Specific expression of COX‐2 in type 1 muscle fibers

Abstract

A skeletal muscle biopsy is important for the diagnosis of muscle diseases. Frozen sections for histochemistry to determine patterns of muscle fiber types are essential for a proper pathological evaluation of skeletal muscle. Many Pathology Laboratories cannot perform histochemistry routinely by many limitations related to proper snap freezing. Recently, Troponin C and Troponin T have been developed for muscular fiber typing; however, they are not widely used. We incidentally discovered expression of cyclooxygenase -2 (COX-2) in skeletal muscle tissue around breast cancer, and the “checkerboard” pattern of COX-2 expression was suggestive of fiber typing of the skeletal muscle. We performed this study to verify whether COX-2 is expressed in a specific muscle fiber type and to validate applicability of COX-2 immunohistochemistry in the formalin-fixed, paraffin-embedded muscle biopsy specimens. We used 58 cases of muscle biopsy specimens consisting of 27 cases of neurogenic atrophy, 9 cases of muscular dystrophy, 8 cases of inflammatory myopathy, 7 cases of other muscular diseases, and 7 cases of nonspecific changes. Immunohistochemistry was performed with COX-2, Troponin C and Troponin T monoclonal antibodies. Compared with immunohistochemical expression of Troponin-C and Troponin-T, and compared with histochemical studies of NADH-TR and ATPase pH9.4, COX-2 was specifically expressed in type 1 muscle fibers in various muscle diseases and normal skeletal muscle. Specific expression of COX-2 in type 1 myofibers is a brand new finding hitherto undescribed in the literatures.