Blockade of the tumor necrosis factor-related apoptosis inducing ligand death receptor DR5 prevents beta-amyloid neurotoxicity

A DNA robotic switch with regulated autonomous display of cytotoxic ligand nanopatterns

The clustering of death receptors (DRs) at the membrane leads to apoptosis. With the goal of treating tumours, multivalent molecular tools that initiate this mechanism have been developed. However, DRs are also ubiquitously expressed in healthy tissue. Here we present a stimuli-responsive robotic switch nanodevice that can autonomously and selectively turn on the display of cytotoxic ligand patterns in tumour microenvironments. We demonstrate a switchable DNA origami that normally hides six ligands but displays them as a hexagonal pattern 10 nm in diameter once under higher acidity. This can effectively cluster DRs and trigger apoptosis of human breast cancer cells at pH 6.5 while remaining inert at pH 7.4. When administered to mice bearing human breast cancer xenografts, this nanodevice decreased tumour growth by up to 70%. The data demonstrate the feasibility and opportunities for developing ligand pattern switches as a path for targeted treatment.

Microglia either promote or restrain TRAIL-mediated excitotoxicity caused by Aβ1-42 oligomers

BACKGROUND

Alzheimer's disease (AD) features progressive neurodegeneration and microglial activation that results in dementia and cognitive decline. The release of soluble amyloid (Aβ) oligomers into the extracellular space is an early feature of AD pathology. This can promote excitotoxicity and microglial activation. Microglia can adopt several activation states with various functional outcomes. Protective microglial activation states have been identified in response to Aβ plaque pathology in vivo. However, the role of microglia and immune mediators in neurotoxicity induced by soluble Aβ oligomers is unclear. Further, there remains a need to identify druggable molecular targets that promote protective microglial states to slow or prevent the progression of AD.

METHODS

Hippocampal entorhinal brain slice culture (HEBSC) was employed to study mechanisms of Aβ1-42 oligomer-induced neurotoxicity as well as the role of microglia. The roles of glutamate hyperexcitation and immune signaling in Aβ-induced neurotoxicity were assessed using MK801 and neutralizing antibodies to the TNF-related apoptosis-inducing ligand (TRAIL) respectively. Microglial activation state was manipulated using Gi-hM4di designer receptor exclusively activated by designer drugs (DREADDs), microglial depletion with the colony-stimulating factor 1 receptor (CSF1R) antagonist PLX3397, and microglial repopulation (PLX3397 withdrawal). Proteomic changes were assessed by LC-MS/MS in microglia isolated from control, repopulated, or Aβ-treated HEBSCs.

RESULTS

Neurotoxicity induced by soluble Aβ1-42 oligomers involves glutamatergic hyperexcitation caused by the proinflammatory mediator and death receptor ligand TRAIL. Microglia were found to have the ability to both promote and restrain Aβ-induced toxicity. Induction of microglial Gi-signaling with hM4di to prevent pro-inflammatory activation blunted Aβ neurotoxicity, while microglial depletion with CSF1R antagonism worsened neurotoxicity caused by Aβ as well as TRAIL. HEBSCs with repopulated microglia, however, showed a near complete resistance to Aβ-induced neurotoxicity. Comparison of microglial proteomes revealed that repopulated microglia have a baseline anti-inflammatory and trophic phenotype with a predicted pathway activation that is nearly opposite that of Aβ-exposed microglia. mTORC2 and IRF7 were identified as potential targets for intervention.

CONCLUSION

Microglia are key mediators of both protection and neurodegeneration in response to Aβ. Polarizing microglia toward a protective state could be used as a preventative strategy against Aβ-induced neurotoxicity.

Unveiling Immune-related feature genes for Alzheimer's disease based on machine learning

The identification of diagnostic and therapeutic biomarkers for Alzheimer's Disease (AD) remains a crucial area of research. In this study, utilizing the Weighted Gene Co-expression Network Analysis (WGCNA) algorithm, we identified RHBDF2 and TNFRSF10B as feature genes associated with AD pathogenesis. Analyzing data from the GSE33000 dataset, we revealed significant upregulation of RHBDF2 and TNFRSF10B in AD patients, with correlations to age and gender. Interestingly, their expression profile in AD differs notably from that of other neurodegenerative conditions. Functional analysis unveiled their involvement in immune response and various signaling pathways implicated in AD pathogenesis. Furthermore, our study demonstrated the potential of RHBDF2 and TNFRSF10B as diagnostic biomarkers, exhibiting high discrimination power in distinguishing AD from control samples. External validation across multiple datasets confirmed the robustness of the diagnostic model. Moreover, utilizing molecular docking analysis, we identified dinaciclib and tanespimycin as promising small molecule drugs targeting RHBDF2 and TNFRSF10B for potential AD treatment. Our findings highlight the diagnostic and therapeutic potential of RHBDF2 and TNFRSF10B in AD management, shedding light on novel strategies for precision medicine in AD.

