The Molecular Mechanism of Amyloid β42 Peptide Toxicity: The Role of Sphingosine Kinase-1 and Mitochondrial Sirtuins

Notoginsenoside R1 ameliorates the inflammation induced by amyloid‑β by suppressing SphK1‑mediated NF‑κB activation in PC12 cells

Alzheimer's disease (AD) is the most common type of age‑related dementia, and causes progressive memory degradation, neuronal loss and brain atrophy. The pathological hallmarks of AD consist of amyloid‑β (Aβ) plaque accumulation and abnormal neurofibrillary tangles. Amyloid fibrils are constructed from Aβ peptides, which are recognized to assemble into toxic oligomers and exert cytotoxicity. The fibrillar Aβ‑protein fragment 25‑35 (Aβ25‑35) induces local inflammation, thereby exacerbating neuronal apoptosis. Notoginsenoside R1 (NGR1), one of the primary bioactive ingredients isolated from Panax notoginseng, exhibits effective anti‑inflammatory and anti‑oxidative activities. However, NGR1 pharmacotherapies targeting Aβ‑induced inflammation and cell injury cascade remain to be elucidated. The present study investigated the effect and mechanism of NGR1 in Aβ25‑35‑treated PC12 cells. NGR1 doses between 250 and 1,000 µg/ml significantly increased cell viability suppressed by 20 µM Aβ25‑35 peptide treatment. Notably, the present study demonstrated that Aβ25‑35 peptide‑induced sphingosine kinase 1 (SphK1) signaling activation was reduced after NGR1 treatment, further inhibiting the downstream NF‑κB inflammatory signaling pathway. In addition, administration of SphK1 inhibitor II (SKI‑II), a SphK1 inhibitor, also significantly reduced Aβ25‑35 peptide‑induced apoptosis and the ratio of NF‑κB p‑p65/p65. Furthermore, SphK1 knockdown in PC12 cells using small interfering RNA alleviated Aβ‑induced cell apoptosis and inflammation, suggesting a pivotal role of SphK1 signaling in the anti‑inflammatory effect of NGR1. In summary, NGR1 alleviated inflammation and apoptosis stimulated by Aβ25‑35 by inhibiting the SphK1/NF‑κB signaling pathway and may be a promising agent for future AD treatment.

Inhibiting mtDNA-STING-NLRP3/IL-1β axis-mediated neutrophil infiltration protects neurons in Alzheimer's disease

Neutrophil is a pathophysiological character in Alzheimer's disease. The pathogen for neutrophil activation in cerebral tissue is the accumulated amyloid protein. In our present study, neutrophils infiltrate into the cerebra in two models (transgenic model APP/PS1 and stereotactic injection model) and promote neuron apoptosis, releasing their cellular constituents, including mitochondria and mitochondrial DNA (mtDNA). We found that both Aβ1-42 and mtDNA could provoke neutrophil infiltration into the cerebra, and they had synergistic effects when they presented together. This neutrophillic neuroinflammation upregulates expressions of STING, NLRP3 and IL-1β. These inflammatory cytokines with mtDNA constitute the mtDNA-STING-NLRP3/IL-1β axis, which is the prerequisite for neutrophil infiltration. When any factor in this pathway is depleted, the migration of neutrophils into cerebral tissue is ceased, with neurons and cognitive function being protected. Thus, we provide a novel perspective to alleviate the progression of Alzheimer's disease.

Melatonin as a Harmonizing Factor of Circadian Rhythms, Neuronal Cell Cycle and Neurogenesis: Additional Arguments for Its Therapeutic Use in Alzheimer's Disease

The synthesis and release of melatonin in the brain harmonize various physiological functions. The apparent decline in melatonin levels with advanced aging is an aperture to the neurodegenerative processes. It has been indicated that down regulation of melatonin leads to alterations of circadian rhythm components, which further causes a desynchronization of several genes and results in an increased susceptibility to develop neurodegenerative diseases. Additionally, as circadian rhythms and memory are intertwined, such rhythmic disturbances influence memory formation and recall. Besides, cell cycle events exhibit a remarkable oscillatory system, which is downstream of the circadian phenomena. The linkage between the molecular machinery of the cell cycle and complex fundamental regulatory proteins emphasizes the conjectural regulatory role of cell cycle components in neurodegenerative disorders such as Alzheimer's disease. Among the mechanisms intervening long before the signs of the disease appear, the disturbances of the circadian cycle, as well as the alteration of the machinery of the cell cycle and impaired neurogenesis, must hold our interest. Therefore, in the present review, we propose to discuss the underlying mechanisms of action of melatonin in regulating the circadian rhythm, cell cycle components and adult neurogenesis in the context of AD pathogenesis with the view that it might further assist to identify new therapeutic targets.

The Role of Mitochondrial Genes in Neurodegenerative Disorders

Mitochondrial disorders are clinically heterogeneous, resulting from nuclear gene and mitochondrial mutations that disturb the mitochondrial functions and dynamics. There is a lack of evidence linking mtDNA mutations to neurodegenerative disorders, mainly due to the absence of noticeable neuropathological lesions in postmortem samples. This review describes various gene mutations in Alzheimer's disease, Parkinson's disease, amyotrophic lateral sclerosis, multiple sclerosis, and stroke. These abnormalities, including PINK1, Parkin, and SOD1 mutations, seem to reveal mitochondrial dysfunctions due to either mtDNA mutation or deletion, the mechanism of which remains unclear in depth.

