Low dose methotrexate enhances lymphocytic JAM-A expression in rheumatoid arthritis

Endothelial Junction Adhesion Molecule A (JAM-A) functionally manages immune cell infiltration via tight junctions during the pathological development of human immune diseases. However, the expression and function of JAM-A on peripheral lymphocytes are yet to be well understood. The current study aims to identify the expression and functional roles of JAM-A on peripheral lymphocyte in the context of RA treated with low-dose methotrexate (MTX).

The proportion of JAM-A⁺ cells in RA patients and healthy controls were detected by flow cytometry (FCM). Functional validation and the regulatory mechanism between JAM-A and integrin β1 inperipheral lymphocytes were evaluated using quantitative real-time polymerase chain reaction (RT-qPCR), bisulfite sequencing PCR (BSP-PCR), the cell adhesion assay, and MTX treatment in vitro.

In this study, we report that JAM-A mediates lymphocytic cellular adhesion to the extracellular matrix (ECM). Knockdown of JAM-A genes or blocking cell surface JAM-A protein dimerization decreases lymphocyte adhesion to the ECM. Consistently, over-expressing JAM-A enhances lymphocytic ECM adhesion by increasing downstream adhesive proteins, namely integrin β1. In rheumatoid arthritis (RA), we found that increased proportion of JAM-A⁺ cells are associated with low dose MTX clinical treatments. Furthermore, treating lymphocytes with 0.01 μg/ml MTX in vitro elevates JAM-A expression by inhibiting methylation level of CpG islands in the JAM-A promotor region. In addition, we noticed that an increased level of JAM-A expression induced by low dose MTX does not directly counteract MTX's inhibitory effects on cell-to-ECM adhesion.

Regardless, our findings suggest that JAM-A-mediated adhesion of lymphocytes potentially plays an important role during pathogenesis and clinical low dose MTX treatments of RA.