Heat shock proteins (Hsps) have been repeatedly implicated to participate in the pathogenesis of rheumatoid arthritis (RA).
Herein, Hsp70 cell surface and mRNA expression were studied in human fibroblast-like synovial cells, dermal fibroblasts and peripheral blood leukocytes derived from 24 RA patients, who underwent synovectomy by using flow-cytometric analysis and real-time quantitative reverse-transcriptase polymerase chain reaction. For comparison, peripheral blood leukocytes of 17 healthy controls were tested.
Significantly higher Hsp70 membrane positivity was found on fibroblast-like synovial cells in RA patients (average 18.3%, median 16.5%) than on autologous and healthy control peripheral blood lymphocytes (RA patients: average 4.7%, median 2.9%, p = 0.002; healthy controls: average 6.0%, median 4.5%, p = 0.002) and/or autologous dermal fibroblasts (average 5.1%, median 4.3%, p < 0.001). Strong Hsp70 cell surface expression was also found on peripheral blood monocytes of RA patients (average 53.0%, median 58.1%) and healthy controls (average 49.4%, median 47.5%, p = 0.52). Peripheral blood granulocytes of healthy controls (average 41.8%, median 41.4%) showed significantly increased Hsp70 expression comparing with RA patients (average 10.7%, median 6.4%, p = 0.005). Significantly higher Hsp70 gene expression was observed in synovial cells of RA patients (average 2.04, median 1.7) when compared with autologous peripheral blood leukocytes (average 0.75, median 0.68; p < 0.001). However, the difference in Hsp70 gene expression between RA-derived synovial cells and healthy control peripheral blood leukocytes (average 1.69, median 1.64) was not observed (p = 0.83). We also found significantly lower relative gene expression in peripheral blood leukocytes of RA patients in comparison with healthy controls (p < 0.001). Interestingly, we found that Hsp70 gene expression in RA non-affected skin dermis gained from the operation wound was 3.7-fold higher in average (average 7.6, median 8.3) when compared to autologous RA-affected synovial tissue (p < 0.001); 10.1-fold higher in average when compared to autologous peripheral blood leukocytes (p < 0.001) and 4.5-fold higher in average comparing to control peripheral blood leukocytes (p < 0.001).
Hsp70 gene expression in RA-affected synovial tissue is followed by Hsp70 cell surface expression on fibroblast-like synovial cells growing from RA synovial tissue. Hsp70 may be translocated to the cell surface from the cytosol and/or Hsp70 released from inflamed synovial tissue may be captured onto the membrane of synovial cells from the extracellular space via Hsp receptors. As a physiological response to potentially harmful enviromental stress factors, skin dermis produces higher levels of Hsp70 comparing to the cells of internal organs and tissues.