Human iPSC-derived microglia assume a primary microglia-like state after transplantation into the neonatal mouse brain

Abstract

Microglia are essential for maintenance of normal brain function, with dysregulation contributing to numerous neurological diseases. Protocols have been developed to derive microglia-like cells from human induced pluripotent stem cells (hiPSCs). However, primary microglia display major differences in morphology and gene expression when grown in culture, including down-regulation of signature microglial genes. Thus, in vitro differentiated microglia may not accurately represent resting primary microglia. To address this issue, we transplanted microglial precursors derived in vitro from hiPSCs into neonatal mouse brains and found that the cells acquired characteristic microglial morphology and gene expression signatures that closely resembled primary human microglia. Single-cell RNA-sequencing analysis of transplanted microglia showed similar cellular heterogeneity as primary human cells. Thus, hiPSCs-derived microglia transplanted into the neonatal mouse brain assume a phenotype and gene expression signature resembling that of resting microglia residing in the human brain, making chimeras a superior tool to study microglia in human disease.

Human microglia upregulate cytokine signatures and accelerate maturation of neural networks

“…2H, fig. S4F-N), as has been previously reported (19), with the exception of cytokine-associated microglia that formed two separate clusters composed of primary and transplanted cells, respectively ( Fig. 2H, fig.…”

“…In contrast, microglia of the developing brain are highly heterogeneous and follow stepwise maturation trajectory (17). Whether human microglia undergo similar transitions is currently unclear (18), and comprehensive characterization of prenatal human microglia is needed to benchmark and improve in vitro differentiation protocols (19)(20)(21).…”

“…However, the dynamic nature of microglia gene expression and morphology (40) represents a significant challenge for studies involving human microglia. We generated scRNAseq data for microglia that were induced from pluripotent stem cells using a recently established protocol (21) (see Materials and Methods), and we analyzed recently published data for induced microglia that had been transplanted into in vivo mouse brain (19). We co-embedded both datasets in the space of primary microglia and compared the level of mixing with primary cell clusters ( Fig.…”

Emerging Developments in Human Induced Pluripotent Stem Cell-Derived Microglia: Implications for Modelling Psychiatric Disorders With a Neurodevelopmental Origin

“…One possibility to circumvent this issue is the potential for transplanting hiPSC-derived microglial precursors into adult rodent brains to create chimeric model systems (124,125). Excitingly, this has also been recently demonstrated using neonatal mice, as young as postnatal day 0 (38,126). Importantly, in both adult and neonatal rodent brains, the hiPSC-derived microglial precursors integrated successfully and acquired characteristic microglial morphologies and gene expression signatures, closely resembling that of human primary microglia (38,(124)(125)(126).…”

“…As already mentioned, the transplantation procedure means that the microglia express a transcriptomic signature that is much closer to in vivo human microglia, as compared to culture models, even co-culture or organoid-models, although how much this influenced by the age of the host remains to be characterized in depth (38,124,127). Collectively then, experiments done using patient derived microglia and neurons in vitro may be complemented by parallel in vivo studies using chimeric models, which will likely improve the chances of results from such studies translating into effective human treatments (126). There remain however important limitations to this technique that still need to be overcome.…”