Biofluid biomarkers for Alzheimer's disease

Alzheimer's disease (AD) is a multifactorial neurodegenerative disease, with a complex pathogenesis and an irreversible course. Therefore, the early diagnosis of AD is particularly important for the intervention, prevention, and treatment of the disease. Based on the different pathophysiological mechanisms of AD, the research progress of biofluid biomarkers are classified and reviewed. In the end, the challenges and perspectives of future research are proposed.

TNF-Related Apoptosis-Inducing Ligand: Non-Apoptotic Signalling

TNF-related apoptosis-inducing ligand (TRAIL or Apo2 or TNFSF10) belongs to the TNF superfamily. When bound to its agonistic receptors, TRAIL can induce apoptosis in tumour cells, while sparing healthy cells. Over the last three decades, this tumour selectivity has prompted many studies aiming at evaluating the anti-tumoral potential of TRAIL or its derivatives. Although most of these attempts have failed, so far, novel formulations are still being evaluated. However, emerging evidence indicates that TRAIL can also trigger a non-canonical signal transduction pathway that is likely to be detrimental for its use in oncology. Likewise, an increasing number of studies suggest that in some circumstances TRAIL can induce, via Death receptor 5 (DR5), tumour cell motility, potentially leading to and contributing to tumour metastasis. While the pro-apoptotic signal transduction machinery of TRAIL is well known from a mechanistic point of view, that of the non-canonical pathway is less understood. In this study, we the current state of knowledge of TRAIL non-canonical signalling.

Implicative role of Cytokines in Neuroinflammation mediated AD and associated signaling pathways: Current Progress in molecular signaling and therapeutics

Alzheimer's Disease (AD) is one of the most devastating age-related disorder causing significant social and economic burden worldwide. It affects the cognitive and social behavior of individuals and characterized by accumulation of Aβ, phosphorylated tau and cytokines formation. The synthesis and release of cytokines are regulated by specific groups of immune and non-immune cells in response to microglia or astrocyte activation through multiple pathways. Physiologically, microglia assert an anti-inflammatory, quiescent state with minimal cytokine expression and little phagocytic activity in motion to carry out their housekeeping role to eliminate pathogens, aggregated Aβ and tau protein. However, they develop a phagocytic nature and overexpress cytokine gene modules in response to certain stimuli in AD. Microglia and astrocytes upon chronic activation release an enormous amount of inflammatory cytokines due to interaction with formed Aβ and neurofibrillary tangle. Gut microbiota dysbiosis also stimulates the release of inflammatory cytokines contributing to AD pathogenesis. In addition, the dysregulation of few signaling pathways significantly influences the development of disease, and the pace of advancement also rises with age. This review sheds light on multiple pathways results into neuroinflammation triggered by activated cytokines worsening AD pathology and making it an appropriate target for AD treatment. This review also included drugs targeting different neuroinflammation pathways under clinical and preclinical studies that are found to be effective in attenuating the disease pathology.

Apoptotic cell death in disease-Current understanding of the NCCD 2023

Apoptosis is a form of regulated cell death (RCD) that involves proteases of the caspase family. Pharmacological and genetic strategies that experimentally inhibit or delay apoptosis in mammalian systems have elucidated the key contribution of this process not only to (post-)embryonic development and adult tissue homeostasis, but also to the etiology of multiple human disorders. Consistent with this notion, while defects in the molecular machinery for apoptotic cell death impair organismal development and promote oncogenesis, the unwarranted activation of apoptosis promotes cell loss and tissue damage in the context of various neurological, cardiovascular, renal, hepatic, infectious, neoplastic and inflammatory conditions. Here, the Nomenclature Committee on Cell Death (NCCD) gathered to critically summarize an abundant pre-clinical literature mechanistically linking the core apoptotic apparatus to organismal homeostasis in the context of disease.

Indirubin Inhibits TRAIL-Induced Activation of Death Receptor 5 in Jurkat Cells

Death receptor 5 (DR5) is an apoptosis-inducing membrane receptor that mediates cell death in several life-threatening conditions. There is a crucial need for the discovery of DR5 antagonists for the therapeutic intervention of conditions in which the overactivation of DR5 underlies the pathophysiology. DR5 activation mediates cell death in non-alcoholic fatty liver disease (NAFLD) and neurodegenerative processes including amyloid-beta (Aβ) accumulation, spinal cord injury (SCI), and brain ischemia. In the current work, we used fluorescence resonance energy transfer (FRET) to monitor the conformational dynamics of DR5 that mediate death signaling. We used a time-resolved FRET screening platform to screen the Selleck library of 2863 U.S. Food and Drug Administration (FDA)-approved compounds. The high-throughput screen (HTS) identified 13 compounds that modulated the FRET between DR5 monomers beyond 5 median absolute deviations (MADs) from the DMSO controls. Of these 13 compounds, indirubin was identified to specifically inhibit tumor necrosis factor-related apoptosis-inducing ligand (TRAIL)-induced caspase-8 activity without modulating DR5 surface expression or TRAIL binding. Indirubin inhibited Fas-associated death domain (FADD) oligomerization and increased cellular FLICE-inhibitory protein (c-FLIP) expression; both are molecular mechanisms involved in inhibiting the DR5 signaling cascade. This study has elucidated previously unknown properties of indirubin that make it a promising candidate for therapeutic investigation of diseases in which overactivation of DR5 underlies pathology.

