Abstract
Current brain spheroids or organoids derived from human induced pluripotent stem cells (hiPSCs) still lack a microglia component, the resident immune cells in the brain. The objective of this study is to engineer brain region-specific organoids from hiPSCs incorporated with isogenic microglia-like cells in order to enhance immune function. In this study, microglia-like cells were derived from hiPSCs using a simplified protocol with stage-wise growth factor induction, which expressed several phenotypic markers, including CD11b, IBA-1, CX3CR1, and P2RY12, and phagocytosed micron-size super-paramagnetic iron oxides. The derived cells were able to upregulate pro-inflammatory gene (TNF-α) and secrete anti-inflammatory cytokines (i.e., VEGF, TGF-β1, and PGE2) when stimulated with amyloid β42 oligomers, lipopolysaccharides, or dexamethasone. The derived isogenic dorsal cortical (higher expression of TBR1 and PAX6) and ventral (higher expression of NKX2.1 and PROX1) spheroids/organoids displayed action potentials and synaptic activities. Co-culturing the microglia-like cells (MG) with the dorsal (D) or ventral (V) organoids showed differential migration ability, intracellular Ca2+ signaling, and the response to pro-inflammatory stimuli (V-MG group had higher TNF-α and TREM2 expression). Transcriptome analysis exhibited 37 microglia-related genes that were differentially expressed in MG and D-MG groups. In addition, the hybrid D-MG spheroids exhibited higher levels of immunoreceptor genes in activating members, but the MG group contained higher levels for most of genes in inhibitory members (except SIGLEC5 and CD200). This study should advance our understanding of the microglia function in brain-like tissue and establish a transformative approach to modulate cellular microenvironment toward the goal of treating various neurological disorders.
Highlights
IntroductionHuman induced pluripotent stem cells (hiPSCs) have shown great potential to generate physiologically relevant neural cells[1], tissues and spheroids (i.e., brain organoids)[2,3,4,5,6,7,8,9,10,11,12,13] for studying neurological disease progression and virus infections (e.g., Zika)[14,15,16,17,18]
The results demonstrate the similarity of human induced pluripotent stem cells (hiPSCs)-derived microglia-like cells with human microglia, suggesting that generating microglia from hiPSCs is possible
vascular endothelial growth factor (VEGF) presence (+VEGF) and absence (−VEGF) conditions were compared in order to elucidate the role of VEGF in microglia (MG) derivation
Summary
Human induced pluripotent stem cells (hiPSCs) have shown great potential to generate physiologically relevant neural cells[1], tissues and spheroids (i.e., brain organoids)[2,3,4,5,6,7,8,9,10,11,12,13] for studying neurological disease progression and virus infections (e.g., Zika)[14,15,16,17,18]. Microglia are resident macrophage-like cells in human brain and account for 5–20% of total neural cells in parenchyma[28,29,30] They have two main functions: immune defense and the maintenance and development of the central nervous system[28,29]. Understanding the roles of microglia in human brain tissue development is expected to greatly facilitate the construction of complex 3D brain-like organoids, thereby advancing neurological disease modeling and drug screening[43,44]. Built on our previous studies, it is hypothesized that incorporation of microglia-like cells enhances immune response ability of cortical spheroids/organoids with different regional identity, i.e., dorsal or ventral. This study should advance our understanding of microglia function in brain-like tissue and establish a transformative approach to modulate cellular microenvironment for treating various neurological disorders through novel drug discovery
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