Anabolic steroids prevent disuse atrophy and reverse atrophy caused by glucocorticoids. To determine whether these beneficial effects extend to denervation atrophy, we tested whether nandrolone blocked denervation atrophy acutely or reversed subacute denervation atrophy. We also tested the association of such anabolic effects with expression of MAFbx, MuRF1 (both of which accelerate denervation atrophy), and IGF-1 (which prevents such atrophy). When begun at the time of denervation, nandrolone did not alter atrophy or expression of MAFbx, MuRF1, or IGF-1 measured 3, 7, or 14 days thereafter. When nandrolone administration was begun 28 days after denervation, atrophy was significantly reduced 7 and 28 days later (16% and 30%, respectively), and this was associated with significant reductions in expression of MAFbx and MuRF1, without alterations in the expression of IGF-1. The findings indicate that the actions of nandrolone depend on time after nerve transection and that the timing of anabolic steroid administration is an important determinant of responses of atrophying muscle to these agents.

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Causes of disuse atrophy include loss of upper motor neurons, which occurs in spinal cord injury (SCI) or lower motor neurons (denervation). Whereas denervation quickly results in muscle fibrillations, SCI causes delayed onset of muscle spasticity. To compare the influence of denervation or SCI on muscle atrophy and atrophy-related gene expression, male rats had transection of either the spinal cord or sciatic nerve and were sacrificed 3, 7, or 14 days later. Rates of atrophy increased gradually over the first week after denervation and then were constant. In contrast, atrophy after SCI peaked at 1 week, then declined sharply. The greater atrophy after SCI compared to denervation was preceded by high levels of ubiquitin ligase genes, MAFbx and MuRF1, which then also markedly declined. After denervation, however, expression of these genes remained elevated at lower levels throughout the 2-week time course. Interestingly, expression of the muscle growth factor, IGF-1 was increased at 3 days after denervation when fibrillation also peaks compared to SCI. Expression of IGF-1R, GADD45, myogenin, and Runx1 were also initially increased after denervation or SCI, with later declines in expression levels which correlated less well with rates of atrophy. Thus, there were significant time-dependent differences in muscle atrophy and MAFbx, MuRF1, and IGF-1 expression following SCI or denervation which may result from distinct temporal patterns of spontaneous muscle contractile activity due to injury to upper versus lower motor neurons.

Testosterone stimulates the expression of IGF-I in cells and tissues that include prostate, muscle and muscle satellite cells, and the uterus. Here, the molecular mechanisms of this effect of testosterone were explored. Testosterone increased IGF-I mRNA levels in HepG2 and LNCaP cells and stimulated the activity of reporter genes controlled by 1.6 kb of the upstream promoter of the human IGF-I gene. An androgen-responsive region that was located between -1320 and -1420 bases upstream of the first codon was identified by truncation studies. The androgen-responsive region was found to contain two sequences resembling known androgen receptor (AR)-binding sites from the Pem1 gene. Reporter genes incorporating these sequences were strongly stimulated by androgens. Each of the androgen-responsive elements (AREs) bound recombinant AR-DNA-binding domain in gel-shift experiments; binding was greatly enhanced by sequences flanking the apparent AR-binding half-sites. Testosterone induced recruitment of AR to sequences of genomic DNA containing these AREs. The two AREs were activated 5-fold more by AR than glucocorticoid receptor. Collectively, these findings indicate the presence of two AREs within the IGF-I upstream promoter that act in cis to activate IGF-I expression. These AREs seem likely to contribute to the up-regulation of the IGF-I gene in prostate tissues, HepG2 cells, and potentially other tissues.

Glucocorticoids are a well-recognized and common cause of muscle atrophy that can be prevented by testosterone. However, the molecular mechanisms underlying such protection have not been described. Thus, the global effects of testosterone on dexamethasone-induced changes in gene expression were evaluated in rat gastrocnemius muscle using DNA microarrays. Gene expression was analyzed after 7-d administration of dexamethasone, dexamethasone plus testosterone, or vehicle. Dexamethasone changed expression of 876 probe sets by at least 2-fold. Among these, 474 probe sets were changed by at least 2-fold in the opposite direction in the dexamethasone plus testosterone group (genes in opposition). Major biological themes represented by genes in opposition included IGF-I signaling, myogenesis and muscle development, and cell cycle progression. Testosterone completely prevented the 22-fold increase in expression of the mammalian target of rapamycin (mTOR) inhibitor regulated in development and DNA damage responses 1 (REDD1), and attenuated dexamethasone induced increased expression of eIF4E binding protein 1, Forkhead box O1, and the p85 regulatory subunit of the IGF-I receptor but prevented decreased expression of IRS-1. Testosterone attenuated increases in REDD1 protein in skeletal muscle and L6 myoblasts and prevented dephosphorylation of p70S6 kinase at the mTOR-dependent site Thr389 in L6 myoblast cells. Effects of testosterone on REDD1 mRNA levels occurred within 1 h, required the androgen receptor, were blocked by bicalutamide, and were due to inhibition of transcriptional activation of REDD1 by dexamethasone. These data suggest that testosterone blocks dexamethasone-induced changes in expression of REDD1 and other genes that collectively would otherwise down-regulate mTOR activity and hence also down-regulate protein synthesis.

The findings demonstrate an ability of LIV to improve selected biomarkers of bone turnover and gene expression and to reduce osteoclastogenesis. The study indicates a possibility that LIV initiated earlier after SCI and/or continued for a longer duration would increase bone mass.

Spinal cord injury (SCI) results in atrophy of skeletal muscle and changes from slow oxidative to fast glycolytic fibers, which may reflect reduced levels of peroxisome proliferator-activated receptor gamma coactivator-1a (PGC-1a), increased myostatin signaling, or both. In animals, testosterone reduces loss of muscle fiber crosssectional area and activity of enzymes of energy metabolism. To identify the molecular mechanisms behind the benefits of androgens on paralyzed muscle, male rats were spinal cord transected and treated for 8 weeks with vehicle, testosterone at a physiological replacement dose, or testosterone plus nandrolone, an anabolic steroid. Treatments were initiated immediately after SCI and continued until the day animals were euthanized. In the SCI animals, gastrocnemius muscle mass was significantly increased by testosterone plus nandrolone, but not by testosterone alone. Both treatments significantly reduced nuclear content of Smad2/3 and mRNA levels of activin receptor IIB and follistatin-like 3. Testosterone alone or with nandrolone reversed SCI-induced declines in cellular and nuclear levels of PGC-1a protein and PGC-1a mRNA levels. For PGC-1a target genes, testosterone plus nandrolone partially reversed SCI-induced decreases in levels of proteins without corresponding increases in their mRNA levels. Thus, the findings demonstrate that following SCI, signaling through activin receptors and Smad2/3 is increased, and that androgens suppress activation of this signaling pathway. The findings also indicate that androgens upregulate PGC-1a in paralyzed muscle and promote its nuclear localization, but that these effects are insufficient to fully activate transcription of PGC-1a target genes. Furthermore, the transcription of these genes is not tightly coupled with their translation.