Athsq1 is an atherosclerosis modifier locus with dramatic effects on lesion area and prominent accumulation of versican

Loss of ADAMTS5 promotes vascular calcification via versican/integrin β1/FAK signal

INTRODUCTION

Extracellular matrix (ECM) proteases have been closely linked to the pathogenesis of vascular calcification. A disintegrin and metalloprotease with thrombospondin motifs-5 (ADAMTS5) is an ECM-degrading enzyme involved in ECM remodeling. Versican, a critical ECM component in the arteries, can be proteolytically cleaved by ADAMTS5 and activates integrin β1. However, whether ADAMTS5 is involved in the regulation of the pathogenesis of vascular calcification remains unclear. This study investigates the regulatory role of ADAMTS5 in vascular calcification and its mechanistic link to versican-integrin β1/FAK signaling.

METHODS AND RESULTS

Western blot, immunofluorescence, and immunohistochemistry analysis revealed that ADAMTS5 expression was significantly downregulated in rat and human vascular smooth muscle cells (VSMCs), as well as in rat and human arteries during vascular calcification. In addition, both pharmacological inhibition of ADAMTS5 and knockdown of ADAMTS5 by siRNA significantly aggravated mineral deposition in rat and human VSMCs under osteogenic conditions. Moreover, adenovirus-mediated ADAMTS5 overexpression markedly attenuated calcification of VSMCs and aortic calcification in rats with chronic kidney disease. Furthermore, inhibition of ADAMTS5 promoted aortic calcification in VitD3-overloaded mice. Mechanistically, overexpression of ADAMTS5 significantly reduced versican protein levels, and inhibited integrin β1 and FAK phosphorylation in rat VSMCs, but increased versikine protein levels. Moreover, either knockdown of versican or pharmacological inhibition of FAK phosphorylation repressed VSMC calcification mediated by loss of ADAMTS5.

CONCLUSIONS

We have demonstrated for the first time that ADAMTS5 deficiency promotes versican accumulation and activates integrin β1/FAK signaling. These findings suggest ADAMTS5 as a potential therapeutic target for vascular calcification.

Comparison Study on the Effect of Mesenchymal Stem Cells-Conditioned Medium Derived from Adipose and Wharton’s Jelly on Versican Gene Expression in Hypoxia

Background:

Mesenchymal stem cells enhance tissue repair through paracrine effects following transplantation. The versican protein is one of the important factors contributing to this repair mechanism. Using MSC conditioned medium for cultivating monocytes may increase versican protein production and could be a good alternative for transplantation of MSCs. This study investigates the effect of culture medium conditioned by human MSCs on the expression of the versican gene in PBMCs under hypoxia-mimetic and normoxic conditions.

Methods:

The conditioned media used were derived from either adipose tissue or from WJ. Flow cytometry for surface markers (CD105, CD73, and CD90) was used to confirm MSCs. The PBMCs were isolated and cultured with the culture media of the MSC derived from either the adipose tissue or WJ. Desferrioxamine and cobalt chloride (200 and 300 µM final concentrations, respectively) were added to monocytes media to induce hypoxia-mimetic conditions. Western blotting was applied to detect HIF-1α protein and confirm hypoxia-mimetic conditions in PBMC. Versican gene expression was assessed in PBMC using RT-PCR. Western blotting showed that the expression of HIF-1α in PBMC increased significantly (p < 0.01).

Results:

RT-PCR results demonstrated that the expression of the versican and VEGF genes in PBMC increased significantly (p < 0.01) in hypoxia-mimetic conditions as compared to normoxia.

Conclusion:

Based on the findings in the present study, the secreted factors of MSCs can be replaced by direct use of MSCs to improve damaged tissues.

Extracellular Matrix in Vascular Disease, Part 2/4: JACC Focus Seminar

Medium-sized and large arteries consist of 3 layers: the tunica intima, tunica media, and tunica adventitia. The tunica media accounts for the bulk of the vessel wall and is the chief determinant of mechanical compliance. It is primarily composed of circumferentially arranged layers of vascular smooth muscle cells that are separated by concentrically arranged elastic lamellae; a form of extracellular matrix (ECM). The tunica media is separated from the tunica intima and tunica adventitia, the innermost and outermost layers, respectively, by the internal and external elastic laminae. This second part of a 4-part JACC Focus Seminar discusses the contributions of the ECM to vascular homeostasis and pathology. Advances in genetics and proteomics approaches have fostered significant progress in our understanding of vascular ECM. This review highlights the important role of the ECM in vascular disease and the prospect of translating these discoveries into clinical disease biomarkers and potential future therapies.

