The galectin profile of the endothelium: altered expression and localization in activated and tumor endothelial cells

Hybrid ligands with calixarene and thiodigalactoside groups: galectin binding and cytotoxicity

Galectins have diverse functions and are involved in many biological processes because of their complex intra- and extracellular activities. Selective and potent inhibitors for galectins will be valuable tools to investigate the biological functions of these proteins. Therefore, we describe here the synthesis of galectin inhibitors with a potential "chelate effect". These compounds are designed to bind to two different binding sites on galectins simultaneously. In this paper a series of asymmetric "hybrid" compounds are prepared, which combine two galectin ligands (1) a substituted thiodigalactoside derivative and (2) an antagonist calixarene-based therapeutic agent. NMR spectroscopy was used to evaluate the interactions of these compounds with Galectin-1 and -3. In addition, cellular experiments were conducted to compare the cytotoxic effects of the hybrids with those of a calixarene derivative. While only the thiodigalactoside part of the hybrids showed strong binding, the calixarene part was responsible for observed cytoxoxicity effects, suggesting that the calixarene moiety may also be addressing a non-galectin target.

Galectin-3 aggravates ox-LDL-induced endothelial dysfunction through LOX-1 mediated signaling pathway

Galectin-3, a biomarker linking oxidative stress and inflammation, participates in different mechanisms related to atherothrombosis, such as inflammation, proliferation, or macrophage chemotaxis. Accumulating evidence indicates that galectin-3 may also promote atherogenesis through inducing endothelial dysfunction. Lectin-like oxidized low-density lipoprotein (oxLDL) receptor-1 (LOX-1), a receptor for oxLDL uptake, contributes to oxLDL-induced endothelial dysfunction. Whether galectin-3 induces endothelial dysfunction through modulation of LOX-1-mediated signaling remains unclear. In the present study, we explored the mechanisms underlying galectin-3 enhanced cytotoxicity of oxLDL in human umbilical vein endothelial cells (HUVECs) and the role of LOX-1. Incubation of HUVECs with galectin-3 increased the expression of LOX-1 in RNA and protein levels. In addition, the expression of LOX-1 induced by oxLDL was promoted by galectin-3. However, pretreatment of LOX-1 antibody reduced LOX-1 mRNA expression level in cells with oxLDL plus galectin-3 incubation. Compared to cells treated with oxLDL alone, reactive oxygen species (ROS) generation via nicotinamide adenine dinucleotide phosphate (NADPH) oxidase activation and subsequent activation of p38 mitogen-activated protein kinases followed by nuclear factor kappa B (NF-κB) activation and related inflammatory responses including adhesion molecule expression, adhesiveness of monocytic cells, and IL-8 release were also aggravated in cells treated with galectin-3 combined with oxLDL. Compared to cells treated with galectin-3 plus oxLDL group. We found that LOX-1 antibody mitigated NADPH oxidase activity, p-38 up-regulation, NF-κB activation, and proinflammatory responses in cells treated with galectin-3 combined with oxLDL. We conclude that galectin-3 enhances endothelial LOX-1 expression and propose a new mechanism by which galectin-3 may promote endothelial dysfunction by inducing inflammation via LOX-1/ROS/p38/NF-κB-mediated signaling pathway.

Pregnancy Galectinology: Insights Into a Complex Network of Glycan Binding Proteins

Galectins are a phylogenetically conserved family of soluble β-galactoside binding proteins, consisting of 15 different types, each with a specific function. Galectins contribute to placentation by regulating trophoblast development, migration, and invasion during early pregnancy. In addition, galectins are critical players regulating maternal immune tolerance to the embedded embryo. Recently, the role of galectins in angiogenesis during decidualization and in placenta formation has gained attention. Altered expression of galectins is associated with abnormal pregnancies and infertility. This review focuses on the role of galectins in pregnancy-associated processes and discusses the relevance of galectin-glycan interactions as potential therapeutic targets in pregnancy disorders.

Galectin-3 is expressed in vascular smooth muscle cells and promotes pulmonary hypertension through changes in proliferation, apoptosis, and fibrosis

A defining characteristic of pulmonary hypertension (PH) is the extensive remodeling of pulmonary arteries (PAs), which results in progressive increases in vascular resistance and stiffness and eventual failure of the right ventricle. There is no cure for PH and identification of novel molecular mechanisms that underlie increased proliferation, reduced apoptosis, and excessive extracellular matrix production in pulmonary artery smooth muscle cells (PASMCs) is a vital objective. Galectin-3 (Gal-3) is a chimeric lectin and potent driver of many aspects of fibrosis, but its role in regulating PASMC behavior in PH remains poorly understood. Herein, we evaluated the importance of increased Gal-3 expression and signaling on PA vascular remodeling and cardiopulmonary function in experimental models of PH. Gal-3 expression was quantified by qRT-PCR, immunoblotting, and immunofluorescence imaging, and its functional role was assessed by specific Gal-3 inhibitors and CRISPR/Cas9-mediated knockout of Gal-3 in the rat. In rat models of PH, we observed increased Gal-3 expression in PASMCs, which stimulated migration and resistance to apoptosis, whereas silencing or genetic deletion reduced cellular migration and PA fibrosis and increased apoptosis. Gal-3 inhibitors attenuated and reversed PA remodeling and fibrosis, as well as hemodynamic indices in monocrotaline (MCT)-treated rats in vivo. These results were supported by genetic deletion of Gal-3 in both MCT and Sugen Hypoxia rat models. In conclusion, our results suggest that elevated Gal-3 levels contribute to inappropriate PA remodeling in PH by enhancing multiple profibrotic mechanisms. Therapeutic strategies targeting Gal-3 may be of benefit in the treatment of PH.

Isolation of tumor endothelial cells from murine cancer

Tumor endothelial cells (TECs), which constitute the lining of the tumor blood vessels, have various characteristics as tumor constituent cells. In this study, we describe a novel method for the isolation of highly pure, fresh TECs, which form a small population within the tumor. Tumors were first dissected from tumor-bearing mice and digested to a single cell suspension with Collagenase Type II; the single cells were then separated by density gradient centrifugation. TECs were enriched by CD31-positive selection using magnetic activated cell sorting and subsequently purified by fluorescence activated cell sorting. The high purity of the obtained cells was verified by flow cytometry. Upon cell culture, the isolated cells showed a polygonal shape and a cobblestone appearance, which are features of the endothelial cells. Furthermore, a functional assay revealed that the TECs suppressed the proliferation of CD8+ T cells in vitro. We believe that the isolation method described in this study will enable the further elucidation of the characteristics of TECs.

