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. 2019 Oct 1;10(5):e02211-19.
doi: 10.1128/mBio.02211-19.

Pseudomonas aeruginosa Quorum Sensing Molecule Alters Skeletal Muscle Protein Homeostasis by Perturbing the Antioxidant Defense System

Affiliations

Pseudomonas aeruginosa Quorum Sensing Molecule Alters Skeletal Muscle Protein Homeostasis by Perturbing the Antioxidant Defense System

Arunava Bandyopadhaya et al. mBio. .

Erratum in

Abstract

Skeletal muscle function is compromised in many illnesses, including chronic infections. The Pseudomonas aeruginosa quorum sensing (QS) signal, 2-amino acetophenone (2-AA), is produced during acute and chronic infections and excreted in human tissues, including the lungs of cystic fibrosis patients. We have shown that 2-AA facilitates pathogen persistence, likely via its ability to promote the formation of bacterial persister cells, and that it acts as an interkingdom immunomodulatory signal that epigenetically reprograms innate immune functions. Moreover, 2-AA compromises muscle contractility and impacts the expression of genes involved in reactive oxygen species (ROS) homeostasis in skeletal muscle and in mitochondrial functions. Here, we elucidate the molecular mechanisms of 2-AA's impairment of skeletal muscle function and ROS homeostasis. Murine in vivo and differentiated C2C12 myotube cell studies showed that 2-AA promotes ROS generation in skeletal muscle via the modulation of xanthine oxidase (XO) activity, NAD(P)H oxidase2 (NOX2) protein level, and the activity of antioxidant enzymes. ROS accumulation triggers the activity of AMP-activated protein kinase (AMPK), likely upstream of the observed locations of induction of ubiquitin ligases Muscle RING Finger 1 (MuRF1) and Muscle Atrophy F-box (MAFbx), and induces autophagy-related proteins. The protein-level perturbation in skeletal muscle of silent mating type information regulation 2 homolog 1 (SIRT1), peroxisome proliferator-activated receptor gamma coactivator 1 (PGC-1), and uncoupling protein 3 (UCP3) is rescued by the antioxidant N-acetyl-l-cysteine (NAC). Together, these results unveil a novel form of action of a QS bacterial molecule and provide molecular insights into the 2-AA-mediated skeletal muscle dysfunction caused by P. aeruginosaIMPORTANCEPseudomonas aeruginosa, a bacterium that is resistant to treatment, causes serious acute, persistent, and relapsing infections in humans. There is increasing evidence that bacterial excreted small molecules play a critical role during infection. We have shown that a quorum sensing (QS)-regulated excreted small molecule, 2-AA, which is abundantly produced by P. aeruginosa, promotes persistent infections, dampens host inflammation, and triggers mitochondrial dysfunction in skeletal muscle. QS is a cell-to-cell communication system utilized by bacteria to promote collective behaviors. The significance of our study in identifying a mechanism that leads to skeletal muscle dysfunction, via the action of a QS molecule, is that it may open new avenues in the control of muscle loss as a result of infection and sepsis. Given that QS is a common characteristic of prokaryotes, it is possible that 2-AA-like molecules promoting similar effects may exist in other pathogens.

Keywords: 2-amino acetophenone (2-AA); NAD(P)H oxidase 2 (NOX2); Pseudomonas aeruginosa; chronic infections; muscle atrophy; muscle dysfunction; quorum sensing (QS); reactive oxygen species (ROS); skeletal muscle; virulence; xanthine oxidase (XO).

