosis were used to characterize plaque morphology. Plaque microarrays (n = 40 and n = 126) were used for bioinformatic deconvolution of immune cell populations. Tissue microarrays (n = 103) were used to histologically validate the contribution of activated and resting MCs in plaques.

RESULTS

Activated MCs and their typical markers were negatively correlated with macrocalcification. The ratio of activated vs. resting MCs was increased in low-calcified plaques from symptomatic patients. There was no modulating effect of medication on MC ratios. In vitro experiments showed that SMC calcification attenuated MC activation, while both active and resting MCs stimulated SMC calcification and induced dedifferentiation towards a pro-inflammatory-, osteochondrocyte-like phenotype, without modulating their migro-proliferative function.

CONCLUSIONS

Integrative analyses from human plaques showed that MC activation is inversely associated with macrocalcification and positively with parameters of plaque vulnerability. Mechanistically, MCs induce SMC osteogenic reprograming, while matrix calcification in turn attenuates MC activation, offering new therapeutic avenues for exploration.

In silico model of atherosclerosis with individual patient calibration to enable precision medicine for cardiovascular disease

OBJECTIVE

Guidance for preventing myocardial infarction and ischemic stroke by tailoring treatment for individual patients with atherosclerosis is an unmet need. Such development may be possible with computational modeling. Given the multifactorial biology of atherosclerosis, modeling must be based on complete biological networks that capture protein-protein interactions estimated to drive disease progression. Here, we aimed to develop a clinically relevant scale model of atherosclerosis, calibrate it with individual patient data, and use it to simulate optimized pharmacotherapy for individual patients.

APPROACH AND RESULTS

The study used a uniquely constituted plaque proteomic dataset to create a comprehensive systems biology disease model for simulating individualized responses to pharmacotherapy. Plaque tissue was collected from 18 patients with 6735 proteins at two locations per patient. 113 pathways were identified and included in the systems biology model of endothelial cells, vascular smooth muscle cells, macrophages, lymphocytes, and the integrated intima, altogether spanning 4411 proteins, demonstrating a range of 39-96% plaque instability. After calibrating the systems biology models for individual patients, we simulated intensive lipid-lowering, anti-inflammatory, and anti-diabetic drugs. We also simulated a combination therapy. Drug response was evaluated as the degree of change in plaque stability, where an improvement was defined as a reduction of plaque instability. In patients with initially unstable lesions, simulated responses varied from high (20%, on combination therapy) to marginal improvement, whereas patients with initially stable plaques showed generally less improvement.

CONCLUSION

In this pilot study, proteomics-based system biology modeling was shown to simulate drug response based on atherosclerotic plaque instability with a power of 90%, providing a potential strategy for improved personalized management of patients with cardiovascular disease.

Therapeutic potential of the Proprotein Convertase Subtilisin/Kexin family in vascular disease

Proprotein convertase subtilisin/kexins (PCSKs) constitute a family of nine related proteases: PCSK1-7, MBTPS1, and PCSK9. Apart from PCSK9, little is known about PCSKs in cardiovascular disease. Here, we aimed to investigate the expression landscape and druggability potential of the entire PCSK family for CVD. We applied an integrative approach, combining genetic, transcriptomic and proteomic data from three vascular biobanks comprising carotid atherosclerosis, thoracic and abdominal aneurysms, with patient clinical parameters and immunohistochemistry of vascular biopsies. Apart from PCSK4, all PCSK family members lie in genetic regions containing variants associated with human cardiovascular traits. Transcriptomic analyses revealed that FURIN, PCSK5, MBTPS1 were downregulated, while PCSK6/7 were upregulated in plaques vs. control arteries. In abdominal aneurysms, FURIN, PCSK5, PCSK7, MBTPS1 were downregulated, while PCSK6 was enriched in diseased media. In thoracic aneurysms, only FURIN was significantly upregulated. Network analyses of the upstream and downstream pathways related to PCSKs were performed on the omics data from vascular biopsies, revealing mechanistic relationships between this protein family and disease. Cell type correlation analyses and immunohistochemistry showed that PCSK transcripts and protein levels parallel each other, except for PCSK9 where transcript was not detected, while protein was abundant in vascular biopsies. Correlations to clinical parameters revealed a positive association between FURIN plaque levels and serum LDL, while PCSK6 was negatively associated with Hb. PCSK5/6/7 were all positively associated with adverse cardiovascular events. Our results show that PCSK6 is abundant in plaques and abdominal aneurysms, while FURIN upregulation is characteristic for thoracic aneurysms. PCSK9 protein, but not the transcript, was present in vascular lesions, suggesting its accumulation from circulation. Integrating our results lead to the development of a novel ‘molecular’ 5D framework. Here, we conducted the first integrative study of the proprotein convertase family in this context. Our results using this translational pipeline, revealed primarily PCSK6, followed by PCSK5, PCSK7 and FURIN, as proprotein convertases with the highest novel therapeutic potential.

Plaque Evaluation by Ultrasound and Transcriptomics Reveals BCLAF1 as a Regulator of Smooth Muscle Cell Lipid Transdifferentiation in Atherosclerosis

BACKGROUND

Understanding the processes behind carotid plaque instability is necessary to develop methods for identification of patients and lesions with stroke risk. Here, we investigated molecular signatures in human plaques stratified by echogenicity as assessed by duplex ultrasound.

METHODS

Lesion echogenicity was correlated to microarray gene expression profiles from carotid endarterectomies (n=96). The findings were extended into studies of human and mouse atherosclerotic lesions in situ, followed by functional investigations in vitro in human carotid smooth muscle cells (SMCs).

RESULTS

Pathway analyses highlighted muscle differentiation, iron homeostasis, calcification, matrix organization, cell survival balance, and BCLAF1 (BCL2 [B-cell lymphoma 2]-associated transcription factor 1) as the most significant signatures. BCLAF1 was downregulated in echolucent plaques, positively correlated to proliferation and negatively to apoptosis. By immunohistochemistry, BCLAF1 was found in normal medial SMCs. It was repressed early during atherogenesis but reappeared in CD68+ cells in advanced plaques and interacted with BCL2 by proximity ligation assay. In cultured SMCs, BCLAF1 was induced by differentiation factors and mitogens and suppressed by macrophage-conditioned medium. BCLAF1 silencing led to downregulation of BCL2 and SMC markers, reduced proliferation, and increased apoptosis. Transdifferentiation of SMCs by oxLDL (oxidized low-denisty lipoprotein) was accompanied by upregulation of BCLAF1, CD36, and CD68, while oxLDL exposure with BCLAF1 silencing preserved MYH (myosin heavy chain) 11 expression and prevented transdifferentiation. BCLAF1 was associated with expression of cell differentiation, contractility, viability, and inflammatory genes, as well as the scavenger receptors CD36 and CD68. BCLAF1 expression in CD68+/BCL2+ cells of SMC origin was verified in plaques from MYH11 lineage-tracing atherosclerotic mice. Moreover, BCLAF1 downregulation associated with vulnerability parameters and cardiovascular risk in patients with carotid atherosclerosis.

CONCLUSIONS

Plaque echogenicity correlated with enrichment of distinct molecular pathways and identified BCLAF1, previously not described in atherosclerosis, as the most significant gene. Functionally, BCLAF1 seems necessary for survival and transdifferentiation of SMCs into a macrophage-like phenotype. The role of BCLAF1 in plaque vulnerability should be further evaluated.

Abstract 218: Integration Of Coronary Artery Disease GWAS With Bulk And Single-cell Transcriptomics From Atherosclerotic Plaques By Deconvolution, Reveals Novel Smooth Muscle Cell Genes

Background and Aim: A central role of vascular smooth muscle cells (SMCs) in atherosclerosis has recently evolved that suggests causal genetic links to disease processes. Single cell sequencing studies of atherosclerotic plaques have identified multiple mesenchymal transition cell populations within the plaques. Here, we correlated cell fractions from plaques to coronary artery disease (CAD) related gene polymorphisms to identify novel SMC targets and study their influence on SMC function in atherosclerosis.

