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.

Effects of Fibroblast Growth Factor 2 on Burn Injury and Repair Process: Analysis Using a Refined Mouse Model.

BACKGROUND: Burn injury is one of the most debilitating traumas, which induces multiple organ dysfunctions, resulting in high levels of morbidity and mortality. Fibroblast growth factor 2 (FGF2) has been applied to burn injury, whose precise mechanisms underlying facilitating the healing have not been fully understood. Although various animal models have been developed in pigs, rabbits, rats, and mice, no mouse model that creates burns consistent in their extent and depth have not been developed. Here, we developed a mouse burn model, and investigated details of the burn process, and elucidated the mechanisms of FGF2 effects. METHODS: A device with an 8-mm metal probe and a temperature controller was developed, which controls the temperature of the probe. Using the device, 1 or 2 of full-thickness burn injuries were generated on the back under catagen/telogen of 6-month-old C57BL/6 male mice. After 24 hours, FGF2 or phosphate-buffered saline was injected into the injured region, and at days 3, 5, and 7, histological and immunohistochemical analysis was performed to observe the injury and repair process. RESULTS: The device constantly generated a mouse full-thickness burn injury. The repair was initiated on the bottom of the burn as well as the margin. Local treatment with FGF2 displayed higher levels of immunostaining for both CD31+ and alpha-smooth muscle actin. CONCLUSIONS: The device we developed is useful to generate a mouse burn injury model. FGF2 facilitates tissue repair with an increased number of both CD31+ and αSMA+ cells.

Regulation of Macrophage and Dendritic Cell Function by Chondroitin Sulfate in Innate to Antigen-Specific Adaptive Immunity.

Chondroitin sulfate (CS), a type of glycosaminoglycan (GAG), is a linear acidic polysaccharide comprised of repeating disaccharides, modified with sulfate groups at various positions. Except for hyaluronan (HA), GAGs are covalently bound to core proteins, forming proteoglycans (PGs). With highly negative charges, GAGs interact with a variety of physiologically active molecules, including cytokines, chemokines, and growth factors, and control cell behavior during development and in the progression of diseases, including cancer, infections, and inflammation. Heparan sulfate (HS), another type of GAG, and HA are well reported as regulators for leukocyte migration at sites of inflammation. There have been many reports on the regulation of immune cell function by HS and HA; however, regulation of immune cells by CS has not yet been fully understood. This article focuses on the regulatory function of CS in antigen-presenting cells, including macrophages and dendritic cells, and refers to CSPGs, such as versican and biglycan, and the cell surface proteoglycan, syndecan.

Accumulation of versican facilitates wound healing: Implication of its initial ADAMTS-cleavage site.

Versican is a large chondroitin sulfate/dermatan sulfate proteoglycan in the extracellular matrix, and is expressed at high levels in tissues during development and remodeling in pathological conditions. Its core protein is cleaved at a region close to the N-terminal end of CSß domain by several members of a disintegrin and metalloproteinase with thrombospondin motifs (ADAMTS) family, i.e., ADAMTS-1, 4, 5, 9, 15, and 20. Here, using a CRISPR/Cas9 system, we generated knock-in mice (V1R), which express an ADAMTS cleavage-resistant versican. Some V1R homozygote mice, termed R/R, exhibit syndactyly and organ hemorrhage. In wound healing experiments, R/R wound shows accumulation of versican and activated TGFß-signaling in the early stage, leading to faster healing than wild type wound. Immunostaining for Ki67, CD31, smooth muscle α-actin, periostin demonstrates higher levels of overall cell proliferation and an increased number of endothelial cells and myofibroblasts. Immunostaining for CD11b and qRT-PCR for macrophage markers revealed increased levels of inflammatory cell infiltration, especially those of M1 macrophages. Cultured R/R dermal fibroblasts revealed increased deposition of versican, type I and III collagens, and hyaluronan, and upregulation of Smad2/3 signaling. Taken together, these results demonstrate that the cleavage site determines versican turnover and that versican plays a central role in the provisional matrix during the wound repair.

The plant alkaloid conophylline inhibits matrix formation of fibroblasts.

