Galectins in Atherosclerotic Disease

Tandem-repeat lectins: structural and functional insights

Multivalency in lectins plays a pivotal role in influencing glycan cross-linking, thereby affecting lectin functionality. This multivalency can be achieved through oligomerization, the presence of tandemly repeated carbohydrate recognition domains, or a combination of both. Unlike lectins that rely on multiple factors for the oligomerization of identical monomers, tandem-repeat lectins inherently possess multivalency, independent of this complex process. The repeat domains, although not identical, display slightly distinct specificities within a predetermined geometry, enhancing specificity, affinity, avidity and even oligomerization. Despite the recognition of this structural characteristic in recently discovered lectins by numerous studies, a unified criterion to define tandem-repeat lectins is still necessary. We suggest defining them multivalent lectins with intrachain tandem repeats corresponding to carbohydrate recognition domains, independent of oligomerization. This systematic review examines the folding and phyletic diversity of tandem-repeat lectins and refers to relevant literature. Our study categorizes all lectins with tandemly repeated carbohydrate recognition domains into nine distinct folding classes associated with specific biological functions. Our findings provide a comprehensive description and analysis of tandem-repeat lectins in terms of their functions and structural features. Our exploration of phyletic and functional diversity has revealed previously undocumented tandem-repeat lectins. We propose research directions aimed at enhancing our understanding of the origins of tandem-repeat lectin and fostering the development of medical and biotechnological applications, notably in the design of artificial sugars and neolectins.

Sex-dependent expression of galectin-1, a cardioprotective β-galactoside-binding lectin, in human calcific aortic stenosis

We aimed to analyze sex-related differences in galectin-1 (Gal-1), a β-galactoside-binding lectin, in aortic stenosis (AS) and its association with the inflammatory and fibrocalcific progression of AS. Gal-1 was determined in serum and aortic valves (AVs) from control and AS donors by western blot and immunohistochemistry. Differences were validated by ELISA and qPCR in AS samples. In vitro experiments were conducted in primary cultured valve interstitial cells (VICs). Serum Gal-1 was not different neither between control and AS nor between men and women. There was no association between circulating and valvular Gal-1 levels. The expression of Gal-1 in stenotic AVs was higher in men than women, even after adjusting for confounding factors, and was associated with inflammation, oxidative stress, extracellular matrix remodeling, fibrosis, and osteogenesis. Gal-1 (LGALS1) mRNA was enhanced within fibrocalcific areas of stenotic AVs, especially in men. Secretion of Gal-1 was up-regulated over a time course of 2, 4, and 8 days in men's calcifying VICs, only peaking at day 4 in women's VICs. In vitro, Gal-1 was associated with similar mechanisms to those in our clinical cohort. β-estradiol significantly up-regulated the activity of an LGALS1 promoter vector and the secretion of Gal-1, only in women's VICs. Supplementation with rGal-1 prevented the effects elicited by calcific challenge including the metabolic shift to glycolysis. In conclusion, Gal-1 is up-regulated in stenotic AVs and VICs from men in association with inflammation, oxidative stress, matrix remodeling, and osteogenesis. Estrogens can regulate Gal-1 expression with potential implications in post-menopause women. Exogenous rGal-1 can diminish calcific phenotypes in both women and men.

Human Galectin-7 Gene LGALS7 Promoter Sequence Polymorphisms and Risk of Spontaneous Intracerebral Hemorrhage: A Prospective Study

Background and purpose

Despite evidence for the role of genetic factors in stroke, only a small proportion of strokes have been clearly attributed to monogenic factors, due to phenotypic heterogeneity. The goal of this study was to determine whether a significant relationship exists between human galectin-7 gene LGALS7 promoter region polymorphisms and the risk of stroke due to non-traumatic intracerebral hemorrhage (ICH).

