α1-Syntrophin is a member of the family of dystrophin-associated proteins and is strongly expressed in the sarcolemma and the neuromuscular junctions. All three syntrophin isoforms have a PDZ domain that appears to participate in protein-protein interactions at the plasma membrane. α1-Syntrophin has additionally been shown to associate with neuronal nitric-oxide synthase (nNOS) through PDZ domains in vitro. These observations suggest that α1-syntrophin may work as a modular adaptor protein that can link nNOS or other signaling enzyme to the sarcolemmal dystrophin complex. In the sarcolemma, nNOS regulates the homeostasis of reactive free radical species and may contribute to the oxidative damage to muscle protein in muscle disease such as Duchenne muscular dystrophy. In this study, we generated α1-syntrophin knock-out mice to clarify the interaction between α1-syntrophin and nNOS in the skeletal muscle. We observed that nNOS, normally expressed in the sarcolemma, was largely absent from the sarcolemma, but considerably remained in the cytosol of the knock-out mice. Even though the distribution of nNOS was altered, the knock-out mice displayed no gross histological changes in the skeletal muscle. We also discovered that muscle contractile properties have not been influenced in the knock-out mice.

The autosomal recessive mouse mutation retinal degeneration 6 (rd6) causes small, white retinal spots and progressive photoreceptor degeneration similar to that observed in human flecked retinal diseases. Using a positional cloning approach, we determined that rd6 mice carry a splice donor mutation in the mouse homolog of the human membrane-type frizzled-related protein (Mfrp) gene that results in the skipping of exon 4. We found that mRNA of Mfrp is predominantly expressed in the eye, and at a lower level in the brain. To determine where in the eye Mfrp is expressed, in situ hybridization was done and showed that Mfrp is expressed specifically in the retinal pigment epithelium (RPE) and ciliary epithelium of the eye. The deduced amino acid sequence of MFRP contains a region with similarities to the cysteine-rich domain (CRD) of frizzled, a gene originally found in Drosophila that controls tissue polarity. The CRD is essential for Wnt binding and signaling. Wnt signaling has been shown to be involved in the control of gene expression, cell adhesion, planar polarity, proliferation and apoptosis. We also observed the localization of Wnt family proteins in the apical membrane of the RPE. Our results provide genetic evidence for an involvement of the Mfrp gene expressed by RPE in the degeneration of photoreceptors.

α1-Syntrophin is a member of the family of dystrophin-associated proteins; it has been shown to recruit neuronal nitric oxide synthase and the water channel aquaporin-4 to the sarcolemma by its PSD-95/SAP-90, Discs-large, ZO-1 homologous domain. To examine the role of α1-syntrophin in muscle regeneration, we injected cardiotoxin into the tibialis anterior muscles of α1-syntrophin–null (α1syn−/−) mice. After the treatment, α1syn−/− muscles displayed remarkable hypertrophy and extensive fiber splitting compared with wild-type regenerating muscles, although the untreated muscles of the mutant mice showed no gross histological change. In the hypertrophied muscles of the mutant mice, the level of insulin-like growth factor-1 transcripts was highly elevated. Interestingly, in an early stage of the regeneration process, α1syn−/− mice showed remarkably deranged neuromuscular junctions (NMJs), accompanied by impaired ability to exercise. The contractile forces were reduced in α1syn−/− regenerating muscles. Our results suggest that the lack of α1-syntrophin might be responsible in part for the muscle hypertrophy, abnormal synapse formation at NMJs, and reduced force generation during regeneration of dystrophin-deficient muscle, all of which are typically observed in the early stages of Duchenne muscular dystrophy patients.

Background: Neuromyelitis optica (NMO) is a disease of the CNS characterized by severe optic neuritis and longitudinally extended transverse myelitis. Recent studies suggest that anti-aquaporin-4 (AQP4) antibodies, NMO-specific biomarkers, are pathogenic and target AQP4-expressing astrocytes in NMO, although an additional event (T-cell response or infection) should occur for anti-AQP4 antibodies and complements to pass through the blood–brain barrier and cause the CNS lesions. AQP4 is the major water channel in the CNS, but it is also expressed in fast-twitch skeletal muscle fibers. However, muscle diseases have not been described in NMO. Methods: We retrospectively examined the serologic database of 733 cases of NMO with anti-AQP4 antibody at the Department of Neurology, Tohoku University School of Medicine. The serum samples were sent to our laboratory for testing anti-AQP4 antibody from around the country during the period from 2006 to 2009. Results: We found 3 anti-AQP4 antibody-positive female patients (7, 34, and 67 years old) with NMO who had episodes of prominent hyperCKemia (12,520, 19,415, and 59,660 IU/L) with general fatigue some weeks before the onset of optic neuritis. HyperCKemia was transient without any treatment in all patients, but recurred once in one of them. Conclusions: These cases suggest that hyperCKemia may be involved in the pathogenesis of neuromyelitis optica (NMO) in a fraction of patients. The causes of transient hyperCKemia are unknown. Further studies are needed to know the frequency of hyperCKemia in NMO and clarify its pathogenic role.