Serum Glycoproteomics and Identification of Potential Mechanisms Underlying Alzheimer’s Disease

Objectives. This study compares glycoproteomes in Thai Alzheimer’s disease (AD) patients with those of cognitively normal individuals. Methods. Study participants included outpatients with clinically diagnosed AD ( $N=136$ ) and healthy controls without cognitive impairment ( $N=183$ ). Blood samples were collected from all participants for biochemical analysis and for $\text{Apolipoprotein}\text{E}$ (APOE) genotyping by real-time TaqMan PCR assays. Comparative serum glycoproteomic profiling by liquid chromatography-tandem mass spectrometry was then performed to identify differentially abundant proteins with functional relevance. Results. Statistical differences in age, educational level, and APOE ɛ3/ɛ4 and ɛ4/ɛ4 haplotype frequencies were found between the AD and control groups. The frequency of the APOE ɛ4 allele was significantly higher in the AD group than in the control group. In total, 871 glycoproteins were identified, including 266 and 259 unique proteins in control and AD groups, respectively. There were 49 and 297 upregulated and downregulated glycoproteins, respectively, in AD samples compared with the controls. Unique AD glycoproteins were associated with numerous pathways, including Alzheimer’s disease-presenilin pathway (16.6%), inflammation pathway mediated by chemokine and cytokine signaling (9.2%), Wnt signaling pathway (8.2%), and apoptosis signaling pathway (6.7%). Conclusion. Functions and pathways associated with protein-protein interactions were identified in AD. Significant changes in these proteins can indicate the molecular mechanisms involved in the pathogenesis of AD, and they have the potential to serve as AD biomarkers. Such findings could allow us to better understand AD pathology.

Quercetin inhibited the proliferation and invasion of hepatoblastoma cells through facilitating SIRT6-medicated FZD4 silence

Hepatoblastoma (HB) is a malignant liver tumor that occurs during childhood. The histone deacetylase SIRT6 functions as a tumor suppressor in diverse cancers. Quercetin, as activators and antioxidants of sirtuins, exhibits remarkable anticancer activity in many tumors. However, whether quercetin ameliorates HB is still unclear. In our study, we found that SIRT6 was downregulated in HB tissues and cell lines. Overexpression of SIRT6 observably suppressed cell proliferation and invasion, promoted cell apoptosis. Mechanistically, SIRT6 suppressed frizzled 4 (FZD4) transcription by deacetylating histone H3K9. Upregulation of SIRT6 reduced the protein levels of FZD4 and H3K9ac. Additionally, quercetin treatment could enhance the expression of SIRT6, repress FZD4 level, cell viability and invasion, and promote apoptosis. Overexpression of FZD4 signally reversed quercetin-treated the promotion effect on cell apoptosis, and the inhibition effects on FZD4 expression, cell viability, invasion and Wnt/β-catenin pathway related proteins. In addition, LiCl, an agonist of Wnt/β-catenin pathway, could recover the inhibition effects of quercetin on Wnt/β-catenin pathway related proteins, cell viability and invasion, and promotion effect on cell apoptosis. In vivo mouse xenograft tumor growth assay revealed that quercetin markedly suppressed tumor growth. In conclusion, these results demonstrated that the molecular mechanism of quercetin suppressing HB cell proliferation and invasion, promoting apoptosis was to promote the deacetylation of SIRT6 on FZD4 and inhibit the activation of Wnt/β-catenin pathway.

Mitochondrial SIRT3 confers neuroprotection in Huntington's disease by regulation of oxidative challenges and mitochondrial dynamics

SIRT3 is a major regulator of mitochondrial acetylome. Here we show that SIRT3 is neuroprotective in Huntington's disease (HD), a motor neurodegenerative disorder caused by an abnormal expansion of polyglutamines in the huntingtin protein (HTT). Protein and enzymatic analysis revealed that increased SIRT3 is a signature in several HD models, including human HD brain, which is regulated by oxidative species. While loss of SIRT3 further aggravated the oxidative phenotype, antioxidant treatment regularized SIRT3 levels. SIRT3 overexpression promoted the antioxidant effect in cells expressing mutant HTT, leading to enhanced mitochondrial function and balanced dynamics. Decreased Fis1 and Drp1 accumulation in mitochondria induced by SIRT3 expression favored mitochondrial elongation, while the SIRT3 activator ε-viniferin improved anterograde mitochondrial neurite transport, sustaining cell survival. Notably, SIRT3 fly-ortholog dSirt2 overexpression in HD flies ameliorated neurodegeneration and extended lifespan. These findings provide a link between oxidative stress and mitochondrial dysfunction hypotheses in HD and offer an opportunity for therapeutic development.

Sirtuins and Their Implications in Neurodegenerative Diseases from a Drug Discovery Perspective

Sirtuins are class III histone deacetylase (HDAC) enzymes that target both histone and non-histone substrates. They are linked to different brain functions and the regulation of different isoforms of these enzymes is touted to be an emerging therapy for the treatment of neurodegenerative diseases (NDs), including Parkinson's disease (PD), Alzheimer's disease (AD), and amyotrophic lateral sclerosis (ALS). The level of sirtuins affects brain health as many sirtuin-regulated pathways are responsible for the progression of NDs. Certain sirtuins are also implicated in aging, which is a risk factor for many NDs. In addition to SIRT1-3, it has been suggested that the less studied sirtuins (SIRT4-7) also play critical roles in brain health. This review delineates the role of each sirtuin isoform in NDs from a disease centric perspective and provides an up-to-date overview of sirtuin modulators and their potential use as therapeutics in these diseases. Furthermore, the future perspectives for sirtuin modulator development and their therapeutic application in neurodegeneration are outlined in detail, hence providing a research direction for future studies.

