Cholesterol Modulation Attenuates the AD-like Phenotype Induced by Herpes Simplex Virus Type 1 Infection.

Cholesterol, a crucial component of cell membranes, influences various biological processes, including membrane trafficking, signal transduction, and host-pathogen interactions. Disruptions in cholesterol homeostasis have been linked to congenital and acquired conditions, including neurodegenerative disorders such as Alzheimer's disease (AD). Previous research from our group has demonstrated that herpes simplex virus type I (HSV-1) induces an AD-like phenotype in several cell models of infection. This study explores the interplay between cholesterol and HSV-1-induced neurodegeneration. The impact of cholesterol was determined by modulating its levels with methyl-beta-cyclodextrin (MßCD) using the neuroblastoma cell lines SK-N-MC and N2a. We have found that HSV-1 infection triggers the intracellular accumulation of cholesterol in structures resembling endolysosomal/autophagic compartments, a process reversible upon MßCD treatment. Moreover, MßCD exhibits inhibitory effects at various stages of HSV-1 infection, underscoring the importance of cellular cholesterol levels, not only in the viral entry process but also in subsequent post-entry stages. MßCD also alleviated several features of AD-like neurodegeneration induced by viral infection, including lysosomal impairment and intracellular accumulation of amyloid-beta peptide (Aß) and phosphorylated tau. In conclusion, these findings highlight the connection between cholesterol, neurodegeneration, and HSV-1 infection, providing valuable insights into the underlying mechanisms of AD.

Herpes Simplex Virus Type 1 Induces AD-like Neurodegeneration Markers in Human Progenitor and Differentiated ReNcell VM Cells.

An increasing body of evidence strongly suggests that infections or reactivations of herpes simplex virus type 1 (HSV-1) may be closely linked to Alzheimer's disease (AD). Promising results have been obtained using cell and animal models of HSV-1 infection, contributing to the understanding of the molecular mechanisms linking HSV-1 infection and AD neurodegeneration. ReNcell VM is a human neural stem cell line that has been used as a model system to study the impact of various infectious agents on the central nervous system. In this study, we demonstrate the suitability of the ReNcell VM cell line for developing a new in vitro model of HSV-1 infection. By following standard differentiation protocols, we were able to derive various nervous cell types, including neurons, astrocytes, and oligodendrocytes, from neural precursors. Additionally, we demonstrated the susceptibility of ReNcell VM cells, including precursor and differentiated cells, to HSV-1 infection and subsequent viral-induced AD-like neurodegeneration. Our findings support the use of this cell line to generate a new research platform for investigating AD neuropathology and its most significant risk factors, which may lead to important discoveries in the context of this highly impactful disease.

Matrix metalloproteinase 14 regulates HSV-1 infection in neuroblastoma cells.

Growing evidence supports that chronic or latent infection of the central nervous system might be implicated in Alzheimer's disease (AD). Among them, Herpes simplex virus type 1 (HSV-1) has emerged as a major factor in the etiology of the disease. Our group is devoted to the study of the relationship among HSV-1, oxidative stress (OS) and neurodegeneration. We have found that HSV-1 induces the main neuropathological hallmarks of AD, including the accumulation of intracellular amyloid beta (Aß), hyperphosphorylated tau protein and autophagic vesicles, that OS exacerbates these effects, and that matrix metalloproteinase 14 (MMP-14) participates in the alterations induced by OS. In this work, we focused on the role of MMP-14 in the degenerative markers raised by HSV-1 infection. Interestingly, we found that MMP-14 blockage is a potent inhibitor of HSV-1 infection efficiency, that also reduces the degeneration markers, accumulation of Aß and hyperphosphorylated tau, induced by the virus. Our results point to MMP-14 as a potent antiviral target to control HSV-1 infection and its associated neurodegenerative effects.

LAMP2 deficiency attenuates the neurodegeneration markers induced by HSV-1 infection.

Mounting evidence suggests a major role of infectious agents in the pathogenesis of sporadic Alzheimer's disease (AD). Among them, herpes simplex virus type 1 (HSV-1) infection has emerged as a major factor in the etiology of AD. HSV-1 is able to induce some of the main alterations of the disease such as hyperphosphorylation of tau protein and accumulation of amyloid-ß peptide. Functional genomic analysis of a cell model of HSV-1 infection and oxidative stress developed in our laboratory revealed lysosomal system to be the main pathway altered, and the lysosome-associated membrane protein 2 (LAMP2) gene one of the most strongly modulated genes. The aim of this work is to study LAMP2 as an AD candidate gene and to investigate its role in the neurodegeneration induced by HSV-1 using a LAMP2 knockdown cell model. LAMP2 deficiency led to a significant reduction of viral DNA replication and formation of infectious particles. In addition, tau hyperphosphorylation and inhibition of Aß secretion induced by the virus were attenuated by the absence of LAMP2. Finally, genetic association studies revealed LAMP2 genetic variants to be associated with AD risk. In summary, our data indicate that LAMP2 could be a suitable candidate to mediate the AD-like phenotype caused by HSV-1.

