Reduced expression of sarcospan in muscles of Fukuyama congenital muscular dystrophy
Yoshihiro Wakayama1, Masahiko Inoue1, Hiroko Kojima1, Sumimasa Yamashita4, Seiji Shibuya1, Takahiro Jimi1, Hajime Hara1, Yoko Matsuzaki2, Hiroaki Oniki3, Motoi Kanagawa5, Kazuhiro Kobayashi5 and Tatsushi Toda5
1Department of Neurology, 2Biochemical and 3Electron Microscopic Laboratory, Showa University Fujigaoka Hospital, Fujigaoka, Aoba-ku, Yokohama, Japan, 4Department of Neurology, Kanagawa Children’s Medical Center, Mutsugawa, Minami-ku, Yokohama, Japan and 5Department of Medical Genetics, Osaka University Graduate School of Medicine, Yamadaoka, Suita, Japan.
Offprint requests to: Yoshihiro Wakayama, MD, PhD, Department of Neurology, Showa University Fujigaoka Hospital, 1-30 Fujigaoka, Aoba-ku, Yokohama 227-8501, Japan. e-mail: firstname.lastname@example.org
Summary. Expression profiles of sarcospan in muscles with muscular dystrophies are scarcely reported. To examine this, we studied five Fukuyama congenital muscular dystrophy (FCMD) muscles, five Duchenne muscular dystrophy (DMD) muscles, five disease control and five normal control muscles. Immunoblot showed reactions of sarcospan markedly decreased in FCMD and DMD muscle extracts. Immunohisto-chemistry of FCMD muscles showed that most large diameter myofibers expressed sarcospan discontinuously at their surface membranes. Immature small diameter FCMD myofibers usually did not express sarcospan. Immunoreactivity of sarcospan in DMD muscles was similarly reduced. With regard to dystroglycans and sarcoglycans, immunohistochemistry of FCMD muscles showed selective deficiency of glycosylated α-dystroglycan, together with reduced expression of ß-dystroglycan and α-, ß-, γ-, δ-sarcoglycans. Although the expression of glycosylated α-dystroglycan was lost, scattered FCMD myofibers showed positive immunoreaction with an antibody against the core protein of α-dystroglycan. The group mean ratios of sarcospan mRNA copy number versus GAPDH mRNA copy number by real-time RT-PCR showed that the ratios between FCMD and normal control groups were not significantly different (P>0.1 by the two-tailed t test). This study implied either O-linked glycosylation defects of α-dystroglycan in the Golgi apparatus of FCMD muscles may lead to decreased expression of sarcoglycan and sarcospan molecules, or selective deficiency of glycosylated α-dystroglycan due to impaired glycosylation in FCMD muscles may affect the molecular integrity of the basal lamina of myofibers. This, in turn, leads to decreased expression of sarcoglycans, and finally of sarcospan at the FCMD myofiber surfaces. Histol Histopathol 23, 1425-1438 (2008)
Key words: Sarcospan, Muscular dystrophy, Immunoblot, Real-time RT-PCR, Immunofluorescence