Emi Hiroki

Tokyo Dental College, Edo, Tōkyō, Japan

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Publications (7)4.39 Total impact

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    ABSTRACT: Muscle regeneration supports muscle function in aging, and plays a role in the functional impairment caused by progressive neuromuscular diseases. Major substances controlling this process are growth factors and the extracellular matrix (ECM). Thus, follistatin is known to antagonize the function of several members of the TGF-β family of secreted signaling factors, including myostatin-the most powerful inhibitor of muscle growth characterized to date. Decorin-a small leucine-rich proteoglycan-traps myostatin and modulates its activity towards myogenic cells in the ECM. In addition, there are few reports concerning the regenerative muscle process of masseter muscles, which are of branchial arch origin, in mdx mice. Thus, in order to clarify the muscle regenerative process of masseter muscle, gene and protein expression of myostatin, follistatin and decorin were examined using the tibialis anterior (TA)muscle as a positive control. In both muscles, a gradual increase in mRNA myostatin, follistatin and decorin expression was detected, with the increase being greater in TA muscle than in masseter muscle. At 2 weeks, both muscles exhibited normal skeletal muscle cells. At 3 weeks, masseter muscle demonstrated scant areas of necrosis, whereas large necrotic zones were seen in TA muscle. At 4 weeks, the formation of necrotic tissue and presence of follistatin protein was observed clearly in masseter muscle. This result indicates that follistatin production is stimulated in the presence of necrosis. Interestingly, both muscles showed the same process of muscular formation, but with different time frames, which could be related to muscle origin.
    Anatomical science international. 03/2011; 86(3):151-9.
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    ABSTRACT: We examined expression of four important members of myogenic regulatory factors (MRFs) in the myoblasts both at mRNA and protein levels, which were subjected to mechanical stretching in in vitro condition. Our results showed that MyoD expression existed both in the stretch and in the control group at all time periods of the mechanical stimulus. Myf-5 expressed only at early stage of the stretch group. Although mRNA and protein expressions of myogenin and MRF4 were detected both in the stretch and in the control group at 12 h after the stretching, their expressions were only shown in the stretch group at 24 h after the mechanical stimulus. However, at 36 and 48 h, none of the MRFs examined except MyoD appeared in both groups. Our results suggest that the MRFs are up-regulated upon mechanical stimulus and each member plays a different major role for either proliferation or differentiation of the myoblasts.
    Anantomia Histologia Embryologia 09/2009; 38(4):305-10. · 0.88 Impact Factor
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    ABSTRACT: Ballistic muscle training leads to hypertrophy of fast type fibers and training for endurance induces that of slow type fibers. Numerous studies have been conducted on electrical, extending and magnetic stimulation of cells, but the effect of centrifugal force on cells remains to be investigated. In this study, we investigated the effect of stimulating cultured myoblasts with centrifugal force at different speeds on cell proliferation and myosin heavy-chain (MyHC) mRNA expression in muscle fiber. Stimulation of myoblasts was carried out at 2 different speeds for 20 min using the Himac CT6D, a desk centrifuge, and cells were observed at 1, 3 and 5 days later. Number of cells 1 and 5 days after centrifugal stimulation was significantly larger in the 62.5 x g and 4,170 x g stimulation groups than in the control group. Expression of MyHC-2b mRNA 1 day after centrifugal stimulation was significantly higher in the 2 stimulation groups than in the control group. Almost no expression of MyHC-2a was observed in any group at 1 and 3 days after centrifugal stimulation. However, 5 days after stimulation, MyHC-2a was strongly expressed in the 2 stimulation groups in comparison to the control group. Three days after centrifugal stimulation, expression of MyHC-1 was significantly higher in the 2 stimulation groups than in the control group. The results of this study clarified the effect of different centrifugal stimulation speeds on muscle fiber characteristics, and suggest that centrifugal stimulation of myoblasts enhances cell proliferation.
    The Bulletin of Tokyo Dental College 12/2008; 49(4):179-84.
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    ABSTRACT: The mouse mylohyoid muscle belongs to the mastication-related suprahyoid muscle group. It shows a plate-like morphology and forms the mouth floor. There have been no reports on the characteristics of the mouse mylohyoid muscle fibers, and especially on their functional role during ingestion action, and many points remain unclear. We examined the mouse mylohyoid muscle at both the transcriptional and protein levels by RT-PCR, immunohistochemistry, and Western Blotting. MyHC-2b, which is expressed in almost all head and neck muscles and is thought to play a role in rapid mastication movement, was not detected in the mouse mylohyoid muscle. This result suggests that the mouse mylohyoid muscle has a special function and does not directly function during ingestion.
