Tuberc Respir Dis.  2012 Dec;73(6):312-319. 10.4046/trd.2012.73.6.312.

Role of IL-15 in Sepsis-Induced Skeletal Muscle Atrophy and Proteolysis

• Kim HC
• Cho HY
• Hah YS

• KMID: 1842924
• DOI: http://doi.org/10.4046/trd.2012.73.6.312

Abstract

BACKGROUND
Muscle wasting in sepsis is associated with increased proteolysis. Interleukin-15 (IL-15) has been characterized as an anabolic factor for skeletal muscles. Our study aims to investigate the role of IL-15 in sepsis-induced muscle atrophy and proteolysis.
METHODS
Mice were rendered septic either by cecal ligation and puncture or by intraperitoneal injection of lipopolysaccharide (LPS, 10 mg/kg i.p.). Expression of IL-15 mRNA and protein was determined by reverse transcriptase polymerase chain reaction and Western blot analysis in the control and septic limb muscles. C2C12 skeletal muscle cells were stimulated in vitro with either LPS or dexamethasone in the presence and absence of IL-15 and sampled at different time intervals (24, 48, or 72 hours). IL-15 (10microg/kg) was intraperitoneally administered 6 hours before sepsis induction and limb muscles were sampled after 24 hours of sepsis. Cathepsin L activity was determined to measure muscle proteolysis. Atrogin-1 and muscle-specific ring finger protein 1 (MuRF1) expressions in limb muscle protein lysates was analyzed.
RESULTS
IL-15 mRNA expression was significantly lower in the limb muscles of septic mice compared to that of controls. Cathepsin L activity in C2C12 cells was significantly lower in presence of IL-15, when compared to that observed with individual treatments of LPS or dexamethasone or tumor necrosis factor alpha. Further, the limb muscles of mice pre-treated with IL-15 prior to sepsis induction showed a lower expression of atrogin-1 and MuRF1 than those not pre-treated.
CONCLUSION
IL-15 may play a role in protection against sepsis-induced muscle wasting; thereby, serving as a potential therapeutic target for sepsis-induced skeletal muscle wasting and proteolysis.

Keyword

Interleukin-15; Muscular Atrophy; Proteolysis; Muscle Retardation; Sepsis

MeSH Terms

Animals
Atrophy
Blotting, Western
Cathepsin L
Dexamethasone
Extremities
Fingers
Injections, Intraperitoneal
Interleukin-15
Ligation
Mice
Muscle Proteins
Muscle, Skeletal
Muscles
Muscular Atrophy
Proteolysis
Punctures
Reverse Transcriptase Polymerase Chain Reaction
RNA, Messenger
Sepsis
Tumor Necrosis Factor-alpha
Cathepsin L
Dexamethasone
Interleukin-15
Muscle Proteins
RNA, Messenger
Tumor Necrosis Factor-alpha

Figure

• 

  Figure 1 IL-15 mRNA expression in the limb muscles of the sepsis animal model. (A) IL-15 mRNA expression was measured in TA and EDL limb muscle samples of septic mice by RT-PCR at 16 hours after sepsis induction. (B) IL-15 mRNA expression was compared to the control with densitometry. IL-15 mRNA expression was significantly lower in both TA and EDL muscle samples of septic mice when compared to the control (p<0.05). CLP: cecal ligation and puncture; CON: control; EDL: extensor digitorum longus; GAPDH: glyceraldehyde 3-phosphate dehydrogenase; IL-15: interleukin-15; LPS: lipopolysaccharide; RT-PCR: reverse transcriptase polymerase chain reaction; TA: tibialis anterior.

• 

  Figure 2 IL-15 protein expression in the limb muscles of the sepsis animal model. (A) IL-15 protein expression was measured in TA, EDL, and GN limb muscle samples of septic mice by western blot analysis at 16 hours after sepsis induction. (B) IL-15 protein was compared to the control with densitometry. IL-15 protein expression was significantly lower in only TA muscle samples of septic mice when compared to the control (p<0.05). CLP: cecal ligation and puncture; CON: control; EDL: extensor digitorum longus; GN: gastrocnemius; IL-15: interleukin-15; LPS: lipopolysaccharide; TA: tibialis anterior.

• 

  Figure 3 Expression of muscle atrophy-related genes in the limb muscles of the sepsis animal model. (A) Atrogin-1 and MuRF1 mRNA expression was measured in TA and EDL limb muscle samples of septic mice by RT-PCR at 16 hours after sepsis induction. (B) Atrogin-1 and MuRF1 mRNA expression was compared to the control with densitometry. The mRNA expression of atrogin-1 and MuRF1 significantly increased in TA samples from CLP sepsis mice and in EDL samples from both LPS and CLP sepsis mice compared to the control (p<0.05). CLP: cecal ligation and puncture; CON: control; EDL: extensor digitorum longus; GAPDH: glyceraldehyde 3-phosphate dehydrogenase; LPS: lipopolysaccharide; MuRF1: muscle-specific ring finger protein 1; RT-PCR: reverse transcriptase polymerase chain reaction; TA: tibialis anterior.

• 

  Figure 4 Effect of IL-15 in muscle atrophy and proteolysis in mouse myoblast (C2C12) cell and in limb muscle of sepsis animal model. (A) Cathepsin L enzyme activity in C2C12 cells when incubated with dexamethasone (100 nM/mL), LPS (10µg/mL), or TNF-α (10µg/mL), in the presence or absence of IL-15 (20µg/mL). The activity of cathepsin L was found to be decreased in C2C12 cells co-stimulated with IL-15. (B) The cathepsin L enzyme activity in TA and EDL muscle lysates of mice pretreated with IL-15 (10µg/kg), prior to the induction of sepsis by CLP was significantly decreases as compared to those obtained from mice that had not been pretreated (p<0.05). CLP: cecal ligation and puncture; Dexa: dexamethasone; EDL: extensor digitorum longus; IL-15: interleukin-15; LPS: lipopolysaccharide; TA: tibialis anterior; TNF: tumor necrosis factor.

• 

  Figure 5 Effect of IL-15 in muscle atrophy-related gene expression in the sepsis animal model. (A) RT-PCR analysis of the mRNA expression levels of the muscle atrophy-related genes, atrogin-1 and MuRF1, in muscle lysates derived from limb muscle samples from mice with and without pretreatment with IL-15-prior to the induction of sepsis by cecal ligation and puncture. A marked decrease was seen in the expression of both atrogin-1 (B) and MuRF1 (C) mRNA in muscle lysates derived from GN limb muscle samples from mice pretreated with IL-15, as compared to those obtained from mice that did not undergo IL-15 pretreatment, as well as the control. CLP: cecal ligation and puncture; CON: control; GAPDH: glyceraldehyde 3-phosphate dehydrogenase; GN: gastrocnemius; IL-15: interleukin-15; MuRF1: muscle-specific ring finger protein 1; RT-PCR: reverse transcriptase polymerase chain reaction.

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