Fibulin-1 is a ligand for the C-type lectin domains of aggrecan and versican

Fibulin-1 promotes intimal hyperplasia after venous stent implantation through ACE mediated angiotensin II signaling

Objective

Stent intimal hyperplasia leads to in stent restenosis and thrombosis. This study determined whether Fibulin-1 activity in smooth muscle cells (SMCs) contributes to stent restenosis or thrombosis.

Methods

Stent implantation was conducted in a pig model. Target vessel samples were stained and analyzed by protein mass spectrometry. Cell experiments and Fibulin-1 SMC specific knockout mice (Fbln1SMKO) were used to investigate the mechanism of Fibulin-1 induced SMC proliferation and thrombosis.

Results

SMC proliferation and phenotypic transition are the main pathological changes of intimal hyperplasia in venous stents. Protein mass spectrometry analysis revealed a total of 67 upregulated proteins and 39 downregulated proteins in intimal hyperplasia after stent implantation compared with normal iliac vein tissues. Among them, Fibulin-1 ranked among the top proteins altered. Fibulin-1 overexpressing human SMCs (Fibulin-1-hSMCs) showed increased migration and phenotypic switching from contractile to secretory type and Fibulin-1 inhibition decreased the activity of SMCs. Mechanistically, Fibulin-1-hSMCs displayed increased levels of angiotensin converting enzyme (ACE) expression and angiotensin II signaling. Inhibition of ACE or angiotensin II signaling alleviated the migration of Fibulin-1-hSMCs. Using Fibulin-1 SMC specific knockout mice (Fbln1SMKO) and venous thrombosis model, we demonstrated that Fibulin-1 deletion attenuated intimal SMCs proliferation and thrombosis. Further, Fibulin-1 concentration was high in iliac vein compression syndrome (IVCS) patients treated with stent and was an independent predictor of venous insufficiency.

Conclusions

Fibulin-1 promotes SMC proliferation partially through ACE secretion and angiotensin II signaling after stent implantation. Fibulin-1 plays a role in venous insufficiency syndrome, implicating the protein in the detection and treatment of IVCS.

V3: an enigmatic isoform of the proteoglycan versican

V3 is an isoform of the extracellular matrix (ECM) proteoglycan (PG) versican generated through alternative splicing of the versican gene such that the two major exons coding for sequences in the protein core that support chondroitin sulfate (CS) glycosaminoglycan (GAG) chain attachment are excluded. Thus, versican V3 isoform carries no GAGs. A survey of PubMed reveals only 50 publications specifically on V3 versican, so it is a very understudied member of the versican family, partly because to date there are no antibodies that can distinguish V3 from the CS-carrying isoforms of versican, that is, to facilitate functional and mechanistic studies. However, a number of in vitro and in vivo studies have identified the expression of the V3 transcript during different phases of development and in disease, and selective overexpression of V3 has shown dramatic phenotypic effects in "gain and loss of function" studies in experimental models. Thus, we thought it would be useful and instructive to discuss the discovery, characterization, and the putative biological importance of the enigmatic V3 isoform of versican.

The C-terminal domains of ADAMTS1 contain exosites involved in its proteoglycanase activity

A disintegrin-like and metalloproteinase with thrombospondin type 1 motifs (ADAMTS1) is a protease involved in fertilization, cancer, cardiovascular development, and thoracic aneurysms. Proteoglycans such as versican and aggrecan have been identified as ADAMTS1 substrates, and Adamts1 ablation in mice typically results in versican accumulation; however, previous qualitative studies have suggested that ADAMTS1 proteoglycanase activity is weaker than that of other family members such as ADAMTS4 and ADAMTS5. Here, we investigated the functional determinants of ADAMTS1 proteoglycanase activity. We found that ADAMTS1 versicanase activity is approximately 1000-fold lower than ADAMTS5 and 50-fold lower than ADAMTS4 with a kinetic constant (kcat/Km) of 3.6 × 103 M-1 s-1 against full-length versican. Studies on domain-deletion variants identified the spacer and cysteine-rich domains as major determinants of ADAMTS1 versicanase activity. Additionally, we confirmed that these C-terminal domains are involved in the proteolysis of aggrecan as well as biglycan, a small leucine-rich proteoglycan. Glutamine scanning mutagenesis of exposed positively charged residues on the spacer domain loops and loop substitution with ADAMTS4 identified clusters of substrate-binding residues (exosites) in β3-β4 (R756Q/R759Q/R762Q), β9-β10 (residues 828-835), and β6-β7 (K795Q) loops. This study provides a mechanistic foundation for understanding the interactions between ADAMTS1 and its proteoglycan substrates and paves the way for development of selective exosite modulators of ADAMTS1 proteoglycanase activity.

Molecular mechanisms regulating extracellular matrix-mediated remodeling in the ductus arteriosus

Progressive remodeling throughout the fetal and postnatal period is essential for anatomical closure of the ductus arteriosus (DA). Internal elastic lamina interruption and subendothelial region widening, elastic fiber formation impairment in the tunica media, and intimal thickening are distinctive features of the fetal DA. After birth, the DA undergoes further extracellular matrix-mediated remodeling. Based on the knowledge obtained from mouse models and human disease, recent studies revealed a molecular mechanism of DA remodeling. In this review, we focus on matrix remodeling and regulation of cell migration/proliferation associated with DA anatomical closure and discuss the role of prostaglandin E receptor 4 (EP4) signaling and jagged1-Notch signaling as well as myocardin, vimentin, and secretory components including tissue plasminogen activator, versican, lysyl oxidase, and bone morphogenetic proteins 9 and 10.

Aggrecan and versican: two brothers close or apart

Aggrecan (Acan) and versican (Vcan) are large chondroitin sulfate proteoglycans of the extracellular matrix. They share the same structural domains at both N and C-termini. The N-terminal G1 domain binds hyaluronan (HA), forms an HA-rich matrix, and regulates HA-mediated signaling. The C-terminal G3 domain binds other extracellular matrix molecules and forms a supramolecular structure that stores TGFb and BMPs and regulates their signaling. EGF-like motifs in the G3 domain may directly act like an EGF ligand. Both Acan and Vcan are present in cartilage, intervertebral disc, brain, heart, and aorta. Their localizations are essentially reciprocal. This review describes their structural domains, expression patterns and functions, and regulation of their expression.

Novel missense ACAN gene variants linked to familial osteochondritis dissecans cluster in the C-terminal globular domain of aggrecan

The cartilage aggrecan proteoglycan is crucial for both skeletal growth and articular cartilage function. A number of aggrecan (ACAN) gene variants have been linked to skeletal disorders, ranging from short stature to severe chondrodyplasias. Osteochondritis dissecans is a disorder where articular cartilage and subchondral bone fragments come loose from the articular surface. We previously reported a missense ACAN variant linked to familial osteochondritis dissecans, with short stature and early onset osteoarthritis, and now describe three novel ACAN gene variants from additional families with this disorder. Like the previously described variant, these are autosomal dominant missense variants, resulting in single amino acid residue substitutions in the C-type lectin repeat of the aggrecan G3 domain. Functional studies showed that neither recombinant variant proteins, nor full-length variant aggrecan proteoglycan from heterozygous patient cartilage, were secreted to the same level as wild-type aggrecan. The variant proteins also showed decreased binding to known cartilage extracellular matrix ligands. Mapping these and other ACAN variants linked to hereditary skeletal disorders showed a clustering of osteochondritis dissecans-linked variants to the G3 domain. Taken together, this supports a link between missense ACAN variants affecting the aggrecan G3 domain and hereditary osteochondritis dissecans.

FBLN1 promotes chondrocyte proliferation by increasing phosphorylation of Smad2

BACKGROUND

The role of fibulin-1 or FBLN1 in chondrocyte proliferation has not been reported so far. In this study, we aimed to verify whether FBLN1 promotes chondrocyte proliferation in elderly patients with knee osteoarthritis by phosphorylating Smad2.

METHODS

Chondrocytes were isolated from cartilage samples collected from elderly patients with osteoarthritis (n = 6) and young patients (n = 6). The isolated chondrocytes were divided into the following three groups: control (medium only); cells transfected with adenovirus expressing green fluorescent protein (Ad-GFP); and those transfected with adenovirus expressing green fluorescent protein and FBLN1 (Ad-GFP-FBLN1). Furthermore, chondrocytes were divided into the following three groups in the mechanistic analysis: group 1, medium only; group 2, Ad-FBLN1; and group 3, Ad-FBLN1+pSmad2 inhibitor. The cells were analyzed for the relevant indicators after culturing for 48 h.

