CIP2A Causes Tau/APP Phosphorylation, Synaptopathy, and Memory Deficits in Alzheimer's Disease

Neuronal double-stranded DNA accumulation induced by DNase II deficiency drives tau phosphorylation and neurodegeneration

BACKGROUND

Deoxyribonuclease 2 (DNase II) plays a key role in clearing cytoplasmic double-stranded DNA (dsDNA). Deficiency of DNase II leads to DNA accumulation in the cytoplasm. Persistent dsDNA in neurons is an early pathological hallmark of senescence and neurodegenerative diseases including Alzheimer's disease (AD). However, it is not clear how DNase II and neuronal cytoplasmic dsDNA influence neuropathogenesis. Tau hyperphosphorylation is a key factor for the pathogenesis of AD. The effect of DNase II and neuronal cytoplasmic dsDNA on neuronal tau hyperphosphorylation remains unclarified.

METHODS

The levels of neuronal DNase II and dsDNA in WT and Tau-P301S mice of different ages were measured by immunohistochemistry and immunolabeling, and the levels of DNase II in the plasma of AD patients were measured by ELISA. To investigate the impact of DNase II on tauopathy, the levels of phosphorylated tau, phosphokinase, phosphatase, synaptic proteins, gliosis and proinflammatory cytokines in the brains of neuronal DNase II-deficient WT mice, neuronal DNase II-deficient Tau-P301S mice and neuronal DNase II-overexpressing Tau-P301S mice were evaluated by immunolabeling, immunoblotting or ELISA. Cognitive performance was determined using the Morris water maze test, Y-maze test, novel object recognition test and open field test.

RESULTS

The levels of DNase II were significantly decreased in the brains and the plasma of AD patients. DNase II also decreased age-dependently in the neurons of WT and Tau-P301S mice, along with increased dsDNA accumulation in the cytoplasm. The DNA accumulation induced by neuronal DNase II deficiency drove tau phosphorylation by upregulating cyclin-dependent-like kinase-5 (CDK5) and calcium/calmodulin activated protein kinase II (CaMKII) and downregulating phosphatase protein phosphatase 2A (PP2A). Moreover, DNase II knockdown induced and significantly exacerbated neuron loss, neuroinflammation and cognitive deficits in WT and Tau-P301S mice, respectively, while overexpression of neuronal DNase II exhibited therapeutic benefits.

CONCLUSIONS

DNase II deficiency and cytoplasmic dsDNA accumulation can initiate tau phosphorylation, suggesting DNase II as a potential therapeutic target for tau-associated disorders.

Revolutionizing Alzheimer's treatment: Harnessing human serum albumin for targeted drug delivery and therapy advancements

Alzheimer's disease (AD) is a neurodegenerative disorder initiated by amyloid-beta (Aβ) accumulation, leading to impaired cognitive function. Several delivery approaches have been improved for AD management. Among them, human serum albumin (HSA) is broadly employed for drug delivery and targeting the Aβ in AD owing to its biocompatibility, Aβ inhibitory effect, and nanoform, which showed blood-brain barrier (BBB) crossing ability via glycoprotein 60 (gp60) receptor and secreted protein acidic and rich in cysteine (SPARC) protein to transfer the drug molecules in the brain. Thus far, there is no previous review focusing on HSA and its drug delivery system in AD. Hence, the reviewed article aimed to critically compile the HSA therapeutic as well as drug delivery role in AD management. It also delivers information on how HSA-incorporated nanoparticles with surfaced embedded ligands such as TAT, GM1, and so on, not only improve BBB permeability but also increase neuron cell targetability in AD brain. Additionally, Aβ and tau pathology, including various metabolic markers likely BACE1 and BACE2, etc., are discussed. Besides, the molecular interaction of HSA with Aβ and its distinctive forms are critically reviewed that HSA can segregate Zn(II) and Cu(II) metal ions from Aβ owing to high affinity. Furthermore, the BBB drug delivery challenges in AD are addressed. Finally, the clinical formulation of HSA for the management of AD is critically discussed on how the HSA inhibits Aβ oligomer and fibril, while glycated HSA participates in amyloid plaque formation, i.e., β-structure sheet formation. This review report provides theoretical background on HSA-based AD drug delivery and makes suggestions for future prospect-related work.

Loss of function variant in CIP2A associated with female infertility with early embryonic arrest and fragmentation

BACKGROUND

Early embryonic arrest and fragmentation (EEAF) is a common cause of female infertility, but the genetic causes remain to be largely unknown. CIP2A encodes the cellular inhibitor of PP2A, playing a crucial role in mitosis and mouse oocyte meiosis.

METHODS

Exome sequencing and Sanger sequencing were performed to identify candidate causative genes in patients with EEAF. The pathogenicity of the CIP2A variant was assessed and confirmed in cultured cell lines and human oocytes through Western blotting, semi-quantitative RT-PCR, TUNEL staining, and fluorescence localization analysis.

FINDINGS

We identified CIP2A (c.1510C > T, p.L504F) as a novel disease-causing gene in human EEAF from a consanguineous family. L504 is highly conserved throughout evolution. The CIP2A variant (c.1510C > T, p.L504F) reduced the expression level of the mutant CIP2A protein, leading to the abnormal aggregation of mutant CIP2A protein and cell apoptosis. Abnormal aggregation of CIP2A protein and chromosomal dispersion occurred in the patient's oocytes and early embryos. We further replicated the patient phenotype by knockdown CIP2A in human oocytes. Additionally, CIP2A deficiency resulted in decreased levels of phosphorylated ERK1/2.

INTERPRETATION

We first found that the CIP2A loss-of-function variant associate with female infertility characterized by EEAF. Our findings suggest the uniqueness and importance of CIP2A gene in human oocyte and early embryo development.

FUNDING

This work was supported by National Key Research and Development Program of China (2023YFC2706302), the National Natural Science Foundation of China (81000079, 81170165, and 81870959), the HUST Academic Frontier Youth Team (2016QYTD02), and the Key Research of Huazhong University of Science and Technology, Tongji Hospital (2022A20).

Targeting tau in Alzheimer's disease: from mechanisms to clinical therapy

ABSTRACT

Alzheimer's disease is the most prevalent neurodegenerative disease affecting older adults. Primary features of Alzheimer's disease include extracellular aggregation of amyloid-β plaques and the accumulation of neurofibrillary tangles, formed by tau protein, in the cells. While there are amyloid-β-targeting therapies for the treatment of Alzheimer's disease, these therapies are costly and exhibit potential negative side effects. Mounting evidence suggests significant involvement of tau protein in Alzheimer's disease-related neurodegeneration. As an important microtubule-associated protein, tau plays an important role in maintaining the stability of neuronal microtubules and promoting axonal growth. In fact, clinical studies have shown that abnormal phosphorylation of tau protein occurs before accumulation of amyloid-β in the brain. Various therapeutic strategies targeting tau protein have begun to emerge, and are considered possible methods to prevent and treat Alzheimer's disease. Specifically, abnormalities in post-translational modifications of the tau protein, including aberrant phosphorylation, ubiquitination, small ubiquitin-like modifier (SUMO)ylation, acetylation, and truncation, contribute to its microtubule dissociation, misfolding, and subcellular missorting. This causes mitochondrial damage, synaptic impairments, gliosis, and neuroinflammation, eventually leading to neurodegeneration and cognitive deficits. This review summarizes the recent findings on the underlying mechanisms of tau protein in the onset and progression of Alzheimer's disease and discusses tau-targeted treatment of Alzheimer's disease.

Chronic stress induces Alzheimer's disease-like pathologies through DNA damage-Chk1-CIP2A signaling

Stress is an important initiating factor in promoting Alzheimer's disease (AD) pathogenesis. However, the mechanism by which stress induces AD-like cognitive impairment remains to be clarified. Here, we demonstrate that DNA damage is increased in stress hormone Corticotropin-releasing factor (CRF)-treated cells and in brains of mice exposed to chronic restraint stress. Accumulation of DNA damage drives activation of cell cycle checkpoint protein kinase 1 (Chk1), upregulation of cancerous inhibitor of PP2A (CIP2A), tau hyperphosphorylation, and Aβ overproduction, eventually resulting in synaptic impairment and cognitive deficits. Pharmacological intervention targeting Chk1 by specific inhibitor and DNA damage by vitamin C, suppress DNA damage-Chk1-CIP2A signaling pathway in chronic stress animal model, which in turn attenuate AD-like pathologies, synaptic impairments and cognitive deficits. Our study uncovers a novel molecular mechanism of stress-induced AD-like pathologies and provides effective preventive and therapeutic strategies targeting this signaling pathway.

