Insulin-like growth factor-I inhibits lysosomal and proteasome-dependent proteolysis in skeletal muscle after burn injury

Fang, C-Hui.; Li, B-Guo.; Wray, C.J.; Hasselgren, P-Olof.

Journal of Burn Care and Rehabilitation 23(5): 318-325


ISSN/ISBN: 0273-8481
PMID: 12352132
DOI: 10.1097/00004630-200209000-00003
Accession: 010857995

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Previous studies suggest that insulin-like growth factor-I (IGF-I) inhibits burn-induced muscle wasting mainly by reducing muscle protein degradation. The intracellular mechanisms of this effect of IGF-I are not known. In the present study, we examined the influence of IGF-I on individual proteolytic pathways in muscles from burned rats. Extensor digitorum longus muscles from burned rats were incubated with specific blockers of lysosomal, calcium-calpain-dependent, and ubiquitin-proteasome-dependent proteolytic pathways in the absence or presence of IGF-I. In addition, cathepsin B and L activities and 20S proteasome activity were determined. IGF-I inhibited lysosomal and ubiquitin-proteasome-dependent protein breakdown in skeletal muscle from burned rats by 70 and 90%, respectively, but did not influence calcium-calpain-dependent protein breakdown. The hormone blocked the burn-induced increase in cathepsin B and L activities but did not reduce 20S proteasome activity. Results are important because they provide novel information about intracellular mechanisms by which IGF-I inhibits the catabolic response to burn injury in skeletal muscle.