New insights into form and function of fibronectin splice variants

Mesenchymal stromal cells: inhibiting PDGF receptors or depleting fibronectin induces mesodermal progenitors with endothelial potential

Realizing the full therapeutic potential of mesenchymal stromal/stem cells (MSCs) awaits improved understanding of mechanisms controlling their fate. Using MSCs cultured as spheroids to recapitulate a three-dimensional cellular environment, we show that perturbing the mesenchymal regulators, platelet-derived growth factor (PDGF) receptors or fibronectin, reverts MSCs toward mesodermal progenitors with endothelial potential that can potently induce neovascularization in vivo. MSCs within untreated spheroids retain their mesenchymal spindle shape with abundant smooth muscle α-actin filaments and fibronectin-rich matrix. Inhibiting PDGF receptors or depleting fibronectin induces rounding and depletes smooth muscle α-actin expression; these cells have characteristics of mesenchymoangioblasts, with enhanced expression of mesendoderm and endoderm transcription factors, prominent upregulation of E-cadherin, and Janus kinase signaling-dependent expression of Oct4A and Nanog. PDGF receptor-inhibited spheroids also upregulate endothelial markers platelet endothelial cell adhesion molecule 1 and vascular endothelial-cadherin and secrete many angiogenic factors, and in vivo they potently stimulate neovascularization, and their MSCs integrate within functional blood vessels that are perfused by the circulation. Thus, MSC potency and vascular induction are regulated by perturbing mesenchymal fate.

Occurrence of soluble supra-molecular FN–fibrin complexes in the plasma of children with recurrent respiratory infection

Objectives

Fibronectin (FN) is able to bind fibrin and FN–fibrin complexes and is found in the plasma of some patients suffering from inflammatory disease. The present study was undertaken to determine whether soluble supra-molecular FN–fibrin complexes were present in the plasma of children with recurrent respiratory infections (RRI).

Design and methods

The frequency of occurrence and relative amounts of the supra-molecular FN–fibrin forms, concentrations of immunoglobulins and numbers of natural killer cells (NK) were determined in the plasma of children with recurrent respiratory infections. The frequencies of these parameters were compared with their frequencies in the plasma of children with acute respiratory infections and plasma from healthy children.

Results

SDS-agarose immunoblotting of patients’ plasma revealed the presence of several additional FN–fibrin bands, with decreasing electrophoretic mobilities and increasing molecular masses of 750 kDa, 1000 kDa, 1300 kDa, 1600 kDa and 1900 kDa. Such FN–fibrin complexes occurred with higher frequency and in larger amounts in the plasma of children with RRI and acute infection than they did in plasma from normal children. Moreover, bands above 1000 kDa were absent in most young healthy individuals. The occurrence of FN–fibrin complexes did not correlate with either immunoglobulin concentrations, or with the number of NK cells.

Conclusions

The occurrence of plasma supra-molecular FN–fibrin complexes is associated with acute and recurrent respiratory infections of children.

Blockade of IL-6 Trans signaling attenuates pulmonary fibrosis

Idiopathic pulmonary fibrosis (IPF) is a lethal lung disease with progressive fibrosis and death within 2-3 y of diagnosis. IPF incidence and prevalence rates are increasing annually with few effective treatments available. Inhibition of IL-6 results in the attenuation of pulmonary fibrosis in mice. It is unclear whether this is due to blockade of classical signaling, mediated by membrane-bound IL-6Rα, or trans signaling, mediated by soluble IL-6Rα (sIL-6Rα). Our study assessed the role of sIL-6Rα in IPF. We demonstrated elevations of sIL-6Rα in IPF patients and in mice during the onset and progression of fibrosis. We demonstrated that protease-mediated cleavage from lung macrophages was important in production of sIL-6Rα. In vivo neutralization of sIL-6Rα attenuated pulmonary fibrosis in mice as seen by reductions in myofibroblasts, fibronectin, and collagen in the lung. In vitro activation of IL-6 trans signaling enhanced fibroblast proliferation and extracellular matrix protein production, effects relevant in the progression of pulmonary fibrosis. Taken together, these findings demonstrate that the production of sIL-6Rα from macrophages in the diseased lung contributes to IL-6 trans signaling that in turn influences events crucial in pulmonary fibrosis.

Extracellular matrix and liver disease

SIGNIFICANCE

The extracellular matrix (ECM) is a dynamic microenvironment that undergoes continuous remodeling, particularly during injury and wound healing. Chronic liver injury of many different etiologies such as viral hepatitis, alcohol abuse, drug-induced liver injury, obesity and insulin resistance, metabolic disorders, and autoimmune disease is characterized by excessive deposition of ECM proteins in response to persistent liver damage.

CRITICAL ISSUES

This review describes the main collagenous and noncollagenous components from the ECM that play a significant role in pathological matrix deposition during liver disease. We define how increased myofibroblasts (MF) from different origins are at the forefront of liver fibrosis and how liver cell-specific regulation of the complex scarring process occurs.

RECENT ADVANCES

Particular attention is paid to the role of cytokines, growth factors, reactive oxygen species, and newly identified matricellular proteins in the regulation of fibrillar type I collagen, a field to which our laboratory has significantly contributed over the years. We compile data from recent literature on the potential mechanisms driving fibrosis resolution such as MF' apoptosis, senescence, and reversal to quiescence.

FUTURE DIRECTIONS

We conclude with a brief description of how epigenetics, an evolving field, can regulate the behavior of MF and of how new "omics" tools may advance our understanding of the mechanisms by which the fibrogenic response to liver injury occurs.

Low level of tracheal cellular fibronectin in extremely premature infants with funisitis: relationship with respiratory distress 1 month after birth

BACKGROUND

Funisitis reflects the fetal systemic inflammatory response in premature infants. Macrophages and neutrophils have been identified as key elements in the inflammatory process of the lungs, and secrete proteases that cause the destruction of the extracellular matrix (ECM). Fibronectin (FN) is the major constituent of the pulmonary ECM and exists in multiple isoforms arising from alternative RNA splicing. Extra domain A (EDA) is the major alternatively spliced segment, and the expression of EDA containing FN (EDA + FN) in the lungs is associated with distal pulmonary cell proliferation during alveolar formation.

OBJECTIVE

To study the relationship between the presence of funisitis and EDA + FN levels in the tracheal aspirate fluid (TAF) of infants of less than 28 weeks' gestation.

METHODS

The subjects included in this study were 26 extremely premature infants of <28 weeks' gestation at <24 hr of age, from whom the TAF was collected. These preterm infants were divided into two groups according to placental histology. The funisitis (+) group (n = 9) was compared with the funisitis (-) group (n = 17). The TAF supernatants were analyzed for IL-1β, IL-6, IL-8, neutrophil elastase, and EDA + FN using enzyme-linked immunosorbent assay (ELISA).

RESULTS

There were no significant differences in gestational age or birthweight between these groups. The funisitis (+) group had a significantly higher ventilator setting (inspired O(2)  × mean airway pressure) at Day 28 than the funisitis (-) group. In the TAF, the concentrations of IL-1β were significantly higher in the funisitis (+) group than in the funisitis (-) group, as were the concentrations of neutrophil elastase. The concentrations of EDA + FN were significantly lower in the funisitis (+) group than in the funisitis (-) group.

CONCLUSIONS

Decreased EDA + FN in TAF might be one of the risk factors leading to respiratory distress in extremely premature infants with funisitis.

