PAX6-positive microglia evolve locally in hiPSC-derived ocular organoids

概要

〔目的(Purpose)〕
Purpose; Microglia are the resident immune cells of the central nervous system (CNS). The CNS is inaccessible to immune cells in general circulation owing to the presence of the blood-brain barrier. Instead, microglial cells in the brain and spinal cord provide the CNS with its immune protection. Microglia deliver immune protection for the posterior eye, including the neural retina, and have involvement with some sight-threatening conditions, such as age-related macular degeneration, uveitis and glaucoma and retinal degeneration. However, it is not known how microglia develop in the eye.

〔方法ならびに成績(Methods/Results)〕
Metliods; We studied human-induced pluripotent stem cells (hiPSCs) that had been expanded into a self-formed ectodermal autonomous multi-zone (SEAM) (Hayashi et al. Nature 2016;531:376-380) of cells that partially mimics human eye development. We searched and investigated microglia-like cells, and sorted the cells. After that, we examined them by qPCR, cytokine analysis, RNA-seq and single-cell RNA-seq.

Results; We generated 2D eye-like organoids from hiPSCs, which we discovered contained immune cells with significant similarity to microglia cells. RNA-sequencing data and qPCR, moreover, showed that the cells are more similar to primary microglia cells than to human immortalised microglia. The results of functional stimulation assays revealed that PPM cells likely govern immune tolerance in ocular tissue. Single-cell RNA sequencing further indicates that they resemble yolk sac-derived myeloid progenitors and not macrophages.

〔総括(Conclusion))
Conclusions; Our results indicated that microglia-like cells, which have characteristics of yolk sac-like linage cells, natxirally develop in two-dimensional eye-like SEAM organoids,which lack any vascular components. These cells are unique in that they are paired box protein 6 (PAX6) positive, yet possess some characteristics of mesoderm. Our data support the possibility of the existence of an isolated, locally developing immune system in the eye, which is independent of the body's vasculature and general immune system.