scRNAseq analysis code: Fernandez Garcia-Agudo, Steixner-Kumar, Curto et al. (2021) - Cell reports

In adult cornu ammonis hippocampi, erythropoietin (EPO) expression drives differentiation of new neurons, independent of DNA synthesis, and increases dendritic spine density. This substantial brain hardware upgrade is part of a regulatory circle: During motor-cognitive challenge, neurons experience ‘functional’ hypoxia, triggering neuronal EPO production, which in turn promotes improved performance (EPO brain doping). Here, we show an unexpected involvement of resident microglia. During EPO upregulation and stimulated neurodifferentiation, either by functional or inspiratory hypoxia, microglia numbers decrease. Treating mice with recombinant human (rh)EPO or exposure to hypoxia recapitulates these changes and reveals involvement of neuronally expressed IL-34 and microglial CSF1R. Surprisingly, EPO affects microglia in phases, initially by inducing apoptosis, later by reducing proliferation, and overall dampens microglia activity and metabolism, as verified by selective genetic targeting of either microglial or pyramidal neuronal EPO receptor. We suggest that during accelerating neuronal differentiation, EPO acts as regulator of the CSF1R-dependent microglia.