IL-7 is expressed and secreted by human skeletal muscle cells

Am J Physiol Cell Physiol. 2010 Apr;298(4):C807-16. doi: 10.1152/ajpcell.00094.2009. Epub 2010 Jan 20.

Abstract

In addition to generating movement, skeletal muscle may have a function as a secretory organ. The aim of the present study was to identify novel proteins with signaling capabilities secreted from skeletal muscle cells. IL-7 was detected in media conditioned by primary cultures of human myotubes differentiated from satellite cells, and concentrations increased with incubation time. By immunoblotting and real-time RT-PCR IL-7 expression was confirmed at both protein and mRNA levels. Furthermore, with immunofluorescence and specific antisera, multinucleated myotubes were found to coexpress IL-7 and myosin heavy chain. During differentiation of human myotubes from satellite cells, IL-7 expression increased at mRNA and protein levels. In contrast, mRNA expression of the IL-7 receptor was 80% lower in myotubes compared with satellite cells. Incubations with recombinant IL-7 under differentiation conditions caused approximately 35% reduction in mRNA for the terminal myogenic markers myosin heavy chain 2 (MYH2) and myogenin (MYOG), suggesting that IL-7 may act on satellite cells to inhibit development of the muscle fiber phenotype. Alternative routes of cell development were investigated, and IL-7 increased migration of satellite cells by 40% after 48 h in a Transwell system, whereas cell proliferation remained unchanged. In vivo, real-time RT-PCR analysis of musculus vastus lateralis (n = 10) and musculus trapezius (n = 7) biopsies taken from male individuals undergoing a strength training program demonstrated that after 11 wk mean IL-7 mRNA increased by threefold (P = 0.01) and fourfold (P = 0.04), respectively. In conclusion, we have demonstrated that IL-7 is a novel myokine regulated both in vitro and in vivo, and it may play a role in the regulation of muscle cell development.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adult
  • Biomarkers / metabolism
  • Cell Differentiation / physiology
  • Cell Proliferation
  • Cells, Cultured
  • Culture Media / chemistry
  • Humans
  • Interleukin-7 / genetics
  • Interleukin-7 / metabolism*
  • Male
  • Middle Aged
  • Muscle Development / physiology
  • Muscle Fibers, Skeletal* / cytology
  • Muscle Fibers, Skeletal* / metabolism
  • Myosin Heavy Chains / genetics
  • Myosin Heavy Chains / metabolism
  • RNA, Messenger / genetics
  • RNA, Messenger / metabolism
  • Receptors, Interleukin-7 / genetics
  • Receptors, Interleukin-7 / metabolism
  • Resistance Training
  • Satellite Cells, Skeletal Muscle / cytology
  • Satellite Cells, Skeletal Muscle / metabolism

Substances

  • Biomarkers
  • Culture Media
  • Interleukin-7
  • RNA, Messenger
  • Receptors, Interleukin-7
  • Myosin Heavy Chains