A role for proteoglycans in vascular disease

The content of proteoglycans (PGs) is low in the extracellular matrix (ECM) of vascular tissue, but increases dramatically in all phases of vascular disease. Early studies demonstrated that glycosaminoglycans (GAGs) including chondroitin sulfate (CS), dermatan sulfate (DS), keratan sulfate (KS) and heparan sulfate (HS) accumulate in vascular lesions in both humans and in animal models in areas of the vasculature that are susceptible to disease initiation (such as at branch points) and are frequently coincident with lipid deposits. Later studies showed the GAGs were covalently attached to specific types of core proteins that accumulate in vascular lesions. These molecules include versican (CSPG), biglycan and decorin (DS/CSPGs), lumican and fibromodulin (KSPGs) and perlecan (HSPG), although other types of PGs are present, but in lesser quantities. While the overall molecular design of these macromolecules is similar, there is tremendous structural diversity among the different PG families creating multiple forms that have selective roles in critical events that form the basis of vascular disease. PGs interact with a variety of different molecules involved in disease pathogenesis. For example, PGs bind and trap serum components that accumulate in vascular lesions such as lipoproteins, amyloid, calcium, and clotting factors. PGs interact with other ECM components and regulate, in part, ECM assembly and turnover. PGs interact with cells within the lesion and alter the phenotypes of both resident cells and cells that invade the lesion from the circulation. A number of therapeutic strategies have been developed to target specific PGs involved in key pathways that promote vascular disease. This review will provide a historical perspective of this field of research and then highlight some of the evidence that defines the involvement of PGs and their roles in the pathogenesis of vascular disease.

Analysis of the 9p21.3 sequence associated with coronary artery disease reveals a tendency for duplication in a CAD patient

Tandem segmental duplications (SDs) greater than 10 kb are widespread in complex genomes. They provide material for gene divergence and evolutionary adaptation, while formation of specific de novo SDs is a hallmark of cancer and some human diseases. Most SDs map to distinct genomic regions termed ‘duplication blocks’. SDs organization within these blocks is often poorly characterized as they are mosaics of ancestral duplicons juxtaposed with younger duplicons arising from more recent duplication events. Structural and functional analysis of SDs is further hampered as long repetitive DNA structures are underrepresented in existing BAC and YAC libraries. We applied Transformation-Associated Recombination (TAR) cloning, a versatile technique for large DNA manipulation, to selectively isolate the coronary artery disease (CAD) interval sequence within the 9p21.3 chromosome locus from a patient with coronary artery disease and normal individuals. Four tandem head-to-tail duplicons, each ∼50 kb long, were recovered in the patient but not in normal individuals. Sequence analysis revealed that the repeats varied by 10-15 SNPs between each other and by 82 SNPs between the human genome sequence (version hg19). SNPs polymorphism within the junctions between repeats allowed two junction types to be distinguished, Type 1 and Type 2, which were found at a 2:1 ratio. The junction sequences contained an Alu element, a sequence previously shown to play a role in duplication. Knowledge of structural variation in the CAD interval from more patients could help link this locus to cardiovascular diseases susceptibility, and maybe relevant to other cases of regional amplification, including cancer.

The central role of arterial retention of cholesterol-rich apolipoprotein-B-containing lipoproteins in the pathogenesis of atherosclerosis: a triumph of simplicity

PURPOSE OF REVIEW

Today, it is no longer a hypothesis, but an established fact, that increased plasma concentrations of cholesterol-rich apolipoprotein-B (apoB)-containing lipoproteins are causatively linked to atherosclerotic cardiovascular disease (ASCVD) and that lowering plasma LDL concentrations reduces cardiovascular events in humans. Here, we review evidence behind this assertion, with an emphasis on recent studies supporting the 'response-to-retention' model - namely, that the key initiating event in atherogenesis is the retention, or trapping, of cholesterol-rich apoB-containing lipoproteins within the arterial wall.

RECENT FINDINGS

New clinical trials have shown that ezetimibe and anti-PCSK9 antibodies - both nonstatins - lower ASCVD events, and they do so to the same extent as would be expected from comparable plasma LDL lowering by a statin. These studies demonstrate beyond any doubt the causal role of apoB-containing lipoproteins in atherogenesis. In addition, recent laboratory experimentation and human Mendelian randomization studies have revealed novel information about the critical role of apoB-containing lipoproteins in atherogenesis. New information has also emerged on mechanisms for the accumulation in plasma of harmful cholesterol-rich and triglyceride-rich apoB-containing remnant lipoproteins in states of overnutrition. Like LDL, these harmful cholesterol-rich and triglyceride-rich apoB-containing remnant lipoprotein remnants become retained and modified within the arterial wall, causing atherosclerosis.

