TNF receptor-associated factor 5 limits function of plasmacytoid dendritic cells by controlling IFN regulatory factor 5 expression

The physiological functions of TNF receptor-associated factor 5 (TRAF5) in the skin inflammation and wound healing process are not well characterized. We found that Traf5^-/- mice exhibited an accelerated skin wound healing as compared with wild-type counterparts. The augmented wound closure in Traf5^-/- mice was associated with a massive accumulation of plasmacytoid dendritic cells (pDCs) into skin wounds and an enhanced expression of genes related to wound repair at skin sites. In accordance with this result, adoptive transfer of Traf5^-/- pDCs, but not wild-type pDCs, into the injured skin area in wild-type recipient mice significantly promoted skin wound healing. The expression of skin-tropic chemokine receptor CXCR3 was significantly upregulated in Traf5^-/- pDCs, and treatment with a CXCR3 inhibitor cancelled the promoted wound healing in Traf5^-/- mice, suggesting a pivotal role of CXCR3 in pDC-dependent wound healing. Traf5^-/- pDCs displayed significantly higher expression of IFN regulatory factor 5 (IRF5), which correlated with greater induction of proinflammatory cytokine genes and CXCR3 protein after stimulation with TLR ligands. Consistently, transduction of exogeneous TRAF5 in Traf5^-/- pDCs normalized the levels of abnormally elevated proinflammatory molecules, including IRF5 and CXCR3. Furthermore, knockdown of IRF5 also rescued the abnormal phenotypes of Traf5^-/- pDCs. Therefore, the higher expression and induction of IRF5 in Traf5^-/- pDCs causes proinflammatory and skin-tropic characteristics of the pDCs, which may accelerate skin wound healing responses. Collectively, our results uncover a novel role of TRAF5 in skin wound healing that is mediated by IRF5-dependent function of pDCs.