Mechanisms of U87 astrocytoma cell uptake and trafficking of monomeric versus protofibril Alzheimer's disease amyloid-β proteins

The effect of human PBMCs immobilization on their Аβ42 aggregates-dependent proinflammatory state on a cellular model of Alzheimer's disease

The leading pathological mechanisms of Alzheimer's disease are amyloidosis and inflammation. The presented work was aimed to study the effect of human peripheral blood mononuclear cells (hPBMcs) cells-matrix adhesion on their pro-inflammatory state in vitro. Although direct interaction of Аβ42 to PBMC is not a cellular model of Alzheimer's disease, PBMCs may serve as test cells to detect Аβ42-dependent molecular effects in monitoring disease progression. Peripheral blood mononuclear cells (PBMCs) are used to assess changes in cytokines released in response to diseases or Alzheimer's disease-specific cytotoxic molecules such as Aβ42. The effect of recombinant amyloid β-peptide rАβ42 on the concentration of endogenous amyloid β-peptide Aβ40 and pro-inflammatory cytokines TNFα and IL-1β in human peripheral blood mononuclear cells that were cultured in suspension and immobilized in alginate microcarriers for 24 h were investigated. The localization and accumulation of Aβ40 and rAβ42 peptides in cells, as well as quantitative determination of the concentration of Aβ40 peptide, TNFα and IL-1β cytokines, was performed by intravital fluorescence imaging. The results were qualitatively similar for both cell models. It was determined that the content of TNFα and Aβ40 in the absence of rAβ42 in the incubation medium did not change for 24 h after incubation, and the content of IL-1β was lower compared to the cells that were not incubated. Incubation of cells in vitro with exogenous rAβ42 led to an increase in the intracellular content of TNFα and Aβ40, and no accumulation of IL-1β in cells was observed. The accumulation of Aβ40 in the cytoplasm was accompanied by the aggregation of rAβ42 on the outer surface of the cell plasma membrane. It was shown that the basic levels of indicators and the intensity of the response of immobilized cells to an exogenous stimulus were significantly greater than those of cells in suspension. To explore whether non-neuronal cells effects in alginate microcarriers were cell-matrix adhesion mediated, we tested the effect of blocking β1 integrins on proamyloidogenic and proinflammation cellular state. Immobilization within alginate hydrogels after incubation with the β1 integrins blocking antibodies showed a remarkable inhibition of TNFα and Aβ40 accumulation in rAβ42-treated cells. It can be concluded that activation of signal transduction and synthesizing activity of a portion of mononuclear cells of human peripheral blood is possible (can significantly increase) in the presence of cell-matrix adhesion.

PCSK9 Affects Astrocyte Cholesterol Metabolism and Reduces Neuron Cholesterol Supplying In Vitro: Potential Implications in Alzheimer's Disease

The Proprotein Convertase Subtilisin/Kexin Type 9 (PCSK9) involvement in Alzheimer’s disease (AD) is poorly investigated. We evaluated the in vitro PCSK9 modulation of astrocyte cholesterol metabolism and neuronal cholesterol supplying, which is fundamental for neuronal functions. Moreover, we investigated PCSK9 neurotoxic effects. In human astrocytoma cells, PCSK9 reduced cholesterol content (−20%; p < 0.05), with a greater effect in presence of beta amyloid peptide (Aβ) (−37%; p < 0.01). PCSK9 increased cholesterol synthesis and reduced the uptake of apoE-HDL-derived cholesterol (−36%; p < 0.0001), as well as the LDL receptor (LDLR) and the apoE receptor 2 (ApoER2) expression (−66% and −31%, respectively; p < 0.01). PCSK9 did not modulate ABCA1- and ABCG1-cholesterol efflux, ABCA1 levels, or membrane cholesterol. Conversely, ABCA1 expression and activity, as well as membrane cholesterol, were reduced by Aβ (p < 0.05). In human neuronal cells, PCSK9 reduced apoE-HDL-derived cholesterol uptake (−41%; p < 0.001) and LDLR/apoER2 expression (p < 0.05). Reduced cholesterol internalization occurred also in PCSK9-overexpressing neurons exposed to an astrocyte-conditioned medium (−39%; p < 0.001). PCSK9 reduced neuronal cholesterol content overall (−29%; p < 0.05) and increased the Aβ-induced neurotoxicity (p < 0.0001). Our data revealed an interfering effect of PCSK9, in cooperation with Aβ, on brain cholesterol metabolism leading to neuronal cholesterol reduction, a potentially deleterious effect. PCSK9 also exerted a neurotoxic effect, and thus represents a potential pharmacological target in AD.

Glial Cell-Mediated Neuroinflammation in Alzheimer's Disease

Alzheimer's disease (AD) is a progressive neurodegenerative disorder; it is the most common cause of dementia and has no treatment. It is characterized by two pathological hallmarks, the extracellular deposits of amyloid beta (Aβ) and the intraneuronal deposits of Neurofibrillary tangles (NFTs). Yet, those two hallmarks do not explain the full pathology seen with AD, suggesting the involvement of other mechanisms. Neuroinflammation could offer another explanation for the progression of the disease. This review provides an overview of recent advances on the role of the immune cells' microglia and astrocytes in neuroinflammation. In AD, microglia and astrocytes become reactive by several mechanisms leading to the release of proinflammatory cytokines that cause further neuronal damage. We then provide updates on neuroinflammation diagnostic markers and investigational therapeutics currently in clinical trials to target neuroinflammation.

