A Highly Efficient Human Pluripotent Stem Cell Microglia Model Displays a Neuronal-Co-culture-Specific Expression Profile and Inflammatory Response

TLDR

Microglia, derived from yolk‑sac MYB‑independent macrophages that colonize the developing brain, are increasingly implicated in neurodegenerative diseases such as Alzheimer’s, Parkinson’s, and motor neuron disease through expression of disease‑associated genes. The study aims to develop an authentic, efficient in vitro model of human microglia to investigate pathological mechanisms. The authors differentiate embryonic MYB‑independent iPSC‑derived macrophages into microglia and co‑culture them with iPSC‑derived cortical neurons to recapitulate microglial ontogeny. Co‑cultures maintain neuronal maturity and functionality, while microglia express disease‑relevant markers, exhibit dynamic ramification and phagocytosis, and upon activation become ameboid and release cytokines; importantly, they downregulate pathogen‑response pathways, upregulate homeostatic functions, and promote an anti‑inflammatory, pro‑remodeling cytokine profile, outperforming monocultures for modeling authentic microglial physiology.

Abstract

Microglia are increasingly implicated in brain pathology, particularly neurodegenerative disease, with many genes implicated in Alzheimer's, Parkinson's, and motor neuron disease expressed in microglia. There is, therefore, a need for authentic, efficient in vitro models to study human microglial pathological mechanisms. Microglia originate from the yolk sac as MYB-independent macrophages, migrating into the developing brain to complete differentiation. Here, we recapitulate microglial ontogeny by highly efficient differentiation of embryonic MYB-independent iPSC-derived macrophages then co-culture them with iPSC-derived cortical neurons. Co-cultures retain neuronal maturity and functionality for many weeks. Co-culture microglia express key microglia-specific markers and neurodegenerative disease-relevant genes, develop highly dynamic ramifications, and are phagocytic. Upon activation they become more ameboid, releasing multiple microglia-relevant cytokines. Importantly, co-culture microglia downregulate pathogen-response pathways, upregulate homeostatic function pathways, and promote a more anti-inflammatory and pro-remodeling cytokine response than corresponding monocultures, demonstrating that co-cultures are preferable for modeling authentic microglial physiology.