Background: Heme oxygenase-1 (HO-1) is induced in many cell types as a defense mechanism against stress. We have investigated the possible role of endogenous HO-1 in the effector phase of arthritis using the K/BxN serum transfer model of arthritis in HO-1 heterozygous and homozygous knock-out mice.
Methodology/principal findings: Arthritis was induced in C57/Black-6 xFVB (HO-1(+/+), HO-1(+/-) and HO-1(-/-)) mice by intraperitoneal injection of 150 µl serum from arthritic K/BxN mice at days 0 and 2. Blood was collected and animals were sacrificed at day 10. Histological analysis was performed in ankle sections. The levels of inflammatory mediators were measured in serum and paw homogenates by enzyme-linked immunosorbent assay or Multiplex technology. The incidence of arthritis was higher in HO-1(+/-) and HO-1(-/-) groups compared with HO-1(+/+). The inflammatory response was aggravated in HO-1(+/-) mice as shown by arthritic score and the migration of inflammatory cells that could be related to the enhancement of CXCL-1 production. In addition, the HO-1(+/-) group showed proteoglycan depletion significantly higher than HO-1(+/+) mice. Serum levels of matrix metalloproteinase-3, monocyte chemotactic protein-1, plasminogen activator inhibitor-1, E-selectin and intercellular adhesion molecule-1 were increased in arthritic HO-1(-/-) mice, whereas vascular endothelial growth factor and some cytokines such as interferon-γ showed a reduction compared to HO-1(+/+) or HO-1(+/-) mice. In addition, down-regulated gene expression of ferritin, glutathione S-reductase A1 and superoxide dismutase-2 was observed in the livers of arthritic HO-1(+/-) animals.
Conclusion/significance: Endogenous HO-1 regulates the production of systemic and local inflammatory mediators and plays a protective role in K/BxN serum transfer arthritis.