Heparan Sulfate Proteoglycans (HSPGs) Serve as the Mediator Between Monomeric Tau and Its Subsequent Intracellular ERK1/2 Pathway Activation

The conversion of soluble tau protein to insoluble, hyperphosphorylated neurofibrillary tangles (NFTs) is a major hallmark leading to neuronal death observed in neurodegenerative tauopathies. Unlike NFTs, the involvement of monomeric tau in the progression of tau pathology has been less investigated. Using live-cell confocal microscopy and flow cytometry, we demonstrate that soluble 0N4R monomers were rapidly endocytosed by SH-SY5Y and C6 glioma cells via actin-dependent macropinocytosis. Further, cellular endocytosis of monomeric tau has been demonstrated to be HSPG-dependent, as shown in C6 glial cells with genetic knockouts of xylosyltransferase-1-a key enzyme in HSPG synthesis-with a reduced level of tau uptake. Tau internalization subsequently triggers ERK1/2 activation and therefore, the upregulation of IL-6 and IL-1β. The role of ERK1/2 in regulating the levels of pro-inflammatory gene transcripts was confirmed by inhibiting the MEK-ERK1/2 signaling pathway, which led to the attenuated IL-6 and IL-1β expressions but not that of TNF-α. Moreover, as a key regulator of tau internalization, LRP1 (low-density lipoprotein receptor-related protein 1) levels were downregulated in response to monomeric tau added to C6 cells, while it was upregulated in HSPG-deficient cells, suggesting that the involvement of LRP1 in tau uptake depends on the presence of HSPGs on the cell surface. The subsequent LRP1 knockdown experiment we performed shows that LRP1 deficiency leads to an attenuated propensity for tau uptake and further elevated IL-6 gene expression. Collectively, our data suggest that tau has multiple extracellular binding partners that mediate its internalization through distinct mechanisms. Additionally, this study demonstrates the important role of both HSPGs and LRP1 in regulating cellular immune responses to tau protein monomers, providing a novel target for alleviating the neuroinflammatory environment before the formation of neurofibrillary tangles.

Amyloid Beta Is Internalized via Macropinocytosis, an HSPG- and Lipid Raft-Dependent and Rac1-Mediated Process

Intracellular amyloid β peptide (Aβ) accumulation has drawn attention in relation to the pathophysiology of Alzheimer’s disease in addition to its extracellular deposition as senile plaque. Cellular uptake of extracellular Aβ is one of the possible mechanisms by which intracellular Aβ deposits form. Given the relevance of Aβ inside cells, it is important to understand the mechanism by which it is taken up by them. In this study, we elucidated that Neuro2A and SH-SY5Y cells internalize specifically oligomerized Aβ in a time- and dose-dependent manner. The depletion of plasma membrane cholesterol with methyl-β-cyclodextrin or treatment with trypsin diminished the internalization of oAβ, suggesting that the oAβ uptake might be both a lipid raft-dependent and heparan sulfate proteoglycan-mediated process. Treatment with a macropinocytosis inhibitor (ethylisopropyl amiloride and wortmannin) also drastically reduced the uptake of oligomer-Aβ (oAβ). oAβ-treated cells exhibited an increase in Rac1 activity, indicating that macropinocytosis induced by oAβ is regulated by these small GTPases. These findings suggest that macropinocytosis is a major endocytic route through which oAβ42 enters cells.

Development of curcumin-based amyloid β aggregation inhibitors for Alzheimer's disease using the SAR matrix approach

Amyloid β (Aβ) aggregation inhibitor activity cliff involving a curcumin structure was predicted using the SAR Matrix method on the basis of 697 known Aβ inhibitors from ChEMBL (data set 2487). Among the compounds predicted, compound B was found to possess approximately 100 times higher inhibitory activity toward Aβ aggregation than curcumin. TEM images indicate that compound B induced the shortening of Aβ fibrils and increased the generation of Aβ oligomers in a concentration dependent manner. Furthermore, compound K, in which the methyl ester of compound B was replaced by the tert-butyl ester, possessed low cytotoxicity on N2A cells and attenuated Aβ-induced cytotoxicity, indicating that compound K would have an ability for preventing neurotoxicity caused by Aβ aggregation.

Deep Brain Stimulation for Alzheimer's Disease: Stimulation Parameters and Potential Mechanisms of Action

Deep brain stimulation (DBS) is a neurosurgical technique that regulates neuron activity by using internal pulse generators to electrodes in specific target areas of the brain. As a blind treatment, DBS is widely used in the field of mental and neurological diseases, although its mechanism of action is still unclear. In the past 10 years, DBS has shown a certain positive effect in animal models and patients with Alzheimer's disease (AD), but there are also different results that may be related to the stimulation parameters of DBS. Based on this, determining the optimal stimulation parameters for DBS in AD and understanding its mechanism of action are essential to promote the clinical application of DBS in AD. This review aims to explore the therapeutic effect of DBS in AD, and to analyze its stimulation parameters and potential mechanism of action. The keywords "Deep brain stimulation" and "Alzheimer's Disease" were used for systematic searches in the literature databases of Web of Science and PubMed (from 1900 to September 29, 2020). All human clinical studies and animal studies were reported in English, including individual case studies and long-term follow-up studies, were included. These studies described the therapeutic effects of DBS in AD. The results included 16 human clinical studies and 14 animal studies, of which 28 studies clearly demonstrated the positive effect of DBS in AD. We analyzed the current stimulation parameters of DBS in AD from stimulation target, stimulation frequency, stimulation start time, stimulation duration, unilateral/bilateral treatment and current intensity, etc., and we also discussed its potential mechanism of action from multiple aspects, including regulating related neural networks, promoting nerve oscillation, reducing β-amyloid and tau levels, reducing neuroinflammation, regulating the cholinergic system, inducing the synthesis of nerve growth factor.

Critical Molecular and Cellular Contributors to Tau Pathology

Tauopathies represent a group of neurodegenerative diseases including Alzheimer's disease (AD) that are characterized by the deposition of filamentous tau aggregates in the brain. The pathogenesis of tauopathies starts from the formation of toxic 'tau seeds' from hyperphosphorylated tau monomers. The presence of specific phosphorylation sites and heat shock protein 90 facilitates soluble tau protein aggregation. Transcellular propagation of pathogenic tau into synaptically connected neuronal cells or adjacent glial cells via receptor-mediated endocytosis facilitate disease spread through the brain. While neuroprotective effects of glial cells-including phagocytotic microglial and astroglial phenotypes-have been observed at the early stage of neurodegeneration, dysfunctional neuronal-glial cellular communication results in a series of further pathological consequences as the disease progresses, including abnormal axonal transport, synaptic degeneration, and neuronal loss, accompanied by a pro-inflammatory microenvironment. Additionally, the discovery of microtubule-associated protein tau (MAPT) gene mutations and the strongest genetic risk factor of tauopathies-an increase in the presence of the ε2 allele of apolipoprotein E (ApoE)-provide important clues to understanding tau pathology progression. In this review, we describe the crucial signaling pathways and diverse cellular contributors to the progression of tauopathies. A systematic understanding of disease pathogenesis provides novel insights into therapeutic targets within altered signaling pathways and is of great significance for discovering effective treatments for tauopathies.