TRAIL-R Deficient Mice Are Protected from Neurotoxic Effects of Amyloid-β

TRAIL, a member of TNF superfamily, is a potent inducer of neuronal death. Neurotoxic effects of TRAIL appear mediated by its death receptor TRAIL-R2/DR5. To assess the role of TRAIL/TRAIL-R2 pathway in AD-related neurodegeneration, we studied the impact of the treatment with amyloid-β (Aβ) upon cell viability and inflammation in TRAIL-R-deficient mice (TRAIL-R^−/−). Here, we demonstrate that the lack of TRAIL-R2 protects from death cultured TRAIL-R^−/− mouse embryonic hippocampal cells after treatment with either Aβ1-42 or TRAIL. Consistently, stereotaxic injection of Aβ1-42 resulted in blunted caspase activation, as well as in reduction of JNK phosphorylation and increased AKT phosphorylation in TRAIL-R^−/− mice. Moreover, the lack of TRAIL-R2 was associated with blunted constitutive p53 expression in mice that have undergone Aβ1-42 treatment, as well as in decrease of phosphorylated forms of tau and GSK3β proteins. Likewise, TRAIL-R2 appears essential to both TRAIL and Aβ-mediated neurotoxicity and inflammation. Indeed, hippocampi of TRAIL-R^−/− mice challenged with Aβ1-42, showed a slight expression of microglial (Iba-1) and astrocytic (GFAP) markers along with attenuated levels of IL-1β, TNF-α, NOS2 and COX2. In conclusion, the bulk of these results demonstrate that the constitutive lack of TRAIL-R2 is associated with a substantial reduction of noxious effects of Aβ1-42, providing further evidence on the prominent role played by TRAIL in course of Aβ-related neurodegeneration and confirming that the TRAIL system represents a potential target for innovative AD therapy.

PARP-1-Associated Pathological Processes: Inhibition by Natural Polyphenols

Poly (ADP-ribose) polymerase-1 (PARP-1) is a nuclear enzyme involved in processes of cell cycle regulation, DNA repair, transcription, and replication. Hyperactivity of PARP-1 induced by changes in cell homeostasis promotes development of chronic pathological processes leading to cell death during various metabolic disorders, cardiovascular and neurodegenerative diseases. In contrast, tumor growth is accompanied by a moderate activation of PARP-1 that supports survival of tumor cells due to enhancement of DNA lesion repair and resistance to therapy by DNA damaging agents. That is why PARP inhibitors (PARPi) are promising agents for the therapy of tumor and metabolic diseases. A PARPi family is rapidly growing partly due to natural polyphenols discovered among plant secondary metabolites. This review describes mechanisms of PARP-1 participation in the development of various pathologies, analyzes multiple PARP-dependent pathways of cell degeneration and death, and discusses representative plant polyphenols, which can inhibit PARP-1 directly or suppress unwanted PARP-dependent cellular processes.

The immune system on the TRAIL of Alzheimer's disease

Alzheimer's disease (AD) is the most common form of dementia, characterized by progressive degeneration and loss of neurons in specific regions of the central nervous system. Chronic activation of the immune cells resident in the brain, peripheral immune cell trafficking across the blood-brain barrier, and release of inflammatory and neurotoxic factors, appear critical contributors of the neuroinflammatory response that drives the progression of neurodegenerative processes in AD. As the neuro-immune network is impaired in course of AD, this review is aimed to point out the essential supportive role of innate and adaptive immune response either in normal brain as well as in brain recovery from injury. Since a fine-tuning of the immune response appears crucial to ensure proper nervous system functioning, we focused on the role of the TNF superfamily member, TNF-related apoptosis-inducing ligand (TRAIL), which modulates both the innate and adaptive immune response in the pathogenesis of several immunological disorders and, in particular, in AD-related neuroinflammation. We here summarized mounting evidence of potential involvement of TRAIL signaling in AD pathogenesis, with the aim to provide clearer insights about potential novel therapeutic approaches in AD.

