Characterization of three-dimensional cancer cell migration in mixed collagen-Matrigel scaffolds using microfluidics and image analysis

Microfluidic devices are becoming mainstream tools to recapitulate in vitro the behavior of cells and tissues. In this study, we use microfluidic devices filled with hydrogels of mixed collagen-Matrigel composition to study the migration of lung cancer cells under different cancer invasion microenvironments. We present the design of the microfluidic device, characterize the hydrogels morphologically and mechanically and use quantitative image analysis to measure the migration of H1299 lung adenocarcinoma cancer cells in different experimental conditions. Our results show the plasticity of lung cancer cell migration, which turns from mesenchymal in collagen only matrices, to lobopodial in collagen-Matrigel matrices that approximate the interface between a disrupted basement membrane and the underlying connective tissue. Our quantification of migration speed confirms a biphasic role of Matrigel. At low concentration, Matrigel facilitates migration, most probably by providing a supportive and growth factor retaining environment. At high concentration, Matrigel slows down migration, possibly due excessive attachment. Finally, we show that antibody-based integrin blockade promotes a change in migration phenotype from mesenchymal or lobopodial to amoeboid and analyze the effect of this change in migration dynamics, in regards to the structure of the matrix. In summary, we describe and characterize a robust microfluidic platform and a set of software tools that can be used to study lung cancer cell migration under different microenvironments and experimental conditions. This platform could be used in future studies, thus benefitting from the advantages introduced by microfluidic devices: precise control of the environment, excellent optical properties, parallelization for high throughput studies and efficient use of therapeutic drugs.

Cyclic loading of human articular cartilage: The transition from compaction to fatigue

Osteoarthritis and articular cartilage injuries are common conditions in human joints and a frequent cause of pain and disability. Unfortunately, cartilage is avascular and has limited capabilities for self-repair. Despite the societal impact, there is little information on the dynamic process of cartilage degeneration. We performed a series of cyclic unconfined compression tests motivated by in vivo loading conditions and designed to generate mechanical fatigue. We examined the functional (both stress-stretch and creep) responses of the tissue after recovery from a specified number of loading cycles, as well as histology and second harmonic generation microscopy images. The effect of compaction was complimented by the effect of fatigue in our unconfined compression tests. A three-way, repeated-measures mixed model ANOVA showed significant differences between loading with a physiologically relevant low magnitude, and two more severe loading magnitudes, in terms of the resulting specimen stiffness, time to equilibrium and thickness. There was a statistically significant effect of loading frequency on a specimen's time to equilibrium and significant interaction of force and frequency on specimen thickness and time to equilibrium. Increasing the number of loading cycles significantly impacted a specimen's effective stiffness and resulting thickness. We attribute permanent loss of mechanical function under cyclic loading to rearrangement and disruption of the collagen network and resulting proteoglycan (PG) aggregation, as seen in histological and second harmonic generation images, as a result of induced mechanical fatigue.

Austromegabalanus psittacus barnacle shell structure and proteoglycan localization and functionality

Comparative analyzes of biomineralization models have being crucial for the understanding of the functional properties of biominerals and the elucidation of the processes through which biomacromolecules control the synthesis and structural organization of inorganic mineral-based biomaterials. Among calcium carbonate-containing bioceramics, egg, mollusk and echinoderm shells, and crustacean carapaces, have being fairly well characterized. However, Thoraceca barnacles, although being crustacea, showing molting cycle, build a quite stable and heavily mineralized shell that completely surround the animal, which is for life firmly cemented to the substratum. This makes barnacles an interesting model for studying processes of biomineralization. Here we studied the main microstructural and ultrastructural features of Austromegabalanus psittacus barnacle shell, characterize the occurrence of specific proteoglycans (keratan-, dermatan- and chondroitin-6-sulfate proteoglycans) in different soluble and insoluble organic fractions extracted from the shell, and tested them for their ability to crystallize calcium carbonate in vitro. Our results indicate that, in the barnacle model, proteoglycans are good candidates for the modification of the calcite crystal morphology, although the cooperative effect of some additional proteins in the shell could not be excluded.

Role of epidermal growth factor receptor (EGFR) in corneal remodelling in diabetes

PURPOSE

This study examined the role of epidermal growth factor receptor (EGFR) signalling on the organization and remodelling of collagen fibrils (CFs) and proteoglycans (PGs) in the stroma of diabetic rat cornea.

METHODS

Diabetes was induced in female Wistar rats (n = 5) by streptozotocin (STZ) injection (55 mg/kg). Treatment with a selective inhibitor of EGFR tyrosine kinase, AG1478, was started on the same day as the induction of diabetes and administered every other day for 4 weeks. Corneas were fixed in 4% paraformaldehyde at 4 degrees to allow for analysis of CF diameters and in 2.5% glutaraldehyde in sodium acetate buffer containing cuprolinic blue to enable the study of PG distribution. AnalySIS soft imaging software was used to analyse CFs and PGs.

RESULTS

Epithelial thickness, and median diameter and area fraction of CF in corneal stroma were decreased in diabetic rat cornea compared with normal cornea (p < 0.001), whereas the median PG area and area fractions were significantly increased (p < 0.001). Treatment with AG1478, although it had no action on normal cornea, prevented these diameter and area fraction changes in CFs and PGs. The cornea of AG1478-treated diabetic rats showed a slight increase in CF diameter and area fraction and a decreased number density.

CONCLUSIONS

These data show that the distribution of corneal stroma CFs and PGs was altered after 4 weeks of diabetes and that, furthermore, treatment with an EGFR signalling inhibitor normalized these abnormalities. The data suggest that EGFR plays an important role in the development of diabetes-induced corneal remodelling.

Altered structural and mechanical properties in decellularized rabbit carotid arteries

Recently, major achievements in creating decellularized whole tissue scaffolds have drawn considerable attention to decellularization as a promising approach for tissue engineering. Decellularized tissues are expected to have mechanical strength and structure similar to the native tissues from which they are derived. However, numerous studies have shown that mechanical properties change after decellularization. Often, tissue structure is observed by histology and electron microscopy, but the structural alterations that may have occurred are not always evident. Here, a variety of techniques were used to investigate changes in tissue structure and relate them to altered mechanical behavior in decellularized rabbit carotid arteries. Histology and scanning electron microscopy revealed that major extracellular matrix components were preserved and fibers appeared intact, although collagen appeared looser and less crimped after decellularization. Transmission electron microscopy confirmed the presence of proteoglycans (PG), but there was decreased PG density and increased spacing between collagen fibrils. Mechanical testing and opening angle measurements showed that decellularized arteries had significantly increased stiffness, decreased extensibility and decreased residual stress compared with native arteries. Small-angle light scattering revealed that fibers had increased mobility and that structural integrity was compromised in decellularized arteries. Taken together, these studies revealed structural alterations that could be related to changes in mechanical properties. Further studies are warranted to determine the specific effects of different decellularization methods on the structure and performance of decellularized arteries used as vascular grafts.

Ultrastructural analysis of collagen fibrils and proteoglycans in keratoconus

PURPOSE

To investigate ultrastructural alterations in the distribution of collagen fibrils (CFs) and proteoglycans (PGs) in the keratoconus cornea.

METHODS

Four normal corneas (donor age 24-75 years) and four severe and one mild keratoconus corneas (donor age 24-47 years) were fixed in 2.5% glutaraldehyde containing 0.05% cuprolinic blue dye for electron microscopy. Analyses were carried out on approximately 39 000 CF and 66 000 PG filaments in the anterior, middle and posterior stroma, using analySIS soft imaging software.

RESULTS

In severe keratoconus, stromal lamellae were seen to undulate in most regions, whereas in mild keratoconus only the middle and posterior lamellae were affected. In keratoconus corneas the mean diameter and interfibrillar spacing of CFs was reduced in all zones (p < 0.0001) and the CF and PG number density and area fractions were significantly increased (p < 0.0001) compared with in normal corneas and were higher (p < 0.0001) in the corneas with severe keratoconus than in that with mild keratoconus. The lamellae contained microfibrils (8-9 nm wide) and, in addition, PGs embedded within CFs. Degenerate keratocytes containing PGs were found in all keratoconus corneas.

