1178 Mechanisms of type I interferon-mediated UVB sensitivity in human keratinocytes

Photosensitivity is a characteristic feature of some inflammatory skin diseases, including cutaneous lupus erythematosus (CLE) and dermatomyositis (DM). Among the various hypotheses that explain this phenomenon, an aberrant sensitivity of keratinocytes (KC) deserves more attention, especially in the case of UVB photosensitivity, as the epidermis almost entirely absorbs UVB. However, the underlying mechanisms of UVB-induced KC death in an inflammatory milieu are unknown. Single-cell RNA sequencing on skin specimens from healthy volunteers and patients with CLE and DM showed a robust type-I-interferon (IFN-I) signature in basal KC, even in non-lesional skin, suggesting subclinical priming for subsequent inflammatory insults. ELISA on interstitial skin fluid from DM patients revealed elevated levels of IFN-beta. We, therefore, sought to investigate how IFN-Is affect KC death after UVB irradiation. Usingin vitroassays, we found pyroptosis, and not cell lysis, as the primary mechanism of UVB-induced inflammatory death in KCs, which was mediated through host-encoded pore-forming protein gasderminE (GSDME). Further, we discovered that GSDME cleavage happens in a caspase 3 (CASP3)-dependent manner. Using ZAK-alpha knockout KCs, we found a significant reduction in cleaved CASP3 and GSDME, suggesting ribotoxic stress as a mechanism of UVB-induced KC pyroptosis. Pretreatment of cultured KC with type I IFNs (IFN-alpha and beta) (p<0.0001) but not IFN-gamma enhanced GSDME-mediated pyroptosis and led to an increased release of interleukin-1 cytokine (p=0.01) following UVB exposure, which was blunted by pan-caspase inhibition. Bulk-RNA sequencing of KCs, we identified upregulation of apoptotic-related genes, including TXNIP, GCH1, and ATF3, after treatment with type I IFNs, suggesting them as targets that could prime KC sensitivity to UVB. These findings provide insight into the underlying mechanisms of UVB photosensitivity in IFN-I-mediated skin diseases.