Identity of the core proteins of the large chondroitin sulphate proteoglycans synthesized by skeletal muscle and prechondrogenic mesenchyme

Austromegabalanus psittacus barnacle shell structure and proteoglycan localization and functionality

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

Quantifying load-induced solute transport and solute-matrix interaction within the osteocyte lacunar-canalicular system

Osteocytes, the most abundant cells in bone, are essential in maintaining tissue homeostasis and orchestrating bone's mechanical adaptation. Osteocytes depend upon load-induced convection within the lacunar-canalicular system (LCS) to maintain viability and to sense their mechanical environment. Using the fluorescence recovery after photobleaching (FRAP) imaging approach, we previously quantified the convection of a small tracer (sodium fluorescein, 376 Da) in the murine tibial LCS under intermittent cyclic loading. In the present study, we first expanded the investigation of solute transport using a larger tracer (parvalbumin, 12.3 kDa), which is comparable in size to some signaling proteins secreted by osteocytes. Murine tibiae were subjected to sequential FRAP tests under rest-inserted cyclic loading while the loading magnitude (0, 2.8, or 4.8 N) and frequency (0.5, 1, or 2 Hz) were varied. The characteristic transport rate k and the transport enhancement relative to diffusion (k/k0) were measured under each loading condition, from which the peak solute velocity in the LCS was derived using our LCS transport model. Both the transport enhancement and solute velocity increased with loading magnitude and decreased with loading frequency. Furthermore, the solute-matrix interaction, quantified in terms of the reflection coefficient through the osteocytic pericellular matrix (PCM), was measured and theoretically modeled. The reflection coefficient of parvalbumin (σ = 0.084) was derived from the differential fluid and solute velocities within loaded bone. Using a newly developed PCM sieving model, the PCM's fiber configurations accounting for the measured interactions were obtained for the first time. The present study provided not only new data on the micro-fluidic environment experienced by osteocytes in situ but also a powerful quantitative tool for future study of the PCM, the critical interface that controls both outside-in and inside-out signaling in osteocytes during normal bone adaptation and in pathological conditions.

Distribution of PG-M/versican variants in human tissues and de novo expression of isoform V3 upon endothelial cell activation, migration, and neoangiogenesis in vitro

We have carried out a comprehensive molecular mapping of PG-M/versican isoforms V0-V3 in adult human tissues and have specifically investigated how the expression of these isoforms is regulated in endothelial cells in vitro. A survey of 21 representative tissues highlighted a prevalence of V1 mRNA; demonstrated that the relative frequency of expression was V1 > V2 > V3 >or= V2; and showed that <15% of the tissues transcribed significant levels of all four isoforms. By employing novel and previously described anti-versican antibodies we verified a ubiquitous versican deposition in normal and tumor-associated vascular structures and disclosed differences in the glycanation profiles of versicans produced in different vascular beds. Resting endothelial cells isolated from different tissue sources transcribed several of the versican isoforms but consistently failed to translate these mRNAs into detectable proteoglycans. However, if stimulated with tumor necrosis factor-alpha or vascular endothelial growth factor, they altered their versican expression by de novo transcribing the V3 isoform and by exhibiting a moderate V1/V2 production. Induced versican synthesis and de novo V3 expression was also observed in endothelial cells elicited to migrate in a wound-healing model in vitro and in angiogenic endothelial cells forming tubule-like structures in Matrigel or fibrin clots. The results suggest that, independent of the degree of vascularization, human adult tissues show a limited expression of versican isoforms V0, V2, and V3 and that endothelial cells may contribute to the deposition of versican in vascular structures, but only following proper stimulation.

