Aggrecan, the Primary Weight-Bearing Cartilage Proteoglycan, Has Context-Dependent, Cell-Directive Properties in Embryonic Development and Neurogenesis: Aggrecan Glycan Side Chain Modifications Convey Interactive Biodiversity

This review examines aggrecan's roles in developmental embryonic tissues, in tissues undergoing morphogenetic transition and in mature weight-bearing tissues. Aggrecan is a remarkably versatile and capable proteoglycan (PG) with diverse tissue context-dependent functional attributes beyond its established role as a weight-bearing PG. The aggrecan core protein provides a template which can be variably decorated with a number of glycosaminoglycan (GAG) side chains including keratan sulphate (KS), human natural killer trisaccharide (HNK-1) and chondroitin sulphate (CS). These convey unique tissue-specific functional properties in water imbibition, space-filling, matrix stabilisation or embryonic cellular regulation. Aggrecan also interacts with morphogens and growth factors directing tissue morphogenesis, remodelling and metaplasia. HNK-1 aggrecan glycoforms direct neural crest cell migration in embryonic development and is neuroprotective in perineuronal nets in the brain. The ability of the aggrecan core protein to assemble CS and KS chains at high density equips cartilage aggrecan with its well-known water-imbibing and weight-bearing properties. The importance of specific arrangements of GAG chains on aggrecan in all its forms is also a primary morphogenetic functional determinant providing aggrecan with unique tissue context dependent regulatory properties. The versatility displayed by aggrecan in biodiverse contexts is a function of its GAG side chains.

Biophysical Stimuli: A Review of Electrical and Mechanical Stimulation in Hyaline Cartilage

OBJECTIVE

Hyaline cartilage degenerative pathologies induce morphologic and biomechanical changes resulting in cartilage tissue damage. In pursuit of therapeutic options, electrical and mechanical stimulation have been proposed for improving tissue engineering approaches for cartilage repair. The purpose of this review was to highlight the effect of electrical stimulation and mechanical stimuli in chondrocyte behavior.

DESIGN

Different information sources and the MEDLINE database were systematically revised to summarize the different contributions for the past 40 years.

RESULTS

It has been shown that electric stimulation may increase cell proliferation and stimulate the synthesis of molecules associated with the extracellular matrix of the articular cartilage, such as collagen type II, aggrecan and glycosaminoglycans, while mechanical loads trigger anabolic and catabolic responses in chondrocytes.

CONCLUSION

The biophysical stimuli can increase cell proliferation and stimulate molecules associated with hyaline cartilage extracellular matrix maintenance.

Glycosaminoglycans are differentially involved in bacterial binding to healthy and cystic fibrosis lung cells

BACKGROUND

Glycosaminoglycans (GAGs) are essential in many infections, including recurrent bacterial respiratory infections, the main cause of mortality in cystic fibrosis (CF) patients.

METHODS

Using a cellular model of healthy and CF lung epithelium, a comparative transcriptomic study of GAG encoding genes was performed using qRT-PCR, and their differential involvement in the adhesion of bacterial pathogens analyzed by enzymatic degradation and binding competition experiments.

RESULTS

Various alterations in gene expression in CF cells were found which affect GAG structures and seem to influence bacterial adherence to lung epithelium cells. Heparan sulfate appears to be the most important GAG species involved in bacterial binding.

CONCLUSIONS

Adherence to lung epithelial cells of some of the main pathogens involved in CF is dependent on GAGs, and the expression of these polysaccharides is altered in CF cells, suggesting it could play an essential role in the development of infectious pathology.

In the absence of overt urothelial damage, chondroitinase ABC digestion of the GAG layer increases bladder permeability in ovariectomized female rats

Loss of integrity of the protective impermeability barrier in the urothelium has been identified as significant in bladder dysfunction. In this study, we tested the theory that the luminal layer of glycosaminoglycans (GAG) serves as an important component of barrier function. The peptide polycation protamine sulfate (PS), 1 mg/ml, was instilled intravesically for 10 min into rat bladders. Chondroitinase ABC (ChABC), 63 IU/ml, was instilled into an additional six rats for 30 min to digest the GAG layer. Unmanipulated controls and sham-injected controls were also performed. After 24 h, the rats were euthanized, the bladders were removed, and permeability was assessed in the Ussing chamber and by diffusion of FITC-labeled dextran (4 kDa) to measure macromolecular permeability. The status of tight junctions was assessed by immunofluorescence and electron microscopy. In control and sham treated rat bladders, the transepithelial electrical resistance were means of 2.5 ± 1.1 vs. 2.6 ± 1.1 vs 1.2 ± 0.5 and 1.01 ± 0.7 kΩ·cm(2) in the PS-treated and ChABC-treated rat bladders (P = 0.0016 and P = 0.0039, respectively). Similar differences were seen in dextran permeability. Histopathology showed a mild inflammation following PS treatment, but the ChABC-treated bladders were indistinguishable from controls. Tight junctions generally remained intact. ChABC digestion alone induced bladder permeability, confirming the importance of the GAG layer to bladder barrier function and supports that loss of the GAG layer seen in bladder biopsies of interstitial cystitis patients could be a significant factor producing symptoms for at least some interstitial cystitis/painful bladder syndrome patients.

A vessel active contour model for vascular segmentation

This paper proposes a vessel active contour model based on local intensity weighting and a vessel vector field. Firstly, the energy function we define is evaluated along the evolving curve instead of all image points, and the function value at each point on the curve is based on the interior and exterior weighted means in a local neighborhood of the point, which is good for dealing with the intensity inhomogeneity. Secondly, a vascular vector field derived from a vesselness measure is employed to guide the contour to evolve along the vessel central skeleton into thin and weak vessels. Thirdly, an automatic initialization method that makes the model converge rapidly is developed, and it avoids repeated trails in conventional local region active contour models. Finally, a speed-up strategy is implemented by labeling the steadily evolved points, and it avoids the repeated computation of these points in the subsequent iterations. Experiments using synthetic and real vessel images validate the proposed model. Comparisons with the localized active contour model, local binary fitting model, and vascular active contour model show that the proposed model is more accurate, efficient, and suitable for extraction of the vessel tree from different medical images.