Putative Molecular Mechanisms Underpinning the Inverse Roles of Mitochondrial Respiration and Heme Function in Lung Cancer and Alzheimer's Disease

Mitochondria are the powerhouse of the cell. Mitochondria serve as the major source of oxidative stress. Impaired mitochondria produce less adenosine triphosphate (ATP) but generate more reactive oxygen species (ROS), which could be a major factor in the oxidative imbalance observed in Alzheimer's disease (AD). Well-balanced mitochondrial respiration is important for the proper functioning of cells and human health. Indeed, recent research has shown that elevated mitochondrial respiration underlies the development and therapy resistance of many types of cancer, whereas diminished mitochondrial respiration is linked to the pathogenesis of AD. Mitochondria govern several activities that are known to be changed in lung cancer, the largest cause of cancer-related mortality worldwide. Because of the significant dependence of lung cancer cells on mitochondrial respiration, numerous studies demonstrated that blocking mitochondrial activity is a potent strategy to treat lung cancer. Heme is a central factor in mitochondrial respiration/oxidative phosphorylation (OXPHOS), and its association with cancer is the subject of increased research in recent years. In neural cells, heme is a key component in mitochondrial respiration and the production of ATP. Here, we review the role of impaired heme metabolism in the etiology of AD. We discuss the numerous mitochondrial effects that may contribute to AD and cancer. In addition to emphasizing the significance of heme in the development of both AD and cancer, this review also identifies some possible biological connections between the development of the two diseases. This review explores shared biological mechanisms (Pin1, Wnt, and p53 signaling) in cancer and AD. In cancer, these mechanisms drive cell proliferation and tumorigenic functions, while in AD, they lead to cell death. Understanding these mechanisms may help advance treatments for both conditions. This review discusses precise information regarding common risk factors, such as aging, obesity, diabetes, and tobacco usage.

Disruption of the Na+/K+-ATPase-purinergic P2X7 receptor complex in microglia promotes stress-induced anxiety

Na+/K+-ATPase (NKA) plays an important role in the central nervous system. However, little is known about its function in the microglia. Here, we found that NKAα1 forms a complex with the purinergic P2X7 receptor (P2X7R), an adenosine 5'-triphosphate (ATP)-gated ion channel, under physiological conditions. Chronic stress or treatment with lipopolysaccharide plus ATP decreased the membrane expression of NKAα1 in microglia, facilitated P2X7R function, and promoted microglia inflammatory activation via activation of the NLRP3 inflammasome. Accordingly, global deletion or conditional deletion of NKAα1 in microglia under chronic stress-induced aggravated anxiety-like behavior and neuronal hyperexcitability. DR5-12D, a monoclonal antibody that stabilizes membrane NKAα1, improved stress-induced anxiety-like behavior and ameliorated neuronal hyperexcitability and neurogenesis deficits in the ventral hippocampus of mice. Our results reveal that NKAα1 limits microglia inflammation and may provide a target for the treatment of stress-related neuroinflammation and diseases.

Astrocyte-derived lactoferrin reduces β-amyloid burden by promoting the interaction between p38 kinase and PP2A phosphatase in male APP/PS1 transgenic mice

BACKGROUND AND PURPOSE

Overexpression of astrocytic lactoferrin (Lf) was observed in the brain of Alzheimer's disease (AD) patients, whereas the role of astrocytic Lf in AD progression remains unexplored. In this study, we aimed to evaluate the effects of astrocytic Lf on AD progression.

EXPERIMENTAL APPROACH

Male APP/PS1 mice with astrocytes overexpressing human Lf were developed to evaluate the effects of astrocytic Lf on AD progression. N2a-sw cells also were employed to further uncover the mechanism of astrocytic Lf on β-amyloid (Aβ) production.

KEY RESULTS

Astrocytic Lf overexpression increased protein phosphatase 2A (PP2A) activity and reduced amyloid precursor protein (APP) phosphorylation, Aβ burden and tau hyperphosphorylation in APP/PS1 mice. Mechanistically, astrocytic Lf overexpression promoted the uptake of astrocytic Lf into neurons in APP/PS1 mice, and conditional medium from astrocytes overexpressing Lf inhibited p-APP (Thr668) expression in N2a-sw cells. Furthermore, recombinant human Lf (hLf) significantly enhanced PP2A activity and inhibited p-APP expression, whereas inhibition of p38 or PP2A activities abrogated the hLf-induced p-APP down-regulation in N2a-sw cells. Additionally, hLf promoted the interaction of p38 and PP2A via p38 activation, thereby enhancing PP2A activity, and low-density lipoprotein receptor-related protein 1 (LRP1) knockdown significantly reversed the hLf-induced p38 activation and p-APP down-regulation.

CONCLUSIONS AND IMPLICATIONS

Our data suggested that astrocytic Lf promoted neuronal p38 activation, via targeting to LRP1, subsequently promoting p38 binding to PP2A to enhance PP2A enzyme activity, which finally inhibited Aβ production via APP dephosphorylation. In conclusion, promoting astrocytic Lf expression may be a potential strategy against AD.

LINKED ARTICLES

This article is part of a themed issue From Alzheimer's Disease to Vascular Dementia: Different Roads Leading to Cognitive Decline. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v181.6/issuetoc.

KIBRA repairs synaptic plasticity and promotes resilience to tauopathy-related memory loss

Synaptic plasticity is obstructed by pathogenic tau in the brain, representing a key mechanism that underlies memory loss in Alzheimer's disease (AD) and related tauopathies. Here, we found that reduced levels of the memory-associated protein KIdney/BRAin (KIBRA) in the brain and increased KIBRA protein levels in cerebrospinal fluid are associated with cognitive impairment and pathological tau levels in disease. We next defined a mechanism for plasticity repair in vulnerable neurons using the C-terminus of the KIBRA protein (CT-KIBRA). We showed that CT-KIBRA restored plasticity and memory in transgenic mice expressing pathogenic human tau; however, CT-KIBRA did not alter tau levels or prevent tau-induced synapse loss. Instead, we found that CT-KIBRA stabilized the protein kinase Mζ (PKMζ) to maintain synaptic plasticity and memory despite tau-mediated pathogenesis. Thus, our results distinguished KIBRA both as a biomarker of synapse dysfunction and as the foundation for a synapse repair mechanism to reverse cognitive impairment in tauopathy.

Hippocampal synaptic plasticity injury mediated by SIRT1 downregulation is involved in chronic pain-related cognitive dysfunction

AIMS

Cognitive dysfunction associated with chronic pain may be caused by impaired synaptic plasticity. Considering the impact of silent information regulator 1 (SIRT1) on synaptic plasticity, we explored the exact role of SIRT1 in cognitive impairment caused by chronic pain.

METHODS

We evaluated the memory ability of mice with the fear conditioning test (FCT) after spared nerve injury (SNI) model. Western blotting and immunofluorescence were used to analyze the expression levels of SIRT1. Hippocampal synaptic plasticity was detected with Golgi staining, transmission electron microscopy, and long-term potentiation (LTP). In the intervention study, AAV9-CaMKIIα-Cre-EGFP was injected to SIRT1flox/flox mice to knockdown the expression levels of SIRT1. Besides, SNI mice were injected with AAV2/9-CaMKIIα-SIRT1-3*Flag-GFP or SRT1720 to increase the expression levels or enzymatic activity of SIRT1.

RESULTS

Our current results indicated that cognitive function in SNI mice was impaired, SIRT1 expression in glutaminergic neurons in the hippocampal CA1 area was downregulated, and synaptic plasticity was altered. Selective knockdown of SIRT1 in hippocampus damaged synaptic plasticity and cognitive function of healthy mice. In addition, the impaired synaptic plasticity and cognitive dysfunction of SNI mice could be improved by the upregulation of SIRT1 expression or enzyme activity.

CONCLUSIONS

Reduced SIRT1 expression in hippocampus of SNI mice may induce cognitive impairment associated with chronic pain by mediating the impaired synaptic plasticity.

