Expression profiling reveals alternative macrophage activation and impaired osteogenesis in periprosthetic osteolysis

Abstract

Interactions between periprosthetic cells and prosthetic wear debris have been recognized as an important event in the development of osteolysis and aseptic loosening. Although the ability of wear debris to activate pro-inflammatory macrophage signaling has been documented, the full repertoire of macrophage responses to wear particles has not been established. Here, we examined the involvement of alternative macrophage activation and defective osteogenic signaling in osteolysis. Using real-time RT-PCR analysis of periprosthetic soft tissue from osteolysis patients, we detected elevated levels of expression of alternative macrophage activation markers (CHIT1, CCL18), chemokines (IL8, MIP1 a) and markers of osteoclast precursor cell differentiation and multinucleation (Cathepsin K, TRAP, DC-STAMP) relative to osteoarthritis controls. The presence of cathepsin K positive multinuclear cells was confirmed by immunohistochemistry. Reduced expression levels of the osteogenic signaling components BMP4 and FGF18 were detected. Expression levels of TNF-a, IL-6, and RANKL were unchanged, while the anti-osteoclastogenic cytokine OPG was reduced in osteolysis patients, resulting in elevated RANKL:OPG ratios. In vitro studies confirmed the role of particulate debris in alternative macrophage activation and inhibition of osteogenic signaling. Taken together, these results suggest involvement in osteolysis of alternative macrophage activation, accompanied by elevated levels of various chemokines. Increased recruitment and maturation of osteoclast precursors is also observed, as is reduced osteogenesis. These findings provide new insights into the molecular pathogenesis of osteolysis, and identify new potential candidate markers for disease progression and therapeutic targeting. ß

Low dose metal particles can induce monocyte/macrophage survival

“…7 Less evidence has been obtained from human studies, and whether enhanced TNF levels exist has been debated. 14 In our hands, the two materials that we employed were rather poor at inducing secretion by BMM over a 24 h period for TNF and IL-6; these findings are consistent with our particles having little or no contaminating endotoxin, but could be due to particle preparation.…”

“…Perhaps a similar mechanism is operating in the responses described above and if so would be consistent with elevated Bcl-2 expression at the mRNA and protein levels in periprosthetic tissues of osteolysis patients. 14,36 We suggest that if the prosurvival responses described above to wear particles and other poorly degradable particulates were to occur in vivo, shift would occur in the normal balance between macrophage survival and death, thereby maintaining macrophage-lineage numbers in tissues where the particulates are located. 26 Thus, more macrophages would be in an inflammatory lesion, for example, during implant failure, with the potential, following activation and/or differentiation, to perpetuate the particular inflammatory reaction and also to lead to increased osteoclast numbers.…”

“…8 Evidence for the involvement of proinflammatory cytokines in osteolysis is their formation by wear particle-treated macrophages in vitro, their detection in animal models, and their blockade leading to benefit in these models. 14 The cytokine profile observed following macrophage ''activation'' in vitro depends on particle composition. 15 Inflammatory cytokines have been detected around the peri-implant tissue, including TNF, IL-1b, IL-6, IL-8, IL-11, MCP-1, GM-CSF, CSF-1, and TGF-b.…”

“…7 Conversely, conflicting results exist in human studies as to whether TNF levels are raised in failed lesions, suggesting that the involvement of macrophages in osteolysis may not be limited to the action of proinflammatory cytokines. 14 The colony stimulating factor (CSF), macrophage-CSF (M-CSF or CSF-1), controls macrophage lineage development and function in the steady state and during inflammation/pathology 16 ; for example, CSF-1, along with receptor activator of nuclear factor-kB ligand (RANKL), is an important cytokine that controls osteoclast development. CSF-1 blockade can have significant benefit in inflammation/autoimmunity, [16][17][18] and has been implicated in periprosthetic osteolysis.…”

Peri-prosthetic tissue cells show osteogenic capacity to differentiate into the osteoblastic lineage

“…The variation could not be explained by any type of technical error. Literature, presenting RT‐PCR data of peri‐prosthetic tissue cells, shows the use of several different reference genes like GAPDH, 18S, β‐actin, PBGD, HPRT, and RPL32 36, 37, 38, 39. We tested all these genes, widely used as reference genes in peri‐prosthetic tissue samples, but all showed differences in expression between osteogenic and non‐osteogenic conditions in at least some donors.…”