Protein kinase C β_I and β_II are differentially expressed in the developing glomerulus

In the pre- and postnatal period of kidney development, proliferation with subsequent functional maturation of intrinsic glomerular mesangial cells (MCs) continues within the existing framework. Recent work has suggested that PKC β isoform is responsible for the proliferation observed during maturation. We sought to ascertain whether PKC β isoform expression is altered during the development of the mesangium. MCs were subcultured from glomerular explants of Sprague-Dawley rat kidneys, days 1, 3, 5, 8, 15 postnatally, and adult. MCs from rat kidneys postnatally days 1-5 proliferated at a significantly greater rate than adult [> 1.169-fold, P < 0.01] but term day 8 cells did not [< 1.34-fold, not significant)] as assessed by [³H]thymidine incorporation. Western blot analysis using isoform specific antibodies was performed on confluent neonatal and adult MC. We observed that all neonatal and adult MC express β_I PKC (n = 8 kidneys from separate primaries for each date and adult). However, unlike adult MCs, neonatal MC express β_II in postnatal days 1-5 and none thereafter. Immunofluorescent staining of postnatal kidneys confirmed that PKC β_II is present in neonatal MC up to day 5. By day 8, staining of mesangium with PKC β_II begins to disappear and assumes a parietal epithelial pattern. In adult kidneys, there was only PKC β_II staining of the parietal epithelial cells. Our results demonstrate that differential expression of PKC β_II closely parallels the proliferative behavior of the MCs of the maturing glomerulus. Therefore, PKC β_II expression and activation may play a critical role in development.