Aging of connective tissues: experimental facts and theoretical considerations

In this chapter, we describe in detail the age-dependent modifications of connective tissues, separately for their cellular and extracellular compartments. Cell aging was studied by the in vitro method established by Hayflick as well as by ex vivo explant cultures, and results with both methods are discussed. Follows then the description of age changes of macromolecular components of extracellular matrix as well as the decline with age of receptor-mediated cell-matrix interactions. These interactions mediated by several types of receptors, as integrins, the elastin receptor and others, play a crucial role for the definition and regulation of the differentiated cell phenotype. Age-related modifications of both matrix components and receptors are discussed in order to explain the mechanisms of the age-dependent modulations of cell-matrix interactions. Finally, we discuss the relations between age changes of matrix components and the onset of age-related diseases, especially cardiovascular pathologies mostly involved in age-dependence of functions and limitation of longevity.

Development and use of sulodexide in vascular diseases: implications for treatment

Sulodexide (SDX), a sulfated polysaccharide complex extracted from porcine intestinal mucosa, is a blend of two glycosaminoglycan (GAG) entities, namely a fast-moving heparin (HP) fraction and a dermatan sulfate (DS; 20%) component. The compound is unique among HP-like substances in that it is biologically active by both the parenteral and oral routes. A main feature of the agent is to undergo extensive absorption by the vascular endothelium. For this reason, in preclinical studies, SDX administered parenterally displays an antithrombotic action similar to that of HPs but associated with fewer alterations of the blood clotting mechanisms and tests, thus being much less conducive to bleeding risk than HPs. When given orally, SDX is associated with minimal changes in classic coagulation tests, but maintains a number of important effects on the structure and function of endothelial cells (EC), and the intercellular matrix. These activities include prevention or restoration of the integrity and permeability of EC, counteraction versus chemical, toxic or metabolic EC injury, regulation of EC-blood cell interactions, inhibition of microvascular inflammatory and proliferative changes, and other similar effects, thus allowing oral SDX to be considered as an endothelial-protecting agent. The best available clinical evidence of the efficacy of SDX administered orally with or without an initial parenteral phase is the following: alleviation of symptoms in chronic venous disease and especially acceleration of healing of venous leg ulcers; prevention of cardiovascular events in survivors after acute myocardial infarction; marked improvement of intermittent claudication in patients with peripheral occlusive arterial disease; and abatement of proteinuria in patients with diabetic nephropathy that may contribute to the amelioration or stabilization of kidney function. Although further clinical trials are warranted, SDX is presently widely accepted in many countries as an effective and safe long-term, endothelial-protecting drug.

GAG depletion increases the stress-relaxation response of tendon fascicles, but does not influence recovery

Cyclic and static loading regimes are commonly used to study tenocyte metabolism in vitro and to improve our understanding of exercise-associated tendon pathologies. The aims of our study were to investigate if cyclic and static stress relaxation affected the mechanical properties of tendon fascicles differently, if this effect was reversible after a recovery period, and if the removal of glycosaminoglycans (GAGs) affected sample recovery. Tendon fascicles were dissected frombovine-foot extensors and subjected to 14% cyclic (1Hz) or static tensile strain for 30min. Additional fascicles were incubated overnight in buffer with 0.5U chondroitinase ABC or in buffer alone prior to the static stress-relaxation regime. To assess the effect of different stress-relaxation regimes, a quasi-static test to failure was carried out, either directly post loading or after a 2h recovery period, and compared with unloaded control fascicles. Both stress-relaxation regimes led to a significant reduction in fascicle failure stress and strain, but this was more pronounced in the cyclically loaded specimens. Removal of GAGs led to more stress relaxation and greater reductions in failure stress after static loading compared to controls. The reduction in mechanical properties was partially reversible in all samples, given a recovery period of 2h. This has implications for mechanical testing protocols, as a time delay between fatiguing specimens and characterization of mechanical properties will affect the results. GAGs appear to protect tendon fascicles from fatigue effects, possibly by enabling sample hydration.

[Role of glycosaminoglycans in pathogenesis of atherosclerosis]

In this review we summarize the role of glycosaminoglycans and proteoglycans in pathogenesis of atherosclerosis and possibilities for correction of lesions of atherosclerotic vessels via influence on their metabolism.

Deformation simulation of cells seeded on a collagen-GAG scaffold in a flow perfusion bioreactor using a sequential 3D CFD-elastostatics model

Tissue-engineered bone shows promise in meeting the huge demand for bone grafts caused by up to 4 million bone replacement procedures per year, worldwide. State-of-the-art bone tissue engineering strategies use flow perfusion bioreactors to apply biophysical stimuli to cells seeded on scaffolds and to grow tissue suitable for implantation into the patient's body. The aim of this study was to quantify the deformation of cells seeded on a collagen-GAG scaffold which was perfused by culture medium inside a flow perfusion bioreactor. Using a microCT scan of an unseeded collagen-GAG scaffold, a sequential 3D CFD-deformation model was developed. The wall shear stress and the hydrostatic wall pressure acting on the cells were computed through the use of a CFD simulation and fed into a linear elastostatics model in order to calculate the deformation of the cells. The model used numerically seeded cells of two common morphologies where cells are either attached flatly on the scaffold wall or bridging two struts of the scaffold. Our study showed that the displacement of the cells is primarily determined by the cell morphology. Although cells of both attachment profiles were subjected to the same mechanical load, cells bridging two struts experienced a deformation up to 500 times higher than cells only attached to one strut. As the scaffold's pore size determines both the mechanical load and the type of attachment, the design of an optimal scaffold must take into account the interplay of these two features and requires a design process that optimizes both parameters at the same time.

Physiological changes in tissues denervated by spinal cord injury tissues and possible effects on wound healing

There are many metabolic and physiological changes that happen to the tissues below the level of a spinal cord injury. These deficits are examined in relation to the series of events that has to take place for wound healing - the "wound healing cascade". The conclusion is that every step of the wound healing process is impaired by the physiological deficits inherent post-spinal cord injury. This may explain, in part, why pressure ulcers on these patients are so difficult to close and to maintain closed.

Extracellular matrix in the trabecular meshwork

The extracellular matrix (ECM) of the trabecular meshwork (TM) is thought to be important in regulating intraocular pressure (IOP) in both normal and glaucomatous eyes. IOP is regulated primarily by a fluid resistance to aqueous humor outflow. However, neither the exact site nor the identity of the normal resistance to aqueous humor outflow has been established. Whether the site and nature of the increased outflow resistance, which is associated with open-angle glaucoma, is the same or different from the normal resistance is also unclear. The ECMs of the TM beams, juxtacanalicular region (JCT) and Schlemm's canal (SC) inner wall are comprised of fibrillar and non-fibrillar collagens, elastin-containing microfibrils, matricellular and structural organizing proteins, glycosaminoglycans (GAGs) and proteoglycans. Both basement membranes and stromal ECM are present in the TM beams and JCT region. Cell adhesion proteins, cell surface ECM receptors and associated binding proteins are also present in the beams, JCT and SC inner wall region. The outflow pathway ECM is relatively dynamic, undergoing constant turnover and remodeling. Regulated changes in enzymes responsible for ECM degradation and biosynthetic replacement are observed. IOP homeostasis, triggered by pressure changes or mechanical stretching of the TM, appears to involve ECM turnover. Several cytokines, growth factors and drugs, which affect the outflow resistance, change ECM component expression, mRNA alternative splicing, cellular cytoskeletal organization or all of these. Changes in ECM associated with open-angle glaucoma have been identified.

