Dose-dependent tandem responses of osteoblasts during osteogenesis

Irisin, a myokine mainly secreted from contracted skeleton muscle, plays a profound role in bone formation and remodeling. Although irisin has been revealed to elevate bone mass in vivo, details whether there is a dosedependent relationship between irisin and bone formation remain unclear. In this study, we explored the dosedependent effects of irisin on osteoblast proliferation and differentiation. Our results first demonstrated a remarkable increase in cell proliferation rate and viability in response to elevated concentrations of r-irisin, which was further enhanced over time. Notably, this increase was subject to complex dose-response relationships as the proliferation-enhancing effects of r-irisin may have a saturation point between 10 ng/ml and 100 ng/ml. Furthermore, we determined that 1, 10, and 100 ng/ml r-irisin were able to upregulate the expression of osteogenic transcription factors (Runx2, Osx, and Atf4), as well as osteogenic markers (Alp, Col1a1 and Spp1), albeit without significant difference among these 3 concentrations. Interestingly, nutrient-depleted osteoblasts and those with standard culture showed distinct responses to higher doses of irisin regarding osteogenic differentiation. Further investigation is required to uncover the molecular mechanisms underlying the observed tandem effects of irisin on osteogenesis.