Development of an Enzyme Immunoassay Specific for a Core Protein Epitope of a Novel Small Basement Membrane Associated Heparan Sulphate Proteoglycan from Human Kidney

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Abstract
Heparan sulphate proteoglycans are major components of the glomerular basement membrane and play a key role in their molecular organization and function. Moreover, their presence is essential for the maintenance of the selective permeability of the glomerular basement membrane. Recently, we have isolated and characterized a novel, small basement membrane associated heparan sulphate proteoglycan from human aorta and kidney. Using specific monoclonal antibodies we have shown that the novel heparan sulphate proteoglycan is predominantly located in the glomerular basement membrane, to a lesser extent in the basement membrane of tubuli, and also in the mesangium. Turnover or, in the course of kidney diseases, degradation of heparan sulphate proteoglycan from glomerular basement membranes may lead to urinary excretion of heparan sulphate proteoglycan. Therefore, changes in the structure and function of glomerular basement membranes may be directly detected by measuring the excretion of a component of this basement menbrane, e. g. heparan sulphate proteoglycan into urine. Here we describe the establishment of an enzyme immunoassay for the sensitive detection of the novel, small heparan sulphate proteoglycan in urine. In this assay the specific monoclonal antibody 1F10/B8, which recognizes a core protein epitope, was used to detect the polyanionic heparan sulphate proteoglycan bound to the surface of a cationic charge modified microtitre plate. This assay allows the sensitive and specific detection of the small heparan sulphate proteoglycan, which is released from the glomerular basement membrane into urine during normal turnover and also in the course of kidney diseases.