Proteolytic gene expression differs at rest and after resistance exercise between young and old women

Abstract

Background. Skeletal muscle atrophy in rodents is associated with increased gene expression of proteolytic markers muscle-RING-finger protein 1 (MuRF-1) and atrogin-1. In humans with age-related muscle atrophy, known as sarcopenia, little is known about these key proteolytic biomarkers. Therefore, the purpose of this investigation was 2-fold: (i) measure messenger RNA (mRNA) expression of proteolytic genes MuRF-1, atrogin-1, forkhead box (FOXO)3A, and tumor necrosis factor-α (TNF-α) in young and old women at rest, and (ii) measure these proteolytic genes in response to an acute resistance exercise (RE) bout, a known hypertrophic stimulus. Methods. A group of old women (OW: n = 6, 85 ± 1 years, thigh muscle = 89 ± 4 cm2) and young women (YW: n = 8, 23 ± 2 years, thigh muscle = 122 ± 6 cm2) performed three sets of 10 knee extensions at 70% of one-repetition maximum. Muscle biopsies were taken from the vastus lateralis before and 4 hours after RE. Using real-time reverse transcription-polymerase chain reaction (RT-PCR), mRNA was amplified and normalized to GAPDH. Results. At rest, OW expressed higher mRNA levels of MuRF-1 (p = .04) and FOXO3A (p = .001) compared to YW. In response to RE, there was an age effect (p = .01) in the induction of atrogin-1 (OW: 2.5-fold). Both YW and OW had an induction (p = .001) in MuRF-1 (YW: 3.6-fold; OW: 2.6-fold) with RE. Conclusions. These data show that the regulation of ubiquitin proteasome-related genes involved with muscle atrophy are altered in very old women (> 80 years). This finding is manifested both at rest and in response to RE, which may contribute to the large degree of muscle loss with age. Copyright 2007 by The Gerontological Society of America.