Caspase-8 Variant G Regulates Rheumatoid Arthritis Fibroblast-Like Synoviocyte Aggressive Behavior.

Area of Science:

• Molecular Biology
• Immunology
• Epigenetics

Background:

• Fibroblast-like synoviocytes (FLS) are key drivers of synovial inflammation and joint damage in rheumatoid arthritis (RA).
• An imprinted epigenetic state contributes to the aggressive phenotype of RA FLS.
• CASP8, encoding caspase-8, was identified as a differentially marked gene in RA FLS.

Purpose of the Study:

• To investigate the pathogenic role of caspase-8 in rheumatoid arthritis fibroblast-like synoviocytes (RA FLS).
• To evaluate the specific contribution of caspase-8 isoforms to FLS aggressive functions.

Main Methods:

• RA FLS lines were cultured and treated with small interfering RNA to silence caspase-8.
• Cell adhesion, migration, and invasion assays were performed.
• Quantitative reverse transcription PCR, western blot, and caspase-8 selective inhibitors were used to analyze gene and protein expression and enzymatic activity. Caspase-8 isoform transcripts, epigenetic marks, and crystal structures were also analyzed.

Main Results:

• Caspase-8 deficiency in RA FLS reduced cell adhesion, migration, and invasion independently of its catalytic activity.
• Caspase-8 variant G was identified as the dominant (~80%) and PDGF-induced isoform in RA FLS.
• Selective knockdown of caspase-8G, not caspase-8B, was responsible for reduced calpain activity and cell invasion.

Conclusions:

• Targeting caspase-8 variant G specifically can decrease FLS invasion in rheumatoid arthritis.
• This isoform-specific inhibition offers a potential therapeutic strategy to mitigate joint damage in RA without the adverse effects of broad caspase-8 inhibition.