BMP-7 protects mesangial cells from injury by polymeric IgA

Bone morphogenetic protein-7 (BMP-7) is a potential therapeutic agent for acute and chronic renal diseases. Here we found that addition of polymeric IgA, isolated from patients with IgA nephropathy, increased the synthesis of tumor necrosis factor-α (TNF-α), interleukin-6 (IL-6), transforming growth factor-β (TGF-β) and fibronectin in cultured human mesangial cells, effects blunted by BMP-7. When mesangial cells were cultured with both polymeric IgA and BMP-7 there was an increase in the expression of peroxisome proliferator-activated receptor-γ (PPAR-γ). The activation of NFκB and TNF-α synthesis induced by polymeric IgA or TNF-α were downregulated by BMP-7 or rosiglitazone. BMP-7 inhibited TNF-α release from polymeric IgA-stimulated mesangial cells by activation of PPAR-γ but suppressed TGF-β release by mechanisms independent of PPAR-γ. The expression of inhibitory Smad6 and 7 was increased whereas the expression of active Smad2 and 3 was reduced in these mesangial cells by BMP-7. Our study shows that BMP-7 ameliorates IgA nephropathy-derived polymeric IgA-induced TNF-α and TGF-β synthesis in human mesangial cells through multiple mechanisms involving inhibitory Smads and PPAR-γ.