KIBRA repairs synaptic plasticity and promotes resilience to tauopathy-related memory loss

Synaptic plasticity is obstructed by pathogenic tau in the brain, representing a key mechanism that underlies memory loss in Alzheimer's disease (AD) and related tauopathies. Here, we define a mechanism for plasticity repair in vulnerable neurons using the C-terminus of the KIdney/BRAin (KIBRA) protein (CT-KIBRA). We show that CT-KIBRA restores plasticity and memory in transgenic mice expressing pathogenic human tau; however, CT-KIBRA did not alter tau levels or prevent tau-induced synapse loss. Instead, we find that CT-KIBRA binds to and stabilizes protein kinase Mζ (PKMζ) to maintain synaptic plasticity and memory despite tau-mediated pathogenesis. In humans we find that reduced KIBRA in brain and increased KIBRA in cerebrospinal fluid are associated with cognitive impairment and pathological tau levels in disease. Thus, our results distinguish KIBRA both as a novel biomarker of synapse dysfunction in AD and as the foundation for a synapse repair mechanism to reverse cognitive impairment in tauopathy.

Does modulation of tau hyperphosphorylation represent a reasonable therapeutic strategy for Alzheimer's disease? From preclinical studies to the clinical trials

Protein kinases (PKs) have emerged as one of the most intensively investigated drug targets in current pharmacological research, with indications ranging from oncology to neurodegeneration. Tau protein hyperphosphorylation was the first pathological post-translational modification of tau protein described in Alzheimer's disease (AD), highlighting the role of PKs in neurodegeneration. The therapeutic potential of protein kinase inhibitors (PKIs)) and protein phosphatase 2 A (PP2A) activators in AD has recently been explored in several preclinical and clinical studies with variable outcomes. Where a number of preclinical studies demonstrate a visible reduction in the levels of phospho-tau in transgenic tauopathy models, no reduction in neurofibrillary lesions is observed. Amongst the few PKIs and PP2A activators that progressed to clinical trials, most failed on the efficacy front, with only a few still unconfirmed and potential positive trends. This suggests that robust preclinical and clinical data is needed to unequivocally evaluate their efficacy. To this end, we take a systematic look at the results of preclinical and clinical studies of PKIs and PP2A activators, and the evidence they provide regarding the utility of this approach to evaluate the potential of targeting tau hyperphosphorylation as a disease modifying therapy.

Microglia activation mediates circadian rhythm disruption-induced cognitive impairment in mice

Alzheimer's disease (AD) is the leading cause of dementia and there are no effective treatments for this disease currently. Circadian rhythm disruption (CRD) is a hallmark of modern society that appears to be on the rise. It is well reported that AD is associated with disrupted circadian functioning and CRD can impair cognitive function. However, the cellular mechanisms underlying CRD-associated cognitive decline remain elusive. In this study, we investigated whether microglia are involved in CRD-induced cognitive decline. We established experimental 'jet lag' (phase delay of the light/dark cycles)-induced CRD mouse model and observed significant impairment of spatial learning and memory function in these mice. In the brain, CRD resulted in neuroinflammation, which was characterized by microglia activation and increased pro-inflammatory cytokine production, impairments in neurogenesis and reduction of synaptic proteins in the hippocampus. Interestingly, elimination of microglia with the colony stimulating factor-1 receptor inhibitor PLX3397 prevented CRD-induced neuroinflammation, cognitive decline, impairment of neurogenesis and loss of synaptic proteins. These findings collectively suggest that microglia activation plays a key role in CRD-induced cognitive deficit most likely through neuroinflammation-mediated impairments in adult neurogenesis and synapses.

The Multifaceted Role of WNT Signaling in Alzheimer's Disease Onset and Age-Related Progression

The evolutionary conserved WNT signaling pathway orchestrates numerous complex biological processes during development and is critical to the maintenance of tissue integrity and homeostasis in the adult. As it relates to the central nervous system, WNT signaling plays several roles as it relates to neurogenesis, synaptic formation, memory, and learning. Thus, dysfunction of this pathway is associated with multiple diseases and disorders, including several neurodegenerative disorders. Alzheimer's disease (AD) is characterized by several pathologies, synaptic dysfunction, and cognitive decline. In this review, we will discuss the various epidemiological, clinical, and animal studies that demonstrate a precise link between aberrant WNT signaling and AD-associated pathologies. In turn, we will discuss the manner in which WNT signaling influences multiple molecular, biochemical, and cellular pathways upstream of these end-point pathologies. Finally, we will discuss how merging tools and technologies can be used to generate next generation cellular models to dissect the relationship between WNT signaling and AD.

The Effects of PP2A Disruption on ER-Mitochondria Contact and Mitochondrial Functions in Neuronal-like Cells

Mitochondria-associated membranes (MAMs) regulate several cellular processes, including calcium homeostasis and mitochondrial function, and dynamics. While MAMs are upregulated in Alzheimer’s disease (AD), the mechanisms underlying this increase remain unknown. A possible mechanism may include dysregulation of protein phosphatase 2A (PP2A), which is reduced in the AD brain. Furthermore, PP2A has been previously reported to modulate MAM formation in hepatocytes. However, it is unknown whether PP2A and MAMs are linked in neuronal cells. Here, to test the correlation between PP2A and MAMs, we inhibited the activity of PP2A to mimic its low levels in AD brains and observed MAM formation, function, and dynamics. MAMs were significantly increased after PP2A inhibition, which correlated with elevated mitochondrial Ca2+ influx and disrupted mitochondrial membrane potential and mitochondrial fission. This study highlights the essential role PP2A plays in regulating MAM formation and mitochondrial function and dynamics for the first time in neuronal-like cells.

C-glycosides analogues of the okadaic acid central fragment exert neuroprotection via restoration of PP2A-phosphatase activity: A rational design of potential drugs for Alzheimer's disease targeting tauopathies

Protein phosphatase 2A (PP2A) is an important Ser/Thr phosphatase that participates in the regulation of multiple cellular processes. This implies that any deficient activity of PP2A is the responsible of severe pathologies. For instance, one of the main histopathological features of Alzheimer's disease is neurofibrillary tangles, which are mainly comprised by hyperphosphorylated forms of tau protein. This altered rate of tau phosphorylation has been correlated with PP2A depression AD patients. With the goal of preventing PP2A inactivation in neurodegeneration scenarios, we have aimed to design, synthesize and evaluate new ligands of PP2A capable of preventing its inhibition. To achieve this goal, the new PP2A ligands present structural similarities with the central fragment C19-C27 of the well-established PP2A inhibitor okadaic acid (OA). Indeed, this central moiety of OA does not exert inhibitory actions. Hence, these compounds lack PP2A-inhibiting structural motifs but, in contrast, compete with PP2A inhibitors, thus recovering phosphatase activity. Proving this hypothesis, most compounds showed a good neuroprotective profile in neurodegeneration models related to PP2A impairment, highlighting derivative 10, named ITH12711, as the most promising one. This compound (1) restored in vitro and cellular PP2A catalytic activity, measured on a phospho-peptide substrate and by western-blot analyses, (2) proved good brain penetration measured by PAMPA, and (3) prevented LPS-induced memory impairment of mice in the object recognition test. Thus, the promising outcomes of the compound 10 validate our rational approach to design new PP2A-activating drugs based on OA central fragment.

Structural mechanism for inhibition of PP2A-B56α and oncogenicity by CIP2A

The protein phosphatase 2A (PP2A) heterotrimer PP2A-B56α is a human tumour suppressor. However, the molecular mechanisms inhibiting PP2A-B56α in cancer are poorly understood. Here, we report molecular level details and structural mechanisms of PP2A-B56α inhibition by an oncoprotein CIP2A. Upon direct binding to PP2A-B56α trimer, CIP2A displaces the PP2A-A subunit and thereby hijacks both the B56α, and the catalytic PP2Ac subunit to form a CIP2A-B56α-PP2Ac pseudotrimer. Further, CIP2A competes with B56α substrate binding by blocking the LxxIxE-motif substrate binding pocket on B56α. Relevant to oncogenic activity of CIP2A across human cancers, the N-terminal head domain-mediated interaction with B56α stabilizes CIP2A protein. Functionally, CRISPR/Cas9-mediated single amino acid mutagenesis of the head domain blunted MYC expression and MEK phosphorylation, and abrogated triple-negative breast cancer in vivo tumour growth. Collectively, we discover a unique multi-step hijack and mute protein complex regulation mechanism resulting in tumour suppressor PP2A-B56α inhibition. Further, the results unfold a structural determinant for the oncogenic activity of CIP2A, potentially facilitating therapeutic modulation of CIP2A in cancer and other diseases.

