p53 in neurodegenerative diseases and brain cancers

α-synuclein expression in glioblastoma restores tumor suppressor function and rescues temozolomide drug resistance

Several studies have shown that Parkinson's disease causative gene products, including α-synuclein (α-syn), display tight links with the tumor suppressor p53. The purpose of this study is to determine the implication of α-syn in glioblastoma development and elucidate how it elicits a tumor suppressor function. We show that the expression of α-syn, a TP53 transcriptional target and a key molecular player in Parkinson's disease, is detected in 1p/19q-codeleted and isocitrate dehydrogenase (IDH)-mutant oligodendroglioma and in IDH-wild-type glioblastoma, while reduced in glioblastoma biopsies, corroborating the link of α-syn expression with a better prognosis among all glioma patients. Accordingly, protein expression is drastically reduced in oligodendrogliomas and glioblastoma biopsies. This could be accounted for by a reduction of p53 transcriptional activity in these samples. Interestingly, genetic manipulation of p53 in glioblastoma cells and in mouse brain shows that p53 up-regulates α-synuclein, a phenotype fully abolished by the prominent p53 hot spot mutation R175H. Downstream to its p53-linked control, α-syn lowers cyclin D1 protein and mRNA levels and reduces glioblastoma cells proliferation in a cyclin D1-dependent-manner. Further, in temozolomide (TMZ)-resistant U87 cells, α-syn reduces O6-methylguanine-DNA methyltransferase (MGMT) expression and rescues drug sensitivity by a mechanism implying its transcriptional activation by X-box binding protein 1 (XBP1), an effector of the UPR response. Furthermore, α-syn lowers MGMT and cyclin D1 (CCDN1) expressions and reduces tumor development in allografted mice. Overall, our data reveals a new role of α-syn as an oligodendroglioma biomarker and as a glioblastoma tumor suppressor capable of either potentiate TMZ effect or avoid TMZ-associated resistance.

Neuroprotective effects of activated fibroblast growth factor receptor 1 via the suppression of p53 accumulation against poly-PR-mediated toxicity

A GGGGCC hexanucleotide repeat expansion (HRE) within the C9orf72 gene is a major causative factor in amyotrophic lateral sclerosis (ALS). This aberrant HRE results in the generation of five distinct dipeptide repeat proteins (DPRs). Among the DPRs, poly-PR accumulates in the nucleus and exhibits particularly strong toxicity to motor and cortical neurons. Fibroblast growth factor receptor 1 (FGFR1) is known to promote neurogenesis and inhibit apoptosis in neurons. Nevertheless, there has been no previous report of its neuroprotective effects against poly-PR toxicity. The objective of this study was to investigate the neuroprotective effects of FGFR1 activation in poly-PR-expressing NSC34 motor neuron-like cells. RT-qPCR analysis in NSC34 cells showed that Fgfr1 was the most highly expressed member of the Fgfr family in NSC34 cells. The activation of FGFR1 by FGF2, a common ligand for all FGFRs, exerted neuroprotective effects against the toxicity of poly-PR. Additionally, FGFR1 activation was observed to enhance cell viability through the PI3K-AKT pathway, while the contribution of the MEK-ERK pathway was found to be limited. Furthermore, FGFR1 activation suppressed the accumulation of p53 protein and promoted its degradation through increased murine double minute 2 (MDM2), an E3 ubiquitin ligase that targets p53. The neuroprotective effects were attenuated by PD173074, a selective FGFR1 inhibitor or Nutlin-3a, an inhibitor of the p53-MDM2 interaction. Overall, these findings suggest that FGFR1 activation provides neuroprotection against poly-PR toxicity. Consequently, this study suggests the potential utility of FGFR1 activation as a therapeutic strategy for ALS.

Understanding the complexity of p53 in a new era of tumor suppression

p53 was discovered 45 years ago as an SV40 large T antigen binding protein, coded by the most frequently mutated TP53 gene in human cancers. As a transcription factor, p53 is tightly regulated by a rich network of post-translational modifications to execute its diverse functions in tumor suppression. Although early studies established p53-mediated cell-cycle arrest, apoptosis, and senescence as the classic barriers in cancer development, a growing number of new functions of p53 have been discovered and the scope of p53-mediated anti-tumor activity is largely expanded. Here, we review the complexity of different layers of p53 regulation, and the recent advance of the p53 pathway in metabolism, ferroptosis, immunity, and others that contribute to tumor suppression. We also discuss the challenge regarding how to activate p53 function specifically effective in inhibiting tumor growth without harming normal homeostasis for cancer therapy.

A common molecular and cellular pathway in developing Alzheimer and cancer

Globally cancer and Alzheimer's disease (AD) are two major diseases and still, there is no clearly defined molecular mechanism. There is an opposite relation between cancer and AD which are the proportion of emerging cancer was importantly slower in AD patients, whereas slow emerging AD in patients with cancer. In cancer, regulation of cell mechanisms is interrupted by an increase in cell survival and proliferation, while on the contrary, AD is related to augmented neuronal death, that may be either produced by or associated with amyloid-β (Aβ) and tau deposition. Stated that the probability that disruption of mechanisms takes part in the regulation of cell survival/death and might be implicated in both diseases. The mechanism of actions such as DNA-methylation, genetic polymorphisms, or another mechanism of actions that induce alteration in the action of drugs with significant roles in resolving the finding to repair and live or die might take part in the pathogenesis of these two ailments. The functions of miRNA, p53, Pin1, the Wnt signaling pathway, PI3 KINASE/Akt/mTOR signaling pathway GRK2 signaling pathway, and the pathophysiological role of oxidative stress are presented in this review as potential candidates which hypothetically describe inverse relations between cancer and AD. Innovative materials almost mutual mechanisms in the aetiology of cancer and AD advocates novel treatment approaches. Among these treatment strategies, the most promising use treatment such as tyrosine kinase inhibitor, nilotinib, protein kinase C, and bexarotene.

Targeting p53 for neuroinflammation: New therapeutic strategies in ischemic stroke

Ischemic stroke (IS) is characterized by high incidence, high recurrence, and high mortality and places a heavy burden on society and families. The pathological mechanisms of IS are complex, among which secondary neurological impairment mediated by neuroinflammation is considered to be the main factor in cerebral ischemic injury. At present, there is still a lack of specific therapies to treat neuroinflammation. The tumor suppressor protein p53 has long been regarded as a key substance in the regulation of the cell cycle and apoptosis in the past. Recently, studies have found that p53 also plays an important role in neuroinflammatory diseases, such as IS. Therefore, p53 may be a crucial target for the regulation of the neuroinflammatory response. Here, we provide a comprehensive review of the potential of targeting p53 in the treatment of neuroinflammation after IS. We describe the function of p53, the major immune cells involved in neuroinflammation, and the role of p53 in inflammatory responses mediated by these cells. Finally, we summarize the therapeutic strategies of targeting p53 in regulating the neuroinflammatory response after IS to provide new directions and ideas for the treatment of ischemic brain injury.

P53 protein and the diseases in central nervous system

P53 protein is the product of P53 gene, which is a well acknowledged tumor suppressor gene. The function of P53 and the relevant mechanisms of anti-neoplasm have raised the interest of researchers since many years ago. It is demonstrated that P53 is a basic cell cycle regulator and a strong inhibitor for versatile cancers in humans. However, most research focuses on other organs and systems instead of the central nervous system (CNS). In fact, in recent years, more and more studies have been suggesting that P53 plays a significant role in multiple CNS tumors and other diseases and disorders such as cerebral stroke and neurodegenerative diseases. In this work, we mainly reviewed the P53's relationship with CNS tumors, cerebral stroke and neurodegenerative diseases, together with the relevant mechanisms, aiming to summarize the research achievements and providing new insight to the future study on diseases in CNS.

