Exploring New Inflammatory Biomarkers and Pathways during LPS-Induced M1 Polarization

Abstract

Identification of mediators triggering microglia activation and transference of noncoding microRNA (miRNA) into exosomes are critical to dissect the mechanisms underlying neurodegeneration. We used lipopolysaccharide- (LPS-) induced N9 microglia activation to explore new biomarkers/signaling pathways and to identify inflammatory miRNA (inflamma-miR) in cells and their derived exosomes. Upregulation of iNOS and MHC-II (M1-markers) and downregulation of arginase 1, FIZZ1 (M2-markers), and CX3CR1 (M0/M2 polarization) confirmed the switch of N9 LPS-treated cells into the M1 phenotype, as described for macrophages/microglia. Cells showed increased proliferation, activated TLR4/TLR2/NF-κB pathway, and enhanced phagocytosis, further corroborated by upregulated MFG-E8. We found NLRP3-inflammasome activation in these cells, probably accounting for the increased extracellular content of the cytokine HMGB1 and of the MMP-9 we have observed. We demonstrate for the first time that the inflamma-miR profiling (upregulated miR-155 and miR-146a plus downregulated miR-124) in M1 polarized N9 cells, noticed by others in activated macrophages/microglia, was replicated in their derived exosomes, likely regulating the inflammatory response of recipient cells and dissemination processes. Data show that LPS-treated N9 cells behave like M1 polarized microglia/macrophages, while providing new targets for drug discovery. In particular, the study yields novel insights into the exosomal circulating miRNA during neuroinflammation important for emerging therapeutic approaches targeting microglia activation.

Exosomes derived from pro‐inflammatory bone marrow‐derived mesenchymal stem cells reduce inflammation and myocardial injury via mediating macrophage polarization

“…Numerous studies have revealed that the activation and polarization of macrophages could be mediated by many signalling pathways, including PI3K/AKT, JAK/STAT and NF‐κB signalling pathways . In LPS‐induced inflammation, the NF‐κB signalling pathway is the most important activation and effector pathway, in which IκB is an inhibitor of NF‐κB, and the activation of IκB promotes NF‐κB p65 to translocate to the cell nucleus and induces transcription and secretion of pro‐inflammatory cytokines . In our study, firstly we observed that L‐Exo significantly reduced the phosphorylation level of IκB, which indicated that L‐Exo might inhibit the LPS‐dependent NF‐κB signalling pathway.…”

Increased miR‐124‐3p in microglial exosomes following traumatic brain injury inhibits neuronal inflammation and contributes to neurite outgrowthviatheir transfer into neurons

“…miR-124-3p has been identified in surveillant microglia and anti-inflamatory M2 microglia. It is revealed to switch cell polarization from the M1 to the M2 phenotype in various subsets of monocyte cells and microglia (52). Down-regulation of its expression level is an indicator of neuroinflammation in various diseases, such as experimental autoimmune encephalomyelitis (53) and intracerebral hemorrhage (54).…”

Analgecine inhibits NF-kB to regulate microglia polarization by TLR4 MyD88-dependent and MyD88-independent pathways in ischemic stroke

“…The expression of M1 markers (CD16 and CD32) of microglia increased significantly after OGD/R, and AGC could down-regulated the number of CD16/32-positive cells, indicating AGC attenuated the microglia polarized to the M1 phenotype. The M1 phenotype microglia can be induced by lipopolysaccharide (LPS) or interferon-gamma (IFN-γ) with increased production of proinflammatory cytokines [30]. Treatment with AGC suppressed LPS/IFN-γ-mediated the expression of M1 marker CD16/32 and tended to elevate the CD206-positive M2 microglia number, demonstrating AGC could switch microglia M1 to M2 transition.…”