Activation of thyroid hormone receptors α and β by perfluoroalkyl carboxylic acid revealed by in vitro and in silico methods

Abstract

Perfluoroalkyl carboxylates (PFCAs), with similar structures to perfluorooctanoic acid (PFOA), have become ubiquitous in the environment. However, thyroid hormone-disrupting effects and underlying mechanisms of PFCAs remain poorly understood. In this study, we explored and compared the TR-mediated activities of four typical PFCAs. Cell proliferation assays showed that PFHxA, PFNA, and PFDA promoted the proliferation of GH3 cells, whereas PFHpA showed no such effect. The observed enhancement was likely caused by thyroid hormone receptors (TRs) activation, as a TR antagonist significantly inhibited the pro-proliferation effect. The results of the luciferase reporter gene assays revealed that PFHxA, PFNA, and PFDA activated the transcriptional activity of both subtypes of TRs (TRα and TRβ), suggesting that TRs are potential targets for these 3 compounds. Notably, the ability of all three PFCAs to activate TRα transcriptional activity was more robust than that for TRβ, indicating that they may have a subtype-selective interaction with TRα. The strength of TR-mediated activation followed the order: PFNA (9-carbon chain) > PFHxA (6-carbon chain) > PFDA (10-carbon chain). Molecular docking analysis suggested that weaker activity of PFDA may be attributed to steric hindrance from its longer carbon chain, reducing binding affinity toward TRs. Overall, this research demonstrated that PFHxA, PFNA, and PFDA exerted TR-mediated activation via TR-mediated pathways, with distinct differences in their interactions with the two TR subtypes, TRα and TRβ.