Chondroitin sulfate proteoglycan is a potent enhancer in the processing of procathepsin L

The acceleration effect of chondroitin-4-sulfate(CS-) proteoglycan on the processing of procathepsin L in vitro was investigated using enzyme purified from the culture medium of MLC cells. Procathepsin L was slightly processed even when it was incubated without CS-proteoglycan for 60 min in 50 mm acetate buffer, pH 5.5, and trace amounts of the 31 kDa mature form and 35-38 kDa intermediates of cathepsin L were formed. On the other hand, in the presence of CS-proteoglycan, procathepsin L was completely converted to the mature form within the same 60 minute time period. Moreover, Z-Phe-Arg-MCA hydrolyzing activity was increased significantly by the incubation with CS-proteoglycan, while no considerable increase in the activity was observed during the incubation without CS-proteoglycan. Since the specific cathepsin L inhibitor, CLIK-195, inhibited the processing of procathepsin L accelerated by CS-proteoglycan, the trace amount of cathepsin L activity may participate in the processing. These results suggest that CS-proteoglycan may play a role in accelerating the processing of procathepsin L as an endogenous enhancer in the extracellular environment in vivo.

Secretion pattern, ultrastructural localization and function of extracellular matrix molecules involved in eggshell formation

The chicken eggshell is a composite bioceramic containing organic and inorganic phases. The organic phase contains, among other constituents, type X collagen and proteoglycans (mammillan, a keratan sulfate proteoglycan, and ovoglycan, a dermatan sulfate proteoglycan), whose localization depends on a topographically defined and temporally regulated deposition. Although the distribution of these macromolecules in the eggshell has been well established, little is known about their precise localization within eggshell substructures and oviduct cells or their pattern of production and function during eggshell formation. By using immunofluorescent and immuno-ultrastructural analyses, we examined the distribution of these macromolecules in oviduct cells at different post-oviposition times. To understand the role of proteoglycan sulfation on eggshell formation, we studied the effects of inhibition of proteoglycan sulfation by treatment with sodium chlorate. We showed that these macromolecules are produced by particular oviduct cell populations and at precise post-oviposition times. Based on the precise ultrastructural localization of these macromolecules in eggshell substructures, the timing of the secretion of these macromolecules by oviduct cells and the effects on eggshell formation caused by the inhibition of proteoglycan sulfation, the putative role of mammillan is in the nucleation of the first calcite crystals, while that of ovoglycan is to regulate the growth and orientation of the later forming crystals of the chicken eggshell.

Monoclonal antibodies to mineralized matrix molecules of the avian eggshell

The extracellular matrix of the mineralizing eggshell contains molecules hypothesized to be regulators of biomineralization. To study eggshell matrix molecules, a bank of monoclonal antibodies was generated that bound demineralized eggshell matrix or localized to oviduct epithelium. Immunofluorescence staining revealed several staining patterns for antibodies that recognized secretory cells: staining for a majority of columnar lining cells, staining for a minor sub-set of columnar lining cells, intensified staining within epithelial crypts, and staining of the entire tubular gland. Western blotting with the antibody Epi2 on eggshell matrix showed binding to molecules with the apparent molecular weight of eggshell matrix dermatan sulfate proteoglycan (eggshell DSPG). Immunoblots of cyanogen bromide-cleaved eggshell DSPG revealed broad band of reactivity that shifted to 25 kDa after chondroitinase digestion; indicating that the Epi2 binding site is located on a fragment which contains dermatan sulfate side chains. Immunogold labeling showed that Epi2 binds to secretory vesicles within the non-ciliated cells of the columnar epithelium, while the antibodies Tg1 and Tg2 bind to secretory vesicles of tubular gland cells. Immunogold labeling of demineralized shell matrix showed binding of Epi2, Tg1, and Tg2 to the matrix of the palisade layer, and showed little reactivity to other regions of the shell matrix. Quantification of the immunogold particles within the eggshell matrix revealed that antibodies Epi2 and Tg1 bind all calcified regions equally while antibody Tg2 has a greater affinity for the baseplate region of the calcium reserve assembly.

