Activation of vitamin D receptor inhibits Tau phosphorylation is associated with reduction of iron accumulation in APP/PS1 transgenic mice

The role of protein phosphorylation modifications mediated by iron metabolism regulatory networks in the pathogenesis of Alzheimer's disease

Alzheimer's disease (AD) is a severe neurodegenerative disease characterized mainly by the formation of amyloid beta (Aβ) plaques and abnormal phosphorylation of tau. In recent years, an imbalance in iron homeostasis has been recognized to play a key role in the pathological process of AD. Abnormal iron accumulation can activate various kinases such as glycogen synthase kinase-3β, cyclin-dependent kinase 5, and mitogen-activated protein kinase, leading to abnormal phosphorylation of tau and amyloid precursor protein, and accelerating the formation of Aβ plaques and neurofibrillary tangles. In addition, iron-mediated oxidative stress not only triggers neuronal damage, but also exacerbates neuronal dysfunction by altering the phosphorylation of N-methyl-D-aspartate receptors and γ-aminobutyric acid type A receptors. Iron accumulation also affects the phosphorylation status of tyrosine hydroxylase, the rate-limiting enzyme for dopamine synthesis, interfering with the dopamine signaling pathway. On the other hand, iron affects iron transport and metabolism in the brain by regulating the phosphorylation of transferrin, further disrupting iron homeostasis. Therapeutic strategies targeting iron metabolism show promise by reducing iron accumulation, inhibiting oxidative stress, and reducing abnormal phosphorylation of key proteins. This article reviews the molecular mechanisms of phosphorylation modifications mediated by iron homeostasis imbalance in AD, and discusses the potential of interventions that regulate iron metabolism and related signaling pathways, providing a new theoretical basis for the treatment of AD.

Vitamin D3 Exerts a Neuroprotective Effect in Metabolic Syndrome Rats: Role of BDNF/TRKB/Akt/GS3Kβ Pathway

Metabolic syndrome (MetS) is usually associated with cognitive impairment, neuropathic pain, and reduced brain-derived neurotrophic factor (BDNF) levels. BDNF via tropomyosin receptor kinase B (TrkB) exerts neuroprotection by activating protein kinase B (Akt) to inhibit glycogen synthase kinase-3β (GSK3β). Although Vitamin D3 (VitD3) has demonstrated favorable metabolic and neuronal outcomes in MetS, the precise molecular mechanisms underlying its neuroprotective effects remain poorly elucidated. We aimed to test the hypothesis that VitD3 mitigates MetS-induced cognition deficits and neuropathic pain via modulating the BDNF/TRKB/Akt/GS3Kβ signaling pathway. MetS was induced in male rats by 10% fructose-supplemented water and 3% salt-enriched diet. After 6 weeks, normal and MetS rats received either vehicle or VitD3 (10 µg/kg/day) for an additional 6 weeks. Glycemic status, lipid profile, and behavioral changes were assessed. The advanced glycation end products (AGEs), and markers of inflammation (TNF-α and NF-κB), oxidative stress (malondialdehyde), and apoptosis (caspase3), as well as BDNF, TrkB, PI3K, Akt, GSK3β, phosphorylated tau, and amyloid beta (Aβ) were assessed in the cerebral cortex. MetS rats had deteriorated glycemic and lipid profiles, higher AGEs, reduced levels of BDNF, TrkB, PI3K, and active Akt, along with increased GSK3β levels, inflammation, oxidative stress, and apoptosis. These changes were associated with higher levels of cognitive impairment markers phosphorylated tau and Aβ, as well as behavioral changes indicative of cognitive impairment and neuropathic pain. VitD3 improved the cognitive and behavioral alterations, while mitigating the associated molecular derangements. Our results indicate that VitD3 may exert neuroprotective effects by modulating the BDNF/TrkB/PI3K/Akt/GSK3β signaling pathway.