Methods

This two-stage genetic association study included an initial exploratory stage followed by a discovery stage. During the exploratory stage, transgenic galectin-7 mice or transgenic mice with the scrambled sequence of the hairpin structure –silenced down gene LGALS7—were generated and then expressed differentially expressed proteins and galectin-7-interacting proteins were identified through proteomic analysis. During the discovery stage, a single-nucleotide polymorphism (SNP) genotyping approach was used to determine associations between 2 LGALS7 SNPs and ICH stroke risk for a cohort of 24 patients with stroke of the Chinese Han population and 70 controls.

Results

During the exploratory phase, LGALS7 expression was found to be decreased in TGLGALS–DOWN mice as compared to its expression in TGLGALS mice. During the discovery phase, analysis of LGALS7 sequences of 24 non-traumatic ICH cases and 70 controls led to the identification of 2 ICH susceptibility loci: a genomic region on 19q13.2 containing two LGALS7 SNPs, rs567785577 and rs138945880, whereby the A allele of rs567785577 and the T allele of rs138945880 were associated with greater risk of contracting ICH [for T and A vs. C and G, unadjusted odds ratio (OR) = 13.5; 95% CI = 2.249–146.5; p = 0.002]. This is the first study to genotype the galectin-7 promoter in patients with hemorrhagic stroke. Genotype and allele association tests and preliminary analysis of patients with stroke revealed that a single locus may be a genetic risk factor for hemorrhagic stroke.

Conclusion

A and T alleles of two novel SNP loci of 19q13.2, rs567785577 and rs138945880, respectively, were evaluated for associations with susceptibility to ICH. Further studies with expanded case numbers that include subjects of other ethnic populations are needed to elucidate mechanisms underlying associations between these SNPs and ICH risk.

Galectin-3 is associated with severe heart failure and death: A hospital-based study in Chinese patients

Heart failure (HF) is a serious disease syndrome characterized by elevated pro-inflammatory cytokines and inflammatory mediators presume to have significant contribution on disease progression. Galectins are carbohydrate-binding proteins responsible of various physiological functions. Role of galectins in heart failure has been ill-defined. In the present case-controls study, 136 patients clinically diagnosed with heart failure and 125 healthy Chinese controls were recruited. Levels of galectins (Gal-1, 3 and 9) and cytokines (IFN-γ, IL-17A, IL-4 and TGF-β) were quantified by ELISA. Increased levels of galectin-1 and 3 was observed in HF patients and associated with clinical severity. In addition, pro-inflammatory cytokines such as IFN-γ and IL-17A were increased in patients whereas, anti-inflammatory TGFβ was decreased. Galectin-3 was positively correlated with IFN-γ, IL-17A and inversely with TGF-β. Furthermore, ROC curve analysis suggested galectin-3 as a promising biomarker for diagnosis and HF and clinical severity. Interestingly, a two-year follow-up indicated significant association of elevated galectin-3 with mortality due to HF. In conclusion, galectin-3 associated with HF and clinical manifestations possibly by inducing pro-inflammatory cytokines and could be a possible biomarker of HF and severe clinical conditions.

Galectins in the Pathogenesis of Cerebrovascular Accidents: An Overview

Due to limitations of neuroimaging, such as the isodense appearance of blood to neuronal tissue in subacute hemorrhagic stroke, a body of studies have been performed to evaluate candidate biomarkers which may aid in accurate determination of cerebrovascular accident type. Beyond aiding in the delineation of stroke cause, biomarkers could also confer useful prognostic information to help clinicians plan use of resources. One of the candidate biomarkers studied for detection of cerebrovascular accident (CVA) includes a class of proteins called galectins. Galectins bind β-galactoside through a highly conserved carbohydrate recognition domain, endowing an ability to interact with carbohydrate moieties on glycoproteins, some of which are relevant to CVA response. Furthermore, galectins-1, -2, -3, -9, and -12 are expressed in tissues relevant to CVA, and some exhibit characteristics (eg, extracellular secretion) that could render feasible their detection in serum. Galectins-1 and -3 appear to have the largest amounts of preclinical evidence, consistently demonstrating increased activity and expression levels during CVA. However, a lack of standardization of biochemical assays across cohort studies limits further translation of these basic science studies. This review aims to increase awareness of the biochemical roles of galectins in CVA, while also highlighting challenges and remaining questions preventing the translation of basic science observations into a clinically useful test.

