Relaxin-2 promotes osteoblastic differentiation mediated by epidermal growth factor and epidermal growth factor receptor signaling.

Loss of osteogenic differentiation potential of osteoblasts has been associated with the pathogenesis of osteoporosis. Thus, stimulation of osteoblastic differentiation is a therapeutic strategy for osteoporosis. Relaxin-2 is a peptide hormone with potent biological functions. However, the effects of Relaxin-2 in osteoblastic differentiation and osteoporosis have not been reported before. Here, we report a novel physiological role of Relaxin-2 in promoting osteoblastic differentiation and mineralization of MC3T3-E1 cells. Our results indicate that exposure to Relaxin-2 upregulated the expression, and elevated the activity of alkaline phosphatase (ALP) when MC3T3-E1 cells were cultured in osteogenic differentiation medium (OM). Additionally, Relaxin-2 upregulated the mRNA levels of osteocalcin (ocn), osteopontin (opn), and collagen type I alpha 1 (Col1a1). The alizarin red S staining assay revealed that Relaxin-2 promoted the mineralization of MC3T3-E1 cells. We also found that Relaxin-2 increased the expression of Runx-2 as well as the epidermal growth factor (EGF) and epidermal growth factor receptor (EGFR). Importantly, silencing of EGF abolished the effects of Relaxin-2 in osteoblastic differentiation and related gene expression. These findings suggest that Relaxin-2 stimulates osteogenic differentiation through activating EGF/EGFR signaling.