TREM2 and Microglia Contribute to the Synaptic Plasticity: from Physiology to Pathology

Synapses are bridges for information transmission in the central nervous system (CNS), and synaptic plasticity is fundamental for the normal function of synapses, contributing substantially to learning and memory. Numerous studies have proven that microglia can participate in the occurrence and progression of neurodegenerative diseases (NDDs), such as Alzheimer's disease (AD), by regulating synaptic plasticity. In this review, we summarize the main characteristics of synapses and synaptic plasticity under physiological and pathological conditions. We elaborate the origin and development of microglia and the two well-known microglial signaling pathways that regulate synaptic plasticity. We also highlight the unique role of triggering receptor expressed on myeloid cells 2 (TREM2) in microglia-mediated regulation of synaptic plasticity and its relationship with AD. Finally, we propose four possible ways in which TREM2 is involved in regulating synaptic plasticity. This review will help researchers understand how NDDs develop from the perspective of synaptic plasticity.

The regulatory role of Pin1 in neuronal death

Regulated cell death predominantly involves apoptosis, autophagy, and regulated necrosis. It is vital that we understand how key regulatory signals can control the process of cell death. Pin1 is a cis-trans isomerase that catalyzes the isomerization of phosphorylated serine or threonine-proline motifs of a protein, thereby acting as a crucial molecular switch and regulating the protein functionality and the signaling pathways involved. However, we know very little about how Pin1-associated pathways might play a role in regulated cell death. In this paper, we review the role of Pin1 in regulated cell death and related research progress and summarize Pin1-related pathways in regulated cell death. Aside from the involvement of Pin1 in the apoptosis that accompanies neurodegenerative diseases, accumulating evidence suggests that Pin1 also plays a role in regulated necrosis and autophagy, thereby exhibiting distinct effects, including both neurotoxic and neuroprotective effects. Gaining an enhanced understanding of Pin1 in neuronal death may provide us with new options for the development of therapeutic target for neurodegenerative disorders.

CIP2A deficiency promotes depression-like behaviors in mice through inhibition of dendritic arborization

Major depressive disorder (MDD) is a severe mental illness. Decreased brain plasticity and dendritic fields have been consistently found in MDD patients and animal models; however, the underlying molecular mechanisms remain to be clarified. Here, we demonstrate that the deletion of cancerous inhibitor of PP2A (CIP2A), an endogenous inhibitor of protein phosphatase 2A (PP2A), leads to depression-like behaviors in mice. Hippocampal RNA sequencing analysis of CIP2A knockout mice shows alterations in the PI3K-AKT pathway and central nervous system development. In primary neurons, CIP2A stimulates AKT activity and promotes dendritic development. Further analysis reveals that the effect of CIP2A in promoting dendritic development is dependent on PP2A-AKT signaling. In vivo, CIP2A deficiency-induced depression-like behaviors and impaired dendritic arborization are rescued by AKT activation. Decreased CIP2A expression and impaired dendrite branching are observed in a mouse model of chronic unpredictable mild stress (CUMS). Indicative of clinical relevance to humans, CIP2A expression is found decreased in transcriptomes from MDD patients. In conclusion, we discover a novel mechanism that CIP2A deficiency promotes depression through the regulation of PP2A-AKT signaling and dendritic arborization.

Discovering new peripheral plasma biomarkers to identify cognitive decline in type 2 diabetes

Type 2 diabetes mellitus (T2DM) is an independent risk factor of Alzheimer's disease (AD), and thus identifying who among the increasing T2DM populations may develop into AD is important for early intervention. By using TMT-labeling coupled high-throughput mass spectrometry, we conducted a comprehensive plasma proteomic analysis in none-T2DM people (Ctrl, n = 30), and the age-/sex-matched T2DM patients with mild cognitive impairment (T2DM-MCI, n = 30) or T2DM without MCI (T2DM-nMCI, n = 25). The candidate biomarkers identified by proteomics and bioinformatics analyses were verified by ELISA, and their diagnostic capabilities were evaluated with machine learning. A total of 53 differentially expressed proteins (DEPs) were identified in T2DM-MCI compared with T2DM-nMCI patients. These DEPs were significantly enriched in multiple biological processes, such as amyloid neuropathies, CNS disorders, and metabolic acidosis. Among the DEPs, alpha-1-antitrypsin (SERPINA1), major viral protein (PRNP), and valosin-containing protein (VCP) showed strong correlation with AD high-risk genes APP, MAPT, APOE, PSEN1, and PSEN2. Also, the levels of PP2A cancer inhibitor (CIP2A), PRNP, corticotropin-releasing factor-binding protein (CRHBP) were significantly increased, while the level of VCP was decreased in T2DM-MCI patients compared with that of the T2DM-nMCI, and these changes were correlated with the Mini-Mental State Examination (MMSE) score. Further machine learning data showed that increases in PRNP, CRHBP, VCP, and rGSK-3β(T/S9) (ratio of total to serine-9-phosphorylated glycogen synthase kinase-3β) had the greatest power to identify mild cognitive decline in T2DM patients.

Combined DiI and Antibody Labeling Reveals Complex Dysgenesis of Hippocampal Dendritic Spines in a Mouse Model of Fragile X Syndrome

Structural, functional, and molecular alterations in excitatory spines are a common hallmark of many neurodevelopmental disorders including intellectual disability and autism. Here, we describe an optimized methodology, based on combined use of DiI and immunofluorescence, for rapid and sensitive characterization of the structure and composition of spines in native brain tissue. We successfully demonstrate the applicability of this approach by examining the properties of hippocampal spines in juvenile Fmr1 KO mice, a mouse model of Fragile X Syndrome. We find that mutant mice display pervasive dysgenesis of spines evidenced by an overabundance of both abnormally elongated thin spines and cup-shaped spines, in combination with reduced density of mushroom spines. We further find that mushroom spines expressing the actin-binding protein Synaptopodin-a marker for spine apparatus-are more prevalent in mutant mice. Previous work identified spines with Synaptopodin/spine apparatus as the locus of mGluR-LTD, which is abnormally elevated in Fmr1 KO mice. Altogether, our data suggest this enhancement may be linked to the preponderance of this subset of spines in the mutant. Overall, these findings demonstrate the sensitivity and versatility of the optimized methodology by uncovering a novel facet of spine dysgenesis in Fmr1 KO mice.

SPIN90 Deficiency Ameliorates Amyloid β Accumulation by Regulating APP Trafficking in AD Model Mice

Alzheimer’s disease (AD), a common form of dementia, is caused in part by the aggregation and accumulation in the brain of amyloid β (Aβ), a product of the proteolytic cleavage of amyloid precursor protein (APP) in endosomes. Trafficking of APP, such as surface-intracellular recycling, is an early critical step required for Aβ generation. Less is known, however, about the molecular mechanism regulating APP trafficking. This study investigated the mechanism by which SPIN90, along with Rab11, modulates APP trafficking, Aβ motility and accumulation, and synaptic functionality. Brain Aβ deposition was lower in the progeny of 5xFAD-SPIN90KO mice than in 5xFAD-SPIN90WT mice. Analysis of APP distribution and trafficking showed that the surface fraction of APP was locally distinct in axons and dendrites, with these distributions differing significantly in 5xFAD-SPIN90WT and 5xFAD-SPIN90KO mice, and that neural activity-driven APP trafficking to the surface and intracellular recycling were more actively mobilized in 5xFAD-SPIN90KO neurons. In addition, SPIN90 was found to be cotrafficked with APP via axons, with ablation of SPIN90 reducing the intracellular accumulation of APP in axons. Finally, synaptic transmission was restored over time in 5xFAD-SPIN90KO but not in 5xFAD-SPIN90WT neurons, suggesting SPIN90 is implicated in Aβ production through the regulation of APP trafficking.

Dysfunctional Glucose Metabolism in Alzheimer’s Disease Onset and Potential Pharmacological Interventions

Alzheimer’s disease (AD) is the most common age-related dementia. The alteration in metabolic characteristics determines the prognosis. Patients at risk show reduced glucose uptake in the brain. Additionally, type 2 diabetes mellitus increases the risk of AD with increasing age. Therefore, changes in glucose uptake in the cerebral cortex may predict the histopathological diagnosis of AD. The shifts in glucose uptake and metabolism, insulin resistance, oxidative stress, and abnormal autophagy advance the pathogenesis of AD syndrome. Here, we summarize the role of altered glucose metabolism in type 2 diabetes for AD prognosis. Additionally, we discuss diagnosis and potential pharmacological interventions for glucose metabolism defects in AD to encourage the development of novel therapeutic methods.

