Aim: To examine the effect of NADPH oxidase Nox4 deletion in diabetic nephropathy (DN) using a global Nox4 deficient mice as well as podocyte specific Nox4 deficient mice.
Background: Chronic kidney failure is a major complication of diabetes. However, the underlying causes remain unclear. NADPH oxidase, particularly Nox4 derived reactive oxygen species (ROS) in the kidney play a crucial role in the development and progression of diabetic nephropathy. Albuminuria is a key feature of diabetic nephropathy and podocyte injury leads to the development of albuminuria in diabetes.
Methods: Nox4-/-ApoE-/- and Nox4+/+ApoE-/- mice as well as podNox4KO and floxedNox4 mice were rendered diabetic via streptozotocin injection. At week 20 urine samples were collected for the measurement of albuminuria. Animals were culled after 20 weeks and kidneys were removed for assessment of structural damage, oxidative stress markers, as well as measurement of the protein expression of extracellular matrix (ECM), pro-fibrotic and pro-inflammatory markers. In vitro, Nox4 was silenced in human podocytes and exposed to high glucose for gene expression analysis and ROS measurements.
Results: Global deletion of Nox4 as well podocyte specific Nox4 deletion resulted in attenuation of the diabetes induced increase in albuminuria in respective diabetic mice. Global deletion of Nox4 preserved renal structure, reduced glomerular accumulation of ECM proteins as well as attenuated glomerular macrophage infiltration and MCP-1 expression. However, no significant changes in renal structure were observed in diabetic podNox4KO when compared with floxedNox4 mice. In human podocytes, silencing of the Nox4 gene resulted in reduced ROS production and down-regulation of profibrotic markers that are implicated in diabetic nephropathy.
Conclusions: Collectively, these results identify Nox4 is a key source of ROS responsible for kidney injury including damage to podocytes in diabetes. These studies provide proof of principle for an innovative small molecule approach targeting Nox4 to treat and/or prevent DN.