Upregulation of HSP72 in Reloading Rat Soleus Muscle after Prolonged Hindlimb Unloading

Abstract

The hind-limb suspension is an established method to unload hind-limb muscles and is largely known to induce muscle fiber atrophy, especially in an antigravity slow soleus muscle. The ankle joints of rat are hyper-extended in response to hind-limb suspension, therefore, the soleus muscles are passively shortened and tension development is inhibited even when the active electromyogram (EMG) is present [1,2]. The hind-limb unloading (HU) changes the myosin heavy chain (MHC) phenotypes and contractile properties in the rat soleus muscle toward the "fast" type [3][4][5][6]. These responses are very similar to those observed after exposure to actual microgravity [1,[7][8][9][10][11]. Thus the functional properties of the soleus muscle seem to depend on the gravitational and/or weight-bearing conditions.Heat shock proteins (HSPs) are observed in any types of tissues or organs [12]. Within several types of HSPs, a 70 kDa HSP called HSP72 is known as a heat-or stress-inducible protein in mammalian skeletal muscles [13][14][15]. It is proposed that HSPs including HSP72 have an important role to maintain the homeostasis of cells and to protect tissues and organs from heat or other types of stresses [12,13]. Although the exact functions are not clear in mammalian skeletal muscles, some studies suggest that HSP72 can protect muscle damage or atrophy [16,17]. We have previously reported that HSP72 was decreased in the slow soleus and fast plantaris muscles of rats following short-term (5 d) of HU combined with tenotomy and/or denervation, and the expression level of HSP72 was paralleled to the muscle weight [18]. Our results Japanese Journal of Physiology Vol. 53, No. 4, 2003 281Japanese Journal of Physiology, 53, 281-286, 2003 Key words: heat shock protein, hind-limb unloading, reloading, soleus, rat. Abstract:To clarify the changes of heat shock protein (HSP) 72 in the rat soleus muscle after hind-limb unloading (HU) and during reloading, 7-week-old male Wistar rats were hind-limb-suspended for 9 weeks, thereafter ambulatory recovery was permitted for 8 weeks. The body and absolute soleus weights were significantly lower in the HU than in the age-matched control group after HU and during reloading. The soleus weight relative to body weight was also significantly lower in the HU than in the age-matched control group at the end of 9 weeks of suspension, but returned to the control level after 2 weeks of reloading. The HSP72 content decreased to 38%of the control level after HU and conversely increased to 165 and 175% of the control level after 2 and 4 weeks of reloading, respectively. The HSP72 content returned to the control level after 8 weeks of reloading. Thus our results showed that the expression of HSP72 was downregulated by HU and upregulated temporally over the level of the control during the reloading period, and they suggested that these down-and up-regulations of HSP72 may be related to many factors including mechanical stress or load applied to the muscle.

Role(s) of nucleoli and phosphorylation of ribosomal protein S6 and/or HSP27 in the regulation of muscle mass

“…It was also reported that the protein synthesis activity was suppressed in the soleus muscle following the hindlimb unloading by tail suspension (10). Furthermore, the expression of the heat shock protein (HSP), which is a molecular chaperone, decreased by the unloading of muscle (14,31). These results clearly indicate that load applied is an important factor for muscle plasticity.…”

Diathermy treatment increases heat shock protein expression in female, but not male skeletal muscle

“…In animal models of unloading there is a substantial decline in Hsp70 (Desplanches et al 2004;Lawler et al 2006;Oishi et al 2003b) and Hsp27p (Huey et al 2005;Huey et al 2004) content, suggesting they may play important roles in the maintenance of muscle mass. The role of Hsps as cytoprotective agents has shown promise.…”

Gene Expression Levels of Heat Shock Proteins in the Soleus and Plantaris Muscles of Rats after Hindlimb Suspension or Spaceflight

“…It has been reported that gravitational unloading as a result of actual spacefl ight [1][2][3] or of simulation model, i.e., hindlimb suspension [4][5][6][7], inhibits the antigravity activity of skeletal muscles and modulates the neuromuscular properties in rats. Fiber atrophy and a shift from the slowto the fast-twitch phenotype in the fibers of rat skeletal muscles, predominantly in the antigravity slow-twitch muscles, are observed following hindlimb suspension [8].…”