Myofibroblast differentiation: main features, biomedical relevance, and the role of reactive oxygen species

SIGNIFICANCE

Myofibroblasts are prototypical fibrotic cells, which are involved in a number of more or less pathological conditions, from foreign body reactions to scarring, from liver, kidney, or lung fibrosis to neoplastic phenomena. The differentiation of precursor cells (not only of fibroblastic nature) is characterized by a complex interplay between soluble factors (growth factors such as transforming growth factor β1, reactive oxygen species [ROS]) and material properties (matrix stiffness).

RECENT ADVANCES

The last 15 years have seen very significant advances in the identification of appropriate differentiation markers, in the understanding of the differentiation mechanism, and above all, the involvement of ROS as causative and persistence factors.

CRITICAL ISSUES

The specific mechanisms of action of ROS remain largely unknown, although evidence suggests that both intracellular and extracellular phenomena play a role.

FUTURE DIRECTIONS

Approaches based on antioxidant (ROS-scavenging) principles and on the potentiation of nitric oxide signaling hold much promise in view of a pharmacological therapy of fibrotic phenomena. However, how to make the active principles available at the target sites is yet a largely neglected issue.

What have we learned about non-involved psoriatic skin from large-scale gene expression studies?

Psoriasis is a chronic inflammatory skin disorder; its genetic background has been widely studied in recent decades. Recognition of novel factors contributing to the pathogenesis of this disorder was facilitated by potent molecular biology tools developed during the 1990s. Large-scale gene expression studies, including differential display and microarray, have been used in experimental dermatology to a great extent; moreover, skin was one of the first organs analyzed using these methods. We performed our first comprehensive gene expression analysis in 2000. With the help of differential display and microarray, we have discovered several novel factors contributing to the inherited susceptibility for psoriasis, including the EDA+ fibronectin splice variant and PRINS. The long non-coding PRINS RNA is expressed at higher levels in non-involved skin compared to healthy and involved psoriatic epidermis and might be a factor contributing cellular stress responses and, specifically, to the development of psoriatic symptoms. This review summarizes the most important results of our large-scale gene expression studies.

Scaffold biomaterials for nano-pathophysiology

This review is intended to provide an overview of tissue engineering strategies using scaffold biomaterials to develop a vascularized tissue engineered construct for nano-pathophysiology. Two primary topics are discussed. The first is the biological or synthetic microenvironments that regulate cell behaviors in pathological conditions and tissue regeneration. Second is the use of scaffold biomaterials with angiogenic factors and/or cells to realize vascularized tissue engineered constructs for nano-pathophysiology. These topics are significantly overlapped in terms of three-dimensional (3-D) geometry of cells and blood vessels. Therefore, this review focuses on neovascularization of 3-D scaffold biomaterials induced by angiogenic factors and/or cells. The novel strategy of this approach in nano-pathophysiology is to utilize the vascularized tissue engineered construct as a tissue model to predict the distribution and subsequent therapeutic efficacy of a drug delivery system with different physicochemical and biological properties.

An intron polymorphism of the fibronectin gene is associated with end-stage knee osteoarthritis in a Han Chinese population: two independent case-control studies

Background

Knee osteoarthritis (OA) is a complex disease involving both biomechanical and metabolic factors that alter the tissue homeostasis of articular cartilage and subchondral bone. The catabolic activities of extracellular matrix degradation products, especially fibronectin (FN), have been implicated in mediating cartilage degradation. Chondrocytes express several members of the integrin family which can serve as receptors for FN including integrins α5β1, αvβ3, and αvβ5. The purpose of this study was to determine whether polymorphisms in the FN (FN-1) and integrin genes are markers of susceptibility to, or severity of, knee OA in a Han Chinese population.

Methods

Two independent case–control studies were conducted on 928 patients with knee OA and 693 healthy controls. Ten single nucleotide polymorphisms (SNPs) of FN-1 and the integrin αV gene (ITGAV) were detected using the ABI 7500 real-time PCR system.

Results

The AT heterozygote in FN-1 (rs940739A/T) was found to be significantly associated with knee OA (adjusted OR = 1.44; 95% CI = 1.16–1.80) in both stages of the study. FN-1 rs6725958C/A and ITGAV rs10174098A/G SNPs were only associated with knee OA when both study groups were combined. Stratifying the participants by Kellgren-Lawrence (KL) score identified significant differences in the FN-1 rs6725958C/A and rs940739 A/T genotypes between patients with grade 4 OA and controls. Haplotype analyses revealed that TGA and TAA were associated with a higher risk of OA, and that TAG conferred a lower risk of knee OA in the combined population.

Conclusions

Our study suggests that the FN-1 rs940739A/T polymorphism may be an important risk factor of genetic susceptibility to knee OA in the Han Chinese population.

FibronectinEDA promotes chronic cutaneous fibrosis through Toll-like receptor signaling

Scleroderma is a progressive autoimmune disease affecting multiple organs. Fibrosis, the hallmark of scleroderma, represents transformation of self-limited wound healing into a deregulated self-sustaining process. The factors responsible for maintaining persistent fibroblast activation in scleroderma and other conditions with chronic fibrosis are not well understood. Toll-like receptor 4 (TLR4) and its damage-associated endogenous ligands are implicated in immune and fibrotic responses. We now show that fibronectin extra domain A (Fn(EDA)) is an endogenous TLR4 ligand markedly elevated in the circulation and lesional skin biopsies from patients with scleroderma, as well as in mice with experimentally induced cutaneous fibrosis. Synthesis of Fn(EDA) was preferentially stimulated by transforming growth factor-β in normal fibroblasts and was constitutively up-regulated in scleroderma fibroblasts. Exogenous Fn(EDA) was a potent stimulus for collagen production, myofibroblast differentiation, and wound healing in vitro and increased the mechanical stiffness of human organotypic skin equivalents. Each of these profibrotic Fn(EDA) responses was abrogated by genetic, RNA interference, or pharmacological disruption of TLR4 signaling. Moreover, either genetic loss of Fn(EDA) or TLR4 blockade using a small molecule mitigated experimentally induced cutaneous fibrosis in mice. These observations implicate the Fn(EDA)-TLR4 axis in cutaneous fibrosis and suggest a paradigm in which aberrant Fn(EDA) accumulation in the fibrotic milieu drives sustained fibroblast activation via TLR4. This model explains how a damage-associated endogenous TLR4 ligand might contribute to converting self-limited tissue repair responses into intractable fibrogenesis in chronic conditions such as scleroderma. Disrupting sustained TLR4 signaling therefore represents a potential strategy for the treatment of fibrosis in scleroderma.

Non-collagenous ECM proteins in blood vessel morphogenesis and cancer

BACKGROUND

The extracellular matrix (ECM) is constituted by diverse composite structures, which determine the specific to each organ, histological architecture and provides cells with biological information, mechanical support and a scaffold for adhesion and migration. The pleiotropic effects of the ECM stem from the dynamic changes in its molecular composition and the ability to remodel in order to effectively regulate biological outcomes. Besides collagens, fibronectin and laminin are two major fiber-forming constituents of various ECM structures.

SCOPE OF REVIEW

This review will focus on the properties and the biological functions of non-collagenous extracellular matrix especially on laminin and fibronectin that are currently emerging as important regulators of blood vessel formation and function in health and disease.

MAJOR CONCLUSIONS

The ECM is a fundamental component of the microenvironment of blood vessels, with activities extending beyond providing a vascular scaffold; extremely versatile it directly or indirectly modulates all essential cellular functions crucial for angiogenesis, including cell adhesion, migration, proliferation, differentiation and lumen formation. Specifically, fibronectin and laminins play decisive roles in blood vessel morphogenesis both during embryonic development and in pathological conditions, such as cancer.

