Here is an interesting article on the effects of IL-15 on muscle
Overexpression of Interleukin-15 Induces Skeletal Muscle
Hypertrophy in Vitro: Implications for Treatment of 
Muscle Wasting Disorders
LeBris S. Quinnb, a, 1, Barbara G. Andersonc, a, Rolf H. Drivdahlc, d, Belén Alvareze and Josep M. Argilése
a Division of Gerontology and Geriatric Medicine, Department of Medicine, University of Washington, Seattle, Washington, 98195
d Division of Nutrition, Endocrinology, and Metabolism, Department of Medicine, University of Washington, Seattle, Washington, 98195
b Geriatric Research, Education, and Clinical Center, VA Puget Sound Health Care System, Tacoma, Washington, 98493
c Research Service, VA Puget Sound Health Care System, Tacoma, Washington, 98493
e Department of Biochemistry and Molecular Biology, University of Barcelona, Barcelona, Spain
Received 18 April 2002; revised 12 July 2002. Available online 2 October 2002.
Abstract
Interleukin-15 (
IL-15) is a novel anabolic factor for skeletal
muscle which inhibits
muscle wasting associated with cancer (cachexia) in a rat model. To develop a cell culture system in which the mechanism of the anabolic action of
IL-15 on skeletal
muscle could be examined, the mouse C2 skeletal myogenic cell line was transduced with a retroviral expression vector for
IL-15 and compared to sister cells transduced with a control vector. Overexpression of
IL-15 induced fivefold higher levels of sarcomeric myosin heavy chain and
-actin accumulation in differentiated myotubes. Secreted factors from
IL-15-overexpressing myogenic cells, but not from control cells, induced increased myofibrillar protein accumulation in cocultured control myotubes.
IL-15 overexpression induced a hypertrophic myotube morphology similar to that described for cultured myotubes which overexpressed the well-characterized anabolic factor insulin-like growth factor-I (IGF-I). However, in contrast to IGF-I, the hypertrophic action of
IL-15 on skeletal myogenic cells did not involve stimulation of skeletal myoblast proliferation or differentiation.
IL-15 induced myotube hypertrophy at both low and high IGF-I concentrations. Furthermore, in contrast to IGF-I, which stimulated only protein synthesis under these culture conditions,
IL-15 both stimulated protein synthesis and inhibited protein degradation in cultured skeletal myotubes. These findings indicate that
IL-15 action on skeletal myogenic cells is distinct from that of IGF-I. Due to the ability of IGF-I to stimulate cell division and its association with several forms of cancer, controversy exists concerning the advisability of treating cachexia or age-associated
muscle wasting with IGF-I. Administration of
IL-15 or modulation of the
IL-15 signaling pathway may represent an alternative strategy for maintaining skeletal
muscle mass under these conditions.
, 
, a and LeBris S. Quinn