Proteoglycan-collagen interactions

Mouse placental scaffolds: a three-dimensional environment model for recellularization

The rich extracellular matrix (ECM) and availability make placenta eligible as alternative biomaterial source. Herein we produced placental mouse scaffolds by decellularization, and structure, composition, and cytocompatibility were evaluated to be considered as a biomaterial. We obtained a cell-free scaffold containing 9.42 ± 5.2 ng dsDNA per mg of ECM, presenting well-preserved structure and composition. Proteoglycans were widespread throughout ECM without cell nuclei and cell remnants. Collagen I, weak in native placenta, clearly appears in the scaffold after recellularization, opposite distribution was observed for collagen III. Fibronectin was well-observed in placental scaffolds whereas laminin and collagen IV were strong expressed. Placental scaffolds recellularization potential was confirmed after mouse embryonic fibroblasts 3D dynamic culture, resulting in massive scaffold repopulation with cell–cell interactions, cell-matrix adhesion, and maintenance of natural morphology. Our small size scaffolds provide a useful tool for tissue engineering to produce grafts and organ fragments, as well as for cellular biology purposes for tridimensional culture substrate.

Differential expression of lumican and fibromodulin regulate collagen fibrillogenesis in developing mouse tendons

Collagen fibrillogenesis is finely regulated during development of tissue-specific extracellular matrices. The role(s) of a leucine-rich repeat protein subfamily in the regulation of fibrillogenesis during tendon development were defined. Lumican-, fibromodulin-, and double-deficient mice demonstrated disruptions in fibrillogenesis. With development, the amount of lumican decreases to barely detectable levels while fibromodulin increases significantly, and these changing patterns may regulate this process. Electron microscopic analysis demonstrated structural abnormalities in the fibrils and alterations in the progression through different assembly steps. In lumican-deficient tendons, alterations were observed early and the mature tendon was nearly normal. Fibromodulin-deficient tendons were comparable with the lumican-null in early developmental periods and acquired a severe phenotype by maturation. The double-deficient mice had a phenotype that was additive early and comparable with the fibromodulin-deficient mice at maturation. Therefore, lumican and fibromodulin both influence initial assembly of intermediates and the entry into fibril growth, while fibromodulin facilitates the progression through growth steps leading to mature fibrils. The observed increased ratio of fibromodulin to lumican and a competition for the same binding site could mediate these transitions. These studies indicate that lumican and fibromodulin have different developmental stage and leucine-rich repeat protein specific functions in the regulation of fibrillogenesis.

Transient and cyclic responses of strain-generated potential in rabbit patellar tendon are frequency and pH dependent

The goal of this study was to expand understanding of strain-generated potential (SGP) in ligamentous or tendinous tissues. Most SGP studies in the past have focused on cartilage or bone. Herein, rabbit patellar tendon (PT) was used as a model. Each patellar tendon had two Ag/AgCl electrodes inserted at axial positions of 1/4 and 1/2 from patellar to tibial insertions. Each specimen was electrically isolated, gripped in a servohydraulic test system, and then subjected to a short session of uniaxial haversine tension (2.5 percent maximum strain) at a frequency of 0.5, 1.0, 2.0, or 5.0 Hz. A cyclic (sinusoidal) electrical potential superimposed upon a larger transient (exponentially asymptotic) potential was consistently observed. Upon termination of loading, the cyclic SGP ended, and the shifted baseline of the SGP exponentially decayed and asymptotically returned to a residual potential which over all specimens was not different than the original potential. The transient and cyclic SGPs were frequency dependent (P < 0.001, P = 0.06, respectively). To our knowledge, this transient portion of the SGP, although theoretically predicted by Suh (1996, Biorheology, 33, pp. 289-304) and Chen (1996, Ph.D. thesis, University of Wisconsin-Madison) has not been observed in other experiments using different protocols. Additional PTs were dehydrated and the rehydrated in solution at different pH levels. The magnitude of SGPs increased in basic solution (pH 9.5) but diminished in pH 4.7 buffer. This pH dependency suggests that electrokinetics is the dominant mechanism for the transient and cyclic responses of the SGPs, although this study does not provide direct evidence.

