Functions of PI3K and MAPK on Wnt5a Expression in THP-1

Objectives: Wingless was first characterized as a segment polarity gene in Drosophila, which is essential in embryonic segmentation and patterning. Various homologs of the Wingless protein, termed Wnt, are involved in embryonic development and differentiation, and in tumorigenesis. Recent studies suggested that it was secreted by activated antigen presenting cells and by inflammatory synoviocytes from rheumatoid arthritis and atherosclerotic lesions. We previously demonstrated that Wnt5a mRNA expression was up-regulated in chronic periodontitis tissue and that Porphyromonas gingivalis lipopolysaccharide (LPS)-induced Wnt5a in human monocytic cell line THP-1 was dependent upon NF-κB and STAT1. In this study, we investigated the additional mechanism of Wnt5a mRNA expression by P. gingivalis LPS. Methods: Human monocytic cell line THP-1 cells were stimulated with P. gingivalis LPS. In addition, THP-1 cells were pretreated with specific inhibitors for JNK (JNK inhibitor II), MEK1/2 (U0126), p38 (SB203580), PI3K (Wortmannin, LY294002), mTOR (Rapamycin), and STAT3 (STA21) before the stimulation. The expression levels of Wnt5a mRNA were determined by real-time RT-PCR. Results: In THP-1 cells, Wnt5a expression was significantly up-regulated by P. gingivalis LPS. P. gingivalis LPS-induced Wnt5a mRNA levels were suppressed by a JNK inhibitor (JNK inhibitor II). On the other hand, the induction of Wnt5a mRNA expression was augmented by a PI3K inhibitor (Wortmannin), a mTOR inhibitor (Rapamycin), and a STAT3 inhibitor (STA21). Conclusion: Our study suggests that Wnt5a up-regulation by P. gingivalis LPS in THP-1 cells might be dependent upon JNK and that PI3K-Akt pathway would be a negative regulator of the expression of Wnt5a. These signaling molecules are thought to be associated with periodontal disease. (This study was supported by grants from the Japanese Ministry of Education (GCOE) Program, International Research Center for Molecular Science in Tooth and Bone Diseases, and the JSPS Invitation Fellowship for Research in Japan)