Maturation-related changes in proteoglycans of fetal articular cartilage

Advancements in hydrogel design for articular cartilage regeneration: A comprehensive review

This review paper explores the cutting-edge advancements in hydrogel design for articular cartilage regeneration (CR). Articular cartilage (AC) defects are a common occurrence worldwide that can lead to joint breakdown at a later stage of the disease, necessitating immediate intervention to prevent progressive degeneration of cartilage. Decades of research into the biomedical applications of hydrogels have revealed their tremendous potential, particularly in soft tissue engineering, including CR. Hydrogels are highly tunable and can be designed to meet the key criteria needed for a template in CR. This paper aims to identify those criteria, including the hydrogel components, mechanical properties, biodegradability, structural design, and integration capability with the adjacent native tissue and delves into the benefits that CR can obtain through appropriate design. Stratified-structural hydrogels that emulate the native cartilage structure, as well as the impact of environmental stimuli on the regeneration outcome, have also been discussed. By examining recent advances and emerging techniques, this paper offers valuable insights into developing effective hydrogel-based therapies for AC repair.

Decrease in Glycosaminoglycan with Aging in Normal Rat Articular Cartilage Is Greater in Females than in Males

OBJECTIVE

Osteoarthritis (OA) is more prevalent in females. We hypothesized that changes in articular cartilage (AC) constituents with aging may cause differences. Herein, we aimed to compare the changes in AC constituents with aging in male and female normal rats.

DESIGN

The glycosaminoglycan (GAG) and collagen (COL) contents of the AC in knee, hip, and shoulder joints of male and female rats were quantified and compared between age groups and sexes.

RESULTS

The amount of GAG was decreased in multiple joints in both males and females with aging. In females, it had a significant decrease in all joints measured. The decrease in GAG with aging was more severe in females than in males. Even in young rats, the amount of knee joint GAG was significantly less in females than in males. The amount of COL in the AC was unchanged with aging in both sexes.

CONCLUSIONS

The drastic GAG decrease with aging in female normal rats may explain the higher prevalence and more severe OA in females.

Location-Specific Study of Young Rabbit Femoral Cartilage by Quantitative µMRI and Polarized Light Microscopy

OBJECTIVE

Microscopic magnetic resonance imaging (µMRI) and polarized light microscopy (PLM) are used to characterize the structural variations at different anatomical locations of femoral cartilage in young rabbits (12-14 weeks old).

DESIGN

Four intact knees were imaged by µMRI at 86 µm resolution. Three small cartilage-bone specimens were harvested from each of 2 femoral medial condyles and imaged by quantitative µMRI (T2 anisotropy) at 9.75 µm resolution (N = 6). These specimens, as well as the other 2 intact femoral condyles, were used for histology and imaged by quantitative PLM (retardation and angle) at 0.25 µm to 4 µm resolutions.

RESULTS

Quantitative MRI relaxation data and PLM fibril data revealed collaboratively distinct topographical variations in both cartilage thickness and its collagen organization in the juvenile joint. Cartilage characteristics from the central location have a 3-zone arcade-like fibril structure and a distinct magic angle effect, commonly seen in mature articular cartilage, while cartilage at the anterior location lacks these characteristics. Overall, the lowest retardation values and isotropic T2 values have been found in the distal femur (trochlear ridge), with predominant parallel fibers with respect to the articular surface. Central cartilage is the thickest (~550 µm), approximately twice as thick as the anterior and posterior locations.

CONCLUSION

Distinctly different characteristics of tissue properties were found in cartilage at different topographical locations on femoral condyle in rabbits. Knowledge of location-specific structural differences in the collagen network over the joint surface can improve the understanding of local mechanobiology and provide insights to tissue engineering and degradation repairs.

A genome-wide transcriptomic analysis of articular cartilage during normal maturation in pigs

OBJECTIVE

The articular cartilage undergoes dramatic changes in structure and composition during post-natal maturation, but the associated transcriptional changes are not well characterized. Compared to a mature stage, the immature articular cartilage shows developmental features such as increased thickness, presence of blood vessels, and the presence of a deep layer of growth cartilage which undergoes endochondral ossification. These features decrease during normal development. Following maturation, the articular cartilage is known to undergo few minor modifications. Since mature articular cartilage has poor regenerative and repair capacity compared to the immature articular cartilage, a better understanding of the molecular changes during the normal postnatal articular cartilage development might reveal insights on the molecular adaptation. It may also provide new therapeutic strategies. The purpose of this study was to determine the differential expression of genes in the femoral head articular cartilage of 6-weeks old and 6-months old pigs using a genome-wide transcriptomic analysis.

METHODS

The articular cartilage of the femoral head of 6-weeks and 6-months old normal pigs was assessed for thickness and vascularity (number of vascular canals) using Safranin O/Fast Green staining of paraffin sections (n=4 pigs/age group). The measurements were determined using Image J software. RNA was isolated from the femoral head articular cartilage from 6-weeks and 6-months old pigs (n=8 pigs/age group). A microarray analysis was performed using an Affymetrix Porcine GeneChip Array. A gene enrichment analysis and a functional clustering analysis were performed by DAVID and STRING software, respectively. The differential expression of selected genes was confirmed by a quantitative RTPCR analysis.

RESULTS

The femoral head articular cartilage showed a significant decrease in thickness and number of vascular canals in 6-months old compared to 6-weeks old pigs. A microarray analysis revealed a differential gene expression of 576 genes, with 206 genes that were significantly upregulated and 370 genes that were significantly downregulated (>2-fold change, p<0.05) at 6-months compared to 6-weeks of age. Among the upregulated genes, DAVID analysis revealed that a significant number of genes represented the biological processes of responses to external stimuli, and wounding and inflammation at 6-months of age. These processes involved genes representing secretory and signaling proteins such as MMP-1, MMP-3, IL-8 and STAT3 suggesting increased inflammatory activity. In addition, an assessment of the downregulated genes indicated a decrease in the expression of genes representing the biological processes of developmental processes (e.g. BMPR1A, BMPR2, ACVR2, periostin, SFRP2, COL5A3) and regulation of blood vessel size (e.g. alpha adrenergic receptor 1B, alpha-SMA) at 6-months of age. A real-time qRTPCR analysis of selected upregulated genes, fibronectin, MMP-3, IL-8 and downregulated genes, BMPR2, PECAM, CCL2, TLR4 confirmed the differential gene expression in the microarray analysis.

CONCLUSION

During the process of articular cartilage maturation from 6-weeks to 6-months of age in normal pigs, genes associated with inflammatory responses to injury were upregulated and genes involved in the development and vascular responses were downregulated. These findings suggest that during articular cartilage maturation, the transcriptional changes might increase the susceptibility of cartilage to inflammatory damage and decrease the regenerative capacity.

A compositional analysis of cadaveric human nasal septal cartilage

OBJECTIVES/HYPOTHESIS

To localize quantitatively the major biochemical constituents of native adult human septal cartilage across whole septa.

STUDY DESIGN

Prospective, basic science.

METHODS

The nasal septa from seven cadavers were partitioned into 24 separate regions: six from caudal to cephalic and four from dorsal to ventral. Biochemical assays were used to determine the quantities, relative to wet weight, of the major constituents of cartilage: chondrocytes, collagen, and sulfated glycosaminoglycan.