Restoring Age-Related Cognitive Decline through Environmental Enrichment: A Transcriptomic Approach

Cognitive decline is one of the greatest health threats of old age and the maintenance of optimal brain function across a lifespan remains a big challenge. The hippocampus is considered particularly vulnerable but there is cross-species consensus that its functional integrity benefits from the early and continuous exercise of demanding physical, social and mental activities, also referred to as environmental enrichment (EE). Here, we investigated the extent to which late-onset EE can improve the already-impaired cognitive abilities of lifelong deprived C57BL/6 mice and how it affects gene expression in the hippocampus. To this end, 5- and 24-month-old mice housed in standard cages (5mSC and 24mSC) and 24-month-old mice exposed to EE in the last 2 months of their life (24mEE) were subjected to a Barnes maze task followed by next-generation RNA sequencing of the hippocampal tissue. Our analyses showed that late-onset EE was able to restore deficits in spatial learning and short-term memory in 24-month-old mice. These positive cognitive effects were reflected by specific changes in the hippocampal transcriptome, where late-onset EE affected transcription much more than age (24mSC vs. 24mEE: 1311 DEGs, 24mSC vs. 5mSC: 860 DEGs). Remarkably, a small intersection of 72 age-related DEGs was counter-regulated by late-onset EE. Of these, Bcl3, Cttnbp2, Diexf, Esr2, Grb10, Il4ra, Inhba, Rras2, Rps6ka1 and Socs3 appear to be particularly relevant as key regulators involved in dendritic spine plasticity and in age-relevant molecular signaling cascades mediating senescence, insulin resistance, apoptosis and tissue regeneration. In summary, our observations suggest that the brains of aged mice in standard cage housing preserve a considerable degree of plasticity. Switching them to EE proved to be a promising and non-pharmacological intervention against cognitive decline.

Identification of 3-Phenylquinoline Derivative PQ1 as an Antagonist of p53 Transcriptional Activity

Transcription factor p53 regulates cellular responses to environmental perturbations via the transcriptional activation of downstream target genes. Inappropriate p53 activation can trigger abnormal cellular responses, therefore leading to acute or chronic tissue damage, human developmental syndromes, and neurodegenerative diseases. Antagonists of p53 transcriptional activity provide prospective therapeutic applications and molecular probes. In this article, we identified five 3-phenylquinoline derivatives as potential p53 inhibitors through screening a chemical library consisting of 120 compounds, in which PQ1 was the most active compound. PQ1 had no effect on p53 protein levels and decreased the expression of p53 target gene p21. PQ1 thermally stabilizes the wild-type p53 protein. Further, transcriptomics confirmed that PQ1 exposure generated a similar regulatory effect to transcription profiles with a reported p53 transcriptional inhibitor pifithrin-α. However, compared to pifithrin-α, PQ1 increased the sensitivity of SW480 cells to 5FU. Taken together, PQ1 was a novel antagonist of p53 transcriptional activity. We propose that PQ1 could be developed as a chemical tool to pinpoint the physiological functions of p53 and a novel lead compound for targeting dysfunctional p53 activation.

Adeno-associated virus-delivered alpha synuclein inhibits bladder cancer growth via the p53/p21 signaling pathway

Alpha-synuclein (α-syn), encoded by the SNCA gene, is a major participant in the pathophysiology of Parkinson's disease (PD). Its functions have been reported to be related to apoptosis induction, the elevation of oxidative stress, mitochondrial homeostasis, cell-cycle aberrations, and DNA-related interactions. Evidence obtained in recent studies suggests a possible link between α-syn and cancer development. Bladder cancer (BCa) is the second most common genitourinary malignancy, with the population of survivors of BCa increasing worldwide. In this study, we show that α-syn expression was significantly downregulated in BCa. In vitro and in vivo experiments showed that α-syn could significantly inhibit BCa cell proliferation by arresting the cell cycle in the S phase via upregulation of p53 expression mediated by DNA damages. Further experiments showed that overexpression of α-syn delivered by adeno-associated viruses (AAVs) exerted inhibitory effects on the growth of BCa tumors. These findings indicate that αα-syn is a functional tumor suppressor that can inhibit the proliferation of BCa cells by activating the p53/p21 signaling pathway. Our present study provides insights into the roles of α-syn in BCa and suggests that α-syn may be a novel therapeutic target for the treatment of BCa.

NO-Dependent Mechanisms of p53 Expression and Cell Death in Rat’s Dorsal Root Ganglia after Sciatic-Nerve Transection

Peripheral-nerve injury is a frequent cause of disability. Presently, no clinically effective neuroprotectors have been found. We have studied the NO-dependent expression of p53 in the neurons and glial cells of the dorsal root ganglia (DRG) of a rat’s spinal cord, as well as the role of NO in the death of these cells under the conditions of axonal stress, using sciatic-nerve axotomy as a model. It was found out that axotomy led to the nuclear–cytoplasmic redistribution of p53 in neurons, 24 h after trauma. The NO donor led to a considerable increase in the level of p53 in nuclei and, to a smaller degree, in the cytoplasm of neurons and karyoplasm of glial cells 4 and 24 h after axotomy. Application of a selective inhibitor of inducible NO-synthase (iNOS) provided the opposite effect. Introduction of the NO donor resulted in a significant increase in cell death in the injured ipsilateral DRG, 24 h and 7 days after trauma. The selective inhibitor of iNOS demonstrated a neuroprotective effect. Axotomy was shown to upregulate the iNOS in nuclei and cytoplasm of DRG cells. The NO-dependent expression of p53, which is particularly achieved through iNOS activation, is believed to be a putative signaling mechanism of neural and glial-cell death after axotomy.

Parkin as a Molecular Bridge Linking Alzheimer’s and Parkinson’s Diseases?

Alzheimer’s (AD) and Parkinson’s (PD) diseases are two distinct age-related pathologies that are characterized by various common dysfunctions. They are referred to as proteinopathies characterized by ubiquitinated protein accumulation and aggregation. This accumulation is mainly due to altered lysosomal and proteasomal clearing processes and is generally accompanied by ER stress disturbance, autophagic and mitophagic defects, mitochondrial structure and function alterations and enhanced neuronal cell death. Genetic approaches aimed at identifying molecular triggers responsible for familial forms of AD or PD have helped to understand the etiology of their sporadic counterparts. It appears that several proteins thought to contribute to one of these pathologies are also likely to contribute to the other. One such protein is parkin (PK). Here, we will briefly describe anatomical lesions and genetic advances linked to AD and PD as well as the main cellular processes commonly affected in these pathologies. Further, we will focus on current studies suggesting that PK could well participate in AD and thereby act as a molecular bridge between these two pathologies. In particular, we will focus on the transcription factor function of PK and its newly described transcriptional targets that are directly related to AD- and PD-linked cellular defects.

Genetic Deficiency of p53 Leads to Structural, Functional, and Synaptic Deficits in Primary Somatosensory Cortical Neurons of Adult Mice

The tumor suppressor p53 plays a crucial role in embryonic neuron development and neurite growth, and its involvement in neuronal homeostasis has been proposed. To better understand how the lack of the p53 gene function affects neuronal activity, spine development, and plasticity, we examined the electrophysiological and morphological properties of layer 5 (L5) pyramidal neurons in the primary somatosensory cortex barrel field (S1BF) by using in vitro whole-cell patch clamp and in vivo two-photon imaging techniques in p53 knockout (KO) mice. We found that the spiking frequency, excitatory inputs, and sag ratio were decreased in L5 pyramidal neurons of p53KO mice. In addition, both in vitro and in vivo morphological analyses demonstrated that dendritic spine density in the apical tuft is decreased in L5 pyramidal neurons of p53KO mice. Furthermore, chronic imaging showed that p53 deletion decreased dendritic spine turnover in steady-state conditions, and prevented the increase in spine turnover associated with whisker stimulation seen in wildtype mice. In addition, the sensitivity of whisker-dependent texture discrimination was impaired in p53KO mice compared with wildtype controls. Together, these results suggest that p53 plays an important role in regulating synaptic plasticity by reducing neuronal excitability and the number of excitatory synapses in S1BF.

