A Common Polymorphism in Extracellular Superoxide Dismutase Affects Cardiopulmonary Disease Risk by Altering Protein Distribution

Abstract

Background The enzyme extracellular superoxide dismutase (EC-SOD; SOD3) is a major antioxidant defense in lung and vasculature. A nonsynonomous single nucleotide polymorphism (SNP) in EC-SOD (rs1799895) leads to an arginine to glycine (Arg->Gly) amino acid substitution at position 213 (R213G) in the heparin-binding domain (HBD). In recent human genetic association studies, this SNP attenuates the risk of lung disease, yet paradoxically increases the risk of cardiovascular disease. Methods and Results Capitalizing on the complete sequence homology between human and mouse in the HBD, we created an analogous R213G SNP knockin mouse. The R213G SNP did not change enzyme activity, but shifted the distribution of EC-SOD from lung and vascular tissue to extracellular fluid (e.g. bronchoalveolar lavage fluid (BALF) and plasma). This shift reduces susceptibility to lung disease (lipopolysaccharide-induced lung injury) and increases susceptibility to cardiopulmonary disease (chronic hypoxic pulmonary hypertension). Conclusions We conclude that EC-SOD provides optimal protection when localized to the compartment subjected to extracellular oxidative stress: thus, the redistribution of EC-SOD from the lung and pulmonary circulation to the extracellular fluids is beneficial in alveolar lung disease but detrimental in pulmonary vascular disease. These findings account for the discrepant risk associated with R213G in humans with lung diseases compared with cardiovascular diseases.

The R213G polymorphism in SOD3 protects against allergic airway inflammation

“…As we have previously reported, R213G mice have no other changes in antioxidant expression or activity, but only in its distribution (22,23). In general, higher airway EC-SOD, either through the R213G SNP or EC-SOD OE, resulted in lower inflammatory responses to both the OVA model and the Alternaria model.…”

“…We used 4 different C57BL/6 mice strains: wild-type (WT) control mice, heterozygous (HET), and homozygous (HM) mice that were genetically modified with an R213G knockin to mimic the human R213G SNP (22), and mice that overexpressed lung SOD3 via an SPC promoter (OE) (33). Mice were sensitized and challenged with OVA ( Figure 3A), and it had no effect on the EC-SOD activity among the treatment groups (data not shown).…”

“…ECM binding region of SOD3 (rs1799895) results in an arginine to glycine amino acid change at position 213 (R213G), thereby disrupting the positive charge and releasing the protein from the ECM (21) and redistributing EC-SOD to extracellular fluids such as plasma and epithelial lining fluids (22,23). People who carry the R213G SNP have attenuated risk of exacerbations of chronic obstructive pulmonary disease (COPD) (24), but the role of the rs1799895 SNP in asthma is unknown.…”

Selective depletion of vascular EC-SOD augments chronic hypoxic pulmonary hypertension

“…Lung tissue was homogenized in SOD activity assay buffer, and EC-SOD was separated from intracellular SOD (SOD1 and SOD2) using the Glycoprotein Isolation Kit, ConA (Pierce Biotechnology), as recently described (16). Activity levels were determined using the SOD assay kit-WST (Dojindo Molecular Technologies), according to the manufacturer's instructions.…”

“…Collagen deposition around pulmonary arteries Ͻ200 m associated with terminal bronchioles was analyzed by nonlinear second harmonic generation (SHG) imaging, as recently described (16). Collagen fibrils are able to intrinsically generate an SHG signal, which can be quantified to reflect collagen content (22).…”