Spectrum Of Activation States Research Articles

Peroxiredoxin-1 is an H2O2 safe-guard antioxidant and signalling enzyme in M1 macrophages

Macrophages are characterised by their high plasticity and ability to adapt their phenotype and functionality in response to environmental cues, resulting in a spectrum of activation states the two extremes of which are M1 and M2. Reactive oxygen species, such as hydrogen peroxide, are among the cues that impact macrophage polarisation. Moreover, high levels of hydrogen peroxide play a role in the phagocytic response executed by M1 macrophages. Therefore, macrophages must balance the need to shield themselves from the harmful effects of hydrogen peroxide bursts with the ability to interpret hydrogen peroxide signals from the surroundings and initiate a cellular response. Peroxiredoxins (PRDX) are proteins capable of performing both roles. Specifically, PRDX1 and PRDX5 have been demonstrated to safeguard macrophages against reactive oxygen species while also impacting their polarisation status. Previously conducted studies did not differentiate between the polarisation state of macrophages or investigate the signalling events triggered by PRDXs. In this study, we utilised bone marrow-derived murine macrophages polarised to the M1 and M2 states. Our findings revealed that the expression of PRDX1 was significantly higher in M1 macrophages than in M2 and unpolarised macrophages. Moreover, we present evidence that in M1 macrophages, PRDX1 interacts with ASK1, its established interaction partner, and also binds to other proteins that regulate the cellular antioxidant response. Interestingly, we found that pharmacological elevation of hydrogen peroxide levels leads to an increase in PRDX1 expression on the mRNA level, but not in the highly related PRDX2 expression. Taken together, our findings suggest that PRDX1 plays a critical role in macrophage antioxidant defence and redox signalling, and provide scope for exploring redox-signalling proteins as highly sought-after candidates for macrophage repolarisation.

Macrophages in periodontitis: A dynamic shift between tissue destruction and repair.

Periodontitis is a chronic inflammatory disease associated with a dysbiotic bacterial biofilm in the subgingival environment that may disturb the balance between the oral microbiome and its host. The inability of the immune system to eliminate inflammation may result in the progressive destruction of tooth-support tissues. Macrophages are crucial cellular components of the innate immune system and play important roles in diverse physiological and pathological processes. In response to periodontitis-associated bacterial communities, macrophages contribute to inflammation and restoration of tissue homeostasis through pattern recognition receptor-induced signaling cascades; therefore, targeting macrophages can be a feasible strategy to treat patients with periodontitis. Although recent studies indicate that macrophages have a spectrum of activation states, ranging from pro-inflammatory to anti-inflammatory, the regulatory mechanism of the macrophage response to dysbiosis in a tissue-specific manner remains largely unclear. Herein, we attempt to summarize the potential role of macrophage activation in the progression of periodontitis, as well as its relevance to future approaches in the treatment of periodontitis.

The effects of myelin on macrophage activation are phenotypic specific via cPLA2 in the context of spinal cord injury inflammation

Spinal cord injury (SCI) produces chronic, pro-inflammatory macrophage activation that impairs recovery. The mechanisms driving this chronic inflammation are not well understood. Here, we detail the effects of myelin debris on macrophage physiology and demonstrate a novel, activation state-dependent role for cytosolic phospholipase-A2 (cPLA2) in myelin-mediated potentiation of pro-inflammatory macrophage activation. We hypothesized that cPLA2 and myelin debris are key mediators of persistent pro-inflammatory macrophage responses after SCI. To test this, we examined spinal cord tissue 28-days after thoracic contusion SCI in 3-month-old female mice and observed both cPLA2 activation and intracellular accumulation of lipid-rich myelin debris in macrophages. In vitro, we utilized bone marrow-derived macrophages to determine myelin’s effects across a spectrum of activation states. We observed phenotype-specific responses with myelin potentiating only pro-inflammatory (LPS + INF-γ; M1) macrophage activation, whereas myelin did not induce pro-inflammatory responses in unstimulated or anti-inflammatory (IL-4; M2) macrophages. Specifically, myelin increased levels of pro-inflammatory cytokines, reactive oxygen species, and nitric oxide production in M1 macrophages as well as M1-mediated neurotoxicity. PACOCF3 (cPLA2 inhibitor) blocked myelin’s detrimental effects. Collectively, we provide novel spatiotemporal evidence that myelin and cPLA2 play an important role in the pathophysiology of SCI inflammation and the phenotype-specific response to myelin implicate diverse roles of myelin in neuroinflammatory conditions.

