Nuclear Accumulation of HSP70 in Mouse Skeletal Muscles in Response to Heat Stress, Aging, and Unloading With or Without Reloading.

Antonios Apostolopoulos,Megumi Aoshima,Kodai Nakamura,Rika Ito,Katsumasa Goto,Ayane Nakamura,Shingo Yokoyama,Risa Fujimoto

doi:10.3389/fgene.2018.00617

Antonios Apostolopoulos, Megumi Aoshima + Show 6 more

Open Access

https://doi.org/10.3389/fgene.2018.00617

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Abstract

The purpose of this study was to investigate the nuclear accumulation of heat shock protein 70 (HSP70), a molecular chaperonin in mouse skeletal muscle in response to aging, heat stress, and hindlimb unloading with or without reloading. Profiles of HSP70-specific nuclear transporter Hikeshi in skeletal muscles were also evaluated. Heat stress-associated nuclear accumulation of HSP70 was observed in slow soleus (SOL) and fast plantaris (PLA) muscles of young (10-week-old) mice. Mean nuclear expression level of HSP70 in slow medial gastrocnemius (MGAS) and PLA muscles of aged (100-week-old) mice increased ~4.8 and ~1.7 times, compared to that of young (10-week-old) mice. Reloading following 2-week hindlimb unloading caused accumulation of HSP70 in myonuclei in MGAS and PLA of young mice ( p < 0.05). However, reloading-associated nuclear accumulation of HSP70 was not observed in both types of muscles of aged mice. On the other hand, 2-week hindlimb unloading had no impact on the nuclear accumulation of HSP70 in both muscles of young and aged mice. Nuclear expression level of Hikeshi in both MGAS and PLA in mice was suppressed by aging. No significant changes in the nuclear Hikeshi in both muscles were induced by unloading with or without reloading. Results of this study indicate that the nuclear accumulation of HSP70 might show a protective response against cellular stresses in skeletal muscle and that the protective response may be suppressed by aging. Protective response to aging might depend on muscle fiber types.

Highlights

Skeletal muscle has a great potential in response to various environmental stimuli
We investigated the effects of 1-h heat stress on the nuclear accumulation of heat shock protein 70 (HSP70) in slow SOL and fast PLA muscles
The present study demonstrated heat stress-associated nuclear accumulation of HSP70 in slow SOL and fast PLA muscles

Summary

Introduction

Mechanical loading is one of the most important factors that regulates skeletal muscle mass. Increase in mechanical load on skeletal muscle results in hypertrophy, whereas unloading such as in spaceflight or hindlimb suspension results in atrophy Aging causes decrease in skeletal muscle function and mass, so-called sarcopenia (Rosenberg, 1997; Frontera et al, 2000), which is dominant in fast muscle (Evans and Cambell, 1993). The molecular mechanism of sarcopenia might be different from that of unloading-associated muscle atrophy, which is dominant in slow skeletal muscle, and a slow-to-fast transition shift of myosin phenotypes is observed in unloading-associated atrophied muscle (Templeton et al, 1984; Ohira et al, 1992). The reason why aging-associated muscle atrophy is dominant in fast muscle remains unclear

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