Background: The olfactomedin domain proteins Olfm-1 and myocilin are expressed in podocytes. Myocilin stimulates the formation of focal contacts and actin stress fibres in podocytes and other cell types, effects that are mediated through the Wnt signalling pathway. Here, we tested if the expression of both proteins is modified during puromycin aminonucleoside (PAN) nephrosis, which leads to structural changes in the actin cytoskeleton of podocytes.
Methods: Rats were treated with PAN, and the effectiveness of treatment was analysed by electron microscopy of podocytes and protein detection in the urine. The expression of Olfm-1 and myocilin was studied by immunohistochemistry, western blot analysis of glomerular proteins and real-time RT-PCR of glomerular proteins. In parallel experiments, the expression of Olfm-1 was studied in cultured podocytes treated with dexamethasone, TGF-β, TNF-α and PAN.
Results: Between Days 5 and 22 after treatment, the amounts of the BMZ and BMY splice variants of Olfm-1 and their mRNA were markedly elevated in proteins and mRNA from isolated glomeruli. Immunohistochemistry showed that the expression of Olfm-1 was confined to podocytes. Essentially, comparable results were obtained for myocilin. The BMZ variant of Olfm-1 appeared to be secreted from podocytes and was found in high amounts in urine of treated animals. Treatment of cultured podocytes with dexamethasone and PAN caused an increase in Olfm-1 expression, while treatment with recombinant Olfm-1 increased the formation of actin stress fibres.
Conclusions: Olfm-1 and myocilin are markedly induced in podocytes during PAN nephrosis and appear to be involved in the processes that govern the reorganization of the actin cytoskeleton during podocyte repair.