ABCB5 identifies RPE progenitor cells required for normal retinal development and aging

Abstract

Purpose : RPE might contain subpopulations of progenitor cells with multipotent differentiation potential; however, no specific molecular marker for such subpopulations has been described to date. Recently, we identified ATP binding cassette member B5 (ABCB5) as a marker for mammalian limbal stem cells, with essential roles in normal corneal development and repair. In the current study, we describe that ABCB5 also identifies a novel progenitor subpopulation among RPE with essential functions in retinal development and regeneration.

Methods : RPE cells were recovered from choroidal flat mounts isolated from 2 months-old C57BL/6J mice and from human cadaveric donors. Analysis of ABCB5 expression in mouse and human RPE was done by dual-color flow cytometry using two distinct murine and human anti-ABCB5 monoclonal antibodies (mAb) described previously (Ksander et al., Nature 2014). Abcb5 knock out (KO) mice were generated as previously described (Ksander et al., Nature 2014) and maintained on a 129S6/SvEvTac/C57BL/6 mixed genetic background. Gender-matched littermates were used as controls for experimental analyses. Comparative histopathology of Abcb5 WT and Abcb5 KO retinas was done by examination of H&E-stained sections of 9 months old mice.

Results : Flow cytometric analyses of human and murine RPE cell suspensions revealed that ABCB5 was expressed in 2-8% of RPE cells. Additional studies demonstrated that a portion of ABCB5-positive cells did not express the marker of differentiated RPE cells, RPE65. Moreover, histological examination of Abcb5 KO mice revealed significantly reduced RPE cell numbers associated with abnormal RPE morphology and vacuolization. Additionally, Abcb5 KO animals also exhibited thinning and attenuation of the overlaying photoreceptor outer and inner segments, and reduced cell numbers in the outer nuclear layer.

Conclusions : ABCB5 identifies a novel progenitor cell population in RPE, which lacks expression of the RPE differentiation marker RPE65, but is essential for retinal development and regeneration.

This is an abstract that was submitted for the 2016 ARVO Annual Meeting, held in Seattle, Wash., May 1-5, 2016.