Avian neural crest cell migration is diversely regulated by the two major hyaluronan-binding proteoglycans PG-M/versican and aggrecan

It has been proposed that hyaluronan-binding proteoglycans play an important role as guiding cues during neural crest (NC) cell migration, but their precise function has not been elucidated. In this study, we examine the distribution, structure and putative role of the two major hyaluronan-binding proteoglycans, PG-M/versicans and aggrecan, during the course of avian NC development. PG-M/versicans V0 and V1 are shown to be the prevalent isoforms at initial and advanced phases of NC cell movement, whereas the V2 and V3 transcripts are first detected following gangliogenesis. During NC cell dispersion, mRNAs for PG-M/versicans V0/V1 are transcribed by tissues lining the NC migratory pathways, as well as by tissues delimiting nonpermissive areas. Immunohistochemistry confirm the deposition of the macromolecules in these regions and highlight regional differences in the density of these proteoglycans. PG-M/versicans assembled within the sclerotome rearrange from an initially uniform distribution to a preferentially caudal localization, both at the mRNA and protein level. This reorganization is a direct consequence of the metameric NC cell migration through the rostral portion of the somites. As suggested by previous in situ hybridizations, aggrecan shows a virtually opposite distribution to PG-M/versicans being confined to the perinotochordal ECM and extending dorsolaterally in a segmentally organized manner eventually to the entire spinal cord at axial levels interspacing the ganglia. PG-M/versicans purified from the NC migratory routes are highly polydispersed, have an apparent M(r) of 1,200-2,000 kDa, are primarily substituted with chondroitin-6-sulfates and, upon chondroitinase ABC digestion, are found to be composed of core proteins with apparent M(r)of 360–530, 000. TEM/rotary shadowing analysis of the isolated PG-M/versicans confirmed that they exhibit the characteristic bi-globular shape, have core proteins with sizes predicted for the V0/V1 isoforms and carry relatively few extended glycosaminoglycan chains. Orthotopical implantation of PG-M/versicans immobilized onto transplantable micromembranes tend to ‘attract’ moving cells toward them, whereas similar implantations of a notochordal type-aggrecan retain both single and cohorts of moving NC cells in close proximity of the implant and thereby perturb their spatiotemporal migratory pattern. NC cells fail to migrate through three-dimensional collagen type I-aggrecan substrata in vitro, but locomote in a haptotactic manner through collagen type I-PG-M/versican V0 substrata via engagement of HNK-1 antigen-bearing cell surface components. The present data suggest that PG-M/versicans and notochordal aggrecan exert divergent guiding functions during NC cell dispersion, which are mediated by both their core proteins and glycosaminoglycan side chains and may involve ‘haptotactic-like’ motility phenomena. Whereas aggrecan defines strictly impenetrable embryonic areas, PG-M/versicans are central components of the NC migratory pathways favoring the directed movement of the cells.

Age-related changes in the proteoglycans of human skin

Skin undergoes dramatic age-related changes in its mechanical properties, including changes in tissue hydration and resiliency. Proteoglycans are macromolecular conjugates of protein and carbohydrate (glycosaminoglycan) which are involved in these tissue properties. In order to examine whether age-related changes in skin proteoglycans may contribute to the age-related changes in the mechanical properties of skin, proteoglycans from human skin of various ages were extracted and analyzed. Samples were obtained from two different fetal ages, from mature skin, and from senescent skin. As a function of age, there is a decrease in the proportion of large chondroitin sulfate proteoglycans (versican) and a concomitant increase in the proportion of small dermatan sulfate proteoglycans (decorin). Based on reactivity with antibodies to various chondroitin sulfate epitopes, fetal versican differs from the versican found in older skin with respect to the chondroitin sulfate chains. Also, the decorin of fetal skin is slightly larger, while the decorin of older skin shows greater polydispersity in both its size and its charge to mass ratio. There are also age-related differences in the size and polydispersity of the core proteins of decorin. The most pronounced change in skin proteoglycans is the appearance in mature skin of a proteoglycan which is smaller than decorin, but which has the same amino terminal amino acid sequence as decorin. This small proteoglycan is abundant in mature skin and may be a catabolic fragment of decorin or an alternatively spliced form of decorin. In light of the known ability of decorin to influence collagen fibrillogenesis and fibril diameter, the appearance of this small decorin-related proteoglycan may have a significant effect on skin elasticity. The observation that proteoglycans in skin show dramatic age-related differences suggests that these changes may be involved in the age-related changes in the physical properties of skin.