SUMMARY

LDL and other cholesterol-rich, apoB-containing lipoproteins, once they become retained and modified within the arterial wall, cause atherosclerosis. This simple, robust pathophysiologic understanding may finally allow us to eradicate ASCVD, the leading killer in the world.

Enhanced Megakaryopoiesis and Platelet Activity in Hypercholesterolemic, B6-Ldlr-/-, Cdkn2a-Deficient Mice

BACKGROUND

Genome-wide association studies for coronary artery disease/myocardial infarction revealed a 58 kb risk locus on 9p21.3. Refined genetic analyses revealed unique haplotype blocks conferring susceptibility to atherosclerosis per se versus risk for acute complications in the presence of underlying coronary artery disease. The cell proliferation inhibitor locus, CDKN2A, maps just upstream of the myocardial infarction risk block, is at least partly regulated by the noncoding RNA, ANRIL, overlapping the risk block, and has been associated with platelet counts in humans. Thus, we tested the hypothesis that CDKN2A deficiency predisposes to increased platelet production, leading to increased platelet activation in the setting of hypercholesterolemia.

METHODS AND RESULTS

Platelet production and activation were measured in B6-Ldlr(-/-)Cdkn2a(+/-) mice and a congenic strain carrying the region of homology with the human 9p21.3/CDKN2A locus. The strains exhibit decreased expression of CDKN2A (both p16(INK4a) and p19(ARF)) but not CDKN2B (p15(INK4b)). Compared with B6-Ldlr(-/-) controls, both Cdkn2a-deficient strains exhibited increased platelet counts and bone marrow megakaryopoiesis. The platelet overproduction phenotype was reversed by treatment with cyclin-dependent kinase 4/6 inhibitor, PD0332991/palbociclib, that mimics the endogenous effect of p16(INK4a). Western diet feeding resulted in increased platelet activation, increased thrombin/antithrombin complex, and decreased bleeding times in Cdkn2a-deficient mice compared with controls.

CONCLUSIONS

Together, the data suggest that one or more Cdkn2a transcripts modulate platelet production and activity in the setting of hypercholesterolemia, amenable to pharmaceutical intervention. Enhanced platelet production and activation may predispose to arterial thrombosis, suggesting an explanation, at least in part, for the association of 9p21.3 and myocardial infarction.

A disintegrin and metalloproteinase with thrombospondin motif 1 (ADAMTS1) expression increases in acute aortic dissection

Acute aortic dissection (AAD) is a life-threatening cardiovascular disease caused by progressive medial degeneration of the aortic wall. A disintegrin and metalloproteinase with thrombospondin motifs 1 (ADAMTS1) is a recently identified extracellular metalloproteinase participating in the development of vascular disease, such as atherosclerosis. In the present study, we found that ADAMTS1 was significantly elevated in blood samples from AAD patients compared with patients with acute myocardial infarction and healthy volunteers. Based on these findings, we established an AAD model by infusing angiotensin II in older mice. AAD was successfully developed in aorta tissues, with an incidence of 42% after 14 days in the angiotensin II group. Macrophage and neutrophil infiltration was observed in the media of the aorta, and ADAMTS1 overexpression was found in the aorta by Western blot and immunohistochemistry. Double immunofluorescence staining showed the expression of ADAMTS1 in macrophages and neutrophils. Consistent with the upregulation of ADAMTS1 in aortic dissection tissues, versican (a proteoglycan substrate of ADAMTS1) was degraded significantly more in these tissues than in control aortic tissues. These data suggest that the increased expression of ADAMTS1 protein in macrophages and neutrophils that infiltrated aortic tissues may promote the progression of AAD by degrading versican.

Mechanisms of Hypoxic Up-Regulation of Versican Gene Expression in Macrophages

Hypoxia is a hallmark of many pathological tissues. Macrophages accumulate in hypoxic sites and up-regulate a range of hypoxia-inducible genes. The matrix proteoglycan versican has been identified as one such gene, but the mechanisms responsible for hypoxic induction are not fully characterised. Here we investigate the up-regulation of versican by hypoxia in primary human monocyte-derived macrophages (HMDM), and, intriguingly, show that versican mRNA is up-regulated much more highly (>600 fold) by long term hypoxia (5 days) than by 1 day of hypoxia (48 fold). We report that versican mRNA decay rates are not affected by hypoxia, demonstrating that hypoxic induction of versican mRNA is mediated by increased transcription. Deletion analysis of the promoter identified two regions required for high level promoter activity of luciferase reporter constructs in human macrophages. The hypoxia-inducible transcription factor HIF-1 has previously been implicated as a key potential regulator of versican expression in hypoxia, however our data suggest that HIF-1 up-regulation is unlikely to be principally responsible for the high levels of induction observed in HMDM. Treatment of HMDM with two distinct specific inhibitors of Phosphoinositide 3-kinase (PI3K), LY290042 and wortmannin, significantly reduced induction of versican mRNA by hypoxia and provides evidence of a role for PI3K in hypoxic up-regulation of versican expression.