Methods: Deconvolution analysis was performed on bulk microarray data from carotid plaques in the Biobank of Karolinska Endarterectomies (BiKE, n=127) using single cell sequencing data from coronary plaques (n=5). CAD-associated GWAS loci associated with mesenchymal cell fractions were identified, followed by functional analyses of these genes in SMC in vitro using migration, proliferation and apoptosis assays.

Results: We identified 5 mesenchymal cell-specific genetic variants associated with CAD, BiKE patient symptomatology and gene expression eQTLs in BiKE plaque tissue and GTex normal arteries. These variants were harbored in genetic loci of ARNTL, LDLR, MIA3, PAK1 and ARHGAP15 . Microarray analysis revealed increased expression of ARHGAP15 and PAK1 and decreased levels of LDLR in carotid plaques compared with normal arteries (n=127 vs. 10 respectively, student’s t-test). Immunohistochemistry demonstrated increased expression of corresponding proteins in the fibrous cap of plaques compared to normal arteries (n=5). To investigate their function in SMCs, the genes were silenced using siRNAs followed by migration, proliferation and apoptosis assays. Preliminary results indicated that silencing of MIA3, LDLR and ARNTL inhibited SMC proliferation.

Conclusions: The results of this project may reveal novel SMC-specific genetic links to the disease, which may serve as therapeutic targets to be explored for improved treatment of atherosclerosis.

Abstract 420: Proprotein Convertase Subtilisin/Kexin 6 Is Involved In Lipid Metabolism In Liver

Introduction: PCSK6 is a protease that activates cytokines and growth factors and strongly enriched in healthy human liver, however its function in this context has not been explored. We have previously shown that PCSK6 is induced in atherosclerotic plaques from patients with symptoms of stroke and important for regulating several cell types in this context. Here, we aimed to investigate the role of PCSK6 in lipid metabolism in liver, particularly in the context of atherosclerosis and non-alcoholic fatty liver disease (NAFLD).

Methods: We used publically available datasets and several atherosclerosis biobanks to investigate the expression of PCSK6 in healthy and diseased human tissues. In addition, we used full Pcsk6 -/- mice as well as liver specific conditional Pcsk6 -/- knockout mice compared to littermate controls, to investigate the effects of PCSK6 ablation on lipid metabolism.

Results: Genetic analyses of the PCSK6 locus identified a variant, rs7181043, that was significantly associated with PCSK6 mRNA expression in healthy human adipose tissue, liver and in atherosclerotic plaques. The same variant was associated specifically with plaque fat content and atherosclerotic patient’s plasma LDL levels. In addition, PCSK6 mRNA expression in plaques was positively correlated with total plasma cholesterol and LDL levels in atherosclerotic patients as well as lipid metabolism associated pathways within the carotid plaque. Microarray comparison of the livers from Pcsk6 -/- mice and controls showed that VLDL particle assembly was one of the upregulated processes. I n vivo studies showed that Pcsk6 -/- mice have higher plasma cholesterol and LPL levels at baseline compared to controls, and lower levels of LDLR in their liver. These findings were further confirmed in liver specific conditional knockouts. Preliminary results show that liver specific knockout mice develop increased liver steatosis and fibrosis on a modified western diet.

Conclusions: Our data suggests that PCSK6 is involved in cholesterol and metabolic control in liver. Breeding of liver specific Pcsk6 knockout mice on an ApoE -/- background is currently ongoing and will provide insight into the role of liver PCSK6 in atherosclerosis and NAFLD development.

Abstract 419: Therapeutic Potential Of The Proprotein Convertase Subtilisin/Kexin (PCSK) Family In Vascular Disease

Introduction: Proprotein convertase subtilisin/kexins (PCSKs) constitute a family of 7 related proteases (PCSK1-7) and 2 distant ones (MBTPS1, PCSK9), with unexplored role in cardiovascular disease (CVD), apart from PCSK9 in lipid metabolism. Here, we aimed to investigate the expression landscape and therapeutic targeting potential of the entire PCSK family for ameliorating CVD.

Methods: An integrative approach was applied with genetic, transcriptomic and proteomic data mining from public databases and three independent vascular biobanks comprising carotid atherosclerosis, thoracic and abdominal aneurysms. Omics analyses were followed by gene expression association with patient clinical parameters and immunohistochemistry in vascular biopsies.

Results: Genetic studies revealed that, apart from PCSK4 , all PCSK family members lie in regions containing variants associated with human cardiovascular traits. Transcriptomic analyses showed that FURIN, PCSK5, MBTPS1 were downregulated, while PCSK6/7 were upregulated in atherosclerotic plaques vs. normal arteries. In abdominal aneurysms, FURIN, PCSK5, PCSK7, MBTPS1 were downregulated, while PCSK6 was enriched in diseased media. In thoracic aneurysms, only FURIN was significantly upregulated. To understand the mechanistic relationships of this protein family with the disease, network analyses of the upstream and downstream pathways related to PCSKs were done on the omics data from vascular biopsies. Immunohistochemistry indicated that PCSK protein levels correspond to the mRNA expression, except in the case of PCSK9 protein that was abundant in vascular biopsies. Correlation to clinical parameters in a carotid endarterectomy cohort revealed positive associations for PCSK5/6/7 with adverse cardiovascular events.

Conclusions: Our results show that PCSK6 is the most enriched PCSK in plaques and abdominal aneurysms, while FURIN upregulation is characteristic for thoracic aneurysms. PCSK9 protein but not the transcript, was present in vascular lesions, suggesting its accumulation from circulation. Overall evaluation revealed that PCSK6 is the most attractive protease from this family to target for drug development in CVD.

Abstract 217: PCSK6 Is A Key Regulator Of Immune Status In Mice And Its Ablation Increases Atherosclerotic Plaque Burden In A Bone Marrow Transplant Model

Introduction: Proprotein convertase subtilisins/kexins (PCSKs) activate cytokines and growth factors and have been implicated in various cancers. We have previously shown that PCSK6 is a key protease modulating smooth muscle cell response in atherosclerosis, but its expression also correlated positively with typical markers of T lymphocytes and macrophages in plaques and it was localised in the proximity of these cells. Here, we hypothesized that PCSK6 may be involved in modulating inflammatory responses and aimed to elucidate its role in a hyperlipidemic mice model.

Methods: Detailed immunophenotyping using histology, FACS-, OLINK- and ELISA-based analyses and primary cell cultures was used to compare Pcsk6 -/- and littermate controls. Atherosclerosis was evaluated in Ldlr -/- mice upon bone marrow transplant with Pcsk6 -/- or wild-type bone-marrow.

Results: At baseline Pcks6 -/- mice showed an enrichment of pro-inflammatory cytokines Ccl2, Ccl3, Ccl20, Cxcl1 and in particular Il17a and Il17f in plasma compared controls. Spleens of Pcsk6 -/- mice had an increased number of germinal centres and FACS analysis showed that they contained significantly more CD8+ T cells. Microarray analysis of spleens from Pcsk6 -/- vs. controls confirmed that T cell markers CD4, CD3E and CD3G were upregulated. In vitro , splenocytes isolated from Pcsk6 -/- mice secreted more IFN-γ, IL-2 and IL-10 than controls upon stimulation with α-CD3 and α-CD28 antibodies. Moreover, peritoneal macrophages from Pcsk6 -/- mice secreted more TNF-α, MCP-1, IL-6 and IL-10 compared to control mice upon LPS stimulation. Interestingly, bone marrow derived macrophages from Pcsk6 -/- mice were also more prone to lipid uptake. Finally, in vivo transplantation of Pcsk6 -/- bone marrow to Ldlr -/- mice led to increased atherosclerotic plaque burden compared to controls, as quantified in the aortic root.

Conclusions: PCSK6 ablation led to increased number of CD8+ T cells, as well as macrophage and cytokine activation. Transplantation of Pcsk6 -/- bone marrow resulted in an increase in atherosclerotic plaque burden compared to controls. Taken together, these results indicate that PCSK6 is a key regulator of the immune system, though the exact mechanisms involved require further investigation.