Chemokines: novel targets for breast cancer metastasis

Recent studies have highlighted the possible involvement of chemokines and their receptors in breast cancer progression and metastasis. Chemokines and their receptors constitute a superfamily of signalling factors whose prognosis value in breast cancer progression remains unclear. We will examine here the expression pattern of chemokines and their receptors in mammary gland physiology and carcinogenesis. The nature of the cells producing chemokines or harboring chemokine receptors appears to be crucial in certain conditions for example, the infiltration of the primary tumor by leukocytes and angiogenesis. In addition, chemokines, their receptors and the interaction with glycosaminoglycan (GAGs) are key players in the homing of cancer cells to distant metastasis sites. Several lines of evidence, including in vitro and in vivo models, suggest that the mechanism of action of chemokines in cancer development involves the modulation of proliferation, apoptosis, invasion, leukocyte recruitment or angiogenesis. Furthermore, we will discuss the regulation of chemokine network in tumor neovascularity by decoy receptors. The reasons accounting for the deregulation of chemokines and chemokine receptors expression in breast cancer are certainly crucial for the comprehension of chemokine role in breast cancer and are in several cases linked to estrogen receptor status. The targeting of chemokines and chemokine receptors by antibodies, small molecule antagonists, viral chemokine binding proteins and heparins appears as promising tracks to develop therapeutic strategies. Thus there is significant interest in developing strategies to antagonize the chemokine function, and an opportunity to interfere with metastasis, the leading cause of death in most patients.

Proteoglycanomics: tools to unravel the biological function of glycosaminoglycans

Glycosylation is the most frequent PTM and contributes significantly to the function of proteins depending on the type of glycosylation. Especially glycan structures like the glycosaminoglycans are considered to constitute themselves the major function of the glycoconjugate which is therefore termed proteoglycan. Here we review recent views on and novel tools for analysing the proteoglycanome, which are directly related to the type of glycanation under investigation. We define the major function of the proteoglycanome to be its interaction with various proteins in many different (patho-)physiological conditions. This is exemplified by the differential glycosaminoglycan-interactome of healthy versus arthritic patient sera.

A tissue engineered osteochondral plug: an in vitro morphological evaluation

Articular cartilage lesions have a poor intrinsic healing potential. The repair tissue is often fibrous, having insufficient biomechanical properties, which could frequently lead to the development of early osteoarthritis. In the last decade, tissue engineering approaches addressed this topic in order to restore joint function with a differentiated and functional tissue. Many biomaterials and techniques have been proposed and some of them applied in clinical practice, even though several concerns have been raised on the quality of the engineered tissue and on its integration in the host joint. In this study, we focused on engineering in vitro a biphasic composite made of cellular fibrin glue and a calcium-phosphate scaffold. Biphasic composites are the latest products of tissue engineering applied to articular cartilage and they seem to allow a more efficient integration of the engineered tissue with the host. However, a firm in vitro bonding between the two components of the composite is a necessary condition to validate this model. Our study demonstrated a gross and microscopic integration of the two components and a cartilage-like quality of the newly formed matrix. Moreover, we noticed an improvement of this integration and GAGs production during the in vitro culture.

A new technique for calculating individual dermal fibroblast contractile forces generated within collagen-GAG scaffolds

Cell-mediated contraction plays a critical role in many physiological and pathological processes, notably organized contraction during wound healing. Implantation of an appropriately formulated (i.e., mean pore size, chemical composition, degradation rate) three-dimensional scaffold into an in vivo wound site effectively blocks the majority of organized wound contraction and results in induced regeneration rather than scar formation. Improved understanding of cell contraction within three-dimensional constructs therefore represents an important area of study in tissue engineering. Studies of cell contraction within three-dimensional constructs typically calculate an average contractile force from the gross deformation of a macroscopic substrate by a large cell population. In this study, cellular solids theory has been applied to conventional column buckling relationships to quantify the magnitude of individual cell contraction events within a three-dimensional, collagen-glycosaminoglycan scaffold. This new technique can be used for studying cell mechanics with a wide variety of porous scaffolds that resemble low-density, open-cell foams. It extends previous methods for analyzing cell buckling of two-dimensional substrates to three-dimensional constructs. From data available in the literature, the mean contractile force (Fc) generated by individual dermal fibroblasts within the collagen-glycosaminoglycan scaffold was calculated to range between 11 and 41 nN (Fc=26+/-13 nN, mean+/-SD), with an upper bound of cell contractility estimated at 450 nN.

Utility and control of proteoglycans in tissue engineering

This review addresses various methods of integrating proteoglycans (PGs) into the design of engineered tissues and provides insight for designing tissue-engineered disease models that leverage current knowledge of PG biology. Even though PGs show immense possibilities in tissue-engineering applications, they have seldom been used to their full potential. The most common tissue-engineering application of PGs has been in scaffolds (matrigels and collagen-chondroitin sulfate matrices), in which PGs or their glycosaminoglycan (GAG) chains are incorporated into the scaffold to promote cell growth, tissue remodeling, and intracellular signaling. In addition, many studies have reported the total amount of PGs synthesized within engineered tissues but have not delineated which specific PGs or GAG classes are involved in engineered tissue development. In native tissues, various PGs are dynamically and differentially regulated to achieve specific biophysical and biological functions, such as compressibility and transparency. Therefore, the targeted modulation of specific PGs (via exogenous addition, endogenous stimulation with growth factors, or mechanical stimulation) may help engineered tissues to achieve native tissue properties. The PG composition of engineered tissues could also be modified to achieve disease models in vitro and thus provide a way to study the effect of external agents on PG-related disease mechanisms.