Small Molecule Phenotypic Screen Identifies Novel Regulators of LDLR Expression

Alzheimer's Disease (AD) is a progressive neurodegenerative disease and the most common cause of dementia. The current treatment options for AD are limited to ameliorating cognitive decline temporarily and not reversing or preventing the progression of dementia. Hence, more effective therapeutic strategies are needed to combat this devastating disease. The low-density lipoprotein receptor has been shown to modulate the neuronal metabolism of cholesterol and apolipoprotein E, a major genetic risk factor for AD. LDLR overexpression in mice has been shown to increase amyloid-β clearance and reduce amyloid deposition. We conducted a phenotypic screen to identify novel signaling pathways and targets that regulate LDLR expression in glial cells using an annotated compound library of approximately 29 000 compounds. The screen identified novel targets such as polo like kinase 1 (PLK1), activin receptor like kinase 5 (ALK5), and serotonin transporter (SERT). We used genetic, chemical biology and pathway analysis to confirm the target hypothesis. This work highlights that phenotypic screening is a promising strategy to identify novel mechanisms and targets for therapeutic intervention of complex neurodegenerative disorders.

pH-bioresponsive poly(ε-caprolactone)-based polymersome for effective drug delivery in cancer and protein glycoxidation prevention

Artificial nanostructures using polymers to produce polymeric vesicles are inspired by the many intricate structures found in living organisms. Polymersomes are a class of self-assembled vesicles known for their great stability and application in drug delivery. They can be tuned according to their intended use by changing their components and introducing activable block copolymers that transform these polymersomes into smart nanocarriers. In this study, we propose the synthesis of a poly (ethylene oxide)-poly (ε-caprolactone)-based polymersome (PEO-PCL) loaded with GSH as a pH-responsive drug delivery molecule for cancer and protein alteration inhibition. Initially, the nanocarrier was synthesized and characterized by DLS, TEM/SEM microscopy as well as gel permeation chromatography (GPC) and ¹H NMR. Their CMC formation, encapsulation efficiency, and pH responsiveness were analyzed. In addition, empty and GSH-loaded PEO-PCL polymersomes were tested for their toxicity and therapeutic effect on normal and cancer cells via an MTT test. Subsequently, protein alteration models (aggregation, glycation, and oxidation) were performed in vitro where the polymersomes were tested. Results showed that other than being non-toxic and able to highly encapsulate and release the GSH in response to acidic conditions, the nanocomposites do not hinder its content's ameliorative effects on cancer cells and protein alterations. This infers that polymeric nanocarriers can be a base for future smart biomedicine applications and theranostics.

Investigating the effect of sugar-terminated nanoparticles on amyloid fibrillogenesis of β-lactoglobulin

In vivo tissue deposition of fibrillar protein aggregates is the cause of several degenerative diseases. Evidence suggests that interfering with the pathology-associated amyloid fibrillogenesis by inhibitory molecules is envisaged as the primary therapeutic strategy. Amyloid fibril formation of proteins has been demonstrated to be influenced by nanoparticles/nanomaterials. As compared with their molecular form counterpart, this work examined the effect of sucrose-terminated nanoparticles on the in vitro amyloid fibrillogenesis and structural properties of β-lactoglobulin at pH 2.0 and 80 °C. ThT binding and electron microscopy results demonstrated that sucrose-terminated nanoparticles were able to suppress β-lactoglobulin fibrillogenesis in a concentration-dependent fashion. Importantly, sucrose-terminated nanoparticles showed better β-lactoglobulin fibril-inhibiting ability than sucrose molecules. ANS fluorescence and right-angle light scattering results showed reduced solvent exposure and decreased aggregation, respectively, in the β-lactoglobulin samples upon treatment with sucrose-terminated nanoparticles. Moreover, fluorescence quenching analyses revealed that the static quenching mechanism and formation of a non-fluorescent fluorophore-nanoparticle complex are involved in the nanoparticle-β-lactoglobulin interaction. We believe that the results from this study may suggest that the nanoparticle form of biocompatible sugar-related osmolytes may serve as effective inhibiting/suppressing agents toward protein fibrillogenesis.

Anodal Transcranial Direct Current Stimulation Can Improve Spatial Learning and Memory and Attenuate Aβ42 Burden at the Early Stage of Alzheimer's Disease in APP/PS1 Transgenic Mice

Alzheimer’s disease (AD) is an irreversible progressive neurodegenerative disease. Intervention in the early stage of AD is a new path for AD treatment that is being explored. The behavioral and pathological effects of anodal transcranial direct current stimulation (AtDCS) at the early stage of AD in the mouse model, amyloid precursor protein (APP)/presenilin-1 (PS1) transgenic mice, were investigated based on our previous studies. Thirty-three 6-month-old male APP/PS1 mice were randomly divided into the model group (AD group), model + sham stimulation group (ADST group) and stimulation group (ADT group). Eleven 6-month-old male C57 wild-type mice were randomly selected as a control group (CTL group). The ADT group received 10 AtDCS sessions. The Morris water maze (MWM) task and novel object recognition (NOR) task were used to test mouse memory. Nissl staining, Western blot (WB), immunohistochemistry and immunofluorescence staining of β-amyloid (Aβ₄₂), glial fibrillary acidic protein (GFAP) and NF200 were conducted for pathological analysis. The ADT group and the CTL group had a shorter escape latency and more platform-region crossings than the AD group and ADST group in the MWM. There was no significant difference in the discrimination index among the groups in the NOR task. Pathological analysis showed visible differences between the AD group and ADT group. This study revealed that early-stage APP/PS1 transgenic mice did not show recognition memory impairment. AtDCS effectively improved spatial learning and memory in the early-stage APP/PS1 transgenic mouse model of AD, alleviating Aβ burden and having a protective effect on neurons. AtDCS could improve AD-related symptoms by activating many glial cells to promote the degradation and clearance of Aβ or directly affecting production and degradation of Aβ to reduce glial activation. AtDCS is an effective means of early intervention in the early stage of AD.