CONCLUSIONS

These studies suggest that as keratoconus progresses, the PG content of the stroma increases, whereas fibril diameter is reduced. The altered stromal content of PGs may influence CF diameters and their organization in keratoconus, weakening lateral cohesion and resulting in significant disorder of CF packing.

Formation of stromal collagen fibrils and proteoglycans in the developing zebrafish cornea

PURPOSE

Collagen fibrils and proteoglycans are the main components of the corneal extracellular matrix and corneal transparency depends crucially on their proper arrangement. In the present study, we investigated the formation of collagen fibrils and proteoglycans in the developing cornea of the zebrafish, a model organism used to study vertebrate embryonic development and genetic disease.

METHODS

We employed thin-section electron microscopy to investigate the ultrastructure of the zebrafish cornea at different developmental stages.

RESULTS

The layering of the zebrafish cornea into an epithelium, a Bowman's layer, stroma and endothelium was observed starting at 72 hr post-fertilization. At this stage, the stroma contained orthogonally arranged collagen fibrils and small proteoglycans. The density of proteoglycans increased gradually throughout subsequent development of the cornea. In the stroma of 2-week-old larvae, the collagen fibrils were organized into thin lamellae and were separated by very large, randomly distributed proteoglycans. At 4 weeks, a regular arrangement of proteoglycans in relation to the collagen fibrils was observed for the first time and the lamellae were also thickened.

CONCLUSION

The present study, for the first time, provides ultrastructural details of collagen fibril and proteoglycan development in the zebrafish cornea. Furthermore, it directly correlates the collagen fibril and proteoglycan composition of the zebrafish cornea with that of the human cornea. The similarities between the two species suggest that the zebrafish could serve as a model for investigating the genetics of human corneal development and diseases.

A model of the early mineralization process of mantle dentin

The aim of this study was to investigate the relationship between proteoglycans (PGs) and collagen fibrils at the early mineralization process of mantle dentin. Ten first molar dental germs of rats were removed and fixed in glutaraldehyde/formaldehyde in cacodylate buffer and post-fixed in osmium tetroxide. The samples were dehydrated and embedded in epoxy resin. Ultrathin sections were contrasted and analyzed in TEM before and after treatment with EDTA, chondroitinases AC and ABC. After EDTA treatment, a electrondense substance associated with collagen fibril was removed, and did not stain again. A high magnification of these areas showed globular structures with 15 nm diameter surrounding collagen fibrils. In advanced mineralization areas, collagen fibrils showed a banded pattern and at high magnification the fibrils presented a light 10 nm ring inside and a dark 10 nm ring outside. After chondroitinase treatment, the electrondense substance associated with collagen fibrils was removed, showing a banded pattern of clear and dark areas along them. From morphological data, the authors proposed a model of interaction between PGs and collagen fibrils, where glicosaminoglycans chains are inside the fibrils, while the protein core remains outside. That stereochemical arrangement would start the crystal nucleation.

Quantifying the contributions of structure to annulus fibrosus mechanical function using a nonlinear, anisotropic, hyperelastic model

The annulus fibrosus of the intervertebral disc is comprised of concentric lamella of oriented collagen fibers embedded in a hydrated proteoglycan matrix with smaller amounts of minor collagens, elastin, and small proteoglycans. Its structure and composition enable the disc to withstand complex loads and result in inhomogeneous, anisotropic, and nonlinear mechanical behaviors. The specific contributions of the annulus fibrosus constituent structures to mechanical function remain unclear. Therefore, the objective of this study was to use a structurally motivated, anisotropic, nonlinear strain energy model of annulus fibrosus to determine the relative contributions of its structural components to tissue mechanical behavior. A nonlinear, orthotropic hyperelastic model was developed for the annulus fibrosus. Terms to describe fibers, matrix, and interactions between annulus fibrosus structures (shear and normal to the fiber directions) were explicitly included. The contributions of these structures were analyzed by including or removing terms and determining the effect on the fit to multidimensional experimental data. Correlation between experimental and model-predicted stress, a Bland-Altman analysis of bias and standard deviation of residuals, and the contribution of structural terms to overall tissue stress were calculated. Both shear and normal interaction terms were necessary to accurately model multidimensional behavior. Inclusion of shear interactions more accurately described annulus fibrosus nonlinearity. Fiber stretch and shear interactions dominated contributions to circumferential direction stress, while normal and shear interactions dominated axial stress. The results suggest that interactions between fibers and matrix, perhaps facilitated by crosslinks, elastin, or minor collagens, augment traditional (i.e., fiber-uncrimping) models of nonlinearity.

Fourier transform infrared imaging and MR microscopy studies detect compositional and structural changes in cartilage in a rabbit model of osteoarthritis

Assessment of subtle changes in proteoglycan (PG) and collagen, the primary macromolecular components of cartilage, which is critical for diagnosis of the early stages of osteoarthritis (OA), has so far remained a challenge. In this study we induced osteoarthritic cartilage changes in a rabbit model by ligament transection and medial meniscectomy and monitored disease progression by infrared fiber optic probe (IFOP) spectroscopy, Fourier transform infrared imaging spectroscopy (FT-IRIS), and magnetic resonance imaging (MRI) microscopy. IFOP studies combined with chemometric partial least-squares analysis enabled us to monitor progressive cartilage surface changes from two to twelve weeks post-surgery. FT-IRIS studies of histological sections of femoral condyle cartilage revealed that compared with control cartilage the OA cartilage had significantly reduced PG content 2 and 4 weeks post-surgery, collagen fibril orientation changes 2 and 4 weeks post-surgery, and changes in collagen integrity 2 and 10 weeks post-surgery, but no significant changes in collagen content at any time. MR microscopy studies revealed reduced fixed charge density (FCD), indicative of reduced PG content, in the OA cartilage, compared with controls, 4 weeks post-surgery. A non-significant trend toward higher apparent MT exchange rate, k(m), was also found in the OA cartilage at this time point, suggesting changes in collagen structural features. These two MR findings for FCD and k(m) parallel the FT-IRIS findings of reduced PG content and altered collagen integrity, respectively. MR microscopy studies of the cartilage at the 12-week time point also found a trend toward longer T (2) values and reduced anisotropy in the deep zone of the OA cartilage, consistent with increased hydration and less ordered collagen. These studies reveal that FT-IRIS and MR microscopy provide complementary data on compositional changes in articular cartilage in the early stages of osteoarthritic degradation.

Engineering three-dimensional pulmonary tissue constructs

In this paper, we report on engineering 3-D pulmonary tissue constructs in vitro. Primary isolates of murine embryonic day 18 fetal pulmonary cells (FPC) were comprised of a mixed population of epithelial, mesenchymal, and endothelial cells as assessed by immunohistochemistry and RT-PCR of 2-D cultures. The alveolar type II (AE2) cell phenotype in 2-D and 3-D cultures was confirmed by detection of SpC gene expression and presence of the gene product prosurfactant protein C. Three-dimensional constructs of FPC were generated utilizing Matrigel hydrogel and synthetic polymer scaffolds of poly-lactic-co-glycolic acid (PLGA) and poly-L-lactic-acid (PLLA) fabricated into porous foams and nanofibrous matrices, respectively. Three-dimensional Matrigel constructs contained alveolar forming units (AFU) comprised of cells displaying AE2 cellular ultrastructure while expressing the SpC gene and gene product. The addition of tissue-specific growth factors induced formation of branching, sacculated epithelial structures reminiscent of the distal lung architecture. Importantly, 3-D culture was necessary for inducing expression of the morphogenesis-associated distal epithelial gene fibroblast growth factor receptor 2 (FGFr2). PLGA foams and PLLA nanofiber scaffolds facilitated ingrowth of FPC, as evidenced by histology. However, these matrices did not support the survival of distal lung epithelial cells, despite the presence of tissue-specific growth factors. Our results may provide the first step on the long road toward engineering distal pulmonary tissue for augmenting and/or replacing dysfunctional native lung in diseases, such as neonatal pulmonary hypoplasia.

