Interleukin-15

[Twitch]

posted by nandi..CEM

Many readers may already be familiar Interleukin-15. This abstract provides a nice introduction to the properties of this cytokine as they relate to anabolism:

Int J Mol Med. 2005 Sep;16(3):471-6. Related Articles, Links


Interleukin-15 decreases proteolysis in skeletal muscle: A direct effect.

Busquets S, Figueras MT, Meijsing S, Carbo N, Quinn LS, Almendro V, Argiles JM, Lopez-Soriano FJ.

Departament de Bioquimica i Biologia Molecular, Facultat de Biologia, Universitat de Barcelona, Diagonal 645, 08028 Barcelona, Spain.

Incubation of rat isolated skeletal muscles (extensor digitorum longus) in the presence of 100 ng/ml of human recombinant interleukin-15 (IL-15) resulted in a significant decrease in total proteolytic rate, while it had no effect on total protein synthesis as measured by the incorporation of (14)C-phenylalanine into muscle protein. In addition, IL-15 had no effect on either amino acid uptake (as determined by the tissue uptake of labelled [1-(14)C]MeAIB) or alanine utilization by incubated skeletal muscles. Similarly, a single injection of IL-15 (100 microg/kg) in vivo did not result in any changes in amino acid uptake (as measured by the tissue uptake of alpha-[1-(14)C]AIB) or alanine metabolism, with the exception of alanine carbon incorporation into lipids, which was significantly increased in adipose tissue as a result of IL-15 administration. The results suggest that the main mechanism involved in the anabolic effects of IL-15 in skeletal muscle relies on a decrease in the proteolytic rate.
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So basically it works by inhibiting protein breakdown

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As a side note, I found this interesting as well. IL-15 fights fat as well as promoting anabolism:

Cell Biol Int. 2005 Jun 23; [Epub ahead of print] Related Articles, Links


Interleukin-15 stimulates adiponectin secretion by 3T3-L1 adipocytes: Evidence for a skeletal muscle-to-fat signaling pathway.

Quinn LS, Strait-Bodey L, Anderson BG, Argiles JM, Havel PJ.

Geriatric Research, Education, and Clinical Center, University of Washington, Seattle, WA, USA; Division of Gerontology and Geriatric Medicine, Department of Medicine, University of Washington, Seattle, WA, USA.

Interleukin-15 (IL-15) is a cytokine that is highly expressed in skeletal muscle tissue, and that has anabolic effects on skeletal muscle protein dynamics both in vivo and in vitro. Additionally, administration of IL-15 to rats and mice inhibits white adipose tissue deposition.To determine if the action of IL-15 on adipose tissue is direct, the capacity of cultured murine 3T3-L1 preadipocytes and adipocytes to respond to IL-15 was examined. IL-15 administration inhibited lipid accumulation in differentiating 3T3-L1 preadipocytes, and stimulated secretion of the adipocyte-specific hormone adiponectin by differentiated 3T3-L1 adipocytes. The latter observation constitutes the first report of a cytokine or growth factor that stimulates adiponectin production. IL-15 mRNA expression by cultured 3T3-L1 adipogenic cells and C2C12 murine skeletal myogenic cells was also examined. Quantitative real-time PCR indicated IL-15 mRNA was expressed by C2C12 skeletal myogenic cells, and was upregulated more than 10-fold in differentiated skeletal myotubes compared to undifferentiated myoblasts. In contrast, 3T3-L1 cells expressed little or no IL-15 mRNA at either the undifferentiated preadipocyte or differentiated adipocyte stages. These findings provide support for the hypothesis that IL-15 functions in a muscle-to-fat endocrine axis that modulates fat:lean body composition and insulin sensitivity.




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