N 1 -methylpseudouridine-incorporated mRNA enhances exogenous protein expression and suppresses immunogenicity in primary human fibroblast-like synoviocytes

Studies conducted using murine arthritis models have indicated that the use of in vitro -transcribed messenger RNA (IVT mRNA) is an effective therapeutic approach for joint diseases. However, the use of IVT mRNA in human synovial cells has not been widely studied. Recently, the outbreak of the novel coronavirus disease has accelerated the development of innovative mRNA vaccines such as those containing a modified nucleic acid, N 1 -methylpseudouridine-5′-triphosphate (m1ψ). IVT mRNA is an attractive tool for biological experiments and drug discovery. To verify the protein expression of IVT mRNA in vitro , primary cultured human fibroblast-like synoviocytes (FLS) were transfected with enhanced green fluorescent protein (EGFP) mRNA with or without m1ψ incorporation. EGFP was detected using western blotting and fluorescence microscopy. A multiplex assay was performed to comprehensively understand IVT mRNA-induced immunogenicity. FLS transfected EGFP mRNA containing m1ψ generated higher levels of EGFP than unmodified EGFP mRNA or control RNAs. The multiplex assay of the FLS culture supernatant revealed that concentrations of IL-6, TNF-α, and CXCL10 were upregulated by unmodified EGFP mRNA, whereas they were suppressed by EGFP mRNA with m1ψ. Overall, m1ψ incorporation enhanced protein expression and decreased cytokine expressions in primary cultured FLS. The findings may contribute to arthritis research.