Role of miR-155 in the pathogenesis of herpetic stromal keratitis

Meeting the Challenge of Controlling Viral Immunopathology

The mission of this review is to identify immune-damaging participants involved in antiviral immunoinflammatory lesions. We argue these could be targeted and their activity changed selectively by maneuvers that, at the same time, may not diminish the impact of components that help resolve lesions. Ideally, we need to identify therapeutic approaches that can reverse ongoing lesions that lack unwanted side effects and are affordable to use. By understanding the delicate balance between immune responses that cause tissue damage and those that aid in resolution, novel strategies can be developed to target detrimental immune components while preserving the beneficial ones. Some strategies involve rebalancing the participation of immune components using various approaches, such as removing or blocking proinflammatory T cell products, expanding regulatory cells, restoring lost protective cell function, using monoclonal antibodies (moAb) to counteract inhibitory molecules, and exploiting metabolic differences between inflammatory and immuno-protective responses. These strategies can help reverse ongoing viral infections. We explain various approaches, from model studies and some clinical evidence, that achieve innate and adaptive immune rebalancing, offering insights into potential applications for controlling chronic viral-induced lesions.

Controlling viral inflammatory lesions by rebalancing immune response patterns

In this review, we discuss a variety of immune modulating approaches that could be used to counteract tissue-damaging viral immunoinflammatory lesions which typify many chronic viral infections. We make the point that in several viral infections the lesions can be largely the result of one or more aspects of the host response mediating the cell and tissue damage rather than the virus itself being directly responsible. However, within the reactive inflammatory lesions along with the pro-inflammatory participants there are also other aspects of the host response that may be acting to constrain the activity of the damaging components and are contributing to resolution. This scenario should provide the prospect of rebalancing the contributions of different host responses and hence diminish or even fully control the virus-induced lesions. We identify several aspects of the host reactions that influence the pattern of immune responsiveness and describe approaches that have been used successfully, mainly in model systems, to modulate the activity of damaging participants and which has led to lesion control. We emphasize examples where such therapies are, or could be, translated for practical use in the clinic to control inflammatory lesions caused by viral infections.

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.

Host-microbe interactions in cornea

Corneal infections result through interaction between microbes and host innate immune receptors. Damage to the cornea occurs as a result of microbial virulence factors and is often exacerbated by lack of a controlled host immune response; the latter contributing to bystander damage to corneal structure. Understanding mechanisms involved in host microbial interactions is critical to development of novel therapeutic targets, ultimate control of microbial pathogenesis, and restoration of tissue homeostasis. Studies on these interactions continue to provide exciting findings directly related to this ultimate goal.

Tear Film MicroRNAs as Potential Biomarkers: A Review

MicroRNAs are non-coding RNAs that serve as regulatory molecules in a variety of pathways such as inflammation, metabolism, homeostasis, cell machinery, and development. With the progression of sequencing methods and modern bioinformatics tools, novel roles of microRNAs in regulatory mechanisms and pathophysiological states continue to expand. Advances in detection methods have further enabled larger adoption of studies utilizing minimal sample volumes, allowing the analysis of microRNAs in low-volume biofluids, such as the aqueous humor and tear fluid. The reported abundance of extracellular microRNAs in these biofluids has prompted studies to explore their biomarker potential. This review compiles the current literature reporting microRNAs in human tear fluid and their association with ocular diseases including dry eye disease, Sjögren's syndrome, keratitis, vernal keratoconjunctivitis, glaucoma, diabetic macular edema, and diabetic retinopathy, as well as non-ocular diseases, including Alzheimer's and breast cancer. We also summarize the known roles of these microRNAs and shed light on the future progression of this field.

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.

Clinical Management of Herpes Simplex Virus Keratitis

Herpes simplex virus (HSV) keratitis is one of the leading causes of blindness worldwide. Additionally, up to 90% of the population in some countries is seropositive for HSV. HSV can cause a wide spectrum of ocular disease ranging from blepharitis to retinitis. Although the initial clinical expressions of HSV-1 and HSV-2 are similar, HSV-2 has been reported more frequently in association with recurrent HSV disease. Besides irreversible vision loss from keratitis, HSV also causes encephalitis and genital forms of the disease. Despite these statistics, there remains no vaccine against HSV. Current treatment therapies for related ocular diseases include the use of oral and topical antivirals and topical corticosteroids. While effective in many cases, they fail to address the latency and elimination of the virus, making it ineffective in addressing recurrences, a factor which increases the risk of vision loss. As such, there is a need for continued research of other potential therapeutic targets. This review utilized several published articles regarding the manifestations of HSV keratitis, antiviral immune responses to HSV infection, and clinical management of HSV keratitis. This review will summarize the current knowledge on the host–virus interaction in HSV infections, as well as highlighting the current and potential antiviral therapeutics.