Targeting protein phosphatases for the treatment of inflammation-related diseases: From signaling to therapy

Inflammation is the common pathological basis of autoimmune diseases, metabolic diseases, malignant tumors, and other major chronic diseases. Inflammation plays an important role in tissue homeostasis. On one hand, inflammation can sense changes in the tissue environment, induce imbalance of tissue homeostasis, and cause tissue damage. On the other hand, inflammation can also initiate tissue damage repair and maintain normal tissue function by resolving injury and restoring homeostasis. These opposing functions emphasize the significance of accurate regulation of inflammatory homeostasis to ameliorate inflammation-related diseases. Potential mechanisms involve protein phosphorylation modifications by kinases and phosphatases, which have a crucial role in inflammatory homeostasis. The mechanisms by which many kinases resolve inflammation have been well reviewed, whereas a systematic summary of the functions of protein phosphatases in regulating inflammatory homeostasis is lacking. The molecular knowledge of protein phosphatases, and especially the unique biochemical traits of each family member, will be of critical importance for developing drugs that target phosphatases. Here, we provide a comprehensive summary of the structure, the "double-edged sword" function, and the extensive signaling pathways of all protein phosphatases in inflammation-related diseases, as well as their potential inhibitors or activators that can be used in therapeutic interventions in preclinical or clinical trials. We provide an integrated perspective on the current understanding of all the protein phosphatases associated with inflammation-related diseases, with the aim of facilitating the development of drugs that target protein phosphatases for the treatment of inflammation-related diseases.

Tau Acts in Concert With Kinase/Phosphatase Underlying Synaptic Dysfunction

Alzheimer's disease (AD) is characterized by two pathological features: neurofibrillary tangles (NFTs), formed by microtubule-associated protein tau, and abnormal accumulation of amyloid-β (Aβ). Multiple evidence placed synaptic tau as the vital fact of AD pathology, especially at the very early stage of AD. In the present review, we discuss tau phosphorylation, which is critical for the dendritic localization of tau and synaptic plasticity. We review the related kinases and phosphatases implicated in the synaptic function of tau. We also review the synergistic effects of these kinases and phosphatases on tau-associated synaptic deficits. We aim to open a new perspective on the treatment of AD.

Inhibitory Effects of Macelignan on Tau Phosphorylation and Aβ Aggregation in the Cell Model of Alzheimer's Disease

Alzheimer's disease (AD) is a neurodegenerative disorder mainly affecting old population. In this study, two Tau overexpressing cell lines (SH-SY5Y/Tau and HEK293/Tau), N2a/SweAPP cell line, and 3× Transgene (APPswe/PS1M146V/TauP301L) mouse primary nerve cell lines were used as AD models to study the activity and molecular mechanism of macelignan, a natural compound extracted from Myristica fragrans, against AD. Our study showed that macelignan could reduce the phosphorylation of Tau at Thr 231 site, Ser 396 site, and Ser 404 site in two overexpressing Tau cell lines. It also could decrease the phosphorylation of Tau at Ser 404 site in mouse primary neural cells. Further investigation of its mechanism found that macelignan could reduce the phosphorylation of Tau by increasing the level of autophagy and enhancing PP2A activity in Tau overexpressing cells. Additionally, macelignan could activate the PERK/eIF2α signaling pathway to reduce BACE1 translation, which further inhibits the cleavage of APP and ultimately suppresses Aβ deposition in N2a/SweAPP cells. Taken together, our results indicate that macelignan has the potential to be developed as a treatment for AD.

Transgenic Mouse Models of Alzheimer's Disease: An Integrative Analysis

Alzheimer's disease (AD) constitutes the most prominent form of dementia among elderly individuals worldwide. Disease modeling using murine transgenic mice was first initiated thanks to the discovery of heritable mutations in amyloid precursor protein (APP) and presenilins (PS) genes. However, due to the repeated failure of translational applications from animal models to human patients, along with the recent advances in genetic susceptibility and our current understanding on disease biology, these models have evolved over time in an attempt to better reproduce the complexity of this devastating disease and improve their applicability. In this review, we provide a comprehensive overview about the major pathological elements of human AD (plaques, tauopathy, synaptic damage, neuronal death, neuroinflammation and glial dysfunction), discussing the knowledge that available mouse models have provided about the mechanisms underlying human disease. Moreover, we highlight the pros and cons of current models, and the revolution offered by the concomitant use of transgenic mice and omics technologies that may lead to a more rapid improvement of the present modeling battery.

Chk1 Inhibition Ameliorates Alzheimer's Disease Pathogenesis and Cognitive Dysfunction Through CIP2A/PP2A Signaling

Alzheimer's disease (AD) is the most common neurodegenerative disease with limited therapeutic strategies. Cell cycle checkpoint protein kinase 1 (Chk1) is a Ser/Thr protein kinase which is activated in response to DNA damage, the latter which is an early event in AD. However, whether DNA damage-induced Chk1 activation participates in the development of AD and Chk1 inhibition ameliorates AD-like pathogenesis remain unclarified. Here, we demonstrate that Chk1 activity and the levels of protein phosphatase 2A (PP2A) inhibitory protein CIP2A are elevated in AD human brains, APP/PS1 transgenic mice, and primary neurons with Aβ treatment. Chk1 overexpression induces CIP2A upregulation, PP2A inhibition, tau and APP hyperphosphorylation, synaptic impairments, and cognitive memory deficit in mice. Moreover, Chk1 inhibitor (GDC0575) effectively increases PP2A activity, decreases tau phosphorylation, and inhibits Aβ overproduction in AD cell models. GDC0575 also reverses AD-like cognitive deficits and prevents neuron loss and synaptic impairments in APP/PS1 mice. In conclusion, our study uncovers a mechanism by which DNA damage-induced Chk1 activation promotes CIP2A-mediated tau and APP hyperphosphorylation and cognitive dysfunction in Alzheimer's disease and highlights the therapeutic potential of Chk1 inhibitors in AD.

PP2A and Its Inhibitors in Helper T-Cell Differentiation and Autoimmunity

Protein phosphatase 2A (PP2A) is a highly complex heterotrimeric Ser/Thr phosphatase that regulates many cellular processes. The role of PP2A as a tumor suppressor has been extensively studied and reviewed. However, emerging evidence suggests PP2A constrains inflammatory responses and is important in autoimmune and neuroinflammatory diseases. Here, we reviewed the existing literature on the role of PP2A in T-cell differentiation and autoimmunity. We have also discussed the modulation of PP2A activity by endogenous inhibitors and its small-molecule activators as potential therapeutic approaches against autoimmunity.

ChK1 activation induces reactive astrogliosis through CIP2A/PP2A/STAT3 pathway in Alzheimer's disease

Cancerous Inhibitor of PP2A (CIP2A), an endogenous PP2A inhibitor, is upregulated and causes reactive astrogliosis, synaptic degeneration, and cognitive deficits in Alzheimer's disease (AD). However, the mechanism underlying the increased CIP2A expression in AD brains remains unclear. We here demonstrated that the DNA damage-related Checkpoint kinase 1 (ChK1) is activated in AD human brains and 3xTg-AD mice. ChK1-mediated CIP2A overexpression drives inhibition of PP2A and activates STAT3, then leads to reactive astrogliosis and neurodegeneration in vitro. Infection of mouse brain with GFAP-ChK1-AAV induced AD-like cognitive deficits and exacerbated AD pathologies in vivo. In conclusion, we showed that ChK1 activation induces reactive astrogliosis, degeneration of neurons, and exacerbation of AD through the CIP2A-PP2A-STAT3 pathway, and inhibiting ChK1 may be a potential therapeutic approach for AD treatment.

Short-Term Efficacy of Transcranial Focused Ultrasound to the Hippocampus in Alzheimer’s Disease: A Preliminary Study

Preclinical studies have suggested that low-intensity transcranial focused ultrasound (tFUS) may have therapeutic potential for Alzheimer’s disease (AD) by opening the blood–brain barrier (BBB), reducing amyloid pathology, and improving cognition. This study investigated the effects of tFUS on BBB opening, regional cerebral metabolic rate of glucose (rCMRglu), and cognitive function in AD patients. Eight patients with AD received image-guided tFUS to the right hippocampus immediately after intravenous injection of microbubble ultrasound contrast agents. Patients completed magnetic resonance imaging (MRI), ¹⁸F-fluoro-2-deoxyglucose positron emission tomography (PET), and cognitive assessments before and after the sonication. No evidence of transient BBB opening was found on T1 dynamic contrast-enhanced MRI. However, immediate recall (p = 0.03) and recognition memory (p = 0.02) were significantly improved on the verbal learning test. PET image analysis demonstrated increased rCMRglu in the right hippocampus (p = 0.001). In addition, increases of hippocampal rCMRglu were correlated with improvement in recognition memory (Spearman’s ρ = 0.77, p = 0.02). No adverse event was observed. Our results suggest that tFUS to the hippocampus of AD patients may improve rCMRglu of the target area and memory in the short term, even without BBB opening. Further larger sham-controlled trials with loger follow-up are warranted to evaluate the efficacy and safety of tFUS in patients with AD.

