Notch, NF-κB, Hippo, Ephrin, and Piezo1/2 signaling pathways also play important roles in osteoblast differentiation. Osteoblast differentiation is inhibited by the Notch and NF-κB signaling pathways, with the Notch signaling pathway’s downstream factors NICD binding to CLS and inhibiting β-catenin. NICD/CLS/Foxo1 complex can promote Hey1 expression, then Hey1 can bind with Runx2 to inhibit Runx2 activity. When NF-κB signaling is stimulated, the P50 and P65 complex translocates into the nucleus and inhibits Smad protein activity. Hippo signaling is a crucial pathway in cell growth and development. The important downstream factors YAP/TAZ in Hippo signaling can regulate osteoblast differentiation-related gene expression. When Hippo signaling is in an “off” state, the YAP/TAZ complex will not be degraded and will translocate into the nucleus to regulate osteoblast-specific gene expression. The snail/slug complex can promote YAP/TAZ activity in nuclear and inhibit YAP/TAZ degradation in the cytoplasm. Ephrin signaling has different regulatory effects on osteoblast differentiation through different pathways and plays a specific role in the regulation of osteoblasts and osteoclasts. The EphrinA2 and EphrinB2 expressed on osteoclast membranes can interact with EphA2 and EphB4 expressed on osteoblast membranes to regulate osteoblast differentiation. Ephrin signaling regulated osteoblast-specific gene expression mainly through RhoA. EphrinA2 binds with EphA2 and promotes RhoA activity, while EphrinB1/2 binds with EphB4 and inhibits RhoA activity. When RhoA is activated, it will inhibit osteoblast differentiation. Piezo1/2 is a recently discovered pathway functioning in osteoblast differentiation. Piezo1/2 can regulate osteoblast-specific gene expression by regulating downstream pathways such as ERK and P38 and interacting with Hippo signaling. Piezo1/2 can regulate β-catenin activation to active Runx2 and regulate osteoblast gene expression. Piezo1/2 can also activate NFATc1 and YAP via calcium signal, and then NFATc1 and YAP can translocate into the nucleus and regulate osteoblast differentiation. Insulin signaling inhibits the production of FoxO1 and Twist2, which can inhibit the expression of Runx2 and Ocn. Ocn improves insulin sensitivity and energy expenditure through multiple mechanisms like activating to β-cells. The direct effect of osteocalcin as an insulin-sensitizing hormone is speculative and remains to be determined.
