His-Rich Domain of Selenoprotein P Ameliorates Neuropathology and Cognitive Deficits by Regulating TrkB Pathway and Zinc Homeostasis in an Alzheimer Model of Mice

The Role of Gut Microbiota in the Neuroprotective Effects of Selenium in Alzheimer's Disease

The objective of the present review was to provide a timely update on the molecular mechanisms underlying the beneficial role of Se in Alzheimer's disease pathogenesis, and discuss the potential role of gut microbiota modulation in this neuroprotective effect. The existing data demonstrate that selenoproteins P, M, S, R, as well as glutathione peroxidases and thioredoxin reductases are involved in regulation of Aβ formation and aggregation, tau phosphorylation and neurofibrillary tangles formation, as well as mitigate the neurotoxic effects of Aβ and phospho-tau. Correspondingly, supplementation with various forms of Se in cellular and animal models of AD was shown to reduce Aβ formation, tau phosphorylation, reverse the decline in brain antioxidant levels, inhibit neuronal oxidative stress and proinflammatory cytokine production, improve synaptic plasticity and neurogenesis, altogether resulting in improved cognitive functions. In addition, most recent findings demonstrate that these neuroprotective effects are associated with Se-induced modulation of gut microbiota. In animal models of AD, Se supplementation was shown to improve gut microbiota biodiversity with a trend to increased relative abundance of Lactobacillus, Bifidobacterium, and Desulfivibrio, while reducing that of Lachnospiracea_NK4A136, Rikenella, and Helicobacter. Moreover, the relative abundance of Se-affected taxa was significantly associated with Aβ accumulation, tau phosphorylation, neuronal oxidative stress, and neuroinflammation, indicative of the potential role of gut microbiota to mediate the neuroprotective effects of Se in AD. Hypothetically, modulation of gut microbiota along with Se supplementation may improve the efficiency of the latter in AD, although further detailed laboratory and clinical studies are required.

New horizons for the role of selenium on cognitive function: advances and challenges

Cognitive deficits associated with oxidative stress and the dysfunction of the central nervous system are present in some neurodegenerative diseases, such as Alzheimer's disease and Parkinson's disease. Selenium (Se), an essential microelement, exhibits cognition-associated functions through selenoproteins mainly owing to its antioxidant property. Due to the disproportionate distribution of Se in the soil, the amount of Se varies greatly in various foods, resulting in a large proportion of people with Se deficiency worldwide. Numerous cell and animal experiments demonstrate Se deficiency-induced cognitive deficits and Se supplementation-improved cognitive performances. However, human studies yield inconsistent results and the mechanism of Se in cognition still remains elusive, which hinder the further exploration of Se in human cognition. To address the urgent issue, the review summarizes Se-contained foods (plant-based foods, animal-based foods, and Se supplements), brain selenoproteins, mechanisms of Se in cognition (improvement of synaptic plasticity, regulation of Zn2+ level, inhibition of ferroptosis, modulation of autophagy and de novo synthesis of L-serine), and effects of Se on cognitive deficits, as well as consequently sheds light on great potentials of Se in the prevention and treatment of cognitive deficits.

Blood Selenium and Serum Glutathione Peroxidase Levels Were Associated with Serum β-Amyloid in Older Adults

BACKGROUND

Studies have established the association between blood β-amyloid (Aβ) levels and Alzheimer's disease, but population-based studies concerning the association between selenium (Se) and Aβ levels in blood samples are very limited. Therefore, we explored the association in an elderly population with Se status and serum Aβ measures.

METHODS

A cross-sectional study on 469 elderly individuals from four rural counties with diverse soil Se levels was carried out. Fasting blood Se, serum selenoprotein P (SELENOP), and glutathione peroxidase (GPX), serum Aβ42, and Aβ40 were measured. Quantile regression models were used to determine the associations of blood Se, serum GPX, and SELENOP with Aβ levels.

RESULTS

Significant negative associations were observed between blood Se and serum Aβ42 and Aβ40 levels at all percentiles (P < 0.05). The associations were generally stronger at higher Aβ42 and Aβ40 percentiles than lower Aβ42 and Aβ40 percentiles. Blood Se was positively associated with serum Aβ42/Aβ40 ratio at 25th, 50th, and 75th percentiles. Significant positive associations were observed between serum GPX and Aβ42 and Aβ40 levels at all percentiles (P < 0.05). The positive associations were generally stronger at higher Aβ42 and Aβ40 percentiles than at lower percentiles. Serum GPX was negatively associated with Aβ42/Aβ40 ratio at 25th, 50th, 75th, and 95th percentiles. No associations with serum SELENOP and Aβ levels were observed.

CONCLUSIONS

Our results suggest that higher Se levels are associated with lower serum Aβ42 and Aβ40 levels and with higher Aβ42/Aβ40 ratio, and the results are specific for different selenoproteins.

