Retinoic acid-elicited RARα/RXRα signaling attenuates Aβ production by directly inhibiting γ-secretase-mediated cleavage of amyloid precursor protein

Ergosterol promotes neurite outgrowth, inhibits amyloid-beta synthesis, and extends longevity: In vitro neuroblastoma and in vivo Caenorhabditis elegans evidence

AIMS

Alzheimer's disease (AD), the most common neurodegenerative disorder associated with aging, is characterized by amyloid-β (Aβ) plaques in the hippocampus. Ergosterol, a mushroom sterol, exhibits neuroprotective activities; however, the underlying mechanisms of ergosterol in promoting neurite outgrowth and preventing Aβ-associated aging have never been investigated. We aim to determine the beneficial activities of ergosterol in neuronal cells and Caenorhabditis elegans (C. elegans).

MATERIALS AND METHODS

The neuritogenesis and molecular mechanisms of ergosterol were investigated in wild-type and Aβ precursor protein (APP)-overexpressing Neuro2a cells. The anti-amyloidosis properties of ergosterol were determined by evaluating in vitro Aβ production and the potential inhibition of Aβ-producing enzymes. Additionally, AD-associated transgenic C. elegans was utilized to investigate the in vivo attenuating effects of ergosterol.

KEY FINDINGS

Ergosterol promoted neurite outgrowth in Neuro2a cells through the upregulation of the transmembrane protein Teneurin-4 (Ten-4) mRNA and protein expressions, phosphorylation of the extracellular signal-regulated kinases (ERKs), activity of cAMP response element (CRE), and growth-associated protein-43 (GAP-43). Furthermore, ergosterol enhanced neurite outgrowth in transgenic Neuro2A cells overexpressing either the wild-type APP (Neuro2a-APPwt) or the Swedish mutant APP (Neuro2a-APPswe) through the Ten-4/ERK/CREB/GAP-43 signaling pathway. Interestingly, ergosterol inhibited Aβ synthesis in Neuro2a-APPwt cells. In silico analysis indicated that ergosterol can interact with the catalytic sites of β- and γ-secretases. In Aβ-overexpressing C. elegans, ergosterol decreased Aβ accumulation, increased chemotaxis behavior, and prolonged lifespan.

SIGNIFICANCE

Ergosterol is a potential candidate compound that might benefit AD patients by promoting neurite outgrowth, inhibiting Aβ synthesis, and enhancing longevity.

The activation of RARα prevents surgery-induced cognitive impairments via the inhibition of neuroinflammation and the restoration of synaptic proteins in elderly mice

Post-operative cognitive dysfunction (POCD) is a multi-etiological symptom mainly occurred in elderly people after surgery. The activation of retinoic acid receptor α (RARα), a transcriptional factor, was previously predicated to be negatively associated with the occurrence of POCD. However, the mechanisms underlying anti-POCD effects of RARα were still unclear. In this study, AM580, a selective agonist of RARα, and all-trans-retinoic acid (ATRA), a pan agonist of RAR, significantly alleviated cognitive dysfunction and increased the expression of RARα in elderly mice after surgery, which was decreased by RO41-5253, an antagonist of RARα. A bioinformatic study further predicted that the activation of RARα might produce anti-POCD effects via the restoration of synaptic proteins. Both agonists inhibited the expression of Toll-like receptor 4 (TLR4), myeloid differentiation factor 88 (Myd88) and the phosphorylation of nuclear factorkappa-B (NF-κB), leading to the prevention of microglial over-activation and pro-inflammatory cytokines secretion in the hippocampal regions of elderly mice after surgery. Moreover, AM580 and ATRA increased the expression of brain-derived neurotrophic factor (BDNF) and postsynaptic density protein 95 (PSD95), and the phosphorylation of extracellular signal-regulated kinase (ERK) and cAMP-response element binding protein (CREB). All these results suggested that the activation of RARα prevented surgery-induced cognitive impairments via the inhibition of neuroinflammation by the reduction of the TLR4/Myd88/NF-κB pathway and the restoration of synaptic proteins by the activation of the BDNF/ERK/CREB pathway, providing a further support that RARα could be developed as a therapeutic target for POCD.

