Induction of adiponectin gene expression in human myotubes by an adiponectin-containing HEK293 cell culture supernatant

Abstract

Aims/hypothesis. Adiponectin, an adipocytokine known to be down-regulated in obesity-linked disorders, is considered to be a potential key mediator of insulin sensitivity. In this study, we asked whether adiponectin is able to regulate ten selected genes possibly associated with insulin sensitivity in human skeletal muscle cells. Methods. To this end, we treated in vitro differentiated human myotubes with the culture supernatant of HEK293 cells stably transfected with human recombinant adiponectin and assessed gene expression by RT-PCR. Intracellular adiponectin protein was quantified by radioimmunoassay and visualized by Western blotting. Results. In contrast to the control supernatant, the adiponectin-containing supernatant consistently induced expression of adiponectin mRNA in human myotubes from eight different donors (mean increase: 90-fold over control; n=8, p<0.001). This increase in mRNA was paralleled by a rise in intracellular adiponectin protein (mean increase: 8.3-fold over control; n=4, p<0.05). Expression of the other nine candidate genes was not altered. In human skin fibroblasts and HepG2 cells, the adiponectin-enriched supernatant did not induce relevant amounts of adiponectin mRNA. Conclusions/interpretation. In conclusion, we show here that adiponectin gene expression is specifically inducible in skeletal muscle cells.