Amyloid-β induced astrocytosis and astrocyte death: Implication of FoxO3a-Bim-caspase3 death signaling

Nobiletin regulates intracellular Ca2+ levels via IP3R and ameliorates neuroinflammation in Aβ42-induced astrocytes

Astrocytes are the major glial cells in the human brain and provide crucial metabolic and trophic support to neurons. The amyloid-β peptide (Aβ) alter the morphological and functional properties of astrocytes and induce inflammation and calcium dysregulation, contributing to Alzheimer's disease (AD) pathology. Recent studies highlight the role of Toll-like receptor (TLR) 4/nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB) signaling in inflammation. Reactive oxygen species (ROS) generated due to Aβ, induce apoptosis in the brain cells worsening AD progression. Astrocytic cell surface receptors, such as purinergic receptors (P2Y1 and P2Y2), metabotropic glutamate receptor (mGLUR)5, α7 nicotinic acetylcholine receptor (α7nAChR), and N-methyl-d-aspartate receptors (NMDARs), have been suggested to interact with inositol trisphosphate receptor (IP3R) on the endoplasmic reticulum (ER) to induce Ca2+ movement from ER to cytoplasm, causing Ca2+ dysregulation. We found that the citrus flavonoid nobiletin (NOB) protected primary astrocytes from Aβ42-induced cytotoxicity and inhibited TLR4/NF-κB signaling in Aβ42-induced primary rat astrocytes. NOB was found to regulate Aβ42-induced ROS levels through Keap1-Nrf2 pathway. The receptors P2Y1, P2Y2, mGLUR5, α7nAChR, and NMDARs induced intracellular Ca2+ levels by activating IP3R and NOB regulated them, thereby regulating intracellular Ca2+ levels. Molecular docking analysis revealed a possible interaction between NOB and IP3R in IP3R regulation. Furthermore, RNA sequencing revealed various NOB-mediated biological signaling pathways, such as the AD-presenilin, AD-amyloid secretase, and Wnt signaling pathway, suggesting possible neuroprotective roles of NOB. To conclude, NOB is a promising therapeutic agent for AD and works by modulating AD pathology at various levels in Aβ42-induced primary rat astrocytes.

An EWAS of dementia biomarkers and their associations with age, African ancestry, and PTSD

BACKGROUND

Large-scale cohort and epidemiological studies suggest that PTSD confers risk for dementia in later life but the biological mechanisms underlying this association remain unknown. This study examined this question by assessing the influences of PTSD, APOE ε4 genotypes, DNA methylation, and other variables on the age- and dementia-associated biomarkers Aβ40, Aβ42, GFAP, NfL, and pTau-181 measured in plasma. Our primary hypothesis was that PTSD would be associated with elevated levels of these markers.

METHODS

Analyses were based on data from a PTSD-enriched cohort of 849 individuals. We began by performing factor analyses of the biomarkers, the results of which identified a two-factor solution. Drawing from the ATN research framework, we termed the first factor, defined by Aβ40 and Aβ42, "Factor A" and the second factor, defined by GFAP, NfL and pTau-181, "Factor TN." Next, we performed epigenome-wide association analyses (EWAS) of the two-factor scores. Finally, using structural equation modeling (SEM), we evaluated (a) the influence of PTSD, age, APOE ε4 genotype and other covariates on levels of the ATN factors, and (b) tested the mediating influence of the EWAS-significant DNAm loci on these associations.

RESULTS

The Factor A EWAS identified one significant locus, cg13053408, in FANCD2OS. The Factor TN analysis identified 3 EWAS-significant associations: cg26033520 near ASCC1, cg23156469 in FAM20B, and cg15356923 in FAM19A4. The SEM showed age to be related to both factors, more so with Factor TN (β = 0.581, p < 0.001) than Factor A (β = 0.330, p < 0.001). Genotype-determined African ancestry was associated with lower Factor A (β = 0.196, p < 0.001). Contrary to our primary hypothesis, we found a modest negative bivariate correlation between PTSD and the TN factor scores (r = - 0.133, p < 0.001) attributable primarily to reduced levels of GFAP (r = - 0.128, p < 0.001).

CONCLUSIONS

This study identified novel epigenetic associations with ATN biomarkers and demonstrated robust age and ancestral associations that will be essential to consider in future efforts to develop the clinical applications of these tests. The association between PTSD and reduced GFAP, which has been reported previously, warrants further investigation.

