Alteration of the sialylation pattern and memory deficits by injection of Aβ(25-35) into the hippocampus of rats

Galectin-9 and Tim-3 are upregulated in response to microglial activation induced by the peptide Amyloid-β (25-35)

Galectins are a group of β-galactoside-binding lectins associated with regulating immunological response. In the brains of AD patients and 5xFAD (familial AD) mice, galectin-3 (Gal-3) was highly upregulated and found to be expressed in microglia associated with Aβ plaques. However, the participation of other galectins, specifically galectin-9 (Gal-9) and T-cell immunoglobulin and mucin domain 3 (Tim-3) receptors, are unknown in the inflammatory response. The experimental model of the Aβ25-35 peptide will allow us to study the mechanisms of neuroinflammation and describe the changes in the expression of the Gal-9 and Tim-3 receptor. This study aimed to evaluate whether Aβ25-35 peptide administration into the lateral ventricles of rats upregulated Gal-9 and Tim-3 implicated in the modulation of neuroinflammation. The vehicle or Aβ25-35 peptide (1 μg/μL) was bilaterally administered into the lateral ventricles of the rat, and control group. After the administration of the Aβ25-35 peptide, animals were tested for learning (day 29) and spatial memory (day 30) in the novel object recognition test (NOR). On day 31, hippocampus was examined for morphological changes by Nilss stain, biochemical changes by NO2 and MDA, immunohistochemical analysis by astrocytes (GFAP), microglia (Iba1), Gal-9 and Tim-3, and western blot. Our results show the administration of the Aβ25-35 peptide into the lateral ventricles of rats induce memory impairment in the NOR by increases the oxidative stress and inflammatory response. This result is associated with an upregulation of Gal-9 and Tim-3 predominantly detected in the microglia cells of Aβ25-35-treated rats with respect to the control group. Gal-9 and Tim-3 are upregulated in activated microglia that could modulate the inflammatory response and damage in neurodegenerative processes induced by the Aβ25-35 peptide. Therefore, we suggest that Gal-9 and Tim-3 participate in the inflammatory process induced by the administration of the Aβ25-35 peptide.

Amyloid-β (25-35) induces the morphological alteration of dendritic spines and decreases NR2B and PSD-95 expression in the hippocampus

Research on the memory impairment caused by the Amyloid-β 25-35 (Aβ25-35) peptide in animal models has provided an understanding of the causes that occurs in Alzheimer's disease. However, it is uncertain whether this cognitive impairment occurs due to disruption of information encoding and consolidation or impaired retrieval of stored memory. The aim of this study was to determine the effect of the Aβ25-35 peptide on the morphology of dendritic spines and the changes in the expression of NR2B and PSD-95 in the hippocampus associated with learning and memory deficit. Vehicle or Aβ25-35 peptide (0.1 µg/µL) was bilaterally administered into the CA1 subfield of the rat hippocampus, then tested for spatial learning and memory in the Morris Water Maze. On Day 39, the morphological changes in the CA1 of the hippocampus and dentate gyrus were examined via Golgi-Cox stain. It was observed that the Aβ25-35 peptide administered in the CA1 region of the rat hippocampus induced changes to the morphology of dendritic spines and the expression of the NR2B subunit of the NMDA receptor co-localized with both the spatial memory and PSD-95 protein in the hippocampus of learning rats. We conclude that, in soluble form, the Aβ25-35 peptide perturbs synaptic plasticity, specifically in the formation of new synapses, thus promoting the progression of memory impairment.

