Weijie Wu,1,2,* Hao Cai,1,* Yunyi Nan,3 Junjie Tang,1 Youhua Wang1 

1Department of Orthopaedics, Affiliated Hospital of Nantong University, Nantong University Medical School, Nantong, Jiangsu, People’s Republic of China; 2Department of Orthopaedics, Affiliated Nantong Hospital of Shanghai University, The Sixth People’s Hospital of Nantong, Nantong, Jiangsu, People’s Republic of China; 3Department of Pain Medicine, Yueqing People’s Hospital, Affiliated Yueqing Hospital of Wenzhou Medical University, Wenzhou, Zhejiang, People’s Republic of China

*These authors contributed equally to this work

Correspondence: Youhua Wang, Email wangyouhua99@163.com

Background: Genetic factors are key determinants of vulnerability to rheumatoid arthritis (RA), a systemic inflammatory disease that causes inflammation, pain, swelling, and destruction of the joints. Expression quantitative trait loci (eQTLs) have been shown to detect novel disease-risk loci in previous studies. In this paper, we identified new susceptibility genes in RA and investigated their underlying mechanisms using integrated Mendelian randomization (MR) analysis.
Methods: Two-sample MR analyses were used to determine the causative links among eQTLs, metabolites, and RA risk. The study was conducted between January 2023 and June 2024. Synovial tissue samples were collected from patients undergoing joint surgery at the Affiliated Hospital of Nantong University. Functional validation of the candidate gene vesicular overexpressed in cancer pro-survival protein 1 (VOPP1) was performed in vitro using rheumatoid arthritis fibroblast-like synoviocytes (RA-FLSs), and in vivo in a collagen-induced arthritis (CIA) rat model. Expression levels of VOPP1 were evaluated by quantitative real-time PCR and Western blot. Additional assays assessed cell proliferation, inflammatory cytokine expression, and activation of the p38 mitogen-activated protein kinase (MAPK) signaling pathway.
Results: Our findings offer the first evidence that RA risk is increased by the VOPP1 eQTL. Furthermore, we discovered that the VOPP1 eQTL positively modulates the X− 23,587 metabolite’s levels, and raising this metabolite may make RA risk worse. Moreover, we demonstrate that VOPP1 is highly expressed in RA synovial tissues and RA-FLSs. VOPP1 stimulates the proliferation of RA-FLSs and the inflammatory response through the p38 MAPK signaling pathway according to functional experiments. We showed that VOPP1 knockdown reduced articular damage and synovial inflammation in vivo using a CIA rat model.
Conclusion: This study identifies VOPP1 as a novel gene associated with rheumatoid arthritis susceptibility. VOPP1 may contribute to disease progression by elevating X− 23,587 metabolite levels and activating the p38 MAPK signaling pathway.

Keywords: Mendelian randomization, expression quantitative trait loci, vesicular overexpressed in cancer pro-survival protein 1, VOPP1, p38 MAPK signaling pathway, rheumatoid arthritis, fibroblast-like synoviocytes