Gal-1 Expression Analysis in the GLIOCAT Multicenter Study: Role as a Prognostic Factor and an Immune-Suppressive Biomarker

Glioblastoma (GBM) is the most frequent primary malignant brain tumor and has a dismal prognosis. Unfortunately, despite the recent revolution of immune checkpoint inhibitors in many solid tumors, these have not shown a benefit in overall survival in GBM patients. Therefore, new potential treatment targets as well as diagnostic, prognostic, and/or predictive biomarkers are needed to improve outcomes in this population. The β-galactoside binding protein Galectin-1 (Gal-1) is a protein with a wide range of pro-tumor functions such as proliferation, invasion, angiogenesis, and immune suppression. Here, we evaluated Gal-1 expression by immunohistochemistry in a homogenously treated cohort of GBM (the GLIOCAT project) and correlated its expression with clinical and molecular data. We observed that Gal-1 is a negative prognostic factor in GBM. Interestingly, we observed higher levels of Gal-1 expression in the mesenchymal/classical subtypes compared to the less aggressive proneural subtype. We also observed a Gal-1 expression correlation with immune suppressive signatures of CD4 T-cells and macrophages, as well as with several GBM established biomarkers, including SHC1, PD-L1, PAX2, MEOX2, YKL-40, TCIRG1, YWHAG, OLIG2, SOX2, Ki-67, and SOX11. Moreover, Gal-1 levels were significantly lower in grade 4 IDH-1 mutant astrocytomas, which have a better prognosis. Our results confirm the role of Gal-1 as a prognostic factor and also suggest its value as an immune-suppressive biomarker in GBM.

Monoamines in glioblastoma: complex biology with therapeutic potential

Glioblastoma (GBM) is characterized by extremely poor prognoses, despite the use of gross surgical resection, alkylating chemotherapeutic agents, and radiotherapy. Evidence increasingly highlights the role of the tumor microenvironment in enabling this aggressive phenotype. Despite this interest, the role of neurotransmitters, brain-specific messengers underlying synaptic transmission, remains murky. These signaling molecules influence a complex network of molecular pathways and cellular behaviors in many CNS-resident cells, including neural stem cells and progenitor cells, neurons, and glia cells. Critically, available data convincingly demonstrate that neurotransmitters can influence proliferation, quiescence, and differentiation status of these cells. This ability to affect progenitors and glia-GBM-initiating cells-and their availability in the CNS strongly support the notion that neurotransmitters participate in the onset and progression of GBM. This review will focus on dopamine and serotonin, as studies indicate they contribute to gliomagenesis. Particular attention will be paid to how these neurotransmitters and their receptors can be utilized as novel therapeutic targets. Overall, this review will analyze the complex biology governing the interaction of GBM with neurotransmitter signaling and highlight how this interplay shapes the aggressive nature of GBM.

A potential impact of Helicobacter pylori-related galectin-3 in neurodegeneration

Neurodegeneration represents a component of the central nervous system (CNS) diseases pathogenesis, either as a disability primary source in the frame of prototype neurodegenerative disorders, or as a secondary effect, following inflammation, hypoxia or neurotoxicity. Galectins are members of the lectin superfamily, a group of endogenous glycan-binding proteins, able to interact with glycosylated receptors expressed by several immune cell types. Glycan-lectin interactions play critical roles in the living systems by involving and mediating a variety of biologically important normal and pathological processes, including cell-cell signaling shaping cell communication, proliferation and migration, immune responses and fertilization, host-pathogen interactions and diseases such as neurodegenerative disorders and tumors. This review focuses in the role of Galectin-3 in shaping responses of the immune system against microbial agents, and concretely, Helicobacter pylori (Hp), thereby potentiating effect of the microbe in areas distant from the ordinary site of colonization, like the CNS. We hereby postulate that gastrointestinal Hp alterations in terms of immune cell functional phenotype, cytokine and chemokine secretion, may trigger systemic responses, thereby conferring implications for remote processes susceptible in immunity disequilibrium, namely, the CNS inflammation and/or neurodegeneration.

Enzymatic Synthesis of N-Acetyllactosamine (LacNAc) Type 1 Oligomers and Characterization as Multivalent Galectin Ligands

Repeats of the disaccharide unit N-acetyllactosamine (LacNAc) occur as type 1 (Galβ1, 3GlcNAc) and type 2 (Galβ1, 4GlcNAc) glycosylation motifs on glycoproteins and glycolipids. The LacNAc motif acts as binding ligand for lectins and is involved in many biological recognition events. To the best of our knowledge, we present, for the first time, the synthesis of LacNAc type 1 oligomers using recombinant β1,3-galactosyltransferase from Escherichia coli and β1,3-N-acetylglucosaminyltranferase from Helicobacter pylori. Tetrasaccharide glycans presenting LacNAc type 1 repeats or LacNAc type 1 at the reducing or non-reducing end, respectively, were conjugated to bovine serum albumin as a protein scaffold by squarate linker chemistry. The resulting multivalent LacNAc type 1 presenting neo-glycoproteins were further studied for specific binding of the tumor-associated human galectin 3 (Gal-3) and its truncated counterpart Gal-3∆ in an enzyme-linked lectin assay (ELLA). We observed a significantly increased affinity of Gal-3∆ towards the multivalent neo-glycoprotein presenting LacNAc type 1 repeating units. This is the first evidence for differences in glycan selectivity of Gal-3∆ and Gal-3 and may be further utilized for tracing Gal-3∆ during tumor progression and therapy.