RESULTS

On average, each milligram of wet cartilage contained 24,900 cells, 73.9 μg collagen, and 17.1 μg sulfated glycosaminoglycan. Cell number showed no significant variation across the septa. In contrast, the caudal regions of the septa were associated with higher levels of collagen, the ventral regions correlated with higher levels of sulfated glycosaminoglycan, and the dorsal regions were associated with an elevated ratio of collagen to sulfated glycosaminoglycan.

CONCLUSIONS

This study represents the first characterization of the biochemical composition of native human septal cartilage across whole septa. Quantities of collagen and sulfated glycosaminoglycan showed region-specific variation across the septum. The localized pattern of collagen and sulfated glycosaminoglycan deposition are consistent with the significance of preserving the L-strut during rhinoplasty and other nasal reconstructive procedures. In addition, it may assist in defining design goals for tissue-engineered septal neocartilage constructs to meet specific reconstructive needs in the future.

Growth-related structural, biochemical, and mechanical properties of the functional bone-cartilage unit

Articular cartilage and subchondral bone act together, forming a unit as a weight-bearing loading-transmitting surface. A close interaction between both structures has been implicated during joint cartilage degeneration, but their coupling during normal growth and development is insufficiently understood. The purpose of the present study was to examine growth-related changes of cartilage mechanical properties and to relate these changes to alterations in cartilage biochemical composition and subchondral bone structure. Tibiae and femora of both hindlimbs from 7- and 13-week-old (each n = 12) female Sprague-Dawley rats were harvested. Samples were processed for structural, biochemical and mechanical analyses. Immunohistochemical staining and protein expression analyses of collagen II, collagen IX, COMP and matrilin-3, histomorphometry of cartilage thickness and COMP staining height were performed. Furthermore, mechanical testing of articular cartilage and micro-CT analysis of subchondral bone was conducted. Growth decreased cartilage thickness, paralleled by a functional condensation of the underlying subchondral bone due to enchondral ossification. Cartilage mechanical properties seem to be rather influenced by growth-related changes in the assembly of major ECM proteins such as collagen II, collagen IX and matrilin-3 than by growth-related alterations in its underlying subchondral bone structure. Importantly, the present study provides a first insight into the growth-related structural, biochemical and mechanical interaction of articular cartilage and subchondral bone. Finally, these data contribute to the general knowledge about the cooperation between the articular cartilage and subchondral bone.

Contribution of proteoglycan osmotic swelling pressure to the compressive properties of articular cartilage

The negatively charged proteoglycans (PG) provide compressive resistance to articular cartilage by means of their fixed charge density (FCD) and high osmotic pressure (π(PG)), and the collagen network (CN) provides the restraining forces to counterbalance π(PG). Our objectives in this work were to: 1), account for collagen intrafibrillar water when transforming biochemical measurements into a FCD-π(PG) relationship; 2), compute π(PG) and CN contributions to the compressive behavior of full-thickness cartilage during bovine growth (fetal, calf, and adult) and human adult aging (young and old); and 3), predict the effect of depth from the articular surface on π(PG) in human aging. Extrafibrillar FCD (FCD(EF)) and π(PG) increased with bovine growth due to an increase in CN concentration, whereas PG concentration was steady. This maturation-related increase was amplified by compression. With normal human aging, FCD(EF) and π(PG) decreased. The π(PG)-values were close to equilibrium stress (σ(EQ)) in all bovine and young human cartilage, but were only approximately half of σ(EQ) in old human cartilage. Depth-related variations in the strain, FCD(EF), π(PG), and CN stress profiles in human cartilage suggested a functional deterioration of the superficial layer with aging. These results suggest the utility of the FCD-π(PG) relationship for elucidating the contribution of matrix macromolecules to the biomechanical properties of cartilage.

Age-related differences in human skin proteoglycans

Previous work has shown that versican, decorin and a catabolic fragment of decorin, termed decorunt, are the most abundant proteoglycans in human skin. Further analysis of versican indicates that four major core protein species are present in human skin at all ages examined from fetal to adult. Two of these are identified as the V0 and V1 isoforms, with the latter predominating. The other two species are catabolic fragments of V0 and V1, which have the amino acid sequence DPEAAE as their carboxyl terminus. Although the core proteins of human skin versican show no major age-related differences, the glycosaminoglycans (GAGs) of adult skin versican are smaller in size and show differences in their sulfation pattern relative to those in fetal skin versican. In contrast to human skin versican, human skin decorin shows minimal age-related differences in its sulfation pattern, although, like versican, the GAGs of adult skin decorin are smaller than those of fetal skin decorin. Analysis of the catabolic fragments of decorin from adult skin reveals the presence of other fragments in addition to decorunt, although the core proteins of these additional decorin catabolic fragments have not been identified. Thus, versican and decorin of human skin show age-related differences, versican primarily in the size and the sulfation pattern of its GAGs and decorin in the size of its GAGs. The catabolic fragments of versican are detected at all ages examined, but appear to be in lower abundance in adult skin compared with fetal skin. In contrast, the catabolic fragments of decorin are present in adult skin, but are virtually absent from fetal skin. Taken together, these data suggest that there are age-related differences in the catabolism of proteoglycans in human skin. These age-related differences in proteoglycan patterns and catabolism may play a role in the age-related changes in the physical properties and injury response of human skin.

Chondroitin sulphate: an effective joint lubricant?

OBJECTIVE

The effect of chondroitin sulphate (CS) treatment on the friction and deformation characteristics of native and glycosaminoglycan (GAG) deficient articular cartilage was investigated.

METHODS

Friction tests were conducted at 0.4 MPa load, in Static and Dynamic models, to determine the startup coefficient of friction (COF) and dynamic COF, respectively. Native cartilage: For each cartilage pin and plate couple, the COF was determined under three consecutive tests - (1) baseline COF in PBS (2) COF in CS lubricant and (3) COF again in PBS, after 24h CS treatment. GAG deficient cartilage: For each cartilage pin and plate couple, the baseline COF was determined in PBS initially and again following enzymatic treatment to deplete GAGs. The specimens were then soaked in CS solution for 24h and the COF determined again in PBS. In a similar manner, friction tests were replaced with indentation tests to study the deformation of the tissue.

RESULTS

CS at 50mg/ml significantly lowered the startup COF of native cartilage both as a lubricant and a treatment solution. In the dynamic model, where the fluid load support is sustained at a high level, CS failed to have any effect on the COF of native cartilage. GAG depletion raised the friction and deformation levels of cartilage, and subsequent CS treatment failed to lower them to their native levels.

CONCLUSION

CS proved to be an effective lubricant for cartilage under mixed-mode lubrication conditions. However, supplemental CS that diffused into the specimens had no influence on the fluid load support of cartilage.

Changes in spatial collagen content and collagen network architecture in porcine articular cartilage during growth and maturation

OBJECTIVES

The present study was designed to reveal changes in the collagen network architecture and collagen content in cartilage during growth and maturation of pigs.

METHODS

Femoral groove articular cartilage specimens were collected from 4-, 11- and 21-month-old domestic pigs (n=12 in each group). The animal care conditions were kept constant throughout the study. Polarized light microscopy was used to determine the collagen fibril network birefringence, fibril orientation and parallelism. Infrared spectroscopy was used to monitor changes in the spatial collagen content in cartilage tissue.