RESULTS

There were more EdU-positive cells in the Ad-GFP-FBLN1 group than in the other two groups (both P < 0.05). Compared with the other two groups, the level of pSmad2 and Col2 in the Ad-GFP-FBLN1 group was significantly increased (P < 0.05). The gene expression level of each indicator was consistent with the protein expression level. There was no significant difference in the indicators between groups 1 and 3. The percentage of EdU-positive cells in group 2 was higher than that in the other two groups (P < 0.05). The expression of pSmad2 and Col2 in group 2 was higher than that in the other two groups (both P < 0.05).

CONCLUSION

FBLN1 can promote chondrocyte proliferation in the knee cartilage in elderly patients by phosphorylating Smad2.

The Glomerular Endothelium Restricts Albumin Filtration

Inflammatory activation and/or dysfunction of the glomerular endothelium triggers proteinuria in many systemic and localized vascular disorders. Among them are the thrombotic microangiopathies, many forms of glomerulonephritis, and acute inflammatory episodes like sepsis and COVID-19 illness. Another example is the chronic endothelial dysfunction that develops in cardiovascular disease and in metabolic disorders like diabetes. While the glomerular endothelium is a porous sieve that filters prodigious amounts of water and small solutes, it also bars the bulk of albumin and large plasma proteins from passing into the glomerular filtrate. This endothelial barrier function is ascribed predominantly to the endothelial glycocalyx with its endothelial surface layer, that together form a relatively thick, mucinous coat composed of glycosaminoglycans, proteoglycans, glycolipids, sialomucins and other glycoproteins, as well as secreted and circulating proteins. The glycocalyx/endothelial surface layer not only covers the glomerular endothelium; it extends into the endothelial fenestrae. Some glycocalyx components span or are attached to the apical endothelial cell plasma membrane and form the formal glycocalyx. Other components, including small proteoglycans and circulating proteins like albumin and orosomucoid, form the endothelial surface layer and are bound to the glycocalyx due to weak intermolecular interactions. Indeed, bound plasma albumin is a major constituent of the endothelial surface layer and contributes to its barrier function. A role for glomerular endothelial cells in the barrier of the glomerular capillary wall to protein filtration has been demonstrated by many elegant studies. However, it can only be fully understood in the context of other components, including the glomerular basement membrane, the podocytes and reabsorption of proteins by tubule epithelial cells. Discovery of the precise mechanisms that lead to glycocalyx/endothelial surface layer disruption within glomerular capillaries will hopefully lead to pharmacological interventions that specifically target this important structure.

Proteoglycans and Diseases of Soft Tissues

Proteoglycans consist of protein cores to which at least one glycosaminoglycan chain is attached. They play important roles in the physiology and biomechanical function of tendons, ligaments, cardiovascular system, and other systems through their involvement in regulation of assembly and maintenance of extracellular matrix, and through their participation in cell proliferation together with growth factors. They can be divided into two main groups, small and large proteoglycans. The small proteoglycans are also known as small leucine-rich proteoglycans (SLRPs) which are encoded by 18 genes and are further subclassified into Classes I-V. Several members of Class I and II, such as decorin and biglycan from Class I, and Class II fibromodulin and lumican, are known to regulate collagen fibrillogenesis. Decorin limits the diameter of collagen fibrils during fibrillogenesis. The function of biglycan in fibrillogenesis is similar to that of decorin. Though biomechanical function of tendon is compromised in decorin-deficient mice, decorin can substitute for lack of biglycan in biglycan-deficient mice. New data also indicate an important role for biglycan in disorders of the cardiovascular system, including aortic valve stenosis and aortic dissection. Two members of the Class II of SLRPs, fibromodulin and lumican bind to the same site within the collagen molecule and can substitute for each other in fibromodulin- or lumican-deficient mice.Aggrecan and versican are the major representatives of the large proteoglycans. Though they are mainly found in the cartilage where they provide resilience and toughness, they are present also in tensile portions of tendons and, in slightly different biochemical form in fibrocartilage. Degradation by aggrecanase is responsible for the appearance of different forms of aggrecan and versican in different parts of the tendon where these cleaved forms play different roles. In addition, they are important components of the ventricularis of cardiac valves. Mutations in the gene for versican or in the gene for elastin (which binds to versican ) lead to severe disruptions of normal developmental of the heart at least in mice.

[A new therapeutic target for patent ductus arteriosus]

The ductus arteriosus (DA) maintains the fetal circulation by connecting the aorta and pulmonary arteries. Patent ductus arteriosus (PDA) occurs in >70% extremely-low-birth-weight infants. Patients with PDA exhibit circulatory failure, which is caused by left-to-right shunt. The DA immediately contracts after birth in response to the elevation of blood oxygen tension and to the decline in circulating prostaglandin E₂ (PGE₂). Cyclooxygenase inhibitors targeting smooth muscle cell (SMC) contraction represent only pharmacological treatment for PDA. However, it is important for DA anatomical closure that intimal thickening (IT) is appropriately formed between SMC layer and endothelial cells (EC). IT begins to form before the second-trimester and becomes prominent toward the end of third-trimester as an increase in placenta-derived PGE₂. Immature DAs frequently fail to be close due to poorly formed IT. IT consists of extracellular matrices (ECM) and migrated DA-SMCs from the tunica media. A glycoprotein fibulin-1 is expressed in developing cardiovascular system and binds to multiple ECMs. We found that PGE₂ increased fibulin-1 via EP4 in DA-SMCs, and Fbln1-deficient mice exhibited PDA with poor IT formation. Although EP4 is a Gs-coupled GPCR, fibulin-1 was secreted from DA-SMCs through the phospholipase C-protein kinase C-non-canonical NFκB signaling pathway. Fibulin-1 bound to DA-EC-derived versican which is a binding partner of hyaluronan, which promoted directional DA-SMC migration toward ECs and contributed to IT formation in the DA. Fibulin-1 upregulation by the activation of specific downstream pathway of EP4 may serve a new pharmacological strategy for PDA.

Isolation and Purification of Versican and Analysis of Versican Proteolysis

Versican is a widely distributed chondroitin sulfate proteoglycan that forms large complexes with the glycosaminoglycan hyaluronan (HA). As a consequence of HA binding to its receptor CD44 and interactions of the versican C-terminal globular (G3) domain with a variety of extracellular matrix proteins, versican is a key component of well-defined networks in pericellular matrix and extracellular matrix. Versican is crucial for several developmental processes in the embryo ranging from cardiac development to digit separation, and there is an increasing interest in its roles in cancer and inflammation. Versican proteolysis by ADAMTS proteases is highly regulated, occurs at specific peptide bonds, and is relevant to several physiological and disease mechanisms. In this chapter, methods are described for the isolation and detection of intact and cleaved versican in tissues using morphologic and biochemical techniques. These, together with the methodologies for purification and analysis of recombinant versican and an N-terminal versican fragment named versikine that are provided here, are likely to facilitate further progress on the biology of versican and its proteolysis.

Identification of VCAN as Hub Gene for Diabetic Kidney Disease Immune Injury Using Integrated Bioinformatics Analysis

Background: Diabetic kidney disease (DKD) is a leading cause of chronic kidney disease in China. Tubular injury contributes to the progression of DKD. Our study was conducted to explore the differential gene expression profiles between kidneys from patients with DKD and kidney living donors (LDs).

Methods: In total, seven DKD and eighteen LD gene expression profiles from the GSE104954 dataset were downloaded from the Gene Expression Omnibus database. Differentially expressed genes (DEGs) were analyzed in R with the limma package. DEGs were uploaded to the g:Profiler online database to explore the Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways. Ingenuity pathway analysis (IPA) was carried out using online IPA software. Weighted gene co-expression network analysis (WGCNA) was performed using the WGCNA R package. By integrating DEGs and genes from the top 1 phenotype-gene associated module, we determined the hub gene. We next tested the hub gene, VCAN, in the GSE30122 dataset. We also validated the versican levels in human kidney tissues, explored immune cell type enrichment using an online database xCell, and investigated the correlation between cell types and VCAN expression.

Results: A total of 563 DEGs was identified. A large number of pathways were involved in the immune response process according to the results of GO, KEGG, and IPA. Using WGCNA, we selected the lightcyan module in which genes showed the strongest correlation with the phenotype and smallest P-value. We also identified VCAN as a hub gene by integrating DEG analysis and WGCNA. Versican expression was upregulated in human diabetic kidney tissue. Moreover, versican was speculated to play a role in immune injury according to the enrichment of functions and signaling pathways. VCAN transcript levels correlate with the assembly of immune cells in the kidney.

