Dysfunctional keratinocytes increase dermal inflammation in systemic sclerosis. Results from tissue‐engineered scleroderma epidermis

OBJECTIVE In systemic sclerosis (SSc) evidence suggests abnormal keratinocyte-fibroblast interactions. We investigated the potential epidermal dysfunction in SSc and its effects on dermal homeostasis. METHODS Epidermal equivalents (EE) were generated using keratinocytes from six healthy donor (HD) and four individuals with SSc. Skin and EE expression of markers of proliferation, differentiation, and activation was evaluated by immunohistochemistry. The transcriptomic profile of SSc-EE and HD-EE was identified by RNAseq analysis. EE conditioned medium (CM) was used to stimulate fibroblasts, and their production of interleukin (IL)-6, IL-8, matrix metalloproteinase (MMP)-1, type-I collagen (col-I), and fibronectin was assessed by ELISA. RESULTS Compared to HD, SSc-EE exhibited aberrant differentiation, enhanced expression of activation markers, and lower mitotic rate of basal keratinocytes, reproducing most of the abnormalities observed in SSc epidermis. RNAseq analysis revealed that, compared to HD-EE, SSc-EE were characterized by lower expression of HOX gene family members and by enhanced metabolic and oxidative stress molecular pathways. EE-CM enhanced the fibroblast production of IL-6, IL-8, MMP-1, Col-I, and fibronectin (p<0.05). Except for Col-I and fibronectin, this effect was 2-fold higher in the presence of CM generated form SSc-EE. IL-1 was, at least in part, responsible for keratinocyte-dependent fibroblast activation. CONCLUSIONS SSc-EE recapitulate the in vivo characteristics of SSc epidermis demonstrating that SSc keratinocytes have an intrinsically altered differentiation program possibly due to the dysregulation of genes from the HOX family. The increased metabolic and oxidative stress associated with SSc epidermis may contribute to dermis chronic inflammation and fibrosis.