Astrocyte-derived lactoferrin inhibits neuronal ferroptosis by reducing iron content and GPX4 degradation in APP/PS1 transgenic mice

Increased astrocytic lactoferrin (Lf) expression was observed in the brains of elderly individuals and Alzheimer's disease (AD) patients. Our previous study revealed that astrocytic Lf overexpression improved cognitive capacity by facilitating Lf secretion to neurons to inhibit β-amyloid protein (Aβ) production in APP/PS1 mice. Here, we further discovered that astrocytic Lf overexpression inhibited neuronal loss by decreasing iron accumulation and increasing glutathione peroxidase 4 (GPX4) expression in neurons within APP/PS1 mice. Furthermore, human Lf (hLf) treatment inhibited ammonium ferric citrate (FAC)-induced ferroptosis by chelating intracellular iron. Additionally, machine learning analysis uncovered a correlation between Lf and GPX4. hLf treatment boosted low-density lipoprotein receptor-related protein 1 (LRP1) internalization and facilitated its interaction with heat shock cognate 70 (HSC70), thereby inhibiting HSC70 binds to GPX4, and eventually attenuating GPX4 degradation and FAC-induced ferroptosis. Overall, astrocytic Lf overexpression inhibited neuronal ferroptosis through two pathways: reducing intracellular iron accumulation and promoting GPX4 expression via inhibiting chaperone-mediated autophagy (CMA)-mediated GPX4 degradation. Hence, upregulating astrocytic Lf expression is a promising strategy for combating AD.

Tremendous Fidelity of Vitamin D3 in Age-related Neurological Disorders

Vitamin D3 (VD) is a secosteroid hormone and shows a pleiotropic effect in brain-related disorders where it regulates redox imbalance, inflammation, apoptosis, energy production, and growth factor synthesis. Vitamin D3's active metabolic form, 1,25-dihydroxy Vitamin D3 (1,25(OH)2D3 or calcitriol), is a known regulator of several genes involved in neuroplasticity, neuroprotection, neurotropism, and neuroinflammation. Multiple studies suggest that VD deficiency can be proposed as a risk factor for the development of several age-related neurological disorders. The evidence for low serum levels of 25-hydroxy Vitamin D3 (25(OH)D3 or calcidiol), the major circulating form of VD, is associated with an increased risk of Alzheimer's disease (AD), Parkinson's disease (PD), Huntington's disease (HD), dementia, and cognitive impairment. Despite decades of evidence on low VD association with neurological disorders, the precise molecular mechanism behind its beneficial effect remains controversial. Here, we will be delving into the neurobiological importance of VD and discuss its benefits in different neuropsychiatric disorders. The focus will be on AD, PD, and HD as they share some common clinical, pathological, and epidemiological features. The central focus will be on the different attributes of VD in the aspect of its anti-oxidative, anti-inflammatory, anti-apoptotic, anti-cholinesterase activity, and psychotropic effect in different neurodegenerative diseases.

Transgenerational hormesis in healthy aging and antiaging medicine from bench to clinics: Role of food components

Neurodegenerative diseases have multifactorial pathogenesis, mainly involving neuroinflammatory processes. Finding drugs able to treat these diseases, expecially because for most of these diseases there are no effective drugs, and the current drugs cause undesired side effects, represent a crucial point. Most in vivo and in vitro studies have been concentrated on various aspects related to neurons (e.g. neuroprotection), however, there has not been focus on the prevention of early stages involving glial cell activation and neuroinflammation. Recently, it has been demonstrated that nutritional phytochemicals including polyphenols, the main active constituents of the Mediterranean diet, maintain redox balance and neuroprotection through the activation of hormetic vitagene pathway. Recent lipidomics data from our laboratory indicate mushrooms as strong nutritional neuronutrients with strongly activity against neuroinflammation in Meniere' diseaseas, a model of cochleovestibular neural degeneration, as well as in animal model of traumatic brain injury, or rotenone induced parkinson's disease. Moreover, Hidrox®, an aqueous extract of olive containing hydroxytyrosol, and Boswellia, acting as Nrf2 activators, promote resilience by enhancing the redox potential, and thus, regulate through hormetic mechanisms, cellular stress response mechanisms., Thus, modulation of cellular stress pathways, in particular vitagenes system, may be an innovative approach for therapeutic intervention in neurodegenerative disorders.