GENERAL SIGNIFICANCE

Emerging evidence demonstrates the importance of ECM function during embryonic development, organ formation and tissue homeostasis. A wealth of data also illustrates the crucial role of the ECM in several human pathophysiological processes, including fibrosis, skeletal diseases, vascular pathologies and cancer. Notably, several ECM components have been identified as potential therapeutic targets for various diseases, including cancer. This article is part of a Special Issue entitled Matrix-mediated cell behaviour and properties.

EDA-containing fibronectin increases proliferation of embryonic stem cells

Embryonic stem cells (ESC) need a set of specific factors to be propagated. They can also grow in conditioned medium (CM) derived from a bovine granulosa cell line BGC (BGC-CM), a medium that not only preserves their main features but also increases ESC´s proliferation rate. The mitogenic properties of this medium were previously reported, ascribing this effect to an alternative spliced generated fibronectin isoform that contains the extra domain A (FN EDA⁺). Here, we investigated if the FN EDA⁺ isoform increased proliferation of mouse and human ES cells. We analyzed cell proliferation using conditioned media produced by different mouse embryonic fibroblast (MEF) lines genetically engineered to express FN constitutively including or excluding the EDA domain (FN EDA^-), and in media supplemented with recombinant peptides containing or not the EDA. We found that the presence of EDA in the medium increased mouse and human ESC’s proliferation rate. Here we showed for the first time that this FN isoform enhances ESC’s proliferation. These findings suggest a possible conserved behavior for regulation of ES cells proliferation by this FN isoform and could contribute to improve their culturing conditions both for research and cell therapy.

Damage-associated molecular patterns and their receptors in upper airway pathologies

Inflammation of the nasal (rhinitis) and sinus mucosa (sinusitis) are prevalent medical conditions of the upper airways that are concurrent in many patients; hence the terminology "rhinosinusitis". The disease status is further defined to be "chronic" in case symptoms persist for more than 12 weeks without resolution. A diverse spectrum of external factors including viral and bacterial insults together with epithelial barrier malfunctions could be implicated in the chronicity of the inflammatory responses in chronic rhinosinusitis (CRS). However, despite massive research efforts in an attempt to unveil the pathophysiology, the exact reason for a lack of resolution still remains poorly understood. A novel set of molecules that could be implicated in sustaining the inflammatory reaction may be found within the host itself. Indeed, besides mediators of inflammation originating from outside, some endogenous intracellular and/or extracellular matrix (ECM) components from the host can be released into the extracellular space upon damage induced during the initial inflammatory reaction where they gain functions distinct from those during normal physiology. These "host-self" molecules are known to modulate inflammatory responses under pathological conditions, potentially preventing resolution and contributing to the development of chronic inflammation. These molecules are collectively classified as damage-associated molecular patterns (DAMPs). This review summarizes the current knowledge regarding DAMPs in upper airway pathologies, also covering those that were previously investigated for their intracellular and/or ECM functions often acting as an antimicrobial agent or implicated in tissue/cell homeostasis, and for which their function as a danger signaling molecule was not assessed. It is, however, of importance to assess these molecules again from a point of view as a DAMP in order to further unravel the pathogenesis of CRS.

Cellular fibronectin expression in human trabecular meshwork and induction by transforming growth factor-β2

PURPOSE

Levels of TGF-β2 are higher in POAG aqueous humor, causing deposition of extracellular matrix (ECM) proteins, including fibronectin (FN), in the glaucomatous human trabecular meshwork (HTM) that may be responsible for elevated IOP. The purpose of this study was to identify the expression of cellular FN (cFN) isoforms (EDA and EDB) in HTM cells and tissues, and to determine whether TGF-β2 can induce cFN expression and fibril formation in cultured HTM cells.

METHODS

Expression of cFN mRNA isoforms and induction by recombinant TGF-β2 (5 ng/mL) were determined by quantitative RT-PCR. The TGF-β2 induction of EDA isoform protein expression and FN fibril formation were analyzed using Western immunoblots and immunocytochemistry (ICC), respectively. Immunohistochemistry (IHC) analysis was used to examine total FN and EDA isoform expression in normal (NTM) and glaucomatous (GTM) trabecular meshwork (TM) tissues.

RESULTS

Both cFN mRNA isoforms were expressed in cultured HTM cells and were induced by TGF-β2 after 2, 4, and 7 days (P < 0.05). Similarly, EDA isoform protein and fibril formation were increased after 4 and 7 days of TGF-β2 treatment. Finally, GTM tissues had significantly greater EDA isoform protein levels (1.7-fold, P < 0.05) compared to NTM tissues.

CONCLUSIONS

This study demonstrated that cFN isoforms are expressed and induced in HTM cells by TGF-β2. Also, increased EDA isoform protein levels were seen in GTM tissues. Our findings suggest that induction of cFN isoform expression in the TM ECM may be a novel pathologic mechanism involved in the TM changes associated with glaucoma.

Regulation of alternative splicing by local histone modifications: potential roles for RNA-guided mechanisms

The molecular mechanisms through which alternative splicing and histone modifications regulate gene expression are now understood in considerable detail. Here, we discuss recent studies that connect these two previously separate avenues of investigation, beginning with the unexpected discoveries that nucleosomes are preferentially positioned over exons and DNA methylation and certain histone modifications also show exonic enrichment. These findings have profound implications linking chromatin structure, histone modification and splicing regulation. Complementary single gene studies provided insight into the mechanisms through which DNA methylation and histones modifications modulate alternative splicing patterns. Here, we review an emerging theme resulting from these studies: RNA-guided mechanisms integrating chromatin modification and splicing. Several groundbreaking papers reported that small noncoding RNAs affect alternative exon usage by targeting histone methyltransferase complexes to form localized facultative heterochromatin. More recent studies provided evidence that pre-messenger RNA itself can serve as a guide to enable precise alternative splicing regulation via local recruitment of histone-modifying enzymes, and emerging evidence points to a similar role for long noncoding RNAs. An exciting challenge for the future is to understand the impact of local modulation of transcription elongation rates on the dynamic interplay between histone modifications, alternative splicing and other processes occurring on chromatin.

Role of pseudoexons and pseudointrons in human cancer

In all eukaryotic organisms, pre-mRNA splicing and alternative splicing processes play an essential role in regulating the flow of information required to drive complex developmental and metabolic pathways. As a result, eukaryotic cells have developed a very efficient macromolecular machinery, called the spliceosome, to correctly recognize the pre-mRNA sequences that need to be inserted in a mature mRNA (exons) from those that should be removed (introns). In healthy individuals, alternative and constitutive splicing processes function with a high degree of precision and fidelity in order to ensure the correct working of this machinery. In recent years, however, medical research has shown that alterations at the splicing level play an increasingly important role in many human hereditary diseases, neurodegenerative processes, and especially in cancer origin and progression. In this minireview, we will focus on several genes whose association with cancer has been well established in previous studies, such as ATM, BRCA1/A2, and NF1. In particular, our objective will be to provide an overview of the known mechanisms underlying activation/repression of pseudoexons and pseudointrons; the possible utilization of these events as biomarkers of tumor staging/grading; and finally, the treatment options for reversing pathologic splicing events.

Tissue-specific and SRSF1-dependent splicing of fibronectin, a matrix protein that controls host cell invasion

Matching sets of human primary fibroblasts cocultured with placenta explants are used to compare tissue capacities to support trophoblast invasion. Substituting endometrium with dermis dramatically reduces EVCT interstitial invasion, a phenomenon related to the ECM fibronectin content, FN alternative splicing, and expression of the SR protein SRSF1.

