Rapamycin reveals neuropeptide Y as a regulator of senescence and inflammatory pathways in arthritis.

BACKGROUND: Rheumatoid arthritis (RA) is a chronic inflammatory disease characterized by immune dysregulation and joint destruction. Cellular senescence has been implicated in the progression of RA through the senescence-associated secretory phenotype (SASP), yet its molecular links to inflammation remain unclear. Rapamycin, an mTOR inhibitor with anti-inflammatory and anti-senescence properties, provides a valuable tool for exploring these mechanisms. OBJECTIVE: To investigate the link between senescence and inflammation in a murine model of RA by comparing the transcriptome of diseased joints in rapamycin-treated and untreated mice. METHODS: Collagen-induced arthritis was established in DBA/1 mice, followed by 40 days of rapamycin treatment. RNA sequencing and bioinformatic analyses were performed to identify differentially expressed genes and altered signaling pathways. RT-qPCR and immunohistochemistry validated candidate genes. Functional assays were conducted in fibroblast-like synoviocytes (FLS) following Npy silencing. RESULTS: Rapamycin treatment reduced the incidence and severity of arthritis while modulating senescence- and autophagy-related pathways. Transcriptomic analysis identified neuropeptide Y (Npy) as a differentially expressed gene linking senescence and inflammation, with reduced protein levels following rapamycin treatment, similar to TNF and β-galactosidase. NPY receptor expression (Npy1r and Npy2r) and autophagy-related genes (Sirt1, Sirt6, and Lc3b) were also modulated in vivo. In vitro, Npy silencing in FLS significantly reduced the expression of the SASP cytokines Tnfa, Il1b, and Il6, downregulated Npy1r and Npy2r, and increased Sirt1 expression. CONCLUSION: This study identifies Npy as a modulator of inflammation and senescence-related pathways in arthritis. Its regulation by rapamycin and impact on sirtuins, autophagy, and NPY receptor expression suggest a broader role in RA pathogenesis.