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

Integrated multi-omics analysis and experimental validation reveals the mechanism of tenuifoliside A activity in Alzheimer's disease

ETHNOPHARMACOLOGICAL RELEVANCE

Alzheimer's disease (AD) is characterized by progressive cognitive dysfunction and memory loss. Tenuifoliside A (TFSA) is a constituent of RADIX POLYGALAE, a medicinal herb traditionally used in the clinical treatment of AD in China. However, the therapeutic mechanism of this compound is unknown.

AIM OF THE STUDY

To investigate the effects and pharmacological mechanisms of TFSA in ameliorating AD symptoms in APP/PS1 mice.

MATERIALS AND METHODS

The neuroprotective effects of TFSA were assessed using behavioral tests, transmission electron microscopy, and immunofluorescence staining. The differential metabolites in the feces of model mice were obtained from non-targeted metabolomics analysis. Differential abundances of microbiota in the gut were investigated by 16S rRNA sequencing, and correlations among differential metabolites and microbiota were investigated using an integrated approach.

RESULTS

Cognitive impairment and Aβ burden were mitigated in APP/PS1 mice treated with TFSA. TFSA intervention led to an increase in the diversity of gut microbiota and a reduction in the relative abundance of Firmicutes, Bacteroidetes, and Proteobacteria. There were 71 differential metabolites in mice given high dose of TFSA. In comparison to the AD group, the mice treated with TFSA exhibited a notable enrichment in various pathways including glucose and lipid metabolism, tryptophan metabolism. Based on integrated metabolomics and 16S rRNA sequencing, 23 metabolite-microbiota pairs were different between the TFSA and AD groups, and there was an especially strong correlation between Alistipes and 2,3-dinor-8-epi-prostaglandin F2α. Validation experiment demonstrated TFSA ameliorates AD by regulating metabolism pathways and inhibiting neuroinflammation.

CONCLUSIONS

This study offers a theoretical basis for elucidating the molecular mechanism of TFSA's amelioration of AD. Although the potential pharmacological mechanisms of TFSA are still unknown, we have demonstrated that TFSA inhibits neuroinflammation and improves AD symptoms in APP/PS1 mice by remodeling the microbiota and its metabolites.

Urinary formic acid is associated with cerebral amyloid deposition and glucose metabolism in memory clinic patients

BACKGROUND

Urinary formic acid (FA) has been reported to be a biomarker for Alzheimer's disease (AD). However, the association between FA and pathological changes in memory clinic patients is currently unclear.

OBJECTIVE

This study aims to investigate associations between FA and pathological changes across different cognitive statuses in memory clinic patients.

METHODS

A cohort of patients with mild cognitive impairment (MCI-Aβ- n = 37, MCI-Aβ+ n = 33), AD dementia (n = 39), and cognitively normal subjects (CN-Aβ- n = 98, CN-Aβ+ n = 50) were included. Comprehensive neuropsychological assessment, urinary FA, AD-related plasma biomarkers, MRI scans, [18F]-flurbetapir and [18F]-FDG PET scan data were collected from all participants.

RESULTS

Urinary FA levels were higher in patients with MCI and AD than in CN subjects and higher in Aβ+ (CN- Aβ+, MCI-Aβ+, AD dementia) subjects than in Aβ-subjects (CN- Aβ-, MCI-Aβ-). Urinary FA was positively associated with cerebral Aβ deposition and negatively associated with glucose metabolism, both at the global level and in multiple regions of interest cortical regions in participants with different cognitive statuses. Additionally, urinary FA levels were positively correlated with the severity of white matter hyperintensities and hippocampal atrophy. Urinary FA combined with age, Mini-Mental State Examination, plasma p-tau181, and neurofilament light chain could be used to predict Aβ deposition in the brain.

