To investigate the neuroinflammatory mechanism underlying C-band electromagnetic radiation (EMR)-induced anxiety-like behavior in mice and the protective effect of Astragaloside Ⅳ (AS-Ⅳ).

A mouse model of electromagnetic exposure was established using a 10 mW/cm² C-band EMR source. Anxiety-like behaviors were assessed using the open field test and the elevated plus maze test. The expression levels of the M1-type pro-inflammatory factor C-C motif chemokine ligand 2 (CCL2), C-C chemokine receptor 2 (CCR2), and the transcription factor early growth response protein 1 (EGR-1) in the mouse cortex and BV2 microglial cells were detected by RT-PCR and Western blotting. Bioinformatics analysis was conducted to predict potential binding sites for transcription factor EGR-1 in the promoter regions of the CCL2 and CCR2 genes while siRNA knockdown was used to verify the regulatory role of EGR-1 inCCL2/CCR2 expression. Different doses of AS-Ⅳ were administered prophylactically to mice for 14 days prior to EMR to find out whether it could antagonize EMR-induced anxiety-like behavior and suppress the activation of the EGR-1/CCL2/CCR2 pathway.

C-band EMR exposure induced anxiety-like behavior in mice, as evidenced by significantly reduced entries into and time spent in the center zone of the open field test and the open arms of the elevated plus maze (vs. control). Compared with the control group, the mRNA and protein levels of CCL2 and CCR2 in the mouse cortex were significantly upregulated 24 hours after EMR exposure while EGR-1 expression levels in the mouse cortex and BV2 cells were significantly increased 3 hours after EMR exposure. Knockdown of EGR-1 expression significantly suppressed the upregulation of CCL2 and CCR2 in the BV2 cell line. Prophylactic administration of medium and high doses of AS-Ⅳ significantly ameliorated anxiety-like behavior in EMR-exposed mice and restored the expression levels of EGR-1, CCL2, and CCR2 in the cortex to near-normal levels.

C-band electromagnetic radiation can activate the transcription factor EGR-1, which upregulates the CCL2/CCR2 signaling axis and induces cortical neuroinflammation, ultimately mediating anxiety-like behavior in mice. Astragaloside Ⅳ (AS-Ⅳ) exerts anti-inflammatory and anxiolytic effects by antagonizing the activation of the EGR-1/CCL2/CCR2 pathway.

To investigate the roles and mechanism of deoxycholic acid (DCA) in mediating the neuroinflammatory responses induced by hypobaric hypoxia.

C57BL/6J mice were randomly divided into thecontrol group (Con), tauroursodeoxycholic acid (TUDCA) group, hypoxia group (Hyp) and hypoxia+TUDCA group (Hyp+TUDCA). The mice were exposed in a hypoxic chamber for 48 h, which could mimic the high altitude environment. The levels of total bile acids (BA), lithocholic acid (LCA) and deoxycholic acid (DCA) in the serum and colon of mice were detected using enzyme-linked immunosorbent assay (ELISA), so were levels of DCA in the cortex, hippocampus and hypothalamus. The role of DCA in inducing neuroinflammation and IL-1β and TNF-α expressions was evaluated by knocking down the DCA receptor, farnesoid X receptor (FXR) in the N9 microglial cells and by administrating TUDCA to mice followed by hypoxia exposure. Real-time quantitative PCR (qPCR) and immunofluorescence staining were used to detect the activation of microglia and expression levels of interleukin-1β (IL-1β) and tumor necrosis factor-α (TNF-α) in the cortex of mice in each group.

Hypoxia exposure increased DCA levels in the colon, serum and cortex. Under the same conditions, cortical microglia were activated, along with the elevation of IL-1β and TNF-α levels. DCA treatment increased the expression levels of FXR, IL-1β and TNF-α in N9 microglial cells. Knocking down the expression level of FXR inhibited DCA-induced IL-1β and TNF-α expressions in N9 cells. Furthermore, administration of TUDCA inhibited microglial activation and elevation of IL-1β in the cortex induced by hypoxia.

DCA can serve as a mediator in neuroinflammation by activating FXR in the cortex under hypoxia exposure. TUDCA administration can be used to mitigate neuroinflammation induced by hypoxia.