232 - Peroxiredoxin II Deficiency Contributes to Contraction-Induced Force Loss in the mdx Model of Duchenne Muscular Dystrophy

Abstract

Duchenne muscular dystrophy is a lethal, degenerative muscle disease caused by loss of the protein dystrophin. Eccentric contraction-induced force loss is a hallmark of dystrophin-deficient muscle, although the underlying cause of force loss remains obscure. Here, we employed iTRAQ proteomics to identify proteins that were differentially expressed in skeletal muscle of dystrophin-deficient mdx mice overexpressing γ cyto -actin (mdx/Actg1-TG), a model which displays partial protection from eccentric contraction-induced force loss. We identified peroxiredoxin II (PrxII) as significantly decreased in mdx muscle compared to WT, and recovered to WT levels in mdx/Actg1-TG muscle. PrxII is an antioxidant enzyme that reduces reactive oxygen species (ROS) in the form of hydrogen peroxide to water. Because the sarcolemmal NAPDH oxidase 2 (NOX2) complex exhibits increased expression and activity in mdx mice, and inhibition of NOX2 also partially protects mdx muscle against eccentric contraction-induced force loss, we investigated the relationship between PrxII and NOX2 in WT and mdx muscle. Like NOX2, PrxII was enriched at the sarcolemma. Knockout of the p47 phox subunit of NOX2 in mdx muscle restored PrxII levels back to WT, suggesting that elevated NOX2 activity may drive PrxII hyperoxidation and proteasomal degradation. Most interestingly, force production by mdx/PrxII -/- double knockout muscle exhibited increased sensitivity to eccentric contraction, while transgenic overexpression of PrxII protected mdx muscle from eccentric contraction to a similar extent measured in mdx/Actg1-TG muscle. Our results suggest that PrxII functions as the “off-switch” in the sarcolemmal NOX2 signaling pathway and its loss from dystrophic muscle contributes to pathogenesis associated with excessive ROS production.