Arc Regulates Transcription of Genes for Plasticity, Excitability and Alzheimer’s Disease

The immediate early gene Arc is a master regulator of synaptic function and a critical determinant of memory consolidation. Here, we show that Arc interacts with dynamic chromatin and closely associates with histone markers for active enhancers and transcription in cultured rat hippocampal neurons. Both these histone modifications, H3K27Ac and H3K9Ac, have recently been shown to be upregulated in late-onset Alzheimer’s disease (AD). When Arc induction by pharmacological network activation was prevented using a short hairpin RNA, the expression profile was altered for over 1900 genes, which included genes associated with synaptic function, neuronal plasticity, intrinsic excitability, and signalling pathways. Interestingly, about 100 Arc-dependent genes are associated with the pathophysiology of AD. When endogenous Arc expression was induced in HEK293T cells, the transcription of many neuronal genes was increased, suggesting that Arc can control expression in the absence of activated signalling pathways. Taken together, these data establish Arc as a master regulator of neuronal activity-dependent gene expression and suggest that it plays a significant role in the pathophysiology of AD.

ICAM-1 protects neurons against Amyloid-β and improves cognitive behaviors in 5xFAD mice by inhibiting NF-κB

Alzheimer's disease (AD) is mainly characterized by amyloid beta (Aβ) plaque deposition and neurofibrillary tangle formation due to tau hyperphosphorylation. It has been shown that astrocytes respond to these pathologies very early and exert either beneficial or deleterious effects towards neurons. Here, we identified soluble intercellular adhesion molecule-1 (ICAM-1) which is rapidly increased in astrocyte conditioned medium derived from Aβ_1-42 treated cultured astrocytes (Aβ_1-42-ACM). Aβ_1-42-ACM was found to be neuroprotective, however, Aβ_1-42-ACM deprived of ICAM-1 was unable to protect neurons against Aβ_1-42 mediated toxicity. Moreover, exogenous ICAM-1 renders protection to neurons from Aβ_1-42 induced death. It blocks Aβ_1-42-mediated PARP cleavage and increases the levels of anti-apoptotic proteins such as Bcl-2 and Bcl-xL, and decreases pro-apoptotic protein Bim. In an Aβ-infused rat model of AD and in 5xFAD mouse, intra-peritoneal administration of ICAM-1 revealed a reduction in Aβ load in hippocampal and cortical regions. Moreover, ICAM-1 treatment led to an increment in the expression of the Aβ-degrading enzyme, neprilysin in 5xFAD mice. Finally, we found that ICAM-1 can ameliorate cognitive deficits in Aβ-infused rat and 5xFAD mouse. Interestingly, ICAM-1 could block the NF-κB upregulation by Aβ and inhibition of NF-κB recovers cognitive impairments in 5xFAD mice. Thus, our study finds a neuroprotective role of ICAM-1 and suggests that it can be a major candidate in cytokine-mediated therapy of AD.

Role of FoxO transcription factors in aging and age-related metabolic and neurodegenerative diseases

Aging happens to all of us as we live. Thanks to the improved living standard and discovery of life-saving medicines, our life expectancy has increased substantially across the world in the past century. However, the rise in lifespan leads to unprecedented increases in both the number and the percentage of individuals 65 years and older, accompanied by the increased incidences of age-related diseases such as type 2 diabetes mellitus and Alzheimer’s disease. FoxO transcription factors are evolutionarily conserved molecules that play critical roles in diverse biological processes, in particular aging and metabolism. Their dysfunction is often found in the pathogenesis of many age-related diseases. Here, we summarize the signaling pathways and cellular functions of FoxO proteins. We also review the complex role of FoxO in aging and age-related diseases, with focus on type 2 diabetes and Alzheimer’s disease and discuss the possibility of FoxO as a molecular link between aging and disease risks.

