Characterization and modulation of microglial phenotypes in an animal model of severe sepsis.

Monique Michels,Mariane Rocha Abatti,Celso Carvalho Junior,José Claudio Fonseca Moreira,Diogo Wendhausen,Daniel Pens Gelain,Felipe Dal‐Pizzol,Heloisa Borges,Pricila Ávila,Andriele Vieira,Juciano Gasparotto,Camila Tiefensee Ribeiro

doi:10.1111/jcmm.14606

Abstract

We aim to characterize the kinetics of early and late microglial phenotypes after systemic inflammation in an animal model of severe sepsis and the effects of minocycline on these phenotypes. Rats were subjected to CLP, and some animals were treated with minocycline (10 ug/kg) by i.c.v. administration. Animals were killed 24 hours, 5, 10 and 30 days after sepsis induction, and serum and hippocampus were collected for subsequent analyses. Real‐time PCR was performed for M1 and M2 markers. TNF‐α, IL‐1β, IL‐6, IL‐10, CCL‐22 and nitrite/nitrate levels were measured. Immunofluorescence for IBA‐1, CD11b and arginase was also performed. We demonstrated that early after sepsis, there was a preponderant up‐regulation of M1 markers, and this was not switched to M2 phenotype markers later on. We found that up‐regulation of both M1 and M2 markers co‐existed up to 30 days after sepsis induction. In addition, minocycline induced a down‐regulation, predominantly, of M1 markers. Our results suggest early activation of M1 microglia that is followed by an overlap of both M1 and M2 phenotypes and that the beneficial effects of minocycline on sepsis‐associated brain dysfunction may be related to its effects predominantly on the M1 phenotype.

Highlights

Sepsis is characterized by excessive production of inflammatory mediators resulting in deregulated host response and organ dysfunction that includes brain dysfunction
We have demonstrated that up‐regulation of both M1 and M2 markers co‐exists up to 30 days after sepsis induction
We recently demonstrated that the depletion of microglia before sepsis development is associated with acute exacerbation of brain inflammation

Summary

| INTRODUCTION

Sepsis is characterized by excessive production of inflammatory mediators resulting in deregulated host response and organ dysfunction that includes brain dysfunction. In this context, many studies have already reported microglia activation in animal models and humans.[1,2,3,4,5,6,7] The primary role of microglia is the maintenance of neural cells and synapses during normal functioning of the CNS. Activated microglia are very plastic and may exist in multiple phenotypes that present different responses in accordance to changes in the cerebral microenvironment They can induce brain repair, or cytotoxicity, as well as immune‐regulatory or pro‐inflammatory functions.[8,9]. We aimed to characterize the kinetics of microglial phenotypes early and late after systemic inflammation in an animal model of severe sepsis, and the effects of minocycline on these phenotypes

| MATERIALS AND METHODS

| DISCUSSION

Findings

| CONCLUSION