Versican is upregulated in circulating monocytes in patients with systemic sclerosis and amplifies a CCL2-mediated pathogenic loop

Introduction

Altered phenotypes of circulating monocytes of patients with systemic sclerosis (SSc) have been reported, but the role of these alterations in the pathogenesis of SSc remains unclear. This study was undertaken to identify molecules that are preferentially expressed by SSc monocytes, and to investigate the roles of these molecules in the pathogenic process of SSc.

Methods

We analyzed circulating CD14⁺ monocytes isolated from 36 patients with SSc and 32 healthy control subjects. The monocytes' gene expression profiles were assessed by Oligo GEArray^® (SABiosciences, Frederic, MA, USA) and semiquantitative or quantitative PCR; their protein expression was evaluated in culture supernatants of unstimulated monocytes by immunoblotting or ELISA, and by immunocytostaining. Monocyte chemoattractant activity of CCL2 was assessed in a TransWell^® system (Corning Incorporated, Corning, NY, USA) in the presence or absence of chondroitin sulfate (CS).

Results

A step-wise approach to profiling gene expression identified that versican and CCL2 were upregulated in SSc monocytes. Subsequent analysis of proteins expressed in monocyte culture supernatants confirmed enhanced production of versican and CCL2 in SSc monocytes compared with control monocytes. CCL2 bound to CS chains of versican and colocalized with versican in the monocytes' Golgi apparatus. Finally, CCL2 had a greater ability to mediate monocyte migration when bound to CS chains, because this binding provided efficient formation of CCL2 gradients and protection from protease attack.

Conclusion

Circulating monocytes with elevated versican and CCL2 levels may contribute to the fibrotic process in a subset of SSc patients by amplifying a positive feedback loop consisting of versican, CCL2, and the influx of monocytes.

Pegylation of high-density lipoprotein decreases plasma clearance and enhances antiatherogenic activity

RATIONALE

Infusions of apolipoprotein AI (apoAI), mimetic peptides, or high-density lipoprotein (HDL) remain a promising approach for the treatment of atherosclerotic coronary disease. However, rapid clearance leads to a requirement for repeated administration of large amounts of material and limits effective plasma concentrations.

OBJECTIVE

Because pegylation of purified proteins is commonly used as a method to increase their half-life in the circulation, we determined whether pegylation of apoAI or HDL would increase its plasma half-life and in turn its antiatherogenic potential.

METHODS AND RESULTS

Initial pegylation attempts using lipid-poor apoAI showed a marked tendency to form multi-pegylated (PEG) species with reduced ability to promote cholesterol efflux from macrophage foam cells. However, pegylation of human holo-HDL or reconstituted phospholipid/apoAI particles (rHDL) led to selective N-terminal monopegylation of apoAI with full preservation of cholesterol efflux activity. The plasma clearance of PEG-rHDL was estimated after injection into hypercholesterolemic Apoe-/- mice; the half-life of pegylated PEG-apoAI after injection of PEG-rHDL was increased ≈7-fold compared with apoAI in nonpegylated rHDL. In comparison with nonpegylated rHDL, infusion of PEG-rHDL (40 mg/kg) into hypercholesterolemic Apoe-/- mice led to more pronounced suppression of bone marrow myeloid progenitor cell proliferation and monocytosis, as well as reduced atherosclerosis and a stable plaque phenotype.

CONCLUSIONS

We describe a novel method for effective monopegylation of apoAI in HDL particles, in which lipid binding seems to protect against pegylation of key functional residues. Pegylation of apoAI in rHDL markedly increases its plasma half-life and enhances antiatherogenic properties in vivo.