Neuroinflammation and galectins: a key relationship in neurodegenerative diseases

Neurodegeneration is a pathological condition that is associated with the loss of neuronal function and structure. In neurodegenerative diseases, mounting evidence indicates that neuroinflammation is a common factor that contributes to neuronal damage and neurodegeneration. Neuroinflammation is characterized by the activation of microglia, the neuroimmune cells of the central nervous system (CNS), which have been implicated as active contributors to neuronal damage. Glycan structure modification is defining the outcome of neuroinflammation and neuronal regeneration; moreover, the expression of galectins, a group of lectins that specifically recognize β-galactosides, has been proposed as a key factor in neuronal regeneration and modulation of the inflammatory response. Of the different galectins identified, galectin-1 stimulates the secretion of neurotrophic factors in astrocytes and promotes neuronal regeneration, whereas galectin-3 induces the proliferation of microglial cells and modulates cell apoptosis. Galectin-8 emerged as a neuroprotective factor, which, in addition to its immunosuppressive function, could generate a neuroprotective environment in the brain. This review describes the role of galectins in the activation and modulation of astrocytes and microglia and their anti- and proinflammatory functions within the context of neuroinflammation. Furthermore, it discusses the potential use of galectins as a therapeutic target for the inflammatory response and remodeling in damaged tissues in the central nervous system.

Correlation between Sialylation Status and Cell Susceptibility to Amyloid Toxicity

The interaction between the cell membrane and misfolded protein species plays a crucial role in the development of neurodegeneration. This study was designed to clarify the relationship between plasma membrane composition in terms of the differently linked sialic acid (Sia) content and cell susceptibility to toxic and misfolded Aβ-42 peptides. The sialylation status in different cell lines was investigated by lectin histochemistry and confocal immunofluorescence and then correlated with the different propensities to bind amyloid fibrils and with the relative cell susceptibility to amyloid damage. This study reveals that expressions of Sias α2,3 and α2,6 linked to galactose/N-acetyl-galactosamine, and PolySia are positively correlated with Aβ-42-induced cell toxicity. PolySia shows an early strong interaction with amyloid fibrils, favoring their binding to GM1 ganglioside containing α2,3 galactose-linked Sia and a loss of cell viability. Our findings demonstrate that cell lines with a prevailing plastic neuron-like phenotype and high monoSia and PolySia contents are highly susceptible to amyloid Aβ-42 toxicity. This toxicity may involve a change in neuron metabolism and promote a compensative/protective increase in PolySia, which, in turn, could favor amyloid binding to GM1, thus exacerbating cell dysmetabolism and further amyloid aggregation.

The O-Glycome of Human Nigrostriatal Tissue and Its Alteration in Parkinson's Disease

O-Glycosylation changes in misfolded proteins are of particular interest in understanding neurodegenerative conditions such as Parkinson's disease (PD) and incidental Lewy body disease (ILBD). This work outlines optimizations of a microwave-assisted nonreductive release to limit glycan degradation and employs this methodology to analyze O-glycosylation on the human striatum and substantia nigra tissue in PD, ILBD, and healthy controls, working alongside well-established reductive release approaches. A total of 70 O-glycans were identified, with ILBD presenting significantly decreased levels of mannose-core (p = 0.017) and glucuronylated structures (p = 0.039) in the striatum and PD presenting an increase in sialylation (p < 0.001) and a decrease in sulfation (p = 0.001). Significant increases in sialylation (p = 0.038) in PD were also observed in the substantia nigra. This is the first study to profile the whole nigrostriatal O-glycome in healthy, PD, and ILBD tissues, outlining disease biomarkers alongside benefits of employing orthogonal techniques for O-glycan analysis.

The significance of sialylation on the pathogenesis of Alzheimer's disease

Sialylation, one of the most common and complex modes of glycosylation, corresponds with the development of the infant brain and nervous system. The most prevalent neurodegenerative disease is Alzheimer's disease (AD), which is mainly characterized by cognitive decline and behavioral disorders. However, the relationship between sialylation and AD occurrence is poorly understood. In this article, we reviewed the role of sialylation on the occurrence and development of AD, then discussed the value of sialylation modification for AD diagnosis and treatment.