[Skin changes in amyotrophic lateral sclerosis]

It has been repeatedly noted, but never as yet fully explained, that patients with amyotrophic lateral sclerosis (ALS) do not develop bedsores even at the terminal stage. Furthermore, the skin of ALS patients feels supple, like tanned leather, and loses elasticity. When the skin is stretched, it returns only sluggishly to its original position. We termed this property of skin "delayed return phenomenon (DRP)"; it is usually seen more than 2.5 years after the onset of symptoms. Although it is thought that a phenomena such as DRP and the absence of bedsores are characteristic of this disease, little attention has been paid to these unique features in ALS patients. In this review we summarize recent developments in research on skin from ALS patients. From our own works cited in this review it is clear that not only the motor neuron but also the skin is affected in ALS, and that abnormalities of collagen, glycosaminoglycans, vascular endotherial growth factor (VEGF) and neurotrophic factors like ciliary neurotrophic factor (CNTF), neurotrophin-3 (NT-3) and insulin-like growth factor-1 (IGF-1) do occur in the skin of ALS. Examination of the skin in patients with ALS would be easy to carry out as an additional examination. Further analysis of the complex skin abnormalities will be useful in elucidating the basic pathological mechanism of ALS.

Heparan sulphate proteoglycan as mediator of some adhesive responses and cytoskeletal reorganization of cells on fibronectin matrices: independent versus cooperative functions

Fibronectin is a multifunctional glycoprotein which promotes the adhesion of a variety of cell types to extracellular matrices, including artificial tissue culture substrata. Biochemical analyses of substratum adhesion sites indicated important functions for cell-surface heparan sulphate proteoglycan (HS-PG) in directly mediating adhesive responses by the binding of heparan sulphate sequences to fibronectin. In addition, fibronectin has a binding domain for a cell surface 'receptor' (possibly a 140K glycoprotein) important in these responses. To differentiate the relative importance of these two binding activities, a proteolytically generated cell-binding fragment of fibronectin has been isolated which binds to the 140K 'receptor' but not to HS or to collagen. Platelet factor 4 (PF4), a tetravalent HS-binding protein, provides a model of the tetravalent HS-binding activity of fibronectin, as supported by affinity chromatography studies (these studies also reveal the complexity of HS-PG metabolism in adhesion sites). Responses are measured on substrata coated with the cell-binding fragment of fibronectin, intact fibronectin, or PF4, singly or in combination. Fibroblast-like BALB/c 3T3 cells form both close and tight-focal adhesive contacts with associated microfilament stress fibres on intact fibronectin. Whereas HS-PG binding appears to mediate the formation of close contacts and linear microfilament bundles, a cooperative relationship exists between the HS- and the cell-binding activities of the intact fibronectin molecule in the formation of focal contacts and stress fibres. Human dermal fibroblasts generate different adhesive responses on HS-binding or cell-binding substrata, which are dependent on whether cells have been grown in medium with ascorbate to maximize production of their own collagenous matrix. As with 3T3 cells, focal contact and stress fibre formations of dermal cells require both binding activities in the intact fibronectin molecule. A third system consists of neuroblastoma tumour cells which adhere and extend neurites on fibronectin. Cell-body adherence, but not neurite extension, occurs on HS-binding matrices whereas neurite extension requires only fibronectin's cell-binding activity; the responses of primary peripheral neurons were exactly the opposite and CNS neurons did not respond at all. These studies indicate the diversity of molecular mechanisms by which various cells interact with the multifunctional fibronectin molecule in order to perform specialized functions, as well as the independent or cooperative functions of heparan sulphate proteoglycan on the cell surface in mediating these responses.

The functions of the heparan sulphate proteoglycans

Heparan sulphate (HS)-containing proteoglycans (HS-PGs) are present at the surface of nearly all adherent mammalian cells. The principal mode of attachment is by way of the protein core which is inserted into the plasma membrane. Other forms of HS-PG may be components of pericellular matrices, notably basement membranes. The core proteins of HS-PGs can be small (35K) as in hepatocytes, intermediate (50K) as in many mesenchymal cells, or very large (400K) as in basement membranes. A special case is the HS-PG synthesized by postconfluent fibroblasts. This proteoglycan has a core protein that closely resembles the transferrin receptor glycoprotein. It is possible that this HS-PG is a pro-form of the receptor. Low molecular weight, carbohydrate-rich HS-PG forms are probably derived from larger forms by partial degradation. The HS side-chains can contain 24 different disaccharides in an unknown number of arrangements. The biosynthetic machinery can impose considerable restrictions; for example, the extent of N-sulphation rarely exceeds 40-50%, whereas O-sulphation may range from 20% to 75% of potential sites. Nevertheless, the informational capacity of HS is formidable. By way of the HS chains, HS-PG at the surface of endothelial cells can interact specifically or selectively with a number of plasma proteins. HS-PG at the surface of matrix-producing cells is similarly in a position to interact with matrix proteins, notably collagen, fibronectin and laminin. As the cytoplasmic portion of the HS-PG core protein can bind actin, this proteoglycan can provide a connection between extracellular matrices and the cytoskeleton. A number of studies support a role for HS-PGs in the control of cell growth, and this could be one of their major functions. Whether the HS side-chains or the core protein or both are carrying out such a function remains to be determined.

Plasmodium falciparum ookinetes require mosquito midgut chondroitin sulfate proteoglycans for cell invasion

Malaria transmission entails development of the Plasmodium parasite in its insect vector, the Anopheles mosquito. Parasite invasion of the mosquito midgut is the critical first step and involves adhesion to host epithelial cell ligands. Partial evidence suggests that midgut oligosaccharides are important ligands for parasite adhesion; however, the identity of these glycans remains unknown. We have identified a population of chondroitin glycosaminoglycans along the apical midgut microvilli of Anopheles gambiae and further demonstrated ookinete recognition of these glycans in vitro. By repressing the expression of the peptide-O-xylosyltransferase homolog of An. gambiae by means of RNA interference, we blocked glycosaminoglycan chain biosynthesis, diminished chondroitin sulfate levels in the adult midgut, and substantially inhibited parasite development. We provide evidence for the in vivo role of chondroitin sulfate proteoglycans in Plasmodium falciparum invasion of the midgut and insight into the molecular mechanisms mediating parasite-mosquito interactions.

[Profile of sulphated glycosaminoglycans content in the murine uterus during the different phases of the estrous cycle]

OBJECTIVE

Identification and quantitation of sulphated glycosaminoglycans (GAGs) in the uterus of female mice during the estrous cycle.

