Galectin-3 expression is correlated with abnormal prion protein accumulation in murine scrapie

Increased Gal-3 Mediates Microglia Activation and Neuroinflammation via the TREM2 Signaling Pathway in Prion Infection

Galectin 3 (Gal-3) is one of the major elements for activating microglia and mediating neuroinflammation in some types of neurodegenerative diseases. However, its role in the pathogenesis of prion disease is seldom addressed. In this study, markedly increased brain Gal-3 was identified in three scrapie-infected rodent models at the terminal stage. The increased Gal-3 was mainly colocalized with the activated microglia. Coincidental with the increased brain Gal-3 in prion-infected animals, the expression of brain trigger receptor expressed in myeloid cell 2 (TREM2), one of the Gal-3 receptors, and some components in the downstream pathway also significantly increased, whereas Toll-like receptor 4 (TLR4), another Gal-3 receptor, and the main components in its downstream signaling were less changed. The increased Gal-3 signals were distributed at the areas with PrPSc deposit but looked not to colocalize directly with PrPSc/PrP signals. Similar changing profiles of Gal-3, the receptors TREM2 and TLR4, as well as the proteins in the downstream pathways were also observed in prion-infected cell line SMB-S15. Removal of PrPSc replication in SMB-S15 cells reversed the upregulation of cellular Gal-3, TREM2, and the relevant proteins. Moreover, we presented data for interactions of Gal-3 with TREM2 and with TLR4 morphologically and molecularly in the cultured cells. Stimulation of prion-infected cells or their normal partner cells with recombinant mouse Gal-3 in vitro induced obvious responses for activation of TREM2 signaling and TLR4 signaling. Our data here strongly indicate that prion infection or PrPSc deposit induces remarkably upregulated brain Gal-3, which is actively involved in the microglia activation and neuroinflammation mainly via TREM2 signaling.

Galectins and Their Ligand Glycoconjugates in the Central Nervous System Under Physiological and Pathological Conditions

Galectins are β-galactoside-binding lectins consisting of 15 members in mammals. Galectin-1,-3,-4,-8, and -9 are predominantly expressed in the central nervous system (CNS) and regulate various physiological and pathological events. This review summarizes the current knowledge of the cellular expression and role of galectins in the CNS, and discusses their functions in neurite outgrowth, myelination, and neural stem/progenitor cell niches, as well as in ischemic/hypoxic/traumatic injuries and neurodegenerative diseases such as multiple sclerosis. Galectins are expressed in both neurons and glial cells. Galectin-1 is mainly expressed in motoneurons, whereas galectin-3-positive neurons are broadly distributed throughout the brain, especially in the hypothalamus, indicating its function in the regulation of homeostasis, stress response, and the endocrine/autonomic system. Astrocytes predominantly contain galectin-1, and galectin-3 and−9 are upregulated along with its activation. Activated, but not resting, microglia contain galectin-3, supporting its phagocytic activity. Galectin-1,−3, and -4 are characteristically expressed during oligodendrocyte differentiation. Galectin-3 from microglia promotes oligodendrocyte differentiation and myelination, while galectin-1 and axonal galectin-4 suppress its differentiation and myelination. Galectin-1- and- 3-positive cells are involved in neural stem cell niche formation in the subventricular zone and hippocampal dentate gyrus, and the migration of newly generated neurons and glial cells to the olfactory bulb or damaged lesions. In neurodegenerative diseases, galectin-1,-8, and -9 have neuroprotective and anti-inflammatory activities. Galectin-3 facilitates pro-inflammatory action; however, it also plays an important role during the recovery period. Several ligand glycoconjugates have been identified so far such as laminin, integrins, neural cell adhesion molecule L1, sulfatide, neuropilin-1/plexinA4 receptor complex, triggering receptor on myeloid cells 2, and T cell immunoglobulin and mucin domain. N-glycan branching on lymphocytes and oligodendroglial progenitors mediated by β1,6-N-acetylglucosaminyltransferase V (Mgat5/GnTV) influences galectin-binding, modulating inflammatory responses and remyelination in neurodegenerative diseases. De-sulfated galactosaminoglycans such as keratan sulfate are potential ligands for galectins, especially galectin-3, regulating neural regeneration. Galectins have multitudinous functions depending on cell type and context as well as post-translational modifications, including oxidization, phosphorylation, S-nitrosylation, and cleavage, but there should be certain rules in the expression patterns of galectins and their ligand glycoconjugates, possibly related to glucose metabolism in cells.