Cell invasion targets specific tissues in physiological placental implantation and pathological metastasis, which raises questions about how this process is controlled. We compare dermis and endometrium capacities to support trophoblast invasion, using matching sets of human primary fibroblasts in a coculture assay with human placental explants. Substituting endometrium, the natural trophoblast target, with dermis dramatically reduces trophoblast interstitial invasion. Our data reveal that endometrium expresses a higher rate of the fibronectin (FN) extra type III domain A+ (EDA+) splicing isoform, which displays stronger matrix incorporation capacity. We demonstrate that the high FN content of the endometrium matrix, and not specifically the EDA domain, supports trophoblast invasion by showing that forced incorporation of plasma FN (EDA–) promotes efficient trophoblast invasion. We further show that the serine/arginine-rich protein serine/arginine-rich splicing factor 1 (SRSF1) is more highly expressed in endometrium and, using RNA interference, that it is involved in the higher EDA exon inclusion rate in endometrium. Our data therefore show a mechanism by which tissues can be distinguished, for their capacity to support invasion, by their different rates of EDA inclusion, linked to their SRSF1 protein levels. In the broader context of cancer pathology, the results suggest that SRSF1 might play a central role not only in the tumor cells, but also in the surrounding stroma.

The EDA-containing cellular fibronectin induces epithelial-mesenchymal transition in lung cancer cells through integrin α9β1-mediated activation of PI3-K/AKT and Erk1/2

Cellular fibronectin (cFN) is one of the main components of tissue extracellular matrices and is involved in multiple physiologic and pathologic processes such as embryogenesis, wound healing, inflammation and tumor progression. The function of fibronectin in regulating normal cell adhesion and migration is well documented, but its function in cancer progression is only partially unraveled. We have reported previously that fibronectin stimulates the proliferation and survival of non-small lung carcinoma cells through upregulation of pro-oncogenic signals related to cyclooxygenase-2/phosphatidylinositol-3-kinase/protein kinase B (COX-2/PI3-K/AKT)/mammalian target of rapamycin triggered by activation of the integrin α5β1. Here, we extend these studies by showing that fibronectin promotes epithelial-mesenchymal transition (EMT) in lung cancer cells. We found that cFN, but not plasma fibronectin or type 1 collagen, induces lung carcinoma cell scattering in vitro, promotes cell migration and invasion of Matrigel and stimulates the expression of the mesenchymal marker α-smooth muscle actin while decreasing the expression of the epithelial marker E-cadherin through PI3-K and Erk pathways. Interestingly, the extra domain A (EDA) within cFN was found to be crucial for this process, as confirmed by testing cells overexpressing EDA or cells exposed to EDA-containing matrices. We found that the integrin α9, but not α5, mediated cFN-induced EMT as silencing integrin α9 neutralized cFN-induced EMT. Overall, our findings show that the EDA domain within cFN induces EMT in lung carcinoma cells through integrin α9-mediated activation of PI3-K and Erk.

Human seminal fibronectin fragmentation patterns and their domain immunoreactivities in leucocytospermic patients

The aim of the work was to analyse fibronectin (FN) domain immunoreactivities and profiles of FN fragmentation in seminal plasmas of fertile normozoospermic and infertile leucocytospermic male patients. ELISA with domain-specific monoclonal antibodies and immunoblotting were used in these measurements. Immunoblotting of normal and leucocytospermic seminal plasmas revealed the presence of twelve FN bands of ~70-196kDa with nearly identical FN profiles under reducing and non-reducing conditions. The epitopes of the cell-, fibrin-, collagen-binding FN domains and the extra domain A (EDA) FN segment retained the ability to bind their specific monoclonal antibodies, whereas the fibrin-heparin domain (N-terminal end) and the area around the disulfide bridges (C-terminal end) of the FN polypeptide did not show any reactivities with their respective specific antibodies. The mean values of cell- (338.4±138.4 and 398.3±310mgL(-1)), fibrin- (79.1±38.5 and 145.2±188.8mgL(-1)) and collagen-binding (19±19.8 and 50.9±73.4mgL(-1)) FN domain immunoreactivities and the relative amount of (EDA)FN did not show any significant differences between the normal and leucocytospermic groups. The high values of standard deviations for the FN domain immunoreactivities in the leucocytospermic group probably results from different aetiology of leucocytospermia. The profile of FN fragmentation and alterations of FN domain immunoreactivities in seminal plasma may influence their engagement in the fertilisation process. The analysis of seminal FN molecular status would be helpful for selecting the highest quality spermatozoa for use in assisted reproduction techniques.

Syndecan-2 is upregulated in colorectal cancer cells through interactions with extracellular matrix produced by stromal fibroblasts

BACKGROUND

The extracellular matrix (ECM) influences the structure, viability and functions of cells and tissues. Recent evidence indicates that tumor cells and stromal cells interact through direct cell-cell contact, the production of ECM components and the secretion of growth factors. Syndecans are a family of transmembrane heparan sulfate proteoglycans that are involved in cell adhesion, motility, proliferation and differentiation. Syndecan-2 has been found to be highly expressed in colorectal cancer cell lines and appears to be critical for cancer cell behavior. We have examined the effect of stromal fibroblast-produced ECM on the production of proteoglycans by colorectal cancer cell lines.

RESULTS

Our results showed that in a highly metastatic colorectal cancer cell line, HCT-116, syndecan-2 expression is enhanced by fibroblast ECM, while the expression of other syndecans decreased. Of the various components of the stromal ECM, fibronectin was the most important in stimulating the increase in syndecan-2 expression. The co-localization of syndecan-2 and fibronectin suggests that these two molecules are involved in the adhesion of HCT-116 cells to the ECM. Additionally, we demonstrated an increase in the expression of integrins alpha-2 and beta-1, in addition to an increase in the expression of phospho-FAK in the presence of fibroblast ECM. Furthermore, blocking syndecan-2 with a specific antibody resulted in a decrease in cell adhesion, migration, and organization of actin filaments.

CONCLUSIONS

Overall, these results show that interactions between cancer cells and stromal ECM proteins induce significant changes in the behavior of cancer cells. In particular, a shift from the expression of anti-tumorigenic syndecans to the tumorigenic syndecan-2 may have implications in the migratory behavior of highly metastatic tumor cells.

Alterations in molecular status of plasma fibronectin associated with aging of normal human individuals

OBJECTIVES

Senescence, progressive deterioration of many bodily functions might be associated with age-dependent alterations of plasma fibronectin (FN) molecular status (i.e., domain, glycotope, and molecular form expressions).

DESIGN AND METHODS

FN molecular status was analyzed in 127 plasma samples of healthy individuals in groups of newborns, and subjects aged 3-14, 15-39, 41-59, and 60-82 years by FN-ELISA, lectin-FN-ELISA, and immunoblotting using a set of domain-specific monoclonal antibodies, specific lectins, and monoclonal antibody to FN, respectively.

RESULTS

During the first four decades of human life the levels of cell-binding-, carboxyl-terminal-, collagen-, heparin-, and fibrin-domains of plasma FN gradually increased. In subjects aged up to 82 years the cell-binding and carboxyl-terminal FN domain concentrations did not change, while the heparin, fibrin, and collagen domains significantly increased. The relative reactivity of plasma FN with Maackia amurensis lectin, specific to α2,3-linked sialic acid, significantly decreased after birth, reaching a stable level in the subsequent life period, whereas with Sambucus nigra lectin, specific to α2,6-linked sialic acid, it significantly decreased in the 60-82 year old group. Moreover, the appearance of 280-kDa and 320-kDa FN bands, absent in young and mature healthy individuals, was found in the groups of 41-59 and 60-82 year olds.

