Collagen and proteoglycan interactions in bovine articular cartilage

Walking on water: revisiting the role of water in articular cartilage biomechanics in relation to tissue engineering and regenerative medicine

The importance, and the difficulty, of generating biosynthetic articular cartilage is widely recognized. Problems arise from obtaining sufficient stiffness, toughness and longevity in the material and integration of new material into existing cartilage and bone. Much work has been done on chondrocytes and tissue macromolecular components while water, which comprises the bulk of the tissue, is largely seen as a passive component; the ‘solid matrix’ is believed to be the main load-bearing element most of the time. Water is commonly seen as an inert filler whose restricted flow through the tissue is believed to be sufficient to generate the properties measured. We propose that this model should be turned on its head. Water comprises 70–80% of the matrix and has a bulk modulus considerably greater than that of cartilage. We suggest that the macromolecular components structure the water to support the loads applied. Here, we shall examine the structure and organization of the main macromolecules, collagen, aggrecan and hyaluronan, and explore how water interacts with their polyelectrolyte nature. This may inform the biosynthetic process by identifying starting points to enable developing tissue properties to guide the cells into producing the appropriate macromolecular composition and structure.

Shrinkage Properties and Their Relationship with Degradation of Proteins Linking the Endomysium and Myofibril in Lamb Meat Submitted to Heating or Air Drying

The shrinkage of the connective tissue and myofiber of lamb meat submitted to heat treatment or air drying at different storage stages (1, 5 and 7 days) was evaluated herein. The longitudinal and transverse shrinkage of heated lamb meat was significantly influenced by storage time and water bath heating temperature (50 °C, 70 °C and 90 °C) (p < 0.001). In contrast, the shrinkage of air-dried lamb meat was not influenced by storage time (p > 0.05). The microstructure of heated lamb meat, namely, the distance between muscle fascicles, the distance between myofibril networks, the area of myofibril networks, and the endomysium circumference, was significantly influenced by storage time (p < 0.05). During storage, the proportion of muscle fibers completely detached from endomysium increased, which could be due to the progressive degradation of proteins linking the endomysium and myofibril, including β-dystroglycan, α-dystroglycan, integrin-β1, and dystrophin. However, degradation of such proteins did not influence the shrinkage of lamb meat stored for five days or longer, since the decreased distance between myofibril networks indicated a higher shrinkage ratio of the endomysium compared to myofibers in samples air-dried at 35 °C or heated at 90 °C. The effect of these proteins on the shrinkage of heated lamb meat (raw meat stored for 1 day or less time) requires further elucidation.

Immunohistochemical and biochemical analyses of 20,000-25,000-year-old fossil cartilage

A cracked, irregular pellicle adhering to fossilized bone excavated from the Enlène cave (Ariège) and estimated to date from 20,000-25,000 years BP was examined to verify its cartilaginous nature, suggested previously on the basis of optical and electron microscopic investigations. Immunolabeling of the organic component revealed the presence of type II and IX collagens, associated with residual glycosaminoglycans, in the external zone of the pellicle. The cartilaginous nature of the pellicle was also demonstrated by biochemical identification of type II collagen as the major protein in the demineralized sample: the amino acid compositions of insoluble and soluble fractions were similar to that of pure type II collagen; cyanogen-bromide-generated peptides, prepared after reduction of the sample, had an electrophoretic pattern similar to that of cyanogen bromide peptides derived from type II collagen. The amino acid sequences of four tryptic peptides were identical to the corresponding human type II sequences. It was impossible to isolate intact alpha chains. All of the solubilized fractions were composed of a wide range of low-molecular-mass peptides demonstrating significant degradation of the collagen molecules that was not reflected in the well-preserved fibrillar structure observed at the ultrastructural level. The mineral fraction, characterized by X-ray diffraction, consisted of apatite (as in sub-chondral bone) associated with contaminating poorly crystallized components originating from the cave sediment. Energy dispersive spectrometry showed that the cartilaginous zone contained three times less phosphorus and calcium than the underlying bone. These results confirm the cartilaginous nature of the sample and the preservation of tissue-specific components, and suggest that the process of fossilization is closely related to a mechanism of phosphatization.

Effect of dissociative extraction with 1.5 M calcium chloride on proteoglycans in rat-incisor predentine visualized with cuprolinic blue

Treatment of rat-incisor predentine for 48 h in a 1.5 M CaCl2 solution halved the number and size of the proteoglycan precipitates visualized using a critical MgCl2 concentration and cuprolinic blue staining. About 75 per cent of the aggregable proteoglycans were extracted; 25 per cent resisted extraction. Treatment with CaCl2 also completely abolished the electron density of the amorphous ground substance, an observation consistent with the possible existence of two classes of proteoglycans in predentine.

