Skin fibrosis is characterized by the excessive accumulation of extracellular matrix (ECM) caused by fibrotic disorders of the skin. In recent years, ECM stiffness has emerged as a prominent mechanical cue that precedes skin fibrosis and drives its progression by promoting fibroblasts activation. However, how stiffness influences fibroblasts activation for skin fibrosis progression remains unknown. Here, we report a positive feedback loop mediated by the mechanosensitive ion channel Piezo1 and aberrant tissue mechanics in driving skin fibrosis. Piezo1 is upregulated in fibrotic skin in both humans and mice. Piezo1 knockdown dermal fibroblasts lose their fibroproliferative phenotypes despite being grown on a stiffer substrate. We show that Piezo1 acts through the Wnt2/Wnt11 pathway to mechanically induce secretion of C-C motif chemokine ligand 24 (CCL24, also known as eotaxin-2), a potent cytokine associated with fibrotic disorders. Importantly, adeno-associated virus (AAV)-mediated Piezo1 knockdown ameliorated the progression of skin fibrosis and skin stiffness in mice. Overall, increased matrix stiffness promotes skin fibrosis through the inflammatory Piezo1-Wnt2/Wnt11-CCL24 pathway. In turn, a stiffer skin microenvironment increases Piezo1 expression to exacerbate skin fibrosis aggression. Therefore, targeting Piezo1 represents a strategy to break the positive feedback loop between fibroblasts mechanotransduction and aberrant tissue mechanics in skin fibrosis.

The increased mechanics of fibrotic skin tissue continuously regulate fibroblast functions such as survival and differentiation. Although all these processes consume metabolites, it is unclear whether and how cells adapt their metabolic activity to increased matrix stiffness. Here, we show that transferring mouse dermal fibroblasts from soft to stiff substrates causes an up-regulation of arginine and proline metabolism. Increased matrix stiffness stimulates the expression and activity of key metabolic enzymes, leading to the synthesis of L-proline, a major source of collagen. In addition, the novel mechanosensitive channel Piezo1 was identified as a key regulator of arginine and proline metabolism in fibroblasts under increased stiffness. Consistently, targeting Piezo1 to dermal fibroblasts in vivo effectively reduces fibrosis and arginine-proline metabolism in mouse skin. Therefore, mechanical stiffness is a critical environmental cue for fibroblast metabolism and skin fibrosis progression.

Skin fibrotic diseases are characterized by abnormal fibroblast function and excessive deposition of extracellular matrix. Our previous single-cell sequencing results identified an enriched fibroblast subcluster in skin fibrotic tissues that highly expresses the actin cross-linking cytoskeletal protein Transgelin (TAGLN), which bridges the mechanical environment of tissues and cellular metabolism. Therefore, we aimed to investigate the role of TAGLN in the pathogenesis of skin fibrosis. Transwell, wound healing, collagen gel contraction assay, immunofluorescence and RNA-seq analyses were used to validate and explore the potential mechanisms of the TAGLN-RhoA/ROCK2-SLC2A3-mediated mechano-metabolic axis in dermal fibrosis. The therapeutic efficacy of targeting TAGLN was validated using a bleomycin-induced mouse model of skin fibrosis. Functional assays revealed that downregulation of TAGLN inhibited motility and secretory function of fibroblasts, including invasion, migration, contraction, and collagen secretion. The glucose carrier SLC2A3 was identified as one of the downstream targets of TAGLN by RNA-sequencing analysis and further validation. We further demonstrated that TAGLN regulates the expression of SLC2A3 through the RhoA/ROCK2 pathway, a key pathway of mechanotransduction, thereby affecting glycolysis and motility of fibroblasts. This study reveals the existence of the TAGLN-RhoA/ROCK2-SLC2A3 mechano-metabolic axis in skin fibrotic diseases and provides a promising target for its clinical treatment.

Myofibroblasts contribute to the excessive production, remodeling and cross-linking of the extracellular matrix that characterizes the progression of skin fibrosis. An important insight into the pathogenesis of tissue fibrosis has been the discovery that increased matrix stiffness during fibrosis progression is involved in myofibroblast activation. However, mechanistic basis for this phenomenon remains elusive. To explore the role of fibroblast activation protein-α (FAPα) in mechanical stiffness-induced skin fibrosis progression. RNA-seq was performed to compare differential genes of mouse dermal fibroblasts (MDFs) grown on low or high stiffness plates. This process identified FAPα, which is a membrane protein usually overexpressed in activated fibroblasts, as a suitable candidate. In vitro assay, we investigate the role of FAPα in mechanical stiffness-induced MDFs activation and downstream pathway. By establishing mouse skin fibrosis model and intradermally administrating FAPα adeno-associated virus (AAV) or a selective Fap inhibitor FAPi, we explore the role of FAPα in skin fibrosis in vivo. We show that FAPα, a membrane protein highly expressed in myofibroblasts of skin fibrotic tissues, is regulated by increased matrix stiffness. Genetic deletion or pharmacological inhibition of FAPα significantly inhibits mechanical stiffness-induced activation of myofibroblasts in vitro. Mechanistically, FAPα promotes myofibroblast activation by stimulating the PI3K-Akt pathway. Furthermore, we showed that administration of the inhibitor FAPi or FAPα targeted knockdown ameliorated the progression of skin fibrosis. Taken together, we identify FAPα as an important driver of mechanical stiffness-induced skin fibrosis and a potential therapeutic target for the treatment of skin fibrosis.

Transplantation of adipose‐derived stem cells (ASCs) is a promising option in the field of chronic wounds treatment. However, the effectiveness of ASCs therapies has been hampered by highly inflammatory environment in chronic wound areas. These problems could be partially circumvented using efficient approaches that boost the survival and anti‐inflammatory capacity of transplanted ASCs. Here, by application of mechanical stretch (MS), we show that ASCs exhibits increased survival and immunoregulatory properties in vitro. MS triggers the secretion of macrophage colony stimulating factor (M‐CSF) from ASCs, a chemokine that is linked to anti‐inflammatory M2‐like macrophages polarization. When the MS‐ASCs were transplanted to chronic wounds, the wound area yields significantly faster closure rate and lower inflammatory mediators, largely due to macrophages polarization driven by transplanted MS‐ASCs. Thus, our work shows that mechanical stretch can be harnessed to enhance ASCs transplantation efficiency in chronic wounds treatment.