CONCLUSIONS

Urinary FA is associated with brain pathological changes in memory clinic patients, including cerebral Aβ deposition, glucose metabolism, white matter hyperintensities, and hippocampal atrophy. It could be used as a biomarker for the early diagnosis of AD and predicting Aβ deposition.

Oxidative Stress, Inflammation and Altered Glucose Metabolism Contribute to the Retinal Phenotype in the Choroideremia Zebrafish

Reactive oxygen species (ROS) within the retina play a key role in maintaining function and cell survival. However, excessive ROS can lead to oxidative stress, inducing dysregulation of metabolic and inflammatory pathways. The chmru848 zebrafish models choroideremia (CHM), an X-linked chorioretinal dystrophy, which predominantly affects the photoreceptors, retinal pigment epithelium (RPE), and choroid. In this study, we examined the transcriptomic signature of the chmru848 zebrafish retina to reveal the upregulation of cytokine pathways and glia migration, upregulation of oxidative, ER stress and apoptosis markers, and the dysregulation of glucose metabolism with the downregulation of glycolysis and the upregulation of the oxidative phase of the pentose phosphate pathway. Glucose uptake was impaired in the chmru848 retina using the 2-NBDG glucose uptake assay. Following the overexpression of human PFKM, partial rescue was seen with the preservation of photoreceptors and RPE and increased glucose uptake, but without modifying glycolysis and oxidative stress markers. Therapies targeting glucose metabolism in CHM may represent a potential remedial approach.

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.

New insight into protein glycosylation in the development of Alzheimer's disease

Alzheimer's disease (AD) is a chronic neurodegenerative disease that seriously endangers the physical and mental health of patients, however, there are still no effective drugs or methods to cure this disease up to now. Protein glycosylation is the most common modifications of the translated proteins in eukaryotic cells. Recently many researches disclosed that aberrant glycosylation happens in some important AD-related proteins, such as APP, Tau, Reelin and CRMP-2, etc, suggesting a close link between abnormal protein glycosylation and AD. Because of its complexity and diversity, glycosylation is thus considered a completely new entry point for understanding the precise cause of AD. This review comprehensively summarized the currently discovered changes in protein glycosylation patterns in AD, and especially introduced the latest progress on the mechanism of protein glycosylation affecting the progression of AD and the potential application of protein glycosylation in AD detection and treatment, thereby providing a wide range of opportunities for uncovering the pathogenesis of AD and promoting the translation of glycosylation research into future clinical applications.

Protein glycosylation and glycoinformatics for novel biomarker discovery in neurodegenerative diseases

Glycosylation is a common post-translational modification of brain proteins including cell surface adhesion molecules, synaptic proteins, receptors and channels, as well as intracellular proteins, with implications in brain development and functions. Using advanced state-of-the-art glycomics and glycoproteomics technologies in conjunction with glycoinformatics resources, characteristic glycosylation profiles in brain tissues are increasingly reported in the literature and growing evidence shows deregulation of glycosylation in central nervous system disorders, including aging associated neurodegenerative diseases. Glycan signatures characteristic of brain tissue are also frequently described in cerebrospinal fluid due to its enrichment in brain-derived molecules. A detailed structural analysis of brain and cerebrospinal fluid glycans collected in publications in healthy and neurodegenerative conditions was undertaken and data was compiled to create a browsable dedicated set in the GlyConnect database of glycoproteins (https://glyconnect.expasy.org/brain). The shared molecular composition of cerebrospinal fluid with brain enhances the likelihood of novel glycobiomarker discovery for neurodegeneration, which may aid in unveiling disease mechanisms, therefore, providing with novel therapeutic targets as well as diagnostic and progression monitoring tools.

Agent Orange Causes Metabolic Dysfunction and Molecular Pathology Reminiscent of Alzheimer's Disease

Background

Agent Orange, an herbicide used during the Vietnam War, contains 2,4-dichlorophenoxyacetic acid (2,4-D) and 2,4,5-trichlorophenoxyacetic acid (2,4,5-T). Agent Orange has teratogenic and carcinogenic effects, and population-based studies suggest Agent Orange exposures lead to higher rates of toxic and degenerative pathologies in the peripheral and central nervous system (CNS).