Conophylline is a Vinca alkaloid from leaves of the tropical plant Ervatamia microphylla and has been shown to mimic the effect of the growth and differentiation factor activin A on pancreatic progenitor cells. However, activin A stimulates fibrosis of pancreatic stellate cells, whereas conophylline inhibits it, suggesting that this compound may serve as an antifibrotic drug. Here we investigated the effects of conophylline on human foreskin fibroblasts, especially focusing on extracellular matrix (ECM) proteins. A gene microarray analysis revealed that conophylline remarkably suppressed expression of the gene for hyaluronan synthase 2 (HAS2) and of its antisense RNA, whereas the expression of collagen genes was unaffected. Of note, immunostaining experiments revealed that conophylline substantially inhibits incorporation of versican and collagens into the ECM in cells treated with transforming growth factor ß (TGFß), which promotes collagen synthesis, but not in cells not treated with TGFß. Moreover, a protein biosynthesis assay disclosed that conophylline decreases collagen biosynthesis, concomitant with a decrease in total protein biosynthesis, indicating that conophylline-mediated inhibition of fibrosis is not specific to collagen synthesis. Conophylline affected neither TGFß-induced nuclear translocation of SMAD family member 2/3 (SMAD2/3) nor phosphorylation of SMAD2. However, conophylline substantially inhibited phosphorylation of extracellular signal-regulated kinase 1/2 (ERK1/2), suggesting that conophylline inhibits HAS2 expression via TGFß-mediated activation of the ERK1/2 pathway. Taken together, our results indicate that conophylline may be a useful inhibitor of ECM formation in fibrosis.

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 VcanΔ3/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, VcanΔ3/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 VcanΔ3/Δ3 mice died at the neonatal period (P0). At P0, VcanΔ3/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 VcanΔ3/Δ3 fibroblasts as compared with that in wild type (WT). Transforming growth factor ß (TGFß) signaling mediated through the Smad2/3-dependent pathway was down-regulated in VcanΔ3/Δ3 fibroblasts and a reduced TGFß 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 TGFß 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 TGFß signaling.

Host stromal versican is essential for cancer-associated fibroblast function to inhibit cancer growth.

The stroma provides a microenvironment that regulates tumor cell behavior. The extracellular matrix (ECM) has long been recognized to be important in tumor cell behavior, and previous studies have revealed the impact of individual matrix molecules on tumor progression. Although several reports have highlighted some central roles of tumor cell-expressed versican, the role of host stromal versican is not yet understood. In this study, we demonstrate that versican is an important molecule in the functional ECM structure and maintaining cancer-associated fibroblasts, using versican-negative QRsP11 fibrosarcoma cells. By their subcutaneous injection with cre-expressing adenoviruses to versican-floxed mice, we demonstrate that loss of host stromal versican facilitates tumor cell proliferation, and following angiogenesis, decreases cancer-associated fibroblasts, diminishes collagen fibers and alters hyaluronan distribution, concomitant with upregulation of hyaluronan, TGFß and VEGF-mediated signaling. When the versican V3 variant consisting of G1 and G3 domains was expressed in tumor cells, it was integrated into the ECM, regained collagen fibers and cancer-associated fibroblasts and resulted in successful recovery of tumor growth inhibition, indicating that whatever cells produce, the G1 and G3 domains are adequate for versican function. Collectively, our results indicate a dynamic function of versican in the ECM that regulates tumor cell behavior. A greater understanding of the regulation of versican expression may contribute to the development of cancer therapies.

Chondroitin sulfate synthase-2 is necessary for chain extension of chondroitin sulfate but not critical for skeletal development.

Chondroitin sulfate (CS) is a linear polysaccharide consisting of repeating disaccharide units of N-acetyl-D-galactosamine and D-glucuronic acid residues, modified with sulfated residues at various positions. Based on its structural diversity in chain length and sulfation patterns, CS provides specific biological functions in cell adhesion, morphogenesis, neural network formation, and cell division. To date, six glycosyltransferases are known to be involved in the biosynthesis of chondroitin saccharide chains, and a hetero-oligomer complex of chondroitin sulfate synthase-1 (CSS1)/chondroitin synthase-1 and chondroitin sulfate synthase-2 (CSS2)/chondroitin polymerizing factor is known to have the strongest polymerizing activity. Here, we generated and analyzed CSS2(-/-) mice. Although they were viable and fertile, exhibiting no overt morphological abnormalities or osteoarthritis, their cartilage contained CS chains with a shorter length and at a similar number to wild type. Further analysis using CSS2(-/-) chondrocyte culture systems, together with siRNA of CSS1, revealed the presence of two CS chain species in length, suggesting two steps of CS chain polymerization; i.e., elongation from the linkage region up to Mr ∼10,000, and further extension. There, CSS2 mainly participated in the extension, whereas CSS1 participated in both the extension and the initiation. Our study demonstrates the distinct function of CSS1 and CSS2, providing a clue in the elucidation of the mechanism of CS biosynthesis.

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.

Chondroitin sulfate synthase-2/chondroitin polymerizing factor has two variants with distinct function.

