Upstream eventInhibition, Deiodinase 2
Reduced, Posterior swim bladder inflation
Key Event Relationship Overview
AOPs Referencing Relationship
|AOP Name||Directness||Weight of Evidence||Quantitative Understanding|
|Deiodinase 2 inhibition leading to reduced young of year survival via posterior swim bladder inflation||indirectly leads to|
|fathead minnow||Pimephales promelas||NCBI|
Life Stage Applicability
How Does This Key Event Relationship Work
Deiodinase or DIO is a peroxidase enzyme that is involved in the activation or deactivition of thyroid hormones. Currently, three types of iodothyronine deiodinases (DIO1-3) have been described in vertebrates that locally activate or inactivate THs and are therefore important mediators of TH action. All deiodinases are integral membrane proteins of the thioredoxin superfamily that contain the amino acid selenocysteine in their catalytic centre. Type I and II deiodinase are capable to convert T4 into T3, thus activating the thyroid hormones. DIO3 on the other hand convertes T4 and T3 to the inactive forms of THs.
Weight of Evidence
The weight of evidence supporting an indirect linkage between these wo KEs, i.e. DIO inhibition and reduced posterior swim bladder inflation, is strong.
Inhibition of DIO activity is widely accepted to directly impact the T3 levels in serum, since the convertion of T4 to T3 is inhibited. In fish, many different adverse effects during early development resulting from disruption of the TH endocrine system have been reported , including effects on swim bladder inflation. As in amphibians, the transition in fish between the different developmental phases, including maturation and inflation of the swim bladder, have been shown to be mediated by THs.
Empirical Support for Linkage
Deiodinases are criticial for normal development. Several defects have already been reported if the TH hormone balance is disturbed. Winata et al., 2009, 2010 reported reduced pigmentation, otic vesicle length and head-trunk angle in DIO1+2 and DIO2 knockdown fish. These effects were rescued after T3 supplementation, indicating the importance of T4 to T3 conversion by deiodinases.
Several implications of the involvement of thyroid hormones in posterior chamber inflation are available in literature as well.
Chang et al., (2012) established a base-line for TH levels during zebrafish development and observed peaks in whole-body T3 content at 5 and 10 dpf, which are linked to specific developmental processes during transition, including posterior chamber inflation.
Bagci et al., 2015 and Heijlen et al., 2014 reported that knockdown of DIO1+2 in zebrafish resulted in impairment of the inflation of the posterior chamber of the swim bladder.
DIO1 and DIO2 mRNA has also been shown to be present in zebrafish swim bladder tissue at 96 hpf using whole mount in situ hybridization (Heijlen et al.,2013 and Dong et al.,2013), suggesting a tissue-specific role of T3 in the inflation process of the posterior chamber.
Exposure to PTU, a very potent DIO1 inhibitor, caused thyroid hypertrophy in X. leavis (Degitz et al., 2005)and resulted in lower serum T3 levels because of the inhibition of the peripheral conversion of T4 to T3 in the rat (Frumess and Larsen, 1975) and resulted in effects on posterior chamber inflation in zebrafish (Jomaa et al., 2014).
Exposure of fathead minnows (Pimephales promelas) to the non-specific deiodinase inhibitor iopanoic acid from 1-6 dpf caused significant reduction in posterior swim bladder inflation (% inflated) and length (Cavallin et al., unpublished).
Therefore, it can be concluded that there is a direct link between the inhibition of deiodinases and the inflation of the posterior chamber.
Uncertainties or Inconsistencies
The mode of action through which reduced T3 hormone concentrations in serum will result in posterior chamber inflation impairment has still to be elucidated.
The development of the posterior chamber inflation starts with a budding phase, during which the posterior bud evaginates from the digestive tract. During the pre-inflation phase, characterised by the formation of three distinct tissue layers (epithelium, mesenchymal layer differentiating into smooth muscle and an outermesothelial layer) (Winata et al., 2010). During the subsequent inflation phase, the posterior chamber inflates and remains inflated during the post-inflation phase.
Based on the developmental stages of the posterior chamber, several hypotheses could explain effects on posterior chamber inflation due to disrupted TH levels.
A first hypothesis includes effects on the budding of the posterior chamber inflation. The effect on posterior chamber inflation could also be caused by disturbing the formation and growth of the three tissue-layers of this organ. It has been reported that the Hedgehog signalling plays an essential role in swim bladder development and is required for growth and differentiation of cells of the swim bladder. The Wnt/ β-catenin signalling is required for the organization and growth of all three tissue layers (Yin et al., 2011, 2012, Winata 2009, Kress et al., 2009). Both pathways have been related to THs in amphibian and rodent species (Kress et al., 2009; Plateroti et al., 2006; Stolow and Shi, 1995).
Heijlen et al., 2015 reported histologically defected tissue layers in DIO3 knockdown zebrafish. As reported in Bagci et al., 2015 and Heijlen et al., 2014, posterior chamber inflation was impaired in DIO3 knockdown zebrafish. DIO 3 is a thyroid hormone inactivating enzyme, which would result in higher levels of T3 in serum. This implicates that presumably not only too low, but also too high T3 levels, will impact posterior chamber inflation.
Several other hypotheses include effects on the capability of initial inflation of the posterior chamber, effect on lactic acid production, which is required for the maintenance of the swim bladder volume, or effects on the production of surfactant, which is crucial to maintain the surface tension necessary for swim bladder inflation.