Pro-inflammatory phenotype of COPD fibroblasts not compatible with repair in COPD lung

Chronic obstructive pulmonary disease (COPD) is characterized by loss of elastic fibres from small airways and alveolar walls, with the decrease in elastin increasing with disease severity. It is unclear why there is a lack of repair of elastic fibres. We have examined fibroblasts cultured from lung tissue from subjects with or without COPD to determine if the secretory profile explains lack of tissue repair. In this study, fibroblasts were cultured from lung parenchyma of patients with mild COPD [Global initiative for chronic Obstructive Lung Disease (GOLD) 1, n= 5], moderate to severe COPD (GOLD 2–3, n= 12) and controls (non-COPD, n= 5). Measurements were made of proliferation, senescence-associated β-galactosidase-1, mRNA expression of IL-6, IL-8, MMP-1, tropoelastin and versican, and protein levels for IL-6, IL-8, PGE_2, tropoelastin, insoluble elastin, and versican. GOLD 2–3 fibroblasts proliferated more slowly (P < 0.01), had higher levels of senescence-associated β-galactosidase-1 (P < 0.001) than controls and showed significant increases in mRNA and/or protein for IL-6 (P < 0.05), IL-8 (P < 0.01), MMP-1 (P < 0.05), PGE₂ (P < 0.05), versican (P < 0.05) and tropoelastin (P < 0.05). mRNA expression and/or protein levels of tropoelastin (P < 0.01), versican (P < 0.05), IL-6 (P < 0.05) and IL-8 (P < 0.05) were negatively correlated with FEV1% of predicted. Insoluble elastin was not increased. In summary, fibroblasts from moderate to severe COPD subjects display a secretory phenotype with up-regulation of inflammatory molecules including the matrix proteoglycan versican, and increased soluble, but not insoluble, elastin. Versican inhibits assembly of tropoelastin into insoluble elastin and we conclude that the pro-inflammatory phenotype of COPD fibroblasts is not compatible with repair of elastic fibres.

RhoGDI2 suppresses lung metastasis in mice by reducing tumor versican expression and macrophage infiltration

Half of patients with muscle-invasive bladder cancer develop metastatic disease, and this is responsible for most of the deaths from this cancer. Low expression of RhoGTP dissociation inhibitor 2 (RhoGDI2; also known as ARHGDIB and Ly-GDI) is associated with metastatic disease in patients with muscle-invasive bladder cancer. Moreover, a reduction in metastasis is observed upon reexpression of RhoGDI2 in xenograft models of metastatic cancer. Here, we show that RhoGDI2 suppresses lung metastasis in mouse models by reducing the expression of isoforms V1 and V3 of the proteoglycan versican (VCAN; also known as chondroitin sulfate proteoglycan 2 [CSPG2]). In addition, we found that high versican levels portended poor prognosis in patients with bladder cancer. The functional importance of tumor expression of versican in promoting metastasis was established in in vitro and in vivo studies in mice that implicated a role for the chemokine CCL2 (also known as MCP1) and macrophages. Further analysis indicated that RhoGDI2 suppressed metastasis by altering inflammation in the tumor microenvironment. In summary, we demonstrate what we believe to be a new mechanism of metastasis suppression that works by reducing host responses that promote metastatic colonization of the lung. Therapeutic targeting of these interactions may provide a novel adjuvant strategy for delaying the appearance of clinical metastasis in patients.

WNT3A induces a contractile and secretory phenotype in cultured vascular smooth muscle cells that is associated with increased gap junction communication

Evidence suggests a role for Wnt signaling in vascular wound repair and remodeling events. Despite this, very little is known about the effect of Wnt ligands on the structure and function of vascular cells. In this study, we treated vascular smooth muscle cells with 250 ng/ml of recombinant Wnt3a for 72 h and observed changes in the cell phenotype. Our data suggest Wnt3a completely alters the phenotype of vascular smooth muscle cells. The Wnt3a-treated cells appeared larger and had increased formation of stress fibers. These cells also had increased expression of the smooth muscle contractile proteins, calponin and smooth muscle α-actin, and contracted a collagen lattice faster than control cells. The Wnt3a-treated smooth muscle cells displayed increased extracellular matrix synthesis, as measured by collagen I and III mRNA expression, along with increased expression of MMP2 and MMP9, but decreased TIMP2 levels. The Wnt3a-induced change in cell phenotype was associated with increased expression of the gap junction protein connexin 43. Consistent with this, Wnt3a-treated smooth muscle cells displayed enhanced intercellular communication, as measured by the scrape-loading dye transfer technique. The canonical Wnt antagonist, dickkopf-related protein 1, completely reversed the contractile protein and connexin 43 expression seen in the Wnt3a-treated cells, suggesting these changes were dependent on canonical Wnt signaling. Collectively, this data suggest Wnt3a promotes a contractile and secretory phenotype in vascular smooth muscle cells that is associated with increased gap junction communication.