Tumor Cell Migration in Three Dimensions

In almost all physiological and pathological situations, cells migrate through three-dimensional environments, yet most studies of cell motility have used two-dimensional substrates. It is clear that two-dimensional substrates do not mimic the in vivo environment accurately, and recent work using three-dimensional environments has revealed many different mechanisms of cell migration (Abbott, 2003; Sahai and Marshall, 2003; Wolf et al., 2003). This chapter will describe methods for generating three-dimensional matrices suitable for studying cell motility, methods for imaging the morphology of motile cells in situ, and methods for quantifying cell migration through three-dimensional environments.

Using three-dimensional acinar structures for molecular and cell biological assays

Epithelial cells grown in three-dimensional matrix allows one to investigate biological processes in a setting that is closer to in vivo conditions than those obtained by growing cells on plastic culture dishes. Here we outline procedures that allow one to investigate molecular mechanisms that regulate formation and disruption of three-dimensional epithelial structures.

Ultrastructural, immunohistochemical and biochemical analysis of glycosaminoglycans and proteoglycans in the mouse pubic symphysis during pregnancy

During pregnancy, an interpubic ligament is formed in the mouse pubic symphysis. In late stages, this ligament undergoes "relaxation" to allow proper delivery, which is expected on the 19th day. Proteoglycans and hyaluronic acid play an important role in the remodeling of the extracellular matrix in these tissues. Glycosaminoglycans and proteoglycans were studied by electron microscopic, immunohistochemical and biochemical methods in samples of mouse pubic symphysis from the 12th to 18th day of pregnancy. At the ultrastructural level, using cuprolinic blue and enzymatic digestion by chondroitin lyases, two types of proteoglycan filaments were observed in the fibrocartilage on the 12th day, as well as in D 15, D 17 and D 18 pubic ligaments. The only sulfated glycosaminoglycan in these filaments was chondroitin sulfate, as shown by chondroitin lyase treatment. Their electrophoretic mobility, before and after enzymatic degradation, corroborated this inference. The ratio of chondroitin sulfate/dry weight of symphysis showed two phases of increase: between D12 and D 15, and between D 17 and D 18. We suggest that the first corresponds mainly to an increase in decorin when the ligament is formed, and the second to versican, during "relaxation". Versican and hyaluronic acid, working as water holding molecules would be responsible for the hydration of the ligament at the end of pregnancy, allowing an increase in resiliency. The presence of hyaluronic acid was confirmed by labeling with HA-probe in the perichondrium, fibrocartilage and ligament. The role of collagen fibers as physical restrictors of the complete expansion of glycosaminoglycans and hyaluronic acid in tissue is discussed.

Atomic force microscopy on human trabecular bone from an old woman with osteoporotic fractures

AFM images were taken of the exterior surface of a single trabecula, extracted from a human femoral head removed during surgery for a hip fracture in an old women with former fractures. The images showed a dense structure of bundled collagen fibrils banded with 67 nm periodicity. Bundles were seen to run in parallel in layers confirming the collagen structure seen by other techniques. Single collagen fibrils were seen to cross the bundles, thus forming cross-links between neighboring bundles of collagen fibrils. Some of these crossing fibrils did not have the 67 nm band pattern and their dimensions were about half compared to the neighboring collagen fibrils. Very little mineral was found on the surface of the trabecula. An AFM image of a fracture plane was also displayed. The trabecula was extracted from a region close to the hip fracture. However, there were in this case no obvious features in the images that could be linked directly to osteoporosis, but altered collagen banding and collagen protrusions may alter mechanical competence. A path to extensive studies of the nanometer scale structure of bone was demonstrated.

Development of an ectopic site for islet transplantation, using biodegradable scaffolds

Clinical islet transplantation in liver has achieved normoglycemia. However, this site may not be ideal for islet survival. To create a more optimal site for islet transplantation, we have developed a construct with biodegradable scaffolds. Islets were seeded in scaffolds and transplanted into the epididymal fat pad of diabetic BALB/c mice. Controls included islets transplanted underneath the kidney capsule or into the fat pad without scaffolds. All animals with islets in scaffolds or the kidney became normoglycemic and maintained this metabolic state. When islets were transplanted without scaffolds the time to achieve normoglycemia was significantly increased and less than 45% of mice survived. An oral glucose tolerance test was performed on the scaffold and kidney groups with similar blood glucose levels and area under the curve values between the groups. Grafts were removed at more than 100 days posttransplantation and all animals became hyperglycemic. There was no significant difference in insulin content between the grafts and all grafts were well vascularized with insulin-positive beta cells. Therefore, islets in scaffolds function and restore diabetic animals to normoglycemic levels, similar to islets transplanted underneath the kidney capsule, suggesting scaffolds can be used to create a site for islet transplantation.

Use of embryonic stem cell-derived endothelial cells as a cell source to generate vessel structures in vitro

Embryonic stem (ES) cells could potentially serve as an excellent cell source for various applications in regenerative medicine and tissue engineering. Our laboratory is particularly interested in generating a reproducible endothelial cell source for the development of prevascularized materials for tissue/organ reconstruction. After developing methods to isolate highly purified (>96%) proliferating populations of endothelial cells from mouse embryonic stem cells, we tested their ability to form three-dimensional (3-D) vascular structures in vitro. The ES cell-derived endothelial cells were embedded in 3-D collagen gel constructs with rat tail collagen type I (2 mg/mL) at a concentration of 10(6) cells/mL of gel. The gels were observed daily with a phase-contrast microscope to analyze the time course for endothelial cell assembly. The first vessels were observed between days 3 and 5 after gel construct formation. The number and complexity of structures steadily increased, reaching a maximum before beginning to regress. By 2 weeks, all vessel-like structures had regressed back to single cells. Histology and fluorescent images of the vessel-like structures verified that tube structures were multicellular and could develop patent lumens. We have shown that endothelial cells derived, purified and expanded in vitro from ES cells sustain an important endothelial cell function, the ability to undergo vasculogenesis in collagen gels, indicating that endothelial products derived in vitro from stem cells could be useful in regenerative medicine applications.

[Alterations in the structure of the epiretinal membranes in PVR -- assumptions and reality]

BACKGROUND

Proliferative vitreoretinopathy (PVR) is known to be the main cause of failure for routine retinal detachment surgery. Our aim was to document the ultrastructural changes in the epiretinal membranes in cases of PVR.

MATERIAL AND METHODS

Epiretinal membranes were taken during vitrectomy of 64 patients with different stages of PVR and further analysed using transmission and scanning electron microscopy.

RESULTS

In the early stages of the disease mainly retinal pigment epithelial (RPE) cells, fibroblasts and occasional glial cells were found. Moreover, some of the RPE cells showed altered characteristics. In contrast, epiretinal membranes from the developed stages of PVR were comprised mostly of fibroblasts and a considerably diminished number of RPE cells. Cells with marks of degeneration were generally found.

CONCLUSIONS

Our results point out that epiretinal membranes in PVR are dynamic structures, constantly changing their cell and matrix composition with the progression of the disease. The morphological changes together with the clinical data are important points to consider when discussing the most appropriate therapeutic approach for each case.

Atypical Composition and Ultrastructure of Proteoglycans in the Mouse Corneal Stroma

PURPOSE

Recently, gene-targeted strains of mice with null mutations for specific proteoglycans (PGs) have been used for investigations of the functional role of these molecules. In the present study, the corneal stroma of the mouse was examined to provide some baseline PG morphologies in this species.

METHODS

Monoclonal antibodies to specific glycosaminoglycan (GAG) chain sulfation patterns were used to characterize PG composition in corneal extracts by SDS-PAGE and Western blot analysis and to identify their tissue distribution by immunofluorescence microscopy. PGs were also visualized by transmission electron microscopy after contrast enhancement with cationic dye fixation.