Isoform-Specific Effects of Apolipoprotein E on Hydrogen Peroxide-Induced Apoptosis in Human Induced Pluripotent Stem Cell (iPSC)-Derived Cortical Neurons

Hydrogen peroxide (H₂O₂)-induced neuronal apoptosis is critical to the pathology of Alzheimer's disease (AD) as well as other neurodegenerative diseases. The neuroprotective effects of apolipoprotein (ApoE) isoforms against apoptosis and the underlying mechanism remains controversial. Here, we have generated human cortical neurons from iPSCs and induced apoptosis with H₂O₂. We show that ApoE2 and ApoE3 pretreatments significantly attenuate neuronal apoptosis, whereas ApoE4 has no neuroprotective effect and higher concentrations of ApoE4 even display toxic effect. We further identify that ApoE2 and ApoE3 regulate Akt/FoxO3a/Bim signaling pathway in the presence of H₂O₂. We propose that ApoE alleviates H₂O₂-induced apoptosis in human iPSC-derived neuronal culture in an isoform specific manner. Our results provide an alternative mechanistic explanation on how ApoE isoforms influence the risk of AD onset as well as a promising therapeutic target for diseases involving neuronal apoptosis in the central nervous system.

Calpain-Mediated Alterations in Astrocytes Before and During Amyloid Chaos in Alzheimer's Disease

One of the changes found in the brain in Alzheimer's disease (AD) is increased calpain, derived from calcium dysregulation, oxidative stress, and/or neuroinflammation, which are all assumed to be basic pillars in neurodegenerative diseases. The role of calpain in synaptic plasticity, neuronal death, and AD has been discussed in some reviews. However, astrocytic calpain changes sometimes appear to be secondary and consequent to neuronal damage in AD. Herein, we explore the possibility of calpain-mediated astroglial reactivity in AD, both preceding and during the amyloid phase. We discuss the types of brain calpains but focus the review on calpains 1 and 2 and some important targets in astrocytes. We address the signaling involved in controlling calpain expression, mainly involving p38/mitogen-activated protein kinase and calcineurin, as well as how calpain regulates the expression of proteins involved in astroglial reactivity through calcineurin and cyclin-dependent kinase 5. Throughout the text, we have tried to provide evidence of the connection between the alterations caused by calpain and the metabolic changes associated with AD. In addition, we discuss the possibility that calpain mediates amyloid-β clearance in astrocytes, as opposed to amyloid-β accumulation in neurons.

Challenges and Opportunities of Targeting Astrocytes to Halt Neurodegenerative Disorders

Neurodegenerative diseases are a heterogeneous group of disorders whose incidence is likely to duplicate in the next 30 years along with the progressive aging of the western population. Non-cell-specific therapeutics or therapeutics designed to tackle aberrant pathways within neurons failed to slow down or halt neurodegeneration. Yet, in the last few years, our knowledge of the importance of glial cells to maintain the central nervous system homeostasis in health conditions has increased exponentially, along with our awareness of their fundamental and multifaced role in pathological conditions. Among glial cells, astrocytes emerge as promising therapeutic targets in various neurodegenerative disorders. In this review, we present the latest evidence showing the astonishing level of specialization that astrocytes display to fulfill the demands of their neuronal partners as well as their plasticity upon injury. Then, we discuss the controversies that fuel the current debate on these cells. We tackle evidence of a potential beneficial effect of cell therapy, achieved by transplanting astrocytes or their precursors. Afterwards, we introduce the different strategies proposed to modulate astrocyte functions in neurodegeneration, ranging from lifestyle changes to environmental cues. Finally, we discuss the challenges and the recent advancements to develop astrocyte-specific delivery systems.

Amyloid and Tau Induce Cell Death Independently of TSPO Polymerization and Density Changes

Apoptosis-dependent cell death of astrocytes has been described in Alzheimer's disease and is linked to the presence of two markers of the pathology: the β-amyloid peptide (Aβ) and the hyperphosphorylated Tau protein. Astrocytes also show reactive states characterized by the overexpression of the 18 kDa translocator protein (TSPO). However, TSPO is also known, in other areas of research, to participate in cell proliferation and death. Regulation of its function by autopolymerization has been described, but its involvement in apoptosis remains unknown. The aim was to determine the effects of Aβ, Tau, and TSPO antagonists on proliferation/cell death and TSPO polymerization in the C6 astrocytic cell line. The dose-effect on cell death in response to Aβ and Tau was observed but without alterations of TSPO density and polymerization. In contrast, nanomolar doses of antagonists stimulated cell proliferation, although micromolar doses induced cell death with a reduction in TSPO density and an increase in the ratio between the 36 and the 72 kDa TSPO polymers. Therefore, an alteration in the density and polymerization of TSPO appears to be related to cell death induced by TSPO antagonisms. In contrast, Aβ- and Tau-induced death seems to be independent of TSPO alterations. In conclusion, even if its role in cell death and proliferation is demonstrated, TSPO seems to, in the context of Alzheimer's disease, rather represent a marker of the activity of astrocytes than of cell death.

