Purpose: Irisin is a hormone-like molecule secreted from skeletal muscle in response to exercise both in mice and in humans and identified as an important effector in the crosstalk between muscle and bone. Although a number of studies report that irisin increased osteoblast differentiation in vitro and cortical bone mass in vivo, the models used are exclusively rodent ones. Due to the lack of reports on human cell models, the aim of our work was to investigate the in vitro effects of irisin on the proliferation and the osteogenic differentiation processes in human adipose tissue-derived mesenchymal stem cells (hAMSCs).
Methods: hAMSCs were obtained by enzymatic digestion and mechanical dispersion, and cultured in growth medium. Cells were exposed to 10 and 100 ng/ml irisin for the entire experimental period and refreshed every two days. The proliferation was performed in growth medium containing 2.5% fetal bovine serum, and measured by cell counting at 24-48-72 hours. Alkaline phosphatase (ALP) activity and Ca2+ depositions were quantified by fluorometric assay during up to 35 days of osteogenic induction.
Results: Cell proliferation assay showed that 100 ng/ml irisin significantly increased the proliferation process (p<0.01) vs control, with a decrease of cell doubling time from 88 to 63 hours. Osteodifferentiation with 10 and 100 ng/ml irisin showed significant increases in ALP activity vs control (p<0.01) after 14 days. Moreover, both tested concentrations of irisin were able to accelerate the deposition of mineralized matrix, resulting in significant increments in the production of Ca2+ nodules vs control after 35 days (p<0.01).
Conclusions: This work showed the in vitro effects of irisin on a human cell model of AMSCs. The preliminary results show this myokine to be an important effector on cell proliferation and during osteo-differentiation of hAMSCs, supporting the hypothesis that irisin could represent a potent new anabolic treatment to bring about gain of bone mass.