Conclusion: Immune processes played an essential role in DKD tubulointerstitium injury. The hub gene VCAN contributed to this process.

Extracellular matrix-mediated remodeling and mechanotransduction in large vessels during development and disease

The vascular extracellular matrix (ECM) is synthesized and secreted during embryogenesis and facilitates the growth and remodeling of large vessels. Proper interactions between the ECM and vascular cells are pivotal for building the vasculature required for postnatal dynamic circulation. The ECM serves as a structural component by maintaining the integrity of the vessel wall while also regulating intercellular signaling, which involves cytokines and growth factors. The major ECM component in large vessels is elastic fibers, which include elastin and microfibrils. Elastin is predominantly synthesized by vascular smooth muscle cells (SMCs) and uses microfibrils as a scaffold to lay down and assemble cross-linked elastin. The absence of elastin causes developmental defects that result in the subendothelial proliferation of SMCs and inward remodeling of the vessel wall. Notably, elastic fiber formation is attenuated in the ductus arteriosus and umbilical arteries. These two vessels function during embryogenesis and close after birth via cellular proliferation, migration, and matrix accumulation. In dynamic postnatal mechano-environments, the elastic fibers in large vessels also serve an essential role in proper signal transduction as a component of elastin-contractile units. Disrupted mechanotransduction in SMCs leads to pathological conditions such as aortic aneurysms that exhibit outward remodeling. This review discusses the importance of the ECM-mainly the elastic fiber matrix-in large vessels during developmental remodeling and under pathological conditions. By dissecting the role of the ECM in large vessels, we aim to provide insights into the role of ECM-mediated signal transduction that can provide a basis for seeking new targets for intervention in vascular diseases.

Elastic tissue disruption is a major pathogenic factor to human vascular disease

Elastic fibers are essential components of the arterial extracellular matrix. They consist of the protein elastin and an array of microfibrils that support the protein and connect it to the surrounding matrix. The elastin gene encodes tropoelastin, a protein that requires extensive cross-linking to become elastin. Tropoelastin is expressed throughout human life, but its expression levels decrease with age, suggesting that the potential to synthesize elastin persists during lifetime although declines with aging. The initial abnormality documented in human atherosclerosis is fragmentation and loss of the elastic network in the medial layer of the arterial wall, suggesting an imbalance between elastic fiber injury and restoration. Damaged elastic structures are not adequately repaired by synthesis of new elastic elements. Progressive collagen accumulation follows medial elastic fiber disruption and fibrous plaques are formed, but advanced atherosclerosis lesions do not develop in the absence of prior elastic injury. Aging is associated with arterial extracellular matrix anomalies that evoke those present in early atherosclerosis. The reduction of elastic fibers with subsequent collagen accumulation leads to arterial stiffening and intima-media thickening, which are independent predictors of incident hypertension in prospective community-based studies. Arterial stiffening precedes the development of hypertension. The fundamental role of the vascular elastic network to arterial structure and function is emphasized by congenital disorders caused by mutations that disrupt normal elastic fiber production. Molecular changes in the genes coding tropoelastin, lysyl oxidase (tropoelastin cross-linking), and elastin-associated microfibrils, including fibrillin-1, fibulin-4, and fibulin-5 produce severe vascular injury due to absence of functional elastin.

Relationship between the Plasma Fibulin-1 Levels, Pulse Wave Velocity, and Vascular Age in Asymptomatic Hyperuricemia

Fibulin-1 (FBLN-1), an elastin-associated extracellular matrix protein, has been found in blood and may play a role in the pathophysiological processes leading to cardiovascular disease (CVD). We aimed to investigate the relationship between fibulin-1 levels and the risk of CVD by evaluating vascular age derived from the Framingham Heart Study and brachial-ankle Pulse Wave Velocity (baPWV) in patients with asymptomatic hyperuricemia (AHU). In total, 66 patients with AHU and 66 gender- and age-matched healthy individuals were enrolled. The plasma fibulin-1 levels were measured by immunochemistry. Patients with AHU presented significantly higher vascular age [median (interquartile range): 54 (22) vs. 48 (14) years, P=0.01] and baPWV [mean±SD: 1373±223 vs. 1291±177 cm/s, P=0.02] than the healthy subjects; however, no significant difference was observed in the plasma fibulin-1 level between the patients with AHU and healthy subjects [median (interquartile range): 4018 (3838) vs. 3099 (3405) ng/mL, P=0.31]. A correlation between fibulin-1 levels and baPWV was observed only in patients with AHU (r=0.29, P=0.02); and there was also a suggestively statistically significant correlation between fibulin-1 levels and vascular age (r=0.22, P=0.08). However, these associations were rendered insignificant after adjustments for potential confounders. In healthy subjects, no correlation was observed between fibulin-1 levels and CVD risk. This study reveals that plasma fibulin-1 levels may reflect the CVD risk in patients with AHU, but the relationship is not robust.

Matrisome Provides a Supportive Microenvironment for Skin Functions of Diverse Species

A biomaterial scaffold is a promising tool employed to drive tissue regeneration. This technology has been successfully applied in human tissue rebuilding, particularly for the skin. Meanwhile, there is still room for further improvement, such as maintaining sufficient functionality of a biomaterial scaffold. Here, we developed a new decellularization method to generate a complete anatomical skin biomatrix scaffold with a preserved extracellular matrix (ECM) architecture. We performed proteomic and bioinformatic analyses of the skin scaffold maps of humans, pigs, and rats and systematically analyzed the interaction between ECM proteins and different cell types in the skin microenvironment. These interactions served to quantify the structure and function of the skin's Matrisome comprising core ECM components and ECM-associated soluble signaling molecules required for the regulation of epidermal development. We primarily found that the properties of the skin ECM were species-specific. For example, the composition and function of the ECM of the human skin were more similar to those of pigs compared with those of rats. However, the skin ECM of the pig was significantly deficient in its enzyme systems and immune regulatory factors compared with that of humans. These findings provide a new understanding of the role of the skin ECM niche as well as an attractive strategy that can apply tissue engineering principles to skin biomatrix scaffold materials, which promises to accelerate and enhance tissue regeneration.

Correlation of Fibulin-2 expression with proliferation, migration and invasion of breast cancer cells

Expression level of Fibulin-2 gene in breast cancer cells was evaluated to explore the impact of Fibulin-2 gene on the proliferation, migration and invasion of breast cancer cells. MDA-MB-231, BT483, MCF-7 and SK-BR-3 breast cancer cells were cultured in vitro. Then, expression of Fibulin-2 in cells was upregulated and downregulated using ribonucleic acid interference (RNAi) and lentiviral transfection techniques, respectively. Thereafter, expression levels of Fibulin-2 messenger RNA (mRNA) and protein were measured via quantitative real-time reverse transcription-polymerase chain reaction and western blotting, respectively. Cell Counting Kit-8 assay was applied to detect the proliferation ability, and wound healing assay was performed to determine the effect of transfection on the metastatic capacity of cells. The influence of transfection on the invasive ability of breast cancer cells was detected through Transwell chamber assay. MDA-MB-231 and MCF-7 cells did not express Fibulin-2, while BT483 and SK-BR-3 cells expressed Fibulin-2. Expression of Fibulin-2 mRNA and protein in SK-BR-3 Fibulin-2 siRNA group was significantly lower than that in SK-BR-3 NC siRNA group 48 h after transfection (P<0.01), while the expression of Fibulin-2 mRNA and protein in MDA-MB-231 Fibulin-2 lentiviral transfection (LAP) group was significantly higher than that in MDA-MB-231 NC LAP group. Compared with the MDA-MB-231 NC LAP group, the cell proliferation, migration and invasion ability of MDA-MB-231 Fibulin-2 LAP group were weakened. The tumor volume and weight of the MDA-MB-231 Fibulin-2 LAP group were significantly lower than those of the MDA-MB-231 NC LAP group. Low expression of Fibulin-2 is able to promote proliferation, migration and invasion of breast cancer cells, and can reduce the rate of tumor growth in nude mice. Therefore, Fibulin-2 may be a potential therapeutic target and an indicator of prognosis for breast cancer.