Amyloid-β1-40 differentially stimulates proliferation, activation of oxidative stress and inflammatory responses in male and female hippocampal astrocyte cultures

Alzheimer's disease (AD) is the most common form of dementia and has a higher incidence in women. The main component of the senile plaques characteristic of AD is amyloid-beta (Aβ), with surrounding astrocytes contributing to the degenerative process. We hypothesized that the sex difference in the incidence of AD could be partially due to differential astrocytic responses to Aβ. Thus, the effect of Aβ_1-40 on cell viability, the inflammatory response, and oxidative status was studied in cultures of hippocampal astrocytes from male and female rats. Aβ_1-40 increased astrocyte viability in both female and male cultures by activating proliferation and survival pathways. Pro-inflammatory and anti-inflammatory responses were induced in astrocytes from both sexes. Aβ_1-40 did not affect endoplasmic reticulum stress although it induced oxidative stress in male and female astrocytes. Interestingly, male astrocytes had an increase in cell number and significantly lower cell death in response to Aβ_1-40. Conversely, astrocytes from females displayed a greater inflammatory response after the Aβ_1-40 challenge. These results suggest that the inflammatory and oxidative environment induced by Aβ_1-40 in female astrocytes may contribute to enhance the vulnerability to AD and warrants further studies to unveil the mechanisms underlying sex differences in astrocytic responses.

P38K and JNK pathways are induced by amyloid-β in astrocyte: Implication of MAPK pathways in astrogliosis in Alzheimer's disease

Astrocyte activation is one of the crucial hallmarks of Alzheimer's disease (AD) along with amyloid-β (Aβ) plaques, neurofibrillary tangles and neuron death. Glial scar and factors secreted from activated astrocytes have important contribution on neuronal health in AD. In this study, we investigated the mechanisms of astrocyte activation both in in vitro and in vivo models of AD. In this regard, mitogen activated protein kinase (MAPK) signalling cascades that control several fundamental and stress related cellular events, has been implicated in astrocyte activation in various neurological diseases. We checked activation of different MAPKs by western blot and immunocytochemistry and found that both JNK and p38K, but not ERK pathways are activated in Aβ-treated astrocytes in culture and in Aβ-infused rat brain cortex. Next, to investigate the downstream consequences of these two MAPKs (JNK and p38K) in Aβ-induced astrocyte activation, we individually blocked these pathways by specific inhibitors in presence and absence of Aβ and checked Aβ-induced cellular proliferation, morphological changes and glial fibrillary acidic protein (GFAP) upregulation. We found that activation of both JNK and p38K signalling cascades are involved in astrocyte proliferation evoked by Aβ, whereas only p38K pathway is implicated in morphological changes and GFAP upregulation in astrocytes exposed to Aβ. To further validate the implication of p38K pathway in Aβ-induced astrocyte activation, we also observed that transcription factor ATF2, a downstream phosphorylation substrate of p38, is phosphorylated upon Aβ treatment. Taken together, our study indicates that p38K and JNK pathways mediate astrocyte activation and both the pathways are involved in cellular proliferation but only p38K pathway contributes in morphological changes triggered by Aβ.

High intake of chicken and pork proteins aggravates high-fat-diet-induced inflammation and disorder of hippocampal glutamatergic system

