Timed Notch Inhibition Drives Photoreceptor Fate Specification in Human Retinal Organoids

PURPOSE. Transplanting photoreceptors from human pluripotent stem cell-derived retinal organoids have the potential to reverse vision loss in affected individuals. However, transplantable photoreceptors are only a subset of all cells in the organoids. Hence, the goal of our current study was to accelerate and synchronize photoreceptor differentiation in retinal organoids by inhibiting the Notch signaling pathway at different developmental time-points using a small molecule, PF-03084014 (PF). METHODS. Human induced pluripotent stem cell- and human embryonic stem cells-derived retinal organoids were treated with 10 mu M PF for 3 days starting at day 45 (D45), D60, D90, and D120 of differentiation. Organoids were collected at post-treatment days 14, 28, and 42 and analyzed for progenitor and photoreceptor markers and Notch pathway inhibition by immunohistochemistry (IHC), quantitative PCR, and bulk RNA sequencing (n = 3-5 organoids from three independent experiments). RESULTS. Retinal organoids collected after treatment showed a decrease in progenitor markers (KI67, VSX2, PAX6, and LHX2) and an increase in differentiated pan-photoreceptor markers (OTX2, CRX, and RCVRN) at all organoid stages except D120. PF-treated organoids at D45 and D60 exhibited an increase in cone photoreceptor markers (RXRG and ARR3). PF treatment at D90 revealed an increase in cone and rod photoreceptors markers (ARR3, NRL, and NR2E3). Bulk RNA sequencing analysis mirrored the immunohistochemistry data and quantitative PCR confirmed Notch effector inhibition. CONCLUSIONS. Timing the Notch pathway inhibition in human retinal organoids to align with progenitor competency stages can yield an enriched population of early cone or rod photoreceptors.

Automated summary

The purpose of this study was to accelerate and synchronize the differentiation of photoreceptors in retinal organoids by inhibiting the Notch signaling pathway at different developmental stages using the small molecule PF-03084014. The results showed that treating the organoids with PF resulted in changes in the expression of progenitor and photoreceptor markers, with an increase in differentiated photoreceptor markers and a decrease in progenitor markers. The findings suggest that timing the inhibition of the Notch pathway can enrich the population of early cone or rod photoreceptors in human retinal organoids.