Haptoglobin and CD163: captor and receptor gating hemoglobin to macrophage lysosomes

The plasma protein haptoglobin and the endocytic hemoglobin receptor HbSR/CD163 are key molecules in the process of removing hemoglobin released from ruptured erythrocytes. Hemoglobin in plasma is instantly bound with high affinity to haptoglobin--an interaction leading to the recognition of the complex by HbSR/CD163 and endocytosis in macrophages. The haptoglobin-dependent HbSR/CD163 scavenging system for hemoglobin clearance prevents toxic effects of hemoglobin in plasma and kidney and explains the decrease in the haptoglobin plasma concentration in patients with accelerated hemolysis. The HbSR/CD163 activity may be of quantitative importance for iron uptake in macrophages in general and for some iron-associated pathological processes, e.g. the atherogenesis-promoting oxidation of LDL leading to foam cell formation and apoptosis in the vessel wall.     

Haemoglobin scavenger receptor: function in relation to disease

Highly efficient systems remove the toxic and proinflammatory haemoglobin from the circulation and local sites of tissue damage. Macrophages are major haemoglobin-clearing cells; CD163 was recently recognized as the specific haemoglobin scavenger receptor (HbSR). It is tightly involved in both physiological as well as pathophysiological processes, such as cytoprotection and inflammation. Haemoglobin functions as a double-edged sword. In moderate quantities and bound to haptoglobin, it forms a ligand for haemoglobin scavenger receptor CD163/HbSR, but when unleashed in large amounts, it can become toxic by mediating oxidative stress and inflammation. CD163/HbSR plays a crucial role in the control of inflammatory processes, probably in part through its effects on both ferritin induction and subsequent induction of antiinflammatory pathways through interleukin-10 and haem oxygenase. Besides the observation that the haemoglobin scavenger receptor provides a promising target for new treatment possibilities, it offers a novel view on the aetiology of diverse physiological as well as pathophysiological processes. In addition, monocyte CD163/HbSR and soluble CD163/HbSR are potential diagnostic tools in a variety of disease states, such as inflammation, atherosclerosis, transplant rejection, and carcinoma.     

Oleacein enhances anti-inflammatory activity of human macrophages by increasing CD163 receptor expression

BackgroundOleacein (dialdehydic form of decarboxymethyl elenolic acid linked to hydroxytyrosol; 3,4-DHPEA-EDA) have been proven to possess antioxidant and anti-inflammatory activity.PurposeIn this study, we examined whether oleacein could increase CD163 and IL-10 receptor expression as well as HO-1 intracellular secretion in human macrophages.MethodsEffect of oleacein (10 and 20 μmol/l) or oleacein together with complexes of haemoglobin (Hb) and haptoglobin 1-1 (Hp11) or haptoglobin 2-2 (Hp22) on expression of IL-10 and CD163 receptor was determined by Flow Cytometry. Expression of CD163mRNA was measured by real-time quantitative RT-PCR. Heme oxygenase 1 (HO-1) intracellular secretion in macrophages was investigated by enzyme-linked immunosorbent assay (ELISA).ResultsOleacein (OC) together with complexes HbHp11 or HbHp22 stimulated the expression of CD163 (30-100-fold), IL-10 (170-300-fold) and HO-1 secretion (60-130-fold) after 5 days of coincubation. The 2-fold (24 h), 4-fold (48 h) increase of CD163 mRNA level and its final (72 h) decrease was also observed.ConclusionOur results suggested that oleacein enhances anti-inflammatory activity of complexes haemoglobin with haptoglobin 1-1 and 2-2 and could play a potential role in the prevention of inflammatory disease related to atherosclerosis.     

CD163: a signal receptor scavenging haptoglobin-hemoglobin complexes from plasma

CD163 is a highly expressed macrophage membrane protein belonging to the scavenger receptor cysteine rich (SRCR) domain family. The CD163 expression is induced by interleukin-6, interleukin-10 and glucocorticoids. Its function has remained unknown until recently when CD163 was identified as the endocytic receptor binding hemoglobin (Hb) in complex with the plasma protein haptoglobin (Hp). This specific receptor-ligand interaction leading to removal from plasma of the Hp-Hb complex-but not free Hp or Hb-now explains the depletion of circulating Hp in individuals with increased intravascular hemolysis. Besides having a detoxificating effect by removing Hb from plasma, the CD163-mediated endocytosis of the Hp-Hb complex may represent a major pathway for uptake of iron in the tissue macrophages.The novel functional linkage of CD163 and Hp, which both are induced during inflammation, also reveal some interesting perspectives relating to the suggested anti-inflammatory properties of the receptor and the Hp phenotypes.     