Matrix Metalloproteinase 14 Mediates APP Proteolysis and Lysosomal Alterations Induced by Oxidative Stress in Human Neuronal Cells.

The alteration of amyloid precursor protein (APP) proteolysis is a hallmark of Alzheimer's disease (AD). Recent studies have described noncanonical pathways of APP processing that seem partly executed by lysosomal enzymes. Our laboratory's in vitro human SK-N-MC model has shown that oxidative stress (OS) alters the lysosomal degradation pathway and the processing/metabolism of APP. The present study identifies the lysosomal protein matrix metalloproteinase 14 (MMP14) as a protease involved in the APP noncanonical processing. Previous expression analyses of the above cells showed MMP14 to be overexpressed under OS. In the present work, its role in changes in OS-induced APP proteolysis and lysosomal load was examined. The results show that MMP14 mediates the accumulation of an ≈85 kDa N-terminal APP fragment and increases the lysosome load induced by OS. These results were validated in neurons and neural progenitor cells generated from the induced pluripotent stem cells of patients with sporadic AD, reinforcing the idea that MMP14 may offer a therapeutic target in this disease.

Tetraspanin CD81 regulates HSV-1 infection.

Different members of the tetraspanin superfamily have been described to regulate different virus infectious cycles at several stages: viral entry, viral replication or virion exit or infectivity. In addition, tetraspanin CD81 regulates HIV reverse transcription through its association with the dNTP hydrolase SAMHD1. Here we aimed at analysing the role of CD81 in Herpes simplex virus 1 infectivity using a neuroblastoma cell model. For this purpose, we generated a CD81 KO cell line using the CRISPR/Cas9 technology. Despite being CD81 a plasma membrane protein, CD81 KO cells showed no defects in viral entry nor in the expression of early protein markers. In contrast, glycoprotein B and C, which require viral DNA replication for their expression, were significantly reduced in CD81 KO infected cells. Indeed, HSV-1 DNA replication and the formation of new infectious particles were severely compromised in CD81 KO cells. We could not detect significant changes in SAMHD1 total expression levels, but a relocalization into endosomal structures was observed in CD81 KO cells. In summary, CD81 KO cells showed impaired viral DNA replication and produced greatly diminished viral titers.

A Free Radical-Generating System Regulates Amyloid Oligomers: Involvement of Cathepsin B.

Amyloid-ß (Aß), a major component of senile plaques, is generated via the proteolysis of amyloid-ß protein precursor (AßPP). This cleavage also produces AßPP fragment-derived oligomers which can be highly neurotoxic. AßPP metabolism/processing is affected by many factors, one of which is oxidative stress (OS). Associated with aging, OS is an important risk factor for Alzheimer's disease. In addition, the protein degradation systems, especially those involving cathepsins, are impaired in aging brains. Moreover, cathepsin B (CTSB) is a cysteine protease with potentially specific roles in AßPP proteolysis (ß-secretase activity) and Aß clearance (Aß degradative activity). The present work examines the effect of OS and the involvement of CTSB in amyloid oligomer formation. The xanthine/xanthine oxidase (X-XOD) free radical generating system induced the partial inhibition of CTSB activity, which was accompanied by an increase in large amyloid oligomers. These were located throughout the cytosol and in endo-lysosomal vesicles. Cells treated with the CTSB inhibitor CA-074Me also showed increased amyloid oligomer levels, whereas those subjected to OS in the presence of the inhibitor showed no such increase. However, CTSB inhibition clearly modulated the AßPP metabolism/processing induced by X-XOD, as revealed by the increase in intracellular AßPP and secreted α-secretase-cleaved soluble AßPP. The present results suggest that CTSB participates in the changes of amyloid oligomer induced by mild OS.

The lysosome system is severely impaired in a cellular model of neurodegeneration induced by HSV-1 and oxidative stress.

