Herpes simplex virus-1 (HSV-1) infection induces a potent but ineffective IFN-λ production in immune cells of AD and PD patients

The Quest for Immunity: Exploring Human Herpesviruses as Vaccine Vectors

Herpesviruses are large DNA viruses that have long been used as powerful gene therapy tools. In recent years, the ability of herpesviruses to stimulate both innate and adaptive immune responses has led to their transition to various applications as vaccine vectors. This vaccinology branch is growing at an unprecedented and accelerated rate. To date, human herpesvirus-based vectors have been used in vaccines to combat a variety of infectious agents, including the Ebola virus, foot and mouth disease virus, and human immunodeficiency viruses. Additionally, these vectors are being tested as potential vaccines for cancer-associated antigens. Thanks to advances in recombinant DNA technology, immunology, and genomics, numerous steps in vaccine development have been greatly improved. A better understanding of herpesvirus biology and the interactions between these viruses and the host cells will undoubtedly foster the use of herpesvirus-based vaccine vectors in clinical settings. To overcome the existing drawbacks of these vectors, ongoing research is needed to further advance our knowledge of herpesvirus biology and to develop safer and more effective vaccine vectors. Advanced molecular virology and cell biology techniques must be used to better understand the mechanisms by which herpesviruses manipulate host cells and how viral gene expression is regulated during infection. In this review, we cover the underlying molecular structure of herpesviruses and the strategies used to engineer their genomes to optimize capacity and efficacy as vaccine vectors. Also, we assess the available data on the successful application of herpesvirus-based vaccines for combating diseases such as viral infections and the potential drawbacks and alternative approaches to surmount them.

Nicotinamide n-Oxide Attenuates HSV-1-Induced Microglial Inflammation through Sirtuin-1/NF-κB Signaling

HSV-1 is a typical neurotropic virus that infects the brain and causes keratitis, cold sores, and occasionally, acute herpes simplex encephalitis (HSE). The large amount of proinflammatory cytokines induced by HSV-1 infection is an important cause of neurotoxicity in the central nervous system (CNS). Microglia, as resident macrophages in CNS, are the first line of defense against neurotropic virus infection. Inhibiting the excessive production of inflammatory cytokines in overactivated microglia is a crucial strategy for the treatment of HSE. In the present study, we investigated the effect of nicotinamide n-oxide (NAMO), a metabolite mainly produced by gut microbe, on HSV-1-induced microglial inflammation and HSE. We found that NAMO significantly inhibits the production of cytokines induced by HSV-1 infection of microglia, such as IL-1β, IL-6, and TNF-α. In addition, NAMO promotes the transition of microglia from the pro-inflammatory M1 type to the anti-inflammatory M2 type. More detailed studies revealed that NAMO enhances the expression of Sirtuin-1 and its deacetylase enzymatic activity, which in turn deacetylates the p65 subunit to inhibit NF-κB signaling, resulting in reduced inflammatory response and ameliorated HSE pathology. Therefore, Sirtuin-1/NF-κB axis may be promising therapeutic targets against HSV-1 infection-related diseases including HSE.

Neuroinflammation in neurodegeneration via microbial infections

Recent epidemiological studies show a noticeable correlation between chronic microbial infections and neurological disorders. However, the underlying mechanisms are still not clear due to the biological complexity of multicellular and multiorgan interactions upon microbial infections. In this review, we show the infection leading to neurodegeneration mediated by multiorgan interconnections and neuroinflammation. Firstly, we highlight three inter-organ communications as possible routes from infection sites to the brain: nose-brain axis, lung-brain axis, and gut-brain axis. Next, we described the biological crosstalk between microglia and astrocytes upon pathogenic infection. Finally, our study indicates how neuroinflammation is a critical player in pathogen-mediated neurodegeneration. Taken together, we envision that antibiotics targeting neuro-pathogens could be a potential therapeutic strategy for neurodegeneration.

