Using human iPSC-derived microglia, the study shows IFNγ reprograms microglial metabolism and lipidome toward a resolving-like phenotype that partially counteracts α-synuclein PFF-driven harmful secretome effects on human dopaminergic neurons.

Identifies actionable immunometabolic and secretome-linked mechanisms (IFNγ signaling, TGM2, TGFβ1, glycolytic/tryptophan/phospholipid pathways) that can be targeted or used as biomarkers to modulate microglia-neuron interactions in α-synuclein-driven Parkinson's pathology.

Microglia play a major role in the pathophysiology of Parkinson's disease, where they regulate both α-synuclein (αSyn) aggregate clearance and inflammatory responses. Interferon gamma (IFNγ) is a strong immunomodulator, but its role in shaping human microglial phenotypes during αSyn exposure remains incompletely understood. Further, whether the secreted factors from microglia after exposure to αSyn pre-formed fibrils (PFFs) and IFNγ can affect morphology and functionality of dopaminergic neurons has not been studied. We used human stem cell-derived microglia to investigate how αSyn PFFs and IFNγ stimulation influence microglial metabolism, lipid composition, and phenotypic state. IFNγ induced broad metabolic and lipidomic remodeling, affecting glycolytic, tryptophan, and phospholipid pathways. Pre-exposure to IFNγ promoted a resolving-like phenotype upon αSyn PFFs challenge, characterized by increased transglutaminase 2 (TGM2) expression and elevated TGFβ1 secretion. Conditioned media (CM) from exposed microglia were applied to human iPSC-derived dopaminergic neurons, and neuronal morphology, protein expression, mitochondrial function, and electrophysiological activity were evaluated. CM from αSyn PFFs-exposed microglia reduced neuronal branching and neurite length. Furthermore, CM from stimulated microglia decreased TUJ1 and TH expression, altered mitochondrial regulators (cytochrome C, MnSOD, iNOS), and disrupted neuronal activity as measured by changes in c-FOS expression and multielectrode array recordings. IFNγ profoundly modulates human microglial states, enhancing resolving-like features and simultaneously driving secretome-mediated neuronal effects. These findings highlight microglial activation state as a critical determinant of neuronal vulnerability in αSyn-associated pathology. Importantly, IFNγ-induced microglial activation can, at least partially, counteract αSyn-driven adverse effects on dopaminergic neurons.