The causal agent(s) and molecular mechanisms of Alzheimer's disease (AD) remain unclear. Mounting evidence suggests that herpes simplex virus type 1 (HSV-1) infection is involved in the AD pathogenesis. Oxidative stress (OS) may also be crucial in the AD development. Our group previously reported that both HSV-1 and OS trigger the appearance of AD-type neurodegeneration markers. The main aim of the present study was to identify the mechanisms involved in this triggering. Expression studies revealed the involvement of a set of OS-regulated genes in HSV-1-infected cells and in cells harboring the Swedish mutation of the amyloid beta precursor protein gene. Functional annotation of these genes revealed the lysosome system to be impaired, suggesting that the interaction of OS with both HSV-1 and amyloid beta precursor protein mutations affects lysosomal function. Functional studies revealed HSV-1 infection and OS to increase the lysosome load, reduce the activity of lysosomal hydrolases, affect cathepsin maturation, and inhibit the endocytosis-mediated degradation of the epidermal growth factor receptor. These findings suggest alterations in the lysosome system to be involved in different forms of AD.

Herpes simplex virus type 2 infection induces AD-like neurodegeneration markers in human neuroblastoma cells.

Herpes simplex virus (HSV) types 1 and 2 are neurotropic viruses that establish lifelong latent infections in neurons. Mounting evidence suggests that HSV-1 infection is involved in the pathogenesis of Alzheimer's disease (AD). The relationships between other herpesvirus infections and events associated with neurodegeneration have not, however, been extensively studied. The present work reports that HSV-2 infection leads to the strong accumulation of hyperphosphorylated tau and the amyloid-ß peptides Aß40 and Aß42 (all major pathological hallmarks of AD) in human SK-N-MC neuroblastoma cells. Infection is also associated with a marked reduction in the amount of Aß40 secreted and in the proteolytic fragments of the amyloid-ß precursor protein (APP) (secreted APPα and the α-C-terminal fragment). These results indicate that HSV-2 infection inhibits the nonamyloidogenic pathway of APP processing and impairs Aß secretion in these cells. In addition, HSV-2 induces the accumulation of intracellular autophagic compartments containing Aß due to a failure in the late stages of autophagy. To our knowledge, this is the first report to show that HSV-2 infection strongly alters the tau phosphorylation state, APP processing, and autophagic process in human neuroblastoma cells, leading to the appearance of AD-like neurodegeneration markers.

Choroid plexus implants rescue Alzheimer's disease-like pathologies by modulating amyloid-ß degradation.

The choroid plexuses (CP) release numerous biologically active enzymes and neurotrophic factors, and contain a subpopulation of neural progenitor cells providing the capacity to proliferate and differentiate into other types of cells. These characteristics make CP epithelial cells (CPECs) excellent candidates for cell therapy aiming at restoring brain tissue in neurodegenerative illnesses, including Alzheimer's disease (AD). In the present study, using in vitro approaches, we demonstrated that CP were able to diminish amyloid-ß (Aß) levels in cell cultures, reducing Aß-induced neurotoxicity. For in vivo studies, CPECs were transplanted into the brain of the APP/PS1 murine model of AD that exhibits advanced Aß accumulation and memory impairment. Brain examination after cell implantation revealed a significant reduction in brain Aß deposits, hyperphosphorylation of tau, and astrocytic reactivity. Remarkably, the transplantation of CPECs was accompanied by a total behavioral recovery in APP/PS1 mice, improving spatial and non-spatial memory. These findings reinforce the neuroprotective potential of CPECs and the use of cell therapies as useful tools in AD.

Oxidative stress enhances neurodegeneration markers induced by herpes simplex virus type 1 infection in human neuroblastoma cells.

Mounting evidence suggests that Herpes simplex virus type 1 (HSV-1) is involved in the pathogenesis of Alzheimer's disease (AD). Previous work from our laboratory has shown HSV-1 infection to induce the most important pathological hallmarks of AD brains. Oxidative damage is one of the earliest events of AD and is thought to play a crucial role in the onset and development of the disease. Indeed, many studies show the biomarkers of oxidative stress to be elevated in AD brains. In the present work the combined effects of HSV-1 infection and oxidative stress on Aß levels and autophagy (neurodegeneration markers characteristic of AD) were investigated. Oxidative stress significantly potentiated the accumulation of intracellular Aß mediated by HSV-1 infection, and further inhibited its secretion to the extracellular medium. It also triggered the accumulation of autophagic compartments without increasing the degradation of long-lived proteins, and enhanced the inhibition of the autophagic flux induced by HSV-1. These effects of oxidative stress were not due to enhanced virus replication. Together, these results suggest that HSV-1 infection and oxidative damage interact to promote the neurodegeneration events seen in AD.

A free radical-generating system regulates AßPP metabolism/processing: involvement of the ubiquitin/proteasome and autophagy/lysosome pathways.