RESULTS

Western blot analysis of pooled corneal extracts and immunofluorescence of tissue sections identified 4-sulfated, but not 6-sulfated, chondroitin sulfate/dermatan sulfate (CS/DS). Keratan sulfate (KS) was present only as a low-sulfated moiety. Electron microscopic histochemistry disclosed a complex array of corneal PGs present as (1) fine filaments radiating from collagen fibrils, and (2) elongate, straplike structures, running either along the fibril axis or weaving across the primary fibril orientation. These large structures were digested by chondroitinase ABC, but not by keratanase.

CONCLUSIONS

KS in the mouse is predominantly undersulfated and generates an immunostaining pattern that differs from that observed in corneas of other mammalian species thus far investigated. The mouse cornea resembles other mammalian corneas in the presence of filamentous arrays of small, collagen-associated stromal PGs visualized by cationic dye staining. However, large dye-positive structures with a CS/DS component are also present and appear to be unique to the cornea of this species.

Dynamin II interacts with syndecan-4, a regulator of focal adhesion and stress-fiber formation

Dynamin is a large mechanochemical GTPase that has been implicated in vesicle formation in multiple cellular compartments. It is believed that dynamin interacts with a variety of cellular proteins to constrict membranes. To identify potential intracellular proteins that interact with the PH domain of dynamin II, we carried out a yeast two-hybrid screen in which the PH domain of dynamin II was used as bait. The cell surface heparan sulfate proteoglycan syndecan-4 that acts in conjunction with integrins to promote the formation of actin stress fibers and focal adhesions was isolated as a binding partner for the PH domain of dynamin II. In vitro binding assays, immunoprecipitation, and confocal microscopy analysis confirmed the association of dynamin II with syndecan-4. Most dramatic finding of our study is that the cytoplasmic distribution of dynamin II and syndecan-4 changes in fibroblasts that have been stimulated to form the focal adhesions and stress fibers with LPA. In quiescent cells, dynamin II is evenly distributed in the cytoplasm and colocalizes with syndecan-4 near the nucleus. Upon treatment with LPA to induce focal adhesions and stress-fiber formation, dynamin II becomes markedly associated with syndecan-4 at focal adhesion sites. We further established the colocalization of syndecan-4 and dynamin with paxillin and actin as marker proteins for focal adhesions and stress fibers, respectively. All of these results suggest that the interaction between dynamin II and syndecan-4 is important in mediating focal adhesion and stress-fiber formation.

Proteoglycans and collagen in the intervertebral disc of the rhesus monkey (Macaca mulatta)

The different varieties of supportive tissues in the intervertebral discs of the rhesus monkeys (Macaca mulatta) were investigated with regard to morphology of the collagen fibrils and distribution and localization of proteoglycans (PG). The annulus fibrosus and the nucleus pulposus of the intervertebral disc were structurally closely integrated into the cartilaginous endplates of the vertebral bodies. The collagen fibrils in the intervertebral disc fell into two categories; i.e. thick (70-110 nm) and thin (40-50 nm) ones. In the outer zone of the annulus fibrosus only thick fibrils occurred, while in the regions of the inner part of the annulus fibrosus, in the periphery of the nucleus pulposus and in the cartilaginous endplates both types of fibrils were found. PG were found free in the matrix and in great numbers in association with collagen fibrils in all regions of the intervertebral disc. They interconnected neighbouring fibrils and decorated the surface of the collagen fibrils in irregular orientation. Only the thick fibrils of the annulus fibrosus contained small regularly arranged intrafibrillar PG precipitates. The free precipitates were usually longer and thicker than the collagen-associated PG, in addition they could be branched. Since rhesus monkeys are closely related to humans, they can serve as model organisms and the findings presented may be of relevance to the understanding of the human intervertebral discs.

Investigating tendon fascicle structure-function relationships in a transgenic-age mouse model using multiple regression models

Proper replacement or repair of damaged tendons or ligaments requires functionally engineered tissue that mimics their native mechanical properties. While tendon structure-function relationships are generally assumed, there exists little quantitative evidence of the roles of distinct tendon components in tendon function. Previous work has used linear correlations to assess the independent, univariate effects of one structural or one biochemical variable on mechanics. The current study's objective was to simultaneously and rigorously evaluate the relative contributions of seven different structural and compositional variables in predicting tissue mechanical properties through the use of multiple regression statistical models. Structural, biochemical, and mechanical analysis were all performed on tail tendon fascicles from different groups of transgenic mice, which provide a reproducible, noninvasive, in vivo model of changes in tendon structure and composition. Interestingly, glycosaminoglycan (GAG) content was observed to be the strongest predictor of mechanical properties. GAG content was also well correlated with collagen content and mean collagen fibril diameter. Collagen fibril area fraction was a significant predictor only of material properties. Therefore, in a large multivariate model, GAG content was the largest predictor of mechanical properties, perhaps both through direct influence and indirectly through its correlation with collagen content and fibril structure.

CAMM Techniques for the Prediction of the Mechanical Properties of Tendons and Ligaments Nanostructures

Theoretical prediction of the mechanical properties of soft tissues usually relies on a top-down approach; that is analysis is gradually refined to observe smaller structures and properties until technical limits are reached. Computer-Assisted Molecular Modeling (CAMM) allows for the reversal of this approach and the performance of bottom-up modeling instead. The wealth of available sequences and structures provides an enormous database for computational efforts to predict structures, simulate docking and folding processes, simulate molecular interactions, and understand them in quantitative energetic terms. Tendons and ligaments can be considered an ideal arena due to their well defined and highly organized architecture which involves not only the main structural constituent, the collagen molecule, but also other important molecular “actors” such as proteoglycans and glycosaminoglycans. In this ideal arena each structure is well organized and recognizable, and using the molecular modeling tool it is possible to evaluate their mutual interactions and to characterize their mechanical function. Knowledge of these relationships can be useful in understanding connective tissue performance as a result of the cooperation and mutual interaction between different biological structures at the nanoscale.

The structure of proteoglycan aggregate determined by atomic force microscopy

Proteoglycan aggregate is the major extracellular matrix component in cartilage, comprising about 18% of the dry weight of hyaline cartilage. The proteoglycan aggregate is the major substance in cartilage which resists compression in the joint. The purpose of this study was to utilize the newly developed imaging technique, Atomic force Microscopy (AFM), to visualize the ultrastructure of proteoglycan aggregates. The proteoglycan aggregate molecules were imaged in air using the tapping mode of the AFM. The images illustrated the ultrastructure of the aggregates, especially the individual proteoglycan and the core hyaluronic acid. In addition to the length and width of each molecule, the height of the proteoglycan aggregates and the individual proteoglycans could be directly measured. The images of the ultrastructures of proteoglycan aggregates visualized from the AFM are comparable with those using conventional electron microscopy approaches. Nevertheless, the sample preparation for AFM imaging does not involve fixation, staining, coating, and other routine procedures required for traditional electron microscopy imaging. Thus, this technique could be a simple alternative approach for future analysis of proteoglycan aggregate and its assembly.

Ultrastructural, tomographic and confocal imaging of the chondrocyte primary cilium in situ

Hyaline cartilage chondrocytes express one primary cilium per cell, but its function remains unknown. We examined the ultrastructure of chick embryo sternal chondrocyte cilia and their interaction with extracellular matrix molecules by transmission electron microscopy (TEM) and, for the first time, double-tilt electron tomography. Ciliary bending was also examined by confocal immunohistochemistry. Tomography and TEM showed the ciliary axoneme to interdigitate amongst collagen fibres and condensed proteoglycans. TEM also revealed the presence of electron-opaque particles in the proximal axoneme which may represent intraciliary-transport (ICT) particles. We observed a wide range of ciliary bending patterns. Some conformed to a heavy elastica model associated with shear stress. Others were acutely deformed, suggesting ciliary deflection by collagen fibres and proteoglycans with which the cilia make contact. We conclude that mechanical forces transmitted through these matrix macromolecules bend the primary cilium, identifying it as a potential mechanosensor involved in skeletal patterning and growth.

