OBJECTIVE: The PIWIL (P-element induced wimpy testis like protein) subfamily of argonaute proteins is essential for Piwi-interacting RNA (piRNA) biogenesis and their function to silence transposons during germ-line development. Here we explored their presence and regulation in rheumatoid arthritis (RA). METHODS: The expression of PIWIL genes in RA and osteoarthritis (OA) synovial tissues and synovial fibroblasts (SF) was analysed by Real-time PCR, immunofluorescence and Western blot. The expression of piRNAs was quantified by next generation small RNA sequencing (NGS). The regulation of PIWI/piRNAs, proliferation and methylation of LINE-1 after silencing of PIWIL genes were studied. RESULTS: PIWIL2 and 4 mRNA were similarly expressed in synovial tissues and SF from RA and OA patients. However, on the protein level only PIWIL4 was strongly expressed in SF. Using NGS up to 300 piRNAs were identified in all SF without significant differences in expression levels between RA and OASF. Of interest, the analysis of the co-expression of the detected piRNAs revealed a less tightly regulated pattern of piRNA-823, -4153 and -16659 expression in RASF. In RASF and OASF, stimulation with TNFα+IL1β/TLR-ligands further significantly increased the expression levels of PIWIL2 and 4 mRNA and piRNA-16659 was significantly (4-fold) induced upon Poly(I:C) stimulation. Silencing of PIWIL2/4 neither affect LINE-1 methylation/expression nor proliferation of RASF. CONCLUSION: We detected a new class of small regulatory RNAs (piRNAs) and their specific binding partners (PIWIL2/4) in synovial fibroblasts. The differential regulation of co-expression of piRNAs in RASF and the induction of piRNA/Piwi-proteins by innate immune stimulators suggest a role in inflammatory processes.

• MeSH
• Argonaute Proteins genetics   metabolism   MeSH
• Cytokines metabolism   MeSH
• Long Interspersed Nucleotide Elements MeSH
• Fibroblasts pathology   MeSH
• Middle Aged MeSH
• Humans MeSH
• RNA, Small Interfering metabolism   MeSH
• Osteoarthritis genetics   metabolism   pathology   MeSH
• RNA-Binding Proteins MeSH
• Proteins genetics   metabolism   MeSH
• Gene Expression Regulation MeSH
• Arthritis, Rheumatoid genetics   metabolism   pathology   MeSH
• Aged, 80 and over MeSH
• Aged MeSH
• Synovial Membrane pathology   MeSH
• Check Tag
• Middle Aged MeSH
• Humans MeSH
• Male MeSH
• Aged, 80 and over MeSH
• Aged MeSH
• Female MeSH
• Publication type
• Journal Article MeSH
• Names of Substances
• Argonaute Proteins MeSH
• Cytokines MeSH
• RNA, Small Interfering MeSH
• PIWIL2 protein, human MeSH Browser
• PIWIL3 protein, human MeSH Browser
• PIWIL4 protein, human MeSH Browser
• RNA-Binding Proteins MeSH
• Proteins MeSH