Corticosteroid enhances heme oxygenase-1 production by circulating monocytes by up-regulating hemoglobin scavenger receptor and amplifying the receptor-mediated uptake of hemoglobin-haptoglobin complex

This study examined the relationship between steroid treatment and CD163-mediated downstream pathways linked to inflammatory resolution. Twelve patients referred for congenital heart disease surgery were divided into two groups based on the severity of intravascular hemolysis during cardiopulmonary bypass surgery. Patients with severe intravascular hemolysis were administered haptoglobin during the procedure. Flow cytometry indicated a peak in monocyte CD163 expression on post-operative day 1 in both groups. Enhanced and prolonged heme oxygenase-1 (HO-1) mRNA expression levels were observed in patients who received haptoglobin. Binding of hemoglobin-haptoglobin complex (Hb/Hp) to CD163 resulted in significant induction of HO-1 by peripheral blood mononuclear cells after exposure to dexamethasone prior to culture. This effect was significantly inhibited by anti-CD163 antibody. Our results demonstrated up-regulation of CD163 expression on the monocyte surface by steroid treatment. Steroid treatment was suggested to facilitate CD163-mediated endocytosis of hemoglobin to monocytes/macrophages and thereby induce acceleration of HO-1 synthesis.     

A unique loop extension in the serine protease domain of haptoglobin is essential for CD163 recognition of the haptoglobin-hemoglobin complex

Haptoglobin and haptoglobin-related protein are homologous hemoglobin-binding proteins consisting of a complement control repeat (alpha-chain) and a serine protease domain (beta-chain). Haptoglobin-hemoglobin complex formation promotes high affinity binding of hemoglobin to the macrophage scavenger receptor CD163 leading to endocytosis and degradation of the haptoglobin-hemoglobin complex. In contrast, complex formation between haptoglobin-related protein and hemoglobin does not promote high affinity interaction with CD163. To define structural components of haptoglobin important for CD163 recognition, we exploited this functional difference to design and analyze recombinant haptoglobin/haptoglobin-related protein chimeras complexed to hemoglobin. These data revealed that only the beta-chain of haptoglobin is involved in receptor recognition. Substitution of 4 closely spaced amino acid residues of the haptoglobin beta-chain (valine 259, glutamate 261, lysine 262, and threonine 264) abrogated the high affinity receptor binding. The 4 residues are encompassed by a part of the primary structure not present in other serine protease domain proteins. Structural modeling based on the well characterized serine protease domain fold suggests that this sequence represents a loop extension unique for haptoglobin and haptoglobin-related protein. A synthetic peptide representing the haptoglobin loop sequence exhibited a pronounced inhibitory effect on receptor binding of haptoglobin-hemoglobin.     

M2 differentiation of MonoMac-1 cell line induced by M-CSF and glucocorticoid pathways

Models of macrophage subtypes require molecular characterization to reliably facilitate their differentiation. Although CD16⁺ (Fc-gamma III receptor) monocytes that express CD163 (a hemoglobin/haptoglobin receptor) have been implicated in a variety of disease states, the conditions necessary to establish lineages of these cell subtypes remains unknown. The current investigations utilize a cell line derived from acute myelogenous leukemia lineage, MonoMac-1, to interrogate the factors that promote the development of CD16⁺ macrophages that express CD163. Results implicate the glucocorticoid pathway as well as c-fms signaling based on the action of dexamethasone and macrophage colony-stimulating factor-1 in promoting CD16⁺ expression, in addition to phorbol myristate acetate and lipopolysaccharides treatment. The ability of glucocorticoid and c-fms receptor antagonists to inhibit CD16⁺ cell formation further establishes the role of these pathways in CD16 expression in this cell line. In view of the inherent difficulty in working with primary cells as well as donor variation, cell lines may be preferable to primary cells for their consistency. We envision that the process we use to induce CD16 expression in this cell type will be useful for screening and identification of drug candidates potentially useful for the treatment of diseases where the etiology involves the expansion of the CD16⁺ monocytes subset or the accumulation of CD163⁺ tissue macrophages.     