Up-regulation of miRNA-151-3p enhanced the neuroprotective effect of dexmedetomidine against β-amyloid by targeting DAPK-1 and TP53

Alzheimer's disease (AD) is the most common cause of dementia and is the leading lethal disease among the elderly. Dexmedetomidine (Dex) has been reported to have multiple neuroprotective effects, but its effect against beta-amyloid (Aβ) has not been completely determined and understood. Dex can activate both α2 adrenoceptor/cAMP/PKA and imidazoline I receptors/ERK1/2 signals. To determine which signal is critical for the effect of Dex on Aβ toxicity, we treated SH-SY5Y and PC12 cells with inhibitors of α2 adrenoceptor and ERK1/2. Dex suppressed the apoptosis of neuronal cells and production of reactive oxygen species induced by Aβ. These suppressive effects were attenuated by both inhibitors. As indicated by western blot, Dex stimulates both pro-apoptosis (activating death-associated protein kinase 1 [DAPK-1] and p53) and anti-apoptotic (up-regulating bcl-2 and bcl-xL) signals in Aβ-treated neuronal cells. This effect is likely associated with ERK1/2 signaling because ERK1/2 inhibitor disrupts the effect of Dex on these signals. To eliminate the pro-apoptotic effect of Dex while retaining its anti-apoptosis action, we screened miRNA-151-3p to target DAPK-1 and p53. Transfection with miRNA-151-3p mimics suppressed DAPK-1 and TP53 expression induced by Dex and increased Nrf-2 and SOD expression. More importantly, increasing miRNA-151-3p enhanced the anti-apoptotic and antioxidative effects of Dex in Aβ-treated neuronal cells. Overall, this study revealed that Dex additionally stimulated pro-apoptosis signaling, although it suppressed Aβ-induced apoptosis of neuronal cells. miRNA-151-3p enhanced the neuroprotective effect of Dex against Aβ by targeting DAPK-1 and TP53.

Decoding the proteome of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) for cell-penetrating peptides involved in pathogenesis or applicable as drug delivery vectors

Synthetic or natural derived cell-penetrating peptides (CPPs) are vastly investigated as tools for the intracellular delivery of membrane-impermeable molecules. As viruses are intracellular obligate parasites, viral originated CPPs have been considered as suitable intracellular shuttling vectors for cargo transportation. A total of 310 CPPs were identified in the proteome of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Screening the proteome of the cause of COVID-19 reveals that SARS-CoV-2 CPPs (SCV2-CPPs) span the regions involved in replication, protein-nucleotide and protein-protein interaction, protein-metal ion interaction, and stabilization of homo/hetero-oligomers. However, to find the most appropriate peptides as drug delivery vectors, one might face several hurdles. Computational analyses showed that 94.3% of the identified SCV2-CPPs are non-toxins, and 38% are neither antigenic nor allergenic. Interestingly, 36.70% of SCV2-CPPs were resistant to all four groups of protease families. Nearly 1/3 of SCV2-CPPs had sufficient inherent or induced helix and sheet conformation leading to increased uptake efficiency. Heliquest lipid-binding discrimination factor revealed that 44.30% of the helical SCV2-CPPs are lipid-binding helices. Although Cys-rich derived CPPs of helicase (NSP13) can potentially fold into a cyclic conformation in endosomes with a higher rate of endosomal release, the most optimal SCV2-CPP candidates as vectors for drug delivery were SCV2-CPP118, SCV2-CPP119, SCV2-CPP122, and SCV2-CPP129 of NSP12 (RdRp). Ten experimentally validated viral-derived CPPs were also used as the positive control to check the scalability and reliability of our protocol in SCV2-CPP retrieval. Some peptides with a cell-penetration ability known as bioactive peptides are adopted as biotherapeutics themselves. Therefore, 59.60%, 29.63%, and 32.32% of SCV2-CPPs were identified as potential antibacterial, antiviral, and antifungals, respectively. While 63.64% of SCV2-CPPs had immuno-modulatory properties, 21.89% were recognized as anti-cancers. Conclusively, the workflow of this study provides a platform for profound screening of viral proteomes as a rich source of biotherapeutics or drug delivery carriers.

Sirtuin 3 mRNA Expression is Downregulated in the Brain Tissues of Alzheimer's Disease Patients: A Bioinformatic and Data Mining Approach

Background

Emerging experimental evidence has shown that sirtuin 3 (SIRT3), which is a class III histone deacetylase, participates in the pathological process of Alzheimer’s disease (AD). However, data mining of current gene expression databases, such as Gene Expression Omnibus (GEO), has not been previously performed to determine whether SIRT3 expression is upregulated or downregulated in the brain tissues of AD patients.

Material/Methods

Eight RNA expression chip datasets of AD brains in the GEO database were selected, and GEO2R analysis was conducted to identify the differentially expressed genes (DEGs) between the AD and control groups. Furthermore, the SIRT3 mRNA levels between the AD and control groups and their relationships with the DEGs and diagnosis of AD were evaluated. Finally, Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) analyses of both the AD-related DEGs and the SIRT3-related DEGs were conducted.

Results

The SIRT3 mRNA levels were downregulated in 7 of 8 databases and were related to the diagnosis of AD in 7 databases, with an area under the curve (AUC) of the receiver operating characteristic curve (ROC curve) greater than 50%. Additionally, GO and KEGG analyses showed that SIRT3 downregulation could affect neuroactive ligand-receptor interactions, the MAPK signaling pathway, long-term potentiation, the calcium signaling pathway and axon guidance in AD patients.

Conclusions

SIRT3 mRNA is downregulated in the brain tissues of AD patients, promoting the progression of AD.