Self-triggered click reaction in an Alzheimer's disease model: in situ bifunctional drug synthesis catalyzed by neurotoxic copper accumulated in amyloid-β plaques

Cu is one of the essential elements for life. Its dyshomeostasis has been demonstrated to be closely related to neurodegenerative disorders, such as Alzheimer's disease (AD), which is characterized by amyloid-β (Aβ) aggregation and Cu accumulation. It is a great challenge as to how to take advantage of neurotoxic Cu to fight disease and make it helpful. Herein, we report that the accumulated Cu in Aβ plaques can effectively catalyze an azide-alkyne bioorthogonal cycloaddition reaction for fluorophore activation and drug synthesis in living cells, a transgenic AD model of Caenorhabditis elegans CL2006, and brain slices of triple transgenic AD mice. More importantly, the in situ synthesized bifunctional drug 6 can disassemble Aβ-Cu aggregates by extracting Cu and photo-oxygenating Aβ synergistically, suppressing Aβ-mediated paralysis and diminishing the locomotion defects of the AD model CL2006 strain. Our results demonstrate that taking the accumulated Cu ions in the Aβ plaque for an in situ click reaction can achieve both a self-triggered and self-regulated drug synthesis for AD therapy. To the best of our knowledge, a click reaction catalyzed by local Cu in a physiological environment has not been reported. This work may open up a new avenue for in situ multifunctional drug synthesis by using endogenous neurotoxic metal ions for the treatment of neurodegenerative diseases.

24S-hydroxycholesterol affects redox homeostasis in human glial U-87 MG cells

The cholesterol metabolite 24(S)-hydroxycholesterol (24S-OHC) allows cholesterol excretion from the brain and was suggested to be critically involved in physiological as well as neurodegenerative processes. It induces on human neuronal cell cultures a dose dependent toxicity associated with increased reactive oxygen species production. Since glial cells play a key role in assisting neuronal function, here we investigated the effects of increased concentrations of 24S-OHC on a glial cell model (human glioblastoma U-87 MG cells). We determined the content of PGC-1α and TFAM, involved in the biogenesis of mitochondria, both mitochondrial complexes activity and protein amount, lipid and protein oxidative damage, cellular reactive oxygen species (ROS) release and both the activities and amount of the antioxidant enzymes glutathione peroxidase and catalase. Low concentration of 24S-OHC increased cellular content of PGC-1α and TFAM and the activities of mitochondrial complexes I and II, with no marked changes in their protein amount. Interestingly, 24S-OHC at lower concentrations reduced while at higher concentration increased lipid and protein oxidative damage. Conversely, the content of nitro-tyrosine increased only with the highest 24S-OHC concentration. Also, cell H₂O₂ release was reduced by lower and increased by higher 24S-OHC used concentrations. The cell activity of glutathione peroxidase was reduced by 24S-OHC at higher concentration while that of catalase was reduced by all the assayed concentrations. Further, a dose dependent decrease of both enzymes levels was observed. In conclusion, we demonstrated that 24S-OHC exerts different effects on U-87 MG cells depending on its level. At lower concentrations it stimulates cellular processes critical to maintain redox homeostasis, while at higher dose its effect on the glial cell here used resemble its action on neurons.

Contribution of syndecans to cellular internalization and fibrillation of amyloid-β(1-42)

Intraneuronal accumulation of amyloid-β(1-42) (Aβ1-42) is one of the earliest signs of Alzheimer's disease (AD). Cell surface heparan sulfate proteoglycans (HSPGs) have profound influence on the cellular uptake of Aβ1-42 by mediating its attachment and subsequent internalization into the cells. Colocalization of amyloid plaques with members of the syndecan family of HSPGs, along with the increased expression of syndecan-3 and -4 have already been reported in postmortem AD brains. Considering the growing evidence on the involvement of syndecans in the pathogenesis of AD, we analyzed the contribution of syndecans to cellular uptake and fibrillation of Aβ1-42. Among syndecans, the neuron specific syndecan-3 isoform increased cellular uptake of Aβ1-42 the most. Kinetics of Aβ1-42 uptake also proved to be fairly different among SDC family members: syndecan-3 increased Aβ1-42 uptake from the earliest time points, while other syndecans facilitated Aβ1-42 internalization at a slower pace. Internalized Aβ1-42 colocalized with syndecans and flotillins, highlighting the role of lipid-rafts in syndecan-mediated uptake. Syndecan-3 and 4 also triggered fibrillation of Aβ1-42, further emphasizing the pathophysiological relevance of syndecans in plaque formation. Overall our data highlight syndecans, especially the neuron-specific syndecan-3 isoform, as important players in amyloid pathology and show that syndecans, regardless of cell type, facilitate key molecular events in neurodegeneration.

Anticancer properties of lipid and poly(ε-caprolactone) nanocapsules loaded with ferrocenyl-tamoxifen derivatives

OBJECTIVE

We synthesized new tamoxifen derivatives as anticancer drug candidates and elaborated on convection-enhanced delivery (CED) as a strategy for delivery.

METHODS

To overcome the issue of their poor solubility, these ferrocenyl-tamoxifen derivatives were esterified and encapsulated into different nanocarriers, that is lipid (LNC) and polymeric nanocapsules (PNL-NC). We describe the chemistry, the encapsulation and the physicochemical characterization of these formulations.

KEY FINDINGS

Starting compounds [phthalimido-ferrocidiphenol and succinimido-ferrocidiphenol], esterified prodrugs and their nanocapsules formulations were characterized. These drug candidates displayed a strong in vitro activity against breast and glioblastoma cancer cells. The ester prodrugs were toxic for glioblastoma cells (IC₅₀ = 9.2 × 10^-2 μm and 6.7 × 10^-2 μm, respectively). The IC₅₀ values for breast cancer cells were higher for these compounds. The encapsulation of the esterified compounds in LNCs (≈50 nm) or PCL-NCs (≈300 nm) did not prevent their efficacy on glioblastoma cells. These anticancer effects were due to both blockade in the S-phase of the cell cycle and apoptosis. Moreover, the tamoxifen derivatives-loaded nanocapsules induced no toxicity for healthy astrocytes and showed no haemolytic properties. Loaded Lipid Nanocapsules (LNCs) presented interesting profiles for the optimal delivery of active compounds.