Inverse Correlation Between Alzheimer's Disease and Cancer: Short Overview

The negative association between Alzheimer's disease (AD) and cancer suggests that susceptibility to one disease may protect against the other. When biological mechanisms of AD and cancer and relationship between them are understood, the unsolved problem of both diseases which still touches the growing human population could be overcome. Actual information about biological mechanisms and common risk factors such as chronic inflammation, age-related metabolic deregulation, and family history is presented here. Common signaling pathways, e.g., p53, Wnt, role of Pin1, and microRNA, are discussed as well. Much attention is also paid to the potential impact of chronic viral, bacterial, and fungal infections that are responsible for the inflammatory pathway in AD and also play a key role to cancer development. New data about common mechanisms in etiopathology of cancer and neurological diseases suggests new therapeutic strategies. Among them, the use of nilotinib, tyrosine kinase inhibitor, protein kinase C, and bexarotene is the most promising.

Therapeutic potential of parkin as a tumor suppressor via transcriptional control of cyclins in glioblastoma cell and animal models

Parkin (PK) is an E3-ligase harboring tumor suppressor properties that has been associated to various cancer types including glioblastoma (GBM). However, PK is also a transcription factor (TF), the contribution of which to GBM etiology remains to be established.

Methods: The impact of PK on GBM cells proliferation was analyzed by real-time impedance measurement and flow cytometry. Cyclins A and B proteins, promoter activities and mRNA levels were measured by western blot, luciferase assay and quantitative real-time PCR. Protein-protein and protein-promoter interactions were performed by co-immunoprecipitation and by ChIP approaches. The contribution of endogenous PK to tumor progression in vivo was performed by allografts of GL261 GBM cells in wild-type and PK knockout mice.

Results: We show that overexpressed and endogenous PK control GBM cells proliferation by modulating the S and G2/M phases of the cell cycle via the trans-repression of cyclin A and cyclin B genes. We establish that cyclin B is regulated by both E3-ligase and TF PK functions while cyclin A is exclusively regulated by PK TF function. PK invalidation leads to enhanced tumor progression in immunocompetent mice suggesting an impact of PK-dependent tumor environment to tumor development. We show that PK is secreted by neuronal cells and recaptured by tumor cells. Recaptured PK lowered cyclins levels and decreased GBM cells proliferation. Further, PK expression is decreased in human GBM biopsies and its expression is inversely correlated to both cyclins A and B expressions.

Conclusion: Our work demonstrates that PK tumor suppressor function contributes to the control of tumor by its cellular environment. It also shows a key role of PK TF function in GBM development via the control of cyclins in vitro and in vivo. It suggests that therapeutic strategies aimed at controlling PK shuttling to the nucleus may prove useful to treat GBM.

The Cellular Prion Protein and the Hallmarks of Cancer

Simple Summary

The cellular prion protein PrP^C is best known for its involvement, under its pathogenic isoform, in a group of neurodegenerative diseases. Notwithstanding, an emerging role for PrP^C in various cancer-associated processes has attracted increasing attention over recent years. PrP^C is overexpressed in diverse types of solid cancers and has been incriminated in various aspects of cancer biology, most notably proliferation, migration, invasion and metastasis, as well as resistance to cytotoxic agents. This article aims to provide a comprehensive overview of the current knowledge of PrP^C with respect to the hallmarks of cancer, a reference framework encompassing the major characteristics of cancer cells.

Abstract

Beyond its causal involvement in a group of neurodegenerative diseases known as Transmissible Spongiform Encephalopathies, the cellular prion protein PrP^C is now taking centre stage as an important contributor to cancer progression in various types of solid tumours. The prion cancer research field has progressively expanded in the last few years and has yielded consistent evidence for an involvement of PrP^C in cancer cell proliferation, migration and invasion, therapeutic resistance and cancer stem cell properties. Most recent data have uncovered new facets of the biology of PrP^C in cancer, ranging from its control on enzymes involved in immune tolerance to its radio-protective activity, by way of promoting angiogenesis. In the present review, we aim to summarise the body of literature dedicated to the study of PrP^C in relation to cancer from the perspective of the hallmarks of cancer, the reference framework defined by Hanahan and Weinberg.

Melatonin Attenuates Thrombin-induced Inflammation in BV2 Cells and Then Protects HT22 Cells from Apoptosis

Increasing evidence has revealed that the uncontrolled thrombin-induced inflammation following intracerebral hemorrhage (ICH) plays a key role in ICH. Oxidative stress and neuroinflammatory responses are interdependent and bidirectional events. Melatonin is now recognized as an antioxidant and a free radical scavenger due to its roles in various physiological and pathological processes. The aim of this study was to explore the molecular mechanisms underlying the effects of melatonin on thrombin-induced microglial inflammation and its indirect protection of HT22 cells from p53-associated apoptosis. Melatonin treatment attenuated the expression of IL-1β, IL-18, cleaved caspase-1, and NLRP3 and decreased the production of reactive oxygen species (ROS), revealing its inhibitory effects against ROS-NLRP3 inflammasome activation. In further experiments investigating the protection conferred by melatonin, incubating HT22 cells with conditioned medium (CM) from thrombin-stimulated microglia induced HT22 cell apoptosis, and this effect was reversed after treating CM with either melatonin or N-acetyl-L-cysteine (NAC). Additionally, the Bax/Bcl-2 ratio and the levels of cleaved caspase-3 and p53 were markedly lower in the cells cultured in thrombin + melatonin-CM than in the cells cultured in thrombin-CM. Furthermore, the levels of MMP, ROS, SOD, MDA, and GSH-PX in bystander HT22 cells suggested that melatonin decreased HT22 cell apoptosis instigated via the p53-associated apoptotic pathway. Therefore, these findings strongly indicate the anti-inflammatory properties of melatonin that may suppress ROS-NLRP3 inflammasome activation and protect HT22 cells against apoptosis by inhibiting the ROS-mediated p53-dependent mitochondrial apoptotic pathway.

Focus on the Complex Interconnection between Cancer, Narcolepsy and Other Neurodegenerative Diseases: A Possible Case of Orexin-Dependent Inverse Comorbidity

Simple Summary

This narrative review first describes from several points of view the complex interrelationship between cancer and neurodegeneration, with special attention to the mechanisms that might underlie an inverse relationship between them. In particular, the mechanisms that might induce an imbalance between cell apoptotic and proliferative stimuli are discussed. Second, the review summarizes findings on orexins and their involvement in narcolepsy, neurodegenerative diseases, and cancer, starting from epidemiological data then addressing laboratory findings, animal models, and human clinical observational and interventional investigations. Important research efforts are warranted on these topics, as they might lead to novel therapeutic approaches to both neurodegenerative diseases and cancer.

Abstract

Conditions such as Alzheimer’s (AD) and Parkinson’s diseases (PD) are less prevalent in cancer survivors and, overall, cancer is less prevalent in subjects with these neurodegenerative disorders. This seems to suggest that a propensity towards one type of disease may decrease the risk of the other. In addition to epidemiologic data, there is also evidence of a complex biological interconnection, with genes, proteins, and pathways often showing opposite dysregulation in cancer and neurodegenerative diseases. In this narrative review, we focus on the possible role played by orexin signaling, which is altered in patients with narcolepsy type 1 and in those with AD and PD, and which has been linked to β-amyloid brain levels and inflammation in mouse models and to cancer in cell lines. Taken together, these lines of evidence depict a possible case of inverse comorbidity between cancer and neurodegenerative disorders, with a role played by orexins. These considerations suggest a therapeutic potential of orexin modulation in diverse pathologies such as narcolepsy, neurodegenerative disorders, and cancer.

