PROTEOGLYCAN EXPRESSION IN THE NORMAL RAT-KIDNEY

Proteoglycans constitute a heterogenous group of complex macromolecule s, consisting of a backbone core protein and a variable number of sulf ated 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 glomeru lar filtration barrier, and to bind and sequester cytokines essential for renal development and function. With the aim of identifying proteo glycan genes expressed in kidney glomeruli, we have performed in situ hybridization for selected proteoglycan core proteins in the normal ra t kidney. Syndecan-4, glypican-1 and biglycan were all expressed in no rmal glomeruli, whereas syndecan-1, perlecan and versican mRNAs were c onfined to the papillary area. Decorin mRNA was detected in interstiti al cells found between tubuli and surrounding larger vessels. No signa l for betaglycan mRNA could be detected. By hybridizing adjacent secti ons with a probe for the podocyte-specific PTPase GLEPP-1, the glomeru lar cells containing mRNA for syndecan-4 and glypican-1 could be ident ified as podocytes, whereas the cells expressing biglycan were identif ied as mesangial cells. These results demonstrate that seven out of th e eight proteoglycans investigated are expressed in the normal kidney in detectable amounts and, importantly, that each proteoglycan gene sh ows a unique pattern of expression. The constitutive expression of syn decan-4, glypican-1 and biglycan in glomerular cells points to a role for these polyanionic molecules in maintaining the integrity of the gl omerular filtration barrier.