Linking Glycation and Glycosylation With Inflammation and Mitochondrial Dysfunction in Parkinson's Disease

The alteration and role of glycoconjugates in Alzheimer's disease

Alzheimer's disease (AD) is a prevalent neurodegenerative disorder characterized by abnormal protein deposition. With an alarming 30 million people affected worldwide, AD poses a significant public health concern. While inhibiting key enzymes such as β-site amyloid precursor protein-cleaving enzyme 1 and γ-secretase or enhancing amyloid-β clearance, has been considered the reasonable strategy for AD treatment, their efficacy has been compromised by ineffectiveness. Furthermore, our understanding of AD pathogenesis remains incomplete. Normal aging is associated with a decline in glucose uptake in the brain, a process exacerbated in patients with AD, leading to significant impairment of a critical post-translational modification: glycosylation. Glycosylation, a finely regulated mechanism of intracellular secondary protein processing, plays a pivotal role in regulating essential functions such as synaptogenesis, neurogenesis, axon guidance, as well as learning and memory within the central nervous system. Advanced glycomic analysis has unveiled that abnormal glycosylation of key AD-related proteins closely correlates with the onset and progression of the disease. In this context, we aimed to delve into the intricate role and underlying mechanisms of glycosylation in the etiopathology and pathogenesis of AD. By highlighting the potential of targeting glycosylation as a promising and alternative therapeutic avenue for managing AD, we strive to contribute to the advancement of treatment strategies for this debilitating condition.

Integrating the analysis of human biopsies using post-translational modifications proteomics

Proteome diversities and their biological functions are significantly amplified by post-translational modifications (PTMs) of proteins. Shotgun proteomics, which does not typically survey PTMs, provides an incomplete picture of the complexity of human biopsies in health and disease. Recent advances in mass spectrometry-based proteomic techniques that enrich and study PTMs are helping to uncover molecular detail from the cellular level to system-wide functions, including how the microbiome impacts human diseases. Protein heterogeneity and disease complexity are challenging factors that make it difficult to characterize and treat disease. The search for clinical biomarkers to characterize disease mechanisms and complexity related to patient diagnoses and treatment has proven challenging. Knowledge of PTMs is fundamentally lacking. Characterization of complex human samples that clarify the role of PTMs and the microbiome in human diseases will result in new discoveries. This review highlights the key role of proteomic techniques used to characterize unknown biological functions of PTMs derived from complex human biopsies. Through the integration of diverse methods used to profile PTMs, this review explores the genetic regulation of proteoforms, cells of origin expressing specific proteins, and several bioactive PTMs and their subsequent analyses by liquid chromatography and tandem mass spectrometry.

Altered expression of Sialyl Lewis X in experimental models of Parkinson's disease

The mechanisms underlying neurodegeneration in Parkinson's disease (PD) are still not fully understood. Glycosylation is an important post-translational modification that affects protein function, cell-cell contacts and inflammation and can be modified in pathologic conditions. Although the involvement of aberrant glycosylation has been proposed for PD, the knowledge of the diversity of glycans and their role in PD is still minimal. Sialyl Lewis X (sLeX) is a sialylated and fucosylated tetrasaccharide with essential roles in cell-to-cell recognition processes. Pathological conditions and pro-inflammatory mediators can up-regulate sLeX expression on cell surfaces, which has important consequences in intracellular signalling and immune function. Here, we investigated the expression of this glycan using in vivo and in vitro models of PD. We show the activation of deleterious glycation-related pathways in mouse striatum upon treatment with 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP), a toxin-based model of PD. Importantly, our results show that MPTP triggers the presentation of more proteins decorated with sLeX in mouse cortex and striatum in a time-dependent manner, as well as increased mRNA expression of its rate-limiting enzyme fucosyltransferase 7. sLeX is expressed in neurons, including dopaminergic neurons, and microglia. Although the underlying mechanism that drives increased sLeX epitopes, the nature of the protein scaffolds and their functional importance in PD remain unknown, our data suggest for the first time that sLeX in the brain may have a role in neuronal signalling and immunomodulation in pathological conditions. KEY MESSAGES: MPTP triggers the presentation of proteins decorated with sLeX in mouse brain. MPTP triggers the expression of sLeX rate-limiting enzyme FUT 7 in striatum. sLeX is expressed in neurons, including dopaminergic neurons, and microglia. sLeX in the brain may have a role in neuronal signalling and immunomodulation.

Triaging between post-translational modification of cell cycle regulators and their therapeutics in neurodegenerative diseases

Neurodegenerative diseases, such as Alzheimer's disease, Parkinson's disease, and Huntington's disease, present challenges in healthcare because of their complicated etiologies and absence of healing remedies. Lately, the emerging role of post-translational modifications (PTMs), in the context of cell cycle regulators, has garnered big interest as a potential avenue for therapeutic intervention. The review explores the problematic panorama of PTMs on cell cycle regulators and their implications in neurodegenerative diseases. We delve into the dynamic phosphorylation, acetylation, ubiquitination, SUMOylation, Glycation, and Neddylation that modulate the key cell cycle regulators, consisting of cyclins, cyclin-dependent kinases (CDKs), and their inhibitors. The dysregulation of these PTMs is related to aberrant cell cycle in neurons, which is one of the factors involved in neurodegenerative pathologies. Moreover, the effect of exogenous activation of CDKs and CDK inhibitors through PTMs on the signaling cascade was studied in postmitotic conditions of NDDs. Furthermore, the therapeutic implications of CDK inhibitors and associated alteration in PTMs were discussed. Lastly, we explored the putative mechanism of PTMs to restore normal neuronal function that might reverse NDDs.

Communal interaction of glycation and gut microbes in diabetes mellitus, Alzheimer's disease, and Parkinson's disease pathogenesis

Diabetes and its complications, Alzheimer's disease (AD), and Parkinson's disease (PD) are increasing gradually, reflecting a global threat vis-à-vis expressing the essentiality of a substantial paradigm shift in research and remedial actions. Protein glycation is influenced by several factors, like time, temperature, pH, metal ions, and the half-life of the protein. Surprisingly, most proteins associated with metabolic and neurodegenerative disorders are generally long-lived and hence susceptible to glycation. Remarkably, proteins linked with diabetes, AD, and PD share this characteristic. This modulates protein's structure, aggregation tendency, and toxicity, highlighting renovated attention. Gut microbes and microbial metabolites marked their importance in human health and diseases. Though many scientific shreds of evidence are proposed for possible change and dysbiosis in gut flora in these diseases, very little is known about the mechanisms. Screening and unfolding their functionality in metabolic and neurodegenerative disorders is essential in hunting the gut treasure. Therefore, it is imperative to evaluate the role of glycation as a common link in diabetes and neurodegenerative diseases, which helps to clarify if modulation of nonenzymatic glycation may act as a beneficial therapeutic strategy and gut microbes/metabolites may answer some of the crucial questions. This review briefly emphasizes the common functional attributes of glycation and gut microbes, the possible linkages, and discusses current treatment options and therapeutic challenges.