Fibulin-1 Integrates Subendothelial Extracellular Matrices and Contributes to Anatomical Closure of the Ductus Arteriosus

OBJECTIVE

The ductus arteriosus (DA) is a fetal artery connecting the aorta and pulmonary arteries. Progressive matrix remodeling, that is, intimal thickening (IT), occurs in the subendothelial region of DA to bring anatomic DA closure. IT is comprised of multiple ECMs (extracellular matrices) and migrated smooth muscle cells (SMCs). Because glycoprotein fibulin-1 binds to multiple ECMs and regulates morphogenesis during development, we investigated the role of fibulin-1 in DA closure. Approach and Results: Fibulin-1-deficient (Fbln1^-/-) mice exhibited patent DA with hypoplastic IT. An unbiased transcriptome analysis revealed that EP4 (prostaglandin E receptor 4) stimulation markedly increased fibulin-1 in DA-SMCs via phospholipase C-NFκB (nuclear factor κB) signaling pathways. Fluorescence-activated cell sorting (FACS) analysis demonstrated that fibulin-1 binding protein versican was derived from DA-endothelial cells (ECs). We examined the effect of fibulin-1 on directional migration toward ECs in association with versican by using cocultured DA-SMCs and ECs. EP4 stimulation promoted directional DA-SMC migration toward ECs, which was attenuated by either silencing fibulin-1 or versican. Immunofluorescence demonstrated that fibulin-1 and versican V0/V1 were coexpressed at the IT of wild-type DA, whereas 30% of versican-deleted mice lacking a hyaluronan binding site displayed patent DA. Fibulin-1 expression was attenuated in the EP4-deficient mouse (Ptger4^-/-) DA, which exhibits patent DA with hypoplastic IT, and fibulin-1 protein administration restored IT formation. In human DA, fibulin-1 and versican were abundantly expressed in SMCs and ECs, respectively.

CONCLUSIONS

Fibulin-1 contributes to DA closure by forming an environment favoring directional SMC migration toward the subendothelial region, at least, in part, in combination with EC-derived versican and its binding partner hyaluronan.

Cell Derived Matrix Fibulin-1 Associates With Epidermal Growth Factor Receptor to Inhibit Its Activation, Localization and Function in Lung Cancer Calu-1 Cells

Epidermal Growth Factor Receptor (EGFR) is a known promoter of tumor progression and is overexpressed in lung cancers. Growth factor receptors (including EGFR) are known to interact with extracellular matrix (ECM) proteins, which regulate their activation and function. Fibulin-1 (FBLN1) is a major component of the ECM in lung tissue, and its levels are known to be downregulated in non-small cell lung cancers (NSCLC). To test the possible role FBLN1 isoforms could have in regulating EGFR signaling and function in lung cancer, we performed siRNA mediated knockdown of FBLN1C and FBLN1D in NSCLC Calu-1 cells. Their loss significantly increased basal (with serum) and EGF (Epidermal Growth Factor) mediated EGFR activation without affecting net EGFR levels. Overexpression of FBLN1C and FBLN1D also inhibits EGFR activation confirming their regulatory crosstalk. Loss of FBLN1C and FBLN1D promotes EGFR-dependent cell migration, inhibited upon Erlotinib treatment. Mechanistically, both FBLN1 isoforms interact with EGFR, their association not dependent on its activation. Notably, cell-derived matrix (CDM) enriched FBLN1 binds EGFR. Calu-1 cells plated on CDM derived from FBLN1C and FBLN1D knockdown cells show a significant increase in EGF mediated EGFR activation. This promotes cell adhesion and spreading with active EGFR enriched at membrane ruffles. Both adhesion and spreading on CDMs is significantly reduced by Erlotinib treatment. Together, these findings show FBLN1C/1D, as part of the ECM, can bind and regulate EGFR activation and function in NSCLC Calu-1 cells. They further highlight the role tumor ECM composition could have in influencing EGFR dependent lung cancers.

Extracellular Interactions between Fibulins and Transforming Growth Factor (TGF)-β in Physiological and Pathological Conditions

Transforming growth factor (TGF)-β is a multifunctional peptide growth factor that has a vital role in the regulation of cell growth, differentiation, inflammation, and repair in a variety of tissues, and its dysregulation mediates a number of pathological conditions including fibrotic disorders, chronic inflammation, cardiovascular diseases, and cancer progression. Regulation of TGF-β signaling is multifold, but one critical site of regulation is via interaction with certain extracellular matrix (ECM) microenvironments, as TGF-β is primarily secreted as a biologically inactive form sequestrated into ECM. Several ECM proteins are known to modulate TGF-β signaling via cell–matrix interactions, including thrombospondins, SPARC (Secreted Protein Acidic and Rich in Cystein), tenascins, osteopontin, periostin, and fibulins. Fibulin family members consist of eight ECM glycoproteins characterized by a tandem array of calcium-binding epidermal growth factor-like modules and a common C-terminal domain. Fibulins not only participate in structural integrity of basement membrane and elastic fibers, but also serve as mediators for cellular processes and tissue remodeling as they are highly upregulated during embryonic development and certain disease processes, especially at the sites of epithelial–mesenchymal transition (EMT). Emerging studies have indicated a close relationship between fibulins and TGF-β signaling, but each fibulin plays a different role in a context-dependent manner. In this review, regulatory interactions between fibulins and TGF-β signaling are discussed. Understanding biological roles of fibulins in TGF-β regulation may introduce new insights into the pathogenesis of some human diseases.

The matrix proteins aggrecan and fibulin-1 play a key role in determining aortic stiffness

Stiffening of the aorta is an important independent risk factor for myocardial infarction and stroke. Yet its genetics is complex and little is known about its molecular drivers. We have identified for the first time, tagSNPs in the genes for extracellular matrix proteins, aggrecan and fibulin-1, that modulate stiffness in young healthy adults. We confirmed SNP associations with ex vivo stiffness measurements and expression studies in human donor aortic tissues. Both aggrecan and fibulin-1 were found in the aortic wall, but with marked differences in the distribution and glycosylation of aggrecan reflecting loss of chondroitin-sulphate binding domains. These differences were age-dependent but the striking finding was the acceleration of this process in stiff versus elastic young aortas. These findings suggest that aggrecan and fibulin-1 have critical roles in determining the biomechanics of the aorta and their modification with age could underpin age-related aortic stiffening.

Versican A-subdomain is required for its adequate function in dermal development

Versican, a large chondroitin sulfate (CS) proteoglycan, serves as a structural macromolecule of the extracellular matrix (ECM) and regulates cell behavior. We determined the function of versican in dermal development using Vcan^Δ3/Δ3 mutant mice expressing versican with deleted A-subdomain of the N-terminal G1 domain. The mutant versican showed a decreased hyaluronan (HA)-binding ability and failed to accumulate in the ECM. In the early developmental stage, Vcan^Δ3/Δ3 dermis showed a decrease in versican expression as compared with WT. As development proceeded, versican expression further decreased to a barely detectable level, and Vcan^Δ3/Δ3 mice died at the neonatal period (P0). At P0, Vcan^Δ3/Δ3 dermis exhibited an impaired ECM structure and decreased cell density. While the level of collagen deposition was similar in both genotypes, collagen biosynthesis significantly decreased in Vcan^Δ3/Δ3 fibroblasts as compared with that in wild type (WT). Transforming growth factor β (TGFβ) signaling mediated through the Smad2/3-dependent pathway was down-regulated in Vcan^Δ3/Δ3 fibroblasts and a reduced TGFβ storage in the ECM was observed. Microarray analysis revealed a decrease in the expression levels of transcription factors, early growth response (Egr) 2 and 4, which act downstream of TGFβ signaling. Thus, our results suggest that A-subdomain is necessary for adequate versican expression in dermis and that versican is involved in the formation of the ECM and regulation of TGFβ signaling.

