Sachiko Hoshino

A Role for the CHC22 Clathrin Heavy-Chain Isoform in Human Glucose Metabolism

GLUT4, Clathrin, and Glucose In human muscle, the GLUT4 glucose transport pathway responds to insulin and is responsible for 70 to 90% of human glucose clearance. In the basal metabolic state, GLUT4 is sequestered away from the cell surface and is released from an intracellular membrane compartment in response to insulin. This GLUT4 membrane pathway is defective in type II diabetes. Vassilopoulos et al. (p. 1192; see the Perspective by Orme and Bogan) now describe a function for CHC22 clathrin, a second isoform of clathrin that is present in humans and not in mice. CHC22 participates in the biogenesis of the intracellular compartment that sequesters the GLUT4 glucose transporter for insulin-stimulated release. Because CHC22 is restricted to humans, mice differ in their pathways that control glucose metabolism, which may restrict the utility of the mouse as a model system in assessing glucose metabolism and diabetes. A human-specific vesicle-forming protein regulates relocation of a glucose transporter to the cell membrane. Intracellular trafficking of the glucose transporter GLUT4 from storage compartments to the plasma membrane is triggered in muscle and fat during the body’s response to insulin. Clathrin is involved in intracellular trafficking, and in humans, the clathrin heavy-chain isoform CHC22 is highly expressed in skeletal muscle. We found a role for CHC22 in the formation of insulin-responsive GLUT4 compartments in human muscle and adipocytes. CHC22 also associated with expanded GLUT4 compartments in muscle from type 2 diabetic patients. Tissue-specific introduction of CHC22 in mice, which have only a pseudogene for this protein, caused aberrant localization of GLUT4 transport pathway components in their muscle, as well as features of diabetes. Thus, CHC22-dependent membrane trafficking constitutes a species-restricted pathway in human muscle and fat with potential implications for type 2 diabetes.

Immunohistochemical staining of dystrophin on formalin-fixed paraffin-embedded sections in Duchenne/Becker muscular dystrophy and manifesting carriers of Duchenne muscular dystrophy.

We succeeded in immunostaining of monoclonal anti-dystrophin antibodies on formalin-fixed and paraffin-embedded muscle sections from patients with Duchenne muscular dystrophy, patients with Becker muscular dystrophy, and manifesting carriers of Duchenne muscular dystrophy using Catalyzed Signal Amplification(TM) system. The Catalyzed Signal Amplification system is an extremely sensitive immunohistochemistry staining procedure based on the peroxidase-catalyzed deposition of a biotinylated phenolic compound. We used three mouse monoclonal antibodies: DYS1, DYS2, and DYS3. Muscle sections were treated using the Target Retrieval Solution(TM) and the Catalyzed Signal Amplification system. In control patients, DYS1 and DYS2 were stained at the sarcolemma, but DYS3 remained unstained. In Duchenne muscular dystrophy patients, DYS1 and DYS2 staining were undetected. In Becker muscular dystrophy patients, the immunolabeling of DYSI and DYS2 were weak and discontinuous. In manifesting carriers of Duchenne muscular dystrophy, DYS1 and DYS2 staining showed a mosaic pattern of dystrophin-positive fibers and dystrophin-negative fibers. DYS1 and DYS2 staining patterns of this study are similar to those of frozen sections using conventional methods previously reported. In cases from whom frozen muscle sections cannot be obtained, immunohistochemical dystrophin analysis using the Catalyzed Signal Amplification system will be beneficial for the diagnosis and the screening of neuromuscular diseases.

The CHC22 clathrin-GLUT4 transport pathway contributes to skeletal muscle regeneration.

Mobilization of the GLUT4 glucose transporter from intracellular storage vesicles provides a mechanism for insulin-responsive glucose import into skeletal muscle. In humans, clathrin isoform CHC22 participates in formation of the GLUT4 storage compartment in skeletal muscle and fat. CHC22 function is limited to retrograde endosomal sorting and is restricted in its tissue expression and species distribution compared to the conserved CHC17 isoform that mediates endocytosis and several other membrane traffic pathways. Previously, we noted that CHC22 was expressed at elevated levels in regenerating rat muscle. Here we investigate whether the GLUT4 pathway in which CHC22 participates could play a role in muscle regeneration in humans and we test this possibility using CHC22-transgenic mice, which do not normally express CHC22. We observed that GLUT4 expression is elevated in parallel with that of CHC22 in regenerating skeletal muscle fibers from patients with inflammatory and other myopathies. Regenerating human myofibers displayed concurrent increases in expression of VAMP2, another regulator of GLUT4 transport. Regenerating fibers from wild-type mouse skeletal muscle injected with cardiotoxin also showed increased levels of GLUT4 and VAMP2. We previously demonstrated that transgenic mice expressing CHC22 in their muscle over-sequester GLUT4 and VAMP2 and have defective GLUT4 trafficking leading to diabetic symptoms. In this study, we find that muscle regeneration rates in CHC22 mice were delayed compared to wild-type mice, and myoblasts isolated from these mice did not proliferate in response to glucose. Additionally, CHC22-expressing mouse muscle displayed a fiber type switch from oxidative to glycolytic, similar to that observed in type 2 diabetic patients. These observations implicate the pathway for GLUT4 transport in regeneration of both human and mouse skeletal muscle, and demonstrate a role for this pathway in maintenance of muscle fiber type. Extrapolating these findings, CHC22 and GLUT4 can be considered markers of muscle regeneration in humans.

