miR-H28 and miR-H29 expressed late in productive infection are exported and restrict HSV-1 replication and spread in recipient cells

Regulatory role of miRNAs in the human immune and inflammatory response during the infection of SARS-CoV-2 and other respiratory viruses: A comprehensive review

miRNAs are single-stranded ncRNAs that act as regulators of different human body processes. Several miRNAs have been noted to control the human immune and inflammatory response during severe acute respiratory infection syndrome (SARS-CoV-2) infection. Similarly, many miRNAs were upregulated and downregulated during different respiratory virus infections. Here, an attempt has been made to capture the regulatory role of miRNAs in the human immune and inflammatory response during the infection of SARS-CoV-2 and other respiratory viruses. Firstly, the role of miRNAs has been depicted in the human immune and inflammatory response during the infection of SARS-CoV-2. In this direction, several significant points have been discussed about SARS-CoV-2 infection, such as the role of miRNAs in human innate immune response; miRNAs and its regulation of granulocytes; the role of miRNAs in macrophage activation and polarisation; miRNAs and neutrophil extracellular trap formation; miRNA-related inflammatory response; and miRNAs association in adaptive immunity. Secondly, the miRNAs landscape has been depicted during human respiratory virus infections such as human coronavirus, respiratory syncytial virus, influenza virus, rhinovirus, and human metapneumovirus. The article will provide more understanding of the miRNA-controlled mechanism of the immune and inflammatory response during COVID-19, which will help more therapeutics discoveries to fight against the future pandemic.

Herpes simplex virus type 1 modifies the protein composition of extracellular vesicles to promote neurite outgrowth and neuroinfection

The highly prevalent herpes simplex virus type 1 (HSV-1) causes a range of diseases, including cold sores, blinding keratitis, and life-threatening encephalitis. HSV-1 initially replicates in epithelial cells, enters the peripheral nervous system via neurites, and establishes lifelong infection in the neuronal cell bodies. Neurites are highly dynamic structures that grow or retract in response to attractive or repulsive cues, respectively. Here, we show that infection with HSV-1, but not with a mutant virus lacking glycoprotein G (gG), reduced the repulsive effect of epithelial cells on neurite outgrowth and facilitated HSV-1 invasion of neurons. HSV-1 gG was required and sufficient to induce neurite outgrowth by modifying the protein composition of extracellular vesicles, increasing the amount of neurotrophic and neuroprotective proteins, including galectin-1. Antibodies directed against galectin-1 neutralized the capacity of extracellular vesicles released from HSV-1-infected cells to promote neurite outgrowth. Our study provides new insights into the neurotropism of HSV-1 and identifies a viral protein that modifies the protein composition of extracellular vesicles to stimulate neurite outgrowth and invasion of the nervous system.IMPORTANCEHerpes simplex virus type 1 (HSV-1) must infect neurites (or nerve endings) to establish a chronic infection in neurons. Neurites are highly dynamic structures that retract or grow in the presence of repulsive or attractive proteins. Some of these proteins are released by epithelial cells in extracellular vesicles and act upon interaction with their receptor present on neurites. We show here that HSV-1 infection of epithelial cells modulated their effect on neurites, increasing neurite growth. Mechanistically, HSV-1 glycoprotein G (gG) modifies the protein composition of extracellular vesicles released by epithelial cells, increasing the amount of attractive proteins that enhance neurite outgrowth and facilitate neuronal infection. These results could inform of therapeutic strategies to block HSV-1 induction of neurite outgrowth and, thereby, neuronal infection.

Viral MicroRNAs in Herpes Simplex Virus 1 Pathobiology

Simplexvirus humanalpha1 (Herpes simplex virus type 1 [HSV-1]) infects millions of people globally, manifesting as vesiculo-ulcerative lesions of the oral or genital mucosa. After primary infection, the virus establishes latency in the peripheral neurons and reactivates sporadically in response to various environmental and genetic factors. A unique feature of herpesviruses is their ability to encode tiny noncoding RNAs called microRNA (miRNAs). Simplexvirus humanalpha1 encodes eighteen miRNA precursors that generate twentyseven different mature miRNA sequences. Unique Simplexvirus humanalpha1 miRNAs repertoire is expressed in lytic and latent stages and exhibits expressional disparity in various cell types and model systems, suggesting their key pathological functions. This review will focus on elucidating the mechanisms underlying the regulation of host-virus interaction by HSV-1 encoded viral miRNAs. Numerous studies have demonstrated sequence- specific targeting of both viral and host transcripts by Simplexvirus humanalpha1 miRNAs. While these noncoding RNAs predominantly target viral genes involved in viral life cycle switch, they regulate host genes involved in antiviral immunity, thereby facilitating viral evasion and lifelong viral persistence inside the host. Expression of Simplexvirus humanalpha1 miRNAs has been associated with disease progression and resolution. Systemic circulation and stability of viral miRNAs compared to viral mRNAs can be harnessed to utilize their potential as diagnostic and prognostic markers. Moreover, functional inhibition of these enigmatic molecules may allow us to devise strategies that have therapeutic significance to contain Simplexvirus humanalpha1 infection.

HSV-1 miRNAs are post-transcriptionally edited in latently infected human ganglia

IMPORTANCE

Herpes simplex virus 1 is an important human pathogen that has been intensively studied for many decades. Nevertheless, the molecular mechanisms regulating its establishment, maintenance, and reactivation from latency are poorly understood. Here, we show that HSV-1-encoded miR-H2 is post-transcriptionally edited in latently infected human tissues. Hyperediting of viral miRNAs increases the targeting potential of these miRNAs and may play an important role in regulating latency. We show that the edited miR-H2 can target ICP4, an essential viral protein. Interestingly, we found no evidence of hyperediting of its homolog, miR-H2, which is expressed by the closely related virus HSV-2. The discovery of post-translational modifications of viral miRNA in the latency phase suggests that these processes may also be important for other non-coding viral RNA in the latency phase, including the intron LAT, which in turn may be crucial for understanding the biology of this virus.

RNA Editing-Dependent and -Independent Roles of Adenosine Deaminases Acting on RNA Proteins in Herpesvirus Infection-Hints on Another Layer of Complexity

The Adenosine Deaminases Acting on RNA (ADAR) catalyze the posttranscriptional deamination of adenosine residues to inosine in double-stranded RNAs (dsRNAs, A-to-I editing), preventing the overactivation of dsRNA sensor molecules and interferons. RNA editing is the cornerstone of innate immunity that distinguishes between self and non-self (virus), and it is essential for normal regulation of cellular homeostasis. Although much is already known about the role of ADAR proteins in RNA virus infection, the role of ADAR proteins in herpesvirus infection remains largely unexplored. In this review, we provide several lines of evidence from studies of different herpesviruses for another level of complexity in regulating the already intricate biphasic life cycle of herpesviruses.

Trick-or-Trap: Extracellular Vesicles and Viral Transmission

Extracellular vesicles (EVs) are lipid membrane-enclosed particles produced by most cells, playing important roles in various biological processes. They have been shown to be involved in antiviral mechanisms such as transporting antiviral molecules, transmitting viral resistance, and participating in antigen presentation. While viral transmission was traditionally thought to occur through independent viral particles, the process of viral infection is complex, with multiple barriers and challenges that viruses must overcome for successful infection. As a result, viruses exploit the intercellular communication pathways of EVs to facilitate cluster transmission, increasing their chances of infecting target cells. Viral vesicle transmission offers two significant advantages. Firstly, it enables the collective transmission of viral genomes, increasing the chances of infection and promoting interactions between viruses in subsequent generations. Secondly, the use of vesicles as vehicles for viral transmission provides protection to viral particles against environmental factors, while also expanding the cell tropism allowing viruses to reach cells in a receptor-independent manner. Understanding the role of EVs in viral transmission is crucial for comprehending virus evolution and developing innovative antiviral strategies, therapeutic interventions, and vaccine approaches.