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 Binding to Neo-Glycoproteins: LacDiNAc Conjugated BSA as Ligand for Human Galectin-3

Carbohydrate-lectin interactions are relatively weak. As they play an important role in biological recognition processes, multivalent glycan ligands are designed to enhance binding affinity and inhibitory potency. We here report on novel neo-glycoproteins based on bovine serum albumin as scaffold for multivalent presentation of ligands for galectins. We prepared two kinds of tetrasaccharides (N-acetyllactosamine and N,N-diacetyllactosamine terminated) by multi-step chemo-enzymatic synthesis utilizing recombinant glycosyltransferases. Subsequent conjugation of these glycans to lysine groups of bovine serum albumin via squaric acid diethyl ester yielded a set of 22 different neo-glycoproteins with tuned ligand density. The neo-glycoproteins were analyzed by biochemical and chromatographic methods proving various modification degrees. The neo-glycoproteins were used for binding and inhibition studies with human galectin-3 showing high affinity. Binding strength and inhibition potency are closely related to modification density and show binding enhancement by multivalent ligand presentation. At galectin-3 concentrations comparable to serum levels of cancer patients, we detect the highest avidities. Selectivity of N,N-diacetyllactosamine terminated structures towards galectin-3 in comparison to galectin-1 is demonstrated. Moreover, we also see strong inhibitory potency of our scaffolds towards galectin-3 binding. These novel neo-glycoproteins may therefore serve as selective and strong galectin-3 ligands in cancer related biomedical research.

Primary Central Nervous System (CNS) Lymphoma B Cell Receptors Recognize CNS Proteins

Primary lymphoma of the CNS (PCNSL) is a diffuse large B cell lymphoma confined to the CNS. To elucidate its peculiar organ tropism, we generated recombinant Abs (recAbs) identical to the BCR of 23 PCNSLs from immunocompetent patients. Although none of the recAbs showed self-reactivity upon testing with common autoantigens, they recognized 1547 proteins present on a large-scale protein microarray, indicating polyreactivity. Interestingly, proteins (GRINL1A, centaurin-α, BAIAP2) recognized by the recAbs are physiologically expressed by CNS neurons. Furthermore, 87% (20/23) of the recAbs, including all Abs derived from IGHV4-34 using PCNSL, recognized galectin-3, which was upregulated on microglia/macrophages, astrocytes, and cerebral endothelial cells upon CNS invasion by PCNSL. Thus, PCNSL Ig may recognize CNS proteins as self-Ags. Their interaction may contribute to BCR signaling with sustained NF-κB activation and, ultimately, may foster tumor cell proliferation and survival. These data may also explain, at least in part, the affinity of PCNSL cells for the CNS.

Galectin-3 up-regulation in hypoxic and nutrient deprived microenvironments promotes cell survival

Galectin-3 (gal-3) is a β-galactoside binding protein related to many tumoral aspects, e.g. angiogenesis, cell growth and motility and resistance to cell death. Evidence has shown its upregulation upon hypoxia, a common feature in solid tumors such as glioblastoma multiformes (GBM). This tumor presents a unique feature described as pseudopalisading cells, which accumulate large amounts of gal-3. Tumor cells far from hypoxic/nutrient deprived areas express little, if any gal-3. Here, we have shown that the hybrid glioma cell line, NG97ht, recapitulates GBM growth forming gal-3 positive pseudopalisades even when cells are grafted subcutaneously in nude mice. In vitro experiments were performed exposing these cells to conditions mimicking tumor areas that display oxygen and nutrient deprivation. Results indicated that gal-3 transcription under hypoxic conditions requires previous protein synthesis and is triggered in a HIF-1α and NF-κB dependent manner. In addition, a significant proportion of cells die only when exposed simultaneously to hypoxia and nutrient deprivation and demonstrate ROS induction. Inhibition of gal-3 expression using siRNA led to protein knockdown followed by a 1.7–2.2 fold increase in cell death. Similar results were also found in a human GBM cell line, T98G. In vivo, U87MG gal-3 knockdown cells inoculated subcutaneously in nude mice demonstrated decreased tumor growth and increased time for tumor engraftment. These results indicate that gal-3 protected cells from cell death under hypoxia and nutrient deprivation in vitro and that gal-3 is a key factor in tumor growth and engraftment in hypoxic and nutrient-deprived microenvironments. Overexpression of gal-3, thus, is part of an adaptive program leading to tumor cell survival under these stressing conditions.