To assess the effect of proprotein convertase subtilisin/kexin type 6 (PCSK6) in the synovial fibroblasts of rheumatoid arthritis (RA). PCSK6 is a proteinase implicated in the proteolytic activity of various precursor proteins and involved in the regulation of protein maturation.
PCSK6 expression was detected in the synovial tissue of 10 patients with RA, 10 controls with osteoarthritis, and 10 controls with ankylosing spondylitis using Western blotting and quantitative real-time PCR. Genotyping of 67 tag single-nucleotide polymorphisms (SNP) was performed using an Illumina VeraCode (Illumina) microarray in a case-control study including 267 patients with RA and 160 healthy controls. Genotyping of 4 other tag SNP was performed using a TaqMan probe genotyping assay in 1056 healthy controls and 1151 patients with RA. Cultured RA synovial fibroblasts (RASF) were transfected with PCSK6 small interfering RNA to study changes in the proliferation, invasion, migration capacity, secretion of inflammatory cytokines, cell cycle, and expression profiles of the RASF.
Expression of PCSK6 mRNA and protein was significantly higher in the synovial tissues of individuals with RA than in control tissues. One SNP, rs8029797, was significantly associated with RA (p = 0.011). Knockdown of PCSK6 by RNA interference significantly decreased proliferation, invasion, and migration of RASF. These changes in RASF appeared to be related to reduced tumor necrosis factor-α secretion, G0/G1 arrest, and altered expression of various proteins including those involved in angiogenesis (matrix metalloproteinase 9, nitric oxide synthase trafficking), hypoxia (hypoxia-inducible factor-α, thioredoxin domain containing 5), proliferation (chromosome 10 open reading frame 116), and inflammation [CCL7, chemokine (C-X-C motif) ligand 9, interleukin 26].
PCSK6 is upregulated in the synovial tissues of patients with RA and has a genetic effect on the risk of RA. Inhibition of PCSK6 may play a protective role in the development of RA.