Extracellular Vesicles as a Translational Approach for the Treatment of COVID-19 Disease: An Updated Overview

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) caused a global pandemic in the years 2020-2022. With a high prevalence, an easy route of transmission, and a long incubation time, SARS-CoV-2 spread quickly and affected public health and socioeconomic conditions. Several points need to be elucidated about its mechanisms of infection, in particular, its capability to evade the immune system and escape from neutralizing antibodies. Extracellular vesicles (EVs) are phospholipid bilayer-delimited particles that are involved in cell-to-cell communication; they contain biological information such as miRNAs, proteins, nucleic acids, and viral components. Abundantly released from biological fluids, their dimensions are highly variable, which are used to divide them into exosomes (40 to 150 nm), microvesicles (40 to 10,000 nm), and apoptotic bodies (100-5000 nm). EVs are involved in many physiological and pathological processes. In this article, we report the latest evidence about EVs' roles in viral infections, focusing on the dual role of exosomes in promoting and inhibiting SARS-CoV-2 infection. The involvement of mesenchymal stromal/stem cells (MSCs) and MSC-derived EVs in COVID-19 treatment, such as the use of translational exosomes as a diagnostical/therapeutic approach, is also investigated. These elucidations could be useful to better direct the discovery of future diagnostical tools and new exosome-derived COVID-19 biomarkers, which can help achieve optimal therapeutic interventions and implement future vaccine strategies.

Viral miRNA regulation of host gene expression

Viruses have evolved a multitude of mechanisms to combat barriers to productive infection in the host cell. Virally-encoded miRNAs are one such means to regulate host gene expression in ways that benefit the virus lifecycle. miRNAs are small non-coding RNAs that regulate protein expression but do not trigger the adaptive immune response, making them powerful tools encoded by viruses to regulate cellular processes. Diverse viruses encode for miRNAs but little sequence homology exists between miRNAs of different viral species. Despite this, common cellular pathways are targeted for regulation, including apoptosis, immune evasion, cell growth and differentiation. Herein we will highlight the viruses that encode miRNAs and provide mechanistic insight into how viral miRNAs aid in lytic and latent infection by targeting common cellular processes. We also highlight how viral miRNAs can mimic host cell miRNAs as well as how viral miRNAs have evolved to regulate host miRNA expression. These studies dispel the myth that viral miRNAs are subtle regulators of gene expression, and highlight the critical importance of viral miRNAs to the virus lifecycle.

Extracellular Vesicles and Infection: From Hijacked Machinery to Therapeutic Tools

Extracellular vesicles (EVs) comprise a broad range of secreted cell-derived membrane vesicles. Beyond their more well-characterized role in cell communication, in recent years, EVs have also been shown to play important roles during infection. Viruses can hijack the biogenesis of exosomes (which are small EVs) to promote viral spreading. Additionally, these exosomes are also important mediators in inflammation and immune responses during both bacterial and viral infections. This review summarizes these mechanisms while also describing the impact of bacterial EVs in regulating immune responses. Finally, the review also focuses on the potential and challenges of using EVs, in particular, to tackle infectious diseases.

Herpes Simplex Virus 1 MicroRNAs: An Update

BACKGROUND

Herpes simplex virus 1 (HSV-1), an important human pathogen, is capable of latent infection in neurons and productive (lytic) infection in other tissue cells. Once infected with HSV-1, the immune system of the organism cannot eliminate the virus and carries it lifelong. HSV-1 possesses approximately 150 kb of double-stranded linear genomic DNA and can encode at least 70 proteins and 37 mature microRNAs (miRNAs) derived from 18 precursor miRNAs (pre-miRNAs).

SUMMARY

These HSV-1-encoded miRNAs are widely involved in multiple processes in the life cycle of the virus and the host cell, including viral latent and lytic infection, as well as host cell immune signaling, proliferation, and apoptosis.

KEY MESSAGE

In this review, we focused primarily on recent advances in HSV-1-encoded miRNA expression, function, and mechanism, which may provide new research ideas and feasible research methods systemically and comprehensively.

miRNAs in Herpesvirus Infection: Powerful Regulators in Small Packages

microRNAs are a class of small, single-stranded, noncoding RNAs that regulate gene expression. They can be significantly dysregulated upon exposure to any infection, serving as important biomarkers and therapeutic targets. Numerous human DNA viruses, along with several herpesviruses, have been found to encode and express functional viral microRNAs known as vmiRNAs, which can play a vital role in host-pathogen interactions by controlling the viral life cycle and altering host biological pathways. Viruses have also adopted a variety of strategies to prevent being targeted by cellular miRNAs. Cellular miRNAs can act as anti- or proviral components, and their dysregulation occurs during a wide range of infections, including herpesvirus infection. This demonstrates the significance of miRNAs in host herpesvirus infection. The current state of knowledge regarding microRNAs and their role in the different stages of herpes virus infection are discussed in this review. It also delineates the therapeutic and biomarker potential of these microRNAs in future research directions.

Exosomes: from biology to immunotherapy in infectious diseases

Exosomes are extracellular vesicles derived from the endosomal compartment, which are released by all kinds of eukaryotic and prokaryotic organisms. These vesicles contain a variety of biomolecules that differ both in quantity and type depending on the origin and cellular state. Exosomes are internalized by recipient cells, delivering their content and thus contributing to cell-cell communication in health and disease. During infections exosomes may exert a dual role, on one hand, they can transmit pathogen-related molecules mediating further infection and damage, and on the other hand, they can protect the host by activating the immune response and reducing pathogen spread. Selective packaging of pathogenic components may mediate these effects. Recently, quantitative analysis of samples by omics technologies has allowed a deep characterization of the proteins, lipids, RNA, and metabolite cargoes of exosomes. Knowledge about the content of these vesicles may facilitate their therapeutic application. Furthermore, as exosomes have been detected in almost all biological fluids, pathogenic or host-derived components can be identified in liquid biopsies, making them suitable for diagnosis and prognosis. This review attempts to organize the recent findings on exosome composition and function during viral, bacterial, fungal, and protozoan infections, and their contribution to host defense or to pathogen spread. Moreover, we summarize the current perspectives and future directions regarding the potential application of exosomes for prophylactic and therapeutic purposes.

Extracellular Vesicles and Viruses: Two Intertwined Entities

Viruses share many attributes in common with extracellular vesicles (EVs). The cellular machinery that is used for EV production, packaging of substrates and secretion is also commonly manipulated by viruses for replication, assembly and egress. Viruses can increase EV production or manipulate EVs to spread their own genetic material or proteins, while EVs can play a key role in regulating viral infections by transporting immunomodulatory molecules and viral antigens to initiate antiviral immune responses. Ultimately, the interactions between EVs and viruses are highly interconnected, which has led to interesting discoveries in their associated roles in the progression of different diseases, as well as the new promise of combinational therapeutics. In this review, we summarize the relationships between viruses and EVs and discuss major developments from the past five years in the engineering of virus-EV therapies.

The Role of Extracellular Vesicles in COVID-19 Pathology

Extracellular vesicles (EVs) have become a trending topic in recent years; they constitute a new intercellular communication paradigm. Extracellular vesicles are 30–4000 nanometers in diameter particles that are limited by a phospholipid bilayer and contain functional biomolecules, such as proteins, lipids, and nucleic acids. They are released by virtually all types of eukaryotic cells; through their cargoes, EVs are capable of triggering signaling in recipient cells. In addition to their functions in the homeostatic state, EVs have gained attention because of their roles in pathological contexts, eventually contributing to disease progression. In the Coronavirus disease 2019 (COVID-19) pandemic, aside from the scientific race for the development of preventive and therapeutic interventions, it is critical to understand the pathological mechanisms involved in SARS-CoV-2 infection. In this sense, EVs are key players in the main processes of COVID-19. Thus, in this review, we highlight the role of EVs in the establishment of the viral infection and in the procoagulant state, cytokine storm, and immunoregulation of innate and adaptive immune responses.