Protective function of StAR in amyloid-β accumulated hippocampal neurotoxicity and neurosteroidogenesis: Mechanistic insights into Alzheimer's disease

The steroidogenic acute regulatory (StAR) protein principally mediates steroid hormone biosynthesis by governing the transport of intramitochondrial cholesterol. Neurosteroids progressively decrease during aging, the key risk factor for Alzheimer's disease (AD), which is triggered by brain-region specific accumulation of amyloid beta (Aβ) precursor protein (APP), a key pathological factor. We demonstrate that hippocampal neuronal cells overexpressing wild-type (WtAPP) and mutant APP (mAPP) plasmids, conditions mimetic to AD, resulted in decreases in StAR mRNA, free cholesterol, and pregnenolone levels. The magnitude of suppression of the steroidogenic response was more pronounced with mAPP than that of WtAPP. While mAPP-waned assorted anomalies correlate to AD pathology, deterioration of APP/Aβ laden StAR expression and neurosteroid biosynthesis was enhanced by retinoid signaling. An abundance of mitochondrially targeted StAR expression partially restored APP/Aβ accumulated diverse neurodegenerative vulnerabilities. Immunofluorescence analyses revealed that overexpression of StAR diminishes mAPP provoked Aβ aggregation. Co-expression of StAR and mAPP in hippocampal neurons substantially reversed the declines in mAPP mediated cell survival, mitochondrial oxygen consumption rate, and ATP production. Concurrently, induction of mAPP induced Aβ loading showed an increase in cholesterol esters, but decrease in free cholesterol, concomitant with pregnenolone biosynthesis, events that were inversely regulated by StAR. Moreover, retinoid signaling was found to augment cholesterol content for facilitating neurosteroid biosynthesis in an AD mimetic condition. These findings provide novel insights into the molecular events by which StAR acts to protect mAPP-induced hippocampal neurotoxicity, mitochondrial dysfunction, and neurosteroidogenesis, and these measures are fundamental for ameliorating and/or delaying dementia in individuals with AD.

Bioinorganic Chemistry of Micronutrients Related to Alzheimer's and Parkinson's Diseases

Metal ions are fundamental to guarantee the regular physiological activity of the human organism. Similarly, vitamins play a key role in many biological functions of the metabolism, among which are coenzymes, redox mediators, and antioxidants. Due to their importance in the human organism, both metals and vitamins have been extensively studied for their involvement in neurodegenerative diseases (NDs). However, the full potential of the interaction between vitamins and metal ions has not been fully explored by researchers yet, and further investigation on this topic is needed. The aim of this review is to provide an overview of the scientific literature on the implications of vitamins and selected metal ions in two of the most common neurodegenerative diseases, Alzheimer's and Parkinson's disease. Furthermore, vitamin-metal ion interactions are discussed in detail focusing on their bioinorganic chemistry, with the perspective of arousing more interest in this fascinating bioinorganic field.

Vitamin A metabolites inhibit ferroptosis

Vitamin A (retinol) is a lipid-soluble vitamin that acts as a precursor for several bioactive compounds, such as retinaldehyde (retinal) and isomers of retinoic acid. Retinol and all-trans-retinoic acid (atRA) penetrate the blood-brain barrier and are reported to be neuroprotective in several animal models. We characterised the impact of retinol and its metabolites, all-trans-retinal (atRAL) and atRA, on ferroptosis-a programmed cell death caused by iron-dependent phospholipid peroxidation. Ferroptosis was induced by erastin, buthionine sulfoximine or RSL3 in neuronal and non-neuronal cell lines. We found that retinol, atRAL and atRA inhibited ferroptosis with a potency superior to α-tocopherol, the canonical anti-ferroptotic vitamin. In contrast, we found that antagonism of endogenous retinol with anhydroretinol sensitises ferroptosis induced in neuronal and non-neuronal cell lines. Retinol and its metabolites atRAL and atRA directly interdict lipid radicals in ferroptosis since these compounds displayed radical trapping properties in a cell-free assay. Vitamin A, therefore, complements other anti-ferroptotic vitamins, E and K; metabolites of vitamin A, or agents that alter their levels, may be potential therapeutics for diseases where ferroptosis is implicated.

