Curcumin prevents lipopolysaccharide‐induced atrogin‐1/MAFbx upregulation and muscle mass loss

Abstract

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. Keywords endotoxemia; ubiquitin-proteasome pathway; p38; AKT; NF-κB Muscle wasting is a major feature of the cachexia associated with such diseases as sepsis, cancer, AIDS, diabetes, uremia, congestive heart failure, and chronic obstructive pulmonary disease (COPD) [Hasselgren, 1995;Tisdale, 1997]. Muscle wasting increases patient morbidity and mortality through disability, injury, osteoporosis, impairment of respiratory function, and depletion of the free amino acid pool for enzyme and antibody production. The progressive loss of body protein becomes lethal when it depletes approximately 40% of lean body mass [Winick, 1979]. However, to date, no drug has been approved for muscle wasting. Muscle wasting is primarily caused by accelerated muscle protein breakdown via the ubiquitin-proteasome pathway . Proteins degraded by this pathway are first covalently linked to a chain of ubiquitin molecules that marks them for rapid breakdown by the 26S proteasome. The selectivity of ubiquitin targeting is primarily a function of ubiquitin ligase (E3 protein) [Hershko and Ciechanover, 1998]. Two muscleenriched ubiquitin ligases, atrogin-1/MAFbx and MuRF1, are rate limiting for muscle protein loss in various catabolic conditions. Expression of these two ubiquitin ligases is upregulated in the muscle of various animal models of muscle atrophy,...

Ghrelin inhibits skeletal muscle protein breakdown in rats with thermal injury through normalizing elevated expression of E3 ubiquitin ligases MuRF1 and MAFbx

“…6). However, there is accumulating evidence to suggest that the pathway(s) mediating muscle proteolysis is (are) more complex than anticipated because there are reports showing 1) that IGF-I downregulated the burn-induced elevation of MuRF1 and MAFbx genes independent of its effect on glucocorticoids (40); 2) that IGF-I could not prevent muscle atrophy induced by proinflammatory cytokines, despite inhibiting MAFbx (9); 3) that TNF-␣ blockade did not prevent the increase of muscle MuRF1 and MAFbx genes in arthritic rats (21); and 4) that MuRF1 and MAFbx genes could be regulated through multiple pathways including those involving AKT, NF-B, and p38 MAPK (34). Moreover, as discussed earlier, direct actions of ghrelin on muscle also could have contributed to attenuated expression of the E3 ligase genes and, hence, to reduced muscle proteolysis (10,20,45,51,67).…”

p38 MAPK links oxidative stress to autophagy-related gene expression in cachectic muscle wasting

“…Since the p38 MAPK pathway has been implicated in mediating oxidative stress-induced muscle-specific E3 ligase MAFbx gene expression and ubiquitin-conjugating activity in skeletal muscle (18,25), which could occur in a fiber typespecific manner (48), we investigated p38 MAPK signaling in glycolytic and oxidative skeletal muscles from endotoxin (LPS, 1 mg/kg ip)-treated mice utilizing an abbreviated time frame (8 h). We measured the relative phosphorylation of p38 in skeletal muscles (presumably ␣/␤-and/or ␥-isoform) and found that phosphorylation of p38 increased in both glycolytic white vastus lateralis muscle (ϩ82%) and oxidative soleus muscle (ϩ41%) compared with control mice injected with saline (Fig.…”

“…A few studies have suggested that the p38 MAPK pathway mediates oxidative stress-induced muscle-specific E3 ligase muscle atrophy F-box protein (MAFbx) gene expression and ubiquitin-conjugating activity in skeletal muscle (18,25), but its role in the autophagy-lysosome system has not been investigated. It is particularly intriguing that oxidative stress-induced activation of p38 MAPK signaling and upregulation of the downstream genes in ubiquitin-proteasome system-mediated protein degradation appears to be independent of the NF-B and the FoxO pathways (9,18). These findings raised the possibility that there is also a link between oxidative stress and the autophagy-lysosome system-mediated protein degradation through the p38 MAPK pathway.…”

Relation between extent of myostatin depletion and muscle growth in mature mice

“…A secondary goal of this study was to examine whether myostatin-deficient muscles have altered expression or phosphorylation of a number of molecules that are thought to be important regulators of muscle mass (10): the serine/ threonine kinase Akt, which promotes mammalian target of rapamycin (mTOR) activity and inhibits Foxo transcription factor activity when activated; p70 S6 kinase (S6k), an mTOR target that promotes protein synthesis when activated by phosphorylation; ribosomal protein S6 (rpS6), a target of S6k; initiation factor 4E-binding protein-1 (4E-BP1), an mTOR target that inhibits translation when it is not phosphorylated; mRNAs encoding the E3 ubiquitin ligases muscle atrophy F-box (MAFbx; also known as atrogin-1) and muscle RING-finger protein-1 (MuRF1), which are regulated by Akt via Foxo transcription factors; and p38 mitogen-activated protein kinase (MAPK), which can promote expression of MAFbx (13,21,43). These molecules were selected for analysis because previous studies have linked the Akt-mTOR and p38 MAPK pathways to myostatin signaling (7,18,22,27,29,32,35,40).…”