Nerve growth factor regulation and production by macrophages in osteoarthritic synovium.

Nerve growth factor (NGF) functions to modulate osteoarthritis (OA)-associated pain. Although recent studies suggest that tumour necrosis factor (TNF)-α and interleukin (IL)-1ß mediate NGF activity in human synovial fibroblasts, the regulation of NGF expression in human synovial macrophages remains unclear. Here, we examined the role of macrophages in the production and regulation of synovial (SYN) NGF in osteoarthritic knee joints by examining the mRNA expression of TNF-α and IL-1ß in freshly isolated CD14-positive (macrophage-rich fraction) and CD14-negative cells (fibroblast-rich fraction) in synovial tissue from OA patients by quantitative polymerase chain reaction. We also examined the effects of IL-1ß and TNF-α on NGF mRNA expression in cultured CD14-positive (macrophage-rich fraction) and CD14-negative cells (fibroblast-rich fraction). In addition, to examine the contribution of macrophages to NGF, TNF-α and IL-1ß expression, we injected clodronate liposomes systemically into STR/Ort mice, an osteoarthritis animal model, to deplete macrophages. TNF-α and IL-1ß mRNA levels in CD14-positive cells from the SYN of OA patients was significantly higher than that in CD14-negative cells, while NGF expression did not differ markedly between the two cell fractions. In addition, treatment of human cultured CD14-positive and -negative cells with IL-1ß and TNF-α enhanced NGF mRNA and protein levels. Expression of NGF, IL-1ß and TNF-α was also reduced significantly in STR/Ort mice upon macrophage depletion. These findings suggest that IL-1ß and TNF-α regulate NGF expression and production in synovial macrophages and fibroblasts in osteoarthritic joints.

Synovial macrophage-derived IL-1ß regulates the calcitonin receptor in osteoarthritic mice.

Recent studies have reported that calcitonin gene-related peptide (CGRP) contributes to joint pain. However, regulation of the CGRP/CGRP receptor signalling in osteoarthritis (OA) is not fully understood. To investigate the regulation of CGRP/CGRP receptor signalling by macrophages in the synovial tissue (ST) of OA joints, we characterized the gene expression profiles of CGRP and CGRP receptors in the ST of OA mice (STR/Ort). In addition, we examined whether macrophage depletion by the systemic injection of clodronate-laden liposomes affected the expression of CGRP and CGRP receptors in ST. CD11c(+) macrophages in the ST of STR/Ort and C57BL/6J mice were analysed by flow cytometry. Real-time polymerase chain reaction (PCR) was used to evaluate the expression of interleukin (IL)-1ß, CGRP, calcitonin receptor-like receptor (CLR) and receptor activity-modifying protein 1 (RAMP1) in F4/80(+) and F4/80(-) cells. The effects of IL-1ß on the expression of CGRP and CLR by cultured synovial cells were also examined. The percentage of CD11c(+) macrophages in the ST of STR/Ort was higher than that in C57/BL6J mice. Notably, the F4/80(+) cell fraction expressed IL-1ß highly, whereas the F4/80(-) cell fraction expressed CGRP, CLR, and RAMP1 highly. In addition, expression of the IL-1ß and CLR genes was increased in ST, but was decreased upon macrophage depletion, and the IL-1ß treatment of cultured synovial cells up-regulated CLR. Taken together, the present findings suggest that synovial macrophages are the major producers of IL-1ß and regulators of CLR in OA mice. Therefore, macrophages and IL-1ß may be suitable therapeutic targets for treating OA pain.