Thwarting Alzheimer's Disease through Healthy Lifestyle Habits: Hope for the Future

Alzheimer's disease (AD) is a neurodegenerative disorder that slowly disintegrates memory and thinking skills. Age is known to be the major risk factor in AD, but there are several nonmodifiable and modifiable causes. The nonmodifiable risk factors such as family history, high cholesterol, head injuries, gender, pollution, and genetic aberrations are reported to expediate disease progression. The modifiable risk factors of AD that may help prevent or delay the onset of AD in liable people, which this review focuses on, includes lifestyle, diet, substance use, lack of physical and mental activity, social life, sleep, among other causes. We also discuss how mitigating underlying conditions such as hearing loss and cardiovascular complications could be beneficial in preventing cognitive decline. As the current medications can only treat the manifestations of AD and not the underlying process, healthy lifestyle choices associated with modifiable factors is the best alternative strategy to combat the disease.

Bidirectional communication between brain and visceral white adipose tissue: Its potential impact on Alzheimer's disease

A variety of axes between brain and abdominal organs have been reported, but the interaction between brain and visceral white adipose tissue (vWAT) remains unclear. In this review, we summarized human studies on the association between brain and vWAT, and generalized their interaction and the underlying mechanisms according to animal and cell experiments. On that basis, we come up with the concept of the brain-vWAT axis (BVA). Furthermore, we analyzed the potential mechanisms of involvement of BVA in the pathogenesis of Alzheimer's disease (AD), including vWAT-derived fatty acids, immunological properties of vWAT, vWAT-derived retinoic acid and vWAT-regulated insulin resistance. The proposal of BVA may expand our understanding to some extent of how the vWAT impacts on brain health and diseases, and provide a novel approach to study the pathogenesis and treatment strategies of neurodegenerative disorders.

Amylin and Secretases in the Pathology and Treatment of Alzheimer's Disease

Alzheimer’s disease remains a prevailing neurodegenerative condition which has an array physical, emotional, and financial consequences to patients and society. In the past decade, there has been a greater degree of investigation on therapeutic small peptides. This group of biomolecules have a profile of fundamentally sound characteristics which make them an intriguing area for drug development. Among these biomolecules, there are four modulatory mechanisms of interest in this review: alpha-, beta-, gamma-secretases, and amylin. These protease-based biomolecules all have a contributory role in the amyloid cascade hypothesis. Moreover, the involvement of various biochemical pathways intertwines these peptides to have shared regulators (i.e., retinoids). Further clinical and translational investigation must occur to gain a greater understanding of its potential application in patient care. The aim of this narrative review is to evaluate the contemporary literature on these protease biomolecule modulators and determine its utility in the treatment of Alzheimer’s disease.

Revisiting APP secretases: an overview on the holistic effects of retinoic acid receptor stimulation in APP processing

Alzheimer's disease (AD) is the leading cause of dementia worldwide and is characterized by the accumulation of the β-amyloid peptide (Aβ) in the brain, along with profound alterations in phosphorylation-related events and regulatory pathways. The production of the neurotoxic Aβ peptide via amyloid precursor protein (APP) proteolysis is a crucial step in AD development. APP is highly expressed in the brain and is complexly metabolized by a series of sequential secretases, commonly denoted the α-, β-, and γ-cleavages. The toxicity of resulting fragments is a direct consequence of the first cleaving event. β-secretase (BACE1) induces amyloidogenic cleavages, while α-secretases (ADAM10 and ADAM17) result in less pathological peptides. Hence this first cleavage event is a prime therapeutic target for preventing or reverting initial biochemical events involved in AD. The subsequent cleavage by γ-secretase has a reduced impact on Aβ formation but affects the peptides' aggregating capacity. An array of therapeutic strategies are being explored, among them targeting Retinoic Acid (RA) signalling, which has long been associated with neuronal health. Additionally, several studies have described altered RA levels in AD patients, reinforcing RA Receptor (RAR) signalling as a promising therapeutic strategy. In this review we provide a holistic approach focussing on the effects of isoform-specific RAR modulation with respect to APP secretases and discuss its advantages and drawbacks in subcellular AD related events.

Role of Retinoid X Receptors (RXRs) and dietary vitamin A in Alzheimer's disease: Evidence from clinicopathological and preclinical studies

BACKGROUND

Vitamin A (VitA), via its active metabolite retinoic acid (RA), is critical for the maintenance of memory function with advancing age. Although its role in Alzheimer's disease (AD) is not well understood, data suggest that impaired brain VitA signaling is associated with the accumulation of β-amyloid peptides (Aβ), and could thus contribute to the onset of AD.

