Human Retina-on-a-Chip: Merging retinal organoids with Organ-on-a-Chip technology

Abstract

Purpose : The development of new compounds for the treatment of hereditary and sporadic retinal diseases demands the use of adequate preclinical models. Currently available models such as animals and static cell cultures do not reflect the human retinal biology in its entirety. The discovery of human induced pluripotent stem cells (iPSC) and the generation of iPSC-derived retina-like tissues called retinal organoids (RO) provides the basis for a paradigm shift in ophthalmic research. ROs harbor all known retinal cell types as well as a physiological layering. However, they still lack a controlled and stable interaction of photoreceptors and retinal pigmented epithelial cells (RPE) as well as a vascularization. To overcome this issue, we integrated ROs and RPE in a tailored microfluidic organ-on-a-chip platform, creating the retina-on-a-chip (RoC).

Methods : Human iPSC-RO and RPE were derived based on a protocol adapted from Zhong et al. (2014). The RoC was designed to enable the adherent culture of iPSC-RPE in close apposition to hydrogel-embedded ROs. The RoC is fabricated via photolithography and replica molding techniques. Photoreceptor segment maturation and phagocytosis were analyzed by immunocytochemistry and electron microscopy.

Results : The RoC enabled the culture of retinal tissue based on RPE and ROs for multiple weeks while being supplied by a vasculature-like perfusion. The proximity-culture of the RO to the RPE induced an in vivo-like dense growth of photoreceptor outer segments featuring an enhanced segment maturation in comparison to classically dish cultured RO and RoCs lacking the RPE. Moreover, the RoC culture enabled the recapitulation of one of the primary physiological features of the inner retina: the phagocytosis of segments by the RPE. Based on immunofluorescence staining and electron microscopy, we were able to confirm the phagocytosis of outer segment-like structures by the epithelial cells. To assess the capability of the RoC as a drug screening platform, we exposed the chips to chloroquine and gentamicin and successfully reproduced the drug-specific retinopathic side effects.

Conclusions : In summary, the RoC provides a powerful new model system of the human retina, which enables for the first time to study the interaction of photoreceptors and RPE cells in vitro. The RoC is a promising tool for testing and developing of new drug compounds as well as for studying (patho)mechanistic questions.

This abstract was presented at the 2019 ARVO Annual Meeting, held in Vancouver, Canada, April 28 - May 2, 2019.