Mineralocorticoid Receptor and Aldosterone-Related Biomarkers of End-Organ Damage in Cardiometabolic Disease

The mineralocorticoid receptor (MR) was first identified as a blood pressure regulator, modulating renal sodium handling in response to its principal ligand aldosterone. The mineralocorticoid receptor is also expressed in many tissues other than the kidney, such as adipose tissue, heart and vasculature. Recent studies have shown that MR plays a relevant role in the control of cardiovascular and metabolic function, as well as in adipogenesis. Dysregulation of aldosterone/MR signaling represents an important cause of disease as high plasma levels of aldosterone are associated with hypertension, obesity and increased cardiovascular risk. Aldosterone displays powerful vascular effects and acts as a potent pro-fibrotic agent in cardiovascular remodeling. Mineralocorticoid receptor activation regulates genes involved in vascular and cardiac fibrosis, calcification and inflammation. This review focuses on the role of novel potential biomarkers related to aldosterone/MR system that could help identify cardiovascular and metabolic detrimental conditions, as a result of altered MR activation. Specifically, we discuss: (1) how MR signaling regulates the number and function of different subpopulations of circulating and intra-tissue immune cells; (2) the role of aldosterone/MR system in mediating cardiometabolic diseases induced by obesity; and (3) the role of several MR downstream molecules as novel potential biomarkers of cardiometabolic diseases, end-organ damage and rehabilitation outcome.

Molecular profiling of colorectal tumors stratified by the histological tumor-stroma ratio - Increased expression of galectin-1 in tumors with high stromal content

The tumor microenvironment is a dominant determinant of cancer cell behavior. Reactive tumor stroma is associated with poor outcome perspective. The tumor-stroma ratio (TSR) is a strong independent prognostic factor in colorectal cancer and is easily assessed using conventional hematoxylin and eosin (H&E) stained paraffin sections at the invasive margin of the tumor. We aim to understand the biology of the tumor stroma in colorectal cancer by investigating the transcriptomic profiles of tumors classified by the TSR method. The TSR was assessed in a cohort of 71 colorectal cancer patients undergoing surgery without (neo)adjuvant therapy. In the cohort, stroma-high tumors were distinguished from stroma-low tumors at gene expression level in the upregulation of biological pathways related to extracellular matrix (ECM) remodeling and myogenesis. The activated microenvironment in stroma-high tumors overexpressed different types of collagen genes, THBS2 and 4 as well as INHBA, COX71A and LGALS1/galectin-1. The upregulation of THBS2, COX7A1 and LGALS1/galectin-1. The upregulation of THBS2, COX7A1 and LGALS1/galectin-1 in stroma-high tumors was validated in The Cancer Genome Atlas. In conclusion, the gene expression data reflects the high stromal content of tumors assessed based on the histological method, the TSR. The composition of the microenvironment suggests an altered proteolysis resulting in ECM remodeling and invasive capacity of tumor cells.

Galectin-9 binds to O-glycans on protein disulfide isomerase

Changes in the T cell surface redox environment regulate critical cell functions, such as cell migration, viral entry and cytokine production. Cell surface protein disulfide isomerase (PDI) contributes to the regulation of T cell surface redox status. Cell surface PDI can be released into the extracellular milieu or can be internalized by T cells. We have found that galectin-9, a soluble lectin expressed by T cells, endothelial cells and dendritic cells, binds to and retains PDI on the cell surface. While endogenous galectin-9 is not required for basal cell surface PDI expression, exogenous galectin-9 mediated retention of cell surface PDI shifted the disulfide/thiol equilibrium on the T cell surface. O-glycans on PDI are required for galectin-9 binding, and PDI recognition appears to be specific for galectin-9, as galectin-1 and galectin-3 do not bind PDI. Galectin-9 is widely expressed by immune and endothelial cells in inflamed tissues, suggesting that T cells would be exposed to abundant galectin-9, in cis and in trans, in infectious or autoimmune conditions.

Galectins: Multitask signaling molecules linking fibroblast, endothelial and immune cell programs in the tumor microenvironment

Tumor cells corrupt surrounding normal cells instructing them to support proliferative, pro-angiogenic and immunosuppressive networks that favor tumorigenesis and metastasis. This dynamic cross-talk is sustained by a range of intracellular signals and extracellular mediators produced by both tumoral and non-tumoral cells. Galectins -whether secreted or intracellularly expressed- play central roles in the tumorigenic process by delivering regulatory signals that contribute to reprogram fibroblasts, endothelial and immune cell programs. Through glycosylation-dependent or independent mechanisms, these endogenous lectins control a variety of cellular events leading to tumor cell proliferation, survival, migration, inflammation, angiogenesis and immune escape. Here we discuss the role of galectin-driven pathways, particularly those activated in non-tumoral stromal cells, in modulating tumor progression.

Different angioregulatory activity of monovalent galectin-9 isoforms

Galectin-9 consists of two peptide-linked carbohydrate recognition domains (CRDs), but alternative splicing and proteolytic processing can give rise to multiple galectin-9 isoforms. Some of these consist of a single CRD and can exert different functions in cell biology. Here, we explored the role of these galectin-9 isoforms in endothelial cell function and angiogenesis. For this, we compared the effects of the two separate CRDs (Gal-9N and Gal-9C) with the tandem repeat galectin-9M on endothelial cell proliferation, migration, sprouting and tube formation in vitro as well as on angiogenesis in vivo using the chicken chorioallantoic membrane (CAM) assay. Galectin-9 isoforms significantly affected proliferation in quiescent endothelial cells and migration in activated endothelial cells. Interestingly, both monovalent gal-9 CRDs displayed opposite effects compared to gal-9M on proliferation and migration. Sprouting was significantly inhibited by gal-9C, while all isoforms appeared to stimulate tube formation. Angiogenesis in vivo was hampered by all three isoforms with predominant effects on vessel length. In general, the isoforms induced only subtle concentration-dependent effects in vitro as well as in vivo. Collectively, the effects of different galectin-9 isoforms in endothelial cell biology depend on the cellular activation status. While opposing effects can be observed on a cellular level in vitro, all galectin-9 isoforms hamper angiogenesis in vivo. This warrants further investigation of the regulatory mechanisms that underlie the diverging roles of galectin-9 isoforms in endothelial cell biology since this could provide therapeutic opportunities.

Overall Survival of Ovarian Cancer Patients Is Determined by Expression of Galectins-8 and -9

The evaluation of new prognostic factors that can be targeted in ovarian cancer diagnosis and therapy is of the utmost importance. Galectins are a family of carbohydrate binding proteins with various implications in cancer biology. In this study, the presence of galectin (Gal)-8 and -9 was investigated in 156 ovarian cancer samples using immunohistochemistry (IHC). Staining was evaluated using semi-quantitative immunoreactivity (IR) scores and correlated to clinical and pathological data. Different types of galectin expression were compared with respect to disease-free survival (DFS) and overall survival (OS). Gal-8 served as a new positive prognostic factor for the OS and DFS of ovarian cancer patients. Gal-9 expression determined the DFS and OS of ovarian cancer patients in two opposing ways—moderate Gal-9 expression was correlated with a reduced outcome as compared to Gal-9 negative cases, while patients with high Gal-9 expression showed the best outcome.

