Heat shock transcription factor 1-deficiency attenuates overloading-associated hypertrophy of mouse soleus muscle.

Hypertrophic stimuli, such as mechanical stress and overloading, induce stress response, which is mediated by heat shock transcription factor 1 (HSF1), and up-regulate heat shock proteins (HSPs) in mammalian skeletal muscles. Therefore, HSF1-associated stress response may play a key role in loading-associated skeletal muscle hypertrophy. The purpose of this study was to investigate the effects of HSF1-deficiency on skeletal muscle hypertrophy caused by overloading. Functional overloading on the left soleus was performed by cutting the distal tendons of gastrocnemius and plantaris muscles for 4 weeks. The right muscle served as the control. Soleus muscles from both hindlimbs were dissected 2 and 4 weeks after the operation. Hypertrophy of soleus muscle in HSF1-null mice was partially inhibited, compared with that in wild-type (C57BL/6J) mice. Absence of HSF1 partially attenuated the increase of muscle wet weight and fiber cross-sectional area of overloaded soleus muscle. Population of Pax7-positive muscle satellite cells in HSF1-null mice was significantly less than that in wild-type mice following 2 weeks of overloading (p<0.05). Significant up-regulations of interleukin (IL)-1β and tumor necrosis factor mRNAs were observed in HSF1-null, but not in wild-type, mice following 2 weeks of overloading. Overloading-related increases of IL-6 and AFT3 mRNA expressions seen after 2 weeks of overloading tended to decrease after 4 weeks in both types of mice. In HSF1-null mice, however, the significant overloading-related increase in the expression of IL-6, not ATF3, mRNA was noted even at 4th week. Inhibition of muscle hypertrophy might be attributed to the greater and prolonged enhancement of IL-6 expression. HSF1 and/or HSF1-mediated stress response may, in part, play a key role in loading-induced skeletal muscle hypertrophy

Expressions of heat shock proteins (HSPs) and heat shock cognate protein (HSC) in soleus muscle.

<p>A: Representative protein expression patterns of HSP25, HSP47, HSC70, HSP72, HSP90α and glyceraldehyde-3-phosphate dehydrogenase (GAPDH). C: control muscle, O: overloaded muscle. B: Changes in the mean expression levels of HSP25, HSP47, HSP70, HSP72, and HSP90α proteins. See <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0077788#pone-0077788-g001" target="_blank">figure 1</a> and <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0077788#pone-0077788-g006" target="_blank">6</a> for other abbreviations. Values are means ± SEM. n  =  6 /group at each time point. *: significant difference at p<0.05.</p

Changes in mean mRNA expression levels of heat shock transcription factor (HSF) 1, HSF2, and HSF4 in soleus muscle during the experimental period.

<p><i>hsf1</i>, HSF1 mRNA; <i>hsf2</i>, HSF2 mRNA; <i>hsf4</i>, HSF4 mRNA. See <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0077788#pone-0077788-g001" target="_blank">figure 1</a> for other abbreviations. Values are means ± SEM. n  =  6 /group at each time point. *: significant difference at p<0.05.</p

Changes in mean mRNA expressions of heat shock protein (HSP) 25, HSP47, HSC70, HSP72, and HSP90α.

<p><i>hsp25</i>, HSP25 mRNA; <i>hsp47</i>, HSP47 mRNA; <i>hsc70</i>, HSC70 mRNA; <i>hsp72</i>, HSP72 mRNA; <i>hsp90α</i>, HSP90α mRNA. See <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0077788#pone-0077788-g001" target="_blank">figure 1</a> for other abbreviations. Values are means ± SEM. n  =  6 /group at each time point. *: significant difference at p<0.05.</p

The rates of increase in the relative muscle weight and protein content to body weight.

<p>Each bar represents the relative value of overloaded muscle vs. the contralateral control muscle, which is 1.0. See <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0077788#pone-0077788-g001" target="_blank">figure 1</a> for other abbreviations. Values are means ± SEM. n  =  6 /group at each time point. *: significant difference at p<0.05.</p