Integrating human iPSC‐derived macrophage progenitors into retinal organoids to generate a mature retinal microglial niche

Abstract

In the retina, microglia are resident immune cells that are essential for development and function. Retinal microglia play a central role in mediating pathological degeneration in diseases such as glaucoma, retinitis pigmentosa, age‐related neurodegeneration, ischemic retinopathy, and diabetic retinopathy. Current models of mature human retinal organoids (ROs) derived from iPS cell (hiPSC) do not contain resident microglia integrated into retinal layers. Increasing cellular diversity in ROs by including resident microglia would more accurately represent the native retina and better model diseases in which microglia play a key role. In this study, we develop a new 3D in vitro tissue model of microglia‐containing retinal organoids by co‐culturing ROs and hiPSC‐derived macrophage precursor cells (MPCs). We optimized the parameters for successful integration of MPCs into retinal organoids. We show that while in the ROs, MPCs migrate to the equivalent of the outer plexiform layer where retinal microglia cells reside in healthy retinal tissue. While there, they develop a mature morphology characterized by small cell bodies and long branching processes which is only observed in vivo. During this maturation process these MPCs cycle through an activated phase followed by a stable mature microglial phase as seen by the down regulation of pro‐inflammatory cytokines and upregulation of anti‐inflammatory cytokines. Finally, we characterized mature ROs with integrated MPCs using RNAseq showing an enrichment of cell‐type specific microglia markers. We propose that this co‐culture system may be useful for understanding the pathogenesis of retinal diseases involving retinal microglia and for drug discovery directly in human tissue.

Application of patient-derived induced pluripotent stem cells and organoids in inherited retinal diseases

“…However, the lack of vascular networks, immune cells, continuous RPE monolayer, and the central nervous system may limit RO generation and development. Co-culture systems for interaction between multi-organoids, or organoids with cells/spheroids, have been studied to address the constraints of traditional organoid cultivation [ 143 – 147 ]. Meanwhile, establishing an organoid culture system with standardized, high-throughput, and undifferentiated operations is required.…”

The new era of cardiovascular research: revolutionizing cardiovascular research with 3D models in a dish

“…Therefore, integrating immune cells into 3D models of cardiovascular diseases emerges as a pivotal research avenue. In other organoid fields, to address the absence of immune cells involves establishing co-culture of retinal organoids with hiPSC-derived macrophage precursor cells [ 185 ] or co-differentiation of immune cells during the brain organoid differentiation process [ 186 ]. Similar strategies could be applied to cardiac organoids, but with some caution, as immune cells exhibit significant heterogeneity in terms of morphology, gene expression profile, physiological properties, and function, which are determined by their developmental origin and tissue microenvironment [ 187 ].…”

Classical and Innovative Evidence for Therapeutic Strategies in Retinal Dysfunctions

“…Different studies have shown that when human induced pluripotent stem cells (hiPSCs) were treated with RPE-derived factors, or cocultured along with RPE cells, it was possible to observe an improvement in the maturation of organoids and in the differentiation of photoreceptors [224,225]. Recently, Usui-Ouchi and colleagues [226] have generated mature ROs with integrated macrophage precursor cells, thus producing a model implemented with microglial cells that may be of great importance in the study of retinal pathologies involving retinal microglia.…”