Objective

This study examines the potential contribution of Agent Orange exposures to neurodegeneration.

Methods

Human CNS-derived neuroepithelial cells (PNET2) treated with 2,4-D and 2,4,5-T were evaluated for viability, mitochondrial function, and Alzheimer's disease (AD)-related proteins.

Results

Treatment with 250μg/ml 2,4-D or 2,4,5-T significantly impaired mitochondrial function, caused degenerative morphological changes, and reduced viability in PNET2 cells. Correspondingly, glyceraldehyde-3-phosphate dehydrogenase expression which is insulin-regulated and marks the integrity of carbohydrate metabolism, was significantly inhibited while 4-hydroxy-2-nonenal, a marker of lipid peroxidation, was increased. Tau neuronal cytoskeletal protein was significantly reduced by 2,4,5-T, and relative tau phosphorylation was progressively elevated by 2,4,5-T followed by 2,4-D treatment relative to control. Amyloid-β protein precursor (AβPP) was increased by 2,4,5-T and 2,4-D, and 2,4,5-T caused a statistical trend (0.05 < p<0.10) increase in Aβ. Finally, altered cholinergic function due to 2,4,5-T and 2,4-D exposures was marked by significantly increased choline acetyltransferase and decreased acetylcholinesterase expression, corresponding with responses in early-stage AD.

Conclusion

Exposures to Agent Orange herbicidal chemicals rapidly damage CNS neurons, initiating a path toward AD-type neurodegeneration. Additional research is needed to understand the permanency of these neuropathologic processes and the added risks of developing AD in Agent Orange-exposed aging Vietnam Veterans.

Roles of protein post-translational modifications in glucose and lipid metabolism: mechanisms and perspectives

The metabolism of glucose and lipids is essential for energy production in the body, and dysregulation of the metabolic pathways of these molecules is implicated in various acute and chronic diseases, such as type 2 diabetes, Alzheimer's disease, atherosclerosis (AS), obesity, tumor, and sepsis. Post-translational modifications (PTMs) of proteins, which involve the addition or removal of covalent functional groups, play a crucial role in regulating protein structure, localization function, and activity. Common PTMs include phosphorylation, acetylation, ubiquitination, methylation, and glycosylation. Emerging evidence indicates that PTMs are significant in modulating glucose and lipid metabolism by modifying key enzymes or proteins. In this review, we summarize the current understanding of the role and regulatory mechanisms of PTMs in glucose and lipid metabolism, with a focus on their involvement in disease progression associated with aberrant metabolism. Furthermore, we discuss the future prospects of PTMs, highlighting their potential for gaining deeper insights into glucose and lipid metabolism and related diseases.

Long-term dietary folic acid supplementation attenuated aging-induced hippocampus atrophy and promoted glucose uptake in 25-month-old rats with cognitive decline

The brain has high energy demand making it sensitive to changes in energy fuel supply. Aging shrinks brain volume, decreases glucose uptake availability of the brain, and finally, causes cognitive dysfunction. Folic acid supplementation delayed cognitive decline and neurodegeneration. However, whether folic acid affects brain energy metabolism and structural changes is unclear. The study aimed to determine if long-term dietary folic acid supplementation could alleviate age-related cognitive decline by attenuating hippocampus atrophy and promoting brain glucose uptake in Sprague-Dawley (SD) rats. According to folic acid levels in diet, three-month-old male SD rats were randomly divided into four intervention groups for 22 months in equal numbers: folic acid-deficient diet (FA-D) group, folic acid-normal diet (FA-N) group, low folic acid-supplemented diet (FA-L) group, and high folic acid-supplemented diet (FA-H) group. The results showed that serum folate concentrations decreased and serum homocysteine (Hcy) concentrations increased with age, and dietary folic acid supplementation increased serum folate concentrations and decreased Hcy concentrations at 11, 18, and 22 months of intervention. Dietary folic acid supplementation attenuated aging-induced hippocampus atrophy, which was showed by higher fractional anisotropy and lower mean diffusivity in the hippocampus, increased brain ¹⁸F-Fluorodeoxyglucose (¹⁸F-FDG) uptake, then stimulated neuronal survival, and alleviated age-related cognitive decline in SD rats. In conclusion, long-term dietary folic acid supplementation alleviated age-related cognitive decline by attenuating hippocampus atrophy and promoting brain glucose uptake in SD rats.