Radiation-enhanced therapeutic targeting of galectin-1 enriched malignant stroma in triple negative breast cancer

Currently there are no FDA approved targeted therapies for Triple Negative Breast Cancer (TNBC). Ongoing clinical trials for TNBC have focused primarily on targeting the epithelial cancer cells. However, targeted delivery of cytotoxic payloads to the non-transformed tumor associated-endothelium can prove to be an alternate approach that is currently unexplored. The present study is supported by recent findings on elevated expression of stromal galectin-1 in clinical samples of TNBC and our ongoing findings on stromal targeting of radiation induced galectin-1 by the anginex-conjugated arsenic-cisplatin loaded liposomes using a novel murine tumor model. We demonstrate inhibition of tumor growth and metastasis in response to the multimodal nanotherapeutic strategy using a TNBC model with orthotopic tumors originating from 3D tumor tissue analogs (TTA) comprised of tumor cells, endothelial cells and fibroblasts. The ‘rigorous’ combined treatment regimen of radiation and targeted liposomes is also shown to be well tolerated. More importantly, the results presented provide a means to exploit clinically relevant radiation dose for concurrent receptor mediated enhanced delivery of chemotherapy while limiting overall toxicity. The proposed study is significant as it falls in line with developing combinatorial therapeutic approaches for stroma-directed tumor targeting using tumor models that have an appropriate representation of the TNBC microenvironment.

Galectin Targeted Therapy in Oncology: Current Knowledge and Perspectives

The incidence and mortality of cancer have increased over the past decades. Significant progress has been made in understanding the underpinnings of this disease and developing therapies. Despite this, cancer still remains a major therapeutic challenge. Current therapeutic research has targeted several aspects of the disease such as cancer development, growth, angiogenesis and metastases. Many molecular and cellular mechanisms remain unknown and current therapies have so far failed to meet their intended potential. Recent studies show that glycans, especially oligosaccharide chains, may play a role in carcinogenesis as recognition patterns for galectins. Galectins are members of the lectin family, which show high affinity for β-galactosides. The galectin–glycan conjugate plays a fundamental role in metastasis, angiogenesis, tumor immunity, proliferation and apoptosis. Galectins’ action is mediated by a structure containing at least one carbohydrate recognition domain (CRD). The potential prognostic value of galectins has been described in several neoplasms and helps clinicians predict disease outcome and determine therapeutic interventions. Currently, new therapeutic strategies involve the use of inhibitors such as competitive carbohydrates, small non-carbohydrate binding molecules and antibodies. This review outlines our current knowledge regarding the mechanism of action and potential therapy implications of galectins in cancer.

Platelet interaction with activated endothelium: mechanistic insights from microfluidics

Traditionally, in vitro flow chamber experiments and in vivo arterial thrombosis studies have been proved to be of vital importance to elucidate the mechanisms of platelet thrombus formation after vessel wall injury. In recent years, it has become clear that platelets also act as modulators of inflammatory processes, such as atherosclerosis. A key element herein is the complex cross talk between platelets, the coagulation system, leukocytes, and the activated endothelium. This review provides insight into the platelet-endothelial interface, based on in vitro flow chamber studies and cross referenced with in vivo thrombosis studies. The main mechanisms of platelet interaction with the activated endothelium encompass (1) platelet rolling via interaction of platelet glycoprotein Ib-IX-V with endothelial-released von Willebrand factor with a supporting role for the P-selectin/P-selectin glycoprotein ligand 1 axis, followed by (2) firm platelet adhesion to the endothelium via interaction of platelet α_IIbβ₃ with endothelial α_vβ₃ and intercellular adhesion molecule 1, and (3) a stimulatory role for thrombin, the thrombospondin-1/CD36 axis and cyclooxygenase 1 in subsequent platelet activation and stable thrombus formation. In addition, the molecular mechanisms underlying the stimulatory effect of platelets on leukocyte transendothelial migration, a key mediator of atheroprogression, are discussed. Throughout the review, emphasis is placed on recommendations for setting up, reporting, interpreting, and comparing endothelial-lined flow chamber studies and suggestions for future studies.

A genomic screen for angiosuppressor genes in the tumor endothelium identifies a multifaceted angiostatic role for bromodomain containing 7 (BRD7)

Tumor angiogenesis is characterized by deregulated gene expression in endothelial cells (EC). While studies until now have mainly focused on overexpressed genes in tumor endothelium, we here describe the identification of transcripts that are repressed in tumor endothelium and thus have potential suppressive effects on angiogenesis. We identified nineteen putative angiosuppressor genes, one of them being bromodomain containing 7 (BRD7), a gene that has been assigned tumor suppressor properties. BRD7 was studied in more detail, and we demonstrate that BRD7 expression is inversely related to EC activation. Ectopic expression of BRD7 resulted in a dramatic reduction of EC proliferation and viability. Furthermore, overexpression of BRD7 resulted in a bromodomain-dependent induction of NFκB-activity and NFκB-dependent gene expression, including ICAM1, enabling leukocyte–endothelial interactions. In silico functional annotation analysis of genome-wide expression data on BRD7 knockdown and overexpression revealed that the transcriptional signature of low BRD7 expressing cells is associated with increased angiogenesis (a.o. upregulation of angiopoietin-2, VEGF receptor-1 and neuropilin-1), cytokine activity (a.o. upregulation of CXCL1 and CXCL6), and a reduction of immune surveillance (TNF-α, NFκB, ICAM1). Thus, combining in silico and in vitro data reveals multiple pathways of angiosuppressor and anti-tumor activities of BRD7.

Combined Anti-VEGF and Anti-CTLA-4 Therapy Elicits Humoral Immunity to Galectin-1 Which Is Associated with Favorable Clinical Outcomes

The combination of anti-VEGF blockade (bevacizumab) with immune checkpoint anti-CTLA-4 blockade (ipilimumab) in a phase I study showed tumor endothelial activation and immune cell infiltration that were associated with favorable clinical outcomes in patients with metastatic melanoma. To identify potential immune targets responsible for these observations, posttreatment plasma from long-term responding patients were used to screen human protein arrays. We reported that ipilimumab plus bevacizumab therapy elicited humoral immune responses to galectin-1 (Gal-1), which exhibits protumor, proangiogenesis, and immunosuppressive activities in 37.2% of treated patients. Gal-1 antibodies purified from posttreatment plasma suppressed the binding of Gal-1 to CD45, a T-cell surface receptor that transduces apoptotic signals upon binding to extracellular Gal-1. Antibody responses to Gal-1 were found more frequently in the group of patients with therapeutic responses and correlated with improved overall survival. In contrast, another subgroup of treated patients had increased circulating Gal-1 protein instead, and they had reduced overall survival. Our findings suggest that humoral immunity to Gal-1 may contribute to the efficacy of anti-VEGF and anti-CTLA-4 combination therapy. Gal-1 may offer an additional therapeutic target linking anti-angiogenesis and immune checkpoint blockade. Cancer Immunol Res; 5(6); 446-54. ©2017 AACR.

The clinical application of angiostatic therapy in combination with radiotherapy: past, present, future

Although monotherapy with angiostatic drugs is still far from effective, there is abundant evidence that angiostatic therapy can improve the efficacy of conventional treatments like radiotherapy. This has instigated numerous efforts to optimize and clinically implement the combination of angiostatic drugs with radiation treatment. The results from past and present clinical trials that explored this combination therapy indeed show encouraging results. However, current findings also show that the combination has variable efficacy and is associated with increased toxicity. This indicates that combining radiotherapy with angiostatic drugs not only holds opportunities but also provides several challenges. In the current review, we provide an update of the most recent insights from clinical trials that evaluated the combination of angiostatic drugs with radiation treatment. In addition, we discuss the outstanding questions for future studies in order to improve the clinical benefit of combining angiostatic therapy with radiation therapy.

