Genetic Targeting or Pharmacologic Inhibition of NADPH Oxidase Nox4 Provides Renoprotection in Long-Term Diabetic Nephropathy

Abstract

Diabetic nephropathy may occur, in part, as a result of intrarenal oxidative stress. NADPH oxidases comprise the only known dedicated reactive oxygen species (ROS)-forming enzyme family. In the rodent kidney, three isoforms of the catalytic subunit of NADPH oxidase are expressed (Nox1, Nox2, and Nox4). Here we show that Nox4 is the main source of renal ROS in a mouse model of diabetic nephropathy induced by streptozotocin administration in ApoE 2/2 mice. Deletion of Nox4, but not of Nox1, resulted in renal protection from glomerular injury as evidenced by attenuated albuminuria, preserved structure, reduced glomerular accumulation of extracellular matrix proteins, attenuated glomerular macrophage infiltration, and reduced renal expression of monocyte chemoattractant protein-1 and NF-kB in streptozotocin-induced diabetic ApoE 2/2 mice. Importantly, administration of the most specific Nox1/4 inhibitor, GKT137831, replicated these renoprotective effects of Nox4 deletion. In human podocytes, silencing of the Nox4 gene resulted in reduced production of ROS and downregulation of proinflammatory and profibrotic markers that are implicated in diabetic nephropathy. Collectively, these results identify Nox4 as a key source of ROS responsible for kidney injury in diabetes and provide proof of principle for an innovative small molecule approach to treat and/or prevent chronic kidney failure.

Myocardin-related Transcription Factor Regulates Nox4 Protein Expression

“…However, results obtained with whole body Nox4 knock-out mice are controversial or more complex. One study found that Nox4 deletion indeed mitigated the progression of DKD on the apoE Ϫ/Ϫ background (29). 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.…”

“…There is strong evidence that Nox4 is up-regulated during and is required for fibroblast-myofibroblast transition in vitro (19,(21)(22)(23). Moreover, Nox4 down-regulation by siRNA or antisense oligonucleotides proved to be protective in a lung fibrosis model (22) and reduced matrix deposition in diabetic kidney disease (DKD) (27), whereas new Nox1/4-selective pharmacological inhibitors exerted potent kidney-protective and antifibrotic effects in DKD models (28,29). All these findings suggest that Nox4 protein levels rise under fibrogenic (predominantly diabetic) conditions, and this contributes to the ensuing nephropathy and fibrosis.…”

“…Nox4-mediated reactive oxygen species (ROS) production was found to be necessary for the induction of key myofibroblast features, including contractility, matrix production (extra domain A fibronectin, collagen), and SMA expression (19,22,26). Accordingly, interventions that suppress ROS signaling or directly target Nox4 have been shown to attenuate fibrosis in mouse models of chronic kidney disease (27)(28)(29). Moreover, we found that EMyT is also associated with Smad3-dependent Nox4 expression (30).…”

Increased Muscle Mass Protects Against Hypertension and Renal Injury in Obesity

“…In metabolically compromised animals, oxidant stress is thought to be an important link between glucose disturbances and impaired function of the kidney. Several reports have described a causal role for NOX4 in renal dysfunction that can lead to hypertension 50, 51. In salt‐sensitive rats, urinary hydrogen peroxide has been shown to be elevated with increased renal perfusion pressure, and deletion of renal NOX4 attenuates hypertension 52, 53, 54.…”

Recent novel approaches to limit oxidative stress and inflammation in diabetic complications

“…One mechanism leading to enhanced NOX activity includes hyperglycaemia‐driven formation of intermediate Amadori products which are oxidised to form AGEs that activate RAGE and stimulate NOX to produce ROS 2. A clear role for elevated NOX1 activity has been shown in the promotion of diabetes‐associated atherosclerosis,9 whilst NOX4 appears critical in driving diabetic nephropathy 10…”