iPSC-derived human microglia-like cells to study neurological diseases

Microglia are essential for CNS health and are heavily implicated in neurological disorders like Alzheimer's disease (AD). However, studying human microglia is hindered by the scarcity and difficulty of obtaining primary tissue. This study seeks to generate a scalable, renewable, and functional source of human microglia using induced pluripotent stem cells (iPSCs) that can be used to investigate microglial function and disease mechanisms.

Researchers developed a two-step, serum-free, fully defined differentiation protocol. First, iPSCs are directed toward hematopoietic progenitors (iHPCs) over 10 days, followed by a 25-day microglia differentiation phase using key cytokines (M-CSF, IL-34, TGF-β1) to mimic the developmental environment. The resulting iMGLs were rigorously validated using whole-transcriptome sequencing, comparing them to primary fetal and adult microglia. Functional validation included assays for cytokine secretion, calcium transients (via P2RY12 activation), phagocytosis of synaptosomes and Alzheimer's-related proteins (beta-amyloid, tau oligomers), and transplantation into mouse models and human 3D brain organoids.

The generated iMGLs highly resemble primary human microglia at the transcriptomic level and are distinct from other myeloid cells like monocytes or macrophages. They display key physiological behaviors: they secrete inflammatory cytokines when stimulated, migrate and undergo calcium flux in response to ADP (mediated by the purinergic receptor P2RY12), and phagocytose neuronal substrates such as synaptosomes and amyloid-beta fibrils. Importantly, the researchers used iMGLs to show that synaptic pruning is predominantly mediated by the C1q/CR3 pathway rather than the MERTK pathway. Furthermore, the researchers utilized iMGLs to examine AD-associated GWAS genes, observing that specific disease-related pathologies (fAβ, tau oligomers) significantly alter the expression of genes linked to AD risk, demonstrating the platform's utility for mechanistic study.