Angiomodulators in cancer therapy: New perspectives

The formation of new blood vessels plays a crucial for the development and progression of pathophysiological changes associated with a variety of disorders, including carcinogenesis. Angiogenesis inhibitors (anti-angiogenics) are an important part of treatment for some types of cancer. Some natural products isolated from marine invertebrates have revealed antiangiogenic activities, which are diverse in structure and mechanisms of action. Many preclinical studies have generated new models for further modification and optimization of anti-angiogenic substances, and new information for mechanistic studies and new anti-cancer drug candidates for clinical practice. Moreover, in the last decade it has become apparent that galectins are important regulators of tumor angiogenesis, as well as microRNA. MicroRNAs have been validated to modulate endothelial cell migration or endothelial tube organization. In the present review we summarize the current knowledge regarding the role of marine-derived natural products, galectins and microRNAs in tumor angiogenesis.

Galectin-9: From cell biology to complex disease dynamics

Galectins is a family of non-classically secreted, beta-galactoside-binding proteins that has recently received considerable attention in the spatio-temporal regulation of surface 'signal lattice' organization, membrane dynamics, cell-adhesion and disease therapeutics. Galectin-9 is a unique member of this family, with two non-homologous carbohydrate recognition domains joined by a linker peptide sequence of variable lengths, generating isoforms with distinct properties and functions in both physiological and pathological settings, such as during development, immune reaction, neoplastic transformations and metastasis. In this review, we summarize the latest knowledge on the structure, receptors, cellular targets, trafficking pathways and functional properties of galectin-9 and discuss how galectin-9-mediated signalling cascades can be exploited in cancers and immunotherapies.

miR-455-5p functions as a potential oncogene by targeting galectin-9 in colon cancer

Although there is evidence that galectin-9 is a critical factor in health and disease, the upstream regulatory microRNA (miRNA or miR) of the protein remains poorly defined. miR-455-5p is characterized as a tumor-associated miRNA in cancer research. However, the actual role of miR-455-5p with respect to inhibiting or promoting tumorigenesis in colon cancer is unclear. The present study aimed to investigate the expression, role and target regulation association of galectin-9 and miR-455-5p in colon cancer. Western blot analysis and reverse transcription-quantitative polymerase chain reaction were used for the detection of the expression levels of galectin-9 and miRNAs. Cell Counting kit-8 test was used for the evaluation of cell proliferation, while flow cytometry was used for cell apoptosis analysis. A potential interaction between galectin-9 and miR-455-5p was predicted by target prediction programs and confirmed by luciferase assay and transfection with miRNA mimics. The present study revealed that elevated expression of galectin-9 and miR-455-5p in colon cancer was associated with HT29 cell proliferation and apoptosis. Furthermore, the present study demonstrated that miR-455-5p reduced galectin-9 expression by directly targeting its 3'-untranslated region. These data suggest that miR-455-5p functions as a potential oncogene in colon cancer by targeting galectin-9.

Cancer Therapy Due to Apoptosis: Galectin-9

Dysregulation of apoptosis is a major hallmark in cancer biology that might equip tumors with a higher malignant potential and chemoresistance. The anti-cancer activities of lectin, defined as a carbohydrate-binding protein that is not an enzyme or antibody, have been investigated for over a century. Recently, galectin-9, which has two distinct carbohydrate recognition domains connected by a linker peptide, was noted to induce apoptosis in thymocytes and immune cells. The apoptosis of these cells contributes to the development and regulation of acquired immunity. Furthermore, human recombinant galectin-9, hG9NC (null), which lacks an entire region of the linker peptide, was designed to resist proteolysis. The hG9NC (null) has demonstrated anti-cancer activities, including inducing apoptosis in hematological, dermatological and gastrointestinal malignancies. In this review, the molecular characteristics, history and apoptosis-inducing potential of galectin-9 are described.

Galectin-3 inhibition ameliorates hypoxia-induced pulmonary artery hypertension

Galectin-3 (Gal-3) is a β-galactoside-binding lectin, which is important in inflammation, fibrosis and heart failure. The present study aimed to investigate the role and mechanism of Gal-3 in hypoxia-induced pulmonary arterial hypertension (PAH). Male C57BL/6J and Gal-3^−/− mice were exposed to hypoxia, then the right ventricular systolic pressure (RVSP) and Fulton's index were measured, and Gal-3 mRNA and protein expression in the pulmonary arteries was analyzed by reverse transcription-quantitative polymerase chain reaction and western blotting. Compared with the control, hypoxia increased the mRNA and protein expression levels of Gal-3 in wild type murine pulmonary arteries. Gal-3 deletion reduced the hypoxia-induced upregulation of RVSP and Fulton's index. Furthermore, human pulmonary arterial endothelial cells (HPAECs) and human pulmonary arterial smooth muscle cells (HPASMCs) were stimulated by hypoxia in vitro, and Gal-3 expression was inhibited by small interfering RNA. The inflammatory response of HPAECs, and the proliferation and cell cycle distribution of HPASMCs was also analyzed. Gal-3 inhibition alleviated the hypoxia-induced inflammatory response in HPAECs, including tumor necrosis factor-α and interleukin-1 secretion, expression of intercellular adhesion molecule-1 and adhesion of THP-1 monocytes. Gal-3 inhibition also reduced hypoxia-induced proliferation of HPASMCs, partially by reducing cyclin D1 expression and increasing p27 expression. Furthermore, Gal-3 inhibition suppressed HPASMC switching from a ‘contractile’ to a ‘synthetic’ phenotype. In conclusion, Gal-3 serves a fundamental role in hypoxia-induced PAH, and inhibition of Gal-3 may represent a novel therapeutic target for the treatment of hypoxia-induced PAH.

Histological chorioamnionitis in preterm prelabor rupture of the membranes is associated with increased expression of galectin-3 by amniotic epithelium

PURPOSE

Gal-3, which can regulate immune responses upon infection and inflammation, was not studied so far in intrauterine infection leading to preterm prelabor rupture of the membranes (PPROM), although gal-1 was reported to be implicated in the process. Gal-3 mRNA and protein expression in amnion and its changes during histological chorioamnionitis were studied here.

MATERIALS AND METHODS

Fetal membranes were obtained from women with PPROM with (n =15) and without histological chorioamnionitis (n =15) during second and third trimester. Immunohistochemical reactivity was evaluated semiquantitatively and analyzed using t-test. Galectin profile of amniotic epithelia was determined by polymerase chain reaction (PCR) and change assessed in gal-3 in PPROM with (n =5) or without histological chorioamnionitis (n =5) by real-time PCR.

RESULTS

Human amniotic epithelium was found to express gal-1, gal-3, gal-7 and gal-8 mRNA. Gal-3 mRNA and protein is increased in fetal membranes and in the amniotic epithelium in patients with chorionamnionitis.

