39 - Prenatal Alcohol Exposure and Disrupted Ear Development: Investigating the Role of the Sonic Hedgehog Signaling Pathway

Poster Board Number: 39
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Co-authors:

Alyssa Moore - Graduate Student, University of Western Ontario; Brian Allman - Associate Professor, University of Western Ontario; Katherine Willmore - Assistant Professor, University of Western Ontario

Abstract Body : Introduction: Prenatal alcohol exposure (PAE) can lead to adverse fetal outcomes collectively known as fetal alcohol spectrum disorder (FASD). One such outcome experienced by 57% of children with FASD is hearing loss, including conductive (damage to middle ear ossicles) and sensorineural (damage to cochlear cells and the auditory nerve), yet the molecular underpinnings of this hearing loss are unknown. A possible candidate is the sonic hedgehog (Shh) pathway, as Shh plays a key role in ossicle and cochlear development and its expression is disrupted following PAE. Although Shh signaling plays a critical role in ear development, and PAE disrupts Shh signaling, the effect of PAE on Shh signaling in the developing ossicles and cochlea, remain unknown. Using a mouse model of PAE, we will test the hypothesis that PAE disrupts middle and inner ear development by altering Shh signaling.

Methods: To determine the effects of PAE on Shh signaling in ear development, pregnant C57BL/6 dams will be administered water (vehicle) or ethanol (PAE) via oral gavage on gestational day (GD) 7.5. To verify that outcomes following PAE are caused by altered Shh signaling, a subset of vehicle dams will receive vismodegib a Shh inhibitor (ShhDef), and a subset of PAE dams will receive SAG, a small molecule Shh signaling agonist (PAE + Shh). The middle ear ossicles receive Shh signaling from pharyngeal arch (PA) ectoderm during their development. We will investigate the effect of PAE on Shh gene and protein expression within the PAs and developing ossicles as well as expression of key Shh targets Gli1 and Ptch1. The cochlea develops from the ventral otocyst and receives Shh signaling from the neural tube and notochord. Thus, we will measure gene and protein expression of Shh, Gli1 and Ptch1 in the developing otocyst, neural tube and notochord. We will also determine the effects of PAE and Shh signaling on fully developed ossicle and cochlear morphology. Ossicle shape of postnatal day (P) 10 offspring will be measured from 3D landmark data obtained from high-resolution micro-CT images. Morphology of the sensory hair cells and spiral ganglion neurons within the cochlea will be assessed using immunofluorescence in P60 offspring.

Expected Outcomes & Significance: We predict that PAE alters Shh signaling in the developing ossicles and cochlea and as such, patterns of signaling and morphological outcomes will be similar in our PAE and ShhDef groups. Moreover, we expect that administering Shh will help rescue the effects of PAE and that signaling and phenotypic outcomes in our Shh + PAE offspring will resemble vehicle mice. Our results may uncover a key molecular pathway involved in hearing loss following PAE that could help guide pharmacological intervention.

Funding: Children’s Health Research Institute Internal Grant Fund