Molecular characterization of the haptoglobin.hemoglobin receptor CD163. Ligand binding properties of the scavenger receptor cysteine-rich domain region

CD163 is the macrophage receptor for endocytosis of haptoglobin.hemoglobin complexes. The extracellular region consisting of nine scavenger receptor cysteine rich (SRCR) domains also circulates in plasma as a soluble protein. By ligand binding analysis of a broad spectrum of soluble CD163 truncation variants, the amino-terminal third of the SRCR region was shown to be crucial for the binding of haptoglobin.hemoglobin complexes. By Western blotting of the CD163 variants, a panel of ten monoclonal antibodies was mapped to SRCR domains 1, 3, 4, 6, 7, and 9, respectively. Only the two antibodies binding to SRCR domain 3 exhibited effective inhibition of ligand binding. Furthermore, analysis of purified native CD163 revealed that proteolytic cleavage in SRCR domain 3 inactivates ligand binding. Calcium protects against cleavage in this domain. Analysis of the calcium sensitivity of ligand binding to CD163 demonstrated that optimal ligand binding requires physiological plasma calcium concentrations, and an immediate ligand release occurs at the low calcium concentrations measured in acidifying endosomes. In conclusion, SRCR domain 3 of CD163 is an exposed domain and a critical determinant for the calcium-sensitive coupling of haptoglobin.hemoglobin complexes.     

Regulation of CD163 associated casein kinase II activity is haptoglobin genotype dependent

Free hemoglobin is now recognized as a major mediator of a variety of vascular diseases. The abundant serum protein haptoglobin irreversibly binds to hemoglobin and promotes the uptake of hemoglobin via the macrophage CD163 receptor. The haptoglobin gene is polymorphic in man with two common alleles denoted 1 and 2. The haptoglobin genotype specifies the nature of the response of the macrophage to free hemoglobin. Hp 1-Hb complexes stimulate an anti-inflammatory macrophage phenotype while Hp 2-Hb complexes do not. We have previously demonstrated that Hp 1-Hb induced anti-inflammatory cytokine production is critically dependent on casein kinase II. In this study we set out to determine whether the amount or the activity of casein kinase II associated with CD163 was altered by the binding of Hp 1-1-Hb to CD163. Our results indicate that casein kinase II activity is increased by the binding of Hp 1-1-Hb to CD163.     

Diagnostic value of serum concentrations of high‐mobility group‐box protein 1 and soluble hemoglobin scavenger receptor in brucellosis

Both cluster of differentiation (CD)4⁺ and CD8⁺ T lymphocytes play key roles in immunity to Brucella, in part because they secrete interferon (IFN)‐γ and activate bactericidal functions in macrophages. Therefore, use of markers of macrophage activation may have diagnostic and prognostic significance. High‐mobility group‐box 1 protein (HMGB1), a late‐onset pro‐inflammatory cytokine, is secreted by activated macrophages. Soluble hemoglobin scavenger receptor (sCD163) is a specific marker of anti‐inflammatory macrophages. The aim of this study was to investigate the diagnostic value of HMGB1 and sCD163 concentrations in brucellosis and its various clinical forms. Serum HMGB1 and sCD163 concentrations in 49 brucellosis patients were compared with those in 52 healthy control subjects. Both serum HMGB1 and sCD163 concentrations were significantly higher in brucellosis patients than in healthy controls (P < 0.001). There were no statistically significant differences in serum concentrations of HMGB1 and sCD163 between cases of acute, subacute and chronic brucellosis. Additionally, serum HMGB1 concentrations were positively correlated with sCD163 concentrations, whereas neither HMGB1 nor sCD163 concentrations were correlated with C‐reactive protein concentrations, white cell counts or erythrocyte sedimentation rates. Therefore, serum concentrations of HMGB1 and sCD163 may be diagnostic markers for brucellosis, but neither can be used to differentiate the three different forms of this disease (acute, subacute and chronic).     

