The interactions of cartilage proteoglycans with collagens are determined by their structures

A Bio-inspired Latent TGF-β Conjugated Scaffold Improves Neocartilage Development

In cartilage tissue engineering, active TGF-β is conventionally supplemented in culture medium at highly supraphysiologic doses to accelerate neocartilage development. While this approach enhances cartilage extracellular matrix (ECM) biosynthesis, it further promotes tissue features detrimental to hyaline cartilage function, including the induction of tissue swelling, hyperplasia, hypertrophy, and ECM heterogeneities. In contrast, during native cartilage development, chondrocytes are surrounded by TGF-β configured in a latent complex (LTGF-β), which undergoes cell-mediated activation, giving rise to moderated, physiologic dosing regimens that enhance ECM biosynthesis while avoiding detrimental features associated with TGF-β excesses. Here, we explore a bio-inspired strategy, consisting of LTGF-β-conjugated scaffolds, providing TGF-β exposure regimens that are moderated and uniformly administered throughout the construct. Specifically, we evaluate the performance of LTGF-β scaffolds to improve neocartilage development with bovine chondrocyte-seeded agarose constructs compared to outcomes from active TGF-β media supplementation (MS) at a physiologic 0.3 ng/mL dose (MS-0.3), supraphysiologic 10 ng/mL dose (MS-10), or TGF-β free. For small-size constructs (∅3×2 mm), LTGF-β scaffolds yield neocartilage that achieves native-matched mechanical properties (800-925 kPa) and sGAG content (6.6%-7.1%), while providing a cell morphology and collagen distribution more reminiscent of hyaline cartilage. LTGF-β scaffolds further afford an optimal chondrogenic phenotype, marked by a 12-to 28-fold reduction of COL-I expression relative to TGF-β-free and a 7-to 17-fold reduction of COL-X expression relative to MS-10. Further, for large-size constructs, which approach the dimensions needed for clinical cartilage repair, LTGF-β scaffolds significantly reduce mechanical and biochemical heterogeneities relative to MS-0.3 and MS-10. Overall, the use of LTGF-β scaffolds improves the composition, structure, material properties, and cell phenotype of neocartilage.

Versican binds collagen via its G3 domain and regulates the organization and mechanics of collagenous matrices

Type I collagen is the most abundant structural protein in the body and, with other fibrillar collagens, forms the fibrous network of the extracellular matrix. Another group of extracellular matrix polymers, the glycosaminoglycans, and glycosaminoglycan-modified proteoglycans, play important roles in regulating collagen behaviors and contribute to the compositional, structural, and mechanical complexity of the extracellular matrix. While the binding between collagen and small leucine-rich proteoglycans has been studied in detail, the interactions between collagen and the large bottlebrush proteoglycan versican are not well understood. Here, we report that versican binds collagen directly and regulates collagen structure and mechanics. Versican colocalizes with collagen fibers in vivo and binds to collagen via its C-terminal G3 domain (a non-GAG-modified domain present in all known versican isoforms) in vitro; it promotes the deposition of a highly aligned collagen-rich matrix by fibroblasts. Versican also shows an unexpected effect on the rheology of collagen gels in vitro, causing decreased stiffness and attenuated shear strain stiffening, and the cleavage of versican in the liver results in reduced tissue compression stiffening. Thus, versican is an important collagen-binding partner and plays a role in modulating collagen organization and mechanics.

Age-dependent changes in collagen crosslinks reduce the mechanical toughness of human meniscus

The mechanical resilience of the knee meniscus is provided by a group of structural proteins in the extracellular matrix. Aging can alter the quantity and molecular structure of these proteins making the meniscus more susceptible to debilitating tears. In this study, we determined the effect of aging on the quantity of structural proteins and collagen crosslinks in human lateral meniscus, and examined whether the quantity of these molecules was predictive of tensile toughness (area under the stress-strain curve). Two age groups were tested: a young group under 40 and an older group over 65 years old. Using mass spectrometry, we quantified the abundance of proteins and collagen crosslinks in meniscal tissue that was adjacent to the dumbbell-shaped specimens used to measure uniaxial tensile toughness parallel or perpendicular to the circumferential fiber orientation. We found that the enzymatic collagen crosslink deoxypyridinoline had a significant positive correlation with toughness, and reductions in the quantity of this crosslink with aging were associated with a loss of toughness in the ground substance and fibers. The non-enzymatic collagen crosslink carboxymethyl-lysine increased in quantity with aging, and these increases corresponded to reductions in ground substance toughness. For the collagenous (Types I, II, IV, VI, VIII) and non-collagenous structural proteins (elastin, decorin, biglycan, prolargin) analyzed in this study, only the quantity of collagen VIII was predictive of toughness. This study provides valuable insights on the structure-function relationships of the human meniscus, and how aging causes structural adaptations that weaken the tissue's mechanical integrity.

