Proteoglycan-collagen arrangements in developing rat tail tendon. An electron microscopical and biochemical investigation

Abstract

1. Developing tail tendons from rats (19-day foetal to 126 days post partum) were examined by electron microscopy after staining for proteoglycan with a cationic copper phthalocyanin dye. Cuprolinic Blue, in a "critical electrolyte concentration" method. Hydroxyproline was measured on papain digests of tendons, from which glycosaminoglycuronans were isolated, characterized and quantified. 2. Mean collagen fibril diameters increased more than 10-fold with age according to a sigmoid curve, the rapid growth phase 2 being during 30-90 days after conception. Fibril periodicities were considerably smaller (50-55 nm) in phases 1 and 2 than in phase 3 (greater than 62 nm). 3. Dermatan sulphate is the main glycosaminoglycuronan in mature tendon. Chondroitin sulphate and hyaluronate preponderate in foetal tissue. 4. Proteoglycan was seen around but not inside collagen fibrils. Proteoglycan and collagen were quantified from electron micrographs. Their ratios behaved similarly to uronic acid/hydroxyproline and hyaluronate/hydroxyproline ratios, which decreased rapidly around birth, and then levelled off to a low plateau coincident with the onset of rapid growth in collagen fibril diameter. 5. Dermatan sulphate/hydroxyproline ratios suggest that the proteoglycan orthogonal array around the fibril is largely dermatan sulphate. In the foetus hyaluronate and chondroitin sulphate exceed that expected to be bound to collagen. 6. An inhibiting action of chondroitin sulphate-rich proteoglycan on fibril diameter growth is suggested. 7. The distributions of hyaluronate, chondroitin sulphate and dermatan sulphate are discussed in the light of secondary structures suggested to be present in hyaluronate and chondroitin sulphate, but not in dermatan sulphate.

Effects of Cysteine Proteases on the Structural and Mechanical Properties of Collagen Fibers

“…Only recently, the fine structure of collagen fibrils has been better understood (41). The morphology of collagen fibers is characterized by a regular arrangement of fibrils tightly bundled together through GAGmediated proteoglycan interactions as shown in previous reports (15,39,42,43). We and others (24) have previously demonstrated the unique collagenase activity of catK, which is able to cleave at multiple sites within the triple helical region of tropocollagen.…”

“…Proteoglycans consist of leucine-rich repeat core proteins such as biglycans, decorins, and fibromodulins with covalently attached glycosaminoglycan chains of dermatan sulfate (DS) (12,13), keratan sulfate (11), or chondroitin sulfate (14). These GAG chains are associated with nearby GAG chains through electrostatic interactions and build bridges between proteoglycan core proteins present on the collagen fibril surface (15). Several studies have shown that polysaccharide chains of these interfibrillar bridges are responsible for the mechanical integrity between collagen fibrils in connective tissues (16,17).…”

Phenotype of arylsulfatase A-deficient mice: Relationship to human metachromatic leukodystrophy

“…Vibratome slices cut from glutaraldehyde-fixed material were incubated with 0.025% alcian blue at pH 5.7 in 0.025 M sodium acetate buffer containing 0.3 M MgCl 2 (15). Frozen sections from unfixed tissues were stained with 0.1% toluidine blue or 1% alcian blue at pH 1 (16).…”

A role for glycosaminoglycans in the development of collagen fibrils

“…We propose that during this second stage of fibril development the inhibition of the lateral growth of fibrils imposed by the hyaluronic acid is removed by the proportionate increase of chondroitin sulphate [34] and/or dermatan sulphate synthesised preferentially by the cells in response to their changing mechanical or microelectrical environment [35,36]. Chondroitin sulphate, unlike hyaluronic acid, establishes weak inonic interactions with collagen under physiological conditions.…”