Expression and Regulation of PIWIL-Proteins and PIWI-Interacting RNAs in Rheumatoid Arthritis.

Area of Science:

• Molecular Biology
• Immunology
• Genetics

Background:

• Piwi-interacting RNAs (piRNAs) and PIWIL proteins are crucial for germline development and transposon silencing.
• Their role in inflammatory diseases like rheumatoid arthritis (RA) is largely unexplored.

Purpose of the Study:

• To investigate the presence and regulation of PIWIL proteins and piRNAs in rheumatoid arthritis (RA) synovial tissues and cells.
• To explore the functional impact of PIWIL/piRNA pathways in RA synovial fibroblasts.

Main Methods:

• Quantitative real-time PCR, immunofluorescence, and Western blotting were used to analyze PIWIL gene and protein expression.
• Next-generation sequencing (NGS) quantified piRNA expression.
• PIWIL gene silencing was performed to assess effects on LINE-1 methylation, expression, and fibroblast proliferation.

Main Results:

• PIWIL2 and PIWIL4 mRNA were expressed in RA and osteoarthritis (OA) synovial tissues and fibroblasts; PIWIL4 protein was highly expressed.
• NGS identified numerous piRNAs, with distinct co-expression patterns for specific piRNAs (e.g., piRNA-16659) in RA synovial fibroblasts.
• Stimulation with inflammatory cytokines (TNFα+IL1β) and TLR ligands increased PIWIL2/4 mRNA and piRNA-16659 expression.
• Silencing PIWIL2/4 did not impact LINE-1 methylation/expression or fibroblast proliferation.

Conclusions:

• A novel class of piRNAs and their binding partners, PIWIL2/4, were identified in synovial fibroblasts.
• Differential piRNA co-expression in RA synovial fibroblasts and their induction by innate immune stimuli suggest a role in RA pathogenesis and inflammation.