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Alzheimer's Risk Gene TREM2 Determines Functional Properties of New Type of Human iPSC-Derived Microglia
Marvin Reich1,2, Iñaki Paris1,3, Martin Ebeling4
1Roche Pharma Research and Early Development, Neuroscience and Rare Diseases Discovery and Translational Area, Roche Innovation Center Basel, F. Hoffmann-La Roche Ltd, Basel, Switzerland.
Abstract:
Microglia are key in the homeostatic well-being of the brain and microglial dysfunction has been implicated in neurodegenerative disorders such as Alzheimer's disease (AD). Due to the many limitations to study microglia in situ or isolated for large scale drug discovery applications, there is a high need to develop robust and scalable human cellular models of microglia with reliable translatability to the disease. Here, we describe the generation of microglia-like cells from human induced pluripotent stem cells (iPSC) with distinct phenotypes for mechanistic studies in AD. We started out from an established differentiation protocol to generate primitive macrophage precursors mimicking the yolk sac ontogeny of microglia. Subsequently, we tested 36 differentiation conditions for the cells in monoculture where we exposed them to various combinations of media, morphogens, and extracellular matrices. The optimized protocol generated robustly ramified cells expressing key microglial markers. Bulk mRNA sequencing expression profiles revealed that compared to cells obtained in co-culture with neurons, microglia-like cells derived from a monoculture condition upregulate mRNA levels for Triggering Receptor Expressed On Myeloid Cells 2 (TREM2), which is reminiscent to the previously described disease-associated microglia. TREM2 is a risk gene for AD and an important regulator of microglia. The regulatory function of TREM2 in these cells was confirmed by comparing wild type with isogenic TREM2 knock-out iPSC microglia. The TREM2-deficient cells presented with stronger increase in free cytosolic calcium upon stimulation with ATP and ADP, as well as stronger migration towards complement C5a, compared to TREM2 expressing cells. The functional differences were associated with gene expression modulation of key regulators of microglia. In conclusion, we have established and validated a work stream to generate functional human iPSC-derived microglia-like cells by applying a directed and neuronal co-culture independent differentiation towards functional phenotypes in the context of AD. These cells can now be applied to study AD-related disease settings and to perform compound screening and testing for drug discovery.
Insights
Researchers developed a new method to create human microglia-like cells from stem cells for Alzheimer's disease (AD) research. These cells mimic disease-associated microglia and offer a scalable model for drug discovery and studying AD mechanisms.
Area of Science:
- Neuroscience
- Stem Cell Biology
- Immunology
Background:
- Microglia are crucial for brain health, but their dysfunction is linked to neurodegenerative diseases like Alzheimer's disease (AD).
- Studying microglia in their natural environment or isolating them for drug discovery is challenging.
- There is a significant need for effective, scalable human cellular models of microglia for AD research.
Purpose of the Study:
- To generate functional human microglia-like cells from induced pluripotent stem cells (iPSCs) for AD mechanistic studies.
- To develop a robust and scalable differentiation protocol independent of neuronal co-culture.
- To create models that mimic disease-associated microglia phenotypes for drug discovery.
Main Methods:
- Utilized an established protocol to generate primitive macrophage precursors from iPSCs, mimicking yolk sac-derived microglia.
- Systematically tested 36 monoculture differentiation conditions using various media, morphogens, and extracellular matrices.
- Performed bulk mRNA sequencing to analyze gene expression profiles and validated findings using TREM2 knock-out iPSC microglia.
Main Results:
- Optimized protocol yielded ramified microglia-like cells expressing key microglial markers.
- Monoculture-derived cells showed upregulated Triggering Receptor Expressed On Myeloid Cells 2 (TREM2) mRNA, similar to disease-associated microglia.
- TREM2-deficient cells exhibited altered calcium signaling and enhanced migration responses compared to TREM2-expressing cells.
Conclusions:
- Established a validated workflow for generating functional, iPSC-derived microglia-like cells in a monoculture system.
- The developed cells exhibit distinct phenotypes relevant to AD, including TREM2 modulation.
- These human iPSC-microglia models are suitable for studying AD pathogenesis and for compound screening in drug discovery.
