Tetramethylpyrazine Protects Blood-Spinal Cord Barrier Integrity by Modulating Microglia Polarization Through Activation of STAT3/SOCS3 and Inhibition of NF-кB Signaling Pathways in Experimental Autoimmune Encephalomyelitis Mice

Abstract

We previously reported that tetramethylpyrazine (TMP) alleviates experimental autoimmune encephalomyelitis (EAE) by decreasing glia activation. Activated microglia has been shown to mediate blood-spinal cord barrier (BSCB) disruption, which is a primary and continuous pathological characteristic of multiple sclerosis (MS). Therefore, in this study, we further investigated whether TMP protects the BSCB integrity by inhibition of glia activation to alleviate EAE. Extravasation of evans blue was used to detect the BSCB disruption. Tumor necrosis factor-α (TNF-α)/interlukine-1β (IL-1β) and interlukine-4 (IL-4)/interlukine-10 (IL-10) were determined by enzyme-linked immunosorbent assay. BV2 glial cells stimulated by interferon-γ (IFN-γ) were co-cultured with human brain microvascular endothelial cells to investigate the effect of TMP on the BSCB disruption. Flow cytometry was used to analyze the microglia phenotype. Western blot was performed to reveal the signaling pathways involved in the microglia activation. In this study, most importantly, we found that TMP protects the BSCB integrity by modulating microglia polarization from M1 phenotype to M2 phenotype through activation of STAT3/SOCS3 and inhibition of NF-кB signaling pathways. Moreover, TMP significantly preserves the tight junction proteins, reduces the secretion of pro-inflammatory cytokines (TNF-α, IL-1β) and increases the secretion of anti-inflammatory cytokines (IL-4, IL-10) from IFN-γ-stimulated BV2 microglia cells. Consequently, protection of the BSCB integrity leads to alleviation of clinical symptoms and demyelination in EAE mice. Therefore, TMP might be an effective therapeutic agent for cerebral disorders with BBB or BSCB disruption, such as ischemic stroke, MS, and traumatic brain injury.

Regulation of blood–brain barrier integrity by microglia in health and disease: A therapeutic opportunity

“…83 Recently, microglia treated with tetramethylpyrazine, a drug that promotes M2 microglial polarization, were shown to preserve functional integrity of the blood-spinal cord barrier in a murine model of experimental autoimmune encephalomyelitis (EAE). 84 This is the first study to directly show that microglial cells with an anti-inflammatory phenotype can protect brain barriers against pathological stressors.…”

The Role of Microglia in Modulating Neuroinflammation after Spinal Cord Injury

“…Further, using a blocker of fibrinogen and microglial integrin receptor Mac-1, microglia-mediated vascular repair/maintenance was hindered. Another study looked to bias microglial polarization towards the M2 state using tetramethylpyrazine and found that TMP-treated M2 microglia through activation of STAT3/SOCS3 and inhibition of NK-κB promote blood-spinal cord barrier integrity in EAE mice [ 56 ]. Taken together, these studies demonstrate the importance of microglia in the maintenance and repair of the blood-spinal cord barrier.…”

Microglia Polarization: A Novel Target of Exosome for Stroke Treatment

“…When microglia are polarized to the M2 phenotype, they can better protect the blood-brain barrier by producing IL-10 and TGF- β 1, as well as VEGF, IL-8 and pro-MMP-9 to promote vascular remodeling ( Jiang et al, 2018b ). The use of tetramethylpyrazine (TMP) in experimental autoimmune encephalomyelitis animal models protects the blood-spinal cord barrier by activating the signal transducer and activator of transcription 3 (STAT3)/Suppressor of Cytokine Signaling 3 (SOCS3) signaling pathway and promoting microglia polarization from M1 to M2 phenotype ( Zhang et al, 2021b ). M1-type microglia not only secrete pro-inflammatory cytokines, but also secrete chemokines such as chemokine (C-C motif) ligand 2 (CCL2) and Chemokine C-X-C ligand 10 (CXCL10) to recruit more immune cells and compromise the integrity of the blood-brain barrier ( Jiang et al, 2018b ).…”