GSK3: A potential target and pending issues for treatment of Alzheimer's disease

Glycogen synthase kinase-3 (GSK3), consisting of GSK3α and GSK3β subtypes, is a complex protein kinase that regulates numerous substrates. Research has observed increased GSK3 expression in the brains of Alzheimer's disease (AD) patients and models. AD is a neurodegenerative disorder with diverse pathogenesis and notable cognitive impairments, characterized by Aβ aggregation and excessive tau phosphorylation. This article provides an overview of GSK3's structure and regulation, extensively analyzing its relationship with AD factors. GSK3 overactivation disrupts neural growth, development, and function. It directly promotes tau phosphorylation, regulates amyloid precursor protein (APP) cleavage, leading to Aβ formation, and directly or indirectly triggers neuroinflammation and oxidative damage. We also summarize preclinical research highlighting the inhibition of GSK3 activity as a primary therapeutic approach for AD. Finally, pending issues like the lack of highly specific and affinity-driven GSK3 inhibitors, are raised and expected to be addressed in future research. In conclusion, GSK3 represents a target in AD treatment, filled with hope, challenges, opportunities, and obstacles.

Heavy metals toxicity on epigenetic modifications in the pathogenesis of Alzheimer's disease (AD)

Alzheimer's disease (AD) is a progressive decline in cognitive ability and behavior which eventually disrupts daily activities. AD has no cure and the progression rate varies unlikely. Among various causative factors, heavy metals are reported to be a significant hazard in AD pathogenesis. Metal-induced neurodegeneration has been focused globally with thorough research to unravel the mechanistic insights in AD. Recently, heavy metals suggested to play an important role in epigenetic alterations which might provide evidential results on AD pathology. Epigenetic modifications are known to play towards novel therapeutic approaches in treating AD. Though many studies focus on epigenetics and heavy metal implications in AD, there is a lack of research on heavy metal influence on epigenetic toxicity in neurological disorders. The current review aims to elucidate the plausible role of cadmium (Cd), iron (Fe), arsenic (As), copper (Cu), and lithium (Li) metals on epigenetic factors and the increase in amyloid beta and tau phosphorylation in AD. Also, the review discusses the common methods of heavy metal detection to implicate in AD pathogenesis. Hence, from this review, we can extend the need for future research on identifying the mechanistic behavior of heavy metals on epigenetic toxicity and to develop diagnostic and therapeutic markers in AD.

Vitamin D, Alzheimer's disease and related dementia

Vitamin D has been proposed as a potential strategy to mitigate age-related cognitive decline and dementia, including Alzheimer's dementia, the predominant type of dementia. Rodent studies have provided insight into the potential mechanisms underlying the role of vitamin D in Alzheimer's disease and dementia. However, inconsistencies with respect to age, sex, and genetic background of the rodent models used poses some limitations regarding scientific rigor and translation. Several human observational studies have evaluated the association of vitamin D status with cognitive decline and dementia, and the results are conflicting. Randomized clinical trials of vitamin D supplementation have included cognitive outcomes. However, most of the available trials have not been designed specifically to test the effect of vitamin D on age-related cognitive decline and dementia, so it remains questionable how much additional vitamin D will improve cognitive performance. Here we evaluate the strengths and limitations of the available evidence regarding the role of vitamin D in AD, cognitive decline, dementia.

Iron homeostasis imbalance and ferroptosis in brain diseases

Brain iron homeostasis is maintained through the normal function of blood-brain barrier and iron regulation at the systemic and cellular levels, which is fundamental to normal brain function. Excess iron can catalyze the generation of free radicals through Fenton reactions due to its dual redox state, thus causing oxidative stress. Numerous evidence has indicated brain diseases, especially stroke and neurodegenerative diseases, are closely related to the mechanism of iron homeostasis imbalance in the brain. For one thing, brain diseases promote brain iron accumulation. For another, iron accumulation amplifies damage to the nervous system and exacerbates patients' outcomes. In addition, iron accumulation triggers ferroptosis, a newly discovered iron-dependent type of programmed cell death, which is closely related to neurodegeneration and has received wide attention in recent years. In this context, we outline the mechanism of a normal brain iron metabolism and focus on the current mechanism of the iron homeostasis imbalance in stroke, Alzheimer's disease, and Parkinson's disease. Meanwhile, we also discuss the mechanism of ferroptosis and simultaneously enumerate the newly discovered drugs for iron chelators and ferroptosis inhibitors.

Reply to Pluta, R. Comment on "Minich et al. Is Melatonin the "Next Vitamin D"?: A Review of Emerging Science, Clinical Uses, Safety, and Dietary Supplements. Nutrients 2022, 14, 3934"

We would like to thank Dr. Pluta for his thoughtful comments [...].

