Preventing Ethanol-Induced Brain and Eye Morphology Defects Using Optogenetics

Abstract

Background: Embryonic exposure to the teratogen ethanol leads to dysmorphias, including eye and brain morphology defects associated with fetal alcohol spectrum disorder (FASD). Exposure of Xenopus laevis embryos to ethanol leads to similar developmental defects, including brain and eye dysmorphism, confirming our work and the work of others showing Xenopus as a useful system for studies of the brain and eye birth defects associated with FASD. Several targets of ethanol action have been hypothesized, one being regulation of Kir2.1 potassium channel. Endogenous ion fluxes and membrane voltage variation (bioelectric signals) have been shown to be powerful regulators of embryonic cell behaviors that are required for correct brain and eye morphology. Disruptions to these voltage patterns lead to spatially correlated disruptions in gene expression patterns and corresponding morphology. Materials and Methods: Here, we use controlled membrane voltage modulation to determine when and where voltage modulation is sufficient to rescue ethanol-induced brain and eye defects in Xenopus embryos. Results: We found (1) that modulating membrane voltage using light activation of the channelrhodopsin-2 variant D156A rescues ethanol exposed embryos, resulting in normal brain and eye morphologies; (2) hyperpolarization is required for the full duration of ethanol exposure; (3) hyperpolarization of only superficial ectoderm is sufficient for this effect; and(4) the rescue effect acts at a distance. Conclusions: These results, particularly the last, raise the exciting possibility of using bioelectric modulation to treat ethanol-induced brain and eye birth defects, possibly with extant ion channel drugs already prescribed to pregnant women. This may prove to be a simple and cost-effective strategy for reducing the impact of FASD.

HCN2 channel‐induced rescue of brain, eye, heart and gut teratogenesis caused by nicotine, ethanol and aberrant notch signalling

“…[97][98][99] Xenopus is a wellestablished model for ethanol-induced brain and eye morphology defects. 69,[99][100][101][102] We first tested whether HCN2 expression can rescue ethanol-induced brain and eye defects. Ethanol (2%) exposure was applied at stages 9-40 based on our previous analysis of exposure regime that is most effective at disrupting brain and eye patterning.…”

“…Several different teratogenic influences (including nicotine, ethanol and Notch disruption) exert their effect by wiping out or reducing the bioelectric difference that serve as boundaries of developmental compartments 20,21,23,41,68,69 (Figure 1A). A computational model of nicotineinduced brain teratogenesis caused by such bioelectrical change identified HCN2 as a candidate intervention that could reverse the effects by sharpening and restoring those bioelectrical differences.…”

Alcohol and the Eye

“…[41] More recently, modulation of ion channel has been studied for their potential ability in reducing ocular defects in FAS. [46] In animal models, blue light-mediated hyperpolarization of membranes through ChR2D156A channels rescued ethanolinduced eye structural defects. [46]…”

“…[46] In animal models, blue light-mediated hyperpolarization of membranes through ChR2D156A channels rescued ethanolinduced eye structural defects. [46]…”

Zebrafish models of fetal alcohol spectrum disorders

“…For instance, animal models have proven crucial in showing that ethanol is the teratogenic source of FASD, developing our understanding of FASD and the gene‐ethanol interactions that underlie it (Ali, Champagne, Alia, & Richardson, 2011; Kiecker, 2016; C. B. Lovely, 2020; C. B. Lovely, Fernandes, & Eberhart, 2016; Riley, Infante, & Warren, 2011; Smith, Garic, Flentke, & Berres, 2014; Stockard, 1910; Sulik, 2005). To fully recapitulate the impact of prenatal ethanol exposure on human development, many different species have been used, including nonhuman primates, rodents, birds, frogs, and fish (Comeau et al, 2015; Fainsod & Kot‐Leibovich, 2018; Fujisawa et al, 2019; Hong & Zha, 2019; Kelly et al, 2009; Kiecker, 2016; Kot‐Leibovich & Fainsod, 2009, p.; Pai & Adams, 2019; Patten et al, 2014; Sulik, 2005; Wang, Williams, Haasch, & Dasmahapatra, 2006; Wentzel & Eriksson, 2008). By combing the strengths of all these model systems, we have made great inroads in understanding the mechanistic underpinnings of the gene‐ethanol interactions driving FASD.…”