Interaction of the small interstitial proteoglycans biglycan, decorin and fibromodulin with transforming growth factor beta

We have analysed the interactions of three proteoglycans of the decorin family, decorin, biglycan and fibromodulin, with transforming growth factor beta (TGF-beta). The proteoglycan core proteins, expressed from human cDNAs as fusion proteins with Escherichia coli maltose-binding protein, each bound TGF-beta 1. They showed only negligible binding to several other growth factors. Intact decorin, biglycan and fibromodulin isolated from bovine tissues competed with the fusion proteins for the TGF-beta binding. Affinity measurements suggest a two-site binding model with Kd values ranging from 1 to 20 nM for a high-affinity binding site and 50 to 200 nM for the lower-affinity binding site. The stoichiometry indicated that the high-affinity binding site was present in one of ten proteoglycan core molecules and that each molecule contained a low-affinity binding site. Tissue-derived biglycan and decorin were less effective competitors for TGF-beta binding than fibromodulin or the non-glycosylated fusion proteins; removal of the chondroitin/dermatan sulphate chains of decorin and biglycan (fibromodulin is a keratan sulphate proteoglycan) increased the activities of decorin and biglycan, suggesting that the glycosaminoglycan chains may hinder the interaction of the core proteins with TGF-beta. The fusion proteins competed for the binding of radiolabelled TGF-beta to Mv 1 Lu cells and endothelial cells. Affinity labelling showed that the binding of TGF-beta to betaglycan and the type-I receptors in Mv 1 Lu cells and to endoglin in endothelial cells was reduced, but the binding to the type-II receptors was unaffected. TGF-beta 2 and 3 also bound to all three fusion proteins. Latent recombinant TGF-beta 1 precursor bound slightly to fibromodulin and not at all to decorin and biglycan. The results show that the three decorin-type proteoglycans each bind TGF-beta isoforms and that slight differences exist in their binding properties. They may regulate TGF-beta activities by sequestering TGF-beta into extracellular matrix.

The chemical morphology of extracellular matrix in experimental rat liver fibrosis resembles that of normal developing connective tissue

The time course of development of extracellular matrix (ECM) in experimentally induced fibrosis (thioacetamide administration followed for 12 weeks or bile duct ligation for 8 weeks) in adult rats was examined by light and electron microscopy, using Alcian blue or Cupromeronic blue staining for sulphated proteoglycans (PGs) in critical electrolyte concentration techniques. Proteodermatan sulphate (PDS) was regularly observed at the gap zone of the collagen fibrils. Morphometry of uranyl acetate-stained collagen fibrils, polarity of their banding patterns (a-e), statistics of d/e band occupancies by PDS, and lengths and thicknesses of PG filaments were quantified. Biochemical analyses showed that the ECM components collagen, hyaluronan, chondroitin and dermatan sulphates increased by 5-10 fold, roughly in parallel, as did heparan sulphate and DNA. Water and lipid contents also increased sharply. Thioacetamide treatment was much slower than bile duct ligation in producing fibrotic changes of equal severity. Sulphation of anionic glycosaminoglycans (AGAGs) decreased with increasing severity of fibrosis. Biochemical and ultrastructural methods correlated well. The large increase in dermatan sulphate was quantitatively as expected, given that it is collagen fibril surface-associated, and there was an increase of collagen content together with a decrease in fibril thicknesses. The increase in DNA reflected the marked increase in cell numbers in fibrotic livers. The chemical morphology of the new connective tissue closely resembled that in e.g. developing young tendon, in that fibrils were thinner, and AGAG levels were higher. The collagen fibrils were often disarranged, rather than ordered and parallel as in normal ECM. No other indication of abnormality in the new ECM was obtained.

Isolation and characterization of proteoglycans synthesized by mouse osteoblastic cells in culture during the mineralization process

Proteoglycans in mineralized (0.5 M-EDTA/4 M-guanidinium chloride-extractable) and non-mineralized (4 M-guanidinium chloride-extractable) matrices synthesized by a mouse osteoblastic-cell line MC3T3-E1 were characterized at different phases of mineralization in vitro. Cell cultures were labelled with [35S]sulphate and either [3H]glucosamine or 3H-labelled amino acids. At the mineralization phase a large majority of proteoglycans were extracted with 4 M-guanidinium chloride (G extract), and at least five species of labelled proteoglycans were identified; dermatan sulphate proteoglycans (DSPG), apparent Mr approx. 120,000 and 70,000), heparan sulphate proteoglycans (HSPG, apparent Mr approx. 200,000 and 120,000) and DS chains with very little core protein. DSPGs weakly bound to an octyl-Sepharose CL-4B column and HSPGs bound more tightly, whereas DS chains did not bind to the column. Amounts of labelled proteoglycans extracted with 0.5 M-EDTA/4 M-guanidinium chloride (EDTA extract) were much less than those in G extract. Although the predominant species in the EDTA extract were comparable with the DS or DSPGs in the G extract, none of them bound to octyl-Sepharose CL-4B, indicating their lack of hydrophobicity. At the nonmineralizing phase a large chondroitin sulphate proteoglycan (Mr greater than 600,000) was found in the matrix in addition to the five proteoglycan species similar to those at the mineralization phase. Although DS chains at the early phase were similar in size to those at the mineralization phase, the ratio of 2-acetamido-2-deoxy-3-O-(beta-D-gluco-4-enepyranosyluronic acid)-4-O-sulpho-D-galactose to 2-acetamido-2-deoxy-3-O-(beta-D-gluculo-4-enepyranosyluronic acid)-6-O-sulpho-D-galactose was less than that at the mineralization phase. These results agree with those of previous studies performed in vivo and suggest that alteration in the synthesis of proteoglycans is involved in the mineralization process. They also suggest that at the osteoblastic mineralization front proteoglycans undergo partial degradation and lose their hydrophobicity.

