Pope Research Group
The main focus of Dr. Pope's laboratory is the biology of macrophages in the pathogenesis of rheumatoid arthritis (RA). These studies are directed at defining the mechanisms that promote resistance to apoptosis or programmed cell death and the role of endogenous Toll Like Receptor (TLR) ligands in the pathogensis of RA.
His laboratory has identified the upregulation of the anti-apoptotic protein, Flice Like Inhibitory Protein (FLIP), during monocyte to macrophage differentiation. They have demonstrated that FLIP is highly expressed in the rheumatoid joint and is responsible for protecting RA macrophages from Fas-mediated apoptosis. These studies have been extended to examine the in vivo relevance of FLIP to macrophage biology. Mice with FLIP conditionally deleted in myeloid cells are not capable of developing macrophages. The relevance of these observations to chronic inflammatory arthritis is currently under investigation. Since macrophages are critical to the pathogenesis of RA, future studies will focus on macrophage specific FLIP as a therapeutic target in RA.
Additional studies in the laboratory are focusing on the role of endogenous TLR ligands as potential contributors to the persistent activation of macrophages in the RA joint. The Pope laboratory has identified an endoplasmic reticulum (ER) localized protein called gp96, which binds to TLRs within ER of macrophages and correctly transports them to the cell membrane or endosome. In patients with RA, gp96 is highly increased in RA synovial tissue, particularly in macrophages, and is found in RA synovial fluid in high concentrations. gp96 binds to the extracellular domains of TLR2 and TLR4. Both recombinant gp96 and gp96 present in the RA synovial fluid is capable of activating TLR2 and to a lesser degree TLR4. Ongoing studies in the laboratory are further characterizing the mechanisms by which gp96 and other endogenous TLR ligands might contribute to the pathogenesis of RA employing in vitro studies utilizing cells isolated from the joints of patients with RA and experimental murine models of RA.
Additional studies are ongoing in the laboratory to further identify and define the potential clinical relevance of endogenous TLR ligands in the RA joint employing three approaches which are dependent upon binding to endogenous ligands to TLRs. These approaches include the use of recombinant IgG Fc-TLR2 and IgG Fc-TLR4 to pull down TLR ligands from cells isolated from the RA joint; the use of HEK-TLR2 and HEK-TLR4 cells to bind endogenous TLR ligands in RA synovial fluid which will be identified employing a proteomics approach, and utilizing a yeast 2 hybrid system where mRNA from inflammatory RA synovial tissue has been employed to develop the bait, while the extracellular domains to TLR2 and TLR4 are being used as the prey. Each of these approaches have identified candidate molecules which are being further characterized for a potential role in the pathogenesis of RA.