Alterations to adipose tissue morphology during inflammatory arthritis is indicative of vasculopathology in DBA/1 mice

The physiologic function of adipose tissue is altered by the host's inflammatory response; the implications for maintaining human health and regulating inflammation-associated disease progression are ill defined. However, this cannot be investigated in humans, therefore the use of animal models is required. With the aim to determine morphological and molecular alterations to perivascular and organ-associated adipose tissues during inflammatory arthritis, collagen-induced arthritis (CIA) was established in male DBA/1 mice. Emerging evidence from this study signposts CIA in the DBA/1 mouse as a model that is relevant to study the development and treatment of early cardiovascular pathology associated with inflammatory arthritis. Here, we show global morphological changes in adipose tissue and the thoracic aorta in animals induced with CIA compared with the non-immunized controls. In CIA, we concluded that the increased cell count in PVAT was, at least in part, caused by an ingress and/or expansion of macrophages that had a mixed phenotype. A substantial increase of galectin-3 was expressed in PVAT from mice with CIA. Galectin-3 is elevated in the blood of patients with CVDs, however, it has never before been measured in PVAT in rodents or humans. Here, PVAT-associated galectin-3 is identified as a potential biomarker for detecting early vascular pathology in CIA and a promising candidate for translation to RA.

Serum levels of galectin-1, galectin-3, and galectin-9 are associated with large artery atherosclerotic stroke

The aim of this study was to assess the expression patterns of serum galectin-1 (Gal-1), galectin-3 (Gal-3), galectin-9 (Gal-9), and galectin-3 binding protein (Gal-3BP) and their associations with stroke outcome in large artery atherosclerotic (LAA) stroke. The serum levels of Gal-1, Gal-3, Gal-9, and Gal-3BP were measured by ELISA in 130 patients with LAA stroke and 130 age- and sex-matched controls. Serum samples were collected from the patients on day 1, day 6, and in the 4th week after ischaemic stroke (IS). An unfavourable outcome was defined as a modified Rankin Scale score of >2 on day 90 after IS. Our results indicated that the Gal-3 and Gal-9 levels were higher in patients with LAA stroke than in controls. A higher Gal-3 level was independently associated with an unfavourable outcome both on day 1 and day 6 after IS. In addition, Gal-9 and Gal-1 levels were upregulated on day 6 and in the 4th week after IS, respectively. For Gal-3BP, no difference was detected between patients and controls and no predictive value was found in patients. In conclusion, these findings suggest that the serum levels of Gal-1, Gal-3, and Gal-9 may be associated with LAA stroke.

Galectin-3 and prediction of therapeutic response to renal sympathetic denervation

The profibrotic mediator Galectin-3 (Gal-3) has been associated with aldosterone-mediated vascular inflammation, fibrosis, and stiffness. We evaluated whether the Gal-3 levels and change in Gal-3 as associated with renal denervation can serve as prediction of therapeutic response to renal denervation. A total of 42 patients with resistant hypertension undergoing renal sympathetic denervation (RDN) were included. Blood pressure was evaluated by 24-h ambulatory measurement before RDN and 1, 3 and 6 months after RDN. Treatment response was defined as a drop in systolic ambulatory blood pressure of >5 mm Hg after 6 months. Blood samples were assessed for Gal-3 levels. For the entire group, a significant drop in mean systolic ambulatory blood pressure of 5.2 ± 18.6 mm Hg was observed (p = 0.032). The responder rate was 50% (n = 21). At baseline, Gal-3 levels were significantly higher in responders (14.5 ± 6.0 vs. 10.95 ± 4.6 ng/ml, p = 0.017). There were no significant changes of Gal-3 levels during the follow-up period. The profibrotic biomarker may help to identify patients suitable for RDN.