Recent progress of nanomedicine in the treatment of Alzheimer's disease

Alzheimer's disease (AD) is the most common cause of memory disruption in elderly subjects, with the prevalence continuing to rise mainly because of the aging world population. Unfortunately, no efficient therapy is currently available for the AD treatment, due to low drug potency and several challenges to delivery, including low bioavailability and the impediments of the blood-brain barrier. Recently, nanomedicine has gained considerable attention among researchers all over the world and shown promising developments in AD treatment. A wide range of nano-carriers, such as polymer nanoparticles, liposomes, solid lipid nanoparticles, dendritic nanoparticles, biomimetic nanoparticles, magnetic nanoparticles, etc., have been adapted to develop successful new treatment strategies. This review comprehensively summarizes the recent advances of different nanomedicine for their efficacy in pre-clinical studies. Finally, some insights and future research directions are proposed. This review can provide useful information to guide the future design and evaluation of nanomedicine in AD treatment.

The protective effects of Esculentoside A through AMPK in the triple transgenic mouse model of Alzheimer's disease

BACKGROUND

Neurofibrillary tangles comprising hyperphosphorylated tau are vital factors associated with the pathogenesis of Alzheimer's disease (AD). The elimination or reduction of hyperphosphorylated and abnormally aggregated tau is a valuable measure in AD therapy. Esculentoside A (EsA), isolated from Phytolacca esculenta, exhibits pharmacotherapeutic efficacy in mice with amyloid beta-induced AD. However, whether EsA affects tau pathology and its specific mechanism of action in AD mice remains unclear.

PURPOSE

To investigate the roles and mechanisms of EsA in cognitive decline and tau pathology in a triple transgenic AD (3 × Tg-AD) mouse model.

METHODS

EsA (5 and 10 mg/kg) was administered via intraperitoneal injection to 8-month-old AD mice for eight consecutive weeks. Y-maze and novel object recognition tasks were used to evaluate the cognitive abilities of mice. Potential signaling pathways and targets in EsA-treated AD mice were assessed using quantitative proteomic analysis. The NFT levels and hippocampal synapse numbers were investigated using Gallyas-Braak silver staining and transmission electron microscopy, respectively. Western blotting and immunofluorescence assays were used to measure the expression of tau-associated proteins.

RESULTS

EsA administration attenuated memory and recognition deficits and synaptic damage in AD mice. Isobaric tags for relative and absolute quantitation proteomic analysis of the mouse hippocampus revealed that EsA modulated the expression of some critical proteins, including brain-specific angiogenesis inhibitor 3, galectin-1, and Ras-related protein 24, whose biological roles are relevant to synaptic function and autophagy. Further research revealed that EsA upregulated AKT/GSK3β activity, in turn, inhibited tau hyperphosphorylation and promoted autophagy to clear abnormally phosphorylated tau. In hippocampus-derived primary neurons, inhibiting AMP-activated protein kinase (AMPK) activity through dorsomorphin could eliminate the effect of EsA, as revealed by increased tau hyperphosphorylation, downregulated activity AKT/GSK3β, and blocked autophagy.

CONCLUSIONS

To our knowledge, this study is the first to demonstrate that EsA attenuates cognitive decline by targeting the pathways of both tau hyperphosphorylation and autophagic clearance in an AMPK-dependent manner and it shows a high reference value in AD pharmacotherapy research.

The role of selenoproteins in neurodevelopment and neurological function: Implications in autism spectrum disorder

Selenium and selenoproteins play a role in many biological functions, particularly in brain development and function. This review outlines the role of each class of selenoprotein in human brain function. Most selenoproteins play a large antioxidant role within the brain. Autism spectrum disorder (ASD) has been shown to correlate with increased oxidative stress, and the presumption of selenoproteins as key players in ASD etiology are discussed. Further, current literature surrounding selenium in ASD and selenium supplementation studies are reviewed. Finally, perspectives are given for future directions of selenoprotein research in ASD.

Human PSEN1 Mutant Glia Improve Spatial Learning and Memory in Aged Mice

The PSEN1 ΔE9 mutation causes a familial form of Alzheimer's disease (AD) by shifting the processing of amyloid precursor protein (APP) towards the generation of highly amyloidogenic Aβ42 peptide. We have previously shown that the PSEN1 ΔE9 mutation in human-induced pluripotent stem cell (iPSC)-derived astrocytes increases Aβ42 production and impairs cellular responses. Here, we injected PSEN1 ΔE9 mutant astrosphere-derived glial progenitors into newborn mice and investigated mouse behavior at the ages of 8, 12, and 16 months. While we did not find significant behavioral changes in younger mice, spatial learning and memory were paradoxically improved in 16-month-old PSEN1 ΔE9 glia-transplanted male mice as compared to age-matched isogenic control-transplanted animals. Memory improvement was associated with lower levels of soluble, but not insoluble, human Aβ42 in the mouse brain. We also found a decreased engraftment of PSEN1 ΔE9 mutant cells in the cingulate cortex and significant transcriptional changes in both human and mouse genes in the hippocampus, including the extracellular matrix-related genes. Overall, the presence of PSEN1 ΔE9 mutant glia exerted a more beneficial effect on aged mouse brain than the isogenic control human cells likely as a combination of several factors.