Porcine nasal septum cartilage-derived decellularized matrix promotes chondrogenic differentiation of human umbilical mesenchymal stem cells without exogenous growth factors

BACKGROUND

In the domain of plastic surgery, nasal cartilage regeneration is of significant importance. The extracellular matrix (ECM) from porcine nasal septum cartilage has shown potential for promoting human cartilage regeneration. Nonetheless, the specific biological inductive factors and their pathways in cartilage tissue engineering remain undefined.

METHODS

The decellularized matrix derived from porcine nasal septum cartilage (PN-DCM) was prepared using a grinding method. Human umbilical cord mesenchymal stem cells (HuMSCs) were cultured on these PN-DCM scaffolds for 4 weeks without exogenous growth factors to evaluate their chondroinductive potential. Subsequently, proteomic analysis was employed to identify potential biological inductive factors within the PN-DCM scaffolds.

RESULTS

Compared to the TGF-β3-cultured pellet model serving as a positive control, the PN-DCM scaffolds promoted significant deposition of a Safranin-O positive matrix and Type II collagen by HuMSCs. Gene expression profiling revealed upregulation of ACAN, COL2A1, and SOX9. Proteomic analysis identified potential chondroinductive factors in the PN-DCM scaffolds, including CYTL1, CTGF, MGP, ITGB1, BMP7, and GDF5, which influence HuMSC differentiation.

CONCLUSION

Our findings have demonstrated that the PN-DCM scaffolds promoted HuMSC differentiation towards a nasal chondrocyte phenotype without the supplementation of exogenous growth factors. This outcome is associated with the chondroinductive factors present within the PN-DCM scaffolds.

Heparanase-mediated histone 3 acetylation regulates VEGF gene transcription in the hyperglycemia and hypoxia human retinal endothelial cells

Heparanase (HPA) is believed that might mediate histone 3 lysine 9 acetylation (H3K9ac) to regulate vascular endothelial growth factor (VEGF) gene expressions in the hyperglycemia and hypoxia human retinal endothelial cells (HRECs). Cultured human retinal endothelial cells (HRECs) in hyperglycemia, hypoxia, siRNA, and normal medium, respectively. Distributions of H3K9ac and HPA in HRECs were analyzed by immunofluorescence. Western blot and real-time PCR were respectively used to evaluate the expression of HPA, H3K9ac, and VEGF. The differences in occupancies of H3K9ac and RNA polymerase II at VEGF gene promoter among three groups were studied by Chromatin immunoprecipitation (ChIP) combined with real-time PCR. Co-immunoprecipitation (Co-IP) was used to measure the status of HPA and H3K9ac. Re-ChIP was used to verify whether HPA and H3K9ac associate to the transcription of VEGF gene. HPA was consistent with that of H3K9ac in the hyperglycemia and hypoxia groups. And the fluorescent lights of H3K9ac and HPA in siRNA groups were similar to the control group, fainter than that of hyperglycemia, hypoxia, and non-silencing groups. Western blot results showed that the expressions of HPA, H3K9ac, and VEGF in hyperglycemia and hypoxia HRECs were statistically higher than that of the control. HPA, H3K9ac, and VEGF expressions in siRNA groups were statistically lower than hyperglycemia and hypoxia HRECs. The same trends also were found in real-time PCR. ChIP exhibited the occupancies of H3K9ac and RNA Pol II at VEGF gene promoter in hyperglycemia and hypoxia groups were significantly more increased than in the control group. Co-IP revealed that HPA combined with H3K9ac in hyperglycemia and hypoxia groups; while it was not discovered in the control group. Re-ChIP showed that HPA combined with H3K9ac at VEGF gene promoter in the hyperglycemia and hypoxia HRECs nuclear. In our study HPA can influence expressions of H3K9ac and VEGF in the hyperglycemia and hypoxia HRECs. HPA can probably combine with H3K9ac and regulate the transcription of the VEGF gene in the hyperglycemia and hypoxia HRECs.