MAP/ERK Signaling in Developing Cognitive and Emotional Function and Its Effect on Pathological and Neurodegenerative Processes

The signaling pathway of the microtubule-associated protein kinase or extracellular regulated kinase (MAPK/ERK) is a common mechanism of extracellular information transduction from extracellular stimuli to the intracellular space. The transduction of information leads to changes in the ongoing metabolic pathways and the modification of gene expression patterns. In the central nervous system, ERK is expressed ubiquitously, both temporally and spatially. As for the temporal ubiquity, this signaling system participates in three key moments: (i) Embryonic development; (ii) the early postnatal period; and iii) adulthood. During embryonic development, the system is partly responsible for the patterning of segmentation in the encephalic vesicle through the FGF8-ERK pathway. In addition, during this period, ERK directs neurogenesis migration and the final fate of neural progenitors. During the early postnatal period, ERK participates in the maturation process of dendritic trees and synaptogenesis. During adulthood, ERK participates in social and emotional behavior and memory processes, including long-term potentiation. Alterations in mechanisms related to ERK are associated with different pathological outcomes. Genetic alterations in any component of the ERK pathway result in pathologies associated with neural crest derivatives and mental dysfunctions associated with autism spectrum disorders. The MAP-ERK pathway is a key element of the neuroinflammatory pathway triggered by glial cells during the development of neurodegenerative diseases, such as Parkinson's and Alzheimer's disease, Huntington's disease, and amyotrophic lateral sclerosis, as well as prionic diseases. The process triggered by MAPK/ERK activation depends on the stage of development (mature or senescence), the type of cellular element in which the pathway is activated, and the anatomic neural structure. However, extensive gaps exist with regards to the targets of the phosphorylated ERK in many of these processes.

Histidyl-Proline Diketopiperazine Isomers as Multipotent Anti-Alzheimer Drug Candidates

Cyclic dipeptides administered by both parenteral and oral routes are suggested as promising candidates for the treatment of neurodegeneration-related pathologies. In this study, we tested Cyclo (His-Pro) isomers (cHP1-4) for their anti-Alzheimer potential using a differentiated human neuroblastoma cell line (SH-SY5Y) as an Alzheimer’s disease (AD) experimental model. The SH-SY5Y cell line was differentiated by the application of all-trans retinoic acid (RA) to obtain mature neuron-like cells. Amyloid-beta 1-42 (Aβ_1-42) peptides, the main effector in AD, were administered to the differentiated cell cultures to constitute the in vitro disease model. Next, we performed cell viability analyses 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) and lactate dehydrogenase (LDH) release assays) to investigate the neuroprotective concentrations of cyclodipeptides using the in vitro AD model. We evaluated acetylcholinesterase (AChE), α- and β-secretase activities (TACE and BACE1), antioxidant potency, and apoptotic/necrotic properties and performed global gene expression analysis to understand the main mechanism behind the neuroprotective features of cHP1-4. Moreover, we conducted sister chromatid exchange (SCE), micronucleus (MN), and 8-hydroxy-2′-deoxyguanosine (8-OHdG) analyses to evaluate the genotoxic damage potential after applications with cHP1-4 on cultured human lymphocytes. Our results revealed that cHP1-4 isomers provide a different degree of neuroprotection against Aβ_1-42-induced cell death on the in vitro AD model. The applications with cHP1-4 isomers altered the activity of AChE but not the activity of TACE and BACE1. Our analysis indicated that the cHP1-4 increased the total antioxidant capacity without altering total oxidative status levels in the cellular AD model and that cHP1-4 modulated the alterations of gene expressions by Aβ_1-42 exposure. We also observed that cHP1-4 exhibited noncytotoxic and non-genotoxic features in cultured human whole blood cells. In conclusion, cHP1-4 isomers, especially cHP4, have been explored as novel promising therapeutics against AD.

Silent Mating-Type Information Regulation 2 Homolog 1 Attenuates the Neurotoxicity Associated with Alzheimer Disease via a Mechanism Which May Involve Regulation of Peroxisome Proliferator-Activated Receptor Gamma Coactivator 1-α

To investigate the neuroprotective role of silent mating-type information regulation 2 homolog 1 (SIRT1) in Alzheimer disease (AD), brain tissues from patients with AD and APP/PS1 mice as well as primary rat neurons exposed to oligomers of amyloid-β peptide were examined. The animals were treated with resveratrol (RSV) or suramin for 2 months. Cell cultures were treated with RSV, suramin, and the peroxisome proliferator-activated receptor gamma coactivator 1-α (PGC-1α) stimulator ZLN005. Cells were transiently transfected with PGC-1α silencing RNA. The level of SIRT1 in brain tissues from patients with AD and APP/PS1 mice, including nuclear and mitochondrial proteins, as well as in primary neurons exposed to oligomers of amyloid-β peptide, was decreased. Overexpression of APP/PS1 impaired learning and memory of mice; produced more senile plaques, disrupted membranes, and resulted in broken or absent cristae of mitochondria in the brain; decreased levels of A disintegrin and metallopeptidase domain 10, beta-secretase 2, 8-oxoguanine DNA glycosylase-1, PGC-1α, and NAD+; and increased levels of beta-secretase 1 and apoptosis. Interestingly, these changes were attenuated significantly by RSV treatment but enhanced by suramin administration. By activating PGC-1α but inhibiting SIRT1, apoptotic cell death was significantly decreased; however, by activating SIRT1 but inhibiting PGC-1α with small interfering PGC-1α, these levels remained unchanged. These findings indicate that SIRT1 may protect against AD-associated neurotoxicity, which might involve PGC-1α regulation.

Alterations of Transcription of Genes Coding Anti-oxidative and Mitochondria-Related Proteins in Amyloid β Toxicity: Relevance to Alzheimer's Disease