High-fat diets have been associated with neurodegenerative diseases, which are also largely related to the type and amount of dietary proteins. However, to our knowledge, it is little known how dietary proteins affect neurodegenerative changes. In this study, we investigated the effects of dietary proteins in a high-fat diet on hippocampus functions related to enteric glial cells (EGCs) in Wistar rats that were fed either 40% or 20% (calorie) casein, chicken protein or pork protein for 12 weeks (n=10 each group). Inflammatory factors, glutamatergic system, EGCs, astrocytes and nutrient transporters were measured. A high-chicken-protein diet significantly increased the levels of systemic inflammatory factors, Tau protein and amyloid precursor protein mRNA level in the rat hippocampus. The type and level of dietary proteins in high-fat diets did not affect the gene expression of glial fibrillary acidic protein and α-synuclein (P>.05), indicating a negligible effect on astrocyte activity. However, the high-protein diets up-regulated glutamate transporters compared with the low-protein diets (P<.05), while they reduced the γ-aminobutyric acid content in high-chicken and -pork-protein diets (P<.05). Thus, compared with a low-protein diet (20%), a high-chicken or -pork-protein diet (40%) under a high-fat background could alter the balance between glutamatergic system and neurotransmitter and have a stronger effect on the interactions between hippocampal glutamatergic system and EGCs.

Isoforsythiaside Attenuates Alzheimer's Disease via Regulating Mitochondrial Function Through the PI3K/AKT Pathway

Improving mitochondrial dysfunction and inhibiting apoptosis has always been regarded as a treatment strategy for Alzheimer's disease (AD). Isoforsythiaside (IFY), a phenylethanoid glycoside isolated from the dried fruit of Forsythia suspensa, displays antioxidant activity. This study examined the neuroprotective effects of IFY and its underlying mechanisms. In the L-glutamate (L-Glu)-induced apoptosis of HT22 cells, IFY increased cell viability, inhibited mitochondrial apoptosis, and reduced the intracellular levels of reactive oxygen species (ROS), caspase-3, -8 and -9 after 3 h of pretreatment and 12-24 h of co-incubation. In the APPswe/PSEN1dE9 transgenic (APP/PS1) model, IFY reduced the anxiety of mice, improved their memory and cognitive ability, reduced the deposition of beta amyloid (Aβ) plaques in the brain, restrained the phosphorylation of the tau protein to form neurofibrillary tangles, inhibited the level of 4-hydroxynonenal in the brain, and improved phosphatidylinositol 3-kinase (PI3K)/protein kinase B (AKT) signaling pathway-related mitochondrial apoptosis. In Aβ1-42-induced U251 cells, IFY relieved the mitochondrial swelling, crest ruptures and increased their electron density after 3 h of pretreatment and 18-24 h of co-incubation. The improved cell viability and mitochondrial function after IFY incubation was blocked by the synthetic PI3K inhibitor LY294002. Taken together, these results suggest that IFY exerts a protective effect against AD by enhancing the expression levels of anti-apoptosis proteins and reducing the expression levels of pro-apoptosis proteins of B-cell lymphoma-2 (BCL-2) family members though activating the PI3K/AKT pathway.

TIMP-1: A key cytokine released from activated astrocytes protects neurons and ameliorates cognitive behaviours in a rodent model of Alzheimer's disease

Alzheimer's disease (AD) is characterized by two pathologic species, extracellular amyloid-β (Aβ) plaques and intracellular neurofibrillary tangles. Astrocytes that maintain normal homeostasis in the brain undergo a set of molecular, cellular and functional changes called reactive astrogliosis in various neurological diseases including AD. It is hypothesized that reactive astrocytes initially tend to protect neurons by reducing Aβ load and by secreting a plethora of cytokines, however, their functions have only been poorly investigated. Our studies on the kinetics of activation of cortical astrocytes following Aβ-exposure revealed significant level of activation as early as in 6 h. The astrocyte conditioned medium (ACM) from 6 h Aβ-treated astrocytes (Aβ-ACM) provided significant neuroprotection of cultured cortical neurons against Aβ insults. Analysis of the secreted proteins in Aβ-ACM revealed a marked increase of Tissue inhibitor of Metalloproteinase-1 (TIMP-1) within 6 h. Interestingly, we found that neutralization of TIMP-1 with antibody or knockdown with siRNA in astrocytes abolished most of the neuroprotective ability of the 6 h Aβ-ACM on Aβ-treated cultured neurons. Furthermore addition of exogenous rat recombinant TIMP-1 protein protects primary neurons from Aβ mediated toxicity. In a well characterized Aβ-infused rodent model of AD, intra-cerebroventricular administration of TIMP-1 revealed a reduction in Aβ load and apoptosis in hippocampal and cortical regions. Finally, we found that TIMP-1 can ameliorate Aβ-induced cognitive dysfunctions through restoration of Akt and its downstream pathway and maintenance of synaptic integrity. Thus, our results not only provide a functional clarity for TIMP-1, secreted by activated astrocytes, but also support it as a major candidate in cytokine-mediated therapy of AD especially at the early phase of disease progression.

