Influence Of Perfluoroalkyl Acids And Other Parameters On Circulating Thyroid Hormones And Immune-Related Microrna Expression In Free-Ranging Nestling Peregrine Falcons

Exposure to certain perfluoroalkyl acids (PFAAs) can have considerable effects on the endocrine and immune systems, although such effects remain largely uncharacterized inwildlife. Using an apex avian predator, we investigated possible relationships of thyroid hormones (THs), specifically free (F) and total (T) thyroxine (FT4; TT4) and triiodothyronine (FT3; TT3), and the expression of an immune-related microRNA biomarker (i.e., miR-155), with the concentrations of 11 PFAAs in nestling peregrine falcons (Falco peregrinus). Nestling peregrines (n = 56; usually two chicks of each sex per nest) were blood sampled when 23 +/- 4 days old in urban and rural regions of the Laurentian Great Lakes Basin (Ontario, Canada) in 2016 and 2018. The circulating concentrations of several PFAAswere significantly associatedwith THs and estimated thyroid gland activity (TT3:TT4; FT3: FT4), including PFHxS (FT3; FT3:FT4), PFDS (TT3; TT3:TT4), PFOA (TT4; FT3:FT4), PFTeDA (TT4; FT3:FT4), PFHxDA (TT4; TT3:TT4) and SPFCAs (TT4). Our novel evaluation ofmiR-155 in peregrine nestlings identified significantly negative relationships of plasmamiR-155 counts with PFHxS and PFOA concentrations, indicating potential down-regulation of miR-155 expression and impaired immunity. Several PFAA homologues significantly predicted the variation in THs and miR-155 in conjunction with year (e.g., inter-annual differences in weather, ambient temperature, rainfall), region (urban/rural), nestling age, and/or diet (trophic position; delta N-15), which suggests thatmultiple environmental and biological stressors, including PFAA exposure, influenced thyroid activity and immune function in these nestlings. Further research is warranted to identify the mechanisms and additional impacts of PFAA-related thyroid and immune disruption on the growth, development, and health risks in developing birds. Crown Copyright (C) 2021 Published by Elsevier B.V. All rights reserved.