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.

Galectin-2 induces a proinflammatory, anti-arteriogenic phenotype in monocytes and macrophages

Galectin-2 is a monocyte-expressed carbohydrate-binding lectin, for which increased expression is genetically determined and associated with decreased collateral arteriogenesis in obstructive coronary artery disease patients. The inhibiting effect of galectin-2 on arteriogenesis was confirmed in vivo, but the mechanism is largely unknown. In this study we aimed to explore the effects of galectin-2 on monocyte/macrophage phenotype in vitro and vivo, and to identify the receptor by which galectin-2 exerts these effects. We now show that the binding of galectin-2 to different circulating human monocyte subsets is dependent on monocyte surface expression levels of CD14. The high affinity binding is blocked by an anti-CD14 antibody but not by carbohydrates, indicating a specific protein-protein interaction. Galectin-2 binding to human monocytes modulated their transcriptome by inducing proinflammatory cytokines and inhibiting pro-arteriogenic factors, while attenuating monocyte migration. Using specific knock-out mice, we show that galectin-2 acts through the CD14/toll-like receptor (TLR)-4 pathway. Furthermore, galectin-2 skews human macrophages to a M1-like proinflammatory phenotype, characterized by a reduced motility and expression of an anti-arteriogenic cytokine/growth factor repertoire. This is accompanied by a switch in surface protein expression to CD40-high and CD206-low (M1). In a murine model we show that galectin-2 administration, known to attenuate arteriogenesis, leads to increased numbers of CD40-positive (M1) and reduced numbers of CD206-positive (M2) macrophages surrounding actively remodeling collateral arteries. In conclusion galectin-2 is the first endogenous CD14/TLR4 ligand that induces a proinflammatory, non-arteriogenic phenotype in monocytes/macrophages. Interference with CD14-Galectin-2 interaction may provide a new intervention strategy to stimulate growth of collateral arteries in genetically compromised cardiovascular patients.

Galectin-8 elicits pro-inflammatory activities in the endothelium

Galectins (Gals), a family of mammalian lectins, play diverse roles under physiological and pathological conditions. Here, we analyzed the tandem-repeat Gal-8 synthesis, secretion and effects on the endothelium physiology. Gal-8M and Gal-8L isoforms were secreted under basal conditions by human microvascular endothelial cells (HMEC-1). However, expression and secretion of the Gal-8M isoform, but not Gal-8L, were increased in response to bacterial lipopolysaccharide (LPS) stimulus and returned to control values after LPS removal. Similarly, cell surface Gal-8 exposure was increased after stimulation with LPS. To evaluate Gal-8 effects on the endothelium physiology, HMEC-1 cells were incubated in the presence of recombinant Gal-8M. Pretreated HMEC-1 cells became proadhesive to human normal platelets, indicating that Gal-8 actually activates endothelial cells. This effect was specific for lectin activity as it was prevented by the simultaneous addition of lactose, but not by sucrose. Endothelial cells also increased their exposition of von Willebrand factor after Gal-8 treatment, which constitutes another feature of cell activation that could be, in turn, responsible for the observed platelet adhesion. Several pro-inflammatory molecules were abundantly produced by Gal-8 stimulated endothelial cells: CXCL1 (GRO-α), GM-CSF, IL-6 and CCL5 (RANTES), and in a lower degree CCL2 (MCP-1), CXCL3 (GRO-γ) and CXCL8 (IL-8). In agreement, Gal-8M induced nuclear factor kappa B phosphorylation. Altogether, these results not only confirm the pro-inflammatory role we have already proposed for Gal-8 in other cellular systems but also suggest that this lectin is orchestrating the interaction between leukocytes, platelets and endothelial cells.