Genetic Editing and Pharmacogenetics in Current And Future Therapy Of Neurocognitive Disorders

Dementia is an important issue in western societies, and in the following years, this problem will also rise in the developing regions, such as Africa and Asia. The most common types of dementia in adults are Alzheimer's Disease (AD), Dementia with Lewy Bodies (DLB), Frontotemporal Dementia (FTD) and Vascular Dementia (VaD), of which, AD accounts for more than half of the cases. The most prominent symptom of AD is cognitive impairment, currently treated with four drugs: Donepezil, rivastigmine, and galantamine, enhancing cholinergic transmission; as well as memantine, protecting neurons against glutamate excitotoxicity. Despite ongoing efforts, no new drugs in the treatment of AD have been registered for the last ten years, thus multiple studies have been conducted on genetic factors affecting the efficacy of antidementia pharmacotherapy. The researchers investigate the effects of variants in multiple genes, such as ABCB1, ACE, CHAT, CHRNA7, CYP2C9, CYP2C19, CYP2D6, CYP3A4, CYP3A5, CYP3A7, NR1I2, NR1I3, POR, PPAR, RXR, SLC22A1/2/5, SLC47A1, UGT1A6, UGT1A9 and UGT2B7, associated with numerous pathways: the development of pathological proteins, formation and metabolism of acetylcholine, transport, metabolism and excretion of antidementia drugs and transcription factors regulating the expression of genes responsible for metabolism and transport of drugs. The most promising results have been demonstrated for APOE E4, dementia risk variant, BCHE-K, reduced butyrylcholinesterase activity variant, and CYP2D6 UM, ultrarapid hepatic metabolism. Further studies investigate the possibilities of the development of emerging drugs or genetic editing by CRISPR/Cas9 for causative treatment. In conclusion, the pharmacogenetic studies on dementia diseases may improve the efficacy of pharmacotherapy in some patients with beneficial genetic variants, at the same time, identifying the carriers of unfavorable alleles, the potential group of novel approaches to the treatment and prevention of dementia.

Tantalizing role of p53 molecular pathways and its coherent medications in neurodegenerative diseases

Neurodegenerative diseases are incongruous, commonly age-related disorders characterized by progressive neuronal loss, comprising the most prevalent being Alzheimer's disease, Parkinson's disease, and Huntington's disease. Perilous health states are anticipated following the neurodegeneration. Their etiology remains largely ambiguous, while various mechanisms are ascribed to their pathogenesis. A recommended conception is regarding the role of p53, as a transcription factor regulating numerous cellular pathways comprising apoptosis. Neuronal fates are a feasible occurrence that contributes to all neurodegenerative diseases. In this work, we review the research investigated the potential role of p53 in the pathogenesis of these diseases. We put special emphasis on intricate We not only describe aberrant changes in p53 level/activity observed in CNS regions affected by particular diseases but, most importantly, put special attention to the complicated reciprocal tuning connections prevailing between p53 and molecules considered in pathological hallmarks of these disorders. Natural and synthetic medications regulating p53 expression are regarded as well.

Cancer and Alzheimer's disease inverse relationship: an age-associated diverging derailment of shared pathways

Several epidemiological studies show an inverse association between cancer and Alzheimer's disease (AD). It is debated whether this association is the consequence of biological mechanisms shared by both these conditions or may be related to the pharmacological treatments carried out on the patients. The latter hypothesis, however, is not sustained by the available evidence. Hence, the focus of this review is to analyze common biological mechanisms for both cancer and AD and to build up a biological theory useful to explain the inverse correlation between AD and cancer. The review proposes a hypothesis, according to which several molecular players, prominently PIN1 and p53, have been investigated and considered involved in complex molecular interactions putatively associated with the inverse correlation. On the other hand, p53 involvement in both diseases seems to be a consequence of the aberrant activation of other proteins. Instead, PIN1 may be identified as a novel key regulator at the crossroad between cancer and AD. PIN1 is a peptidyl-prolyl cis-trans isomerase that catalyzes the cis-trans isomerization, thus regulating the conformation of different protein substrates after phosphorylation and modulating protein function. In particular, trans-conformations of Amyloid Precursor Protein (APP) and tau are functional and "healthy", while cis-conformations, triggered after phosphorylation, are pathogenic. As an example, PIN1 accelerates APP cis-to-trans isomerization thus favoring the non-amyloidogenic pathway, while, in the absence of PIN1, APP is processed through the amyloidogenic pathway, thus predisposing to neurodegeneration. Furthermore, a link between PIN1 and tau regulation has been found, since when PIN1 function is inhibited, tau is hyperphosphorylated. Data from brain specimens of subjects affected by mild cognitive impairment and AD have revealed a very low PIN1 expression. Moreover, polymorphisms in PIN1 promoter correlated with an increased PIN1 expression are associated with a delay of sporadic AD age of onset, while a polymorphism related to a reduced PIN1 expression is associated with a decreased risk of multiple cancers. In the case of dementias, in particular of Alzheimer's disease, new biological markers and targets based on the discussed players can be developed based on a theoretical approach relying on different grounds compared to the past. An unbiased expansion of the rationale and of the targets may help to achieve in the field of neurodegenerative dementias similar advances to those attained in the case of cancer treatment.

Cancer and Parkinson's Disease: Common Targets, Emerging Hopes

Cancer and neurodegeneration are two major leading causes of morbidity and death worldwide. At first sight, the two fields do not seem to share much in common and, if anything, might be placed on opposite ends of a spectrum. Although neurodegeneration results in excessive neuronal cell death, cancer emerges from increased proliferation and resistance to cell death. Therefore, one might expect significant differences in the underlying pathophysiological mechanisms. However, the more we deepen our understanding of these two types of diseases, the more we appreciate the unexpected overlap between them. Although most epidemiological studies support an inverse association between the risk for development of neurodegenerative diseases and cancer, increasing evidence points to a positive correlation between specific types of cancer, like melanoma, and neurodegenerative diseases, like Parkinson's disease (PD). We believe that deciphering the molecular processes and pathways underlying one of these diseases may significantly increase our understanding about the other. Therefore, the identification of novel biomarkers and therapeutic approaches in cancer, may lead to improved diagnosis and treatment of neurodegeneration, and vice versa. In this Viewpoint, we summarize recent findings connecting both diseases and speculate that insights from one disease may inform on mechanisms, and help identify novel biomarkers and targets for intervention, possibly leading to improved management of both diseases. © 2020 International Parkinson and Movement Disorder Society.

DEPTOR is a direct p53 target that suppresses cell growth and chemosensitivity

DEP-domain containing mTOR-interacting protein (DEPTOR), a natural mTOR inhibitor, has essential roles in several processes, including cell growth, metabolism, apoptosis, and immunity. DEPTOR expression has been shown to be diversely controlled at transcriptional levels in cell- and context-specific manners. However, whether there is a general mechanism for the regulation of DEPTOR expression remains largely unknown. Here, we report that DEPTOR is a downstream target of the tumor suppressor, p53, whose activity is positively correlated with DEPTOR expression both in vitro in cell cultures and in vivo in mouse tissues. Mechanistically, p53 directly binds to the DEPTOR promoter and transactivates its expression. Depletion of the p53-binding site on the DEPTOR promoter by CRISPR-Cas9 technology decreases DEPTOR expression and promotes cell proliferation and survival by activating AKT signaling. Importantly, inhibition of AKT by small molecular inhibitors or genetic knockdown abrogates the induction of cell growth and survival induced by deletion of the p53-binding region on the DEPTOR promoter. Furthermore, p53, upon activation by the genotoxic agent doxorubicin, induces DEPTOR expression, leading to cancer cell resistance to doxorubicin. Together, DEPTOR is a direct p53 downstream target and contributes to p53-mediated inhibition of cell proliferation, survival, and chemosensitivity.