Sialometabolism in Brain Health and Alzheimer's Disease

Sialic acids refer to a unique family of acidic sugars with a 9-carbon backbone that are mostly found as terminal residues in glycan structures of glycoconjugates including both glycoproteins and glycolipids. The highest levels of sialic acids are expressed in the brain where they regulate neuronal sprouting and plasticity, axon myelination and myelin stability, as well as remodeling of mature neuronal connections. Moreover, sialic acids are the sole ligands for microglial Siglecs (sialic acid-binding immunoglobulin-type lectins), and sialic acid-Siglec interactions have been indicated to play a critical role in the regulation of microglial homeostasis in a healthy brain. The recent discovery of CD33, a microglial Siglec, as a novel genetic risk factor for late-onset Alzheimer's disease (AD), highlights the potential role of sialic acids in the development of microglial dysfunction and neuroinflammation in AD. Apart from microglia, sialic acids have been found to be involved in several other major changes associated with AD. Elevated levels of serum sialic acids have been reported in AD patients. Alterations in ganglioside (major sialic acid carrier) metabolism have been demonstrated as an aggravating factor in the formation of amyloid pathology in AD. Polysialic acids are linear homopolymers of sialic acids and have been implicated to be an important regulator of neurogenesis that contributes to neuronal repair and recovery from neurodegeneration such as in AD. In summary, this article reviews current understanding of neural functions of sialic acids and alterations of sialometabolism in aging and AD brains. Furthermore, we discuss the possibility of looking at sialic acids as a promising novel therapeutic target for AD intervention.

PSA mimetic 5-nonyloxytryptamine protects cerebellar neurons against glutamate induced excitotoxicity: An in vitro perspective

PSA-NCAM is a molecule of therapeutic interest for its key role in promoting neuritogenesis and synaptic plasticity. The current study was aimed to investigate the neuroregenerative potential of 5-nonyloxytryptamine (5-NOT) as PSA mimetic compound against glutamate induced excitotoxicity. 2D and 3D cultures of cerebellar neurons challenged with glutamate were used to ascertain the effect of 5-NOT on neurite outgrowth, migration and expression of neuronal plasticity markers. Glutamate excitotoxicity is one of the major underlying pathological factor responsible for neurodegeneration in various neurological disorders such as trauma, stroke, ischemia, epilepsy and neurodegenerative diseases.5-NOT treatment was observed to promote axonal growth and defasiculation in glutamate challenged neurons as well as promoted the migration of cerebellar neurons in both wound scratched area and cerebellar explant cultures. Further, 5-NOT treatment upregulated the expression of synaptic plasticity and cell survival pathway proteins which showed reduced expression after glutamate induced excitotoxicity. Thus, this preliminary data reveals thatPSA-mimetic,5-NOT may prove to be a potential neuroprotective candidate for neurodegenerative diseases.

The therapeutic potential of galectin-1 and galectin-3 in the treatment of neurodegenerative diseases

Introduction: Neuroinflammation has been proposed as a common factor and one of the main inducers of neuronal degeneration. Galectins are a group of β-galactoside-binding lectins, that play an important role in the immune response, adhesion, proliferation, differentiation, migration and cell growth. Up to 15 members of the galectin's family have been identified; however, the expression of galectin-1 and galectin-3 has been considered a key factor in neuronal regeneration and modulation of the inflammatory response. Galectin-1 is necessary to stimulate the secretion of neurotrophic factors in astrocytes and promoting neuronal regeneration. In contrast, galectin-3 fosters the proliferation of microglial cells and modulates cellular apoptosis, therefore these proteins are considered a useful alternative for the treatment of degenerative diseases.Areas covered: This review describes the roles of galectin-1 and galectin-3 in the modulation of neuroinflammation and their potential as therapeutic targets in the treatment for neurodegenerative diseases.Expert opinion: Although data in the literature vary, the effects of galectin-1 and galectin-3 on the activation and modulation of astrocytes and microglia has been described. Due to its anti-inflammatory effects, galectin-1 is proposed as a molecule with therapeutic potential, whereas the inhibition of galectin-3 could contribute to reduce the neuroinflammatory response in neurodegenerative diseases.