Mechanical interactions between collagen and proteoglycans: implications for the stability of lung tissue

Collagen and elastin are thought to dominate the elasticity of the connective tissue including lung parenchyma. The glycosaminoglycans on the proteoglycans may also play a role because osmolarity of interstitial fluid can alter the repulsive forces on the negatively charged glycosaminoglycans, allowing them to collapse or inflate, which can affect the stretching and folding pattern of the fibers. Hence, we hypothesized that the elasticity of lung tissue arises primarily from 1) the topology of the collagen-elastin network and 2) the mechanical interaction between proteoglycans and fibers. We measured the quasi-static, uniaxial stress-strain curves of lung tissue sheets in hypotonic, normal, and hypertonic solutions. We found that the stress-strain curve was sensitive to osmolarity, but this sensitivity decreased after proteoglycan digestion. Images of immunofluorescently labeled collagen networks showed that the fibers follow the alveolar walls that form a hexagonal-like structure. Despite the large heterogeneity, the aspect ratio of the hexagons at 30% uniaxial strain increased linearly with osmolarity. We developed a two-dimensional hexagonal network model of the alveolar structure incorporating the mechanical properties of the collagen-elastin fibers and their interaction with proteoglycans. The model accounted for the stress-strain curves observed under all experimental conditions. The model also predicted how aspect ratio changed with osmolarity and strain, which allowed us to estimate the Young's modulus of a single alveolar wall and a collagen fiber. We therefore identify a novel and important role for the proteoglycans: they stabilize the collagen-elastin network of connective tissues and contribute to lung elasticity and alveolar stability at low to medium lung volumes.

Strain-Rate Sensitive Mechanical Properties of Tendon Fascicles From Mice With Genetically Engineered Alterations in Collagen and Decorin

Tendons have complex mechanical behaviors that are nonlinear and time dependent. It is widely held that these behaviors are provided by the tissue’s composition and structure. It is generally thought that type I collagen provides the primary elastic strength to tendon while proteoglycans, such as decorin, play a role in failure and viscoelastic properties. This study sought to quantify such structure-function relationships by comparing tendon mechanical properties between normal mice and mice genetically engineered for altered type I collagen content and absence of decorin. Uniaxial tensile ramp to failure experiments were performed on tail tendon fascicles at two strain rates, 0.5%/s and 50%/s. Mutations in type I collagen led to reduced failure load and stiffness with no changes in failure stress, modulus or strain rate sensitivity. Fascicles without decorin had similar elastic properties to normal fascicles, but reduced strain rate sensitivity. Fascicles from immature mice, with increased decorin content compared to adult fascicles, had inferior elastic properties but higher strain rate sensitivity. These results showed that tendon viscoelasticity is affected by decorin content but not by collagen alterations. This study provides quantitative evidence for structure-function relationships in tendon, including the role of proteoglycan in viscoelasticity.

Ultrastructural and immunohistochemical analysis of proteoglycans in mouse pubic symphysis

Proteoglycans were accurately localized in mouse pubic symphyseal tissues using the cuprolinic blue method. Specific glycosaminoglycans degradative enzymes, together with chondroitin sulfate and decorin antibodies, allowed the identification of glycosaminoglycans. Chondroitin sulfate proteoglycans were the main proteoglycans observed in hyaline cartilage, fibrocartilage, and dense connective tissue. Ultrastructurally, they were seen as electron-dense granules and filaments. The granules, rich in chondroitin sulfate chains, were exclusively found in hyaline cartilage, whereas filaments were present in cartilage, fibrocartilage, and dense connective tissue. The latter were classified by size and susceptibility to enzyme digestion into F1, F2 and F3 filaments: F1 filaments were small, thin, and collagen fibril-associated; F2 filaments were thick, heavily stained, and localized around individual collagen fibrils and between bundles of collagen fibrils; and F3 filaments were scattered throughout elastic fiber surfaces. Considering their localization, susceptibility to chondroitinase AC and immunohistochemical detection, the symphysial F1 filaments were found to be preferentially decorin substituted with chondroitin sulfate side chains. The F2 filaments were also susceptible to chondroitinase AC treatment, whereas F3 filaments could be digested by heparitinase. The data thus obtained on the localization and identification of pubic symphyseal proteoglycans in virgin mice may be useful in the study of structural modifications that occur throughout pregnancy.

The Structure and Swelling of Corneal Scar Tissue in Penetrating Full-Thickness Wounds

OBJECTIVE

The purpose of this study was to determine corneal thickness and to examine the collagen and proteoglycans in full-thickness corneal scars up to 16 months following wounding.

METHODS

Ultrasound pachymetry was used to measure the depths of penetrating central scars and their surrounding areas in 16 rabbit corneas. Measurements were taken at regular intervals: 5, 10, 12, and 16 months after healing. Transmission electron microscopy was then used to study the stroma of the resulting scars to observe the collagen organization and the amount, as well as the size, of cuprolinic blue-stained proteoglycan filaments within the stroma. Furthermore, ex vivo swelling of selected wounded contralateral excised corneas was undertaken by the measured addition of distilled water.

RESULTS

In vivo, the thickness of the scar tissue was significantly less than that of the surrounding tissue throughout the period studied. By 12 months the proteoglycan filaments within the scar were of a similar size and number to those within the adjacent tissue, whereas the collagen fibrils within the scar were still disorganized (collagen interweaving, lack of a lamellar structure). Once excised and allowed to swell in water, scar tissue thickness remained relatively unchanged, whereas the surrounding tissue swelled considerably.

CONCLUSION

Disorganized fibril arrangement inhibits the normal swelling of the scar tissue, which remains reduced. Furthermore, even after many months of healing, collagen remodeling in corneal scar tissue is not complete.

A new three-dimensional model of the organization of proteoglycans and collagen fibrils in the human corneal stroma

The purpose of the present study was to re-evaluate the three-dimensional organization of collagen fibrils and proteoglycans (PGs) in the human corneal stroma using an improved ultrastructural approach. After a short aldehyde prefixation, one half of seven fresh corneal buttons was stained for PGs with Quinolinic Phtalocyanin (QP) or Cupromeronic Blue (CB). Strips of 1 mm width were cut, subsequently treated with aqueous phosphotungstic acid (PTA) and further processed for light and electron microscopy. The other half of the corneas served as control and was routinely processed with OsO4. Embedding was as such that ultrathin sections could be cut precisely parallel (frontal sections) or perpendicular (cross sections) to the corneal surface. The mutual connections between collagen fibrils and PGs were studied and the length of PGs and their mutual distance were measured manually at a calibrated final magnification of 70,000 x. Prefixed fresh corneal tissue treated with QP and CB shows no signs of swelling and exhibits well contrasted PGs. In cross sections PGs form a repeating network of ring-like structures (approximately 45 nm) around the collagen fibrils. In frontal sections PGs are aligned orthogonal to the collagen fibrils, are equidistant (approximately 42 nm) attached to the collagen fibrils along their full length and have a thickness of approximately 11 nm and a length of approximately 54 nm. The observed maximal length of the PGs and the occurrence of ring-like structures enwrapping the collagen fibrils urged us to revisit the prevailing model of maurice (1962) on the organization of the corneal stroma. In the new model hexagonal arranged collagen fibrils are interconnected at regular distances with their next-nearest neighbours by groups of six PGs, attached orthogonal to the circumference of the fibrils. In this way a regular meshwork of ring-like structures enwrapping the collagen fibrils is formed. It is discussed that this new model more convincingly explains corneal resistance to compression and stretching and further rationalizes corneal transparency because of the low refractive index difference between the regularly arranged collagen fibrils and their inter-space filled with PGs.

