The myokine interleukin-7 may influence differentiation and migration of cultured satellite cells

Abstract

Regular physical activity has beneficial effects on health. The relations between exercise and health are not fully understood. Myokines are secretory peptides of skeletal muscle origin with auto-, para- or endocrine functions. So far interleukin (IL)-6 is the best explored myokine. The identification of this myokine has made the basis for many new hypotheses. For example, can IL-6 or other muscle-derived factors explain some of the beneficial health effects of physical activity?

Recently, our group demonstrated production of IL-7 by cultivated skeletal muscle cells of human origin. The aim of this Master thesis was to investigate if IL-7 can influence skeletal muscle cell development in a paracrine manner.

To do this, we incubated skeletal muscle progenitor cells (satellite cells) with recombinant human (rh) IL-7. Gene expression analyses by real time polymerase chain reaction (RT-PCR), showed that rhIL-7 incubation during myogenesis significantly reduced the expression of the late differentiation marker gene myosin heavy chain 2 (MYH2) by 37 ± 4 % (mean ± SEM) at mRNA level after 7 days. Shorter incubation time (6 hours) with rhIL-7 significantly down-regulated the expression of early myogenic differentiating marker gene myogenic differentiation 1 (MYOD1) and the late myogenic differentiating marker gene myosin heavy chain 2 (MYH2). These findings indicate that IL-7 may influence differentiation of satellite cells into fully developed skeletal muscle cells. Radioactively labelled thymidine, glucose and oleic acid were used to monitor the influence of rhIL-7 on satellite cell proliferation, and on glucose and fatty acid metabolism. Recombinant hIL-7 incubation did not influence these parameters in satellite cells. Migration of satellite cells was measured using BD Falcon Insert Systems together with green fluorescence dye staining, picture analytical software and manual counting. Relative to control the migration was increased 40 ± 13 % (mean ± SEM) after 48 hours incubation with rhIL-7.

In conclusion: IL-7 may influence differentiation and migration of cultured satellite cells.