PFOA substitute GenX at a sub-cytotoxic level exhibits thyroid-disrupting effects by inhibiting the expression of thyroid transcription factor 1

While the occurrence of GenX, a novel alternative for perfluorooctanoic acid (PFOA), in the environment and its cytotoxicity at high concentrations to thyroid cells are well documented, limited information is available regarding its impact at low concentrations. GenX is detected to be as low as 0.001 ng/mL in drinking water and 0.04-1 ng/mL in human serum. In this study, we investigated the impact of GenX at levels similar to that from drinking water and human serum on thyroid function in vitro and in vivo. Our data showed that GenX from 0.001 to 0.1 ng/mL was sub-cytotoxic and did not exhibit apparent impact on thyroid cell viability. However, GenX at 0.001 ng/mL significantly reduced the expression of Thyroid Transcription Factor 1 (TTF-1) on both mRNA and protein levels. Further analysis showed that GenX suppressed TTF-1 expression through the inhibition of Wnt/β-catenin pathway. Furthermore, we tested as a proof-of-concept that inhibition of GSK-3β, a negative regulator in the Wnt/β-catenin pathway, using specific inhibitors could rescue GenX-induced TTF-1 reduction in thyroid cells. Together, our findings have not only provided evidence that GenX at a low but human exposure-relevant concentration could cause thyroid disruption, but also proposed potential underlying mechanism and treatment approach. This information will be useful for the guidance of the future use of GenX.