A MIF-p38-GSDMD inflammatory loop in keratinocytes underlies UVB-induced cutaneous lupus.

Ultraviolet B (UVB) is a well-recognized trigger of cutaneous lupus erythematosus (CLE), yet its molecular basis remains largely undefined. Here, using single-cell transcriptomics and a lupus-prone mouse model, we identify keratinocyte-derived macrophage migration inhibitory factor (MIF) as a key amplifier of cutaneous inflammation through a self-sustaining feedback loop. Single-cell RNA sequencing reveals elevated MIF expression specifically within pathogenic, interferon-high keratinocyte subclusters associated with CLE, which is further validated across major CLE subtypes in clinical skin samples. In vitro, UVB irradiation dose-dependently induces the release of MIF from keratinocytes, which in turn promotes inflammatory signaling and matrix remodeling in both keratinocytes and fibroblasts. Mechanistically, we demonstrate that UVB irradiation activates the ribotoxic stress response (RSR), leading to the p38-C/EBPβ-mediated transcriptional upregulation of NLRP3 and GSDMD cleavage in keratinocytes. The ensuing GSDMD-dependent pyroptosis facilitates the release of MIF, primarily through GSDMD pores rather than vesicular secretion, which in turn amplifies the p38-C/EBPβ signaling pathway. Therapeutic disruption of this loop either by gene silencing via AAVs or pharmacological inhibition via microneedles, markedly attenuates epidermal hyperplasia and cytokine imbalance in lupus-prone mice. These findings uncover a previously unrecognized MIF-p38-GSDMD inflammatory loop contributes to the UVB-induced cutaneous lupus, offering both mechanistic insights and translational opportunities for CLE.