Pre-eclamptic sera induce nephrin shedding from podocytes through endothelin-1 release by endothelial glomerular cells

In pre-eclampsia (PE), proteinuria has been associated with a reduced expression of nephrin by podocytes. In the present study, we investigated in vitro on human cultured podocytes the mechanism responsible for nephrin loss in PE. Sera from patients with PE did not directly downregulated the expression of nephrin. In contrast, conditioned medium obtained from glomerular endothelial cells incubated with PE sera induced loss of nephrin and synaptopodin , but not of podocin, from podocytes. Nephrin loss was related to a rapid shedding of the protein from the cell surface due to cleavage of its extracellular domain by proteases and to cytoskeleton redistribution. The absence of nephrin mRNA downregulation together with nephrin re-expression within 24 hours confirm that the loss of nephrin was not related to a reduced synthesis. Studies with an endothelin-1 (ET1) receptor antagonist, that abrogated the loss of nephrin triggered by glomerular endothelial conditioned medium of PE sera, indicated that ET1 was the main effector of nephrin loss. Indeed, ET1 was synthesized and released from glomerular endothelial cells when incubated with PE sera and recombinant ET1 triggered nephrin shedding from podocytes. Moreover, VEGF blockade induced ET-1 release from endothelial cells and in turn the conditioned medium obtained triggered nephrin loss. In conclusion, the present study identifies a potential mechanism of nephrin loss in PE that may link the endothelial injury with the enhanced glomerular permeability. Key words: nephrin, pre-eclampsia, podocytes, slit diaphragm.