Serum galectin-3 levels are decreased in schizophrenia

Objective:

To determine whether changes in serum galectin-3 (gal-3) concentrations in schizophrenia patients have etiopathogenetic importance. Since very little research has assessed the connection between galectins and schizophrenia, we wanted to examine alterations in the inflammatory marker gal-3 in schizophrenia and investigate possible correlations between clinical symptomatology and serum concentrations.

Methods:

Forty-eight schizophrenia patients and 44 healthy controls were included in this study. The Scale for the Assessment of Positive Symptoms (SAPS) and the Scale for the Assessment of Negative Symptoms (SANS) were administered to determine symptom severity. Venous blood samples were collected, and serum gal-3 levels were measured.

Results:

Mean serum gal-3 levels were significantly lower in schizophrenia patients, and there were no significant differences in age or sex with the control group. There was also a significant positive correlation between serum gal-3 concentrations and negative schizophrenia symptoms according to the SANS.

Conclusion:

The results indicate that gal-3 is decreased in schizophrenia patients, which could contribute to inflammation in the pathogenesis of schizophrenia.

The role of galectin-3 in modulation of anxiety state level in mice

Galectin-3 (Gal-3), a member of lectin family that binds to oligosaccharides, is involved in several biological processes, including maturation and function of nervous system. It had been reported that Gal-3 regulates oligodendrocytes differentiation and that Gal-3/Toll-like receptor-4 (TLR4) axis is involved in neuroinflammation. As both, central nervous system (CNS) maturation and neuroinflammation may affect behavior, the principle aim of this study was to examine the effects of Gal-3 gene deletion on behavior. Here we provide the evidence that Gal-3 deficiency shows clear anxiogenic effect in mature untreated animals (basal conditions). This was accompanied with lower interleukin-6 (IL-6) and tumor necrosis factor-α (TNF-α) relative gene expression and hippocampal content, with no effect on TLR4 expression. Gal-3 deficiency was also accompanied with lower brain-derived neurotrophic factor (BDNF) relative gene expression and immunoreactivity in hippocampus (predominantly in CA1 region). Besides, the Gal-3 gene deletion resulted in attenuation of the hippocampal relative gene expression of GABA-A receptor subunits 2 and 5 (GABA-AR2S and GABA-AR5S), On the other hand, Gal-3 deficiency attenuates LPS-induced neuroinflammation. The anxiogenic effect of acute neuroinflammation was accompanied with increased hippocampal IL-6, TNF-α and TLR4 gene expression, as well as decreased gene and immunohistochemical BDNF expression in hippocampus, with significant decline in GABA-AR2S in wild type (WT) mice in comparison to basal conditions. Gal-3 gene deletion prevented the increase in IL-6, the decline in BDNF gene expression and immunoreactivity, and reduction in hippocampal GABA-AR2S, and therefore attenuated the anxiogenic effect of neuroinflammation. In summary, our data demonstrate that apparently opposite effects of Gal-3 deficiency on anxiety levels (anxiogenic effect under basal conditions and anxiolytic action during neuroinflammation) seem to be related to the shift in IL-6, TNF-α and hippocampal BDNF.

Galectin-3-Mediated Glial Crosstalk Drives Oligodendrocyte Differentiation and (Re)myelination

Galectin-3 (Gal-3) is the only chimeric protein in the galectin family. Gal-3 structure comprises unusual tandem repeats of proline and glycine-rich short stretches bound to a carbohydrate-recognition domain (CRD). The present review summarizes Gal-3 functions in the extracellular and intracellular space, its regulation and its internalization and secretion, with a focus on the current knowledge of Gal-3 role in central nervous system (CNS) health and disease, particularly oligodendrocyte (OLG) differentiation, myelination and remyelination in experimental models of multiple sclerosis (MS). During myelination, microglia-expressed Gal-3 promotes OLG differentiation by binding glycoconjugates present only on the cell surface of OLG precursor cells (OPC). During remyelination, microglia-expressed Gal-3 favors an M2 microglial phenotype, hence fostering myelin debris phagocytosis through TREM-2b phagocytic receptor and OLG differentiation. Gal-3 is necessary for myelin integrity and function, as evidenced by myelin ultrastructural and behavioral studies from LGALS3^-/- mice. Mechanistically, Gal-3 enhances actin assembly and reduces Erk 1/2 activation, leading to early OLG branching. Gal-3 later induces Akt activation and increases MBP expression, promoting gelsolin release and actin disassembly and thus regulating OLG final differentiation. Altogether, findings indicate that Gal-3 mediates the glial crosstalk driving OLG differentiation and (re)myelination and may be regarded as a target in the design of future therapies for a variety of demyelinating diseases.