CONCLUSION

Histological chorioamnionitis is associated with increased gal-3 expression and strong immunoreactivity of the amnion. Gal-3 may participate in the regulation of the inflammatory responses to chorioamniotic infection and/or direct interaction with pathogens.

The Role of Galectin-1 in Cancer Progression, and Synthetic Multivalent Systems for the Study of Galectin-1

This review discusses the role of galectin-1 in the tumor microenvironment. First, the structure and function of galectin-1 are discussed. Galectin-1, a member of the galectin family of lectins, is a functionally dimeric galactoside-binding protein. Although galectin-1 has both intracellular and extracellular functions, the defining carbohydrate-binding role occurs extracellularly. In this review, the extracellular roles of galectin-1 in cancer processes are discussed. In particular, the importance of multivalent interactions in galectin-1 mediated cellular processes is reviewed. Multivalent interactions involving galectin-1 in cellular adhesion, mobility and invasion, tumor-induced angiogenesis, and apoptosis are presented. Although the mechanisms of action of galectin-1 in these processes are still not well understood, the overexpression of galectin-1 in cancer progression indicates that the role of galectin-1 is significant. To conclude this review, synthetic frameworks that have been used to modulate galectin-1 processes are reviewed. Small molecule oligomers of carbohydrates, carbohydrate-functionalized pseudopolyrotaxanes, cyclodextrins, calixarenes, and glycodendrimers are presented. These synthetic multivalent systems serve as important tools for studying galectin-1 mediated cancer cellular functions.

Galectin-8 enhances adhesion of multiple myeloma cells to vascular endothelium and is an adverse prognostic factor

Multiple myeloma is characterized by abnormal infiltration of malignant plasma cells into bone marrow. Testing the hypothesis that bivalent galectin-8 (Gal-8) may influence homing of myeloma cells to vascular endothelium as a key prerequisite for infiltration, we analyzed the two Gal-8 splice variants (Gal-8S, Gal-8L). They differ in the length of their linker peptide connecting the two lectin domains. Both Gal-8 isoforms bind to cells of the myeloma lines Gal-8⁺ MOLP-8 and Gal-8^- LP-1 in a glycan-inhibitable manner. Both Gal-8 isoforms led to enhanced adhesion of myeloma cells to vascular endothelium under dynamic shear stress conditions, Gal-8L (by more than 40-fold) even stronger than Gal-8S. Additional treatment of endothelial cells with tumour necrosis factor prior to the dynamic shear stress assay entailed an almost 100-fold enhanced adhesion of myeloma cells without addition of Gal-8 variants and a further 1.5-1.7-fold enhancement by addition of Gal-8 variants. We also found that elevated expression of Gal-8 in native multiple myeloma cells is an adverse prognostic factor for overall and event-free survival using patients' gene expression profile data of the total therapy 2 and 3 myeloma studies. Also, elevated concentrations of Gal-8 were detected (45%, 19/42 patients) in sera of multiple myeloma patients compared to those of healthy, age-matched donors. Both experimental and clinical data strongly point to the significance of Gal-8 for multiple myeloma development.

Galectin-1 and Galectin-3 Constitute Novel-Binding Partners for Factor VIII

OBJECTIVE

Recent studies have demonstrated that galectin-1 (Gal-1) and galectin-3 (Gal-3) can bind von Willebrand factor and directly modulate von Willebrand factor-dependent early thrombus formation in vivo. Because the glycans expressed on human factor VIII (FVIII) are similar to those of von Willebrand factor, we investigated whether galectins might also bind and modulate the activity of FVIII.

APPROACH AND RESULTS

Immunosorbant assays and surface plasmon resonance analysis confirmed that Gal-1 and Gal-3 bound purified FVIII with high affinity. Exoglycosidase removal of FVIII N-linked glycans significantly reduced binding to both Gal-1 and Gal-3. Moreover, combined removal of both the N- and O-glycans of FVIII further attenuated Gal-3 binding. Notably, specific digestion of FVIII high-mannose glycans at N239 and N2118 significantly impaired FVIII affinity for Gal-1. Importantly Gal-1, but not Gal-3, bound to free FVIII in the plasma milieu, and significantly inhibited FVIII functional activity. Interestingly, commercial recombinant FVIII (rFVIII) concentrates are manufactured in different cell lines and differ in their glycosylation profiles. Although the biological mechanism has not been defined, recent studies in previously untreated patients with severe hemophilia A reported significant differences in inhibitor development associated with different rFVIII products. Interestingly, Gal-1 and Gal-3 both displayed enhanced affinity for BHK-rFVIII compared with CHO-rFVIII. Furthermore, binding of Gal-1 and Gal-3 to BDD-FVIII was markedly reduced compared with full-length rFVIII.

CONCLUSIONS

We have identified Gal-1 and Gal-3 as novel-binding partners for human FVIII and demonstrated that Gal-1 binding can influence the procoagulant activity of FVIII.

"Kill" the messenger: Targeting of cell-derived microparticles in lupus nephritis

Immune complex (IC) deposition in the glomerular basement membrane (GBM) is a key early pathogenic event in lupus nephritis (LN). The clarification of the mechanisms behind IC deposition will enable targeted therapy in the future. Circulating cell-derived microparticles (MPs) have been proposed as major sources of extracellular autoantigens and ICs and triggers of autoimmunity in LN. The overabundance of galectin-3-binding protein (G3BP) along with immunoglobulins and a few other proteins specifically distinguish circulating MPs in patients with systemic lupus erythematosus (SLE), and this is most pronounced in patients with active LN. G3BP co-localizes with deposited ICs in renal biopsies from LN patients supporting a significant presence of MPs in the IC deposits. G3BP binds strongly to glomerular basement membrane proteins and integrins. Accordingly, MP surface proteins, especially G3BP, may be essential for the deposition of ICs in kidneys and thus for the ensuing formation of MP-derived electron dense structures in the GBM, and immune activation in LN. This review focuses on the notion of targeting surface molecules on MPs as an entirely novel treatment strategy in LN. By targeting MPs, a double hit may be achieved by attenuating both the autoantigenic fueling of immune complexes and the triggering of the adaptive immune system. Thereby, early pathogenic events may be blocked in contrast to current treatment strategies that primarily target and modulate later events in the cellular and humoral immune response.

The emerging role of galectins in cardiovascular disease

Galectins are an ancient family of β-galactoside-specific lectins and consist of 15 different types, each with a specific function. They play a role in the immune system, inflammation, wound healing and carcinogenesis. In particular the role of galectin in cancer is widely studied. Lately, the role of galectins in the development of cardiovascular disease has gained attention. Worldwide cardiovascular disease is still the leading cause of death. In ischemic heart disease, atherosclerosis limits adequate blood flow. Angiogenesis and arteriogenesis are highly important mechanisms relieving ischemia by restoring perfusion to the post-stenotic myocardial area. Galectins act ambiguous, both relieving ischemia and accelerating atherosclerosis. Atherosclerosis can ultimately lead to myocardial infarction or ischemic stroke, which are both associated with galectins. There is also a role for galectins in the development of myocarditis by their influence on inflammatory processes. Moreover, galectin acts as a biomarker for the severity of myocardial ischemia and heart failure. This review summarizes the association between galectins and the development of multiple cardiovascular diseases such as myocarditis, ischemic stroke, myocardial infarction, heart failure and atrial fibrillation. Furthermore it focuses on the association between galectin and more general mechanisms such as angiogenesis, arteriogenesis and atherosclerosis.

