Brucella abortus-activated microglia induce neuronal death through IL-6 signaling

JULIA RODRÍGUEZ; JULIA DE SANTIS ARÉVALO; ARIADNA M. FIORILLO EVEQUOZ; ANA M. RODRÍGUEZ; GUILLERMO H. GIAMBARTOLOMEI

Congreso; First Meeting Glia Club Southern Cone: The good, the bad, the nice and the ugly of glial cells; 2022

Facultad de Farmacia y Bioquímica (FFyB), Universidad de Buenos Aires

Neurobrucellosis is an inflammatory disease caused by Brucella spp infection of the central nervous system. We have previously demonstrated that soluble mediators released by B. abortus-infected astrocytes induce an inflammatory state in microglia, and this bystander activated-microglia elicit neuronal death through phagocytosis of viable neurons. The aim of this work was to investigate possible mediators involved in this mechanism. For this, we use monoclonal antibodies to neutralize TNF-α and IL-6 cytokines in neurons/microglia co-cultures treated with supernatants from B. abortus-infected astrocytes. Neutralization of IL-6, but not TNF- α, prevented neuronal loss (evaluated by fluorescence microscopy; p<0.05) and caused a decrease in the phagocytic activity of microglia (evaluated by phagocytosis assay with negatively charged fluorescent beads; p<0.005). Considering that both astrocytes and microglia are capable of secrete IL-6, we further investigate the contribution of each cell type in this phenomenon. Astrocytes from wild type (WT) and IL-6 KO mice were infected or not with B. abortus for 24 h. After that, cell-free culture supernatants were used to stimulate primary murine co-cultures of WT and IL-6 KO microglia with neurons during 48 h. Treatment of WT co-cultures with supernatants from IL-6 KO infected astrocytes caused a partial inhibition of neuronal death (p<0.05). Similar results were obtained when neurons/IL-6 KO microglia co-cultures were treated with supernatants from WT- infected astrocytes (p<0.05). Neuronal loss was totally prevented in co-cultures of neurons/IL-6 KO microglia treated with IL-6 KO infected astrocytes (p<0.05). Moreover, B. abortus-activated microglia from IL-6 KO mice were unable to induce neuronal death (p<0.05). These results indicate that both paracrine and autocrine IL-6 signaling in microglia can be sufficient to induce phagocytosis of viable neurons in the context of a B. abortus infection, and could highlight the relevance of this cytokine in neuropathological mechanisms caused by Brucella spp.