The expression of α-dystrobrevin and dystrophin during skeletal muscle regeneration

The expression of α-dystrobrevin and dystrophin in rat tibialis anterior muscles was chronologically evaluated during a cycle of regeneration after myonecrosis induced by the injection of cardiotoxin. In immunohistochemical studies, α-dystrobrevin and dystrophin were first stained weakly at the sarcolemma of some regenerating muscle fibers on day 5. On day 7, α-dystrobrevin was still stained weakly, whereas dystrophin was stained conspicuously. After day 10, α-dystrobrevin and dystrophin were both stained conspicuously on almost all regenerating muscle fibers. In the Western blot analysis, α-dystrobrevin and dystrophin were first detected as visible bands on days 5 and 7, respectively. The bands of α-dystrobrevin and dystrophin both darkened sequentially up to day 10. The protein levels based on the densitometrical analysis of the bands on each day were converted to the percentage of the protein level on day 28, which was taken as 100%. The sequential line based on these data showed that α-dystrobrevin and dystrophin reached 50% of the protein level on day 28 by 6.6 and 5.3 days, respectively. These data provide evidence that α-dystrobrevin regenerates more slowly than dystrophin in skeletal muscle.

Bilateral gustatory disturbance caused by a unilateral pontine lesion.

To the Editor: Uesaka et al.1 described a patient with unilateral gustatory loss caused by a lesion in the ipsilateral pontine tegmentum. They concluded that the parabrachial nucleus probably plays an important role in the gustatory system in the human. We encountered a case with bilateral taste disturbance caused by a small lesion of the right pontine tegmentum. Case report. A 17-year-old girl presented bilateral gustatory disturbance. Taste was examined carefully using 0.5 M NaCl, 10% glucose, and 0.2 M acetic acid. She showed a whole bilateral taste disturbance (right dominant) for all three solutions. She also had gaze nystagmus and vertigo and sensory disturbance on the right side of her face. Other cranial nerves were normal. Her strength, muscle tonus, and deep tendon reflexes were normal. She did not have cerebellar signs. Immunoglobulin G (IgG) index in CSF was slightly increased, but cell count, protein, and glucose content were normal. Myelin basic …

The expression of dystrophin and alpha1-syntrophin during skeletal muscle regeneration.

The expression of dystrophin and α1-syntrophin in rat tibialis anterior muscles were evaluated during a cycle of regeneration after myonecrosis induced by the injection of cardiotoxin. Immunohistochemical studies were performed in cryosections of muscles on days 1, 3, 5, 7, 10, 14, 21 and 28 after injection of cardiotoxin. Western blot analysis was also examined in muscle on days 1, 3, 5, 7, 10, 14, 21 and 28. In immunohistochemical studies, dystrophin was stained weakly at the sarcolemma of some regenerating muscle fibers on day 3, and by day 10 it was stained strongly on almost all regenerating muscle fibers. α1-syntrophin was stained weakly at the sarcolemma of some regenerating fibers on day 5, and by day 14 it was detected on all regenerating muscle fibers. In Western blot analysis, dystrophin (DYS1) and α1-syntrophin (α1S) were completely absent on day 1. Re-expression of DYS1 and α1S was visible by day 5 and accelerated thereafter. The Western blots of DYS1 and α1S were densitometrically analyzed on each day. The protein levels on each day were converted to the percentage of the protein level on day 28, which was taken as 100%. From the sequential line based on these data, the following results were obtained on the chronological course of DYS1 and α1S. DYS1: 25% of the protein level on day 28 was reached by 3.5 days, 50% was reached by 5.3 days, and 90% was reached by 6.9 days. α1S: 25% of the protein level on day 28 was reached by 4.6 days, 50% was reached by 6.0 days, and 90% was reached by 12.5 days. In this study, DYS1 regenerated earlier than α1S at the sarcolemma of regenerating muscle fibers.

The expression of dystrophin, α-sarcoglycan, and β-dystroglycan during skeletal muscle regeneration: immunohistochemical and western blot studies

Summary We evaluated re-expression of dystrophin, α-sarcoglycan and β-dystroglycan in regenerating skeletal muscles of rats after cardiotoxin-induced myonecrosis in order to understand the dynamic behaviour of these proteins during the regeneration process. Immunohistochemical staining of these proteins almost disappeared in the sarcolemma of necrotic fibers on the 1st day, and was obscured due to non-specific staining on the 3rd day. Dystrophin was labeled faintly at the sarcolemma of regenerating muscle fibers on the 5th day. From the 5th day to the 10th day, levels of immunostaining of dystrophin increased. After the 14th day, dystrophin was stained conspicuously. α-Sarcoglycan was labeled weakly at the sarcolemma of small regenerating muscle fibers on the 5th day and was labeled conspicuously after the 7th day. β-Dystroglycan was labeled moderately at the sarcolemma of regenerating muscle fibers on the 5th day and was labeled conspicuously after the 7th day. In western blot analysis, β-dystroglycan persisted throughout the entire cycle of myonecrosis and regeneration, and re-expression of α-sarcoglycan progressed faster than that of dystrophin. We speculate that regeneration advances from the basement membrane side to the subsarcolemmal side, and that proteins at the basement membrane side resist disruption and have a high capacity for regeneration.

