Aryl Hydrocarbon Receptor 2 Mediates 2,3,7,8-Tetrachlorodibenzo-p-dioxin Developmental Toxicity in Zebrafish

Abstract

In order to use the zebrafish as a model vertebrate to investigate the developmental toxicity of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), it is essential to know whether one or both forms of the zebrafish aryl hydrocarbon receptor (AHR), zfAHR1 or zfAHR2, mediate toxicity. To determine the role of zfAHR2, an antisense morpholino approach was used to knock down translation of the protein. No effect of the zfahr2 morpholino (zfahr2-MO) was seen on normal development in embryos not treated with TCDD. Injection of embryos at the 1-2 cell stage with zfahr2-MO decreased TCDD-induced transcription of zfCYP1A mRNA until 96 h post fertilization (hpf), and immuno-histochemical detection of zfCYP1A protein in embryos at 72 hpf revealed a dramatic decrease in expression. The zfahr2-MO completely protected embryos from TCDD-induced edema and anemia and provided protection against TCDD-induced reductions in peripheral blood flow initially; however, a slight reduction in blood flow was observed at later times when the morpholino was no longer effective. Due to persistence of TCDD and decreasing effectiveness of the zfahr2-MO over time, the morpholino provided only transient protection against TCDD-induced inhibition of chondrogenesis of the lower jaw, and no protection against an effect of TCDD that was initiated late in development, blockade of swimbladder inflation. The zfahr2-MO did not protect embryos from TCDD-induced mortality but did produce a 48 h delay in its onset. Endpoints of TCDD developmental toxicity manifested in zfahr2 morphants at late stages of development, beyond 144 hpf, were clearly different from TCDD-exposed embryos injected with a control morpholino. Most strikingly, zfahr2 morphants exposed to TCDD never developed edema. Taken together, these results demonstrate that zfAHR2 mediates several endpoints of TCDD developmental toxicity in zebrafish.

Transcriptional expression analysis of ABC efflux transporters and xenobiotic-metabolizing enzymes in the Chinese rare minnow

“…Previous studies have reported the AHR-mediated induction of CYP1A expression by various environmental pollutants (e.g., PAHs) in fish (Prasch et al, 2003;Timme-Laragy et al, 2007). Pyrene is considered to be a weak AHR agonist (Barron et al, 2004).…”

When evolution is the solution to pollution: Key principles, and lessons from rapid repeated adaptation of killifish (Fundulus heteroclitus) populations

“…AHR activation during embryonic development leads to altered gene expression, malformations, and decreased survivorship (Billiard, Meyer, Wassenberg, Hodson, & Di Giulio, 2008; King‐Heiden et al., 2012). Experimental knockout or knockdown of AHR function protects against HAH‐ and PAH‐induced toxicity (Billiard, Timme‐Laragy, Wassenberg, Cockman, & Di Giulio, 2006; Clark, Matson, Jung, & Di Giulio, 2010; Fernandez‐Salguero, Hilbert, Rudikoff, Ward, & Gonzalez, 1996; Goodale et al., 2012; Incardona, Day, Collier, & Scholz, 2006; Incardona et al., 2005; Jönsson, Jenny, Woodin, Hahn, & Stegeman, 2007; Prasch et al., 2003); thus, evolved desensitization of this signaling pathway is plausibly causative for adaptive pollutant tolerance in killifish.…”

“…However, sustained activation of AHR, such as occurs by exposure to poorly metabolizable DLCs or constant exposure to labile AHR agonists, leads to toxicity through sustained misregulation of genes involved in cellular homeostasis. The AHR is thus an integral component of the mechanism by which DLCs and some PAHs cause toxicity, and loss of AHR function protects against these effects (Fernandez‐Salguero et al., 1996; Goodale et al., 2012; Mimura et al., 1997; Prasch et al., 2003). Although the AHR is now known to participate in a variety of additional, noncanonical interactions and pathways (Jackson, Joshi, & Elferink, 2015), the primary mechanism of toxicity appears to involve canonical interactions requiring nuclear localization, dimerization with ARNT, and binding to AHREs (Bunger et al., 2003, 2008; Nukaya, Walisser, Moran, Kennedy, & Bradfield, 2010; Walisser, Bunger, Glover, Harstad, & Bradfield, 2004).…”

“…Thus, AHR regulates adaptive and toxic responses to DLC and some PAH exposures in fish as in mammals, and loss of AHR function ameliorates these effects (Billiard et al., 2006; Goodale et al., 2012; Jönsson et al., 2007; Prasch et al., 2003). Despite the fundamental similarities, however, there are also differences in the AHR pathway among vertebrates—including fish—that may be important in their adaptive evolutionary response to pollution.…”

“…Fish typically have four AHR genes, products of a tandem gene duplication ( AHR1 and AHR2 ) and paralogs of each of these (designated “a” and “b”), the result of a whole‐genome duplication at the base of the teleost lineage, after its divergence from the lineage leading to tetrapods (Hahn et al., 2006, 2017). The relative roles of each AHR are not yet fully understood, but the AHR2 paralogs appear to mediate many of the toxic and adaptive responses to DLCs and some PAHs (Antkiewicz, Peterson, & Heideman, 2006; Billiard et al., 2006; Clark et al., 2010; Dong, Teraoka, Tsujimoto, Stegeman, & Hiraga, 2004; Goodale et al., 2012; Incardona et al., 2006; Jönsson et al., 2007; Lanham, Prasch, Weina, Peterson, & Heideman, 2011; Prasch et al., 2003; Waits & Nebert, 2011). For some chemicals, however, responses may be mediated by AHR1 (Goodale et al., 2012; Incardona et al., 2006).…”