Mechanism of electroacupuncture inhibiting psoriasis recurrence by regulating CD8⁺ memory T cells based on the TRAF2/NF-κB signaling pathway

To investigate the therapeutic effect of electroacupuncture (EA) on mice with recurrent psoriasis, so as to explore its mechanism from the perspective of memory T cell differentiation and the tumor necrosis factor receptor-associated factor 2 (TRAF2)/nuclear factor-κB (NF-κB) signaling pathway.

BALB/c mice were divided into batches for establishment of recurrent psoriasis model and mechanism verification experiments. The recurrence experiment included blank control group, model group, EA group, methotrexate(MTX) group, and EA + MTX group. The verification experiment additionally set up EA + NF-κB inhibitor group and EA + NF-κB agonist group. The recurrent psoriasis model was induced by topical imiquimod (IMQ) application on the back skin. EA was applied at “Quchi” (LI11) and “Zusanli” (ST36) with sparse-dense wave, frequency of 2 Hz/30 Hz and intensity of 1 mA, once daily for 7 consecutive days, 15 min each time. Lesion changes were observed and psoriasis area and severity index (PASI) scores were evaluated. HE staining was adopted to observe histopathological alterations of lesional skin tissues. ELISA was used to detect the contents of interleukin (IL)-6, IL-17A and tumor necrosis factor α (TNF-α) in lesional skin tissues. Real-time quantitative PCR was performed to detect mRNA expressions of IL-15, C-X-C motif chemokine ligand (CXCL) 9, CXCL10 and C-X-C chemokine receptor 3 (CXCR3) in lesional skin tissue. Flow cytometry was applied to detect the proportions of CD8⁺ tissue-resident memory T cells (T_RM) and CD4⁺ T_RM in skin lesions. Western blot was used to test protein expression of phosphorylated NF-κB p65 (p-NF-κB p65), NF-κB p52, phosphorylated TRAF2 (p-TRAF2), and phosphorylated p38 mitogen-activated protein kinase (p-p38 MAPK) in lesional skin tissues.

Compared with the blank control group, the model group exhibited significantly increased PASI score, contents of IL-6, TNF-α and IL-17A, proportions of CD8⁺ T_RM and CD4⁺ T_RM, mRNA expressions of IL-15, CXCL9, CXCL10, CXCR3, as well as protein expressions of p-TRAF2, p-NF-κB p65 and NF-κB p52 (P<0.01, P<0.05). Compared with the model group, all above indicators were markedly reversed in the EA group and EA + MTX group (P<0.01, P<0.05, except for the proportion of CD4⁺ T_RM). Except for the proportion of CD4⁺ T_RM and IL-17A, the remaining indicators were significantly lower in the two EA-related groups than those in the MTX group (P<0.01, P<0.05). Compared with the EA group, the EA + MTX group showed further decreased proportion of CD8⁺CD103⁺ T_RM, down-regulated mRNA expressions of CXCL9, CXCL10 and reduced p-NF-κB p65 protein expression (P<0.01, P<0.05). In verification experiments, compared with the model group, the EA group and EA + NF-κB inhibitor group presented obvious improvements in skin lesions, inflammatory factors, proportions of CD8⁺CD103⁺ T_RM and CD4⁺ T_RM, protein expressions of p-TRAF2, p-NF-κB p65, and mRNA levels of CXCL9, CXCL10, CXCR3 (P<0.01, P<0.05). Compared with the EA group, these indicators (except for PASI score) were further decreased in the EA + inhibitor group (P<0.01, P<0.05)； in the EA + agonist group, all these indicators were significantly elevated (P<0.01, P<0.05).

EA can effectively alleviate symptoms of recurrent psoriasis. Its underlying mechanism may be related to inhibiting the activation of the TRAF2/NF-κB signaling pathway and specifically down-regulating the level of CD8⁺ memory T cells.