Protein phosphatase 2A restrains DLK signaling to promote proper Drosophila synaptic development and mammalian cortical neuron survival

Protein phosphatase 2A (PP2A) is a major cellular phosphatase with many protein substrates. As expected for a signaling molecule with many targets, inhibition of PP2A disrupts fundamental aspects of cellular physiology including cell division and survival. In post-mitotic neurons, the microtubule associated protein Tau is a particularly well-studied PP2A substrate as hyperphosphorylation of Tau is a hallmark of Alzheimer's disease. Although many cellular targets are likely altered by loss of PP2A, here we find that activation of a single pathway can explain important aspects of the PP2A loss-of-function phenotype in neurons. We demonstrate that PP2A inhibits activation of the neuronal stress kinase DLK and its Drosophila ortholog Wallenda. In the fly, PP2A inhibition activates a DLK/Wallenda-regulated transcriptional program that induces synaptic terminal overgrowth at the neuromuscular junction. In cultured mammalian neurons, PP2A inhibition activates a DLK-dependent apoptotic program that induces cell death. Since hyperphosphorylated Tau is toxic, we wished to test the hypothesis that dephosphorylation of Tau by PP2A is required for neuronal survival. Contrary to expectations, in the absence of Tau PP2A inhibition still activates DLK and induces neuronal cell death, demonstrating that hyperphosphorylated Tau is not required for cell death in this model. Moreover, hyperphosphorylation of Tau following PP2A inhibition does not require DLK. Hence, loss of PP2A function in cortical neurons triggers two independent neuropathologies: 1) Tau hyperphosphorylation and 2) DLK activation and subsequent neuronal cell death. These findings demonstrate that inhibition of the DLK pathway is an essential function of PP2A required for normal Drosophila synaptic terminal development and mammalian cortical neuron survival.

Proteomic and Transcriptomic Analyses Reveal Pathological Changes in the Entorhinal Cortex Region that Correlate Well with Dysregulation of Ion Transport in Patients with Alzheimer's Disease

Alzheimer's disease (AD) is the most common neurodegenerative disorder. The earliest neuropathology of AD appears in entorhinal cortex (EC) regions. Therapeutic strategies and preventive measures to protect against entorhinal degeneration would be of substantial value in the early stages of AD. In this study, transcriptome based on the Illumina RNA-seq and proteome based on TMT-labelling were performed for RNA and protein profiling on AD EC samples and non-AD control EC samples. Immunohistochemistry was used to validate proteins expressions. After integrated analysis, 57 genes were detected both in transcriptome and proteome data, including 51 in similar altering trends (7 upregulated, 44 downregulated) and 6 in inverse trends when compared AD vs. control. The top 6 genes (GABRG2, CACNG3, CACNB4, GABRB2, GRIK2, and SLC17A6) within the 51 genes were selected and related to "ion transport". Correlation analysis demonstrated negative relationship of protein expression level with the neuropathologic changes. In conclusion, the integrate transcriptome and proteome analysis provided evidence for dysregulation of ion transport across brain regions in AD, which might be a critical signaling pathway that initiates pathology. This study might provide new insight into the earliest changes occurring in the EC of AD and novel targets for AD prevention and treatment.

Protein Phosphatase 2A (PP2A) mutations in brain function, development, and neurologic disease

By removing Ser/Thr-specific phosphorylations in a multitude of protein substrates in diverse tissues, Protein Phosphatase type 2A (PP2A) enzymes play essential regulatory roles in cellular signalling and physiology, including in brain function and development. Here, we review current knowledge on PP2A gene mutations causally involved in neurodevelopmental disorders and intellectual disability, focusing on PPP2CA, PPP2R1A and PPP2R5D. We provide insights into the impact of these mutations on PP2A structure, substrate specificity and potential function in neurobiology and brain development.

Dendritic/Post-synaptic Tau and Early Pathology of Alzheimer's Disease

Microtubule-associated protein tau forms insoluble neurofibrillary tangles (NFTs), which is one of the major histopathological hallmarks of Alzheimer's disease (AD). Many studies have demonstrated that tau causes early functional deficits prior to the formation of neurofibrillary aggregates. The redistribution of tau from axons to the somatodendritic compartment of neurons and dendritic spines causes synaptic impairment, and then leads to the loss of synaptic contacts that correlates better with cognitive deficits than amyloid-β (Aβ) aggregates do in AD patients. In this review, we discuss the underlying mechanisms by which tau is mislocalized to dendritic spines and contributes to synaptic dysfunction in AD. We also discuss the synergistic effects of tau and oligomeric forms of Aβ on promoting synaptic dysfunction in AD.

A Comprehensive Review of Alzheimer's Association with Related Proteins: Pathological Role and Therapeutic Significance

Alzheimer's is an insidious, progressive, chronic neurodegenerative disease which causes the devastation of neurons. Alzheimer's possesses complex pathologies of heterogeneous nature counting proteins as one major factor along with enzymes and mutated genes. Proteins such as amyloid precursor protein (APP), apolipoprotein E (ApoE), presenilin, mortalin, calbindin-D28K, creactive protein, heat shock proteins (HSPs), and prion protein are some of the chief elements in the foremost hypotheses of AD like amyloid-beta (Aβ) cascade hypothesis, tau hypothesis, cholinergic neuron damage, etc. Disturbed expression of these proteins results in synaptic dysfunction, cognitive impairment, memory loss, and neuronal degradation. On the therapeutic ground, attempts of developing anti-amyloid, anti-inflammatory, anti-tau therapies are on peak, having APP and tau as putative targets. Some proteins, e.g., HSPs, which ameliorate oxidative stress, calpains, which help in regulating synaptic plasticity, and calmodulin-like skin protein (CLSP) with its neuroprotective role are few promising future targets for developing anti-AD therapies. On diagnostic grounds of AD C-reactive protein, pentraxins, collapsin response mediator protein-2, and growth-associated protein-43 represent the future of new possible biomarkers for diagnosing AD. The last few decades were concentrated over identifying and studying protein targets of AD. Here, we reviewed the physiological/pathological roles and therapeutic significance of nearly all the proteins associated with AD that addresses putative as well as probable targets for developing effective anti-AD therapies.

Vitamin D Attenuates Alzheimer-like Pathology Induced by Okadaic Acid

Many elderly individuals suffer from Alzheimer's disease (AD), which causes a growing concern. We investigated the mechanism underlying the effects of vitamin D (VD) as a prophylactic treatment. A mouse model of okadaic-acid-induced AD-like pathology was used in vivo and in vitro. Morris water maze and field trials were used to assess cognitive function. The expression levels of VDR, MTHFR, LCMT-1, PP2A, p-TAU (Thr396), and T-TAU and the methylation level of PP2A were measured by Western blotting, and a reversal of the increase in the levels of these proteins in an AD cell model was observed. We used MTHFR-knockdown SH-SY5Y cells to further test the effects of VD, treated these cells with cycloheximide and MG132, and used RT-PCR to explore the mechanism underlying MTHFR targeting. We found that the effects of VD on AD were impaired by MTHFR knockdown through a pretranscriptional mechanism. In addition, VD attenuated AD-induced cognitive impairment and significantly suppressed the expression of TAU. Our findings indicated that VD treatment alleviated TAU accumulation and rescued methylated PP2A by increasing the expression of LCMT-1 and MTHFR.

Prophylactic effects of sporoderm-removed Ganoderma lucidum spores in a rat model of streptozotocin-induced sporadic Alzheimer's disease

ETHNOPHARMACOLOGICAL RELEVANCE

Ganoderma lucidum (G. lucidum, Lingzhi), also known as "immortality mushroom" has been broadly used to improve health and longevity for thousands of years in Asia. G. lucidum and its spores have been used to promote health, based on its broad pharmacological and therapeutic activity. This species is recorded in Chinese traditional formula as a nootropic and has been suggested to improve cognitive dysfunction in Alzheimer's disease. However, little is known about the nootropic effects and molecular mechanism of action of G. lucidum spores.

