Human cytomegalovirus activates glucose transporter 4 expression to increase glucose uptake during infection

Glucose-independent human cytomegalovirus replication is supported by metabolites that feed upper glycolytic branches

Viruses with broad tissue distribution and cell tropism successfully replicate in various nutrient environments in the body. Several viruses reprogram metabolism for viral replication. However, many studies focus on metabolic reprogramming in nutrient-rich conditions that do not recapitulate physiological environments in the body. Here, we investigated how viruses may replicate when a metabolite thought to be essential for replication is limited. We use human cytomegalovirus infection in glucose-free conditions as a model to determine how glucose supports virus replication and how physiologically relevant nutrients contribute to glucose-independent virus production. We find that glucose supports viral genome synthesis, viral protein production and glycosylation, and infectious virus production. Notably, supplement of glucose-free cultures with uridine, ribose, or UDP-GlcNAc-metabolites that feed upper glycolytic branches like the pentose phosphate pathway-results in partially restored virus replication, including low levels of infectious virus production. Supplementing lower glycolysis in glucose-free cultures using pyruvate fails to restore virus replication. These results indicate that nutrients can compensate for glucose via feeding upper glycolytic branches to sustain low levels of virus production. More broadly, our findings suggest that viruses may successfully replicate in diverse metabolic niches, including those in the body with low glucose levels, through alternative nutrient usage.

Virus-Induced Histone Lactylation Promotes Virus Infection in Crustacean

As "non-cellular organisms", viruses need to infect living cells to survive themselves. The virus infection must alter host's metabolisms. However, the influence of the metabolites from the altered metabolisms of virus-infected host cells on virus-host interactions remains largely unclear. To address this issue, shrimp, a representative species of crustaceans, is challenged with white spot syndrome virus (WSSV) in this study. The in vivo results presented that the WSSV infection enhanced shrimp glycolysis, leading to the accumulation of lactate. The lactate accumulation in turn promoted the site-specific histone lactylation (H3K18la and H4K12la) in a p300/HDAC1/HDAC3-dependent manner. H3K18la and H4K12la are enriched in the promoters of 75 target genes, of which the H3K18la and H4K12la modification upregulated the expression of ribosomal protein S6 kinases 2 (S6K2) in the virus-infected hosts to promote the virus infection. Further data revealed that the virus-encoded miR-N20 targeted hypoxia inducible factor-1α (HIF-1α) to inhibit the host glycolysis, leading to the suppression of H3K18la and H4K12la. Therefore, the findings contributed novel insights into the effects and the underlying mechanism of the virus-induced histone lactylation on the virus-host interactions, providing new targets for the control of virus infection.

Immunometabolites in viral infections: Action mechanism and function

The interplay between viral pathogens and host metabolism plays a pivotal role in determining the outcome of viral infections. Upon viral detection, the metabolic landscape of the host cell undergoes significant changes, shifting from oxidative respiration via the tricarboxylic acid (TCA) cycle to increased aerobic glycolysis. This metabolic shift is accompanied by elevated nutrient accessibility, which is vital for cell function, development, and proliferation. Furthermore, depositing metabolites derived from fatty acids, TCA intermediates, and amino acid catabolism accelerates the immunometabolic transition, facilitating pro-inflammatory and antimicrobial responses. Immunometabolites refer to small molecules involved in cellular metabolism regulating the immune response. These molecules include nutrients, such as glucose and amino acids, along with metabolic intermediates and signaling molecules adenosine, lactate, itaconate, succinate, kynurenine, and prostaglandins. Emerging evidence suggests that immunometabolites released by immune cells establish a complex interaction network within local niches, orchestrating and fine-tuning immune responses during viral diseases. However, our current understanding of the immense capacity of metabolites to convey essential cell signals from one cell to another or within cellular compartments remains incomplete. Unraveling these complexities would be crucial for harnessing the potential of immunometabolites in therapeutic interventions. In this review, we discuss specific immunometabolites and their mechanisms of action in viral infections, emphasizing recent findings and future directions in this rapidly evolving field.

Enteric coronavirus PDCoV evokes a non-Warburg effect by hijacking pyruvic acid as a metabolic hub

The Warburg effect, also referred as aerobic glycolysis, is a common metabolic program during viral infection. Through targeted metabolomics combined with biochemical experiments and various cell models, we investigated the central carbon metabolism (CCM) profiles of cells infected with porcine deltacoronavirus (PDCoV), an emerging enteropathogenic coronavirus with zoonotic potential. We found that PDCoV infection required glycolysis but decreased glycolytic flux, exhibiting a non-Warburg effect characterized by pyruvic acid accumulation. Mechanistically, PDCoV enhanced pyruvate kinase activity to promote pyruvic acid anabolism, a process that generates pyruvic acid with concomitant ATP production. PDCoV also hijacked pyruvic acid catabolism to increase biosynthesis of non-essential amino acids (NEAAs), suggesting that pyruvic acid is an essential hub for PDCoV to scavenge host energy and metabolites. Furthermore, PDCoV facilitated glutaminolysis to promote the synthesis of NEAA and pyrimidines for optimal proliferation. Our work supports a novel CCM model after viral infection and provides potential anti-PDCoV drug targets.

