Angiogenesis is involved in rheumatoid arthritis since it allows leukocytes and inflammatory mediators infiltration in the synovium. In turn, inflammation also keeps angiogenesis going as inflammatory mediators stimulate endothelial cell proliferation.
We aimed to evaluate the reciprocical relationship between synovium inflammation and angiogenesis in mice with collagen-induced arthritis (CIA), a model for rheumatoid arthritis.
CIA was induced by immunization of DBA/1 mice with collagen II in adjuvant. Endothelial cells were detected using a GSL-1 lectin-specific immunohistochemical staining on knee slides. Angiogenesis, clinical scores and histological signs of arthritis were evaluated each week from the induction of CIA to the end of the experiment. Angiogenesis was quantified by counting both the isolated endothelial cells and vessels stained on each slide. To evaluate the effect of an angiogenesis increase on CIA, vascular endothelial growth factor (VEGF) gene transfer was performed with adeno-associated virus VEGF (AAV-VEGF) injection in the muscles of mice with CIA (1010 AAV-VEGF particles intramuscularly 3 weeks before CIA induction). The AAV vectors used in this study contained either mVEGF164 (AAV-VEGF) or lacZ (AAV-lacZ) cDNA, whose expression were driven by the cytomegalo virus promoter.
As expected, clinical and histological scores of arthritis, evaluated each week from day 0 to day 55 after induction of CIA, were correlated (P < 0.0001, r = 0.74, Spearman correlation test). More importantly, angiogenesis increased as a function of the disease course. A correlation was observed between joint vascularization and clinical scores of arthritis (P < 0.0001, r = 0.61). A correlation was also shown between vascularization and histological scores (P = 0.0006, r = 0.51). The overexpression of VEGF induced by gene transfer was followed by an aggravation of arthritis as compared with the AAV-lacZ control group (P < 0.0001, analysis of variance test). Histological and quantification of angiogenesis are in progress in this experiment.
Angiogenesis and inflammation evolved in the same way during the course of CIA. Stimulation of angiogenesis in mice with CIA led to a worse clinical inflammation. These results suggest an early involvement of angiogenesis in joint inflammation development, and emphasize the critical role of angiogenesis in chronic inflammatory arthritis.
GC was supported by Societe Francaise de Rhumatologie.