Cutaneous lupus erythematosus (CLE) is a disfiguring and common manifestation in systemic lupus erythematosus (SLE), and the etiology of this predisposition for cutaneous inflammation is unknown. Here, we sought to examine the keratinocyte as an important source of IL-6 and define the mechanism for its increased production in CLE. Evaluation of discoid and subacute cutaneous lupus erythematosus lesions revealed significant epidermal upregulation of IL-6 when compared with control via real-time PCR and immunohistochemistry. Keratinocytes from unaffected skin of lupus patients produced significantly more IL-6 compared with healthy controls following exposure to TLR2, 3, or 4 agonists, or exposure to UVB radiation. Importantly, pretreatment with type I interferons (IFNα and IFNκ) increased IL-6 production by control keratinocytes, and type I IFN blockade decreased IL-6 secretion by lupus keratinocytes. Secretion of keratinocyte-specific IFNκ was significantly increased after TLR2 and UVB treatment in lupus keratinocytes and neutralization of IFNκ decreased IL-6 production by lupus keratinocytes. Thus, lupus keratinocytes are primed for IL-6 hyper-production in a type I IFN-dependent manner. Increased production of IFNκ by lupus keratinocytes drives this response, indicating that IFNκ may play a pathogenic role in CLE and serve as a novel target for treatment.
Cutaneous lupus erythematosus (CLE) is a common manifestation of systemic lupus erythematosus (SLE), and CLE can also develop without systemic involvement. CLE can be difficult to treat and negatively contributes to quality of life. Despite the importance of CLE, our knowledge of what differentiates cutaneous lupus subtypes is limited. Here, we utilized a large cohort of 90 CLE lesional biopsies to compare discoid lupus erythematosus (DLE) and subacute cutaneous lupus (SCLE) in patients with and without associated SLE in order to discern the drivers of disease activity and possibly uncover better treatment targets. Overall, we found that DLE and SCLE share many differentially expressed genes (DEG) reflecting type I interferon (IFN) signaling and repression of EGFR pathways. No differences between CLE only and SLE-associated CLE lesions were found. Of note, DLE uniquely expresses an IFN-γ node. Unbiased cluster analysis of the DEGs identified two groups separated by neutrophilic vs. monocytic signatures that did not sort the patients based on clinical phenotype or disease activity. This suggests that unbiased analysis of the pathobiology of CLE lesions may be important for personalized medicine and targeted therapeutic decision making.
Purpose of Review
Cutaneous lupus erythematosus (CLE) is a common manifestation among systemic lupus patients. There are no FDA approved therapies for CLE, and these lesions are frequently disfiguring and refractory to treatment. This will review will cover the recent inroads made into understanding the mechanisms behind CLE lesions and discuss promising therapeutic developments.
Recent Findings
The definition of cutaneous lupus is being refined to facilitate diagnostic and research protocols. Research into the pathogenesis of CLE is accelerating, and discoveries are now identifying genetic and epigenetic changes which may predispose to particular disease manifestations. Further, unique features of disease subtypes are being defined. Murine work supports a connection between cutaneous inflammation and systemic lupus disease activity. Importantly, human trials of type I interferon blockade hold promise for improving our treatment armamentarium for refractory CLE lesions.
Summary
Continued research to understand the mechanisms driving CLE will provide new methods for prevention and treatment of cutaneous lesions. These improvements may also have important effects on systemic disease activity, and thus, efforts to understand this link should be supported.
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