Liposomes surface conjugated with human hemoglobin target delivery to macrophages

Current strategies to deliver therapeutic molecules to specific cell and tissue types rely on conjugation of antibodies and other targeting ligands directly to the therapeutic molecule itself or its carrier. This work describes a novel strategy to deliver therapeutic molecules into macrophages that takes advantage of the native hemoglobin (Hb) scavenging activity of plasma haptoglobin (Hp) and the subsequent uptake of the Hb-Hp complex into macrophages via CD163 receptor-mediated endocytosis. The drug delivery system described in this work consists of Hb decorated liposomes that can encapsulate any therapeutic molecule of interest, in this case the model fluorescent dye calcein was used in this study. The results of this study clearly demonstrate that this delivery system is specific towards macrophages and demonstrates the feasibility of using this approach in targeted drug delivery.     

Susceptible cell lines for the production of porcine reproductive and respiratory syndrome virus by stable transfection of sialoadhesin and CD163

Background  

Porcine reproductive and respiratory syndrome virus (PRRSV) causes major economic losses in the pig industry worldwide. In vivo, the virus infects a subpopulation of tissue macrophages. In vitro, PRRSV only replicates in primary pig macrophages and African green monkey kidney derived cells, such as Marc-145. The latter is currently used for vaccine production. However, since virus entry in Marc-145 cells is different compared to entry in primary macrophages, specific epitopes associated with virus entry could potentially alter upon growth on Marc-145 cells. To avoid this, we constructed CHO and PK15 cell lines recombinantly expressing the PRRSV receptors involved in virus entry into macrophages, sialoadhesin (Sn) and CD163 (CHO^Sn-CD163 and PK15^Sn-CD163) and evaluated their potential for production of PRRSV.     

The reaction of hydrogen peroxide with hemoglobin induces extensive alpha-globin crosslinking and impairs the interaction of hemoglobin with endogenous scavenger pathways

Cell-free hemoglobin (Hb) enhances the oxidation-related toxicity associated with inflammation, ischemia, and hemolytic disorders. Hb is highly vulnerable to oxidative damage, and irreversible structural changes involving iron/heme oxidation, heme-adduct products, and amino acid oxidation have been reported. Specific structural features of Hb, such as unconstrained alpha-chains and molecular size, determine the efficiency of interactions between the endogenous Hb scavengers haptoglobin (Hp) and CD163. Using HPLC, mass spectrometry, and Western blotting, we show that H(2)O(2)-mediated Hb oxidation results in the formation of covalently stabilized globin multimers, with prominent intramolecular crosslinking between alpha-globin chains. These structural alterations are associated with reduced Hp binding, reduced CD163 interaction, and severely impaired endocytosis of oxidized Hb by the Hp-CD163 pathway. As a result, when exposed to oxidized Hb, CD163-positive HEK293 cells and human macrophages do not increase hemeoxygenase-1 (HO-1) expression, the physiological anti-oxidative macrophage response to Hb exposure. Failed Hb clearance, inadequate HO-1 expression, and the subsequent accumulation of oxidatively damaged Hb species might thus contribute to pathologies related to oxidative stress.     

The Clinical Significance of the CD163+ and CD68+ Macrophages in Patients with Hepatocellular Carcinoma

Our previous study has found that the abundance of peritumoral CD68⁺ macrophages was associated with poor prognosis in hepatocellular carcinoma (HCC) after resection. However, CD68 staining could not discriminate the protumoral or tumoricidal subpopulations from pan-macrophages. CD163 is a marker of alternatively activated macrophages. In this study, the clinical significance of CD163⁺ cells in tumors and peritumoral liver tissues was evaluated in a cohort of 295 patients with HCC after curative resection. We found that the density of CD163⁺ cells was well correlated with that of CD68⁺ cells in both tumors and peritumoral liver tissues but was much more. Immunostaining on consecutive sections and flow cytometry assay on surgical resected specimens further supported the findings that the CD163⁺ cells was more abundant than CD68⁺ cells. The density of peritumoral CD68⁺ cells was associated with poor recurrence-free survival (RFS) and poor overall survival (OS) (P = 0.004 and P = 0.001, respectively), whereas the CD163⁺ cells have no prognostic values either in tumors or in peritumoral liver tissues. In another cohort of 107 HCC patients, preoperative plasma concentration of soluble form of CD163 (sCD163) was associated with active hepatitis-related factors but not associated with the markers of tumor invasion. In conclusion, both the CD163⁺ cells local infiltration and plasma sCD163 were of limited significance in HCC, and they were more likely markers related to active hepatitis rather than tumor progression.     