Differential Spatiotemporal Patterns of Galectin Expression are a Hallmark of Endotheliochorial Placentation

PROBLEM

Galectins influence the progress of pregnancy by regulating key processes associated with embryo-maternal cross talk, including angiogenesis and placentation. Galectin family members exert multiple roles in the context of hemochorial and epitheliochorial placentation; however, the galectin prolife in endotheliochorial placenta remains to be investigated.

METHOD OF STUDY

Here, we used immunohistochemistry to analyze galectin (gal)-1, gal-3 and gal-9 expression during early and late endotheliochorial placentation in two different species (dogs and cats).

RESULTS

We found that during early feline gestation, all three galectin members were more strongly expressed on trophoblast and maternal vessels compared to the decidua. This was accompanied by an overall decrease of gal-1, gal-3 and gal-9 expressions in late feline gestation. In canine early pregnancy, we observed that gal-1 and gal-9 were expressed strongly in cytotrophoblast (CTB) cells compared to gal-3, and no galectin expression was observed in syncytiotrophoblast (STB) cells. Progression of canine gestation was accompanied by increased gal-1 and gal-3 expressions on STB cells, whereas gal-9 expression remained similar in CTB and STB.

CONCLUSION

These data suggest that both the maternal and fetal compartments are characterized by a spatiotemporal regulation of galectin expression during endotheliochorial placentation. This strongly suggests the involvement of the galectin family in important developmental processes during gestation including immunemodulation, trophoblast invasion and angiogenesis. A conserved functional role for galectins during mammalian placental development emerges from these studies.

The great escape; the hallmarks of resistance to antiangiogenic therapy

The concept of antiangiogenic therapy in cancer treatment has led to the approval of different agents, most of them targeting the well known vascular endothelial growth factor pathway. Despite promising results in preclinical studies, the efficacy of antiangiogenic therapy in the clinical setting remains limited. Recently, awareness has emerged on resistance to antiangiogenic therapies. It has become apparent that the intricate complex interplay between tumors and stromal cells, including endothelial cells and associated mural cells, allows for escape mechanisms to arise that counteract the effects of these targeted therapeutics. Here, we review and discuss known and novel mechanisms that contribute to resistance against antiangiogenic therapy and provide an outlook to possible improvements in therapeutic approaches.

Circulating Galectin-1 and 90K/Mac-2BP Correlated with the Tumor Stages of Patients with Colorectal Cancer

Background. The simultaneous correlation of serum galectin-1, galectin-3, and 90K/Mac-2BP levels with clinical stages of patients with colorectal cancer has not yet been clarified. We plan to measure the serum levels of galectin-1, galectin-3, and 90K/Mac-2BP of patients at different stages of colorectal cancer and analyze the correlation of these galectins with stages of colorectal cancers. Methods. 198 colorectal cancer patients (62 ± 13 (range 31–85) years old, 43.6% female) were recruited for this study. Subjects' blood samples were checked for serum galectin-1, galectin-3, 90K/Mac-2BP, and carcinoembryonic antigen by sandwich enzyme-linked immunosorbent assay. We determined the correlation between plasma concentrations with clinical tumor stages. Results. Colorectal cancer patients with larger cancer sizes (stages T3, T4 rather than T1, T2) have higher serum 90K/Mac-2BP (P = 0.014) and patients with lymph node metastasis have higher serum galectin-1 (P = 0.002) but there was not a significant correlation between galectin-3 and tumor staging of colon cancer. In colorectal cancer patients even with normal carcinoembryonic antigen, serum galectin-1 could predict more lymph node metastasis. Conclusions. We found 90K/Mac-2BP correlated with the size of colorectal cancer. Galectin-1 but not galectin-3 was associated with lymph node metastasis. Galectin-1 could predict more lymph node metastasis in colorectal cancer patients with normal serum carcinoembryonic antigen.

3D tumor tissue analogs and their orthotopic implants for understanding tumor-targeting of microenvironment-responsive nanosized chemotherapy and radiation

An appropriate representation of the tumor microenvironment in tumor models can have a pronounced impact on directing combinatorial treatment strategies and cancer nanotherapeutics. The present study develops a novel 3D co-culture spheroid model (3D TNBC) incorporating tumor cells, endothelial cells and fibroblasts as color-coded murine tumor tissue analogs (TTA) to better represent the tumor milieu of triple negative breast cancer in vitro. Implantation of TTA orthotopically in nude mice, resulted in enhanced growth and aggressive metastasis to ectopic sites. Subsequently, the utility of the model is demonstrated for preferential targeting of irradiated tumor endothelial cells via radiation-induced stromal enrichment of galectin-1 using anginex conjugated nanoparticles (nanobins) carrying arsenic trioxide and cisplatin. Demonstration of a multimodal nanotherapeutic system and inclusion of the biological response to radiation using an in vitro/in vivo tumor model incorporating characteristics of tumor microenvironment presents an advance in preclinical evaluation of existing and novel cancer nanotherapies.

FROM THE CLINICAL EDITOR

Existing in-vivo tumor models are established by implanting tumor cells into nude mice. Here, the authors described their approach 3D spheres containing tumor cells, enodothelial cells and fibroblasts. This would mimic tumor micro-environment more realistically. This interesting 3D model should reflect more accurately tumor response to various drugs and would enable the design of new treatment modalities.

Galectin-3 blockade inhibits cardiac inflammation and fibrosis in experimental hyperaldosteronism and hypertension

Hypertensive cardiac remodeling is accompanied by molecular inflammation and fibrosis, 2 mechanisms that finally affect cardiac function. At cardiac level, aldosterone promotes inflammation and fibrosis, although the precise mechanisms are still unclear. Galectin-3 (Gal-3), a β-galactoside-binding lectin, is associated with inflammation and fibrosis in the cardiovascular system. We herein investigated whether Gal-3 inhibition could block aldosterone-induced cardiac inflammation and fibrosis and its potential role in cardiac damage associated with hypertension. Aldosterone-salt-treated rats presented hypertension, cardiac inflammation, and fibrosis that were prevented by the pharmacological inhibition of Gal-3 with modified citrus pectin. Cardiac inflammation and fibrosis presented in spontaneously hypertensive rats were prevented by modified citrus pectin treatment, whereas Gal-3 blockade did not modify blood pressure levels. In the absence of blood pressure modifications, Gal-3 knockout mice were resistant to aldosterone-induced cardiac inflammation. In human cardiac fibroblasts, aldosterone increased Gal-3 expression via its mineralocorticoid receptor. Gal-3 and aldosterone enhanced proinflammatory and profibrotic markers, as well as metalloproteinase activities in human cardiac fibroblasts, effects that were not observed in Gal-3-silenced cells treated with aldosterone. In experimental hyperaldosteronism, the increase in Gal-3 expression was associated with cardiac inflammation and fibrosis, alterations that were prevented by Gal-3 blockade independently of blood pressure levels. These data suggest that Gal-3 could be a new molecular mechanism linking cardiac inflammation and fibrosis in situations with high-aldosterone levels, such as hypertension.

