Evidence of 5-lipoxygenase overexpression in the skin of patients with systemic sclerosis: A newly identified pathway to skin inflammation in systemic sclerosis

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Abstract
Objective Leukotrienes are a family of arachidonic acid derivatives with potent proinflammatory and profibrotic properties, and 5‐lipoxygenase (5‐LOX) catalyzes two key steps in the leukotriene biosynthetic pathway. Since inflammatory cell infiltrates and excessive fibrosis are hallmarks of systemic sclerosis (SSc) skin lesions, we undertook the present study to investigate the expression of 5‐LOX in skin biopsy specimens from patients with SSc. Methods Expression of 5‐LOX in skin sections from 10 SSc patients and 8 healthy controls was examined by in situ hybridization with specific riboprobes and by immunohistochemistry analysis with 5‐LOX monoclonal antibodies. Synthesis of 5‐LOX by cultured dermal fibroblasts from 7 patients with SSc and 4 controls was measured by fluorescence‐activated cell sorter analysis. In addition, concentrations of leukotriene B4 (LTB4) and LTE4 in fibroblast supernatants after stimulation were determined using enzyme immunoassays. Results Expression of 5‐LOX was found in all skin sections from SSc patients as well as from controls. However, the number and percentage of 5‐LOX–positive cells were significantly higher in SSc skin sections compared with control sections. Expression of 5‐LOX was seen in cells within perivascular inflammatory infiltrates as well as in fibroblasts throughout the skin. The experiments with cultured skin fibroblasts revealed that 5‐LOX was constitutively expressed in these cells, which resulted in the production of leukotrienes after cell stimulation. Whereas no difference was found for LTE4, SSc fibroblasts produced significantly higher amounts of LTB4 after stimulation, compared with healthy control fibroblasts. Conclusion The results of this study suggest that the 5‐LOX pathway may be of significance in the pathogenesis of SSc and may represent a target for new treatment strategies.

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