AIM OF THE STUDY

The present study investigated the protective effects of sporoderm-deficient Ganoderma lucidum spores (RGLS) against learning and memory impairments and its mechanism of action.

MATERIALS AND METHODS

In the Morris water maze, the effects of RGLS on learning and memory impairments were evaluated in a rat model of sporadic Alzheimer's disease that was induced by an intracerebroventricular injection of streptozotocin (STZ). Changes in amyloid β (Aβ) expression, Tau expression and phosphorylation, brain-derived neurotrophic factor (BDNF), and the BDNF receptor tropomyosin-related kinase B (TrkB) in the hippocampus were evaluated by Western blot.

RESULTS

Treatment with RGLS (360 and 720 mg/kg) significantly enhanced memory in the rat model of STZ-induced sporadic Alzheimer's disease and reversed the STZ-induced increases in Aβ expression and Tau protein expression and phosphorylation at Ser199, Ser202, and Ser396. The STZ-induced decreases in neurotrophic factors, including BDNF, TrkB and TrkB phosphorylation at Tyr816, were reversed by treatment with RGLS.

CONCLUSION

These findings indicate that RGLS prevented learning and memory impairments in the present rat model of STZ-induced sporadic Alzheimer's disease, and these effects depended on a decrease in Aβ expression and Tau hyperphosphorylation and the modulation of BDNF-TrkB signaling in the hippocampus.

STAT3 ameliorates cognitive deficits via regulation of NMDAR expression in an Alzheimer's disease animal model

Background: Abnormal tau accumulation in the brain has a positively correlation with neurodegeneration and memory deterioration, but the mechanism underlying tau-associated synaptic and cognitive impairments remains unclear. Our previous work has found that human full length tau (hTau) accumulation activated signal transducer and activator of transcription-1 (STAT1) to suppress N-methyl-D-aspartate receptors (NMDARs) expression, followed by memory deficits. STAT3 also belongs to STAT protein family and is reported to involve in regulation of synaptic plasticity and cognition. Here, we investigated the role of STAT3 in the cognitive deficits induced by hTau accumulation. Methods: In vitro studies HEK293 cells were used. EMSA, Luciferase reporter assay, and Immunoprecipitation were applied to detect STAT3 activity. In vivo studies, AAV virus were injected into the hippocampal CA3 region of C57 mice. Western blotting, quantitative real-time polymerase chain reaction, and immunofluorescence were applied to examine the level of synaptic proteins. Electrophysiological analysis, behavioral testing and Golgi impregnation were used to determine synaptic plasticity and memory ability recovery after overexpressing STAT3 or non-acetylated STAT1. Results: Our results showed that hTau accumulation acetylated STAT1 to retain STAT3 in the cytoplasm by increasing the binding of STAT1 with STAT3, and thus inactivated STAT3. Overexpressing STAT3 or non-acetylated STAT1 ameliorated hTau-induced synaptic loss and memory deficits by increasing the expression of NMDARs. Conclusions: Taken together, our study indicates that hTau accumulation impaired synaptic plasticity through STAT3 inactivation induced suppression of NMDARs expression, revealing a novel mechanism for hTau-associated synapse and memory deficits.

Sirtuin 3 protects against anesthesia/surgery-induced cognitive decline in aged mice by suppressing hippocampal neuroinflammation

BACKGROUND

Postoperative cognitive dysfunction (POCD) is a very common complication that might increase the morbidity and mortality of elderly patients after surgery. However, the mechanism of POCD remains largely unknown. The NAD-dependent deacetylase protein Sirtuin 3 (SIRT3) is located in the mitochondria and regulates mitochondrial function. SIRT3 is the only sirtuin that specifically plays a role in extending lifespan in humans and is associated with neurodegenerative diseases. Therefore, the aim of this study was to evaluate the effect of SIRT3 on anesthesia/surgery-induced cognitive impairment in aged mice.

METHODS

SIRT3 expression levels were decreased after surgery. For the interventional study, an adeno-associated virus (AAV)-SIRT3 vector or an empty vector was microinjected into hippocampal CA1 region before anesthesia/surgery. Western blotting, immunofluorescence staining, and enzyme-linked immune-sorbent assay (ELISA) were used to measure the oxidative stress response and downstream microglial activation and proinflammatory cytokines, and Golgi staining and long-term potentiation (LTP) recording were applied to evaluate synaptic plasticity.

RESULTS

Overexpression of SIRT3 in the CA1 region attenuated anesthesia/surgery-induced learning and memory dysfunction as well as synaptic plasticity dysfunction and the oxidative stress response (superoxide dismutase [SOD] and malondialdehyde [MDA]) in aged mice with POCD. In addition, microglia activation (ionized calcium binding adapter molecule 1 [Iba1]) and neuroinflammatory cytokine levels (tumor necrosis factor-alpha [TNF-α], interleukin [IL]-1β and IL-6) were regulated after anesthesia/surgery in a SIRT3-dependent manner.

CONCLUSION

The results of the current study demonstrate that SIRT3 has a critical effect in the mechanism of POCD in aged mice by suppressing hippocampal neuroinflammation and reveal that SIRT3 may be a promising therapeutic and diagnostic target for POCD.

Identification of new BACE1 inhibitors for treating Alzheimer's disease

Alzheimer's disease (AD) is a type of brain disorder, wherein a person experiences gradual memory loss, state of confusion, hallucination, agitation, and personality change. AD is marked by the presence of extracellular amyloid plaques and intracellular neurofibrillary tangles (NFTs) and synaptic losses. Increased cases of AD in recent times created a dire need to discover or identify chemical compounds that can cease the development of AD. This study focuses on finding potential drug molecule(s) active against β-secretase, also known as β-site amyloid precursor protein cleaving enzyme 1 (BACE1). Clustering analysis followed by phylogenetic studies on microarray datasets retrieved from GEO browser showed that BACE1 gene has genetic relatedness with the RCAN1 gene. A ligand library comprising 60 natural compounds retrieved from literature and 25 synthetic compounds collected from DrugBank were screened. Further, 350 analogues of potential parent compounds were added to the library for the docking purposes. Molecular docking studies identified 11-oxotigogenin as the best ligand molecule. The compound showed the binding affinity of - 11.1 Kcal/mole and forms three hydrogen bonds with Trp124, Ile174, and Arg176. The protein-ligand complex was subjected to 25 ns molecular dynamics simulation and the potential energy of the complex was found to be - 1.24579e+06 Kcal/mole. In this study, 11-oxotigogenin has shown promising results against BACE1, which is a leading cause of AD, hence warrants for in vitro and in vivo validation of the same. In addition, in silico identification of 11-oxotigogenin as a potential anti-AD compound paves the way for designing of chemical scaffolds to discover more potent BACE1 inhibitors.Graphical abstract.

Protein interactome of the Cancerous Inhibitor of protein phosphatase 2A (CIP2A) in Th17 cells

Cancerous inhibitor of protein phosphatase 2A (CIP2A) is involved in immune response, cancer progression, and Alzheimer's disease. However, an understanding of the mechanistic basis of its function in this wide spectrum of physiological and pathological processes is limited due to its poorly characterized interaction networks. Here we present the first systematic characterization of the CIP2A interactome by affinity-purification mass spectrometry combined with validation by selected reaction monitoring targeted mass spectrometry (SRM-MS) analysis in T helper (Th) 17 (Th17) cells. In addition to the known regulatory subunits of protein phosphatase 2A (PP2A), the catalytic subunits of protein PP2A were found to be interacting with CIP2A. Furthermore, the regulatory (PPP1R18, and PPP1R12A) and catalytic (PPP1CA) subunits of phosphatase PP1 were identified among the top novel CIP2A interactors. Evaluation of the ontologies associated with the proteins in this interactome revealed that they were linked with RNA metabolic processing and splicing, protein traffic, cytoskeleton regulation and ubiquitin-mediated protein degradation processes. Taken together, this network of protein-protein interactions will be important for understanding and further exploring the biological processes and mechanisms regulated by CIP2A both in physiological and pathological conditions.

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The first characterisation of the CIP2A interactome in Th17 ​cells.

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Key interactions validated by targeted SRM-MS proteomics, western blot and confocal microscopy.

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Pathway analysis of the interactome revealed interrelationships with proteins across a broad range of cellular processes.

