Upregulation of NADPH Oxidase 2 Contributes to Renal Fibrosis in pcy Mice: An Experimental Model of Nephronophthisis

<b><i>Background:</i></b> DBA/2FG-<i>pcy</i> (<i>pcy</i>) mice harbor a homozygous <i>Nphp3</i> missense mutation and develop nephronophthisis with renal interstitial fibrosis. Previous studies have shown that aberrant oxygen homeostasis contributes to the renal pathology in <i>pcy</i> mice, but the underlying molecular mechanism remains largely unknown. <b><i>Methods:</i></b> <i>pcy</i> mice and a control strain, DBA/2N (DBA) mice, were used. Renal levels of 62 mRNAs involved in oxygen homeostasis were investigated by real-time PCR, and the resulting data were used for extraction of pathological pathways. On the basis of the genes found to be upregulated and pathway analysis, further studies were performed using immunoblotting, immunohistochemistry, and pharmacological intervention. <b><i>Results:</i></b> In comparison with DBA mice, the levels of 18 mRNAs were altered by &#x3e;2-fold in <i>pcy</i> mice. Pathway analysis extracted molecular pathways related to oxidative stress, inflammation, and cell adhesion. As the levels of mRNAs relevant to the NADPH oxidase 2 (NOX2) pathway were prominently (4 genes &#x3e;5-fold) increased in <i>pcy</i> mice, we further analyzed the molecules related to this pathway. A time course study suggested that the pathway was gradually activated in <i>pcy</i> mice from at least 5 weeks of age. Immunohistochemistry study revealed that NOX2 protein was colocalized with a macrophage marker protein in the renal interstitium. Moreover, treatment of <i>pcy</i> mice with apocynin, an inhibitor of the NOX2 pathway, ameliorated the renal fibrosis. <b><i>Conclusion:</i></b> Our findings suggest that the activation of the NOX2 pathway, possibly mediated by macrophage infiltration, plays a pivotal role in progressive renal fibrosis in <i>pcy</i> mice.