Identification of specific binding sites for keratan sulphate proteoglycans and chondroitin-dermatan sulphate proteoglycans on collagen fibrils in cornea by the use of cupromeronic blue in 'critical-electrolyte-concentration' techniques

Proteoglycans (PGs) in bovine corneal stroma were stained with Cupromeronic Blue in 'critical-electrolyte-concentration' (CEC) methods for electron microscopy, and were located vis-à-vis collagen fibril a-e banding patterns. Keratanase and chondroitin ABC lyase digestion showed that a + c-band- and d + e-band-associated PGs were keratan sulphate-rich and chondroitin (dermatan) sulphate-rich respectively. The CEC pattern proved that the keratan sulphate PGs at the a and c bands differed. Comparison of their CECs with their behaviour on anion-exchange chromatography confirmed previous (indirect) attempts at identification [Scott & Haigh (1985) Biosci. Rep. 5, 765-774]. Similar arguments were applied to the dermatan sulphate PGs at the d and e bands. These results strongly support the one-PG-one-binding-site hypothesis [e.g. Scott (1988) Biochem. J. 252, 313-323]. Remarkable inter-species variations in the keratan sulphate PG patterns contrast with the relatively constant picture of dermatan sulphate PG-collagen fibril interactions.

Proteoglycan-fibrillar collagen interactions

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Ultrastructural localization of proteoglycans in tissue using cuprolinic blue according to the critical electrolyte concentration method: comparison with biochemical data from the literature

Several connective tissues were stained for proteoglycans using the cationic dye Cuprolinic Blue according to the critical electrolyte concentration method. With this method, proteoglycans are visualized as electron-dense filaments. In most tissues, two types of proteoglycan filaments are present: a small (maximum length 60 nm), thin, collagen fibril-associated filament, and a thick, heavily-staining filament which is predominantly localized between bundles of collagen fibrils. Cartilage contains very large (about 300 nm) proteoglycan filaments while in cornea they are very small. Comparison with biochemical data from the literature suggests that the appearance of the proteoglycan filaments may be indicative for the glycosaminoglycan-protein ratio and for the molecular weight of the part of the protein core to which glycosaminoglycans are attached. The data thus obtained on the localization and structure of a proteoglycan may be useful when planning a strategy for its isolation.

Dermatan sulphate proteoglycans from sclera examined by rotary shadowing and electron microscopy

Two dermatan sulphate-containing proteoglycans from bovine sclera were examined by rotary shadowing and electron microscopy, and the results were compared with previous biochemical findings. Both the large iduronate-poor proteoglycan (PGI) and the small iduronate-rich proteoglycan (PGII) possessed a globular proteinaceous region. Whereas PGI had a branched extension from the globular region, with five to eight side chains attached to it, PGII had only a single tail, which was of glycosaminoglycuronan. PGII aggregated via globular-region interactions, which were much diminished by reduction and alkylation. PGI aggregated via side chains and globular-region interactions. Although a few PGI aggregates were large, and similar to the hyaluronan-cartilage proteoglycan aggregates [Weidemann, Paulsson, Timpl, Engel & Heinegård (1984) Biochem. J. 224, 331-333], hyaluronan did not cause enhanced aggregation. PGII is very similar in shape to the small cartilage chondroitin sulphate proteoglycan, whereas PGI somewhat resembles the large cartilage chondroitin sulphate proteoglycan, although with many fewer glycosaminoglycan side chains, and probably only one globular region as opposed to two in the cartilage proteoglycan.