A pathological convergence theory for non-communicable diseases

The current paradigm considers the study of non-communicable diseases (NCDs), which are the main causes of mortality, as individual disorders. Nevertheless, this conception is being solidly challenged by numerous remarkable studies. The clear fact that the mortality, by virtually all NCDs, tends to cluster at old ages (with the exception of congenital malformations and certain types of cancer, among a few others); makes us intuitive to assume that the common convergence mechanism that exponentially increases mortality by almost all NCDs in older ages is cell aging. Moreover, when we study NCDs, we are not analyzing which disorders cause the mortality of the populations, rather that which disorders kill us before others do, because the aging of the individuals causes inevitably their death by one cause or another. This is not a defeatist perspective, but a challenging and efficient one. These intuitive assumptions have been supported by studies from the pathophysiologic, epidemiologic, and genetic fields, leading to the affirmation that, as NCDs share genetic and pathophysiological mechanisms (derived from mostly the same risk factors), they should no longer be considered independently. Those studies should make us reconsider our current conceptions of studying NCDs as individual disorders, and to hypothesize about a paradigm that would consider most NCDs (cancer, neurological pathologies, cardiovascular diseases, type II diabetes mellitus, chronic respiratory diseases, osteoarthritis, and osteoporosis, among others) different manifestations of the same process: the cell aging.

Microbial-Immune Crosstalk in Elderly-Onset Inflammatory Bowel Disease: Unchartered Territory

Elderly-onset inflammatory bowel disease [IBD] patients exhibit a distinct natural history compared to younger IBD patients, with unique disease phenotypes, differential responses to therapy, and increased surgical morbidity and mortality. Despite the foreseeable high demand for personalized medicine and specialized IBD care in the elderly, current paradigms of IBD management fail to capture the required nuances of care for elderly-onset IBD patients. Our review postulates the roles of systemic and mucosal immunosenescence, inflammageing and a dysbiotic microbial ecosystem in the pathophysiology of elderly-onset IBD. Ultimately, a better understanding of elderly-onset IBD can lead to improved patient outcomes and the tailoring of future preventative and treatment strategies.

Dessert or Poison? The Roles of Glycosylation in Alzheimer's, Parkinson's, Huntington's Disease, and Amyotrophic Lateral Sclerosis

Ministry of Education and Key Laboratory of Neurons and glial cells of the central nervous system (CNS) are modified by glycosylation and rely on glycosylation to achieve normal neural function. Neurodegenerative disease is a common disease of the elderly, affecting their healthy life span and quality of life, and no effective treatment is currently available. Recent research implies that various glycosylation traits are altered during neurodegenerative diseases, suggesting a potential implication of glycosylation in disease pathology. Herein, we summarized the current knowledge about glycosylation associated with Alzheimer's disease (AD), Parkinson's disease (PD), Huntington's disease (HD), and Amyotrophic lateral sclerosis (ALS) pathogenesis, focusing on their promising functional avenues. Moreover, we collected research aimed at highlighting the need for such studies to provide a wealth of disease-related glycosylation information that will help us better understand the pathophysiological mechanisms and hopefully specific glycosylation information to provide further diagnostic and therapeutic directions for neurodegenerative diseases.

Saccharomyces cerevisiae DJ-1 paralogs maintain genome integrity through glycation repair of nucleic acids and proteins

Reactive carbonyl species (RCS) such as methylglyoxal and glyoxal are potent glycolytic intermediates that extensively damage cellular biomolecules leading to genetic aberration and protein misfolding. Hence, RCS levels are crucial indicators in the progression of various pathological diseases. Besides the glyoxalase system, emerging studies report highly conserved DJ-1 superfamily proteins as critical regulators of RCS. DJ-1 superfamily proteins, including the human DJ-1, a genetic determinant of Parkinson's disease, possess diverse physiological functions paramount for combating multiple stressors. Although S. cerevisiae retains four DJ-1 orthologs (Hsp31, Hsp32, Hsp33, and Hsp34), their physiological relevance and collective requirement remain obscure. Here, we report for the first time that the yeast DJ-1 orthologs function as novel enzymes involved in the preferential scavenge of glyoxal and methylglyoxal, toxic metabolites, and genotoxic agents. Their collective loss stimulates chronic glycation of the proteome, and nucleic acids, inducing spectrum of genetic mutations and reduced mRNA translational efficiency. Furthermore, the Hsp31 paralogs efficiently repair severely glycated macromolecules derived from carbonyl modifications. Also, their absence elevates DNA damage response, making cells vulnerable to various genotoxins. Interestingly, yeast DJ-1 orthologs preserve functional mitochondrial content, maintain ATP levels, and redistribute into mitochondria to alleviate the glycation damage of macromolecules. Together, our study uncovers a novel glycation repair pathway in S. cerevisiae and a possible neuroprotective mechanism of how hDJ-1 confers mitochondrial health during glycation toxicity.

A new metabolic model of Drosophila melanogaster and the integrative analysis of Parkinson's disease

High conservation of the disease-associated genes between flies and humans facilitates the common use of Drosophila melanogaster to study metabolic disorders under controlled laboratory conditions. However, metabolic modeling studies are highly limited for this organism. We here report a comprehensively curated genome-scale metabolic network model of Drosophila using an orthology-based approach. The gene coverage and metabolic information of the draft model derived from a reference human model were expanded via Drosophila-specific KEGG and MetaCyc databases, with several curation steps to avoid metabolic redundancy and stoichiometric inconsistency. Furthermore, we performed literature-based curations to improve gene-reaction associations, subcellular metabolite locations, and various metabolic pathways. The performance of the resulting Drosophila model (8,230 reactions, 6,990 metabolites, and 2,388 genes), iDrosophila1 (https://github.com/SysBioGTU/iDrosophila), was assessed using flux balance analysis in comparison with the other currently available fly models leading to superior or comparable results. We also evaluated the transcriptome-based prediction capacity of iDrosophila1, where differential metabolic pathways during Parkinson's disease could be successfully elucidated. Overall, iDrosophila1 is promising to investigate system-level metabolic alterations in response to genetic and environmental perturbations.

Quantitative proteomics and phosphoproteomics of urinary extracellular vesicles define putative diagnostic biosignatures for Parkinson's disease

BACKGROUND

Mutations in the leucine-rich repeat kinase 2 (LRRK2) gene have been recognized as genetic risk factors for Parkinson's disease (PD). However, compared to cancer, fewer genetic mutations contribute to the cause of PD, propelling the search for protein biomarkers for early detection of the disease.

METHODS

Utilizing 138 urine samples from four groups, healthy individuals (control), healthy individuals with G2019S mutation in the LRRK2 gene (non-manifesting carrier/NMC), PD individuals without G2019S mutation (idiopathic PD/iPD), and PD individuals with G2019S mutation (LRRK2 PD), we applied a proteomics strategy to determine potential diagnostic biomarkers for PD from urinary extracellular vesicles (EVs).

RESULTS

After efficient isolation of urinary EVs through chemical affinity followed by mass spectrometric analyses of EV peptides and enriched phosphopeptides, we identify and quantify 4476 unique proteins and 2680 unique phosphoproteins. We detect multiple proteins and phosphoproteins elevated in PD EVs that are known to be involved in important PD pathways, in particular the autophagy pathway, as well as neuronal cell death, neuroinflammation, and formation of amyloid fibrils. We establish a panel of proteins and phosphoproteins as novel candidates for disease biomarkers and substantiate the biomarkers using machine learning, ROC, clinical correlation, and in-depth network analysis. Several putative disease biomarkers are further partially validated in patients with PD using parallel reaction monitoring (PRM) and immunoassay for targeted quantitation.

CONCLUSIONS

These findings demonstrate a general strategy of utilizing biofluid EV proteome/phosphoproteome as an outstanding and non-invasive source for a wide range of disease exploration.