RESULTS

During growth, gradual alterations were recorded in the collagen network properties. At 4 months of age, a major part of the collagen fibrils was oriented parallel to the cartilage surface throughout the tissue. However, the fibril orientation changed considerably as skeletal maturation progressed. At 21 months of age, the fibrils of the deep zone cartilage ran predominantly at right angles to the cartilage surface. The collagen content increased and its depthwise distribution changed during growth and maturation. A significant increase of the collagen network birefringence was observed in the deep tissue at the age of 21 months.

CONCLUSIONS

The present study revealed dynamic changes of the collagen network during growth and maturation of the pigs. The structure of the collagen network of young pigs gradually approached a network with the classical Benninghoff architecture. The probable explanation for the alterations is growth of the bone epiphysis with simultaneous adaptation of the cartilage to increased joint loading. The maturation of articular cartilage advances gradually with age and offers, in principle, the possibility to influence the quality of the tissue, especially by habitual joint loading. These observations in porcine cartilage may be of significance with respect to the maturation of human articular cartilage.

Regulation of immature cartilage growth by IGF-I, TGF-beta1, BMP-7, and PDGF-AB: role of metabolic balance between fixed charge and collagen network

Cartilage growth may involve alterations in the balance between the swelling tendency of proteoglycans and the restraining function of the collagen network. Growth factors, including IGF-I, TGF-beta1, BMP-7, and PDGF-AB, regulate chondrocyte metabolism and, consequently, may regulate cartilage growth. Immature bovine articular cartilage explants from the superficial and middle zones were incubated for 13 days in basal medium or medium supplemented with serum, IGF-I, TGF-beta1, BMP-7, or PDGF-AB. Variations in tissue size, accumulation of proteoglycan and collagen, and tensile properties were assessed. The inclusion of serum, IGF-I, or BMP-7 resulted in expansive tissue growth, stimulation of proteoglycan deposition but not of collagen, and a diminution of tensile integrity. The regulation of cartilage metabolism by TGF-beta1 resulted in tissue homeostasis, with maintenance of size, composition, and function. Incubation in basal medium or with PDGF-AB resulted in small volumetric and compositional changes, but a marked decrease in tensile integrity. These results demonstrate that the phenotype of cartilage growth, and the associated balance between proteoglycan content and integrity of the collagen network, is regulated differentially by certain growth factors.

Cartilage growth and remodeling: modulation of balance between proteoglycan and collagen network in vitro with beta-aminopropionitrile

OBJECTIVE

To examine the effect of beta-aminopropionitrile (BAPN), an inhibitor of lysyl oxidase, on growth and remodeling of immature articular cartilage in vitro.

DESIGN

Immature bovine articular cartilage explants from the superficial and middle layers were cultured for 13 days in serum-containing medium with or without BAPN. Variations in tissue size, accumulation of proteoglycan and collagen (COL), and tensile mechanical properties were assessed.

RESULTS

The inclusion of serum resulted in expansive tissue growth, stimulation of proteoglycan and COL deposition, and a diminution of tensile integrity. Supplementation of medium with BAPN accentuated this phenotype in terms of a further increase in tissue size in explants from the superficial layer and further diminution of tensile integrity, without affecting the contents of proteoglycan and COL in explants from both the superficial and middle layers.

CONCLUSION

COL crosslinking is a major factor in modulating the phenotype of cartilage growth and the associated balance between proteoglycan content and integrity of the COL network.

Mechanisms of cartilage growth: modulation of balance between proteoglycan and collagen in vitro using chondroitinase ABC

OBJECTIVE

To examine the cartilage growth-associated effects of a disruption in the balance between the swelling pressure of glycosaminoglycans (GAGs) and the restraining function of the collagen network, by diminishing GAG content prior to culture using enzymatic treatment with chondroitinase ABC.

METHODS

Immature bovine articular cartilage explants from the superficial and middle layers were analyzed immediately or after incubation in serum-supplemented medium for 13 days. Other explants were treated with chondroitinase ABC to deplete tissue GAG and also either analyzed immediately or after incubation in serum-supplemented medium for 13 days. Treatment- and incubation-associated variations in tissue volume, contents of proteoglycan and collagen network components, and tensile mechanical properties were assessed.

RESULTS

Incubation in serum-supplemented medium resulted in expansive growth with a marked increase in tissue volume that was associated with a diminution of tensile integrity. In contrast, chondroitinase ABC treatment on day 0 led to a marked reduction of GAG content and enhancement of tensile integrity, and subsequent incubation led to maturational growth with minimal changes in tissue volume and maintenance of tensile integrity at the enhanced levels.

CONCLUSION

The data demonstrate that a manipulation of GAG content in articular cartilage explants can distinctly alter the growth phenotype of cartilage. This may have practical utility for tissue engineering and cartilage repair. For example, the expansive growth phenotype may be useful to fill cartilage defects, while the maturational growth phenotype may be useful to induce matrix stabilization after filling defect spaces.

Effect of tissue maturity on cell viability in load-injured articular cartilage explants

OBJECTIVE

During joint maturation, articular cartilage undergoes compositional, structural, and biomechanical changes, which could affect how the chondrocytes within the cartilage matrix respond to load-induced injury. The objective of this study was to determine the effects of tissue maturity on chondrocyte viability when explanted cartilage was subjected to load-induced injury.

DESIGN

Cartilage explants from immature (4-8-week-old) and mature (1.5-2-year-old) bovine humeral heads were cyclically loaded at 0.5 hertz in confined compression with a stress of 1 or 5 megapascals for 0.5, 1, 3, 6 and 16 h. Cell death was assessed at 0, 24 and 48 h after load removal using cell viability dyes and terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling assay. The organization of pericellular matrix (PCM), biochemical composition and biomechanical properties of the cartilage were also determined.

RESULTS

For the immature and mature cartilage, cell death began at the articular surface and increased in depth with loading time up to 6h. No increase of cell death was found after load removal for up to 48 h. In both groups, cell death increased at a faster rate with the increase of stress level. The depth of cell death in the immature cartilage was greater than the mature cartilage, despite the immature cartilage having a higher bulk aggregate modulus. A less organized PCM in immature cartilage was found as indicated by the weak staining of type VI collagen.

CONCLUSION

Cells in the mature cartilage are less vulnerable to load-induced injury than those in immature cartilage.

Growth of immature articular cartilage in vitro: correlated variation in tensile biomechanical and collagen network properties

Articular cartilage biochemical composition and mechanical properties evolve during in utero and in vivo growth, with marked differences between fetus, newborn, and young adult. The objectives of this study were to test whether in vitro growth of bovine fetal and newborn calf articular cartilage explants resulted in changes in biochemical and tensile properties during up to 6 weeks of free-swelling culture in serum-supplemented medium. During this culture period, both fetal and calf cartilage grew markedly in size, increasing in dry and wet mass by 150-270%. This was due in part to increases in sulfated glycosaminoglycan (+248%), collagen (+96%), and pyridinoline cross-link (+133%). This was accompanied by an increase in water content so that the concentration of matrix components decreased, despite the overall net increase in mass. The ratio of pyridinoline cross-link to collagen remained low and characteristic of immature tissue. The equilibrium and dynamic tensile moduli and strength of both fetal and calf cartilage decreased during the culture period. The biochemical and biomechanical properties of the cartilage explants were correlated, such that the low values of modulus and strength were associated with low concentrations of collagen and pyridinoline. Thus, the tested culture conditions supported growth and maintenance cartilage in an immature state, but did not induce biomechanical or collagen network maturation.

