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

Abstract

Background: Microglia polarization plays an important role in poststroke recovery. Inhibition of proinflammatory (M1) polarization and promotion of anti-inflammatory (M2) polarization of microglia are potential therapeutic strategies for inflammation reduction and neuronal recovery after stroke. Analgecine (AGC), the extracts of Vaccin a variola-inoculated rabbit skin, is used to treat patients with chronic low back pain due to degenerative vertebral disorders. Here, we evaluated the neuroprotective effect of AGC in stroke and investigate anti-inflammatory mechanism of AGC on microglia-mediated neural damage.Methods: Sprague-Dawley (SD) rats underwent 120 min of middle cerebral artery occlusion (MCAO) followed by reperfusion. We injected AGC intravenously into rats starting 3 h after the onset of MCAO. Then we investigated the effect of AGC on neurological impairment, neuronal loss and inflammatory cytokines. For in vitro study, we examined the effect of AGC on microglial polarization in oxygen-glucose deprivation/reperfusion (OGD/R) or LPS/IFN-γ induced microglia cells and further investigated neuroprotective effect of ACG in microglia-mediated neural damage based on the direct or indirect co-culture systems. Finally, TLR4/Myd88/ NF-κB pathway was detected in OGD/R-induced microglia cells with or without Myd88 siRNA transfection.Results: AGC treatment reduced the neurological deficits and suppressed neuronal loss. In terms of inflammatory cytokines, AGC inhibited the release of pro-inflammatory cytokines and elevated the content of anti-inflammatory cytokines in vivo (SD rats) and in vitro (microglia). We further showed that AGC promoted M1 to M2 phenotypic transition of microglia in OGD/R or LPS/IFN-γ induced microglia cells. Based on the direct or indirect co-culture systems, we found AGC indirectly inhibits LPS/IFN-γ-induced neuronal damage by modulating microglial polarization. Moreover, AGC suppressed the nuclear translocation of the phosphorylation of NF-κB p65 by inhibiting the TLR4/Myd88/TRAF6 but not TLR9 signaling. We also confirmed that AGC-regulated TLR4 inhibition partly dependent on Myd88 in a Myd88 depletion cell line.Conclusion: Our findings provide a new understanding of AGC in neuroprotection by inhibiting M1 microglial polarization and promoting anti-inflammation by suppressing TLR4 MyD88-dependent and MyD88-independent pathways. Thus, AGC treatment may represent a novel approach in inflammation reduction or poststroke recovery.