Effect of amyloid-Β (25-35) in hyperglycemic and hyperinsulinemic rats, effects on phosphorylation and O-GlcNAcylation of tau protein

Regulation of Tau protein phosphorylation by glucosamine-induced O-GlcNAcylation as a neuroprotective mechanism in a brain ischemia-reperfusion model

Purpose:Tau hyperphosphorylation is a modification frequently observed after brain ischemia which has been related to the aggregation of this protein, with subsequent cytoskeletal damage, and cellular toxicity. The present study tests the hypothesis of using glucosamine, an agent that increases protein O-GlcNAcylation, to decrease the levels of phosphorylation in Tau during ischemia-reperfusion.Material and methods: Transient focal ischemia was artificially induced in male Wistar rats by occlusion of the middle cerebral artery (MCAO) with an intraluminal monofilament. A single dose of intraperitoneal glucosamine of 200 mg/kg diluted in normal saline (SSN) was administered 60 min before ischemia. Histological brain sections were processed using indirect immunofluorescence with primary antibodies (anti-O-GlcNAc and anti pTau-ser 396). The Image J software was used to calculate the immunofluorescence signal intensity.Results: The phosphorylation of Tau at the serine residue 396 had a significant decrease with the administration of glucosamine during ischemia-reperfusion compared with the administration of placebo.Conclusions: These results show that glucosamine can reduce the phosphorylation levels of Tau in rodents subjected to ischemia and cerebral reperfusion, which implies a neuroprotective role of glucosamine.

Implications of Glycosylation in Alzheimer's Disease

Alzheimer's disease (AD) is the most common cause of dementia, affecting millions of people worldwide, and no cure is currently available. The major pathological hallmarks of AD are considered to be amyloid beta plaques and neurofibrillary tangles, generated by respectively APP processing and Tau phosphorylation. Recent evidence imply that glycosylation of these proteins, and a number of other AD-related molecules is altered in AD, suggesting a potential implication of this process in disease pathology. In this review we summarize the understanding of glycans in AD pathogenesis, and discuss how glycobiology can contribute to early diagnosis and treatment of AD, serving as potential biomarkers and therapeutic targets. Furthermore, we look into the potential link between the emerging topic neuroinflammation and glycosylation, combining two interesting, and until recent years, understudied topics in the scope of AD. Lastly, we discuss how new model platforms such as induced pluripotent stem cells can be exploited and contribute to a better understanding of a rather unexplored area in AD.

Crucial players in Alzheimer's disease and diabetes mellitus: Friends or foes?

Alzheimer's disease (AD) and diabetes mellitus, especially type 2 (T2DM), are very common and widespread diseases in contemporary societies, and their incidence is steadily on the increase. T2DM is a multiple metabolic disorder, with several mechanisms including hyperglycaemia, insulin resistance, insulin receptor and insulin growth factor disturbances, glucose toxicity, formation of advanced glycation end products (AGEs) and the activity of their receptors. AD is the most common form of dementia, characterized by the accumulation of extracellular beta amyloid peptide aggregates and intracellular hyper-phosphorylated tau proteins, which are thought to drive and/or accelerate inflammatory and oxidative stress processes leading to neurodegeneration. The aim of this paper is to provide a comprehensive review of the evidence linking T2DM to the onset and development of AD and highlight the unknown or poorly studied "nooks and crannies" of this interesting relationship, hence providing an opportunity to stimulate new ideas for the analysis of comorbidities between AD and DM. Despite, indication of possible biomarkers of early diagnosis of T2DM and AD, this review is also an attempt to answer the question as to whether the crucial factors in the development of both conditions support the link between DM and AD.

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.

The combination of luteolin and l-theanine improved Alzheimer disease-like symptoms by potentiating hippocampal insulin signaling and decreasing neuroinflammation and norepinephrine degradation in amyloid-β-infused rats

Luteolin and l-theanine have anti-inflammatory, antioxidant, and possible antidiabetic activities, and they may synergistically protect against dementia. Here, we hypothesized that a combination of luteolin and l-theanine would synergistically act to improve memory function and glucose disturbances in rats infused with amyloid-β, and the mechanisms underlying these actions were investigated. Rats that received an amyloid-β(25-35) infusion into the CA1 region of the hippocampus were fed dextrin (AD-CON), 0.1% luteolin (AD-Lut), 0.2% l-theanine (AD-Thea), or both 0.05% luteolin and 0.1% l-theanine (AD-LuTh) in conjunction with a high-fat diet over 8 weeks. AD-LuTh improved memory function, as determined by water maze and passive avoidance tests, by potentiating the hippocampal insulin signaling and reducing inflammation: Luteolin mainly potentiated insulin signaling via the pAkt➔pGSK➔pTau pathway, and l-theanine primarily reduced tumor necrosis factor-α. In the metabolomics analysis of the hippocampus lysates, the concentration of proline, phenylpyruvic acid, and normetanephrine decreased in the AD-LuTh compared to AD-CON. Norepinephrine contents were lower in the AD-CON than non-AD rats with a high fat diet with 0.2% dextrin, whereas AD-Thea and AD-LuTh inhibited the decrease. Both the AD-Lut and AD-LuTh increased glucose infusion rates and decreased hepatic glucose output under basal and hyperinsulinemic conditions, indicating improved whole-body and hepatic insulin sensitivity. Disturbances in glucose-stimulated insulin secretion during hyperglycemic clamp were most effectively corrected by the AD-Lut and AD-LuTh treatments. In conclusion, the hypothesis of the study was accepted. The combination of luteolin and l-theanine prevented Alzheimer disease-like symptom, possibly by improving hippocampal insulin signaling, norepinephrine metabolisms, and decreasing neuroinflammation. The combination of luteolin and l-theanine may be a useful therapeutic option for preventing and/or delaying the progression of memory dysfunction.

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.