The intrathecal CD163-haptoglobin-hemoglobin scavenging system in subarachnoid hemorrhage

Delayed cerebral ischemia resulting from extracellular hemoglobin is an important determinant of outcome in subarachnoid hemorrhage. Hemoglobin is scavenged by the CD163-haptoglobin system in the circulation, but little is known about this scavenging pathway in the human CNS. The components of this system were analyzed in normal cerebrospinal fluid and after subarachnoid hemorrhage. The intrathecal presence of the CD163-haptoglobin-hemoglobin scavenging system was unequivocally demonstrated. The resting capacity of the CD163-haptoglobin-hemoglobin system in the normal CNS was 50 000-fold lower than that of the circulation. After subarachnoid hemorrhage, the intrathecal CD163-haptoglobin-hemoglobin system was saturated, as shown by the presence of extracellular hemoglobin despite detectable haptoglobin. Hemoglobin efflux from the CNS was evident, enabling rescue hemoglobin scavenging by the systemic circulation. Therefore, the CNS is not capable of dealing with significant intrathecal hemolysis. Potential therapeutic options to prevent delayed cerebral ischemia ought to concentrate on augmenting the capacity of the intrathecal CD163-haptoglobin-hemoglobin scavenging system and strategies to encourage hemoglobin efflux from the brain.     

Structural Basis for Inflammation-driven Shedding of CD163 Ectodomain and Tumor Necrosis Factor-α in Macrophages

The haptoglobin-hemoglobin receptor CD163 and proTNF-α are transmembrane macrophage proteins subjected to cleavage by the inflammation-responsive protease ADAM17. This leads to release of soluble CD163 (sCD163) and bioactive TNF-α. Sequence comparison of the juxtamembrane region identified similar palindromic sequences in human CD163 (¹⁰⁴⁴Arg-Ser-Ser-Arg) and proTNF-α (⁷⁸Arg-Ser-Ser-Ser-Arg). In proTNF-α the Arg-Ser-Ser-Ser-Arg sequence is situated next to the previously established ADAM17 cleavage site. Site-directed mutagenesis revealed that the sequences harbor essential information for efficient cleavage of the two proteins upon ADAM17 stimulation. This was further evidenced by analysis of mouse CD163 that, like CD163 in other non-primates, does not contain the palindromic CD163 sequence in the juxtamembrane region. Mouse CD163 resisted endotoxin- and phorbol ester-induced shedding, and ex vivo analysis of knock-in of the Arg-Ser-Ser-Arg sequence in mouse CD163 revealed a receptor shedding comparable with that of human CD163. In conclusion, we have identified an essential substrate motif for ADAM17-mediated CD163 and proTNF-α cleavage in macrophages. In addition, the present data indicate that CD163, by incorporation of this motif in late evolution, underwent a modification that allows for an instant down-regulation of surface CD163 expression and inhibition of hemoglobin uptake. This regulatory modality seems to have coincided with the evolution of an enhanced hemoglobin-protecting role of the haptoglobin-CD163 system in primates.     

Revealing the link between macrophage in microenvironment of osteosarcoma and poor prognosis by utilizing the Integrated analysis

Objectives:Osteosarcoma (OS) is the most common type of primary malignant bone tumor, The effect of tumor microenvironment components on OS oncogenesis remains unknown.Methods:To investigate the function of immune cells in osteosarcoma, we provided a text-based GMT (Gene Matrix Transposed) file in which each line defines one of lm22 with their markers. We used STRING to draw DEG’s PPI network and selected hub genes and modules. Then, survival analysis was conducted to hub genes. We identified 10,390 common genes, and identified 218 DEGs based on the combined t-value and Z scores.Results:The KEGG and GSEA enrichment analysis showed that macrophages are significantly activated in osteosarcoma. PPI network analysis revealed that hub gene CD163 molecule. We found that the expression of CD163 was negatively associated with the OS of osteosarcoma patients. These results suggest that macrophages are a risk factor in patients with osteosarcoma.Conclusions:This study has systematically validated results of the studies carried out previously and filled up the gap in the field of OS on large-scaled meta-analysis. In addition, for the hub gene (CD163) and the macrophage cell capable of being used as a novel biomarker in promoting early diagnosis and development of therapeutic approaches.     