CONCLUSIONS

The alterations of FN molecular status throughout growth, maturation and senescence might be associated not only with disturbances in the balance of FN production rate and degradation, but concomitantly with conformational rearrangements of FN and its engagement in age-related vascular remodeling processes.

Genetic polymorphisms associated with intervertebral disc degeneration

BACKGROUND CONTEXT

Disc degeneration (DD) is a multifaceted chronic process that alters the structure and function of the intervertebral discs and can lead to painful conditions. The pathophysiology of degeneration is not well understood, but previous studies suggest that certain genetic polymorphisms may be important contributing factors leading to an increased risk of DD.

PURPOSE

To review the genetic factors in DD with a focus on polymorphisms and their putative role in the pathophysiology of degeneration. Elucidating the genetic components that are associated with degeneration could provide insights into the mechanism of the process. Furthermore, defining these relationships and eventually using them in a clinical setting may allow an identification and early intervention for those who are at a high risk for painful DD.

STUDY DESIGN

Literature review.

METHODS

This literature review focused on the studies concerning genetic polymorphisms and their associations with DD.

RESULTS

Genetic polymorphisms in 20 genes have been analyzed in association with DD, including vitamin D receptor, growth differentiation factor 5 (GDF5), aggrecan, collagen Types I, IX, and XI, fibronectin, hyaluronan and proteoglycan link protein 1 (HAPLN1), thrombospondin, cartilage intermediate layer protein (CILP), asporin, MMP1, 2, and 3, parkinson protein 2, E3 ubiquitin protein ligase (PARK2), proteosome subunit β type 9 (PSMB9), tissue inhibitor of metalloproteinase (TIMP), cyclooxygenase-2 (COX2), and IL1α, IL1β, and IL6. Each genetic polymorphism codes for a protein that has a functional role in the pathogenesis of DD.

CONCLUSIONS

There are known associations between several genetic polymorphisms and DD. Of the 20 genes analyzed, polymorphisms in vitamin D receptor, aggrecan, Type IX collagen, asporin, MMP3, IL1, and IL6 show the most promise as functional variants. Genetic studies are crucial for understanding the mechanism of the degeneration. This genetic information could eventually be used as a predictive model for determining a patient's risk for symptomatic DD.

Tissue mechanics and fibrosis

Mechanical forces are essential to the development and progression of fibrosis, and are likely to be as important as soluble factors. These forces regulate the phenotype and proliferation of myofibroblasts and other cells in damaged tissues, the activation of growth factors, the structure and mechanics of the matrix, and, potentially, tissue patterning. Better understanding of the variety and magnitude of forces, the characteristics of those forces in biological tissues, and their impact on fibrosis in multiple tissues is needed and may lead to identification of important new therapeutic targets. This article is part of a Special Issue entitled: Fibrosis: Translation of basic research to human disease.

The myofibroblast matrix: implications for tissue repair and fibrosis

Myofibroblasts, and the extracellular matrix (ECM) in which they reside, are critical components of wound healing and fibrosis. The ECM, traditionally viewed as the structural elements within which cells reside, is actually a functional tissue whose components possess not only scaffolding characteristics, but also growth factor, mitogenic, and other bioactive properties. Although it has been suggested that tissue fibrosis simply reflects an 'exuberant' wound-healing response, examination of the ECM and the roles of myofibroblasts during fibrogenesis instead suggest that the organism may be attempting to recapitulate developmental programmes designed to regenerate functional tissue. Evidence of this is provided by the temporospatial re-emergence of embryonic ECM proteins by fibroblasts and myofibroblasts that induce cellular programmatic responses intended to produce a functional tissue. In the setting of wound healing (or physiological fibrosis), this occurs in a highly regulated and exquisitely choreographed fashion which results in cessation of haemorrhage, restoration of barrier integrity, and re-establishment of tissue function. However, pathological tissue fibrosis, which oftentimes causes organ dysfunction and significant morbidity or mortality, likely results from dysregulation of normal wound-healing processes or abnormalities of the process itself. This review will focus on the myofibroblast ECM and its role in both physiological and pathological fibrosis, and will discuss the potential for therapeutically targeting ECM proteins for treatment of fibrotic disorders.

Matrix metalloproteinase 9 and cellular fibronectin plasma concentrations are predictors of the composite endpoint of length of stay and death in the intensive care unit after severe traumatic brain injury

BACKGROUND

The relationship between severe traumatic brain injury (TBI) and blood levels of matrix metalloproteinase-9 (MMP-9) or cellular fibronectin (c-Fn) has never been reported. In this study, we aimed to assess whether plasma concentrations of MMP-9 and c-Fn could have predictive values for the composite endpoint of intensive care unit (ICU) length of stay (LOS) of survivors and mortality after severe TBI. Secondary outcomes were the state of consciousness measured with the Glasgow Coma Scale (GCS) of survivors at 14 days and Glasgow Outcome Scale Extended (GOSE) at 3 months.

METHODS

Forty-nine patients with abbreviated injury scores of the head region ≥ 4 were included. Blood was sampled at 6, 12, 24 and 48 hours after injury. MMP-9 and c-Fn concentrations were measured by ELISA. The values of MMP-9 and c-Fn, and, for comparison, the value of the GCS on the field of the accident (fGCS), as predictors of the composite outcome of ICU LOS and death were assessed by logistic regression.

RESULTS

There was a linear relationship between maximal MMP-9 concentration, measured during the 6-12-hour period, and maximal c-Fn concentration, measured during the 24-48-hour period. The risk of staying longer than 9 days in the ICU or of dying was increased in patients with a maximal early MMP-9 concentration ≥ 21.6 ng/ml (OR = 5.0; 95% CI: 1.3 to 18.6; p = 0.02) or with a maximal late c-Fn concentration ≥ 7.7 μg/ml (OR = 5.4; 95% CI: 1.4 to 20.8; p = 0.01). A similar risk association was observed with fGCS ≤8 (OR, 4.4; 95% CI, 1.2-15.8; p = 0.02). No relationship was observed between MMP-9, c-Fn concentrations or fGCS and the GCS at 14 days of survivors and GOSE at 3 months.

CONCLUSIONS

Plasma MMP-9 and c-Fn concentrations in the first 48 hours after injury are predictive for the composite endpoint of ICU LOS and death after severe TBI but not for consciousness at 14 days and outcome at 3 months.

Clinical significance of heparanase splice variant (t5) in renal cell carcinoma: evaluation by a novel t5-specific monoclonal antibody

T5 is a novel splice variant of heparanase, an endo-β-D-glucuronidase capable of cleaving heparan sulfate side chains at a limited number of sites. T5 splice variant is endowed with pro-tumorigenic properties, enhancing cell proliferation, anchorage independent growth and tumor xenograft development despite lack of heparan sulfate-degrading activity typical of heparanase. T5 is over expressed in the majority of human renal cell carcinoma biopsies examined, suggesting that this splice variant is clinically relevant. T5 is thought to assume a distinct three-dimensional conformation compared with the wild type heparanase protein. We sought to exploit this presumed feature by generating monoclonal antibodies that will recognize the unique structure of T5 without, or with minimal recognition of heparanase, thus enabling more accurate assessment of the clinical relevance of T5. We provide evidence that such a monoclonal antibody, 9c9, preferentially recognizes T5 compared with heparanase by ELISA, immunoblotting and immunohistochemistry. In order to uncover the clinical significance of T5, a cohort of renal cell carcinoma specimens was subjected to immunostaining applying the 9c9 antibody. Notably, T5 staining intensity was significantly associated with tumor size (p = 0.004) and tumor grade (p = 0.02). Our results suggest that T5 is a functional, pro-tumorigenic entity.