Developmental regulation of proteoglycan synthesis and decorin expression during turkey embryonic skeletal muscle formation

To delineate the role of proteoglycans in turkey skeletal muscle development, proteoglycan expression was examined in pectoral muscle from 14-, 20-, and 25-d-old embryos. Proteoglycans were separated by DEAE (diethylaminoethyl cellulose) anion exchange and molecular sieve chromatography. Glycosaminoglycan composition was measured by enzyme digestion and nitrous acid deamination. The proteoglycan decorin was analyzed at each of these stages of development for core protein size by polyacrylamide gel electrophoresis and for spatial distribution by immunohistochemistry. Chondroitin sulfate-containing proteoglycans were the predominant proteoglycans found throughout turkey embryonic skeletal muscle development. However, in 20- and 25-d-old pectoral muscle, higher levels of heparan and dermatan sulfate were observed compared with their values at 14 d. Two decorin core protein bands with molecular weights of 45 and 46 kDa were detected. Immunostaining for decorin showed that, as the connective tissue layers developed, decorin was localized in the perimysium and epimysium. These data indicate that turkey embryonic skeletal muscle proteoglycan expression is dynamic and changes from a matrix that is rich in a large chondroitin sulfate proteoglycan to one containing dermatan sulfate, heparan sulfate, and chondroitin sulfate proteoglycans, and suggests the presence of two forms of decorin.

A monoclonal antibody which recognizes a glycosaminoglycan epitope in both dermatan sulfate and chondroitin sulfate proteoglycans of human skin

Studies have been initiated to identify various cell surface and matrix components of normal human skin through the production and characterization of murine monoclonal antibodies. One such antibody, termed PG-4, identifies both cell surface and matrix antigens in extracts of human foetal and adult skin as the dermatan sulfate proteoglycans, decorin and biglycan, and the chondroitin sulfate proteoglycan versican. Treatment of proteoglycans with chondroitinases completely abolishes immunoreactivity for all of these antigens which suggests that the epitope resides within their glycosaminoglycan chains. Further evidence for the carbohydrate nature of the epitope derives from competition studies where protein-free chondroitin sulfate chains from shark cartilage react strongly; however, chondroitin sulfate chains from bovine tracheal cartilage fail to exhibit a significant reactivity, an indication that the epitope, although present in some chondroitin sulfate chains, does not consist of random chondroitin 4- or 6-sulfate disaccharides. The presence of the epitope on dermatan sulfate chains and on decorin was also demonstrated using competition assays. Thus, PG-4 belongs to a class of antibodies that recognize native epitopes located within glycosaminoglycan chains. It differs from previously described antibodies in this class in that it identifies both chondroitin sulfate and dermatan sulfate proteoglycans. These characteristics make PG-4 a useful monoclonal antibody probe to identify the total population of proteoglycans in human skin.