Genetic targeting of astrocytes to combat neurodegenerative disease

Astrocytes, glial cells that interact extensively with neurons and other support cells throughout the central nervous system, have recently come under the spotlight for their potential contribution to, or potential regenerative role in a host of neurodegenerative disorders. It is becoming increasingly clear that astrocytes, in concert with microglial cells, activate intrinsic immunological pathways in the setting of neurodegenerative injury, although the direct and indirect consequences of such activation are still largely unknown. We review the current literature on the astrocyte’s role in several neurodegenerative diseases, as well as highlighting recent advances in genetic manipulation of astrocytes that may prove critical to modulating their response to neurological injury, potentially combatting neurodegenerative damage.

A drug library screen identifies Carbenoxolone as novel FOXO inhibitor that overcomes FOXO3-mediated chemoprotection in high-stage neuroblastoma

The transcription factor FOXO3 has been associated in different tumor entities with hallmarks of cancer, including metastasis, tumor angiogenesis, maintenance of tumor-initiating stem cells, and drug resistance. In neuroblastoma (NB), we recently demonstrated that nuclear FOXO3 promotes tumor angiogenesis in vivo and chemoresistance in vitro. Hence, inhibiting the transcriptional activity of FOXO3 is a promising therapeutic strategy. However, as no FOXO3 inhibitor is clinically available to date, we used a medium-throughput fluorescence polarization assay (FPA) screening in a drug-repositioning approach to identify compounds that bind to the FOXO3-DNA-binding-domain (DBD). Carbenoxolone (CBX), a glycyrrhetinic acid derivative, was identified as a potential FOXO3-inhibitory compound that binds to the FOXO3-DBD with a binding affinity of 19 µM. Specific interaction of CBX with the FOXO3-DBD was validated by fluorescence-based electrophoretic mobility shift assay (FAM-EMSA). CBX inhibits the transcriptional activity of FOXO3 target genes, as determined by chromatin immunoprecipitation (ChIP), DEPP-, and BIM promoter reporter assays, and real-time RT-PCR analyses. In high-stage NB cells with functional TP53, FOXO3 triggers the expression of SESN3, which increases chemoprotection and cell survival. Importantly, FOXO3 inhibition by CBX treatment at pharmacologically relevant concentrations efficiently repressed FOXO3-mediated SESN3 expression and clonogenic survival and sensitized high-stage NB cells to chemotherapy in a 2D and 3D culture model. Thus, CBX might be a promising novel candidate for the treatment of therapy-resistant high-stage NB and other "FOXO-resistant" cancers.

Interactions between BIM Protein and Beta-Amyloid May Reveal a Crucial Missing Link between Alzheimer's Disease and Neuronal Cell Death

Extensive neuronal cell death is among the pathological hallmarks of Alzheimer's disease. While neuron death is coincident with formation of plaques comprising the beta-amyloid (Aβ) peptide, a direct causative link between Aβ (or other Alzheimer's-associated proteins) and cell toxicity is yet to be found. Here we show that BIM-BH3, the primary proapoptotic domain of BIM, a key protein in varied apoptotic cascades of which elevated levels have been found in brain cells of patients afflicted with Alzheimer's disease, interacts with the 42-residue amyloid isoform Aβ42. Remarkably, BIM-BH3 modulated the structure, fibrillation pathway, aggregate morphology, and membrane interactions of Aβ42. In particular, BIM-BH3 inhibited Aβ42 fibril-formation, while it simultaneously enhanced protofibril assembly. Furthermore, we discovered that BIM-BH3/Aβ42 interactions induced cell death in a human neuroblastoma cell model. Overall, our data provide a crucial mechanistic link accounting for neuronal cell death in Alzheimer's disease patients and the participation of both BIM and Aβ42 in the neurotoxicity process.

Novel Treatment Strategies for the Nervous System: Circadian Clock Genes, Non-coding RNAs, and Forkhead Transcription Factors

BACKGROUND

With the global increase in lifespan expectancy, neurodegenerative disorders continue to affect an ever-increasing number of individuals throughout the world. New treatment strategies for neurodegenerative diseases are desperately required given the lack of current treatment modalities.

