Abstract
Purpose :
Microglia are the resident immune cells of the central nervous system (CNS). Since the immune cells from the general circulation cannot reach the CNS due to the blood-brain barrier, the brain and spinal cord microglial cells provide immune protection for CNS. Also, the microglia provide immune protection to the posterior eye, including the neural retina, and are involved in some sight-threatening conditions, such as age-related macular degeneration, uveitis, glaucoma, and retinal degeneration. However, it is not known how the microglia develop in the eye.
Methods :
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 mimicked the human eye development. We searched and investigated the microglia-like cells, sorted them, and examined them by quantitative polymerase chain reaction (qPCR), cytokine analysis, RNA sequencing (seq), and single-cell RNA seq.
Results :
We discovered that they contained immune cells that were significantly similar to the microglia cells in SEAM. Moreover, the RNA-seq data and qPCR showed that the cells were more similar to primary microglia cells than to immortalized human microglia. The results of the functional stimulation assays revealed that the sorted cells are likely govern immune tolerance in the ocular tissue. Furthermore, single-cell RNA seq revealed that the cells resembled yolk sac-derived myeloid progenitors and not macrophages.
Conclusions :
Our results showed that microglia-like cells showing characteristics of yolk sac-like linage cells naturally develop in SEAM organoids, which lack vascular components. These cells are unique because they are paired box protein 6 (PAX6)-positive, yet possess some characteristics of the mesoderm. Our data support the possibility of the existence of an isolated and locally developing immune system in the eye, which is independent of the body’s vasculature and general immune system.
This abstract was presented at the 2022 ARVO Annual Meeting, held in Denver, CO, May 1-4, 2022, and virtually.