[Interaction of mesangial cells and the extracellular matrix in the glomerulus]

Different lesions of the renal glomerulus can cause very different responses of glomerular cells and alterations of the extracellular matrix (ECM). Whatever the initial glomerular abnormality, increases of the ECM are invariably found in chronic glomerular disease. Widening of the ECM is most prominent in the glomerular mesangium and this frequently precedes chronic sklerotic changes of the glomerular capillary tuft. Immunochemical examination of renal tissue sections have shown that scarred glomeruli contain not only basement membrane collagens (type IV and V) but also express and produce the interstitial collagens, type I and III. Mesangial cells in culture produce these 4 collagen types and also show expression of their gene transcripts. Further studies have shown that the production of ECM in culture is affected by cell density, proliferative activity and by the composition of the underlying ECM, such as presence of laminin or type IV collagen. The available results have led the conclusion that the solid-phase ECM might well affect mesangial cells in culture with regard to their growth behaviour and to their activity to secrete ECM. It is, thus, conceivable that the ECM components might have an autocrine effect on mesangial cell behaviour, not only in cell culture but, possibly, also in situ. It remains to be seen whether the presence of abnormal types and amounts of ECM components in diseased glomeruli max contribute to increased cell proliferation as well as ECM production.