Cellular distribution of Hsp70 expression in rat skeletal muscles. Effects of moderate exercise training and chronic hypoxia

Abstract

Rat hindlimb muscles constitutively express the inducible heat shock protein 72 (Hsp70), apparently in proportion to the slow myosin content. Since it remains controversial whether chronic Hsp70 expression reflects the overimposed stress, we investigated Hsp70 cellular distribution in fast muscles of the posterior rat hindlimb after (1) mild exercise training (up to 30 m/min treadmill run for 1 h/day), which induces a remodeling in fast fiber composition, or (2) prolonged exposure to normobaric hypoxia (10%O 2 ), which does not affect fiber-type composition. Both conditions increased significantly protein Hsp70 levels in the skeletal muscle. Immunohistochemistry showed the labeling for Hsp70 in subsets of both slow/ type 1 and fast/type 2A myofibers of control, sedentary, and normoxic rats. Endurance training increased about threefold the percentage of Hsp70-positive myofibers (P<0.001), and changed the distribution of Hsp70 immunoreactivity, which involved a larger subset of both type 2A and intermediate type 2A/2X myofibers (P<0.001) and vascular smooth muscle cells. Hypoxia induced Hsp70 immunoreactivity in smooth muscle cells of veins and did not increase the percentage of Hsp70-positive myofibers; however, sustained exposure to hypoxia affected the distribution of Hsp70 immunoreactivity, which appeared detectable in a very small subset of type 2A fibers, whereas it concentrated in type 1 myofibers (P<0.05) together with the labeling for heme-oxygenase isoform 1, a marker of oxidative stress. Therefore, the chronic induction of Hsp70 expression in rat skeletal muscles is not obligatory related to the slow fiber phenotype but reveals the occurrence of a stress response.

Effects of Combination Therapy of Heat Stress and Muscle Contraction Exercise Induced by Neuromuscular Electrical Stimulation on Disuse Atrophy in the Rat Gastrocnemius

“…Hsp72 expression in cells is also stimulated by heat stress, depletion of glucose, and/or hypoxia [11][12][13][14][15][16][17] . Furthermore, Hsp72 has an important function as a molecular chaperone, whose expression may promote an increased rate of protein synthesis 18,19) .…”

hsp70 mRNA temporal localization in rat skeletal myofibers and blood vessels post-exercise

“…shown to experience greater blood flow (Laughlin and Armstrong 1982) and Hsp70 protein content (Locke et al 1991;Tarricone et al 2008) under resting conditions as compared to white muscle. Indeed, results demonstrated greater hsp70 mRNA ISH signal localized to the skeletal myofibers ( Fig.…”

“…Indeed, Watkins et al (2007) observed minimal variability in intramuscular temperature as measured through probing the belly of vastus lateralis post-exercise (40±0.2°C). However, various modes of exercise tend to induce Hsp70 protein expression in the phenotypically slower contracting and more oxidative myofibers of various skeletal muscles (O'Neill et al 2006;Tarricone et al 2008;Tupling et al 2007), which creates a pattern of differential expression as compared to the neighboring faster and more glycolytic myofibers. In addition to elevated body temperature, the physiologic stress associated with exercise can pose selective homeostatic perturbations to recruited myofibers such as mechanical damage, hypoxia, lowered pH, impaired calcium homeostasis, reactive oxygen species generation, decreased ATP pools, glycogen depletion, and a rise in circulating catecholamines, which have all been implicated in contributing to the activation of the heat shock response (see Noble et al 2008 for review).…”

“…However, Hsp70 protein expression pattern in the vasculature is tissue-specific. For example, in the vasculature of skeletal muscle, enhanced Hsp70 protein expression has been observed to be predominantly localized throughout the smooth muscle portion post-exercise (Tarricone et al 2008). While it is clear that the myocardium becomes protected in response to both exercise and heat stress per se, the role of elevated temperature in inducing Hsp70 protein expression in the vasculature of exercised skeletal muscle remains unknown.…”

Impact of phosphatidylinositide 3-kinase signaling pathway on the cardioprotection induced by intermittent hypoxia

“…This increase was blunted in mice treated with wortmannin, in analogy with the effect led by this PI3K inhibitor on Akt phosphorylation (see later). By contrast, the expression level of Heat Shock Protein 70 kDa (HSP-70) and glucose-regulated protein 94 (GRP94), stress-proteins that were demonstrated to be up-regulated by hypoxia [21,22], remained unchanged. The pro-apoptotic factor endoplasmic reticulum stress-induced transcription factor C/EBP homologous protein (CHOP) was decreased by IH, without any effect led by wortmannin.…”