MicroRNA Regulation of Human Herpesvirus Latency

Herpesviruses are ubiquitous human pathogens. After productive (lytic) infection, all human herpesviruses are able to establish life-long latent infection and reactivate from it. Latent infection entails suppression of viral replication, maintenance of the viral genome in infected cells, and the ability to reactivate. Most human herpesviruses encode microRNAs (miRNAs) that regulate these processes during latency. Meanwhile, cellular miRNAs are hijacked by herpesviruses to participate in these processes. The viral or cellular miRNAs either directly target viral transcripts or indirectly affect viral infection through host pathways. These findings shed light on the molecular determinants that control the lytic-latent switch and may lead to novel therapeutics targeting latent infection. We discuss the multiple mechanisms by which miRNAs regulate herpesvirus latency, focusing on the patterns in these mechanisms.

Studies of Infection and Experimental Reactivation by Recombinant VZV with Mutations in Virally-Encoded Small Non-Coding RNA

Locked-nucleotide analog antagonists (LNAA) to four varicella zoster virus small non-coding RNA (VZVsncRNA 10-13) derived from the mRNA of the open reading frame (ORF) 61 gene individually reduce VZV replication in epithelial cells and fibroblasts. To study the potential roles VZVsncRNA 10-13 have in neuronal infection we generated two recombinant VZV; one in which 8 nucleotides were changed in VZVsncRNA10 without altering the encoded residues of ORF61 (VZVsnc10MUT) and a second containing a 12-nucleotide deletion of the sequence common to VZVsncRNA12 and 13, located in the ORF61 mRNA leader sequence (VZVsnc12-13DEL). Both were developed from a VZV BAC with a green fluorescent protein (GFP) reporter fused to the N terminal of the capsid protein encoded by ORF23. The growth of both mutant VZV in epithelial cells and fibroblasts was similar to that of the parental recombinant virus. Both mutants established productive infections and experimental latency in neurons derived from human embryonic stem cells (hESC). However, neurons that were latently infected with both VZV mutant viruses showed impaired ability to reactivate when given stimuli that successfully reactivated the parental virus. These results suggest that these VZVsncRNA may have a role in VZV latency maintenance and/or reactivation. The extension of these studies and confirmation of such roles could potentially inform the development of a non-reactivating, live VZV vaccine.

Neuronal miR-138 Represses HSV-2 Lytic Infection by Regulating Viral and Host Genes with Mechanistic Differences from HSV-1

HSV-1 and HSV-2 are closely related viruses with major differences. Both viruses establish latency in neurons from which they reactivate to cause disease.

A Comprehensive Insight into the Role of Exosomes in Viral Infection: Dual Faces Bearing Different Functions

Extracellular vesicles (EVs) subtype, exosome is an extracellular nano-vesicle that sheds from cells’ surface and originates as intraluminal vesicles during endocytosis. Firstly, it was thought to be a way for the cell to get rid of unwanted materials as it loaded selectively with a variety of cellular molecules, including RNAs, proteins, and lipids. However, it has been found to play a crucial role in several biological processes such as immune modulation, cellular communication, and their role as vehicles to transport biologically active molecules. The latest discoveries have revealed that many viruses export their viral elements within cellular factors using exosomes. Hijacking the exosomal pathway by viruses influences downstream processes such as viral propagation and cellular immunity and modulates the cellular microenvironment. In this manuscript, we reviewed exosomes biogenesis and their role in the immune response to viral infection. In addition, we provided a summary of how some pathogenic viruses hijacked this normal physiological process. Viral components are harbored in exosomes and the role of these exosomes in viral infection is discussed. Understanding the nature of exosomes and their role in viral infections is fundamental for future development for them to be used as a vaccine or as a non-classical therapeutic strategy to control several viral infections.

A Role for Extracellular Vesicles in SARS-CoV-2 Therapeutics and Prevention

Extracellular vesicles (EVs) are the common designation for ectosomes, microparticles and microvesicles serving dominant roles in intercellular communication. Both viable and dying cells release EVs to the extracellular environment for transfer of cell, immune and infectious materials. Defined morphologically as lipid bi-layered structures EVs show molecular, biochemical, distribution, and entry mechanisms similar to viruses within cells and tissues. In recent years their functional capacities have been harnessed to deliver biomolecules and drugs and immunological agents to specific cells and organs of interest or disease. Interest in EVs as putative vaccines or drug delivery vehicles are substantial. The vesicles have properties of receptors nanoassembly on their surface. EVs can interact with specific immunocytes that include antigen presenting cells (dendritic cells and other mononuclear phagocytes) to elicit immune responses or affect tissue and cellular homeostasis or disease. Due to potential advantages like biocompatibility, biodegradation and efficient immune activation, EVs have gained attraction for the development of treatment or a vaccine system against the severe acute respiratory syndrome coronavirus 2 (SARS CoV-2) infection. In this review efforts to use EVs to contain SARS CoV-2 and affect the current viral pandemic are discussed. An emphasis is made on mesenchymal stem cell derived EVs' as a vaccine candidate delivery system.

Latency-Associated Transcript-Derived MicroRNAs in Herpes Simplex Virus Type 1 Target SMAD3 and SMAD4 in TGF-β/Smad Signaling Pathway

Background

During its latent infection, hepatic stellate cell (HSV-1) produces only a micro RNA (miRNA) precursor called latency-associated transcript (LAT), which encodes six distinct miRNAs. Recent studies have suggested that some of these miRNAs could target cellular mRNAs. One of the key cell signaling pathways that can be affected by HSV-1 is the TGF-β/Smad pathway. Herein, we investigated the potential role of the LAT as well as three LAT-derived miRNAs in targeting SMAD3 and SMAD4, as two main mediators in TGF-β/Smad.

Methods

The selection of LAT-derived miRNAs was based on the search results obtained from an online miRNA prediction tool. HEK293T cells were transfected with each miRNA-expressing lentivector and with the construct-expressing LAT. To survey the effect of LAT on the expression of pro-fibrotic markers, we transfected LX-2 cells with LAT construct. The impact of viral miRNA overexpression on SMADs and fibrotic markers was measured by quantitative PCR and luciferase assays.

Results

Among the LAT-derived miRNAs, miR-H2, miR-H3, and miR-H4 were selected for the study. Our results demonstrated that while miR-H2 binds to both SMAD mRNAs, miR-H3 and miR-H4 inhibit only the expression of the SMAD4 and SMAD3, respectively. Transfection of the LX-2 with LAT also decreased pro-fibrotic genes expression.

Conclusion

Our findings display that LAT negatively regulates TGF-β/Smad through targeting SMAD3 and SMAD4 by its miRNAs. These viral miRNAs can also contribute to the development of therapeutic interventions in diseases for which prevention or treatment can be achieved through targeting TGF-β pathway.

Latency-Associated Transcript-Derived MicroRNAs in Herpes Simplex Virus Type 1 Target SMAD3 and SMAD4 in TGF-β/Smad Signaling Pathway

Background:

During its latent infection, HSV-1 produces only a miRNA precursor called LAT, which encodes six distinct miRNAs. Recent studies have suggested that some of these miRNAs could target cellular mRNAs. One of the key cell signaling pathways that can be affected by HSV-1 is the TGF-β/Smad pathway. Herein, we investigated the potential role of the LAT as well as three LAT-derived miRNAs in targeting SMAD3 and SMAD4, as two main mediators in TGF-β/Smad.

Methods:

The selection of LAT-derived miRNAs was based on the search results obtained from an online miRNA prediction tool. HEK293T cells were transfected with each miRNA-expressing lentivector and with the construct-expressing LAT. To survey the effect of LAT on the expression of pro-fibrotic markers, we transfected LX-2 cells with LAT construct. The impact of viral miRNA overexpression on SMADs and fibrotic markers was measured by qPCR and luciferase assays.

Results:

Among the LAT-derived miRNAs, miR-H2, miR-H3, and miR-H4 were selected for the study. Our results demonstrated that while miR-H2 binds to both SMAD mRNAs, miR-H3 and miR-H4 inhibit only the expression of the SMAD4 and SMAD3, respectively. Transfection of the LX-2 with LAT also decreased pro-fibrotic genes expression.