The Vitamin D Receptor as a Potential Target for the Treatment of Age-Related Neurodegenerative Diseases Such as Alzheimer's and Parkinson's Diseases: A Narrative Review

The vitamin D receptor (VDR) belongs to the nuclear receptor superfamily of transcription factors. The VDR is expressed in diverse brain regions and has been implicated in the neuroprotective, antiaging, prosurvival, and anti-inflammatory action of vitamin D. Accordingly, a relationship between vitamin D insufficiency and susceptibility to neurodegenerative diseases has been suggested. However, due to the multitargeted mechanisms of vitamin D and its often overlapping genomic and nongenomic effects, the role of the VDR in brain pathologies remains obscure. In this narrative review, we present progress in deciphering the molecular mechanism of nuclear VDR-mediated vitamin D effects on prosurvival and anti-inflammatory signaling pathway activity within the central nervous system. In line with the concept of the neurovascular unit in pathomechanisms of neurodegenerative diseases, a discussion of the role of the VDR in regulating the immune and vascular brain systems is also included. Next, we discuss the results of preclinical and clinical studies evaluating the significance of vitamin D status and the efficacy of vitamin D supplementation in the treatment of Parkinson's and Alzheimer's diseases, emphasizing the possible role of the VDR in these phenomena. Finally, the associations of some VDR polymorphisms with higher risks and severity of these neurodegenerative disorders are briefly summarized.

The metal ion hypothesis of Alzheimer's disease and the anti-neuroinflammatory effect of metal chelators

Alzheimer's disease (AD), characterized by the β-amyloid protein (Aβ) deposition and tau hyperphosphorylation, is the most common dementia with uncertain etiology. The clinical trials of Aβ monoclonal antibody drugs have almost failed, giving rise to great attention on the other etiologic hypothesis regarding AD such as metal ions dysmetabolism and chronic neuroinflammation. Mounting evidence revealed that the metal ions (iron, copper, and zinc) were dysregulated in the susceptible brain regions of AD patients, which was highly associated with Aβ deposition, tau hyperphosphorylation, neuronal loss, as well as neuroinflammation. Further studies uncovered that iron, copper and zinc could not only enhance the production of Aβ but also directly bind to Aβ and tau to promote their aggregations. In addition, the accumulation of iron and copper could respectively promote ferroptosis and cuproptosis. Therefore, the metal ion chelators were recognized as promising agents for treating AD. This review comprehensively summarized the effects of metal ions on the Aβ dynamics and tau phosphorylation in the progression of AD. Furthermore, taking chronic neuroinflammation contributes to the progression of AD, we also provided a summary of the mechanisms concerning metal ions on neuroinflammation and highlighted the metal ion chelators may be potential agents to alleviate neuroinflammation under the condition of AD. Nevertheless, more investigations regarding metal ions on neuroinflammation should be taken into practice, and the effects of metal ion chelators on neuroinflammation should gain more attention. Running title: Metal chelators against neuroinflammation.

Vitamin D, a Secosteroid Hormone and Its Multifunctional Receptor, Vitamin D Receptor, in Alzheimer's Type Neurodegeneration

Vitamin D is a secosteroid hormone exerting neurosteroid-like properties. Its well-known nuclear hormone receptor, and recently proposed as a mitochondrial transcription factor, vitamin D receptor, acts for its primary functions. The second receptor is an endoplasmic reticulum protein, protein disulfide isomerase A3 (PDIA3), suggested to act as a rapid response. Vitamin D has effects on various systems, particularly through calcium metabolism. Among them, the nervous system has an important place in the context of our subject. Recent studies have shown that vitamin D and its receptors have numerous effects on the nervous system. Neurodegeneration is a long-term process. Throughout a human life span, so is vitamin D deficiency. Our previous studies and others have suggested that the out-come of long-term vitamin D deficiency (hypovitaminosis D or inefficient utilization of vitamin D), may lead neurons to be vulnerable to aging and neurodegeneration. We suggest that keeping vitamin D levels at adequate levels at all stages of life, considering new approaches such as agonists that can activate vitamin D receptors, and utilizing other derivatives produced in the synthesis process with UVB are crucial when considering vitamin D-based intervention studies. Given most aspects of vitamin D, this review outlines how vitamin D and its receptors work and are involved in neurodegeneration, emphasizing Alzheimer's disease.