Beyond genome-wide association studies: the usefulness of mouse genetics in understanding the complex etiology of atherosclerosis

The development of population-based genome-wide association studies has led to the rapid identification of large numbers of genetic variants associated with coronary artery disease (CAD) and related traits. Together with large-scale gene-centric studies, at least 35 loci associated with CAD per se have been identified with replication. The majority of these associations are with common single-nucleotide polymorphisms exhibiting modest effects on relative risk. The modest nature of the effects, coupled with ethical/practical constraints associated with human sampling, makes it difficult to answer important questions beyond gene/locus localization and allele frequency via human genetic studies. Questions related to gene function, disease-causing mechanism(s), and effective interventions will likely require studies in model organisms. The use of the mouse model for further detailed studies of CAD-associated loci identified by genome-wide association studies is highlighted herein.

Genetic analysis of atherosclerosis and glucose homeostasis in an intercross between C57BL/6 and BALB/cJ apolipoprotein E-deficient mice

BACKGROUND

Diabetic patients have an increased risk of developing atherosclerosis and related complications compared with nondiabetic individuals. The increased cardiovascular risk associated with diabetes is due in part to genetic variations that influence both glucose homeostasis and atherosclerotic lesion growth. Mouse strains C57BL/6J (B6) and BALB/cJ (BALB) exhibit distinct differences in fasting plasma glucose and atherosclerotic lesion size when deficient in apolipoprotein E (Apoe(-/-)). Quantitative trait locus (QTL) analysis was performed to determine genetic factors influencing the 2 phenotypes.

METHODS AND RESULTS

Female F(2) mice (n=266) were generated from an intercross between B6.Apoe(-/-) and BALB.Apoe(-/-) mice and fed a Western diet for 12 weeks. Atherosclerotic lesions in the aortic root, fasting plasma glucose, and body weight were measured. 130 microsatellite markers across the entire genome were genotyped. Four significant QTLs, Ath1 on chromosome (Chr) 1, Ath41 on Chr2, Ath42 on Chr5, and Ath29 on Chr9, and 1 suggestive QTL on Chr4, were identified for atherosclerotic lesion size. Four significant QTLs, Bglu3 and Bglu12 on Chr1, Bglu13 on Chr5, Bglu15 on Chr12, and 2 suggestive QTLs on Chr9 and Chr15 were identified for fasting glucose levels on the chow diet. Two significant QTLs, Bglu3 and Bglu13, and 1 suggestive locus on Chr8 were identified for fasting glucose on the Western diet. One significant locus on Chr1 and 2 suggestive loci on Chr9 and Chr19 were identified for body weight. Ath1 and Ath42 coincided with Bglu3 and Bglu13, respectively, in the confidence interval.

CONCLUSIONS

We have identified novel QTLs that have major influences on atherosclerotic lesion size and glucose homeostasis. The colocalization of QTLs for atherosclerosis and diabetes suggests possible genetic connections between the 2 diseases.

Cdkn2a is an atherosclerosis modifier locus that regulates monocyte/macrophage proliferation

OBJECTIVE

Common genetic variants in a 58-kb region of chromosome 9p21, near the CDKN2A/CDKN2B tumor suppressor locus, are strongly associated with coronary artery disease. However, the underlying mechanism of action remains unknown.

METHODS AND RESULTS

We previously reported a congenic mouse model harboring an atherosclerosis susceptibility locus and the region of homology with the human 9p21 locus. Microarray and transcript-specific expression analyses showed markedly decreased Cdkn2a expression, including both p16(INK4a) and p19(ARF), but not Cdkn2b (p15(INK4b)), in macrophages derived from congenic mice compared with controls. Atherosclerosis studies in subcongenic strains revealed genetic complexity and narrowed 1 locus to a small interval including Cdkn2a/b. Bone marrow (BM) transplantation studies implicated myeloid lineage cells as the culprit cell type, rather than resident vascular cells. To directly test the role of BM-derived Cdkn2a transcripts in atherogenesis and inflammatory cell proliferation, we performed a transplantation study using Cdkn2a(-/-) cells in the Ldlr(-/-) mouse model. Cdkn2a-deficient BM recipients exhibited accelerated atherosclerosis, increased Ly6C proinflammatory monocytes, and increased monocyte/macrophage proliferation compared with controls.

CONCLUSION

These data provide a plausible mechanism for accelerated atherogenesis in susceptible congenic mice, involving decreased expression of Cdkn2a and increased proliferation of monocyte/macrophages, with possible relevance to the 9p21 human locus.