The Involvement of Post-Translational Modifications in Regulating the Development and Progression of Alzheimer's Disease

Post-translational modifications (PTMs) have been recently reported to be involved in the development and progression of Alzheimer's disease (AD). In detail, PTMs include phosphorylation, glycation, acetylation, sumoylation, ubiquitination, methylation, nitration, and truncation, which are associated with pathological functions of AD-related proteins, such as β-amyloid (Aβ), β-site APP-cleavage enzyme 1 (BACE1), and tau protein. In particular, the roles of aberrant PTMs in the trafficking, cleavage, and degradation of AD-associated proteins, leading to the cognitive decline of the disease, are summarized under AD conditions. By summarizing these research progress, the gaps will be filled between PMTs and AD, which will facilitate the discovery of potential biomarkers, leading to the establishment of novel clinical intervention methods against AD.

In Silico Localization of Perilymph Proteins Enriched in Meńier̀e Disease Using Mammalian Cochlear Single-cell Transcriptomics

Hypothesis

Proteins enriched in the perilymph proteome of Meńier̀e disease (MD) patients may identify affected cell types. Utilizing single-cell transcriptome datasets from the mammalian cochlea, we hypothesize that these enriched perilymph proteins can be localized to specific cochlear cell types.

Background

The limited understanding of human inner ear pathologies and their associated biomolecular variations hinder efforts to develop disease-specific diagnostics and therapeutics. Perilymph sampling and analysis is now enabling further characterization of the cochlear microenvironment. Recently, enriched inner ear protein expression has been demonstrated in patients with MD compared to patients with other inner ear diseases. Localizing expression of these proteins to cochlear cell types can further our knowledge of potential disease pathways and subsequent development of targeted therapeutics.

Methods

We compiled previously published data regarding differential perilymph proteome profiles amongst patients with MD, otosclerosis, enlarged vestibular aqueduct, sudden hearing loss, and hearing loss of undefined etiology (controls). Enriched proteins in MD were cross-referenced against published single-cell/single-nucleus RNA-sequencing datasets to localize gene expression to specific cochlear cell types.

Results

In silico analysis of single-cell transcriptomic datasets demonstrates enrichment of a unique group of perilymph proteins associated with MD in a variety of intracochlear cells, and some exogeneous hematologic and immune effector cells. This suggests that these cell types may play an important role in the pathology associated with late MD, suggesting potential future areas of investigation for MD pathophysiology and treatment.

Conclusions

Perilymph proteins enriched in MD are expressed by specific cochlear cell types based on in silico localization, potentially facilitating development of disease-specific diagnostic markers and therapeutics.

Critical appraisal on mitochondrial dysfunction in Alzheimer's disease

It is widely recognized that Alzheimer's disease (AD) is a common type of progressive neurodegenerative disorder that results in cognitive impairment over time. Approximately 152 million cases of AD are predicted to be reported by 2050. Amyloid plaques and tau proteins are two major hallmarks of AD which can be seen under electron microscope. Mitochondria plays a vital role in the pathogenesis of AD and mitochondria disruption leads to mitochondrial DNA (mtDNA) dysfunction, alteration of mitochondria dependent Ca2+ homeostasis, copper dysfunction, immune cell dysfunction, etc. In this review, we try to cover all the mechanisms related with mitochondrial dysfunction and mitochondrial pathogenesis that may help us to better understand AD as well as open a new era for therapeutic target of AD and treat this progressive disease.