A Glance of p53 Functions in Brain Development, Neural Stem Cells, and Brain Cancer

p53 is one of the most intensively studied tumor suppressors. It transcriptionally regulates a broad range of genes to modulate a series of cellular events, including DNA damage repair, cell cycle arrest, senescence, apoptosis, ferroptosis, autophagy, and metabolic remodeling, which are fundamental for both development and cancer. This review discusses the role of p53 in brain development, neural stem cell regulation and the mechanisms of inactivating p53 in gliomas. p53 null or p53 mutant mice show female biased exencephaly, potentially due to X chromosome inactivation failure and/or hormone-related gene expression. Oxidative cellular status, increased PI3K/Akt signaling, elevated ID1, and metabolism are all implicated in p53-loss induced neurogenesis. However, p53 has also been shown to promote neuronal differentiation. In addition, p53 mutations are frequently identified in brain tumors, especially glioblastomas. Mechanisms underlying p53 inactivation in brain tumor cells include disruption of p53 protein stability, gene expression and transactivation potential as well as p53 gene loss or mutation. Loss of p53 function and gain-of-function of mutant p53 are both implicated in brain development and tumor genesis. Further understanding of the role of p53 in the brain may provide therapeutic insights for brain developmental syndromes and cancer.

The P53/microRNA network: A potential tumor suppressor with a role in anticancer therapy

MicroRNAs (miRNAs) are endogenous and small non-coding RNAs that have been identified as mediators of tumor suppression as well as stress responses mediated by p53 suppressors. MiRNAs may act as tumor suppressors under certain conditions. MiRNAs regulated by p53 may control the expression of processes such as cell cycle progression, cell survival, and angiogenesis. P53 activity and expression are also controlled by miRNA; consequently alterations in the p53-miRNA network may be essential for tumor initiation and progression. Future studies on the p53-miRNA network presumably would find it helpful in diagnostic and therapeutic approaches or as tools for various cancers.

Protective role of anticancer drugs in neurodegenerative disorders: A drug repurposing approach

The disease heterogeneity and little therapeutic progress in neurodegenerative diseases justify the need for novel and effective drug discovery approaches. Drug repurposing is an emerging approach that reinvigorates the classical drug discovery method by divulging new therapeutic uses of existing drugs. The common biological background and inverse tuning between cancer and neurodegeneration give weight to the conceptualization of repurposing of anticancer drugs as novel therapeutics. Many studies are available in the literature, which highlights the success story of anticancer drugs as repurposed therapeutics. Among them, kinase inhibitors, developed for various oncology indications evinced notable neuroprotective effects in neurodegenerative diseases. In this review, we shed light on the salient role of multiple protein kinases in neurodegenerative disorders. We also proposed a feasible explanation of the action of kinase inhibitors in neurodegenerative disorders with more attention towards neurodegenerative disorders. The problem of neurotoxicity associated with some anticancer drugs is also highlighted. Our review encourages further research to better encode the hidden potential of anticancer drugs with the aim of developing prospective repurposed drugs with no toxicity for neurodegenerative disorders.

Tumor suppressor p53 cross-talks with TRIM family proteins

p53 is a key tumor suppressor. As a transcription factor, p53 accumulates in cells in response to various stress signals and selectively transcribes its target genes to regulate a wide variety of cellular stress responses to exert its function in tumor suppression. In addition to tumor suppression, p53 is also involved in many other physiological and pathological processes, e.g. anti-infection, immune response, development, reproduction, neurodegeneration and aging. To maintain its proper function, p53 is under tight and delicate regulation through different mechanisms, particularly the posttranslational modifications. The tripartite motif (TRIM) family proteins are a large group of proteins characterized by the RING, B-Box and coiled-coil (RBCC) domains at the N-terminus. TRIM proteins play important roles in regulation of many fundamental biological processes, including cell proliferation and death, DNA repair, transcription, and immune response. Alterations of TRIM proteins have been linked to many diseases including cancer, infectious diseases, developmental disorders, and neurodegeneration. Interestingly, recent studies have revealed that many TRIM proteins are involved in the regulation of p53, and at the same time, many TRIM proteins are also regulated by p53. Here, we review the cross-talk between p53 and TRIM proteins, and its impact upon cellular biological processes as well as cancer and other diseases.

Tumor suppressor p53 and metabolism

p53 plays a key role in tumor suppression. The tumor suppressive function of p53 has long been attributed to its ability to induce apoptosis, cell cycle arrest, and senescence in cells. However, recent studies suggest that other functions of p53 also contribute to its role as a tumor suppressor, such as its function in metabolic regulation. p53 regulates various metabolic pathways to maintain the metabolic homeostasis of cells and adapt cells to stress. In addition, recent studies have also shown that gain-of-function (GOF) mutant p53 proteins drive metabolic reprogramming in cancer cells, contributing to cancer progression. Further understanding of p53 and its GOF mutants in metabolism will provide new opportunities for cancer therapy.

Inhibition of p53 DNA binding by a small molecule protects mice from radiation toxicity

Transcription factors are attractive therapeutic targets that are considered non-druggable because they do not have binding sites for small drug-like ligands. We established a cell-free high-throughput screening assay to search for small molecule inhibitors of DNA binding by transcription factors. A screen was performed using p53 as a target, resulting in the identification of NSC194598 that inhibits p53 sequence-specific DNA binding in vitro (IC₅₀ = 180 nM) and in vivo. NSC194598 selectively inhibited DNA binding by p53 and homologs p63/p73, but did not affect E2F1, TCF1, and c-Myc. Treatment of cells with NSC194598 alone paradoxically led to p53 accumulation and modest increase of transcriptional output owing to disruption of the MDM2-negative feedback loop. When p53 was stabilized and activated by irradiation or chemotherapy drug treatment, NSC194598 inhibited p53 DNA binding and induction of target genes. A single dose of NSC194598 increased the survival of mice after irradiation. The results suggest DNA binding by p53 can be targeted using small molecules to reduce acute toxicity to normal tissues by radiation and chemotherapy.

Activation of BDNF-AS/ADAR/p53 Positive Feedback Loop Inhibits Glioblastoma Cell Proliferation

Despite progress in conventional treatment for glioblastoma (GBM), the prognosis remains poor due to high tumor recurrence. Therefore, identification of new molecular mechanisms is a pressing need for betterment of GBM patient outcomes. qRT-PCR was used to determine BDNF-AS expression in GBM cells. CCK-8, EdU incorporation, and caspase-3 activity assays were employed to analyze biological functions of BDNF-AS. RIP and RNA pull-down were conducted to detect the interactions among BDNF-AS, ADAR, and p53. Actinomycin D was utilized to examine the stability of p53 mRNA. ChIP and luciferase reporter assays were performed to detect transcriptional activation of BDNF-AS by p53. We found that BDNF-AS was significantly downregulated in GBM cell lines, and its overexpression inhibited GBM cell growth, and promoted apoptosis. Importantly, we illustrated that BDNF-AS coupled with ADAR protein to potentiate stability of p53 mRNA and thus upregulate p53. Interestingly, we further identified p53 as a transcription factor of BDNF-AS, activating transcription of BNDF-AS. This study firstly demonstrated that BDNF-AS acted as a tumor suppressor in GBM and the positive feedback circuit of BDNF-AS/ADAR/p53 served an important mechanism to control GBM proliferation. Targeting this auto-regulatory loop may provide a potential therapeutic strategy for GBM patients.