Dynamic expression of proteoglycans during chicken skeletal muscle development and maturation

Skeletal muscle development is a complex process in which cell migration and adhesion play important roles. Because these cellular activities involve cell surface and extracellular matrix molecules, proteoglycan analysis was performed for developing chick skeletal muscle. Proteoglycans are macromolecular conjugates of protein and carbohydrate found in the extracellular matrix and at the cell surface. In developing muscle, both in vivo and in vitro, there is a development-related progression from synthesis of primarily large proteoglycans at earlier stages to mainly small proteoglycans at later stages. This progression was demonstrated by radiolabeling developing muscle and extracting and characterizing the proteoglycans. The large proteoglycans synthesized earlier in myogenesis have been identified as the large chondroitin sulfate proteoglycan, versican. Among the small proteoglycans synthesized at later stages is the small dermatan sulfate proteoglycan, decorin. Immunolocalization of these proteoglycans shows that versican is initially present in pericellular locations around developing myotubes, whereas decorin is observed in the epimysium early in development, and then its distribution gradually spreads to also include the perimysium and endomysium. Studies of regenerating muscle show that there is a recapitulation of the embryonic pattern of proteoglycan synthesis, which, coupled with the results from embryonic muscle development, suggests a role for versican in some early aspect of myogenesis.

Dermatan sulfate proteoglycans from the mineralized matrix of the avian eggshell

The eggshell of the chicken is a useful model to study matrix components which affect biomineralization. As an extension of our previous immunohistochemical work which suggested the presence of dermatan sulfate proteoglycans in the mineralized region of the eggshell, a study was undertaken to characterize these molecules biochemically. After demineralization with HCl and extraction with 4 M guanidinium chloride containing protease inhibitors, the extract was partitioned by anion exchange chromatography. Step elution with 0.25 M and 1.0 M sodium chloride resulted in the generation of two fractions, both of which contain chondroitinase-sensitive proteoglycans with molecular weights estimated at 200,000 by gel electrophoresis. The proteoglycans in each fraction have core proteins with molecular weights of approximately 120,000 and glycosaminoglycans with average molecular weights of 22,000. Based on differential sensitivity to chondroitinase ABC and AC II, these glycosaminoglycans contain a small proportion of dermatan sulfate. The disaccharide compositions of these glycosaminoglycans differ for the proteoglycans eluted with 0.25 M and 1.0 M sodium chloride. Those eluted with lower sodium chloride are enriched in unsulfated chondroitin and have much more 4-sulfated than 6-sulfated disaccharides; those eluted with 1.0 M sodium chloride contain primarily 4-sulfated disaccharides, a small amount of 6-sulfated disaccharides, and less unsulfated disaccharides than the proteoglycans eluted with 0.25 M sodium chloride. The large difference in the proportions of unsulfated chondroitin may be the reason for the elution at different sodium chloride concentrations. Both of the anion exchange column fractions contain other proteins in addition to the proteoglycans. These proteins are not separated from the proteoglycans by a second anion exchange column or by molecular sieve chromatography under dissociative conditions. Of particular interest is the observation that the eggshell proteoglycans and their core proteins are recognized by a monoclonal antibody which recognizes an epitope on the core protein of avian versican. This suggests that, in spite of the large differences in the sizes of the core proteins of versican and the eggshell proteoglycans, these core proteins share some homology. Because anionic molecules are thought to be important regulators of biomineralization, and because preparations like those analyzed in this study have been shown to influence in vitro calcium carbonate crystallization, the eggshell proteoglycans may play a role in eggshell mineralization.

Decorin and collagen type I gene expression in avian low score normal pectoral muscle

The avian Low Score Normal (LSN) genetic muscle weakness is phenotypically characterized by a reduction in the ability of the birds to right themselves from a supine position. Compared to normal skeletal muscle, LSN muscle has normal myosin isoform switching and cell-cell recognition, elevated glycosaminoglycan and decorin levels at embryonic Day 20, and a large increase in collagen crosslinking at 6 wk posthatch. To begin to determine the biological mechanism involved in the elevated decorin protein concentration at embryonic Day 20, the steady-state levels of transcripts encoding both decorin and collagen Type I at embryonic Days 14, 19, and 20, and at 1 d and 6 wk posthatch were measured. On embryonic Day 20, collagen Type I transcripts were not different from the control but there was a significant elevation in decorin transcript levels. At 1 d and 6 wk posthatch, transcript levels of decorin and collagen Type I were not different between LSN and controls. The change in decorin transcript steady-state levels is limited to late embryonic development and suggests an alteration in a signal transduction pathway regulating decorin transcription.