Glycosylation and behavioral symptoms in neurological disorders

Glycosylation, the addition of glycans or carbohydrates to proteins, lipids, or other glycans, is a complex post-translational modification that plays a crucial role in cellular function. It is estimated that at least half of all mammalian proteins undergo glycosylation, underscoring its importance in the functioning of cells. This is reflected in the fact that a significant portion of the human genome, around 2%, is devoted to encoding enzymes involved in glycosylation. Changes in glycosylation have been linked to various neurological disorders, including Alzheimer's disease, Parkinson's disease, autism spectrum disorder, and schizophrenia. Despite its widespread occurrence, the role of glycosylation in the central nervous system remains largely unknown, particularly with regard to its impact on behavioral abnormalities in brain diseases. This review focuses on examining the role of three types of glycosylation: N-glycosylation, O-glycosylation, and O-GlcNAcylation, in the manifestation of behavioral and neurological symptoms in neurodevelopmental, neurodegenerative, and neuropsychiatric disorders.

Altered expression of glycobiology-related genes in Parkinson's disease brain

The precise mechanisms initiating and perpetuating the cellular degeneration in Parkinson's disease (PD) remain unclear. There is decreased expression of the main brain gangliosides, and GM1 ganglioside in particular, in the PD brain along with decreased expression of the genes coding for the glycosyltranferase and the sialyltransferase responsible for the synthesis of these brain gangliosides. However, potentially important pathogenic mechanisms contributing to the neurodegeneration in PD may also include altered levels of expression of genes involved in glycosylation, sialylation and sphingolipid synthesis and metabolism. Although various studies have described pathological lipid and glycolipid changes in PD brain, there have been limited studies of expression of glycobiology-related genes in PD brain. The current study was performed as an initial attempt to gain new information regarding potential changes in glycoprotein and glycolipid-related genes in PD by investigating the gene expression status for select glycosyltransferases, sialyltransferases, sialidases, sphingosine kinases, and lysosomal enzymes in the substantia nigra and putamen from patients with PD and neurologically normal controls. Results showed altered expression of glycosyltransferase genes (B3GALT2 and B4GALT1) potentially involved in microglial activation and neuroinflammation, sphingosine-1-phosphate (S1P) modulators (SPHK1, SPHK2, and SGPL1) involved in sphingolipid synthesis and metabolism, polysialyltransferase genes (ST8SIA2 and ST8SIA4) that encode enzymes responsible for polysialic acid (polySia) biosynthesis, and the sialidase NEU4, expression of which has been linked to the clearance of storage materials from lysosomes. The data presented here underscore the complexity of the glycolipid/sphingolipid dysregulation in the PD brain and continued and expanded study of these processes may not only provide a greater understanding of the complex roles of aberrant glycosylation sialylation, and sphingolipid synthesis/metabolism in the pathophysiology of PD but may identify potential druggable targets for PD therapeutics.

Recent developments in nucleic acid-based therapies for Parkinson’s disease: Current status, clinical potential, and future strategies

Parkinson’s disease is the second most common progressive neurodegenerative disease diagnosed mainly based on clinical symptoms caused by loss of nigrostriatal dopaminergic neurons. Although currently available pharmacological therapies provide symptomatic relief, however, the disease continues to progress eventually leading to severe motor and cognitive decline and reduced quality of life. The hallmark pathology of Parkinson’s disease includes intraneuronal inclusions known as Lewy bodies and Lewy neurites, including fibrillar α-synuclein aggregates. These aggregates can progressively spread across synaptically connected brain regions leading to emergence of disease symptoms with time. The α-synuclein level is considered important in its fibrillization and aggregation. Nucleic acid therapeutics have recently been shown to be effective in treating various neurological diseases, raising the possibility of developing innovative molecular therapies for Parkinson’s disease. In this review, we have described the advancements in genetic dysregulations in Parkinson’s disease along with the disease-modifying strategies involved in genetic regulation with particular focus on downregulation of α-synuclein gene using various novel technologies, notably antisense oligonucleotides, microRNA, short interfering RNA, short hairpin RNAs, DNA aptamers, and gene therapy of vector-assisted delivery system-based therapeutics. In addition, the current status of preclinical and clinical development for nucleic acid-based therapies for Parkinson’s disease have also been discussed along with their limitations and opportunities.

Concerted Regulation of Glycosylation Factors Sustains Tissue Identity and Function

Glycosylation is a fundamental cellular process affecting human development and health. Complex machinery establishes the glycan structures whose heterogeneity provides greater structural diversity than other post-translational modifications. Although known to present spatial and temporal diversity, the evolution of glycosylation and its role at the tissue-specific level is poorly understood. In this study, we combined genome and transcriptome profiles of healthy and diseased tissues to uncover novel insights into the complex role of glycosylation in humans. We constructed a catalogue of human glycosylation factors, including transferases, hydrolases and other genes directly involved in glycosylation. These were categorized as involved in N-, O- and lipid-linked glycosylation, glypiation, and glycosaminoglycan synthesis. Our data showed that these glycosylation factors constitute an ancient family of genes, where evolutionary constraints suppressed large gene duplications, except for genes involved in O-linked and lipid glycosylation. The transcriptome profiles of 30 healthy human tissues revealed tissue-specific expression patterns preserved across mammals. In addition, clusters of tightly co-expressed genes suggest a glycosylation code underlying tissue identity. Interestingly, several glycosylation factors showed tissue-specific profiles varying with age, suggesting a role in ageing-related disorders. In cancer, our analysis revealed that glycosylation factors are highly perturbed, at the genome and transcriptome levels, with a strong predominance of copy number alterations. Moreover, glycosylation factor dysregulation was associated with distinct cellular compositions of the tumor microenvironment, reinforcing the impact of glycosylation in modulating the immune system. Overall, this work provides genome-wide evidence that the glycosylation machinery is tightly regulated in healthy tissues and impaired in ageing and tumorigenesis, unveiling novel potential roles as prognostic biomarkers or therapeutic targets.

Complementary proteome and glycoproteome access revealed through comparative analysis of reversed phase and porous graphitic carbon chromatography

Continual developments in instrumental and analytical techniques have aided in establishing rigorous connections between protein glycosylation and human illness. These illnesses, such as various forms of cancer, are often associated with poor prognoses, prompting the need for more comprehensive characterization of the glycoproteome. While innovative instrumental and computational strategies have largely benefited glycoproteomic analyses, less attention is given to benefits gained through alternative, optimized chromatographic techniques. Porous graphitic carbon (PGC) chromatography has gained considerable interest in glycomics research due to its mobile phase flexibility, increased retention of polar analytes, and improved structural elucidation at higher temperatures. PGC has yet to be systematically compared against or in tandem with standard reversed phase liquid chromatography (RPLC) in high-throughput bottom-up glycoproteomic experiments, leaving the potential benefits unexplored. Performing comparative analysis of single and biphasic separation regimes at a range of column temperatures illustrates complementary advantages for each method. PGC separation is shown to selectively retain shorter, more hydrophilic glycopeptide species, imparting higher average charge, and exhibiting greater microheterogeneity coverage for identified glycosites. Additionally, we demonstrate that liquid-phase separation of glycopeptide isomers may be achieved through both single and biphasic PGC separations, providing a means towards facile, multidimensional glycopeptide characterization. Beyond this, we demonstrate how utilization of multiple separation regimes and column temperatures can aid in profiling the glycoproteome in tumorigenic and aggressive prostate cancer cells. RAW MS proteomic and glycoproteomic datasets have been deposited to the ProteomeXchange Consortium via the PRIDE partner repository with the dataset identifier PXD024196 (10.6019/PXD024196) and PXD024195, respectively.

