Nox-2 Is a Modulator of Fibrogenesis in Kidney Allografts

Abstract

We studied the role of classical phagocytic NADPH oxidase (Nox) in the pathogenesis of kidney allograft tubulointerstitial fibrosis. Immunofluorescence studies showed that Nox-2 and p22phox (electron transfer subunits of Nox) colocalized in the tubulointerstitium of human kidney allografts. Tubular Nox-2 also colocalized with α -SMA in areas of injury, suggestive of epithelial-to-mesenchymal transition (EMT). Interstitial macrophages (CD68+) and myofibroblasts (α -SMA+) expressed Nox-2 while graft infiltrating T cells (CD3+) and mature fibroblasts (S100A4+) were Nox-2−. These results were confirmed in the Fisher-to-Lewis rat kidney transplant model. Areas of tubulitis were associated with Nox-2 and α -SMA, suggestive of EMT. Immunoblot analyses showed that Nox-2 upregulation was associated with oxidative stress (nitrotyrosine) and fibrogenesis (α -SMA and phospho-Smad2) at 3 weeks and 6 months. Allografts treated with Nox inhibitors (DPI or apocynin) for 1 week showed reduced fibronectin and phospho-Smad2 and increased E-cadherin levels. Cyclosporine A, TGF-β1 and angiotensin II increased Nox-2 mRNA levels 2- to 7-fold in vitro (NRK52E cells). Treatment with specific Nox inhibitors (DPI or apocynin) prevented the downregulation of E-cadherin and upregulation of fibronectin transcripts. In aggregate, these studies suggest that Nox-2 is involved in the pathogenesis of allograft tubulointerstitial fibrosis via activation transcription factor Smad2, EMT and myofibroblasts.

Renal Allograft Fibrosis: Biology and Therapeutic Targets

“…Oxidative stress is increased in kidney allografts and associated with renal interstitial fibrosis (323). Inhibition of superoxide anion release with apocynin and diphenyleneiodonium prevented allograft fibrosis in the Fisher-to-Lewis model and antagonized the profibrotic effects of cyclosporine A (324,325). L-arginine, but not vitamin E, another antioxidant, exerted similar effects (326,327).…”

“…Some immunosuppressants such as mycophenolic acid exert antifibrotic actions via downregulation of NOX in renal cells (270). Experimentally, NOX inhibitors (diphenylene iodonium or apocynin) reduced allograft tubulointerstitial fibrosis (324). However, the function of NOX may be context-dependent and, for example, NOX-4 deficiency markedly aggravated fibrosis (185).…”

Epithelial-to-Mesenchymal Transdifferentiation of Renal Tubular Epithelial Cell Mediated by Oxidative Stress and Intervention Effect of Probucol in Diabetic Nephropathy Rats

“…4 Oxidative stress has been known to play an important role in the development and progression of DKD. 15 Recent studies have suggested that oxidative stress is a key component in the development of dissociation of renal proximal tubular epithelial cell-cell junctions primarily through activation of mitogen-activated protein kinase (MAPK), 16 Smad 17,18 , and/or extracellular signalregulated kinase 1/2 (ERK1/2) 19 pathway in the early EMT. Sp1 is believed to play a critical role in the regulation of cell growth, differentiation, metastasis, and apoptosis.…”

Involvement of NOX in the Regulation of Renal Tubular Expression of Na/K-ATPase in Acute Unilateral Ureteral Obstruction Rats

“…The source of ROS in tissue injury is largely dependent on the types of enzymes activated. The NOX family has been identified as a major source of superoxide and hydrogen peroxide in the kidney during health and disease [13,22,23,24,25]. NOX consists of at least one membrane-bound NOX/p22-phox complex and cytosolic subunits p67-phox, p47-phox, p40-phox as well as the small GTPase rac1 or rac2.…”