Phenotypic modulation of parietal epithelial cells of Bowman's capsule in culture.

The origin of cobblestone-like polygonal cells (the most numerous in renal glomerular cell culture) remains controversial; they could be either dedifferentiated podocytes or parietal epithelial cells (PECs) of Bowman's capsule. Poor cellular outgrowth from glomeruli devoid of Bowman's capsule (decapsulated glomeruli) hinders podocytes being obtained without contamination of PECs in culture. Since podocytes are easily damaged during the isolation of glomeruli by the conventional sieving method, we devised a gentle isolation method without forced sieving, resulting in substantial numbers of arborized cells growing out from decapsulated glomeruli. The cells were distinctly different from cobblestone-like polygonal cells in their irregular and often arborized shape and extended long cytoplasmic processes that often crossed over adjacent cells. The arborized cells from decapsulated glomeruli showed intense staining for a podocyte-specific marker, podocalyxin, but no staining for markers specific to PECs (pan cadherin), mesangial cells (Thy-1) or endothelial cells (von Willebrand factor, RECA-1), indicating their podocyte origin. Polygonal cells growing out from encapsulated glomeruli were negative for podocalyxin and positive for pan cadherin at the peripheral cell-cell contact. Thus, the cell population from decapsulated glomeruli is distinctly different from that from encapsulated glomeruli, supporting the idea that polygonal cells originate from PECs, although immunocytochemical markers specific to podocytes in vivo such as WT1, synaptopodin, HSP27 and P-31 antigen were expressed significantly in the polygonal cells. Occasionally, large irregular-shaped cells appeared at the periphery of the outgrowths from encapsulated glomeruli. They were similar in shape to the arborized cells from decapsulated glomeruli but were identical in antigenic properties to cobblestone-like polygonal cells and thus may be named "pseudo-arborized cells". We conclude that PECs in culture modulate their phenotype to resemble podocytes.