The Effects of Dietary Advanced Glycation End-Products on Neurocognitive and Mental Disorders

Advanced glycation end products (AGEs) are glycated proteins or lipids formed endogenously in the human body or consumed through diet. Ultra-processed foods and some culinary techniques, such as dry cooking methods, represent the main sources and drivers of dietary AGEs. Tissue accumulation of AGEs has been associated with cellular aging and implicated in various age-related diseases, including type-2 diabetes and cardiovascular disease. The current review summarizes the literature examining the associations between AGEs and neurocognitive and mental health disorders. Studies indicate that elevated circulating AGEs are cross-sectionally associated with poorer cognitive function and longitudinally increase the risk of developing dementia. Additionally, preliminary studies show that higher skin AGE accumulation may be associated with mental disorders, particularly depression and schizophrenia. Potential mechanisms underpinning the effects of AGEs include elevated oxidative stress and neuroinflammation, which are both key pathogenetic mechanisms underlying neurodegeneration and mental disorders. Decreasing dietary intake of AGEs may improve neurological and mental disorder outcomes. However, more sophisticated prospective studies and analytical approaches are required to verify directionality and the extent to which AGEs represent a mediator linking unhealthy dietary patterns with cognitive and mental disorders.

Omarigliptin attenuates rotenone-induced Parkinson's disease in rats: Possible role of oxidative stress, endoplasmic reticulum stress and immune modulation

The current study aimed to explore the potential neuroprotective effect of omarigliptin (OG), an antidiabetic drug that crosses the blood-brain barrier (BBB), in a Parkinson's disease (PD) rotenone-based rat-model. Results showed that OG attenuated motor impairment, histological aberrations, α-synuclein accumulation, and rescued the dopaminergic neurons in rotenone-administered rats. Furthermore, OG halted rotenone-induced oxidative stress; as shown by reduced lipid peroxidation, decline in the oxidative stress sensor (nuclear factor erythroid 2-related factor 2) and its downstream heme oxygenase-1. In addition, OG abrogated neuroinflammation and apoptosis in rotenone-treated rats. Moreover, OG ameliorated endoplasmic reticulum (ER) stress in rotenone-administered rats; as evidenced by reduced levels of ER resident proteins such as glucose-regulated protein 78, C/EBP homologous protein and apoptotic caspase-12. In conclusion, this study implies repurposing of OG, as a novel neuroprotective agent due to its antioxidant properties, its effects on ER stress in addition to its anti-inflammatory and anti-apoptotic activities.

Autophagy and Glycative Stress: A Bittersweet Relationship in Neurodegeneration

Autophagy is a fine-tuned proteolytic pathway that moves dysfunctional/aged cellular components into the lysosomal compartment for degradation. Over the last 3 decades, global research has provided evidence for the protective role of autophagy in different brain cell components. Autophagic capacities decline with age, which contributes to the accumulation of obsolete/damaged organelles and proteins and, ultimately, leads to cellular aging in brain tissues. It is thus well-accepted that autophagy plays an essential role in brain homeostasis, and malfunction of this catabolic system is associated with major neurodegenerative disorders. Autophagy function can be modulated by different types of stress, including glycative stress. Glycative stress is defined as a cellular status with abnormal and accelerated accumulation of advanced glycation end products (AGEs). It occurs in hyperglycemic states, both through the consumption of high-sugar diets or under metabolic conditions such as diabetes. In recent years, glycative stress has gained attention for its adverse impact on brain pathology. This is because glycative stress stimulates insoluble, proteinaceous aggregation that is linked to the malfunction of different neuropathological proteins. Despite the emergence of new literature suggesting that autophagy plays a major role in fighting glycation-derived damage by removing cytosolic AGEs, excessive glycative stress might also negatively impact autophagic function. In this mini-review, we provide insight on the status of present knowledge regarding the role of autophagy in brain physiology and pathophysiology, with an emphasis on the cytoprotective role of autophagic function to ameliorate the adverse effects of glycation-derived damage in neurons, glia, and neuron-glia interactions.

Methylglyoxal disrupts the functionality of rat liver mitochondria

Methylglyoxal (MG) is a reactive metabolite derived from different physiological pathways. Its production can be harmful to cells via glycation reactions of lipids, DNA, and proteins. But, the effects of MG on mitochondrial functioning and bioenergetic responses are still elusive. Then, the effects of MG on key parameters of mitochondrial functionality were examined here. Isolated rat liver mitochondria were exposed to 0.1-10 mM of MG to determine its toxicity in the mitochondrial viability, membrane potential (Δψm), swelling and the superoxide (O2•-) production. Besides, mitochondrial oxidative phosphorylation parameters were analyzed by high-resolution respiratory (HRR) assay. In this set of experiments, routine state, PM state (pyruvate/malate), oxidative phosphorylation (OXPHOS), LEAK respiration, electron transport system (ETS) and oxygen residual (ROX) states were evaluated. HRR showed that PM state, OXPHOS CI-Linked, LEAK respiration, ETS CI/CII-Linked and ETS CII-Linked/ROX were significantly inhibited by MG exposure. MG also inhibited the complex II activity, and decreased Δψm and the viability of mitochondria. Taken together, our data indicates that MG is an inductor of mitochondrial dysfunctions and impairs important steps of respiratory chain, effects that can alter bioenergetics responses.

Utilizing liquid chromatography, ion mobility spectrometry, and mass spectrometry to assess INLIGHT™ derivatized N-linked glycans in biological samples

Glycosylation is a ubiquitous co- and post-translational modification involved in the sorting, folding, and trafficking of proteins in biological systems; in humans, >50% of gene products are glycosylated with the cellular machinery of glycosylation compromising ~2% of the genome. Perturbations in glycosylation have been implicated in a variety of diseases including neurodegenerative diseases and certain types of cancer. However, understanding the relationship between a glycan and its biological role is often difficult due to the numerous glycan isomers that exist. To address this challenge, nanoflow liquid chromatography, ion mobility spectrometry, and mass spectrometry (nLC-IMS-MS) were combined with the Individuality Normalization when Labeling with the Isotopic Glycan Hydrazide Tags (INLIGHT™) strategy to study a series of glycan standards and those enzymatically released from the glycoproteins horseradish peroxidase, fetuin, and pooled human plasma. The combination of IMS and the natural (NAT) and stable-isotope label (SIL) in the INLIGHT™ strategy provided additional confidence for each glycan identification due to the mobility aligned NAT- and SIL-labeled glycans and further capabilities for isomer examinations. Additionally, molecular trend lines based on the IMS and MS dimensions were investigated for the INLIGHT™ derivatized glycans, facilitating rapid identification of putative glycans in complex biological samples.

Rethinking the necessity of low glucose intervention for cerebral ischemia/reperfusion injury

Glucose is the essential and almost exclusive metabolic fuel for the brain. Ischemic stroke caused by a blockage in one or more cerebral arteries quickly leads to a lack of regional cerebral blood supply resulting in severe glucose deprivation with subsequent induction of cellular homeostasis disturbance and eventual neuronal death. To make up ischemia-mediated adenosine 5′-triphosphate depletion, glucose in the ischemic penumbra area rapidly enters anaerobic metabolism to produce glycolytic adenosine 5′-triphosphate for cell survival. It appears that an increase in glucose in the ischemic brain would exert favorable effects. This notion is supported by in vitro studies, but generally denied by most in vivo studies. Clinical studies to manage increased blood glucose levels after stroke also failed to show any benefits or even brought out harmful effects while elevated admission blood glucose concentrations frequently correlated with poor outcomes. Surprisingly, strict glycaemic control in clinical practice also failed to yield any beneficial outcome. These controversial results from glucose management studies during the past three decades remain a challenging question of whether glucose intervention is needed for ischemic stroke care. This review provides a brief overview of the roles of cerebral glucose under normal and ischemic conditions and the results of managing glucose levels in non-diabetic patients. Moreover, the relationship between blood glucose and cerebral glucose during the ischemia/reperfusion processes and the potential benefits of low glucose supplements for non-diabetic patients are discussed.