Distinct effects of different matrix proteoglycans on collagen fibrillogenesis and cell-mediated collagen reorganization

The extracellular matrix (ECM) is a complex mixture composed of fibrillar collagens as well as additional protein and carbohydrate components. Proteoglycans (PGs) contribute to the heterogeneity of the ECM and play an important role in its structure and function. While the small leucine rich proteoglycans (SLRPs), including decorin and lumican, have been studied extensively as mediators of collagen fibrillogenesis and organization, the function of large matrix PGs in collagen matrices is less well known. In this study, we showed that different matrix PGs have distinct roles in regulating collagen behaviors. We found that versican, a large chondroitin sulfate PG, promotes collagen fibrillogenesis in a turbidity assay and upregulates cell-mediated collagen compaction and reorganization, whereas aggrecan, a structurally-similar large PG, has different and often opposing effects on collagen. Compared to versican, decorin and lumican also have distinct functions in regulating collagen behaviors. The different ways in which matrix PGs interact with collagen have important implications for understanding the role of the ECM in diseases such as fibrosis and cancer, and suggest that matrix PGs are potential therapeutic targets.

Recombinant Extracellular Matrix Protein Fragments Support Human Embryonic Stem Cell Chondrogenesis

We previously developed a 14-day culture protocol under potentially GMP, chemically defined conditions, to generate chondroprogenitors from human embryonic stem cells (hESCs). In vivo work has confirmed the cartilage repair capacity of these cells in a nude rat osteochondral defect model. Aiming to enhance hESC-chondrogenesis, we screened a range of extracellular matrix (ECM) molecules for their ability to support differentiation of hESCs toward chondrocytes. We identified two novel ECM protein fragments that supported hESC-chondrogenesis: Fibronectin III (fibronectin 7-14 protein fragments, including the RGD domain, syndecan-binding domain, and heparin-binding domain) and fibrillin-1 (FBN1) fragment PF8 (encoded by exons 30-38, residues 1238-1605, which contains the RGD motif but not heparin-binding site). These two protein fragments support hESC-chondrogenesis compared with the substrates routinely used previously (a mixture of fibronectin and gelatin) in our directed chondrogenic protocol. We have identified recombinant fibronectin fragment (FN III) and FBNI fragment (PF8) as alternative coating substrates to promote expression of genes known to regulate chondrocytes and code for chondrocyte ECM components. These recombinant protein fragments are likely to have better batch to batch stability than full-length molecules, especially where extracted from tissue/serum.

Hydrogel based cartilaginous tissue regeneration: recent insights and technologies

Hydrogel based technologies has been extensively employed in both exploratory research and clinical applications to address numerous existing challenges in the regeneration of articular cartilage and intervertebral disc.

A Pathway Toward Tumor Cell-Selective CPPs?

Despite the great potential of CPPs in therapeutics and diagnosis, their application still suffers from a non-negligible drawback: a complete lack of cell-type specificity. In the innumerous routes proposed for CPP cell entry there is common agreement that electrostatic interactions between cationic CPPs and anionic components in membranes, including lipids and glycosaminoglycans, play a crucial role. Tumor cells have been shown to overexpress certain glycosaminoglycans at the cell membrane surface and to possess a higher amount of anionic lipids in their outer leaflet when compared with healthy cells. Such molecules confer tumor cell membranes an enhanced anionic character, a property that could be exploited by CPPs to preferentially target these cells. Herein, these aspects are discussed in an attempt to confer CPPs certain selectivity toward cancer cells.

Dentin sialophosphoprotein (DSPP) plays an essential role in the postnatal development and maintenance of mouse mandibular condylar cartilage

Recently, dentin sialophosphoprotein (DSPP) was found to be expressed in the mandibular condylar cartilage (MCC), but the possible roles of this molecule in the formation, growth, and maintenance of the cartilage are largely unclear. To analyze such roles, we examined Dspp null mice compared with wild-type mice to assess the consequences of Dspp deletion on the morphology and structure of the MCC. Our data showed that DSPP is expressed in the prechondroblastic, chondroblastic, hypertrophic layers of the MCC. Dspp null mice exhibited decreases in the amount of MCC, with reduced formation of articular and prechondroblastic layers in which progenitor cell proliferation levels were distinctly affected. The expression of extracellular matrix molecules, including biglycan and collagen II, IX, and X, was remarkably altered. The findings in this study indicate that continuous DSPP action is required for the growth and/or maintenance of the MCC.