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The study identifies for the first time the interaction of phosphatase PP1 with CIP2A.

Association of Genes Involved in the Metabolic Pathways of Amyloid-β and Tau Proteins With Sporadic Late-Onset Alzheimer's Disease in the Southern Han Chinese Population

The genes involved in the metabolic pathways of amyloid-β (Aβ) and tau proteins significantly influence the etiology of Alzheimer's disease (AD). Various studies have explored the associations between some of these genes and AD in the Caucasian population; however, researches regarding these associations remain limited in the Chinese population. To systematically evaluate the associations of these genes with AD, we investigated 19 genes involved in the metabolism of Aβ and tau based on previous studies selected using the PubMed database. This study included 372 patients with sporadic late-onset AD (sLOAD) and 345 cognitively healthy individuals from southern China. The results were replicated in the International Genomics of Alzheimer's Project (IGAP). Protein-protein interactions were determined using the STRING v11 database. We found that a single-nucleotide polymorphism, rs11682128, of BIN1 conferred susceptibility to sLOAD after adjusting for age, sex, and APOE ε4 status and performing the Bonferroni correction {corrected P = 0.000153, odds ratio (OR) [95% confidence interval (CI)] = 1.403 (1.079-1.824)}, which was replicated in the IGAP. Protein-protein interactions indicated that BIN1 was correlated with MAPT. Moreover, rare variants of NEP and FERMT2 (0.0026 < corrected P < 0.05), and the Aβ degradation, tau pathology, and tau phosphatase pathways (0.01 < corrected P < 0.05), were nominally significantly associated with sLOAD. This study suggested that the genes involved in the metabolic pathways of Aβ and tau contributed to the etiology of sLOAD in the southern Han Chinese population.

Polyphyllin I attenuates cognitive impairments and reduces AD-like pathology through CIP2A-PP2A signaling pathway in 3XTg-AD mice

Polyphyllin I (PPI) is a natural phytochemical drug isolated from plants which can inhibit the proliferation of cancer cells. One of the PPI tumor-inhibitory effects is through downregulating the expression of Cancerous Inhibitor of PP2A (CIP2A), the latter, is found upregulated in Alzheimer's disease (AD) brains and participates in the development of AD. In this study, we explored the application of PPI in experimental AD treatment in CIP2A-overexpressed cells and 3XTg-AD mice. In CIP2A-overexpressed HEK293 cells or primary neurons, PPI effectively reduced CIP2A level, activated PP2A, and decreased the phosphorylation of tau/APP and the level of Aβ. Furthermore, synaptic protein levels were restored by PPI in primary neurons overexpressing CIP2A. Animal experiments in 3XTg-AD mice revealed that PPI treatment resulted in decreased CIP2A expression and PP2A re-activation. With the modification of CIP2A-PP2A signaling, the hyperphosphorylation of tau/APP and Aβ overproduction were prevented, and the cognitive impairments of 3XTg-AD mice were rescued. In summary, PPI ameliorated AD-like pathology and cognitive impairment through modulating CIP2A-PP2A signaling pathway. It may be a potential drug candidate for the treatment of AD.

Small molecule therapeutics for tauopathy in Alzheimer's disease: Walking on the path of most resistance

Alzheimer's disease (AD) is the most common form of dementia characterized by presence of extracellular amyloid plaques and intracellular neurofibrillary tangles composed of tau protein. Currently there are close to 50 million people living with dementia and this figure is expected to increase to 75 million by 2030 putting a huge burden on the economy due to the health care cost. Considering the effects on quality of life of patients and the increasing burden on the economy, there is an enormous need of new disease modifying therapies to tackle this disease. The current therapies are dominated by only symptomatic treatments including cholinesterase inhibitors and N-methyl-D-aspartate receptor blockers but no disease modifying treatments exist so far. After several failed attempts to develop drugs against amyloidopathy, tau targeting approaches have been in the main focus of drug development against AD. After an overview of the tauopathy in AD, this review summarizes recent findings on the development of small molecules as therapeutics targeting tau modification, aggregation, and degradation, and tau-oriented multi-target directed ligands. Overall, this work aims to provide a comprehensive and critical overview of small molecules which are being explored as a lead candidate for discovering drugs against tauopathy in AD.

Tau-induced upregulation of C/EBPβ-TRPC1-SOCE signaling aggravates tauopathies: A vicious cycle in Alzheimer neurodegeneration

Intracellular accumulating of the hyperphosphorylated tau plays a pivotal role in neurodegeneration of Alzheimer disease (AD), but the mechanisms underlying the gradually aggravated tau hyperphosphorylation remain elusive. Here, we show that increasing intracellular tau could upregulate mRNA and protein levels of TRPC1 (transient receptor potential channel 1) with an activated store‐operated calcium entry (SOCE), an increased intraneuronal steady‐state [Ca²⁺]_i, an enhanced endoplasmic reticulum (ER) stress, an imbalanced protein kinases and phosphatase, and an aggravated tauopathy. Furthermore, overexpressing TRPC1 induced ER stress, kinases‐phosphatase imbalance, tau hyperphosphorylation and cognitive deficits in cultured neurons and mice, while pharmacological inhibiting or knockout TRPC1 attenuated the hTau‐induced deregulations in SOCE, ER homeostasis, kinases‐phosphatase balance, and tau phosphorylation level with improved synaptic and cognitive functions. Finally, an increased CCAAT‐enhancer‐binding protein (C/EBPβ) activity was observed in hTau‐overexpressing cells and the hippocampus of the AD patients, while downregulating C/EBPβ by siRNA abolished the hTau‐induced TRPC1 upregulation. These data reveal that increasing intracellular tau can upregulate C/EBPβ‐TRPC1‐SOCE signaling and thus disrupt phosphorylating system, which together aggravates tau pathologies leading to a chronic neurodegeneration.

High-frequency transcranial magnetic stimulation protects APP/PS1 mice against Alzheimer's disease progress by reducing APOE and enhancing autophagy

INTRODUCTION

The repetitive transcranial magnetic stimulation (rTMS) has clinically wide application prospect of psychiatry and neuroscience, for its painless, noninvasive, and high efficiency. So far, rTMS has been used in the treatment of Alzheimer's disease (AD) but the underlying mechanism is not clear.

METHODS AND RESULTS

The APP/PS1 mice at 3-month-old were treated by 5 Hz high-frequency (HF) rTMS for two weeks. After rTMS treatment, the AD-like cognitive impairments of APP/PS1 mice were investigated subsequently, and molecular mechanisms underlying was further explored. The study showed that the 2-week rTMS at 5Hz frequency improved cognitive impairments and AD-like pathology (including a decrease in p-Tau, APP, Aβ, and PP2A expression) of APP/PS1 mice. Although BDNF-TrkB signaling was significantly enhanced, no differences of SYN, PSD95 and p-AKT were observed in the brain of APP/PS1 mice. On the contrary, the LC3Ⅱ/LC3Ⅰ ratio was elevated with a significant reduction of ApoE and p62 in mice.

CONCLUSIONS

rTMS exerts a potentially protective role in the prevention and treatment of AD by reducing ApoE expression and promoting autophagic flux, which provides a new insight into the mechanism of rTMS.

Codonopsis pilosula polysaccharide attenuates Aβ toxicity and cognitive defects in APP/PS1 mice

Codonopsis pilosula Polysaccharides (CPPs), a traditional Chinese medicine used for thousands of years, is a potential neuroprotective polysaccharide via a relatively poorly understood mechanism. We previously reported that CPPs attenuated tau pathology in hTau transfected mice and therefore in the current work investigated the effect of CPPs on Aβ toxicity and cognitive defects in APP/PS1 mice model. It was found that one-month intragastric administration of CPPs significantly ameliorated cognitive defects in APP/PS1 mice. In addition, CPPs treatment mitigated the loss of the synaptic plasticity and increased the synaptic proteins including synaptotagmin and PSD95. The expression of Aβ42 and Aβ40 was remarkably decreased in the hippocampus of APP/PS1 mice after CPPs treatment. We also found that CPPs coincubation significantly reduced the amount of APPβ and Aβ42 expression in cells. Intriguingly, the activity of BACE1 was decreased following CPPs treatment in both the hippocampus of APP/PS1 mice and in vitro experiments. Collectively, these results indicated that CPPs attenuated Aβ pathology in APP/PS1 mice, and down-regulating BACE1 might be the underlaying mechanism which could be a therapeutic target for alleviating cognitive defects in AD pathology.