Altered versican cleavage in ADAMTS5 deficient mice; a novel etiology of myxomatous valve disease

In fetal valve maturation the mechanisms by which the relatively homogeneous proteoglycan-rich extracellular matrix (ECM) of endocardial cushions is replaced by a specialized and stratified ECM found in mature valves are not understood. Therefore, we reasoned that uncovering proteases critical for 'remodeling' the proteoglycan rich (extracellular matrix) ECM may elucidate novel mechanisms of valve development. We have determined that mice deficient in ADAMTS5, (A Disintegrin-like And Metalloprotease domain with ThromboSpondin-type 1 motifs) which we demonstrated is expressed predominantly by valvular endocardium during cardiac valve maturation, exhibited enlarged valves. ADAMTS5 deficient valves displayed a reduction in cleavage of its substrate versican, a critical cardiac proteoglycan. In vivo reduction of versican, in Adamts5(-/-) mice, achieved through Vcan heterozygosity, substantially rescued the valve anomalies. An increase in BMP2 immunolocalization, Sox9 expression and mesenchymal cell proliferation were observed in Adamts5(-/-) valve mesenchyme and correlated with expansion of the spongiosa (proteoglycan-rich) region in Adamts5(-/-) valve cusps. Furthermore, these data suggest that ECM remodeling via ADAMTS5 is required for endocardial to mesenchymal signaling in late fetal valve development. Although adult Adamts5(-/-) mice are viable they do not recover from developmental valve anomalies and have myxomatous cardiac valves with 100% penetrance. Since the accumulation of proteoglycans is a hallmark of myxomatous valve disease, based on these data we hypothesize that a lack of versican cleavage during fetal valve development may be a potential etiology of adult myxomatous valve disease.

Neointima formed by arterial smooth muscle cells expressing versican variant V3 is resistant to lipid and macrophage accumulation

OBJECTIVE

Extracellular matrix (ECM) of neointima formed following angioplasty contains elevated levels of versican, loosely arranged collagen, and fragmented deposits of elastin, features associated with lipid and macrophage accumulation. ECM with a low versican content, compact structure, and increased elastic fiber content can be achieved by expression of versican variant V3, which lacks chondroitin sulfate glycosaminoglycans. We hypothesized that V3-expressing arterial smooth muscle cells (ASMC) can be used to form a neointima resistant to lipid and macrophage accumulation associated with hypercholesterolemia.

METHODS AND RESULTS

ASMC transduced with V3 cDNA were seeded into ballooned rabbit carotid arteries, and animals were fed a chow diet for 4 weeks, followed by a cholesterol-enriched diet for 4 weeks, achieving plasma cholesterol levels of 20 to 25 mmol/L. V3 neointimae at 8 weeks were compact, multilayered, and elastin enriched. They were significantly thinner (57%) than control neointimae; contained significantly more elastin (118%), less collagen (22%), and less lipid (76%); and showed significantly reduced macrophage infiltration (85%). Mechanistic studies demonstrated that oxidized low-density lipoprotein stimulated the formation of a monocyte-binding ECM, which was inhibited in the presence of V3 expressing ASMC.

CONCLUSION

These results demonstrate that expression of V3 in vessel wall creates an elastin-rich neointimal matrix that in the presence of hyperlipidemia is resistant to lipid deposition and macrophage accumulation.

Developing vasculature and stroma in engineered human myocardium

We recently developed a scaffold-free patch of human myocardium with human embryonic stem cell-derived cardiomyocytes and showed that stromal and endothelial cells form vascular networks in vitro and improve cardiomyocyte engraftment. Here, we hypothesize that stromal cells regulate the angiogenic phenotype by modulating the extracellular matrix (ECM). Human marrow stromal cells (hMSCs) support the greatest degree of endothelial cell organization, at 1.3- to 2.4-fold higher than other stromal cells tested. Stromal cells produce abundant ECM components in patches, including fibrillar collagen, hyaluronan, and versican. We identified two clonal hMSC lines that supported endothelial networks poorly and robustly. Interestingly, the pro-angiogenic hMSCs express high levels of versican, a chondroitin sulfate proteglycan that modulates angiogenesis and wound healing, whereas poorly angiogenic hMSCs produce little versican. When transplanted onto uninjured athymic rat hearts, patches with proangiogenic hMSCs develop ~ 50-fold more human vessels and form anastomoses with the host circulation, resulting in chimeric vessels containing erythrocytes. Thus, stromal cells play a key role in supporting vascularization of engineered human myocardium. Different stromal cell types vary widely in their proangiogenic ability, likely due in part to differences in ECM synthesis. Comparison of these cells defines an in vitro predictive platform for studying vascular development.

