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

Rapid transcription of the survival transcript, inducible heat shock protein 70 (hsp70), is critical for mounting cytoprotection against severe cellular stress, like elevated temperature. Previous investigations have demonstrated that exercise-induced expression of Hsp70 protein occurs in a fiber-specific pattern; however, the activation pattern of hsp70 mRNA expression remains unclear in skeletal muscle. Consequentially, the temporal localization of hsp70 mRNA was characterized via in situ hybridization (ISH) experiments examining fast-muscle, white vastus: 1, 3, 10, and 24 h after a single bout of intense treadmill running (1 h, 30 m/min, 6% grade) in rats. The role that the physiologic temperature stress associated with exercise (raising core body temperature to 40.0°C for 15 min (HS-40.0°C)) might play in inducing hsp70 mRNA expression was also explored. In skeletal muscle myofibers (SkM), hsp70 mRNA ISH signal was observed to be concentrated in a punctate manner that was associated with nuclei post-exercise. HS-40°C treatment produced minimal detectable hsp70 mRNA ISH signal in SkM. In large intermyofibrillar blood vessels (BV), peak hsp70 mRNA signal, distributed throughout the vessel wall, was observed 1 h post-exercise. In BV, no differences in hsp70 mRNA signal were observed between HS-40°C and EX-1 h. Results indicate that the majority of hsp70 mRNA is retained in a perinuclear localization in SkM post-exercise. They further suggest a muscle-type specific time course for peak hsp70 mRNA expression. This investigation suggests that the physiologic rise in core temperature associated with exercise per se is not the key stimulus responsible for inducing hsp70 mRNA transcription in SkM.