E3 ligase RNF5 inhibits type I interferon response in herpes simplex virus keratitis through the STING/IRF3 signaling pathway

Herpes simplex keratitis (HSK), caused by the herpes simplex virus 1 (HSV-1), is a major blinding disease in developed countries. HSV-1 can remain latent in the host for life and cannot be eradicated. The infection causes the secretion of various cytokines and aggregation of inflammatory cells. In the early stage of inflammation, mainly neutrophils infiltrate the cornea, and CD4⁺ T cells mediate the immunopathological changes in herpetic stromal keratitis in the subsequent progression. The STING/IRF3-mediated type I interferon (IFN) response can effectively inhibit viral replication and control infection, but the activity of STING is affected by various ubiquitination modifications. In this study, we found that the expression of RNF5 was elevated in corneal tissues and corneal epithelial cells after infection with HSV-1. Immunofluorescence staining confirmed that RNF5 was mainly expressed in the corneal epithelial layer. We silenced and overexpressed RNF5 expression in corneal epithelial cells and then inoculated them with HSV-1. We found that the expressions of STING, p-IRF3, p-TBK1, and IFN-β mRNA increased after RNF5 silencing. The opposite results were obtained after RNF5 overexpression. We also used siRNA to silence RNF5 in the mouse cornea and then established the HSK model. Compared with the siRNA-control group, the siRNA-RNF5 group showed significantly improved corneal inflammation, reduced clinical scores and tear virus titers, and significantly increased corneal IFN-β expression. In addition, the expressions of the proinflammatory cytokines IL-6 and TNF-α in the corneal tissue were significantly decreased, indicating that RNF5 silencing could effectively promote IFN-I expression, inhibit virus replication, alleviate inflammation, and reduce corneal inflammatory damage. In summary, our results suggest that RNF5 limits the type I IFN antiviral response in HSV corneal epithelitis by inhibiting STING/IRF3 signaling.

The Virus-Induced Upregulation of the miR-183/96/182 Cluster and the FoxO Family Protein Members Are Not Required for Efficient Replication of HSV-1

Herpes simplex virus 1 (HSV-1) expresses a large number of miRNAs, and their function is still not completely understood. In addition, HSV-1 has been found to deregulate host miRNAs, which adds to the complexity of the regulation of efficient virus replication. In this study, we comprehensively addressed the deregulation of host miRNAs by massive-parallel sequencing. We found that only miRNAs expressed from a single cluster, miR-183/96/182, are reproducibly deregulated during productive infection. These miRNAs are predicted to regulate a great number of potential targets involved in different cellular processes and have only 33 shared targets. Among these, members of the FoxO family of proteins were identified as potential targets for all three miRNAs. However, our study shows that the upregulated miRNAs do not affect the expression of FoxO proteins, moreover, these proteins were upregulated in HSV-1 infection. Furthermore, we show that the individual FoxO proteins are not required for efficient HSV-1 replication. Taken together, our results indicate a complex and redundant response of infected cells to the virus infection that is efficiently inhibited by the virus.

miR-155: An Important Role in Inflammation Response

MicroRNAs (miRNAs) are a class of small, mature, noncoding RNA that lead to posttranscriptional gene silencing to regulate gene expression. miRNAs are instrumental in biological processes such as cell development, cell differentiation, cell proliferation, and cell apoptosis. The miRNA-mediated gene silencing is an important part of the regulation of gene expression in many kinds of diseases. miR-155, one of the best-characterized miRNAs, has been found to be closely related to physiological and pathological processes. What is more, miR-155 can be used as a potential therapeutic target for inflammatory diseases. We analyze the articles about miR-155 for nearly five years, review the advanced study on the function of miR-155 in different inflammatory cells like T cells, B cells, DCs, and macrophages, and then summarize the biological functions of miR-155 in different inflammatory cells. The widespread involvement of miR-155 in human diseases has led to a novel therapeutic approach between Chinese and Western medicine.

Analysis of MicroRNA Expression in Tears of Patients with Herpes Epithelial Keratitis: A Preliminary Study

Purpose

Herpes epithelial keratitis (HEK) is the most common form of herpes simplex virus (HSV) eye involvement, and understanding the molecular mechanisms underlying HEK is important. We investigated the expression of microRNAs (miRNAs) in the tears of patients with HEK.

Methods

Tear samples from eight patients with HEK and seven age-matched controls were evaluated. Clinical ophthalmologic evaluation was performed, and an anterior segment photograph was obtained after fluorescence staining. Dendritic or geographic ulcer areas were measured using ImageJ software. The expression of 43 different miRNAs in tears was measured using real-time polymerase chain reaction and compared between patients with HEK and controls. Differences in miRNA expression between the dendritic and geographic ulcer groups and correlations involving miRNA expression and ulcer area were evaluated.

Results

Of the 43 miRNAs, 23 were upregulated in patients with HEK compared to normal controls. MiR-15b-5p, miR-16-5p, miR-20b-5p, miR-21-5p, miR-23b-3p, miR-25-3p, miR-29a-3p, miR-30a-3p, miR-30d-5p, miR-92a-3p, miR-124-3p, miR-127-3p, miR-132-3p, miR-142-3p, miR-145-5p, miR-146a-5p, miR-146b-5p, miR-155-5p, miR-182-5p, miR-183-5p, miR-221-3p, miR-223-3p, and miR-338-5p were significantly upregulated in patients with HEK. MiR-29a-3p exhibited significant differences between the dendritic and geographic ulcer groups. All 23 miRNAs with significant differences between patients with HEK and the control group were not significantly correlated with ulcer area.

Conclusions

Twenty-three miRNAs were significantly upregulated in the tears of patients with HEK, and the expression of miRNAs may play important roles in herpes infection in relation to host immunity.