A growing body of evidence indicates that pathological forms of amyloid beta (Aβ) peptide contribute to neuronal degeneration and synaptic loss in Alzheimer's disease (AD). In this study, we investigated the impact of exogenous Aβ1-42 oligomers (AβO) and endogenously liberated Aβ peptides on transcription of genes for anti-oxidative and mitochondria-related proteins in cell lines (neuronal SH-SY5Y and microglial BV2) and in brain cortex of transgenic AD (Tg-AD) mice, respectively. Our results demonstrated significant AβO-evoked changes in transcription of genes in SH-SY5Y cells, where AβO enhanced expression of Sod1, Cat, mt-Nd1, Bcl2, and attenuated Sirt5, Sod2 and Sdha. In BV2 line, AβO increased the level of mRNA for Sod2, Dnm1l, Bcl2, and decreased for Gpx4, Sirt1, Sirt3, mt-Nd1, Sdha and Mfn2. Then, AβO enhanced free radicals level and impaired mitochondrial membrane potential only in SH-SY5Y cells, but reduced viability of both cell types. Inhibitor of poly(ADP-ribose)polymerase-1 and activator of sirtuin-1 more efficiently enhanced viability of SH-SY5Y than BV2 affected by AβO. Analysis of brain cortex of Tg-AD mice confirmed significant downregulation of Sirt1, Mfn1 and mt-Nd1 and upregulation of Dnm1l. In human AD brain, changes of microRNA pattern (miRNA-9, miRNA-34a, miRNA-146a and miRNA-155) seem to be responsible for decrease in Sirt1 expression. Overall, our results demonstrated a diverse response of neuronal and microglial cells to AβO toxicity. Alterations of genes encoding Sirt1, Mfn1 and Drp1 in an experimental model of AD suggest that modulation of mitochondria dynamics and Sirt1, including miRNA strategy, may be crucial for improvement of AD therapy.

S1PR2 antagonist ameliorate high glucose-induced fission and dysfunction of mitochondria in HRGECs via regulating ROCK1

Aims

Sphingosine-1-phosphate receptor 2 (S1PR2) is a G-protein-coupled receptor that regulates sphingosine-1-phosphate-triggered cellular response. However, the role of S1PR2 in diabetes-induced glomerular endothelial cell dysfunction remains unclear. This study aims to investigate the effect of S1PR2 blockade on the morphology and function of mitochondria in human renal glomerular endothelial cells (HRGECs).

Methods

HRGECs were pretreated with a S1PR2 antagonist (JTE-013) or a Rho-associated coiled coil-containing protein kinase 1 (ROCK1) inhibitor (Y27632) for 30 min and then cultured with normal glucose (5.5 mM) or high glucose (30 mM) for 72 h. The protein expression levels of RhoA, ROCK1, and Dynmin-related protein-1(Drp1) were evaluated by immunoblotting; mitochondrial morphology was observed by electron microscopy; intracellular levels of ATP, ROS, and Ca²⁺ were measured by ATPlite, DCF-DA, and Rhod-2 AM assays, respectively. Additionally, the permeability, apoptosis, and migration of cells were determined to evaluate the effects of S1PR2 and ROCK1 inhibition on high glucose-induced endothelial dysfunction.

Results

High glucose induced mitochondrial fission and dysfunction, indicated by increased mitochondrial fragmentation, ROS generation, and calcium overload but decreased ATP production. High glucose also induced endothelial cell dysfunction, indicated by increased permeability and apoptosis but decreased migration. However, inhibition of either S1PR2 or ROCK1 almost completely blocked these high glucose-mediated cellular responses. Furthermore, inhibiting S1PR2 resulted in the deceased expression of RhoA, ROCK1, and Drp1 while inhibiting ROCK1 led to the downregulated expression of Drp1.

Conclusions

S1PR2 antagonist modulates the morphology and function of mitochondria in HRGECs via the positive regulation of the RhoA/ROCK1/Drp1 signaling pathway, suggesting that the S1PR2/ROCK1 pathway may play a crucial role in high glucose milieu.

Electronic supplementary material

The online version of this article (10.1186/s12882-019-1323-0) contains supplementary material, which is available to authorized users.

Sirtuins in Alzheimer's Disease: SIRT2-Related GenoPhenotypes and Implications for PharmacoEpiGenetics

Sirtuins (SIRT1-7) are NAD⁺-dependent protein deacetylases/ADP ribosyltransferases with important roles in chromatin silencing, cell cycle regulation, cellular differentiation, cellular stress response, metabolism and aging. Sirtuins are components of the epigenetic machinery, which is disturbed in Alzheimer’s disease (AD), contributing to AD pathogenesis. There is an association between the SIRT2-C/T genotype (rs10410544) (50.92%) and AD susceptibility in the APOEε4-negative population (SIRT2-C/C, 34.72%; SIRT2-T/T 14.36%). The integration of SIRT2 and APOE variants in bigenic clusters yields 18 haplotypes. The 5 most frequent bigenic genotypes in AD are 33CT (27.81%), 33CC (21.36%), 34CT (15.29%), 34CC (9.76%) and 33TT (7.18%). There is an accumulation of APOE-3/4 and APOE-4/4 carriers in SIRT2-T/T > SIRT2-C/T > SIRT2-C/C carriers, and also of SIRT2-T/T and SIRT2-C/T carriers in patients who harbor the APOE-4/4 genotype. SIRT2 variants influence biochemical, hematological, metabolic and cardiovascular phenotypes, and modestly affect the pharmacoepigenetic outcome in AD. SIRT2-C/T carriers are the best responders, SIRT2-T/T carriers show an intermediate pattern, and SIRT2-C/C carriers are the worst responders to a multifactorial treatment. In APOE-SIRT2 bigenic clusters, 33CC carriers respond better than 33TT and 34CT carriers, whereas 24CC and 44CC carriers behave as the worst responders. CYP2D6 extensive metabolizers (EM) are the best responders, poor metabolizers (PM) are the worst responders, and ultra-rapid metabolizers (UM) tend to be better responders that intermediate metabolizers (IM). In association with CYP2D6 genophenotypes, SIRT2-C/T-EMs are the best responders. Some Sirtuin modulators might be potential candidates for AD treatment.

