Human microglia are central regulators and actors in brain infections and neuro-inflammatory pathologies. However, access to such cells is limited, and studies systematically mapping the spectrum of their inflammatory states are scarce. Here, we generated microglia-like cells (MGLCs) from human induced pluripotent stem cells and characterized them as a robust, accessible model system for studying inflammatory activation. We validated lineage identity through transcriptome profiling, revealing selective upregulation of microglial signature genes and enrichment of microglia/macrophage-related gene sets. MGLCs displayed distinct morphologies and produced stimulus- and time-dependent cytokine secretion profiles upon exposure to diverse inflammatory stimuli, including pro-inflammatory cytokines (TNFα, interferon-γ) and agonists of the Toll-like receptors TLR2 (FSL-1), TLR3 (Poly(I:C)), TLR4 (lipopolysaccharide, LPS), and TLR7 (imiquimod). Transcriptome profiling and bioinformatics analysis revealed distinct activation signatures. Functional assays demonstrated stimulus-specific engagement of NFκB and JAK-STAT signaling pathways. The shared NFκB nuclear translocation response of TLR ligands and TNFα was reflected in overlapping transcriptome profiles: they shared modules (e.g., oxidative stress response and TNFα-related signaling) identified by weighted gene co-expression network analysis. Finally, the potential consequences of microglia activation for neighboring cells were studied on the example of microglia-astrocyte crosstalk. The capacity of MGLC supernatants to stimulate astrocytes was measured by quantifying astrocytic NFκB translocation. MGLCs stimulated with FSL-1, LPS, or Poly(I:C) indirectly activated astrocytes via a strictly TNFα-dependent mechanism, highlighting the role of soluble mediators in the signal propagation. Altogether, this platform enables a dissection of microglia activation states and multi-parametric characterization of subsequent neuroinflammation.

Little is known about how nicotinic signalling in human astrocytes may contribute to the functional neurotoxicity of compounds related to tobacco alkaloids and neonicotinoid pesticides. We generated a single-cell Ca²⁺-imaging assay in induced pluripotent stem cell (iPSC)-derived astrocytes, and profiled functional expressions of some neurotoxicologically relevant receptors. Responses to pharmacological tool compounds indicated the expression of nicotinic, muscarinic, purinergic, glutamatergic receptors and voltage-gated Na⁺/Ca²⁺ channels. Closer investigation of the nicotinic system, e.g., using the alpha7 nicotinic acetylcholine receptor (nAChR)-selective positive allosteric modulator PNU-120596 and alpha7-preferring agonist (AR-R17779) demonstrated that Ca²⁺ signals elicited by nicotine and neonicotinoids are dominated by alpha7 nAChRs and depend on the downstream activation of L-type Ca²⁺ channels and tetrodotoxin-sensitive Na⁺ channels. Crosstalk of nAChR activation/desensitization was not observed for the inflammatory response elicited by TNF or for activation of glutamatergic or purinergic signalling. However, pre-stimulation of nAChR by neonicotinoids significantly blunted the response to the neurotransmitter acetylcholine. Comparative experiments in the human neuronal cultures (LUHMES cells) revealed similar potency ranges and pharmacological fingerprints for several neonicotinoids and their human-relevant metabolites descyanothiacloprid and desnitroimidacloprid. The pesticide metabolites showed a high potency, compared with their respective parent compounds. After this basic system characterization, the hitherto data-poor pesticides cycloxaprid and flupyradifurone were comparatively profiled in astrocytic and neuronal test systems. They showed the typical features of alpha7 nAChR agonists. The disruption of cholinergic signalling in astrocytes suggests that neonicotinoids affect not only neurons in human brains. Therefore, future neurotoxicity screening approaches may need to consider astrocyte toxicity.