Role of AP-2β Transcription Factor in Early Postnatal Development of the Trabecular Meshwork

Abstract

Purpose : Anterior segment dysgenesis (ASD) is a group of disorders stemming from anomalies in anterior ocular structures, including the trabecular meshwork (TM), leading to abnormalities in aqueous humor production and outflow. Previously, our lab showed that AP-2β transcription factor deletion in neural crest cells contributing to the periocular mesenchyme (POM) resulted in ASD, including absence of a corneal endothelium, iridocorneal adhesions, outflow pathway defects and raised intraocular pressure (IOP). In order to more specifically target the outflow pathway tissue, including the TM, a novel MgpCre mouse line was used to delete AP-2β from the developing TM region (TMR) of the eye.

Methods : MgpCre^+/-;Tfap2b^+/- mice were bred with Tfap2b^lox/lox;tdTomato^lox/lox mice to generate MgpCre^+/-;Tfap2b^-/lox;tdTomato^lox/+ mice (AP-2β TMR KO) with Tfap2b, encoding AP-2β, deleted in the TMR. When crossed with tdTomato mice, control and KO mice express an RFP variant in the presence of Cre, which was used to trace MgpCre-expressing cells. H&E and immunohistochemistry of paraffin sections from AP-2β TMR KO and control eyes was carried out using antibodies for AP-2β and the TM markers, αSMA and myocilin, while IOP was acquired using a rebound tonometer.

Results : In the MgpCre^+/-;tdTomato^lox/+ mice at embryonic day (E) 15.5, MgpCre expression was observed in the POM giving rise to the future TM, and at postnatal day (P) 7 and P14, expression was localized mainly to the iridocorneal angle region. At E15.5 in AP-2β TMR KO mice, tdTomato expression was similar to MgpCre^+/-;tdTomato^lox/+ mice, but by P7 and P14, there were fewer tdTomato-positive cells in the TMR of KO mice. At P14, AP-2β deletion was confirmed in the TMR of mutant mice. Fewer TM cells were observed in the KOs compared to controls, as seen using H&E staining, and αSMA and myocilin expression was reduced in the TM of KO mice. At P30 and P40, IOP was significantly higher in AP-2β TMR KO eyes when compared with control eyes.

Conclusions : The reduced expression of TM markers in the AP-2β TMR KO mice and the reduction in the number of tdTomato-positive cells in the KO suggests that AP-2β expression in the iridocorneal angle region is critical for proper development of TM cells. The increased IOP at P30 and P40 in the KO mice likely resulted from abnormal differentiation of the POM cells into TM cells, which typically contribute to IOP regulation.

This is a 2020 ARVO Annual Meeting abstract.