Fibrotic skin disease represents a major global healthcare burden, characterized by fibroblast hyperproliferation and excessive accumulation of extracellular matrix. Fibroblasts are found to be heterogeneous in multiple fibrotic diseases, but fibroblast heterogeneity in fibrotic skin diseases is not well characterized. In this study, we explore fibroblast heterogeneity in keloid, a paradigm of fibrotic skin diseases, by using single-cell RNA-seq. Our results indicate that keloid fibroblasts can be divided into 4 subpopulations: secretory-papillary, secretory-reticular, mesenchymal and pro-inflammatory. Interestingly, the percentage of mesenchymal fibroblast subpopulation is significantly increased in keloid compared to normal scar. Functional studies indicate that mesenchymal fibroblasts are crucial for collagen overexpression in keloid. Increased mesenchymal fibroblast subpopulation is also found in another fibrotic skin disease, scleroderma, suggesting this is a broad mechanism for skin fibrosis. These findings will help us better understand skin fibrotic pathogenesis, and provide potential targets for fibrotic disease therapies.

Keloids are regarded as benign fibroproliferative diseases with unknown pathogenesis that only occur in humans. Keloid tissue proliferates abnormally and bulges beyond the edge of the skin lesion.Keloid tissue not only affects the appearance and causes pain and itching but also causes physical and mental illness in patients. 1 Keloids are characterized by fibroblast proliferation and excessive collagen deposition in the dermis. 2 Although several factors, such as hyperactive inflammation, genetic predisposition, cell heterogeneity and tension, have been shown to play crucial roles in keloid development, the pathogenesis of keloids is still unclear. 3,4 It has been reported that multiple signalling pathways are involved in the pathogenesis of keloids. For instance, the overactive TGFβ-SMAD signalling pathway is the most studied, and it stimulates collagen synthesis and fibroblast proliferation by interacting with

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The NLRP3 inflammasome and IL-1β are essential for scleroderma pathogenesis. Nevertheless, the role of pyroptosis executor gasdermin D(GSDMD), which is a downstream molecule of NLRP3 and is required for IL-1β release in some situations, has not yet been well elucidated in scleroderma. Here, we found that GSDMD was significantly up-regulated and activated in the skin of scleroderma patients and bleomycin-induced mouse model. What’s more, the ablation of GSDMD ameliorates bleomycin-induced skin fibrosis according to HE staining, Masson staining and the detection of hydroxyproline contents. GSDMD deficiency also impaired macrophages infiltration and reduced inflammation response. Furthermore, the loss of GSDMD reduced Th17 differentiation in vivo and in vitro. Collectively, these findings provide the first demonstration that GSDMD related pyroptosis plays an important role in scleroderma pathogenesis.

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