Neutrophil extracellular traps mediate bone erosion in rheumatoid arthritis by enhancing RANKL‐induced osteoclastogenesis

• Published in: British journal of pharmacology Vol. 181; no. 3; pp. 429 - 446
• Main Authors: Schneider, Ayda Henriques, Taira, Thaise Mayumi, Públio, Gabriel Azevedo, Silva Prado, Douglas, Donate Yabuta, Paula Barbim, Santos, Jéssica Cristina, Machado, Caio Cavalcante, Souza, Flávio Falcão Lima, Rodrigues Venturini, Lucas Gabriel, Oliveira, Renê Donizeti Ribeiro, Cunha, Thiago Mattar, Alves‐Filho, José Carlos, Louzada‐Júnior, Paulo, Aparecida da Silva, Tarcília, Fukada, Sandra Yasuyo, Cunha, Fernando Queiróz
• Format: Journal Article
• Language: English
• Published: England Blackwell Publishing Ltd 01-02-2024
• Subjects: Animals; Arthritis, Rheumatoid - metabolism; Autoimmune diseases; bone damage; Bone loss; Deoxyribonuclease; Deoxyribonucleases - metabolism; Extracellular Traps - metabolism; Humans; Inflammation; Leukocytes (neutrophilic); Mice; NETs; Neutrophils; Osteoarthritis; Osteoblasts; Osteoclastogenesis; Osteoclasts; Osteoclasts - metabolism; Osteogenesis; Osteoprotegerin; Osteoprotegerin - metabolism; Osteoprotegerin - pharmacology; Protein-arginine deiminase; RANK Ligand - metabolism; Rheumatoid arthritis; Synovial fluid; TLR4 protein; TLR9 protein; Toll-Like Receptor 4 - metabolism; Toll-Like Receptor 9 - metabolism; Toll-like receptors; TRANCE protein; Western blotting; NETs; bone damage; osteoclastogenesis; rheumatoid arthritis; osteoclasts
• ISSN: 0007-1188; 1476-5381
• DOI: 10.1111/bph.16227

Background and Purpose
Rheumatoid arthritis (RA) is a chronic autoimmune disease that can cause bone erosion due to increased osteoclastogenesis. Neutrophils involvement in osteoclastogenesis remains uncertain. Given that neutrophil extracellular traps (NETs) can act as inflammatory mediators in rheumatoid arthritis, we investigated the role of NETs in stimulating bone loss by potentiating osteoclastogenesis during arthritis.
Experimental Approach
The level of NETs in synovial fluid from arthritis patients was assessed. Bone loss was evaluated by histology and micro‐CT in antigen‐induced arthritis (AIA)‐induced WT mice treated with DNase or in Padi4‐deficient mice (Padi4flox/flox LysMCRE). The size and function of osteoclasts and the levels of RANKL and osteoprotegerin (OPG) released by osteoblasts that were incubated with NETs were measured. The expression of osteoclastogenic marker genes and protein levels were evaluated by qPCR and western blotting. To assess the participation of TLR4 and TLR9 in osteoclastogenesis, cells from Tlr4−/− and Tlr9−/− mice were cultured with NETs.
Key Results
Rheumatoid arthritis patients had higher levels of NETs in synovial fluid than osteoarthritis patients, which correlated with increased levels of RANKL/OPG. Moreover, patients with bone erosion had higher levels of NETs. Inhibiting NETs with DNase or Padi4 deletion alleviated bone loss in arthritic mice. Consistently, NETs enhanced RANKL‐induced osteoclastogenesis that was dependent on TLR4 and TLR9 and increased osteoclast resorptive functions in vitro. In addition, NETs stimulated the release of RANKL and inhibited osteoprotegerin in osteoblasts, favouring osteoclastogenesis.
Conclusions and Implications
Inhibiting NETs could be an alternative strategy to reduce bone erosion in arthritis patients.