Lesional Accumulation of CD163-Expressing Cells in the Gut of Patients with Inflammatory Bowel Disease

Monocytes/macrophages displaying different markers of activation/differentiation infiltrate the inflamed gut of patients with inflammatory bowel diseases (IBD), but the role that each monocyte/macrophage subpopulation plays in the pathogenesis of IBD is not fully understood. The hemoglobin scavenger receptor CD163, a specific marker of monocytes/macrophages, has been associated with either anti-inflammatory or inflammatory functions of macrophages in several pathologies. In this study we examined the tissue distribution and function of CD163-expressing monocytes/macrophages in IBD. CD163 RNA and protein expression was more pronounced in IBD in comparison to normal controls, with no significant difference between Crohn''s disease and Ulcerative colitis. In IBD, over-expression of CD163 was restricted to areas with active inflammation and not influenced by current therapy. Immunohistochemical analysis confirmed the accumulation of CD163-expressing cells in IBD, mostly around and inside blood vessels, thus suggesting that these cells are partly recruited from the systemic circulation. Indeed, FACS analysis of circulating mononuclear cells showed that the fractions of CD163-positive monocytes were increased in IBD patients as compared to controls. Functionally, interleukin-6 up-regulated CD163 expression in lamina propria mononuclear cells and mucosal explants of normal subjects. In IBD blood and mucosal cell cultures, cross-linking of CD163 with a specific monoclonal anti-CD163 antibody enhanced tumor necrosis factor-α synthesis. These findings indicate that IBD mucosa is abundantly infiltrated with CD163-positive cells, which could contribute to amplify the inflammatory cytokine response.     

A comparative study on root and bark extracts of Eleutherococcus senticosus and their effects on human macrophages

BackgroundEleutherococcus senticosus or Siberian ginseng is a medicinal plant containing adaptogenic substances believed to regulate immune responses. Both, the root and stem bark are commonly used in traditional medicines.PurposeThe purpose of the present study is to chemically characterize E. senticosus root and bark extracts and to compare their effects on functions of human primary macrophages.Study design and methodsHPLC-DAD-MS analysis was used to characterize chemical constituents of alcoholic extracts from E. senticosus root and bark. The data obtained and available databases were combined for network pharmacology analysis. Involvement of predicted pathways was further functionally confirmed by using monocyte-derived human macrophages and endotoxin-free E. senticosus root and bark extracts.ResultsChemical analysis showed that the root extract contained more syringin, caffeic acid, and isofraxidin than the bark extract. At variance, bark extract contained more sesamin and oleanolic acid. Coniferyl aldehyde and afzelin were below the limit of quantification in both extracts. Network pharmacology analysis indicated that constituents of E. senticosus might affect the immune cell phenotype and signaling pathways involved in cell metabolism and cytoskeleton regulation. Indeed, both extracts promoted actin polymerization, migration, and phagocytosis of E. coli by macrophages pointing to macrophage polarization towards the M2 phenotype. In addition, treatment with E. senticosus root and bark extracts decreased phosphorylation of Akt on Ser473 and significantly reduced expression of the hemoglobin scavenger receptor CD163 by macrophages. Neither extract affected expression of CD11b, CD80, or CD64 by macrophages. In addition, macrophages treated with the bark extract, but not with the root extract, exhibited activated p38 MAPK and NF-κB and released increased, but still moderate, amounts of proinflammatory TNF-α and IL-6, anti-inflammatory IL-10, and chemotactic CCL1, which all together point to a M2b-like macrophage polarization. Differently, the root extract increased the IL-4-induced expression of anti-inflammatory CD200R. These changes in monocytes are in agreement with an increased M2a macrophage polarization.ConclusionThe ability of E. senticosus root and bark extracts to promote polarization of human macrophages towards anti-inflammatory M2a and M2b phenotypes, respectively, might underlay the immunoregulatory activities and point to potential wound healing promoting effects of this medicinal plant.