CONCLUSIONS

Phthalimido- and Succinimido-esters represent an innovative approach to treat cancers with cerebral localizations such as glioblastoma or brain metastases from breast cancers.

Lopinavir/Ritonavir Treatment Induces Oxidative Stress and Caspaseindependent Apoptosis in Human Glioblastoma U-87 MG Cell Line

Background:

Lopinavir and Ritonavir (LPV/r) treatment is widely used to prevent HIV mother-to-child transmission. Nevertheless, studies related to the impact of these compounds on patients, in particular in the foetus and newborns, are strictly required due to the controversial findings reported in the literature concerning possible neurologic side effects following the administration of these drugs.

Objectives:

In our study, we evaluated the impact of LPV/r treatment on the human glioblastoma U- 87 MG cell line.

Methods:

In order to evaluate the influence of Lopinavir and Ritonavir in terms of oxidative stress (ROS production), mitochondrial morphology and apoptotic cell death, the latter either in the presence or in the absence of caspase-3 and -9 inhibitors, we treated U-87 MG with increasing doses (0.1-1-10-25-50 µM) of Lopinavir and Ritonavir for 24h, either in single formulation or in combination. ROS production was measured by flow cytometry using H2DCFDA dye, mitochondrial morphology was evaluated using MitoRed dye and apoptotic cell death was monitored by flow cytometry using Annexin V-FITC and Propidium Iodide.

Results:

We observed that co-treatment with Lopinavir and Ritonavir (25 and 50 µM) promoted a significant increase in ROS production, caused mitochondrial network damage and induced apoptosis in a caspase-independent manner.

Conclusion:

Based on our findings, concordant with others reported in the literature, we hypothesize that LPV/r treatment could not be entirely free from side effects, being aware of the need of validation in in vivo models, necessary to confirm our results.

TFEB enhances astroglial uptake of extracellular tau species and reduces tau spreading

Martini-Stoica et al. demonstrate that the TFEB-mediated lysosomal pathway in astrocytes is increased in tauopathy and plays a functional role in modulating extracellular tau and the propagation of neuronal tau pathology in a mouse model of tau spreading.

The progression of tau pathology in Alzheimer’s disease follows a stereotyped pattern, and recent evidence suggests a role of synaptic connections in this process. Astrocytes are well positioned at the neuronal synapse to capture and degrade extracellular tau as it transits the synapse and hence could potentially have the ability to inhibit tau spreading and delay disease progression. Our study shows increased expression and activity of Transcription Factor EB (TFEB), a master regulator of lysosomal biogenesis, in response to tau pathology in both human brains with dementia and transgenic mouse models. Exogenous TFEB expression in primary astrocytes enhances tau fibril uptake and lysosomal activity, while TFEB knockout has the reverse effect. In vivo, induced TFEB expression in astrocytes reduces pathology in the hippocampus of PS19 tauopathy mice, as well as prominently attenuates tau spreading from the ipsilateral to the contralateral hippocampus in a mouse model of tau spreading. Our study suggests that astrocytic TFEB plays a functional role in modulating extracellular tau and the propagation of neuronal tau pathology in tauopathies such as Alzheimer’s disease.

Amyloid clearance defect in ApoE4 astrocytes is reversed by epigenetic correction of endosomal pH

Endosomes have emerged as a central hub and pathogenic driver of Alzheimer's disease (AD). The earliest brain cytopathology in neurodegeneration, occurring decades before amyloid plaques and cognitive decline, is an expansion in the size and number of endosomal compartments. The strongest genetic risk factor for sporadic AD is the ε4 allele of Apolipoprotein E (ApoE4). Previous studies have shown that ApoE4 potentiates presymptomatic endosomal dysfunction and defective endocytic clearance of amyloid beta (Aβ), although how these two pathways are linked at a cellular and mechanistic level has been unclear. Here, we show that aberrant endosomal acidification in ApoE4 astrocytes traps the low-density lipoprotein receptor-related protein (LRP1) within intracellular compartments, leading to loss of surface expression and Aβ clearance. Pathological endosome acidification is caused by ε4 risk allele-selective down-regulation of the Na⁺/H⁺ exchanger isoform NHE6, which functions as a critical leak pathway for endosomal protons. In vivo, the NHE6 knockout (NHE6^KO) mouse model showed elevated Aβ in the brain, consistent with a causal effect. Increased nuclear translocation of histone deacetylase 4 (HDAC4) in ApoE4 astrocytes, compared with the nonpathogenic ApoE3 allele, suggested a mechanistic basis for transcriptional down-regulation of NHE6. HDAC inhibitors that restored NHE6 expression normalized ApoE4-specific defects in endosomal pH, LRP1 trafficking, and amyloid clearance. Thus, NHE6 is a downstream effector of ApoE4 and emerges as a promising therapeutic target in AD. These observations have prognostic implications for patients who have Christianson syndrome with loss of function mutations in NHE6 and exhibit prominent glial pathology and progressive hallmarks of neurodegeneration.

Effects and mechanism of amyloid β1-42 on mitochondria in astrocytes

Amyloid β (Aβ)_1–42 is strongly associated with Alzheimer's disease (AD). The effects of Aβ_1–42 on astrocytes remain largely unknown. The present study focused on the effects of Aβ_1–42 on U87 human glioblastoma cells as astrocytes for in vitro investigation and mouse brains for in vivo investigation. The mechanism and regulation of mitochondria and cytochrome P450 reductase (CPR) were also investigated. As determined by MTT assays, low doses of Aβ_1–42 (<1 µM) marginally promoted astrocytosis compared with the 0 µM group within 24 h, however, after 48 h treatment these doses reduced cellular growth compared with the 0 µM group. Furthermore, Aβ_1–42 doses >5 µM inhibited the growth of U87 cells compared with the 0 µM group after 24 and 48 h treatment. Immunofluorescence analysis demonstrated that astrocytosis was also observed in early stage AD mice compared with wild-type (WT) mice. In addition, concentrations of Aβ_1–42 were also significantly higher in early stage AD mice compared with WT mice, however, the levels were markedly lower compared with later stage AD mice, as determined by ELISA. In addition to increased levels of Aβ_1–42 in mice with later stage AD, reduced astrocyte staining was observed compared with WT mice. Western blotting indicated that the effect of Aβ_1–42 on U87 cell apoptosis may be regulated via Bcl-2 and caspase-3 located in mitochondria, whose functions, including adenosine triphosphate generation, electron transport chain and mitochondrial membrane potential, were inhibited by Aβ_1–42. During this process, the expression and activity of cytochrome P450 reductase was also downregulated. The current study provides novel insight into the effects of Aβ_1–42 on astrocytes and highlights a potential role for astrocytes in the protection against AD.