METHODS

Four groups (n = 10 each) of virgin, 100-day old female mice were assembled according to the estrous cycle phase: proestrus, estrus, metaestrus and diestrus. Samples of the median portion of uterine horns were processed for light microscopy examination (H/E and Alcian blue + PAS). The GAGs were extracted and characterized by agarose gel electrophoresis. Data were analyzed by the unpaired Student's t-test.

RESULTS

At light microscopy GAGs appear in all layers of the uterus, especially in the endometrium, between collagen fibers, in the basal membrane and around fibroblasts. Biochemical analyses disclosed presence of dermatan sulphate (DS), chondroitin sulphate (CS and heparan sulphate (HS) during all estral cycle phases. There was no clear electrophoretic separation between DS and CS, thus these two GAGs were considered together (DS+CS) (proestrus = 0.854 +/- 0.192; estrus = 1.073 +/- 0.254; metaestrus = 1.003 +/- 0.255; diestrus = 0.632 +/- 0.443 microg/mg). HS was as follows: proestrus = 0.092 +/- 0.097; estrus = 0.180 +/- 0.141; metaestrus = 0.091 +/- 0.046; diestrus = 0.233 +/- 0.147 microg/mg. The uterine content of DS+CS peaked at estrus (estrogenic action) and that of HS at diestrus (progestagen action).

CONCLUSION

Due to a constant turnover process, there are definite alterations in the uterine profile of GAGs content during the estrous cycle in mice, which may be modulated by female sex hormones.

The glycosaminoglycan chain of decorin plays an important role in collagen fibril formation at the early stages of fibrillogenesis

Decorin is a multifunctional small leucine-rich proteoglycan involved in the regulation of collagen fibrillogenesis. In patients with a variant of Ehlers-Danlos syndrome, about half of the secreted decorin lacks the single glycosaminoglycan side chain. Notably, these patients have a skin-fragility phenotype that resembles that of decorin null mice. In this study, we investigated the role of glycanated and unglycanated decorin on collagen fibrillogenesis. Glycosaminoglycan-free decorin, generated by mutating Ser4 of the mature protein core into Ala (DCN-S4A), showed reduced inhibition of fibrillogenesis compared with the decorin proteoglycan. Interestingly, using a 3D matrix generated by decorin-null fibroblasts, an increase in fibril diameter was found after the addition of decorin, and even greater effects were observed with DCN-S4A. To avoid potential side effects of artificial tags, adenoviruses containing decorin and DCN-S4A were used to transduce decorin-null fibroblasts prior to matrix formation. Both molecules were efficiently incorporated into the matrix, with no changes in collagen composition and network formation, or altered expression of the related proteoglycan biglycan. Both decorin and DCN-S4A mutants increased the collagen fibril diameter, with the latter showing the most prominent effects. These data show that at early stages of fibrillogenesis, the glycosaminoglycan chain of decorin has a reducing effect on collagen fibril diameter.

Glycosaminoglycans and proteoglycans: overlooked entities?

BACKGROUND

By virtue of their high net negative charge, glycosaminoglycans and proteoglycans play pivotal roles in biologic processes such as cell-cell and cell-matrix interactions, sequestration of growth factors, activation of chemokines and cytokines, and permselectivity of basement membranes.

METHODS

The present article reviews the putative roles of glycosaminoglycans and proteoglycans in the peritoneal cavity during normal peritoneal homeostasis and chronic inflammation, the latter induced by constant exposure of the peritoneum to non-physiologic peritoneal dialysis (PD) solutions.

RESULTS

Glycosaminoglycans have been identified in the mesothelial glycocalyx, a slippery, non-adhesive layer that protects the peritoneal membrane from abrasion and infection. Dermatan sulfate proteoglycans can neutralize the activity of transforming growth factor beta1 and can thus play an essential role in modulating peritoneal fibrosis. Heparan sulfate proteoglycans play a crucial role in the sequestration of growth factors; they also modulate selective permeability of proteins across the peritoneal cavity. Reduced expression of perlecan, a heparan sulfate proteoglycan of the basement membrane, is observed in peritoneal biopsies obtained from established PD patients, consequent to prolonged exposure to the elevated glucose concentrations in conventional PD solutions. Supplementation of PD fluids with glycosaminoglycans has been shown to be beneficial to both the structural and functional integrity of the peritoneum.

CONCLUSIONS

Recent advances in the field of glycobiology have revealed a multitude of biologic processes that are controlled or influenced by glycosaminoglycans and proteoglycans. Altered synthesis of these macromolecules during PD has serious implications for the peritoneal transport of proteins, host defense, wound healing, inflammation, and fibrosis.

Regenerative healing in fetal skin: a review of the literature

In mature skin, wound repair typically begins with hemostasis and inflammation. This is followed by a proliferative phase with reepithelialization, angiogenesis, and collagen production, and ends with the generation of a permanent scar. However, animal studies and clinical observations have shown that a different type of healing occurs in fetal skin in the first two trimesters of development. In early fetal skin, wounds exhibit a unique pattern of wound healing leading to regeneration. Notably, repair in the fetus takes place with little or no inflammation, faster reepithelialization, and no scarring. Although research in scarless fetal healing began several decades ago, the exact mechanisms of how this regenerative process takes place remain unknown. Knowing how the fetus will respond to potential injury from invasive diagnostic procedures or surgery is essential, especially given the development of less invasive fetal surgical techniques which could increase the number of fetal surgeries. In addition, insights into regenerative healing may provide information about how to accelerate postnatal wound healing as well as how to improve healing from a cosmetic standpoint. Future research directions include identification of the molecular controls responsible for scarless healing, with the intention that this new information will lead to improved therapeutic strategies for wound healing.

Transitions in Early Embryonic Atrioventricular Valvular Function Correspond With Changes in Cushion Biomechanics That Are Predictable by Tissue Composition

Endocardial cushions are critical to maintain unidirectional blood flow under constantly increasing hemodynamic forces, but the interrelationship between endocardial cushion structure and the mechanics of atrioventricular junction function is poorly understood. Atrioventricular (AV) canal motions and blood velocities of embryonic chicks at Hamburger and Hamilton (HH) stages 17, 21, and 25 were quantified using ultrasonography. Similar to the embryonic zebrafish heart, the HH17 AV segment functions like a suction pump, with the cushions expanding in a wave during peak myocardial contraction and becoming undetectable during the relaxation phase. By HH25, the AV canal contributes almost nothing to the piston-like propulsion of blood, but the cushions function as stoppers apposing blood flow with near constant thickness. Using a custom built mesomechanical testing system, we quantified the nonlinear pseudoelastic biomechanics of developing AV cushions, and found that both AV cushions increased in effective modulus between HH17 and HH25. Enzymatic digestion of major structural constituent collagens or glycosaminoglycans resulted in distinctly different stress-strain curves suggestive of their individual contributions. Mixture theory using histologically determined volume fractions of cells, collagen, and glycosaminoglycans showed good prediction of cushion material properties regardless of stage and cushion position. These results have important implications in valvular development, as biomechanics may play a larger role in stimulating valvulogenic events than previously thought.

