An APOC1+ inflammatory CAF-like state drives a senescent, treatment-resistant niche in rheumatoid arthritis

Risa Yoshihara; Sotaro Nakajima; Reo Yamazato; Tomoya Yoshida; Ikuo Takazawa; Yasunori Omata; Teh-Wei Wang; Kazuyoshi Ishigaki; Takahiro Itamiya; Mineto Ota; Yoichi Yasunaga; Yuichiro Fujieda; Takumi Matsumoto; Hirofumi Shoda; Kazuhiko Yamamoto; Naoto Tamura; Toshihide Mimura; Koichiro Ohmura; Akio Morinobu; Tatsuya Atsumi; Yoshiya Tanaka; Tsutomu Takeuchi; Yutaka Suzuki; Makoto Nakanishi; Tomohisa Okamura; Sakae Tanaka; Haruka Tsuchiya; Keishi Fujio

doi:10.64898/2026.04.17.718831

ImmunologybioRxivJun 29, 2026

Preprint

An APOC1+ inflammatory CAF-like state drives a senescent, treatment-resistant niche in rheumatoid arthritis

Risa Yoshihara iD, Sotaro Nakajima iD, Reo Yamazato, Tomoya Yoshida, Ikuo Takazawa iD, Yasunori Omata iD, Teh-Wei Wang iD, Kazuyoshi Ishigaki iD, Takahiro Itamiya iD, Mineto Ota iD, Yoichi Yasunaga iD, Yuichiro Fujieda iD, Takumi Matsumoto iD, Hirofumi Shoda iD, Kazuhiko Yamamoto iD, Naoto Tamura iD, Toshihide Mimura iD, Koichiro Ohmura iD, Akio Morinobu iD, Tatsuya Atsumi iD, Yoshiya Tanaka iD, Tsutomu Takeuchi iD, Yutaka Suzuki, Makoto Nakanishi iD, Tomohisa Okamura iD, , Keishi Fujio iD

Abstract

ObjectivesRheumatoid arthritis (RA) synovitis frequently persists despite cytokine-targeted therapies, suggesting the existence of pathogenic stromal programs that sustain chronic inflammation independently of canonical immune pathways. Although synovial fibroblasts (SF) are increasingly implicated in treatment resistance, the pathogenic fibroblast states driving refractory disease and their therapeutic vulnerabilities remain poorly defined. MethodsWe integrated multimodal single-cell and spatial profiling of synovial tissue from 54 patients with RA with prospective treatment-response data and functional studies in human fibroblasts and experimental arthritis models. ResultsWe identified a C-X-C motif chemokine 12 (CXCL12)hi Apolipoprotein C1 (APOC1)+ fibroblast population selectively enriched in treatment-refractory synovitis. Spatial analyses demonstrated that these fibroblasts establish CXCL12-dependent plasmablast niches within inflamed synovium, resembling inflammatory cancer-associated fibroblasts (iCAF) that orchestrate immune cell recruitment in the tumor microenvironment. CXCL12hi APOC1+ fibroblasts exhibited a senescence-associated iCAF-like transcriptional program characterized by STAT3-C/EBP activation and APOC1 expression and were associated with poor response to TNF and IL-6 pathway inhibition. Mechanistically, APOC1 knockdown in RA-SF attenuated invasive mesenchymal behavior and disrupted senescence-associated inflammatory programs, identifying APOC1 as a central regulator of pathogenic fibroblast reprogramming. Importantly, genetic or pharmacological elimination of senescent cells ameliorated experimental arthritis and enhanced the efficacy of TNF blockade. ConclusionsThese findings implicate iCAF-like fibroblasts with senescent properties as a mechanistic driver of refractory RA synovitis and highlight stromal senescence programs as preclinically actionable therapeutic targets beyond cytokine inhibition.

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