Regulation of thyroid hormones and branchial iodothyronine deiodinases during freshwater acclimation in tilapia. (1st December 2021)

• Record Type: Journal Article
• Authors: Seale, Lucia A.; Gilman, Christy L.; Zavacki, Ann Marie; Larsen, P. Reed; Inokuchi, Mayu; Breves, Jason P.; Seale, Andre P.
• Is Part Of: Molecular and cellular endocrinology. Volume 538(2021)
• Publication Date: 2021-12-01
• Subjects: Deiodinase -- Thyroid hormones -- T3 -- T4 -- TSH -- Fish -- Freshwater -- Salinity -- Osmoregulation -- Gill; Endocrinology -- Periodicals; Molecular biology -- Periodicals; Cytology -- Periodicals; Endocrinology -- Periodicals; Hormones -- Periodicals; Endocrinologie -- Périodiques; Cytology; Endocrinology; Molecular biology; Periodicals; 573.4
• DOI: 10.1016/j.mce.2021.111450
• Languages: English
• ISSNs: 0303-7207

Abstract

Abstract: Euryhaline fishes are capable of maintaining osmotic homeostasis in a wide range of environmental salinities. Several pleiotropic hormones, including prolactin, growth hormone, and thyroid hormones (THs) are mediators of salinity acclimation. It is unclear, however, the extent to which THs and the pituitary-thyroid axis promote the adaptive responses of key osmoregulatory organs to freshwater (FW) environments. In the current study, we characterized circulating thyroxine (T4) and 3-3'-5-triiodothyronine (T3) levels in parallel with the outer ring deiodination (ORD) activities of deiodinases (dios) and mRNA expression of dio1, dio2, and dio3 in gill during the acclimation of Mozambique tilapia ( Oreochromis mossambicus ) to FW. Tilapia transferred from seawater (SW) to FW exhibited reduced plasma T4 and T3 levels at 6 h. These reductions coincided with an increase in branchial dio2-like activity and decreased branchial dio1 gene expression. To assess whether dios respond to osmotic conditions and/or systemic signals, gill filaments were exposed to osmolalities ranging from 280 to 450 mOsm/kg in an in vitro incubation system. Gene expression of branchial dio1, dio2, and dio3 was not directly affected by extracellular osmotic conditions. Lastly, we observed that dio1 and dio2 expression was stimulated by thyroid-stimulating hormone in hypophysectomized tilapia, suggesting that branchial TH metabolism is regulated by systemic signals. Our collective findings suggest that THs are involved in the FW acclimation of Mozambique tilapia through their interactions with branchial deiodinases that modulate their activities in a key osmoregulatory organ. Highlights: Transfer of Mozambique tilapia from seawater to fresh water reduces circulating thyroid hormones. T4 outer ring deiodination activity is transiently increased upon transfer to fresh water. Branchial dio1 is transiently downregulated upon transfer to fresh water. Branchial dios are insensitive to extracellular osmolality in vitro . Branchial dio1 and dio2 are reduced following pituitary removal and stimulated by TSH replacement.