Osteomodulin attenuates smooth muscle cell osteogenic transition in vascular calcification

Rationale

Vascular calcification is a prominent feature of late‐stage diabetes, renal and cardiovascular disease (CVD), and has been linked to adverse events. Recent studies in patients reported that plasma levels of osteomodulin (OMD), a proteoglycan involved in bone mineralisation, associate with diabetes and CVD. We hypothesised that OMD could be implicated in these diseases via vascular calcification as a common underlying factor and aimed to investigate its role in this context.

Methods and results

In patients with chronic kidney disease, plasma OMD levels correlated with markers of inflammation and bone turnover, with the protein present in calcified arterial media. Plasma OMD also associated with cardiac calcification and the protein was detected in calcified valve leaflets by immunohistochemistry. In patients with carotid atherosclerosis, circulating OMD was increased in association with plaque calcification as assessed by computed tomography. Transcriptomic and proteomic data showed that OMD was upregulated in atherosclerotic compared to control arteries, particularly in calcified plaques, where OMD expression correlated positively with markers of smooth muscle cells (SMCs), osteoblasts and glycoproteins. Immunostaining confirmed that OMD was abundantly present in calcified plaques, localised to extracellular matrix and regions rich in α‐SMA⁺ cells. In vivo, OMD was enriched in SMCs around calcified nodules in aortic media of nephrectomised rats and in plaques from ApoE^−/− mice on warfarin. In vitro experiments revealed that OMD mRNA was upregulated in SMCs stimulated with IFNγ, BMP2, TGFβ1, phosphate and β‐glycerophosphate, and by administration of recombinant human OMD protein (rhOMD). Mechanistically, addition of rhOMD repressed the calcification process of SMCs treated with phosphate by maintaining their contractile phenotype along with enriched matrix organisation, thereby attenuating SMC osteoblastic transformation. Mechanistically, the role of OMD is exerted likely through its link with SMAD3 and TGFB1 signalling, and interplay with BMP2 in vascular tissues.

Conclusion

We report a consistent association of both circulating and tissue OMD levels with cardiovascular calcification, highlighting the potential of OMD as a clinical biomarker. OMD was localised in medial and intimal α‐SMA⁺ regions of calcified cardiovascular tissues, induced by pro‐inflammatory and pro‐osteogenic stimuli, while the presence of OMD in extracellular environment attenuated SMC calcification.

Carotid Plaque Phenotyping by Correlating Plaque Morphology from Computed Tomography Angiography with Transcriptional Profiling

OBJECTIVE

Ischaemic strokes can be caused by unstable carotid atherosclerosis, but methods for identification of high risk lesions are lacking. Carotid plaque morphology imaging using software for visualisation of plaque components in computed tomography angiography (CTA) may improve assessment of plaque phenotype and stroke risk, but it is unknown if such analyses also reflect the biological processes related to lesion stability. Here, we investigated how carotid plaque morphology by image analysis of CTA is associated with biological processes assessed by transcriptomic analyses of corresponding carotid endarterectomies (CEAs).

METHODS

Carotid plaque morphology was assessed in patients undergoing CEA for symptomatic or asymptomatic carotid stenosis consecutively enrolled between 2006 and 2015. Computer based analyses of pre-operative CTA was performed to define calcification, lipid rich necrotic core (LRNC), intraplaque haemorrhage (IPH), matrix (MATX), and plaque burden. Plaque morphology was correlated with molecular profiles obtained from microarrays of corresponding CEAs and models were built to assess the ability of plaque morphology to predict symptomatology.

RESULTS

Carotid plaques (n = 93) from symptomatic patients (n = 61) had significantly higher plaque burden and LRNC compared with plaques from asymptomatic patients (n = 32). Lesions selected from the transcriptomic cohort (n = 40) with high LRNC, IPH, MATX, or plaque burden were characterised by molecular signatures coupled with inflammation and extracellular matrix degradation, typically linked with instability. In contrast, highly calcified plaques had a molecular signature signifying stability with enrichment of profibrotic pathways and repressed inflammation. In a cross validated prediction model for symptoms, plaque morphology by CTA alone was superior to the degree of stenosis.

CONCLUSION

The study demonstrates that CTA image analysis for evaluation of carotid plaque morphology, also reflects prevalent biological processes relevant for assessment of plaque phenotype. The results support the use of CTA image analysis of plaque morphology for risk stratification and management of patients with carotid stenosis.

Abstract P140: Molecular Signatures Of The Delayed Healing Response To Arterial Injury In Diabetic Rats

Aim: Atherosclerosis is a major complication of diabetes mellitus and a leading cause of mortality in diabetic patients. Vascular interventions in diabetic patients can lead to complications attributed to defective vascular remodeling and impaired healing response. In this study, we aim to elucidate the physiological and molecular differences in the vascular healing response over time using a rat model of arterial injury applied in healthy and diabetic conditions.

Methods: Wistar (healthy) and Goto-Kakizaki (GK, diabetic) rats (n = 40 per strain) were subjected to left common carotid artery (CCA) balloon injury and euthanized at different timepoints: 0 and 24 hours, 5 days, 2, 4 and 6 weeks. Non-invasive morphological and physiological assessment, and microarray profiling of the CCA was performed for each timepoint. Bioinformatic analyses were conducted using R software, DAVID bioinformatic tool, online STRING database and Cytoscape software.

Results: Significant increase in the neointimal thickness (p<0.01; 2-way ANOVA) was observed after 2 weeks of injury in diabetic compared to heathy rats, which was confirmed by histological analyses. Moreover, a decrease in the reendothelialization rate was also detected in the diabetic rats at 4 and 6 weeks after injury. Bioinformatic analyses showed that expression of early response genes related to inflammation and proliferation were delayed in diabetic rats, coupled with the dysregulation of key pathways related to vascular healing. Defective expression patterns were observed for endothelial, macrophage and lymphocyte markers indicating potential faults on cell regulation level. TF-PPI analysis provided mechanistic evidence wherein an array of transcription factors was dysregulated in diabetic rats specifically from 2 weeks after injury.

Conclusions: In this study, we investigated the effect of diabetes on vessel wall healing. We demonstrate that diabetic rats exhibit impaired arterial remodelling characterised by a delayed healing response. These results further corroborate the higher prevalence of restenosis in diabetic patients and provide vital molecular insights into the mechanisms contributing to the impaired arterial healing response in diabetes.

Proteoglycan 4 Modulates Osteogenic Smooth Muscle Cell Differentiation during Vascular Remodeling and Intimal Calcification

Calcification is a prominent feature of late-stage atherosclerosis, but the mechanisms driving this process are unclear. Using a biobank of carotid endarterectomies, we recently showed that Proteoglycan 4 (PRG4) is a key molecular signature of calcified plaques, expressed in smooth muscle cell (SMC) rich regions. Here, we aimed to unravel the PRG4 role in vascular remodeling and intimal calcification. PRG4 expression in human carotid endarterectomies correlated with calcification assessed by preoperative computed tomographies. PRG4 localized to SMCs in early intimal thickening, while in advanced lesions it was found in the extracellular matrix, surrounding macro-calcifications. In experimental models, Prg4 was upregulated in SMCs from partially ligated ApoE-/- mice and rat carotid intimal hyperplasia, correlating with osteogenic markers and TGFb1. Furthermore, PRG4 was enriched in cells positive for chondrogenic marker SOX9 and around plaque calcifications in ApoE-/- mice on warfarin. In vitro, PRG4 was induced in SMCs by IFNg, TGFb1 and calcifying medium, while SMC markers were repressed under calcifying conditions. Silencing experiments showed that PRG4 expression was driven by transcription factors SMAD3 and SOX9. Functionally, the addition of recombinant human PRG4 increased ectopic SMC calcification, while arresting cell migration and proliferation. Mechanistically, it suppressed endogenous PRG4, SMAD3 and SOX9, and restored SMC markers' expression. PRG4 modulates SMC function and osteogenic phenotype during intimal remodeling and macro-calcification in response to TGFb1 signaling, SMAD3 and SOX9 activation. The effects of PRG4 on SMC phenotype and calcification suggest its role in atherosclerotic plaque stability, warranting further investigations.

Virtual Transcriptomics: Noninvasive Phenotyping of Atherosclerosis by Decoding Plaque Biology From Computed Tomography Angiography Imaging

[Figure: see text].