Insight into the divergent role of TRAIL in non-neoplastic neurological diseases

Tumour necrosis factor–related apoptosis‐inducing ligand (TRAIL) is a member of the tumour necrosis factor (TNF) superfamily which mainly induces apoptosis of tumour cells and transformed cell lines with no systemic toxicity, whereas they share high sequence homology with TNF and CD95L. These unique effects of TRAIL have made it an important molecule in oncology research. However, the research on TRAIL‐related antineoplastic agents has lagged behind and has been limited by the extensive drug resistance in cancer cells. Given the several findings showing that TRAIL is involved in immune regulation and other pleiotropic biological effects in non‐malignant cells, TRAIL and its receptors have attracted widespread attention from researchers. In the central nervous system (CNS), TRAIL is highly correlated with malignant tumours such as glioma and other non‐neoplastic disorders such as acute brain injury, CNS infection and neurodegenerative disease. Many clinical and animal studies have revealed the dual roles of TRAIL in which it causes damage by inducing cell apoptosis, and confers protection by enhancing both pro‐ and non‐apoptosis effects in different neurological disorders and at different sites or stages. Its pro‐apoptotic effect produces a pro‐survival effect that cannot be underestimated. This review extensively covers in vitro and in vivo experiments and clinical studies investigating TRAIL. It also provides a summary of the current knowledge on the TRAIL signalling pathway and its involvement in pathogenesis, diagnosis and therapeutics of CNS disorders as a basis for future research.

Electrochemical Biosensors Based on Nanomaterials for Early Detection of Alzheimer's Disease

Alzheimer's disease (AD) is an untreatable neurodegenerative disease that initially manifests as difficulty to remember recent events and gradually progresses to cognitive impairment. The incidence of AD is growing yearly as life expectancy increases, thus early detection is essential to ensure a better quality of life for diagnosed patients. To reach that purpose, electrochemical biosensing has emerged as a cost-effective alternative to traditional diagnostic techniques, due to its high sensitivity and selectivity. Of special relevance is the incorporation of nanomaterials in biosensors, as they contribute to enhance electron transfer while promoting the immobilization of biological recognition elements. Moreover, nanomaterials have also been employed as labels, due to their unique electroactive and electrocatalytic properties. The aim of this review is to add value in the advances achieved in the detection of AD biomarkers, the strategies followed for the incorporation of nanomaterials and its effect in biosensors performance.

Circulating Dkk1 and TRAIL Are Associated With Cognitive Decline in Community-Dwelling, Older Adults With Cognitive Concerns

Background

Osteoporosis and Alzheimer's disease are common diseases of aging that would seem to be unrelated, but may be linked through the influence of bone-derived signals on brain function. The aim of the current study is to investigate the relationship between circulating levels of bone-related biomarkers and cognition.

Methods

The population included 103 community-dwelling older individuals with memory concerns but without cognitive impairment. A global cognition summary measure was collected at baseline and 6, 12, and 18 months post-enrollment by converting raw scores from 19 cognitive function tests to z-scores and averaging. Baseline plasma concentrations of bone-related biomarkers, including undercarboxylated, carboxylated, and total osteocalcin, parathyroid hormone, C-terminal telopeptide of collagen 1 (CTX-1), procollagen type 1 amino-terminal propeptide, osteoprotegrin, osteopontin, Dickkopf WNT signaling pathway inhibitor 1 (Dkk1), sclerostin, and amyloid β peptides (Aβ40 and Aβ42), were measured.

Results

Using sex, age, and education-adjusted mixed-effects models, we found that baseline levels of TNF-related apoptosis-inducing ligand (TRAIL; p < .001), Dkk1 (p = .014), and CTX-1 (p = .046) were related to the annual rate of change of global cognition over the 18 month follow-up. In cognitive domain-specific analysis, baseline TRAIL was found to be positively related to the annual rate of change in episodic (p < .001) and working memory (p = .016), and baseline Dkk1 was positively related to semantic memory (p = .027) and negatively related to working memory (p = .016).

Conclusions

These results further confirm the link between bone and brain health and suggest that circulating levels of bone-related biomarkers may have diagnostic potential to predict worsening cognition.

Competitive electrochemical immunosensor for the detection of unfolded p53 protein in blood as biomarker for Alzheimer's disease

Alzheimer's disease is one of the most common causes of dementia nowadays, and its prevalence increases over time. Because of this and the difficulty of its diagnosis, accurate methods for the analysis of specific biomarkers for an early diagnosis of this disease are much needed. Recently, the levels of unfolded isoform of the multifunctional protein p53 in plasma have been proved to increase selectively in Alzheimer's Disease patients in comparison with healthy subjects, thus entering the list of biomarkers that can be used for the diagnosis of this illness. We present here the development of an electrochemical immunosensor based on nanostructured screen-printed carbon electrodes for the quantification of unfolded p53 in plasma samples. The sensor shows a suitable linear range (from 2 to 50 nM) for its application in real blood samples and a very low limit of detection (0.05 nM). The concentration of unfolded p53 has been accurately detected in plasma of elderly people in healthy conditions, subjects with mild cognitive impairment (MCI) and Alzheimer's Disease (AD) subjects, obtaining results with no significant differences to those provided by an ELISA assay. These results support the possibility of measuring unfolded p53 levels with a cheap, simple and miniaturized device with a promising future for point-of-care applications in the early diagnosis of Alzheimer's dementia.