Tensile mechanical properties of bovine articular cartilage: variations with growth and relationships to collagen network components

One approach to repairing articular defects is to regenerate cartilage by recapitulating the changes that occur during fetal and postnatal growth into adulthood, and to thereby restore functional biomechanical properties, especially those of the normally strong superficial region. The objectives of this study were (1) to characterize and compare tensile biomechanical properties of the superficial region of articular cartilage of the patellofemoral groove (PFG) and femoral condyle (FC) from bovine animals over a range of growth stages (third-trimester fetal, 1-3 week-old calf, and adult), and (2) to determine if these properties were correlated with collagen network components. With growth from the fetus to the adult, the equilibrium and dynamic tensile moduli and strength of cartilage samples increased by an average of 391-1060%, while the strain at the failure decreased by 43%. The collagen concentration (per wet weight) increased by 98%, and the pyridinoline cross-link concentration increased by 730%, while the glycosaminoglycan concentration remained unchanged or decreased slightly. Some growth-associated changes were location-specific, with tensile moduli and strength attaining higher values in the PFG than the FC. The growth-associated variation in tensile moduli and strength were associated strongly with variation in the contents of collagen and pyridinoline cross-link, but not sulfated glycosaminoglycan. The marked changes in the tensile properties and collagen network components of articular cartilage with growth suggest that such parameters may be used to evaluate the degrees to which regenerated cartilage recapitulates normal development and growth.

A growth mixture theory for cartilage with application to growth-related experiments on cartilage explants

In this paper, we present a growth mixture model for cartilage. The main features of this model are illustrated in a simple equilibrium boundary-value problem that is chosen to illustrate how a mechanical theory of cartilage growth may be applied to growth-related experiments on cartilage explants. The cartilage growth mixture model describes the independent growth of the proteoglycan and collagen constituents due to volumetric mass deposition, which leads to the remodeling of the composition and the mechanical properties of the solid matrix. The model developed here also describes how the material constants of the collagen constituent depend on a scalar parameter that may change over time (e.g., crosslink density); this leads to a remodeling of the structural and mechanical properties of the collagen constituent. The equilibrium boundary-value problem that describes the changes observed in cartilage explants harvested at different stages of a growth or a degenerative process is formulated. This boundary-value problem is solved using existing experimental data for developing bovine cartilage explants harvested at three developmental stages. The solution of the boundary-value problem in conjunction with existing experimental data suggest the types of experimental studies that need to be conducted in the future to determine model parameters and to further refine the model.

A compositional analysis of human nasal septal cartilage

BACKGROUND

Nasal septal cartilage is well established as an autograft material. Tissue engineering methods are now being developed to synthesize cartilage constructs with the properties of this type of cartilage. However, important baseline data on the composition of native septal cartilage is sparse.

OBJECTIVES

To characterize quantitatively the major biochemical constituents of native adult human septal cartilage and determine age- or sex-related variation in composition.

METHODS

Cartilage was harvested from the inferior region of the nasal septum in 33 patients (mean +/- SD age, 47.0 +/- 13.5 years; range, 24-80 years) during routine septoplasty or septorhinoplasty. Biochemical assays were used to determine the quantities, relative to wet weight, of the major constituents of cartilage: water, collagen (from hydroxyproline), sulfated glycosaminoglycan (sGAG), and chondrocytes (from DNA).

RESULTS

On average, each gram of wet cartilage contained 77.7% water, 7.7% collagen, 2.9% sGAG, and 24.9 million cells. Hydration and collagen content showed no significant age variation. Advancing age was associated with a reduction in sGAG content (7.7% per decade, P =.02) and cellularity (7.4% per decade, P =.05). No significant sex differences were found in any of these cartilage constituents.

CONCLUSIONS

This study represents the first biochemical characterization of the composition of native human septal cartilage. The data serve as a baseline for future comparison of the properties of tissue-engineered neocartilage constructs. Furthermore, the age-associated variations in cartilage composition have implications for patient selection for reconstructive procedures.

Development-associated differences in integrative cartilage repair: roles of biosynthesis and matrix

A recurring problem in tissue transplantation therapies for articular cartilage defects is the lack of integration between the implant and the host cartilage. Previous studies have shown that in vitro integration between explants of calf cartilage is markedly higher than that between fetal cartilage, despite similarly high levels of deposition of newly synthesized collagen. The aim of this study was to determine if cellular biosynthesis and extracellular matrix each contribute to these development-associated differences in integrative repair in vitro. The approach taken was to examine integration between specific combinations of cartilage explants that were apposed for two weeks. The cartilage matrix showed different propensities for repair, as integration of calf live cartilage to calf devitalized cartilage was greater than that of calf live cartilage to fetal devitalized cartilage. An inhibiting factor appeared to be present in fetal cartilage matrix since guanidine treatment of fetal devitalized cartilage was able to enhance its integration. The difference between integration to living cartilage and integration to devitalized cartilage, for calf and fetal tissue, indicated that the biosynthetic contribution to integration by calf cartilage was greater than the biosynthetic contribution by fetal cartilage. Thus, the increasing level of integration between fetal and fetal cartilage, fetal and calf cartilage, and calf and calf cartilage appeared to reflect both biosynthetic and matrix differences. Therapeutic strategies to enhance integration to cartilage may thus target both the extracellular components and the cellular biosynthetic activities of implants and host cartilage.

Biologic resurfacing of the patella: current status

The techniques of biologic resurfacing of the patella, like other joint surfaces, are still evolving. Currently none of them is free from criticism. In this regard it is our hope that progress in the basic science will offer in the near future new and more optimistic therapeutic possibilities (i.e., the restoration of a reparative cartilage that is structurally and functionally comparable to the native one). The greater expectancies come perhaps from the present experimental investigations about the combined use of tissue-engineered implants embedded with staminal cells and growth factors. Many problems remain to be solved, however, before reliable applicability in humans. From a general point of view, stem cells obtained from various sources (e.g., adult bone marrow, umbilical cord) offer the same finalities as the embryonic stem cells, without the ethical obstacles related to the latter. Therefore, it may be that restoration of part or all of the articular surface of a joint will be possible by way of these mesenchymal progenitors that have the ability to differentiate into the chondrogenic and osteogenic lines, which is required for the restoration of the various layers of a normal articular cartilage and subchondral bone.

Integrative articular cartilage repair: dependence on developmental stage and collagen metabolism

OBJECTIVES

The objectives of this research were to determine whether the integrative repair of bovine cartilage explants was dependent on developmental stage, and whether observed differences in integration with developmental stage were related to deposition of newly synthesized collagen and lysyl oxidase-mediated collagen cross-linking.

METHODS

Pairs of fetal, newborn calf, and adult bovine cartilage blocks were cultured in partial apposition for 2 weeks in medium supplemented with serum, ascorbate, and [3H]proline. Following culture, mechanical integration between apposed cartilage blocks was assessed by measuring adhesive strength in a single-lap shear configuration. Formation and stabilization of newly synthesized protein and collagen was investigated by determination of [3H]proline and [3H]hydroxyproline in tissue digests and guanidine extracts.

