Myricetin alleviates DNCB-induced atopic dermatitis by modulating macrophage M1/M2 polarization

Abstract

Background: Atopic dermatitis (AD), a chronic and relapsing inflammatory skin disease, is characterized by recurrent eczema, itch, and pain. Conventional treatments, such as topical corticosteroids, are associated with various adverse effects. Previous studies have shown that Myricetin (Myr) effectively treats AD and inflammation induced by DNFB and MC903. However, the mechanism of Myricetin remains poorly understood. This study aims to investigate the therapeutic effects of Myricetin on DNCB-induced AD and to elucidate the underlying mechanisms.

Methods: An AD model was established with DNCB to evaluate the effectiveness of Myricetin by daily intraperitoneal injection at dosages of 2, 4, and 6 mg/kg. The Enzyme-linked immunosorbent assay (ELISA) was used for measuring levels of inflammatory cytokines/chemokines in ear tissues, Masson's staining was used to assess collagen loss, Immunofluorescence was used to identify macrophage infiltration in skin tissue, and Western blot was employed to detect the expression of proteins associated with M1 and M2 macrophage polarization. To investigate the underlying mechanism in vitro, RAW264.7 cells were employed for macrophage polarization analysis. M1 macrophages phenotype was induced with LPS + IFN-γ, whereas M2 macrophages phenotype was induced by IL-4. The Griess assay method was used to detect the content of NO, and the Enzyme-linked immunosorbent assay (ELISA) was used for measuring levels of IL-6, TNF-α, IL-1β, and IL-10 in M1 macrophage culture medium. Western blot was employed to detect the proteins expression of JAK1, JAK2, STAT1, IκB-α, P65, and iNOS in M1 macrophages. In M2 macrophages, Western blot was employed to detect the proteins expression of JAK1, JAK2, STAT1, STAT6, and Arg-1.

Results: Myricetin ameliorated skin lesions of DNCB-induced AD mice by reduced levels of pro-inflammatory chemokines/cytokines (IL-18, CXCL-9, CXCL-10), attenuated collagen loss in ear lesions, increased levels of the anti-inflammatory factors TGF-β1 and IL-10, increased the number of F4/80/CD206 positive cells and decreased the infiltration of F4/80/CD86 positive cells, suppressed iNOS protein expression and reduced the phosphorylation of STAT1, IκB-α, and P65, while enhancing Arg-1 expression and STAT6 phosphorylation. In vitro studies have demonstrated that Myricetin effectively suppressed the content of inflammatory factors such as IL-6, TNF-α, NO, and IL-1β, while elevating IL-10 concentration, reduced the proteins expression of p-JAK1, p-STAT1 (Tyr701), p-IκB-α, p-P65, and iNOS, in M1 macrophages. In M2 macrophages, Myricetin increased the expression of Arg-1 and phosphorylation of STAT6 protein expression, lowered the expression of phosphorylation of JAK1 protein expression.

Conclusions: Our findings demonstrate that Myricetin significantly ameliorates skin lesions of DNCB-induced AD mice and reduces inflammatory factor levels by inhibiting the STAT1 and NF-κB signaling pathways to prevent M1 macrophage polarization, while activating the STAT6 signaling pathway to promote M2 macrophage polarization.

Keywords: Anti-inflammatory; Atopic dermatitis; M1/M2 phenotype; Macrophage polarization; Myricetin; NF-κB signaling; STAT signaling.