Fibronectin in the vitreous body - distribution and possible functional role

The presence of fibronectin in the bovine vitreous was demonstrated by immu nohistochemical procedures which showed a uniform coating of the vitreous c ollagen network. A fractional extraction of bovine vitreous was carried out in order to determine the distribution of fibronectin and glycosaminoglyca ns as related to collagen fibers. About half of total fibronectin could be extracted with aqueous buffers with increasing concentrations of KCl, part of fibronectin remained however strongly associated with the insoluble coll agen network even after a final extraction with 4 M urea and 0.05 M DTT. To tal extractable fibronectin was of the order of 76 mug per vitreous, corres ponding to approximately 0.17 nM fibronectin. Total quantity of GAG-s deter mined as uronic acid were of the order of 2200 mug/vitreous corresponding a pproximately to 4400 mug disaccharide units that is to about 11 nM disaccha ride units of GAG per vitreous. The persistence of fibronectin, strongly as sociated with the collagen fibers even after repeated KCI and urea-DTT extr actions was confirmed using immune-gold labelling of vitreous collagen fibe rs. Gold particle density on the collagen fibers increased with the molarit y of KC[ used for the extractions. These findings suggest that KCI mainly r emoved fiber associated components probably GAG-s, which hindered the immun e recognition of fiber-bound fibronectin. The strong association of fibrone ctin with vitreous collagen suggested a modified model for vitreous structu re taking in account the binding of fibronectin both by collagen and GAG-s. (C) 2001 Editions scientifiques et medicales Elsevier SAS.