RESULTS

Calf cartilage exhibited a relatively high integrative repair phenotype, achieving an adhesive strength that was three--four-fold that of adult or fetal specimens. The low and high integrative repair phenotypes appeared related in part to different levels of collagen biosynthesis, which was approximately four--five-fold higher in calf cartilage samples than in the adult. However, fetal cartilage also exhibited a high level of biosynthesis. The different integrative repair phenotypes were not associated with marked differences in the kinetics of chemical stabilization of newly synthesized collagen, as the proportion of incorporated [3H]proline and newly-formed [3H]hydroxyproline that was resistant to extraction by 4M guanidine-HCl following culture was similar for cartilage from all developmental stages. Integration of calf cartilage appeared to depend on lysyl oxidase-mediated collagen cross-link formation, since inclusion of beta-aminopropionitrile (BAPN) in the culture medium completely eliminated development of adhesive strength. BAPN treatment also increased the percentage of newly synthesized protein in the guanidine extracts from 10% to 36% of the total, and that of newly synthesized collagen from 2% to 20%, while having only slight inhibitory effects on overall protein and collagen biosynthesis.

CONCLUSION

The finding that cartilage exhibits enhanced integrative repair at a certain developmental stage suggests that it may ultimately be possible to enhance repair when needed in clinical situations.

Compressive properties and function-composition relationships of developing bovine articular cartilage

The composition of cartilage is known to change during fetal and postnatal development. The objectives of this study were to characterize the compressive biomechanical properties of the 1 mm thick articular layer of cartilage of the distal femur from third-trimester bovine fetuses, from 1 to 3 week old bovine calf and from young adult bovine knees, and to correlate these properties with tissue components. The confined compression modulus increased 180% from the fetus to the calf and adult. The hydraulic permeability at 45% offset compression (relative to the free-swelling thickness) decreased by 70% from fetus to adult. These development-associated changes in biomechanical properties were primarily associated with a marked (approximately 2-3-fold) increase during development in collagen content and no detectable change in glycosaminoglycan (GAG) content. A role for collagen in the compressive properties of cartilage and the gradual increase in collagen during development suggest that collagen metabolism is critical for cartilage tissue engineering and repair therapies.

Age-associated changes in decorin in rat mandibular condylar cartilage

The small proteoglycan decorin strongly binds the fibrils of collagen types I and II; this interaction is thought to play a part in the maintenance of tissue integrity and biomechanical properties. In limb articular cartilage, there is evidence that decorin synthesis increases with age and that it is elevated in response to increased loading or in osteoarthritic cartilage. The aim here was to characterize the presence and relative amount of decorin in the condylar cartilage of the temporomandibular joint (TMJ) with maturation by Western blotting, and to assess its tissue localization by immunohistochemistry. Comparative data were obtained from tibial articular cartilage, which has been extensively studied. Cartilage from the mandibular condyle and tibial plateau was harvested from 24-day-old (growing) and 161-day-old (young adult) female Sprague-Dawley rats. In growing animals, decorin appeared slightly more abundant in the mandibular condylar cartilage than in articular cartilage, whereas in young adult animals the decorin content in the TMJ cartilage was noticeably less than in limb articular cartilage. Although there was an increase in decorin abundance with age at the TMJ, the increase in decorin with age in limb articular cartilage was considerably more pronounced. These data indicate that, although decorin is present in mandibular condylar cartilage, its abundance in adults is less than in limb articular cartilage; thus, maturation-associated changes may be dissimilar in magnitude from those documented for limb articular cartilage.

Human aggrecan keratan sulfate undergoes structural changes during adolescent development

Alkaline borohydride-reduced keratan sulfate chains were isolated from human articular cartilage aggrecan from individuals of various ages (0-85 years old). The chains were structurally characterized using 1H NMR spectroscopy, gel permeation chromatography, and oligosaccharide profiling (after digestion with the enzymes keratanase and keratanase II). The results show that from birth to early adolescence (0-9 years) the levels of alpha(1-3)-fucosylation, alpha(2-3)-sialylation, and galactose sulfation increase. Also, the weight-average molecular weight of the chains increases. During maturation (9-18 years) the levels of fucosylation and galactose sulfation continue to increase and alpha(2-6)-sialylation of the chains occurs. In adult life (18-85 years) there is little change in the weight-average molecular weight of the chains, and the levels of fucosylation, sialylation, and sulfation remain fairly constant.

Principles of cartilage repair and regeneration

An experimental approach and logic are presented for the regeneration of skeletal tissues that focus on the recapitulation of embryonic events starting with an uncommitted progenitor cell population that the authors refer to as mesenchymal stem cells. The repair and regeneration of articular cartilage, which itself has no repair potential, is the subject of this presentation. Full thickness cartilage defects were created in the medial condyle of the distal femur. Self repair (empty defects), articular chondrocytes (allografts), and autologous mesenchymal stem cells were used and the results are reported in selected examples from more than 800 rabbit knees. The optimal number of the appropriate cells delivered in a supportive vehicle to a defect pretreated with a dilute trypsin solution to optimize the integration of repair with normal host cartilage provides a methodology in which regeneration of articular cartilage can be observed. The principles have relevance to the clinical repair and regeneration of cartilage and other skeletal defects.

Changes in the chemical composition of the bovine temporomandibular joint disc with age

The bovine temporomandibular joint disc is a fibrocartilaginous structure composed largely of collagen and proteoglycans. Little is known about changes in its composition accompanying growth and maturation. Discs were collected from immature foetuses (3-5 months), mature foetuses (6-8 months, adolescents (18 months), young adults (2-3 yr) and mature adults (over 4 yr), dissected free of fibrous attachments, and separated into outer and inner tissues. For the outer tissues the major findings were that: (1) water content in postnatal specimens was less than in prenatal specimens: (2) collagen content (relative to tissue dry weight) increased up to adolescence with little change thereafter; (3) total glycosaminoglycan, chondroitin sulphate and hyaluronic acid contents decreased during foetal development and then remained relatively constant, and (4) dermatan sulphate (the major glycosaminoglycan at all ages) decreased at maturity while keratan sulphate increased slightly. Results for the inner tissues were similar except that: (1) total glycosaminoglycan content was much higher in postnatal animals; (2) chondroitin sulphate was the major glycosaminoglycan after birth; and (3) keratan sulphate, which was barely detectable in the foetal specimens, increased rapidly after birth. Evidence was also obtained for changes in the copolymeric nature of galactosaminoglycans in the inner tissue. These findings, especially the different pattern of age-related changes in outer (presumably non-compressed) and inner (presumably compressed) tissue, suggest that the disc has the capacity to continually modify its composition in response to the mechanical stresses placed on it.

Length variation in the keratan sulfate domain of mammalian aggrecan

The keratan sulfate domain of aggrecan consists of a series of tandemly repeating hexapeptides which have the consensus sequence Glu-Glu/Lys-Pro-Phe-Pro-Ser, where the serine side-chains presumably provide sites for the attachment of keratan sulfate (KS) chains. The number of hexapeptide repeats varies between species, ranging from four in rat (Doege et al., 1987) and mouse (Walcz et al., 1992) to 13 in human (Doege et al., 1991) and 23 in bovine aggrecan (Antonsson et al., 1989). Chicken aggrecan (Chandrasekaran and Tanzer, 1992) does not contain a KS domain with a recognizable hexapeptide motif. The extent of this variation among mammalian and avian species is not known, and there is currently no explanation to predict how differences in the size of the KS domain would affect aggrecan function. We used polymerase chain reaction (PCR) to amplify the portion of the human, canine and porcine aggrecan gene that codes for the KS domain. We sequenced the amplified products in each case. Human aggrecan, with 13 hexapeptide repeats (Doege et al., 1987), was used as reference and found to be essentially identical to published data. The canine and porcine KS domains consisted of six and ten hexapeptide repeats respectively. The same PCR protocol was used to amplify the KS domain from genomic DNA of eight other mammalian species. Comparison of the size of these amplified products, as determined by agarose gel electrophoresis, with those for which sequence data are available allowed us to estimate the number of repeats in the KS domain. In almost half the species examined, the KS domain consisted of 13 hexapeptide repeats.