METHODS

We evaluated the protective action of a six-month-long dietary VitA-supplementation (20 IU/g), starting at 8 months of age, on the memory and the neuropathology of the 3xTg-AD mouse model of AD (n = 11-14/group; including 4-6 females and 7-8 males). We also measured protein levels of Retinoic Acid Receptor β (RARβ) and Retinoid X Receptor γ (RXRγ) in homogenates from the inferior parietal cortex of 60 participants of the Religious Orders study (ROS) divided in three groups: no cognitive impairment (NCI) (n = 20), mild cognitive impairment (MCI) (n = 20) and AD (n = 20).

RESULTS

The VitA-enriched diet preserved spatial memory of 3xTg-AD mice in the Y maze. VitA-supplementation affected hippocampal RXR expression in an opposite way according to sex by tending to increase in males and decrease in females their mRNA expression. VitA-enriched diet also reduced the amount of hippocampal Aβ₄₀ and Aβ₄₂, as well as the phosphorylation of tau protein at sites Ser396/Ser404 (PHF-1) in males. VitA-supplementation had no effect on tau phosphorylation in females but worsened their hippocampal Aβ load. However, the expression of Rxr-β in the hippocampus was negatively correlated with the amount of both soluble and insoluble Aβ in both males and females. Western immunoblotting in the human cortical samples of the ROS study did not reveal differences in RARβ levels. However, it evidenced a switch from a 60-kDa-RXRγ to a 55-kDa-RXRγ in AD, correlating with ante mortem cognitive decline and the accumulation of neuritic plaques in the brain cortex.

CONCLUSION

Our data suggest that (i) an altered expression of RXRs receptors is a contributor to β-amyloid pathology in both humans and 3xTg-AD mice, (ii) a chronic exposure of 3xTg-AD mice to a VitA-enriched diet may be protective in males, but not in females.

The protective variant rs7173049 at LOXL1 locus impacts on retinoic acid signaling pathway in pseudoexfoliation syndrome

LOXL1 (lysyl oxidase-like 1) has been identified as the major effect locus in pseudoexfoliation (PEX) syndrome, a fibrotic disorder of the extracellular matrix and frequent cause of chronic open-angle glaucoma. However, all known PEX-associated common variants show allele effect reversal in populations of different ancestry, casting doubt on their biological significance. Based on extensive LOXL1 deep sequencing, we report here the identification of a common non-coding sequence variant, rs7173049A>G, located downstream of LOXL1, consistently associated with a decrease in PEX risk (odds ratio, OR = 0.63; P = 6.33 × 10⁻³¹) in nine different ethnic populations. We provide experimental evidence for a functional enhancer-like regulatory activity of the genomic region surrounding rs7173049 influencing expression levels of ISLR2 (immunoglobulin superfamily containing leucine-rich repeat protein 2) and STRA6 [stimulated by retinoic acid (RA) receptor 6], apparently mediated by allele-specific binding of the transcription factor thyroid hormone receptor beta. We further show that the protective rs7173049-G allele correlates with increased tissue expression levels of ISLR2 and STRA6 and that both genes are significantly downregulated in tissues of PEX patients together with other key components of the STRA6 receptor-driven RA signaling pathway. siRNA-mediated downregulation of RA signaling induces upregulation of LOXL1 and PEX-associated matrix genes in PEX-relevant cell types. These data indicate that dysregulation of STRA6 and impaired retinoid metabolism are involved in the pathophysiology of PEX syndrome and that the variant rs7173049-G, which represents the first common variant at the broad LOXL1 locus without allele effect reversal, mediates a protective effect through upregulation of STRA6 in ocular tissues.

Reduction BACE1 expression via suppressing NF-κB mediated signaling by Tamibarotene in a mouse model of Alzheimer's disease

This present study examined the effect of Tamibarotene (AM80) in APP/PS1 mice, a well-established AD mouse model. AM80 was intraperitoneal administered to 3-month-old APP/PS1 mice at a dose of 5 mg/kg/day for 16 weeks. The results clearly showed that AM80 could reduce amyloid-β peptides through impact on APP processing and reduce microglia and astrocyte activation in APP/PS1 mice. The most notable finding in the present study was that inhibitory effect on BACE1 mediated by NF-κB pathway underlies the anti-inflammatory action of AM80. Moreover, AM80 could significantly decrease synaptic loss and enhance the expressions of Synapsin and Drebrin. Therefore, AM80 treatment may have the preclinical prevention of AD with new therapeutic strategies.

