Abstract
Lipopolysaccharide (LPS) has been implicated in mesenchymal stem cell differentiation processes. Wnt5a, one of the “non-canonical” Wnt family members, is important in signaling stem cell differentiation and in the inflammatory responses of immune cells. Here we studied whether LPS can regulate the expression of Wnt5a in human dental pulp stem cells (hDPSCs) and investigated the intracellular signaling pathways activated by LPS.
Wnt5a mRNA and protein expression changes in hDPSCs were investigated by real-time polymerase chain reaction analysis and enzyme-linked immunosorbent assay. In addition, real-time polymerase chain reaction, enzyme-linked immunosorbent assay, and luciferase activity assays were used to determine whether toll-like receptor 4 (TLR4), myeloid differentiating factor 88 (MyD88), nuclear factor kappa B (NF-kB), or the phosphatidylinositol 3-OH kinase (PI3K)/AKT pathways are involved in LPS-induced Wnt5a expression. The activation of PI3K and AKT in hDPSCs was measured by Western blot analysis.
Wnt5a mRNA and protein expression was rapidly increased in response to LPS in a time- and dose-dependent manner. LPS-induced Wnt5a expression was effectively attenuated by administration of a TLR4 neutralizing antibody, MyD88 inhibitory peptide, PI3-kinase inhibitors (LY294002 and wortmannin), an AKT inhibitor, or NF-κB inhibitor (pyrrolidine dithiocarbamate), IκBa phosphorylation inhibitor (Bay 117082), or IκB protease inhibitor (L-1-tosylamido-2-phenylethyl chloromethyl ketone). Treatment of hDPSCs with LPS activated PI3-kinase (p85) and AKT signaling in a time-dependent manner. Moreover, LPS-mediated increases in κB-luciferase activity were diminished by the overexpression of dominant negative mutants of TLR4, MyD88, p85, AKT, and IκBa.
These results demonstrated that LPS-induced Wnt5a expression was mediated through the TLR4/MyD88/PI3-kinase/AKT pathway, which then initiated NF-κB activation in hDPSCs.