Age-related changes in cartilage proteoglycans: quantitative electron microscopic studies

Biochemical and biophysical studies have shown that the composition and sedimentation velocity of cartilage proteoglycans change with age, but these investigations cannot demonstrate the alterations in molecular structure responsible for these changes. Development of quantitative electron microscopic methods has made it possible to define the age-related structural changes in aggregating proteoglycans and to correlate the alterations in their structure with changes in tissue composition and morphology. Electron microscopic measurement of human and animal hyaline cartilage proteoglycans has shown that with increasing age the length of the chondroitin sulfate-rich region of aggregating proteoglycan monomers (aggrecan molecules) decreases, the variability in aggrecan length increases, the density of aggrecan keratan sulfate chains increases, the number of monomers per aggregate decreases, and the proportion of monomers that aggregate declines. Proteoglycans from the nucleus pulposus of the intervertebral disc show similar but more dramatic age-related alterations. At birth, nucleus pulposus aggrecan molecules are smaller and more variable in length than those found in articular cartilage. Within the first year of human life, the populations of aggregates and large aggrecan molecules analogous to those found in articular cartilage decline until few if any of these molecules remain in the central disc tissues of skeletally mature individuals. The mechanisms of the age-related changes in cartilage proteoglycans have not been fully explained, but measurement of proteoglycans synthesized by chondrocytes of different ages suggests that alterations in synthesis produce at least some of the age-related changes in aggrecan molecules. Degradation of aggrecan chondroitin sulfate-rich regions in the matrix probably also contributes to the structural changes seen by electron microscopy. Age-related changes in proteoglycan aggregation may be due to alterations in link protein function or inhibition of aggregation of newly synthesized aggrecan molecules by accumulation of degraded aggrecan molecules.

Mesenchymal cell-based repair of large, full-thickness defects of articular cartilage

Osteochondral progenitor cells were used to repair large, full-thickness defects of the articular cartilage that had been created in the knees of rabbits. Adherent cells from bone marrow, or cells from the periosteum that had been liberated from connective tissue by collagenase digestion, were grown in culture, dispersed in a type-I collagen gel, and transplanted into a large (three-by-six-millimeter), full-thickness (three-millimeter) defect in the weight-bearing surface of the medial femoral condyle. The contralateral knee served as a control: either the defect in that knee was left empty or a cell-free collagen gel was implanted. The periosteal and the bone-marrow-derived cells showed similar patterns of differentiation into articular cartilage and subchondral bone. Specimens of reparative tissue were analyzed with use of a semiquantitative histological grading system and by mechanical testing with employment of a porous indenter to measure the compliance of the tissue at intervals until twenty-four weeks after the operation. There was no apparent difference between the results obtained with the cells from the bone marrow and those from the periosteum. As early as two weeks after transplantation, the autologous osteochondral progenitor cells had uniformly differentiated into chondrocytes throughout the defects. This repair cartilage was subsequently replaced with bone in a proximal-to-distal direction, until, at twenty-four weeks after transplantation, the subchondral bone was completely repaired, without loss of overlying articular cartilage. The mechanical testing data were a useful index of the quality of the long-term repair. Twenty-four weeks after transplantation, the reparative tissue of both the bone-marrow and the periosteal cells was stiffer and less compliant than the tissue derived from the empty defects but less stiff and more compliant than normal cartilage.

CLINICAL RELEVANCE

The current modalities for the repair of defects of the articular cartilage have many disadvantages. The transplantation of progenitor cells that will form cartilage and bone offers a possible alternative to these methods. As demonstrated in this report, autologous, bone-marrow-derived, osteochondral progenitor cells can be isolated and grown in vitro without the loss of their capacity to differentiate into cartilage or bone. Sufficient autologous cells can be generated to initiate the repair of articular cartilage and the reformation of subchondral bone. The repair tissues appear to undergo the same developmental transitions that originally led to the formation of articular tissue in the embryo.(ABSTRACT TRUNCATED AT 400 WORDS)

Variability in the G3 domain content of bovine aggrecan from cartilage extracts and chondrocyte cultures

The content of the globular domains G1, G2 and G3 on the core protein of high-density (A1D1) aggrecan isolated from newborn and mature bovine cartilage and from cultures of bovine chondrocytes was examined. Quantitation based on the 220 nm absorbance of tryptic marker peptides from each domain isolated by reversed-phase HPLC showed that while the content of G1 and G2 was essentially the same for all samples, the content of G3 varied markedly. The molar yield of G3 and G1 marker peptides indicated that approximately 55% of the G1-bearing aggrecan from immature cartilage carried the G3 domain, while for mature cartilage this figure was markedly reduced, at about 35%. Aggrecan prepared from the cell layer matrix of calf chondrocyte cultures had an apparent G3 content similar to newborn cartilage (55%), whereas aggrecan prepared from the medium of these cultures had a markedly higher G3 content, at about 80%. The high content of G3 in cell medium samples compared to cartilage extracts was supported by electron microscopic analysis of A1D1 preparations. The G3 content of the two subpopulations of aggrecan present in mature cartilage and separable by flat bed agarose gel electrophoresis was also determined at about 45% (Band I) and 20% (Band II) respectively. These results are discussed in terms of the likely origin of the marked variability in the G3 domain content of aggrecan.

Composition of proteoglycans synthesized in different layers of cultured anatomically intact articular cartilage

Calf articular cartilage was cultured anatomically intact on its natural bone-support. At day 0 and day 7, respectively, the cartilage was radiolabeled, washed and harvested in 3 successive layers parallel to the articular surface. The proteoglycans were studied after extraction by 4 M guanidine hydrochloride. In the deep layer, the endogenous proteoglycan monomers were slightly smaller, showed an increased polydispersity and the relative amount of keratan sulfate was lower. In addition, chondroitin sulfate side chains were slightly larger and the sulfation degree and proportion of 4-sulfated disaccharides was elevated. At day 0, deep layer chondrocytes incorporated about twice as much [35S]-sulfate into glycosaminoglycans as did superficial chondrocytes. The newly synthesized proteoglycan monomers were the same in all layers with respect to size, dispersity, relative amount of keratan sulfate and size of chondroitin sulfate side chains. The sulfation-pattern, however, changed with depth in the same way as noted in the endogenous proteoglycan population. Small endogenous proteoglycan was present in all layers, but its synthesis was only prominent in the upper layer and decreased with depth. After 7 days culture, the [35S]-sulfate incorporation had increased in the upper half of the cartilage. There was a strong increment in the proportion of 6-sulfated disaccharides of newly synthesized glycosaminoglycan in all layers. The synthesis of small proteoglycan was markedly reduced, especially in the upper layer.

Micromechanical spectroscopy of cartilage proteoglycans: hydration

Proteoglycan subunits extracted from calf cartilage have been studied with a high resolving power mechanical spectroscopy: the Thermostimulated Creep (TSC). The influence of hydration on TSC spectra shows the existence of two types of bound water: the weakly bound water increases the inertia of proteoglycan and stiffens their structure; the strongly bound water is responsible to a compensation law indicating the existence of a resonance phenomenon at the physiological temperature. Because of the looseness of bonds in weakly bound water, an increase of the local pressure may induce, in vivo, a release of water in tissues. This hypothesis explains perfectly the role of a water pump of proteoglycans in cartilage.