Conclusion:

Our findings display that LAT negatively regulates TGF-β/Smad through targeting SMAD3 and SMAD4 by its miRNAs. These viral miRNAs can also contribute to the development of therapeutic interventions in diseases for which prevention or treatment can be achieved through targeting TGF-β pathway.

Herpesvirus latency

Herpesviruses infect virtually all humans and establish lifelong latency and reactivate to infect other humans. Latency requires multiple functions: maintaining the herpesvirus genome in the nuclei of cells; partitioning the viral genome to daughter cells in dividing cells; avoiding recognition by the immune system by limiting protein expression; producing noncoding viral RNAs (including microRNAs) to suppress lytic gene expression or regulate cellular protein expression that could otherwise eliminate virus-infected cells; modulating the epigenetic state of the viral genome to regulate viral gene expression; and reactivating to infect other hosts. Licensed antivirals inhibit virus replication, but do not affect latency. Understanding of the mechanisms of latency is leading to novel approaches to destroy latently infected cells or inhibit reactivation from latency.

Herpes Simplex Virus 1 MicroRNA miR-H8 Is Dispensable for Latency and Reactivation In Vivo

The regulatory functions of 10 individual viral microRNAs (miRNAs) that are abundantly expressed from the herpes simplex virus 1 (HSV-1) latency-associated transcript (LAT) region remain largely unknown. Here, we focus on HSV-1 miRNA miR-H8, which is within the LAT 3p exon, antisense to the first intron of ICP0, and has previously been shown to target a host glycosylphosphatidylinositol (GPI)-anchoring pathway. However, the functions of this miRNA have not been assessed in the context of the viral genome during infection. Therefore, we constructed a recombinant virus lacking miR-H8 (17dmiR-H8) and compared it to the parental wild-type and rescue viruses to characterize phenotypic differences. In rabbit skin cells, 17dmiR-H8 exhibited only subtle reductions in viral yields. In contrast, we found significant decreases in both viral yields (8-fold) and DNA replication (9.9-fold) in murine neuroblastoma cells, while 17dmiR-H8 exhibited a 3.6-fold increase in DNA replication in differentiated human neuronal cells (Lund human mesencephalic [LUHMES] cells). These cell culture phenotypes suggested potential host- and/or neuron-specific roles for miR-H8 in acute viral replication. To assess whether miR-H8 plays a role in HSV latency or reactivation, we used a human in vitro reactivation model as well as mouse and rabbit reactivation models. In the LUHMES cell-induced reactivation model, there was no difference in viral yields at 48 h postreactivation. In the murine dorsal root ganglion explant and rabbit ocular adrenergic reactivation models, the deletion of miR-H8 had no detectable effect on genome loads during latency or reactivation. These results indicate that miR-H8 is dispensable for the establishment of HSV-1 latency and reactivation.IMPORTANCE Herpesviruses have a remarkable ability to sustain lifelong infections by evading host immune responses, establishing a latent reservoir, and maintaining the ability to reactivate the lytic cascade to transmit the virus to the next host. The HSV-1 latency-associated transcript region is known to regulate many aspects of HSV-1 latency and reactivation, although the mechanisms for these functions remain unknown. To this end, we characterize an HSV-1 recombinant containing a deletion of a LAT-encoded miRNA, miR-H8, and demonstrate that it plays no detectable role in the establishment of latency or reactivation in differentiated human neurons (LUHMES cells) and mouse and rabbit models. Therefore, this study allows us to exclude miR-H8 from phenotypes previously attributed to the LAT region. Elucidating the genetic elements of HSV-1 responsible for establishment, maintenance, and reactivation from latency may lead to novel strategies for combating persistent herpesvirus infections.

Extracellular Vesicles in Viral Pathogenesis: A Case of Dr. Jekyll and Mr. Hyde

Secretion of extracellular vesicles (EVs) is a fundamental property of living cells. EVs are known to transfer biological signals between cells and thus regulate the functional state of recipient cells. Such vesicles mediate the intercellular transport of many biologically active molecules (proteins, nucleic acids, specific lipids) and participate in regulation of key physiological processes. In addition, EVs are involved in the pathogenesis of multiple diseases: infectious, neurodegenerative, and oncological. The current EV classification into microvesicles, apoptotic bodies, and exosomes is based on their size, pathways of cellular biogenesis, and molecular composition. This review is focused on analysis of the role of EVs (mainly exosomes) in the pathogenesis of viral infection. We briefly characterize the biogenesis and molecular composition of various EV types. Then, we consider EV-mediated pro- and anti-viral mechanisms. EV secretion by infected cells can be an important factor of virus spread in target cell populations, or a protective factor limiting viral invasion. The data discussed in this review, on the effect of EV secretion by infected cells on processes in neighboring cells and on immune cells, are of high significance in the search for new therapeutic approaches and for design of new generations of vaccines.

Extracellular Vesicles in Viral Infections: Two Sides of the Same Coin?

Extracellular vesicles are small membrane structures containing proteins and nucleic acids that are gaining a lot of attention lately. They are produced by most cells and can be detected in several body fluids, having a huge potential in therapeutic and diagnostic approaches. EVs produced by infected cells usually have a molecular signature that is very distinct from healthy cells. For intracellular pathogens like viruses, EVs can have an even more complex function, since the viral biogenesis pathway can overlap with EV pathways in several ways, generating a continuum of particles, like naked virions, EVs containing infective viral genomes and quasi-enveloped viruses, besides the classical complete viral particles that are secreted to the extracellular space. Those particles can act in recipient cells in different ways. Besides being directly infective, they also can prime neighbor cells rendering them more susceptible to infection, block antiviral responses and deliver isolated viral molecules. On the other hand, they can trigger antiviral responses and cytokine secretion even in uninfected cells near the infection site, helping to fight the infection and protect other cells from the virus. This protective response can also backfire, when a massive inflammation facilitated by those EVs can be responsible for bad clinical outcomes. EVs can help or harm the antiviral response, and sometimes both mechanisms are observed in infections by the same virus. Since those pathways are intrinsically interlinked, understand the role of EVs during viral infections is crucial to comprehend viral mechanisms and respond better to emerging viral diseases.

Viral MicroRNAs: Interfering the Interferon Signaling

Interferons are secreted cytokines with potent antiviral, antitumor and immunomodulatory functions. As the first line of defense against viruses, this pathway restricts virus infection and spread. On the contrary, viruses have evolved ingenious strategies to evade host immune responses including the interferon pathway. Multiple families of viruses, in particular, DNA viruses, encode microRNA (miR) that are small, non-protein coding, regulatory RNAs. Virus-derived miRNAs (v-miR) function by targeting host and virus-encoded transcripts and are critical in shaping host-pathogen interaction. The role of v-miRs in viral pathogenesis is emerging as demonstrated by their function in subverting host defense mechanisms and regulating fundamental biological processes such as cell survival, proliferation, modulation of viral life-cycle phase. In this review, we will discuss the role of v-miRs in the suppression of host genes involved in the viral nucleic acid detection, JAK-STAT pathway, and cytokine-mediated antiviral gene activation to favor viral replication and persistence. This information has yielded new insights into our understanding of how v-miRs promote viral evasion of host immunity and likely provide novel antiviral therapeutic targets.

The role of extracellular vesicles in COVID-19 virus infection

Extracellular vesicles releasing from various types of cells contribute to intercellular communication via delivering bio-molecules like nucleic acids, proteins, and lipids to recipient cells. Exosomes are 30-120 nm extracellular vesicles that participate in several pathological conditions. Virus-infected cells release exosomes that are implicated in infection through transferring viral components such as viral-derived miRNAs and proteins. As well, exosomes contain receptors for viruses that make recipient cells susceptible to virus entry. Since December 2019, SARS-CoV-2 (COVID-19) infection has become a worldwide urgent public health concern. There is currently no vaccine or specific antiviral treatment existing for COVID-19 virus infection. Hence, it is critical to find a safe and effective therapeutic tool to patients with severe COVID-19 virus infection. Extracellular vesicles may contribute to spread this virus as they transfer such receptors as CD9 and ACE2, which make recipient cells susceptible to virus docking. Upon entry, COVID-19 virus may be directed into the exosomal pathway, and its component is packaged into exosomes for secretion. Exosome-based strategies for the treatment of COVID-19 virus infection may include following items: inhibition of exosome biogenesis and uptake, exosome-therapy, exosome-based drug delivery system, and exosome-based vaccine. Mesenchymal stem cells can suppress nonproductive inflammation and improve/repair lung cells including endothelial and alveolar cells, which damaged by COVID-19 virus infection. Understanding molecular mechanisms behind extracellular vesicles related COVID-19 virus infection may provide us with an avenue to identify its entry, replication, spreading, and infection to overcome its adverse effects.

