Microglia-like Cells Promote Neuronal Functions in Cerebral Organoids

Abstract

Human cerebral organoids, derived from induced pluripotent stem cells, offer a unique in vitro research window to the development of the cerebral cortex. However, a key player in the developing brain, the microglia, do not natively emerge in cerebral organoids. Here we show that erythromyeloid progenitors (EMPs), differentiated from induced pluripotent stem cells, migrate to cerebral organoids, and mature into microglia-like cells and interact with synaptic material. Patch-clamp electrophysiological recordings show that the microglia-like population supported the emergence of more mature and diversified neuronal phenotypes displaying repetitive firing of action potentials, low-threshold spikes and synaptic activity, while multielectrode array recordings revealed spontaneous bursting activity and increased power of gamma-band oscillations upon pharmacological challenge with NMDA. To conclude, microglia-like cells within the organoids promote neuronal and network maturation and recapitulate some aspects of microglia-neuron co-development in vivo, indicating that cerebral organoids could be a useful biorealistic human in vitro platform for studying microglia-neuron interactions.

Electrophysiological Properties of Human Cortical Organoids: Current State of the Art and Future Directions

“…Erythromyeloid progenitors (EMPs), microglia precursors, were generated from iPSCs and incorporated to cerebral organoids at an early maturation stage (Fagerlund et al, 2021).…”

“…Due to the different germ layer origin, microglial cells are not present in cortical organoids and need to be infiltrated from external sources ( Figure 1 ). Transplantation of primary human fetal microglia or iPSC-derived microglial progenitors ( Fagerlund et al, 2021 ; Popova et al, 2021 ) showed that microglia or their precursors can spontaneously integrate in the organoid tissue, eventually transitioning from an immature amoeboid state to a ramified morphology indicating a homeostatic surveillance role ( Fagerlund et al, 2021 ; Popova et al, 2021 ).…”

“…Erythromyeloid progenitors (EMPs), microglia precursors, were generated from iPSCs and incorporated to cerebral organoids at an early maturation stage ( Fagerlund et al, 2021 ). The incorporated EMPs infiltrated the organoid, establishing a microglial population, which then colonized the organoid.…”

“…Differentiated microglia were found to interact with synapses, reducing the number of synaptic puncta, without inducing an inflammatory response. Interestingly, when recorded using whole-cell patch clamping between 107–165 days in culture, organoids containing microglia showed increases in both sodium and potassium current densities, without any changes in the basal electrophysiological parameters of the neurons ( Fagerlund et al, 2021 ). This translated in an increased prevalence of neurons able to fire repetitive APs ( Fagerlund et al, 2021 ).…”

“…Interestingly, when recorded using whole-cell patch clamping between 107–165 days in culture, organoids containing microglia showed increases in both sodium and potassium current densities, without any changes in the basal electrophysiological parameters of the neurons ( Fagerlund et al, 2021 ). This translated in an increased prevalence of neurons able to fire repetitive APs ( Fagerlund et al, 2021 ). Importantly, in this model sEPSCs were recorded in cerebral organoids with microglia but not in those without.…”