METHODS

Here, we examine novel strategies for neurodegenerative disorders that include circadian clock genes, non-coding Ribonucleic Acids (RNAs), and the mammalian forkhead transcription factors of the O class (FoxOs).

RESULTS

Circadian clock genes, non-coding RNAs, and FoxOs offer exciting prospects to potentially limit or remove the significant disability and death associated with neurodegenerative disorders. Each of these pathways has an intimate relationship with the programmed death pathways of autophagy and apoptosis and share a common link to the silent mating type information regulation 2 homolog 1 (Saccharomyces cerevisiae) (SIRT1) and the mechanistic target of rapamycin (mTOR). Circadian clock genes are necessary to modulate autophagy, limit cognitive loss, and prevent neuronal injury. Non-coding RNAs can control neuronal stem cell development and neuronal differentiation and offer protection against vascular disease such as atherosclerosis. FoxOs provide exciting prospects to block neuronal apoptotic death and to activate pathways of autophagy to remove toxic accumulations in neurons that can lead to neurodegenerative disorders.

CONCLUSION

Continued work with circadian clock genes, non-coding RNAs, and FoxOs can offer new prospects and hope for the development of vital strategies for the treatment of neurodegenerative diseases. These innovative investigative avenues have the potential to significantly limit disability and death from these devastating disorders.

Non-aggregated Aβ25-35 Upregulates Primary Astrocyte Proliferation In Vitro

Amyloid beta (Aβ) is a peptide cleaved from amyloid precursor protein that contributes to the formation of senile plaques in Alzheimer’s disease (AD). The relationship between Aβ and astrocyte proliferation in AD remains controversial. Despite pathological findings of increased astrocytic mitosis in AD brains, in vitro studies show an inhibitory effect of Aβ on astrocyte proliferation. In this study, we determined the effect of an active fragment of Aβ (Aβ_25-35) on the cell cycle progression of primary rat astrocytes. We found that Aβ_25-35 (0.3–1.0 μg/ml) enhanced astrocyte proliferation in vitro in a time- and concentration-dependent manner. Increased DNA synthesis by Aβ_25-35 was observed during the S phase of the astrocyte cell cycle, as indicated by proliferation kinetics and bromodeoxyuridine immunocytochemical staining. Aggregation of Aβ_25-35 abolished the upregulatory effect of Aβ on astrocyte proliferation. Further examination indicated that Aβ_25-35 affected astrocyte proliferation during early or mid-G₁ phase but had no effect on DNA synthesis at the peak of S phase. These results provide insight into the relationship between Aβ_25-35 and astrocyte cell cycling in AD.

Astrocyte and Alzheimer's disease

The past several decades have given rise to more insights into the role of astrocytes in normal brain function and diseases. Astrocytes elicit an effect which may be neuroprotective or deleterious in the process of Alzheimer's disease (AD). Impairments in astrocytes and their other functions, as well as physiological reactions of astrocytes to external injury, can trigger or exacerbate hyperphosphorylated tau and amyloid-beta (Aβ) pathologies, leading to the formation of both amyloid plaques and neurofibrillary tangles (NFTs), as well as neuronal dysfunction. This review addresses the involvement of astrocytes in the Aβ pathology, where the main mechanisms include the generation and clearance of Aβ, and the formation of NFTs. It is also discussed that metabolic dysfunction from astrocytes acts as an initiating factor in the pathogenesis of AD and a contributor to the onset and development of clinical presentation in AD.

Forkhead Transcription Factors: Formulating a FOXO Target for Cognitive Loss

BACKGROUND

With almost 47 million individuals worldwide suffering from some aspect of dementia, it is clear that cognitive loss impacts a significant proportion of the global population. Unfortunately, definitive treatments to resolve or prevent the onset of cognitive loss are limited. In most cases such care is currently non-existent prompting the need for novel treatment strategies.

METHODS

Mammalian forkhead transcription factors of the O class (FoxO) are one such avenue of investigation that offer an exciting potential to bring new treatments forward for disorders that involve cognitive loss. Here we examine the background, structure, expression, and function of FoxO transcription factors and their role in cognitive loss, programmed cell death in the nervous system with apoptosis and autophagy, and areas to target FoxOs for dementia and specific disorders such as Alzheimer's disease.

