Insulin-like growth factor binding protein-2 modulates podocyte mitogenesis

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Abstract
To study the role of insulin-like growth factors (IGF) in podocyte maturation, we isolated and characterized fetal visceral glomerular epithelial cells from human kidneys obtained at 8-18 weeks gestation. Cells were identified as podocyte lineage by their cobblestone morphology and immunoreactivity with synaptopodin, Wilms tumor-1 suppressor gene product (WT-1), complement receptor CR1, and cytoskeletal proteins smooth muscle actin and vimentin. Stimulation of the podocyte cell monolayers with IGF-II resulted in a slight increase in mitogenesis, an effect that was concentration and time dependent and abrogated by co-incubation with exogenous IGF binding protein 2 (IGFBP-2). Western blot analysis of conditioned media revealed that cultured podocytes expressed endogenous IGFBP-2 exclusively. IGF-II stimulation enhanced IGFBP-2 production in a dose- and time-dependent fashion and was associated with an increase in IGFBP-2 mRNA production. These data demonstrate that IGF-II-stimulated IGFBP-2 production appears to inhibit the mitogenic effect of IGF-II, and may have an autocrine effect on the maturation, differentiation, and survival of fetal podocytes.