Expression of linear and novel circular forms of an INK4/ARF-associated non-coding RNA correlates with atherosclerosis risk

Human genome-wide association studies have linked single nucleotide polymorphisms (SNPs) on chromosome 9p21.3 near the INK4/ARF (CDKN2a/b) locus with susceptibility to atherosclerotic vascular disease (ASVD). Although this locus encodes three well-characterized tumor suppressors, p16^INK4a, p15^INK4b, and ARF, the SNPs most strongly associated with ASVD are ∼120 kb from the nearest coding gene within a long non-coding RNA (ncRNA) known as ANRIL (CDKN2BAS). While individuals homozygous for the atherosclerotic risk allele show decreased expression of ANRIL and the coding INK4/ARF transcripts, the mechanism by which such distant genetic variants influence INK4/ARF expression is unknown. Here, using rapid amplification of cDNA ends (RACE) and analysis of next-generation RNA sequencing datasets, we determined the structure and abundance of multiple ANRIL species. Each of these species was present at very low copy numbers in primary and cultured cells; however, only the expression of ANRIL isoforms containing exons proximal to the INK4/ARF locus correlated with the ASVD risk alleles. Surprisingly, RACE also identified transcripts containing non-colinear ANRIL exonic sequences, whose expression also correlated with genotype and INK4/ARF expression. These non-polyadenylated RNAs resisted RNAse R digestion and could be PCR amplified using outward-facing primers, suggesting they represent circular RNA structures that could arise from by-products of mRNA splicing. Next-generation DNA sequencing and splice prediction algorithms identified polymorphisms within the ASVD risk interval that may regulate ANRIL splicing and circular ANRIL (cANRIL) production. These results identify novel circular RNA products emanating from the ANRIL locus and suggest causal variants at 9p21.3 regulate INK4/ARF expression and ASVD risk by modulating ANRIL expression and/or structure.

Unbiased studies of the human genome have identified strong genetic determinants of atherosclerotic vascular disease (ASVD) on chromosome 9p21.3. This region of the genome does not encode genes previously linked to ASVD, but does contain the INK4/ARF tumor suppressor locus. Products of the INK4/ARF locus regulate cell division, a process thought to be important in ASVD pathology. We and others have suggested that genetic variants in 9p21.3 influence INK4/ARF gene expression; however, the mechanisms by which these distant polymorphisms (>100,000 bp away) influence transcription of the locus is unknown. The ASVD–associated genetic variants lie within the predicted structure of a non-coding RNA (ncRNA) called ANRIL. Based upon recent work suggesting that other ncRNAs can repress nearby coding genes, we considered the possibility that ANRIL structure may regulate INK4/ARF gene expression. Coupling molecular analysis with state-of-the-art sequencing technologies in a wide variety of cell types from normal human donors and cancer cells, we found that ANRIL encodes a heterogeneous species of rare RNA transcripts. Moreover, we identified novel, circular ANRIL isoforms (cANRIL) whose expression correlated with INK4/ARF transcription and ASVD risk. These studies suggest a new model wherein ANRIL structure influences INK4/ARF expression and susceptibility to atherosclerosis.

Synthesis and organization of hyaluronan and versican by embryonic stem cells undergoing embryoid body differentiation

Embryonic stem cells (ESCs) provide a convenient model to probe the molecular and cellular dynamics of developmental cell morphogenesis. ESC differentiation in vitro via embryoid bodies (EBs) recapitulates many aspects of early stages of development, including the epithelial-mesenchymal transition (EMT) of pluripotent cells into more differentiated progeny. Hyaluronan and versican are important extracellular mediators of EMT processes, yet the temporal expression and spatial distribution of these extracellular matrix (ECM) molecules during EB differentiation remains undefined. Thus, the objective of this study was to evaluate the synthesis and organization of hyaluronan and versican by using murine ESCs during EB differentiation. Hyaluronan and versican (V0 and V1 isoforms), visualized by immunohistochemistry and evaluated biochemically, accumulated within EBs during the course of differentiation. Interestingly, increasing amounts of a 70-kDa proteolytic fragment of versican were also detected over time, along with ADAMTS-1 and -5 protein expression. ESCs expressed each of the hyaluronan synthases (HAS) -1, -2, and -3 and versican splice variants (V0, V1, V2, and V3) throughout EB differentiation, but HAS-2, V0, and V1 were expressed at significantly increased levels at each time point examined. Hyaluronan and versican exhibited overlapping expression patterns within EBs in regions of low cell density, and versican expression was excluded from clusters of epithelial (cytokeratin-positive) cells but was enriched within the vicinity of mesenchymal (N-cadherin-positive) cells. These results indicate that hyaluronan and versican synthesized by ESCs within EB microenvironments are associated with EMT processes and furthermore suggest that endogenously produced ECM molecules play a role in ESC differentiation. This manuscript contains online supplemental material at http://www.jhc.org. Please visit this article online to view these materials.