Exosomes containing miRNAs targeting HER2 synthesis and engineered to adhere to HER2 on tumor cells surface exhibit enhanced antitumor activity

BACKGROUND

Exosomes are small, cellular membrane-derived vesicles with a diameter of 50-150 nm. Exosomes are considered ideal drug delivery systems with a wide range of applications in various diseases, including cancer. However, nonspecific delivery of therapeutic agents by exosomes in vivo remains challenging. Human epidermal growth factor receptor 2 (HER2) is an epidermal growth factor receptor tyrosine kinase, and its overexpression is usually associated with cell survival and tumor progression in various cancers. In this study, we aim to develop novel exosomes with dual HER2-targeting ability as a nanoparticle delivery vehicle to enhance antitumor efficacy in vivo.

RESULTS

Here, we report the generation of two kinds of exosomes carrying miRNAs designed to block HER2 synthesis, which consequently showed a distinct anti-tumor effect. The 293-miR-HER2 exosomes package and deliver miRNAs targeting HER2 to recipient cells to block HER2 synthesis. The anti-tumor effect of these exosomes on cancer cells dependent on HER2 for survival but do not affect cells that lack HER2 or that are engineered to express HER2 but are not dependent on it for survival. In contrast, 293-miR-XS-HER2 exosomes carry an additional peptide, which enables them to adhere to HER2 on the surface of cancer cells. Consequently, these exosomes preferentially enter these cells with surface expression of HER2 and further displayed a tumoricidal effect. The 293-miR-XS-HER2 exosomes are significantly more effective than the 293-miR-HER2 exosomes in shrinking HER2-positive tumors implanted in mice.

CONCLUSIONS

Collectively, as novel antitumor drug delivery vehicles, HER2 dual-targeting exosomes exhibit increased target-specific delivery efficiency and can be further utilized to develop new nanoparticle-based targeted therapies.

Extracellular Vesicles in Viral Replication and Pathogenesis and Their Potential Role in Therapeutic Intervention

Extracellular vesicles (EVs) have shown their potential as a carrier of molecular information, and they have been involved in physiological functions and diseases caused by viral infections. Virus-infected cells secrete various lipid-bound vesicles, including endosome pathway-derived exosomes and microvesicles/microparticles that are released from the plasma membrane. They are released via a direct outward budding and fission of plasma membrane blebs into the extracellular space to either facilitate virus propagation or regulate the immune responses. Moreover, EVs generated by virus-infected cells can incorporate virulence factors including viral protein and viral genetic material, and thus can resemble noninfectious viruses. Interactions of EVs with recipient cells have been shown to activate signaling pathways that may contribute to a sustained cellular response towards viral infections. EVs, by utilizing a complex set of cargos, can play a regulatory role in viral infection, both by facilitating and suppressing the infection. EV-based antiviral and antiretroviral drug delivery approaches provide an opportunity for targeted drug delivery. In this review, we summarize the literature on EVs, their associated involvement in transmission in viral infections, and potential therapeutic implications.

Human Cytomegalovirus Utilizes Extracellular Vesicles To Enhance Virus Spread

Human cytomegalovirus (HCMV) manipulates cellular processes associated with secretory pathways within an infected cell to facilitate efficient viral replication. However, little is known about how HCMV infection alters the surrounding cellular environment to promote virus spread to uninfected cells. Extracellular vesicles (EVs) are key signaling molecules that are commonly altered in numerous disease states. Previous reports have shown that viruses commonly alter EVs, which can significantly impact infection. This study finds that HCMV modulates EV biogenesis machinery through upregulation of the endosomal sorting complex required for transport (ESCRT) proteins. This regulation appears to increase the activity of EV biogenesis, since HCMV-infected fibroblasts have increased vesicle release and altered vesicle size compared to EVs from uninfected cells. EVs generated through ESCRT-independent pathways are also beneficial to virus spread in fibroblasts, as treatment with the EV inhibitor GW4869 slowed the efficiency of HCMV spread. Importantly, the transfer of EVs purified from HCMV-infected cells enhanced virus spread. This suggests that HCMV modulates the EV pathway to transfer proviral signals to uninfected cells that prime the cellular environment for incoming infection and enhance the efficiency of virus spread.IMPORTANCE Human cytomegalovirus (HCMV) is a herpesvirus that leads to serious health consequences in neonatal or immunocompromised patients. Clinical management of infection in these at-risk groups remains a serious concern even with approved antiviral therapies available. It is necessary to increase our understanding of the cellular changes that occur during infection and their importance to virus spread. This may help to identify new targets during infection that will lead to the development of novel treatment strategies. Extracellular vesicles (EVs) represent an important method of intercellular communication in the human host. This study finds that HCMV manipulates this pathway to increase the efficiency of virus spread to uninfected cells. This finding defines a new layer of host manipulation induced by HCMV infection that leads to enhanced virus spread.

Extracellular Vesicles in Viral Infections of the Nervous System

Almost all types of cells release extracellular vesicles (EVs) into the extracellular space. EVs such as exosomes and microvesicles are membrane-bound vesicles ranging in size from 30 to 1000 nm in diameter. Under normal conditions, EVs mediate cell to cell as well as inter-organ communication via the shuttling of their cargoes which include RNA, DNA and proteins. Under pathological conditions, however, the number, size and content of EVs are found to be altered and have been shown to play crucial roles in disease progression. Emerging studies have demonstrated that EVs are involved in many aspects of viral infection-mediated neurodegenerative diseases. In the current review, we will describe the interactions between EV biogenesis and the release of virus particles while also reviewing the role of EVs in various viral infections, such as HIV-1, HTLV, Zika, CMV, EBV, Hepatitis B and C, JCV, and HSV-1. We will also discuss the potential uses of EVs and their cargoes as biomarkers and therapeutic vehicles for viral infections.

Varicella-Zoster Virus (VZV) Small Noncoding RNAs Antisense to the VZV Latency-Encoded Transcript VLT Enhance Viral Replication

Small noncoding RNAs (sncRNA), including microRNA (miR), are expressed by many viruses to provide an additional layer of gene expression regulation. Our work has shown that varicella-zoster virus (VZV; also called human herpesvirus 3 [HHV3]), the human alphaherpesvirus causing varicella and herpes zoster, expresses 24 virally encoded sncRNA (VZVsncRNA) in infected cells. Here, we demonstrate that several VZVsncRNA can modulate VZV growth, including four VZVsncRNA (VZVsncRNA10, -11, -12, and -13) that are antisense to VLT, a transcript made in lytic infections and associated with VZV latency. The influence on productive VZV growth and spread was assessed in epithelial cells transfected with locked nucleotide analog antagonists (LNAA). LNAA to the four VZVsncRNA antisense to VLT significantly reduced viral spread and progeny titers of infectious virus, suggesting that these sncRNA promoted lytic infection. The LNAA to VZVsncRNA12, encoded in the leader to ORF61, also significantly increased the levels of VLT transcripts. Conversely, overexpression of VZVsncRNA13 using adeno-associated virus consistently increased VZV spread and progeny titers. These results suggest that sncRNA antisense to VZV may regulate VZV growth, possibly by affecting VLT expression. Transfection of LNAA to VZVsncRNA14 and VZVsncRNA9 decreased and increased VZV growth, respectively, while LNAA to three other VZVsncRNA had no significant effects on replication. These data strongly support the conclusion that VZV replication is modulated by multiple virally encoded sncRNA, revealing an additional layer of complexity of VZV regulation of lytic infections. This may inform the development of novel anti-sncRNA-based therapies for treatment of VZV diseases.IMPORTANCE Varicella-zoster virus (VZV) causes herpes zoster, a major health issue in the aging and immunocompromised populations. Small noncoding RNAs (sncRNA) are recognized as important actors in modulating gene expression. This study extends our previous work and shows that four VZVsncRNA clustering in and near ORF61 and antisense to the latency-associated transcript of VZV can positively influence productive VZV infection. The ability of multiple exogenous small oligonucleotides targeting VZVsncRNA to inhibit VZV replication strengthens the possibility that they may inform development of novel treatments for painful herpes zoster.