Proteoglycans in predentin: the last 15 micrometers before mineralization

Small leucine-rich proteoglycans (SLRPs) regulate extracellular matrix organization. In order to investigate the distribution and potential functions of decorin, biglycan (BGN), and fibromodulin (3 SLRPs, potentially related to dentinogenesis), we performed light and electron immunochemistry on teeth from rats, and on wild-type and biglycan knockout mice (BGN KO). Immunohistochemical data demonstrate that chondroitin sulfate/dermatan sulfate (CS/DS) and keratan sulfate (KS) distributions displayed reverse gradients in predentin. The decrease of CS/DS labeling from the proximal to the distal predentin contrasted with the sharp decorin increase observed in the distal predentin near the predentin/dentin transition, an effect possibly attributable to the deglycosylation action of stromelysin-1. In contrast, BGN concentration was apparently constant throughout the whole predentin. Additional immunolabelings showed, for the first time, the presence of fibromodulin in predentin. Compared with the wild-type mouse, the mean diameter of collagen fibrils in the BGN KO was smaller in the proximal predentin but larger in the central and distal predentin, the metadentin was broader, and the dentin mineralization appeared altered and heterogeneous. Altogether, our data suggest an important role for BGN in dentin formation and mineralization.

Functional role of test cells in swimming larvae of Ascidia malaca: ultrastructural and cytochemical investigations

The functional role played by test cells in larvae of various ascidian species consists in depositing sub-microscopic structures known as ornaments and/or proteoglycan substances on the larval test surface. According to the data reported in the literature, the deposition of ornaments together with proteoglycan substances on the larval test would render the latter hydrophilic and thus allow the larva to swim being immersed in water. Ornament deposition on the larval test does not occur in all the ascidian species. Ultrastructural investigations made on larvae belonging to the Cionidae and Ascididae families, for instance, have failed to evidence the presence of ornaments on the test. For these ascidian families it has been hypothesized that in swimming larvae test cells secrete an amorphous substance that would allow them to adhere to the larval test. In order to ascertain the functional role played by test cells in swimming larvae of the Ascididae family, the presently reported ultrastructural and cytochemical investigations have been made on larvae of Ascidia malaca. Besides suggesting that test cells, tightly adherent to the test surface, present an amoeboidic behaviour, the ultrastructural investigations have evidenced that these cells are still metabolically active. Their cytoplasm, characterized by the presence of a Golgi apparatus actively involved in synthesis, is almost entirely filled with very large granules; some of them gradually empty their contents turning into vacuoles containing scarce residues of electrondense particles. The present ultrastructural observations support the hypothesis that the adhesion of test cells on the larval test could be very likely eased by the secretion of substances synthesized by the Golgi and released through pseudopodes which test cells then wedge into the test. The cytochemical investigations were based on a reaction (fixation in glutaraldehyde-tannic acid) which evidences the presence, at the ultrastructural level, of proteoglycan substances such as glycosaminoglycans (Singley and Solursh, 1980). The reaction has given positive results in test cell granules undergoing emptying, on the outer membrane of the same cells, and on the outer cuticular layer C1 of the larval test. The present investigations, besides confirming the absence of ornament deposition on the test surface by test cells of Ascidia malaca swimming larvae, have evidenced that the secretion products deposited on the larval test surface by test cells consist of glycosaminoglycans, i.e. proteoglycan substances. In agreement with the data reported in the literature, it is hypothesized that the deposition of glycosaminoglycans on the surface of Ascidia malaca larval test makes the larval tunic hydrophilic and thus the larva is able to swim being immersed in water.

Individual cartilage aggrecan macromolecules and their constituent glycosaminoglycans visualized via atomic force microscopy

Atomic force microscopy was used in ambient conditions to directly image dense and sparse monolayers of bovine fetal epiphyseal and mature nasal cartilage aggrecan macromolecules adsorbed on mica substrates. Distinct resolution of the non-glycosylated N-terminal region from the glycosaminoglycan (GAG) brush of individual aggrecan monomers was achieved, as well as nanometer-scale resolution of individual GAG chain conformation and spacing. Fetal aggrecan core protein trace length (398+/-57 nm) and end-to-end length (257+/-87 nm) were both larger than that of mature aggrecan (352+/-88 and 226+/-81 nm, respectively). Similarly, fetal aggrecan GAG chain trace length (41+/-7 nm) and end-to-end (32+/-8 nm) length were both larger than that of mature aggrecan GAG (32+/-5 and 26+/-7 nm, respectively). GAG-GAG spacing along the core protein was significantly smaller in fetal compared to mature aggrecan (3.2+/-0.8 and 4.4+/-1.2nm, respectively). Together, these differences between the two aggrecan types were likely responsible for the greater persistence length of the fetal aggrecan (110 nm) compared to mature aggrecan (82 nm) calculated using the worm-like chain model. Measured dimensions and polymer statistical analyses were used in conjunction with the results of Western analyses, chromatographic, and carbohydrate electrophoresis measurements to better understand the dependence of aggrecan structure and properties on its constituent GAG chains.

Proteoglycan alterations and collagen reorganisation in the secondary avian cornea during development

PURPOSE

It is thought that proteoglycan (PG) alterations, collagen matrix reorganisation and the onset of corneal transparency in the developing avian cornea might be related events. The current histochemical study was designed to establish the character and distribution of corneal PG filaments in relation to collagen organisation during tissue morphogenesis.

METHODS

Corneas from days 13-18 developing chicken embryos were treated with cuprolinic blue (CuB) to examine sulphated PGs by transmission electron microscopy and quantitative image analysis.

RESULTS

On developmental day 13, corneas contained poorly defined lamellae and a large number of both small and large CuB-stained PG filaments, randomly distributed and often in collagen-free regions. By day 14 and after, the large CuB-stained PG filaments were much less abundant. At this time, too, collagen fibrils displayed an axial alignment and an occasional periodic arrangement of small CuB-stained PG filaments along their axes. By developmental day 15, lamellae were well formed and continued to increase in number and size thereafter. Between developmental days 16 and 17, there was a significant increase (p < 0.001) in the number of small, collagen-associated PG filaments. This increase persisted into day 18.

CONCLUSIONS

The size, number and distribution of sulphated, CuB-stained PG filaments in the developing avian cornea change over time. This is particularly true between developmental days 13 and 14 and between days 16 and 17, concurrent with previously documented structural changes.

Age-related liquefaction of the human vitreous body: LM and TEM evaluation of the role of proteoglycans and collagen

PURPOSE

To evaluate morphologic aspects of age-related liquefaction of the human vitreous body by light and electron microscopy to provide a basis from which future studies directed at the pathogenesis of this phenomenon can be undertaken. The study focuses on changes in fibrillar collagen and proteoglycans (PGs).

METHODS

Morphologic aspects of intravitreal liquefied spaces and matrix areas surrounding them were examined in 13 adult human donor eyes (aged 21-80 years) by light (LM) and transmission electron microscopy (TEM). Collagen fibrils were visualized by using standard contrasting methods. PGs were specifically stained by cupromeronic blue (CB).

RESULTS

Eyes from older donors contained larger spaces than eyes from younger ones. Transitions between matrix and spaces were abrupt or gradual. In transition areas of all specimens, a gradual decrease in the number of collagen fibers, and to a lesser extent of PGs was observed. In addition, a fragmentation of collagen fibers and an aggregation of PG-molecules around these fragments were found. Neither cells nor their fragments were observed in these areas.

CONCLUSIONS

This is the first study to evaluate vitreous liquefaction at the light and electron microscopic level. A breakdown of collagen fibrils into smaller fragments seems to be crucial to the pathogenesis of age-related liquefaction of the human vitreous body. The mechanism inducing fragmentation of vitreous fibrils has yet to be elucidated. From the absence of cells and cellular remnants in all specimens, it is tentatively concluded that an extracellular process is involved.

The small proteoglycan biglycan is associated with thick collagen fibrils in the mouse decidua

In mice, embryo implantation induces profound changes in the endometrium. These changes include redifferentiation of endometrial fibroblasts and extensive remodeling of extracellular matrix components. We have previously shown that, during this process, there is an impressive increase in the thickness of collagen fibrils present in decidualised areas that surround the implantation site, while collagen fibrils in non-decidualised areas and in the interimplantation site remain thin. In vitro and in vivo experiments have identified small leucine rich proteoglycans (SLRPs) as regulators of collagen fibrillogenesis. In a previous study, we demonstrated a difference between the pre-implantation and the post-implantation expression and distribution of four SLRPs types in uterine tissues. The present study, utilising immunocytochemical electron microscopy, shows that biglycan is associated with the presence of thick collagen fibrils in decidualised regions of the endometrium and that decorin is associated exclusively with thin collagen fibrils in non-decidualised endometrial areas. These results strongly indicate that biglycan plays a role in collagen fibrillogenesis and probably participates in the determination of collagen fibril thickness in the mouse decidua.