Investigation of Gal-3 Expression Pattern in Serum and Cerebrospinal Fluid of Patients Suffering From Neurodegenerative Disorders

We performed this study to investigate the possibility of a definitive pattern of Galectin-3 (Gal-3) expression in the cerebrospinal fluid (CSF) and serum of Alzheimer’s disease (AD) and Amyotrophic Lateral Sclerosis (ALS) patients. In our study, we collected the CSF and serum samples of 31 AD patients, 19 ALS patients and 50 normal healthy subjects (controls). Quantitative ELISA measured Gal-3 concentrations in CSF and serum samples. A comparative analysis was performed to analyze and understand the Gal-3 expression pattern. A number of neuropsychological assessments and statistical analyses were carried out to validate our findings. Recent researches have established the role of galectins in various neurodegenerative disorders (NDDs), but a definitive pattern of galectin expression is still elusive. A significant difference was observed in serum and CSF Gal-3 concentrations between AD patients and healthy controls. The difference in serum and CSF Gal-3 concentrations between ALS patients vs. controls was lesser as compared to AD patients vs. controls. The difference in serum and CSF Gal-3 concentrations of AD vs. ALS patients was not significant. The MMSE score and serum and CSF Gal-3 concentrations in AD and ALS patients, and controls exhibited a significant positive correlation. The findings of the present study are expected to provide an insight into the definitive pattern of Gal-3 expression in AD and ALS patients, and might thus establish Gal-3 as a strong biomarker. This in turn will open up new and promising research avenues targeting the expression of galectins to modulate the progression of NDDs, and pave the way for novel therapeutic options.

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.

Sialylation Controls Prion Fate in Vivo

Prions or PrPSc are proteinaceous infectious agents that consist of misfolded, self-replicating states of a sialoglycoprotein called the prion protein or PrPC The current work tests a new hypothesis that sialylation determines the fate of prions in an organism. To begin, we produced control PrPSc from PrPC using protein misfolding cyclic amplification with beads (PMCAb), and also generated PrPSc with reduced sialylation levels using the same method but with partially desialylated PrPC as a substrate (dsPMCAb). Syrian hamsters were inoculated intraperitoneally with brain-derived PrPSc or PrPSc produced in PMCAb or dsPMCAb and then monitored for disease. Animals inoculated with brain- or PMCAb-derived PrPSc developed prion disease, whereas administration of dsPMCAb-derived PrPSc with reduced sialylation did not cause prion disease. Animals inoculated with dsPMCAb-derived material were not subclinical carriers of scrapie, as no PrPSc was detected in brains or spleen of these animals by either Western blotting or after amplification by serial PMCAb. In subsequent experiments, trafficking of brain-, PMCAb-, and dsPMCAb-derived PrPSc to secondary lymphoid organs was monitored in wild type mice. PrPSc sialylation was found to be critical for effective trafficking of PrPSc to secondary lymphoid organs. By 6 hours after inoculation, brain- and PMCAb-derived PrPSc were found in spleen and lymph nodes, whereas dsPMCAb-derived PrPSc was found predominantly in liver. This study demonstrates that the outcome of prion transmission to a wild type host is determined by the sialylation status of the inoculated PrPSc Furthermore, this work suggests that the sialylation status of PrPSc plays an important role in prion lymphotropism.

Cellular Prion Protein Combined with Galectin-3 and -6 Affects the Infectivity Titer of an Endogenous Retrovirus Assayed in Hippocampal Neuronal Cells

Prion diseases are infectious and fatal neurodegenerative diseases which require the cellular prion protein, PrP^C, for development of diseases. The current study shows that the PrP^C augments infectivity and plaque formation of a mouse endogenous retrovirus, MuLV. We have established four neuronal cell lines expressing mouse PrP^C, PrP^+/+; two express wild type PrP^C (MoPrP^wild) and the other two express mutant PrP^C (MoPrP^mut). Infection of neuronal cells from various PrP^+/+ and PrP^-/- (MoPrP^KO) lines with MuLV yielded at least three times as many plaques in PrP^+/+ than in PrP^-/-. Furthermore, among the four PrP^+/+ lines, one mutant line, P101L, had at least 2.5 times as many plaques as the other three PrP^+/+ lines. Plaques in P101L were four times larger than those in other PrP^+/+ lines. Colocalization of PrP and CAgag was seen in MuLV-infected PrP^+/+ cells. In the PrP-MuLV interaction, the involvement of galectin-3 and -6 was observed by immunoprecipitation with antibody to PrP^C. These results suggest that PrP^C combined with galectin-3 and -6 can act as a receptor for MuLV. P101L, the disease form of mutant PrP^C results suggest the genetic mutant form of PrP^C may be more susceptible to viral infection.

