title: Macrophage deficiency in osteopetrotic (op/op) mice inhibits activation of satellite cells and prevents hypertrophy in single soleus fibers.
abstract: Effects of macrophage on the responses of soleus fiber size to hind limb unloading and reloading were studied in osteopetrotic homozygous (op/op) mice with inactivated mutation of macrophage colony-stimulating factor (M-CSF) gene and in wild-type (+/+) and heterozygous (+/op) mice. The basal levels of mitotically active and quiescent satellite cell (-46 and -39% vs. +/+, and -40 and -30% vs. +/op) and myonuclear number (-29% vs. +/+ and -28% vs. +/op) in fibers of op/op mice were significantly less than controls. Fiber length and sarcomere number in op/op were also less than +/+ (-22%) and +/op (-21%) mice. Similar trend was noted in fiber cross-sectional area (CSA, -15% vs. +/+, P = 0.06, and -14% vs. +/op, P = 0.07). The sizes of myonuclear domain, cytoplasmic volume per myonucleus, were identical in all types of mice. The CSA, length, and the whole number of sarcomeres, myonuclei, and mitotically active and quiescent satellite cells, as well as myonuclear domain, in single muscle fibers were decreased after 10 days of unloading in all types of mice, although all of these parameters in +/+ and +/op mice were increased toward the control values after 10 days of reloading. However, none of these levels in op/op mice were recovered. Data suggest that M-CSF and/or macrophages are important to activate satellite cells, which cause increase of myonuclear number during fiber hypertrophy. However, it is unclear why their responses to general growth and reloading after unloading are different.
authors: Space Biomedical Research Office, Japan Aerospace Exploration Agency, Tsukuba City, Ibaraki, Japan;
authors: T
authors: T
authors: Ohira
authors: Graduate School of Medicine, Osaka University, Toyonaka City, Osaka, Japan;
authors: X D
authors: XD
authors: Wang
authors: Laboratory Animal Center, Yamagata University School of Medicine, Yamagata City, Yamagata, Japan;
authors: T
authors: T
authors: Ito
authors: Graduate School of Medicine, Osaka University, Toyonaka City, Osaka, Japan;
authors: F
authors: F
authors: Kawano
authors: Graduate School of Health Sciences, Toyohashi SOZO University, Toyohashi City, Aichi, Japan;
authors: K
authors: K
authors: Goto
authors: Graduate School of Health and Sports Science, Doshisha University, Kyotanabe City, Kyoto, Japan; Research Center for Adipocyte and Muscle Science, Doshisha University, Kyotanabe City, Kyoto, Japan; and.
authors: T
authors: T
authors: Izawa
authors: Department of Molecular Predictive Medicine and Sport Science, School of Medicine, Kyorin University, Mitaka City, Tokyo, Japan.
authors: H
authors: H
authors: Ohno
authors: Department of Molecular Predictive Medicine and Sport Science, School of Medicine, Kyorin University, Mitaka City, Tokyo, Japan.
authors: T
authors: T
authors: Kizaki
authors: Graduate School of Health and Sports Science, Doshisha University, Kyotanabe City, Kyoto, Japan; Research Center for Adipocyte and Muscle Science, Doshisha University, Kyotanabe City, Kyoto, Japan; and yohira@mail.doshisha.ac.jp.
authors: Y
authors: Y
authors: Ohira
mesh_terms: D000818:Animals; D004195:Disease Models, Animal; D006984:Hypertrophy / Q000378:metabolism / Q000517:prevention & control; D008264:Macrophages / Q000473:pathology*; D008297:Male; D051379:Mice; D018485:Muscle Fibers, Skeletal / Q000473:pathology*; D018482:Muscle, Skeletal / Q000378:metabolism; D009133:Muscular Atrophy / Q000378:metabolism; D032446:Myoblasts / Q000378:metabolism; D010022:Osteopetrosis / Q000378:metabolism; D032496:Satellite Cells, Skeletal Muscle / Q000378:metabolism*
keywords: muscle fiber size; myonuclei; osteopetrotic mice; satellite cells; unloading and reloading