MicroRNA-155 and antiviral immune responses

The microRNA, miR-155 regulates both adaptive and innate immune responses. In viral infections, miR-155 can affect both innate immunity (interferon response, natural killer cell activity, and macrophage polarization) and adaptive immunity (including generation of anti-viral antibodies, CD8⁺ cytotoxic T lymphocytes, Th17, Th2, Th1, Tfh and Treg cells). In many viral infections, the proper and timely regulation of miR-155 expression is critical for the induction of an effective anti-virus immune response and viral clearance without any harmful immunopathologic consequences. MiR-155 may also exert pro-viral effects, mainly through the inhibition of the anti-viral interferon response. Thus, dysregulated expression of miR-155 can result in virus persistence and disruption of the normal response to viral infections. This review provides a thorough discussion of the role of miR-155 in immune responses and immunopathologic reactions during viral infections, and highlights its potential as a therapeutic target.

Inhibiting Glucose Metabolism Results in Herpes Simplex Encephalitis

This report evaluates how HSV enters the brain to cause herpes simplex encephalitis following infection at a peripheral site. We demonstrate that encephalitis regularly occurred when BALB/c mice were infected with HSV and treated daily with 2-deoxy-d-glucose (2DG), which inhibits glucose use via the glycolysis pathway. The outcome of infection in the trigeminal ganglion (TG), the site to which the virus spreads, replicates, and establishes latency, showed marked differences in viral and cellular events between treated and untreated animals. In control-untreated mice, the replicating virus was present only during early time points, whereas in 2DG recipients, replicating virus remained for the 9-d observation period. This outcome correlated with significantly reduced numbers of innate inflammatory cells as well as T cells in 2DG-treated animals. Moreover, T cells in the TG of treated animals were less activated and contained a smaller fraction of expressed IFN-γ production compared with untreated controls. The breakdown of latency was accelerated when cultures of TG cells taken from mice with established HSV latency were cultured in the presence of 2DG. Taken together, the results of both in vivo and in vitro investigations demonstrate that the overall effects of 2DG therapy impaired the protective effects of one or more inflammatory cell types in the TG that normally function to control productive infection and prevent spread of virus to the brain.

Inhibiting miR-129-5p alleviates inflammation and modulates autophagy by targeting ATG14 in fungal keratitis

To investigate the role of miR-129-5p in inflammation and autophagy in fungal keratitis, we established a keratitis mouse model infected with Fusarium solani (F. solani) and conducted experiments on corneal stromal cells infected with F. solani. The expression of miR-129-5p was detected via quantitative real-time polymerase chain reaction (PCR). The miR-129-5p antagomir was used to transfect cells and mice to study the regulatory role of miR-129-5p in autophagy and inflammation after fungal infection. The expression of Beclin1 and LC3B and colocalization of LC3B with lysosomes were detected via Western blotting and immunofluorescence. CCK-8 was used to determine the viability of corneal stromal cells. The expression of IL-1β were detected by ELISA. Bioinformatics software was used to predict the potential targets of miR-129-5p, which were verified by a luciferase reporter gene assay. RT-PCR showed that miR-129-5p expression in mouse corneas was significantly increased after infection with F. solani. Subconjunctival injection of the miR-129-5p antagomir significantly enhanced the proteins Beclin-1 and LC3B. At the same time, inhibiting miR-129-5p expression could reduce the inflammatory response in FK and significantly increase the viability of corneal stromal cells infected with F. solan. Moreover, the dual luciferase reporter assay indicated that Atg14 was a direct target of miR-129-5p. Our study shows that miR-129-5p is a novel small molecule that regulates autophagy by targeting Atg14, indicating that it may be a proinflammatory and therapeutic target for fungal keratitis.

The miRNA: a small but powerful RNA for COVID-19

Coronavirus disease 2019 (COVID-19) caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is a severe and rapidly evolving epidemic. Now, although a few drugs and vaccines have been proved for its treatment and prevention, little systematic comments are made to explain its susceptibility to humans. A few scattered studies used bioinformatics methods to explore the role of microRNA (miRNA) in COVID-19 infection. Combining these timely reports and previous studies about virus and miRNA, we comb through the available clues and seemingly make the perspective reasonable that the COVID-19 cleverly exploits the interplay between the small miRNA and other biomolecules to avoid being effectively recognized and attacked from host immune protection as well to deactivate functional genes that are crucial for immune system. In detail, SARS-CoV-2 can be regarded as a sponge to adsorb host immune-related miRNA, which forces host fall into dysfunction status of immune system. Besides, SARS-CoV-2 encodes its own miRNAs, which can enter host cell and are not perceived by the host's immune system, subsequently targeting host function genes to cause illnesses. Therefore, this article presents a reasonable viewpoint that the miRNA-based interplays between the host and SARS-CoV-2 may be the primary cause that SARS-CoV-2 accesses and attacks the host cells.

