An active fraction from Spatholobus suberectus dunn inhibits the inflammatory response by regulating microglia activation, switching microglia polarization from M1 to M2 and suppressing the TLR4/MyD88/NF-κB pathway in LPS-stimulated BV2 cells

Abstract

Neurodegenerative disorders are known to be associated with neuroinflammation caused by microglia. Therefore, regulation of microglia activation and polarization to inhibit neuroinflammatory reactions seems to hold promise as a therapeutic approach in neurodegenerative disorders. Spatholobus suberectus Dunn (SSD) has been utilized as a traditional Chinese medicine remedy for brain diseases for thousands of years. SSD possesses various pharmacological activities, such as circulation invigoration, neuroprotection, and anti-inflammatory. The objective of this research was to examine the anti-neuroinflammatory effects and molecular mechanisms of an active fraction from SSD (ASSD) in vitro culture BV2 cells, a type of mouse microglia cell line. The inflammatory responses in BV2 cells were induced by stimulating them with 1 μg/mL lipopolysaccharide (LPS) and the effects of ASSD on LPS-stimulated inflammation were monitored. Besides, by using the methods of Western blot, immunofluorescence, and RT-PCR, the mechanisms of ASSD on microglia activation, M1/M2 polarization, and the TLR4/MyD88/NF-κB pathway were investigated. Our findings demonstrate that the treatment doses of ASSD neither induce cytotoxicity nor promote the production of inflammatory cytokines. In addition, immunofluorescence analysis show that ASSD inhibited the expression of ionized calcium-binding adapter molecule 1(Iba1) and inducible nitricoxide synthase (iNOS), and induced arginase 1 (Arg1) expression. Moreover, Western blot analysis indicated that ASSD significantly down-regulated TLR4, MyD88, p-IκB, NF-κB p65, and NF-κB p-p65 protein expression levels. Furthermore, RT-qPCR assay show that ASSD significantly down-regulated iNOS, TLR4, MyD88, and NF-κB mRNA expression levels, and up-regulated Arg1 mRNA expression level. According to the findings, ASSD can suppress microglia-mediated inflammatory responses by modulating microglia activation, inducing a shift from M1 to M2 polarization, and inhibiting the TLR4/MyD88/NF-κB signaling pathway.