The Localization of p53 in the Crayfish Mechanoreceptor Neurons and Its Role in Axotomy-Induced Death of Satellite Glial Cells Remote from the Axon Transection Site

Neuron and glia death after axon transection is regulated by various signaling proteins. Protein p53 is a key regulator of diverse cell functions including stress response, DNA repair, proliferation, and apoptosis. We showed that p53 was overexpressed in crayfish ganglia after bilateral axotomy. In the isolated crayfish stretch receptor, a simple natural neuroglial preparation, which consists of a single mechanoreceptor neuron (MRN) enveloped by glial cells, p53 regulated axotomy-induced death of glial cells remote from the axon transection site. In MRN, p53 immunofluorescence was highest in the nucleolus and in the narrow cytoplasmic ring around the nucleus; its levels in the nucleus and cytoplasm were lower. After axotomy, p53 accumulated in the neuronal perikaryon. Its immunofluorescence also increased in the neuronal and glial nuclei. However, p53 immunofluorescence in the most of neuronal nucleoli disappeared. Axotomy-induced apoptosis of remote glial cells increased in the presence of p53 activators WR-1065 and nutlin-3 but reduced by pifithrin-α that inhibits transcriptional activity of p53. Pifithrin-μ that inhibits p53 effect on mitochondria increased axotomy-induced apoptosis of remote glial cells but reduced their necrosis. Therefore, axotomy-induced apoptosis of remote glial cells was associated with p53 effect on transcription processes, whereas glial necrosis was rather associated with transcription-independent p53 effect on mitochondria. Apparently, the fate of remote glial cells in the axotomized crayfish stretch receptor is determined by the balance between different modalities of p53 activity.

The p53 inactivators pifithrin-μ and pifithrin-α mitigate TBI-induced neuronal damage through regulation of oxidative stress, neuroinflammation, autophagy and mitophagy

Traumatic brain injury (TBI) is one of the most common causes of death and disability worldwide. We investigated whether inhibition of p53 using pifithrin (PFT)-α or PFT-μ provides neuroprotective effects via p53 transcriptional dependent or -independent mechanisms, respectively. Sprague Dawley rats were subjected to controlled cortical impact TBI followed by the administration of PFTα or PFT-μ (2 mg/kg, i.v.) at 5 h after TBI. Brain contusion volume, as well as sensory and motor functions were evaluated at 24 h after TBI. TBI-induced impairments were mitigated by both PFT-α and PFT-μ. Fluoro-Jade C staining was used to label degenerating neurons within the TBI-induced cortical contusion region that, together with Annexin V positive neurons, were reduced by PFT-μ. Double immunofluorescence staining similarly demonstrated that PFT-μ significantly increased HO-1 positive neurons and mRNA expression in the cortical contusion region as well as decreased numbers of 4-hydroxynonenal (4HNE)-positive cells. Levels of mRNA encoding for p53, autophagy, mitophagy, anti-oxidant, anti-inflammatory related genes and proteins were measured by RT-qPCR and immunohistochemical staining, respectively. PFT-α, but not PFT-μ, significantly lowered p53 mRNA expression. Both PFT-α and PFT-μ lowered TBI-induced pro-inflammatory cytokines (IL-1β and IL-6) mRNA levels as well as TBI-induced autophagic marker localization (LC3 and p62). Finally, treatment with PFT-μ mitigated TBI-induced declines in mRNA levels of PINK-1 and SOD2. Our data suggest that both PFT-μ and PFT-α provide neuroprotective actions through regulation of oxidative stress, neuroinflammation, autophagy, and mitophagy mechanisms, and that PFT-μ, in particular, holds promise as a TBI treatment strategy.

Identifying circRNA-associated-ceRNA networks in the hippocampus of Aβ1-42-induced Alzheimer's disease-like rats using microarray analysis

Alzheimer’s disease (AD) is the most common form of dementia worldwide. Accumulating evidence indicates that non-coding RNAs are strongly implicated in AD-associated pathophysiology. However, the role of these ncRNAs remains largely unknown. In the present study, we used microarray analysis technology to characterize the expression patterns of circular RNAs (circRNAs), microRNAs (miRNAs), and mRNAs in hippocampal tissue from Aβ_1-42-induced AD model rats, to integrate interaction data and thus provide novel insights into the mechanisms underlying AD. A total of 555 circRNAs, 183 miRNAs and 319 mRNAs were identified to be significantly dysregulated (fold-change ≥ 2.0 and p-value < 0.05) in the hippocampus of AD rats. Quantitative real-time polymerase chain reaction (qRT-PCR) was then used to validate the expression of randomly-selected circRNAs, miRNAs and mRNAs. Next, GO and KEGG pathway analyses were performed to further investigate ncRNAs biological functions and potential mechanisms. In addition, we constructed circRNA-miRNA and competitive endogenous RNA (ceRNA) regulatory networks to determine functional interactions between ncRNAs and mRNAs. Our results suggest the involvement of different ncRNA expression patterns in the pathogenesis of AD. Our findings provide a novel perspective for further research into AD pathogenesis and might facilitate the development of novel therapeutics targeting ncRNAs.

Signal Transduction Pathways of Acupuncture for Treating Some Nervous System Diseases

In this article, we review signal transduction pathways through which acupuncture treats nervous system diseases. We electronically searched the databases, including PubMed, MEDLINE, clinical Key, the Cochrane Library, and the China National Knowledge Infrastructure from their inception to December 2018 using the following MeSH headings and keywords alone or in varied combination: acupuncture, molecular, signal transduction, genetic, cerebral ischemic injury, cerebral hemorrhagic injury, stroke, epilepsy, seizure, depression, Alzheimer's disease, dementia, vascular dementia, and Parkinson's disease. Acupuncture treats nervous system diseases by increasing the brain-derived neurotrophic factor level and involves multiple signal pathways, including p38 MAPKs, Raf/MAPK/ERK 1/2, TLR4/ERK, PI3K/AKT, AC/cAMP/PKA, ASK1-JNK/p38, and downstream CREB, JNK, m-TOR, NF-κB, and Bcl-2/Bax balance. Acupuncture affects synaptic plasticity, causes an increase in neurotrophic factors, and results in neuroprotection, cell proliferation, antiapoptosis, antioxidant activity, anti-inflammation, and maintenance of the blood-brain barrier.

The Transcription Factor Function of Parkin: Breaking the Dogma

PRKN (PARK2) is a key gene involved in both familial and sporadic Parkinson’s disease that encodes parkin (PK). Since its discovery by the end of the 90s, both functional and more recently, structural studies led to a consensual view of PK as an E3 ligase only. It is generally considered that this function conditions the cellular load of a subset of cytosolic proteins prone to proteasomal degradation and that a loss of E3 ligase function triggers an accumulation of potentially toxic substrates and, consequently, a neuronal loss. Furthermore, PK molecular interplay with PTEN-induced kinase 1 (PINK1), a serine threonine kinase also involved in recessive cases of Parkinson’s disease, is considered to underlie the mitophagy process. Thus, since mitochondrial homeostasis significantly governs cell health, there is a huge interest of the scientific community centered on PK function. In 2009, we have demonstrated that PK could also act as a transcription factor (TF) and induces neuroprotection via the downregulation of the pro-apoptotic and tumor suppressor factor, p53. Importantly, the DNA-binding properties of PK and its nuclear localization suggested an important role in the control of several genes. The duality of PK subcellular localization and of its associated ubiquitin ligase and TF functions suggests that PK could behave as a key molecular modulator of various physiological cellular signaling pathways that could be disrupted in pathological contexts. Here, we update the current knowledge on PK direct and indirect TF-mediated control of gene expression.

Montelukast attenuates rotenone-induced microglial activation/p38 MAPK expression in rats: Possible role of its antioxidant, anti-inflammatory and antiapoptotic effects

Montelukast (MK),a cysteinyl leukotriene (CysLT1) receptor antagonist, latterly exhibited a remarkable neuroprotective activity in various neurodegenerative disorders. This study aims to elucidate the neuroprotective effect of MK in rotenone-induced Parkinson's disease(PD) model in rats. Ninety six male rats were split into four groups: vehicle control (0.2 ml/kg/48 h, sc), MK (10 mg/kg/day, ip), rotenone (1.5 mg/kg/48 h, sc.) and rotenone pretreated with MK. Rotenone treatment led to significant reduction in motor functioning and elevation in oxidative stress markers. Additionally, upregulation of p38 mitogen-activated protein kinase (p38 MAPK) and CysLT1 receptor expressions were anchored with enhanced striatal microglial activation generating a severe neuro-inflammatory milieu. Furthermore, an augmentation in p53 expression and cleaved caspases-3 activity increased apoptotic neurodegeneration synchronized with reduction of striatal tyrosine hydroxylase (TH) content. Changes in neuronal morphology was also noted. MK administration significantly mitigated motor impairment and rise in oxidative stress mediators. As well, the anti-inflammatory activity of MK was manifested by hindering the principal controller of inflammatory pathway, nuclear factor-kappa B, followed by its downstream pro-inflammatory cytokines (tumor necrosis factor-alpha and interleukin-1 beta), by attenuating striatal microglial activation and hampering the expression of both p38 MAPK and CysLT1. Moreover, MK revealed a decline in p53 expression with its downstream cleaved caspases-3 which resulted in preservation of striatal TH terminals as verified by increased striatal TH content and improvement in the histopathological changes incited by rotenone. In conclusion, MK endowed neuroprotective effects in rotenone-induced PD animal model via attenuation of microglial cell activation and p38 MAPK expression.