Exosomes derived from thymic stromal lymphopoietin-treated dendritic cells regulate T helper 17/regulatory T cell differentiation via miR-21/Smad7 axis

Thymic stromal lymphopoietin (TSLP) is associated with fungal keratitis. This work aims to investigate whether TSLP can regulate T helper (Th) 17 and regulatory T cell (Treg) differentiation. We separated dendritic cells (DCs) from peripheral blood of healthy volunteers. DCs were treated with TSLP to activate DCs, and exosomes were obtained. CD⁺ T cells were incubated with exosomes from TSLP-treated DCs. We found that exosomes from TSLP-treated DCs notably promoted the proportions of Th17 cells and inhibited the proportions of Tregs in the CD4⁺ T cells. Moreover, exosomes from TSLP-treated DCs enhanced the expression of retinoid-related orphan receptor γt (RORγt) and interleukin 17 (IL-17), and repressed the expression of forkhead box protein P3 (Foxp3) and interleukin 10 (IL-10) in the CD4⁺ T cells. Furthermore, miR-21 was highly expressed in exosomes from TSLP-treated DCs. Exosomes from TSLP-treated miR-21-silenced DCs promoted Treg differentiation and suppressed Th17 differentiation. Smad7 up-regulation repressed Th17 differentiation and enhanced Treg differentiation, which was abolished by miR-21 overexpression. Smad7 overexpression rescued the effect of exosomes from TSLP-treated DCs on Th17/Treg differentiation. In conclusion, our article confirms that TSLP induces DCs to deliver miR-21 by secreting exosomes, and thus miR-21 regulates Th17/Treg differentiation by inhibiting Smad7. Thus, this work further reveals the biological role of miR-21 in fungal keratitis.

Immune Response to Herpes Simplex Virus Infection and Vaccine Development

Herpes simplex virus (HSV) infections are among the most common viral infections and usually last for a lifetime. The virus can potentially be controlled with vaccines since humans are the only known host. However, despite the development and trial of many vaccines, this has not yet been possible. This is normally attributed to the high latency potential of the virus. Numerous immune cells, particularly the natural killer cells and interferon gamma and pathways that are used by the body to fight HSV infections have been identified. On the other hand, the virus has developed different mechanisms, including using different microRNAs to inhibit apoptosis and autophagy to avoid clearance and aid latency induction. Both traditional and new methods of vaccine development, including the use of live attenuated vaccines, replication incompetent vaccines, subunit vaccines and recombinant DNA vaccines are now being employed to develop an effective vaccine against the virus. We conclude that this review has contributed to a better understanding of the interplay between the immune system and the virus, which is necessary for the development of an effective vaccine against HSV.

Pathogenesis of Herpes Stromal Keratitis: Immune Inflammatory Response Mediated by Inflammatory Regulators

Herpes stromal keratitis (HSK) is one of the primary diseases that cause vision loss or even blindness after herpes simplex virus (HSV)-1 infection. HSK-associated vision impairment is predominantly due to corneal scarring and neovascularization caused by inflammation. In the infected cornea, HSV can activate innate and adaptive immune responses of host cells, which triggers a cascade of reactions that leads to the release of inflammatory cytokines, chemokines, microRNA, and other regulatory factors that have stimulating or inhibitory effects on tissue. Physiologically, host cells show homeostasis. In this review, we summarize the factors involved in HSK pathogenesis from the perspective of immunity, molecules, and pathological angiogenesis. We also describe in detail the pathogenesis of chronic inflammatory lesions of the corneal stroma in response to HSV-1 infection.

Epigenetic regulation of anterior segment diseases and potential therapeutics

In recent years, technological advances in sequencing have accelerated our understanding of epigenetics in ocular development and ophthalmic diseases. We now know that epigenetic modifications are necessary for normal ocular development and biological processes such as corneal wound healing and ocular surface repair, while aberrant epigenetic regulation underlies the pathogenesis of a wide range of ocular diseases, including cataracts and various diseases of the ocular surface. As the epigenetics of the eye is a constantly changing field of medicine, this comprehensive review focuses on innovations and scientific discoveries related to epigenetic control of anterior segment diseases that were published in the English literature in the past five years. These recent studies attempt to elucidate therapeutic targets for the anterior segment pathological processes. Already, recent studies have shown therapeutic potential in targeting epigenetic mechanisms of ocular diseases, and new epigenetic therapies are on the verge of being introduced to clinical practice. New drug targets can potentially emerge as we make further discoveries within this field.

Cellular microRNA-155 Regulates Virus-Induced Inflammatory Response and Protects against Lethal West Nile Virus Infection

West Nile virus (WNV) is a flavivirus that has disseminated globally as a significant cause of viral encephalitis in humans. MircoRNA-155 (miR-155) regulates various aspects of innate and adaptive immune responses. We previously reported that WNV infection induces upregulation of miR-155 in mice brains. In the current study, we demonstrate the critical role of miR-155 in restricting the pathogenesis of WNV infection in mice. Compared to wild-type (WT) mice, miR-155 knockout mice exhibited significantly higher morbidity and mortality after infection with either a lethal strain, WNV NY99, or a non-lethal strain, WNV Eg101. Increased mortality in miR-155^−/− mice was associated with significantly high WNV burden in the serum and brains. Protein levels of interferon (IFN)-α in the serum and brains were higher in miR-155^−/− mice. However, miR-155^−/− mice exhibited significantly lower protein levels of anti-viral interleukin (IL)-1β, IL-12, IL-6, IL-15, and GM-CSF despite the high viral load. Primary mouse cells lacking miR-155 were more susceptible to infection with WNV compared to cells derived from WT mice. Besides, overexpression of miR-155 in human neuronal cells modulated anti-viral cytokine response and resulted in significantly lower WNV replication. These data collectively indicate that miR-155 restricts WNV production in mouse and human cells and protects against lethal WNV infection in mice.

