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Skeletal muscle interleukin 15 promotes CD8(+) T-cell function and autoimmune myositis.

Huang PL, Hou MS, Wang SW, Chang CL, Liou YH, Liao NS - Skelet Muscle (2015)

Bottom Line: Consistently, deficiency of endogenous IL-15 affected neither skeletal muscle growth nor its responses to TNF-α and IFN-γ.On the other hand, the cytokine-stimulated skeletal muscle cells presented antigen and provided IL-15 to promote the effector function of memory-like CD8(+) T cells.These findings together indicate that skeletal muscle IL-15 directly regulates immune effector cells but not muscle cells and thus presents a potential therapeutic target for myositis.

View Article: PubMed Central - PubMed

Affiliation: Molecular Cell Biology, Taiwan International Graduate Program, Institute of Molecular Biology, Academia Sinica, and Graduate Institute of Life Sciences, National Defense Medical Center, Taipei, Taiwan ; Institute of Molecular Biology, Academia Sinica, Taipei, 11529 Taiwan.

ABSTRACT

Background: Interleukin 15 (IL-15) is thought to be abundant in the skeletal muscle under steady state conditions based on RNA expression; however, the IL-15 RNA level may not reflect the protein level due to post-transcriptional regulation. Although exogenous protein treatment and overexpression studies indicated IL-15 functions in the skeletal muscle, how the skeletal muscle cell uses IL-15 remains unclear. In myositis patients, IL-15 protein is up-regulated in the skeletal muscle. Given the supporting role of IL-15 in CD8(+) T-cell survival and activation and the pathogenic role of cytotoxic CD8(+) T cells in polymyositis and inclusion-body myositis, we hypothesize that IL-15 produced by the inflamed skeletal muscle promotes myositis via CD8(+) T cells.

Methods: Expression of IL-15 and IL-15 receptors at the protein level by skeletal muscle cells were examined under steady state and cytokine stimulation conditions. The functions of IL-15 in the skeletal muscle were investigated using Il15 knockout (Il15 (-/-) ) mice. The immune regulatory role of skeletal muscle IL-15 was determined by co-culturing cytokine-stimulated muscle cells and memory-like CD8(+) T cells in vitro and by inducing autoimmune myositis in skeletal-muscle-specific Il15 (-/-) mice.

Results: We found that the IL-15 protein was not expressed by skeletal muscle cells under steady state condition but induced by tumor necrosis factor alpha (TNF-α) and interferon gamma (IFN-γ) stimulation and expressed as IL-15/IL-15 receptor alpha (IL-15Rα) complex. Skeletal muscle cells expressed a scanty amount of IL-15 receptor beta (IL-15Rβ) under either conditions and only responded to a high concentration of IL-15 hyperagonist, but not IL-15. Consistently, deficiency of endogenous IL-15 affected neither skeletal muscle growth nor its responses to TNF-α and IFN-γ. On the other hand, the cytokine-stimulated skeletal muscle cells presented antigen and provided IL-15 to promote the effector function of memory-like CD8(+) T cells. Genetic ablation of Il15 in skeletal muscle cells greatly ameliorated autoimmune myositis in mice.

Conclusions: These findings together indicate that skeletal muscle IL-15 directly regulates immune effector cells but not muscle cells and thus presents a potential therapeutic target for myositis.

No MeSH data available.