25-Hydroxycholesterol and inflammation in Lovastatin-deregulated mevalonate pathway

Mevalonate pathway deregulation has been observed in several diseases, including Mevalonate kinase deficiency (MKD). MKD is a hereditary auto-inflammatory disorder, due to mutations at mevalonate kinase gene (MVK), encoding mevalonate kinase (MK) enzyme. MVK mutations have been reported as associated with impairment of mevalonate pathway with consequent decrease of protein prenylation levels, defective autophagy and increase of IL-1β secretion, followed by cell death. Since 25-hydroxycholesterol (25-HC), a metabolite of cholesterol, can suppress IL-1β production, thus reducing inflammation, we evaluated the effect of 25-HC in an in vitro model of mevalonate pathway alteration, obtained using Lovastatin. Human glioblastoma cell line (U87-MG) was chosen to mimic, at least in part, the central nervous system impairment observed in MKD; 25-HC effects were evaluated aimed at disclosing if this compound could be considered as novel potential drug for MKD. Our results showed that 25-HC is able to reduce inflammation but it is ineffective to restore autophagy flux and to decrease apoptosis levels, both caused by lower protein prenylation; so, in spite of its anti-inflammatory action it is not useful to rescue defective prenylation/autophagy impairment-driven apoptosis in Lovastatin impaired mevalonate pathway. We hypothesize the presence in the mevalonate pathway of alternative mechanisms acting between inflammation and apoptotic autophagy impairment.

Diversity of astroglial responses across human neurodegenerative disorders and brain aging

Astrogliopathy refers to alterations of astrocytes occurring in diseases of the nervous system, and it implies the involvement of astrocytes as key elements in the pathogenesis and pathology of diseases and injuries of the central nervous system. Reactive astrocytosis refers to the response of astrocytes to different insults to the nervous system, whereas astrocytopathy indicates hypertrophy, atrophy/degeneration and loss of function and pathological remodeling occurring as a primary cause of a disease or as a factor contributing to the development and progression of a particular disease. Reactive astrocytosis secondary to neuron loss and astrocytopathy due to intrinsic alterations of astrocytes occur in neurodegenerative diseases, overlap each other, and, together with astrocyte senescence, contribute to disease-specific astrogliopathy in aging and neurodegenerative diseases with abnormal protein aggregates in old age. In addition to the well-known increase in glial fibrillary acidic protein and other proteins in reactive astrocytes, astrocytopathy is evidenced by deposition of abnormal proteins such as β-amyloid, hyper-phosphorylated tau, abnormal α-synuclein, mutated huntingtin, phosphorylated TDP-43 and mutated SOD1, and PrPres , in Alzheimer's disease, tauopathies, Lewy body diseases, Huntington's disease, amyotrophic lateral sclerosis and Creutzfeldt-Jakob disease, respectively. Astrocytopathy in these diseases can also be manifested by impaired glutamate transport; abnormal metabolism and release of neurotransmitters; altered potassium, calcium and water channels resulting in abnormal ion and water homeostasis; abnormal glucose metabolism; abnormal lipid and, particularly, cholesterol metabolism; increased oxidative damage and altered oxidative stress responses; increased production of cytokines and mediators of the inflammatory response; altered expression of connexins with deterioration of cell-to-cell networks and transfer of gliotransmitters; and worsening function of the blood brain barrier, among others. Increased knowledge of these aspects will permit a better understanding of brain aging and neurodegenerative diseases in old age as complex disorders in which neurons are not the only players.

Role of LRP1 in the pathogenesis of Alzheimer's disease: evidence from clinical and preclinical studies

Among the LDL receptor (LDLR) family members, the roles of LDLR-related protein (LRP)1 in the pathogenesis of Alzheimer's disease (AD), especially late-onset AD, have been the most studied by genetic, neuropathological, and biomarker analyses (clinical studies) or cellular and animal model systems (preclinical studies) over the last 25 years. Although there are some conflicting reports, accumulating evidence from preclinical studies indicates that LRP1 not only regulates the metabolism of amyloid-β peptides (Aβs) in the brain and periphery, but also maintains brain homeostasis, impairment of which likely contributes to AD development in Aβ-independent manners. Several preclinical studies have also demonstrated an involvement of LRP1 in regulating the pathogenic role of apoE, whose gene is the strongest genetic risk factor for AD. Nonetheless, evidence from clinical studies is not sufficient to conclude how LRP1 contributes to AD development. Thus, despite very promising results from preclinical studies, the role of LRP1 in AD pathogenesis remains to be further clarified. In this review, we discuss the potential mechanisms underlying how LRP1 affects AD pathogenesis through Aβ-dependent and -independent pathways by reviewing both clinical and preclinical studies. We also discuss potential therapeutic strategies for AD by targeting LRP1.