The extensive role of miR-155 in malignant and non-malignant diseases

MicroRNAs (miRNAs) have rapidly emerged as key molecules in cancer initiation and development, showing the capability to regulate pivotal oncogenic pathways. MiR-155 has gathered an increased attention especially in oncology, but also in non-malignanat pathologies. Nowadays, this noncoding RNA is one of the most important miRNAs in cancer, due to the extensive signaling network associated with it, implication in immune system regulation and also deregulation in disease states. Therefore, numerous research protocols are focused on preclinical modulation of miR-155 for therapeutic purposes, or investigation of its dynamic expression for diagnostic/prognostic assessments, with the final intention of bringing this miRNA into the clinical setting. This review comprehensively presents the extended role of miR-155 in cancer and other pathologies, where its expression is dysregulated. Finally, we assess the future steps toward miR-155 based therapeutics.

MicroRNAs in Ocular Infection

MicroRNAs (miRNAs) are small, non-coding, regulatory RNA molecules and constitute a newly recognized, important layer of gene-expression regulation at post-transcriptional levels. miRNAs quantitatively fine tune the expression of their downstream genes in a cell type- and developmental stage-specific fashion. miRNAs have been proven to play important roles in the normal development and function as well as in the pathogenesis of diseases in all tissues and organ systems. miRNAs have emerged as new therapeutic targets and biomarkers for treatment and diagnosis of various diseases. Although miRNA research in ocular infection remains in its early stages, a handful of pioneering studies have provided insight into the roles of miRNAs in the pathogenesis of parasitic, fungal, bacterial, and viral ocular infections. Here, we review the current status of research in miRNAs in several major ocular infectious diseases. We predict that the field of miRNAs in ocular infection will greatly expand with the discovery of novel miRNA-involved molecular mechanisms that will inform development of new therapies and identify novel diagnostic biomarkers.

Identification of lncRNA-155 encoded by MIR155HG as a novel regulator of innate immunity against influenza A virus infection

Long noncoding RNAs (lncRNAs) are single-stranded RNA molecules longer than 200 nt that regulate many cellular processes. MicroRNA 155 host gene (MIR155HG) encodes the microRNA (miR)-155 that regulates various signalling pathways of innate and adaptive immune responses against viral infections. MIR155HG also encodes a lncRNA that we call lncRNA-155. Here, we observed that expression of lncRNA-155 was markedly upregulated during influenza A virus (IAV) infection both in vitro (several cell lines) and in vivo (mouse model). Interestingly, robust expression of lncRNA-155 was also induced by infections with several other viruses. Disruption of lncRNA-155 expression in A549 cells diminished the antiviral innate immunity against IAV. Furthermore, knockout of lncRNA-155 in mice significantly increased IAV replication and virulence in the animals. In contrast, overexpression of lncRNA-155 in human cells suppressed IAV replication, suggesting that lncRNA-155 is involved in host antiviral innate immunity induced by IAV infection. Moreover, we found that lncRNA-155 had a profound effect on expression of protein tyrosine phosphatase 1B (PTP1B) during the infection with IAV. Inhibition of PTP1B by lncRNA-155 resulted in higher production of interferon-beta (IFN-β) and several critical interferon-stimulated genes (ISGs). Together, these observations reveal that MIR155HG derived lncRNA-155 can be induced by IAV, which modulates host innate immunity during the virus infection via regulation of PTP1B-mediated interferon response.

Long non-coding RNA H19 promotes corneal neovascularization by targeting microRNA-29c

Long non-coding RNA (lncRNA) H19 has been implicated in tumor angiogenesis. However, whether H19 regulates the progression of corneal neovascularization (CNV) is unclear. The present study aimed to determine the function of H19 in CNV and its possible molecular mechanism. Here, we found that the H19 levels were remarkably increased in vascularized corneas and basic fibroblast growth factor (bFGF)-treated human umbilical vein endothelial cells (HUVECs). In vitro, H19 up-regulation promoted proliferation, migration, tube formation and vascular endothelial growth factor A (VEGFA) expression in HUVECs, and it was found to down-regulate microRNA-29c (miR-29c) expression. Bioinformatics analysis revealed that H19 mediated the above effects by binding directly to miR-29c. In addition, miR-29c expression was markedly reduced in vascularized corneas and its expression also decreased in bFGF-treated HUVECs in vitro. MiR-29c targeted the 3′ untranslated region (3′-UTR) of VEGFA and decreased its expression. These data suggest that H19 can enhance CNV progression by inhibiting miR-29c, which negatively regulates VEGFA. This novel regulatory axis may serve as a potential therapeutic target for CNV.