The Role of the Urinary Epithelium in the Pathogenesis of Interstitial Cystitis/Prostatitis/Urethritis

The urothelium plays a pivotal role as a barrier between urine and its solutes and the underlying bladder. Bladder surface mucus is a critical component of this function. The biologic activity of mucus that imparts this barrier function is generated by the highly anionic polysaccharide components (eg, glycosaminoglycans), which are extremely hydrophilic and trap water at the outer layer of the umbrella cell. This trapped water forms a barrier at the critical interface between urine and the bladder. The result is a highly impermeable urothelium that serves as a key protective barrier for the bladder interstitium. In interstitial cystitis (IC), disruption of the urothelial barrier may initiate a cascade of events in the bladder, leading to symptoms and disease. Specifically, epithelial dysfunction leads to the migration of urinary solutes, in particular, potassium, that depolarize nerves and muscles and cause tissue injury. Exogenous heparinoids can restore the barrier function of the urothelium and thus successfully treat patients with IC. Groups of patients who have been given a diagnosis of IC, chronic prostatitis, and urethritis have been shown to have IC by virtue of their shared potassium sensitivity. It would seem, therefore, that mucous deficiency may be present throughout the lower urinary tract. If one is to rename these diseases, perhaps it is best to do so in reference to a shared loss of epithelial barrier function. A name such as lower urinary dysfunctional epithelium would incorporate all of these diseases under a single pathophysiologic process. As a result of these discoveries, a new paradigm for diagnosis and treatment is emerging.

Bench-to-bedside review: the role of glycosaminoglycans in respiratory disease

The extracellular matrix (ECM) plays a significant role in the mechanical behaviour of the lung parenchyma. The ECM is composed of a three-dimensional fibre mesh that is filled with various macromolecules, among which are the glycosaminoglycans (GAGs). GAGs are long, linear and highly charged heterogeneous polysaccharides that are composed of a variable number of repeating disaccharide units. There are two main types of GAGs: nonsulphated GAG (hyaluronic acid) and sulphated GAGs (heparan sulphate and heparin, chondroitin sulphate, dermatan sulphate, and keratan sulphate). With the exception of hyaluronic acid, GAGs are usually covalently attached to a protein core, forming an overall structure that is referred to as proteoglycan. In the lungs, GAGs are distributed in the interstitium, in the sub-epithelial tissue and bronchial walls, and in airway secretions. GAGs have important functions in lung ECM: they regulate hydration and water homeostasis; they maintain structure and function; they modulate the inflammatory response; and they influence tissue repair and remodelling. Given the great diversity of GAG structures and the evidence that GAGs may have a protective effect against injury in various respiratory diseases, an understanding of changes in GAG expression that occur in disease may lead to opportunities to develop innovative and selective therapies in the future.

Les chimiokines : un réseau sophistiqué de guidage cellulaire

The immune system relies on the motility on various cell types that roam the host through the blood, the peripheral tissues and the lymphoid organs, looking for pathogens. Along their maturation and/or activation, the cell migratory capacities change in order to allow them to leave organs where they have been produced such as thymus and bone marrow, to locate in strategic sites to sense surrounding microbes, to meet and interact with other cells, and finally to access peripheral tissues and organs to eradicate the pathogens. This cell traffic is a highly organized process that involves numerous protein families such as adhesion molecules, proteases and chemotactic factors. Among the latter, chemokines are in the front line. We will here summarize the recent findings stressing out their physiopathological relevance and will describe thereafter their possible therapeutic use.

Biochemical markers of the mechanical quality of engineered hyaline cartilage

The aim of this study was to determine whether or not biochemical markers can be used as surrogate measures for the mechanical quality of tissue engineered cartilage. The biochemical composition of tissue engineered cartilage constructs were altered by varying either (i) the initial cell seeding density of the scaffold (seeding density protocol) or (ii) the length of time the engineered tissue was cultured (culture period protocol). The aggregate or Young's moduli of the constructs were measured (by confined or unconfined compression respectively), and compared with the composition of the extracellular matrix by quantitative measurement of the glycosaminoglycan (GAG), hydroxyproline, collagen I and collagen II and collagen cross-links. The aggregate modulus correlated positively with both GAG and collagen II content, but not with collagen I content. Young's modulus correlated positively with GAG, collagen II and collagen I content, and the ratio of mature to immature cross-links. There was no significant correlation of Young's Modulus with total collagen measured as hydroxyproline content. These results suggested that hydroxyproline determination may be an unreliable indicator of mechanical quality of tissue engineered cartilage, and that a measure of collagen II and GAG content is required to predict the biomechanical quality of tissue engineered cartilage.

Roles of cellular activation and sulfated glycans in Haemophilus somnus adherence to bovine brain microvascular endothelial cells

Haemophilus somnus can cause a devastating fibrinopurulent meningitis with thrombotic vasculitis and encephalitis in cattle. The mechanisms used by H. somnus to migrate from the bloodstream into the central nervous system (CNS) are unknown. In this study, we demonstrate that H. somnus adheres to, but does not invade, bovine brain endothelial cells (BBEC) in vitro. The number of adherent H. somnus was significantly increased by prior activation of the BBEC with tumor necrosis factor alpha (TNF-alpha). Addition of exogenous glycosaminoglycans significantly reduced H. somnus adherence to resting and TNF-alpha-activated BBEC. Heparinase digestion of the endothelial cell's glycocalyx or sodium chlorate inhibition of endothelial cell sulfated glycan synthesis significantly reduced the number of adherent H. somnus. In contrast, addition of hyaluronic acid, a nonsulfated glycosaminoglycan, had no inhibitory effect. These findings suggest a critical role for both cellular activation and sulfated glycosaminoglycans in adherence of H. somnus to BBEC. Using heparin-labeled agarose beads, we demonstrated a high-molecular-weight heparin-binding protein expressed by H. somnus. Heparin was also shown to bind H. somnus in a 4 degrees C binding assay. These data suggest that heparin-binding proteins on H. somnus could serve as initial adhesins to sulfated proteoglycans on the endothelial cell surface, thus contributing to the ability of H. somnus to infect the bovine CNS.

