Based on these results, we evaluated the consequences of reducing Nurr1 expression in microglia on LPS responses. Knockdown of Nurr1 expression in BV2 microglia using specific lentivirus-encoded shRNAs led to significant increases in LPS-dependent expression of inflammatory mediators, including TNFα, iNOS and IL-1β (Fig. 2D-F). Similar results were observed in the primary mouse (Fig. S5 and S6A-C) and human (data not shown) microglia. To explore whether loss of Nurr1 in microglia resulted in secretion of mediators exhibiting preferential toxicity for TH+ neurons, we knocked down Nurr1 expression using lentivirus-encoded shRNAs in BV2 cells and tested the activity of conditioned media (CM) after LPS stimulation on in vitro differentiated neurons and glial cells derived from mouse neuronal stem cells (NSC). CM from shNurr1-BV2 cells resulted in the death of nearly all TH+ neurons, with a significantly smaller effect on gamma-aminobutyric acid (GABA)-positive neurons and no significant effect on glial fibrillary acidic protein (GFAP)-positive astroglial cells (Fig. 2G–I).
