Increased expression of manganese superoxide dismutase is associated with that of nitrotyrosine in myopathies with rimmed vacuoles

Abstract

Oxidative stress has been suggested as one of the pathogenetic mechanisms of inclusion body myositis (IBM). To study the role of antioxidant enzymes in myopathies with rimmed vacuoles, we examined expressions of copper, zinc superoxide dismutase (Cu, Zn-SOD) and manganese superoxide dismutase (Mn-SOD), and the relationship between SODs and other proteins localized in rimmed vacuoles in muscle biopsy specimens from three cases of sporadic IBM and two of distal myopathy with rimmed vacuoles (DMRV) as well as eight control cases of myopathies without rimmed vacuoles. Immunoblot analysis showed distinct protein bands of both SODs in IBM and DMRV using subtype-specific antibodies. Intensities of immunoreactive bands for Mn-SOD in IBM and DMRV were stronger than those in the control cases. Immunohistochemistry disclosed accumulation of both SODs in vacuolated muscle fibers in all cases of IBM and DMRV. Immunoreactivity for Mn-SOD was often colocalized with that of nitrotyrosine, cytochrome oxidase, tau, and lysosome-associated membrane proteins 2 (LAMP-2) in vacuolated fibers. Some of the Cu, Zn-SOD-positive vacuolated fibers were associated with ubiquitin. The two SODs may have different roles for cell protection, and the expression of Mn-SOD is associated with nitric oxide-induced oxidative damage in myopathies with rimmed vacuoles.