Vascular dysfunction in Rheumatoid arthritis: a possible role for matrix metalloproteinase-9

Sophie Reynolds, Anwen Williams, Derek Lang

Cardiff University, Cardiff, UK

Matrix metalloproteinases (MMPs) play key roles in the development of cardiovascular disease (CVD) (Raffetto & Khalil, 2008) and synovial tissue damage in rheumatoid arthritis (RA) (Burrage et al., (2006). Interestingly, elevated plasma levels of the gelatinase MMP-9 have been independently demonstrated in both CVD and RA affected patients. Given that CVD is the major cause of mortality in RA patients we propose that increased expression/activity of MMP-9 may be a compounding factor in the vascular dysfunction that characterises these inflammatory conditions. The aim of the present study was to test this hypothesis in an experimental model of RA, namely murine collagen-induced arthritis (mCIA).

Immunisation with type II collagen in complete Freund’s adjuvant was utilised to establish arthritis in male DBA/1 mice (6-8 weeks, 18-22g) (Campbell et al., 2000). Rings of thoracic aorta (1-2mm) from arthritic and non-immunised aged-matched control mice were mounted in wire myographs (in oxygenated Krebs’ solution at 37°C) for assessment of vascular function by isometric tension recording. Tissues were consecutively exposed to KCl (6x10-2M), washing and then increasing cumulative concentrations of 5-hydoxytryptamine (5HT, 10-9-10-5M). Subsequently, and following washing and re-constriction with 5HT (10-7-10-6M), endothelium-dependent relaxation to increasing concentrations of acetylcholine (10-9-10-5M) was assessed. In other studies total MMP-9 levels were quantified in aortic homogenates and blood plasma by ELISA and normalised to sample protein content of volume respectively. All data are expressed as mean±sem (n≥4). Concentration-response curves were fitted using GraphPad Prism. Between group differences in the various parameters were determined using unpaired t tests.

Maximum developed constriction in the aorta of arthritic animals was significantly (p<0.01) reduced compared to controls following exposure to KCl (3.14±0.24 cf. 6.96±0.42mN respectively) and 5HT (7.49±0.25 cf. 10.74±0.27mN respectively). The observed contractile dysfunction in tissues from arthritic animals was not accompanied by impaired endothelium-dependent relaxation. MMP-9 levels were significantly (p<0.05) elevated in both arthritic aortic homogenates (96.58±14.00 cf. 41.03±15.68pg/mg protein respectively) and plasma (21.86±3.73 cf. 8.67±2.26ng/ml respectively) compared to control samples.

These data suggest that increased tissue levels of MMP-9 may be associated with the contractile dysfunction observed in this experimental model of RA. Future in vivo therapeutic strategies aimed at modifying MMP activation in RA may alleviate the burden of CVD in affected individuals.

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