The effects of prenatal protein-energy malnutrition on ossification of fetal rat bones: a biochemical study

In fetal rats whose dams were fed a low-protein diet, 35S sulfate uptake into the growth plate of the long bone and rib was higher than in the control group. The elution pattern of guanidine-HCl extract in gel chromatography revealed that the malnourished group had more high molecular weight proteoglycans in the dissociative condition and a larger aggregated portion in the associative condition than did the control group; however, the same chondroitin-sulfate chain size existed. Calcium content did not differ in both groups. Aggregated proteoglycan or a high molecular weight proteoglycan that existed in the malnourished group probably played an inhibitory role in calcification. Prenatal protein-energy malnutrition may delay the change of proteoglycan character, which could affect mineralization of fetal bones.

Age-related changes in the composition of proteoglycans in sheep cartilages

Age-related changes in the proteoglycans of costal, tracheal, nasal and xiphoid cartilages of sheep, starting at 100 days in utero to 1 year postnatally and in scapular cartilages up to 13 years of age, have been assessed. The amino acid compositions of the core proteins in the proteoglycans from one-year-old cartilages are indistinguishable on the basis of kind of cartilage or of earlier stages of development. At 13 years of age, the core protein in the proteoglycans of scapular cartilages contains less glutamic acid/glutamine and glycine and more lysine, histidine, arginine, and threonine than at one year of age. Relative to the protein, the amount of chondroitin sulfates decreases with age but the amount of keratan sulfate increases. In part, this is a reflection of a decrease in the size of the chondroitin sulfate chains and an increase in the size of the keratan sulfate chains. Up to one year of age, the ratio of chondroitin-4-sulfate to chondroitin-6-sulfate increases in the scapular cartilages. From two to nine years of age, this ratio remains relatively constant at 1.7. At 100 days in utero, about 12% of the disaccharide repeats in the chondroitin sulfate are notsulfated, and this fraction progressively decreases to about 1% by two years postnatally. After one year of age, the size of the proteoglycan monomers decreases. As indicated by sedimentation velocity analysis, the proportion of monomers in aggregate form increases up to 1-2 years of age and then decreases. At 100 days of age the "immature" core protein does not react in vitro with hyaluronan and link proteins to form aggregates discernable in the ultracentrifuge.

Maturation of proteoglycan matrix in articular cartilage under increased and decreased joint loading. A study in young rabbits

The right knees of 4-month-old NZW rabbits were splinted in extension for 1 to 8 weeks. Biochemical changes of the knee articular cartilage were noted after decreased (splinted leg) and increased loading (created by the shift of body weight onto the left, contralateral limb). Increased loading accelerated changes associated with maturation of articular cartilage, which include accumulation of hyaluronic acid (HA) and keratan sulfate-rich proteoglycans (KS, PG) that are tightly bound to the tissue. After 8-weeks of splinting the content of extractable PGs in the tibial medial condyle decreased. The lost material was apparently replaced by PGs with a higher degree of sulfation of the chondroitin sulfate (Ch-S) chains. Reduced loading disturbed normal maturation as evidenced by inhibition of the accumulation of KS-rich, non-extractable PGs. Collagen content increased in all samples of different joint sites and groups during the 8-week experiment. The content of extractable PGs decreased slightly, while the content of non-extractable, especially KS-rich PGs increased. The greatest changes occurred in the tibial medial condyle, where the KS content was highest.

Undersulfated chondroitin sulfate in cartilage from a miniature poodle with spondyloepiphyseal dysplasia

In order to determine if either the proteoglycans or collagen in the cartilagenous epiphyses of a Miniature Poodle with spondyloepiphyseal dysplasia were abnormal, the cartilage was dissociatively extracted in 4 M guanidine HCl in the presence of protease inhibitors and subjected to isopycnic cesium chloride dissociative density gradient ultracentrifugation. Dissociative extraction solubilized 97% of the uronic acid and 88% of the protein. Uronic acid distributed anomalously in the density gradient in that about 1/3 was recovered in each of the D1 (1.58 g/ml), D2 (1.49 g/ml) and D3 (1.44 g/ml) fractions. Proteoglycans in the D1, D2 and D3 fractions also eluted from Sepharose CL-2B columns in a manner indicative of monomers of a smaller apparent hydrodynamic size than those from normal canine growth plate or articular cartilage. D1, D2 and D3 monomers subjected to the sodium borohydride reaction followed by chromatography on a Sepharose CL-6B column yielded glycosaminoglycan chain molecular weights of 10,200 (D1), 7600 (D2) and 6200 (D3). High pressure liquid chromatography on a Whatman Partisil 10PAC column of the chondroitinase AC II digests of D1, D2 and D3 fractions revealed that 60% of the D1, 81% of the D2 and 88% of the D3 unsaturated disaccharides eluted in the delta DiOS-delta DiHA position. Subsequent HPLC of the unsaturated disaccharides on the Hypersil APS column resulted in the recovery of 97% of the nonsulfated unsaturated disaccharides in the delta DiOS position. Associative extraction in 0.5 M guanidine followed by associative gradient ultracentrifugation resulted in the recovery of 27% of the uronic acid in the aA1 and 47% in the aA2 fractions. Two dimensional SDS gel electrophoresis of the CNBr peptides of the collagen isolated by pepsin digestion and 0.9 M NaCl precipitation revealed type II collagen. This study has demonstrated that spondyloepiphyseal dysplasia in a Miniature Poodle is characterized by cartilage containing undersulfated chondroitin sulfate proteoglycan.

Absence of keratan sulphate from skeletal tissues of mouse and rat

The absence of keratan sulphate synthesis from skeletal tissues of young and mature mice and rats has been confirmed by (1) analysis of specific enzyme degradation products of newly synthesized glycosaminoglycans, and (2) immunohistochemistry and radioimmunoassay using a monoclonal antibody directed against keratan sulphate. Approx. 98% of the [35S]glycosaminoglycans synthesized in vivo by mouse and rat costal cartilage, and all of those of lumbar disc, are chondroitin sulphate. The remainder in costal cartilage were identified as heparan sulphate in mature rats. In contrast, [35S]glycosaminoglycans synthesized by cornea of both species comprised both chondroitin sulphate and keratan sulphate. In mice keratan sulphate accounted for 12-25% and in rats 40-50% of the total [35S]glycosaminoglycans, depending on the age of the animal. Experiments in vitro with organ culture of cartilage and cornea confirm these results. Absence of keratan sulphate from mouse costal cartilage and lumbar disc D1-proteoglycans was corroborated by inhibition radioimmunoassay with the monoclonal antibody MZ15 and by lack of staining for keratan sulphate in indirect immunofluorescence studies using the same antibody.

