Adenosine receptor expression in rheumatoid synovium: a basis for methotrexate action

Abstract

IntroductionMethotrexate (MTX) exerts at least part of its anti-inflammatory effects through adenosine receptors (ADOR). The aims of this study were to determine the expression of all four adenosine receptor genes (ADORA1, ADORA2A, ADORA2B, ADORA3 and ADORA3variant) in rheumatoid synovial tissue and any influence of MTX exposure on this expression. Furthermore, we investigated whether polymorphisms within ADORA3 were associated with response and/or adverse effects associated with MTX.MethodsAdenosine receptor gene expression was undertaken using PCR in 20 rheumatoid arthritis (RA) synovial samples. A separate cohort of 225 RA patients receiving MTX was genotyped for SNPs in the ADORA3 receptor gene. Double immunofluorescence was used to identify cells expressing ADOR protein.ResultsAll ADOR genes were expressed in all synovial samples. ADORA3 and A3variant were the dominant subtypes expressed irrespective of MTX therapy. Expression of ADORA2A and ADORA2B was increased in patients receiving MTX compared to those not receiving MTX. There was no association between the ADORA3 rs1544224 SNP and high and low disease activity or MTX-associated adverse effects. ADORA2B protein expression was most obvious in vascular endothelial cells whereas ADORA3 protein was more abundant and expressed by synovial fibroblasts.ConclusionsWe have shown that adenosine receptors are expressed in RA synovium. There is differential expression of receptors such that ADORA3 is expressed at significantly higher levels. This evidence demonstrates the potential for MTX to exert its anti-inflammatory effects at the primary site of pathology within the joints of patients with RA.

The human lymph node microenvironment unilaterally regulates T-cell activation and differentiation

“…A2AR signals reduce secretion of proinflammatory IL-1β and IL-6 [22], both of which are produced at high levels by FRCs in response to inflammation [11], and increases production of collagen I [44]. …”

Adenosine signaling during acute and chronic disease states

“…In the context of ethanol-induced liver cirrhosis, increased adenosine levels, as a consequence of ethanol metabolism [77, 78], contribute to the development of cirrhosis [19, 63]. In support of these findings is the observation that many of the drugs used to treat rheumatoid arthritis, most notably methotrexate (MTX), cause increases in extracellular adenosine that appear to be pivotal for the beneficial effects of MTX [68, 79, 80]; however, a well-documented side effect of MTX is its capacity to induce liver fibrosis [81], a phenomenon consistent with the heightened levels of extracellular adenosine.…”

The A3Adenosine Receptor: History and Perspectives

“…Recently, A 3 AR stimulating degranulation has been demonstrated also in LAD2 bone marrow-derived human mast cells (Leung et al, 2014). Human eosinophils were the first cells in which native hA 3 AR was detected by using radioligand binding (Kohno et al, 1996a;Morschl et al, 2008), and this was then followed by human neutrophils (Bouma et al, 1997;Gessi et al, 2002;Chen et al, 2006;van der Hoeven et al, 2008;Corriden et al, 2013;Mulloy et al, 2013), monocytes (Broussas et al, 1999(Broussas et al, , 2002Thiele et al, 2004), macrophages (McWhinney et al, 1996;Szabo et al, 1998;Gessi et al, 2010a), foam cells (Gessi et al, 2010a), dendritic cells (Panther et al, 2001;Fossetta et al, 2003;Dickenson et al, 2003;Hofer et al, 2003), lymphocytes (Gessi et al, 2004b;Varani et al, 2009Varani et al, , 2010b, splenocytes, bone marrow cells, lymphonodes , and synoviocytes (Varani et al, 2008(Varani et al, , 2010cStamp et al, 2012). Human chondrocytes and osteoblasts, two key cell types in the skeletal system, were recently found to express A 3 AR .…”