Analysis of protein isoforms: can we do it better?

Protein isoforms/splice variants can play important roles in various biological processes and can potentially be used as biomarkers or therapeutic targets/mediators. Thus, there is a need for efficient and, importantly, accurate methods to distinguish and quantify specific protein isoforms. Since protein isoforms can share a high percentage of amino acid sequence homology and dramatically differ in their cellular concentration, the task for accuracy and efficiency in methodology and instrumentation is challenging. The analysis of intact proteins has been perceived to provide a more accurate and complete result for isoform identification/quantification in comparison to analysis of the corresponding peptides that arise from protein enzymatic digestion. Recently, novel approaches have been explored and developed that can possess the accuracy and reliability important for protein isoform differentiation and isoform-specific peptide targeting. In this review, we discuss the recent development in methodology and instrumentation for enhanced detection of protein isoforms as well as the examples of their biological importance.

Type III and V collagens modulate the expression and assembly of EDA(+) fibronectin in the extracellular matrix of defective Ehlers-Danlos syndrome fibroblasts

BACKGROUND

Alternative splicing of EDA fibronectin (FN) region is a cell type- and development-regulated mechanism controlled by pathological processes, growth factors and extracellular matrix (ECM). Classic and vascular Ehlers-Danlos syndrome (cEDS and vEDS) are connective tissue disorders caused by COL5A1/COL5A2 and COL3A1 gene mutations, leading to an in vivo abnormal collagen fibrillogenesis and to an in vitro defective organisation in the ECM of type V (COLLV) and type III collagen (COLLIII). These defects induce the FN-ECM disarray and the decrease of COLLs and FN receptors, the α2β1 and α5β1 integrins. Purified COLLV and COLLIII restore the COLL-FN-ECMs in both EDS cell strains.

METHODS

Real-time PCR, immunofluorescence microscopy, and Western blotting were used to investigate the effects of COLLs on FN1 gene expression, EDA region alternative splicing, EDA(+)-FN-ECM assembly, α5β1 integrin and EDA(+)-FN-specific α9 integrin subunit organisation, α5β1 integrin and FAK co-regulation in EDS fibroblasts.

RESULTS

COLLV-treated cEDS and COLLIII-treated vEDS fibroblasts up-regulate the FN1 gene expression, modulate the EDA(+) mRNA maturation and increase the EDA(+)-FN levels, thus restoring a control-like FN-ECM, which elicits the EDA(+)-FN-specific α9β1 integrin organisation, recruits the α5β1 integrin and switches on the FAK binding and phosphorylation.

CONCLUSION

COLLs regulate the EDA(+)-FN-ECM organisation at transcriptional and post-transcriptional level and activate the α5β1-FAK complexes. COLLs also recruit the α9β1 integrin involved in the assembly of the EDA(+)-FN-ECM in EDS cells.

GENERAL SIGNIFICANCE

The knowledge of the COLLs-ECM role in FN isotype expression and in EDA(+)-FN-ECM-mediated signal transduction adds insights in the ECM remodelling mechanisms in EDS cells.

Induction of epithelial-mesenchymal transition with O-glycosylated oncofetal fibronectin

Epithelial-mesenchymal transition (EMT) has been shown to play a key role in embryogenesis and cancer progression. We previously found that fibronectin (FN) carrying O-GalNAc at a specific site is selectively expressed in cancer and fetal cells/tissues, and termed oncofetal FN (onfFN). Here, we show that (i) a newly-established monoclonal antibody against FN lacking the O-GalNAc, termed normalFN (norFN), is useful for isolation of onfFN, (ii) onfFN, but not norFN, can induce EMT in human lung carcinoma cells, (iii) onfFN has a synergistic effect with transforming growth factor (TGF)β1 in EMT induction.

Mitogen-activated protein kinase phosphorylation of splicing factor 45 (SPF45) regulates SPF45 alternative splicing site utilization, proliferation, and cell adhesion

The regulation of alternative mRNA splicing factors by extracellular cues and signal transduction cascades is poorly understood. Using an engineered extracellular signal-regulated kinase 2 (ERK2) that can utilize ATP analogs, we have identified the alternative mRNA splicing factor 45 (SPF45), which is overexpressed in cancer, as a novel coimmunoprecipitating ERK2 substrate. ERK2 phosphorylated SPF45 on Thr71 and Ser222 in vitro and in cells in response to H-RasV12, B-RAF-V600E, and activated MEK1. Jun N-terminal kinase 1 (JNK1) and p38α also phosphorylated SPF45 in vitro and associated with SPF45 in cells. SPF45 was differentially phosphorylated in cells by all three mitogen-activated protein (MAP) kinases in response to phorbol myristate acid (PMA), H(2)O(2), UV, and anisomycin stimulation. ERK and p38 activation decreased SPF45-dependent exon 6 exclusion from fas mRNA in a minigene assay in cells. Stable overexpression of SPF45 in SKOV-3 cells dramatically inhibited cell proliferation in a phosphorylation-dependent manner through inhibition of ErbB2 expression. SPF45 overexpression also induced EDA inclusion into fibronectin transcripts and fibronectin expression in a phosphorylation-dependent and -independent manner, respectively, specifically affecting cellular adhesion to a fibronectin matrix. These data identify SPF45 as the first splicing factor regulated by multiple MAP kinase pathways and show effects of both SPF45 overexpression and phosphorylation.

Plasma fibronectin deficiency impedes atherosclerosis progression and fibrous cap formation

Atherosclerotic lesions are asymmetric focal thickenings of the intima of arteries that consist of lipids, various cell types and extracellular matrix (ECM). These lesions lead to vascular occlusion representing the most common cause of death in the Western world. The main cause of vascular occlusion is rupture of atheromatous lesions followed by thrombus formation. Fibronectin (FN) is one of the earliest ECM proteins deposited at atherosclerosis-prone sites and was suggested to promote atherosclerotic lesion formation. Here, we report that atherosclerosis-prone apolipoprotein E-null mice lacking hepatocyte-derived plasma FN (pFN) fed with a pro-atherogenic diet display dramatically reduced FN depositions at atherosclerosis-prone areas, which results in significantly smaller and fewer atherosclerotic plaques. However, the atherosclerotic lesions from pFN-deficient mice lacked vascular smooth muscle cells and failed to develop a fibrous cap. Thus, our results demonstrate that while FN worsens the course of atherosclerosis by increasing the atherogenic plaque area, it promotes the formation of the protective fibrous cap, which in humans prevents plaques rupture and vascular occlusion.

Fibronectin extra domain-A promotes hepatic stellate cell motility but not differentiation into myofibroblasts

BACKGROUND & AIMS

Myofibroblasts are the primary cell type involved in physiologic wound healing and its pathologic counterpart, fibrosis. Cellular fibronectin that contains the alternatively spliced extra domain A (EIIIA) is up-regulated during these processes and is believed to promote myofibroblast differentiation. We sought to determine the requirement for EIIIA in fibrosis and differentiation of myofibroblasts in rodent livers.

METHODS

We used a mechanically tunable hydrogel cell culture system to study differentiation of primary hepatic stellate cells and portal fibroblasts from rats into myofibroblasts. Liver fibrosis was induced in mice by bile duct ligation or administration of thioacetamide.