Astrocytic LRP1 Mediates Brain Aβ Clearance and Impacts Amyloid Deposition

Accumulation and deposition of amyloid-β (Aβ) in the brain represent an early and perhaps necessary step in the pathogenesis of Alzheimer's disease (AD). Aβ accumulation leads to the formation of Aβ aggregates, which may directly and indirectly lead to eventual neurodegeneration. While Aβ production is accelerated in many familial forms of early-onset AD, increasing evidence indicates that impaired clearance of Aβ is more evident in late-onset AD. To uncover the mechanisms underlying impaired Aβ clearance in AD, we examined the role of low-density lipoprotein receptor-related protein 1 (LRP1) in astrocytes. Although LRP1 has been shown to play critical roles in brain Aβ metabolism in neurons and vascular mural cells, its role in astrocytes, the most abundant cell type in the brain responsible for maintaining neuronal homeostasis, remains unclear. Here, we show that astrocytic LRP1 plays a critical role in brain Aβ clearance. LRP1 knockdown in primary astrocytes resulted in decreased cellular Aβ uptake and degradation. In addition, silencing of LRP1 in astrocytes led to downregulation of several major Aβ-degrading enzymes, including matrix metalloproteases MMP2, MMP9, and insulin-degrading enzyme. More important, conditional knock-out of the Lrp1 gene in astrocytes in the background of APP/PS1 mice impaired brain Aβ clearance, exacerbated Aβ accumulation, and accelerated amyloid plaque deposition without affecting its production. Together, our results demonstrate that astrocytic LRP1 plays an important role in Aβ metabolism and that restoring LRP1 expression and function in the brain could be an effective strategy to facilitate Aβ clearance and counter amyloid pathology in AD.SIGNIFICANCE STATEMENT Astrocytes represent a major cell type regulating brain homeostasis; however, their roles in brain clearance of amyloid-β (Aβ) and underlying mechanism are not clear. In this study, we used both cellular models and conditional knock-out mouse models to address the role of a critical Aβ receptor, the low-density lipoprotein receptor-related protein 1 (LRP1) in astrocytes. We found that LRP1 in astrocytes plays a critical role in brain Aβ clearance by modulating several Aβ-degrading enzymes and cellular degradation pathways. Our results establish a critical role of astrocytic LRP1 in brain Aβ clearance and shed light on specific Aβ clearance pathways that may help to establish new targets for AD prevention and therapy.

The characteristics of astrocyte on Aβ clearance altered in Alzheimer's disease were reversed by anti-inflammatory agent (+)-2-(1-hydroxyl-4-oxocyclohexyl) ethyl caffeate

Astrocytes are closely related to the amyloid-β (Aβ) deposition in the brain and play crucial roles in Alzheimer's disease (AD) pathology. Meanwhile, inflammation in the CNS has been increasingly demonstrated as a prominent hallmark in AD. Our data from animal models and subjects with Alzheimer's disease (AD) showed GFAP immunoreactivity altered in different stage of AD and had a positive correlation with neprilysin (NEP), suggesting astrocytes might take a protective role in pathogenetic course of AD. Here, we investigate the role of astrocyte in the mechanism of Aβ removal. ELISA and western blotting were performed to determine the ability of astrocyte to clear Aβ1-42. In this study, we demonstrated that cultured astrocytes removed extracellular oligomeric Aβ. However, cultured astrocytes from an AD mouse model showed less capacity to clear extracellular Aβ42 but with hyper-expression of NEP protein than normal astrocytes. In addition, LPS-induced inflammation rather than continuous Aβ stimuli inhibited the capacity of Aβ clearance by astrocytes indicating that inflammation possibly contributed to astrocytic dysfunction. Lastly, HOEC which exhibited anti-inflammatory effects restored the capacity of injured or aged astrocytes to clear Aβ. In conclusion, astrocytes have been shown to exert a direct role in Aβ clearance and undergo functional impair associated with inflammation in the pathogenesis of AD. Therefore, anti-inflammatory treatments aimed at restoring astrocyte functions may represent an appropriate approach to treat AD.

Efficient Inhibition of Protein Aggregation, Disintegration of Aggregates, and Lowering of Cytotoxicity by Green Tea Polyphenol-Based Self-Assembled Polymer Nanoparticles

Green tea polyphenol epigallocatechin-3-gallate (EGCG) is known for its antiamyloidogenic property, and it is observed that molecular EGCG binds with amyloid structure, redirects fibrillation kinetics, remodels mature fibril, and lowers the amyloid-derived toxicity. However, this unique property of EGCG is difficult to utilize because of their poor chemical stability and substandard bioavailability. Here we report a nanoparticle form of EGCG of 25 nm size (nano-EGCG) which is 10-100 times more efficient than molecular EGCG in inhibiting protein aggregation, disintegrating mature protein aggregates, and lowering amyloidogenic cytotoxicity. The most attractive advantage of nano-EGCG is that it efficiently protects neuronal cells from the toxic effect of extracellular amyloid beta or intracellular mutant huntingtin protein aggregates by preventing their aggregation. We found that the better performance of nano-EGCG is due to the combined effect of increased chemical stability of EGCG against degradation, stronger binding with protein aggregates, and efficient entry into the cell for interaction with aggregated protein structure. This result indicates that the nanoparticle form of antiamyloidogenic molecules can be more powerful in prevention and curing of protein aggregation derived diseases.

TSPO PIGA Ligands Promote Neurosteroidogenesis and Human Astrocyte Well-Being

The steroidogenic 18 kDa translocator protein (TSPO) is an emerging, attractive therapeutic tool for several pathological conditions of the nervous system. Here, 13 high affinity TSPO ligands belonging to our previously described N,N-dialkyl-2-phenylindol-3-ylglyoxylamide (PIGA) class were evaluated for their potential ability to affect the cellular Oxidative Metabolism Activity/Proliferation index, which is used as a measure of astrocyte well-being. The most active PIGA ligands were also assessed for steroidogenic activity in terms of pregnenolone production, and the values were related to the metabolic index in rat and human models. The results showed a positive correlation between the increase in the Oxidative Metabolism Activity/Proliferation index and the pharmacologically induced stimulation of steroidogenesis. The specific involvement of steroid molecules in mediating the metabolic effects of the PIGA ligands was demonstrated using aminoglutethimide, a specific inhibitor of the first step of steroid biosynthesis. The most promising steroidogenic PIGA ligands were the 2-naphthyl derivatives that showed a long residence time to the target, in agreement with our previous data. In conclusion, TSPO ligand-induced neurosteroidogenesis was involved in astrocyte well-being.