Synthetic Fragments of Receptor for Advanced Glycation End Products Bind Beta-Amyloid 1-40 and Protect Primary Brain Cells From Beta-Amyloid Toxicity

Receptor for advanced glycation end products (RAGE) is involved in the pathogenesis of Alzheimer's disease. We have previously revealed that RAGE fragment sequence (60-76) and its shortened analogs sequence (60-70) and (60-65) under intranasal insertion were able to restore memory and improve morphological and biochemical state of neurons in the brain of bulbectomized mice developing major AD features. In the current study, we have investigated the ability of RAGE peptide (60-76) and five shortened analogs to bind beta-amyloid (Aβ) 1-40 in an fluorescent titration test and show that all the RAGE fragments apart from one [sequence (65-76)] were able to bind Aβ in vitro. Moreover, we show that all RAGE fragments apart from the shortest one (60-62), were able to protect neuronal primary cultures from amyloid toxicity, by preventing the caspase 3 activation induced by Aβ 1-42. We have compared the data obtained in the present research with the previously published data in the animal model of AD, and offer a probable mechanism of neuroprotection of the RAGE peptide.

Neuronal sphingosine kinase 2 subcellular localization is altered in Alzheimer's disease brain

Background

Alzheimer’s disease (AD) is characterized by the accumulation of β-amyloid (Aβ) peptides and hyperphosphorylated tau protein accompanied by neuronal loss. Aβ accumulation has been associated with an impaired sphingosine 1-phosphate (S1P) metabolism. S1P is generated by sphingosine kinases (SphKs), of which there are two isoenzymes SphK1 and SphK2, and degraded by the sphingosine 1-phosphate lyase (SPL). We previously reported, that both a decrease in SphK1 expression and an increase in SPL expression, correlated with amyloid deposits in the entorhinal cortex of AD brains, suggesting a global loss of pro-survival S1P in AD neurons. SphK2 contribution has also been examined in AD yielding to conflicting results that may reflect the complexity of SphK2 regulation. The subcellular localization of SphK2, hence the compartmentalization of generated S1P, is recognized to play a crucial role in dictating either its pro-survival or pro-apoptotic functions. We therefore aimed at studying the expression of SphK2 and notably its subcellular localization in brain tissues from patients with AD.

Results

We report that a decrease in SphK2 protein cytosolic expression correlated with the density of amyloid deposits in a cohort of 25 post-mortem brains. Interestingly, we observed that the equilibrium between cytoplasmic and nuclear SphK2 is disrupted and showed that SphK2 is preferentially localized in the nucleus in AD brain extracts as compared to control extracts, with a marked increase of cleaved SphK2.

Conclusions

Our results suggest that a shift in the subcellular localization of the S1P generating SphK2 may compromise the well established pro-survival cytosolic S1P by favoring the production of nuclear S1P associated with adverse effects in AD pathogenesis.

Electronic supplementary material

The online version of this article (10.1186/s40478-018-0527-z) contains supplementary material, which is available to authorized users.

Inhibition of cyclin-dependent kinase 5 affects early neuroinflammatory signalling in murine model of amyloid beta toxicity

BACKGROUND

Cyclin-dependent kinase 5 (Cdk5) belongs to the family of proline-directed serine/threonine kinases and plays a critical role in neuronal differentiation, migration, synaptogenesis, plasticity, neurotransmission and apoptosis. The deregulation of Cdk5 activity was observed in post mortem analysis of brain tissue of Alzheimer's disease (AD) patients, suggesting the involvement of Cdk5 in the pathomechanism of this neurodegenerative disease. However, our recent study demonstrated the important function of Cdk5 in regulating inflammatory reaction.

METHODS

Since the role of Cdk5 in regulation of inflammatory signalling in AD is unknown, we investigated the involvement of Cdk5 in neuroinflammation induced by single intracerebroventricular (icv) injection of amyloid beta protein (Aβ) oligomers in mouse. The brain tissue was analysed up to 35 days post injection. Roscovitine (intraperitoneal administration) was used as a potent Cdk5 inhibitor. The experiments were also performed on human neuroblastoma SH-SY5Y as well as mouse BV2 cell lines treated with exogenous oligomeric Aβ.

RESULTS

Our results demonstrated that single injection of Aβ oligomers induces long-lasting activation of microglia and astrocytes in the hippocampus. We observed also profound, early inflammatory response in the mice hippocampus, leading to the significant elevation of pro-inflammatory cytokines expression (e.g. TNF-α, IL-1β, IL-6). Moreover, Aβ oligomers elevated the formation of truncated protein p25 in mouse hippocampus and induced overactivation of Cdk5 in neuronal cells. Importantly, administration of roscovitine reduced the inflammatory processes evoked by Aβ in the hippocampus, leading to the significant decrease of cytokines level.

CONCLUSIONS

These studies clearly show the involvement of Cdk5 in modulation of brain inflammatory response induced by Aβ and may indicate this kinase as a novel target for pharmacological intervention in AD.

Alpha-synuclein alters differently gene expression of Sirts, PARPs and other stress response proteins: implications for neurodegenerative disorders

Alpha-synuclein (ASN) is a presynaptic protein that can easily change its conformation under different types of stress. It's assumed that ASN plays an important role in the pathogenesis of Parkinson's and Alzheimer's disease. However, the molecular mechanism of ASN toxicity has not been elucidated. This study focused on the role of extracellular ASN (eASN) in regulation of transcription of sirtuins (Sirts) and DNA-bound poly(ADP-ribose) polymerases (PARPs) - proteins crucial for cells' survival/death. Our results indicate that eASN enhanced the free radicals level, decreased mitochondria membrane potential, cells viability and activated cells' death. Concomitantly eASN activated expression of antioxidative proteins (Sod2, Gpx4, Gadd45b) and DNA-bound Parp2 and Parp3. Moreover, eASN upregulated expression of Sirt3 and Sirt5, but downregulated of Sirt1, which plays an important role in cell metabolism including Aβ precursor protein (APP) processing. eASN downregulated gene expression of APP alpha secretase (Adam10) and metalloproteinases Mmp2, Mmp10 but upregulated Mmp11. Additionally, expression and activity of pro-survival sphingosine kinase 1 (Sphk1), Akt kinase and anti-apoptotic protein Bcl2 were inhibited. Moreover, higher expression of pro-apoptotic protein Bax and enhancement of apoptotic cells' death were observed. Summarizing, eASN significantly modulates transcription of Sirts and enzymes involved in APP/Aβ metabolism and through these mechanisms eASN toxicity may be enhanced. The inhibition of Sphk1 and Akt by eASN may lead to disturbances of survival pathways. These results suggest that eASN through alteration of transcription and by inhibition of pro-survival kinases may play important pathogenic role in neurodegenerative disorders.

