Deficiency of myeloid-related proteins 8 and 14 (Mrp8/Mrp14) does not block inflammaging but prevents steatosis

Imiquimod-induced skin inflammation is relieved by knockdown of sodium channel Nax

Na_x is an atypical sodium channel that mediates inflammatory pathways in pathological conditions of the skin. In this study, we developed a skin inflammation model in the rabbit ear through application of imiquimod (IMQ). Knockdown of Na_x using RNAi attenuated IMQ-induced skin inflammation, including skin erythema, scaling and papule formation. Histologic analysis showed that thickening and insufficient differentiation of the epidermis found in psoriasis-like skin were normalized by administration of Na_x -RNAi. Excessive infiltration of inflammatory cells found in inflammatory lesions, such as mast cells, eosinophils, neutrophils, T cells and macrophages, was reduced by Na_x -RNAi. Expression of S100A9, which is a downstream gene of Na_x and a mediator of inflammation, was decreased by Na_x -RNAi. Our results demonstrated that knockdown of Na_x ameliorated IMQ-induced psoriasis-like skin inflammation in vivo. Thus, targeting of Na_x may represent a potential therapeutic option for the treatment of psoriasis.

Imiquimod has strain-dependent effects in mice and does not uniquely model human psoriasis

BACKGROUND

Imiquimod (IMQ) produces a cutaneous phenotype in mice frequently studied as an acute model of human psoriasis. Whether this phenotype depends on strain or sex has never been systematically investigated on a large scale. Such effects, however, could lead to conflicts among studies, while further impacting study outcomes and efforts to translate research findings.

METHODS

RNA-seq was used to evaluate the psoriasiform phenotype elicited by 6 days of Aldara (5% IMQ) treatment in both sexes of seven mouse strains (C57BL/6 J (B6), BALB/cJ, CD1, DBA/1 J, FVB/NJ, 129X1/SvJ, and MOLF/EiJ).

RESULTS

In most strains, IMQ altered gene expression in a manner consistent with human psoriasis, partly due to innate immune activation and decreased homeostatic gene expression. The response of MOLF males was aberrant, however, with decreased expression of differentiation-associated genes (elevated in other strains). Key aspects of the IMQ response differed between the two most commonly studied strains (BALB/c and B6). Compared with BALB/c, the B6 phenotype showed increased expression of genes associated with DNA replication, IL-17A stimulation, and activated CD8+ T cells, but decreased expression of genes associated with interferon signaling and CD4+ T cells. Although IMQ-induced expression shifts mirrored psoriasis, responses in BALB/c, 129/SvJ, DBA, and MOLF mice were more consistent with other human skin conditions (e.g., wounds or infections). IMQ responses in B6 mice were most consistent with human psoriasis and best replicated expression patterns specific to psoriasis lesions.

CONCLUSIONS

These findings demonstrate strain-dependent aspects of IMQ dermatitis in mice. We have shown that IMQ does not uniquely model psoriasis but in fact triggers a core set of pathways active in diverse skin diseases. Nonetheless, our findings suggest that B6 mice provide a better background than other strains for modeling psoriasis disease mechanisms.