Activation of nuclear factor-kappa B by podocytes in the autologous phase of passive Heymann nephritis

Abstract

Background: The present study examined whether activation of nuclear factor-kappa B (NF-kappa B) occurs within podocytes in passive Heymann nephritis (PHN) and contributes to the pathogenesis of proteinuria.

Methods: Electrophoretic mobility shift assays (EMSAs) were used to detect NF-kappa B activation, and supershift assays were used to determine the subunits involved. Localization of the activated NF-kappa B subunit p50 was performed by immunohistochemistry. Expression of the NF-kappa B-dependent genes interleukin-1 beta (IL-1 beta) and matrix metalloproteinase-9 (MMP-9) were determined by reverse transcription-polymerase chain reaction and, for IL-1 beta, immunohistochemistry. To inhibit activation of NF-kappa B in vivo, pyrrolidone dithiocarbamate (PDTC) was administered for 10 days following induction of PHN.

Results: Glomerular nuclear extracts from rats with PHN showed increased NF-kappa B binding activity in comparison to normal rats. The major Rel/NF-kappa B proteins in these activated complexes were p65 and p50. Immunohistochemistry showed that nuclear translocation of p50 occurred predominantly within podocytes. IL-1 beta mRNA was increased in the PHN rats, and increased IL-1 beta protein was localized predominantly to podocytes by immunohistochemistry. To investigate whether activation of NF-kappa B is involved in the pathogenesis of proteinuria, PDTC was administered to rats with PHN. Electrophoretic mobility shift assays of glomerular nuclear extracts showed a significant reduction in NF-kappa B binding activity in the PDTC-treated rats with a striking reduction in MMP-9 mRNA. Compared with control rats, there was a significant reduction in albuminuria at days 15 (P < 0.001) and 20 (P < 0.001) when PHN was induced with a suboptimal dose of anti-Fx1A antiserum. There was no detectable difference in the systemic immune response to sheep Ig in the treated rats.

Conclusions: These data show that NF-kappa B is activated within podocytes in PHN and suggest that it contributes to autologous phase proteinuria. The critical genes regulated by NF-kappa B in the podocyte have not yet been determined, but may include MMP-9.