Emerging role of targeting macrophages in rheumatoid arthritis: Focus on polarization,metabolism and apoptosis

Macrophages maintain a dynamic balance in physiology. Various known or unknown microenvironmental signals influence the polarization, activation and death of macrophages, which creates an imbalance that leads to disease. Rheumatoid arthritis (RA) is characterized by the massive infiltration of a variety of chronic inflammatory cells in synovia. Abundant activated macrophages found in RA synovia are an early hallmark of RA, and the number of these macrophages can be decreased after effective treatment. In RA, the proportion of M1 (pro‐inflammatory macrophages) is higher than that of M2 (anti‐inflammatory macrophages). The increased pro‐inflammatory ability of macrophages is related to their excessive activation and proliferation as well as an enhanced anti‐apoptosis ability. At present, there are no clinical therapies specific to macrophages in RA. Understanding the mechanisms and functional consequences of the heterogeneity of macrophages will aid in confirming their potential role in inflammation development. This review will outline RA‐related macrophage properties (focus on polarization, metabolism and apoptosis) as well as the origin of macrophages. The molecular mechanisms that drive macrophage properties also be elucidated to identify novel therapeutic targets for RA and other autoimmune disease.     

Amelogenins modulate cytokine expression in LPS-challenged cultured human macrophages

Amelogenins are enamel matrix proteins with a proven ability to restore tissues in patients with advanced periodontitis and chronic skin wounds. To explore the mechanisms of action of amelogenins in wound inflammation, the in vitro effect on the expression of selected cell mediators involved in inflammation and tissue repair from human monocyte-derived macrophages was studied. Macrophages were treated with amelogenins in serum-enriched medium with simultaneous lipopolysaccharide (LPS) stimulation, for 6, 24 and 72 h, and the conditioned culture medium was analysed for 28 different cytokines. Amelogenin treatment directed the LPS-induced release of both pro- and anti-inflammatory cytokines towards an alternatively activated macrophage phenotype. This change in activation was also demonstrated by the amelogenin-induced secretion of alternative macrophage activation-associated CC chemokine-1 (AMAC-1, also known as CCL18; p<0.001), a well-documented marker of alternative activation. Amelogenins were also shown significantly to increase the macrophage expression of vascular endothelial growth factor and, to a lesser but significant extent, insulin-like growth factor-1 after 24h of culture. The results of the present in vitro study show that monocyte-derived macrophages stimulated by inflammatory agonist LPS respond to the treatment with amelogenins by reducing the pro-inflammatory activity and increasing the expression of tissue repair mediators.     

Molecular aspects of rheumatoid arthritis: chemokines in the joints of patients

Rheumatoid arthritis (RA) is a chronic symmetric polyarticular joint disease that primarily affects the small joints of the hands and feet. The inflammatory process is characterized by infiltration of inflammatory cells into the joints, leading to proliferation of synoviocytes and destruction of cartilage and bone. In RA synovial tissue, the infiltrating cells such as macrophages, T cells, B cells and dendritic cells play important role in the pathogenesis of RA. Migration of leukocytes into the synovium is a regulated multi-step process, involving interactions between leukocytes and endothelial cells, cellular adhesion molecules, as well as chemokines and chemokine receptors. Chemokines are small, chemoattractant cytokines which play key roles in the accumulation of inflammatory cells at the site of inflammation. It is known that synovial tissue and synovial fluid from RA patients contain increased concentrations of several chemokines, such as monocyte chemoattractant protein-4 (MCP-4)/CCL13, pulmonary and activation-regulated chemokine (PARC)/CCL18, monokine induced by interferon-gamma (Mig)/CXCL9, stromal cell-derived factor 1 (SDF-1)/CXCL12, monocyte chemotactic protein 1 (MCP-1)/CCL2, macrophage inflammatory protein 1alpha (MIP-1alpha)/CCL3, and Fractalkine/CXC3CL1. Therefore, chemokines and chemokine-receptors are considered to be important molecules in RA pathology.     

