Interleukin-6 maintains glucose homeostasis to support strenuous masseter muscle activity in mice.
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.
Division of Aging and Geriatric Dentistry, Tohoku University Graduate School of Dentistry, Sendai, Japan. tsuchiya-thk@umin.ac.jp
Masahiro
M
Tsuchiya
Tomomi
T
Kiyama
Shinobu
S
Tsuchiya
Hirohisa
H
Takano
Eiji
E
Nemoto
Keiichi
K
Sasaki
Makoto
M
Watanabe
Shunji
S
Sugawara
Yasuo
Y
Endo
D000818:Animals; D005502:Food; D005786:Gene Expression Regulation; D005947:Glucose / Q000378:metabolism*; D006003:Glycogen / Q000378:metabolism; D006244:Hardness; D006706:Homeostasis; D015850:Interleukin-6 / Q000097:blood / Q000235:genetics / Q000378:metabolism*; D008406:Masseter Muscle / Q000378:metabolism*; D008409:Mastication / Q000235:genetics; D051379:Mice; D008807:Mice, Inbred BALB C; D018345:Mice, Knockout; D008954:Models, Biological; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D012149:Restraint, Physical; D000071223:Suppressor of Cytokine Signaling 3 Protein; D050826:Suppressor of Cytokine Signaling Proteins / Q000235:genetics / Q000378:metabolism
D015850:Interleukin-6; D012333:RNA, Messenger; C491411:Socs3 protein, mouse; D000071223:Suppressor of Cytokine Signaling 3 Protein; D050826:Suppressor of Cytokine Signaling Proteins; C577686:interleukin-6, mouse; D006003:Glycogen; D005947:Glucose