Gpnmb Is Induced in Macrophages by IFN-γ and Lipopolysaccharide and Acts as a Feedback Regulator of Proinflammatory Responses

Abstract

The process of inflammation requires the selective expression of a suite of genes in cells of the macrophage lineage. To identify candidate regulators of inflammation, we used cDNA microarrays to compare the transcriptome of inflammatory macrophages (thioglycolate-elicited peritoneal macrophages), bone marrow-derived macrophages, nonadherent spleen cells, and fibroblasts. We identified genes that were macrophage restricted and further elevated in inflammatory macrophages, and characterized the function of one such gene, gpnmb. Gpnmb mRNA expression was enriched in myelomonocytic cell lines and macrophage-related tissues and strongly up-regulated during macrophage differentiation. Epitope-tagged GPNMB expressed in RAW264.7 cells exhibited a perinuclear distribution and colocalized with the Golgi marker coat protein β. Upon activation of macrophages with IFN-γ and LPS, GPNMB translocated from the Golgi apparatus to vesicular compartments scattered toward the periphery. Gpnmb overexpression in RAW264.7 cells caused a 2-fold reduction in the production of the cytokines IL-6 and IL-12p40 and the inflammatory mediator NO in response to LPS. DBA mice, which have an inactivating point mutation in the gpnmb gene, exhibited reduced numbers of myeloid cells, elevated numbers of thioglycolate-elicited peritoneal macrophages, and higher levels of proinflammatory cytokines in response to LPS. Thus, GPNMB acts as a negative regulator of macrophage inflammatory responses.

Rapid Temporal Dynamics of Transcription, Protein Synthesis, and Secretion during Macrophage Activation

“…The fast release of Ldlr (already detected at 1 h) may prevent the neutralization of LPS by lipoproteins that would inhibit LPS-induced antibacterial programs (81). LPS-induced secretion of Gpnmb has been shown to act as a feedback regulator of the pro-inflammatory response (82), and its shedding in melanocytes has been demonstrated to be mediated by matrix metalloproteinases (83). Furthermore, the described profile is seen for all detected H-2 class I histocompatibility proteins, which have been proposed to undergo extracellular domain cleavage mediated by ␣-secretases (84).…”

“…3, category L), indicating enhanced secretion via vesicles and exosomes specifically induced by LPS. In this respect, an intriguing protein is Gpnmb, which has been implicated in the repression of pro-inflammatory cytokines (82) and is a marker protein for melanosomes (86). This might imply that melanosome formation and secretion are an integral part of the innate immune response.…”

Histone Deacetylase 7 Promotes Toll-like Receptor 4-dependent Proinflammatory Gene Expression in Macrophages

“…Previously, we used comparisons of inflammatory macrophages (TEPMs) versus BMMs to identify genes that regulate macrophage inflammatory responses (30). Therefore, we analyzed the mRNA expression of all classical Hdacs (Hdac1-11) in TEPMs, BMMs, and RAW264 cells.…”

Osteal Tissue Macrophages Are Intercalated throughout Human and Mouse Bone Lining Tissues and Regulate Osteoblast Function In Vitro and In Vivo

“…BMMs were differentiated from C57BL/6 bone marrow progenitors as previously described (15). Enriched calvarial osteoblasts (1.2 ϫ 10 4 ) were cocultured with macrophages (1.8 ϫ 10 3 ; bone macrophages or BMMs) using 24-Transwell plates with 0.4-m pore size (Corning Life Sciences).…”

“…Total RNA was isolated, reverse transcribed, and analyzed using quantitative real time RT-PCR as previously described (15). The sequences of primers used are described in Table I.…”