Inhibition of poly(ADP-ribose) polymerase-1 alters expression of mitochondria-related genes in PC12 cells: relevance to mitochondrial homeostasis in neurodegenerative disorders

Alzheimer's disease (AD) is characterized by the release of amyloid beta peptides (Aβ) in the form of monomers/oligomers which may lead to oxidative stress, mitochondria dysfunction, synaptic loss, neuroinflammation and, in consequence, to overactivation of poly(ADP-ribose) polymerase-1 (PARP-1). However, Aβ peptides are also released in the brain ischemia, traumatic injury and in inflammatory response. PARP-1 is suggested to be a promising target in therapy of neurodegenerative disorders. We investigated the impact of PARP-1 inhibition on transcription of mitochondria-related genes in PC12 cells. Moreover, the effect of PARP-1 inhibitor (PJ34) on cells subjected to Aβ oligomers (AβO) - evoked stress was analyzed. Our data demonstrated that inhibition of PARP-1 in PC12 cells enhanced the transcription of genes for antioxidative enzymes (Sod1, Gpx1, Gpx4), activated genes regulating mitochondrial fission/fusion (Mfn1, Mfn2, Dnm1l, Opa1, Fis1), subunits of ETC complexes (mt-Nd1, Sdha, mt-Cytb) and modulated expression of several TFs, enhanced Foxo1 and decreased Nrf1, Stat6, Nfkb1. AβO elevated free radicals concentration, decreased mitochondria membrane potential (MMP) and cell viability after 24h. Gene transcription was not affected by AβO after 24h, but was significantly downregulated after 96h. In AβO stress, PJ34 exerted stimulatory effect on expression of several genes (Gpx1, Gpx4, Opa1, Mfn2, Fis1 and Sdha), decreased transcription of numerous TFs (Nrf1, Tfam, Stat3, Stat6, Trp53, Nfkb1) and prevented oxidative stress. Our results indicated that PARP-1 inhibition significantly enhanced transcription of genes involved in antioxidative defense and in regulation of mitochondria function, but was not able to ameliorate cells viability affected by Aβ.

Resveratrol activation of AMPK-dependent pathways is neuroprotective in human neural stem cells against amyloid-beta-induced inflammation and oxidative stress

Alzheimer's disease (AD) is a neurodegenerative disorder with progressive memory loss resulting in dementia. Amyloid-beta (Aβ) peptides play a critical role in the pathogenesis of this disease, and are thought to promote inflammation and oxidative stress leading to neurodegeneration in the neocortex and hippocampus of the AD brains. AMP-activated protein kinase (AMPK) is a master regulator of cellular energy homeostasis, and cell survival in response to inflammation and oxidative stress. However, the neuroprotective mechanisms by which AMPK achieves these beneficial effects in human neural stem cells (hNSCs) exposed to Aβ is still not well understood. Resveratrol is a potent activator of AMPK suggesting it may have therapeutic potential against AD. Therefore, we will test the hypothesis that the AMPK activator resveratrol protects against Aβ mediated neuronal impairment (inflammation and oxidative stress) in hNSCs. Here, Aβ-treated hNSCs had significantly decreased cell viability that correlated with increased TNF-α and IL-1β inflammatory cytokine expression. Co-treatment with resveratrol significantly abrogated the Aβ-mediated effects in hNSCs, and was effectively blocked by the addition of the AMPK-specific antagonist (Compound C). These results suggest the neuroprotective effects of resveratrol are mediated by an AMPK-dependent pathway. In addition, resveratrol rescued the transcript expression levels of inhibitory kappa B kinase (IKK) in Aβ-treated hNSCs. NF-κB is a transcription factor with a key role in the expression of a variety of genes involved in inflammatory responses. Resveratrol prevented the Aβ-mediated increases in NF-κB mRNA and protein levels, and its nuclear translocation in hNSCs. Co-treatment with resveratrol also significantly restored iNOS and COX-2 levels in Aβ-treated hNSCs. Furthermore, hNSCs co-treated with resveratrol were significantly rescued from Aβ-induced oxidative stress, which correlated with reversal of the Aβ-induced mRNA decrease in oxidative defense genes (SOD-1, NRF2, Gpx1, Catalase, GSH and HO-1). Taken together, these novel findings show that activation of AMPK-dependent signaling by resveratrol rescues Aβ-mediated neurotoxicity in hNSCs, and provides evidence supporting a neuroprotective role for AMPK activating drugs in Aβ-related diseases such as AD.

Molecular Cloning and Expression of Osmotin in a Baculovirus-Insect System: Purified Osmotin Mitigates Amyloid-beta Deposition in Neuronal Cells

Osmotin is a pathogenesis-related plant protein, have gained focus of research because of its homology with mammalian adiponectin. The therapeutic properties of osmotin have been explored in recent years as it exhibits neuroprotective effects against amyloid beta-, glutamate- and ethanol-induced synaptic dysfunction and neurodegeneration. In the present study, the full-length gene of the tobacco plant osmotin was cloned and expressed in the Sf9 insect cell line using the baculovirus expression system. In vitro analysis of purified Osmotin protein showed excellent cell viability, p-AMPK activation and a reduction in amyloid-beta deposition. Immunofluorescent analysis showed significant reduction in amyloid beta deposition in APP over expressing neuronal cells. Osmotin inhibited amyloid beta deposition by influencing expression of APP processing genes including APP, ADAM 10 and BACE 1. Purified Osmotin showed reduction in amyloid beta deposition in different in vitro models as well. Osmotin showed similar mechanism when compared with mammalian adiponectin in different in vitro models. The present method will be an excellent approach for the efficient and cost-effective production of the functional protein to be utilized for therapeutic purposes. Reduction in amyloid beta deposition by activation of p-AMPK influencing APP processing genes makes osmotin a potent therapeutic candidate for neurodegenerative diseases.

