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Altered Expression of ARPP Protein in Skeletal Muscles of Patients with Muscular Dystrophy, Congenital Myopathy and Spinal Muscular Atrophy

Objectives: Ankyrin-repeated protein with PEST and a proline-rich region (ARPP) is a recently identified protein with 4 ankyrin-repeated motifs in its central portion. Type 1 myofibers of skeletal muscle express high levels of ARPP. Recently, we have found that ARPP expression was induced in mouse denervated skeletal muscle. This led us to hypothesize that ARPP expression might be induced in skeletal muscle under some pathological conditions. Methods: In this study, we performed immunohistochemical analysis of ARPP expression in biopsy specimens of muscle tissue from 15 patients with muscular dystrophies (MDs), 13 with congenital myopathies and 11 with spinal muscular atrophies (SMAs). Results: The ARPP expression levels of all the specimens from MD patients appeared to be lower than control muscle levels. In contrast, the specimens from the 13 patients with congenital myopathies were all ARPP positive. We also found increased numbers of ARPP-positive myofibers in patients with congenital myopathies, and these myofibers co-expressed the slow myosin heavy chain. Indeed, it has been reported that type 1 myofibers are predominant in patients with congenital myopathies, suggesting that increased numbers of ARPP-positive myofibers in such patients may be associated with increased numbers of type 1 fibers. In patients with SMAs, we found that ARPP-positive myofibers tended to be distributed in groups. As grouped myofibers have been reported to result from the process of denervation, innervation and subsequent denervation of re-innervated myofibers, the grouped ARPP-positive myofibers in SMA patients may result from denervation of the motor units. Conclusions: These findings suggest that evaluation of ARPP may be helpful for the histological diagnosis of muscle diseases.