Coralsnake Venomics: Analyses of Venom Gland Transcriptomes and Proteomes of Six Brazilian Taxa

Venom gland transcriptomes and proteomes of six Micrurus taxa (M. corallinus, M. lemniscatus carvalhoi, M. lemniscatus lemniscatus, M. paraensis, M. spixii spixii, and M. surinamensis) were investigated, providing the most comprehensive, quantitative data on Micrurus venom composition to date, and more than tripling the number of Micrurus venom protein sequences previously available. The six venomes differ dramatically. All are dominated by 2-6 toxin classes that account for 91-99% of the toxin transcripts. The M. s. spixii venome is compositionally the simplest. In it, three-finger toxins (3FTxs) and phospholipases A₂ (PLA₂s) comprise >99% of the toxin transcripts, which include only four additional toxin families at levels ≥0.1%. Micrurus l. lemniscatus venom is the most complex, with at least 17 toxin families. However, in each venome, multiple structural subclasses of 3FTXs and PLA₂s are present. These almost certainly differ in pharmacology as well. All venoms also contain phospholipase B and vascular endothelial growth factors. Minor components (0.1-2.0%) are found in all venoms except that of M. s. spixii. Other toxin families are present in all six venoms at trace levels (<0.005%). Minor and trace venom components differ in each venom. Numerous novel toxin chemistries include 3FTxs with previously unknown 8- and 10-cysteine arrangements, resulting in new 3D structures and target specificities. 9-cysteine toxins raise the possibility of covalent, homodimeric 3FTxs or heterodimeric toxins with unknown pharmacologies. Probable muscarinic sequences may be reptile-specific homologs that promote hypotension via vascular mAChRs. The first complete sequences are presented for 3FTxs putatively responsible for liberating glutamate from rat brain synaptosomes. Micrurus C-type lectin-like proteins may have 6-9 cysteine residues and may be monomers, or homo- or heterodimers of unknown pharmacology. Novel KSPIs, 3× longer than any seen previously, appear to have arisen in three species by gene duplication and fusion. Four species have transcripts homologous to the nociceptive toxin, (MitTx) α-subunit, but all six species had homologs to the β-subunit. The first non-neurotoxic, non-catalytic elapid phospholipase A₂s are reported. All are probably myonecrotic. Phylogenetic analysis indicates that the six taxa diverged 15-35 million years ago and that they split from their last common ancestor with Old World elapines nearly 55 million years ago. Given their early diversification, many cryptic micrurine taxa are anticipated.

Glycoproteomic Analysis of Malignant Ovarian Cancer Ascites Fluid Identifies Unusual Glycopeptides

Ovarian cancer is a major cause of cancer mortality among women, largely due to late diagnosis of advanced metastatic disease. More extensive molecular analysis of metastatic ovarian cancer is needed to identify post-translational modifications of proteins, especially glycosylation that is particularly associated with metastatic disease to better understand the metastatic process and identify potential therapeutic targets. Glycoproteins in ascites fluid were enriched by affinity binding to lectins (ConA or WGA) and other affinity matrices. Separate glycomic, proteomic, and glycopeptide analyses were performed. Relative abundances of different N-glycan groups and proteins were identified from ascites fluids and a serum control. Levels of biomarkers CA125, MUC1, and fibronectin were also monitored in OC ascites samples by Western blot analysis. N-Glycan analysis of ascites fluids showed the presence of large, highly fucosylated and sialylated complex and hybrid glycans, some of which were not observed in normal serum. OC ascites glycoproteins, haptoglobin, fibronectin, lumican, fibulin, hemopexin, ceruloplasmin, alpha-1-antitrypsin, and alpha-1-antichymotrypsin were more abundant in OC ascites or not present in serum control samples. Further glycopeptide analysis of OC ascites identified N- and O-glycans in clusterin, hemopexin, and fibulin glycopeptides, some of which are unusual and may be important in OC metastasis.

Fibulin-1 purification from human plasma using affinity chromatography on Factor H-Sepharose

A method is reported to purify Fibulin-1 from human plasma resulting in a 36% recovery. The steps involve removal of the cryoglobulin and the vitamin K dependent proteins followed by polyethylene glycol and ammonium sulfate precipitations, DEAE-Sephadex column chromatography and finally Factor H-Sepharose affinity purification. The procedure is designed to be integrated into an overall scheme for the isolation of over 30 plasma proteins from a single batch of human plasma. Results from mass spectroscopy, SDS-PAGE, and Western blotting indicate that human plasma Fibulin-1 is a single chain of the largest isotype. Functional binding assays demonstrated calcium ion dependent interaction of Fibulin-1 for fibrinogen, fibronectin, and Factor H. The procedure described is the first to our knowledge that enables a large scale purification of Fibulin-1 from human plasma.

Temporospatial expression of fibulin-1 after acute spinal cord injury in rats

OBJECTIVE

Fibulin-1 is a matricellular protein that plays important roles in motility inhibition in a variety of cells and blocks the proliferation of cultured neural stem cells. The biological function of fibulin-1 in the spinal cord has not been fully elucidated.

METHODS

To clarify the expressions and possible functions of fibulin-1 in spinal cord injury (SCI), we performed an acute spinal cord contusion injury model in adult rats. Our work studied the temporospatial expression patterns of fibulin-1.

RESULTS

Western blot analysis revealed that fibulin-1 levels significantly increased 5 days after spinal cord contusion. Immunohistochemistry confirmed an increased number of fibulin-1 immunopositive cells about 2 mm from the lesion site. Moreover, double immunofluorescence labeling suggested that these changes were especially prominent in neurons and microglia.

CONCLUSION

These findings suggest that fibulin-1 may be involved in neuronal apoptosis and microglial activation after SCI.

Versican localizes to the nucleus in proliferating mesenchymal cells

OBJECTIVE

Versican is a versatile and highly interactive chondroitin sulfate proteoglycan that is found in the extracellular matrix (ECM) of many tissues and is a major component of developing and developed lesions in atherosclerotic vascular disease. In this paper, we present data to indicate that versican may have important intracellular functions in addition to its better known roles in the ECM.

METHODS AND RESULTS

Rat aortic smooth muscle cells were fixed and immunostained for versican and images of fluorescently labeled cells were obtained by confocal microscopy. Intracellular versican was detected in the nucleus and cytosol of vascular smooth muscle cells. The use of a synthetic neutralizing peptide eliminated versican immunostaining, demonstrating the specificity of the antibody used in this study. Western blot of pure nuclear extracts confirmed the presence of versican in the nucleus, and multifluorescent immunostaining showed strong colocalization of versican and nucleolin, suggesting a nucleolar localization of versican in nondividing cells. In dividing valve interstitial cells, a strong signal for versican was observed in and around the condensed chromosomes during the various stages of mitosis. Multifluorescent immunostaining for versican and tubulin revealed versican aggregated at opposing poles of the mitotic spindle during metaphase. Knockdown of versican expression using siRNA disrupted the organization of the mitotic spindle and led to the formation of multipolar spindles during metaphase.

CONCLUSIONS

Collectively, these data suggest an intracellular function for versican in vascular cells where it appears to play a role in mitotic spindle organization during cell division. These observations open a new avenue for studies of versican, suggesting even more diverse roles in vascular health and disease.

Proteoglycans in Normal and Healing Skin

Significance: Proteoglycans have a distinct spatial localization in normal skin and are essential for the correct structural development, organization, hydration, and functional properties of this tissue. The extracellular matrix (ECM) is no longer considered to be just an inert supportive material but is a source of directive, spatial and temporal, contextual information to the cells via components such as the proteoglycans. There is a pressing need to improve our understanding of how these important molecules functionally interact with other matrix structures, cells and cellular mediators in normal skin and during wound healing. Recent Advances: New antibodies to glycosaminoglycan side chain components of skin proteoglycans have facilitated the elucidation of detailed localization patterns within skin. Other studies have revealed important proliferative activities of proteinase-generated fragments of proteoglycans and other ECM components (matricryptins). Knockout mice have further established the functional importance of skin proteoglycans in the assembly and homeostasis of the normal skin ECM. Critical Issues: Our comprehension of the molecular and structural complexity of skin as a complex, dynamic, constantly renewing, layered connective tissue is incomplete. The impact of changes in proteoglycans on skin pathology and the wound healing process is recognized as an important area of pathobiology and is an area of intense investigation. Future Directions: Advanced technology is allowing the development of new artificial skins. Recent knowledge on skin proteoglycans can be used to incorporate these molecules into useful adjunct therapies for wound healing and for maintenance of optimal tissue homeostasis in aging skin.

Isolation and purification of versican and analysis of versican proteolysis

Versican is a widely distributed chondroitin sulfate proteoglycan that forms large complexes with the glycosaminoglycan hyaluronan (HA). As a consequence of HA binding to its receptor CD44 and interactions of the versican C-terminal globular (G3) domain with a variety of extracellular matrix proteins, versican is a key component of well-defined networks in pericellular matrix and extracellular matrix. It is crucial for several developmental processes in the embryo and there is increasing interest in its roles in cancer and inflammation. Versican proteolysis by ADAMTS proteases is highly regulated, occurs at specific peptide bonds, and is relevant to several physiological and disease mechanisms. In this chapter, methods are described for the isolation and detection of intact and cleaved versican in tissues using morphologic and biochemical techniques. These, together with the methodologies for purification and analysis of recombinant versican and a versican fragment provided here, are likely to facilitate further progress on the biology of versican and its proteolysis.