Differential binding of chemokines to macrophages and neutrophils in the human inflamed synovium

In chronic inflammatory foci, such as the rheumatoid joint, there is enhanced recruitment of phagocytes from the blood into the tissues. Chemokines are strongly implicated in directing the migration of these cells, although little is known regarding the chemokine receptors that could mediate their chemotaxis into the joint tissue. Therefore the objective of the study was to identify chemokine binding sites on macrophages and neutrophils within the rheumatoid synovium using radiolabeled ligand binding and in situ autoradiography. Specific binding sites for CCL3 (macrophage inflammatory protein-1α), CCL5 (RANTES), CCL2 (monocyte chemoattractant protein-1) and CXCL8 (IL-8) were demonstrated on CD68⁺ macrophages in the subintimal and intimal layers. The number and percentage of intimal cells that bound chemokines were greater in inflamed regions compared to noninflamed regions. The intensity of intimal binding varied between chemokines with the rank order, CCL3 > CCL5 > CCL2 > CXCL8. Neutrophils throughout the synovium bound CXCL8 but did not show any signal for binding CCL2, CCL3 or CCL5.     

Differential binding of chemokines to macrophages and neutrophils in the human inflamed synovium

In chronic inflammatory foci, such as the rheumatoid joint, there is enhanced recruitment of phagocytes from the blood into the tissues. Chemokines are strongly implicated in directing the migration of these cells, although little is known regarding the chemokine receptors that could mediate their chemotaxis into the joint tissue. Therefore the objective of the study was to identify chemokine binding sites on macrophages and neutrophils within the rheumatoid synovium using radiolabeled ligand binding and in situ autoradiography. Specific binding sites for CCL3 (macrophage inflammatory protein-1alpha), CCL5 (RANTES), CCL2 (monocyte chemoattractant protein-1) and CXCL8 (IL-8) were demonstrated on CD68+ macrophages in the subintimal and intimal layers. The number and percentage of intimal cells that bound chemokines were greater in inflamed regions compared to noninflamed regions. The intensity of intimal binding varied between chemokines with the rank order, CCL3 > CCL5 > CCL2 > CXCL8. Neutrophils throughout the synovium bound CXCL8 but did not show any signal for binding CCL2, CCL3 or CCL5. Immunohistochemistry showed that both CXCR1 and CXCR2 are expressed by macrophages and neutrophils in the rheumatoid and nonrheumatoid synovia, suggesting that both of these receptors are responsible for the CXCL8 binding. The chemokine binding sites described on phagocytes may be involved in the migration of these cells into the inflamed joint.     

Zinc finger protein tristetraprolin interacts with CCL3 mRNA and regulates tissue inflammation

Zinc finger protein tristetraprolin (TTP) modulates macrophage inflammatory activity by destabilizing cytokine mRNAs. In this study, through a screen of TTP-bound mRNAs in activated human macrophages, we have identified CCL3 mRNA as the most abundantly bound TTP target mRNA and have characterized this interaction via conserved AU-rich elements. Compared to the wild-type cells, TTP(-/-) macrophages produced higher levels of LPS-induced CCL3. In addition, the plasma level of CCL3 in TTP(-/-) mice was markedly higher than that in wild-type mice. To determine the in vivo significance of TTP-regulated CCL3, we generated CCL3(-/-)TTP(-/-) double-knockout mice. Along with decreased proinflammatory cytokines in their paw joints, there were significant functional and histologic improvements in the inflammatory arthritis of TTP(-/-) mice when CCL3 was absent, although cachexia, reflecting systemic inflammation, was notably unaffected. Furthermore, the marked exacerbation of aortic plaque formation caused by TTP deficiency in the APOE(-/-) mouse model of atherosclerosis was also rescued by disrupting CCL3. Taken together, our data indicate that the interaction between TTP and CCL3 mRNA plays an important role in modulating localized inflammatory processes in tissues that are dissociated from the systemic manifestations of chronic inflammation.     

Effect of peroxisome proliferator-activated receptor-alpha ligands in the interaction between adipocytes and macrophages in obese adipose tissue

