Redox‐Mediated Angiogenesis in the Hypoxic Joint of Inflammatory Arthritis

Abstract

Objective. Inflammatory arthritis is associated with joint inflammation, synovial tissue proliferation, and degradation of articular cartilage and bone. Angiogenesis is an early and fundamental component of synovial inflammation. Oxygen metabolism is recognized as an important mediator of joint vascular remodeling. The aim of this study was to determine whether in vivo synovial hypoxia (tissue PO 2 [tPO 2 ]) and tumor necrosis factor (TNF) blocking therapy alter synovial vascular expression of NADPH oxidase (NOX) and how this action regulates angiogenic mechanisms.Methods. NOX-2 protein and messenger RNA expression was examined in patients with inflammatory arthritis before and after receiving TNF inhibitor (TNFi) therapy and in mice with collagen-induced arthritis (CIA). Proangiogenic processes were assessed in human microvascular endothelial cells (HMVECs) following culture with NOX-2 activators (TNF␣ and 4-hydroxynonenal), small interfering RNA (siRNA) for NOX, and the inhibitor diphenyleneiodonium (DPI) under conditions of normoxia or 3% hypoxia.Results. We demonstrated significantly increased NOX-2 expression in the joints of patients with inflammatory arthritis and the joints of mice with CIA as compared to controls. NOX-2 expression was higher in patients with synovial tPO 2 levels <3% than in those with tPO 2 levels >3% (P < 0.05), and correlated with in vivo macroscopic/microscopic measures of angiogenesis, such as vascularity and levels of vascular endothelial growth factor, angiopoietin 2, factor VIII, neural cell adhesion molecule, and ␣-smooth muscle actin (P < 0.05 for all). A decrease in NOX-2 expression was paralleled by an increase in in vivo tPO 2 levels only in those patients who were defined as TNFi responders. In vitro NOX-2 activators and 3% hypoxia significantly promoted HMVEC migration, angiogenic tube formation, and secretion of proangiogenic mediators, effects that were blocked by siRNA for NOX-2 or the NOX-2 inhibitor DPI.Conclusion. We demonstrated that hypoxia activates NOX-2 protein expression, and NOX-2-induced oxidative stress may be an initiating factor in driving angiogenesis.

IL-35 Inhibits Angiogenesis through VEGF/Ang2/Tie2 Pathway in Rheumatoid Arthritis

“…Administration of anti-VEGF antiserum before, but not after the onset of the disease delays arthritis progression, suggesting that VEGF plays a critical role in early disease development [37]. Ang2 has been implicated in hypoxia-driven synovial angiogenesis in patients with inflammatory arthritis [38]. Gene therapy against the Ang receptor Tie2 before and after disease onset attenuates severity of arthritis [15].…”

Dysregulated bioenergetics: a key regulator of joint inflammation

“…27 We have previously shown increased mitochondrial DNA mutation frequency and mitochondrial dysfunction in the RA joint, 28 which is associated with oxidative stress, angiogenesis, proinflammatory cytokines and activation of the NLRP3 inflammasome. [29][30][31][32][33] Furthermore, in RA, studies have shown increased nicotinamide adenine dinucleotide phosphate (NADPH) oxidase/Nox2 in circulating leucocytes and synovium, 34 demonstrated altered expression of 6-phosphofructo-2kinase/fructose-2, 6-bisphosphatase 3 (PFKFB3) in naive CD4T cells, 35 and shown synovial deficiency of cytochrome C oxidase. 32 The ability of synovial cells to adapt their metabolism in response to the inflammatory microenvironment suggests dysregulated bioenergetics may be an important regulator in RA pathogenesis.…”

Glucose-6-Phosphate Isomerase (G6PI) Mediates Hypoxia-Induced Angiogenesis in Rheumatoid Arthritis

“…3% of oxygen level has been confirmed to represent the joint environment in RA13. Furthermore, the hypoxia level in inflamed joint is inversely correlated with the levels of vascularity, oxidative damage and synovial inflammation1415. HIF-1α, a key gene related to hypoxia, is highly expressed in the synovial tissue16.…”