Fibulins and their role in cardiovascular biology and disease

Fibulins are a group of extracellular matrix proteins of which many are present in high amounts in the cardiovascular system. They share common biochemical properties and are often found in relation to basement membranes or elastic fibers. Observations in humans with specific mutations in fibulin genes, together with results from genetically engineered mice and data from human cardiovascular tissue suggest that the fibulin family of proteins play important functional roles in the cardiovascular system. Moreover, fibulin-1 circulates in high concentrations in plasma and may function as a cardiovascular disease marker.

Determinants of versican-V1 proteoglycan processing by the metalloproteinase ADAMTS5

Proteolysis of the Glu(441)-Ala(442) bond in the glycosaminoglycan (GAG) β domain of the versican-V1 variant by a disintegrin-like and metalloproteinase domain with thrombospondin type 1 motif (ADAMTS) proteases is required for proper embryo morphogenesis. However, the processing mechanism and the possibility of additional ADAMTS-cleaved processing sites are unknown. We demonstrate here that if Glu(441) is mutated, ADAMTS5 cleaves inefficiently at a proximate upstream site but normally does not cleave elsewhere within the GAGβ domain. Chondroitin sulfate (CS) modification of versican is a prerequisite for cleavage at the Glu(441)-Ala(442) site, as demonstrated by reduced processing of CS-deficient or chondroitinase ABC-treated versican-V1. Site-directed mutagenesis identified the N-terminal CS attachment sites Ser(507) and Ser(525) as essential for processing of the Glu(441)-Ala(442) bond by ADAMTS5. A construct including only these two GAG chains, but not downstream GAG attachment sites, was cleaved efficiently. Therefore, CS chain attachment to Ser(507) and Ser(525) is necessary and sufficient for versican proteolysis by ADAMTS5. Mutagenesis of Glu(441) and an antibody to a peptide spanning Thr(432)-Gly(445) (i.e. containing the scissile bond) reduced versican-V1 processing. ADAMTS5 lacking the C-terminal ancillary domain did not cleave versican, and an ADAMTS5 ancillary domain construct bound versican-V1 via the CS chains. We conclude that docking of ADAMTS5 with two N-terminal GAG chains of versican-V1 via its ancillary domain is required for versican processing at Glu(441)-Ala(442). V1 proteolysis by ADAMTS1 demonstrated a similar requirement for the N-terminal GAG chains and Glu(441). Therefore, versican cleavage can be inhibited substantially by mutation of Glu(441), Ser(507), and Ser(525) or by an antibody to the region of the scissile bond.

The functional diversity of essential genes required for mammalian cardiac development

Genes required for an organism to develop to maturity (for which no other gene can compensate) are considered essential. The continuing functional annotation of the mouse genome has enabled the identification of many essential genes required for specific developmental processes including cardiac development. Patterns are now emerging regarding the functional nature of genes required at specific points throughout gestation. Essential genes required for development beyond cardiac progenitor cell migration and induction include a small and functionally homogenous group encoding transcription factors, ligands and receptors. Actions of core cardiogenic transcription factors from the Gata, Nkx, Mef, Hand, and Tbx families trigger a marked expansion in the functional diversity of essential genes from midgestation onwards. As the embryo grows in size and complexity, genes required to maintain a functional heartbeat and to provide muscular strength and regulate blood flow are well represented. These essential genes regulate further specialization and polarization of cell types along with proliferative, migratory, adhesive, contractile, and structural processes. The identification of patterns regarding the functional nature of essential genes across numerous developmental systems may aid prediction of further essential genes and those important to development and/or progression of disease. genesis 52:713–737, 2014.

Functional analysis of candidate genes in 2q13 deletion syndrome implicates FBLN7 and TMEM87B deficiency in congenital heart defects and FBLN7 in craniofacial malformations

Recurrent 2q13 deletion syndrome is associated with incompletely penetrant severe cardiac defects and craniofacial anomalies. We used an atypical, overlapping 1.34 Mb 2q13 deletion in a patient with pathogenically similar congenital heart defects (CHD) to narrow the putative critical region for CHD to 474 kb containing six genes. To determine which of these genes is responsible for severe cardiac and craniofacial defects noted in the patients with the deletions, we used zebrafish morpholino knockdown to test the function of each orthologue during zebrafish development. Morpholino-antisense-mediated depletion of fibulin-7B, a zebrafish orthologue of fibulin-7 (FBLN7), resulted in cardiac hypoplasia, deficient craniofacial cartilage deposition and impaired branchial arch development. TMEM87B depletion likewise resulted in cardiac hypoplasia but with preserved branchial arch development. Depletion of both fibulin-7B and TMEM87B resulted in more severe defects of cardiac development, suggesting that their concurrent loss may enhance the risk of a severe cardiac defect. We postulate that heterozygous loss of FBLN7 and TMEM87B account for some of the clinical features, including cardiac defects and craniofacial abnormalities associated with 2q13 deletion syndrome.

Genes encoding proteoglycans are associated with the risk of anterior cruciate ligament ruptures

BACKGROUND

Genetic variants within genes involved in fibrillogenesis have previously been implicated in anterior cruciate ligament (ACL) injury susceptibility. Proteoglycans also have important functions in fibrillogenesis and maintaining the structural integrity of ligaments. Genes encoding proteoglycans are plausible candidates to be investigated for associations with ACL injury susceptibility; polymorphisms within genes encoding the proteoglycans aggrecan (ACAN), biglycan (BGN), decorin (DCN), fibromodulin (FMOD) and lumican (LUM) were examined.

METHODS

A case-control genetic association study was conducted. 227 participants with surgically diagnosed ACL ruptures (ACL group) and 234 controls without any history of ACL injury were genotyped for 10 polymorphisms in 5 proteoglycan genes. Inferred haplotypes were constructed for specific regions.

RESULTS

The G allele of ACAN rs1516797 was significantly under-represented in the controls (p=0.024; OR=0.72; 95% CI 0.55 to 0.96) compared with the ACL group. For DCN rs516115, the GG genotype was significantly over-represented in female controls (p=0.015; OR=9.231; 95%CI 1.16 to 73.01) compared with the ACL group and the AA genotype was significantly under-represented in controls (p=0.013; OR=0.33; 95% CI 0.14 to 0.78) compared with the female non-contact ACL injury subgroup. Haplotype analyses implicated regions overlapping ACAN (rs2351491 C>T-rs1042631 T>C-rs1516797 T>G), BGN (rs1126499 C>T-rs1042103 G>A) and LUM-DCN (rs2268578 T>C-rs13312816 A>T-rs516115 A>G) in ACL injury susceptibility.

CONCLUSIONS

These independent associations and haplotype analyses suggest that regions within ACAN, BGN, DCN and a region spanning LUM-DCN are associated with ACL injury susceptibility. Taking into account the functions of these genes, it is reasonable to propose that genetic sequence variability within the genes encoding proteoglycans may potentially modulate the ligament fibril properties.

Versican and the regulation of cell phenotype in disease

BACKGROUND

Versican is an extracellular matrix (ECM) proteoglycan that is present in the pericellular environment of most tissues and increases in many different diseases. Versican interacts with cells to influence the ability of cells to proliferate, migrate, adhere and assemble an ECM.

SCOPE OF REVIEW

The structure of the versican molecule is briefly reviewed and studies highlighting those factors that promote versican synthesis and degradation and their impact on cell phenotype in disease are discussed. Particular attention is given to vascular disease, but other diseases where versican is important are covered as well, most notably different forms of cancers. Attention is given to mechanisms(s) by which versican influences cell behaviors through either direct or indirect processes. Versican produced by either stromal cells or myeloid cells can have a major impact influencing immunity and inflammation. Finally, studies controlling versican accumulation that either delay or inhibit the progression of disease will be highlighted.

MAJOR CONCLUSIONS

Versican is one component of the ECM that can influence the ability of cells to proliferate, migrate, adhere, and remodel the ECM. Targeting versican as a way to control cell phenotype offers a novel approach in the treatment of disease.

SIGNIFICANCE

ECM molecules such as versican contribute to the structural integrity of tissues and interact with cells through direct and indirect means to regulate, in part, cellular events that form the basis of disease. This article is part of a Special Issue entitled Matrix-mediated cell behaviour and properties.