The effect of moving point of contact stimulation on chondrocyte gene expression and localization in tissue engineered constructs

Tissue engineering is a promising approach for articular cartilage repair. However, using current technologies, the developed engineered constructs generally do not possess an organized superficial layer, which contributes to the tissue's durability and unique mechanical properties. In this study, we investigated the efficacy of applying a moving point of contract-type stimulation (MPS) to stimulate the production of a superficial-like layer in the engineered constructs. MPS was applied to chondrocyte-agarose hydrogels at a frequency of 0.5, 1 or 2 Hz, under a constant compressive load of 10 mN for durations between 5 and 60 min over 3 consecutive days. Expression and localization of superficial zone constituents was conducted by qRT-PCR and in situ hybridization. Finite element modeling was also constructed to gain insight into the relationship between the applied stimulus and superficial zone constituent expression. Gene expression of superficial zone markers were affected in a frequency dependent manner with a physiologic frequency of 1 Hz producing maximal expression of PRG4, biglycan, decorin and collagen II. In situ hybridization revealed that localization of these markers predominantly occurred at 500-1000 μm below the construct surface which correlated to sub-surface strains between 10 and 25% as determined by finite element modeling. These results indicate that while mechanical stimuli can be used to enhance the expression of superficial zone constituents in engineered cartilage constructs, the resultant subsurface loading is a critical factor for localizing expression. Future studies will investigate altering the applied stimulus to further localize superficial zone constituent expression at the construct surface.

The regulatory roles of small leucine-rich proteoglycans in extracellular matrix assembly

Small leucine-rich proteoglycans (SLRPs) are involved in a variety of biological and pathological processes. This review focuses on their regulatory roles in matrix assembly. SLRPs have protein cores and hypervariable glycosylation with multivalent binding abilities. During development, differential interactions of SLRPs with other molecules result in tissue-specific spatial and temporal distributions. The changing expression patterns play a critical role in the regulation of tissue-specific matrix assembly and therefore tissue function. SLRPs play significant structural roles within extracellular matrices. In addition, they play regulatory roles in collagen fibril growth, fibril organization and extracellular matrix assembly. Moreover, they are involved in mediating cell-matrix interactions. Abnormal SLRP expression and/or structures result in dysfunctional extracellular matrices and pathophysiology. Altered expression of SLRPs has been found in many disease models, and structural deficiency also causes altered matrix assembly. SLRPs regulate assembly of the extracellular matrix, which defines the microenvironment, modulating both the extracellular matrix and cellular functions, with an impact on tissue function.

The location-specific role of proteoglycans in the flexor carpi ulnaris tendon

Tendons like the flexor carpi ulnaris (FCU) that contain region-specific distributions of proteoglycans (PGs) as a result of the heterogeneous, multi-axial loads they are subjected to in vivo provide valuable models for understanding structure-function relationships in connective tissues. However, the contributions of specific PGs to FCU tendon mechanical properties are unknown. Therefore, the objective of this study was to determine how the location-dependent, viscoelastic mechanical properties of the FCU tendon are impacted individually by PG-associated glycosaminoglycans (GAGs) and by two small leucine-rich proteoglycans (SLRPs), biglycan and decorin. Full length FCU tendons from biglycan- and decorin-null mice were compared to wild-type (WT) mice to evaluate the effects of specific SLRPs, while chondroitinase ABC digestion of isolated specimens removed from the tendon midsubstance was used to determine how chondroitin/dermatan sulfate (CS/DS) GAGs impact mechanics in mature FCU tendons. A novel combined genetic knockout/digestion technique also was employed to compare SLRP-null and WT tendons in the absence of CS/DS GAGs that may impact properties in the mature state. In all genotypes, mechanical properties in the FCU tendon midsubstance were not affected by GAG digestion. Full-length tendons exhibited complex, multi-axial deformation under tension that may be associated with their in vivo loading environment. Mechanical properties were adversely affected by the absence of biglycan, and a decreased modulus localized in the center of the tendon was measured. These results help elucidate the role that local alterations in PG levels may play in processes that adversely impact tendon functionality including injury and pathology.