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Figures

FIG 1
FIG 1
Antioxidant treatment rescues 2-AA-induced oxidative stress in murine gastrocnemius muscle. (a) Schematic diagram of 2-AA and NAC treatment in mice. Mice were injected with 2-AA (6.75 mg/kg; i.p.) once, and NAC was given (10 mg/kg; i.p.) once per day. (b and c) ROS production (b) and TAC (c) were measured in skeletal muscle 1 day (1d), 2 days (2d), and 4 days (4d) after 2-AA treatment and 2-AA-plus-NAC treatment (n = 5). The results were expressed as means ± standard deviations (SD). P < 0.05, one-way ANOVA.
FIG 2
FIG 2
Antioxidant enzyme activity in skeletal muscle of 2-AA-treated mice. (a) Levels of SOD (percent inhibition), (b) catalase, (c) GPX, and (d) GST activity were measured in skeletal muscle 1 day, 2 days, and 4 days after 2-AA treatment and 2-AA-plus-NAC treatment (n = 5). The results were expressed as means ± SD. P < 0.05, one-way ANOVA.
FIG 3
FIG 3
Assessment of XO activity and NOX2 protein expression in skeletal muscle of 2-AA-treated mice. (a) XO activity was measured in skeletal muscle 1 day, 2 days, and 4 days after 2-AA treatment and 2-AA-plus-NAC treatment (n = 5 in each group). The results were expressed as means ± SD. P < 0.05, one-way ANOVA. (b) Representative immunoblot of NOX2 in skeletal muscle 1 day, 2 days, and 4 days after 2-AA treatment and 2-AA-plus-NAC treatment. HPRT (bottom) was used as the loading control. Histograms show the relative expression levels of proteins. n = 5 in each group; data represent means ± SD. P < 0.05, one-way ANOVA.
FIG 4
FIG 4
XO and NOX2 inhibitors support the involvement of XO and NOX2 in the 2-AA-mediated initial cellular ROS production in skeletal muscle. (a) Cellular ROS production was measured in differentiated C2C12 myotubes 1 h, 2 h, 3 h, 6 h, 12 h, and 24 h after 2-AA treatment (n = 3; values represent means ± SD; P < 0.05, Student's t test). (b) Inhibition of cellular ROS generation was measured in 2-AA (400 μM)-treated cells with or without allopurinol (50 μM), with or without apocynin (10 μM), with or without gp91ds-tat (50 μM), and with or without NAC (5 mM) for 6 h (n = 3; values represent means ± SD; P < 0.05, one-way ANOVA).
FIG 5
FIG 5
Assessment of the expression of oxidative metabolic regulators in skeletal muscle of 2-AA-treated mice. (Top) Representative immunoblots of PGC-1β, UCP3, SIRT1, and ATP5B in skeletal muscle 1 day, 2 days, and 4 days after 2-AA treatment and 2-AA-plus-NAC treatment. HPRT (bottom blot) was used as the loading control. (Bottom) Histograms show the relative expression levels of proteins. n = 5 in each group; data represent means ± SD. P < 0.05, one-way ANOVA.
FIG 6
FIG 6
Activation of AMPK in skeletal muscle following 2-AA treatment. (Top) Representative immunoblots of pAMPKβ1 (Ser182) in skeletal muscle 1 day, 2 days, and 4 days after 2-AA treatment and 2-AA-plus-NAC treatment. AMPKβ1/2 was used as a control. (Bottom) Histograms show the relative expression levels of proteins. n = 5 in each group; data represent means ± SD. P < 0.05, one-way ANOVA.
FIG 7
FIG 7
Antioxidant treatment reduces the degradation of muscle protein in gastrocnemius muscle promoted by 2-AA. (Top) Immunoblots of MYH and tropomyosin in skeletal muscle 1 day, 2 days, and 4 days after 2-AA treatment and 2-AA-plus-NAC treatment. HPRT (bottom blot) was used as the loading control. (Bottom) Histograms show the relative expression levels of proteins. n = 5 in each group; data represent means ± SD. P < 0.05, one-way ANOVA.
FIG 8
FIG 8
Antioxidant treatment reduces the activation of a ubiquitin-mediated proteasomal pathway in gastrocnemius muscle promoted by 2-AA. (Top) Immunoblot of MuRF1 and MAFbx in skeletal muscle 1 day, 2 days, and 4 days after 2-AA treatment and 2-AA-plus-NAC treatment. HPRT (bottom blot) was used as the loading control. (Bottom) Histograms show the relative expression levels of proteins. n = 5 in each group; data represent means ± SD. P < 0.05, one-way ANOVA.
FIG 9
FIG 9
Activation of autophagy markers in skeletal muscle following 2-AA and NAC treatment. (Top) Representative immunoblots of ATG5, LC3B, and SQSTM1/p62 in skeletal muscle 1 day, 2 days, and 4 days after 2-AA treatment and 2-AA-plus-NAC treatment. HPRT (bottom blot) was used as the loading control. (Bottom) Histograms show the relative expression levels of proteins. n = 5 in each group; data represent means ± SD. P < 0.05, one-way ANOVA.
FIG 10
FIG 10
Effect of AMPK and proteasomal inhibitors on the 2-AA-mediated skeletal muscle degradation in vitro. Representative immunoblots of (a) pAMPKβ1, (b) ubiquitin ligases (MuRF1 and MAFbx), (c) autophagy markers (ATG5, LC3B, and SQSTM1), and (d) MYH and tropomyosin in 2-AA (400 μM)-treated mouse C2C12 myotubes with or without dorsomorphin (10 μM), with or without NAC (5 mM), and/or with or without MG132 (10 μM) for 24 h are shown. β-actin (bottom blot) was used as the loading control. Histograms show the relative expression levels of proteins, and data are representative of results from three independent experiments. n = 3, means ± SD. P < 0.05, one-way ANOVA.
FIG 11
FIG 11
Proposed model of 2-AA’s action in skeletal muscle. 2-AA triggers ROS generation via activating XO activity and NOX2 expression and by impairing the activity of antioxidant enzymes as well as by downregulation of SIRT1 protein. Reduction of PGC-1β protein level impairs ROS detoxification, whereas upregulation of UCP3 gene (25) and protein levels impacts the mitochondrial functions (26), resulting in energy depletion. Energetic exhaustion and oxidative stress increases lead to muscle atrophy by activating AMPK, which controls autophagy and proteasomal degradation as assessed by the activation of autophagy markers ATG5, LC3B, and SQSTM1 and autophagy markers MuRF1 and MAFbx, respectively. NAC can ameliorate 2-AA-induced oxidative stress and thus rescue skeletal muscle protein degradation by scavenging the ROS.

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