Control of angiogenesis by galectins involves the release of platelet-derived proangiogenic factors

Platelets contribute to vessel formation through the release of angiogenesis-modulating factors stored in their α-granules. Galectins, a family of lectins that bind β-galactoside residues, are up-regulated in inflammatory and cancerous tissues, trigger platelet activation and mediate vascularization processes. Here we aimed to elucidate whether the release of platelet-derived proangiogenic molecules could represent an alternative mechanism through which galectins promote neovascularization. We show that different members of the galectin family can selectively regulate the release of angiogenic molecules by human platelets. Whereas Galectin (Gal)-1, -3, and -8 triggered vascular endothelial growth factor (VEGF) release, only Gal-8 induced endostatin secretion. Release of VEGF induced by Gal-8 was partially prevented by COX-1, PKC, p38 and Src kinases inhibitors, whereas Gal-1-induced VEGF secretion was inhibited by PKC and ERK blockade, and Gal-3 triggered VEGF release selectively through a PKC-dependent pathway. Regarding endostatin, Gal-8 failed to stimulate its release in the presence of PKC, Src and ERK inhibitors, whereas aspirin or p38 inhibitor had no effect on endostatin release. Despite VEGF or endostatin secretion, platelet releasates generated by stimulation with each galectin stimulated angiogenic responses in vitro including endothelial cell proliferation and tubulogenesis. The platelet angiogenic activity was independent of VEGF and was attributed to the concerted action of other proangiogenic molecules distinctly released by each galectin. Thus, secretion of platelet-derived angiogenic molecules may represent an alternative mechanism by which galectins promote angiogenic responses and its selective blockade may lead to the development of therapeutic strategies for angiogenesis-related diseases.

Galectin-3 expression in response to LPS, immunomodulatory drugs and exogenously added galectin-3 in monocyte-like THP-1 cells

Galectin-3, a structurally unique beta-galactoside-binding lectin, through the specific protein-protein and protein-carbohydrate interactions participates in numerous biological processes, such as cell proliferation and apoptosis, adhesion and activation. Its expression and secretion by until now an unknown mechanism are modulated by diverse molecules and are dependent on different physiological and pathophysiological conditions. By autocrine and paracrine actions, galectin-3 modulates many immune reactions and affects various immune cells, particularly those of monocyte-macrophage lineage. This is why galectin-3 has recently become an attractive therapeutic target. However, molecular mechanisms of its actions as well as regulatory mechanism of its expression and activation are still largely unknown. In this study, we show that lipopolysaccharide (LPS) provokes upregulation of galectin-3 expression on both gene and protein level in monocyte-like THP-1 cells, which can be inhibited by dexamethasone, but not with non-steroidal anti-inflammatory drugs aspirin and indomethacin. Resting and LPS-challenged monocyte-like THP-1 cells do not have detectable amount of surface-bound galectin-3, but are able to bind exogenously added galectin-3 with the same capacity. Although galectin-3 is generally considered to be a pro-inflammatory molecule, here we show that the exogenously added galectin-3 does not affect interleukin (IL)-1β, IL-6, IL-8, IL-10, IL-12p70 and TNF-α production in resting and LPS-activated monocyte-like THP-1 cells nor influences its own gene expression level in those cells.

Pre-feeding of a glycolipid binding protein LEC-8 from Caenorhabditis elegans revealed enhanced tolerance to Cry1Ac toxin in Helicoverpa armigera

Crystal toxins from Bacillus thuringiensis bind to glycolipids and glycoproteins using two different lectin domains in the toxin protein. Our previous observations suggested that the sequestration of crystal toxin depends on the functional interaction of a toxin lectin with glycolipids. Given the finding that competition of a galectin LEC-8 with Cry5B for binding to glycolipids resulting in reduced Bt toxicity in nematode, it is interesting to explore the role of LEC-8 in insects. Here, we reported that the LEC-8 can also be exploited by insect for their survival when they were fed with Bt toxin food. Bioassay with LEC-8 showed that pre-feeding of Helicoverpa armigera larvae reduced the Cry1Ac susceptibility. Both LEC-8 and Cry1Ac bind to the midgut glycolipid in a similar way. Further ELISA indicated that LEC-8 interacts with glycolipid from insect midgut, thus reduce Cry1Ac binding to glycolipid. This in turn enhances insect tolerance to Cry1Ac toxin. The sugar determinants of LEC-8 were studied by using haemagglutination (HA) and haemagglutination inhibition (HAI) assay. It was suggested that the terminal sugar of LEC-8 has multiple sugar binding property.

