Effect of beta-D-xyloside on the glomerular proteoglycans. I. Biochemical studies.

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Abstract
The effect of p-nitrophenyl-.beta.-D-xylopyranoside on glomerular extracellular matrices (glomerular basement membrane and mesangial matrix) proteoglycans was studied. The proteoglycans of rat kidneys were labeled with [35S]sulfate in the presence or absence of .beta.-xyloside (2.5 mM) by using an isolated organ perfusion system. The proteoglycans from the glomeruli and perfusion medium were isolated and characterized by Sepharose CL-6B chromatography and by their behavior in CsCl density gradients. With xyloside treatment there was a 2-fold decrease in 35S-labeled macromolecules in the tissues but a 2-fold increase in those recovered in the medium as compared with the control. The labeled proteoglycans extracted from control kidneys eluted as a single peak with Kav = 0.5 (MW = .apprx. 130,000) and .apprx. 95% of the radioactivity was associated with heparan sulfate proteoglycan (HS-PG), the remainder with chondroitin (or dermatan) sulfate proteoglycan (CS-PG). In the xyloside-treated kidneys, the proteoglycans extracted from the tissue eluted as 2 peaks, Kav = 0.25 (Mr = .apprx. 130,000) and 0.41 (MW = .apprx. 46,000), which contained .apprx. 40 and .apprx. 60% of the total radioactivity, respectively. The 1st peak contained mostly the HS-PG (.apprx. 90%) while the 2nd peak had a mixture of HS-PG (.apprx. 70%) and CS-PG (.apprx. 30%). In controls, .apprx. 90% of the radioactivity, mostly HS-PG, was confined to high density fractions of a CsCl density gradient. In contrast, in xyloside experiments, both HS-PG and CS-PG were distributed in variable proportions throughout the gradient. The incorporated 35S activity in the medium of xyloside-treated kidneys was twice that of the controls and had 3-4 times the amount of free chondroitin (or dermatan) sulfate glycosaminoglycan chains. Evidently, .beta.-xyloside inhibits the addition of de novo synthesized glycosaminoglycan chains onto the core protein of proteoglycans and at the same time stimulates the synthesis of chondroitin or dermatan sulfate chains which are mainly discharged into the perfusion medium.