    ZOOLOGICAL SCIENCE 09/2008; 25(8):806-10. · 1.08 Impact Factor
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    ABSTRACT: Mammals exhibit marked morphological differences in the muscles surrounding the jaw bone due to differences in eating habits. Furthermore, the myofiber properties of the muscles differ with function. Since the muscles in the oral region have various functions such as eating, swallowing, and speech, it is believed that the functional role of each muscle differs. Therefore, to clarify the functional role of each masticatory muscle, the myofiber properties of the adult mouse masticatory muscles were investigated at the transcriptional level. Expression of MyHC-2b with a fast contraction rate and strong force was frequently noted in the temporal and masseter muscles. This suggests that the temporal and masseter muscles are closely involved in rapid antero-posterior masticatory movement, which is characteristic in mice. Furthermore, expression of MyHC-1 with a low contraction rate and weak continuous force was frequently detected in the lateral pterygoid muscle. This suggests that, in contrast to other masticatory muscles, mouse lateral pterygoid muscle is not involved in fast masticatory movement, but is involved in functions requiring continuous force such as retention of jaw position. This study revealed that muscles with different roles function comprehensively during complicated masticatory movement.
    The Bulletin of Tokyo Dental College 06/2008; 49(2):53-8.
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    ABSTRACT: It has been reported that the synthesis, degradation, and metabolism of muscle proteins in myoblasts, as well as the proliferation and differentiation of cells, are influenced by various related to extracellular signaling molecules, such as neural transmitters, growth factors, and hormones, when muscle tissue has been exposed to mechanical stimulation. However, reports regarding the expression of growth factors during mechanical stimulation of myoblasts are few, and many questions remain unanswered. We examined the mRNA expression of insulin-like growth factor 1 (IGF-1) in myoblasts subjected to mechanical stretching in vitro. In addition, apoptosis caused by intracellular stress has been reported to occur during muscle development at the embryonic stage. To clarify the expression of intracellular stress factors, we here investigated related gene expression. Expression of IGF-1 increased in the early stage of cell stretching, followed by a decrease in the late stage. This suggests that mechanical stimulation resulted in an immediate increase in IGF-1 expression, followed by a decrease as cells acclimated to the inducing environment. Caspase was significantly expressed in a stretch group at 12 hours after the beginning of mechanical stimulation, compared with a control group. This suggests that cellular proliferation is also regulated by intracellular stress factors involving the endoplasmic reticulum, mitochondria, and other organelles during the process of muscle proliferation and differentiation.
    ZOOLOGICAL SCIENCE 04/2008; 25(3):242-7. · 1.08 Impact Factor
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    ABSTRACT: The mdx mouse, a model of muscular dystrophy, lacks dystrophin, a cell membrane protein. It is known that the lack of dystrophin causes muscle fiber necrosis from 2 weeks after birth, and the majority of necrotic muscle fibers are replaced by regenerated muscle fibers by 4 weeks after birth. A recent study indicated the possibility that mitochondria-mediated intracellular stress, a phenomenon similar to apoptosis, may be produced during muscle fiber necrosis, but did not analyze endoplasmic reticulum-mediated intracellular stress. Therefore, we examined the expression of the caspase-12 gene involved in the endoplasmic reticulum stress pathway and the Bax, caspase-9, and caspase-3 genes involved in the mitochondrial stress pathway in the mdx masseter muscle. We found over-expression of caspase-12 in cells at 2-3 weeks after birth when muscle fiber necrosis was not prominent. This suggests that stress occurs in the endoplasmic reticulum to maintain cell morphology in the absence of dystrophin. In addition, Bax was abundantly expressed in the mdx masseter muscle at 3 weeks after birth, and the expression of caspase-9 and -3 was prominent at 3-4 weeks after birth when necrosis and regeneration were marked. These results indicate that endoplasmic reticulum and mitochondrial stresses are produced during necrosis of the mdx masseter muscle, and suggest that these events are a phenomenon similar to apoptosis.
    Journal of Muscle Research and Cell Motility 02/2007; 28(4-5):243-7. · 1.36 Impact Factor