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

Abstract

Developing tail tendons from rats (19 day fetal to 126 days post partum) were examined by EM 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. Mean collagen fibril diameters increased more than 10-fold with age according to a sigmoid curve, the rapid growth phase 2 occurring 30-90 days after conception. Fibril periodicities were considerably smaller (50-55 nm) in phases 1 and 2 than in phase 3 (> 62 nm). Dermatan sulfate is the main glycosaminoglycuronan in mature tendon. Chondroitin sulfate and hyaluronate preponderate in fetal tissue. Proteoglycan was seen around but not inside collagen fibrils. Proteoglycan and collagen were quantified from EM. Their ratios behaved similarly to uronic acid/hydroxyproline and hyaluronate/hydroxyproline ratios, which decreased rapidly around birth and then leveled off to a low plateau coincident with the onset of rapid growth in collagen fibril diameter. Dermatan sulfate/hydroxyproline ratios suggest that the proteoglycan orthogonal array around the fibril is largely dermatan sulfate. In the fetus hyaluronate and chondroitin sulfate exceed that expected to be bound to collagen. An inhibiting action of chondroitin sulfate-rich proteoglycan on fibril diameter growth is suggested. Distributions of hyaluronate, chondroitin sulfate and dermatan sulfate are discussed in the light of secondary structures suggested to be present in hyaluronate and chondroitin sulfate but not in dermatan sulfate.