Galectin-3 plasma levels and coronary artery disease: a new possible biomarker of acute coronary syndrome

Inflammation plays a key role in atherosclerosis. Galectin-3 is a macrophage- and endothelium-derived mediator actively involved in the regulation of many aspects of inflammatory cell behaviour. The aim of this study is to quantify plasma Galectin-3 in patients with coronary artery disease (CAD) and different clinical manifestation at the moment of observation in order to verify whether Galectin-3 could be a useful biomarker of atherosclerotic state. We enrolled 125 patients affected by CAD, angiographically documented (70 stable, 55 unstable). They underwent accurate examinations and anamnestic data was collected. The most important traditional risk factors, such as age, hypertension, and body mass index, were reported. Plasma Galectin-3 was quantified using an ELISA kit. Unstable patients (n = 55) had a higher plasma Galectin-3 levels in respect to the stable subjects (27.75 ng/mL (19.27-39.09) vs 6.48 ng/ml (4.88-8.83), p<0.001. A trend in correlation between plasma Galectin-3 levels and number of vessels compromised seems to be present: CAD patients with three-vessel disease had higher levels of Galectin-3 than patients with one-or two-vessel disease (17.39 ng/ml (10.75-29.82) vs 9.18 ng/ml (5.56-23.22), p= 0.058. The significantly higher plasma Galectin-3 levels in patients with unstable angina in respect to the stable angina confirm the involvement of Galectin-3 in promoting macrophage activation and monocyte attraction. Despite the distribution of CAD in patients with acute and chronic coronary disease being similar, we may hypothesize that Galectin-3 could be a useful biomarker of atherosclerotic plaque and in particular of its destabilization.

Identification of galectins as novel regulators of platelet signaling and function

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. Platelets can be activated by soluble molecules including thrombin, TXA2 , adenosine diphosphate (ADP), and serotonin or by adhesive extracellular matrix (ECM) proteins such as von Willebrand factor and collagen. In this article, we review recent advances on the role of galectins in platelet physiology. By acting in either soluble or immobilized form, these glycan-binding proteins trigger platelet activation 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.

Human platelets express and are activated by galectin-8

Gals (galectins) are proteins with glycan affinity that are emerging as mediators of atherosclerosis. Despite the similarities in structure and sequence, different Gals exert distinct effects on their target cells. We have shown that Gal-1 triggers platelet activation, suggesting a role for Gals in thrombus formation. Since Gal-8 is expressed upon endothelial activation and also contributes to inflammation, to understand further the role of these lectins in haemostasis, we evaluated the effect of Gal-8 on human platelets. Gal-8 bound specific glycans in the platelet membrane and triggered spreading, calcium mobilization and fibrinogen binding. It also promoted aggregation, thromboxane generation, P-selectin expression and granule secretion. GP (glycoprotein) αIIb and Ib-V were identified as putative Gal-8 counter-receptors by MS. Studies performed using platelets from Glanzmann's thromboasthenia and Bernard-Soulier syndrome patients confirmed that GPIb is essential for transducing Gal-8 signalling. Accordingly, Src, PLC2γ (phospholipase C2γ), ERK (extracellular-signal-regulated kinase) and PI3K (phosphoinositide 3-kinase)/Akt downstream molecules were involved in the Gal-8 signalling pathway. Gal-8 fragments containing either the N- or C-terminal carbohydrate-recognition domains showed that activation is exerted through the N-terminus. Western blotting and cytometry showed that platelets not only contain Gal-8, but also expose Gal-8 after thrombin activation. These findings reveal Gal-8 as a potent platelet activator, supporting a role for this lectin in thrombosis and inflammation.