1. Division of Paediatric Dentistry and Orthodontics, Faculty of Dentistry, The University of Hong Kong, Hong Kong SAR, China.
2. Division of Periodontology and Implant Dentistry, Faculty of Dentistry, The University of Hong Kong, Hong Kong SAR, China.
3. School of Dentistry, University of California, Los Angeles, Los Angeles, CA 90095, USA.
4. Division of Restorative Dental Sciences, Faculty of Dentistry, The University of Hong Kong, Hong Kong SAR, China.
Macrophages exhibit diverse functions within various tissues during the inflammatory response, and the physical properties of tissues also modulate the characteristics of macrophages. However, the underlying N6-methyladenosine (m6A)-associated molecular mechanisms remain unclear. Accordingly, we examined the potential role of m6A in macrophage activation and stiffness sensing. Intriguingly, we found that the macrophage inflammatory response and global levels of m6A were stiffness-dependent and that this was due to mechanically loosening the chromatin and epigenetic modification (H3K36me2 and HDAC3). In addition, we targeted suppressor of cytokine signalling 1 (Socs1) m6A methylation in a stiffness-dependent manner by screening the sequencing data and found that a higher stiffness hydrogel activated Jak-STAT and NFκB signalling and suppressed Fto gene expression. Next, by using the CRISPR/Cas9 system to knockout the FTO gene in macrophages, we demonstrated that FTO affects the stiffness-controlled macrophage inflammatory response by sustaining the negative feedback generated by SOCS1. Finally, we determined that the m6A reader YTHDF1 binds Socs1 mRNA and thereby maintains expression of SOCS1. Our results suggest that the FTO/Socs1/YTHDF1 regulatory axis is vital to the stiffness-controlled macrophage inflammatory response and that the deletion of FTO affects the negative feedback control exerted by SOCS1. Our findings increase understanding of the regulatory mechanisms involved in macrophage activation and the control of inflammation.
Keywords: m6A, FTO, SOCS1, Hydrogel stiffness, inflammatory response