Expression of syndecan-1 in rabbit neointima following de-endothelialization by a balloon catheter

An in situ hybridization study of syndecan family during the late stages of developing mouse molar tooth germ

Expression of syndecan-1, 2, 3, and 4 mRNAs during the late stages of tooth germ formation was investigated by in situ hybridization, using [³⁵S]-UTP-labeled cRNA probes. Syndecan-1 mRNA was mainly expressed in the stellate reticulum and stratum intermedium as well as at the cervical region of dental papilla/dental follicle during E18.5-P3.0. Expression in the dental epithelium was enhanced during the postnatal periods, which was supported by real-time RT-PCR analysis. These spatiotemporal expression patterns may suggest specific roles of syndecan-1 in tooth formation such as tooth eruption or root formation. Syndecan-3 mRNA expression became evident in odontoblasts at E18.5, but compared to collagen type I mRNA, which was strongly expressed at this stage, syndecan-3 expression in odontoblast was restricted in mature odontoblasts beneath the cusps during the postnatal periods. This result was also supported by real-time RT-PCR analysis, and indicated that syndecan-3 may be involved in the progress of dentinogenesis rather than in the initiation of it. Syndecan-4 mRNA roughly showed comparable expression patterns to those of syndecan-3. Syndecan-2 mRNA did not show significant expression during the experimental period, but real-time RT-PCR analysis suggested that syndecan-2 expression might be enhanced with hard tissue formation.

Syndecan-1 regulates alphavbeta3 and alphavbeta5 integrin activation during angiogenesis and is blocked by synstatin, a novel peptide inhibitor

Syndecan-1 (Sdc1) is a matrix receptor shown to associate via its extracellular domain with the α_vβ₃ and α_vβ₅ integrins, potentially regulating cell adhesion, spreading, and invasion of cells expressing these integrins. Using Sdc1 deletion mutants expressed in human mammary carcinoma cells, we identified the active site within the Sdc1 core protein and derived a peptide inhibitor called synstatin (SSTN) that disrupts Sdc1's interaction with these integrins. Because the α_vβ₃ and α_vβ₅ integrins are critical in angiogenesis, a process in which a role for Sdc1 has been uncertain, we used human vascular endothelial cells in vitro to show that the Sdc1 regulatory mechanism is also required for integrin activation on these cells. We found Sdc1 expressed in the vascular endothelium during microvessel outgrowth from aortic explants in vitro and in mouse mammary tumors in vivo. Moreover, we show that SSTN blocks angiogenesis in vitro or when delivered systemically in a mouse model of angiogenesis in vivo, and impairs mammary tumor growth in an orthotopic mouse tumor model. Thus, Sdc1 is a critical regulator of these two important integrins during angiogenesis and tumorigenesis, and is inhibited by the novel SSTN peptide.

Evidence of a role for osteoprotegerin in the pathogenesis of pulmonary arterial hypertension

Pulmonary artery smooth muscle cell (PA-SMC) migration and proliferation are key processes in the pathogenesis of pulmonary arterial hypertension (PAH). Recent information suggests that abnormalities in the bone morphogenetic protein (BMP) receptor 2 (BMP-R2) signaling pathway are important in PAH pathogenesis. It remains unclear whether and how this pathway interacts with, for example, serotonin (5-HT) and inflammation to trigger and/or sustain the development of PAH. The secreted glycoprotein osteoprotegerin (OPG) is emerging as an important regulatory molecule in vascular biology and is modulated by BMPs, 5-HT, and interleukin-1 in other cell types. However, whether OPG is expressed by PA-SMCs within PAH lesions and plays a role in PAH is unknown. Immunohistochemistry of human PAH lesions demonstrated increased OPG expression, and OPG was significantly increased in idiopathic PAH patient serum. Recombinant OPG stimulated proliferation and migration of PA-SMCs in vitro, and BMP-R2 RNA interference increased OPG secretion. Additionally, both 5-HT and interleukin-1 also increased OPG secretion. These data are the first to demonstrate that OPG is increased in PAH and that it can regulate PA-SMC proliferation and migration. OPG may provide a common link between the different pathways associated with the disease, potentially playing an important role in the pathogenesis of PAH.

