Transforming growth factor beta induced PD-L1 expression promotes pro-fibrotic signaling

Immune checkpoint proteins such as programmed death-ligand 1 (PD-L1) retain general immune homeostasis and self-tolerance. PD-L1 binds to programmed cell death protein 1 (PD-1) and inhibits T cell activation or protects tumor cells from T cell-mediated killing. PD-L1 has recently been shown to be up-regulated in invasive lung fibroblasts by p53 and focal adhesion kinase (FAK), any potential role of transforming growth factor-beta (TGFβ) in PD-L1 action is unknown in fibrosis. TGFβ is a mysterious protein with various roles in healthy tissue homeostasis/development as well as the development or progression of cancer, fibrotic disorders, and immune modulation, et al. In the current study, we showed that TGFβ induces the expression of the immunoinhibitory molecule PD-L1 in human and murine fibroblasts in a Smad2/3- and YAP/TAZ-dependent manner. Furthermore, PD-L1 knockdown decreased the TGFβ-dependent induction of extracellular matrix proteins, including collagen Ia1 (colIa1) and alpha-smooth muscle actin (α-SMA), and cell migration/wound healing. In addition to an endogenous role for PD-L1 in profibrotic TGFβ signaling, TGFβ stimulated-human lung fibroblast-derived PD-L1 into extracellular vesicles (EVs) capable of inhibiting T-cell proliferation in response to T cell receptor stimulation and mediating fibroblast cell migration. These findings provide new insights and potential targets for a variety of fibrotic and malignant diseases.