The vestibular system is critical for the changes in muscle and bone induced by hypergravity in mice.

Naoyuki Kawao,Hiroshi Kaji,Koji Obata,Yukinori Tamura,Hironobu Morita,Katsumi Okumoto

doi:10.14814/phy2.12979

Naoyuki Kawao, Hiroshi Kaji + Show 4 more

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https://doi.org/10.14814/phy2.12979

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Abstract

Gravity changes concurrently affect muscle and bone as well as induce alterations in vestibular signals. However, the role of vestibular signals in the changes in muscle and bone induced by gravity changes remains unknown. We therefore investigated the effects of vestibular lesions (VL) on the changes in muscle and bone induced by 3 g hypergravity for 4 weeks in C57BL/6J mice. Quantitative computed tomography analysis revealed that hypergravity increased muscle mass surrounding the tibia and trabecular bone mineral content, adjusting for body weight in mice. Hypergravity did not affect cortical bone and fat masses surrounding the tibia. Vestibular lesions blunted the increases in muscle and bone masses induced by hypergravity. Histological analysis showed that hypergravity elevated the cross‐sectional area of myofiber in the soleus muscle. The mRNA levels of myogenic genes such as MyoD, Myf6, and myogenin in the soleus muscle were elevated in mice exposed to hypergravity. Vestibular lesions attenuated myofiber size and the mRNA levels of myogenic differentiation markers enhanced by hypergravity in the soleus muscle. Propranolol, a β‐blocker, antagonized the changes in muscle induced by hypergravity. In conclusion, this study is the first to demonstrate that gravity changes affect muscle and bone through vestibular signals and subsequent sympathetic outflow in mice.

Highlights

Mechanical stress markedly influences both muscle and bone (Wu et al 2011)
The reduction in food intake induced by hypergravity was gradually ameliorated, the body weight of the rats subjected to hypergravity was still lower than that of the control rats at day 14 (Abe et al 2010)
We considered that the body weight reductions induced by hypergravity in the present study might conceal the changes in muscle, bone, and fat mass

Summary

Introduction

Mechanical stress markedly influences both muscle and bone (Wu et al 2011). Several studies suggest that lowmagnitude mechanical impacts affect muscle and bone in an anabolic manner (Colnot et al 2012; Evans et al 2013). Muscle wasting and osteoporosis are serious problems in conditions of reduced mechanical stress such as immobilization. Physiological Reports published by Wiley Periodicals, Inc. on behalf of the American Physiological Society and The Physiological Society.

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