Proteoglycan Expression in the Normal Rat Kidney

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Abstract
Proteoglycans constitute a heterogenous group of complex macromolecules, consisting of a backbone core protein and a variable number of sulfated polysaccharide side chains covalently linked to the core. A dual function for these polyanionic glycosaminoglycans in kidney physiology has been proposed: to maintain a fixed negative charge in the glomerular filtration barrier, and to bind and sequester cytokines essential for renal development and function. With the aim of identifying proteoglycan genes expressed in kidney glomeruli, we have performed in situ hybridization for selected proteoglycan core proteins in the normal rat kidney. Syndecan-4, glypican-1 and biglycan were all expressed in normal glomeruli, whereas syndecan-1, perlecan and versican mRNAs were confined to the papillary area. Decorin mRNA was detected in interstitial cells found between tubuli and surrounding larger vessels. No signal for betaglycan mRNA could be detected. By hybridizing adjacent sections with a probe for the podocyte-specific PTPase GLEPP-1, the glomerular cells containing mRNA for syndecan-4 and glypican-1 could be identified as podocytes, whereas the cells expressing biglycan were identified as mesangial cells. These results demonstrate that seven out of the eight proteoglycans investigated are expressed in the normal kidney in detectable amounts and, importantly, that each proteoglycan gene shows a unique pattern of expression. The constitutive expression of syndecan-4, glypican-1 and biglycan in glomerular cells points to a role for these polyanionic molecules in maintaining the integrity of the glomerular filtration barrier.

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