Cloaked Viruses and Viral Factors in Cutting Edge Exosome-Based Therapies

Extracellular vesicles (EVs) constitute a heterogeneous group of vesicles released by all types of cells that play a major role in intercellular communication. The field of EVs started gaining attention since it was realized that these vesicles are not waste bags, but they carry specific cargo and they communicate specific messages to recipient cells. EVs can deliver different types of RNAs, proteins, and lipids from donor to recipient cells and they can influence recipient cell functions, despite their limited capacity for cargo. EVs have been compared to viruses because of their size, cell entry pathways, and biogenesis and to viral vectors because they can be loaded with desired cargo, modified, and re-targeted. These properties along with the fact that EVs are stable in body fluids, they can be produced and purified in large quantities, they can cross the blood-brain barrier, and autologous EVs do not appear to cause major adverse effects, have rendered them attractive for therapeutic use. Here, we discuss the potential for therapeutic use of EVs derived from virus infected cells or EVs carrying viral factors. We have focused on six major concepts: (i) the role of EVs in virus-based oncolytic therapy or virus-based gene delivery approaches; (ii) the potential use of EVs for developing viral vaccines or optimizing already existing vaccines; (iii) the role of EVs in delivering RNAs and proteins in the context of viral infections and modulating the microenvironment of infection; (iv) how to take advantage of viral features to design effective means of EV targeting, uptake, and cargo packaging; (v) the potential of EVs in antiviral drug delivery; and (vi) identification of novel antiviral targets based on EV biogenesis factors hijacked by viruses for assembly and egress. It has been less than a decade since more attention was given to EV research and some interesting concepts have already been developed. In the coming years, additional information on EV biogenesis, how they are hijacked and utilized by pathogens, and their impact on the microenvironment of infection is expected to indicate avenues to optimize existing therapeutic tools and develop novel approaches.

MicroRNA Involvement in Signaling Pathways During Viral Infection

The study of miRNAs started in 1993, when Lee et al. observed their involvement in the downregulation of a crucial protein known as LIN-14 in the nematode Caenorhabditis elegans. Since then, great progress has been made regarding research on microRNAs, which are now known to be involved in the regulation of various physiological and pathological processes in both animals and humans. One such example is represented by their interaction with various signaling pathways during viral infections. It has been observed that these pathogens can induce the up-/downregulation of various host miRNAs in order to elude the host's immune system. In contrast, some miRNAs studied could have an antiviral effect, enabling the defense mechanisms to fight the infection or, at the very least, they could induce the pathogen to enter a latent state. At the same time, some viruses encode their own miRNAs, which could further modulate the host's signaling pathways, thus favoring the survival and replication of the virus. The goal of this extensive literature review was to present how miRNAs are involved in the regulation of various signaling pathways in some of the most important and well-studied human viral infections. Further on, knowing which miRNAs are involved in various viral infections and what role they play could aid in the development of antiviral therapeutic agents for certain diseases that do not have a definitive cure in the present. The clinical applications of miRNAs are extremely important, as miRNAs targeted inhibition may have substantial therapeutic impact. Inhibition of miRNAs can be achieved through many different methods, but chemically modified antisense oligonucleotides have shown the most prominent effects. Though scientists are far from completely understanding all the molecular mechanisms behind the complex cross-talks between miRNA pathways and viral infections, the general knowledge is increasing on the different roles played by miRNAs during viral infections.

Exosomal miRNAs: novel players in viral infection

Exosomes are secreted nanovesicles that are able to transfer their cargo (such as miRNAs) between cells. To determine to what extent exosomes and exosomal miRNAs are involved in the pathogenesis, progression and diagnosis of viral infections. The scientific literature (PubMed and Google Scholar) was searched from 1970 to 2019. The complex biogenesis of exosomes and miRNAs was reviewed. Exosomes contain both viral and host miRNAs that can be used as diagnostic biomarkers for viral diseases. Viral proteins can alter miRNAs, and conversely miRNAs can alter the host response to viral infections in a positive or negative manner. It is expected that exosomal miRNAs will be increasingly used for diagnosis, monitoring and even treatment of viral infections.

Host microRNAs and exosomes that modulate influenza virus infection

MicroRNAs (miRNAs) are small non-coding RNAs that post-transcriptionally regulate over half of human protein-coding genes and play a vital role in cellular development, proliferation, metabolism, and homeostasis. Exosomes are rounded or cup-like extracellular vesicles that carry proteins, mRNAs, miRNAs, and lipids for release and exchange messages between cells involved in various cellular processes. Influenza virus is a substantial public health challenge. The expression of host miRNAs is altered in response to stimulation by influenza virus. These dysregulated miRNAs directly or indirectly target viral genes to regulate viral replication and stimulate or suppress innate immune responses and cell apoptosis during viral infection. Exosomes released by infected cells are associated with the transfer of antigens and key molecules that activate and modulate immune function. Dysregulation of miRNAs and secretion of exosomes are associated with pathogenicity and immune regulation during influenza infection. This review provides a comprehensive summary of the information available regarding host miRNAs and exosomes that are involved in the modulation of influenza virus infection and will facilitate the development of preventative or therapeutic strategies against influenza virus.

Immunomodulatory roles of human herpesvirus-encoded microRNA in host-virus interaction

Human herpesviruses (HHV) are large, double stranded, DNA viruses with high seroprevalence across the globe. Clinical manifestation of primary HHV infection resolve shortly, however, this period is prolonged in immunocompromised patients or individuals with suppressed immunity. Examining molecular mechanisms of HHV-encoded virulence factors can provide finer details of HHV-host interaction. A unique genetic feature of most members of HHV is that they encode multiple microRNAs (miR). In this review, I will provide mechanistic insights into the immunomodulatory functions of herpesvirus-encoded viral miR (v-miR) that favor viral persistence and spread by ingenious immune evasion schemes. Similar to host miR, v-miR can simultaneously regulate expression of multiple transcripts including host- and virus-derived. V-miRs, by virtue of their direct interaction with various transcripts, can regulate expression of critical components of host innate and adaptive immune system. V-miRs are also exported through exosomal route and gain entry into various cells even at distant sites, thereby allowing HHV to manipulate cellular and tissue immunity. Targeting v-miR may serve as a novel and promising therapeutic candidate to mitigate HHV-mediated clinical manifestations.

Herpes Simplex Virus 1 MicroRNA miR-H28 Exported to Uninfected Cells in Exosomes Restricts Cell-to-Cell Virus Spread by Inducing Gamma Interferon mRNA

An earlier report showed that herpes simplex virus 1 (HSV-1) expresses two microRNAs (miRNAs), miR-H28 and miR-H29, late in the infectious cycle. The miRNAs are packed in exosomes and, in recipient cells, restrict the transmission of virus from infected cells to uninfected cells. We now report that (i) miR-H28 induced the synthesis of gamma interferon (IFN-γ) in both infected cells and cells transfected with miR-H28, (ii) IFN-γ accumulated concurrently with viral proteins in infected cells, (iii) IFN-γ was produced in HEp-2 cells derived from cancer tissue and in HEK293T cells derived from normal tissue, and (iv) HSV-1 replication was affected by exposure to IFN-γ before infection but not during or after infection. The results presented in this report support the growing body of evidence indicating that HSV-1 encodes functions designed to reduce the spread of infection from infected cells to uninfected cells, possibly in order to maximize the transmission of virus from infected individuals to uninfected individuals.IMPORTANCE In this report, we show that IFN-γ is produced by HSV-1 viral miR-H28 and viral replication is blocked in cells exposed to IFN-γ before infection but not during or after infection. The inevitable conclusion is that HSV-1 induces IFN-γ to curtail its spread from infected cells to uninfected cells. In essence, this report supports the hypothesis that HSV-1 encodes functions that restrict the transmission of virus from cell to cell.