Related in: MedlinePlus

IL-15 deficiency does not affect the responses of primary myotube to TNF-α and IFN-γ stimulation. a–c Expression profiling of genes involved in the regulation of skeletal muscle mass and immune system in wt and Il15−/− primary myotubes. Samples were collected 24 h after TNF-α and IFN-γ treatment and analyzed by qPCR. Data are mean ± SEM of triplicates. Data are representative of two independent experiments with similar results. *p < 0.05, **p < 0.01, ***p < 0.001
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Fig4: IL-15 deficiency does not affect the responses of primary myotube to TNF-α and IFN-γ stimulation. a–c Expression profiling of genes involved in the regulation of skeletal muscle mass and immune system in wt and Il15−/− primary myotubes. Samples were collected 24 h after TNF-α and IFN-γ treatment and analyzed by qPCR. Data are mean ± SEM of triplicates. Data are representative of two independent experiments with similar results. *p < 0.05, **p < 0.01, ***p < 0.001

Mentions: As TNF-α and IFN-γ induced abundant expression of IL-15/IL-15Rα on skeletal muscle cells, the local concentration of IL-15/IL-15Rα trans-presentation may be high enough to trigger signaling through the limited number of IL-15Rβ/γc on adjacent muscle cells. We thus examined whether IL-15 affects the response of the skeletal muscle to TNF-α and IFN-γ by comparing wild type (wt) and Il15−/− primary myotubes. As TNF-α and IFN-γ induce muscle wasting under cancer cachexia and IL-15 was shown to prevent it [16, 42, 43], we first examined genes that regulate muscle mass. Upon TNF-α and IFN-γ stimulation, wt and Il15−/− primary myotubes showed similar reduction in the hypertrophy-related genes Igf1 and Myh4 and increase in the atrophy-related gene iNos (Fig. 4a). We next examined the immune regulatory genes affected by IL-15 in immune cells [44–48]. We found that TNF-α and IFN-γ induced the expression of immune regulatory genes in wt and Il15−/− primary myotubes to similar extents, including molecules in the MHC class I antigen presentation pathway and for T-cell co-stimulation and inhibition, chemokines, and cell adhesion molecules (Fig. 4b, c). These results indicate that skeletal muscle IL-15 does not affect the expression of protein homeostasis and immune regulation genes by skeletal muscle cells in response to TNF-α and IFN-γ, which is consistent with the idea that the muscle cells do not use their own IL-15.Fig. 4


Skeletal muscle interleukin 15 promotes CD8(+) T-cell function and autoimmune myositis.

Huang PL, Hou MS, Wang SW, Chang CL, Liou YH, Liao NS - Skelet Muscle (2015)

IL-15 deficiency does not affect the responses of primary myotube to TNF-α and IFN-γ stimulation. a–c Expression profiling of genes involved in the regulation of skeletal muscle mass and immune system in wt and Il15−/− primary myotubes. Samples were collected 24 h after TNF-α and IFN-γ treatment and analyzed by qPCR. Data are mean ± SEM of triplicates. Data are representative of two independent experiments with similar results. *p < 0.05, **p < 0.01, ***p < 0.001
© Copyright Policy - OpenAccess
Related In: Results  -  Collection

License 1 - License 2
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getmorefigures.php?uid=PMC4584479&req=5

Fig4: IL-15 deficiency does not affect the responses of primary myotube to TNF-α and IFN-γ stimulation. a–c Expression profiling of genes involved in the regulation of skeletal muscle mass and immune system in wt and Il15−/− primary myotubes. Samples were collected 24 h after TNF-α and IFN-γ treatment and analyzed by qPCR. Data are mean ± SEM of triplicates. Data are representative of two independent experiments with similar results. *p < 0.05, **p < 0.01, ***p < 0.001
Mentions: As TNF-α and IFN-γ induced abundant expression of IL-15/IL-15Rα on skeletal muscle cells, the local concentration of IL-15/IL-15Rα trans-presentation may be high enough to trigger signaling through the limited number of IL-15Rβ/γc on adjacent muscle cells. We thus examined whether IL-15 affects the response of the skeletal muscle to TNF-α and IFN-γ by comparing wild type (wt) and Il15−/− primary myotubes. As TNF-α and IFN-γ induce muscle wasting under cancer cachexia and IL-15 was shown to prevent it [16, 42, 43], we first examined genes that regulate muscle mass. Upon TNF-α and IFN-γ stimulation, wt and Il15−/− primary myotubes showed similar reduction in the hypertrophy-related genes Igf1 and Myh4 and increase in the atrophy-related gene iNos (Fig. 4a). We next examined the immune regulatory genes affected by IL-15 in immune cells [44–48]. We found that TNF-α and IFN-γ induced the expression of immune regulatory genes in wt and Il15−/− primary myotubes to similar extents, including molecules in the MHC class I antigen presentation pathway and for T-cell co-stimulation and inhibition, chemokines, and cell adhesion molecules (Fig. 4b, c). These results indicate that skeletal muscle IL-15 does not affect the expression of protein homeostasis and immune regulation genes by skeletal muscle cells in response to TNF-α and IFN-γ, which is consistent with the idea that the muscle cells do not use their own IL-15.Fig. 4