RESULTS

EIIIA was not required for differentiation of rat hepatic stellate cells or portal fibroblasts into fibrogenic myofibroblasts. Instead, hepatic stellate cells cultured on EIIIA-containing cellular fibronectin formed increased numbers of lamellipodia; their random motility and chemotaxis also increased. These increases required the receptor for EIIIA, the integrin α(9)β(1). In contrast, the motility of portal fibroblasts did not increase on EIIIA, and these cells expressed little α(9)β(1). Male EIIIA(-/-) mice were modestly protected from thioacetamide-induced fibrosis, which requires motile hepatic stellate cells, but not from bile duct ligation-induced fibrosis, in which portal fibroblasts are more important. Notably, myofibroblasts developed during induction of fibrosis with either thioacetamide or bile duct ligation in EIIIA(-/-) mice.

CONCLUSIONS

EIIIA is dispensable for differentiation of hepatic stellate cells and portal fibroblasts to myofibroblasts, both in culture and in mouse models of fibrosis. Our findings, however, indicate a role for EIIIA in promoting stellate cell motility and parenchymal liver fibrosis.

Extra-domain B in oncofetal fibronectin structurally promotes fibrillar head-to-tail dimerization of extracellular matrix protein

The type III extra-domain B (ED-B) is specifically spliced into fibronectin (Fn) during embryogenesis and neoangiogenesis, including many cancers. The x-ray structure of the recombinant four-domain fragment Fn(III)7B89 reveals a tightly associated, extended head-to-tail dimer, which is stabilized via pair-wise shape and charge complementarity. A tendency toward ED-B-dependent dimer formation in solution was supported by size exclusion chromatography and analytical ultracentrifugation. When amending the model with the known three-dimensional structure of the Fn(III)10 domain, its RGD loop as well as the adhesion synergy region in Fn(III)9-10 become displayed on the same face of the dimer; this should allow simultaneous binding of at least two integrins and, thus, receptor clustering on the cell surface and intracellular signaling. Insertion of ED-B appears to stabilize overall head-to-tail dimerization of two separate Fn chains, which, together with alternating homodimer formation via disulfide bridges at the C-terminal Fn tail, should lead to the known macromolecular fibril formation.

A collapsin response mediator protein 2 isoform controls myosin II-mediated cell migration and matrix assembly by trapping ROCK II

Collapsin response mediator protein 2 (CRMP-2) is known as a regulator of neuronal polarity and differentiation through microtubule assembly and trafficking. Here, we show that CRMP-2 is ubiquitously expressed and a splice variant (CRMP-2L), which is expressed mainly in epithelial cells among nonneuronal cells, regulates myosin II-mediated cellular functions, including cell migration. While the CRMP-2 short form (CRMP-2S) is recognized as a substrate of the Rho-GTP downstream kinase ROCK in neuronal cells, a CRMP-2 complex containing 2L not only bound the catalytic domain of ROCK II through two binding domains but also trapped and inhibited the kinase. CRMP-2L protein levels profoundly affected haptotactic migration and the actin-myosin cytoskeleton of carcinoma cells as well as nontransformed epithelial cell migration in a ROCK activity-dependent manner. Moreover, the ectopic expression of CRMP-2L but not -2S inhibited fibronectin matrix assembly in fibroblasts. Underlying these responses, CRMP-2L regulated the kinase activity of ROCK II but not ROCK I, independent of GTP-RhoA levels. This study provides a new insight into CRMP-2 as a controller of myosin II-mediated cellular functions through the inhibition of ROCK II in nonneuronal cells.

Alternatively-spliced extra domain A of fibronectin promotes acute inflammation and brain injury after cerebral ischemia in mice

BACKGROUND AND PURPOSE

The fibronectin isoform containing the alternatively spliced extra domain A (EDA(+)-FN) is normally absent from the circulation, but plasma levels of EDA(+)-FN can become markedly elevated in several human pathological conditions associated with inflammation including ischemic stroke. It remains unknown whether EDA(+)-FN contributes to stroke pathogenesis or is simply an associative marker. Several in vitro studies suggest that EDA(+)-FN can activate Toll-like receptor 4, an innate immune receptor that triggers proinflammatory responses. We undertook a genetic approach in mice to investigate the ability of EDA(+)-FN to mediate inflammatory brain damage in a focal cerebral ischemia/reperfusion injury model.

METHODS

We used genetically modified EDA(+/+) mice, which constitutively express EDA(+)-FN. Extent of injury, neurological outcome, and inflammatory mechanisms were assessed after 1-hour cerebral ischemia/23-hour reperfusion injury and compared with wild-type mice.

RESULTS

We found that EDA(+/+) mice developed significantly larger infarcts and severe neurological deficits that were associated with significant increased neutrophil and macrophage infiltration as quantitated by immunohistochemistry. Additionally, we found upregulation of nuclear factor-κB, cyclo-oxygenase-2, and inflammatory cytokines tumor necrosis factor-α, interleukin-1β, and interleukin-6 in the EDA(+/+) mice compared with wild-type mice. Interestingly, increased brain injury and neurological deficits were largely abrogated in EDA(+/+) mice by treatment with a specific Toll-like receptor 4 inhibitor.

CONCLUSIONS

These findings provide the first evidence that EDA(+)-FN promotes inflammatory brain injury after ischemic stroke and suggest that the elevated levels of plasma EDA(+)-FN observed in chronic inflammatory conditions could worsen injury and outcome in patients after acute stroke.

Anti-citrullinated fibronectin antibodies in rheumatoid arthritis are associated with human leukocyte antigen-DRB1 shared epitope alleles

Introduction

Fibronectin is one of the most abundant proteins present in the inflamed joint. Here, we characterized the citrullination of fibronectin in the joints of rheumatoid arthritis (RA) patients and studied the prevalence, epitope specificity and human leukocyte antigen (HLA) association of autoantibodies against citrullinated fibronectin in RA.

Methods

Citrullinated residues in fibronectin isolated from RA patient synovial fluid were identified by mass spectrometry. The corresponding citrullinated and non-citrullinated peptides were synthesized and used to analyze the presence of autoantibodies to these peptides in RA sera and sera from other diseases and healthy controls by ELISA. The data were compared with risk factors like shared epitope HLA alleles and smoking, and with clinical features.

Results

Five citrullinated residues were identified in fibronectin from RA synovial fluid. RA sera reacted in a citrulline-dependent manner with two out of four citrullinated fibronectin peptides, one of which contains two adjacent citrulline residues, in contrast to non-RA sera, which were not reactive. The most frequently recognized peptide (FN-Cit_1035,1036, LTVGLTXXGQPRQY, in which × represents citrulline) was primarily targeted by anti-CCP (cyclic citrullinated peptide) 2-positive RA patients. Anti-FN-Cit_1035,1036 autoantibodies were detected in 50% of established anti-CCP2-positive RA patients and in 45% of such patients from a early arthritis clinic. These antibodies appeared to be predominantly of the immunoglobulin G (IgG) isotype and to be associated with HLA shared epitope alleles (odds ratio = 2.11).

Conclusions

Fibronectin in the inflamed synovia of RA patients can be citrullinated at least at five positions. Together with the flanking amino acids, three of these citrullinated residues comprise two epitopes recognized by RA autoantibodies. Anti-citrullinated fibronectin peptide antibodies are associated with HLA shared epitope alleles.

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.