Immunohistochemical Localization of Syndecan-1 in the Dental Follicle of Postnatal Mouse Teeth

BACKGROUND

Syndecans are cell surface heparan sulfate proteoglycans that modulate the action of growth factors and extracellular matrix components. Syndecan-1 plays important roles during early tooth development, and it is expressed in the dental follicle of fetal tooth germ. However, no studies have followed its expression in the dental follicle during the postnatal period. We hypothesized that syndecan-1 protein expression in the dental follicle may be important for postnatal tooth development, and, thus, examined its expression patterns.

METHODS

Syndecan-1 protein expression in the dental follicle of the lower first molar was investigated by immunohistochemistry using embryonic day (E) 18.5 to 21-day-old (d 21) mice. Immunoelectron microscopy was applied to the dental follicle and pulp cells to confirm its membrane localization in mesenchymal cells.

RESULTS

Strong syndecan-1 immunostaining was maintained in the dental follicle and the adjacent dental pulp surrounded by the Hertwig's epithelial root sheath (HERS) from d 4 to d 14, but reduced staining was noted at d 21 with the near-completion of tooth eruption. Three dimensionally, syndecan-1-positive areas plugged the apical foramina surrounded by HERS. However, immunostaining was detected constantly in the dental follicle and the dental pulp of the lower incisor at d 21. In addition, membrane localization of syndecan-1 protein was confirmed for the first time in mesenchymal cells, including dental follicle and pulp cells, by immunoelectron microscopy.

CONCLUSION

The spatial and temporal expression of syndecan-1 in the dental follicle suggests that this proteoglycan is important for the maintenance of proliferation and/or movement of cells in this region during tooth eruption.

Mechanical strain induces a persistent upregulation of syndecan-1 expression in smooth muscle cells

Syndecan-1 belongs to a family of transmembrane proteoglycans, acts as a coreceptor for growth factor binding, as well as cell-matrix and cell-cell interactions, and is induced in smooth muscle cells (SMCs) following balloon catheter injury. In this report, we investigated syndecan-1 expression in SMCs in response to several distinct biomechanical force profiles and the related syndecan shedding response. Syndecan-1 mRNA expression increased in response to 5% and 10% cyclic strain (24 h: 206 +/- 40% and 278 +/- 33%, respectively, P < 0.05) when compared to unstrained controls. When subjected to 10% cyclic strain for periods of up to 48 h, syndecan-1 mRNA levels remained elevated at 294 +/- 31%. Notably, the SMC mechanosensor mechanism remained responsive after an initial 24 h "preconditioning" period, as evident by a fivefold increase in syndecan-1 gene expression following a change in cyclic stress from 10% to 20% (48 h: 516 +/- 55%, P < 0.05). Of note, similar behavior was not observed in an analysis of syndecan-2 mRNA levels. Commensurate with mRNA responses, mechanical stress induced an increase in cell-associated syndecan-1 protein levels with an associated increase in protein shedding. Given the varied functions of syndecan-1, stress-induced effects on SMC syndecan-1 expression and shedding may represent an additional component of the pro-inflammatory, growth-stimulating pathways that are activated in response to changes in the mechanical microenvironment of the vascular wall. Syndecan-1 expression is uniquely influenced by changes in the phase and magnitude of the local stress field.

Syndecans in wound healing, inflammation and vascular biology

Syndecans are heparan sulphate proteoglycans consisting of a type I transmembrane core protein modified by heparan sulphate and sometimes chondroitin sulphate chains. They are major proteoglycans of many organs including the vasculature, along with glypicans and matrix proteoglycans. Heparan sulphate chains have potential to interact with a wide array of ligands, including many growth factors, cytokines, chemokines and extracellular matrix molecules relevant to growth regulation in vascular repair, hypoxia, angiogenesis and immune cell function. This is consistent with the phenotypes of syndecan knock-out mice, which while viable and fertile, show deficits in tissue repair. Furthermore, there are potentially important changes in syndecan distribution and function described in a variety of human vascular diseases. The purpose of this review is to describe syndecan structure and function, consider the role of syndecan core proteins in transmembrane signalling and also their roles as co-receptors with other major classes of cell surface molecules. Current debates include potential redundancy between syndecan family members, the significance of multiple heparan sulphate interactions, regulation of the cytoskeleton and cell behaviour and the switch between promoter and inhibitor of important cell functions, resulting from protease-mediated shedding of syndecan ectodomains.