Chondroitin sulfate (CS) is a polysaccharide consisting of repeating disaccharide units of N-acetyl-D-galactosamine and d-glucuronic acid residues, modified with sulfated residues at various positions. To date six glycosyltransferases for chondroitin synthesis have been identified, and the complex of chondroitin sulfate synthase-1 (CSS1)/chondroitin synthase-1 (ChSy-1) and chondroitin sulfate synthase-2 (CSS2)/chondroitin polymerizing factor is assumed to play a major role in CS biosynthesis. We found an alternative splice variant of mouse CSS2 in a data base that lacks the N-terminal transmembrane domain, contrasting to the original CSS2. Here, we investigated the roles of CSS2 variants. Both the original enzyme and the splice variant, designated CSS2A and CSS2B, respectively, were expressed at different levels and ratios in tissues. Western blot analysis of cultured mouse embryonic fibroblasts confirmed that both enzymes were actually synthesized as proteins and were localized in both the endoplasmic reticulum and the Golgi apparatus. Pulldown assays revealed that either of CSS2A, CSS2B, and CSS1/ChSy-1 heterogeneously and homogeneously interacts with each other, suggesting that they form a complex of multimers. In vitro glycosyltransferase assays demonstrated a reduced glucuronyltransferase activity in CSS2B and no polymerizing activity in CSS2B co-expressed with CSS1, in contrast to CSS2A co-expressed with CSS1. Radiolabeling analysis of cultured COS-7 cells overexpressing each variant revealed that, whereas CSS2A facilitated CS biosynthesis, CSS2B inhibited it. Molecular modeling of CSS2A and CSS2B provided support for their properties. These findings, implicating regulation of CS chain polymerization by CSS2 variants, provide insight in elucidating the mechanisms of CS biosynthesis.

Versican facilitates chondrocyte differentiation and regulates joint morphogenesis.

Versican/PG-M is a large chondroitin sulfate proteoglycan in the extracellular matrix, which is transiently expressed in mesenchymal condensation areas during tissue morphogenesis. Here, we generated versican conditional knock-out mice Prx1-Cre/Vcan(flox/flox), in which Vcan is pruned out by site-specific Cre recombinase driven by the Prx1 promoter. Although Prx1-Cre/Vcan(flox/flox) mice are viable and fertile, they develop distorted digits. Histological analysis of newborn mice reveals hypertrophic chondrocytic nodules in cartilage, tilting of the joint, and a slight delay of chondrocyte differentiation in digits. By immunostaining, whereas the joint interzone of Prx1-Cre/Vcan(+/+) shows an accumulation of TGF-beta, concomitant with versican, that of Prx1-Cre/Vcan(flox/flox) without versican expression exhibits a decreased incorporation of TGF-beta. In a micromass culture system of mesenchymal cells from limb bud, whereas TGF-beta and versican are co-localized in the perinodular regions of developing cartilage in Prx1-Cre/Vcan(+/+), TGF-beta is widely distributed in Prx1-Cre/Vcan(flox/flox). These results suggest that versican facilitates chondrogenesis and joint morphogenesis, by localizing TGF-beta in the extracellular matrix and regulating its signaling.

Alteration of chondroitin sulfate composition on proteoglycan produced by knock-in mouse embryonic fibroblasts whose versican lacks the A subdomain.

Versican/proteoglycan-mesenchymal (PG-M) is a large chondroitin sulfate (CS) proteoglycan of the extracellular matrix (ECM) that is constitutively expressed in adult tissues such as dermis and blood vessels. It serves as a structural macromolecule of the ECM, while in embryonic tissue it is transiently expressed at high levels and regulates cell adhesion, migration, proliferation, and differentiation. Knock-in mouse embryonic (Cspg2(Delta3/Delta3)) fibroblasts whose versican lack the A subdomain of the G1 domain exhibit low proliferation rates and acquire senescence. It was suspected that chondroitin sulfate on versican core protein would be altered when the A subdomain was disrupted, so fibroblasts were made from homozygous Cspg2(Delta3/Delta3) mouse embryos to investigate the hypothesis. Analysis of the resulting versican deposition demonstrated that the total versican deposited in the Cspg2(Delta3/Delta3) fibroblasts culture was approximately 50% of that of the wild type (WT), while the versican deposited in the ECM of Cspg2(Delta3/Delta3) fibroblasts culture was 35% of that of the WT, demonstrating the lower capacity of mutant (Cspg2(Delta3/Delta3)) versican deposited in the ECM. The analysis of CS expression in the Cspg2(Delta3/Delta3) fibroblasts culture compared with wild-type fibroblasts showed that the composition of the non-sulfate chondroitin sulfate isomer on the versican core protein increased in the cell layer but decreased in the culture medium. Interestingly, chondroitin sulfate E isomer was found in the culture medium. The amount of CS in the Cspg2(Delta3/Delta3) cell layer of fibroblasts with mutant versican was dramatically decreased, contrasted to the amount in the culture medium, which increased. It was concluded that the disruption of the A subdomain of the versican molecule leads to lowering of the amount of versican deposited in the ECM and the alteration of the composition and content of CS on the versican molecule.