Identification and immune characteristics of molecular subtypes related to protein glycosylation in Alzheimer's disease

BACKGROUND

Protein glycosylation has been confirmed to be involved in the pathological mechanisms of Alzheimer's disease (AD); however, there is still a lack of systematic analysis of the immune processes mediated by protein glycosylation-related genes (PGRGs) in AD.

MATERIALS AND METHODS

Transcriptomic data of AD patients were obtained from the Gene Expression Omnibus database and divided into training and verification datasets. The core PGRGs of the training set were identified by weighted gene co-expression network analysis, and protein glycosylation-related subtypes in AD were identified based on k-means unsupervised clustering. Protein glycosylation scores and neuroinflammatory levels of different subtypes were compared, and functional enrichment analysis and drug prediction were performed based on the differentially expressed genes (DEGs) between the subtypes. A random forest model was used to select important DEGs as diagnostic markers between subtypes, and a line chart model was constructed and verified in other datasets. We evaluated the differences in immune cell infiltration between the subtypes through the single-sample gene set enrichment analysis, analyzed the correlation between core diagnostic markers and immune cells, and explored the expression regulation network of the core diagnostic markers.

RESULTS

Eight core PGRGs were differentially expressed between the training set and control samples. AD was divided into two subtypes with significantly different biological processes, such as vesicle-mediated transport in synapses and neuroactive ligand-receptor interactions. The high protein glycosylation subtype had a higher level of neuroinflammation. Riluzole and sulfasalazine were found to have potential clinical value in this subtype. A reliable construction line chart model was constructed based on nine diagnostic markers, and SERPINA3 was identified as the core diagnostic marker. There were significant differences in immune cell infiltration between the two subtypes. SERPINA3 was found to be closely related to immune cells, and the expression of SERPINA3 in AD was found to be regulated by a competing endogenous RNA network that involves eight long non-coding RNAs and seven microRNAs.

CONCLUSION

Protein glycosylation and its corresponding immune process play an important role in the occurrence and development of AD. Understanding the role of PGRGs in AD may provide a new potential therapeutic target for AD.

Effects of Ultramicronized Palmitoylethanolamide on Mitochondrial Bioenergetics, Cerebral Metabolism, and Glutamatergic Transmission: An Integrated Approach in a Triple Transgenic Mouse Model of Alzheimer's Disease

The therapeutic potential of ultramicronized palmitoylethanolamide (um-PEA) was investigated in young (6-month-old) and adult (12-month-old) 3 × Tg-AD mice, which received um-PEA for 3 months via a subcutaneous delivery system. Mitochondrial bioenergetics, ATP homeostasis, and magnetic resonance imaging/magnetic resonance spectroscopy were evaluated in the frontal cortex (FC) and hippocampus (HIPP) at the end of um-PEA treatment. Glutamate release was investigated by in vivo microdialysis in the ventral HIPP (vHIPP). We demonstrated that chronic um-PEA treatment ameliorates the decrease in the complex-I respiration rate and the FoF1-ATPase (complex V) activity, as well as ATP content depletion in the cortical mitochondria. Otherwise, the impairment in mitochondrial bioenergetics and the release of glutamate after depolarization was not ameliorated by um-PEA treatment in the HIPP of both young and adult 3 × Tg-AD mice. Moreover, progressive age- and pathology-related changes were observed in the cortical and hippocampal metabolism that closely mimic the alterations observed in the human AD brain; these metabolic alterations were not affected by chronic um-PEA treatment. These findings confirm that the HIPP is the most affected area by AD-like pathology and demonstrate that um-PEA counteracts mitochondrial dysfunctions and helps rescue brain energy metabolism in the FC, but not in the HIPP.

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.