Downregulated apoptosis and autophagy after anti-Aβ immunotherapy in Alzheimer's disease

Aβ immunization of Alzheimer's disease (AD) patients in the AN1792 (Elan Pharmaceuticals) trial caused Aβ removal and a decreased density of neurons in the cerebral cortex. As preservation of neurons may be a critical determinant of outcome after Aβ immunization, we have assessed the impact of previous Aβ immunization on the expression of a range of apoptotic proteins in post-mortem human brain tissue. Cortex from 13 AD patients immunized with AN1792 (iAD) and from 27 nonimmunized AD (cAD) cases was immunolabeled for proapoptotic proteins implicated in AD pathophysiology: phosphorylated c-Jun N-terminal kinase (pJNK), activated caspase3 (a-casp3), phosphorylated GSK3β on tyrosine 216 (GSK3βtyr216 ), p53 and Cdk5/p35. Expression of these proteins was analyzed in relation to immunization status and other clinical data. The antigen load of all of these proapoptotic proteins was significantly lower in iAD than cAD (P < 0.0001). In cAD, significant correlations (P < 0.001) were observed between: Cdk5/p35 and GSK3βtyr216 ; a-casp3 and Aβ42 ; p53 and age at death. In iAD, significant correlations were found between GSK3βtyr216 and a-casp3; both spongiosis and neuritic curvature ratio and Aβ42 ; and Cdk5/p35 and Aβ-antibody level. Although neuronal loss was increased by immunization with AN1792, our present findings suggest downregulation of apoptosis in residual neurons and other cells.

Does traumatic brain injury hold the key to the Alzheimer's disease puzzle?

INTRODUCTION

Neurodegenerative disorders have been a graveyard for hundreds of well-intentioned efforts at drug discovery and development. Concussion and other traumatic brain injuries (TBIs) and Alzheimer's disease (AD) share many overlapping pathologies and possible clinical links.

METHODS

We searched the literature since 1995 using MEDLINE and Google Scholar for the terms concussion, AD, and shared neuropathologies. We also studied a TBI animal model as a supplement to transgenic (Tg) mouse AD models for evaluating AD drug efficacy by preventing neuronal losses. To evaluate TBI/AD pathologies and neuronal self-induced cell death (apoptosis), we are studying brain extracellular vesicles in plasma and (-)-phenserine pharmacology to probe, in animal models of AD and humans, apoptosis and pathways common to concussion and AD.

RESULTS

Neuronal cell death and a diverse and significant pathological cascade follow TBIs. Many of the developing pathologies are present in early AD. The use of an animal model of concussion as a supplement to Tg mice provides an indication of an AD drug candidate's potential for preventing apoptosis and resulting progression toward dementia in AD. This weight drop supplementation to Tg mouse models, the experimental drug (-)-phenserine, and plasma-derived extracellular vesicles enriched for neuronal origin to follow biomarkers of neurodegenerative processes, each and in combination, show promise as tools useful for probing the progression of disease in AD, TBI/AD pathologies, apoptosis, and drug effects on rates of apoptosis both preclinically and in humans. (-)-Phenserine both countered many subacute post-TBI pathologies that could initiate clinical AD and, in the concussion and other animal models, showed evidence consistent with direct inhibition of neuronal preprogrammed cell death in the presence of TBI/AD pathologies.

DISCUSSION

These findings may provide support for expanding preclinical Tg mouse studies in AD with a TBI weight drop model, insights into the progression of pathological targets, their relations to apoptosis, and timing of interventions against these targets and apoptosis. Such studies may demonstrate the potential for drugs to effectively and safely inhibit preprogrammed cell death as a new drug development strategy for use in the fight to defeat AD.

Possible Role of the Polyglutamine Elongation in Evolution of Amyloid-Related Evolvability

The polyglutamine (polyQ) diseases, such as Huntington's disease and the spinocerebellar ataxias, are characterized by the accumulation of elongated polyQ sequences (epolyQ) and mostly occur during midlife. Considering that polyQ disorders have not been selected out in evolution, there might be important physiological functions of epolyQ during development and/or reproduction. In a similar context, the physiological functions of neurodegeneration-associated amyloidogenic proteins (APs), such as β-amyloid in Alzheimer's disease and α-synuclein in Parkinson's disease, remain elusive. In this regard, we recently proposed that evolvability for coping with diverse stressors in the brain, which is beneficial for offspring, might be relevant to the physiological functions of APs. Given analogous properties of APs and epolyQ in terms of neurotoxic amyloid-fibril formation, the objective of this paper is to determine whether evolvability could also be applied to the physiological functions of epolyQ. Indeed, APs and epolyQ are similar in many ways, including functional redundancy of non-amyloidogenic homologues, hormesis conferred by the heterogeneity of the stress-induced protein aggregates, the transgenerational prion-like transmission of the protein aggregates via germ cells, and the antagonistic pleiotropy relationship between evolvability and neurodegenerative disease. Given that epolyQ is widely expressed from microorganisms to human brain, whereas APs are only identified in vertebrates, evolvability of epolyQ is considered to be much more primitive compared to those of APs during evolution. Collectively, epolyQ may be not only be important in the pathophysiology of polyQ diseases, but also in the evolution of amyloid-related evolvability.

Relevance of the p53-MDM2 axis to aging

In response to varying stress signals, the p53 tumor suppressor is able to promote repair, survival, or elimination of damaged cells - processes that have great relevance to organismal aging. Although the link between p53 and cancer is well established, the contribution of p53 to the aging process is less clear. Delineating how p53 regulates distinct aging hallmarks such as cellular senescence, genomic instability, mitochondrial dysfunction, and altered metabolic pathways will be critical. Mouse models have further revealed the centrality and complexity of the p53 network in aging processes. While naturally aged mice have linked longevity with declining p53 function, some accelerated aging mice present with chronic p53 activation, whose phenotypes can be rescued upon p53 deficiency. Further, direct modulation of the p53-MDM2 axis has correlated elevated p53 activity with either early aging or with delayed-onset aging. We speculate that p53-mediated aging phenotypes in these mice must have (1) stably active p53 due to MDM2 dysregulation or chronic stress or (2) shifted p53 outcomes. Pinpointing which p53 stressors, modifications, and outcomes drive aging processes will provide further insights into our understanding of the human aging process and could have implications for both cancer and aging therapeutics.

Putting p53 in Context

TP53 is the most frequently mutated gene in human cancer. Functionally, p53 is activated by a host of stress stimuli and, in turn, governs an exquisitely complex anti-proliferative transcriptional program that touches upon a bewildering array of biological responses. Despite the many unveiled facets of the p53 network, a clear appreciation of how and in what contexts p53 exerts its diverse effects remains unclear. How can we interpret p53's disparate activities and the consequences of its dysfunction to understand how cell type, mutation profile, and epigenetic cell state dictate outcomes, and how might we restore its tumor-suppressive activities in cancer?