Abstract 3061: Tumor-derived PAI-1 promotes macrophage M2 polarization by stimulating an autocrine IL-6 /STAT3 pathway

Abstract Macrophages can exhibit a spectrum of activation states ranging from a pro-inflammatory and antitumorigenic M1 (CD80+; IL-12high; iNOShigh) to a pro-tumorigenic M2 [CD163+; IL-10high; CD206+; Arg+ (mouse)] phenotype. Plasminogen activator inhibitor-1 (PAI-1) is overexpressed in many cancers and although it acts as a protease inhibitor it is paradoxically correlated with poor outcome. PAI-1 exerts its pro-tumorigenic role via pro-angiogenic and anti-apoptotic functions. Increasing evidence points towards the importance of PAI-1 in inflammation and tumorigenesis, but its influence on the immune component of the tumor microenvironment has not yet been investigated. Here we report a novel observation that PAI-1 is a regulator of macrophage polarization. We observe that in PAI-1 KO mice xenotransplanted with 3 human cancer cell lines (HT1080, A549, HCT116) in which PAI-1 was knocked down (KD), tumors were less infiltrated with macrophages with lower Arg expression compared to WT mice implanted with PAI-1 pos. tumors. We demonstrate that recombinant PAI-1 through its uPA interactive domain increased the expression of M2 polarization markers (CD163, IL-10) and decreased or did not affect the expression of M1 polarization markers (iNOS, CD80) in human peripheral blood monocytes. Further investigation demonstrated that treatment of monocytes with PAI-1 induced a rapid (2 h.) increase in IL-6 mRNA and secretion (4 h.) of the protein that was followed by phosphorylation (8-24 h.) of signal transduction and activation of transcription 3 (STAT3) in monocytes. Further linking STAT3 activation to PAI-1, we observed a decreased pSTAT3 in monocytes co-cultured with HT1080 cells upon PAI-1 downregulation. We found that STAT3 activation was downstream of IL-6 and responsible for M2 polarization, as the blockage of the IL-6 receptor with a function blocking antibody (tocilizumab) or inhibition of STAT3 activation by a JAK2/STAT3 inhibitor (ruxolitinib) prevented M2 polarization of monocytes by PAI-1. The contribution of PAI-1 to M2 polarization of macrophages was tested in PAI-1 KO mice implanted with human tumors in which PAI-1 expression was controlled by doxycycline. These experiments demonstrated that induction of PAI-1 in established tumors increased the presence of tumor associated macrophages (TAM) (F4/80+) and decreased the presence of M1 (iNOS+) TAM. Further supporting the presence of an autocrine PAI-1/IL-6 pathway in macrophage polarization in human cancers, a meta-analysis of gene expression array data indicated strong correlations between PAI-1 and IL-6 expression in breast (P=<0.05) and colon (P<0.01) cancers and between PAI-1 and CD163 in colon cancer (P<0.0001). The data thus identify a new pro-tumorigenic function for PAI-1 in the communication between tumor cells and macrophages where tumor-derived PAI-1 activates an autocrine IL-6/STAT3 pathway that promotes M2 polarization. Citation Format: Marta H. Kubala, Veronica R. Placencio, Yves A. DeClerck. Tumor-derived PAI-1 promotes macrophage M2 polarization by stimulating an autocrine IL-6 /STAT3 pathway [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 3061. doi:10.1158/1538-7445.AM2017-3061

Abstract SY06-01: Tumor-associated myelomonocytic cells as therapeutic targets

Abstract SY06-01: Tumor-associated myelomonocytic cells as therapeutic targets

Tumor associated macrophages and neutrophils in tumor progression

Tumor-associated macrophages (TAMs) are a key component of the tumor microenvironment and orchestrate various aspects of cancer. Diversity and plasticity are hallmarks of cells of the monocyte-macrophage lineage. In response to distinct signals macrophages undergo M1 (classical) or M2 (alternative) activation, which represent extremes of a continuum in a spectrum of activation states. Metabolic adaptation is a key component of macrophage plasticity and polarization, instrumental to their function in homeostasis, immunity and inflammation. Generally, TAMs acquire an M2-like phenotype that plays important roles in many aspects of tumor growth and progression. There is now evidence that also neutrophils can be driven towards distinct phenotypes in response to microenvironmental signals. The identification of mechanisms and molecules associated with macrophage and neutrophil plasticity and polarized activation provides a basis for new diagnostic and therapeutic strategies.