Articular cartilage collagen and proteoglycans. Their functional interdependency

By use of an in vitro experimental system which permits the observation at high resolution of articular cartilage in a physiologic condition, its biomechanical response to compression was investigated before and after enzymatic digestion of the proteoglycan components with testicular hyaluronidase. The study provides further insight into the functional interplay between the collagen network and the hydrated proteoglycans. Certain structural features associated with age-related and osteoarthritic changes occurring in vivo in human articular cartilage were mimicked in the compressive response of the enzymatically digested tissue.

Studies on extractable and resistant proteoglycans from metaphyseal and cortical bone and cartilage

Soluble proteoglycans (SPG) were extracted from bovine (BCC) and human (HCC) costal cartilages by the dissociative method using 4 M guanidinium chloride (GuHCl). Proteoglycans which are resistant to extraction (RPG) were obtained following collagenase digestion or hydroxylamine treatment of the cartilage residues. Similarly, SPG were extracted from bovine metaphyseal and cortical bone using EDTA. The RPG were extracted from the bones using hydroxylamine. Density gradient fractionation under dissociative conditions of cartilage SPG and RPG followed by chromatography on Sepharose 2B revealed that A1D1 RPG are smaller than the SPG. SPG reacted with either collagenase or hydroxylamine are also smaller than the parent SPG. A1D1 fractions obtained from BCC-SPG and RPG or from mixtures of SPG and acid-soluble collagen are free of hydroxyproline. Hydroxyproline is not completely separated from HCC-RPG. Density gradient fractionation of bone proteoglycans and Sepharose chromatography of the A1 and A1D1 fractions showed that those obtained from metaphysis are larger than those from cortical bone. This was attributed to the presence of calcified cartilage in metaphyseal bone. The A1D1 fractions of the metaphyseal proteoglycans seemed to undergo self-association since this fraction is larger than the A1 fraction from which it is derived. Cortical bone proteoglycans do not behave similarly. Density gradient purification under dissociative conditions failed to separate hydroxyproline from the proteoglycans obtained from bone. It is hypothesized that in bone proteoglycans and collagen might be linked.

Cockroach collagen: isolation, biochemical and biophysical characterization

Collagen fibrils from the mesenteric connective sheath of the adult cockroach Periplaneta americana were extracted by enzymatic digestion with pepsin and were purified. Chromatographic studies and sodium dodecylsulfate electrophoresis revealed the presence of a single chain. It was demonstrated that the structure of this collagen could be represented by the formula (alpha)3. The amino acid composition is typical of collagens (one-third glycine, and a high imino acid content) and similar to that of type II. The carbohydrate content was high (8.8%), and the cyanogen bromide pattern was different from that of known collagens. The chains were linked by the stable intermolecular bond dihydroxylysinonorleucine. The banding patterns of the segment-long-spacing crystallites and of the reconstituted fibrils were similar to type I collagen. The molecular weight (Mr 280,000) and length (285 nm) were typical, but the denaturation temperature was high (38.5 degrees C). It was concluded that cockroach mesenteric collagen showed the characteristic features of invertebrate mesodermal collagens, except that of the thermal stability of the triple-helical structure.

Resistant proteoglycans in epiphyseal plate cartilage. Variations in their distribution in relationship to age and species

The localizations of resistant proteoglycans (RPGs) in the epiphyseal plates of rats, dogs, and humans are similar. In the epiphysial plates from young rats, dogs, and humans, the RPGs form a stratum at the junction of the zones of resting and proliferating cells. Non-calcified cartilage RPGs are associated with cells which have the potential for proliferation or column organization. As the individuals age, RPGs are found in intercolumnar regions or at times are even absent. There is also a type of RPGs in calcified cartilage, including the calcified cartilage subjacent to the articular surface, in all species. In human epiphyseal plates, looser fibrillar RPGs change abruptly to a more condensed type in the zone of provisional calcification. Calcified cartilage RPGs stain more intensely with toluidine blue and may represent a different type of RPGs.

Insoluble collagen of methylcholanthrene induced sarcoma

The insoluble collagen from methylcholanthrene induced sarcoma was isolated and characterized. It contains more glycine, hydroxyproline and acidic amino acids than normal connective tissue collagen. An anionic character of tumour collagen was stated (pI 6.1). No typical collagen subunits in this protein were found. The tumour collagen is strongly bound to acidic glycoprotein containing a significant amount of hydroxylysine. Such an insoluble complex is resistant to the dispersing action of EDTA. It dissociates during heating in concentrated urea.