Tissue- and cell-specific localization of galectins, β-galactose-binding animal lectins, and their potential functions in health and disease

Fifteen galectins, β-galactose-binding animal lectins, are known to be distributed throughout the body. We herein summarize current knowledge on the tissue- and cell-specific localization of galectins and their potential functions in health and disease. Galectin-3 is widely distributed in epithelia, including the simple columnar epithelium in the gut, stratified squamous epithelium in the gut and skin, and transitional epithelium and several regions in nephrons in the urinary tract. Galectin-2 and galectin-4/6 are gut-specific, while galectin-7 is found in the stratified squamous epithelium in the gut and skin. The reproductive tract mainly contains galectin-1 and galectin-3, and their expression markedly changes during the estrous/menstrual cycle. The galectin subtype expressed in the corpus luteum (CL) changes in association with luteal function. The CL of women and cows displays a "galectin switch" with coordinated changes in the major galectin subtype and its ligand glycoconjugate structure. Macrophages express galectin-3, which may be involved in phagocytotic activity. Lymphoid tissues contain galectin-3-positive macrophages, which are not always stained with the macrophage marker, F4/80. Subsets of neurons in the brain and dorsal root ganglion express galectin-1 and galectin-3, which may contribute to the regeneration of damaged axons, stem cell differentiation, and pain control. The subtype-specific contribution of galectins to implantation, fibrosis, and diabetes are also discussed. The function of galectins may differ depending on the tissues or cells in which they act. The ligand glycoconjugate structures mediated by glycosyltransferases including MGAT5, ST6GAL1, and C2GnT are important for revealing the functions of galectins in healthy and disease states.

Increases of Galectin-1 and its S-nitrosylated form in the Brain Tissues of Scrapie-Infected Rodent Models and Human Prion Diseases

Galectin-1 (Gal-1) shows neuroprotective activity in brain ischemia, spinal cord injury, and autoimmune neuroinflammation. To evaluate the Gal-1 situation in the brains of prion disease, the brain levels of Gal-1 in several scrapie-infected experimental rodent models were tested by Western blot, including agents 263K-infected hamsters, 139A-, ME7-, and S15-infected mice. Remarkable increases of brain Gal-1 were observed in all tested scrapie-infected rodents at the terminal stage. The brain levels of Gal-1 showed time-dependent increases along with the prolonging of incubation times. Immunohistochemical assays illustrated much stronger stainings in the brain sections of scrapie-infected rodents. Quantitative RT-PCR of Gal-1 gene demonstrated increased transcription in the brains of scrapie-infected mice. Gal-1 was colocalized with GFAP- and NeuN-positive cells, but not with Iba-1-positive cells in immunofluorescent test. Increases of Gal-1 were also detected in the several postmortem cortex regions of human prion diseases. Moreover, the S-nitrosylated forms of Gal-1 in the brains of scrapie-infected rodents were significantly higher than those of normal ones. Our finding here demonstrates markedly increased brain Gal-1 and S-nitrosylated Gal-1 both in scrapie-infected rodents and human prion diseases.

Elevated Galectin-3 Levels in the Serum of Patients With Alzheimer's Disease

Alzheimer's disease (AD) is a neurodegenerative disorder of the central nervous system. Galectin-3 (Gal-3) is characterized by a conserved sequence within the carbohydrate recognition domain. The effect of Gal-3 in AD is presently unknown. In this study, we found significantly increased Gal-3 serum levels in patients with AD compared to control participants (P=.017). There was no significant difference between patients with mild cognitive impairment (MCI) and healthy controls (P=.143) or between patients with AD and MCI (P=.688). The degree of cognitive impairment, as measured by the Mini-Mental Status Examination score, was found to have a significant correlation with the Gal-3 serum levels in all patients and healthy controls. These data suggest that Gal-3 potentially plays a role in the neuropathogenesis of AD. The Gal-3 found in serum could be a potential candidate for a biomarker panel for AD diagnosis.

The pleiotropic effects of galectin-3 in neuroinflammation: a review

The β-galactoside-binding lectin, galectin-3, is expressed in a variety of mammalian cells and tissues. It is involved in cell adhesion, activation, proliferation, apoptosis and cell migration. It also plays an important role in inflammation as a pro-inflammatory mediator. The involvement of galectin-3 in various inflammation models, including those of autoimmune disease, skin disease, and cancer, has been investigated extensively. Moreover, galectin-3 has been suggested to be a therapeutic target for various diseases. The present review deals with the expression of galectin-3 in central nervous system (CNS) tissues during normal development and in various models of inflammation. The available information indicates that galectin-3 is essential for normal brain development and plays diverse roles in CNS inflammation, combining pro-inflammatory roles with re-modeling capacity in damaged CNS tissues.