Versican/PG-M Assembles Hyaluronan into Extracellular Matrix and Inhibits CD44-mediated Signaling toward Premature Senescence in Embryonic Fibroblasts.

Versican/PG-M is a large chondroitin sulfate proteoglycan of the extracellular matrix which interacts with hyaluronan at the N-terminal G1 domain, composed of A, B, and B' subdomains. Recently, we generated knock-in mice Cspg2(Delta3/Delta3), whose versican, without the A subdomain, has decreased hyaluronan (HA) binding affinity, thereby exhibiting reduced deposition of versican in the extracellular matrix. Here, we show that the Cspg2(Delta3/Delta3) fibroblasts within 20 passages proliferate more slowly and acquire senescence. Whereas the extracellular matrix of the wild type fibroblasts exhibited a network structure of hyaluronan and versican, that of the Cspg2(Delta3/Delta3) fibroblasts exhibited approximately 35 and approximately 85% deposition of versican and HA, without such a structure. The Cspg2(Delta3/Delta3) fibroblasts showed a substantial increase of ERK1/2 phosphorylation and expression of senescence markers p53, p21, and p16. Treatment of wild type fibroblasts with hyaluronidase and exogenous hyaluronan enhanced ERK1/2 phosphorylation, and treatment with an anti-CD44 antibody that blocks HA-CD44 interaction inhibited the phosphorylation. These results demonstrate that versican is essential for matrix assembly involving hyaluronan and that diminished versican deposition increases free hyaluronan fragments that interact with CD44 and increase phosphorylation of ERK1/2, leading to cellular senescence.

Mutations and aberrant DNA methylation of the PROX1 gene in hematologic malignancies.

The homeobox gene PROX1 is related to the Drosophila prospero gene, which is expressed in the developing central nervous system and lens-secreting cone cells. We found that the PROX1 gene had missense and nonsense mutations in 4 of 29 hematologic cell lines analyzed. Decreased mRNA expression was also observed in half of these cell lines by RT-PCR. The restoration of PROX1 gene expression after treatment with the demethylating agent 5-aza-2'-deoxycytidine, as well as bisulfite sequencing analysis, indicated that gene silencing is caused by DNA hypermethylation at intron 1. Such hypermethylation was also seen in primary lymphomas (56.3%, 18/32) in a tumor-specific manner. These findings indicate that the profile of the PROX1 gene corresponds to that of a candidate tumor-suppressor gene.

The MAGE-A1 gene expression is not determined solely by methylation status of the promoter region in hematological malignancies.

Tumor antigens such as MAGE-A1 are aberrantly expressed in many human tumors and could be recognized by CTL. Thus, they could be targets for cancer immunotherapy. It is presently considered that the expression of the MAGE-A1 gene is regulated by methylation of its promoter region. To estimate the possibility of activating the MAGE-A1 gene with demethylating agents with a view toward clinical use, we assessed the methylation status of its CpG-rich promoter by sodium bisulfite mapping both of samples that express the gene and those that do not. Cell lines and samples from patients with hematological malignancies were examined. Surprisingly, the methylation status of the MAGE-A1 gene did not clearly correlate with the expression of the gene. Our results indicate that the MAGE-A1 gene expression is not determined solely by the methylation status of the promoter region in hematological malignancies.

Aberrant DNA methylation of p57(KIP2) gene in the promoter region in lymphoid malignancies of B-cell phenotype.

The cyclin-dependent kinase inhibitor p57(KIP2) is thought to be a potential tumor suppressor gene (TSG). The present study examines this possibility. We found that the expression of p57(KIP2) gene is absent in various hematological cell lines. Exposing cell lines to the DNA demethylating agent 5-aza-2'-deoxycytidine restored p57(KIP2) gene expression. Bisulfite sequencing analysis of its promoter region showed that p57(KIP2) DNA was completely methylated in cell lines that did not express the p57(KIP2) gene. Thus, DNA methylation of its promoter might lead to inactivation of the p57(KIP2) gene. DNA methylation of this region is thought to be an aberrant alteration, since DNA was not methylated in normal peripheral blood mononuclear cells or in reactive lymphadenitis. Methylation-specific polymerase chain reaction analysis found frequent DNA methylation of the p57(KIP2) gene in primary diffuse large B-cell lymphoma (54.9%) and in follicular lymphoma (44.0%), but methylation was infrequent in myelodysplastic syndrome and adult T-cell leukemia (3.0% and 2.0%, respectively). These findings directly indicate that the profile of the p57(KIP2) gene corresponds to that of a TSG.