Homotypic versican G1 domain interactions enhance hyaluronan incorporation into fibrillin microfibrils

Versican G1 domain-containing fragments (VG1Fs) have been identified in extracts from the dermis in which hyaluronan (HA)-versican-fibrillin complexes are found. However, the molecular assembly of VG1Fs in the HA-versican-microfibril macrocomplex has not yet been elucidated. Here, we clarify the role of VG1Fs in the extracellular macrocomplex, specifically in mediating the recruitment of HA to microfibrils. Sequential extraction studies suggested that the VG1Fs were not associated with dermal elements through HA binding properties alone. Overlay analyses of dermal tissue sections using the recombinant versican G1 domain, rVN, showed that rVN deposited onto the elastic fiber network. In solid-phase binding assays, rVN bound to isolated nondegraded microfibrils. rVN specifically bound to authentic versican core protein produced by dermal fibroblasts. Furthermore, rVN bound to VG1Fs extracted from the dermis and to nondenatured versican but not to fibrillin-1. Homotypic binding of rVN was also seen. Consistent with these binding properties, macroaggregates containing VG1Fs were detected in high molecular weight fractions of sieved dermal extracts and visualized by electron microscopy, which revealed localization to microfibrils at the microscopic level. Importantly, exogenous rVN enhanced HA recruitment both to isolated microfibrils and to microfibrils in tissue sections in a dose-dependent manner. From these data, we propose that cleaved VG1Fs can be recaptured by microfibrils through VG1F homotypical interactions to enhance HA recruitment to microfibrils.

Plasma levels of the arterial wall protein fibulin-1 are associated with carotid-femoral pulse wave velocity: a cross-sectional study

BACKGROUND

The arterial system in diabetic patients is characterized by generalized non-atherosclerotic alterations in the vascular extracellular matrix causing increased arterial stiffness compared with subjects without diabetes. The underlying pathophysiology remains elusive. The elastin-associated extracellular matrix protein, fibulin-1, was recently found in higher concentrations in the arterial wall and in plasma in patients with long duration type 2 diabetes. Furthermore, plasma fibulin-1 independently predicted total mortality and was associated with pulse pressure, an indirect measure of arterial stiffness. Whether plasma fibulin-1 is associated with arterial stiffness at earlier phases of type 2 diabetes has not been determined.

METHODS

In this cross-sectional study, we examined 90 patients with recently diagnosed type 2 diabetes (< 5 years) and 90 gender- and age-matched controls. Plasma fibulin-1 was measured immunochemically. Arterial stiffness was assessed by carotid-femoral Pulse Wave Velocity (PWV). Differences in means were assessed by t-tests. Associations were assessed by multivariate regression analyses.

RESULTS

Plasma fibulin-1 levels were lower in the diabetic group compared with the control group, 93 ± 28 vs 106 ± 30 μg/mL, p = 0.005. In unadjusted analysis of the total study sample, plasma fibulin-1 was not associated with PWV, p = 0.46. However, with adjustment for the confounders age, gender, mean blood pressure, heart rate, body mass index, diabetes and glomerular filtration rate, a 10 μg/mL increase in plasma fibulin was associated with 0.09 ± 0.04 m/s increase in PWV, p < 0.05. In subgroup analysis, plasma fibulin-1 was associated with PWV in the diabetes group, (0.16 ± 0.07 m/s increase in PWV per 10 μg/mL increase in plasma fibulin-1, p<0.05), but not controls, β = 0.021 ± 0.057 m/s per 10 μg/mL, p = 0.70. The association remained significant in the diabetes group after adjustment for covariates, p < 0.05.

CONCLUSIONS

Plasma fibulin-1 is independently associated with PWV. Yet, as the plasma level of fibulin-1 was lower in patients with recently diagnosed type 2 diabetes than in healthy controls, plasma fibulin-1 levels are not a simple marker of the degree of arterial stiffening. Further studies are needed to determine the exact role of fibulin-1 in arterial stiffness and cardiovascular risk in patients with type 2 diabetes.

The C-type lectin of the aggrecan G3 domain activates complement

Excessive complement activation contributes to joint diseases such as rheumatoid arthritis and osteoarthritis during which cartilage proteins are fragmented and released into the synovial fluid. Some of these proteins and fragments activate complement, which may sustain inflammation. The G3 domain of large cartilage proteoglycan aggrecan interacts with other extracellular matrix proteins, fibulins and tenascins, via its C-type lectin domain (CLD) and has important functions in matrix organization. Fragments containing G3 domain are released during normal aggrecan turnover, but increasingly so in disease. We now show that the aggrecan CLD part of the G3 domain activates the classical and to a lesser extent the alternative pathway of complement, via binding of C1q and C3, respectively. The complement control protein (CCP) domain adjacent to the CLD showed no effect on complement initiation. The binding of C1q to G3 depended on ionic interactions and was decreased in D2267N mutant G3. However, the observed complement activation was attenuated due to binding of complement inhibitor factor H to CLD and CCP domains. This was most apparent at the level of deposition of terminal complement components. Taken together our observations indicate aggrecan CLD as one factor involved in the sustained inflammation of the joint.

The different roles of aggrecan interaction domains

The aggregating proteoglycans of the lectican family are important components of extracellular matrices. Aggrecan is the most well studied of these and is central to cartilage biomechanical properties and skeletal development. Key to its biological function is the fixed charge of the many glycosaminoglycan chains, that provide the basis for the viscoelastic properties necessary for load distribution over the articular surface. This review is focused on the globular domains of aggrecan and their role in anchoring the proteoglycans to other extracellular matrix components. The N-terminal G1 domain is vital in that it binds the proteoglycan to hyaluronan in ternary complex with link protein, retaining the proteoglycan in the tissue. The importance of the C-terminal G3 domain interactions has recently been emphasized by two different human hereditary disorders: autosomal recessive aggrecan-type spondyloepimetaphyseal dysplasia and autosomal dominant familial osteochondritis dissecans. In these two conditions, different missense mutations in the aggrecan C-type lectin repeat have been described. The resulting amino acid replacements affect the ligand interactions of the G3 domain, albeit with widely different phenotypic outcomes.

Therapeutic targeting of hyaluronan in the tumor stroma

The tumor stroma, consisting of non-malignant cells and the extracellular matrix, undergoes significant quantitative and qualitative changes throughout malignant transformation and tumor progression. With increasing recognition of the role of the tumor microenvironment in disease progression, stromal components of the tumor have become attractive targets for therapeutic intervention. Stromal accumulation of the glycosaminoglycan hyaluronan occurs in many tumor types and is frequently associated with a negative disease prognosis. Hyaluronan interacts with other extracellular molecules as well as cellular receptors to form a complex interaction network influencing physicochemical properties, signal transduction, and biological behavior of cancer cells. In preclinical animal models, enzymatic removal of hyaluronan is associated with remodeling of the tumor stroma, reduction of tumor interstitial fluid pressure, expansion of tumor blood vessels and facilitated delivery of chemotherapy. This leads to inhibition of tumor growth and increased survival. Current evidence shows that abnormal accumulation of hyaluronan may be an important stromal target for cancer therapy. In this review we highlight the role of hyaluronan and hyaluronan-mediated interactions in cancer, and discuss historical and recent data on hyaluronidase-based therapies and the effect of hyaluronan removal on tumor growth.

Versican/PG-M is essential for ventricular septal formation subsequent to cardiac atrioventricular cushion development

Versican (Vcan)/proteoglycan (PG)-M is a large chondroitin sulfate proteoglycan which forms a proteoglycan/hyaluronan (HA) aggregate in the extracellular matrix (ECM). We tried to generate the Vcan knockout mice by a conventional method, which resulted in mutant mice Vcan(Δ3/Δ3) whose Vcan lacks the A subdomain of the G1 domain. The Vcan knockout embryos died during the early development stage due to heart defects, but some Vcan(Δ3/Δ3) embryos survived through to the neonatal period. The hearts in Vcan(Δ3/Δ3) newborn mice showed normal cardiac looping, but had ventricular septal defects. Their atrioventricular canal (AVC) cushion was much smaller than those of wild-type (WT) embryos, and the extracellular space for cardiac jelly was narrow. The Vcan deposition in the Vcan(Δ3/Δ3) AVC cushion had decreased, whereas the HA deposition was maintained and condensed. In the tip of ventricular septa, both Vcan and HA had decreased. The cell proliferation based on the number of Ki67-positive cells had remarkably increased in both the AVC cushion and ventricular septa, compared with that of WT embryos. Vcan(Δ3/Δ3) seemed to have endocardial and mesenchymal mixed characteristics. When the ex vivo explant culture of these regions was performed on the collagen gel, hardly any migration to make sufficient space for the ECM construction was apparent. Our results suggest that the proteoglycan aggregates are necessary in both the AVC cushion and ventricular septa to fuse interventricular septa, and the Vcan A subdomain plays an essential role for the interventricular septal formation by constituting the proteoglycan aggregates.