Beneficial effects of curtailing immune susceptibility in an Alzheimer's disease model

BACKGROUND

Currently, there are no effective therapeutic options for Alzheimer's disease, the most common, multifactorial form of dementia, characterized by anomalous amyloid accumulation in the brain. Growing evidence points to neuroinflammation as a major promoter of AD. We have previously shown that the proinflammatory cytokine TNFSF10 fuels AD neuroinflammation, and that its immunoneutralization results in improved cognition in the 3xTg-AD mouse.

METHODS

Here, we hypothesize that inflammatory hallmarks of AD might parallel with central and peripheral immune response dysfunction. To verify such hypothesis, we used a triple transgenic mouse model of AD. 3xTg-AD mice were treated for 12 months with an anti-TNFSF10 antibody, and thereafter immune/inflammatory markers including COX2, iNOS, IL-1β and TNF-α, CD3, GITR, and FoxP3 (markers of regulatory T cells) were measured in the spleen as well as in the hippocampus.

RESULTS

Spleens displayed accumulation of amyloid-β1-42 (Aβ1-42), as well as high expression of Treg cell markers FoxP3 and GITR, in parallel with the increased levels of inflammatory markers COX2, iNOS, IL-1β and TNF-α, and blunted IL-10 expression. Moreover, CD3 expression was increased in the hippocampus, consistently with FoxP3 and GITR. After chronic treatment of 3xTg-AD mice with an anti-TNFSF10 antibody, splenic FoxP3, GITR, and the above-mentioned inflammatory markers expression was restored to basal levels, while expression of IL-10 was increased. A similar picture was observed in the hippocampus. Such improvement of peripheral and CNS inflammatory/immune response was associated with decreased microglial activity in terms of TNFα production, as well as decreased expression of both amyloid and phosphorylated tau protein in the hippocampus of treated 3xTg-AD mice. Interestingly, we also reported an increased expression of both CD3 and FoxP3, in sections from human AD brain.

CONCLUSIONS

We suggest that neuroinflammation in the brain of 3xTg-AD mice triggered by TNFSF10 might result in a more general overshooting of the immune response. Treatment with an anti-TNFSF10 antibody blunted inflammatory processes both in the spleen and hippocampus. These data confirm the detrimental role of TNFSF10 in neurodegeneration, and corroborate the hypothesis of the anti-TNFSF10 strategy as a potential treatment to improve outcomes in AD.

Clinical perspectives of TRAIL: insights into central nervous system disorders

The TNF-related apoptosis inducing ligand TRAIL is a member of the TNF superfamily that has been firstly studied and evaluated for its anti-cancer activity, and the insights into its biology have already led to the identification of several TRAIL-based anticancer strategies with strong clinical therapeutic potentials. Nonetheless, the TRAIL system is far more complex and it can lead to a wider range of biological effects other than the ability of inducing apoptosis in cancer cells. By virtue of the different receptors and the different signalling pathways involved, TRAIL plays indeed a role in the regulation of different processes of the innate and adaptive immune system and this feature makes it an intriguing molecule under consideration in the development/progression/treatment of several immunological disorders. In this context, central nervous system represents a peculiar anatomic site where, despite its "status" of immune-privileged site, both innate and adaptive inflammatory responses occur and are involved in several pathological conditions. A number of studies have evaluated the role of TRAIL and of TRAIL-related pathways as pro-inflammatory or protective stimuli, depending on the specific pathological condition, confirming a twofold nature of this molecule. In this light, the aim of this review is to summarize the main preclinical evidences of the potential/involvement of TRAIL molecule and TRAIL pathways for the treatment of central nervous system disorders and the key suggestions coming from their assessment in preclinical models as proof of concept for future clinical studies.

Activation of TRAIL-DR5 pathway promotes sensorineural degeneration in the inner ear

Tumor necrosis factor (TNF) family cytokines are important mediators of inflammation. Elevated levels of serum TNF‐α are associated with human sensorineural hearing loss via poorly understood mechanisms. We demonstrate, for the first time, expression of TNF‐related apoptosis‐inducing ligand (TRAIL) and its signaling death receptor 5 (DR5) in the murine inner ear and show that exogenous TRAIL can trigger hair cell and neuronal degeneration, which can be partly prevented with DR5‐blocking antibodies.

A Study of the Impact of Death Receptor 4 (DR4) Gene Polymorphisms in Alzheimer's Disease

BACKGROUND

Excessive apoptosis is believed to play a role in many degenerative and non-degenerative neurological diseases including Alzheimer's disease (AD). Much recent data suggest that apoptotic mechanisms may represent the missing link between Aβ deposition and proteolysis of tau protein. However, there is emerging evidence that apoptotic mechanisms may play a role in Alzheimer's Disease pathogenesis in the absence of overt apoptosis. TNF-related apoptosis inducing ligand receptor 1 (Death Receptor 4, DR4) might impair the apoptotic signal transduction and lead to dysregulation of the homeostasis between cell survival and cell death.