Vitamins: a nutritional intervention to modulate the Alzheimer's disease progression

Background: Alzheimer's disease is known as one of the fastest growing lethal diseases worldwide where we have limited and undesired ways for regulating its pathological progress. Now-a-days, nutritional compounds have been using to treat several brain disorders and one of them; vitamins were strongly reported to combat cognition and memory deterioration in neurodegenerative diseases including Alzheimer's disease. Objective: Here, the author tried to find the precise physiological roles, status, and worth of vitamins in the brain and how exactly these nutrients modulate progression of Alzheimer's disease. Results & Discussion: After a comprehensive and systematic literature review, the author reports that vitamins have various targets in Alzheimer's disease pathogenesis by which they act to avert the neuronal dysfunction in the disease. Several Alzheimer's disease-associated neurological deficits have reported regulating by vitamin intake but the beneficial effects identified mostly in combinatorial and long-term studies. Conclusion: In this way, the author suggests that it might be better to test vitamins with other components over single vitamin approach for a compatible and synergistic effect as well as using a combination of vitamin with other compounds can target multiple pathways. This strategy may help in deteriorating memory dysfunction and cognition impairment in Alzheimer's disease pathophysiology.Abbreviations: APOE: apolipoprotein E; APP: amyloid precursor protein; ATP: adenosine triphosphate; Aβ- β-amyloid; cGMP: cyclic guanine monophosphate; CNS: central nervous system; DNA: deoxyribonucleic acid; IU: international units; RA: retinoic acid; RAR: retinoic acid receptor; RNA: ribonucleic acid; ROS: reactive oxygen species; tHcy: total homocysteine; α: alpha; β: beta; γ: gama; ε: epsilon; g: gram; µ: micron; mg: milligram; ⬆: increased,⬇: decreased.

Neuroprotection against Amyloid-β-Induced DNA Double-Strand Breaks Is Mediated by Multiple Retinoic Acid-Dependent Pathways

In this study, we have investigated the role of all-trans-retinoic acid (RA) as a neuroprotective agent against Aβ_1-42-induced DNA double-strand breaks (DSBs) in neuronal SH-SY5Y and astrocytic DI TNC₁ cell lines and in murine brain tissues, by single-cell gel electrophoresis. We showed that RA does not only repair Aβ_1-42-induced DSBs, as already known, but also prevents their occurrence. This effect is independent of that of other antioxidants studied, such as vitamin C, and appears to be mediated, at least in part, by changes in expression, not of the RARα, but of the PPARβ/δ and of antiamyloidogenic proteins, such as ADAM10, implying a decreased production of endogenous Aβ. Whereas Aβ_1-42 needs transcription and translation for DSB production, RA protects against Aβ_1-42-induced DSBs at the posttranslational level through both the RARα/β/γ and PPARβ/δ receptors as demonstrated by using specific antagonists. Furthermore, it could be shown by a proximity ligation assay that the PPARβ/δ-RXR interactions, not the RARα/β/γ-RXR interactions, increased in the cells when a 10 min RA treatment was followed by a 20 min Aβ_1-42 treatment. Thus, the PPARβ/δ receptor, known for its antiapoptotic function, might for these short-time treatments play a role in neuroprotection via PPARβ/δ-RXR heterodimerization and possibly expression of antiamyloidogenic genes. Overall, this study shows that RA can not only repair Aβ_1-42-induced DSBs but also prevent them via the RARα/β/γ and PPARβ/δ receptors. It suggests that the RA-dependent pathways belong to an anti-DSB Adaptative Gene Expression (DSB-AGE) system that can be targeted by prevention strategies to preserve memory in Alzheimer's disease and aging.

Natural Compounds for Alzheimer's Disease Therapy: A Systematic Review of Preclinical and Clinical Studies

Alzheimer's Disease (AD) is a neurodegenerative disorder related with the increase of age and it is the main cause of dementia in the world. AD affects cognitive functions, such as memory, with an intensity that leads to several functional losses. The continuous increase of AD incidence demands for an urgent development of effective therapeutic strategies. Despite the extensive research on this disease, only a few drugs able to delay the progression of the disease are currently available. In the last years, several compounds with pharmacological activities isolated from plants, animals and microorganisms, revealed to have beneficial effects for the treatment of AD, targeting different pathological mechanisms. Thus, a wide range of natural compounds may play a relevant role in the prevention of AD and have proven to be efficient in different preclinical and clinical studies. This work aims to review the natural compounds that until this date were described as having significant benefits for this neurological disease, focusing on studies that present clinical trials.