Bioinformatically-predicted varicella zoster virus small non-coding RNAs are expressed in lytically-infected epithelial cells and neurons

Most herpesviruses use both host and viral small non-coding RNAs (sncRNA), especially microRNA, to modulate infection. Bioinformatic analyses of NGS data obtained from Varicella Zoster virus (VZV)-infected cells predicted 24 VZVsncRNA, seven of which were confirmed to be expressed in infected fibroblasts and neurons using stem-loop quantitative reverse transcription PCR (SL-PCR). We here assayed for the expression of all 24 of the bioinformatically predicted VZVsncRNA in cells productively infected by VZV using SL-PCR. 23 of the 24 predicted sequences were detected in VZV-infected ARPE19 cells and 19 of the 24 sequences in infected human neurons generated by two methods from embryonic stem cells. We also show that blocking one of two newly-tested VZV-encoded sncRNA using locked nucleotide antagonists significantly increased viral replication. These findings suggest that further study of VZV encoded sncRNA could elucidate an additional level of regulation of the life cycle of this pathogenic human herpesvirus.

The Role of Extracellular Vesicles in Viral Infection and Transmission

Extracellular vesicles (EVs) have been found to be released by any type of cell and can be retrieved in every circulating body fluid, namely blood (plasma, serum), saliva, milk, and urine. EVs were initially considered a cellular garbage disposal tool, but later it became evident that they are involved in intercellular signaling. There is evidence that viruses can use EV endocytic routes to enter uninfected cells and hijack the EV secretory pathway to exit infected cells, thus illustrating that EVs and viruses share common cell entry and biogenesis mechanisms. Moreover, EVs play a role in immune response against viral pathogens. EVs incorporate and spread both viral and host factors, thereby prompting or inhibiting immune responses towards them via a multiplicity of mechanisms. The involvement of EVs in immune responses, and their potential use as agents modulating viral infection, will be examined. Although further studies are needed, the engineering of EVs could package viral elements or host factors selected for their immunostimulatory properties, to be used as vaccines or tolerogenic tools in autoimmune diseases.

Herpes Simplex Virus Type 1-Encoded miR-H2-3p Manipulates Cytosolic DNA-Stimulated Antiviral Innate Immune Response by Targeting DDX41

Herpes simplex virus type 1 (HSV-1), one of the human pathogens widely epidemic and transmitted among various groups of people in the world, often causes symptoms known as oral herpes or lifelong asymptomatic infection. HSV-1 employs many sophisticated strategies to escape host antiviral immune response based on its multiple coding proteins. However, the functions involved in the immune evasion of miRNAs encoded by HSV-1 during lytic (productive) infection remain poorly studied. Dual-luciferase reporter gene assay and bioinformatics revealed that Asp-Glu-Ala-Asp (DEAD)-box helicase 41 (DDX41), a cytosolic DNA sensor of the DNA-sensing pathway, was a putative direct target gene of HSV-1-encoded miR-H2-3p. The transfection of miR-H2-3p mimics inhibited the expression of DDX41 at the level of mRNA and protein, as well as the expression of interferon beta (IFN-β) and myxoma resistance protein I (MxI) induced by HSV-1 infection in THP-1 cells, and promoted the viral replication and its gene transcription. However, the transfection of miR-H2-3p inhibitor showed opposite effects. This finding indicated that HSV-1-encoded miR-H2-3p attenuated cytosolic DNA-stimulated antiviral immune response by manipulating host DNA sensor molecular DDX41 to enhance virus replication in cultured cells.

Effect of Loss-of-function of the Herpes Simplex Virus-1 microRNA H6-5p on Virus Replication

To date, 29 distinct microRNAs (miRNAs) have been reported to be expressed during herpes simplex virus infections. Sequence analysis of mature herpes simplex virus-1 (HSV-1) miRNAs revealed five sets of miRNAs that are complementary to each other: miR-H6-5p/H1-3p, miR-H6-3p/H1-5p, H2-5p/H14-3p, miR-H2-3p/H14-5p, and miR-H7/H27. However, the roles of individual miRNAs and consequences of this complementarity remain unclear. Here, we focus on two of these complementary miRNAs, miR-H6-5p and miR-H1-3p, using loss-of-function experiments in vitro and in a mouse model of infection using an miRNA sponge approach, including tandem multiplex artificial miRNA-binding sequences that do not match perfectly to the target miRNA inserted downstream of a green fluorescent protein reporter gene. Infection with recombinant virus expressing the miR-H6-5p sponge reduced viral protein levels and virus yield. Decreased accumulation of viral proteins was also observed at early stages of infection in the presence of both an miR-H6-5p inhibitor and plasmid-expressed miR-H1-3p. Moreover, establishment of latency and reactivation did not differ between the recombinant virus expressing the miR-H6-5p sponge and wild-type HSV-1. Taken together, these data suggest that miR-H6-5p has an as-yet-unidentified role in the early stages of viral infection, and its complement miR-H1-3p suppresses this role in later stages of infection. This report extends understanding of the roles of miRNAs in infection by herpes simplex viruses, supporting a model of infection in which the production of virus and its virulent effects are tightly controlled to maximize persistence in the host and population.

Herpes Simplex Virus 1 Lytic Infection Blocks MicroRNA (miRNA) Biogenesis at the Stage of Nuclear Export of Pre-miRNAs

Various mechanisms have been identified by which viruses target host small RNA biogenesis pathways to achieve optimal infection outcomes. Herpes simplex virus 1 (HSV-1) is a ubiquitous human pathogen whose successful persistence in the host entails both productive (“lytic”) and latent infection. Although many HSV-1 miRNAs have been discovered and some are thought to help control the lytic/latent switch, little is known about regulation of their biogenesis. By characterizing expression of both pre-miRNAs and mature miRNAs under various conditions, this study revealed striking differences in miRNA biogenesis between lytic and latent infection and uncovered a regulatory mechanism that blocks pre-miRNA nuclear export and is dependent on viral protein ICP27 and viral DNA synthesis. This mechanism represents a new virus-host interaction that could limit the repressive effects of HSV-1 miRNAs hypothesized to promote latency and may shed light on the regulation of miRNA nuclear export, which has been relatively unexplored.

Herpes simplex virus 1 (HSV-1) switches between two infection programs, productive (“lytic”) and latent infection. Some HSV-1 microRNAs (miRNAs) have been hypothesized to help control this switch, and yet little is known about regulation of their expression. Using Northern blot analyses, we found that, despite inherent differences in biogenesis efficiency among six HSV-1 miRNAs, all six exhibited high pre-miRNA/miRNA ratios during lytic infection of different cell lines and, when detectable, in acutely infected mouse trigeminal ganglia. In contrast, considerably lower ratios were observed in latently infected ganglia and in cells transduced with lentiviral vectors expressing the miRNAs, suggesting that HSV-1 lytic infection blocks miRNA biogenesis. This phenomenon is not specific to viral miRNAs, as a host miRNA expressed from recombinant HSV-1 also exhibited high pre-miRNA/miRNA ratios late during lytic infection. The levels of most of the mature miRNAs remained stable during infection in the presence of actinomycin D, indicating that the high ratios are due to inefficient pre-miRNA conversion to miRNA. Cellular fractionation experiments showed that late (but not early) during infection, pre-miRNAs were enriched in the nucleus and depleted in the cytoplasm, indicating that nuclear export was blocked. A mutation eliminating ICP27 expression or addition of acyclovir reduced pre-miRNA/miRNA ratios, but mutations drastically reducing Us11 expression did not. Thus, HSV-1 lytic infection inhibits miRNA biogenesis at the step of nuclear export and does so in an ICP27- and viral DNA synthesis-dependent manner. This mechanism may benefit the virus by reducing expression of repressive miRNAs during lytic infection while permitting elevated expression during latency.