MicroRNAs in Neuroinflammation: Implications in Disease Pathogenesis, Biomarker Discovery and Therapeutic Applications

The central nervous system can respond to threat via the induction of an inflammatory response. Under normal circumstances this response is tightly controlled, however uncontrolled neuroinflammation is a hallmark of many neurological disorders. MicroRNAs are small non-coding RNA molecules that are important for regulating many cellular processes. The ability of microRNAs to modulate inflammatory signaling is an area of ongoing research, which has gained much attention in recent years. MicroRNAs may either promote or restrict inflammatory signaling, and either exacerbate or ameliorate the pathological consequences of excessive neuroinflammation. The aim of this review is to summarize the mode of regulation for several important and well-studied microRNAs in the context of neuroinflammation, including miR-155, miR-146a, miR-124, miR-21 and let-7. Furthermore, the pathological consequences of miRNA deregulation during disorders that feature neuroinflammation are discussed, including Multiple Sclerosis, Alzheimer’s disease, Parkinson’s disease, Prion diseases, Japanese encephalitis, Herpes encephalitis, ischemic stroke and traumatic brain injury. There has also been considerable interest in the use of altered microRNA signatures as biomarkers for these disorders. The ability to modulate microRNA expression may even serve as the basis for future therapeutic strategies to help treat pathological neuroinflammation.

MiR-155-5p modulates HSV-1 replication via the epigenetic regulation of SRSF2 gene expression

A previous study reported that miR-155-5p knockout mice were more resistant to herpes simplex virus type I (HSV-1) infection. However, the exact underlying molecular mechanism remains to be elucidated. Here, we demonstrated that HSV-1 infection upregulates miR-155-5p expression. By binding to the promoter of serine/arginine-rich splicing factor 2 (SRSF2), which is an important transcriptional activator of HSV-1 genes that was previously reported by our group, and altering the histone modification located near the transcription start site (TSS) of the SRSF2 gene, miR-155-5p promotes the transcription of the SRSF2 gene, ultimately increasing viral replication and viral gene expression. Our results provide insight for an understanding of the roles and molecular mechanism of miR-155-5p in HSV-1 replication and the epigenetic control of SRSF2 gene expression.

MicroRNAs in the cornea: Role and implications for treatment of corneal neovascularization

With no safe and efficient approved therapy available for treating corneal neovascularization, the search for alternative and effective treatments is of great importance. Since the discovery of miRNAs as key regulators of gene expression, knowledge of their function in the eye has expanded continuously, facilitated by high throughput genomic tools such as microarrays and RNA sequencing. Recently, reports have emerged implicating miRNAs in pathological and developmental angiogenesis. This has led to the idea of targeting these regulatory molecules as a therapeutic approach for treating corneal neovascularization. With the growing volume of data generated from high throughput tools applied to study corneal neovascularization, we provide here a focused review of the known miRNAs related to corneal neovascularization, while presenting new experimental data and insights for future research and therapy development.

Pathogenesis of herpes simplex keratitis: The host cell response and ocular surface sequelae to infection and inflammation

Herpes simplex virus type 1 (HSV) keratitis is a leading cause of infectious blindness. Clinical disease occurs variably throughout the cornea from epithelium to endothelium and recurrent HSV stromal keratitis is associated with corneal scarring and neovascularization. HSV keratitis can be associated with ocular pain and subsequent neutrophic keratopathy. Host cell interactions with HSV trigger an inflammatory cascade responsible not only for clearance of virus but also for progressive corneal opacification due to inflammatory cell infiltrate, angiogenesis, and corneal nerve loss. Current antiviral therapies target viral replication to decrease disease duration, severity and recurrence, but there are limitations to these agents. Therapies directed towards viral entry into cells, protein synthesis, inflammatory cytokines and vascular endothelial growth factor pathways in animal models represent promising new approaches to the treatment of recurrent HSV keratitis.

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.

Targeting corneal inflammation by gene therapy: Emerging strategies for keratitis

Inflammation is the underlying process of several diseases within the eye, specifically in the cornea. Current treatment options for corneal inflammation or keratitis, and related neovascularization, are restricted by limited efficacy, adverse effects, and short duration of action. Gene therapy has shown great potential for the treatment of diseases affecting the ocular surface, and major efforts are being targeted to inflammatory mediators and neovascularization, in order to develop potential treatments for corneal inflammation. Gene therapy to treat ocular disorders is still starting, and current therapies are primarily experimental, with most human clinical trials still in research state, although some of them have already shown encouraging results. In this review, we focus on the progress and challenges of gene therapy to treat corneal inflammation. After introducing the inflammation process, we present the main nucleic acid delivery systems, including viral and non-viral vectors, and the most studied strategies to address the therapy: control of neovascularization and regulation of pro- and anti-inflammatory cytokines.

Application of our understanding of pathogenesis of herpetic stromal keratitis for novel therapy

HSV-1 ocular infection can cause herpes stromal keratitis (SK), an immunopathological lesion. Frequent recurrences can lead to progressive corneal scaring which can result in vision impairment if left untreated. Currently, the acute and epithelial forms of SK are usually controlled using anti-viral drugs. However, chronic forms of SK which are inflammatory in nature, require the addition of a topical corticosteroid to the anti-viral treatment regimen. In this review, we highlight the essential events involved in SK pathogenesis which can be targeted for improved therapy. We also examine some approaches which can be combined with the current treatments to effectively control SK.