Small Molecule Natural Products and Alzheimer's Disease

Alzheimer's disease (AD) is a progressive and deadly neurodegenerative disease that is characterized by memory loss, cognitive impairment and dementia. Several hypotheses have been proposed for the pathogenesis based on the pathological changes in the brain of AD patients during the last few decades. Unfortunately, there is no effective agents/therapies to prevent or control AD at present. Currently, only a few drugs, which function as acetylcholinesterase (AChE) inhibitors or N-methyl-Daspartate (NMDA) receptor antagonists, are available to alleviate symptoms. Since many small molecule natural products have shown their functions as agonists or antagonists of receptors, as well as inhibitors of enzymes and proteins in the brain during the development of central nervous system (CNS) drugs, it is likely that natural products will play an important role in anti-AD drug development. We review recent papers on using small molecule natural products as drug candidates for the treatment of AD. These natural products possess antioxidant, anti-inflammatory, anticholinesterase, anti-amyloidogenic and neuroprotective activities. Moreover, bioactive natural products intended to be used for preventing AD, reducing the symptoms of AD and the new targets for treatment of AD are summarized.

MicroRNA in Alzheimer's disease revisited: implications for major neuropathological mechanisms

Pathology of Alzheimer's disease (AD) goes far beyond neurotoxicity resulting from extracellular deposition of amyloid β (Aβ) plaques. Aberrant cleavage of amyloid precursor protein and accumulation of Aβ in the form of the plaque or neurofibrillary tangles are the known primary culprits of AD pathogenesis and target for various regulatory mechanisms. Hyper-phosphorylation of tau, a major component of neurofibrillary tangles, precipitates its aggregation and prevents its clearance. Lipid particles, apolipoproteins and lipoprotein receptors can act in favor or against Aβ and tau accumulation by altering neural membrane characteristics or dynamics of transport across the blood-brain barrier. Lipids also alter the oxidative/anti-oxidative milieu of the central nervous system (CNS). Irregular cell cycle regulation, mitochondrial stress and apoptosis, which follow both, are also implicated in AD-related neuronal loss. Dysfunction in synaptic transmission and loss of neural plasticity contribute to AD. Neuroinflammation is a final trail for many of the pathologic mechanisms while playing an active role in initiation of AD pathology. Alterations in the expression of microRNAs (miRNAs) in AD and their relevance to AD pathology have long been a focus of interest. Herein we focused on the precise pathomechanisms of AD in which miRNAs were implicated. We performed literature search through PubMed and Scopus using the search term: ('Alzheimer Disease') OR ('Alzheimer's Disease') AND ('microRNAs' OR 'miRNA' OR 'MiR') to reach for relevant articles. We show how a limited number of common dysregulated pathways and abnormal mechanisms are affected by various types of miRNAs in AD brain.

Long-term in vitro culture and preliminary establishment of chicken primordial germ cell lines

Primordial germ cells (PGCs) are precursors of functional gametes and can be used as efficient transgenic tools and carriers in bioreactors. Few methods for long-term culture of PGCs are available. In this study, we tested various culture conditions for PGCs, and used the optimum culture system to culture chicken gonad PGCs for about three hundred days. Long-term-cultured PGCs were detected and characterized by karyotype analysis, immunocytochemical staining of SSEA-1, c-kit, Sox2, cDAZL, and quantitative RT-PCR for specific genes like Tert, DAZL, POUV, and NANOG. Cultured PGCs labeled with PKH26 were reinjected into Stage X recipient embryos and into the dorsal aorta of Stage 14–17 embryos to assay their ability of migration into the germinal crescent and gonads, respectively. In conclusion, the most suitable culture system for PGCs is as follows: feeder layer cells treated with 20 μg/mL mitomycin C for 2 hours, and with 50% conditioned medium added to the factor culture medium. PGCs cultured in this system retain their pluripotency and the unique ability of migration without transformation, indicating the successful preliminary establishment of chicken primordial germ cell lines and these PGCs can be considered for use as carriers in transgenic bioreactors.