Propagation and differentiation of human Wharton's jelly stem cells on three-dimensional nanofibrous scaffolds

Stem cells isolated from the Wharton's jelly of the human umbilical cord (hWJSCs) are unique compared to other stem cell types as they lie in between embryonic stem cells (ESCs) and adult mesenchymal stem cells (MSCs) on the developmental map and share stemness markers of ESCs and MSCs. Yet, they do not induce tumorigenesis and are hypoimmunogenic and proliferative and fresh cell numbers can be harvested painlessly in abundance from discarded umbilical cords. Additionally, they secrete important soluble bioactive molecules from the interleukin and cell adhesion family, hyaluronic acid, collagen, glycosoaminoglycans, and chondroitin sulfate. Many of these molecules are involved in bone, cartilage, and joint repair. It has also been shown that hWJSCs attach, proliferate, and differentiate efficiently in the stem cell niches of three-dimensional matrices, particularly nanofibrous scaffolds. Thus, tissue constructs made up of hWJSCs and biodegradable nanofibrous scaffolds will facilitate clinical translation and improved functional outcome for arthritis, bone, and cartilage diseases. When applied in vivo, the hWJSCs from the tissue construct may improve repair either by differentiating into new chondrocytes or osteocytes and/or release of important factors that favor repair through paracrine functions. The nanofibrous scaffold is expected to provide the architecture and niches for the hWJSCs to perform and will later biodegrade encouraging engraftment. This chapter provides a step-by-step protocol for the preparation of such tissue constructs involving hWJSCs and nanofibrous scaffolds. The methodology also includes the targeted in vitro differentiation of the hWJSCs to osteogenic and chondrogenic lineages when attached to the nanofibrous scaffolds.

Non-enzymatic decomposition of collagen fibers by a biglycan antibody and a plausible mechanism for rheumatoid arthritis

Rheumatoid arthritis (RA) is a systemic autoimmune inflammatory and destructive joint disorder that affects tens of millions of people worldwide. Normal healthy joints maintain a balance between the synthesis of extracellular matrix (ECM) molecules and the proteolytic degradation of damaged ones. In the case of RA, this balance is shifted toward matrix destruction due to increased production of cleavage enzymes and the presence of (autoimmune) immunoglobulins resulting from an inflammation induced immune response. Herein we demonstrate that a polyclonal antibody against the proteoglycan biglycan (BG) causes tissue destruction that may be analogous to that of RA affected tissues. The effect of the antibody is more potent than harsh chemical and/or enzymatic treatments designed to mimic arthritis-like fibril de-polymerization. In RA cases, the immune response to inflammation causes synovial fibroblasts, monocytes and macrophages to produce cytokines and secrete matrix remodeling enzymes, whereas B cells are stimulated to produce immunoglobulins. The specific antigen that causes the RA immune response has not yet been identified, although possible candidates have been proposed, including collagen types I and II, and proteoglycans (PG's) such as biglycan. We speculate that the initiation of RA associated tissue destruction in vivo may involve a similar non-enzymatic decomposition of collagen fibrils via the immunoglobulins themselves that we observe here ex vivo.

The bladder extracellular matrix. Part I: architecture, development and disease

From the earliest studies with epithelial cells implanted into detrusor muscle to later experiments on smooth muscle in defined collagen gels, cell niche and extracellular matrix (ECM) have been clearly shown to orchestrate cellular behavior and fate whether quiescent, migratory, or proliferative. Normal matrix can revert transformed cells to quiescence, and damaged matrix can trigger malignancy or dedifferentiation. ECM influence in disease, development, healing and regeneration has been demonstrated in many other fields of study, but a thorough examination of the roles of ECM in bladder cell activity has not yet been undertaken. Structural ECM proteins, in concert with adhesive proteins, provide crucial structural support to the bladder. Both structural and nonstructural components of the bladder have major effects on smooth muscle function, through effects on matrix rigidity and signaling through ECM receptors. While many ECM components and receptors identified in the bladder have specific known functions in the vascular smooth musculature, their function in the bladder is often less well defined. In cancer and obstructive disease, the ECM has a critical role in pathogenesis. The challenge in these settings will be to find therapies that prevent hyperproliferation and encourage proper differentiation, through an understanding of matrix effects on cell biology and susceptibility to therapeutics.

Effect of dermatan sulfate on the indentation and tensile properties of articular cartilage

OBJECTIVE

This paper examines the hypothesis that the dermatan sulfate (DS) chain on decorin is a load carrying element in cartilage and that its damage or removal will alter the material properties.

