Dopamine induces functional extracellular traps in microglia

Dopamine (DA) is central to neurological functions like motivation, movement and reward (Klein et al. 2019). While its role in diseases like Parkinson’s, Alzheimer’s and schizophrenia are well studied, its role in regulating immune functions have just started to unfold. DA receptors are present on almost all immune cells and they regulate innate and adaptive immunity (Matt and Gaskill 2020). We have investigated the role of DA in the formation of extracellular traps (ETs) in microglia. We report that DA can induce ETs in BV2 microglia cell line and primary adult human microglia. ETs are composed of decondensed chromatin and are embedded with proteins including antimicrobial proteins like myeloperoxidase and histone. We confirmed ETs formation by staining them with DAPI, myeloperoxidase and/or DNA/Histone H1. The presence of traps in culture supernatant was confirmed by measuring SYTOX Green absorbance. To check for the mechanism of ETs formation by BV2 cells, we performed MTT assay and treated cells with N-acetyl L-cysteine or cytochalasin D. We saw that the traps were formed independent of cell death, reactive oxygen species (ROS) and actin polymerization. We further confirmed that DA induced microglia traps are functional as they were able to trap FITC tagged Escherichia coli. Lastly we checked the presence of microglia ETs in Glioblastoma multiforme tissues as recently glioma cells have been reported to secrete DA and possess DA receptors (Caragher et al. 2019). We confirmed and quantified the traps present in GBM by an unbiased algorithm. Our findings demonstrate that DA may play significant role in sterile neuro-inflammation by inducing microglia ETs.