Oxidative stress is an early event in the pathogenesis of Alzheimer's disease (AD). We previously reported that, in SK-N-MC cells, the xanthine/xanthine oxidase (X-XOD) free radical generating system regulates the metabolism/processing of the amyloid-ß protein precursor (AßPP). Oxidative stress alters the two main cellular proteolytic machineries, the ubiquitin/proteasome (UPS) and the autophagy/lysosome systems, and recent studies have established connections between the malfunctioning of these and the pathogenesis of AD. The aim of the present work was to examine the involvement of these proteolytic systems in the regulation of AßPP metabolism by X-XOD. The proteasome inhibitor MG132 was found to accelerate the metabolism/processing of AßPP promoted by X-XOD because it significantly enhances the secretion of α-secretase-cleaved soluble AßPP and also the levels of both carboxy-terminal fragments (CTFs) produced by α- and ß-secretase. Further, MG132 modulated the intracellular accumulation of holo-AßPP and/or AßPP CTFs. This indicates that the X-XOD modulation of AßPP metabolism/processing involves the UPS pathway. With respect to the autophagy/lysosome pathway, the AßPP processing and intracellular location patterns induced by X-XOD treatment closely resembled those produced by the lysosome inhibitor ammonium chloride. The present results suggest that the regulation of AßPP metabolism/processing by mild oxidative stress requires UPS activity with a simultaneous reduction in that of the autophagy/lysosome system.

Herpes simplex virus type I induces an incomplete autophagic response in human neuroblastoma cells.

Autophagy is a homeostatic process involved in the turnover or elimination of cytoplasmic components, damaged organelles, and protein aggregates via a lysosomal degradation mechanism. Autophagy also provides a mechanism of innate immunity, known as xenophagy, designed to protect cells from intracellular pathogens, but it may unfortunately be subverted to act as a pro-viral pathway facilitating the replication of certain viruses. Herpes simplex virus type I (HSV-1) is a neurotropic virus that remains latent in host neurons; it is the most common cause of sporadic viral encephalitis. Moreover, HSV-1 has been related to the pathogenesis of Alzheimer's disease. HSV-1 can modulate the autophagic process through a mechanism mediated by the viral protein ICP34.5. Here we report that HSV-1 induces a strong increase in GFP-LC3 and endogenous LC3 lipidation, and triggers the accumulation of intracellular autophagic compartments (mainly autophagosomes) without enhancing autophagic long-lived protein degradation in the late stages of infection. Autophagy inhibition mediated by ATG5 gene silencing had no effect on viral growth. The present results suggest that HSV-1 infection activates the host autophagic machinery and strongly controls the autophagic process, blocking the fusion of autophagosomes with lysosomes. These events might be important in the neurodegenerative process associated with HSV-1 infection.

Herpes simplex virus type 1 induces nuclear accumulation of hyperphosphorylated tau in neuronal cells.

Herpes simplex virus type 1 (HSV-1) is a neurotropic virus that remains latent in host neurons. Viral DNA replication is a highly structured process in which the redistribution of nuclear proteins plays an important role. Although tau is most widely known as a microtubule-associated protein found in a hyperphosphorylated state in the brains of patients with Alzheimer's disease (AD), this protein has also been detected at other sites such as the nucleolus. Here, we establish that HSV-1 infection gives rise to an increase in tau phosphorylation and that hyperphosphorylated tau accumulates in the nucleus, forming defined structures in HSV-1-infected neuronal cells reminiscent of the common sites of viral DNA replication. When tau expression in human neuroblastoma cells was specifically inhibited using an adenoviral vector expressing a short hairpin RNA to tau, viral DNA replication was not affected, indicating that tau is not required for HSV-1 growth in neuronal cells. Given that HSV-1 is considered a risk factor for AD, our results suggest a new way in which to understand the relationships between HSV-1 infection and the pathogenic mechanisms leading to AD.

Herpes simplex virus type I induces the accumulation of intracellular ß-amyloid in autophagic compartments and the inhibition of the non-amyloidogenic pathway in human neuroblastoma cells.

Mounting evidence suggests that herpes simplex virus type 1 (HSV-1) is involved in the pathogenesis of Alzheimer's disease (AD). Epidemiological analyses have shown that HSV-1 is a risk factor for AD in people with at least 1 type 4 allele of the apolipoprotein E gene. Recent studies have also suggested that HSV-1 contributes to the appearance of the biochemical anomalies characteristic of AD brains. In addition, autophagic activity appears to be reduced with aging, and the final stages of autophagy in neurodegenerative process appear to be impaired. The present work reports that HSV-1 provokes the strong intracellular accumulation of both the main species of ß-amyloid (Aß) in the autophagic compartments and that it is associated with a marked inhibition of Aß secretion. Autophagosomes containing Aß failed to fuse with lysosomes in HSV-1-infected cells, indicating the impaired degradation of Aß localized in the autophagic vesicles. In addition, HSV-1 infection was associated with the inhibition of the nonamyloidogenic pathway of amyloid precursor protein (APP) processing without significantly affecting the activity of the secretases involved in the amyloidogenic pathway. Taken together, these data suggest that HSV-1 infection modulates autophagy and amyloid precursor protein processing, contributing to the accumulation of Aß characteristic of AD.