AMPA-Type Glutamate Receptors Associated With Vascular Smooth Muscle Cell Subpopulations in Atherosclerosis and Vascular Injury

Objectives and Aims: Vascular smooth muscle cells (VSMCs) are key constituents of both normal arteries and atherosclerotic plaques. They have an ability to adapt to changes in the local environment by undergoing phenotypic modulation. An improved understanding of the mechanisms that regulate VSMC phenotypic changes may provide insights that suggest new therapeutic targets in treatment of cardiovascular disease (CVD). The amino-acid glutamate has been associated with CVD risk and VSMCs metabolism in experimental models, and glutamate receptors regulate VSMC biology and promote pulmonary vascular remodeling. However, glutamate-signaling in human atherosclerosis has not been explored. Methods and Results: We identified glutamate receptors and glutamate metabolism-related enzymes in VSMCs from human atherosclerotic lesions, as determined by single cell RNA sequencing and microarray analysis. Expression of the receptor subunits glutamate receptor, ionotropic, α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic (AMPA)-type subunit 1 (GRIA1) and 2 (GRIA2) was restricted to cells of mesenchymal origin, primarily VSMCs, as confirmed by immunostaining. In a rat model of arterial injury and repair, changes of GRIA1 and GRIA2 mRNA level were most pronounced at time points associated with VSMC proliferation, migration, and phenotypic modulation. In vitro, human carotid artery SMCs expressed GRIA1, and selective AMPA-type receptor blocking inhibited expression of typical contractile markers and promoted pathways associated with VSMC phenotypic modulation. In our biobank of human carotid endarterectomies, low expression of AMPA-type receptor subunits was associated with higher content of inflammatory cells and a higher frequency of adverse clinical events such as stroke. Conclusion: AMPA-type glutamate receptors are expressed in VSMCs and are associated with phenotypic modulation. Patients suffering from adverse clinical events showed significantly lower mRNA level of GRIA1 and GRIA2 in their atherosclerotic lesions compared to asymptomatic patients. These results warrant further mapping of neurotransmitter signaling in the pathogenesis of human atherosclerosis.

A neutralizing antibody against DKK1 does not reduce plaque formation in classical murine models of atherosclerosis: Is the therapeutic potential lost in translation?

BACKGROUND AND AIMS

Clinical interventions targeting nonlipid risk factors are needed given the high residual risk of atherothrombotic events despite effective control of dyslipidemia. Dickkopf-1 (DKK1) plays a lipid-independent role in vascular pathophysiology but its involvement in atherosclerosis development and its therapeutic attractiveness remain to be established.

METHODS

Patient data, in vitro studies and pharmacological intervention in murine models of atherosclerosis were utilized.

RESULTS

In patients' material (n = 127 late stage plaque specimens and n = 10 control vessels), DKK1 mRNA was found to be higher in atherosclerotic plaques versus control arteries. DKK1 protein was detected in the luminal intimal area and in the necrotic core of plaques. DKK1 was released from isolated primary human platelets (~12 - 21-fold) and endothelial cells (~1.4-2.5-fold) upon stimulation with different pathophysiological stimuli. In ApoE^-/- and Ldlr^-/- mice, plasma DKK1 concentrations were similar to those observed in humans, whereas DKK1 expression in different atheroprone arterial segments was very low/absent. Chronic treatment with a neutralizing DKK1 antibody effectively reduced plasma concentrations, however, plaque lesion area was not reduced in ApoE^-/- and Ldlr^-/- mice fed a western diet for 14 and 16 weeks. Anti-DKK1 treatment increased bone volume and bone mineral content.

CONCLUSIONS

Functional inhibition of DKK1 with an antibody does not alter atherosclerosis progression in classical murine models. This may reflect the absence of DKK1 expression in plaques and more advanced animal disease models could be needed to evaluate the role and therapeutic attractiveness of DKK1 in late stage complications such as plaque destabilization, calcification, rupture and thrombosis.

Lack of PCSK6 Increases Flow-Mediated Outward Arterial Remodeling in Mice

Proprotein convertases (PCSKs) process matrix metalloproteases and cytokines, but their function in the vasculature is largely unknown. Previously, we demonstrated upregulation of PCSK6 in atherosclerotic plaques from symptomatic patients, localization to smooth muscle cells (SMCs) in the fibrous cap and positive correlations with inflammation, extracellular matrix remodeling and cytokines. Here, we hypothesize that PCSK6 could be involved in flow-mediated vascular remodeling and aim to evaluate its role in the physiology of this process using knockout mice. Pcsk6^−/− and wild type mice were randomized into control and increased blood flow groups and induced in the right common carotid artery (CCA) by ligation of the left CCA. The animals underwent repeated ultrasound biomicroscopy (UBM) examinations followed by euthanization with subsequent evaluation using wire myography, transmission electron microscopy or histology. The Pcsk6^−/− mice displayed a flow-mediated increase in lumen circumference over time, assessed with UBM. Wire myography revealed differences in the flow-mediated remodeling response detected as an increase in lumen circumference at optimal stretch with concomitant reduction in active tension. Furthermore, a flow-mediated reduction in expression of SMC contractile markers SMA, MYH11 and LMOD1 was seen in the Pcsk6^−/− media. Absence of PCSK6 increases outward remodeling and reduces medial contractility in response to increased blood flow.

Transcriptomic profiling of experimental arterial injury reveals new mechanisms and temporal dynamics in vascular healing response

Objective

Endovascular interventions cause arterial injury and induce a healing response to restore vessel wall homeostasis. Complications of defective or excessive healing are common and result in increased morbidity and repeated interventions. Experimental models of intimal hyperplasia are vital for understanding the vascular healing mechanisms and resolving the clinical problems of restenosis, vein graft stenosis, and dialysis access failure. Our aim was to systematically investigate the transcriptional, histologic, and systemic reaction to vascular injury during a prolonged time.

Methods

Balloon injury of the left common carotid artery was performed in male rats. Animals (n = 69) were euthanized before or after injury, either directly or after 2 hours, 20 hours, 2 days, 5 days, 2 weeks, 6 weeks, and 12 weeks. Both injured and contralateral arteries were subjected to microarray profiling, followed by bioinformatic exploration, histologic characterization of the biopsy specimens, and plasma lipid analyses.

Results

Immune activation and coagulation were key mechanisms in the early response, followed by cytokine release, tissue remodeling, and smooth muscle cell modulation several days after injury, with reacquisition of contractile features in later phases. Novel pathways related to clonal expansion, inflammatory transformation, and chondro-osteogenic differentiation were identified and immunolocalized to neointimal smooth muscle cells. Analysis of uninjured arteries revealed a systemic component of the reaction after local injury, underlined by altered endothelial signaling, changes in overall tissue bioenergy metabolism, and plasma high-density lipoprotein levels.

Conclusions

We demonstrate that vascular injury induces dynamic transcriptional landscape and metabolic changes identifiable as early, intermediate, and late response phases, reaching homeostasis after several weeks. This study provides a temporal “roadmap” of vascular healing as a publicly available resource for the research community.

Endovascular intervention causes an injury to the arterial wall that subsequently induces a healing response to restore the vessel wall homeostasis. Complications after vascular interventions related to defective or excessive healing response, such as thrombosis or restenosis, are common and result in increased morbidity, suffering of the patient, need for repeated interventions, and possibly death. Thus, there is a need for better understanding of the underlying molecular mechanisms during vascular injury and healing response to identify and to assess the risk of complications in patients. Using an experimental model of vascular injury, this study demonstrates the full landscape of dynamic transcriptional changes in the resolution of vascular injury, accompanied also by systemic variations in plasma lipid levels and reaching homeostasis several weeks after injury. These results can guide the development of new strategies and molecular targets for modulation of the intimal response on endovascular interventions.

Dipeptidyl peptidase-4 is increased in the abdominal aortic aneurysm vessel wall and is associated with aneurysm disease processes

BACKGROUND

Abdominal aortic aneurysm (AAA) is a potentially life-threatening disease, and until today there is no other treatment available than surgical intervention. Dipeptidyl peptidase-4 (DPP4)-inhibitors, used clinically to treat type 2 diabetes, have in murine models been shown to attenuate aneurysm formation and decrease aortic wall matrix degradation, inflammation and apoptosis. Our aim was to investigate if DPP4 is present, active and differentially expressed in human AAA.