Quantitative Understanding of the Linkage
In vitro DIO2 inhibition assays were performed using potential thyroid disrupting compounds (Stinckens et al., Unpublished). Using dose-respons curves, the IC50 values were determined and used to caterogize the chemicals according to their potentcy. For DIO2, at least 9 potent DIO inhibitors were found. Six chemicals were tested in the zebrafish embryo to investigate the effects on posterior chamber inflation. Five out of six chemicals resulted in an effect on posterior chamber inflation, with only 1 false positive prediction. Furthermore, 4 chemicals of which no DIO inhibitory capacity was found, were used in a zebrafish embryo test. None of the chemicals resulted in an impact on posterior chamber inflation. These results cleary emphasis the key event relationship between DIO inhibition and posterior chamber inflation.
Evidence Supporting Taxonomic Applicability
The evidence for a relationship between DIO2 inhibition and inflation of the posterior chamber of the swim bladder currently comes from work on zebrafish and fathead minnow.
Winata, C.L., Korzh, S., Kondrychyn, I., Zheng, W., Korzh, V., Gong, Z. 2009. Development of zebrafish swimbladder: the requirement of Hedgehog signaling in specification and organization of the three tissue layers. Dev. Biol.331, 222–236, http://dx.doi.org/10.1016/j.ydbio.2009.04.035.
Winata, C.L., Korzh, S., Kondrychyn, I., Korzh, V., Gong, Z. 2010. The role of vasulature and blood circulation in zebrafish swim bladder development. Dev. Biol. 10:3.
Chang, J., Wang, M., Gui, W., Zhao, Y., Yu, L., Zhu, G., 2012. Changes in thyroidhormone levels during zebrafish development. Zool. Sci. 29, 181–184, http://dx.doi.org/10.2108/zsj.29.181.
Bagci, E., Heijlen, M., Vergauwen, L., Hagenaars, A., Houbrechts, A.M., Esguerra, C.V.,Blust, R., Darras, V.M., Knapen, D., 2015. Deiodinase knockdown during early zebrafish development affects growth, development, energy metabolism,motility and phototransduction. PLoS One 10, e0123285, http://dx.doi.org/10.1371/journal.pone.0123285.
Heijlen, M., Houbrechts, A.M., Bagci, E., Van Herck, S.L.J., Kersseboom, S., Esguerra,C.V., Blust, R., Visser, T.J., Knapen, D., Darras, V.M., 2014. Knockdown of type 3iodothyronine deiodinase severely perturbs both embryonic and early larval development in zebrafish. Endocrinology 155, 1547–1559, http://dx.doi.org/10.1210/en.2013-1660.
Heijlen, M., Houbrechts, A.M., Darras, V.M., 2013. Zebrafish as a model to study peripheral thyroid hormone metabolism in vertebrate development. Gen.Comp. Endocrinol. 188, 289–296, http://dx.doi.org/10.1016/j.ygcen.2013.04.004.
Dong, W., Macaulay, L., Kwok, K.W.H., Hinton, D.E., Stapleton, H.M., 2013. Using whole mount in situ hydridization to examine thyroid hormone deiodinase expression in embryonic and larval zebrafish: a tool for examining OH-BDE toxicity to early life stages. Aquat. Toxicol. 132–133, 190–199, http://dx.doi.org/10.1016/j.biotechadv.2011.08.021.Secreted.
Degitz, S.J., Holcombe, G.W., Flynn, K.M., Kosian, P.A., Korte, J.J., Tietge, J.E., 2005.Progress towards development of an amphibian-based screening assay usinXenopus laevis. Organismal and thyroidal responses to the model compounds6-propylthiouracil, methimazole, and thyroxine. Toxicol. Sci. 87, 353–364.
Frumess, R.D., Larsen, P.R. 1975. Correlation of serum triiodothyronine (T3) and thyroxine (T4) with biological effects of thyroid hormone replacement in propylthiouracil-treated rats. Metabolism 24:4.
Jomaa, B., Hermsen, S.A.B., Kessels, M.Y., Van Den Berg, J.H.J., Peijnenburg, A.A.C.M.,Aarts, J.M.M.J.G., Piersma, A.H., Rietjens, I.M.C.M., 2014. Developmental toxicity of thyroid-active compounds in a zebrafish embryotoxicity test. ALTEX 31,303–317, http://dx.doi.org/10.14573/altex.1402011.
Yin, A., Korzh, S., Winata, C.L., Korzh, V., Gong, Z., 2011. Wnt signaling is required for early development of zebrafish swimbladder. PLoS One 6, http://dx.doi.org/10.1371/journal.pone.0018431.
Yin, A., Korzh, V., Gong, Z., 2012. Perturbation of zebrafish swim bladder development by enhancing Wnt signaling in Wif1 morphants. Biochim.Biophys. Acta—Mol. Cell Res. 1823, 236–244, http://dx.doi.org/10.1016/j.bbamcr.2011.09.018.
Kress, E., Rezza, A., Nadjar, J., Samarut, J., Plateroti, M., 2009. The frizzled-relatedsFRP2 gene is a target of thyroid hormone receptor alfa1 and activates beta-catenin signaling in mouse intestine. J. Biol. Chem. 284, 1234–1241, http://dx.doi.org/10.1074/jbc.M806548200.
Plateroti, M., Kress, E., Mori, J.I., Samarut, J., 2006. Thyroid hormone receptor alpha1 directly controls transcription of the beta-catenin gene in intestinal epithelial cells. Mol. Cell. Biol. 26, 3204–3214, http://dx.doi.org/10.1128/MCB.26.8.3204.
Stolow, M.A., Shi, Y.B., 1995. Xenopus sonic hedgehog as a potential morphogen during embryogenesis and thyroid hormone-dependent metamorphosis.Nucleic Acids Res. 23, 2555–2562, http://dx.doi.org/10.1093/nar/23.13.2555.