We previously identified a common set of genes, termed atrogenes, whose expression is coordinately induced or suppressed in muscle during systemic wasting states (fasting, cancer cachexia, renal failure, diabetes). To determine whether this transcriptional program also functions during atrophy resulting from loss of contractile activity and whether atrogene expression correlates with the rate of muscle weight loss, we used cDNA microarrays and RT-polymerase chain reaction to analyze changes in mRNA from rat gastrocnemius during disuse atrophy induced by denervation or spinal cord isolation. Three days after Den or SI, the rate of muscle weight loss was greatest, and 78% of the atrogenes identified during systemic catabolic states were induced or repressed. Of particular interest were the large inductions of key ubiquitin ligases, atrogin-1 (35- to 44-fold) and MuRF1 (12- to 22-fold), and the suppression of PGC-1alpha and PGC-1beta coactivators (15-fold). When atrophy slowed (day 14), the expression of 92% of these atrogenes returned toward basal levels. At 28 days, the atrophy-inducing transcription factor, FoxO1, was still induced and may be important in maintaining the "atrophied" state. Thus, 1) the atrophy associated with systemic catabolic states and following disuse involves similar transcriptional adaptations; and 2) disuse atrophy proceeds through multiple phases corresponding to rapidly atrophying and atrophied muscles that involve distinct transcriptional patterns.

Sacheck, Jennifer M., Akira Ohtsuka, S. Christine McLary, and Alfred L. Goldberg. IGF-I stimulates muscle growth by suppressing protein breakdown and expression of atrophy-related ubiquitin ligases, atrogin-1 and MuRF1. Am J Physiol Endocrinol Metab

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The impact of aging on the cytokine response of human skeletal muscle to exercise-induced injury remains poorly understood. We enrolled physically active, young (23-35 years old, n=15) and old (66-78 years old, n=15) men to perform 45 min of downhill running (16% descent) at 75% VO2max. Biopsies of vastus lateralis were obtained 24 h before and 72 h after acute eccentric exercise. Transcripts for inflammatory (TNF-alpha, IL-1beta) and anti-inflammatory cytokines (IL-6, TGF-beta1) were quantified by real-time PCR. Before exercise, cytokine transcripts did not differ with age. At old age, exercise induced a blunted accumulation of transcripts encoding the pan-leukocyte surface marker CD18 (young: 10.1-fold increase, P<0.005; old: 4.7-fold increase, P=0.02; young vs. old: P<0.05). In both age groups, CD18 transcript accumulation strongly correlated with TNF-alpha (young, r=0.87, P<0.001; old, r=0.72, P=0.002) and TGF-beta1 transcript accumulation (young, r=0.80, P<0.001; old, r=0.64, P=0.008). At old age, there was no correlation between IL-1beta and CD18 transcript accumulation. Furthermore, exercise induced IL-6 transcript accumulation in young (3.6-fold, P=0.057) but not in old men. Our results suggest that aging impairs the adaptive response of human skeletal muscle to eccentric exercise by differential modulation of a discrete set of inflammatory and anti-inflammatory cytokine genes.