Cell surface and relative mRNA expression of heat shock protein 70 in human synovial cells

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.