Objective: This study was designed to examine the effect of peroxisome proliferator‐activated receptor‐α (PPAR‐α) ligands on the inflammatory changes induced by the interaction between adipocytes and macrophages in obese adipose tissue. Methods and Procedures: PPAR‐α ligands (Wy‐14,643 and fenofibrate) were added to 3T3‐L1 adipocytes, RAW264 macrophages, or co‐culture of 3T3‐L1 adipocytes and RAW264 macrophages in vitro, and monocyte chemoattractant protein‐1 (MCP‐1) and tumor necrosis factor‐α (TNF‐α) mRNA expression and secretion were examined. PPAR‐α ligands were administered to genetically obese ob/ob mice for 2 weeks. Moreover, the effect of PPAR‐α ligands was also evaluated in the adipose tissue explants and peritoneal macrophages obtained from PPAR‐α‐deficient mice. Results: In the co‐culture of 3T3‐L1 adipocytes and RAW264 macrophages, PPAR‐α ligands reduced MCP‐1 and TNF‐α mRNA expression and secretion in vitro relative to vehicle‐treated group. The anti‐inflammatory effect of Wy‐14,643 was observed in adipocytes treated with macrophage‐conditioned media or mouse recombinant TNF‐α and in macrophages treated with adipocyte‐conditioned media or palmitate. Systemic administration of PPAR‐α ligands inhibited the inflammatory changes in adipose tissue from ob/ob mice. Wy‐14,643 also exerted an anti‐inflammatory effect in the adipose tissue explants but not in peritoneal macrophages obtained from PPAR‐α‐deficient mice. Discussion: This study provides evidence for the anti‐inflammatory effect of PPAR‐α ligands in the interaction between adipocytes and macrophages in obese adipose tissue, thereby improving the dysregulation of adipocytokine production and obesity‐related metabolic syndrome.     

Inflammation and macrophage modulation in adipose tissues

The adipose tissue is an active endocrine organ that harbours not only mature and developing adipocytes but also a wide array of immune cells, including macrophages, a key immune cell in determining metabolic functionality. With adipose tissue expansion, M1 pro‐inflammatory macrophage infiltration increases, activates other immune cells, and affects lipid trafficking and metabolism, in part via inhibiting mitochondrial function and increasing reactive oxygen species (ROS). The pro‐inflammatory cytokines produced and released interfere with insulin signalling, while inhibiting M1 macrophage activation improves systemic insulin sensitivity. In healthy adipose tissue, M2 alternative macrophages predominate and associate with enhanced lipid handling and mitochondrial function, anti‐inflammatory cytokine production, and inhibition of ROS. The sequence of events leading to macrophage infiltration and activation in adipose tissue remains incompletely understood but lipid handling of both macrophages and adipocytes appears to play a major role.     

Fas death receptor signaling represses monocyte numbers and macrophage activation in vivo

Over 1 billion monocytes are produced daily, with a small percentage differentiating into macrophages, suggesting that excess monocytes are deleted through a tightly regulated process. Although the in vivo mechanism governing monocyte/macrophage homeostasis is unknown, deletion of monocytes in culture is mediated by the Fas death pathway and is blocked by M-CSF. To determine the in vivo significance of Fas in monocyte development, mice lacking Fas (lpr/lpr) and mice deficient in Fas and M-CSF were examined. Compared with congenic control C57BL/6 (B6) mice, lpr/lpr mice displayed increased numbers of circulating monocytes. The lack of Fas in M-CSF-deficient mice resulted in an enhanced percentage, but not total numbers, of monocytes. Fas deficiency led to an increase in myeloid bone marrow progenitor potential only in M-CSF-intact mice. Although lpr/lpr and B6 mice had similar numbers of tissue macrophages, the loss of Fas in M-CSF-deficient mice was sufficient to increase the number of macrophages in a subset of tissues. Additionally, after stimulation with thioglycolate, lpr/lpr and B6 mice showed equivalent numbers of peritoneal macrophages. However, Fas-deficient peritoneal macrophages displayed a marked increase in spontaneous and LPS-induced proinflammatory molecule production. Moreover, Fas-deficient mice showed enhanced systemic inflammatory arthritis associated with up-regulation of IL-1beta and CCL2 secretion, elevated numbers of inflammatory monocytes, and increased numbers of tissue macrophages. Collectively, these data suggest that Fas may be required for maintaining circulating monocytes and for suppressing macrophage activation and recruitment that are stimulus dependent.     