Regional variations in the distribution and colocalization of extracellular matrix proteins in the juvenile bovine meniscus

A deeper understanding of the composition and organization of extracellular matrix molecules in native, healthy meniscus tissue is required to fully appreciate the degeneration that occurs in joint disease and the intricate environment in which an engineered meniscal graft would need to function. In this study, regional variations in the tissue-level and pericellular distributions of collagen types I, II and VI and the proteoglycans aggrecan, biglycan and decorin were examined in the juvenile bovine meniscus. The collagen networks were extensively, but not completely, colocalized, with tissue-level organization that varied with radial position across the meniscus. Type VI collagen exhibited close association with large bundles composed of type I and II collagen and, in contrast to type I and II collagen, was further concentrated in the pericellular matrix. Aggrecan was detected throughout the inner region of the meniscus but was restricted to the pericellular matrix and sheaths of collagen bundles in the middle and outer regions. The small proteoglycans biglycan and decorin exhibited regional variations in staining intensity but were consistently localized in the intra- and/or peri-cellular compartments. These results provide insight into the complex hierarchy of extracellular matrix organization in the meniscus and provide a framework for better understanding meniscal degeneration and disease progression and evaluating potential repair and regeneration strategies.

Interleukin-11 promotes the progress of gastric carcinoma via abnormally expressed versican

Versican, a ubiquitous component of the extracellular matrix (ECM), accumulates both in tumor stroma and cancer cells and is highly regulated by various cytokines. The aberrant expression of versican and its isoforms is known to modulate cell proliferation, differentiation, and migration, all of which are features of the invasion and metastasis of cancer; versican is also known to favour the homeostasis of the ECM. Interleukin-11 (IL-11) is an important cytokine that exhibits a wide variety of biological effects in gastric cancer development. Here, we analysed the expression of versican isoforms and found that the major isoforms expressed by both gastric carcinoma tissue and gastric cell lines were V0 and V1, and V1 was significantly higher in gastric carcinoma tissue. The treatment of the gastric cell lines AGS and MKN45 with rhIL-11 resulted in a significant increase in the expression of V0 and V1. Exogenous IL-11 increased migration in AGS and MKN45 cells, whereas these effects were reversed when the expression of V0 and V1 were abolished by siRNA targeting versican V0/V1. Collectively, these findings suggest that the abnormally expressed versican and its isoforms participate, at least in part, in the progress of gastric carcinoma triggered by IL-11.

Matrikines and the lungs

The extracellular matrix is a complex network of fibrous and nonfibrous molecules that not only provide structure to the lung but also interact with and regulate the behaviour of the cells which it surrounds. Recently it has been recognised that components of the extracellular matrix proteins are released, often through the action of endogenous proteases, and these fragments are termed matrikines. Matrikines have biological activities, independent of their role within the extracellular matrix structure, which may play important roles in the lung in health and disease pathology. Integrins are the primary cell surface receptors, characterised to date, which are used by the matrikines to exert their effects on cells. However, evidence is emerging for the need for co-factors and other receptors for the matrikines to exert their effects on cells. The potential for matrikines, and peptides derived from these extracellular matrix protein fragments, as therapeutic agents has recently been recognised. The natural role of these matrikines (including inhibitors of angiogenesis and possibly inflammation) make them ideal targets to mimic as therapies. A number of these peptides have been taken forward into clinical trials. The focus of this review will be to summarise our current understanding of the role, and potential for highly relevant actions, of matrikines in lung health and disease.

Fibulin-1 is required during cardiac ventricular morphogenesis for versican cleavage, suppression of ErbB2 and Erk1/2 activation, and to attenuate trabecular cardiomyocyte proliferation

BACKGROUND

Trabeculation is an integral component of cardiac ventricular morphogenesis and is dependent on the matrix metalloproteinase, ADAMTS1. A substrate of ADAMTS1 is the proteoglycan versican which is expressed in the developing ventricle and which has been implicated in trabeculation. Fibulin-1 is a versican and ADAMTS1-binding extracellular matrix protein required for ventricular morphogenesis. Here we investigated the involvement of fibulin-1 in ADAMTS1-mediated cleavage of versican in vitro, and the involvement of fibulin-1 in versican cleavage in ventricular morphogenesis.

RESULTS

We show that fibulin-1 is a cofactor for ADAMTS1-dependent in vitro cleavage of versican V1, yielding a 70-kDa amino-terminal fragment. Furthermore, fibulin-1-deficiency in mice was found to cause a significant reduction (>90%) in ventricular levels of the 70-kDa versican V1 cleavage product and a 2-fold increase in trabecular cardiomyocyte proliferation. Decreased versican V1 cleavage and augmented trabecular cardiomyocyte proliferation in fibulin-1 null hearts is accompanied by increased ventricular activation of ErbB2 and Erk1/2. By contrast, versican deficiency was found to lead to decreased cardiomyocyte proliferation and reduced ventricular trabeculation.

CONCLUSION

We conclude that fibulin-1 regulates versican-dependent events in ventricular morphogenesis by promoting ADAMTS1 cleavage of versican leading to suppression of trabecular cardiomyocyte proliferation mediated by the ErbB2-Map kinase pathway.

Pericellular versican regulates the fibroblast-myofibroblast transition: a role for ADAMTS5 protease-mediated proteolysis

The cell and its glycosaminoglycan-rich pericellular matrix (PCM) comprise a functional unit. Because modification of PCM influences cell behavior, we investigated molecular mechanisms that regulate PCM volume and composition. In fibroblasts and other cells, aggregates of hyaluronan and versican are found in the PCM. Dermal fibroblasts from Adamts5(-/-) mice, which lack a versican-degrading protease, ADAMTS5, had reduced versican proteolysis, increased PCM, altered cell shape, enhanced α-smooth muscle actin (SMA) expression and increased contractility within three-dimensional collagen gels. The myofibroblast-like phenotype was associated with activation of TGFβ signaling. We tested the hypothesis that fibroblast-myofibroblast transition in Adamts5(-/-) cells resulted from versican accumulation in PCM. First, we noted that versican overexpression in human dermal fibroblasts led to increased SMA expression, enhanced contractility, and increased Smad2 phosphorylation. In contrast, dermal fibroblasts from Vcan haploinsufficient (Vcan(hdf/+)) mice had reduced contractility relative to wild type fibroblasts. Using a genetic approach to directly test if myofibroblast transition in Adamts5(-/-) cells resulted from increased PCM versican content, we generated Adamts5(-/-);Vcan(hdf/+) mice and isolated their dermal fibroblasts for comparison with dermal fibroblasts from Adamts5(-/-) mice. In Adamts5(-/-) fibroblasts, Vcan haploinsufficiency or exogenous ADAMTS5 restored normal fibroblast contractility. These findings demonstrate that altering PCM versican content through proteolytic activity of ADAMTS5 profoundly influenced the dermal fibroblast phenotype and may regulate a phenotypic continuum between the fibroblast and its alter ego, the myofibroblast. We propose that a physiological function of ADAMTS5 in dermal fibroblasts is to maintain optimal versican content and PCM volume by continually trimming versican in hyaluronan-versican aggregates.

Integrin-mediated cell-matrix interaction in physiological and pathological blood vessel formation

Physiological as well as pathological blood vessel formation are fundamentally dependent on cell-matrix interaction. Integrins, a family of major cell adhesion receptors, play a pivotal role in development, maintenance, and remodeling of the vasculature. Cell migration, invasion, and remodeling of the extracellular matrix (ECM) are integrin-regulated processes, and the expression of certain integrins also correlates with tumor progression. Recent advances in the understanding of how integrins are involved in the regulation of blood vessel formation and remodeling during tumor progression are highlighted. The increasing knowledge of integrin function at the molecular level, together with the growing repertoire of integrin inhibitors which allow their selective pharmacological manipulation, makes integrins suited as potential diagnostic markers and therapeutic targets.