METHODS AND RESULTS

DPP4 gene expression was elevated in both media and adventitia of AAA tissue compared with control tissue, as measured by microarrays and qPCR, with consistent findings in external data. The plasma activity of DPP4 was however lower in male patients with AAA compared with age- and gender-matched controls, independently of comorbidity or medication. Immunohistochemical double staining revealed co-localization of DPP4 with cells positive for CD68, CD4 and -8, CD20, and SMA. Gene set enrichment analysis demonstrated that expression of DPP4 in AAA tissue correlated with expression of biological processes related to B- and T-cells, extracellular matrix turnover, peptidase activity, oxidative stress and angiogenesis whereas it correlated negatively with muscle-/actin-related processes.

CONCLUSION

DPP4 is upregulated in both media and adventitia of human AAA and correlates with aneurysm pathophysiological processes. These results support previous murine mechanistic studies and implicate DPP4 as a target in AAA disease.

PCSK6 Is a Key Protease in the Control of Smooth Muscle Cell Function in Vascular Remodeling

RATIONALE

PCSKs (Proprotein convertase subtilisins/kexins) are a protease family with unknown functions in vasculature. Previously, we demonstrated PCSK6 upregulation in human atherosclerotic plaques associated with smooth muscle cells (SMCs), inflammation, extracellular matrix remodeling, and mitogens.

OBJECTIVE

Here, we applied a systems biology approach to gain deeper insights into the PCSK6 role in normal and diseased vessel wall.

METHODS AND RESULTS

Genetic analyses revealed association of intronic PCSK6 variant rs1531817 with maximum internal carotid intima-media thickness progression in high-cardiovascular risk subjects. This variant was linked with PCSK6 mRNA expression in healthy aortas and plaques but also with overall plaque SMA+ cell content and pericyte fraction. Increased PCSK6 expression was found in several independent human cohorts comparing atherosclerotic lesions versus healthy arteries, using transcriptomic and proteomic datasets. By immunohistochemistry, PCSK6 was localized to fibrous cap SMA+ cells and neovessels in plaques. In human, rat, and mouse intimal hyperplasia, PCSK6 was expressed by proliferating SMA+ cells and upregulated after 5 days in rat carotid balloon injury model, with positive correlation to PDGFB (platelet-derived growth factor subunit B) and MMP (matrix metalloprotease) 2/MMP14. Here, PCSK6 was shown to colocalize and cointeract with MMP2/MMP14 by in situ proximity ligation assay. Microarrays of carotid arteries from Pcsk6^-/- versus control mice revealed suppression of contractile SMC markers, extracellular matrix remodeling enzymes, and cytokines/receptors. Pcsk6^-/- mice showed reduced intimal hyperplasia response upon carotid ligation in vivo, accompanied by decreased MMP14 activation and impaired SMC outgrowth from aortic rings ex vivo. PCSK6 silencing in human SMCs in vitro leads to downregulation of contractile markers and increase in MMP2 expression. Conversely, PCSK6 overexpression increased PDGFBB (platelet-derived growth factor BB)-induced cell proliferation and particularly migration.

CONCLUSIONS

PCSK6 is a novel protease that induces SMC migration in response to PDGFB, mechanistically via modulation of contractile markers and MMP14 activation. This study establishes PCSK6 as a key regulator of SMC function in vascular remodeling. Visual Overview: An online visual overview is available for this article.

Early Inhibition of P-Selectin/P-Selectin Glycoprotein Ligand-1 Reduces Intimal Hyperplasia in Murine Vein Grafts through Platelet Adhesion

Inflammatory processes contribute to intimal hyperplasia (IH) and long-term failure of vein grafts used in bypass surgery. Leukocyte recruitment on endothelial cells of vessels during inflammation is regulated by P-selectin and P-selectin glycoprotein ligand-1 (PSGL-1), which also mediates the interaction between platelets and endothelial cells in vein grafts transferred to arteries. However, how this pathway causes IH in vein grafts is unclear. In this study, we used a murine model of vein grafting to investigate P-selectin-mediated platelet adhesion, followed by IH. On the luminal surface of the vein graft, leukocyte recruitment occurred mainly in areas with adhered platelets rather than on endothelial cells without adherent platelets 1 hour after vein grafting. Blockage of either P-selectin or PSGL-1 reduced platelet adhesion and leukocyte recruitment on the luminal surface of vein grafts. Inhibition of the P-selectin pathway in vein grafts significantly reduced platelet-mediated leukocyte recruitment and IH of vein grafts 28 days after surgery. The study demonstrates that functional blockage of the P-selectin/PSGL-1 pathway in the early inflammatory phase after vein grafting reduced leukocyte invasion in the vein graft wall and later IH development. The findings imply an attractive early time window for prevention of vein graft failure by manipulating platelet adhesion.

Noninvasive in vivo Assessment of the Re-endothelialization Process Using Ultrasound Biomicroscopy in the Rat Carotid Artery Balloon Injury Model

OBJECTIVES

Ultrasound biomicroscopy (UBM), or ultra high-frequency ultrasound, is a technique used to assess the anatomy of small research animals. In this study, UBM was used to assess differences in intimal hyperplasia thickness as a surrogate measurement of the re-endothelialization process after carotid artery balloon injury in rats.

METHODS

Ultrasound biomicroscopic data from 3 different experiments and rat strains (Sprague Dawley, Wistar, and diabetic Goto-Kakizaki) were analyzed. All animals were subjected to carotid artery balloon injury and examined with UBM (30-70 MHz) 2 and 4 weeks after injury. Re-endothelialization on UBM was defined as the length from the carotid bifurcation to the most distal visible edge of the intimal hyperplasia. En face staining with Evans blue dye was performed at euthanasia 4 weeks after injury, followed by tissue harvesting for histochemical and immunohistochemical evaluations.

RESULTS

A significant correlation (Spearman r = 0.63; P < .0001) was identified when comparing all measurements of re-endothelialization obtained from UBM and en face staining. The findings revealed a similar pattern for all rat strains: Sprague Dawley (Spearman r = 0.70; P < .0001), Wistar (Spearman r = 0.36; P < .081), and Goto-Kakizaki (Spearman r = 0.70; P < .05). A Bland-Altman test showed agreement between en face staining and UBM. Immunohistochemical staining confirmed the presence of the endothelium in the areas detected as re-endothelialized by the UBM assessment.

CONCLUSIONS

Ultrasound biomicroscopy can be used for repeated in vivo assessment of re-endothelialization after carotid artery balloon injury in rats.

Correlation of computed tomography with carotid plaque transcriptomes associates calcification with lesion-stabilization

BACKGROUND AND AIMS

Unstable carotid atherosclerosis causes stroke, but methods to identify patients and lesions at risk are lacking. We recently found enrichment of genes associated with calcification in carotid plaques from asymptomatic patients. Here, we hypothesized that calcification represents a stabilising feature of plaques and investigated how macro-calcification, as estimated by computed tomography (CT), correlates with gene expression profiles in lesions.

METHODS

Plaque calcification was measured in pre-operative CT angiographies. Plaques were sorted into high- and low-calcified, profiled with microarrays, followed by bioinformatic analyses. Immunohistochemistry and qPCR were performed to evaluate the findings in plaques and arteries with medial calcification from chronic kidney disease patients.

RESULTS

Smooth muscle cell (SMC) markers were upregulated in high-calcified plaques and calcified plaques from symptomatic patients, whereas macrophage markers were downregulated. The most enriched processes in high-calcified plaques were related to SMCs and extracellular matrix (ECM) organization, while inflammation, lipid transport and chemokine signaling were repressed. These findings were confirmed in arteries with high medial calcification. Proteoglycan 4 (PRG4) was identified as the most upregulated gene in association with plaque calcification and found in the ECM, SMA+ and CD68+/TRAP + cells.

