Abstract Dysferlin is a newly identified sarcolemmal pro- tein related to Miyoshi myopathy and limb-girdle muscu- lar dystrophy. Although its function is still unknown, it is inferred from the presence of C2 domains and a transmem- brane domain in its sequence that dysferlin may be ex- pressed or located not only at the sarcolemma but also in other membranous organelles to interact with Ca 2+ . Tubu- lar aggregates (TAs) are derived from sarcoplasmic retic- ulum (SR) and found in various myopathies, especially in those related to disturbed intra-sarcoplasmic Ca 2+ homeo- stasis. To clarify the expression of dysferlin in TAs and the relationship among TA formation, dysferlin expres- sion, and endoplasmic reticulum (ER) stress, we examined the expression of dysferlin and other sarcolemmal pro- teins by immunohistochemistry in 12 muscle biopsy spec- imens with TAs from 11 cases of periodic paralysis and 1 case of myalgia/cramps syndrome. Moreover, the expres- sion of glucose-regulated protein 78 (GRP78) and GRP94, which are up-regulated under ER stress, was also examined by immunohistochemistry and immunoblotting. TAs showed strong expression of dysferlin. GRP78 and GRP94 were also intensely expressed in TAs. Total amounts of GRP78 and GRP94 were significantly increased in muscles with TAs compared with normal controls. These results indi- cate that muscles with TAs seem to be under ER stress, probably resulting from disturbed intra-sarcoplasmic Ca 2+ homeostasis. Strong expression of dysferlin in TAs sug- gests the possibility that it is located not only at the sar- colemma but also in the SR, at least in the pathological conditions. Keywords Dysferlin · Endoplasmic reticulum stress · Tubular aggregates · Periodic paralysis · Sarcoplasmic reticulum Introduction Dysferlin is a transmembrane protein defect of which causes limb-girdle muscular dystrophy 2B (LGMD2B) and Miyoshi myopathy (MM) [4, 10]. Its physiological role is still unknown. Although it locates at the sarcolemma of normal skeletal muscle, dysferlin is not a component of a dystrophin-glycoprotein complex [3, 13]. However, fer-1, a homologous protein of dysferlin in C. elegans is essen- tial in the fusion of the sperm to other membranous or- ganelles [1]. In addition, dysferlin has six C2 domains in its sequence [10]. C2 domains have the capacity to bind Ca 2+ , to mediate Ca 2+ -dependent signaling events, and are present in many membrane-associated proteins [5, 18]. Tubular aggregates (TAs) are pathological organelles found in various myopathies: periodic paralysis [16], con- genital myasthenic syndromes [21], myalgia/cramps syn- drome [19], and malignant hyperthermia [17]. TAs have been so far reported to be derived from the sarcoplasmic reticulum (SR) [20, 28]. The machinery to form them and their function are still unknown. However, it is quite pos- sible that TAs are related to the maintenance of intra-sar- coplasmic Ca 2+ homeostasis because: (1) the SR functions in intra-sarcoplasmic Ca 2+ homeostasis, (2) TAs are re- ported to have Ca 2+ -loading capacity [25], and (3) peri- odic paralysis, myalgia/cramps syndrome and malignant hyperthermia are related to disturbed intra-sarcoplasmic Ca 2+ homeostasis [11, 23, 25, 26]. From these lines of evidence, it seemed possible that dysferlin is expressed in the SR or TAs, at least in patho- logical conditions. To test this hypothesis, we examined Koji Ikezoe · Hirokazu Furuya · Yasumasa Ohyagi · Manabu Osoegawa · Ichizo Nishino · Ikuya Nonaka · Jun-ichi Kira Dysferlin expression in tubular aggregates: their possible relationship to endoplasmic reticulum stress Acta Neuropathol (2003) 105 : 603–609 DOI 10.1007/s00401-003-0686-1 Received: 17 December 2002 / Accepted: 15 January 2003 / Published online: 8 March 2003 REGULAR PAPER K. Ikezoe (✉) · H. Furuya · Y. Ohyagi · M. Osoegawa · J. Kira Department of Neurology, Neurological Institute, Graduate School of Medical Sciences, Kyushu University 60, 812-8582 Fukuoka, Japan Tel.: +81-92-6425340, Fax: +81-92-6425352, e-mail: kikezoe@neuro.med.kyushu-u.ac.jp I. Nishino Department of Neuromuscular Research, National Institute of Neuroscience, National Center of Neurology and Psychiatry (NCNP), 187-8502 Kodaira, Tokyo, Japan I. Nonaka National Center Hospital for Mental, Nervous and Muscular Disorders, NCNP, 187-8551 Kodaira, Tokyo, Japan © Springer-Verlag 2003