Structural and Functional Changes of Reconstituted High-Density Lipoprotein (HDL) by Incorporation of α-synuclein: A Potent Antioxidant and Anti-Glycation Activity of α-synuclein and apoA-I in HDL at High Molar Ratio of α-synuclein

α-synuclein (α-syn) is a major culprit of Parkinson's disease (PD), although lipoprotein metabolism is very important in the pathogenesis of PD. α-syn was expressed and purified using the pET30a expression vector from an E. coli expression system to elucidate the physiological effects of α-syn on lipoprotein metabolism. The human α-syn protein (140 amino acids) with His-tag (8 amino acids) was expressed and purified to at least 95% purity. Isoelectric focusing gel electrophoresis showed that the isoelectric point (pI) of α-syn and apoA-I were pI = 4.5 and pI = 6.4, respectively. The lipid-free α-syn showed almost no phospholipid-binding ability, while apoA-I showed rapid binding ability with a half-time (T_1/2) = 8 ± 0.7 min. The α-syn and apoA-I could be incorporated into the reconstituted HDL (rHDL, molar ratio 95:5:1:1, palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC):cholesterol:apoA-I:α-syn with the production of larger particles (92 Å) than apoA-I-rHDL (86 and 78 Å) and α-syn-rHDL (65 Å). An rHDL containing both apoA-I and α-syn showed lower α-helicity around 45% with a red shift of the Trp wavelength maximum fluorescence (WMF) from 339 nm, while apoA-I-HDL showed 76% α-helicity and 337 nm of WMF. The denaturation by urea addition showed that the incorporation of α-syn in rHDL caused a larger increase in the WMF than apoA-I-rHDL, suggesting that the destabilization of the secondary structure of apoA-I by the addition of α-syn. On the other hand, the addition of α-syn induced two-times higher resistance to rHDL glycation at apoA-I:α-syn molar ratios of 1:1 and 1:2. Interestingly, low α-syn in rHDL concentrations, molar ratio of 1:0.5 (apoA-I:α-syn), did not prevent glycation with more multimerization of apoA-I. In the lipid-free and lipid-bound state, α-syn showed more potent antioxidant activity than apoA-I against cupric ion-mediated LDL oxidation. On the other hand, microinjection of α-syn (final 2 μM) resulted in 10% less survival of zebrafish embryos than apoA-I. A subcutaneous injection of α-syn (final 34 μM) resulted in less tail fin regeneration than apoA-I. Interestingly, incorporation of α-syn at a low molar ratio (apoA-I:α-syn, 1:0.5) in rHDL resulted destabilization of the secondary structure and impairment of apoA-I functionality via more oxidation and glycation. However, at a higher molar ratio of α-syn in rHDL (apoA-I:α-syn = 1:1 or 1:2) exhibited potent antioxidant and anti-glycation activity without aggregation. In conclusion, there might be a critical concentration of α-syn and apoA-I in HDL-like complex to prevent the aggregation of apoA-I via structural and functional enhancement.

Blocked O-GlcNAc cycling alters mitochondrial morphology, function, and mass

O-GlcNAcylation is a prevalent form of glycosylation that regulates proteins within the cytosol, nucleus, and mitochondria. The O-GlcNAc modification can affect protein cellular localization, function, and signaling interactions. The specific impact of O-GlcNAcylation on mitochondrial morphology and function has been elusive. In this manuscript, the role of O-GlcNAcylation on mitochondrial fission, oxidative phosphorylation (Oxphos), and the activity of electron transport chain (ETC) complexes were evaluated. In a cellular environment with hyper O-GlcNAcylation due to the deletion of O-GlcNAcase (OGA), mitochondria showed a dramatic reduction in size and a corresponding increase in number and total mitochondrial mass. Because of the increased mitochondrial content, OGA knockout cells exhibited comparable coupled mitochondrial Oxphos and ATP levels when compared to WT cells. However, we observed reduced protein levels for complex I and II when comparing normalized mitochondrial content and reduced linked activity for complexes I and III when examining individual ETC complex activities. In assessing mitochondrial fission, we observed increased amounts of O-GlcNAcylated dynamin-related protein 1 (Drp1) in cells genetically null for OGA and in glioblastoma cells. Individual regions of Drp1 were evaluated for O-GlcNAc modifications, and we found that this post-translational modification (PTM) was not limited to the previously characterized residues in the variable domain (VD). Additional modification sites are predicted in the GTPase domain, which may influence enzyme activity. Collectively, these results highlight the impact of O-GlcNAcylation on mitochondrial dynamics and ETC function and mimic the changes that may occur during glucose toxicity from hyperglycemia.

Glycoconjugate journal special issue on: the glycobiology of Parkinson's disease

Parkinson's disease (PD) is a neurodegenerative disorder that affects over 10 million aging people worldwide. This condition is characterized by the degeneration of dopaminergic neurons in the pars compacta region of the substantia nigra (SNpc) and by aggregation of proteins, commonly α-synuclein (SNCA). The formation of Lewy bodies that encapsulate aggregated proteins in lipid vesicles is a hallmark of PD. Glycosylation of proteins and neuroinflammation are involved in the pathogenesis. SNCA has many posttranslational modifications and interacts with components of membranes that affect aggregation. The large membrane lipid dolichol accumulates in the brain upon age and has a significant effect on membrane structure. The replacement of dopamine and dopaminergic neurons are at the forefront of therapeutic development. This review examines the role of membrane lipids, glycolipids, glycoproteins and dopamine in the aggregation of SNCA and development of PD. We discuss the SNCA-dopamine-neuromelanin-dolichol axis and the role of membranes in neuronal stem cells that could be a regenerative therapy for PD patients.

Cholinergic Receptor Modulation as a Target for Preventing Dementia in Parkinson's Disease

Parkinson’s disease (PD) is a neurodegenerative condition characterized by the loss of dopaminergic neurons in the substantia nigra pars compacta (SNpc) in the midbrain resulting in progressive impairment in cognitive and motor abilities. The physiological and molecular mechanisms triggering dopaminergic neuronal loss are not entirely defined. PD occurrence is associated with various genetic and environmental factors causing inflammation and mitochondrial dysfunction in the brain, leading to oxidative stress, proteinopathy, and reduced viability of dopaminergic neurons. Oxidative stress affects the conformation and function of ions, proteins, and lipids, provoking mitochondrial DNA (mtDNA) mutation and dysfunction. The disruption of protein homeostasis induces the aggregation of alpha-synuclein (α-SYN) and parkin and a deficit in proteasome degradation. Also, oxidative stress affects dopamine release by activating ATP-sensitive potassium channels. The cholinergic system is essential in modulating the striatal cells regulating cognitive and motor functions. Several muscarinic acetylcholine receptors (mAChR) and nicotinic acetylcholine receptors (nAChRs) are expressed in the striatum. The nAChRs signaling reduces neuroinflammation and facilitates neuronal survival, neurotransmitter release, and synaptic plasticity. Since there is a deficit in the nAChRs in PD, inhibiting nAChRs loss in the striatum may help prevent dopaminergic neurons loss in the striatum and its pathological consequences. The nAChRs can also stimulate other brain cells supporting cognitive and motor functions. This review discusses the cholinergic system as a therapeutic target of cotinine to prevent cognitive symptoms and transition to dementia in PD.

