Tubular NF-κB and AP-1 activation in human proteinuric renal disease.

Nuclear factor-κB (NF-κB) and activated protein-1 (AP-1) are transcription factors that regulate many genes involved in the progression of renal disease. Recent data have shown that NF-κB is activated in tubules and glomeruli in various experimental models of renal injury. In vitro studies also suggest that proteinuria could be an important NF-κB activator. We therefore approached the idea that NF-κB may be an indicator of renal damage progression.

Paraffin-embedded renal biopsy specimens from 34 patients with intense proteinuria [14 with minimal change disease (MCD) and 20 with idiopathic membranous nephropathy (MN)] and from 7 patients with minimal or no proteinuria (IgA nephropathy) were studied by Southwestern histochemistry for the in situ detection of activated transcription factors NF-κB and AP-1. In addition, by immunohistochemistry, we performed staining for the NF-κB subunits (p50 and p65) and AP-1 subunits (c-fos, c-jun). By immunohistochemistry and/or in situ hybridization, the expression of some chemokines [monocyte chemoattractant protein-1 (MCP-1), RANTES, osteopontin (OPN)] and profibrogenic cytokines [transforming growth factor-β (TGF-β)], whose genes are regulated by NF-κB and/or AP-1, were studied further.

NF-κB was detected mainly in the tubules of proteinuric patients, but rarely in nonproteinuric IgA nephropathy (IgAN) patients. In addition, there was a significant relationship between the intensity of proteinuria and NF-κB activation in MCD (r = 0.64, P = 0.01) and MN patients (r = 0.64, P < 0.01). Unexpectedly, patients with MCD had a significantly higher NF-κB tubular activation than those with MN (P < 0.01). To assess whether there was a different composition of NF-κB protein components, immunostaining was performed for the NF-κB subunits p50 and p65. However, no differences were noted between MCD and MN patients. In those patients, there was a lower tubular activation of AP-1 compared with NF-κB. Moreover, a strong correlation in the expression of both transcription factors was observed only in MN (r = 0.7, P = 0.004). Patients with progressive MN had an overexpression of MCP-1, RANTES, OPN, and TGF-β, mainly in the proximal tubules, while no significant expression was found in MCD patients.

On the whole, our results show that a tubular overactivation of NF-κB and AP-1 and a simultaneous up-regulation of certain proinflammatory and profibrogenic genes are markers of progressive renal disease in humans. Increased activation of solely NF-κB and/or AP-1 may merely indicate the response of tubular renal cells to injury.