Marius Wernig: Human iPS cell-derived microtissues to study neurodegenerative disease

Human induced pluripotent stem cells \(iPSCs\) and embryonic stem cells \(ESCs\) havebecome valuable tools to investigate disease mechanisms because they can bedifferentiated into various somatic cell types, including those of the central nervoussystem \(CNS\), which are difficult to obtain from primary sources. Microglia are theimmune cells of the central nervous system and are thought to be key players inboth physiological and disease conditions. Several microglial features are poorlyconserved between mice and human, such as the function of the neurodegeneration-associated immune receptor Trem2. iPSC-derived microglia offer a powerfulopportunity to generate and study human microglia. However, human iPSC-derivedmicroglia often exhibit activated phenotypes in vitro, and assessing their impact onother brain cell types remains challenging due to limitations in current co-culturesystems. We developed fully defined brain microtissues, composed of human iPSC-derived neurons, astrocytes, and microgl ia, co-cultured in 2D or 3D formats. Ourmicrotissues are stable and self-sufficient over time, requiring no exogenouscytokines or growth factors. All three cell types exhibit morphologies characteristicof their in vivo environment and show functional properties. Co-cultured microgliadevelop more homeostatic phenotypes compared to microglia exposed toexogenous cytokines. Hence, these tri-cultures provide a unique approach toinvestigate cell-cell interactions between brain cell types. We found that astrocytesand not neurons are sufficient for microglial survival and maturation, and thatastrocyte-derived M-CSF is essential for microglial survival. Single-cell and single-nucleus RNA sequencing analyses nominated a network of reciprocalcommunication between cell types. Brain microtissues faithfully recapitulatedpathogenic α-synuclein seeding and aggregation, suggesting their usefulness ashuman cell models to study not only normal but also pathological cell biologicalprocesses.Division\(s\): MTx \(Molecular Therapeutics\)ision\(s\): MTx \(Molecular Therapeutics\)