A free radical-generating system regulates APP metabolism/processing.

Oxidative stress, a risk factor in the pathophysiology of Alzheimer's disease, is intimately associated with aging. We previously reported that the X-XOD free radical generating system acts as a modulator of lipid metabolism and a mild inducer of apoptotic death. Using the same cell model, the present study examines the metabolism/processing of the amyloid precursor protein (APP). Prior to inducing cell death, X-XOD promoted the secretion of α-secretase-cleaved soluble APP (sAPPα) and increased the level of APP carboxy-terminal fragments produced by α and γ secretase (αCTF and γCTF/AICD). In contrast, it reduced the activity of ß-secretase and the level of secreted Aß. The present results indicate that mild oxidative stress maintained throughout culturing regulates APP metabolism/processing in SK-N-MC human neuroblastoma cells.

PLA2G3, a gene involved in oxidative stress induced death, is associated with Alzheimer's disease.

Oxidative stress, which plays a critical role in the pathogenesis of neurodegenerative diseases such as Alzheimer's disease (AD), is intimately linked to aging, the best established risk factor for AD. Studies in neuronal cells subjected to oxidative stress, mimicking such stress in AD brains, are therefore of great interest. PLA2G3 is the most overexpressed gene in a human neuronal model of oxidative stress induced by the free radical-generating xanthine/xanthine oxidase (X-XOD) system, which provokes apoptotic cell death. In this work, we describe that PLA2G3 gene silencing produced a marked inhibition of X-XOD induced cell death, and that PLA2G3 polymorphisms are associated with AD in a Spanish case-control sample. The capacity to respond to oxidative stress may therefore modulate the risk of AD, and PLA2G3 is a potential target to regulate neuronal damage induced by free radicals.

A free radical-generating system induces the cholesterol biosynthesis pathway: a role in Alzheimer's disease.

Oxidative stress, which plays a critical role in the pathogenesis of neurodegenerative diseases such as Alzheimer's disease (AD), is intimately linked to aging - the best established risk factor for AD. Studies in neuronal cells subjected to oxidative stress, mimicking the situation in AD brains, are therefore of great interest. This paper reports that, in human neuronal cells, oxidative stress induced by the free radical-generating xanthine/xanthine oxidase (X-XOD) system leads to apoptotic cell death. Microarray analyses showed a potent activation of the cholesterol biosynthesis pathway following reductions in the cell cholesterol synthesis caused by the X-XOD treatment; furthermore, the apoptosis was reduced by inhibiting 3-hydroxy-3-methylglutaryl-coenzyme A reductase (HMGCR) expression with an interfering RNA. The potential importance of this mechanism in AD was investigated by genetic association, and it was found that HMGCR, a key gene in cholesterol metabolism and among those most strongly upregulated, was associated with AD risk. In summary, this work presents a human cell model prepared to mimic the effect of oxidative stress in neurons that might be useful in clarifying the mechanism involved in free radical-induced neurodegeneration. Gene expression analysis followed by genetic association studies indicates a possible link among oxidative stress, cholesterol metabolism and AD.

Presenilin 1 polymorphism associated with Alzheimer's disease in apolipoprotein E4 carriers.

Mutations of presenilin 1 (PSEN1) are associated with monogenic Alzheimer's disease (AD); polymorphisms at this gene may therefore be associated with the sporadic form of the disease. In fact, recent meta-analyses and whole-genome association studies indicate PSEN1 as one of the few genes significantly associated with AD risk. Several polymorphisms have been analyzed in PSEN1. The present work examined the possible modulation of the risk of AD by a PSEN1 polymorphism (dbSNP rs3025786) located in intron 7, which we found during a denaturing gradient gel electrophoresis mutation screening of the gene, and which was previously reported as 'suspected' in the public databases. The study of a Spanish case-control sample of 1,183 individuals showed this polymorphism to be associated with AD in an apolipoprotein E (APOE)-specific manner: more specifically, to carry the PSEN1 C allele was associated with a decreased AD risk among carriers of the APOE4 allele. Thus, the present results reinforce the possible involvement of PSEN1 in sporadic AD.