SALL4 promotes osteoblast differentiation by deactivating NOTCH2 signaling

Background: The Spalt-Like Transcription Factor 4 (SALL4) is reported to regulate cell proliferation, migration and invasion. However, the roles of SALL4 in osteoblast differentiation are unclear. This study was aimed to explore the underlying mechanism of SALL4 in osteoporosis. Methods: Firstly, the expression of SALL4 was assessed in vivo and in vitro at various stages of development of rats (E14, E20, postnatal 2, 4, and 9 day) or different incubation time (0, 6, 9, 12 and 15 day) of C2C12 and MC3T3-E1 cells. Then, alkaline phosphatase (ALP) activities and positive cells percentages were respectively detected after oeSall4 or siSall4 transfection. Cell differentiation related markers and chondrogenesis-related genes expressions in C2C12 cells were tested by western blot assay and qRT-PCR. Finally, the connection and interaction between SALL4 and NOTCH2 were studied. Results: The results showed that SALL4 expression was increased in vivo and in vitro with the growth of rats or the incubation of cells. SALL4 overexpression promoted osteoblast differentiation; on the contrary, SALL4 knockdown inhibited osteoblast differentiation. Moreover, SALL4 participated in the middle and late stages of cell differentiation. Then, SALL4 and NOTCH2 interacted with each other. NOTCH2 expression was decreased both in vivo and in vitro, and negatively regulated by SALL4. Besides, SALL4 overexpression suppressed NOTCH2 target genes expressions and nuclear entry, while deactivated NOTCH2 signaling. Conclusions: Our study found that SALL4 played very important roles in the process of osteoblast differentiation by deactivating NOTCH2 signaling. These findings might provide a new insight for treatment of osteoporosis.