The p38 mitogen-activated protein kinase signaling pathway is involved in regulating low-density lipoprotein receptor-related protein 1-mediated β-amyloid protein internalization in mouse brain

Alzheimer's disease (AD) is one of the most common neurodegenerative diseases. Recently, increasing evidence suggests that intracellular β-amyloid protein (Aβ) alone plays a pivotal role in the progression of AD. Therefore, understanding the signaling pathway and proteins that control Aβ internalization may provide new insight for regulating Aβ levels. In the present study, the regulation of Aβ internalization by p38 mitogen-activated protein kinases (MAPK) through low-density lipoprotein receptor-related protein 1 (LRP1) was analyzed in vivo. The data derived from this investigation revealed that Aβ1-42 were internalized by neurons and astrocytes in mouse brain, and were largely deposited in mitochondria and lysosomes, with some also being found in the endoplasmic reticulum. Aβ1-42-LRP1 complex was formed during Aβ1-42 internalization, and the p38 MAPK signaling pathway was activated by Aβ1-42 via LRP1. Aβ1-42 and LRP1 were co- localized in the cells of parietal cortex and hippocampus. Furthermore, the level of LRP1-mRNA and LRP1 protein involved in Aβ1-42 internalization in mouse brain. The results of this investigation demonstrated that Aβ1-42 induced an LRP1-dependent pathway that related to the activation of p38 MAPK resulting in internalization of Aβ1-42. These results provide evidence supporting a key role for the p38 MAPK signaling pathway which is involved in the regulation of Aβ1-42 internalization in the parietal cortex and hippocampus of mouse through LRP1 in vivo.

Amyloid-β and Astrocytes Interplay in Amyloid-β Related Disorders

Amyloid-β (Aβ) pathology is known to promote chronic inflammatory responses in the brain. It was thought previously that Aβ is only associated with Alzheimer's disease and Down syndrome. However, studies have shown its involvement in many other neurological disorders. The role of astrocytes in handling the excess levels of Aβ has been highlighted in the literature. Astrocytes have a distinctive function in both neuronal support and protection, thus its involvement in Aβ pathological process may tip the balance toward chronic inflammation and neuronal death. In this review we describe the involvement of astrocytes in Aβ related disorders including Alzheimer's disease, Down syndrome, cerebral amyloid angiopathy, and frontotemporal dementia.

Astrocytes: a central element in neurological diseases

The neurone-centred view of the past disregarded or downplayed the role of astroglia as a primary component in the pathogenesis of neurological diseases. As this concept is changing, so is also the perceived role of astrocytes in the healthy and diseased brain and spinal cord. We have started to unravel the different signalling mechanisms that trigger specific molecular, morphological and functional changes in reactive astrocytes that are critical for repairing tissue and maintaining function in CNS pathologies, such as neurotrauma, stroke, or neurodegenerative diseases. An increasing body of evidence shows that the effects of astrogliosis on the neural tissue and its functions are not uniform or stereotypic, but vary in a context-specific manner from astrogliosis being an adaptive beneficial response under some circumstances to a maladaptive and deleterious process in another context. There is a growing support for the concept of astrocytopathies in which the disruption of normal astrocyte functions, astrodegeneration or dysfunctional/maladaptive astrogliosis are the primary cause or the main factor in neurological dysfunction and disease. This review describes the multiple roles of astrocytes in the healthy CNS, discusses the diversity of astroglial responses in neurological disorders and argues that targeting astrocytes may represent an effective therapeutic strategy for Alexander disease, neurotrauma, stroke, epilepsy and Alzheimer's disease as well as other neurodegenerative diseases.

Arf6 controls beta-amyloid production by regulating macropinocytosis of the Amyloid Precursor Protein to lysosomes

Alzheimer’s disease (AD) is characterized by the deposition of Beta-Amyloid (Aβ) peptides in the brain. Aβ peptides are generated by cleavage of the Amyloid Precursor Protein (APP) by the β − and γ − secretase enzymes. Although this process is tightly linked to the internalization of cell surface APP, the compartments responsible are not well defined. We have found that APP can be rapidly internalized from the cell surface to lysosomes, bypassing early and late endosomes. Here we show by confocal microscopy and electron microscopy that this pathway is mediated by macropinocytosis. APP internalization is enhanced by antibody binding/crosslinking of APP suggesting that APP may function as a receptor. Furthermore, a dominant negative mutant of Arf6 blocks direct transport of APP to lysosomes, but does not affect classical endocytosis to endosomes. Arf6 expression increases through the hippocampus with the development of Alzheimer’s disease, being expressed mostly in the CA1 and CA2 regions in normal individuals but spreading through the CA3 and CA4 regions in individuals with pathologically diagnosed AD. Disruption of lysosomal transport of APP reduces both Aβ40 and Aβ42 production by more than 30 %. Our findings suggest that the lysosome is an important site for Aβ production and that altering APP trafficking represents a viable strategy to reduce Aβ production.

Neurotrophic Activity of Cultured Cell Line U87 is Up-Regulated by Proline-Rich Polypeptide Complex and Its Constituent Nonapeptide

Neurotrophins such as nerve growth factor (NGF) and brain-derived neurotrophic factor, as well as cytokines, for example, interleukin-6 (IL-6) play an important role in neuroprotection and in the control of the central nervous system (CNS) function. Reduced expression of neurotrophic factors can lead to dysregulation of neuron function and neuronal death. There is also evidence for mutual interactions between neurotrophins and IL-6. Therefore, the up-regulating the level of neuroprotective substances is one of the key manners to control the nervous system development and function. It can be a promising aim in the therapy of neurodegenerative disease in which the decreased level of neurotrophins is observed. In our recent studies, the role of proline-rich polypeptide complex (PRP) and its nonapeptide fragment (NP) in the regulation of neurotrophic activity in cultured astrocytes was shown. PRP and NP stimulate human astrocytoma cell line U87 to release the significant amounts of NGF to the extracellular space both in its precursor and mature form. We also provide the evidence that in NP-treated cells, the level of βNGF mRNA was increased. NP-treated cells used in this study produced also increasing amounts of IL-6. This finding indicates that PRP and its nonapeptide fragment NP up-regulate neurotrophic activity of U87 cell line by increase of NGF synthesis and its release into the extracellular space. It was also shown that NP-dependent increased production of IL-6 can enhance the NGF activity.