Abstract: Objective To investigate the involvement of apolipoprotein D (APOD) in the proliferation and differentiation of dental pulp cells (DPCs) by activating Wnt/β-catenin signaling pathway in Drosophila melanogaster. 
Methods Human dental pulp cells (HDPCs) were cultured in vitro and divided into blank group, low-dose APOD group, high-dose APOD group and si-APOD group. Cells in the blank group were cultured in DMEM medium without any treatment. APOD 2 nmol/L and 32 nmol/L were added to the low-dose APOD group and high-dose APOD group, respectively. HDPCs cells in the si-APOD group were transfected with APOD si-RNA. RT-qPCR was used to detect the expression of APOD mRNA, and CCK-8 was used to detect cell proliferation. Alkaline phosphatase (ALP) activity was used to detect osteogenic differentiation, and Western Blot was used to detect Wnt/β-catenin pathway protein expression. 
Results Compared with blank group, APOD mRNA level and cell viability were increased, ALP activity was increased at 7 d and 14 d, and Wnt5a and β-catenin proteins were up-regulated in low- and high-dose APOD groups (P＜0.05). In si-APOD group, APOD mRNA level and cell viability were decreased, ALP activity at 7 d and 14 d was decreased, and Wnt5a and β-catenin proteins were down-regulated (P＜0.05). Compared with the low-dose APOD group, the APOD mRNA level and cell viability were increased, the ALP activity was increased at 7 d and 14 d, and the Wnt5a and β-catenin proteins were up-regulated in the high-dose group (P＜0.05). In si-APOD group, APOD mRNA level and cell viability were decreased, ALP activity at 7 d and 14 d was decreased, and Wnt5a and β-catenin protein were down-regulated (P＜0.05). Compared with the high-dose APOD group, the mRNA level and cell viability of APOD were significantly decreased, the activity of ALP at 7 d and 14 d was decreased, and the proteins of Wnt5a and β-catenin were down-regulated in si-APOD group (P＜0.05). 
Conclusion APOD can promote the proliferation and differentiation of HDPCs cells, and its mechanism may be related to the activation of Wnt/β-catenin signaling pathway.  

Key words: dental pulp, cell proliferation, apolipoproteins D