Are miRNAs critical determinants in herpes simplex virus pathogenesis?

miRNAs are small noncoding RNA that play a crucial role in gene regulation by inhibiting translation or promoting mRNA degradation. Viruses themselves express miRNAs that can target either the host or viral mRNA transcriptome. Moreover, viral infection of cells causes a drastic change in host miRNAs. This complex interaction between the host and viruses often favors the virus to evade immune elimination and favors the establishment and maintenance of latency. In this review we discuss the function of both host and viral miRNAs in regulating herpes simplex virus pathogenesis and also discuss the prospect of using miRNAs as biomarkers and therapeutic tools.

Expression of miR-155 associated with Toll-like receptors 3, 7, and 9 transcription in the olfactory bulbs of cattle naturally infected with BHV5

Bovine herpesvirus 5 (BHV5) infection of young cattle is frequently associated with fatal neurological disease and, as such, represents an attractive model for studying the pathogenesis of viral-induced meningoencephalitis. Following replication in the nasal mucosa, BHV5 invades the central nervous system (CNS) mainly through the olfactory pathway. The innate immune response triggered by the host face to virus replication through the olfactory route is poorly understood. Recently, an upregulation of conserved pathogen-associated molecular pattern, as Toll-like receptors (TLRs), has been demonstrated in the CNS of BHV5 experimentally infected cows. A new perspective to understand host-pathogen interactions has emerged elucidating microRNAs (miRNAs) network that interact with innate immune response during neurotropic viral infections. In this study, we demonstrated a link between the expression of TLRs 3, 7, and 9 and miR-155 transcription in the olfactory bulbs (OB) of 16 cows suffering from acute BHV5-induced neurological disease. The OBs were analyzed for viral antigens and genome, miR-155 and TLR 3, 7, and 9 expression considering three major regions: olfactory receptor neurons (ORNs), glomerular layer (GL), and mitral cell layer (ML). BHV5 antigens and viral genomes, corresponding to glycol-C gene, were detected in all OBs regions by fluorescent antibody assay (FA) and PCR, respectively. TLR 3, 7, and 9 transcripts were upregulated in ORNs and ML, yet only ORN layers revealed a positive correlation between TLR3 and miR-155 transcription. In ML, miR-155 correlated positively with all TLRs studied. Herein, our results evidence miR-155 transcription in BHV5 infected OB tissue associated to TLRs expression specifically ORNs which may be a new window for further studies.

Decoding Noncoding RNAs: Role of MicroRNAs and Long Noncoding RNAs in Ocular Neovascularization

Ocular neovascularization is a pathological sequel of multiple eye diseases. Based on the anatomical site into which the abnormal neovessels grow, ocular neovascularization can be categorized into corneal neovascularization, choroidal neovascularization, and retinal neovascularization. Each category is intractable, and may lead to blindness if not appropriately treated. However, the current therapeutic modalities, including laser photocoagulation, vitrectomy surgery, and anti-VEGF drugs, raise concerns due to limited efficacy, damage on retinal parenchyma and vasculature, and the patients' unresponsiveness to the treatments. Therefore, the in-depth study on pathogenesis of and the search for novel therapeutic targets to the ocular neovascularization are needed. During the last 10 years or so, a large number of literatures have emerged indicating a critical role of noncoding RNAs, particularly microRNAs (miRNAs) and long noncoding RNAs (lncRNAs), in the pathogenesis and regulation of the ocular neovascularization. This review summarizes the current understanding of the biosynthesis and functions of the miRNAs and lncRNAs, the regulation of the miRNAs and lncRNAs in neovascular eye diseases, as well as the roles of these noncoding RNAs in the disease models of ocular neovascularization, in the hope that it could provide clues for the pathogenesis of and molecular targets to the ocular neovascularization.

The Plasticity and Stability of Regulatory T Cells during Viral-Induced Inflammatory Lesions

Ocular infection with HSV causes a chronic T cell-mediated inflammatory lesion in the cornea. Lesion severity is affected by the balance of different CD4 T cell subsets, with greater severity occurring when the activity of regulatory T cells (Tregs) is compromised. In this study, fate-mapping mice were used to assess the stability of Treg function in ocular lesions. We show that cells that were once Foxp3⁺ functional Tregs may lose Foxp3 and become Th1 cells that could contribute to lesion expression. The instability primarily occurred with IL-2R^lo Tregs and was shown, in part, to be the consequence of exposure to IL-12. Lastly, in vitro-generated induced Tregs (iTregs) were shown to be highly plastic and capable of inducing stromal keratitis when adoptively transferred into Rag1^-/- mice, with 95% of iTregs converting into ex-Tregs in the cornea. This plasticity of iTregs could be prevented when they were generated in the presence of vitamin C and retinoic acid. Importantly, adoptive transfer of these stabilized iTregs to HSV-1-infected mice prevented the development of stromal keratitis lesions more effectively than did control iTregs. Our results demonstrate that CD25^lo Treg and iTreg instability occurs during a viral immunoinflammatory lesion and that its control may help to avoid lesion chronicity.