Connecting nanoscale images of proteins with their genetic sequences

We present a technique for reconstructing biomolecular structures from scanning force microscope data. The technique works by iteratively refining model molecules by comparison of simulated and experimental images. It can remove instrument artifacts to yield accurate dimensional measurements from tip-broadened data. The result of the reconstruction is a model that can be chosen to include the physically significant parameters for the system at hand. We demonstrate this by reconstructing scanning force microscope images of the cartilage proteoglycan aggrecan. By explicitly including the protein backbone in the model, we are able to associate measured three-dimensional structures with sites in the protein primary structure. The distribution of aggrecan core protein lengths that we measure suggests that 48% of aggrecan molecules found in vivo have been partially catabolized at either the E(1480)-(1481)G or E(1667)-(1668)G aggrecanase cleavage site.

Proteoglycan alterations in the rabbit corneal stroma after a lamellar incision

PURPOSE

To investigate proteoglycans under minimally damaged epithelium after a lamellar microkeratome incision.

SETTING

Collaborating university departments.

METHODS

Anterior lamellar caps were excised from rabbit corneas and then resutured in place. Healing tissue was examined by electron microscopy with proteoglycan staining.

RESULTS

In the weeks after surgery, regions of disorganized stromal matrix were populated by sulfated proteoglycan filaments that were much larger (up to 300 nm long) than those in quiescent stroma.

CONCLUSIONS

Large, sulfated proteoglycans existed in rabbit corneas healing from lamellar incisions. These molecules appear to be a normal feature of corneal wound healing; because of their water-binding capacity, they might aid tissue restructuring.

Experimental induction of anterior disk displacement of the rabbit craniomandibular joint: an immuno-electron microscopic study of collagen and proteoglycan occurrence in the condylar cartilage

BACKGROUND

Results from our previous studies suggest that surgical induction of anterior disk displacement (ADD) in the rabbit craniomandibular joint (CMJ) leads to histopathological alterations consistent with osteoarthritis. In addition, molecular changes in collagens and glycosaminoglycans (GAGs) were observed using immunohistochemistry. The purpose of the present study was to further characterize those molecular changes in collagens and GAGs using immuno-electron microscopy.

METHODS

The right joint of 15 rabbits was exposed surgically and all discal attachments were cut except for the posterior attachment (the bilaminar zone). The disc was then repositioned anteriorly and sutured to the zygomatic arch. The left joint was used as a sham-operated control. Ten additional joints were used as non-operated controls. Mandibular condyles were removed 2 weeks following surgery and processed for light and immuno-electron microscopy using colloidal gold-labeled antibodies against collagen type I, II, VI and IX and against keratan sulfate, chondroitin-4 and -6-sulfate, and link protein.

RESULTS

Light microscopic results showed osteoarthritic changes. Immuno-electron microscopy of osteoarthritic cartilage demonstrated a decline in type II collagen, the abnormal presence of type I collagen and loss of type VI and IX collagens. Quantitative colloidal gold immuno-electron microscopy confirmed the depletion of keratan sulfate, chondroitin-4 and -6-sulfate, and link protein in osteoarthritic cartilage.

CONCLUSION

Anterior disk displacement leads to molecular alterations in both the collagen and the proteoglycans of rabbit condylar cartilage characteristic of osteoarthritis in other synovial joints. These alterations are consistent with loss of the shock absorber function of the cartilage and injury of the underlying bone.

Age-related changes in the composition, the molecular stoichiometry and the stability of proteoglycan aggregates extracted from human articular cartilage

The heterogeneity of the components of proteoglycan aggregates, their stoichiometry within the aggregate and the aggregates' stability was investigated in normal human articular cartilage specimens (age-range newborn to 63 years). Proteoglycans were extracted from tissue by sequentially extracting them with PBS alone, PBS containing oligosaccharides of hyaluronan, and PBS containing solutions of increasing guanidinium chloride concentration (1 M, 2 M, 3 M and 4 M). A high proportion of each of the components of the proteoglycan aggregate, i.e. uronic acid, sulphated glycosaminoglycan, hyaluronan binding domain of aggrecan (G1-domain), link protein (LP) and hyaluronan, was extracted from immature cartilage by PBS alone and PBS containing oligosaccharides of hyaluronan. This was in marked contrast to adult cartilage, which required high concentrations of guanidinium chloride for the efficient extraction of these components. The molar ratios of total G1-domain:LP and the G1-domain associated with aggrecan:LP also differed markedly between immature and mature cartilage and between each of the sequential extracts. The concentration of LP was less than that of the G1-domain in all extracts of cartilage from individuals over 13 years, but this was particularly noticeable in the 1 M guanidinium chloride extracts, and it was surmised that a deficiency in LP produces unstable aggregates in situ. The fragmentation of LP, which is known to occur with advancing age, did not influence the extractability of LP, and fragments were present in each of the sequential extracts. Therefore the generally accepted model of proteoglycan aggregation presented in the literature, which is mostly derived from analysis of immature animal cartilage, cannot be used to describe the structure and organization of aggregates in adult human articular cartilage, where a heterogeneous population of complexes exist that have varying degrees of stability.

Modulation of vascular smooth muscle cells proteoglycan synthesis by the extracellular matrix

In this study, we investigated the effect of the extracellular matrix (ECM) secreted by vascular cells on proteoglycan (PG) synthesis by vascular smooth muscle cells in culture. PG synthesis of human aortic smooth muscle cells plated on plastic or the matrices derived from vascular endothelial cells, vascular smooth muscle cells, or THP-1 macrophages was characterized. Smooth muscle cell and macrophage matrices increased both secreted and cellular smooth muscle cells PG production by 2.5-fold to 3.9-fold, respectively, over plastic and endothelial cell matrix. Macrophage matrix was more potent than smooth muscle cell matrix in this regard. Selective enzymatic removal of chondroitin sulfates, collagen, and elastin from smooth muscle cell matrix enhanced the stimulation of PG synthesis, as did the removal of chondroitin sulfates from macrophage matrix. PG turnover rates were similar for smooth muscle cells plated on the three matrices. The newly synthesized PG from cultures plated on smooth muscle cell-, and macrophage-derived matrices had greater charge density, larger molecular size, and longer glycosaminoglycan chains than those from endothelial cell matrix cultures. These data show that the ECM plays a major role in modulating vascular smooth muscle cell PG metabolism in vitro.

Circular proteoglycans from sponges: first members of the spongican family

Species-specific cell adhesion in marine sponges is mediated by a new family of modular proteoglycans whose general supramolecular structure resembles that of hyalectans. However, neither their protein nor their glycan moieties have significant sequence homology to other proteoglycans, despite having protein subunits equivalent to link proteins and to proteoglycan monomer core proteins, and glycan subunits equivalent to hyaluronan and to the glycosaminoglycans of hyalectans. In some species, these molecular components are assembled into a structure with a circular core formed by the link protein- and hyaluronan-like subunits. Besides their involvement in cell adhesion, these sponge proteoglycans, for which we propose the term spongicans, participate in signal transduction processes and are suspected to play a role in sponge self-nonself recognition. Their in vivo roles and the mild methods used to purify large amounts of functionally active spongicans make them ideal models to study the functions and possible new applications of proteoglycans in biomedical research.

