IL-17A Dissociates Inflammation from Fibrogenesis in Systemic Sclerosis

IL-17A is abundant in scleroderma but its role in fibrogenesis is controversial. We interrogated the role of IL-17A in extracellular matrix deposition and inflammation by investigating its effects on keratinocytes and fibroblasts cross-talk and in organotypic skin cultures. Keratinocyte-conditioned media of resting, IL-17A-, and/or transforming growth factor-beta-primed primary keratinocytes were used to stimulate healthy donors and scleroderma fibroblasts. Alternatively, organotypic cultures of full human skin were challenged with these cytokines. Keratinocyte-conditioned media tilted the balance of col-I to matrix metalloproteinase-1 production by fibroblasts in favor of matrix metalloproteinase-1, significantly more so in healthy donors than in scleroderma, resulting in enhanced extracellular matrix turnover, further increased by IL-17A. In organotypic skin, transforming growth factor-beta induced an extensive pro-fibrotic gene signature, including the enhanced expression of several collagen genes associated with Wnt signaling. IL-17A strongly promoted the expression of proinflammatory genes, with no direct effects on collagen genes, and attenuated Wnt signaling induced by transforming growth factor-beta. In this model, at the protein level, IL-17A significantly decreased col-I production. Our data strongly support a pro-inflammatory and antifibrogenic activity of IL-17A in the context of keratinocyte-fibroblast interaction and in full skin. These data help in directing and interpreting targeted therapeutic approaches in scleroderma.