AIMS

The aim of our study was to further investigate the relationship between genetic variants of DR4 and Alzheimer's Disease.

STUDY DESIGN

Case control study.

METHODS

Sixty-eight patients with AD were included in the study. The control group comprised 72 subjects without signs of neurodegenerative diseases, as evidenced by the examination.DNA was extracted from whole blood using the salting-out procedure. Genotypes were identified by restriction fragment length polymorphism analysis of polymerase chain reaction (PCR-RFLP) products.

RESULTS

We observed significant differences in the genotypic distribution of the rs6557634 polymorphism in AD patients compared with controls (p<0.05); our data suggest that the GA genotype in rs6557634 could be protective against AD (p<0.05). However, there were no significant differences between AD patients and control groups in terms of the DR4 rs20575 polymorphism (p>0.05) and the DR4 rs20576 polymorphism (p>0.05). According to haplotype analysis of the DR4 gene for rs6557634, rs20575 and rs20576 polymorphisms, GCA and GCC haplotypes might be a risk factor for AD. Also, we have shown that ACA, GGC and GGA haplotypes might be protective factors against AD.

CONCLUSION

The present results indicate for the first time the possible contribution of the DR4 gene rs6557634, rs20575, rs20576 polymorphisms in Alzheimer's Disease, which may influence susceptibility to Alzheimer's Disease.

TRAIL death receptors DR4 and DR5 mediate cerebral microvascular endothelial cell apoptosis induced by oligomeric Alzheimer's Aβ

Vascular deposition of amyloid-β (Aβ) in sporadic and familial Alzheimer's disease, through poorly understood molecular mechanisms, leads to focal ischemia, alterations in cerebral blood flow, and cerebral micro-/macro-hemorrhages, significantly contributing to cognitive impairment. Here, we show that tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) death receptors DR4 and DR5 specifically mediate oligomeric Aβ induction of extrinsic apoptotic pathways in human microvascular cerebral endothelial cells with activation of both caspase-8 and caspase-9. The caspase-8 inhibitor cellular FLICE-like inhibitory protein (cFLIP) is downregulated, and mitochondrial paths are engaged through BH3-interacting domain death agonist (Bid) cleavage. Upregulation of DR4 and DR5 and colocalization with Aβ at the cell membrane suggests their involvement as initiators of the apoptotic machinery. Direct binding assays using receptor chimeras confirm the specific interaction of oligomeric Aβ with DR4 and DR5 whereas apoptosis protection achieved through RNA silencing of both receptors highlights their active role in downstream apoptotic pathways unveiling new targets for therapeutic intervention.

Alzheimer's disease: redox dysregulation as a common denominator for diverse pathogenic mechanisms

Alzheimer's disease (AD) is the most common cause of dementia and a progressive neurodegeneration that appears to result from multiple pathogenic mechanisms (including protein misfolding/aggregation, involved in both amyloid β-dependent senile plaques and tau-dependent neurofibrillary tangles), metabolic and mitochondrial dysfunction, excitoxicity, calcium handling impairment, glial cell dysfunction, neuroinflammation, and oxidative stress. Oxidative stress, which could be secondary to several of the other pathophysiological mechanisms, appears to be a major determinant of the pathogenesis and progression of AD. The identification of oxidized proteins common for mild cognitive impairment and AD suggests that key oxidation pathways are triggered early and are involved in the initial progression of the neurodegenerative process. Abundant data support that oxidative stress, also considered as a main factor for aging, the major risk factor for AD, can be a common key element capable of articulating the divergent nature of the proposed pathogenic factors. Pathogenic mechanisms influence each other at different levels. Evidence suggests that it will be difficult to define a single-target therapy resulting in the arrest of progression or the improvement of AD deterioration. Since oxidative stress is present from early stages of disease, it appears as one of the main targets to be included in a clinical trial. Exploring the articulation of AD pathogenic mechanisms by oxidative stress will provide clues for better understanding the pathogenesis and progression of this dementing disorder and for the development of effective therapies to treat this disease.