Glycan changes in the olfactory mucosa of rats with experimental autoimmune encephalomyelitis

Glycans are components of glycoconjugates and function in odorant recognition and cell signaling in the olfactory mucosa. However, little is known about glycan expression in the olfactory mucosa in the presence of neuroinflammatory disorders, which can influence olfaction. We evaluated the changes in glycan in the olfactory mucosa of rats with experimental autoimmune encephalomyelitis (EAE) by histochemical analyses of 21 lectins. In the olfactory mucosa of normal control rats, 16 lectins bound to olfactory sensory neurons, supporting cells, basal cells, nerve and Bowman's glands, and their expression did not significantly change during the course of EAE. In rats with paralytic-stage EAE, five lectins showed different reactivities with the olfactory mucosa compared to those of normal control rats. Of them, Bandeiraea simplicifolia lectin (BSL)-II and BSL-I showed transiently downregulated binding to olfactory sensory neurons and supporting cells in rats with EAE. The reactivities of Lens culinaris agglutinin for the basement membrane, Vicia villosa agglutinin for Bowman's glands and Dolichos biflorus agglutinin for all nuclei were upregulated in the olfactory mucosa of EAE rats. These results suggest that BSL-II-binding N-acetyl-glucosamine and BSL-I-binding N-acetyl-galactose are involved in transient olfactory dysfunction in EAE, which may hamper odor perception and/or signal processing in olfactory sensory neurons.

Goat milk attenuates mimetic aging related memory impairment via suppressing brain oxidative stress, neurodegeneration and modulating neurotrophic factors in D-galactose-induced aging model

One of the most significant hallmarks of aging is cognitive decline. D-galactose administration may impair memory and mimic the effects of natural aging. In this study, the efficiency of goat milk to protect against memory decline was tested. Fifty-two male Sprague-Dawley rats were randomly divided into four groups: (i) control group, (ii) goat milk treated group, (iii) D-galactose treated group, and (iv) goat milk plus D-galactose treated group. Subcutaneous injections of D-galactose at 120 mg/kg and oral administrations of goat milk at 1 g/kg were chosen for the study. Goat milk and D-galactose were administered concomitantly for 6 weeks, while the control group received saline. After 6 weeks, novel object recognition and T-maze tests were performed to evaluate memory of rats. Following behavioral tests, the animals were sacrificed, and right brain homogenates were analyzed for levels of lipid peroxidation, antioxidant enzymes and neurotrophic factors. The left brain hemisphere was used for histological study of prefrontal cortex and hippocampus. There was a significant memory impairment, an increase in oxidative stress and neurodegeneration and a reduction in antioxidant enzymes and neurotrophic factors levels in the brain of D-galactose treated rats compared to controls. Goat milk treatment attenuated memory impairment induced by D-galactose via suppressing oxidative stress and neuronal damage and increasing neurotrophic factors levels, thereby suggesting its potential role as a geroprotective food.

The Acute Activation of the CB1 Receptor in the Hippocampus Decreases Neurotoxicity and Prevents Spatial Memory Impairment in Rats Lesioned with β-Amyloid 25-35

Given their anti-inflammatory properties, cannabinoids have been shown to be neuroprotective agents and to reduce excitotoxicity, through the activation of the Cannabinoid receptor type 1 (CB1r). These properties have led to CB1r being proposed as pharmacological targets for the treatment of various neurodegenerative diseases. Amyloid-β 25-35 (Aβ_25-35) induces the expression of inducible nitric oxide synthase (iNOS) and increases nitric oxide (NO●) levels. It has been observed that increased NO● concentrations trigger biochemical pathways that contribute to neuronal death and cognitive damage. This study aimed to evaluate the neuroprotective effect of an acute activation of CB1r on spatial memory and its impact on iNOS protein expression, NO● levels, gliosis and the neurodegenerative process induced by the injection of Aβ_(25-35) into the CA1 subfield of the hippocampus. ACEA [1 μM/1 μL] and Aβ_(25-35) [100 μM/1 μL] and their respective vehicle groups were injected into the CA1 subfield of the hippocampus. The animals were tested for spatial learning and memory in the eight-arm radial maze, with the results revealing that the administration of ACEA plus Aβ_(25-35) improves learning and memory processes, in contrast with the Aβ_(25-35) group. Moreover, ACEA plus Aβ_(25-35) prevented both the increase in iNOS protein and NO● levels and the reactive gliosis induced by Aβ_(25-35). Importantly, neurodegeneration was significantly reduced by the administration of ACEA plus Aβ_(25-35) in the CA1 subfield of the hippocampus. The data obtained in the present research suggest that the acute early activation of CB1r is crucial for neuroprotection.