METHODS

To test this hypothesis, indentation and tensile testing of cartilage from bovine patella were performed before and after digestion with chondroitinase B (cB). Removal of significant amounts of DS by cB digestion was verified by Western blot analysis of proteoglycans extracted from whole and sectioned specimens. Specimens (control and treated) were subjected to a series of step-hold displacements. Elastic modulus during the step rise (rapid modulus) and at equilibrium (equilibrium modulus), and the relaxation function during each step was measured for test (cB and buffer) and control (buffer alone) conditions.

RESULTS

cB had no effect on any of the viscoelastic mechanical properties measured, either in indentation or tension.

CONCLUSION

Removing or damaging approximately 50% of the DS had no effect on the mechanical properties, strongly suggesting that DS either carries very low load or no load.

Characterization of collagen II fibrils containing biglycan and their effect as a coating on osteoblast adhesion and proliferation

Collagen has been used as a coating material for titanium-based implants for bone contact and as a component of scaffolds for bone tissue engineering. In general collagen type I has been used, however very little attention has been focussed on collagen type II. Collagen-based coatings and scaffolds have been enhanced by the incorporation of the glycosaminoglycan chondroitin sulphate (CS), however the proteglycan biglycan, which is found in bone and contains glycosaminoglycan chains consisting of CS, has not been used as a biomaterial component. The study had the following aims: firstly, five different collagen II preparations were compared with regard to their ability to bind CS and biglycan and the changes in fibril morphology thereby induced. Secondly, the effects of biglycan on the adhesion of primary rat osteoblasts (rO) as well as the proliferation of rO, primary human osteoblasts (hO) and the osteoblast-like cell line 7F2 were studied by culturing the cells on surfaces coated with collagen II fibrils containing biglycan. Fibrils of the collagen II preparation which bound the most biglycan were used to coat titanium surfaces. Bare titanium, titanium coated with collagen II fibrils and titanium coated with collagen II fibrils containing biglycan were compared. It was found that different collagen II preparations showed different affinities for CS and biglycan. In four of the five preparations tested, biglycan reduced fibril diameter, however the ability of a preparation to bind more biglycan did not appear to lead to a greater reduction in fibril diameter. Fibrils containing biglycan promoted the formation of focal adhesions by rO and significantly enhanced the proliferation of hO but not of rO or 7F2 cells. These results should encourage further investigation of biglycan as a component of collagen-based scaffolds and/or coatings.

Influence of collagen-fibril-based coatings containing decorin and biglycan on osteoblast behavior

Collagen is used as a scaffold material for tissue engineering as well as a coating material for implants with a view to enhancing osseointegration by mimicry of the bone extracellular matrix in vivo. The biomimicry strategy can be taken further by incorporating the small leucine-rich proteoglycans (SLRPs) decorin and biglycan, which are expressed in bone. Both bind to fibrils during fibrillogenesis in vitro. In this study, the ability of collagen types I, II, and III to bind decorin and biglycan was compared. Collagen type II bound significantly more SLRPs in fibrils than collagen I and III, with more biglycan than decorin bound by all three collagen types. Therefore, type II fibrils with bound decorin or biglycan or neither were used to coat titanium surfaces. Bioavailability of SLRPs was confirmed by direct ELISA after SLRP biotinilation. The in vitro behavior of osteoblasts from rat calvaria (rOs) and human knee (hOs) cultured on different surfaces was compared. Proliferation and collagen synthesis were determined. Also, the influence of SLRPs on the formation of focal adhesions by rO was investigated. Biglycan enhanced the formation of focal adhesions after 2 and 24 h. Decorin and biglycan affected rO and hO proliferation and collagen synthesis differently. Biglycan stimulated hO proliferation significantly but had no effect on rO proliferation, and also inhibited rO collagen synthesis significantly while not affecting hO collagen synthesis. Decorin promoted hO proliferation slightly but did not influence rO proliferation. The results could be relevant when designing implant coatings or tissue engineering scaffolds.

Pre-eclampsia-associated alterations in decorin, biglycan and versican of the umbilical cord vein wall

OBJECTIVE

The role of proteoglycans in the rearrangement of the extracellular matrix of the umbilical cord vein wall in pre-eclampsia is not known. Decorin, biglycan and versican are the main proteoglycans of the umbilical cord vein wall. We decided to test whether the amounts of these proteoglycans alter in pre-eclampsia.

