Multifactorial Genetic and Environmental Hedgehog Pathway Disruption Sensitizes Embryos to Alcohol‐Induced Craniofacial Defects

Abstract

Background: Prenatal alcohol exposure (PAE) is perhaps the most common environmental cause of human birth defects. These exposures cause a range of structural and neurological defects, including facial dysmorphologies, collectively known as fetal alcohol spectrum disorders (FASD). While PAE causes FASD, phenotypic outcomes vary widely. It is thought that multifactorial genetic and environmental interactions modify the effects of PAE. However, little is known of the nature of these modifiers. Disruption of the Hedgehog (Hh) signaling pathway has been suggested as a modifier of ethanol teratogenicity. In addition to regulating the morphogenesis of craniofacial tissues commonly disrupted in FASD, a core member of the Hh pathway, Smoothened, is susceptible to modulation by structurally diverse chemicals. These include environmentally prevalent teratogens like piperonyl butoxide (PBO), a synergist found in thousands of pesticide formulations. Methods: Here, we characterize multifactorial genetic and environmental interactions using a zebrafish model of craniofacial development. Results: We show that loss of a single allele of shha sensitized embryos to both alcohol-and PBO-induced facial defects. Co-exposure of PBO and alcohol synergized to cause more frequent and severe defects. The effects of this co-exposure were even more profound in the genetically susceptible shha heterozygotes. Conclusions: Together, these findings shed light on the multifactorial basis of alcohol-induced craniofacial defects. In addition to further implicating genetic disruption of the Hh pathway in alcohol teratogenicity, our findings suggest that co-exposure to environmental chemicals that perturb Hh signaling may be important variables in FASD and related craniofacial disorders.

Concepts in Multifactorial Etiology of Developmental Disorders: Gene-Gene and Gene-Environment Interactions in Holoprosencephaly

“…environmental risk factors further interacted with heterozygous mutation of shh (Everson et al, 2020). It should be emphasized that many potential environmental risk factors may require complementary insults for their effects to manifest [e.g., THC in 129S6 mice (Lo et al, 2021)].…”

“…Animal models will be helpful here. A recent study showed that PAE and PBO synergized in a zebrafish model of craniofacial defects, some of which resemble HPE; moreover, this combination of environmental risk factors further interacted with heterozygous mutation of shh ( Everson et al, 2020 ). It should be emphasized that many potential environmental risk factors may require complementary insults for their effects to manifest [e.g., THC in 129S6 mice ( Lo et al, 2021 )].…”

Involvement of homeobox transcription factor Mohawk in palatogenesis

“…3 Notably, alcohol-induced craniofacial defects in zebrafish are increased by loss of a single allele of SHH or by exposure to piperonyl butoxide, another inhibitor of SHH signaling. 4 Several small molecules, including 17-β-estradiol and tolnaftate, have been identified as hedgehog signaling inhibitors with relevant human exposure. 35 Thus, a combination of Mkx mutation and environmental or genetic insults to SHH signaling may increase the risk of cleft palate.…”

Variation in phenotypes from a Bmp-Gata3 genetic pathway is modulated by Shh signaling

“…A growing body of research demonstrates that the Shh pathway is extremely sensitive to environmental attenuation. For instance, the common chemical synergist piperonyl butoxide (PBO) and many dietary molecules such as tomatidine and solanidine can inhibit Shh signaling [47][48][49]. Microsomia is thought to have a large environmental component [26].…”