Tohoku J. Exp. Med., 2012, 227(2)

Interleukin-6 Maintains Glucose Homeostasis to Support Strenuous Masseter Muscle Activity in Mice

MASAHIRO TSUCHIYA,¹ TOMOMI KIYAMA,² SHINOBU TSUCHIYA,³ HIROHISA TAKANO,⁴ EIJI NEMOTO,⁵ KEIICHI SASAKI,² MAKOTO WATANABE,¹ SHUNJI SUGAWARA⁶ and YASUO ENDO⁶

¹Division of Aging and Geriatric Dentistry, Tohoku University Graduate School of Dentistry, Sendai, Japan
²Division of Advanced Prosthetic Dentistry, Tohoku University Graduate School of Dentistry, Sendai, Japan
³Division of Oral Dysfunction Science, Tohoku University Graduate School of Dentistry, Sendai, Japan
⁴Environmental Health Sciences Division, National Institute for Environmental Studies, Tsukuba, Japan
⁵Division of Periodontology and Endodontology, Tohoku University Graduate School of Dentistry, Sendai, Japan
⁶Division of Oral Immunology, Tohoku University Graduate School of Dentistry, Sendai, Japan

The cytokine interleukin-6 (IL-6) is released from working skeletal muscles and reportedly plays key roles in their glucose homeostasis. However, it is unclear whether IL-6 plays such roles in the masseter muscle (MM), which is important in normal and pathological chewing behaviors, such as bruxism and/or prolonged clenching. When restrained (R+) in a narrow cylinder blocked at the front end with a thin plastic strip, a mouse gnaws away (G+) the strip to escape. The absolute weight of plastic gnawed away serves as an index of MM activity. Using this model, we examined the roles of IL-6 in MM with the following results. R+G+ increased the expression levels of IL-6 and glucose transporter 4 (Glut4) mRNAs in MM and the serum level of IL-6 protein. IL-6-deficient mice exhibited about 60% less gnawing activity than wild-type mice at 3-4 h after the start of R+G+, slower recovery of glycogen levels (indicating poorer glucose supply) in MM after R+G+, and no significant change in Glut4 mRNA in MM upon R+G+. During an R+G+ test conducted after “training” (repeated R+G+ sessions), wild-type mice exhibited greater gnawing activity than untrained controls, but no increase in IL-6 mRNA in MM. IL-6 mRNA increased in MM when hard food was eaten by mice raised on soft food for 3 weeks from weaning, but not in those raised on (accustomed to) hard food. Thus, IL-6 may maintain glucose homeostasis in MM in support of unusually strenuous activity, but not of accustomed activity levels.

keywords —— fatigue; glucose homeostasis; interleukin-6; masseter muscle; mastication

© 2012 Tohoku University Medical Press

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Tohoku J. Exp. Med., 2012, 227, 109-117

Correspondence: Masahiro Tsuchiya, D.D.S., Ph.D., Division of Aging and Geriatric Dentistry, Tohoku University Graduate School of Dentistry, 4-1 Seiryo-machi, Aoba-ku, Sendai, Miyagi 980-8575, Japan.

e-mail: tsuchiya-thk@umin.ac.jp