Basement membrane alterations during development and regression of tubular cysts

Tubular cysts consisting of dilatation of the collecting ducts at the level of the subcapsular zone of the kidney were induced in newborn rabbits by a single injection of methylprednisolone acetate. We describe here the structural and compositional modifications of the tubular basement membrane (BM) during the formation, growth, and regression of the tubular cysts. During development of the tubular cysts the cystic BM appeared thickened and multilayered, with numerous matrix vesicles. Alcian blue- (AB) and ruthenium red- (RR) positive material distributed differently along the BM of control and cystic tubuli. While the amount of RR-positive material appeared increased in the cystic BM, no differences in the intensity of the AB staining could be discerned between normal and cystic tubuli. Immunofluorescent staining for laminin and type IV collagen appeared to be slightly decreased in the cystic tubuli. However, the amount of fibronectin appeared clearly increased. These changes in the cystic BM appear at the beginning of the tubular dilatation and are not observed in other renal BM. We suggest that there is a causal relationship between the modifications of the BM and the development of the tubular cysts. Glucocorticoids appear to modify the synthesis and/or secretion of the BM components. An abnormal BM should modify the spatial and chemical signals encoded within the BM that, in turn, could lead to abnormal behavior of the tubular cells. This may result in a loss of the normal developmental constraints imposed upon the tubular epithelium, which then undergoes cystic dilatation. During the regression of the cysts, the abnormalities of the BM progressively disappear. The sharp increase in the number of interstitial cells, which show close relationships with the components of the BM, suggests that these cells may be involved in the removal of the cyst BM.