Integrins and their extracellular matrix ligands in lymphangiogenesis and lymph node metastasis

In the 1970s, the late Judah Folkman postulated that tumors grow proportionately to their blood supply and that tumor angiogenesis removed this limitation promoting growth and metastasis. Work over the past 40 years, varying from molecular examination to clinical trials, verified this hypothesis and identified a host of therapeutic targets to limit tumor angiogenesis, including the integrin family of extracellular matrix receptors. However, the propensity for some tumors to spread through lymphatics suggests that lymphangiogenesis plays a similarly important role. Lymphangiogenesis inhibitors reduce lymph node metastasis, the leading indicator of poor prognosis, whereas inducing lymphangiogenesis promotes lymph node metastasis even in cancers not prone to lymphatic dissemination. Recent works highlight a role for integrins in lymphangiogenesis and suggest that integrin inhibitors may serve as therapeutic targets to limit lymphangiogenesis and lymph node metastasis. This review discusses the current literature on integrin-matrix interactions in lymphatic vessel development and lymphangiogenesis and highlights our current knowledge on how specific integrins regulate tumor lymphangiogenesis.

Fibronectin splice variants: understanding their multiple roles in health and disease using engineered mouse models

The extracellular matrix (ECM) is a highly dynamic network of proteins, glycoproteins, and proteoglycans. Numerous diseases result from mutation in genes coding for ECM proteins, but only recently it has been reported that mutations in the fibronectin (FN) gene were associated with a human disorder. FN is one of the main components of the ECM. It generates protein diversity through alternative splicing of a single pre-mRNA, having at least 20 different isoforms in humans. The precise function of these protein isoforms has remained obscure in most cases. Only in the recent few years, it was possible to shed light on the multiple roles of the alternatively spliced FN isoforms. This substantial progress was achieved basically with the knowledge derived from engineered mouse models bearing subtle mutations in specific FN domains. These data, together with a recent report associating mutations in the FN gene to a form of glomerulopathy, clearly show that mutations in constitutive exons or misregulation of alternatively spliced domains of the FN gene may have nonlethal pathological consequences. In this review, we focus on the pathological consequences of mutations in the FN gene, by connecting the function of alternatively spliced isoforms of fibronectin to human diseases.

Recipient-derived EDA fibronectin promotes cardiac allograft fibrosis

Advances in donor matching and immunosuppressive therapies have decreased the prevalence of acute rejection of cardiac grafts; however, chronic rejection remains a significant obstacle for long-term allograft survival. While initiating elements of anti-allograft immune responses have been identified, the linkage between these factors and the ultimate development of cardiac fibrosis is not well understood. Tissue fibrosis resembles an exaggerated wound healing response, in which extracellular matrix (ECM) molecules are central. One such ECM molecule is an alternatively spliced isoform of the ubiquitous glycoprotein fibronectin (FN), termed extra domain A-containing cellular fibronectin (EDA cFN). EDA cFN is instrumental in fibrogenesis; thus, we hypothesized that it might also regulate fibrotic remodelling associated with chronic rejection. We compared the development of acute and chronic cardiac allograft rejection in EDA cFN-deficient (EDA(-/-)) and wild-type (WT) mice. While EDA(-/-) mice developed acute cardiac rejection in a manner indistinguishable from WT controls, cardiac allografts in EDA(-/-) mice were protected from fibrosis associated with chronic rejection. Decreased fibrosis was not associated with differences in cardiomyocyte hypertrophy or intra-graft expression of pro-fibrotic mediators. Further, we examined expression of EDA cFN and total FN by whole splenocytes under conditions promoting various T-helper lineages. Conditions supporting regulatory T-cell (Treg) development were characterized by greatest production of total FN and EDA cFN, though EDA cFN to total FN ratios were highest in Th1 cultures. These findings indicate that recipient-derived EDA cFN is dispensable for acute allograft rejection responses but that it promotes the development of fibrosis associated with chronic rejection. Further, conditions favouring the development of regulatory T cells, widely considered graft-protective, may drive production of ECM molecules which enhance deleterious remodelling responses. Thus, EDA cFN may be a therapeutic target for ameliorating fibrosis associated with chronic cardiac allograft rejection.

Cell signals influencing hepatic fibrosis

Liver fibrosis is the result of the entire organism responding to a chronic injury. Every cell type in the liver contributes to the fibrosis. This paper first discusses key intracellular signaling pathways that are induced during liver fibrosis. The paper then examines the effects of these signaling pathways on the major cell types in the liver. This will provide insights into the molecular pathophysiology of liver fibrosis and should identify therapeutic targets.

Comparison of fibronectin in human marginal gingiva and interdental papilla using immunohistochemistry

BACKGROUND

The differences between marginal gingiva and interdental papilla may be due to variation in the molecular composition of these two different anatomical structures. The aim of this study was to evaluate the staining intensity of fibronectin in human marginal gingiva and interdental papilla.

MATERIALS AND METHODS

In a prospective analytical study, 16 healthy subjects needing crown lengthening surgery were selected. All participants were medically healthy, non-smokers, with no medication intake, and a healthy periodontium. During surgery, facial/buccal marginal gingiva and interdental papilla were separately harvested. The specimens were subjected to hematoxylin and eosin, histochemical (Masson' strichorom, reticulin, and elastic), and immunohistochemical staining for evaluation of morphology and inflammation; assessment of connective tissue fibers (collagen, reticulin, and elastic); and determination of fibronectin staining intensity. The data were analyzed by Spsssoftware, Wilcoxon, and Spearman tests. P<0.05 was considered to be statistically significant.

RESULTS

From a total of 32 specimens, 21 specimens were found to be normal or having mild inflammation, while the remaining specimens had moderate to severe inflammation in some parts. Collagen fibers were found to be dense in reticular connective tissue and degenerated in the region of inflammation. Reticulin fibers strongly stained near epithelium. Elastic fibers were sparsely found. Mean fibronectin staining intensity between marginal gingiva and interdental papilla was not statically significant (P=0.44). There is no statistically significant correlation between tissue inflammation and fibronectin staining intensity (P=0.76 for marginal gingival and P=0.20 for interdental papilla). Considering all specimens, fibronectin staining intensity of connective tissue adjacent to Sulcular/Junctional epithelium was higher than reticular connective tissue (P=0.003) and higher than connective tissue adjacent to oral epithelium (P<0.001).

CONCLUSION

This study did not show any difference in interdental papilla and marginal gingival with respect to fibronectin composition. More studies in this context are needed.

Involvement of O-glycosylation defining oncofetal fibronectin in epithelial-mesenchymal transition process

The process termed "epithelial-mesenchymal transition" (EMT) was originally discovered in ontogenic development, and has been shown to be one of the key steps in tumor cell progression and metastasis. Recently, we showed that the expression of some glycosphingolipids (GSLs) is down-regulated during EMT in human and mouse cell lines. Here, we demonstrate the involvement of GalNAc-type (or mucin-type) O-glycosylation in EMT process, induced with transforming growth factor β (TGF-β) in human prostate epithelial cell lines. We found that: (i) TGF-β treatment caused up-regulation of oncofetal fibronectin (onfFN), which is defined by mAb FDC6, and expressed in cancer or fetal cells/tissues, but not in normal adult cells/tissues. The reactivity of mAb FDC6 requires the addition of an O-glycan at a specific threonine, inside the type III homology connective segment (IIICS) domain of FN. (ii) This change is associated with typical EMT characteristics; i.e., change from epithelial to fibroblastic morphology, enhanced cell motility, decreased expression of a typical epithelial cell marker, E-cadherin, and enhanced expression of mesenchymal markers. (iii) TGF-β treatment up-regulated mRNA level of FN containing the IIICS domain and GalNAc-T activity for the IIICS domain peptide substrate containing the FDC6 onfFN epitope. (iv) Knockdown of GalNAc-T6 and T3 inhibited TGF-β-induced up-regulation of onfFN and EMT process. (v) Involvement of GSLs was not detectable with the EMT process in these cell lines. These findings indicate the important functional role of expression of onfFN, defined by site-specific O-glycosylation at IIICS domain, in the EMT process.