CONCLUSIONS

Macro-calcification in carotid lesions correlated with a transcriptional profile typical for stable plaques, with altered SMC phenotype and ECM composition and repressed inflammation. PRG4, previously not described in atherosclerosis, was enriched in the calcified ECM and localized to activated macrophages and smooth muscle-like cells. This study strengthens the notion that assessment of calcification may aid evaluation of plaque phenotype and stroke risk.

Novel Multiomics Profiling of Human Carotid Atherosclerotic Plaques and Plasma Reveals Biliverdin Reductase B as a Marker of Intraplaque Hemorrhage

Clinical tools to identify individuals with unstable atherosclerotic lesions are required to improve prevention of myocardial infarction and ischemic stroke. Here, a systems-based analysis of atherosclerotic plaques and plasma from patients undergoing carotid endarterectomy for stroke prevention was used to identify molecular signatures with a causal relationship to disease. Local plasma collected in the lesion proximity following clamping prior to arteriotomy was profiled together with matched peripheral plasma. This translational workflow identified biliverdin reductase B as a novel marker of intraplaque hemorrhage and unstable carotid atherosclerosis, which should be investigated as a potential predictive biomarker for cardiovascular events in larger cohorts.

Integrated Human Evaluation of the Lysophosphatidic Acid Pathway as a Novel Therapeutic Target in Atherosclerosis

Variants in the PLPP3 gene encoding for lipid phosphate phosphohydrolase 3 have been associated with susceptibility to atherosclerosis independently of classical risk factors. PLPP3 inactivates lysophosphatidic acid (LPA), a pro-inflammatory, pro-thrombotic product of phospholipase activity. Here we performed the first exploratory analysis of PLPP3, LPA, and LPA receptors (LPARs 1–6) in human atherosclerosis. PLPP3 transcript and protein were repressed when comparing plaques versus normal arteries and plaques from symptomatic versus asymptomatic patients, and they were negatively associated with risk of adverse cardiovascular events. PLPP3 localized to macrophages, smooth muscle, and endothelial cells (ECs) in plaques. LPAR 2, 5, and especially 6 showed increased expression in plaques, with LPAR6 localized in ECs and positively correlated to PLPP3. Utilizing in situ mass spectrometry imaging, LPA and its precursors were found in the plaque fibrous cap, co-localizing with PLPP3 and LPAR6. In vitro, PLPP3 silencing in ECs under LPA stimulation resulted in increased expression of adhesion molecules and cytokines. LPAR6 silencing inhibited LPA-induced cell activation, but not when PLPP3 was silenced simultaneously. Our results show that repression of PLPP3 plays a key role in atherosclerosis by promoting EC activation. Altogether, the PLPP3 pathway represents a suitable target for investigations into novel therapeutic approaches to ameliorate atherosclerosis.

Abstract 627: Combined Plaque Evaluation by Ultrasound and Microarrays Reveals Bclaf1 as a Novel Regulator of Smooth Muscle Cell Transdifferentiation in Atherosclerosis

Objective: Understanding molecular processes behind carotid plaque instability is necessary to develop methods that can identify patients and lesions at risk of stroke. Here, we investigated molecular signatures in human plaques stratified by echogenicity as assessed by duplex ultrasound (US).

Results: Plaque echogenicity measured by US was correlated to microarray profiles from lesions retrieved at surgery (n=96). Pathway analyses highlighted enrichment of cell apoptosis and proliferation, and BCLAF1 (BCL2 associated factor 1) as the most significantly dysregulated gene (adjusted p<0.0001). BCLAF1 was strongly downregulated in plaques vs. control tissues, positively correlated to markers of cell proliferation and negatively to apoptosis, at both transcriptomic and proteomic level. Immunohistochemistry showed that BCLAF1 was localized in smooth muscle cells (SMCs) nuclei and repressed early during atherogenesis, but reappeared in CD68+ cells in advanced plaques. Proximity ligation assay demonstrated interaction of BCLAF1 with previously reported interaction partners THRAP3 and BCL2, in normal arteries and plaques. In vitro , stimulation of SMCs with pro-survival factors EGF, bFGF, PDGFB resulted in induction of BCLAF1, while it was suppressed by macrophage-conditioned medium. Moreover, BCLAF1 silencing in SMCs led to downregulation of BCL2 and SMC markers, and a decrease in proliferation and adhesion (p<0.0001). Transdifferentiation of SMCs using oxLDL, confirmed by CD68 upregulation and MYH11 repression, was accompanied by upregulation of BCLAF1. However, a combination of oxLDL exposure and BCLAF1 silencing, resulted in preserved expression of MYH11 and prevented transdifferentiation. Finally, BCLAF1 expression in CD68+/BCL2+ cells of SMC origin, was verified in plaques from MYH11-lineage tracing atherosclerotic mice.

Conclusions: Carotid plaque echogenicity correlated with enrichment of molecular pathways associated with cell survival and apoptosis and identified BCLAF1, previously not described in atherosclerosis, as the most dysregulated gene. Functionally, BCLAF1 appeared to promote SMC survival by transdifferentiation into macrophage-like phenotype, by interacting with BCL2 and THRAP3.

Neutrophil Elastase-Derived Fibrin Degradation Products Indicate Presence of Abdominal Aortic Aneurysms and Correlate with Intraluminal Thrombus Volume

Background The intraluminal thrombi (ILT) of abdominal aortic aneurysms (AAA) contain neutrophils, which can secrete elastase. We evaluated whether plasma neutrophil elastase-derived cross-linked fibrin degradation products (E-XDP) could reveal the presence, size and mechanical stress of AAAs and its ILTs.

Methods E-XDP and D-dimer were measured in plasma from 37 male patients with AAA and 42 male controls. The ILT volumes of the AAAs and any coexisting aneurysms could be measured in 29 patients and finite element analysis was performed to estimate mechanical stress of the ILT. E-XDP, neutrophil elastase and neutrophil marker CD66acd were evaluated in aortic tissue with immunohistochemistry (IHC). The association between ILT volume and E-XDP was validated in a separate cohort (n = 51).

Results E-XDP levels were elevated in patients with AAA compared with controls (p = 5.8e-13), indicated AAA with 98% sensitivity, 86% specificity and increased with presence of coexisting aneurysms. The association between AAA and increased E-XDP was independent of smoking, comorbidities and medication. E-XDP correlated with volume of all ILTs (r = 0.76, p = 4.5e-06), mean ILT stress (r = 0.46, p = 0.013) and the volume of the AAA-associated ILT (r = 0.64, p = 0.00017). E-XDP correlated stronger with ILT volume compared with D-dimer (r = 0.76 vs. r = 0.64, p = 0.018). The correlation between E-XDP and ILT volume was validated in the separate cohort (r = 0.53, p = 7.6e-05). IHC revealed E-XDP expression in the ILT, spatially related to neutrophil elastase and neutrophils.

Conclusion E-XDP is a marker of the presence of AAA and coexisting aneurysms as well as the volume and mechanical stress of the ILT.

Platelet adhesion on endothelium early after vein grafting mediates leukocyte recruitment and intimal hyperplasia in a murine model

Intimal hyperplasia (IH) is the substrate for accelerated atherosclerosis and limited patency of vein grafts. However, there is still no specific treatment targeting IH following graft surgery. In this study, we used a mouse model of vein grafting to investigate the potential for early intervention with platelet function for later development of graft IH. We transferred the inferior vena cava (IVC) from donor C57BL/6 mice to the carotid artery in recipients using a cuff technique. We found extensive endothelial injury and platelet adhesion one hour following grafting. Adhesion of leukocytes was distinct in areas of platelet adhesion. Platelet and leukocyte adhesion was strongly reduced in mice receiving a function-blocking antibody against the integrin αIIbβ3. This was followed by a reduction of IH one month following grafting. Depletion of platelets using antiserum also reduced IH at later time points. These findings indicate platelets as pivotal to leukocyte recruitment to the wall of vein grafts. In conclusion, the data also highlight early intervention of platelets and inflammation as potential treatment for later formation of IH and accelerated atherosclerosis following bypass surgery.

