Timed Notch Inhibition drives Photoreceptor fate specification in Human Retinal Organoids

PurposeTransplanting 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). MethodsHuman induced pluripotent stem cell (hiPSC)- and embryonic stem cells (hESC)-derived retinal organoids were treated with 10M PF for three days at day 45 (D45), D60, D90 and D120 of differentiation. Organoids collected at 14-, 28-, and 42-days post-PF treatment were analyzed for progenitor and photoreceptor markers and Notch pathway inhibition by immunohistochemistry (IHC), quantitative PCR (qPCR) and bulk RNA-seq (n=3-5 organoids from 3 independent experiments). ResultsRetinal organoids collected at 14-days post-PF 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-seq analysis mirrored the IHC data and qPCR confirmed Notch effector inhibition. ConclusionsTiming 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.