Zinc in Cognitive Impairment and Aging

Zinc, an essential micronutrient for life, was first discovered in 1869 and later found to be indispensable for the normal development of plants and for the normal growth of rats and birds. Zinc plays an important role in many physiological and pathological processes in normal mammalian brain development, especially in the development of the central nervous system. Zinc deficiency can lead to neurodegenerative diseases, mental abnormalities, sleep disorders, tumors, vascular diseases, and other pathological conditions, which can cause cognitive impairment and premature aging. This study aimed to review the important effects of zinc and zinc-associated proteins in cognitive impairment and aging, to reveal its molecular mechanism, and to highlight potential interventions for zinc-associated aging and cognitive impairments.

Impact of Zinc Transport Mechanisms on Embryonic and Brain Development

The trace element zinc (Zn) binds to over ten percent of proteins in eukaryotic cells. Zn flexible chemistry allows it to regulate the activity of hundreds of enzymes and influence scores of metabolic processes in cells throughout the body. Deficiency of Zn in humans has a profound effect on development and in adults later in life, particularly in the brain, where Zn deficiency is linked to several neurological disorders. In this review, we will summarize the importance of Zn during development through a description of the outcomes of both genetic and early dietary Zn deficiency, focusing on the pathological consequences on the whole body and brain. The epidemiology and the symptomology of Zn deficiency in humans will be described, including the most studied inherited Zn deficiency disease, Acrodermatitis enteropathica. In addition, we will give an overview of the different forms and animal models of Zn deficiency, as well as the 24 Zn transporters, distributed into two families: the ZIPs and the ZnTs, which control the balance of Zn throughout the body. Lastly, we will describe the TRPM7 ion channel, which was recently shown to contribute to intestinal Zn absorption and has its own significant impact on early embryonic development.

A Pan-Cancer Analysis of the Role of Selenoprotein P mRNA in Tumorigenesis

Background

Selenium (Se) exhibits its anti-carcinogenic properties by regulating the redox system. However, the relationship between selenoprotein P (SeP), mRNA (SELENOP mRNA) and tumorigenesis remains unclear. Plasma SeP transports Se to various target tissues and has antioxidant characteristics. The present study aimed to explore the multifaceted pan-cancer properties of SELENOP in terms of its tissue-specific expression, prognostic value, immune function, and signaling pathway enrichment.

Patients and Methods

The expression profile of SELENOP was determined in 33 tumor types and survival, pathway enrichment, and correlation analyses were conducted based on TCGA database. The relationship between SELENOP expression and immune infiltration and macrophage subtype gene markers was investigated using the TIMER and GEPIA.

Results

SELENOP gene expression was decreased in many cancer tissues, but was upregulated in brain lower grade glioma (LGG). Furthermore, SELENOP expression was associated with a better prognosis in most cancers, but a poorer prognosis in LGG and uterine corpus endometrioid carcinoma (UCEC). Our results showed that SELENOP was correlated with infiltration level of six immune cell types, where SELENOP also showed a strong correlation with macrophages in some cancer types. However, we failed to determine macrophage polarization in 33 tumor types. SELENOP negatively regulated vascular endothelial cell proliferation in LGG and UCEC and epidermal cell differentiation in six tumor types. In contrast, upregulation was related to immune function, including T cell activation, B cell-mediated immunity, adaptive immune response and immune response regulation cell surface receptor signaling pathways in another six tumor types.

Conclusion

These findings highlighted the tissue-specific expression, prognostic value and immune characteristics of SELENOP in pan-cancer, and provided insights for illustrating the role of SELENOP in tumorigenesis.

Roles of Selenoproteins in Brain Function and the Potential Mechanism of Selenium in Alzheimer's Disease

Selenium (Se) and its compounds have been reported to have great potential in the prevention and treatment of Alzheimer's disease (AD). However, little is known about the functional mechanism of Se in these processes, limiting its further clinical application. Se exerts its biological functions mainly through selenoproteins, which play vital roles in maintaining optimal brain function. Therefore, selenoproteins, especially brain function-associated selenoproteins, may be involved in the pathogenesis of AD. Here, we analyze the expression and distribution of 25 selenoproteins in the brain and summarize the relationships between selenoproteins and brain function by reviewing recent literature and information contained in relevant databases to identify selenoproteins (GPX4, SELENOP, SELENOK, SELENOT, GPX1, SELENOM, SELENOS, and SELENOW) that are highly expressed specifically in AD-related brain regions and closely associated with brain function. Finally, the potential functions of these selenoproteins in AD are discussed, for example, the function of GPX4 in ferroptosis and the effects of the endoplasmic reticulum (ER)-resident protein SELENOK on Ca²⁺ homeostasis and receptor-mediated synaptic functions. This review discusses selenoproteins that are closely associated with brain function and the relevant pathways of their involvement in AD pathology to provide new directions for research on the mechanism of Se in AD.