Hypoxia enhances the proliferative response of macrophages to CSF-1 and their pro-survival response to TNF.

In chronic inflammatory lesions there are increased numbers of macrophages with a possible contribution of enhanced survival/proliferation due, for example, to cytokine action; such lesions are often hypoxic. Prior studies have found that culture in low oxygen can promote monocyte/macrophage survival. We show here, using pharmacologic inhibitors, that the hypoxia-induced pro-survival response of macrophages exhibits a dependence on PI3-kinase and mTOR activities but surprisingly is suppressed by Akt and p38 MAPK activities. It was also found that in hypoxia at CSF-1 concentrations, which under normoxic conditions are suboptimal for macrophage proliferation, macrophages can proliferate more strongly with no evidence for alteration in CSF-1 receptor degradation kinetics. TNF promoted macrophage survival in normoxic conditions with an additive effect in hypoxia. The enhanced hypoxia-dependent survival and/or proliferation of macrophages in the presence of CSF-1 or TNF may contribute to their elevated numbers at a site of chronic inflammation.

Extracellular proteomes of M-CSF (CSF-1) and GM-CSF-dependent macrophages.

Macrophage colony-stimulating factor (M-CSF) (also known as CSF-1) and granulocyte-macrophage colony-stimulating factor (GM-CSF) have distinct effects on macrophage lineage populations, which are likely to be contributing to their functional heterogeneity. A comparative proteomic analysis of proteins released into culture media from such populations after M-CSF and GM-CSF exposure was carried out. Adherent macrophage populations, termed bone marrow-derived macrophage (BMM) and GM-BMM, were generated after treatment of murine bone marrow precursors with M-CSF and GM-CSF, respectively. Proteins in 16-h serum-free conditioned media (CM) were identified by two-dimensional gel electrophoresis and mass spectrometry. Respective protein profiles from BMM and GM-BMM CM were distinct and there was the suggestion of a switch from primarily signal peptide-driven secretion to non-classical secretion pathways from BMM to GM-BMM. Extracellular expression of cathepsins (lysosomal proteases) and their inhibitors seems to be a characteristic difference between these macrophage cell types with higher levels usually observed in BMM-CM. Furthermore, we have identified a number of proteins in BMM-CM and GM-BMM-CM that could be involved in various tissue regeneration and inflammatory (immune) processes, respectively. The uncharacterized protein C19orf10, a protein found at high levels in the synovial fluid of arthritis patients, was also differentially regulated; its extracellular levels were upregulated in the presence of GM-CSF.

Low dose metal particles can induce monocyte/macrophage survival.

Aseptic loosening results in pain, loss of function, and ultimately prosthetic joint failure and revision surgery. The generation of wear particles from the prosthesis is a major factor in local osteolysis. We investigated the effects of such wear particles on the survival of monocytes and macrophages, populations implicated in wear particle-driven pathology. Particles from titanium aluminum vanadium (TiAlV) and cobalt chromium (CoCr) alloys were generated in-house and were equivalent in size (0.5-3 microm) to those seen in patients. Human CD14(+) monocytes and murine bone marrow-derived macrophages (BMM) were treated with TiAlV and CoCr particles in vitro, and cell survival was assayed. Both particles increased monocyte and macrophage survival in a dose-dependent manner, with an optimal concentration of around 10(7) particles/mL. Conditioned media from particle-treated BMM also increased macrophage survival. Studies with antibody blockade and gene-deficient mice suggest that particle-induced BMM survival is independent of endogenous CSF-1 (M-CSF), GM-CSF, and TNFalpha. These data indicate that wear particles can promote monocyte/macrophage survival in vitro possibly via an endogenous mediator. If this phenomenon occurs in vivo, it could mean that increased numbers of macrophages (and osteoclasts) would be found at a site of joint implant failure, which could contribute to the local inflammatory reaction and osteolysis.