Sirolimus interacts with pathways essential for podocyte integrity

Background. The specific mTor inhibitor sirolimus has been implicated in the pathogenesis of renal glomerular lesions and nephrotic syndrome appearance after transplantation. Podocyte injury and focal segmental glomerulosclerosis have been related to sirolimus therapy in some patients but the pathways underlying these lesions remain hypothetical. Methods. To go further in the comprehension of these mechanisms, primary cultures of human podocytes were exposed to therapeutic-range concentrations of sirolimus. Results. Cell viability was not affected after 2 days' exposure to the drug but changes in cell phenotype and cytoskeleton reorganization were observed. We also evidenced that vascular endothelial growth factor (VEGF) synthesis and Akt phosphorylation were decreased by sirolimus addition. We did not observe any loss of podocyte differentiation markers with the notable exception of WT1, a transcription factor essential for maintaining podocyte integrity. WT1 gene and protein expression in podocytes were decreased in a dose-dependent manner after incubation with sirolimus. Conclusion. Taken together, these data suggest that sirolimus could impair pathways essential for podocyte integrity and therefore predisposes to glomerular injury.