Microglial Cells Depletion Increases Inflammation and Modifies Microglial Phenotypes in an Animal Model of Severe Sepsis

Sepsis-associated encephalopathy is highly prevalent and has impact both in early and late morbidity and mortality. The mechanisms by which sepsis induces brain dysfunction include neuroinflammation, disrupted blood-brain barrier, oxidative stress, and microglial activation, but the cellular and molecular mechanisms involved in these events are not completely understood. Our objective was to determine the effects of microglial depletion in the early systemic and brain inflammatory response and its impact in phenotypes expression in an animal model of sepsis. Animals were subjected to CLP, and depletion of microglial cells was accomplished by administration of (Lipo)-encapsulated clodronate and microglial repopulation by doxycycline. Clod-lip treatment was effective in decreasing microglia density in the hippocampus of animals. Pro-inflammatory cytokines were increased in the CLP+PBS, and liposomes administration increased even further these cytokines mainly 7 days, suggesting that microglial depletion exacerbates both local and systemic inflammation. In contrast, repopulation with doxycycline was able to revert the cytokine levels in both serum and cerebral structures on day 7 and 14 after repopulation. There were no differences in the correlation between M1 and M2 markers by real-time PCR, but immunohistochemistry showed significant increase in CD11b expression in CLP+PBS with greater expression in CLP + liposomes in the hippocampus. These results suggest that the depletion of microglia during severe sepsis development could be associated with early exacerbation of brain and systemic inflammation and repopulation is able to revert this condition, once a rapid neurological recovery is noticed until 7 days after sepsis.