Marginal vitamin A deficiency facilitates Alzheimer's pathogenesis

Deposition of amyloid β protein (Aβ) to form neuritic plaques in the brain is the unique pathological hallmark of Alzheimer's disease (AD). Aβ is derived from amyloid β precursor protein (APP) by β- and γ-secretase cleavages and turned over by glia in the central nervous system (CNS). Vitamin A deficiency (VAD) has been shown to affect cognitive functions. Marginal vitamin A deficiency (MVAD) is a serious and widespread public health problem among pregnant women and children in developing countries. However, the role of MVAD in the pathogenesis of AD remains elusive. Our study showed that MVAD is approximately twofold more prevalent than VAD in the elderly, and increased cognitive decline is positively correlated with lower VA levels. We found that MVAD, mostly prenatal MVAD, promotes beta-site APP cleaving enzyme 1 (BACE1)-mediated Aβ production and neuritic plaque formation, and significantly exacerbates memory deficits in AD model mice. Supplementing a therapeutic dose of VA rescued the MVAD-induced memory deficits. Taken together, our study demonstrates that MVAD facilitates AD pathogenesis and VA supplementation improves cognitive deficits. These results suggest that VA supplementation might be a potential approach for AD prevention and treatment.

Linking deregulation of non-coding RNA to the core pathophysiology of Alzheimer's disease: An integrative review

The human genome encodes a vast repertoire of protein non-coding RNAs (ncRNA), some specific to the brain. MicroRNAs, which interfere with the translation of target mRNAs, are of particular interest since their deregulation has been implicated in neurodegenerative disorders like Alzheimer's disease (AD). However, it remains challenging to link the complex body of observations on miRNAs and AD into a coherent framework. Using extensive graphical support, this article discusses how a diverse panoply of miRNAs convergently and divergently impact (and are impacted by) core pathophysiological processes underlying AD: neuroinflammation and oxidative stress; aberrant generation of β-amyloid-42 (Aβ42); anomalies in the production, cleavage and post-translational marking of Tau; impaired clearance of Aβ42 and Tau; perturbation of axonal organisation; disruption of synaptic plasticity; endoplasmic reticulum stress and the unfolded protein response; mitochondrial dysfunction; aberrant induction of cell cycle re-entry; and apoptotic loss of neurons. Intriguingly, some classes of miRNA provoke these cellular anomalies, whereas others act in a counter-regulatory, protective mode. Moreover, changes in levels of certain species of miRNA are a consequence of the above-mentioned anomalies. In addition to miRNAs, circular RNAs, piRNAs, long non-coding RNAs and other types of ncRNA are being increasingly implicated in AD. Overall, a complex mesh of deregulated and multi-tasking ncRNAs reciprocally interacts with core pathophysiological mechanisms underlying AD. Alterations in ncRNAs can be detected in CSF and the circulation as well as the brain and are showing promise as biomarkers, with the ultimate goal clinical exploitation as targets for novel modes of symptomatic and course-altering therapy.

Molecular Anti-inflammatory Mechanisms of Retinoids and Carotenoids in Alzheimer's Disease: a Review of Current Evidence

Alzheimer's disease (AD) is considered as one of the most prevalent neurodegenerative disorders characterized by progressive loss of mental function and ability to learn. AD is a multifactorial disorder. Various hypotheses are suggested for the pathophysiology of AD including "Aβ hypothesis," "tau hypothesis," and "cholinergic hypothesis." Recently, it has been demonstrated that neuroinflammation is involved in the pathogenesis of AD. Neuroinflammation causes synaptic dysfunction and neuronal death within the brain. Excessive production of pro-inflammatory mediators induces Aβ peptide production/accumulation and hyperphosphorylated tau generating inflammatory molecules and cytokines. These inflammatory molecules disrupt blood-brain barrier integrity and increase the production of Aβ42 oligomers. Retinoids and carotenoids are potent antioxidants and anti-inflammatory agents having neuroprotective properties. They are able to prevent disease progression through several mechanisms such as suppression of Aβ peptide production/accumulation, oxidative stress, and pro-inflammatory mediator's secretion as well as improvement of cognitive performance. These observations, therefore, confirm the neuroprotective role of retinoids and carotenoids through multiple pathways. Therefore, the administration of these nutrients is considered as a promising approach to the prevention and/or treatment of AD in the future. The aim of this review is to present existing evidences regarding the beneficial effects of retinoids and carotenoids on AD's risk and outcomes, seeking the mechanism of their action.

