Component Of Glomerular Basement Membrane Research Articles

The origin, turnover and removal of glomerular basement-membrane.

A comprehensive account of the natural history of normal glomerular basement membrane is prerequisite to elucidating the pathogenesis of numerous renal diseases. The experimental argyric technique was investigated, adapted and applied in a long term sequential, electron microscopic study of normal glomerular basement membrane in the rat. The results demonstrate that a major component of glomerular basement membrane is secreted by the visceral epithelial cells. This component is laid down on the epithelial side and slowly moves towards the endothelial side of the basement membrane as new basement membrane material continues to be secreted. The old basement membrane material is removed from the endothelial aspect of the membrane and passes by way of the lamina rara interna to the mesangial matrix for subsequent ingestion by the mesangial cells. This process is continuous and slow; the time for complete renewal of the glomerular basement membrane in the rat is of the order of twelve months. Secretion of this component, by the epithelial dells, is effected by a vascular-coated pit mechanism and removal, by the mesangial cells, is effected by a phagocytic mechanism. The results further indicate the presence of a second component in glomerular basement membrane. This second component is probably of endothelial origin and has a much faster turnover rate than the main, or epithelial derived, component. Study was also made of glomeruli from two cases of human argyria and though the observations perforce are limited, the results show that human glomerular basement membrane has a natural history essentially similar to rat glomerular basement membrane. On the basis of these experimental observations, correlated with the results of previous investigations, a model of the functional morphology of glomerular basement membrane is proposed. The potential applications of this model are briefly indicated.

Structural changes in the protein and carbohydrate components of glomerular basement membrane in aminonucleoside nephrosis

The glomerular basement membranes of normal and amino nucleoside nephrotic rats were analyzed chemically. Glomerular basement membrane from nephrotic rats contained significantly less hydroxylysine, hydroxyproline and glycine than the normal. The collagen extracted from glomerular basement membrane of nephrotic rats with 5% trichloroacetic acid contained 1/3 less hydroxylysine, and hydroxyproline and 2/3 more lysine and 1/3 more proline than the normal. No differences were noted in total carbohydrate. However, the glycopeptide from nephrotic rats had a ratio of glucose:galactose:hydroxylysinelrhar22:1:1 compared with a ratio of 1:1:1 from normal rats. These structural differences could account for the functional alterations of nephrotic glomerular basement membrane.

Isolation and characterization of antigenic components of rat glomerular basement membrane.

(1) A method was developed to separate normal rat glomerular basement membrane (GBM) into six components by collagenase digestion, urea extraction, and gel filtration.(2) Treatment of rat GBM with collagenase did not alter nephrotoxic antigenicity of the membrane. Further proteolytic digestion with pronase resulted in loss of ability to elicit nephrotoxic antibody. Rat GBM prepared by mild alkali treatment still retained nephrotoxic antigenicity.(3) Antibodies against isolated components, except two which were retained on Sephadex G-75, localized to GBM and induced proteinuria in rats. One of the components retained on Sephadex G-75 produced localizing, non-nephrotoxic antibodies, while the other produced no localizing antibodies. Multiple antigens and common antigenic determinants among membrane components were demonstrated by gel double diffusion.(4) A specific nephrotoxigenic antigen from rat GBM was characterized as a macromolecular glycoprotein containing 10.7% carbohydrate in the form of galactose, mannose, sialic acid, glucosamine, and galactosamine. On analytical ultracentrifugation in Tris buffer, it gave two peaks with sedimentation constants of 5.93 and 3.49 S, while in 8 M urea it appeared as a single symmetrical peak with lower sedimentation constant (1.33 S) suggesting the presence of aggregate forms of the glycoprotein.(5) Dog GBM and collagenase-solubilized components elicited antibodies which localized to rat GBM but failed to produce proteinuria. Antibody to tendon collagen also localized to rat GBM but had no nephrotoxic effect on normal rats. Antibody to collagen fragments obtained from collagenase digestion failed to localize on rat GBM but still cross-reacted with tendon collagen in gel diffusion.