Review of Genetic Association in the SOD2 Gene with Chronic Kidney Disease: Case-Control Studies and Meta-Analysis Confirm Association with Diabetic Nephropathy

Proximal tubular deletion of superoxide dismutase-2 reveals disparate effects on kidney function in diabetes

There is a large body of evidence implicating mitochondrial reactive oxygen species (ROS) overproduction and oxidative stress in the development of diabetic kidney disease and the deficiency of mitochondrial antioxidant systems in the kidney, such as manganese superoxide dismutase (MnSOD/SOD2) have been identified. The proximal tubules of the kidney are densely packed with mitochondria thereby providing energy via oxidative phosphorylation in order to drive active transport for proximal tubular reabsorption of solutes from the glomerular filtrate. We hypothesized that maintenance of MnSOD function in the proximal tubules would be critical to maintain kidney health in diabetes. Here, we induced targeted deletion of SOD2 in the proximal tubules of the kidney in Ins2Akita diabetic mice (SODptKO mice) and show that 20 weeks of SOD2 deletion leads to no major impairment of kidney function and structure, despite these mice displaying enhanced albuminuria and kidney lipid peroxidation (8-isoprostanes). Plasma cystatin C, which is a surrogate marker of glomerular filtration was not altered in SODptKO diabetic mice and histological assessment of the kidney cortex revealed no change in kidney fibrosis. Thus, our findings suggest that deletion of SOD2 in the proximal tubular compartment of the kidney induces a more subtle phenotype than expected, shedding light on the involvement of SOD2 and the proximal tubular compartment in the pathogenesis of diabetic kidney disease.

Riding the tiger - physiological and pathological effects of superoxide and hydrogen peroxide generated in the mitochondrial matrix

Elevated mitochondrial matrix superoxide and/or hydrogen peroxide concentrations drive a wide range of physiological responses and pathologies. Concentrations of superoxide and hydrogen peroxide in the mitochondrial matrix are set mainly by rates of production, the activities of superoxide dismutase-2 (SOD2) and peroxiredoxin-3 (PRDX3), and by diffusion of hydrogen peroxide to the cytosol. These considerations can be used to generate criteria for assessing whether changes in matrix superoxide or hydrogen peroxide are both necessary and sufficient to drive redox signaling and pathology: is a phenotype affected by suppressing superoxide and hydrogen peroxide production; by manipulating the levels of SOD2, PRDX3 or mitochondria-targeted catalase; and by adding mitochondria-targeted SOD/catalase mimetics or mitochondria-targeted antioxidants? Is the pathology associated with variants in SOD2 and PRDX3 genes? Filtering the large literature on mitochondrial redox signaling using these criteria highlights considerable evidence that mitochondrial superoxide and hydrogen peroxide drive physiological responses involved in cellular stress management, including apoptosis, autophagy, propagation of endoplasmic reticulum stress, cellular senescence, HIF1α signaling, and immune responses. They also affect cell proliferation, migration, differentiation, and the cell cycle. Filtering the huge literature on pathologies highlights strong experimental evidence that 30-40 pathologies may be driven by mitochondrial matrix superoxide or hydrogen peroxide. These can be grouped into overlapping and interacting categories: metabolic, cardiovascular, inflammatory, and neurological diseases; cancer; ischemia/reperfusion injury; aging and its diseases; external insults, and genetic diseases. Understanding the involvement of mitochondrial matrix superoxide and hydrogen peroxide concentrations in these diseases can facilitate the rational development of appropriate therapies.