Senolytic Clearance of p16-High Fibroblasts Reverses Epigenetic Clock Acceleration in Rheumatoid Arthritis Synovium and Restores Biologic DMARD Responsiveness

Background: Rheumatoid arthritis (RA) synovium accumulates senescent p16^INK4a-high fibroblast-like synoviocytes (FLS) that exhibit a senescence-associated secretory phenotype (SASP) enriched in IL-6, MMPs, and CXCL1. These cells drive epigenetic clock acceleration (Horvath delta-age +5-12 years in synovial tissue vs. matched blood). Biologic DMARD non-response in RA correlates with senescent cell burden.

Hypothesis: Targeted senolytic therapy (dasatinib + quercetin or navitoclax) that reduces synovial p16^INK4a-high FLS burden by >=60% will reverse Horvath epigenetic clock acceleration in synovial tissue by >=3 years within 16 weeks AND restore clinical response to previously failed biologic DMARDs (TNFi or IL-6Ri) in >=50% of treatment-refractory RA patients.

Mechanism: Senescent FLS create a paracrine SASP microenvironment that (1) drives epigenetic reprogramming of neighboring stromal cells via IL-6/STAT3-mediated DNMT3A upregulation, (2) maintains pathogenic tissue-resident memory T cells through CXCL9/10 retention signals, and (3) generates a cytokine milieu that competes with biologic mechanisms of action. Senolytic clearance would dismantle this self-reinforcing circuit.

Testable predictions: (1) Pre/post synovial biopsy showing >=60% reduction in p16+/SA-beta-gal+ FLS after 4 weeks of senolytics; (2) Horvath clock reversal >=3 years in synovial (not blood) DNA methylation at week 16; (3) Re-challenge with previously failed biologic achieving ACR50 response in >=50% of subjects by week 28; (4) SASP factor panel (IL-6, MMP-3, CXCL1) reduction >=50% in synovial fluid.

Design: Open-label proof-of-concept, N=24 biologic-refractory RA patients, 2 cycles dasatinib+quercetin (3 days on/28 days off), then biologic re-challenge at week 12. Primary endpoint: ACR50 at week 28. Synovial biopsies at baseline, week 4, week 16.