Thymic stromal lymphopoietin promotes the proliferation of human trophoblasts via phosphorylated STAT3-mediated c-Myc upregulation

Our previous study has demonstrated that thymic stromal lymphopoietin (TSLP) stimulates trophoblast proliferation and invasion, suggesting TSLP plays an important role in the placentation in early human pregnancy, but the intracellular molecular mechanism is currently unknown. The present study is undertaken to investigate whether the STAT3-c-Myc signaling pathway is involved in TSLP-mediated trophoblast proliferation. Primary human first-trimester trophoblasts were treated with TSLP only, or TSLP combined with different signaling inhibitors (STAT3, STAT5, AKT, and ERK). The levels of STAT3 tyrosine phosphorylation and c-Myc expression were determined by using Western blot analysis, and the proliferation of trophoblasts was analyzed by BrdU cell proliferation assay. JEG-3 cells were transfected with siRNA targeting to c-Myc, and the proliferation was determined in JEG-3 cells treated with TSLP only, or TSLP combined with c-Myc silencing. It was revealed that treatment with TSLP significantly enhanced STAT3 phosphorylation and c-Myc expression in human trophoblasts. The effect of TSLP upregulation on trophoblast proliferation was abrogated completely by either STAT3 inhibitor or c-Myc siRNA silence. We further found that the upregulation of TSLP on c-Myc expression was abrogated completely by the STAT3 inhibitor, which suggests that the intracellular STAT3 phosphorylation is an upstream signal of c-Myc expression in the TSLP-stimulated trophoblast proliferation. These results suggest that TSLP may upregulate c-Myc expression through activation of STAT3 pathway, thereby inducing trophoblast proliferation.