Pathogenesis of Glomerular Damage in Glomerulonephritis

Although glomerular disease remains the most common cause of end-stage renal disease worldwide, major advances have been made recently in understanding the cellular and molecular mechanisms which mediate these disorders. Nephrotic syndrome in non-inflammatory lesions such as minimal change/focal sclerosis and membranous nephropathy results from disorders of the GEC which can be simulated in animal models by antibodies to various GEC membrane epitopes. Clarification of how these antibodies effect the GEC to induce a loss of glomerular barrier function should substantially improve understanding of the pathogenesis of minimal change/focal sclerosis. In MN, proteinuria is mediated primarily by C5b-9 through similar mechanisms that also involve the GEC as a target and GEC production of oxidants, proteases and TGF beta in response to sublytic C5b-9 attack. C5b-9 also mediates mesangial proliferative glomerulonephritis induced by anti-measangial cell antibodies and thrombotic microangiopathy induced by antibodies to the glomerular endothelial cell. In all of these lesions induced by antibodies to glomerular cells, cell-bound complement regulatory proteins are important in modulating the injury observed. Upregulation of complement regulatory proteins may prove an effective therapeutic manoeuver in the future. Inflammatory glomerular lesions are induced by circulating inflammatory cells or proliferating resident glomerular cells. Understanding of how these cells induce tissue injury has also evolved considerably over the past decade. Neutrophil-induced disease involves leukocyte adhesion molecules in regulating neutrophil localization; proteases, oxidants and MPO in mediating injury and platelets in augmenting these processes. The activated mesangial cell following immune injury exhibits altered phenotype and proliferation with release of oxidants and proteases. Mesangial cell proliferation may be initiated by bFGF and is maintained by an autocrine mechanism involving PDGF. TGF beta is important in the subsequent development of sclerosis. Finally, recent studies establish the nephritogenic potential of cell-mediated mechanisms alone without humoral immunity, and these mechanisms may be important in glomerulonephritis which occurs in the absence of antibody deposits. As understanding of these areas evolves, numerous new therapeutic strategies can now be devised including agents which selectively block or inhibit complement effects, leukocyte adhesion molecules, oxidants, proteases, growth factors and other cytokines and activated T cells. Appreciation of the role of several natural inhibitors of these mechanisms may also allow therapeutic manipulations that upregulate regulatory proteins with a consequent therapeutic benefit. Thus, these changes in basic understanding of the mechanisms of glomerular disease are likely to translate into new and more specific and effective forms of therapy in the next decade.