Background: Liver-type fatty acid-binding protein (L-FABP) in proximal tubules was reported to have renoprotective roles in experimental tubulointerstitial diseases via its anti-oxidative properties. Since tubuloglomerular cross-talk was recently discussed in the progression of renal diseases, to investigate whether tubular L-FABP may have an impact on the progression of glomerular damage, we induced IgA nephropathy (IgAN) in mice (Tg) transgenically tubular overexpressing human L-FABP (hL-FABP).
Methods: We reconstituted IgAN by bone marrow transplantation (BMT) from IgAN-prone mice into Tg and wild-type (WT) mice. Renal damage was evaluated at 6 and 12 weeks after BMT. During in vitro experiments, mesangial cells (MC) were stimulated by aggragated IgA (AIgA), and their supernatants (AIgA-MC medium) were collected. Stable cell line of mouse proximal tubular cell (mProx) transfected with or without hL-FABP gene was cultured with the AIgA-MC medium.
Results: Although mesangial IgA deposition and serum IgA level were not different between WT (WT/ddY) and Tg (Tg/ddY) recipients, WT/ddY mice showed a significantly higher urinary albumin level and mesangial matrix expansion with a significantly higher glomerular damage score. Furthermore, CD68 + macrophage infiltration was also significantly attenuated in Tg/ddY mice. Up-regulation of renal hL-FABP was associated with significant suppression of renal heme oxygenase-1 (HO-1) expression and accumulation of 4-hydroxy-2-nonenal (4-HNE) and MCP-1 expression in Tg/ddY mice. In vitro experiments showed that AIgA-MC medium and recombinant TNF-α significantly up-regulated hL-FABP expression, which was partially blocked by anti-TNF-α antibody, and major mediators of oxidative stress (HO-1 and 4-HNE) and inflammation (MCP-1). Importantly, such up-regulation of the mediators in mProx with hL-FABP was significantly suppressed much more than that in mProx.
Conclusions: Tubular L-FABP activated by MC-origin humoral factors may lessen progression of glomerular damage at early stages of IgAN by reducing oxidative stress and inflammatory mediators.