The presence of circulating plasma factors (PF)
altering renal permeability to proteins has been previously
described in patients with focal segmental glomerulosclerosis
(FSGS). Since these patients show reduced nephrin
and podocin expression at renal biopsy, we evaluated the
effect of serum and PF from patients with FSGS on nephrin
and podocin expression in human podocytes. We studied 7
sera from patients with steroid-resistant FSGS, 3 from patients
with nephrotic syndrome caused by non-immune disease, and
6 from healthy subjects. PF was prepared from plasmapheresis
eluates of 2 patients with post-transplant recurrence
of FSGS. Purification procedure was based on protein A
Sepharose chromatography and differential precipitation in
ammonium sulphate. Nephrin and podocin expression was
semi-quantitatively evaluated by immunofluorescence. We
found that serum and PF from FSGS patients rapidly induced
redistribution and loss of nephrin in podocytes. This effect was
associated with cytoskeleton redistribution and inhibited by
cytochalasin B and sodium azide. On the contrary, podocin
expression was unchanged after incubation with serum and
PF from FSGS patients for short periods, but markedly
reduced at 24 h. Our results demonstrate that serum and PF
from FSGS patients may directly affect nephrin and podocin
in human podocytes, thus providing new insights into the
mechanisms causing proteinuria in FSGS.
