The role of ADAM10 in retinal development

Abstract

Purpose: ADAM10 belongs to a disintegrin and metalloproteinase (ADAM) family of transmembrane Zn²⁺ proteases that have a role in ectodomain cleavage or “shedding” of membrane bound proteins. Although in vitro studies have identified numerous proteins as ADAM10 substrates, Adam10^-/- mice exhibit lethality at E9.5 and abnormal embryonic phenotypes consistent with defects in Notch signaling. Thus, ADAM10 has been proposed as the principal sheddase involved in cleaving of NOTCH1 although other ADAMs such as ADAM17 have also been shown to be involved. During retinal development Notch signaling plays an essential role in the maintenance of the progenitor pool as well as in the progenitor cell fate specification, however the role of ADAM10 in the retina has never been investigated. The goal of this study was to evaluate the role of ADAM10 during retinal development and its role in Notch signaling.

Methods: CKO Adam10¬Six3-Cre mice were generated by breeding Adam10^f/f to Six3-Cre/+ mice. Embryonic and postnatal retinas were H&E analyzed. Proliferation and apoptosis were evaluated using EdU and TUNEL assays, respectively. Immunohistological analyses were performed using antibodies for ADAM10, ISL1, OTX2, NOTCH1, N1ICD, RBPJ, HES1, HES5, β-catenin, and N-cadherin.

Results: Embryonic and postnatal CKO Adam10¬-Six3-Cre mice exhibited severe retinal disorganization and rosette formation. Immunohistochemical analyses identified alteration in NOTCH1 signaling characterized with a decrease in the number of proliferating progenitors and an increase in the number of cones and a significant increase in the number of ganglion cells. Furthermore, mislocalization of N-cadherin and a loss of β-catenin expression at the apical retinal surface were also identified.

Conclusions: Ablation of Adam10 in the developing retina leads to premature depletion of the progenitor cell pool and upregulation of cone and ganglion cell differentiation. In addition, abnormal N-cadherin/β-catenin expression most likely is responsible for the rosette formation and lamination abnormalities observed in these mice. Collectively these findings suggest that ADAM10 may be involved in both NOTCH1 and NOTCH3 signaling. Currently NICD rescue studies are underway to determine if NOTCH3 or possible other proteins may be ADAM10 targets during retinal development.

Keywords: 698 retinal development • 648 photoreceptors • 531 ganglion cells