Frontline Science: Aspirin-triggered resolvin D1 controls herpes simplex virus-induced corneal immunopathology

Stromal keratitis (SK) is a chronic immunopathological lesion of the eye, caused by HSV-1 infection, and a common cause of vision impairment in humans. The inflammatory lesions in the cornea are primarily caused by neutrophils with the active participation of CD4⁺ T cells. Therefore, the targeting of these immune cell types and their products represents a potentially valuable form of therapy to reduce the severity of disease. Resolvin D1 (RvD1) and its epimer aspirin-triggered RvD1 (AT-RvD1) are lipid mediators derived from docosahexaenoic acid (DHA) and were shown to promote resolution in several inflammatory disease models. In this report, we examined whether AT-RvD1 administration, begun before infection or at a later stage after ocular infection of mice with HSV-1, could control the severity of SK lesions. Treatment with AT-RvD1 significantly diminished the extent of corneal neovascularization and the severity of SK lesions. AT-RvD1-treated mice had fewer numbers of inflammatory cells that included neutrophils as well as Th1 and Th17 cells in the infected cornea. The mechanisms by which AT-RvD1 acts appear to be multiple. These include inhibitory effects on proinflammatory mediators, such as IL-1β, IL-6, IL-12, CXCL1, MCP-1, MIP-2, vascular endothelial growth factor (VEGF)-A, matrix metalloproteinase 9 (MMP-9), and proinflammatory miRNA, such as miR-155, miR-132, and miR-223, which are involved in SK pathogenesis and corneal neovascularization. In addition, AT-RvD1 attenuated STAT1, which plays an important role in Th1 cell differentiation and IFN-γ expression. These findings demonstrate that AT-RvD1 treatment could represent a useful strategy for the management of virus-induced immunopathological lesions.

HSV1 latent transcription and non-coding RNA: A critical retrospective

Virologists have invested great effort into understanding how the herpes simplex viruses and their relatives are maintained dormant over the lifespan of their host while maintaining the poise to remobilize on sporadic occasions. Piece by piece, our field has defined the tissues in play (the sensory ganglia), the transcriptional units (the latency-associated transcripts), and the responsive genomic region (the long repeats of the viral genomes). With time, the observed complexity of these features has compounded, and the totality of viral factors regulating latency are less obvious. In this review, we compose a comprehensive picture of the viral genetic elements suspected to be relevant to herpes simplex virus 1 (HSV1) latent transcription by conducting a critical analysis of about three decades of research. We describe these studies, which largely involved mutational analysis of the notable latency-associated transcripts (LATs), and more recently a series of viral miRNAs. We also intend to draw attention to the many other less characterized non-coding RNAs, and perhaps coding RNAs, that may be important for consideration when trying to disentangle the multitude of phenotypes of the many genetic modifications introduced into recombinant HSV1 strains.

MicroRNA 155 and viral-induced neuroinflammation

MicroRNA (miRNA) regulation of gene expression is becoming an increasingly recognized mechanism by which host immune responses are governed following microbial infection. miRNAs are short, non-coding RNAs that repress translation of target genes, and have been implicated in a number of activities that modulate host immune responses, including the regulation of immune cell proliferation, survival, expansion, differentiation, migration, polarization, and effector function. This review highlights several examples in which mammalian-encoded miR-155 influences immune responses following viral infection of the CNS.

MicroRNA-155 enhances T cell trafficking and antiviral effector function in a model of coronavirus-induced neurologic disease

BACKGROUND

MicroRNAs (miRNAs) are noncoding RNAs that modulate cellular gene expression, primarily at the post-transcriptional level. We sought to examine the functional role of miR-155 in a model of viral-induced neuroinflammation.

METHODS

Acute encephalomyelitis and immune-mediated demyelination were induced by intracranial injection with the neurotropic JHM strain of mouse hepatitis virus (JHMV) into C57BL/6 miR-155 (+/+) wildtype (WT) mice or miR-155 (-/-) mice. Morbidity and mortality, viral load and immune cell accumulation in the CNS, and spinal cord demyelination were assessed at defined points post-infection. T cells harvested from infected mice were used to examine cytolytic activity, cytokine activity, and expression of certain chemokine receptors. To determine the impact of miR-155 on trafficking, T cells from infected WT or miR-155 (-/-) mice were adoptively transferred into RAG1 (-/-) mice, and T cell accumulation into the CNS was assessed using flow cytometry. Statistical significance was determined using the Mantel-Cox log-rank test or Student's T tests.

RESULTS

Compared to WT mice, JHMV-infected miR-155 (-/-) mice developed exacerbated disease concomitant with increased morbidity/mortality and an inability to control viral replication within the CNS. In corroboration with increased susceptibility to disease, miR-155 (-/-) mice had diminished CD8(+) T cell responses in terms of numbers, cytolytic activity, IFN-γ secretion, and homing to the CNS that corresponded with reduced expression of the chemokine receptor CXCR3. Both IFN-γ secretion and trafficking were impaired in miR-155 (-/-) , virus-specific CD4(+) T cells; however, expression of the chemokine homing receptors analyzed on CD4(+) cells was not affected. Except for very early during infection, there were not significant differences in macrophage infiltration into the CNS between WT and miR-155 (-/-) JHMV-infected mice, and the severity of demyelination was similar at 14 days p.i. between WT and miR-155 (-/-) JHMV-infected mice.

CONCLUSIONS

These findings support a novel role for miR-155 in host defense in a model of viral-induced encephalomyelitis. Specifically, miR-155 enhances antiviral T cell responses including cytokine secretion, cytolytic activity, and homing to the CNS in response to viral infection. Further, miR-155 can play either a host-protective or host-damaging role during neuroinflammation depending on the disease trigger.