Sulfated and nonsulfated glycosaminoglycans and glycopeptides are synthesized by kidney in vivo and incorporated into glomerular basement membranes

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Abstract
The biosynthesis of glycosaminoglycans (GAG) and glycopeptides was studied in rat kidney cortex, glomeruli, and isolated glomerular basement membranes (GBM). Rats were given four intraperitoneal injections of [ 35 S]sulfate and [ 3 H]glucosamine (over 10 hr) and sacrificed 14 hr after the last injection. Fractions of kidney glomeruli and purified GBM were prepared. The percent of the label incorporated into specific GAG or into glycopeptides was determined by selective degradative techniques in conjunction with gel filtration chromatography using the methods of Hart [Hart, G. W. (1976) J. Biol. Chem. 251, 6513-6521; Hart, G. W. (1978) Dev. Biol. 62, 78-98]. After digestion with Pronase and chromatography on Sephadex G-50, ≈68% of the total 35 S radioactivity and 10-15% of the total 3 H radioactivity incorporated into cortex, glomeruli, or GBM was found in the GAG fraction, and the remainder (≈32% of 35 S radioactivity and 85-90% of the 3 H radioactivity) was found in glycopeptide fractions. Treatment of GAG fractions isolated from the three sources (cortex, glomeruli, and GBM) with nitrous acid (which degrades heparan sulfates) indicated that the majority (85%, 65%, and 87%) of the 35 S radioactivity as well as the majority (60%, 50%, and 91%) of the 3 H radioactivity from all three sources was degraded by this treatment. When nitrous acid-resistant GAG from GBM were subjected to digestion with Streptomyces hyaluronidase (which degrades hyaluronic acid), ≈6% of the 3 H-labeled material was sensitive to this treatment. The remaining 35 S- and 3 H-labeled GAG isolated from GBM were digested with chondroitinase ABC (which degrades chondroitin sulfates A and C and dermatan sulfate). Although the ratios of the types of GAG synthesized by all three sources were similar, in GBM the ratios of 35 S- to 3 H-labeled GAG and of 3 H-labeled glycopeptides to 3 H-labeled GAG were higher (2.5 times) than those found for glomeruli. The data demonstrate the synthesis of both sulfated and nonsulfated GAG by rat kidney cortex and glomeruli and their transport to and incorporation into the GBM. Heparan sulfate is the major GAG synthesized by glomeruli, but the glomeruli also synthesize smaller amounts of hyaluronic acid and chondroitin sulfates, which are in part incorporated into GBM. In addition, the renal cortex and the glomeruli synthesize glycopeptides, some of which are sulfated, and incorporate them into GBM.