STUDY DESIGN

Study was performed on the umbilical cord veins taken from 10 newborns delivered by healthy mothers (control group) and from 10 newborns delivered by mothers with pre-eclampsia. Proteoglycans were extracted in dissociative conditions, purified by Q-Sepharose anion exchange chromatography and lyophilised. Decorin, biglycan and versican were analysed by SDS-PAGE followed by Western blotting before and after treatment with chondroitinase ABC. The amounts of decorin, biglycan and versican core proteins were assessed by ELISA method.

RESULTS

We found that both control and pre-eclamptic umbilical cord vein wall contained all the three proteoglycans. ELISA assay showed the amounts of the core proteins of decorin, biglycan and versican were distinctly higher in pre-eclamptic material in comparison to control vessel. Western blotting confirmed that the expression of all these proteoglycan core proteins increased in pre-eclampsia. They featured in the same electrophoretic mobility-45 and 47 kDa for decorin, 45 kDa for biglycan, and 300 and 320 kDa for versican.

CONCLUSION

The content of decorin, biglycan and versican in the umbilical cord vein wall is elevated in pre-eclampsia in comparison to the corresponding control vessel. These alterations may affect the mechanical properties of this vessel and disturb foetal blood circulation.

A bimodular polyconvex anisotropic strain energy function for articular cartilage

A strain energy function for finite deformations is developed that has the capability to describe the nonlinear, anisotropic, and asymmetric mechanical response that is typical of articular cartilage. In particular, the bimodular feature is employed by including strain energy terms that are only mechanically active when the corresponding fiber directions are in tension. Furthermore, the strain energy function is a polyconvex function of the deformation gradient tensor so that it meets material stability criteria. A novel feature of the model is the use of bimodular and polyconvex "strong interaction terms" for the strain invariants of orthotropic materials. Several regression analyses are performed using a hypothetical experimental dataset that captures the anisotropic and asymmetric behavior of articular cartilage. The results suggest that the main advantage of a model employing the strong interaction terms is to provide the capability for modeling anisotropic and asymmetric Poisson's ratios, as well as axial stress-axial strain responses, in tension and compression for finite deformations.

Chondrogenic differentiation on perlecan domain I, collagen II, and bone morphogenetic protein-2-based matrices

Extracellular matrix (ECM) molecules in cartilage cooperate with growth factors to regulate chondrogenic differentiation and cartilage development. Domain I of perlecan (Pln) bears heparan sulfate chains that bind and release heparin binding growth factors (HBGFs). We hypothesized that Pln domain I (PlnDI) might be complexed with collagen II (P-C) fibrils to improve binding of bone morphogenetic protein-2 (BMP-2) and better support chondrogenesis and cartilage-like tissue formation in vitro. Our results showed that P-C fibrils bound more BMP-2 than collagen II fibrils alone, and better sustained BMP-2 release. Polylactic acid (PLA)-based scaffolds coated with P-C fibrils immobilized more BMP-2 than either PLA scaffolds or PLA scaffolds coated with collagen II fibrils alone. Multipotential mouse embryonic mesenchymal cells, C3H10T1/2, were cultured on 2-dimensional P-C fibrils or 3-dimensional P-C/BMP-2-coated (P-C-B) PLA scaffolds. Chondrogenic differentiation was indexed by glycosaminoglycan (GAG) production, and expression of the pro-chondrogenic transcription factor, Sox9, as well as cartilaginous ECM proteins, collagen II, and aggrecan. Immunostaining for aggrecan, perlecan, tenascin, and collagen X revealed that both C3H10T1/2 cells and primary mouse embryonic fibroblasts cultured on P-C-B fibrils showed the highest expression of chondrogenic markers among all treatment groups. Safranin O-Fast Green staining indicated that cartilage-like tissue was formed in the P-C-B scaffolds, while no obvious cartilage-like tissue formed in other scaffolds. We conclude that P-C fibrils provide an improved biomimetic material for the binding and retention of BMP-2 and support chondrogenic differentiation.