Inhibition of Poly(ADP-ribose) Polymerase-1 Enhances Gene Expression of Selected Sirtuins and APP Cleaving Enzymes in Amyloid Beta Cytotoxicity

Poly(ADP-ribose) polymerases (PARPs) and sirtuins (SIRTs) are involved in the regulation of cell metabolism, transcription, and DNA repair. Alterations of these enzymes may play a crucial role in Alzheimer's disease (AD). Our previous results indicated that amyloid beta (Aβ) peptides and inflammation led to activation of PARP1 and cell death. This study focused on a role of PARP1 in the regulation of gene expression for SIRTs and beta-amyloid precursor protein (βAPP) cleaving enzymes under Aβ42 oligomers (AβO) toxicity in pheochromocytoma cells (PC12) in culture. Moreover, the effect of endogenously liberated Aβ peptides in PC12 cells stably transfected with human gene for APP wild-type (APPwt) was analyzed. Our results demonstrated that AβO enhanced transcription of presenilins (Psen1 and Psen2), the crucial subunits of γ-secretase. Aβ peptides in APPwt cells activated expression of β-secretase (Bace1), Psen1, Psen2, and Parp1. The inhibitor of PARP1, PJ-34 in the presence of AβO upregulated transcription of α-secretase (Adam10), Psen1, and Psen2, but also Bace1. Concomitantly, PJ-34 enhanced mRNA level of nuclear Sirt1, Sirt6, mitochondrial Sirt4, and Parp3 in PC12 cells subjected to AβOs toxicity. Our data indicated that Aβ peptides through modulation of APP secretases may lead to a vicious metabolic circle, which could be responsible for maintaining Aβ at high level. PARP1 inhibition, besides activation of nuclear SIRTs and mitochondrial Sirt4 expression, enhanced transcription of enzyme(s) involved in βAPP metabolism, and this effect should be considered in its application against Aβ peptide toxicity.

Sirtuins and Their Roles in Brain Aging and Neurodegenerative Disorders

Sirtuins (SIRT1-SIRT7) are unique histone deacetylases (HDACs) whose activity depends on NAD⁺ levels and thus on the cellular metabolic status. SIRTs regulate energy metabolism and mitochondrial function. They orchestrate the stress response and damage repair. Through these functions sirtuins modulate the course of aging and affect neurodegenerative diseases. SIRTSs interact with multiple signaling proteins, transcription factors (TFs) and poly(ADP-ribose) polymerases (PARPs) another class of NAD⁺-dependent post-translational protein modifiers. The cross-talk between SIRTs TFs and PARPs is a highly promising research target in a number of brain pathologies. This review describes updated results on sirtuins in brain aging/neurodegeneration. It focuses on SIRT1 but also on the roles of mitochondrial SIRTs (SIRT3, 4, 5) and on SIRT6 and SIRT2 localized in the nucleus and in cytosol, respectively. The involvement of SIRTs in regulation of insulin-like growth factor signaling in the brain during aging and in Alzheimer's disease was also focused. Moreover, we analyze the mechanism(s) and potential significance of interactions between SIRTs and several TFs in the regulation of cell survival and death. A critical view is given on the application of SIRT activators/modulators in therapy of neurodegenerative diseases.

The effect of ethyl acetate extract from persimmon leaves on Alzheimer's disease and its underlying mechanism

BACKGROUND

Alzheimer's disease (AD) is one of the most prevalent neurodegenerative disorders characterized by neuronal loss in the brain and cognitive impairment. AD is now considered to be the third major cause of death in developed countries, after cardiovascular disease and cancer. Persimmon leaves are used as a popular folk medicine to treat hypertension, angina and internal haemorrhage in Cyangbhina, and it has been reported that ethyl acetate extract of persimmon leaves (EAPL) displays a potential therapeutic effect on neurodegenerative diseases.

HYPOTHESIS/PURPOSE

This study was designed to investigate the effects of EAPL on AD, to clarify the possible mechanism by which EAPL exerts its beneficial effects and prevents AD, and to determine the major constituents involved.

STUDY DESIGN

AD model was established by bilateral injection of Aβ1-42 into the hippocampus of rats. The cognitive performance was determined by the Morris water maze and step-down tests. Superoxide dismutase (SOD), glutathione peroxidase (GSH-Px), malondialdehyde (MDA), apoptosis, total and phosphorylated c-Jun NH2-terminal kinase (JNK/p-JNK), caspase-3, Bax and Bcl-2 were determined. In addition, a sensitive and reliable LC-QTOF-MS method was applied to identify the major compounds present in EAPL.

RESULTS

EAPL at doses of 200mg/kg, 400mg/kg could markedly reduce the latency, significantly increase the time in the first quadrant and number of the target crossing times in Morris water maze test, markedly increase the latency and reduce the number of errors in the step-down test, significantly inhibit the reductions in SOD and GSH-Px activities, and increase the level of MDA. In addition, EAPL treatment attenuated neuronal apoptosis in the hippocampus, reduced the expression of p-JNK, caspase-3, and the relative ratio of Bax/Bcl-2. Meanwhile, 32 constituents were identified by LC-QTOF-MS/MS assays.

CONCLUSION

The results indicate that EAPL has a potent protective effect on cognitive deficits induced by Aβ in rats and this effect appears to be associated with the regulation of the antioxidative defense system and the mechanism of mitochondrial-mediated apoptosis. Furthermore, analysis of the LC-MS data suggests that flavonoids and triterpenoids may be responsible for the potential biological effects of EAPL.