Aberrant heparan sulfate profile in the human diabetic kidney offers new clues for therapeutic glycomimetics

BACKGROUND

Diabetic nephropathy poses an increasing health problem in the Western world, and research to new leads for diagnosis and therapy therefore is warranted. In this respect, heparan sulfates (HSs) offer new possibilities because crude mixtures of these polysaccharides are capable of ameliorating proteinuria. The aim of this study is to immuno(histo)chemically profile HSs from microalbuminuric kidneys from patients with type 1 diabetes and identify specific structural HS alterations associated with early diabetic nephropathy.

METHODS

Renal cryosections of control subjects and patients with type 1 diabetes were analyzed immunohistochemically by using a set of 10 unique phage display-derived anti-HS antibodies. HS structures defined by relevant antibodies were characterized chemically by means of enzyme-linked immunosorbent assay and probed for growth factor binding and presence in HS/heparin-containing drugs.

RESULTS

In all patients, HS structure defined by the antibody LKIV69 consistently increased in basement membranes of proximal tubules. This structure contained N- and 2-O-sulfates and was involved in fibroblast growth factor 2 binding. It was present in HS/heparin-containing drugs shown to decrease albuminuria in patients with diabetes. The HS structure defined by the antibody HS4C3 increased in the renal mesangium of some patients, especially those who developed macroalbuminuria within 8 to 10 years. This structure contained N- and 6-O-sulfates. For 8 other antibodies, no major differences were observed.

CONCLUSION

Specific structural alterations in HSs are associated with early diabetic nephropathy and may offer new leads for early diagnosis and the rational design of therapeutic glycomimetics.

Retroviral DNA integration: viral and cellular determinants of target-site selection

Retroviruses differ in their preferences for sites for viral DNA integration in the chromosomes of infected cells. Human immunodeficiency virus (HIV) integrates preferentially within active transcription units, whereas murine leukemia virus (MLV) integrates preferentially near transcription start sites and CpG islands. We investigated the viral determinants of integration-site selection using HIV chimeras with MLV genes substituted for their HIV counterparts. We found that transferring the MLV integrase (IN) coding region into HIV (to make HIVmIN) caused the hybrid to integrate with a specificity close to that of MLV. Addition of MLV gag (to make HIVmGagmIN) further increased the similarity of target-site selection to that of MLV. A chimeric virus with MLV Gag only (HIVmGag) displayed targeting preferences different from that of both HIV and MLV, further implicating Gag proteins in targeting as well as IN. We also report a genome-wide analysis indicating that MLV, but not HIV, favors integration near DNase I-hypersensitive sites (i.e., +/- 1 kb), and that HIVmIN and HIVmGagmIN also favored integration near these features. These findings reveal that IN is the principal viral determinant of integration specificity; they also reveal a new role for Gag-derived proteins, and strengthen models for integration targeting based on tethering of viral IN proteins to host proteins.

Interaction of Chlamydia trachomatis with mammalian cells is independent of host cell surface heparan sulfate glycosaminoglycans

The hypothesis that host cell surface heparan sulfate is required to promote chlamydial infection was tested using a cell line (CHO-18.4) containing a single retroviral insertion and the concomitant loss of heparan sulfate biosynthesis. Tests of chlamydial infectivity of heparan sulfate-deficient CHO-18.4 cells and parental cells, CHO-22, demonstrated that both were equally sensitive to infection by Chlamydia trachomatis serovars L2 and D. These data do not support the hypothesis and demonstrate that host cell surface heparan sulfate does not serve an essential functional role in chlamydial infectivity.

Protein–GAG interactions: new surface-based techniques, spectroscopies and nanotechnology probes

New approaches, rooted in the physical sciences, have been developed to gain a more fundamental understanding of protein–GAG (glycosaminoglycan) interactions. DPI (dual polarization interferometry) is an optical technique, which measures real-time changes in the mass of molecules bound at a surface and the geometry of the bound molecules. QCM-D (quartz crystal microbalance-dissipation), an acoustic technique, measures the mass and the viscoelastic properties of adsorbates. The FTIR (Fourier-transform IR) amide bands I, II and III, resulting from the peptide bond, provide insight into protein secondary structure. Synchrotron radiation CD goes to much shorter wavelengths than laboratory CD, allowing access to chromophores that provide insights into the conformation of the GAG chain and of β-strand structures of proteins. To tackle the diversity of GAG structure, we are developing noble metal nanoparticle probes, which can be detected at the level of single particles and so enable single molecule biochemistry and analytical chemistry. These new approaches are enabling new insights into structure–function relationships in GAGs and together they will resolve many of the outstanding problems in this field.

Morphological and functional evidence for an important role of the endothelial cell glycocalyx in the glomerular barrier

In this study, we pursued the somewhat controversial issue whether the glycosaminoglycans (GAG) in the endothelial cell glycocalyx are important for glomerular size and charge selectivity. In isoflurane-anesthetized mice, Intralipid droplets were used as indirect markers of the glomerular endothelial cell-surface layer, i.e., the glycocalyx. The mice were given intravenous injections of GAG-degrading enzymes, which due to their high molecular weight remained and acted intravascularly. Flow-arrested kidneys were fixed and prepared for electron microscopy, and the distance between glomerular endothelial cells and the luminal Intralipid droplets was measured. The relative frequency of Intralipid droplets was calculated for each 50-nm increment zone up to 500 nm from the endothelial cell membrane surface as were the mean distances. Glomerular size and charge selectivity were estimated from the clearance data for neutral Ficolls (molecular radii of 12–72 Å), and albumin in isolated kidneys was perfused at 8°C. In enzyme-treated animals (hyaluronidase, heparinase, and chondroitinase), the relative Intralipid droplet frequency in the zone closest to the endothelial cells, i.e., 0–50 nm, was increased ∼2.5 times compared with controls. Also, the mean distance between the Intralipid droplets and the endothelium was decreased from 176 to 115–122 nm by enzyme treatment. These changes were accompanied by an increase in the fractional clearance for albumin. In conclusion, both morphological and functional measurements suggest the endothelial cell glycocalyx to be an important component of the glomerular barrier.

