Herpes Simplex Virus 1 and 2 Infections during Differentiation of Human Cortical Neurons

HSV-1 infection induces phosphorylated tau propagation among neurons via extracellular vesicles

Extracellular vesicles (EV), key players in cell-to-cell communication, may contribute to disease propagation in several neurodegenerative diseases, including Alzheimer's disease (AD), by favoring the dissemination of neurotoxic proteins within the brain. Interestingly, growing evidence supports the role of herpes simplex virus type 1 (HSV-1) infection in the pathogenesis of AD. Here, we investigated whether HSV-1 infection could promote the spread of phosphorylated tau (ptau) among neurons via EV. We analyzed the ptau species that were secreted via EV following HSV-1 infection in neuroblastoma cells and primary neurons, focusing particularly on T205, T181, and T217, the phosphorylation sites mainly associated with AD. Moreover, by overexpressing human tau tagged with GFP (htauGFP), we found that recipient tau knockout (KO) neurons uptook EV that are loaded with HSV-1-induced phtauGFP. Finally, we exploited an in vivo model of acute infection and assessed that cerebral HSV-1 infection promotes the release of ptau via EV in the brain of infected mice. Overall, our data suggest that, following HSV-1 infection, EV play a role in tau spreading within the brain, thus contributing to neurodegeneration.IMPORTANCEHerpes simplex virus type 1 (HSV-1) infection that reaches the brain has been repeatedly linked with the appearance of the pathognomonic markers of Alzheimer's disease (AD), including accumulation of amyloid beta and hyperphosphorylated tau proteins, and cognitive deficits. AD is a multifactorial neurodegenerative disease representing the most common form of dementia in the elderly, and no cure is currently available, thus prompting additional investigation on potential risk factors and pathological mechanisms. Here, we demonstrate that the virus exploits the extracellular vesicles (EV) to disseminate phosphorylated tau (ptau) among brain cells. Importantly, we provide evidence that the HSV-1-induced EV-bearing ptau can be undertaken by recipient neurons, thus likely contributing to misfolding and aggregation of native tau, as reported for other AD models. Hence, our data highlight a novel mechanism exploited by HSV-1 to propagate tau-related damage in the brain.

Type 2 herpes simplex virus-induced anti-N-methyl-D-aspartate receptor encephalitis responsive to immunoglobulin monotherapy

Herpes simplex virus-2 encephalitis (HSV2E) in immunocompetent adults is exceptionally rare, and the subsequent onset of autoimmune encephalitis after HSV2E is even less common. This report presents the inaugural Chinese case of anti-N-methyl-D-aspartate receptor encephalitis (NMDARE) induced by HSV2E, confirmed via metagenomic next-generation sequencing (mNGS). The patient demonstrated a favorable response to intravenous immunoglobulin (IVIG) monotherapy. This case emphasizes the importance of considering autoimmune encephalitis in patients exhibiting new or recurrent neurological symptoms after HSV2E recovery. Comprehensive mNGS and neuronal antibody testing are essential for timely diagnosis. Moreover, IVIG monotherapy can serve as an effective treatment for NMDARE induced by HSV2, providing a viable alternative, particularly when steroid therapy is contraindicated.

Alzheimer's disease and herpes viruses: Current events and perspectives

Alzheimer's disease (AD) is a real and current scientific and societal challenge. Alzheimer's disease is characterised by a neurodegenerative neuroinflammatory process, but the etiopathogenetic mechanisms are still unclear. The possible infectious aetiology and potential involvement of Herpes viruses as triggers for the formation of extracellular deposits of amyloid beta (Aβ) peptide (amyloid plaques) and intraneuronal aggregates of hyperphosphorylated and misfold could be a possible explanation. In fact, the possible genetic interference of Herpes viruses with the genome of the host neuronal cell or the stimulation of the infection to a continuous immune response with a consequent chronic inflammation could constitute those mechanisms underlying the development of AD, with possible implications in the understanding and management of the disease. Herpes viruses could be significantly involved in the pathogenesis of AD and in particular, their ability to reactivate in particular conditions such as immunocompromise and immunosenescence, could explain the neurological damage characteristic of AD. Our review aims to evaluate the state of the art of knowledge and perspectives regarding the potential relationship between Herpes viruses and AD, in order to be able to identify the possible etiopathogenetic mechanisms and the possible therapeutic implications.