Transcriptomic Signatures Associated With Regional Cortical Thickness Changes in Parkinson's Disease

Cortical atrophy is a common manifestation in Parkinson's disease (PD), particularly in advanced stages of the disease. To elucidate the molecular underpinnings of cortical thickness changes in PD, we performed an integrated analysis of brain-wide healthy transcriptomic data from the Allen Human Brain Atlas and patterns of cortical thickness based on T1-weighted anatomical MRI data of 149 PD patients and 369 controls. For this purpose, we used partial least squares regression to identify gene expression patterns correlated with cortical thickness changes. In addition, we identified gene expression patterns underlying the relationship between cortical thickness and clinical domains of PD. Our results show that genes whose expression in the healthy brain is associated with cortical thickness changes in PD are enriched in biological pathways related to sumoylation, regulation of mitotic cell cycle, mitochondrial translation, DNA damage responses, and ER-Golgi traffic. The associated pathways were highly related to each other and all belong to cellular maintenance mechanisms. The expression of genes within most pathways was negatively correlated with cortical thickness changes, showing higher expression in regions associated with decreased cortical thickness (atrophy). On the other hand, sumoylation pathways were positively correlated with cortical thickness changes, showing higher expression in regions with increased cortical thickness (hypertrophy). Our findings suggest that alterations in the balanced interplay of these mechanisms play a role in changes of cortical thickness in PD and possibly influence motor and cognitive functions.

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.

Post-translational modifications: Regulators of neurodegenerative proteinopathies

One of the hallmark features in the neurodegenerative disorders (NDDs) is the accumulation of aggregated and/or non-functional protein in the cellular milieu. Post-translational modifications (PTMs) are an essential regulator of non-functional protein aggregation in the pathogenesis of NDDs. Any alteration in the post-translational mechanism and the protein quality control system, for instance, molecular chaperone, ubiquitin-proteasome system, autophagy-lysosomal degradation pathway, enhances the accumulation of misfolded protein, which causes neuronal dysfunction. Post-translational modification plays many roles in protein turnover rate, accumulation of aggregate and can also help in the degradation of disease-causing toxic metabolites. PTMs such as acetylation, glycosylation, phosphorylation, ubiquitination, palmitoylation, SUMOylation, nitration, oxidation, and many others regulate protein homeostasis, which includes protein structure, functions and aggregation propensity. Different studies demonstrated the involvement of PTMs in the regulation of signaling cascades such as PI3K/Akt/GSK3β, MAPK cascade, AMPK pathway, and Wnt signaling pathway in the pathogenesis of NDDs. Further, mounting evidence suggests that targeting different PTMs with small chemical molecules, which acts as an inhibitor or activator, reverse misfolded protein accumulation and thus enhances the neuroprotection. Herein, we briefly discuss the protein aggregation and various domain structures of different proteins involved in the NDDs, indicating critical amino acid residues where PTMs occur. We also describe the implementation and involvement of various PTMs on signaling cascade and cellular processes in NDDs. Lastly, we implement our current understanding of the therapeutic importance of PTMs in neurodegeneration, along with emerging techniques targeting various PTMs.

l-Theanine ameliorates motor deficit, mitochondrial dysfunction, and neurodegeneration against chronic tramadol induced rats model of Parkinson's disease

Parkinson's disease (PD) is the second most prevalent progressive neurodegenerative disease, characterized by loss of dopaminergic neurons in substantia nigra, with deficiency of dopamine in the striatum. Tramadol is safe analgesic but long-term use confirmed to elevate oxidative stress, neuroinflammation, mitochondrial dysfunction, in brain leads to motor deficits. l-Theanine is an active constituent of green tea which prevents neuronal loss, mitochondrial failure and improves dopamine, gamma-aminobutyric acid (GABA), serotonin levels and in the central nervous system (CNS) via antioxidant, anti-inflammatory, and neuromodulatory properties. In the present study, tramadol was injected intraperitoneally to Wister rats for 28 days at a dose of 50 mg/kg. l-Theanine (25, 50, and 100 mg/kg) was administered orally 3 h before tramadol administration from day 14 to day 28. Behavioral analyses including rotarod, narrow beam walk, open field, and grip strength were used to evaluate motor coordination on a weekly basis. On the day 29, all Wistar rats were sacrificed and striatum homogenates were used for biochemical (lipid peroxidation, nitrite, glutathione, glutathione peroxidase activity, superoxide dismutase, catalase, mitochondrial complex I, IV, and cyclic adenosine monophosphate), neuroinflammatory markers (tumor necrosis factor-α, interleukin-1β, and interleukin-17), and neurotransmitters (dopamine, norepinephrine, serotonin, GABA, and glutamate) analysis. Chronic tramadol treatment caused motor deficits reduced antioxidant enzymes level, increased striatal proinflammatory cytokines release, dysbalanced neurotransmitters, and reduced mitochondrial complex activity I, IV, and cAMP activity. However, l-theanine administration attenuated behavioral, biochemical, neuroinflammatory, neurotransmitters, and mitochondrial activity indicated it as a promising neuroprotective potential against degenerative changes in experimental model of PD.

Differential Glycosite Profiling-A Versatile Method to Compare Membrane Glycoproteomes

Glycosylation is the most prevalent and varied form of post-translational protein modifications. Protein glycosylation regulates multiple cellular functions, including protein folding, cell adhesion, molecular trafficking and clearance, receptor activation, signal transduction, and endocytosis. In particular, membrane proteins are frequently highly glycosylated, which is both linked to physiological processes and of high relevance in various disease mechanisms. The cellular glycome is increasingly considered to be a therapeutic target. Here we describe a new strategy to compare membrane glycoproteomes, thereby identifying proteins with altered glycan structures and the respective glycosites. The workflow started with an optimized procedure for the digestion of membrane proteins followed by the lectin-based isolation of glycopeptides. Since alterations in the glycan part of a glycopeptide cause mass alterations, analytical size exclusion chromatography was applied to detect these mass shifts. N-glycosidase treatment combined with nanoUPLC-coupled mass spectrometry identified the altered glycoproteins and respective glycosites. The methodology was established using the colon cancer cell line CX1, which was treated with 2-deoxy-glucose-a modulator of N-glycosylation. The described methodology is not restricted to cell culture, as it can also be adapted to tissue samples or body fluids. Altogether, it is a useful module in various experimental settings that target glycan functions.

Reactive Oxygen Species and Their Impact in Neurodegenerative Diseases: Literature Landscape Analysis

Significance: The excessive production of reactive oxygen species (ROS) has been linked to neurodegenerative diseases (NDs), and, therefore, many scientific works were published on the impact of ROS on the development of prevalent NDs, such as Alzheimer's disease (AD) and Parkinson's disease (PD). Since quantitative and qualitative bibliometric analyses in this research area have not yet been done, the aim of this work is to explore the scientific literature implying ROS in NDs and to identify the major contributors, mainstream research themes, and topics on the rise. Recent Advances: Overall, 22,885 publications were identified and analyzed within the Web of Science (WoS) Core Collection electronic database (Clarivate Analytics, Philadelphia, PA). Most of the manuscripts were published in the 21st century. The publications were mainly related to the WoS categories Neurosciences and Biochemistry molecular biology. The United States is the major contributor, harboring the most productive authors and institutions. China, South Korea, and India have emerged as upcoming major contributors in the 2010s. Two most productive journals were Journal of Neurochemistry and Free Radical Biology and Medicine. Critical Issues: AD, PD, and amyotrophic lateral sclerosis were much more investigated than multiple sclerosis and Huntington's disease. Vitamin E and curcumin were frequently mentioned as potential antioxidant therapeutics, but their efficacy in treating NDs requires more clinical studies, since the existing evidence was mainly from in vitro experiments and in vivo animal studies. Future Directions: Mitochondrial dysfunction, autophagy, and nuclear factor erythroid 2-related factor 2 were among the author keywords with rising prevalence. Further research in these directions should advance our understanding of the mechanism and treatment of NDs. Antioxid. Redox Signal. 34, 402-420.

