Abstract
BackgroundMacrophage M1 polarization plays a pivotal role in inflammatory diseases. Progranulin (PGRN) has potential anti-inflammation action, however, the effect of PGRN on macrophage M1 polarization has been poorly studied. Our study aimed to investigate the effect of PGRN on lipopolysaccharide (LPS)-induced macrophage M1 polarization and clarify the underlying mechanisms.MethodsRAW264.7 cells were polarized to M1 macrophage by LPS with or without recombinant PGRN (rPGRN) and tumor necrosis factor alpha antibody (anti-TNF-α). A cell counting kit-8 assay (CCK-8), flow cytometry, Quantitative Real-Time PCR assay (q-PCR), Western blot assay and enzyme-linked immunosorbent assay (ELISA) were used to determine the effect of different treatments on cell proliferation, expression of surface phenotype marker and expressions and secretion of inflammatory cytokines. The activation of NF-κB/mitogen-activated protein kinase (MAPK) pathways and the nuclear translocation of NF-κB p65 were detected by Western blot and immunofluorescence respectively. THP-1 and primary bone marrow-derived monocytes (BMDMs) were also used to demonstrate effect of PGRN on expressions and secretion of inflammatory cytokines induced by LPS.ResultsIn RAW264.7 cells, rPGRN at concentrations below 80 ng/ml significantly promoted cell proliferation in dose dependent fashion. rPGRN significantly inhibited LPS-induced change of phenotype (CD86/CD206 ratio) and function (tumor necrosis factor (TNF-α) and inducible nitric oxide synthase (iNOS) expressions). LPS-stimulated secretion of TNF-α and activated phosphorylation of IKKα/β, IкBα, p65, JNK and p38 and the nucleus translocation of NF-кB p65 were also significantly downregulated by rPGRN. In addition, recombinant TNF-α (rTNF-α) significantly boosted TNF-α and iNOS expression vs the control group. Moreover, anti-TNF-α significantly inhibited LPS-induced TNF-α and iNOS expression. In THP-1 and BMDM cells, reversing effect of rPGRN on LPS-enhanced expressions of TNF-α and iNOS and secretion of TNF-α was further demonstrated.ConclusionsPGRN down-regulates LPS-induced macrophage M1 polarization in phenotype and function via NF-κB/MAPK signaling pathways.
Highlights
Macrophage M1 polarization plays a pivotal role in inflammatory diseases
We demonstrated that recombinant PGRN (rPGRN) inhibited LPS-induced macrophage M1 polarization and these effects were associated with NFкB and mitogen-activated protein kinase (MAPK) pathway inhibition
10 ng/ml rPGRN significantly inhibited LPSactivated JNK and p38, though PGRN moderately phosphorylate JNK and p38. These results suggest that NF-кB and MAPK/ JNK/ p38 pathways are involved in reversing action of PGRN for LPS-promoted M1 polarization
Summary
Macrophage M1 polarization plays a pivotal role in inflammatory diseases. Progranulin (PGRN) has potential anti-inflammation action, the effect of PGRN on macrophage M1 polarization has been poorly studied. Some special bacteria initiate periodontal inflammation, the host response motivated by bacterial products, for example, Porphyromonas gingivalis (P.g) LPS, plays an equal important role in mediating periodontal tissue breakdown [2]. Plenty of evidences show that macrophages derived from circulating mononuclear cells and tissue resident cells exist in the diseased tissues of periodontitis and are leading players in immunoreaction against periodontal pathogens, contributing to the initiation of periodontal inflammation [7, 8]. Macrophages in gingival tissue play a dural role in the host’s defense against periodontal pathogen infection and in development of periodontitis depending on their polarization status [10]
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