NADPH-Oxidase 4 Protects against Kidney Fibrosis during Chronic Renal Injury

Abstract

NADPH oxidases synthesize reactive oxygen species that may participate in fibrosis progression. NOX4 and NOX2 are NADPH oxidases expressed in the kidneys, with the former being the major renal isoform, but their contribution to renal disease is not well understood. Here, we used the unilateral urinary obstruction model of chronic renal injury to decipher the role of these enzymes using wild-type, NOX4-, NOX2-, and NOX4/NOX2-deficient mice. Compared with wild-type mice, NOX4-deficient mice exhibited more interstitial fibrosis and tubular apoptosis after obstruction, with lower interstitial capillary density and reduced expression of hypoxia-inducible factor-1a and vascular endothelial growth factor in obstructed kidneys. Furthermore, NOX4-deficient kidneys exhibited increased oxidative stress. With NOX4 deficiency, renal expression of other NOX isoforms was not altered but NRF2 protein expression was reduced under both basal and obstructed conditions. Concomitant deficiency of NOX2 did not modify the phenotype exhibited by NOX4-deficient mice after obstruction. NOX4 silencing in a mouse collecting duct (mCCD cl1 ) cell line increased TGF-b1-induced apoptosis and decreased NRF2 protein along with expression of its target genes. In addition, NOX4 silencing decreased hypoxia-inducible factor-1a and expression of its target genes in response to hypoxia. In summary, these results demonstrate that the absence of NOX4 promotes kidney fibrosis, independent of NOX2, through enhanced tubular cell apoptosis, decreased microvascularization, and enhanced oxidative stress. Thus, NOX4 is crucial for the survival of kidney tubular cells under injurious conditions.

Myocardin-related Transcription Factor Regulates Nox4 Protein Expression

“…However, Babelova et al (35) using four chronic kidney injury models detected no protective effect of Nox4 deletion; in fact, they reported slight deterioration of obstructive nephropathy. Similar results were obtained in another study, claiming that Nox4 protects against kidney fibrosis (80). How can these contradictory findings be reconciled?…”

“…To solve this riddle, a biphasic model has been proposed (81). According to this, limited early Nox4-mediated ROS production may be protective because, presumably through Nrf2 and Hif1␣, it may induce antioxidant genes (80). In addition, Nox4 is a mediator of cellular senescence (82) and autophagy (83), both of which were proposed to lessen fibrosis (84,85).…”

Reversal of Persistent Fibrosis in Aging by Targeting Nox4-Nrf2 Redox Imbalance

“…Previous studies indicate that the Nrf2 response is tightly coupled to Nox4 induction or over-expression (24–26), which may in part explain the contextual effects of Nox4. In order to directly evaluate the role of Nox4 in apoptosis resistance, lung fibroblasts isolated from Nox4 −/− and wild-type mice were evaluated ex vivo .…”

Parsing the Role of NADPH Oxidase Enzymes and Reactive Oxygen Species in Heart Failure

“…It is interesting to note that several other laboratories have independently reported the protective effects of Nox4 in the kidney and vasculature, similar to those we found in the heart and also involving Hif1 or Nrf2 signaling. 8,9,13 Furthermore, the Sadoshima laboratory also subsequently reported cardioprotective effects of Nox4 mediated by specific redox signaling in other pathological settings, such as ischemia-reperfusion. 14,15 Taking the totality of the evidence, there seems little doubt that Nox4-activated redox-signaling pathways have significant potential to exert protective effects in the heart and other organs, depending on the pathological context.…”