Structure and development of parietal podocytes in renal glomerular cysts induced in rabbits with methylprednisolone acetate.

Newborn rabbits were injected with methylprednisolone acetate to induce polycystic kidneys. Two major types of cysts were observed: tubular cysts formed by the dilation of collecting tubules and glomerular cysts formed by the dilation of Bowman's capsular space. We examined the structure and developmental changes of the glomerular cysts of rabbits aged 2 to 75 days. Two types (I and II) of fully developed glomerular cysts were observed. Most were type I, having one small glomerulus and a parietal layer composed entirely of podocytes. Type II had one or several small glomeruli and a parietal layer composed partially of podocytes. In both types I and II cysts, the podocytes in the parietal layer were connected to various structures surrounding the cysts by a basal lamina. These cysts were first detected in the early postnatal stages. During the S-shaped body stage, the presumptive parietal layer was composed of simple columnar cells in contrast to the flat cells of normal S-shaped bodies. In the following stages, Bowman's capsular space was dilated, and podocytes were in the process of differentiation. The sequence of differentiation of the parietal podocytes was similar to that in the visceral layer in normal conditions. These data indicate that the differentiation and maturation of podocytes are not dependent upon the endothelial capillary factors. We hypothesized that an inhibitory factor that stabilizes the phenotype of the parietal cells under normal conditions is absent under conditions that cause glomerular cyst formation.