Objective Skin inflammation and photosensitivity are common in patients with cutaneous lupus erythematosus (CLE) and systemic lupus erythematosus (SLE), yet little is known about the mechanisms that regulate these traits. Here we investigate the role of interferon kappa (IFN-κ) in regulation of type I interferon (IFN) and photosensitive responses and examine its dysregulation in lupus skin.
Methods mRNA expression of type I IFN genes was analysed from microarray data of CLE lesions and healthy control skin. Similar expression in cultured primary keratinocytes, fibroblasts and endothelial cells was analysed via RNA-seq. IFNK knock-out (KO) keratinocytes were generated using CRISPR/Cas9. Keratinocytes stably overexpressing IFN-κ were created via G418 selection of transfected cells. IFN responses were assessed via phosphorylation of STAT1 and STAT2 and qRT-PCR for IFN-regulated genes. Ultraviolet B-mediated apoptosis was analysed via TUNEL staining. In vivo protein expression was assessed via immunofluorescent staining of normal and CLE lesional skin.
Results IFNK is one of two type I IFNs significantly increased (1.5-fold change, false discovery rate (FDR) q<0.001) in lesional CLE skin. Gene ontology (GO) analysis showed that type I IFN responses were enriched (FDR=6.8×10−04) in keratinocytes not in fibroblast and endothelial cells, and this epithelial-derived IFN-κ is responsible for maintaining baseline type I IFN responses in healthy skin. Increased levels of IFN-κ, such as seen in SLE, amplify and accelerate responsiveness of epithelia to IFN-α and increase keratinocyte sensitivity to UV irradiation. Notably, KO of IFN-κ or inhibition of IFN signalling with baricitinib abrogates UVB-induced apoptosis.
Conclusion Collectively, our data identify IFN-κ as a critical IFN in CLE pathology via promotion of enhanced IFN responses and photosensitivity. IFN-κ is a potential novel target for UVB prophylaxis and CLE-directed therapy.
- autoimmune diseases
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JEG and JMK contributed equally.
Handling editor Josef S Smolen
Contributors MKS, GAH, JEG, JMK and JJV designed the study and wrote the manuscript; MKS, GAH, XX, JL, YL, WRS, MP, SS, EPST, RU, MAB, AS, SLB, PWH, SG and JTE collected and analysed data; and CCB and LCT analysed data. All authors reviewed and commented on the manuscript.
Funding The work was in part supported by the University of Michigan Babcock Endowment Fund (MKS, LCT, JTE, JJV and JEG), the National Institute of Arthritis and Musculoskeletal and Skin Diseases of the National Institutes of Health under Award Numbers R03AR066337 (JMK), K08AR063668 (JMK), K08-AR060802 (JEG), T32AR007080 (supporting EPST), R01-AR071384 (JMK) and R01-AR069071 (JEG), the A. Alfred Taubman Medical Research Institute Parfet Emerging Scholar Award (JMK) and Kenneth and Frances Eisenberg Emerging Scholar Award (JEG), Doris Duke Charitable Foundation Grant #2013106 (JEG) and the Rheumatology Research Foundation Career Development K Supplement Award (JMK). EPST received support from the Scleroderma Foundation. LCT is supported by the Dermatology Foundation, Arthritis National Research Foundation and National Psoriasis Foundation.
Competing interests None declared.
Patient consent Obtained.
Ethics approval Skin.
Provenance and peer review Not commissioned; externally peer reviewed.