鲇鱼成鱼和幼鱼中含色素的巨噬细胞集结的诱导发生

通过腹腔注射不同剂量的牛血清白蛋白（ＢＳＡ）或墨汁以刺激巨噬细胞活动,研究了鲇鱼成鱼和幼鱼头肾、肾、脾和肝中含色素的巨噬细胞集结（ＰＭＡ）的发生。鲇鱼淋巴样组织中存在巨噬细胞的不均一性,可分网状／纤维状巨噬细胞,梭状巨噬细胞,圆形红色巨噬细胞,圆形黄红色巨噬细胞和含色素的巨噬细胞。注射ＢＳＡ或墨汁后,头肾、肾,脾和肝中ＰＭＡ和圆形巨噬细胞的数量最终均有不同程度的增加。通过诱导发生实验,表明含色素的     

Acute heart inflammation: ultrastructural and functional aspects of macrophages elicited by Trypanosoma cruzi infection

The heart is the main target organ of the parasite Trypanosoma cruzi , the causal agent of Chagas' disease, a significant public health issue and still a major cause of morbidity and mortality in Latin America. During the acute disease, tissue damage in the heart is related to the intense myocardium parasitism. To control parasite multiplication, cells of the monocytic lineage are highly mobilized. In response to inflammatory and immune stimulation, an intense migration and extravasation of monocytes occurs from the bloodstream into heart. Monocyte differentiation leads to the formation of tissue phagocytosing macrophages, which are strongly activated and direct host defence. Newly elicited monocyte-derived macrophages both undergo profound physiological changes and display morphological heterogeneity that greatly differs from originally non-inflammatory macrophages, and underlie their functional activities as potent inflammatory cells. Thus, activated macrophages play a critical role in the outcome of parasite infection. This review covers functional and ultrastructural aspects of heart inflammatory macrophages triggered by the acute Chagas' disease, including recent discoveries on morphologically distinct, inflammation-related organelles, termed lipid bodies, which are actively formed in vivo within macrophages in response to T. cruzi infection. These findings are defining a broader role for lipid bodies as key markers of macrophage activation during innate immune responses to infectious diseases and attractive targets for novel anti-inflammatory therapies. Modulation of macrophage activation may be central in providing therapeutic benefits for Chagas' disease control.     

Natural antiviral compound silvestrol modulates human monocyte‐derived macrophages and dendritic cells

Outbreaks of infections with viruses like Sars‐CoV‐2, Ebola virus and Zika virus lead to major global health and economic problems because of limited treatment options. Therefore, new antiviral drug candidates are urgently needed. The promising new antiviral drug candidate silvestrol effectively inhibited replication of Corona‐, Ebola‐, Zika‐, Picorna‐, Hepatis E and Chikungunya viruses. Besides a direct impact on pathogens, modulation of the host immune system provides an additional facet to antiviral drug development because suitable immune modulation can boost innate defence mechanisms against the pathogens. In the present study, silvestrol down‐regulated several pro‐ and anti‐inflammatory cytokines (IL‐6, IL‐8, IL‐10, CCL2, CCL18) and increased TNF‐α during differentiation and activation of M1‐macrophages, suggesting that the effects of silvestrol might cancel each other out. However, silvestrol amplified the anti‐inflammatory potential of M2‐macrophages by increasing expression of anti‐inflammatory surface markers CD206, TREM2 and reducing release of pro‐inflammatory IL‐8 and CCL2. The differentiation of dendritic cells in the presence of silvestrol is characterized by down‐regulation of several surface markers and cytokines indicating that differentiation is impaired by silvestrol. In conclusion, silvestrol influences the inflammatory status of immune cells depending on the cell type and activation status.     

GEC-derived SFRP5 Inhibits Wnt5a-Induced Macrophage Chemotaxis and Activation

Aberrant macrophage infiltration and activation has been implicated in gastric inflammation and carcinogenesis. Overexpression of Wnt5a and downregulation of SFRP5, a Wnt5a antagonist, were both observed in gastric cancers recently. This study attempted to explore whether Wnt5a/SFRP5 axis was involved in macrophage chemotaxis and activation. It was found that both Wnt5a transfection and recombinant Wnt5a (rWnt5a) treatment upregulated CCL2 expression in macrophages, involving JNK and NFκB signals. Conditioned medium from Wnt5a-treated macrophages promoted macrophage chemotaxis mainly dependent on CCL2. SFRP5 from gastric epithelial cells (GECs) inhibited Wnt5a-induced CCL2 expression and macrophage chemotaxis. In addition, Wnt5a treatment stimulated macrophages to produce inflammatory cytokines and COX-2/PGE₂, which was also suppressed by SFRP5 from GECs. These results demonstrate that Wnt5a induces macrophage chemotaxis and activation, which can be blocked by GEC-derived SFRP5, suggesting that Wnt5a overproduction and SFRP5 deficiency in gastric mucosa may together play an important role in gastric inflammation and carcinogenesis.