Identification of decorin and chondroitin sulfate proteoglycans in turkey skeletal muscle

Turkey pectoral muscles were examined at 15 through 25 d of embryonic age in order to delineate the developmental pattern of proteoglycan expression during skeletal muscle development. Glycosaminoglycan concentration, decorin, and muscle chondroitin sulfate proteoglycan (M-CSPG) levels were measured at each developmental age. Glycosaminoglycan levels rose during the developmental period studied, whereas decorin and M-CSPG levels were initially high at Day 15 and then decreased. The results from this study demonstrate the presence of both decorin and M-CSPG during turkey skeletal muscle development.

Partial characterization of ovine skeletal muscle proteoglycans and collagen

Ovine longissimus dorsi and biceps femoris muscles were analyzed for proteoglycan content, collagen and lysine aldehyde-derived collagen crosslinking concentrations at 2-4 days, six-month-old, and six-year-old stages of development. Tissue extracted proteoglycan molecular sieve distribution on a Sephacryl S-200HR column revealed two proteoglycan populations with estimated relative molecular weight ranges of 200,000 to 250,000 daltons and 23,000 to 70,000 daltons. The molecular sieve distribution was similar between the two muscles within a developmental age, but changed as a function of developmental age. Primary culture from both the longissimus dorsi and biceps femoris muscle liberated proteoglycans into the culture medium. In contrast to the tissue extracted proteoglycans, at the six-year-old stage of development, culture medium liberated proteoglycan Sephacryl S-200HR molecular sieve distribution differed between the two muscles. In both the tissue extracted and medium liberated proteoglycans at all developmental stages, nitrous acid deamination demonstrated the presence of heparan sulfate. Immunoblot analysis of the tissue extracted proteoglycans indicated the presence of decorin at each developmental stage. Longissimus dorsi and biceps femoris collagen concentrations (5.13 +/- 0.9 vs. 5.53 +/- 1.5%, respectively) and crosslink concentrations (0.07 +/- 0.01 moles HP/mole collagen) were initially similar between the two muscles; however, by six-months the muscles differed in both collagen concentration (1.72 +/- 0.5 and 2.53 +/- 0.7%, respectively) and crosslinking (0.24 +/- 0.02 and 0.27 +/- 0.03 moles HP/mole collagen, respectively). At six years of age, both the longissimus dorsi and biceps femoris exhibited slightly elevated collagen concentrations (2.49 and 3.05%, respectively) while crosslinking values were decreased relative to values at six-months of age (0.11 +/- 0.01 and 0.18 +/- 0.01 moles HP/mole of collagen, respectively). The results from this study indicate that skeletal muscle proteoglycans and collagen show developmental changes, which suggests that they are subject to developmental regulation.

The avian low score normal muscle weakness alters decorin expression and collagen crosslinking

Extracellular matrix development of chicken pectoral muscle was examined in the Low Score Normal (LSN) genetic muscle weakness and compared to both normal and avian muscular dystrophy (MD). At 20 days of embryonic development significant elevations were noted in LSN total glycosaminoglycan concentration and decorin, while at 14 days, LSN glycosaminoglycan and decorin levels were indistinguishable from the controls. Levels of a large skeletal muscle chondroitin sulfate proteoglycan (M-CSPG) appear to be unaffected. Morphologically, at 20 days, the extracellular matrix space between muscle fibers increased to a level characteristic to that observed in avian muscular dystrophy. At six weeks posthatch a marked increase in LSN collagen crosslinking relative to MD or control tissues was observed, while collagen concentration was not altered. By one year posthatch LSN collagen crosslink levels did not significantly differ from normal tissue. These data support the concept that the LSN muscle weakness is associated with changes in both proteoglycan and collagen characteristics.