Visual system development is a highly complex process involving coordination of environmental cues, cell signals, and integration of functional circuits. Consequently, a change to any step, due to a mutation or chemical exposure, can lead to deleterious consequences. One class of chemicals known to have both overt and subtle effects on the visual system is endocrine disrupting compounds (EDCs). EDCs are environmental contaminants; most target estrogen signaling by either preventing estrogen synthesis or binding to estrogen receptors. Developmental disruption of estrogen synthesis in animal models causes apoptotic cell death, thinning in retina and cornea, and abnormal and delayed eye growth, indicating estrogen signaling is critical for proper development. Estrogen also maintains eye function: age-related changes in estrogen levels are associated with neurodegenerative retinal diseases and estrogen modulation as a clinical treatment for breast cancer leads to vision related complications. Unfortunately, we know very little about the mechanisms and long-term impact of abnormal estrogenic signaling on visual sensation and perception. We propose to use zebrafish to address this by directly manipulating estrogenic pathways during constrained periods of visual system development and examining the functional impact on adult retinal anatomy, physiology, and visually guided behaviors. Uniquely, we will compare the effects of two well-known, environmentally relevant compounds, tributyltin (TBT), an estrogen synthesis (aromatase) inhibitor, and bisphenol A (BPA), an estrogen agonist, with the effects of 4-OH-A, a standard inhibitor and cancer treatment drug, and estradiol, the biologically relevant estrogen. Zebrafish (Danio rerio) is the ideal animal model for this study: retinal anatomy is similar to humans, sensory development depends on estrogen signaling, and aromatase and estrogen receptor expression patterns have been well categorized; developmental timing of eye and retina, categorization of vision based behaviors, and physiological responses have also been documented. Our central hypothesis is that developmental manipulation of estrogen signaling will target specific retinal cell types causing functional deficits in vision physiology and behavior in adult animals. We will test this hypothesis by first confirming compound efficacy and mechanism of action ex vivo using whole brain homogenates (Aim. 1.1) and in vivo by direct uptake of compounds via tank water (Aim 1.2). We will then screen for behavioral (Aim 2.1) and physiological (Aim 2.2) changes to the adult zebrafish visual system followed by more detailed patch clamp (Aim 3.1) and histological (Aim 3.2) analyses to identify which retinal cells/circuits are compromised by compound exposure. The expected results are relevant to diseases that involve retinal/visual disruptions, to studies in which therapeutic agents target the endocrine system, and to further examination of mechanisms underlying EDC-associated changes in neuronal function, perception, and/or behavior resulting from aberrant estrogen signaling.
(PUBLIC HEALTH RELEVANCY STATEMENT) This study will test the hypothesis that developmental manipulation of estrogen signaling by endocrine disrupting compounds (EDCs), targets specific retinal cell types causing functional deficits in vision physiology and behavior in adult animals. Estrogen is critical for both the development of the eye and maintenance of proper vision and most EDCs target estrogenic pathways, suggesting a direct effect of these ubiquitous environmental contaminants on the visual system. Our results using zebrafish, an existing vertebrate model, will be relevant to studies of complications from prescribed treatments, clinical diseases that involve retinal/visual disruptions, and long-term EDC effects resulting from abnormal estrogen signaling.