Herpes Simplex Virus 1 Deregulation of Host MicroRNAs

Viruses utilize microRNAs (miRNAs) in a vast variety of possible interactions and mechanisms, apparently far beyond the classical understanding of gene repression in humans. Likewise, herpes simplex virus 1 (HSV-1) expresses numerous miRNAs and deregulates the expression of host miRNAs. Several HSV-1 miRNAs are abundantly expressed in latency, some of which are encoded antisense to transcripts of important productive infection genes, indicating their roles in repressing the productive cycle and/or in maintenance/reactivation from latency. In addition, HSV-1 also exploits host miRNAs to advance its replication or repress its genes to facilitate latency. Here, we discuss what is known about the functional interplay between HSV-1 and the host miRNA machinery, potential targets, and the molecular mechanisms leading to an efficient virus replication and spread.

Herpesviruses and MicroRNAs: New Pathogenesis Factors in Oral Infection and Disease?

The oral cavity incessantly encounters a plethora of microorganisms. Effective and efficient oral innate and adaptive immune responses are incumbent to maintain healthy mucosa. A higher prevalence of Human Herpesviruses (HHV), a family of large enveloped DNA viruses, has been reported in multiple oral inflammatory diseases suggesting their involvement in disease progression. However, the viral components contributing to oral disease remain obscure. MicroRNAs (miRNA) are non-protein coding, single stranded ribonucleic acid (RNA) molecules that post-transcriptionally regulate diverse messenger RNAs. Thus, miRNAs can control large repertoire of biological processes. Changes in miRNA expression are associated with various oral infections and diseases. Cellular miRNAs can act as pro- or anti-viral factors and dysregulation of host miRNA expression occurs during herpesviruses infection. This strongly suggest a critical role of cellular miRNAs in host-herpesvirus interaction. Interestingly, HHV also encode multiple miRNAs (called viral miRNAs) that may play key role in host-pathogen interaction by modulating both host biological pathways and controlling viral life cycle. Recent studies from our laboratory have identified viral miRNAs (v-miRs) in diseased oral tissue biopsies and demonstrate their immunomodulatory roles. This review discusses the association of miRNAs (both host and viral) and herpesviruses in the pathogenesis of oral inflammatory diseases.

Modulation of bovine herpesvirus 1 infection by virally encoded microRNAs

Bovine herpesvirus 1 (BoHV-1), is a member of the subfamily Alphaherpesvirinae in the order Herpesviridae and is a ubiquitous pathogen of cattle responsible for significant economic loss worldwide. The BoHV-1 genome encodes at least 10 BoHV-1 microRNA (miRNA) genes, whose functions remain poorly understood. This study sought to understand the role of three BoHV-1 miRNA genes, Bhv1-miR-B6, Bhv1-miR-B8 and Bhv1-miR-B9, which are located proximal to the BoHV-1 origins of replication (OriS). Therefore, plasmids expressing the precursor miRNA hairpins for the Bhv1-miR-B6, Bhv1-miR-B8, and Bhv1-miR-B9 genes were constructed and transfected into Madin-Darby bovine kidney cells prior to BoHV-1 infection. Interestingly, transient expression of either Bhv1-miR-B8 or Bhv1-miR-B9 in Madin-Darby bovine kidney cells prior to infection resulted in partial suppression of BoHV-1 replication, quantified through estimating levels of glycoprotein C mRNA and protein levels. Putative interactions between the mature miRNA bhv1-miR-B8-3p and bhv1-miR-B9 and BoHV-1 transcripts were identified providing plausible pathways for these molecules to affect virus replication. Therefore, these two miRNAs are implicated in the post-transcriptional regulation of BoHV-1 transcripts important for virus replication and could be used to limit BoHV-1 replication.

Herpes simplex virus 1 miRNA sequence variations in latently infected human trigeminal ganglia

Human herpes simplex virus 1 (HSV-1) expresses numerous miRNAs, the function of which is not well understood. Several qualitative and quantitative analyses of HSV-1 miRNAs have been performed on infected cells in culture and animal models, however, there is very limited knowledge of their expression in human samples. We sequenced small-RNA libraries of RNA derived from human trigeminal ganglia latently infected with HSV-1 and Varicella zoster virus (VZV) and detected only a small subset of HSV-1 miRNA. The most abundantly expressed miRNAs are miR-H2, miRNA that regulates the expression of immediate early gene ICP0, and miR-H3 and -H4, both miRNAs expressed antisense to the transcript encoding the major neurovirulence factor ICP34.5. The sequence of many HSV-1 miRNAs detected in human samples was different from the sequences deposited in miRBase, which might significantly affect targeted functional analyses.

Extracellular Vesicles Released by Herpes Simplex Virus 1-Infected Cells Block Virus Replication in Recipient Cells in a STING-Dependent Manner

Herpes simplex virus 1 (HSV-1)-infected cells release extracellular vesicles (EVs) that deliver to uninfected cells viral factors and host components, such as the stimulator of interferon genes (STING), which activates type I interferon upon foreign DNA sensing. The functions of EVs released by HSV-1-infected cells have remained unknown. Here, we describe a procedure to separate the EVs from HSV-1 virions that is based on an iodixanol/sucrose gradient. STING, along with the EV markers CD63 and CD9, was found in light-density fractions, while HSV components accumulated in heavy-density fractions. HSV-1 infection stimulated the release of EVs from the cells. The EVs derived from infected cells, but not from uninfected cells, activated innate immunity in recipient cells and suppressed viral gene expression and virus replication. Moreover, only the EVs derived from infected cells stimulated the expression of a subset of M1-type markers in recipient macrophages. Conversely, EVs derived from STING-knockdown cells failed to stimulate the expression of these M1-type markers, they activated innate immune responses to a lesser extent in recipient cells, and they did not sustain the inhibition of virus replication. These data suggest that STING from the EV donor cells contributes to the antiviral responses in cells receiving EVs from HSV-1-infected cells. Perturbations in the biogenesis of EVs by silencing CD63 or blocking the activity of the neutral spingomyelinase-2 (nSMase-2) increased the HSV-1 yields. Overall, our data suggest that the EVs released from HSV-1-infected cells negatively impact the infection and could control the dissemination of the virus.IMPORTANCE Extracellular vesicles (EVs) are released by all types of cells as they constitute major mechanism of intercellular communication and have the capacity to alter the functions of recipient cells despite their limited capacity for cargo. How the EVs released by HSV-infected cells could alter the surrounding microenvironment and influence the infection currently remains unknown. The cargo of EVs reflects the physiological state of the cells in which they were produced, so the content of EVs originating from infected cells is expected to be substantially different from that of healthy cells. Our studies indicate that the EVs released by HSV-1-infected cells carry innate immune components such as STING and other host and viral factors; they can activate innate immune responses in recipient cells and inhibit HSV-1 replication. The implication of these data is that the EVs released by HSV-1-infected cells could control HSV-1 dissemination promoting its persistence in the host.

Human cytomegalovirus-infected cells release extracellular vesicles that carry viral surface proteins

Extracellular vesicles (EVs) released by virus-infected cells typically incorporate host and viral components inside the vesicles (cargo molecules). Here, we investigated if human cytomegalovirus (HCMV) proteins are incorporated in EV outer membrane released by HCMV-infected cells. We separated EVs from HCMV using an iodixanol step-gradient and found that the separated vesicles carried EV markers such as the tetraspanin CD63 and Rab27A. Flow analysis of individual EVs demonstrated that on average, 15 ± 3.7% of EVs were positive for gB, 5.3 ± 2.3% were positive for gH and 3.74 ± 1.5% were positive for both gB and gH. In light of previous findings demonstrating HIV envelope proteins in EV membranes, the presence of viral protein at the surface of EVs released by HCMV-infected cells indicated that viral membrane proteins incorporated in EVs released by virus-infected cells may be a general phenomenon.