Background Microglial activation-mediated neuroinflammation plays an important role in the progression of neurodegenerative diseases. Inflammatory activation of microglial cells is often accompanied by a metabolic switch from oxidative phosphorylation to aerobic glycolysis. However, the roles and molecular mechanisms of glycolysis in microglial activation and neuroinflammation are not yet fully understood. Methods The anti-inflammatory effects and its underlying mechanisms of glycolytic inhibition in vitro were examined in lipopolysaccharide (LPS) activated BV-2 microglial cells or primary microglial cells by enzyme-linked immunosorbent assay (ELISA), quantitative reverse transcriptase-polymerase chain reaction (RT-PCR), Western blot, immunoprecipitation, flow cytometry, and nuclear factor kappa B (NF-κB) luciferase reporter assays. The anti-inflammatory and neuroprotective effects of glycolytic inhibitor, 2-deoxoy-d-glucose (2-DG) in vivo were measured in the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-or LPS-induced Parkinson’s disease (PD) models by immunofluorescence staining, behavior tests, and Western blot analysis. Results We found that LPS rapidly increased glycolysis in microglial cells, and glycolysis inhibitors (2-DG and 3-bromopyruvic acid (3-BPA)), siRNA glucose transporter type 1 (Glut-1), and siRNA hexokinase (HK) 2 abolished LPS-induced microglial cell activation. Mechanistic studies demonstrated that glycolysis inhibitors significantly inhibited LPS-induced phosphorylation of mechanistic target of rapamycin (mTOR), an inhibitor of nuclear factor-kappa B kinase subunit beta (IKKβ), and NF-kappa-B inhibitor alpha (IκB-α), degradation of IκBα, nuclear translocation of p65 subunit of NF-κB, and NF-κB transcriptional activity. In addition, 2-DG significantly inhibited LPS-induced acetylation of p65/RelA on lysine 310, which is mediated by NAD-dependent protein deacetylase sirtuin-1 (SIRT1) and is critical for NF-κB activation. A coculture study revealed that 2-DG reduced the cytotoxicity of activated microglia toward MES23.5 dopaminergic neuron cells with no direct protective effect. In an LPS-induced PD model, 2-DG significantly ameliorated neuroinflammation and subsequent tyrosine hydroxylase (TH)-positive cell loss. Furthermore, 2-DG also reduced dopaminergic cell death and microglial activation in the MPTP-induced PD model. Conclusions Collectively, our results suggest that glycolysis is actively involved in microglial activation. Inhibition of glycolysis can ameliorate microglial activation-related neuroinflammatory diseases.

Tumor‐associated microglial cells promote glioma growth, invasion, and chemoresistance by releasing inflammatory factors. Milk fat globule EGF factor 8 protein (MFG‐E8), a secreted glycoprotein, is closely related to tissue homeostasis and anti‐inflammation. In the present study, we investigated the role of MFG‐E8 in microglial polarization and glioma progression in vitro and in vivo. We found that glioma cells secrete comparable amounts of MFG‐E8 in culture media to astrocytes. Recombinant MFG‐E8 triggered microglia to express the M2 polarization markers, such as arginase‐1 (ARG‐1), macrophage galactose‐type C‐type lectin‐2 (MGL‐2), and macrophage mannose receptor (CD206). Forced expression of MFG‐E8 in BV‐2 microglia cells not only promoted IL‐4‐induced M2 polarization but also inhibited lipopolysaccharide (LPS)‐induced M1 microglial polarization. Mechanistic studies demonstrated that recombinant MFG‐E8 markedly induced signal transducer and activator of transcription 3 (STAT3) phosphorylation, and the STAT3 inhibitor stattic significantly blocked MFG‐E8‐induced ARG‐1 expression. Administration of antibody against MFG‐E8 and knockdown of its receptor, integrin β3, significantly attenuated MFG‐E8‐induced ARG‐1 expression. Similarly, knockdown of MFG‐E8 also markedly reduced IL‐4‐induced M2 marker expression and increased LPS‐induced M1 marker expression in microglia cells. Moreover, the knockdown of MFG‐E8 in GL261 glioma cells inhibited cell proliferation and enhanced chemosensitivity to 1,3‐bis(2‐chloroethyl)‐1‐nitrosourea (BCNU), which was likely associated with the downregulation of FAK/AKT activation and STAT3/cyclin D1 signaling. The murine GL261 glioma experimental model demonstrated that knockdown of MFG‐E8 significantly reduced tumor size and extended survival times. Additionally, attenuated CD11b+ cell infiltration and reduced CD206+ expression in CD11b+ cells were also observed in an MFG‐E8 knockdown GL261 murine glioma model. These results suggested that inhibition of MFG‐E8 might hamper the immunosuppressive microenvironment in gliomas and therefore ameliorate tumor progression.

Background Microglial activation-mediated neuroinflammation plays an important role in the progression of neurodegenerative diseases. Inflammatory activation of microglial cells is often accompanied by a metabolic switch from oxidative phosphorylation to aerobic glycolysis. However, the roles and molecular mechanisms of glycolysis in microglial activation and neuroinflammation are not yet fully understood.Methods The anti-inflammatory effects and its underlying mechanisms of glycolytic inhibition in vitro were examined in LPS activated BV-2 microglia or primary microglia cells by ELISA, RT-PCR, Western blot, immunoprecipitation, FACS and NF-κB luciferase reporter assays. The anti-inflammatory and neuroprotective effects of glycolytic inhibitor, 2-DG in vivo were measured in the MPTP-or LPS-induced PD models by immunofluorescence staining, behavior tests and Western blot analysis. Results We found that LPS rapidly increased glycolysis in microglial cells, and glycolysis inhibitors (2-DG and 3-BPA), siRNA Glut-1 and siRNA HK Ⅱ abolished LPS-induced microglial cell activation. Mechanistic studies demonstrated that glycolysis inhibitors significantly inhibited LPS-induced phosphorylation of mTOR, IKKβ and IκB, degradation of IκB, nuclear translocation of p65 and NF-κB transcriptional activity. In addition, 2-DG significantly inhibited LPS-induced acetylation of p65/RelA on lysine 310, which is mediated by NAD+-dependent SIRT1 and is critical for NF-kB activation. A coculture study revealed that 2-DG reduced the cytotoxicity of activated microglia toward MES23.5 dopaminergic neuron cells with no direct protective effect. An in vivo study demonstrated that 2-DG significantly ameliorated neuroinflammation and subsequent DA neuronal cell injuries in an LPS-induced Parkinson’s disease (PD) model. Furthermore, 2-DG also reduced TH-positive cell loss and microglial activation in the MPTP-induced PD model. Conclusions Collectively, our results suggest that glycolysis is actively involved in microglial activation and, hence, that inhibition of glycolysis can ameliorate microglial activation-related neuroinflammatory diseases.