HDAC4 and rheumatoid arthritis: MSCs-derived exosomes of circFBXW7 and miR-320a can inhibit cell proliferation, migration, inflammatory response, and bone damage in RA FLS by directly targeting miR-216a-3p to upregulate histone deacetylase 4 (HDAC4) and C-X-C motif chemokine 9 (CXCL9) (Meng and Qiu, 2020; Chang and Kan, 2021).