Galectin-3 immunohistochemistry in the vomeronasal organ of the domestic pig, Sus scrofa

The immunohistochemical localization of galectin-3, a β-galactoside-binding protein, was studied in the vomeronasal organ (VNO) of fetal, 1-day-old, and 6-month-old pigs. In all age groups, the porcine VNO consisted of vomeronasal sensory epithelium (VSE) located medially and non-sensory vomeronasal respiratory epithelium (VRE) located laterally. In the pig, the VNO epithelium increased in height with postnatal development from fetus to adult. In the VSE of all stages examined, galectin-3 immunostaining was seen in the supporting cells and free border, but not in receptor or basal cells. Galectin-3 immunostaining was seen in all layers of the VRE, and the intensity increased with postnatal development. In the lamina propria, galectin-3 was detected in some ductal epithelial cells and the vomeronasal nerve sheath, but not in the acini of the Jacobson glands in all age groups. In view of these observations, we postulate that galectin-3 plays a role in cell survival and cell adhesion in both the VSE and VRE of porcine VNO in all age groups.

Transcriptional analysis implicates endoplasmic reticulum stress in bovine spongiform encephalopathy

Bovine spongiform encephalopathy (BSE) is a fatal, transmissible, neurodegenerative disease of cattle. To date, the disease process is still poorly understood. In this study, brain tissue samples from animals naturally infected with BSE were analysed to identify differentially regulated genes using Affymetrix GeneChip Bovine Genome Arrays. A total of 230 genes were shown to be differentially regulated and many of these genes encode proteins involved in immune response, apoptosis, cell adhesion, stress response and transcription. Seventeen genes are associated with the endoplasmic reticulum (ER) and 10 of these 17 genes are involved in stress related responses including ER chaperones, Grp94 and Grp170. Western blotting analysis showed that another ER chaperone, Grp78, was up-regulated in BSE. Up-regulation of these three chaperones strongly suggests the presence of ER stress and the activation of the unfolded protein response (UPR) in BSE. The occurrence of ER stress was also supported by changes in gene expression for cytosolic proteins, such as the chaperone pair of Hsp70 and DnaJ. Many genes associated with the ubiquitin-proteasome pathway and the autophagy-lysosome system were differentially regulated, indicating that both pathways might be activated in response to ER stress. A model is presented to explain the mechanisms of prion neurotoxicity using these ER stress related responses. Clustering analysis showed that the differently regulated genes found from the naturally infected BSE cases could be used to predict the infectious status of the samples experimentally infected with BSE from the previous study and vice versa. Proof-of-principle gene expression biomarkers were found to represent BSE using 10 genes with 94% sensitivity and 87% specificity.

Strain-dependent inflammatory responsiveness of rat microglial cells

The aim of this study is to test whether inflammatory responsiveness of rat microglial cells is strain-specific in primary microglia derived from neonatal LEW/N and F344/N rats. In contrast to F344/N microglia, LEW/N microglia constitutively and upon lipopolysaccharide challenge expressed higher levels of mRNA for the majority of inflammatory mediators studied. In addition, LEW/N microglia exhibited enhanced secretion of tumor necrosis factor-alpha and CCL2, as well as elevated nitric oxide production. On the contrary, activated LEW/N microglia transcribed and secreted less interleukin-10. Hence, compared to F344/N microglia, LEW/N microglia might be more reactive to lipopolysaccharide and incompetent to suppress inflammation.

Glycosylation-related genes are variably expressed depending on the differentiation state of a bioaminergic neuronal cell line: implication for the cellular prion protein

A striking feature of the cellular prion protein (PrP(C)) is the heterogeneity of its glycoforms, whose contribution to PrP(C) function has yet to be defined. Using the 1C11 neuronal bioaminergic differentiation model and a glycomics approach, we show here a correlation between differential PrP(C) N-glycosylations in 1C11(5-HT) serotonergic and 1C11(NE) noradrenergic cells compared to their 1C11 precursor cells and a variation of the glycogenome expression status in these cells. In particular, expression of genes involved in N-glycan synthesis or in the modeling of chondroitin and heparan sulfate proteoglycans appeared to be modulated. Our results highlight that, the expression of glycosylation-related genes is regulated during bioaminergic neuronal differentiation, consistent with a participation of glycoconjugates in neuronal development and plasticity. A neuronal regulation of glycosylation processes may have direct implications on some neurospecific functions of PrP(C) and may participate in specific brain targeting of prion strains.