Interaction between Parkin and α-Synuclein in PARK2-Mediated Parkinson's Disease

Parkin and α-synuclein are two key proteins involved in the pathophysiology of Parkinson's disease (PD). Neurotoxic alterations of α-synuclein that lead to the formation of toxic oligomers and fibrils contribute to PD through synaptic dysfunction, mitochondrial impairment, defective endoplasmic reticulum and Golgi function, and nuclear dysfunction. In half of the cases, the recessively inherited early-onset PD is caused by loss of function mutations in the PARK2 gene that encodes the E3-ubiquitin ligase, parkin. Parkin is involved in the clearance of misfolded and aggregated proteins by the ubiquitin-proteasome system and regulates mitophagy and mitochondrial biogenesis. PARK2-related PD is generally thought not to be associated with Lewy body formation although it is a neuropathological hallmark of PD. In this review article, we provide an overview of post-mortem neuropathological examinations of PARK2 patients and present the current knowledge of a functional interaction between parkin and α-synuclein in the regulation of protein aggregates including Lewy bodies. Furthermore, we describe prevailing hypotheses about the formation of intracellular micro-aggregates (synuclein inclusions) that might be more likely than Lewy bodies to occur in PARK2-related PD. This information may inform future studies aiming to unveil primary signaling processes involved in PD and related neurodegenerative disorders.

Kale Attenuates Inflammation and Modulates Gut Microbial Composition and Function in C57BL/6J Mice with Diet-Induced Obesity

Kale (Brassica oleracea var. acephala) is a vegetable common in most cultures but is less studied as a functional food compared to other cruciferous vegetables, such as broccoli. We investigated the effect of supplementing a high-fat diet (HFD) with kale (HFKV) in C57BL/6J mice. We particularly explored its role in metabolic parameters, gut bacterial composition and diversity using 16S rRNA sequencing, systematically compared changes under each phylum and predicted the functional potential of the altered bacterial community using PICRUSt2. Like other cruciferous vegetables, kale attenuated HFD-induced inflammation. In addition, kale modulated HFD-induced changes in cecal microbiota composition. The HFD lowered bacterial diversity, increased the Firmicutes: Bacteroidetes (F/B) ratio and altered composition. Specifically, it lowered Actinobacteria and Bacteroidetes (Bacteroidia, Rikenellaceae and Prevotellaceae) but increased Firmicutes (mainly class Bacilli). Kale supplementation lowered the F/B ratio, increased both alpha and beta diversity and reduced class Bacilli and Erysipelotrichi but had no effect on Clostridia. Within Actinobacteria, HFKV particularly increased Coriobacteriales/Coriobacteriaceae about four-fold compared to the HFD (p < 0.05). Among Bacteroidia, HFKV increased the species Bacteroides thetaiotaomicron by over two-fold (p = 0.05) compared to the HFD. This species produces plant polysaccharide digesting enzymes. Compared to the HFD, kale supplementation enhanced several bacterial metabolic functions, including glycan degradation, thiamine metabolism and xenobiotic metabolism. Our findings provide evidence that kale is a functional food that modulates the microbiota and changes in inflammation phenotype.

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.

The Glucose Metabolic Pathway as A Potential Target for Therapeutics: Crucial Role of Glycosylation in Alzheimer's Disease

Glucose uptake in the brain decreases because of normal aging but this decline is accelerated in Alzheimer’s disease (AD) patients. In fact, positron emission tomography (PET) studies have shown that metabolic reductions in AD patients occur decades before the onset of symptoms, suggesting that metabolic deficits may be an upstream event in at least some late-onset cases. A decrease in availability of glucose content induces a considerable impairment/downregulation of glycosylation, which is an important post-translational modification. Glycosylation is an important and highly regulated mechanism of secondary protein processing within cells and it plays a crucial role in modulating stability of proteins, as carbohydrates are important in achieving the proper three-dimensional conformation of glycoproteins. Moreover, glycosylation acts as a metabolic sensor that links glucose metabolism to normal neuronal functioning. All the proteins involved in β-amyloid (Aβ) precursor protein metabolism have been identified as candidates of glycosylation highlighting the possibility that Aβ metabolism could be regulated by their glycosylation. Within this framework, the present review aims to summarize the current understanding on the role of glycosylation in the etiopathology of AD, emphasizing the idea that glucose metabolic pathway may represent an alternative therapeutic option for targeting AD. From this perspective, the pharmacological modulation of glycosylation levels may represent a ‘sweet approach’ to treat AD targeting new mechanisms independent of the amyloid cascade and with comparable impacts in familial and sporadic AD.

Role of microtubule-associated protein 6 glycosylated with Gal-(β-1,3)-GalNAc in Parkinson's disease

Aberrant glycosylation of proteins has major implications for human diseases. To determine whether protein glycosylation contributes to the pathogenesis of Parkinson’s disease (PD), a mouse model of PD was established by injection of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP). Induction of PD-like features was verified by assessing motor impairment and confirming reductions in biological markers, including dopamine, 5-hydroxytryptamine and tyrosine hydroxylase, as well as the aggregation of α-synuclein. Altered glycosylation was detected using biotinylated agaracus bisporus lectin, which specifically binds exposed Gal-(β-1,3)-GalNAc linked to glycoproteins. Subsequent lectin affinity chromatography coupled with mass spectrometry revealed enhanced glycosylation of microtubule-associated protein 6 (MAP6) in PD mice as compared to healthy controls. In situ dual co-immunofluorescence analysis and immunoblotting confirmed that MAP6 is glycosylated with Gal-(β-1,3)-GalNAc oligosaccharides, which in turn alters the distribution and structure of MAP6 complexes within neurons. This is the first study to described MAP6 as a glycoprotein containing Gal-(β-1,3)-GalNAc oligosaccharides and to show that hyperglycosylation of MAP6 is strongly associated with the pathogenesis of PD. These findings provide potentially valuable information for developing new therapeutic targets for the treatment of PD as well as reliably prognostic biomarkers.

Glycation in Huntington's Disease: A Possible Modifier and Target for Intervention

Glycation is the non-enzymatic reaction between reactive dicarbonyls and amino groups, and gives rise to a variety of different reaction products known as advanced glycation end products (AGEs). Accumulation of AGEs on proteins is inevitable, and is associated with the aging process. Importantly, glycation is highly relevant in diabetic patients that experience periods of hyperglycemia. AGEs also play an important role in neurodegenerative diseases including Alzheimer’s (AD) and Parkinson’s disease (PD). Huntington’s disease (HD) is a hereditary neurodegenerative disease caused by an expansion of a CAG repeat in the huntingtin gene. The resulting expanded polyglutamine stretch in the huntingtin (HTT) protein induces its misfolding and aggregation, leading to neuronal dysfunction and death. HD patients exhibit chorea and psychiatric disturbances, along with abnormalities in glucose and energy homeostasis. Interestingly, an increased prevalence of diabetes mellitus has been reported in HD and in other CAG triplet repeat disorders. However, the mechanisms underlying the connection between glycation and HD progression remain unclear. In this review, we explore the possible connection between glycation and proteostasis imbalances in HD, and posit that it may contribute to disease progression, possibly by accelerating protein aggregation and deposition. Finally, we review therapeutic interventions that might be able to alleviate the negative impact of glycation in HD.

Strategies for the Treatment of Parkinson's Disease: Beyond Dopamine

Parkinson’s disease (PD) is the second-leading cause of dementia and is characterized by a progressive loss of dopaminergic neurons in the substantia nigra alongside the presence of intraneuronal α-synuclein-positive inclusions. Therapies to date have been directed to the restoration of the dopaminergic system, and the prevention of dopaminergic neuronal cell death in the midbrain. This review discusses the physiological mechanisms involved in PD as well as new and prospective therapies for the disease. The current data suggest that prevention or early treatment of PD may be the most effective therapeutic strategy. New advances in the understanding of the underlying mechanisms of PD predict the development of more personalized and integral therapies in the years to come. Thus, the development of more reliable biomarkers at asymptomatic stages of the disease, and the use of genetic profiling of patients will surely permit a more effective treatment of PD.