Effect of hydration on interstitial distribution of charged albumin in rat dermis in vitro

At physiological pH, negatively charged glycosaminoglycans in the extracellular matrix may influence distribution volume of macromolecular probes, a phenomenon of importance for hydration of the interstitium and therefore for body fluid balance. We hypothesized that such charge effect was dependent on hydration. Human serum albumin (HSA) (the pH value for the isoelectric point (pI) = 4.9) was made neutral by cationization (cHSA) (pI = 7.6). Rat dermis was studied in vitro in a specially designed equilibration cell allowing control of hydration. Using a buffer containing labelled native HSA and cHSA, the distribution volumes were calculated relative to that of 51Cr-EDTA, an extracellular tracer. During changes in hydration (H), defined as (wet weight - dry weight) (dry weight)(-1)), the slope of the equation describing the relationship between extracellular fluid volume (V(x)) (in g H2O (g dry weight)(-1)) and H (V(x) = 0.925 H + 0.105) differed significantly from that for available volumes of cHSA (V(a,cHSA) = 0.624 H - 0.538) and HSA (V(a,HSA) = 0.518 H - 0.518). A gradual reduction in H led to a reduction in difference between available volumes for the two albumin species. Screening the fixed charges by 1 m NaCl resulted in similar available and excluded volumes of native HSA and neutral cHSA. We conclude that during gradual dehydration, there is a reduced effect of fixed negative charges on interstitial exclusion of charged macromolecules. This effect may be explained by a reduced hydration domain surrounding tissue and probe macromolecules in conditions of increased electrostatic interactions. Furthermore, screening of negative charges suggested that hyaluronan associated with collagen may influence intrafibrillar volume of collagen and thereby available and excluded volume fraction.

Modulation of acute inflammation by targeting glycosaminoglycan–cytokine interactions

Glycosaminoglycans (GAGs) located on cellular membranes and the extracellular matrix (ECM) are able to interact with chemokines and pro-inflammatory cytokines, leading to local cytokine/chemokine accumulation. The tissue-bound cytokines/chemokines function in promoting leukocyte migration and activation, contributing to local inflammation. Hence, targeting of GAG-cytokine interactions may provide an avenue for the attenuation of inflammatory responses. A cationic peptide (MC2) derived from the heparin-binding sequence of mouse IFN-gamma was previously shown by our laboratory to delay allograft rejection in an animal model. In order to further investigate potential anti-inflammatory properties of the MC2 peptide, we have studied its activity in an acute peritoneal inflammation model. Groups of C57Bl/6 mice were injected intraperitoneally with either ConA or thioglycollate and treated with saline (control), the MC2 peptide or two control cationic peptides, poly-l-lysine (PLL) and poly-l-arginine (PLA). Treatment with the MC2 peptide, but not PLA or PLL, resulted in statistically significant reductions in total cell numbers, concentration of total proteins and concentrations of pro-inflammatory cytokines (TNFalpha, IL-6 or IL-1 beta) in peritoneal lavage fluids, without alterations to the qualitative cellular composition of the exudate. These results suggest that targeting GAG-cytokine interaction is a viable approach to reduce inflammation.

Biochemical analysis of the articular cartilage and subchondral and trabecular bone of the metacarpophalangeal joint of horses with early osteoarthritis

OBJECTIVE

To assess whether site-related changes in biochemical composition are present in the cartilage and subchondral and trabecular bone of the metacarpophalangeal joint of horses with early osteoarthritis.

SAMPLE POPULATION

Right metacarpophalangeal joints from 59 mature warmblood horses.

PROCEDURE

Biochemical data (cross-link, amino acid, DNA, and ash contents; denatured collagen and glycosaminoglycan [GAG] concentrations; bone mineral density; and mineral composition) were obtained from 2 differently loaded sites of phalanx I cartilage and subchondral and trabecular bone samples; data were compared with previously published values from nonosteoarthritic equine joints.

RESULTS

Compared with findings in nonosteoarthritic joints, GAG concentration was lower in cartilage from osteoarthritic joints and there was a loss of site differences in cellularity and lysylpyridinoline (LP) cross-link content. In subchondral bone, LP cross-link content was decreased overall and there was a loss of site differences in osteoarthritic joints; ash content was higher in the osteoarthritic joints. Hydroxyproline content in trabecular bone from osteoarthritic joints was greater than that in nonosteoarthritic trabecular bone. In all 3 layers and at both sites, the linear increase of the pentosidine cross-link content with age had diminished or was not apparent in the horses with osteoarthritic joints.

CONCLUSIONS AND CLINICAL RELEVANCE

In equine metacarpophalangeal joints with early osteoarthritis, distinct biochemical changes were detected in the cartilage and subchondral and trabecular bone. The dissimilarity in response of the different tissues and differences between the sites that are affected may be related to differences in biomechanical loading and transmission and dissipation of force.

Glycosaminoglycan: a candidate to stimulate the repair of chronic wounds

A persistent inflammation with large numbers of neutrophils is found in chronic wounds. Secretory products released from the neutrophils, which include proteinases and a heparin-binding protein, are detrimental to wound healing as they cause degradation of the extracellular matrix and growth factors, and promote further recruitment of neutrophils to the wound area. The neutrophil-derived elastase, cathepsin G, proteinase-3 and heparin-binding protein are cationic, and it is hypothesized that their effects can be inhibited by electrostatic binding with certain anionic polymers such as glycosaminoglycans or functionalized dextrans. A sustained delivery of such compounds alone or in combination from a biodegradable carrier may provide a stimulus for these wounds to pass to the next stage of repair.

Stability and function of glycosaminoglycans in porcine bioprosthetic heart valves

Glycosaminoglycans (GAGs) are important structural and functional components in native aortic heart valves and in glutaraldehyde (Glut)-fixed bioprosthetic heart valves (BHVs). However, very little is known about the fate of GAGs within the extracellular matrix of BHVs and their contribution to BHV longevity. BHVs used in heart valve replacement surgery have limited durability due to mechanical failure and pathologic calcification. In the present study we bring evidence for the dramatic loss of GAGs from within the BHV cusp structure during storage in saline and both short- and long-term Glut fixation. In order to gain insight into role of GAGs, we compared properties of fresh and Glut-fixed porcine heart valve cusps before and after complete GAG removal. GAG removal resulted in significant morphological and functional tissue alterations, including decreases in cuspal thickness, reduction of water content and diminution of rehydration capacity. By virtue of this diminished hydration, loss of GAGs also greatly increased the "with-curvature" flexural rigidity of cuspal tissue. However, removal of GAGs did not alter calcification potential of BHV cups when implanted in the rat subdermal model. Controlling the extent of pre-implantation GAG degradation in BHVs and development of improved GAG crosslinking techniques are expected to improve the mechanical durability of future cardiovascular bioprostheses.