Integrative studies implicate matrix metalloproteinase-12 as a culprit gene for large-artery atherosclerotic stroke

BACKGROUND

Ischaemic stroke and coronary heart disease are important contributors to the global disease burden and share atherosclerosis as the main underlying cause. Recent evidence from a genome-wide association study (GWAS) suggested that single nucleotide polymorphisms (SNP) near the MMP12 gene at chromosome 11q22.3 were associated with large-vessel ischaemic stroke. Here, we evaluated and extended these results by examining the relationship between MMP12 and atherosclerosis in clinical and experimental studies.

METHODS AND RESULTS

Plasma concentrations of MMP12 were measured at baseline in 3394 subjects with high-risk for cardiovascular disease (CVD) using the Olink ProSeek CVD I array. The plasma MMP12 concentration showed association with incident cardiovascular and cerebrovascular events (130 and 67 events, respectively, over 36 months) and carotid intima-media thickness progression (P = 3.6 × 10^-5 ). A GWAS of plasma MMP12 concentrations revealed that SNPs rs499459, rs613084 and rs1892971 at chr11q22.3 were independently associated with plasma MMP12 (P < 5 × 10^-8 ). The lead SNPs showed associations with mRNA levels of MMP12 and adjacent MMPs in atherosclerotic plaques. MMP12 transcriptomic and proteomic levels were strongly significantly increased in carotid plaques compared with control arterial tissue and in plaques from symptomatic versus asymptomatic patients. By combining immunohistochemistry and proximity ligation assay, we demonstrated that MMP12 localizes to CD68 + macrophages and interacts with elastin in plaques. MMP12 silencing in human THP-1-derived macrophages resulted in reduced macrophage migration.

CONCLUSIONS

Our study supports the notion that MMP12 is implicated in large-artery atherosclerotic stroke, functionally by enhancing elastin degradation and macrophage invasion in plaques.

Vessel wall morphology is equivalent for different artery types and localizations of advanced human aneurysms

Aneurysm formation occurs most frequently as abdominal aortic aneurysm (AAA), but is also seen in other localizations like thoracic or peripheral aneurysm. While initial mechanisms for aneurysm induction remain elusive, observations from AAA samples show transmural inflammation with proteolytic imbalance and repair mechanisms triggered by the innate immune system. However, limited knowledge exists about aneurysm pathology, especially for others than AAA. We compared 42 AAA, 15 popliteal, 3 ascending aortic, five iliac, two femoral, two brachial, one visceral and two secondary aneurysms to non-aneurysmatic controls by histologic analysis, immunohistochemistry and cytokine expression. Muscular and elastic type arteries show a uniform way of aneurysm formation. All samples show similar morphology. The changes compared to controls are distinct and include matrix remodeling with smooth muscle cell phenotype switch and angiogenesis, adventitial lymphoid cell accumulation and M1 macrophage homing together with neutrophil inflammation. Inflammatory cytokines are up-regulated accordingly. Comparative analysis of different disease entities can identify characteristic pathomechanisms. The phenotype of human advanced aneurysm disease is observed for elastic and muscular type arteries, does not differ between disease localizations and might, thus, be a unique response of the vasculature to the still unknown trigger of aneurysm formation.

Abstract 245: Non-Invasive in vivo Assessment of the Re-Endothelialization Process Using Ultrasound Biomicroscopy in the Rat Carotid Artery Balloon Injury Model

Objective: Ultrasound BioMicroscopy (UBM), or high-frequency ultrasound, is a novel technique used for assessment of anatomy and physiology small research animals. In this study, we evaluate the UBM assessment of the re-endothelialization process following denudation of the carotid artery in rats.

Methods: Ultrasound BioMicroscopy data from three different experiments were analyzed. A total of 66 rats of three different strains (Sprague-Dawley, Wistar and Goto-Kakizaki) were included in this study. All animals were subjected to common carotid artery balloon injury and examined with UBM 2 and 4 weeks after injury. Re-endothelialization in UBM was measured as the length from the carotid bifurcation to the distal edge of the intimal hyperplasia. En face staining with Evans-blue dye was performed upon euthanization at 4 weeks after injury followed by tissue harvest for morphological and immunohistochemical evaluation.

Results: A significant correlation (Spearman r=0.63,p<0.0001) and an agreement according to Bland-Altman test was identified when comparing all measurements of re-endothelialization in high frequency ultrasound and en face staining. Analysis by animal strain revealed a similar pattern and a significant growth in re-endothelialization length measured in UBM from 2 to 4 weeks could be identified. Immunohistochemical staining for von Willebrand factor confirmed the presence of endothelium in the areas detected as re-endothelialized by the ultrasound assessment.

Conclusion: Ultrasound BioMicroscopy can be used for longitudinal in vivo assessment of the re-endothelialization following arterial injury in rats.

Extracellular matrix proteomics identifies molecular signature of symptomatic carotid plaques

BACKGROUND. The identification of patients with high-risk atherosclerotic plaques prior to the manifestation of clinical events remains challenging. Recent findings question histology- and imaging-based definitions of the “vulnerable plaque,” necessitating an improved approach for predicting onset of symptoms.

METHODS. We performed a proteomics comparison of the vascular extracellular matrix and associated molecules in human carotid endarterectomy specimens from 6 symptomatic versus 6 asymptomatic patients to identify a protein signature for high-risk atherosclerotic plaques. Proteomics data were integrated with gene expression profiling of 121 carotid endarterectomies and an analysis of protein secretion by lipid-loaded human vascular smooth muscle cells. Finally, epidemiological validation of candidate biomarkers was performed in two community-based studies.

RESULTS. Proteomics and at least one of the other two approaches identified a molecular signature of plaques from symptomatic patients that comprised matrix metalloproteinase 9, chitinase 3-like-1, S100 calcium binding protein A8 (S100A8), S100A9, cathepsin B, fibronectin, and galectin-3-binding protein. Biomarker candidates measured in 685 subjects in the Bruneck study were associated with progression to advanced atherosclerosis and incidence of cardiovascular disease over a 10-year follow-up period. A 4-biomarker signature (matrix metalloproteinase 9, S100A8/S100A9, cathepsin D, and galectin-3-binding protein) improved risk prediction and was successfully replicated in an independent cohort, the SAPHIR study.

CONCLUSION. The identified 4-biomarker signature may improve risk prediction and diagnostics for the management of cardiovascular disease. Further, our study highlights the strength of tissue-based proteomics for biomarker discovery.

FUNDING. UK: British Heart Foundation (BHF); King’s BHF Center; and the National Institute for Health Research Biomedical Research Center based at Guy’s and St Thomas’ NHS Foundation Trust and King’s College London in partnership with King’s College Hospital. Austria: Federal Ministry for Transport, Innovation and Technology (BMVIT); Federal Ministry of Science, Research and Economy (BMWFW); Wirtschaftsagentur Wien; and Standortagentur Tirol.

Differential expression of sex hormone receptors in abdominal aortic aneurysms

OBJECTIVE

Male sex is a significant risk factor for abdominal aortic aneurysm (AAA). Female sex hormones have been reported to prevent aneurysm formation in animal models. The study aims to describe the expression profile of sex hormone receptors in the aneurysm wall of men and women with AAA and compare with unaffected controls.

METHODS

Aneurysm wall biopsies were obtained during elective open repair of AAA in men and women (n=16+16). Aortic vessel wall from controls were obtained at organ donation (n=6). Western blot-, mRNA expression- and immunohistochemical analyses were performed to assess the expression profile of the sex hormone receptors - androgen receptor (AR), progesterone receptor (PR), estrogen receptor α (ERα) and β (ERβ).

RESULTS

The mRNA- and protein expression levels of AR were higher in AAA compared with control aorta (7.26 vs. 5.14, P=0.001). mRNA- and protein expression levels of ERβ were lower in AAA compared with control aorta (9.15 vs. 12.29, P<0.001). mRNA expression levels of PR were higher in AAA compared with control aorta (8.73 vs. 6.21, P=0.003), but could not be confirmed on protein level. The expression profile of sex hormone receptors in men and women with AAA was similar.

CONCLUSION

Expression of sex hormone receptors differs in the aneurysmal aorta compared with unaffected aorta in men and women. A higher expression of AR and a lower expression of ERβ suggest that sex hormone activity could be associated with aneurysm development.