Vitamin D and neurodegenerative diseases

Neurodegenerative diseases, featured by progressive loss of structure or function of neurons, are considered incurable at present. Movement disorders like tremor and postural instability, cognitive or behavioral disorders such as memory impairment are the most common symptoms of them and the growing patient population of neurodegenerative diseases poses a serious threat to public health and a burden on economic development. Hence, it is vital to prevent the occurrence of the diseases and delay their progress. Vitamin D can be transformed into a hormone in vivo with both genomic and non-genomic actions, exerting diverse physiological effects. Cumulative evidence indicates that vitamin D can ameliorate neurodegeneration by regulating pertinent molecules and signaling pathways including maintaining Ca2+ homeostasis, reducing oxidative stress, inhibiting inflammation, suppressing the formation and aggregation of the pathogenic protein, etc. This review updates discoveries of molecular mechanisms underlying biological functions of vitamin D in neurodegenerative diseases including Alzheimer's disease, Parkinson's disease, multiple sclerosis, and vascular dementia. Clinical trials investigating the influence of vitamin D supplementation in patients with neurodegenerative diseases are also summarized. The synthesized information will probably provoke an enhanced understanding of the neuroprotective roles of vitamin D in the nervous system and provide therapeutic options for patients with neurodegenerative diseases in the future.

Interdisciplinary Approaches to Deal with Alzheimer's Disease-From Bench to Bedside: What Feasible Options Do Already Exist Today?

Alzheimer's disease is one of the most common neurodegenerative diseases in the western population. The incidence of this disease increases with age. Rising life expectancy and the resulting increase in the ratio of elderly in the population are likely to exacerbate socioeconomic problems. Alzheimer's disease is a multifactorial disease. In addition to amyloidogenic processing leading to plaques, and tau pathology, but also other molecular causes such as oxidative stress or inflammation play a crucial role. We summarize the molecular mechanisms leading to Alzheimer's disease and which potential interventions are known to interfere with these mechanisms, focusing on nutritional approaches and physical activity but also the beneficial effects of cognition-oriented treatments with a focus on language and communication. Interestingly, recent findings also suggest a causal link between oral conditions, such as periodontitis or edentulism, and Alzheimer's disease, raising the question of whether dental intervention in Alzheimer's patients can be beneficial as well. Unfortunately, all previous single-domain interventions have been shown to have limited benefit to patients. However, the latest studies indicate that combining these efforts into multidomain approaches may have increased preventive or therapeutic potential. Therefore, as another emphasis in this review, we provide an overview of current literature dealing with studies combining the above-mentioned approaches and discuss potential advantages compared to monotherapies. Considering current literature and intervention options, we also propose a multidomain interdisciplinary approach for the treatment of Alzheimer's disease patients that synergistically links the individual approaches. In conclusion, this review highlights the need to combine different approaches in an interdisciplinary manner, to address the future challenges of Alzheimer's disease.

Associations Between Intrathecal Levels of Vitamin D, Cytokines, and Core Biomarkers of Alzheimer’s Disease: A Cross-Sectional Study

Background: Several studies have examined association between vitamin D levels in serum and cognition, but little is known of vitamin D levels in cerebrospinal fluid (CSF) and association with Alzheimer’s disease (AD). Objective: In this cross-sectional, explorative study we investigated possible associations of vitamin D in CSF with biomarkers for AD, amyloid-β, tau protein/phosphorylated tau protein in CSF, and with the cytokines IL-6, IL-8, and TNF-α in CSF in patients with cognitive impairment and cognitively healthy controls. Methods: We included 100 outpatients ≥65 years referred for assessment of cognitive impairment and 76 age- and sex-matched cognitively healthy controls. Levels of 25-hydroxyvitamin D (25(OH)D), amyloid-β, tau protein and phosphorylated tau protein, as well as IL-6, IL-8, and TNF-α, were analyzed in CSF in both groups. Results: Higher levels of 25(OH)D in CSF in all groups together were associated with lower levels of tau protein (p = 0.01) and phosphorylated tau protein (p = 0.005). We found no association between 25(OH)D levels in CSF and pathological levels of amyloid-β in CSF nor levels of IL-6 or TNF-α in CSF. Higher levels of 25(OH)D in CSF were associated with higher levels of IL-8 in CSF (p = 0.002). However, vitamin D explained only 6% of variance in IL-8. There was no significant difference between the patient groups and the control group regarding the association between 25(OH)D in CSF and any of the three cytokines in CSF. Conclusion: Participants with higher CSF levels of 25(OH)D exhibited reduced CSF levels of tau protein and phosphorylated tau protein.