Introduction: The human amniotic epithelial cell (hAEC), a type of placental stem cell, has been investigated as a new source of regenerative therapy. We previously demonstrated that the hAECs underwent TGF-β-dependent epithelial-mesenchymal transition (EMT) shortly after starting cell culture, which was sufficiently inhibited by a TGF-β pathway inhibitor, SB-431542. Using comprehensive transcriptome analysis, we found a differentially expressed gene, Traf2- and Nck-interacting kinase (TNIK) significantly enriched in SB-431542-treated hAECs. TNIK is a member of the germinal center kinase family and is ubiquitously expressed with a high level in the brain and small intestine, but low in the placenta. It has been reported that TNIK plays an important role in the regulation of Jun N-terminal kinase pathway activation and cytoskeletal rearrangements. Additionally, TNIK phosphorylates the T-cell factor-4 (TCF4) and is also known as an important activator of the Wnt pathway. In this study, we explored the role of TNIK in hAECs.

Methods: hAECs were isolated from the placentae of 6 patients who underwent scheduled Caesarean sections. The cells were cultured for 7 days with or without SB-431542. Total RNA was extracted on day 0 (naïve cell), day 1, 4, and 7, and then the expressions of TNIK were analyzed by RT-qPCR. Additionally, we cultured the hAECs with supplementation of a TNIK inhibitor, NCB-0846, which binds to TNIK in an inactive conformation and inhibits the phosphorylation of TCF4, and examined the cell proliferation.

Results: We confirmed that TNIK was significantly expressed in cultured hAECs with SB-431542 for 7 days by RT-qPCR. TNIK was not observed in naïve hAECs but gradually expressed in inhibited-EMT hAECs over days. The supplementation of NCB-0846 influenced cell viability and proliferation.

Conclusion: Our data showed that the TNIK expression in hAECs was induced by inhibition of TGF-β-dependent EMT. The blocking TNIK/TCF4 interaction using NCB-0846 interfered with cell proliferation. Further study is needed to clarify the crosstalk between TGF-β and Wnt pathways in hAECs. Regulation of these signaling pathways might be useful to develop a clinical protocol for cell transplantation therapy using hAECs.