MAMDC2, a gene highly expressed in microglia in experimental models of Alzheimers Disease, positively regulates the innate antiviral response during neurotropic virus infection

Microglia, as central nervous system (CNS)-resident macrophages, are the first line of defense against neurotropic virus infection, the immune response of which is implicated in numerous CNS diseases, including Alzheimer's disease (AD). Indeed, the infectious hypothesis for AD has long been recognized, of note herpes simplex virus type 1 (HSV-1), the most common human neurotropic virus. However, the mechanism linking HSV-1 and AD remains obscure. In this study, we analyzed the transcriptome data of microglia in AD mice. We found that MAM domain containing 2 (MAMDC2) is significantly upregulated in microglia isolated from both a series of AD mice established by numerous genetic strategies and mice with HSV-1 infection. Mamdc2-deficient (Mamdc2^-/-) mice are susceptible to HSV-1 infection and show an impaired type I interferon (I-IFN)-based innate antiviral response upon neurotropic HSV-1 infection. The in vitro experiments suggest a similar result. Moreover, lentivirus-mediated overexpression of Mamdc2 in mouse brains enhances the innate antiviral response in microglia and ameliorates herpes simplex encephalitis (HSE) symptoms. Mechanistically, MAMDC2 interacts with STING via its first MAM domain within and enhances the polymerization of STING, activating downstream TBK1-IRF3 signaling to facilitate the expression of I-IFNs. The sulfated glycosaminoglycan-mediated polymerization of STING also largely depends on MAMDC2. Our study uncovers the function of MAMDC2 in the innate antiviral response in microglia, revealing a potential mechanism linking HSV-1 and AD, especially the contribution of Mamdc2 overexpression to the upregulation of I-IFN in the AD brain.

How an increase in the copy number of HSV-1 during latency can cause Alzheimer's disease: the viral and cellular dynamics according to the microcompetition model

Numerous studies observed a link between the herpes smplex virus-1 (HSV-1) and Alzheimer's disease. However, the exact viral and cellular dynamics that lead from an HSV-1 infection to Alzheimer's disease are unknown. In this paper, we use the microcompetition model to formulate these dynamics by connecting seemingly unconnected observations reported in the literature. We concentrate on four pathologies characteristic of Alzheimer's disease. First, we explain how an increase in the copy number of HSV-1 during latency can decrease the expression of BECN1/Beclin1, the degradative trafficking protein, which, in turn, can cause a dysregulation of autophagy and Alzheimer's disease. Second, we show how an increase in the copy number of the latent HSV-1 can decrease the expression of many genes important for mitochondrial genome metabolism, respiratory chain, and homeostasis, which can lead to oxidative stress and neuronal damage, resulting in Alzheimer's disease. Third, we describe how an increase in this copy number can reduce the concentration of the NMDA receptor subunits NR1 and NR2b (Grin1 and Grin2b genes), and brain derived neurotrophic factor (BDNF), which can cause an impaired synaptic plasticity, Aβ accumulation and eventually Alzheimer's disease. Finally, we show how an increase in the copy number of HSV-1 in neural stem/progenitor cells in the hippocampus during the latent phase can lead to an abnormal quantity and quality of neurogenesis, and the clinical presentation of Alzheimer's disease. Since the current understanding of the dynamics and homeostasis of the HSV-1 reservoir during latency is limited, the proposed model represents only a first step towards a complete understanding of the relationship between the copy number of HSV-1 during latency and Alzheimer's disease.

