Mechanical stiffness promotes skin fibrosis through FAPα-AKT signaling pathway

BACKGROUND

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.

OBJECTIVE

To explore the role of fibroblast activation protein-α (FAPα) in mechanical stiffness-induced skin fibrosis progression.

METHODS

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.

RESULTS

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.

CONCLUSION

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.

Fibroblast activation proteins-α suppress tumor immunity by regulating T cells and tumor-associated macrophages

Fibroblast activation protein-α (FAPα) is a type-II cell-surface-bound integral transmembrane serine protease and selectively overexpressed by tumor-associated stromal fibroblasts (TAFs), which are the main components in the tumor microenvironment, in >90% of malignant epithelial carcinomas. FAPα regulates the immunosuppression of tumor cells in the tumor microenvironment. Regulatory T cells (Tregs) and tumor-associated macrophages (TAMs) are the major immunosuppressive cells in the tumor microenvironment. However, the effect of FAPα on Tregs and TAMs is unknown. The non-enzymatic function of FAPα on Treg and TAM was investigated. In this study, we confirm that FAPα can promote the generation of Tregs and TAMs, which suggests that FAPα plays a immunosuppressive role in the tumor microenvironment and provides evidence for FAP α as a potent immunotherapeutic target for cancer.

A novel FAPα-based Z-Gly-Pro epirubicin prodrug for improving tumor-targeting chemotherapy

Fibroblast activation protein-α (FAPα) is a serine protease of the post-prolyl peptidase family that is specifically expressed in the majority of human epithelial tumors, but not in normal tissues. In this study, we demonstrated the anti-tumor activity of a novel targeting drug formed by conjugating epirubicin (EPI) with an FAPα-specific dipeptide (Z-Gly-Pro) and named it Z-GP-EPI. Consistent with this tumor-targeting delivery strategy, the results illustrated that Z-GP-EPI could release EPI efficiently after incubating with FAPα and could exhibit similar antitumor effects as EPI in vitro in FAPα over-expressed tumor cells (4T1/FAPα⁺). Furthermore, the evaluation of antitumor activity of Z-GP-EPI in vivo was implemented in a 4T1/FAPα⁺ tumor-bearing mice xenograft model. Our results illustrated that Z-GP-EPI had similar antitumor effects in 4T1/FAPα⁺ tumor-bearing mice and showed no visible cardiotoxicity side effects compared with free EPI. Thus, our study indicated that this FAPα-activated prodrug targeting strategy may provide a new mechanism for the targeted delivery of antitumor agents and improve their safety levels.

Fibroblast activation protein-α promotes ovarian cancer cell proliferation and invasion via extracellular and intracellular signaling mechanisms

Fibroblast activation protein-α (FAPα) is secreted by activated stromal fibroblasts and can promote ovarian cancer cell proliferation, migration and invasion. However, the molecular mechanism by which FAPα promotes tumor cell proliferation and invasion is unknown. The role of the non-enzymatic activities of FAPα in tumor migration and invasion and the intracellular and extracellular signaling mechanisms of FAPα were investigated. In this study, we confirm that FAPα promote ovarian cancer cell proliferation, migration and invasion by extracellular and intracellular signaling mechanisms. These results provide evidence that FAPα, together with integrin α3β1 and the uPAR signaling complex, mediate cancer cell migration in the HO-8910PM cell line via the small GTPase Rac1. FAPα-mediated upregulation of p-ERK occurred in a time-dependent manner.