Neuroinflammation induced by the peptide amyloid-β (25-35) increase the presence of galectin-3 in astrocytes and microglia and impairs spatial memory

Galectins are animal lectins that bind to β-galactosides, such as lactose and N-acetyllactosamine, contained in glycoproteins or glycolipids. Galectin-1 (Gal-1) and Galectin-3 (Gal-3) are involved in pathologies associated with the inflammatory process, cell proliferation, adhesion, migration, and apoptosis. Recent evidence has shown that the administration of Amyloid-β 25-35 (Aβ_25-35) into the hippocampus of rats increases the inflammatory response that is associated with memory impairment and neurodegeneration. Galectins could participate in the modulation of the neuroinflammation induced by the Aβ_25-35. The aim of this study was to evaluate the presence of Gal-1 and Gal-3 in the neuroinflammation induced by administration of Aβ_25-35 into the hippocampus and to examine spatial memory in the Morris water maze. After the administration of Aβ_25-35, animals were tested for learning and spatial memory in the Morris water maze. Behavioral performance showed that Aβ_25-35 didn't affect spatial learning but did impair memory, with animals taking longer to find the platform. On the day 32, hippocampus was examined for astrocytes (GFAP), microglia (Iba1), Gal-1 and Gal-3 via immunohistochemical analysis, and the cytokines IL-1β, TNF-α, IFN-γ by ELISA. This study's results showed a significant increase in the expression of Gal-3 in the microglia and astrocytes, while Gal-1 didn't increase in the dorsal hippocampus. The expression of galectins is associated with increased cytokines in the hippocampal formation of Aβ_25-35 treated rats. These findings suggest that Gal-3 could participate in the inflammation induced by administration of Aβ_25-35 and could be involved in the neurodegeneration progress and memory impairment.

Sialic Acids in Neurology

Sialic acid (Sia) is involved in many biological activities and commonly occurs as a monosialyl residue at the nonreducing terminal end of glycoconjugates. The loss of activity of UDP-GlcNAc2-epimerase/ManNAc kinase, which is a key enzyme in Sia biosynthesis, is lethal to the embryo, which clearly indicates the importance of Sia in embryogenesis. Occasionally, oligo/polymeric Sia structures such as disialic acid (diSia), oligosialic acid (oligoSia), and polysialic acid (polySia) occur in glycoconjugates. In particular, polySia, a well-known epitope that commonly occurs in neuroinvasive bacteria and vertebrate brains, is one of the most well-known and biologically/neurologically important glycotopes in vertebrates. The biological effects of polySia, especially on neural cell-adhesion molecules, have been well studied, and in-depth knowledge regarding polySia has been accumulated. In addition, the importance of diSia and oligoSia epitopes has been reported. In this chapter, the recent advances in the study of diSia, oligoSia, and polySia residues in glycoproteins in neurology, and their history, definition, occurrence, analytical methods, biosynthesis, and biological functions evaluated by phenotypes of gene-targeted mice, biochemical features, and related diseases are described.

Mental disorders and an acidic glycan-from the perspective of polysialic acid (PSA/polySia) and the synthesizing enzyme, ST8SIA2

Mental disorders, such as schizophrenia, bipolar disorder, and autism spectrum disorder, are challenging to manage, worldwide. Understanding the molecular mechanisms underlying these disorders is essential and required. Studies investigating such molecular mechanisms are well performed and important findings are accumulating apace. Based on the fact that these disorders are due in part to the accumulation of genetic and environmental risk factors, consideration of multi-molecular and/or multi-system dependent phenomena might be important. Acidic glycans are an attractive family of molecules for understanding these disorders, because impairment of the fine-tuned glycan system affects a large number of molecules that are deeply involved in normal brain function. One of the candidates of this important family of glycan epitopes in the brain is polysialic acid (PSA/polySia). PSA is a well-known molecule because of its role as an oncodevelopmental antigen and is also widely used as a marker of adult neurogenesis. Recently, several reports have suggested that PSA and PSA-related genes are associated with multiple mental disorders. The relationships among PSA, PSA-related genes, and mental disorders are reviewed here.