Ontogeny of enhanced decorin levels and distribution within myocardium of failing hearts

The proteoglycan, decorin, is a regulator of collagen fibril organization and its resulting functional properties. The temporal and spatial expression of decorin during the progression to heart failure is not well understood and may play a significant role in extracellular matrix remodeling. Decorin and types I and III collagen levels were measured in male Spontaneously Hypertensive Heart Failure (SHHF) and control Wistar-Furth rats at 2 and 8 mo, and at congestive heart failure (CHF). Decorin levels increased in the SHHF rats relative to the control rats in CHF. Type I collagen levels increased while type III levels decreased in the SHHF rats in CHF relative to the age matched controls. The SHHF rats have 48 and 45 KDa isoforms of the decorin core protein expressed at all ages while control Wistar-Furths produced only a 45 KDa form. Decorin was localized in the outer ventricle wall but during CHF, decorin was expressed throughout the ventricular myocardium. Immunogold localization of decorin demonstrated an increased distribution of decorin along the myocardium collagen fibrils at CHF. The enhanced expression and greater distribution of decorin may be linked to extracellular matrix remodeling which occurs with the development of heart failure.

Aging, articular cartilage chondrocyte senescence and osteoarthritis

The incidence of osteoarthritis (OA), the disease characterized by joint pain and loss of joint form and function due to articular cartilage degeneration, is directly correlated with age. The strong association between age and increasing incidence of osteoarthritis (OA) marks OA as an age related disease. Yet, like many other age related diseases, OA is not an inevitable consequence of aging; instead, aging increases the risk of OA. Articular cartilage aging changes that may lead to articular cartilage degeneration include fraying and softening of the articular surface, decreased size and aggregation of proteoglycan aggrecans and loss of matrix tensile strength and stiffness. These changes most likely are the result of an age related decrease in the ability of chondrocytes to maintain and repair the tissue manifested by decreased mitotic and synthetic activity, decreased responsiveness to anabolic growth factors and synthesis of smaller less uniform aggrecans and less functional link proteins. Our recent work suggests that progressive chondrocyte senescence marked by expression of the senescence associated enzyme beta-galactosidase, erosion of chondrocyte telomere length and mitochondrial degeneration due to oxidative damage causes the age related loss of chondrocyte function. New efforts to prevent the development and progression of OA might include strategies that slow the progression of chondrocyte senescence or replace senescent cells.

Ultrastructure of proteoglycans in tissue-engineered cardiovascular structures

Proteoglycans such as versican, decorin, and perlecan are important components of the extracellular matrix in various tissues. They play an important role in water homeostasis, tissue elasticity, prevention of calcification, and thrombogenicity. The aim of our study was to detect such proteoglycans in engineered tissue and compare them with the proteoglycans of native porcine heart valves. Myofibroblasts were seeded on a type I collagen scaffold. Thereafter, endothelial cells were seeded onto the presettled myofibroblasts. The newly formed tissue was histologically and immunohistochemically examined. Cupromeronic blue was used for ultracytochemical staining of proteoglycans. Radiolabeled proteoglycans were isolated by ion-exchange chromatography and characterized by enzymatic degradation. Three differently sized proteoglycan precipitates were found. The large-sized proteoglycan (154 nm) was located outside the collagen bundles in a rarely structured extracellular matrix compound. The small-sized proteoglycan (46 nm) was aligned along the collagen bundles at intervals of 60 nm. The intermediate-sized proteoglycan (56 nm) was detected on the cell surface of myofibroblasts. The glycosaminoglycans included 80% chondroitin and dermatan sulfate and 20% heparan sulfate. We conclude that proteoglycans play an important role in the functional integrity of cardiovascular tissues. This study shows the successful production of a heart valve-like tissue with proteoglycans resembling, in terms of type, production, and distribution, proteoglycans of native heart valves.

Localization of the transmembrane proteoglycan syndecan-4 and its regulatory kinases in costameres of rat cardiomyocytes: a deconvolution microscopic study

Syndecan-4 (syn-4), a transmembrane heparan sulfate-containing proteoglycan, is unique among the four members of the syndecan family in its specific cellular localization to complex cytoskeletal adhesion sites, i.e., focal adhesions. During early phenotypic redifferentiation of neonatal cardiomyocytes in culture, immunolocalization reveals syn-4 to be heavily concentrated in the perinuclear endoplasmic reticulum-Golgi region, with little found at the peripheral regions. Subsequently, syn-4 becomes localized to a cytoskeletal adhesion complex unique to striated muscle, the costamere. Soon after redifferentiation of myofibrils in cultured neonatal cardiomyocytes, syn-4 is present only in costameres, not in focal adhesions. In cultured adult cardiomyocytes, it is present in both costameres and focal adhesions-the latter in two distinct regions of the spread cardiomyocytes, reflecting localization with two types of actin-containing filaments. The fact that syn-4 is observed early in the costameric regions, as opposed to later in the focal adhesions, suggests that it may play an initial role in early adhesion/signal transduction mechanisms in close proximity to the contractile apparatus, as well as in transmission of contractile force to the collagenous extracellular matrix (ECM) which surrounds the cardiac myofibers in situ. With respect to possible regulatory mechanisms of syn-4, we localized syn-4 with both the epsilon isoform of protein kinase C and the tyrosine kinase pp60(csrc) in costameric regions. These findings suggest that syn-4 may not only play a role in cellular adhesion and contractile force transmission, it may also, through ser, thr, and tyr phosphorylation, be part of an interactive signal transduction mechanism in myocardial functioning via these adhesive cytoskeletal complexes.

Proteoglycan–collagen associations in the non-lactating human breast connective tissue during the menstrual cycle

The human mammary gland undergoes a sequence of histological changes in both epithelial and stromal compartments during the menstrual cycle. Swelling and unswelling of the breast stromal tissue is a characteristic feature of the two phases of the cycle and is mediated by changes in the water content of sulfated proteoglycans in the matrix between the fibrils. In an ultrastructural study we investigated the distribution of sulfated proteoglycans identified as cupromeronic blue-positive needle-like structures and measured the distance between the dermatan sulfate-proteoglycan attachment sites at the d-bands of the collagen fibrils in the loose intralobular connective tissue and in the dense interlobular connective tissue. We characterized the dermatan sulfate proteoglycan by enzyme digestion and by immunogold-labeled antibody. In the follicular phase a relatively constant distance of 46 nm between neighboring proteoglycan attachment sites was found, while in the luteal phase the measured distances are strikingly variable and exceed the follicular value by up to 9 nm. This difference of the two cycle phases is more evident in the loose than in the dense connective tissue. Possibly the changes of the fibril-attached proteoglycans in the luteal phase reflect an influence of the higher water content of the matrix leading to a probably torsional swelling of the collagen fibril.

Ultrastructural changes in the transitional zone between articular cartilage and synovial membrane during the development of experimental osteoarthrosis

We studied the ultrastructural changes that take place in the transitional zone between the articular cartilage and the synovial membrane during the development of experimental osteoarthrosis. We focused special attention on changes involving the proteoglycan complexes within the matrix of articular cartilage. We observed that changes in the transitional zone resemble those seen in articular cartilage during the development of osteoarthrosis. We also found transient cellular forms with fibroblast phenotype regulating the demands of both cartilage and synovial matrix. The transient nature of these elements determines the pronounced lability of this zone, and this may be related to the early development of osteoarthrosis.

Structural aspects of the extracellular matrix of the tendon: an atomic force and scanning electron microscopy study

The mutual interactions of small proteoglycans with collagen fibrils in the extracellular matrix remain to be completely understood. The present research investigated the extracellular matrix of the rat tail tendon by atomic force microscopy (AFM) as well as by scanning electron microscopy (SEM). Observations showed simply dehydrated specimens made of large heterogeneous fibrils, tightly packed in mutual contact with no visible interfibrillar spaces. Proteoglycans usually extended onto neighboring fibrils, forming an intricate interfibrillar weaving highly sensitive to chondroitinase digestion. Pre-treatment with cupromeronic blue only affected the proteoglycans side chains, which appeared better preserved but somewhat thickened. Observation of hydrated specimens by AFM confirmed the close packing of collagen fibrils and the abundance of collagen-bound proteoglycans. Interfibrillar bridges were only occasionally observed in this tissue, whose fibrils are instead tightly bound together by proteoglycans in a structure quite consistent with its functional requirements. The molecular machinery responsible for these interactions is the subject of ongoing research.