Bottom Line: Consistently, deficiency of endogenous IL-15 affected neither skeletal muscle growth nor its responses to TNF-α and IFN-γ.On the other hand, the cytokine-stimulated skeletal muscle cells presented antigen and provided IL-15 to promote the effector function of memory-like CD8(+) T cells.These findings together indicate that skeletal muscle IL-15 directly regulates immune effector cells but not muscle cells and thus presents a potential therapeutic target for myositis.

View Article: PubMed Central - PubMed

Affiliation: Molecular Cell Biology, Taiwan International Graduate Program, Institute of Molecular Biology, Academia Sinica, and Graduate Institute of Life Sciences, National Defense Medical Center, Taipei, Taiwan ; Institute of Molecular Biology, Academia Sinica, Taipei, 11529 Taiwan.

ABSTRACT

Background: Interleukin 15 (IL-15) is thought to be abundant in the skeletal muscle under steady state conditions based on RNA expression; however, the IL-15 RNA level may not reflect the protein level due to post-transcriptional regulation. Although exogenous protein treatment and overexpression studies indicated IL-15 functions in the skeletal muscle, how the skeletal muscle cell uses IL-15 remains unclear. In myositis patients, IL-15 protein is up-regulated in the skeletal muscle. Given the supporting role of IL-15 in CD8(+) T-cell survival and activation and the pathogenic role of cytotoxic CD8(+) T cells in polymyositis and inclusion-body myositis, we hypothesize that IL-15 produced by the inflamed skeletal muscle promotes myositis via CD8(+) T cells.

Methods: Expression of IL-15 and IL-15 receptors at the protein level by skeletal muscle cells were examined under steady state and cytokine stimulation conditions. The functions of IL-15 in the skeletal muscle were investigated using Il15 knockout (Il15 (-/-) ) mice. The immune regulatory role of skeletal muscle IL-15 was determined by co-culturing cytokine-stimulated muscle cells and memory-like CD8(+) T cells in vitro and by inducing autoimmune myositis in skeletal-muscle-specific Il15 (-/-) mice.

Results: We found that the IL-15 protein was not expressed by skeletal muscle cells under steady state condition but induced by tumor necrosis factor alpha (TNF-α) and interferon gamma (IFN-γ) stimulation and expressed as IL-15/IL-15 receptor alpha (IL-15Rα) complex. Skeletal muscle cells expressed a scanty amount of IL-15 receptor beta (IL-15Rβ) under either conditions and only responded to a high concentration of IL-15 hyperagonist, but not IL-15. Consistently, deficiency of endogenous IL-15 affected neither skeletal muscle growth nor its responses to TNF-α and IFN-γ. On the other hand, the cytokine-stimulated skeletal muscle cells presented antigen and provided IL-15 to promote the effector function of memory-like CD8(+) T cells. Genetic ablation of Il15 in skeletal muscle cells greatly ameliorated autoimmune myositis in mice.

Conclusions: These findings together indicate that skeletal muscle IL-15 directly regulates immune effector cells but not muscle cells and thus presents a potential therapeutic target for myositis.

No MeSH data available.


Related in: MedlinePlus