The expression of neuronal nitric oxide synthase and dystrophin in rat regenerating muscles

We investigated the expression of neuronal nitric oxide synthase (nNOS) and dystrophin in the regenerating skeletal muscles of rats after cardiotoxin-induced myonecrosis by immunohistochemical studies and western blot analysis. In normal muscles, nNOS was moderately immunostained on type 2B fibers, but was faintly immunostained on type 2A or type 1 fibers. In immunohistochemical studies of regenerating muscles, nNOS was first observed at the sarcolemma of type 2B fibers on day 10, when the type discrimination between types 2A and 2B was first detected by ATP reactions. Subsequently, the immunostaining of nNOS grew progressively stronger in type 2B fibers, with faint staining in type 2A and type 1 fibers until day 28. Meanwhile, the immunostaining of dystrophin grew stronger equally in all three fibers until day 21. In western blot analysis of regenerating muscles, nNOS regenerated more slowly than dystrophin. The present data suggest that the expression of nNOS is related to the muscle fiber type differentiation, and that the role of nNOS is related to the function of the type 2B fibers of the muscle.

Beta-synemin expression in cardiotoxin-injected rat skeletal muscle

Backgroundβ-synemin was originally identified in humans as an α-dystrobrevin-binding protein through a yeast two-hybrid screen using an amino acid sequence derived from exons 1 through 16 of α-dystrobrevin, a region common to both α-dystrobrevin-1 and -2. α-Dystrobrevin-1 and -2 are both expressed in muscle and co-localization experiments have determined which isoform preferentially functions with β-synemin in vivo. The aim of our study is to show whether each α-dystrobrevin isoform has the same affinity for β-synemin or whether one of the isoforms preferentially functions with β-synemin in muscle.MethodsThe two α-dystrobrevin isoforms (-1 and -2) and β-synemin were localized in regenerating rat tibialis anterior muscle using immunoprecipitation, immunohistochemical and immunoblot analyses. Immunoprecipitation and co-localization studies for α-dystrobrevin and β-synemin were performed in regenerating muscle following cardiotoxin injection. Protein expression was then compared to that of developing rat muscle using immunoblot analysis.ResultsWith an anti-α-dystrobrevin antibody, β-synemin co-immunoprecipitated with α-dystrobrevin whereas with an anti-β-synemin antibody, α-dystrobrevin-1 (rather than the -2 isoform) preferentially co-immunoprecipitated with β-synemin. Immunohistochemical experiments show that β-synemin and α-dystrobrevin co-localize in rat skeletal muscle. In regenerating muscle, β-synemin is first expressed at the sarcolemma and in the cytoplasm at day 5 following cardiotoxin injection. Similarly, β-synemin and α-dystrobrevin-1 are detected by immunoblot analysis as weak bands by day 7. In contrast, immunoblot analysis shows that α-dystrobrevin-2 is expressed as early as 1 day post-injection in regenerating muscle. These results are similar to that of developing muscle. For example, in embryonic rats, immunoblot analysis shows that β-synemin and α-dystrobevin-1 are weakly expressed in developing lower limb muscle at 5 days post-birth, while α-dystrobrevin-2 is detectable before birth in 20-day post-fertilization embryos.ConclusionOur results clearly show that β-synemin expression correlates with that of α-dystrobrevin-1, suggesting that β-synemin preferentially functions with α-dystrobrevin-1 in vivo and that these proteins are likely to function coordinately to play a vital role in developing and regenerating muscle.

Miller Fisher syndrome with sinus arrest

Dysautonomia in Guillain-Barre syndrome (GBS) rarely causes serious cardiovascular complications, such as sinus arrest. Miller Fisher syndrome (MFS) is recognized as a variant of GBS. There have been few reports regarding the association between MFS and dysautonomia. We describe a case of a 68-year-old man with ophthalmoplegia, bulbar palsy, truncal ataxia, and areflexia. He was diagnosed with MFS because he exhibited the classical clinical triad and had elevated serum anti- GQ1b immunoglobulin G levels. A magnetic resonance imaging scan of his head was normal. His 24-hour Holter recording showed sinus arrest. He was treated with intravenous immunoglobulin, whereupon his symptoms gradually improved. This included the sinus arrest, which was considered a symptom of dysautonomia in MFS. Therefore, clinicians should be mindful of dysautonomia not only in GBS patients, but also in cases of MFS.