microRNA-22 downregulation of galectin-9 influences lymphocyte apoptosis and tumor cell proliferation in liver cancer

Galectin-9 (Gal-9) plays an important role in both the immune response and tumor progression, while microRNAs act as tumor regulators to mediate tumorigenesis. However, the underlying molecular mechanisms remain unknown. In the present study, we investigated the relationship between Gal-9 and microRNA-mediated regulation in liver cancer. We examined Gal-9 expression using qRT-PCR and western blot analysis and found that it was markedly upregulated in human liver cancer cells compared with the level in normal hepatocytes. We co-cultured peripheral blood mononuclear cells (PBMCs) and tumor cells and observed that Gal-9 induced lymphocyte apoptosis and tumor cell immune escape using flow cytometric analysis and WST-1 assay. We found that miR-22 was downregulated in liver cancer tissues and cell lines and confirmed that miR-22 directly targeted the Gal-9 3'UTR and negatively regulated Gal-9 expression by luciferase reporter assay and transfection of microRNA mimics. We also observed that the Gal-9/miR-22 axis may influence lymphocyte apoptosis and tumor cell proliferation. These studies contribute to a further understanding of the microRNA‑mediated regulation of the Gal-9 pathway and elucidate novel therapeutic targets for liver cancer.

Galectin-1 suppresses methamphetamine induced neuroinflammation in human brain microvascular endothelial cells: Neuroprotective role in maintaining blood brain barrier integrity

Methamphetamine (Meth) abuse can lead to the breakdown of the blood-brain barrier (BBB) integrity leading to compromised CNS function. The role of Galectins in the angiogenesis process in tumor-associated endothelial cells (EC) is well established; however no data are available on the expression of Galectins in normal human brain microvascular endothelial cells and their potential role in maintaining BBB integrity. We evaluated the basal gene/protein expression levels of Galectin-1, -3 and -9 in normal primary human brain microvascular endothelial cells (BMVEC) that constitute the BBB and examined whether Meth altered Galectin expression in these cells, and if Galectin-1 treatment impacted the integrity of an in-vitro BBB. Our results showed that BMVEC expressed significantly higher levels of Galectin-1 as compared to Galectin-3 and -9. Meth treatment increased Galectin-1 expression in BMVEC. Meth induced decrease in TJ proteins ZO-1, Claudin-3 and adhesion molecule ICAM-1 was reversed by Galectin-1. Our data suggests that Galectin-1 is involved in BBB remodeling and can increase levels of TJ proteins ZO-1 and Claudin-3 and adhesion molecule ICAM-1 which helps maintain BBB tightness thus playing a neuroprotective role. Galectin-1 is thus an important regulator of immune balance from neurodegeneration to neuroprotection, which makes it an important therapeutic agent/target in the treatment of drug addiction and other neurological conditions.

Galectin-1 regulates tissue exit of specific dendritic cell populations

During inflammation, dendritic cells emigrate from inflamed tissue across the lymphatic endothelium into the lymphatic vasculature and travel to regional lymph nodes to initiate immune responses. However, the processes that regulate dendritic cell tissue egress and migration across the lymphatic endothelium are not well defined. The mammalian lectin galectin-1 is highly expressed by vascular endothelial cells in inflamed tissue and has been shown to regulate immune cell tissue entry into inflamed tissue. Here, we show that galectin-1 is also highly expressed by human lymphatic endothelial cells, and deposition of galectin-1 in extracellular matrix selectively regulates migration of specific human dendritic cell subsets. The presence of galectin-1 inhibits migration of immunogenic dendritic cells through the extracellular matrix and across lymphatic endothelial cells, but it has no effect on migration of tolerogenic dendritic cells. The major galectin-1 counter-receptor on both dendritic cell populations is the cell surface mucin CD43; differential core 2 O-glycosylation of CD43 between immunogenic dendritic cells and tolerogenic dendritic cells appears to contribute to the differential effect of galectin-1 on migration. Binding of galectin-1 to immunogenic dendritic cells reduces phosphorylation and activity of the protein-tyrosine kinase Pyk2, an effect that may also contribute to reduced migration of this subset. In a murine lymphedema model, galectin-1(-/-) animals had increased numbers of migratory dendritic cells in draining lymph nodes, specifically dendritic cells with an immunogenic phenotype. These findings define a novel role for galectin-1 in inhibiting tissue emigration of immunogenic, but not tolerogenic, dendritic cells, providing an additional mechanism by which galectin-1 can dampen immune responses.

Reprogramming the tumor microenvironment: tumor-induced immunosuppressive factors paralyze T cells

It has become evident that tumor-induced immuno-suppressive factors in the tumor microenvironment play a major role in suppressing normal functions of effector T cells. These factors serve as hurdles that limit the therapeutic potential of cancer immunotherapies. This review focuses on illustrating the molecular mechanisms of immunosuppression in the tumor microenvironment, including evasion of T-cell recognition, interference with T-cell trafficking, metabolism, and functions, induction of resistance to T-cell killing, and apoptosis of T cells. A better understanding of these mechanisms may help in the development of strategies to enhance the effectiveness of cancer immunotherapies.

Correlations between immune response and vascularization qRT-PCR gene expression clusters in squamous cervical cancer

Background

The tumour microenvironment comprises a network of immune response and vascularization factors. From this network, we identified immunological and vascularization gene expression clusters and the correlations between the clusters. We subsequently determined which factors were correlated with patient survival in cervical carcinoma.

Methods

The expression of 42 genes was investigated in 52 fresh frozen squamous cervical cancer samples by qRT-PCR. Weighted gene co-expression network analysis and mixed-model analyses were performed to identify gene expression clusters. Correlations and survival analyses were further studied at expression cluster and single gene level.

Results

We identified four immune response clusters: ‘T cells’ (CD3E/CD8A/TBX21/IFNG/FOXP3/IDO1), ‘Macrophages’ (CD4/CD14/CD163), ‘Th2’ (IL4/IL5/IL13/IL12) and ‘Inflammation’ (IL6/IL1B/IL8/IL23/IL10/ARG1) and two vascularization clusters: ‘Angiogenesis’ (VEGFA/FLT1/ANGPT2/ PGF/ICAM1) and ‘Vessel maturation’ (PECAM1/VCAM1/ANGPT1/SELE/KDR/LGALS9). The ‘T cells’ module was correlated with all modules except for ‘Inflammation’, while ‘Inflammation’ was most significantly correlated with ‘Angiogenesis’ (p < 0.001). High expression of the ‘T cells’ cluster was correlated with earlier TNM stage (p = 0.007). High CD3E expression was correlated with improved disease-specific survival (p = 0.022), while high VEGFA expression was correlated with poor disease-specific survival (p = 0.032). Independent predictors of poor disease-specific survival were IL6 (hazard ratio = 2.3, p = 0.011) and a high IL6/IL17 ratio combined with low IL5 expression (hazard ratio = 4.2, p = 0.010).

