Arthritis is the major cause of disability and chronic pain in Australia, and rheumatoid arthritis (RA) is one of the most damaging forms, with about 30 % of patients unable to work after 3 years of disease. RA is currently not curable. One of treatment strategies currently under development for this disease is to reinstate immune balance by selectively targeting a subset of immune cells named as dendritic cells. Manipulation of these cells has shown beneficial therapeutic effects in RA animal models and human RA patients. A receptor protein named EPCR has been found to be in high quantities in the RA joint where it attracts high numbers of mature dendritic cells, although the reasons behind this are unknown. This project investigated how EPCR modulates the function of two types of immune cells, dendritic cells and T cells, that play a critical role in RA using a mouse model of human RA.
For this study we used mice that had been genetically modified so they do not express EPCR (known as EPCR knockout mice). Our initial work revealed that these mice develop considerably milder arthritis when compared to control mice. Interestingly, we found that these knockout mice had higher numbers of dendritic cells in their blood, and the maturity of these cells varied markedly when compared to control mice. We also found that bone marrow and spleen cells derived from EPCR knockout mice were less likely to become inflammatory compared to normal cells and correspondingly, T cells from EPCR knockout mice produced less inflammatory molecules. These results help explain why EPCR knockout mice exhibit less severe arthritis compared to normal mice.
This grant set out to delineate potential links between EPCR, dendritic cells and T cells in RA, and how these cells associate with arthritis severity; and whether manipulation of EPCR affects inflammation in these immune cells and in RA.
We found overall dendritic cells were increased in blood, but decreased in peripheral lymph nodes; inflammatory T cells were low and anti-inflammatory T cells high in EPCR knockout mice in comparison to control mice; and that removal of EPCR dramatically affected the inflammatory response of dendritic cells..
This work is important because previously, we found that EPCR is over-presented in RA and promotes the destructive properties of RA synovial cells, but we have no direct evidence whether it contributes to RA. Discovery from this grant provides convincing and direct evidence showing that by removing this gene, the incidence and severity of arthritis is inhibited. Importantly, we found that this protein acts via modulating the function of dendritic cells. These findings support the basis of manipulating dendritic cells as a treatment strategy currently under consideration for RA.
We found that EPCR knockout mice develop considerably milder arthritis when compared to control mice. These knockout mice had higher numbers and more mature dendritic cells in their blood and in the synovial joints. Additionally, bone marrow and spleen cells derived from EPCR knockout mice were resistant to become inflammatory, even after being induced by known inflammatory mediators. When compared to control cells. After isolating T cells, EPCR knockout mice had more inflammatory T cells and less anti-inflammatory T cells compared to control mice. Correspondingly, cells from EPCR knockout mice produced less inflammatory mediators. These data indicate that the reduction in arthritis in EPCR knockout mice is likely achieved via modulating the inflammatory function of these specific immune cells.
Overall, this grant makes the discovery that EPCR is directly associated with RA onset and progression, and knockout of this gene inhibits the incidence and severity of arthritis. These functions of EPCR are achieved via modulating the function of dendritic cells. Modulation of these cells is one of the treatment strategies currently under development for RA. Our results suggest that a more specific approach involving EPCR may be a useful adjunctive therapy for RA.
This is a basic science research project and as such requires further work before it can directly benefit people with musculoskeletal disease.
We anticipate that our finding that EPCR can modify the function of dendritic cells will provide insights into the benefits of pharmacologically manipulating dendritic cell function via EPCR expression in RA patients and facilitate the development of innovative therapeutic interventions to prevent disease progression and improve the overall mobility of RA patients.
The next steps we plan to perform are:
- Detail the exact mechanisms of how EPCR modulates inflammation, focusing particularly on the immune cells.
- Test the therapeutic potential of manipulating EPCR using a mouse arthritis model.
A NHMRC grant application will be lodged to further these studies.