Human microglia in brain assembloids display region- specific diversity and respond to hyperexcitable neurons carrying SCN2A mutation: Microglial diversity and response in assembloids
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Microglia critically shape neuronal circuit development and function, yet their region-specific properties and roles in distinct circuits of the human brain remain poorly understood. In this study, we generated region-specific brain organoids (cortical, striatal, and midbrain), each integrated with human microglia, to fill this critical gap. Single-cell RNA sequencing uncovered six distinct microglial subtypes exhibiting unique regional signatures, including a subtype highly enriched for the GABA B receptor gene within striatal organoids. To investigate the contributions of microglia to neural circuitry, we created microglia-incorporated midbrain-striatal assembloids, modeling a core circuit node for many neuropsychiatric disorders including autism. Using chemogenetics to activate this midbrain-striatal circuit, we observed increased calcium signaling in microglia involving GABA B receptors. Leveraging this model, we examined microglial responses within neural circuits harboring an SCN2A nonsense (C959X) mutation associated with profound autism. Remarkably, microglia displayed heightened calcium responses to SCN2A mutation-mediated neuronal hyperactivity, and engaged in excessive synaptic pruning. These pathological effects were reversed by pharmacological inhibition of microglial GABA B receptors. Collectively, our findings establish an advanced platform to dissect human neuroimmune interactions in sub-cortical regions, highlighting the important role of microglia in shaping critical circuitry related to neuropsychiatric disorders.
Teaser
Modeling regional microglial diversity in sub-cortical regions is challenging. We generated human organoid and assembloid models containing microglia that acquire region-specific heterogeneity. Our work shows dynamic responses of microglia when exposed to hyperexcitable midbrain-striatal circuits, providing an exciting platform to study neuroimmune interactions in human brain development and neuropsychiatric disorders, including SCN2A mutation-mediated monogenic autism.
Highlights
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Single-cell RNA sequencing analyses reveal six distinct microglial subtypes that spontaneously attain unique specialization in human cortical, striatal, and midbrain organoids.
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Microglia facilitate axonal projections across regional organoids, promoting assembloid formation.
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Microglia respond to hyperexcitable neurons via calcium signaling and exhibit excessive pruning of neuronal synapses.
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Blocking microglial GABA B receptors normalizes calcium activity and reduces synaptic pruning, suggesting a potential targeting strategy for synaptic deficits.