Phenotypic Modulation of Smooth Muscle Cells in Atherosclerosis Is Associated With Downregulation of LMOD1, SYNPO2, PDLIM7, PLN, and SYNM

OBJECTIVE

Key augmented processes in atherosclerosis have been identified, whereas less is known about downregulated pathways. Here, we applied a systems biology approach to examine suppressed molecular signatures, with the hypothesis that they may provide insight into mechanisms contributing to plaque stability.

APPROACH AND RESULTS

Muscle contraction, muscle development, and actin cytoskeleton were the most downregulated pathways (false discovery rate=6.99e-21, 1.66e-6, 2.54e-10, respectively) in microarrays from human carotid plaques (n=177) versus healthy arteries (n=15). In addition to typical smooth muscle cell (SMC) markers, these pathways also encompassed cytoskeleton-related genes previously not associated with atherosclerosis. SYNPO2, SYNM, LMOD1, PDLIM7, and PLN expression positively correlated to typical SMC markers in plaques (Pearson r>0.6, P<0.0001) and in rat intimal hyperplasia (r>0.8, P<0.0001). By immunohistochemistry, the proteins were expressed in SMCs in normal vessels, but largely absent in human plaques and intimal hyperplasia. Subcellularly, most proteins localized to the cytoskeleton in cultured SMCs and were regulated by active enhancer histone modification H3K27ac by chromatin immunoprecipitation-sequencing. Functionally, the genes were downregulated by PDGFB (platelet-derived growth factor beta) and IFNg (interferron gamma), exposure to shear flow stress, and oxLDL (oxidized low-density lipoprotein) loading. Genetic variants in PDLIM7, PLN, and SYNPO2 loci associated with progression of carotid intima-media thickness in high-risk subjects without symptoms of cardiovascular disease (n=3378). By eQTL (expression quantitative trait locus), rs11746443 also associated with PDLIM7 expression in plaques. Mechanistically, silencing of PDLIM7 in vitro led to downregulation of SMC markers and disruption of the actin cytoskeleton, decreased cell spreading, and increased proliferation.

CONCLUSIONS

We identified a panel of genes that reflect the altered phenotype of SMCs in vascular disease and could be early sensitive markers of SMC dedifferentiation.

NLRP3 Inflammasome Expression and Activation in Human Atherosclerosis

Background

The NLR family, pyrin domain containing 3 (NLRP3) inflammasome is an interleukin (IL)‐1β and IL‐18 cytokine processing complex that is activated in inflammatory conditions. The role of the NLRP3 inflammasome in the pathogenesis of atherosclerosis and myocardial infarction is not fully understood.

Methods and Results

Atherosclerotic plaques were analyzed for transcripts of the NLRP3 inflammasome, and for IL‐1β release. The Swedish First‐ever myocardial Infarction study in Ac‐county (FIA) cohort consisting of DNA from 555 myocardial infarction patients and 1016 healthy individuals was used to determine the frequency of 4 single nucleotide polymorphisms (SNPs) from the downstream regulatory region of NLRP3. Expression of NLRP3, Apoptosis‐associated speck‐like protein containing a CARD (ASC), caspase‐1 (CASP1), IL1B, and IL18 mRNA was significantly increased in atherosclerotic plaques compared to normal arteries. The expression of NLRP3 mRNA was significantly higher in plaques of symptomatic patients when compared to asymptomatic ones. CD68‐positive macrophages were observed in the same areas of atherosclerotic lesions as NLRP3 and ASC expression. Occasionally, expression of NLRP3 and ASC was also present in smooth muscle cells. Cholesterol crystals and ATP induced IL‐1β release from lipopolysaccharide‐primed human atherosclerotic lesion plaques. The minor alleles of the variants rs4266924, rs6672995, and rs10733113 were associated with NLRP3 mRNA levels in peripheral blood mononuclear cells but not with the risk of myocardial infarction.

Conclusions

Our results indicate a possible role of the NLRP3 inflammasome and its genetic variants in the pathogenesis of atherosclerosis.

Abstract 318: Matrix Metalloproteinase 12 is Causally Implicated in Cardiovascular Disease

Recent evidence suggests that single nucleotide polymorphisms (SNPs) in the matrix metalloproteinase (MMP) gene cluster located at chromosome 11q22.3 are associated with large-vessel stroke. In the present study, we evaluated and extended the reported association by examining the relationship between MMPs and vascular disease in both clinical and experimental samples. Plasma concentrations of MMP-1, MMP-3, MMP-7, MMP-10 and MMP-12 were measured in 3 394 subjects with high-risk for cardiovascular disease (CVD) using the Olink ProSeek CVD array. Plasma MMP-12 concentration showed association with incident cardiovascular events (199 events over 36 months) and intima-media thickness progression over time (p=3.6x10 -5 ). The SNP variant rs1892971 was strongly associated with plasma MMP-12 concentration (p=8x10 -29 ) and weakly with susceptibility to coronary heart disease in the CardiogramplusC4D consortium study (p=8.8x10 -5 ). The same SNP was also significantly associated with MMP-12 gene expression in peripheral blood mononuclear cells using microarrays from patients with carotid atherosclerosis (n=96; p=1.8x10 -4 ). Expression of MMP-12 was strongly increased in carotid plaques (n=127) compared with undiseased arteries (n=10; p<0.0001) and in plaques from symptomatic (n=87) compared to asymptomatic patients (n=40; p=0.03) and localised to CD68+ macrophages. Using proximity ligation assay MMP-12 and elastin was demonstrated to co-interact in plaques in situ, particularly in regions with moderate to strong MMP-12 expression. Silencing of MMP-12 using siRNA in differentiated THP-1 cells indicated that MMP-12 has a role in macrophage migration. In conclusion, our study suggests that MMP-12 is a causal factor in CVD that is highly upregulated in human atherosclerotic plaques where it interacts with elastin and appears to enhance macrophage invasion.

Abstract 173: Proprotein Convertase Subtilisin/Kexin Type 6 is a Key Protease in the Control of Smooth Muscle Cell Function in Vascular Disease

Proprotein convertases (PCSKs) process matrix metalloproteases (MMPs) and cytokines. Apart from PCSK9, the role of these enzymes in vascular disease is largely unknown. Previously, we demonstrated upregulation of PCSK6 in carotid atherosclerosis, primarily localized to smooth muscle cells (SMCs) and positively correlated to inflammation, extracellular matrix remodeling and cytokines. Here, we extended these findings to determine the role of PCSK6 in vascular development and disease. Increased expression of PCSK6 in vascular disease was validated by microarrays from two non-overlapping cohorts of carotid plaques vs. non-atherosclerotic arteries (n=50 patients and n=32 patients, p<0.0001), as well as abdominal (AAA, n=14, p<0.0001) and thoracic aortic aneurysms (TAA, n=244, p=0.012). By eQTL, variants in the PCSK6 gene were found to influence it’s expression in both plaques and aneurysms. Among these, rs6598465 also showed association with maximum progression of carotid intima-media thickness in high-risk coronary artery disease subjects (n=3388, p=0.037). By IHC, PCSK6 localized mainly to SMCs in the fibrous cap and neovessels in atherosclerotic, AAA and TAA tissues. In mouse-, rat-, and human intimal hyperplasia, PCSK6 was expressed in proliferating SMCs. By microarrays, after rat carotid balloon injury there was an early downregulation of PCSK6 followed by an upregulation in later phases during SMC activation, as well as positive correlation to PDGFB and IGF1 (Spearman r>0.7, p<0.0001) and to MMP2 and MMP14 (r>0.5, p<0.0001). In zebrafish embryos, PCSK6 localized to heart and vasculature and its ablation caused defective peripheral vascular patterning with cerebral and myocardial hemorrhage. PCSK6 -/- mice did not present an obvious vascular phenotype but showed reduced intimal hyperplasia compared to wild-type mice after carotid artery ligation (p=0.015). In vitro, PCSK6 overexpression markedly increased SMC migration upon PDGFBB stimulation (p<0.0001). The present study establishes PCSK6 as a key modulator of SMC function in vascular disease and demonstrates a functional link between PCSK6 expression and SMC migration in vascular remodeling.