Interactions between collagen IX and biglycan measured by atomic force microscopy

The stability of the lattice-like type II collagen architecture of articular cartilage is paramount to its optimal function. Such stability not only depends on the rigidity of collagen fibrils themselves, but more importantly, on their interconnections. One known interconnection is through type IX and biglycan molecules. However, the mechanical properties of this interaction and its role in the overall stability remain unrevealed. Using atomic force microscopy, this study directly measured the mechanical strength (or the rupture force) of a single bond between collagen IX and biglycan. The results demonstrated that the rupture force of this single bond was 15pN, which was significantly smaller than those of other known molecule interactions to date. This result suggested that type IX collagen and biglycan interaction may be the weak link in the cartilage collagen architecture, vulnerable to abnormal joint force and associated with disorders such as osteoarthritis.

Characterisation of proteoglycans and their catabolic products in tendon and explant cultures of tendon

Tendons are collagenous tissues made of mainly Type I collagen and it has been shown that the major proteoglycans of tendons are decorin and versican. Little is still known about the catabolism of these proteoglycans in tendon. Therefore, the aim of the study was to characterise the proteoglycans including their catabolic products present in uncultured bovine tendon and in the explant cultures of tendon. In this study, the proteoglycans were extracted from the tensile region of deep flexor tendon and isolated by ion-exchange chromatography and after deglycosylation analysed by SDS-polyacrylamide electrophoresis, Western blotting and amino-terminal amino acid sequence analysis. Based on amino acid sequence analysis, approximately 80% of the total proteoglycan core proteins in fresh tendon was decorin. Other species that were detected were biglycan and the large proteoglycans versican (splice variants V(0) and/or V(1)) and aggrecan. Approximately 35% of decorin present in the matrix showed carboxyl-terminal proteolytic processing at a number of specific sites. The analysis of small proteoglycans lost to the medium of tendon explants showed the presence of biglycan and decorin with the intact core protein as well as decorin fragments that contained the amino terminus of the core protein. In addition, two core protein peptides of decorin starting at residues K(171) and D(180) were observed in the matrix and one core protein with an amino-terminal sequence commencing at G(189) was isolated from the culture medium. The majority of the large proteoglycans present in the matrix of tendon were degraded and did not contain the G1 globular domain. Furthermore the aggrecan catabolites present in fresh tendon and lost to the medium of explants were derived from aggrecanase cleavage of the core protein at residues E(373)-A(374), E(1480)-G(1481) and E(1771)-A(1772). The analysis of versican catabolites (splice variants V(0) and/or V(1)) also showed evidence of degradation of the core protein by aggrecanase within the GAG-beta subdomain, as well as cleavage by other proteinase(s) within the GAG-alpha and GAG-beta subdomains of versican (variants V(0) and/or V(2)). Degradation products from the amino terminal region of type XII collagen were also detected in the matrix and medium of tendon explants. This work suggests a prominent role for aggrecanase enzymes in the degradation of aggrecan and to a lesser extent versican. Other unidentified proteinases are also involved in the degradation of versican and small leucine-rich proteoglycans.

The presence of a novel extracellular hyaluronidase in squid cranial cartilage

A new type of hyaluronidase was isolated from squid cranial cartilage. The enzyme seems to be localised extracellularly, since it is extracted from the tissue by 0.5 M sodium acetate, pH 7.0, in the presence of proteinase inhibitors. Degradation studies suggest that the enzyme belongs to the family of endoglycosidases generating oligosaccharides of rather large size. The best activity of the enzyme was observed at pH 7.0 and 37 degrees C and the optimum buffer for digestion was 0.15 M Tris acetate. It is inactive in sodium phosphate, morpholine acetate and HEPES buffers. The enzyme degrades aggrecan, hyaluronan, chondroitin sulphate and oversulphated chondroitin sulphate.

Solid phase assays in glycoconjugate research: applications to the analysis of proteoglycans, glycosaminoglycans and metalloproteinases

Glycoconjugates are a class of macromolecules consisting of different constituents, one of which is sugar moieties. Glycoconjugates comprise the majority of tissue constituents, both intracellular and extracellular. Extracellular glycoconjugates (glycoproteins and proteoglycans) participate in a wide variety of interactions, through which they maintain tissue integrity. Therefore, their analysis or the study of their possible interactions would give evidence for the state of tissues. Since the amounts of some of the extracellular glycoconjugates are usually low or the amounts of tissue to be examined come from biopsies, specific analytical systems are developed for their study, the most familiar being solid phase assays, which have the advantages of analysis of multiple samples on the same time, cheap instrumentation and high specificity.