Sinomenine inhibits macrophage M1 polarization by downregulating α7nAChR via a feedback pathway of α7nAChR/ERK/Egr-1.

BACKGROUND: Sinomenine (SIN) is an anti-inflammatory drug that has been used for decades in China to treat arthritis. In a previous study, SIN acted on α7 nicotinic acetylcholine receptor (α7nAChR) to inhibit inflammatory responses in macrophages, which indicates a new anti-inflammatory mechanism of SIN. However, the level of α7nAChR was increased in the inflammatory responses and was downregulated by SIN in vitro, so the underlying mechanisms of SIN acting on α7nAChR remain unclear. PURPOSE: To analyze the role of α7nAChR in inflammation and the effect and mechanism of SIN regulation of α7nAChR. METHODS: The effects of SIN on α7nAChR in endotoxemic mice and LPS-stimulated macrophages were observed. Nicotine (Nic) was used as a positive control, and berberine (Ber) was used as a negative control targeting α7nAChR. The antagonists of α7nAChR, α-bungarotoxin (BTX) and mecamylamine (Me), were used to block α7nAChR. In RAW264.7 macrophage cells in vitro, α7nAChR short hairpin RNA (shRNA) was used to knock down α7nAChR. Macrophage polarization was analyzed by the detection of TNF-α, IL-6, iNOS, IL-10, Arg-1, and Fizz1. U0126 was used to block ERK phosphorylation. The cytokines α7nAChR, ERK1/2, p-ERK1/2 and Egr-1 were detected. RESULTS: SIN decreased the levels of TNF-α, IL-6 and the expression of α7nAChR increased by LPS in endotoxemic mice. The above effects of SIN were attenuated by BTX. In the α7nAChR shRNA transfected RAW264.7 cells, compared with the control, α7nAChR was knocked down, and M1 phenotype markers (including TNF-α, IL-6, and iNOS) were significantly downregulated, whereas M2 phenotype markers (including IL-10, Arg-1, and Fizz1) were significantly upregulated when stimulated by LPS. SIN inhibited the expression of p-ERK1/2 and the transcription factor Egr-1 induced by LPS in RAW264.7 cells, and the above effects of SIN were attenuated by BTX. The expression of α7nAChR was suppressed by U0126, which lessened the expression of p-ERK1/2 and Egr-1. CONCLUSIONS: SIN acts on α7nAChR to inhibit inflammatory responses and downregulates high expression of α7nAChR in vivo and in vitro. The increase of α7nAChR expression is correlated with inflammatory responses and participates in macrophage M1 polarization. SIN downregulates α7nAChR via a feedback pathway of α7nAChR/ERK/Egr-1, which contributes to inhibiting macrophage M1 polarization and inflammatory responses.

Sinomenine inhibits fibroblast-like synoviocyte proliferation by regulating α7nAChR expression via ERK/Egr-1 pathway.

Fibroblast like synoviocyte (FLS) is a crucial in the pathogenesis of rheumatoid arthritis (RA), and involved in inflammation and joint destruction. Sinomenine (SIN), an alkaloid derived from the plant Sinomenium acutum, has anti-inflammatory and analgesic effect and been used for RA treatment in China. Alpha 7 nicotinic acetylcholine receptors (α7nAChR), as the key receptor in cholinergic anti-inflammatory pathway (CAP) to inhibit inflammation, has been detected in RA patients synovium, but its role is still unclear. Here we investigated the association between the aggressive proliferation of FLS and α7nAChR expression and the effect of sinomenine. FLS was isolated from synovial tissues of adjuvant-induced-arthritis (AIA) rat. Tumor necrosis factor(TNF)-α was used to induce the aggressive proliferation of FLS. MTT assay was applied to evaluate the proliferation of FLS. The messenger RNA (mRNA) and protein levels of α7nAChR and early growth response gene-1 (Egr-1) were measured. The results showed that TNF-α induced FLS proliferation in vitro (P < .01) and increased the phosphorylation of ERK1/2 and the expression of Egr-1 and α7nAChR (P < .05 or P < .01). U0126, the inhibitor of ERK1/2 inhibited α7nAChR expression and FLS proliferation significantly (P < .05 or P < .01). Specific short interference RNA(siRNA) of α7nAChR decreased α7nAChR expression and inhibited FLS proliferation as well. SIN inhibited the proliferation of FLS and decreased the phosphorylation of ERK1/2, and the expression of Egr-1 and α7nAChR induced by TNF-α (P < .05). In conclusion, the expression of α7nAChR involved in the aggressive proliferation of FLS induced by TNF-α and was regulated by ERK/Egr-1 signal pathway. SIN inhibited FLS proliferation and α7nAChR expression through inhibiting ERK/Egr-1 signal pathway, this may contribute to the anti-inflammatory and anti-arthritic effect of SIN.