The Analysis of Herpes Simplex Virus Type 1 (HSV-1)-Encoded MicroRNAs Targets: A Likely Relationship of Alzheimer's Disease and HSV-1 Infection

Alzheimer's disease (AD), the most frequently diagnosed dementia, is a senile neurodegenerative disorder characterized by amnesia and cognitive dysfunction. Unfortunately, there are still no successful strategies to prevent AD progression. Thus, the vast majority of research focuses on recognizing risk factors for developing and progressing this disease. Human spirochetes, fungi, Borrelia burgdorferi, Chlamydophila pneumoniae, Helicobacter pylori, and human herpes simplex virus type 1 (HSV-1) have all been implicated in the development and progression of AD. Identifying microRNAs (miRs) encoded by DNA viruses has indicated that viruses can be evolved to exploit RNA silencing to regulate host and viral genes. Similar to host miR, v-miR can interact with the 3' untranslated region (UTR) of the target mRNA to regulate gene expression. Although HSV-1 can also encode various miRs, their significance in the development and progression of AD is still unclear. In the present study, utilizing the bioinformatics approach (R software and related packages), we analyzed the differentially expressed genes (DEGs) in AD samples (grey matter) of GSE37263 dataset obtained from the NCBI Gene Expression Omnibus (GEO). Then, the sequences of HSV-1-encoded-miRs were retrieved from miRbase, and their targets were predicted by miRDB. Afterward, the common genes between downregulated DEGs in AD and targets of HSV-1-encoded miRs were identified to shed new light on the relationship between HSV-1 infection and AD development. Our results have indicated that HSV-1-encoded-miRs can target the downregulated DEGs in AD, and these aberrant interactions can offer valuable diagnostic/prognostic biomarkers for affected patients.

Can Control Infections Slow Down the Progression of Alzheimer's Disease? Talking About the Role of Infections in Alzheimer's Disease

Alzheimer’s disease as the most common age-related dementia affects more than 40 million people in the world, representing a global public health priority. However, the pathogenesis of Alzheimer’s disease (AD) is complex, and it remains unclear. Over the past decades, all efforts made in the treatments of AD, with targeting the pathogenic amyloid β (Aβ), neurofibrillary tangles, and misfolded tau protein, were failed. Recently, many studies have hinted that infection, and chronic inflammation that caused by infection are crucial risk factors for AD development and progress. In the review, we analyzed the role of infections caused by bacteria, viruses, and other pathogens in the pathogenesis of AD and its animal models, and explored the therapeutic possibility with anti-infections for AD. However, based on the published data, it is still difficult to determine their causal relationship between infection and AD due to contradictory results. We think that the role of infection in the pathogenesis of AD should not be ignored, even though infection does not necessarily cause AD, it may act as an accelerator in AD at least. It is essential to conduct the longitudinal studies and randomized controlled trials in humans, which can determine the role of infection in AD and clarify the links between infection and the pathological features of AD. Finding targeting infection drugs and identifying the time window for applying antibacterial or antiviral intervention may be more promising for future clinical therapeutic strategies in AD.

A Possible Role for HSV-1-Specific Humoral Response and PILRA rs1859788 Polymorphism in the Pathogenesis of Parkinson's Disease

The etiology of Parkinson's disease (PD), a progressive nervous system disorder that affects movement, is still unknown; both genetic and environmental factor are believed to be involved in onset of the disease and its development. Herpes simplex virus type 1 (HSV-1), in particular, is suspected to have a role in PD. Paired Immunoglobulin-like type 2 receptor alpha (PILRA) is an inhibitory receptor that down-regulates inflammation and is expressed on innate immune cells. The PILRA rs1859788 polymorphism is protective against Alzheimer's disease, even in relation with HSV-1 antibody titers, but no data are available in PD. We analyzed HSV-1 antibody titers and PILRA rs1859788 in PD (n = 51) and age-and sex-matched healthy controls (HC; n = 73). Results showed that HSV-1, but not cytomegalovirus (CMV) or human herpes virus type 6 (HHV-6) antibody titers were significantly higher in PD compared to HC (p = 0.045). The rs1859788 polymorphism was not differentially distributed between PD and HC, but the minor allele A was more frequently carried by PD (68%) compared to HC (50%) (p = 0.06). Notably, the rs1859788 minor allele A was statically more frequent in male PD (65%) compared to male HC (37%) (p = 0.036). Finally, no relation was found between HSV-1 antibody titers and PILRA genotype. Results herein suggest an involvement of HSV-1 in PD and indicate a possible interaction between PILRA gene polymorphisms and this neuropathology.

