Collagen I-discoidin domain receptor 1 signalling promotes inflammation development during keloid formation

Keloid formation is a chronic inflammatory skin disease, characterized by abnormal fibroproliferative scars. There are no effective treatments. Many factors are involved in keloid formation, primarily a highly active inflammatory response, wound tension and hereditary susceptibility. Collagen signalling plays important roles in various diseases, including fibrotic diseases and tumours, but its function in keloid inflammation remains unknown.

To study the roles and mechanisms of collagen signalling in inflammation development during keloid formation.

Normal and keloid keratinocytes along with fibroblasts were isolated from fresh normal skin and keloid tissues. Picrosirius red staining, Western blotting, quantitative polymerase chain reaction, co-immunoprecipitation, APEX2-mediated proximity biotinylation, enzyme-linked immunosorbent assay, immunohistochemistry and immunofluorescence were used to discover the roles of collagen I-discoidin domain receptor 1 (DDR1) signalling in the development of inflammation. Human keloid samples were subcutaneously transplanted onto nude mice to build a keloid xenograft model. The therapeutic potential of a DDR1 inhibitor (7rh) and an ADP-ribosylation factor 6 (ARF6) inhibitor (NAV-2729) was examined in keloid inflammation development.

In keloid tissue, we found significant elevation of both phosphorylated nuclear factor kappa B (NF-κB) and signal transducer and activator of transcription 3 (STAT3). In keloid tissue: (i) collagen I was upregulated and comprised the vast proportion of collagen types; (ii) collagen I signalling promoted activation of the keloid inflammation amplifier by DDR1; (iii) DDR1 and ARF6 were upregulated, and their levels positively correlated with each other; (iv) elevated DDR1 was mainly expressed in fibroblasts, in keloid dermal tissues; (v) collagen I-DDR1 signalling activated NFκB and STAT3 signalling; and (vi) in the keloid xenograft model, 7rh restrained keloid inflammation development and growth. Mechanistically, DDR1 interacted with ARF6, which promoted transport of DDR1 to the plasma membrane and amplified collagen I-induced DDR1 signalling, then facilitated binding of DDR1 to STAT3, leading to STAT3 phosphorylation. The combined inhibition of DDR1 and ARF6 synergistically inhibited the keloid inflammation amplifier.

Collectively, these findings reveal the molecular basis of the activation of NFκB and STAT3 signalling via collagen I-DDR1 signalling, and expose the role of the ARF6-DDR1 axis in promoting keloid inflammation development, indicating that DDR1 and ARF6 may serve as innovative therapeutic targets in keloid scars.