Age-related changes in articular cartilage proteoglycans: electron microscopic studies

Biochemical and biophysical studies have demonstrated that proteoglycan monomers from immature and adult articular cartilage differ in composition and size. To investigate the structural basis of age-related differences in articular cartilage proteoglycan monomers and aggregates, we isolated and purified high buoyant density proteoglycans from the articular cartilages of 2- to 3-month-old calves and 18-month-old steers. The molecular architecture and dimensions of the proteoglycans were examined using the electron microscope monolayer method. Aggregated and nonaggregated monomers from calf cartilage were longer and less variable in length than the corresponding monomers from steer articular cartilage. Calf monomer lengths had unimodal frequency distributions whereas nonaggregated steer monomer lengths had a bimodal distribution. These observations were confirmed by acrylamide-agarose electrophoresis, which demonstrated that the samples contained only one species of proteoglycan monomer in calf but two species in steer. In addition, calf aggregated monomers had longer thin segments indicating that calf and steer monomers differed in structure as well as in size. Steer proteoglycan aggregates were shorter and had fewer monomers than those from calf. These observations demonstrate the existence of significant age-related structural differences in articular cartilage proteoglycans and form the basis for future study of the mechanisms responsible for these differences.

Low buoyant density proteoglycans from saline and dissociative extracts of embryonic chicken retinas

Retinas were labeled in culture with [3H]glucosamine or [3H]leucine and [35S]sulfate and extracted sequentially with physiologically balanced saline and 4 M guanidine HCl. They were dialyzed into associative conditions (0.5 M NaCl) and chromatographed on agarose columns. Under these conditions, some of the proteoglycans were associated in massive complexes that showed low buoyant densities when centrifuged in CsCl density gradients under dissociative conditions (4 M guanidine HCl). Much of the label in these complexes was in molecules other than proteoglycans. Most of the proteoglycans, however, were included on the agarose columns, where they appeared to be constitutionally of low buoyant density. They resisted attempts to separate potential low buoyant density contaminants from the major proteoglycans by direct CsCl density gradient centrifugation or by the fractionation of saline or 8 M urea extracts on diethylaminoethyl-Sephacel. The diethylaminoethyl-Sephacel fractions were either subjected to CsCl density gradient centrifugation or were chromatographed on Sephacryl S-300, in both cases before and after alkaline cleavage, to confirm the presence of typical O-linked glycosaminoglycans. The medium and balanced salt extracts were enriched in chondroitin sulfate and other sulfated macromolecules, possibly highly sulfated oligosaccharides, that resisted digestion by chondroitinase ABC but were electrophoretically less mobile than heparan sulfate. Guanidine HCl or urea extracts of the residues were mixtures of high and low density proteoglycans that were enriched in heparan sulfate.

Keratan sulfate content and articular cartilage maturation during postnatal rabbit growth

This article describes the macromolecular changes in keratan sulfate and proteoglycan that occur in rabbit articular cartilage during postnatal development. Articular cartilage glycosaminoglycans from femoral condyles and the tibial plateaus of rabbits at 8, 12, 18, and 26 weeks and 2 years of age were extracted, fractionated, and quantified. The predominant glycosaminoglycan present in articular cartilage at 8 weeks was chondroitin sulfate. During subsequent maturation the relative proportions of keratan sulfate and chondroitin sulfate varied inversely. The greatest increase in the amount of keratan sulfate present in cartilage was observed between 12 and 26 weeks of age. Hyaluronic acid content was measurable at 12 weeks; afterward the amount remained relatively constant with age. Proteoglycans, extracted from 6-, 12-, and 22-week-old rabbit femoral and tibial cartilage in the presence of protease inhibitors, were analyzed on columns of Sepharose CL-2B. Cartilage proteoglycans decreased in hydrodynamic size between 12 and 22 weeks, corresponding to the period of maximal change in content of keratan and chondroitin sulfate.

Molecular and cell isoforms during development

Development proceeds by way of a discrete yet overlapping series of biosynthetic and restructuring events that result in the continued molding of tissues and organs into highly restricted and specialized states required for adult function. Individual molecules and cells are replaced by molecular and cellular variants, called isoforms; these arise and function during embryonic development or later life. Isoforms, whether molecular or cellular, have been identified by their structural differences, which allow separation and characterization of each variant. These isoforms play a central and controlling role in the continued and dynamic remodeling that takes place during development. Descriptions of the individual phases of the orderly replacement of one isoform for another provides an experimental context in which the process of development can be better understood.

Isolation and characterization of high-buoyant-density proteoglycans from bovine femoral-head cartilage

Proteoglycans were extracted from bovine (15-18 months old) femoral-head cartilage. The heterogeneity of the A1D1 proteoglycan fraction was examined by gel chromatography, sedimentation velocity, sucrose rate-zonal centrifugation and CS2SO4 isopycnic centrifugation. In all cases polydisperse but unimodal distributions were obtained. Chemical analysis of the preparation yielded a galactosamine/glucosamine molar ratio of 7:1, and 13C n.m.r. spectroscopy showed that the chondroitin sulphate comprised equal proportions of the 4- and 6-sulphate isomers. Gel chromatography of a papain and Pronase digest of the proteoglycan indicated that the chondroitin sulphate chains had a Mn of approx. 10500. The mean buoyant density of the proteoglycan in pure CS2SO4 was 1.46 g/ml. Physical characterization of the proteoglycan preparation in 4M-guanidine hydrochloride, pH 7.4, by using conventional light-scattering gave a radius of gyration of 42 nm and a Mw of 0.96 X 10(6). Quasi-elastic light-scattering in the same solvent yielded a translational diffusion coefficient, D020, of 5.41 X 10(-8) cm2 X S-1, and ultracentrifugation gave a sedimentation coefficient, S020, of 12.0S. Thus from sedimentation-diffusion studies a Mw of 1.36 X 10(6) was calculated. The possible origins for the differences in the two molecular-weight estimates are discussed. It is concluded that the high-buoyant-density proteoglycans from bovine articular cartilage are significantly smaller than those from bovine nasal septum, and that this is largely due to the smaller size of their chondroitin sulphate chains.

The effect of serum on biosynthesis of proteoglycans by bovine articular cartilage in culture

Proteoglycan synthesis by slices of adult bovine articular cartilage is stimulated two-to threefold when tissue is cultured in the presence of fetal calf serum for 5-6 days. After this, essentially steady-state conditions are achieved for up to 14 days in which the high synthetic rates are maintained and the amount of proteoglycan in the tissue remains nearly constant. In the absence of fetal calf serum, synthesis declines to a lower level and there is a gradual, net loss of proteoglycan from the tissue. Tissue maintained without serum for several days rapidly increases synthetic rates to the higher levels over 2-3 days after transferring into medium with serum, and vice versa, indicating that the response of the chondrocytes to serum factors is reversible. The structures of the proteoglycans synthesized under all medium conditions were typical for cartilage. Only small differences in glycosaminoglycan chain sizes and a consistent decrease in the relative amount of keratan sulfate to chondroitin sulfate during the first days in the culture were observed. The net capacity of the cells for chondroitin sulfate synthesis, as estimated by incubation in the presence of exogenous beta-xyloside acceptor, increased (or decreased) in parallel with the changes in endogenous proteoglycan synthesis when cultures were transferred from medium without to medium with serum (or vice versa), suggesting that changes in the net amounts of the enzymes for chondroitin sulfate synthesis are closely coordinated with changes in the amount of core protein being processed to proteoglycans. The responses of calf articular cartilage in the same system were somewhat different. Serum in the medium was required to maintain initial high levels of synthesis. The proteoglycans synthesized contained a lower proportion of keratan sulfate than those initially synthesized in the adult tissue, and there was no change in this proportion with time in culture. The maintenance of steady-state conditions for proteoglycan metabolism by either adult or calf tissue in the presence of serum in these cultures should provide a useful model for studying the regulation of synthesis and catabolism of proteoglycans by chondrocytes residing in a nearly normal extracellular matrix for long periods of time.