Background: Reactive oxygen species (ROS) play crucial role in the pathogenesis of diabetic nephropathy (DN). The more recently discovered pro-oxidant enzyme, Nox5 could play a role in DN. Nox5 is present in humans but not in rodents. Thus, there is a paucity of information about Nox5 in animal models of DN. We examined the role of Nox5 in human mesangial cells as well as in a model of human inducible Nox5 transgenic mice expressing Nox5 selectively in vascular smooth muscle cells, the mesangial cells (SM22+Nox5+) in the setting of diabetes.
Methods: SM22+Nox5+ and SM22+Nox5- transgenic mice were rendered diabetic via streptozotocin injections. At week 15 urine and plasma samples were collected for the assessment of renal function including albuminuria and creatinine clearance. Animals were culled and kidneys were removed for the assessment of structural damage as well as gene and protein expression of markers of inflammation, fibrosis and oxidative stress. In vitro, Nox5 was silenced in human mesangial cells and exposed to high glucose and TGF-β for the measurement of gene expression and ROS level.
Results: A 10 fold increase in albuminuria was found in Nox5 negative diabetic mice which was further increased by 20% in Nox5 positive diabetic mice. In addition, a further increase in glomerulosclerosis and markers of fibrosis (fibronectin), inflammation (MCP-1 and F4/80) and oxidative stress (nitrotyrosine) were found in diabetic SM22+Nox5+ when compared to diabetic SM22+Nox5- mice. Diabetes induced increase in creatinine clearance was unchanged in both group of mice. Moreover, silencing of Nox5 in human mesangial cells resulted in reduced ROS production and down-regulation of profibrotic markers that are implicated in DN.
Conclusions: Collectively, these findings suggest that Nox5 is a key source of ROS which accelerates renal injury in diabetes and provide proof of principle for the innovation of a new renoprotective agent in diabetes.