HDAC6 and rheumatoid arthritis: Since both p97 and HDAC6 control the fate of misfolded proteins [9], we first evaluated the expression levels of p97 and HDAC6 by immunohistochemistry in synovial tissues obtained from RA and osteoarthritis (OA) patients, as well as by Western blotting and Real-time PCR in cultured synovial fibroblasts (RASFs and OASFs).