Nell-1 Enhances Osteogenic Differentiation of Pre-Osteoblasts on Titanium Surfaces via the MAPK-ERK Signaling Pathway.

Background/aims: This study aimed to investigate the effect of Nell-1 on the osteogenic behaviors of pre-osteoblasts on titanium (Ti) surfaces and to identify the underlying signaling pathway.

Methods: Nell-1 at different concentrations was added to culture medium to stimulate MC3T3-E1 subclone 14 on Ti surfaces. A CCK-8 colorimetric assay was used to detect cell proliferation. Alkaline phosphatase activity (ALP) assay and enzyme-linked immunosorbent assay (ELISA) were used to evaluate ALP activity and the osteocalcin (OCN) secretion, respectively. Indicators of osteoblastic differentiation were assessed using real-time polymerase chain reaction analysis (RT-PCR). Western blot (WB) assay was used to analyze the expression changes of the osteogenic proteins and the mitogen-activated protein kinase (MAPK) pathway.

Results: Nell-1 significantly increased the osteogenic gene and protein expression levels of ALP, OCN, Runx2, osteoprotegerin (OPG), collagen type I (Col-I), and Osterix (Osx) in pre-osteoblasts on Ti surfaces. The optimal concentration of Nell-1 was 100 ng/ ml. In addition, Nell-1 activated ERK and JNK, but not P38, in MC3T3-E1 cells on the Ti surface. Except for ALP and Col-I, the promotive effects of Nell-1 on the expression of osteogenic markers were suppressed by ERK inhibitor U0126.

Conclusion: Certain concentrations of Nell-1 can promote the osteogenic differentiation of pre-osteoblasts on Ti surfaces by activating the MAPK/ERK signaling pathway.