Cofilin-mediated Neuronal Apoptosis via p53 Translocation and PLD1 Regulation

Amyloid β (Aβ) accumulation is an early event in the pathogenesis of Alzheimer’s disease (AD), leading to mitochondrial and synaptic dysfunction, tau accumulation, and eventual neuronal death. While the p53 apoptotic pathway has clearly been associated with Aβ deposits and neuronal apoptosis, the critical upstream factors contributing to p53 activation in AD are not well understood. We have previously shown that cofilin activation plays a pivotal role in Aβ-induced mitochondrial and synaptic dysfunction. In this study, we show that activated cofilin (S3A) preferentially forms a complex with p53 and promotes its mitochondrial and nuclear localization, resulting in transcription of p53-responsive genes and promotion of apoptosis. Conversely, reduction of endogenous cofilin by knockdown or genetic deficiency inhibits mitochondrial and nuclear translocation of p53 in cultured cells and in APP/PS1 mice. This cofilin-p53 pro-apoptotic pathway is subject to negative regulation by PLD1 thorough cofilin inactivation and inhibition of cofilin/p53 complex formation. Finally, activated cofilin is unable to induce apoptosis in cells genetically lacking p53. These findings taken together indicate that cofilin coopts and requires the nuclear and mitochondrial pro-apoptotic p53 program to induce and execute apoptosis, while PLD1 functions in a regulatory multi-brake capacity in this pathway.

Dopaminergic Neuron-Specific Deletion of p53 Gene Attenuates Methamphetamine Neurotoxicity

p53 plays an essential role in the regulation of cell death in dopaminergic (DA) neurons and its activation has been implicated in the neurotoxic effects of methamphetamine (MA). However, how p53 mediates MA neurotoxicity remains largely unknown. In this study, we examined the effect of DA-specific p53 gene deletion in DAT-p53KO mice. Whereas in vivo MA binge exposure reduced locomotor activity in wild-type (WT) mice, this was significantly attenuated in DAT-p53KO mice and associated with significant differences in the levels of the p53 target genes BAX and p21 between WT and DAT-p53KO. Notably, DA-specific deletion of p53 provided protection of substantia nigra pars reticulata (SNpr) tyrosine hydroxylase (TH) positive fibers following binge MA, with DAT-p53KO mice having less decline of TH protein levels in striatum versus WT mice. Whereas DAT-p53KO mice demonstrated a consistently higher density of TH fibers in striatum compared to WT mice at 10 days after MA exposure, DA neuron counts within the substantia nigra pars compacta (SNpc) were similar. Finally, supportive of these results, administration of a p53-specific inhibitor (PFT-α) provided a similarly protective effect on MA binge-induced behavioral deficits. Neither DA specific p53 deletion nor p53 pharmacological inhibition affected hyperthermia induced by MA binge. These findings demonstrate a specific contribution of p53 activation in behavioral deficits and DA neuronal terminal loss by MA binge exposure.

Mutant presenilin2 promotes apoptosis through the p53/miR-34a axis in neuronal cells

Neurodegenerative disorders have attracted attention in last decades due to their high incidence in the world. The p53/miR-34a axis triggers apoptosis and suppresses viability in multiple types of cells, but little is known about its role in neurodegenerative diseases. In this study, we showed that presenilin (PS)-2, a major gene associated with familial Alzheimer's disease (AD) could trigger the apoptosis through the p53/miR-34a axis in PC12 cells. First we found that PC12 cell viability was downregulated by PS-2 and mutant PS-2 overexpression, especially by mutant PS-2 overexpression. Then, we established a mutant PS-2-overexpressing PC12 cell line and confirmed that mutant PS-2 induced not only p53 but also miR-34a expression. The transfection of miR-34a inhibitor reversed PS-2-induced effects on cellular viability and apoptosis. Mutant PS-2 overexpression promoted caspase-3 expression, reduced Sirt1 and Bcl-2 expression, all of which were miR-34a downstream genes related with cell apoptosis. Moreover, mutant PS-2 also activated the p53/miR-34a axis and induced apoptosis in AD transgenic mice brain. These results implied that mutant PS-2 might promote the apoptosis of neuronal cells through triggering the p53/miR-34a axis. Altogether our results provide a novel insight into neurodegenerative disease and deepen our understandings of AD pathogenic processes.

Activation of p53 in Down Syndrome and in the Ts65Dn Mouse Brain is Associated with a Pro-Apoptotic Phenotype

Down syndrome (DS) is the most common genetic cause of intellectual disability, resulting from trisomy of chromosome 21. The main feature of DS neuropathology includes early onset of Alzheimer's disease (AD), with deposition of senile plaques and tangles. We hypothesized that apoptosis may be activated in the presence of AD neuropathology in DS, thus we measured proteins associated with upstream and downstream pathways of p53 in the frontal cortex from DS cases with and without AD pathology and from Ts65Dn mice, at different ages. We observed increased acetylation and phosphorylation of p53, coupled to reduced MDM2/p53 complex level and lower levels of SIRT1. Activation of p53 was associated with a number of targets (BAX, PARP1, caspase-3, p21, heat shock proteins, and PGC1α) that were modulated in both DS and DS/AD compared with age-matched controls. In particular, the most relevant changes (increased p-p53 and acetyl-p53 and reduced formation of MDM2/p53 complex) were found to be modified only in the presence of AD pathology in DS. In addition, a similar pattern of alterations in the p53 pathway was found in Ts65Dn mice. These results suggest that p53 may integrate different signals, which can result in a pro-apoptotic-phenotype contributing to AD neuropathology in people with DS.

The DNA Damage Response in Neurons: Die by Apoptosis or Survive in a Senescence-Like State?

Neurons are exposed to high levels of DNA damage from both physiological and pathological sources. Neurons are post-mitotic and their loss cannot be easily recovered from; to cope with DNA damage a complex pathway called the DNA damage response (DDR) has evolved. This recognizes the damage, and through kinases such as ataxia-telangiectasia mutated (ATM) recruits and activates downstream factors that mediate either apoptosis or survival. This choice between these opposing outcomes integrates many inputs primarily through a number of key cross-road proteins, including ATM, p53, and p21. Evidence of re-entry into the cell-cycle by neurons can be seen in aging and diseases such as Alzheimer's disease. This aberrant cell-cycle re-entry is lethal and can lead to the apoptotic death of the neuron. Many downstream factors of the DDR promote cell-cycle arrest in response to damage and appear to protect neurons from apoptotic death. However, neurons surviving with a persistently activated DDR show all the features known from cell senescence; including metabolic dysregulation, mitochondrial dysfunction, and the hyper-production of pro-oxidant, pro-inflammatory and matrix-remodeling factors. These cells, termed senescence-like neurons, can negatively influence the extracellular environment and may promote induction of the same phenotype in surrounding cells, as well as driving aging and age-related diseases. Recently developed interventions targeting the DDR and/or the senescent phenotype in a range of non-neuronal tissues are being reviewed as they might become of therapeutic interest in neurodegenerative diseases.

Silibinin ameliorates Aβ25-35-induced memory deficits in rats by modulating autophagy and attenuating neuroinflammation as well as oxidative stress

Alzheimer's disease (AD) is a progressive, neurodegenerative disease. Accumulating evidence suggests that inflammatory response, oxidative stress and autophagy are involved in amyloid β (Aβ)-induced memory deficits. Silibinin (silybin), a flavonoid derived from the herb milk thistle, is well known for its hepatoprotective activities. In this study, we investigated the neuroprotective effect of silibinin on Aβ_25-35-injected rats. Results demonstrated that silibinin significantly attenuated Aβ_25-35-induced memory deficits in Morris water maze and novel object-recognition tests. Silibinin exerted anxiolytic effect in Aβ_25-35-injected rats as determined in elevated plus maze test. Silibinin attenuated the inflammatory responses, increased glutathione (GSH) levels and decreased malondialdehyde (MDA) levels, and upregulated autophagy levels in the Aβ_25-35-injected rats. In conclusion, silibinin is a potential candidate for AD treatment because of its anti-inflammatory, antioxidant and autophagy regulating activities.