RESULTS

FoxO proteins work in concert with a number of other cell survival pathways that involve growth factors, such as erythropoietin and neurotrophins, silent mating type information regulation 2 homolog 1 (Saccharomyces cerevisiae) (SIRT1), Wnt1 inducible signaling pathway protein 1 (WISP1), Wnt signaling, and cancer-related pathways. FoxO transcription factors oversee proinflammatory pathways, affect nervous system amyloid (Aβ) production and toxicity, lead to mitochondrial dysfunction, foster neuronal apoptotic cell death, and accelerate the progression of degenerative disease. However, under some scenarios such as those involving autophagy, FoxOs also can offer protection in the nervous system and reduce toxic intracellular protein accumulations and potentially limit Aβ toxicity.

CONCLUSION

Given the ability of FoxOs to not only promote apoptotic cell death in the nervous system, but also through the induction of autophagy offer protection against degenerative disease that can lead to dementia, a fine balance in the activity of FoxOs may be required to target cognitive loss in individuals. Future work should yield exciting new prospects for FoxO proteins as new targets to treat the onset and progression of cognitive loss and dementia.

Role and regulation of Cdc25A phosphatase in neuron death induced by NGF deprivation or β-amyloid

Neuron death during development and in Alzheimer’s disease (AD) is associated with aberrant regulation/induction of cell cycle proteins. However, the proximal events in this process are unknown. Cell cycle initiation requires dephosphorylation of cyclin-dependent kinases by cell division cycle 25A (Cdc25A). Here, we show that Cdc25A is essential for neuronal death in response to NGF deprivation or β-amyloid (Aβ) treatment and describe the mechanisms by which it is regulated in these paradigms. Cdc25A mRNA, protein and Cdc25A phosphatase activity were induced by NGF deprivation and Aβ treatment. Enhanced Cdc25A expression was also observed in rat brains infused with Aβ and in Aβ-overexpressing AβPPswe-PS1dE9 mice. In cultured neurons Cdc25A inhibition by chemical inhibitors or shRNA prevented cell death and neurite degeneration caused by NGF deprivation or Aβ. Additionally, Cdc25A inhibition diminished distal signaling events including Cdk-dependent elevation of phospho-pRb and subsequent caspase-3 activation. Mechanism studies revealed that Cdc25A induction by NGF deprivation and Aβ is mediated by activation of Forkhead transcription factors that in turn suppress miR-21, a negative regulator of Cdc25A. Our studies thus identify Cdc25A as a required upstream element of the apoptotic cell cycle pathway that is required for neuron death in response to trophic factor deprivation and to Aβ exposure and therefore as a potential target to suppress pathologic neuron death.

Forkhead transcription factors: new considerations for alzheimer's disease and dementia

Life expectancy of individuals in both developed and undeveloped nations continues to rise at an unprecedented rate. Coupled to this increase in longevity for individuals is the rise in the incidence of chronic neurodegenerative disorders that includes Alzheimer's disease (AD). Currently, almost ten percent of the population over the age of 65 suffers from AD, a disorder that is presently without definitive therapy to prevent the onset or progression of cognitive loss. Yet, it is estimated that AD will continue to significantly increase throughout the world to impact millions of individuals and foster the escalation of healthcare costs. One potential target for the development of novel strategies against AD and other cognitive disorders involves the mammalian forkhead transcription factors of the O class (FoxOs). FoxOs are present in "cognitive centers" of the brain to include the hippocampus, the amygdala, and the nucleus accumbens and may be required for memory formation and consolidation. FoxOs play a critical role in determining survival of multiple cell types in the nervous system, drive pathways of apoptosis and autophagy, and control stem cell proliferation and differentiation. FoxOs also interface with multiple cellular pathways that include growth factors, Wnt signaling, Wnt1 inducible signaling pathway protein 1 (WISP1), and silent mating type information regulation 2 homolog 1 (Saccharomyces cerevisiae) (SIRT1) that ultimately may control FoxOs and determine the fate and function of cells in the nervous system that control memory and cognition. Future work that can further elucidate the complex relationship FoxOs hold over cell fate and cognitive function could yield exciting prospects for the treatment of a number of neurodegenerative disorders including AD.