UC San Diego

Heat shock protein 72 (HSP72) is a cytoprotective element that is induced during conditions of cell stress, and which has been shown to restore intracellular homeostasis following cell stress in a variety of tissues, including skeletal muscle. Exercise is a non-specific stress, particularly to skeletal muscle, and it has been previously demonstrated in whole animal and human preparations that exercise can induce elevations in skeletal muscle HSP72 transcription. However, due to fiber -type and muscle recruitment heterogeneity, generation of heat, and the multitude of intracellular disruptions which may occur during whole body exercise, the mechanisms of transcriptional activation remain unknown. This dissertation extends previous knowledge of exercise- induced HSP72 activation from whole animal and human models to the single cell level. Specifically, this dissertation describes the development of an isolated single skeletal muscle fiber model of contraction- activated elevation in HSP72 mRNA via development of quantitative PCR methodology enhanced for these single fibers. This model is used to demonstrate the temporal kinetics of contraction-induced increases in HSP72 mRNA in skeletal muscle, and to test the hypotheses that increased HSP72 mRNA transcription following contractions in single skeletal muscle fibers is independent of the development of heat or extracellular signaling sources, and dependent on the development of fatigue, and on fiber type. Finally this model is employed to test the hypotheses that free cytosolic Ca²⁺, alterations in phosporylation potential and/or reactive oxygen species generation contribute to contraction-induced elevations of HSP72 mRNA in single skeletal muscle fibers