Neurogenesis and morphological-neural alterations closely related to amyloid β-peptide (25-35)-induced memory impairment in male rats

Memory impairment by the Amyloid-β 25-35 (Aβ_25-35) peptide in animal models has provided an understanding of the causes behind the similar deterioration that occurs in Alzheimer's disease. However, it is uncertain if a decrease of dendritic spines and neurogenesis conduces to cognitive impairment by an impairment in the retrieval of stored memory. The aim of this study was to evaluate the consequences of impairment on spatial memory caused by the administration of the Aβ_25-35 peptide in the hippocampus, which is associated whit morphological changes and neurogenesis in the dentate gyrus (DG). The vehicle or Aβ_25-35 peptide (0.1μg/μL) were bilaterally administered in the CA1 subfield of the rat hippocampus. The animals were tested for spatial learning and memory in the Morris Water Maze. In the day's 11, 18 and 32 after administration of the Aβ_25-35 peptide were examined the morphological changes in the DG using a Golgi-Cox stain. In the day 32, the neurogenesis was evaluated by the immunoreactivity to 5-bromo-2'-deoxyuridine (BrdU; 100mg/kg, i.p.) that corresponding to cellular proliferation post damage, the neuronal specific nuclear protein (NeuN) and doublecortin (DCX). This study found a memory retrieval impairment occurring at day 17, a cognitive deficit which had increased significantly at day 31 after the administration of Aβ_25-35 peptide. These results are related to morphological changes in the granular cells of the DG, such as a shorter dendritic length and a decrease in the number of dendritic spines. In neurogenesis, the total number of cells positive to BrdU, NeuN and DCX in the hippocampal granule cell layer was found to have declined in animals treated with Aβ_25-35. The results suggest that the Aβ_25-35 peptide impairs memory retrieval by decreasing the number of dendritic spines and altering neurogenesis in the DG.

Neuroinflammation induced by amyloid β25-35 modifies mucin-type O-glycosylation in the rat's hippocampus

Amyloid-β (Aβ) plays a relevant role in the neurodegenerative process of Alzheimer's disease (AD). The 25-35 peptide of amyloid-β (Aβ25-35) induces the inflammatory response in brain experimental models. Mucin-type O-glycosylation has been associated with inflammation of brain tissues in AD, thus in this work, we aimed at identifying changes in the glycosylation profile generated by the injection of Aβ25-35 into the CA1 of the hippocampus of rats, using histochemistry with lectins. Our results indicate that 100μM Aβ25-35 induce increased recognition of the Amaranthus leucocarpus lectin (ALL) (specific for Galβ1,3-GalNAcα1,0-Ser/Thr); whereas concanavalin A (Con A) (specific for α-Man) showed no differences among treated and control groups of rats. Jacalin and peanut agglutinin (Galβ1,3GalNAcα1,0-Ser/Thr) showed no recognition of brain cells of control or treated rats. After 6-h treatment of the tissue with trypsin or with 200mM GalNAc, the interaction with ALL was inhibited. Immunohistochemistry showed positive anti-NeuN and ALL-recognition of neurons; however, anti-GFAP and anti-CD11b showed no co-localization with ALL. The ALL+ neurons revealed the presence of cytochrome C in the cytosol and active caspase 3 in the cytosol and nucleus. Administration of the interleukin-1 receptor antagonist (IL-1RA) to Aβ25-35-treated rats diminished neuroinflammation and ALL recognition. These results suggest a close relationship among over-expression of mucin-type O-glycosylation, the neuroinflammatory process, and neuronal death.