Conclusions

‘Inflammation’ marker IL6, especially in combination with low levels of IL5 and IL17, was correlated with poor survival. This suggests that IL6 promotes tumour growth, which may be suppressed by a Th17 and Th2 response. Measuring IL6, IL5 and IL17 expression may improve the accuracy of predicting prognosis in cervical cancer.

The bitter side of sweet: the role of Galectin-9 in immunopathogenesis of viral infections

In recent years, a critical role for β-galactoside-binding protein, Galectin-9 (Gal-9) has emerged in infectious disease, autoimmunity, and cancer. It is a ligand for T cell immunoglobulin mucin domain 3 (Tim-3), a type-I glycoprotein that is persistently expressed on dysfunctional T cells during chronic viral infections. Gal-9 exerts its pivotal immunomodulatory effects by inducing apoptosis or suppressing effector functions via engagement with its receptor, Tim-3. Recent studies report elevation of circulating Gal-9 in humans infected with different viral infections. Interaction of soluble Gal-9 with Tim-3 expressed on the surface of activated CD4+ T cells renders them less susceptible to HIV-1 infection, while enhanced HIV infection occurs when Gal-9 interacts with a different receptor than Tim-3. This indicates the versatile role of Gal-9 in viral pathogenesis. For instance, higher expression of Tim-3 during chronic viral infection and elevation of plasma Gal-9 may have evolved to limit persistent immune activation and pathogenic T cells activity. In contrast, Gal-9 can suppress the effectiveness of immunity against viral infections. In agreement, Gal-9 knockout mice mount a more robust and vigorous virus-specific immune response in acute and chronic viral infections resulting in rapid viral clearance. In line with this observation, blocking Gal-9 signals to Tim-3-expressing T cells result in improved immune responses. Here we review the biological and immunological properties of Gal-9 in viral infections (HIV, HCV, HBV, HSV, CMV, influenza, and dengue virus). Manipulating Gal-9 signals may have immunotherapeutic potential and could represent an alternative approach for improving immune responses to viral infections/vaccines.

Melanoma Cell Galectin-1 Ligands Functionally Correlate with Malignant Potential

Galectin-1 (Gal-1)-binding to Gal-1 ligands on immune and endothelial cells can influence melanoma development through dampening antitumor immune responses and promoting angiogenesis. However, whether Gal-1 ligands are functionally expressed on melanoma cells to help control intrinsic malignant features remains poorly understood. Here, we analyzed expression, identity, and function of Gal-1 ligands in melanoma progression. Immunofluorescent analysis of benign and malignant human melanocytic neoplasms revealed that Gal-1 ligands were abundant in severely dysplastic nevi, as well as in primary and metastatic melanomas. Biochemical assessments indicated that melanoma cell adhesion molecule (MCAM) was a major Gal-1 ligand on melanoma cells that was largely dependent on its N-glycans. Other melanoma cell Gal-1 ligand activity conferred by O-glycans was negatively regulated by α2,6 sialyltransferase ST6GalNAc2. In Gal-1-deficient mice, MCAM-silenced (MCAM(KD)) or ST6GalNAc2-overexpressing (ST6(O/E)) melanoma cells exhibited slower growth rates, underscoring a key role for melanoma cell Gal-1 ligands and host Gal-1 in melanoma growth. Further analysis of MCAM(KD) or ST6(O/E) melanoma cells in cell migration assays indicated that Gal-1 ligand-dependent melanoma cell migration was severely inhibited. These findings provide a refined perspective on Gal-1/melanoma cell Gal-1 ligand interactions as contributors to melanoma malignancy.

Assessing the roles of galectins in regulating dendritic cell migration through extracellular matrix and across lymphatic endothelial cells

Leukocyte migration from the bloodstream into tissues, and from tissues to lymph nodes, depends on expression of specific adhesion and signaling molecules by vascular endothelial cells and lymphatic endothelial cells. Tissue damage and microbial infection induce vascular endothelial cells to up-regulate expression of adhesion molecules to facilitate entry of several leukocyte populations from blood into tissues. Many of these cells then leave inflamed tissue and migrate to regional lymph nodes. A critical population that emigrates from inflamed tissue is dendritic cells. Dendritic cells in tissue have to migrate through extracellular matrix and across a layer of lymphatic endothelial cells to enter the lymphatic vasculature. Little is known about the adhesion molecules expressed by lymphatic endothelial cells or the processes required for the critical step of dendritic cell exit from tissues, specifically migration through the extracellular matrix and basal-to-apical migration across the lymphatic endothelial cell layer into lymphatic vasculature.Members of the galectin family of carbohydrate binding proteins are expressed in both vascular and lymphatic endothelial cells. Dynamic changes in galectin expression during inflammation are known to regulate leukocyte tissue entry during inflammation. However, the roles of galectin family members expressed by lymphatic endothelial cells in leukocyte tissue exit remain to be explored.Here, we describe an in vitro transmigration assay that mimics dendritic cell tissue exit in the presence and absence of galectin protein. Fluorescently labeled human dendritic cell migration through extracellular matrix and across human lymphatic endothelial cells is examined in the presence and absence of recombinant human galectin protein.

Galectins in angiogenesis: consequences for gestation

Members of the galectin family have been shown to exert several roles in the context of reproduction. They contribute to placentation, maternal immune regulation and facilitate angiogenesis encompassing decidualisation and placenta formation during pregnancy. In the context of neo-vascularisation, galectins have been shown to augment signalling pathways that lead to endothelial cell activation, cell proliferation, migration and tube formation in vitro in addition to angiogenesis in vivo. Angiogenesis during gestation ensures not only proper foetal growth and development, but also maternal health. Consequently, restriction of placental blood flow has major consequences for both foetus and mother, leading to pregnancy diseases. In this review we summarise both the established and the emerging roles of galectin in angiogenesis and discuss the possible implications during healthy and pathological gestation.

Platelets and galectins

A major function of platelets is keeping the vascular system intact. Platelet activation at sites of vascular injury leads to the formation of a hemostatic plug. Activation of platelets is therefore crucial for normal hemostasis; however, uncontrolled platelet activation may also lead to the formation of occlusive thrombi that can cause ischemic events. Although they are essential for proper hemostasis, platelet function extends to physiologic processes such as tissue repair, wound remodeling and antimicrobial host defense, or pathologic conditions such as thrombosis, atherosclerosis, chronic inflammatory diseases and cancer. Platelets can be activated by soluble molecules including thrombin, thromboxane A2 (TXA2), adenosine diphosphate (ADP), serotonin or by adhesive extracellular matrix (ECM) proteins such as von Willebrand factor (vWF) and collagen. Here we describe recent advances in the activation of platelets by non-canonical platelet agonists such as galectins. By acting either in soluble or immobilized form, these glycan-binding proteins trigger all platelet activation responses through modulation of discrete signaling pathways. We also offer new hypotheses and some speculations about the role of platelet-galectin interactions not only in hemostasis and thrombosis but also in inflammation and related diseases such as atherosclerosis and cancer.