Programmed cell death 4 inhibits proliferation and differentiation and induces apoptosis of human mesenchymal stem cells through suppressing the Wnt/β-catenin pathway

Background: Programmed cell death 4 (PDCD4) has been shown to act as a tumor suppressor involved in several cancers. However, the function and possible molecular mechanisms of PDCD4 in human mesenchymal stem cells (hMSCs) are still unclear. Methods: The expression of PDCD4 mRNA were detected by quantitative real-time PCR (qRT-PCR) in N-hMSCs and OP-hMSCs. Western blot assays were used to examine the protein levels of PDCD4, osteogenic markers Runx2 and Osterix, and Wnt/beta-catenin pathway related proteins beta-catenin, C-myc, CyclinD1 and Wnt1, Lgr5 and Axin2. CCK-8 assay and flow cytometry analysis were performed to determine the proliferation and apoptosis of N-hMSCs and OP-hMSCs, respectively. Results: PDCD4 was expressed more highly in OP-hMSCs than N-hMSCs. The proliferation was decreased, and apoptosis was increased in OP-hMSCs compared with N-hMSCs. PDCD4 knockdown promoted proliferation and differentiation and suppressed apoptosis of OP-hMSCs, while PDCD4 overexpression in N-hMSCs showed the reverse effect. Moreover, suppression of PDCD4 activated the Wnt/beta-catenin pathway in OP-hMSCs, whereas overexpression of PDCD4 blocked the Wnt/beta-catenin pathway in N-hMSCs. Furthermore, Wnt/beta-catenin pathway inhibitor, XAV939, inhibited proliferation and differentiation and induced apoptosis of OP-hMSCs and N-hMSCs. Finally, XAV939 reversed the enhanced proliferation and differentiation and suppressed apoptosis of OP-hMSCs mediated by PDCD4 knockdown. Conclusion: PDCD4 inhibits proliferation and differentiation and induces apoptosis of hMSCs by repressing the Wnt/beta-catenin pathway. The present study elucidates a novel PDCD4-Wnt/beta-catenin regulatory pathway in osteoporosis and provides a promising therapeutic target for osteoporosis.