Glycan Mimetics from Natural Products: New Therapeutic Opportunities for Neurodegenerative Disease

Neurodegenerative diseases (NDs) affect millions of people worldwide. Characterized by the functional loss and death of neurons, NDs lead to symptoms (dementia and seizures) that affect the daily lives of patients. In spite of extensive research into NDs, the number of approved drugs for their treatment remains limited. There is therefore an urgent need to develop new approaches for the prevention and treatment of NDs. Glycans (carbohydrate chains) are ubiquitous, abundant, and structural complex natural biopolymers. Glycans often covalently attach to proteins and lipids to regulate cellular recognition, adhesion, and signaling. The importance of glycans in both the developing and mature nervous system is well characterized. Moreover, glycan dysregulation has been observed in NDs such as Alzheimer's disease (AD), Huntington's disease (HD), Parkinson's disease (PD), multiple sclerosis (MS), and amyotrophic lateral sclerosis (ALS). Therefore, glycans are promising but underexploited therapeutic targets. In this review, we summarize the current understanding of glycans in NDs. We also discuss a number of natural products that functionally mimic glycans to protect neurons, which therefore represent promising new therapeutic approaches for patients with NDs.

Repurposing anti-diabetic drugs for the treatment of Parkinson's disease: Rationale and clinical experience

The most pressing need in Parkinson's disease (PD) clinical practice is to identify agents that might slow down, stop or reverse the neurodegenerative process of Parkinson's disease and therefore avoid the onset of the most disabling, dopa-refractory symptoms of the disease. These include dementia, speech and swallowing problems, poor balance and falling. To date, there have been no agents which have yet had robust trial data to confirm positive effects at slowing down the neurodegenerative disease process of PD. In this chapter we will review the reasons why there is growing interest in drugs currently licensed for the treatment of diabetes as agents which may slow down disease progression in PD, including a review of the published trials regarding exenatide, a GLP-1 receptor agonist licensed to treat type 2 diabetes, and recently shown to be associated with reduced severity of PD in a randomized, placebo controlled washout design trial of 60 patients treated for 48 weeks. This subject is now a major area of interest for multiple pharmaceutical companies hoping to bring GLP-1 receptor agonists forward as treatment options in PD.

Advantages of Vasoactive Intestinal Peptide for the Future Treatment of Parkinson's Disease

Parkinson's disease is the second most common neurodegenerative disorder in adults over the age of 65. The characteristic symptoms of Parkinson's disease, such as resting tremor, muscular rigidity, bradykinesia, postural instability and gait imbalance, are thought to be a result of the progressive degeneration of the dopaminergic neurons of the substantia nigra compacta, resulting in insufficient dopamine integrated signalling on GABAergic medium spiny neurons in the striatum. Despite tremendous research, the molecular mechanisms underlying the pathogenesis of neurodegeneration in Parkinson's disease have remained largely unknown. Although a variety of possible pathogenic mechanisms have been proposed over the years, including excessive release of oxygen free radicals, impairment of mitochondrial function, loss of trophic support, abnormal kinase activity, disruption of calcium homeostasis, dysfunction of protein degradation and neuroinflammation, the pathogenesis is still largely uncertain, and there is currently no effective cure for Parkinson's disease. To develop potential therapies for Parkinson's disease, inflammatory processes, mitochondrial dynamics, oxidative stress, production of reactive aldehydes, excitotoxicity and synucleinopathies are to be targeted. In this respect, vasoactive intestinal peptide has beneficial effects that provide an advantage for the treatment of Parkinson's disease. Vasoactive intestinal peptide is a major neuropeptide-neurotransmitter having antioxidant, anti-inflammatory, neurotropic, neuromodulator, and anti-apoptotic properties. In addition to its direct neuroprotective actions regulating the activity of astrocytes, microglia and brain mast cells, it also plays important roles for neuronal adaptation, maintenance and survival.

Complex regulation of ecto-5'-nucleotidase/CD73 and A2AR-mediated adenosine signaling at neurovascular unit: A link between acute and chronic neuroinflammation

The review summarizes available data regarding the complex regulation of CD73 at the neurovascular unit (NVU) during neuroinflammation. Based on available data we propose the biphasic pattern of CD73 regulation at NVU, with an early attenuation and a postponed up-regulation of CD73 activity. Transient attenuation of CD73 activity on leukocyte/vascular endothelium and leukocyte/astrocyte surface, required for the initiation of a neuroinflammatory response, may be effectuated either by catalytic inhibition of CD73 and/or by shedding of the CD73 molecule from the cell surface, while postponed induction of CD73 is effectuated by transcriptional up-regulation of Nt5e and posttranslational modifications. Neuroinflammatory conditions are also associated with significant enhancement and gain-of-function of A_2AR-mediated adenosine signaling. However, in contrast to the temporary prevalence of A_2AR over A₁R signaling during an acute inflammatory response, prolonged induction of A_2AR and resulting perpetual CD73/A_2AR coupling may be a contributing factors in the transition between acute and chronic neuroinflammation. Thus, pharmacological targeting of the CD73/A_2AR axis may attenuate inflammatory response and ameliorate neurological deficits in chronic neuroinflammatory conditions.

Resveratrol decreases the expression of genes involved in inflammation through transcriptional regulation

Oxidative stress generated during inflammation is associated with a wide range of pathologies. Resveratrol (RESV) displays anti-inflammatory and antioxidant activities, being a candidate for the development of adjuvant therapies for several inflammatory diseases. Despite this potential, the cellular responses induced by RESV are not well known. In this work, transcriptomic analysis was performed following lipopolysaccharide (LPS) stimulation of monocyte cultures in the presence of RESV. Induction of an inflammatory response was observed after LPS treatment and the addition of RESV led to decreases in expression of the inflammatory mediators, tumor necrosis factor-alpha (TNF-α), interleukin-8 (IL-8), and monocyte chemoattractant protein-1 (MCP-1), without cytotoxicity. RNA sequencing revealed 823 upregulated and 2098 downregulated genes (cutoff ≥2.0 or ≤-2.0) after RESV treatment. Gene ontology analysis showed that the upregulated genes were associated with metabolic processes and the cell cycle, consistent with normal cell growth and differentiation under an inflammatory stimulus. The downregulated genes were associated with inflammatory responses, gene expression, and protein modification. The prediction of master regulators using the iRegulon tool showed nuclear respiratory factor 1 (NRF1) and GA-binding protein alpha subunit (GABPA) as the main regulators of the downregulated genes. Using immunoprecipitation and protein expression assays, we observed that RESV was able to decrease protein acetylation patterns, such as acetylated apurinic/apyrimidinic endonuclease-1/reduction-oxidation factor 1 (APE1/Ref-1), and increase histone methylation. In addition, reductions in p65 (nuclear factor-kappa B (NF-κB) subunit) and lysine-specific histone demethylase-1 (LSD1) expression were observed. In conclusion, our data indicate that treatment with RESV caused significant changes in protein acetylation and methylation patterns, suggesting the induction of deacetylase and reduction of demethylase activities that mainly affect regulatory cascades mediated by NF-кB and Janus kinase/signal transducers and activators of transcription (JAK/STAT) signaling. NRF1 and GABPA seem to be the main regulators of the transcriptional profile observed after RESV treatment.