The Vitamin A Derivative All-Trans Retinoic Acid Repairs Amyloid-β-Induced Double-Strand Breaks in Neural Cells and in the Murine Neocortex

The amyloid-β peptide or Aβ is the key player in the amyloid-cascade hypothesis of Alzheimer's disease. Aβ appears to trigger cell death but also production of double-strand breaks (DSBs) in aging and Alzheimer's disease. All-trans retinoic acid (RA), a derivative of vitamin A, was already known for its neuroprotective effects against the amyloid cascade. It diminishes, for instance, the production of Aβ peptides and their oligomerisation. In the present work we investigated the possible implication of RA receptor (RAR) in repair of Aβ-induced DSBs. We demonstrated that RA, as well as RAR agonist Am80, but not AGN 193109 antagonist, repair Aβ-induced DSBs in SH-SY5Y cells and an astrocytic cell line as well as in the murine cortical tissue of young and aged mice. The nonhomologous end joining pathway and the Ataxia Telangiectasia Mutated kinase were shown to be involved in RA-mediated DSBs repair in the SH-SY5Y cells. Our data suggest that RA, besides increasing cell viability in the cortex of young and even of aged mice, might also result in targeted DNA repair of genes important for cell or synaptic maintenance. This phenomenon would remain functional up to a point when Aβ increase and RA decrease probably lead to a pathological state.

Retinoic acid as a therapeutic option in Alzheimer's disease: a focus on cholinergic restoration

Retinoic acid is a potent cell differentiating factor, which through its nuclear receptors affects a vast range of promoter sites in brain neuronal and glial cells in every step of embryonic and postnatal life. Its capacities, facilitating maturation of neurotransmitter phenotype in different groups of neurons, pave the way for its application as a potential therapeutic agent in neurodegenerative diseases including Alzheimer's disease. Retinoic acid was found to exert particularly strong enhancing effects on acetylcholine transmitter functions in brain cholinergic neurons, loss of which is tightly linked to the development of cognitive and memory deficits in course of different cholinergic encephalopathies. Here, we review cholinotrophic properties of retinoic acid and its derivatives, which may justify their application in the management of Alzheimer's disease and the related neurodegenerative conditions.

MicroRNA-138 promotes tau phosphorylation by targeting retinoic acid receptor alpha

Alzheimer's disease (AD) is a progressive neurodegenerative dementia characterized by Aβ deposition and neurofibrillary tangles (NFTs) composed of hyperphosphorylated tau. Emerging evidence shows that microRNAs (miRNAs) contribute to the pathogenesis of AD. Herein, we investigated the role of miR-138, a brain enriched miRNA, which is increased in AD patients. We found that miR-138 is increased in AD models, including N2a/APP and HEK293/tau cell lines. Overexpression of miR-138 activates glycogen synthase kinase-3β (GSK-3β), and increases tau phosphorylation in HEK293/tau cells. Furthermore, we confirm that retinoic acid receptor alpha (RARA) is a direct target of miR-138, and supplement of RARA substantially suppresses GSK-3β activity, and reduces tau phosphorylation induced by miR-138. In conclusion, our data suggest that miR-138 promotes tau phosphorylation by targeting the RARA/GSK-3β pathway.

Pharmacogenomics of Alzheimer's disease: novel therapeutic strategies for drug development

Alzheimer's disease (AD) is a major problem of health and disability, with a relevant economic impact on our society. Despite important advances in pathogenesis, diagnosis, and treatment, its primary causes still remain elusive, accurate biomarkers are not well characterized, and the available pharmacological treatments are not cost-effective. As a complex disorder, AD is a polygenic and multifactorial clinical entity in which hundreds of defective genes distributed across the human genome may contribute to its pathogenesis. Diverse environmental factors, cerebrovascular dysfunction, and epigenetic phenomena, together with structural and functional genomic dysfunctions, lead to amyloid deposition, neurofibrillary tangle formation, and premature neuronal death, the major neuropathological hallmarks of AD. Future perspectives for the global management of AD predict that genomics and proteomics may help in the search for reliable biomarkers. In practical terms, the therapeutic response to conventional drugs (cholinesterase inhibitors, multifactorial strategies) is genotype-specific. Genomic factors potentially involved in AD pharmacogenomics include at least five categories of gene clusters: (1) genes associated with disease pathogenesis; (2) genes associated with the mechanism of action of drugs; (3) genes associated with drug metabolism (phase I and II reactions); (4) genes associated with drug transporters; and (5) pleiotropic genes involved in multifaceted cascades and metabolic reactions. The implementation of pharmacogenomic strategies will contribute to optimize drug development and therapeutics in AD and related disorders.