Hypoxia-ischemia upregulates TRAIL and TRAIL receptors in the immature rat brain

The immature brain is susceptible to inflammatory injury induced by hypoxia-ischemia (HI) or infection, which causes serious neurodevelopmental disabilities in the survivors of preterm births. Recently, tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) and its receptors (death receptor DR4/5 and decoy receptor DcR1/2) were reported to mediate various neuroinflammatory responses. However, little information is available regarding the role of TRAIL and its receptors in the immature brain after HI. The purpose of this study was to evaluate the expression of TRAIL and its receptors in the immature brain after HI and relate this expression to neurological function. We performed right common carotid artery ligation followed by hypoxia (6% O(2), 37°C) for 2.5 h to induce HI in postnatal day 3 rats. The distribution of TRAIL and its receptors, caspase-3 and CD68-labeled microglia/macrophages was evaluated 24 h after HI by immunostaining. The protein and mRNA expression of TRAIL and DR5 was measured by Western blot and real-time PCR, respectively. Delayed neuronal loss was evaluated by NeuN and Nissl staining 7 days after HI. Furthermore, neurological deficits were evaluated by a righting reflex test, time of eye opening and T-maze test. The expression of TRAIL, DR5 and DcR1/2 receptors and caspase-3 was more pronounced in the ipsilateral hemisphere compared with the contralateral part and the control group 24 h after HI. DR5/active caspase-3 double-positive cells were observed at 24 h after HI in the ipsilateral hemisphere but not in the contralateral hemisphere. The TRAIL and CD68 double-labeled cells were more pronounced in the ipsilateral cortical regions compared with the corresponding regions of the contralateral part. HI also resulted in a significant increase in TRAIL and DR5 protein and mRNA expression at 24 h, which corresponded to neuronal cell loss 7 days after HI. Furthermore, the HI group displayed impaired neurobehavioral development compared with the control group (p < 0.05). Altogether our results show that the TNF-α superfamily ligand TRAIL is induced on CD68+ microglia/macrophages after perinatal HI and that one of its receptors, DR5, is induced on neocortical neurons and glial cells. That many DR5+ cells were also caspase-3+ strongly supports the conclusion that these signaling molecules are involved in the delayed loss of neurons in the neocortex and in the neurobehavioral deficits that are often seen after perinatal HI.

Regulation of cell survival mechanisms in Alzheimer's disease by glycogen synthase kinase-3

A pivotal role has emerged for glycogen synthase kinase-3 (GSK3) as an important contributor to Alzheimer's disease pathology. Evidence for the involvement of GSK3 in Alzheimer's disease pathology and neuronal loss comes from studies of GSK3 overexpression, GSK3 localization studies, multiple relationships between GSK3 and amyloid β-peptide (Aβ), interactions between GSK3 and the microtubule-associated tau protein, and GSK3-mediated apoptotic cell death. Apoptotic signaling proceeds by either an intrinsic pathway or an extrinsic pathway. GSK3 is well established to promote intrinsic apoptotic signaling induced by many insults, several of which may contribute to neuronal loss in Alzheimer's disease. Particularly important is evidence that GSK3 promotes intrinsic apoptotic signaling induced by Aβ. GSK3 appears to promote intrinsic apoptotic signaling by modulating proteins in the apoptosis signaling pathway and by modulating transcription factors that regulate the expression of proteins involved in apoptosis. Thus, GSK3 appears to contribute to several neuropathological mechanisms in Alzheimer's disease, including apoptosis-mediated neuronal loss.

Neutralization of tumor necrosis factor-related apoptosis-inducing ligand reduces spinal cord injury damage in mice

Spinal cord injury (SCI) is a major cause of disability, its clinical outcome depending mostly on the extent of damage in which proapoptotic cytokines have a crucial function. In particular, the inducers of apoptosis belonging to TNF receptor superfamily and their respective ligands are upregulated after SCI. In this study, the function of the proapoptotic cytokine tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) in SCI-induced damage was investigated in the mouse. SCI resulted in severe trauma, characterized by prominent inflammation-related damage and apoptosis. Immunostaining for TRAIL and its receptor DR5 was found in the white and gray matter of the perilesional area, as also confirmed by western blotting experiments. Immunoneutralization of TRAIL resulted in improved functional recovery, reduced apoptotic cell number, modulation of molecules involved in the inflammatory response (FasL, TNF-alpha, IL-1beta, and MPO), and the corresponding signaling (caspase-8 and -3 activation, JNK phosphorylation, Bax, and Bcl-2 expression). As glucocorticoid-induced TNF receptor superfamily-related protein (GITR) activated by its ligand (GITRL) contributes to SCI-related inflammation, interactions between TRAIL and GITRL were investigated. SCI was associated with upregulated GITR and GITRL expression, a phenomenon prevented by anti-TRAIL treatment. Moreover, the expression of both TRAIL and DR5 was reduced in tissues from mice lacking the GITR gene (GITR(-/-)) in comparison with wild-type mice suggesting that TRAIL- and GITRL-activated pathways synergise in the development of SCI-related inflammatory damage. Characterization of new targets within such molecular systems may constitute a platform for innovative treatment of SCI.

Pathologies associated with the p53 response

Although p53 is a major cancer preventive factor, under certain extreme stress conditions it may induce severe pathologies. Analyses of animal models indicate that p53 is largely responsible for the toxicity of ionizing radiation or DNA damaging drugs contributing to hematopoietic component of acute radiation syndrome and largely determining severe adverse effects of cancer treatment. p53-mediated damage is strictly tissue specific and occurs in tissues prone to p53-dependent apoptosis (e.g., hematopoietic system and hair follicles); on the contrary, p53 can serve as a survival factor in tissues that respond to p53 activation by cell cycle arrest (e.g., endothelium of small intestine). There are multiple experimental indications that p53 contributes to pathogenicity of acute ischemic diseases. Temporary reversible suppression of p53 by small molecules can be an effective and safe approach to reduce severity of p53-associated pathologies.

