The long-term goal of this project is to delineate the signaling mechanisms of retinoic acid (RA) in the regulation of programmed cell death (PCD) during the early stage of ocular lens and anterior segment development. This precisely controlled PCD is essential for normal separation of the lens vesicle from the overlying surface ectoderm (or the prospective corneal epithelium) in lens morphogenesis. Disruption of this PCD, either by genetic mutations or by environmental insults during human embryogenesis, causes a blinding congenital eye disease, called Peters'anomaly, which is a subtype of anterior segment dysgenesis (ASD). We hypothesize that RA (a vitamin A metabolite) and activation of the mitochondrial apoptosis pathway play an essential role in the induction of PCD during early-stage lens development. Three overlapping specific aims are proposed: 1) Our preliminary studies indicate that loss-of-function mutation in retinol dehydrogenase 10 (Rdh10), an enzyme in the first step of RA synthesis, inhibits PCD and causes formation of a persistent lens stalk between the lens and cornea. This finding suggests that RA-signaling is essential for induction of PCD in lens-corneal separation during eye development.
In Aim 1, we will explore the interactions between the RA- induced apoptotic signal and the cell survival signals activated by fibroblast growth factor (FGF) and bone morphogenic protein (BMP) signaling during lens vesicle development. 2) In Aim 2, we will delineate the position of RA-signaling in the previously established genetic pathway of Pax6-Foxe3. Both transcriptional factors are known to be essential for lens-corneal separation during mouse eye development, and mutations in these genes are linked to Peters'anomaly in humans. 3) Preliminary studies show that in the eyes of apoptosis-defective mutant mice (e.g., Cytochrome cKA/KA knockin mice), a persistent lens stalk is formed and disrupts normal anterior segment morphogenesis. To better understand the pathogenic mechanisms of severe congenital glaucoma in children with Peters'anomaly, in Aim 3, we will examine the manifestations of developmental abnormalities in the anterior segment tissues by using the mutant mice models that are defective in the mitochondrial death pathway. In summary, this project will contribute to the fundamental knowledge of RA-signaling in regulation of PCD during early lens development, and will have an important impact on expanding our understanding of the pathogenesis of Peters'anomaly in children. Overall, this project examines a critical, though neglected, area of eye development and has important implications for pediatric ophthalmology.
This project investigates the mechanisms of vitamin A metabolite retinoic acid (RA)-signaling and programmed cell death (PCD) in the early stage of ocular lens and anterior eye development. During human embryonic eye development, dietary vitamin A deficiency or disruption of PCD by either gene mutations or environmental insults can lead to blinding congenital eye diseases, called Peters'anomaly and anterior segment dysgenesis (ASD). Knowledge gained from this project will contribute to our understanding of human eye development and diseases, and will be helpful in the development of interventions for prevention and treatment of congenital eye disorders.