Assessment of increased glomerular permeability associated with recurrent focal segmental glomerulosclerosis using an in vitro model of the glomerular filtration barrier

The presence of circulating permeability factors (cPFs) has been hypothesized to be associated with recurrence of focal segmental glomerulosclerosis (rFSGS) in renal allografts. The available methods to detect cPFs are complex, not easily repeatable and inappropriate to represent the anatomical characteristics of the three-layer glomerular filtration barrier (GFB). Here we describe a novel method which measures the permeability to bovine serum albumin (BSA) through a three-layer device (3LD). The 3 layers comprise: (1) conditionally immortalized human podocytes (HCiPodo), (2) collagen type IV coated porous membrane and (3) human glomerular endothelial cells (HCiGEnC). Using this method, we found that sera from all rFSGS patients increased albumin permeability, while sera from non recurrent (nrFSGS) and genetic (gFSGS) forms of FSGS did not. The mechanisms underlying the increase of albumin permeability are probably due to endothelial cell damage as an initial event, which was demonstrated by the decrease of Platelet endothelial cell adhesion molecule (PECAM-1 or CD31), while the podocytes’ expressions of synaptopodin and podocin were normal. Furthermore, we also found that the plasmapheretic treatment (PPT) eliminated the effect of increasing BSA permeability in sera from rFSGS patients. These preliminary data suggest that our in vitro GFB model could not only be useful in predicting the recurrence of FSGS after renal transplantation (RTx), but also be a valuable in vitro model to study podocyte and endothelial cell biology.