Microglia Differentiation Protocols

Publication: Guttikonda et al., Nat Neurosci, 2021

Description: Guttikonda et al., describes a method to generate microglia from human pluripotent stem cells (hPSCs) that offers a robust and efficient approach, enabling high purity and functionality of the derived microglia. This method does not require hypoxic conditions or sorting procedures. It is designed to produce microglia that closely resemble their primary counterparts, making it an invaluable tool for researchers working with microglia cultures.

Protocol highlights:

• Reproducible: The protocol reproducibly generated a pure population of IBA1+ microglial cells out of 10 different hPSC lines.
• Similarity to primary microglia: The hPSC-derived microglia express key microglial-specific markers (such as TMEM119, C1QA, CX3CR1, GPR34) at levels comparable to primary human microglia, ensuring functional relevance.
• Efficient and timely production: The protocol allows for the efficient production of microglia within 25 days, making it faster than many existing methods.
• Functional maturation: The protocol mimics in vivo conditions by co-culturing with cortical neurons and using cytokines like IL-34 and M-CSF, which are crucial for microglial survival and maturation.
• Scalability: The method doesn't require sorting process. That would support the generation of large numbers of microglia, which is beneficial for extensive research and potential therapeutic applications.
• In vitro modeling: The derived microglia are capable of performing key functions such as environmental surveying and phagocytosis, similar to their in vivo counterparts, making them suitable for in vitro disease modeling and drug testing.

Publication: Ohtonen et al., Sci Rep, 2023

Description: The Ohtonen et al., (2023) protocol does not require a sorting procedure but requires hypoxic conditions. The protocol guides iPSCs through specific stages using defined cytokines and growth factors, and the resulting microglial-like cells are obtained without the need for sorting.

Protocol highlights:

• No need for cell sorting: The protocol does not require cell sorting, simplifying the process and reducing the time and resources needed.
• High yield of functional cells: The protocol results in a high proportion of functional microglia-like cells that respond to nucleotide stimulation.
• Freezing capability: Microglial progenitors can be frozen at the D8 stage and later thawed for further differentiation, providing flexibility in experimental planning.
• Reproducibility: The use of defined cytokines and growth factors ensures consistent and reproducible microglia differentiation outcomes.
• Scalability: The protocol allows for the generation of large quantities of microglia-like cells, beneficial for extensive experimental setups.
• Comprehensive functional assays: The protocol includes steps for functional assays such as Ca²⁺ transient measurements and phagocytosis, ensuring the generated cells are functionally relevant.
• Versatility for disease modeling: It is effective in modeling neurodegenerative diseases, including Parkinson's disease, using iPSCs derived from patients with specific mutations.
• Adaptability to different genetic backgrounds: The protocol accommodates iPSCs from different sexes and genetic backgrounds, allowing for the microglia culture and study of sex and genetic-specific effects on microglial function.

Publication: Dorion et al., Mol Neurodegener, 2024

Description: The Dorion et al., (2024) microglia differentiation protocol is an improvement over the Blurton-Jones's lab publications (Abud et al., 2017, Mcquade et al., 2018), which is referred to as "2.0" in the publication. This method does not require hypoxic conditions or sorting procedures. The new protocol, named "2.9," offers several enhancements.

Protocol highlights:

• Improved cell yield and adhesive properties: The 2.9 protocol results in a significant improvement in cell yield and adhesive properties compared to the 2.0 protocol.
• Enhanced protein expression and functional competence: Cells derived using the 2.9 protocol show improved protein expression of select microglia markers, enhanced scavenging activities, and a better inflammatory response.
• Closer resemblance to primary microglia: The transcriptomic profile of the resulting induced microglia (iMGLs) more closely resembles that of primary human microglia.
• Simplified and cost-effective: The differentiation medium was simplified, requiring fewer reagents, which allows for a significant cost reduction. Additionally, the protocol does not require cell sorting or the use of a hypoxia chamber, making it more straightforward and accessible.
• Functional validation in disease models: The protocol was validated by generating iMGLs from an ALSP patient carrying a pathogenic CSF1R variant. These cells showed functional alterations in migratory, phagocytic, and inflammatory activities, demonstrating the protocol's utility in microglia culture experiments studying disease-related microglial dysfunction.