Comparative genomics of the syndecans defines an ancestral genomic context associated with matrilins in vertebrates

BACKGROUND

The syndecans are the major family of transmembrane proteoglycans in animals and are known for multiple roles in cell interactions and growth factor signalling during development, inflammatory response, wound-repair and tumorigenesis. Although syndecans have been cloned from several invertebrate and vertebrate species, the extent of conservation of the family across the animal kingdom is unknown and there are gaps in our knowledge of chordate syndecans. Here, we develop a new level of knowledge for the whole syndecan family, by combining molecular phylogeny of syndecan protein sequences with analysis of the genomic contexts of syndecan genes in multiple vertebrate organisms.

RESULTS

We identified syndecan-encoding sequences in representative Cnidaria and throughout the Bilateria. The C1 and C2 regions of the cytoplasmic domain are highly conserved throughout the animal kingdom. We identified in the variable region a universally-conserved leucine residue and a tyrosine residue that is conserved throughout the Bilateria. Of all the genomes examined, only tetrapod and fish genomes encode multiple syndecans. No syndecan-1 was identified in fish. The genomic context of each vertebrate syndecan gene is syntenic between human, mouse and chicken, and this conservation clearly extends to syndecan-2 and -3 in T. nigroviridis. In addition, tetrapod syndecans were found to be encoded from paralogous chromosomal regions that also contain the four members of the matrilin family. Whereas the matrilin-3 and syndecan-1 genes are adjacent in tetrapods, this chromosomal region appears to have undergone extensive lineage-specific rearrangements in fish.

CONCLUSION

Throughout the animal kingdom, syndecan extracellular domains have undergone rapid change and elements of the cytoplasmic domains have been very conserved. The four syndecan genes of vertebrates are syntenic across tetrapods, and synteny of the syndecan-2 and -3 genes is apparent between tetrapods and fish. In vertebrates, each of the four family members are encoded from paralogous genomic regions in which members of the matrilin family are also syntenic between tetrapods and fish. This genomic organization appears to have been set up after the divergence of urochordates (Ciona) and vertebrates. The syndecan-1 gene appears to have been lost relatively early in the fish lineage. These conclusions provide the basis for a new model of syndecan evolution in vertebrates and a new perspective for analyzing the roles of syndecans in cells and whole organisms.

Detection of dissection and remodeling of atherosclerotic lesions in rabbits after balloon angioplasty by magnetic-resonance imaging

OBJECTIVE

To assess the usefulness of magnetic-resonance imaging (MRI) for monitoring acute changes after angioplasty of preexisting lesions in rabbits with basal lesions similar to those observed in humans.

METHODS

A combination of Fogarty balloon injury (1 week after initiation of diet) and a mildly hypercholesterolemic diet (0.2% cholesterol and 5% peanut oil) was used to promote the rapid formation of atherosclerotic lesions in 16 New Zealand white rabbits. After 5 months of the diet, angioplasty was performed on these lesions with a Grüntzig catheter in both iliac arteries and the abdominal aorta. MRI was used to monitor the initial formation of lesions after 3 and 5 months of the diet, and 2 days, 2 weeks, and 1 and 2 months after angioplasty.

RESULTS

The combination of early Fogarty injury and mildly hypercholesterolemic diet induced fibroproliferative lesions similar to type Vb atherosclerotic lesions seen in humans. Angioplasty induced deep dissections at the shoulders of lesions in the majority of animals. These dissections often extended into the media. The cellular, proliferative response after angioplasty was localized and limited to sites of dissection. A significant increase in area of arterial wall was observed after angioplasty at sites of dissection without any loss of lumen. In contrast, proximal and distal to the sites of injury, there was no change in wall area but a transient reduction in lumen area.

CONCLUSIONS

Comparison of MRI results with histology confirmed that changes in the wall and lumen, including small linear dissections in the lesions and arterial remodeling, are detectable by MRI.