Generation of reactive oxygen species by beta amyloid fibrils and oligomers involves different intra/extracellular pathways

A neuropathological characteristic of Alzheimer's disease is the extracellular accumulation of amyloid beta peptide (Abeta) in neuritic plaques. Recent evidences suggested that soluble Abeta oligomers are the predominant neurotoxic species for neurons. Thus, considerable attention has been paid to discriminate the cytotoxic pathways of Abeta pre-fibrillar aggregates and mature fibrils. We showed that the mechanisms by which Abeta oligomers and fibrils generated reactive oxygen species differ in terms of site of production and kinetics, suggesting the involvement of different intra/extracellular pathways.

TNF-related apoptosis-inducing ligand level in Alzheimer's disease

In the present study, we determined the significance of tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) in Alzheimer's disease (AD). We characterized the expression of TRAIL protein in the cerebrospinal fluid (CSF) and serum with ELISA and TRAIL mRNA in the peripheral blood mononuclear cells (PBMCs) with real-time PCR in 22 patients with AD and 20 control cases. We could not find TRAIL protein in the CSF samples. The concentration of TRAIL protein in sera from patients with AD was not different from controls. However, there was an inverse correlation between serum TRAIL levels and Mini-Mental State Examination scores in AD patients. Also we did not find significant difference in TRAIL mRNA in the PBMCs of patients with AD when compared with control group. Our data indicate that TRAIL serum level decreases in the late stage of disease.

Inflammatory response in the hippocampus of PS1M146L/APP751SL mouse model of Alzheimer's disease: age-dependent switch in the microglial phenotype from alternative to classic

Although the microglial activation is concomitant to the Alzheimer's disease, its precise role (neuroprotection vs neurodegeneration) has not yet been resolved. Here, we show the existence of an age-dependent phenotypic change of microglial activation in the hippocampus of PS1xAPP model, from an alternative activation state with Abeta phagocytic capabilities (at 6 months) to a classic cytotoxic phenotype (expressing TNF-alpha and related factors) at 18 months of age. This switch was coincident with high levels of soluble Abeta oligomers and a significant pyramidal neurodegeneration. In vitro assays, using astromicroglial cultures, demonstrated that oligomeric Abeta42 and soluble extracts from 18-month-old PS1xAPP hippocampus produced a potent TNF-alpha induction whereas monomeric Abeta42 and soluble extract from 6- or 18-month-old control and 6-month-old PS1xAPP hippocampi produced no stimulation. This stimulatory effect was avoided by immunodepletion using 6E10 or A11. In conclusion, our results show evidence of a switch in the activated microglia phenotype from alternative, at the beginning of Abeta pathology, to a classical at advanced stage of the disease in this model. This change was induced, at least in part, by the age-dependent accumulation of extracellular soluble Abeta oligomers. Finally, these cytotoxic activated microglial cells could participate in the neuronal lost observed in AD.

Increased p53 level, Bax/Bcl-x(L) ratio, and TRAIL receptor expression in human emphysema

RATIONALE

Emphysema is mainly known for the complex inflammatory processes associated with its development. In addition to lung inflammation, it is now accepted that increased alveolar cell apoptosis is also part of emphysema pathophysiology. However, little is known about the mechanisms involved in alveolar apoptosis. We postulate that oxidative stress and proinflammatory cytokines could lead to p53 accumulation, Bax/Bcl-x(L) ratio elevation, and higher tumor necrosis factor (TNF)-related apoptosis-inducing ligand (TRAIL) receptor levels in the emphysematous lung.

OBJECTIVES

To evaluate the expression of p53, Bax, Bcl-x(L), TRAIL, and TRAIL receptors in lung parenchyma from nonemphysematous nonsmokers and smokers and emphysematous smokers and ex-smokers and to determine whether H2O2 and/or TNF can modulate the expression of these apoptotic proteins.

METHODS

p53, Bax, Bcl-x(L), and TRAIL receptor protein levels in lung parenchyma were measured by Western blot, and TRAIL mRNA levels were measured by real-time polymerase chain reaction. Changes in TRAIL receptor, Bax, Bcl-x(L), and p53 protein levels after in vitro H2O2 and/or TNF stimulation of A549 cells were also assessed by Western blot.

MEASUREMENTS AND MAIN RESULTS

The p53 protein levels, the Bax/Bcl-x(L) ratio, and TRAIL receptors 1, 2, and 3 protein levels were significantly higher in subjects with emphysema. Moreover, they were also increased after H2O2 and TNF treatments of A549 cells.

CONCLUSIONS

These findings suggest that oxidative stress and proinflammatory cytokines may be involved in the elevation of p53 levels, the Bax/Bcl-x(L) ratio, and TRAIL receptor levels, new mechanisms that may be implicated in the increased alveolar cell apoptosis that occurs in emphysema.