Alzheimer's disease as a viral disease: Revisiting the infectious hypothesis

Alzheimer's disease (AD) represents the most frequent type of dementia in elderly people. Two major forms of the disease exist: sporadic - the causes of which have not yet been fully understood - and familial - inherited within families from generation to generation, with a clear autosomal dominant transmission of mutations in Presenilin 1 (PSEN1), 2 (PSEN2) or Amyloid Precursors Protein (APP) genes. The main hallmark of AD consists of extracellular deposits of amyloid-beta (Aβ) peptide and intracellular deposits of the hyperphosphorylated form of the tau protein. An ever-growing body of research supports the viral infectious hypothesis of sporadic forms of AD. In particular, it has been shown that several herpes viruses (i.e., HHV-1, HHV-2, HHV-3 or varicella zoster virus, HHV-4 or Epstein Barr virus, HHV-5 or cytomegalovirus, HHV-6A and B, HHV-7), flaviviruses (i.e., Zika virus, Dengue fever virus, Japanese encephalitis virus) as well as Human Immunodeficiency Virus (HIV), hepatitis viruses (HAV, HBV, HCV, HDV, HEV), SARS-CoV2, Ljungan virus (LV), Influenza A virus and Borna disease virus, could increase the risk of AD. Here, we summarized and discussed these results. Based on these findings, significant issues for future studies are also put forward.

Application of metagenomic next-generation sequencing technique for diagnosing a specific case of necrotizing meningoencephalitis caused by human herpesvirus 2

Reactivation of latent human herpesvirus 2 (HHV-2) can cause spontaneous recovering aseptic meningitis and recurrent meningitis in adults, but it rarely affects the brain parenchyma to cause encephalitis. Here, we report the case of a 37-year-old male patient admitted to our hospital due to fever with a progressive headache for 3 days and paroxysmal episodes of unconsciousness for 1 day. Brain magnetic resonance imaging (MRI) revealed viral meningoencephalitis. Then, metagenomics next-generation sequencing (mNGS) was applied, which detected 12,024 unique sequences of HHV-2 in cerebrospinal fluid (2022), indicating HHV-2 encephalitis. After antiviral treatment, the patient’s symptoms improved, and he was discharged. During the 1-month follow-up, the patient recovered without any new symptoms, but a brain MRI revealed significant atrophy of the original foci. The patient was finally diagnosed with HHV-2 necrotizing meningoencephalitis, which is extremely rare. mNGS helped with the clinical diagnosis and strengthened our understanding of HHV-2 infections in the central nervous system.

Impact of Cultured Neuron Models on α-Herpesvirus Latency Research

A signature trait of neurotropic α-herpesviruses (α-HV) is their ability to establish stable non-productive infections of peripheral neurons termed latency. This specialized gene expression program is the foundation of an evolutionarily successful strategy to ensure lifelong persistence in the host. Various physiological stresses can induce reactivation in a subset of latently-infected neurons allowing a new cycle of viral productive cycle gene expression and synthesis of infectious virus. Recurring reactivation events ensure transmission of the virus to new hosts and contributes to pathogenesis. Efforts to define the molecular basis of α-HV latency and reactivation have been notoriously difficult because the neurons harboring latent virus in humans and in experimentally infected live-animal models, are rare and largely inaccessible to study. Increasingly, researchers are turning to cultured neuron infection models as simpler experimental platforms from which to explore latency and reactivation at the molecular level. In this review, I reflect on the strengths and weaknesses of existing neuronal models and briefly summarize the important mechanistic insights these models have provided. I also discuss areas where prioritization will help to ensure continued progress and integration.

Flavonoids Target Human Herpesviruses That Infect the Nervous System: Mechanisms of Action and Therapeutic Insights

Human herpesviruses (HHVs) are large DNA viruses with highly infectious characteristics. HHVs can induce lytic and latent infections in their host, and most of these viruses are neurotropic, with the capacity to generate severe and chronic neurological diseases of the peripheral nervous system (PNS) and central nervous system (CNS). Treatment of HHV infections based on strategies that include natural products-derived drugs is one of the most rapidly developing fields of modern medicine. Therefore, in this paper, we lend insights into the recent advances that have been achieved during the past five years in utilizing flavonoids as promising natural drugs for the treatment of HHVs infections of the nervous system such as alpha-herpesviruses (herpes simplex virus type 1, type 2, and varicella-zoster virus), beta-herpesviruses (human cytomegalovirus), and gamma-herpesviruses (Epstein–Barr virus and Kaposi sarcoma-associated herpesvirus). The neurological complications associated with infections induced by the reviewed herpesviruses are emphasized. Additionally, this work covers all possible mechanisms and pathways by which flavonoids induce promising therapeutic actions against the above-mentioned herpesviruses.