Podocyte-specific expression of a novel trans-Golgi protein Vear in human kidney

Background. Vear is a recently identified Golgi apparatus-associated protei n. It has been suggested to be involved in vesicular trafficking between th e: Golgi and the vacuolar/lysosomal system, Proteins similar to Vear have a lso been shown to interact with activated ARF proteins (ADP ribosylation fa ctor). and they are probably involved in membrane trafficking from the tran s-Golgi network (TGN). We have previously shown that Vear is widely distrib uted in human tissues, with an especially high level of mRNA in the kidney. This study Further characterizes the distribution and subcellular localiza tion of Vear in normal adult kidney and shows its association with glomerul ogenesis in fetal kidney. Methods. Immunofluorescence and immunoelectron microscopy were used to stud y the expression of Vear in fetal and adult kidney. The expression of Vear in isolated glomeruli was shown by immunoblotting. The distribution of its mRNA was analyzed by using in situ and Northern hybridization. Results. In situ hybridization and immunofluorescence microscopy showed tha t in the kidney, Vear is present in glomerular structures. By fluorescence microscopy. the immunoreactivity for Vear was found only in podocytes, as j udged by its distinct colocalization with podocalyxin and vimentin, well-es tablished marker proteins of podocytes. Its specific expression in the glom eruli versus other compartments of the kidney was also verified by Western blotting. By using immunogold electron microscopy. Vear was seen in the Gol gi apparatus, tubulovesicular structures. and membranes adjacent to the Gol gi complex. In fetal kidney. expression of Vear coincided with the formatio n of segmental structures of the glomeruli. It was first seen close to the undifferentiated luminal cells at the vesicular stage and increasingly in t he differentiating podocytes at the more advanced stages of glomerulogenesi s. Conclusions. In the kidney, Vear shows a distinct, specific. and developmen tally regulated expression in glomerular podocytes. This suggests that Vear has a specific function in podocytes. It could be associated with the know n high secretory and synthetic activity of the podocytes. especially the pr oduction of the basement membrane components, which are critically involved in the glomerulogenesis and the maintenance of the glomerular function.