Transdifferentiation of distal but not proximal tubular epithelial cells from human kidney in culture

Human renal proximal and distal (thick ascending limb and early distal conv oluted tubule) epithelial cells have been isolated according to their speci fic antigen expression. The cells were well characterized by flow cytometry , enzyme cytochemistry and electron microscopy and cultured for up to 3 mon ths. Cultured tubular cells coexpressed cytokeratin and vimentin as interme diate filament proteins. While primary isolated cells, proximal as well as distal, revealed the phenotypic characteristics of their nephron origin, cu ltured distal cells showed the tendency to dedifferentiate/transdifferentia te. Distal cells lost their characteristic expression of Tamm-Horsfall glyc oprotein and started de novo expression of the proximal marker proteins ami nopeptidase M, gamma-glutamyl transferase and dipeptidyl peptidase IV. The expression of these antigens by distal cells could be shown by flowcytometr ic analysis and fluorescence microscopy. Enzyme activity assays revealed th e activity of aminopeptidase M, gamma-glutamyl transferase and dipeptidyl p eptidase IV, but not of the proximal marker enzyme alkaline phosphatase. Th is antigenic shift could not be prevented in different culture media, and t he original phenotype could not be restored. Cultured cells displayed chara cteristic hormonal stimulation patterns indicative of their proximal and di stal origins, as shown by activation of adenylate cyclase by different pept ide hormones. These results indicate that distal tubular cells possibly tra nsdifferentiate to a more proximal phenotype in view of loss of the distal marker enzyme Tamm-Horsfall protein and de novo expression of proximal mark er enzymes like dipeptidyl peptidase IV and aminopeptidase M.