Because elevated ubiquitin ligase atrogin-1/MAFbx and MuRF1 mediate skeletal muscle wasting associated with various catabolic conditions, the signaling pathways involved in the upregulation of these genes under pathological conditions are considered therapeutic targets. AKT and NF-κB have been previously shown to regulate the expression of atrogin-1/MAFbx or MuRF1, respectively. In addition, we recently found that p38 MAPK mediates TNF-α upregulation of atrogin-1/MAFbx expression, suggesting that multiple signaling pathways mediate muscle wasting in inflammatory diseases. To date, however, these advances have not resulted in a practical clinical intervention for disease-induced muscle wasting. In the present study, we tested the effect of curcumin—a non-toxic anti-inflammatory reagent that inhibits p38 and NF-κB—on lipopolysaccharide (LPS)-induced muscle wasting in mice. Daily intraperitoneal (i.p.) injection of curcumin (10–60 µg/kg) for 4 days inhibited, in a dose-dependent manner, the LPS-stimulated (1 mg/kg, i.p.) increase of atrogin-1/MAFbx expression in gastrocnemius and extensor digitorum longus (EDL) muscles, resulting in the attenuation of muscle protein loss. It should also be noted that curcumin administration did not alter the basal expression of atrogin-1/MAFbx, nor did it affect LPS-stimulated MuRF1 and polyubiquitin expression. LPS activated p38 and NF-κB, while inhibiting AKT; whereas, curcumin administration inhibited LPS-stimulated p38 activation, without altering the effect of LPS on NF-κB and AKT. These results indicate that curcumin is effective in blocking LPS-induced loss of muscle mass through the inhibition of p38-mediated upregulation of atrogin-1/MAFbx. J. Cell. Biochem. 100: 960–969, 2007. © 2006 Wiley-Liss, Inc.
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