We have reported that both risk of developing and severity of tissue damage in rheumatoid arthritis (RA) is associated with the C allele of the genetic variant rs26232. Our new data reveals this variant to be an expression quantitative trait locus for Peptidylglycine alpha-Amidating Monooxygenase (PAM). Furthermore, using single cell transcriptomics of inflamed RA synovial tissue, we found high level PAM expression restricted to synovial fibroblasts particularly the tissue damaging F4 subtype. Targeted PAM inhibition in RASFs led to increased proliferation and invasiveness and reduced apoptosis in vitro. These data indicate that genetically determined low expression of PAM in RA synovial fibroblasts leads to more severe tissue damage in RA. The biological activities of PAM includes C-terminal peptide amidation and regulation of gene expression. We will determine the biology of PAM in RA synovial fibroblast by investigating its intracellular expression and regulation, and effects on both peptide amidation and gene expression profiles. We will also use a novel organoid model to determine the influence of PAM on the 3D interactions between RA synovial fibroblasts and macrophages. The study will identify the mechanisms by which PAM modulates the severity of tissue damage mediated by RASFs in RA.