Viral Involvement in Alzheimer's Disease

Alzheimer's disease (AD) is characterized by the presence of β-amyloid plaques (Aβ) and neurofibrillary tangles (NFTs) in the brain. The prevalence of the disease is increasing and is expected to reach 141 million cases by 2050. Despite the risk factors associated with the disease, there is no known causative agent for AD. Clinical trials with many drugs have failed over the years, and no therapeutic has been approved for AD. There is increasing evidence that pathogens are found in the brains of AD patients and controls, such as human herpes simplex virus-1 (HSV-1). Given the lack of a human model, the route for pathogen entry into the brain remains open for scrutiny and may include entry via a disturbed blood-brain barrier or the olfactory nasal route. Many factors can contribute to the pathogenicity of HSV-1, such as the ability of HSV-1 to remain latent, tau protein phosphorylation, increased accumulation of Aβ invivo and in vitro, and repeated cycle of reactivation if immunocompromised. Intriguingly, valacyclovir, a widely used drug for the treatment of HSV-1 and HSV-2 infection, has shown patient improvement in cognition compared to controls in AD clinical studies. We discuss the potential role of HSV-1 in AD pathogenesis and argue for further studies to investigate this relationship.

Herpesviruses and the Type III Interferon System

Type III interferons (IFNs) represent the most recently discovered group of IFNs. Together with type I IFNs (e.g. IFN-α/β), type III IFNs (IFN-λ) are produced as part of the innate immune response to virus infection, and elicit an anti-viral state by inducing expression of interferon stimulated genes (ISGs). It was initially thought that type I IFNs and type III IFNs perform largely redundant functions. However, it has become evident that type III IFNs particularly play a major role in antiviral protection of mucosal epithelial barriers, thereby serving an important role in the first-line defense against virus infection and invasion at contact areas with the outside world, versus the generally more broad, potent and systemic antiviral effects of type I IFNs. Herpesviruseses are large DNA viruses, which enter their host via mucosal surfaces and establish lifelong, latent infections. Despite the importance of mucosal epithelial cells in the pathogenesis of herpesviruses, our current knowledge on the interaction of herpesviruses with type III IFN is limited and largely restricted to studies on the alphaherpesvirus herpes simplex virus (HSV). This review summarizes the current understanding about the role of IFN-λ in the immune response against herpesvirus infections.

Alzheimer's Gone Viral: Could Herpes Simplex Virus Type-1 Be Stealing Your Memories?

Alzheimer's disease (AD) is one of the principal causes of disability and morbidity. It is one of the most expensive illnesses. Despite this, there are no significant data regarding its etiology and optimal treatment. This review concentrates on the viral hypothesis of AD. After a comprehensive PubMed literature search, we analyzed the studies associating herpes simplex virus type-1 (HSV1) infection to AD from the previous 10 years. Molecular mechanisms whereby HSV1 induces AD-related pathophysiology, including neuronal production and accumulation of amyloid-beta (amyloid-β), abnormal phosphorylation of tau proteins, impaired calcium homeostasis, and autophagy, are addressed. The virus also imitates the disease in other ways, showing increased neuroinflammation, oxidative stress, synaptic dysfunction, and neuronal apoptosis. Serological studies correlate HSV1 infection with AD and cognitive impairment. A causal link between HSV1 and AD raises the concept of a simple, efficient, and preventive treatment alternative. Anti-viral agents impede brain degeneration by preventing HSV1 spread and its replication, decreasing hyperphosphorylated tau and amyloid-β; thus providing an efficacious treatment for AD. We also mention brown algae, intravenous immunoglobulin (IVIG), and a synthetic drug, BAY57-1293, with anti-viral properties, as options for treating AD. We want to recommend future researchers to look for more affordable, non-invasive, and swifter techniques to identify HSV1 in the brain and assist in the early detection and prevention of AD.