Does oncolytic viruses-mediated metabolic reprogramming benefit or harm the immune microenvironment?

Oncolytic virus immunotherapy as a new tumor therapy has made remarkable achievements in clinical practice. And metabolic reprogramming mediated by oncolytic virus has a significant impact on the immune microenvironment. This review summarized the reprogramming of host cell glucose metabolism, lipid metabolism, oxidative phosphorylation, and glutamine metabolism by oncolytic virus and illustrated the effects of metabolic reprogramming on the immune microenvironment. It was found that oncolytic virus-induced reprogramming of glucose metabolism in tumor cells has both beneficial and detrimental effects on the immune microenvironment. In addition, oncolytic virus can promote fatty acid synthesis in tumor cells, inhibit oxidative phosphorylation, and promote glutamine catabolism, which facilitates the anti-tumor immune function of immune cells. Therefore, targeted metabolic reprogramming is a new direction to improve the efficacy of oncolytic virus immunotherapy.

Metabolites that feed upper glycolytic branches support glucose independent human cytomegalovirus replication

The broad tissue distribution and cell tropism of human cytomegalovirus indicates that the virus successfully replicates in tissues with various nutrient environments. HCMV requires and reprograms central carbon metabolism for viral replication. However, many studies focus on reprogramming of metabolism in high nutrient conditions that do not recapitulate physiological nutrient environments in the body. In this study, we investigate how HCMV successfully replicates when nutrients are suboptimal. We limited glucose following HCMV infection to determine how glucose supports virus replication and how nutrients potentially present in the physiological environment contribute to successful glucose independent HCMV replication. Glucose is required for HCMV viral genome synthesis, viral protein production and glycosylation, and virus production. However, supplement of glucose-free cultures with uridine, ribose, or UDP-GlcNAc-metabolites that support upper glycolytic branches-resulted in partially restored viral genome synthesis and subsequent partial restoration of viral protein levels. Low levels of virus production were also restored. Supplementing lower glycolysis in glucose-free cultures using pyruvate had no effect on virus replication. These results indicate nutrients that support upper glycolytic branches like the pentose phosphate pathway and hexosamine pathway can compensate for glucose during HCMV replication to support low levels of virus production. More broadly, our findings suggest that HCMV could successfully replicate in diverse metabolic niches, including those in the body with low levels of glucose, through alternative nutrient usage.

Role of solute carrier transporters in regulating dendritic cell maturation and function

Dendritic cells (DCs) are specialized antigen-presenting cells that initiate and regulate innate and adaptive immune responses. Solute carrier (SLC) transporters mediate diverse physiological functions and maintain cellular metabolite homeostasis. Recent studies have highlighted the significance of SLCs in immune processes. Notably, upon activation, immune cells undergo rapid and robust metabolic reprogramming, largely dependent on SLCs to modulate diverse immunological responses. In this review, we explore the central roles of SLC proteins and their transported substrates in shaping DC functions. We provide a comprehensive overview of recent studies on amino acid transporters, metal ion transporters, and glucose transporters, emphasizing their essential contributions to DC homeostasis under varying pathological conditions. Finally, we propose potential strategies for targeting SLCs in DCs to bolster immunotherapy for a spectrum of human diseases.

Metabolic Enzymes in Viral Infection and Host Innate Immunity

Metabolic enzymes are central players for cell metabolism and cell proliferation. These enzymes perform distinct functions in various cellular processes, such as cell metabolism and immune defense. Because viral infections inevitably trigger host immune activation, viruses have evolved diverse strategies to blunt or exploit the host immune response to enable viral replication. Meanwhile, viruses hijack key cellular metabolic enzymes to reprogram metabolism, which generates the necessary biomolecules for viral replication. An emerging theme arising from the metabolic studies of viral infection is that metabolic enzymes are key players of immune response and, conversely, immune components regulate cellular metabolism, revealing unexpected communication between these two fundamental processes that are otherwise disjointed. This review aims to summarize our present comprehension of the involvement of metabolic enzymes in viral infections and host immunity and to provide insights for potential antiviral therapy targeting metabolic enzymes.

Sirtuin 2 promotes human cytomegalovirus replication by regulating cell cycle progression

IMPORTANCE

This study expands the growing understanding that protein acetylation is a highly regulated molecular toggle of protein function in both host anti-viral defense and viral replication. We describe a pro-viral role for the human enzyme SIRT2, showing that its deacetylase activity supports HCMV replication. By integrating quantitative proteomics, flow cytometry cell cycle assays, microscopy, and functional virology assays, we investigate the temporality of SIRT2 functions and substrates. We identify a pro-viral role for the SIRT2 deacetylase activity via regulation of CDK2 K6 acetylation and the G1-S cell cycle transition. These findings highlight a link between viral infection, protein acetylation, and cell cycle progression.

Reprogramming of glucose metabolism in virus infected cells

Viral infection is a kind of cellular stress that leads to the changes in cellular metabolism. Many metabolic pathways in a host cell such as glycolysis, amino acid and nucleotide synthesis are altered following virus infection. Both oncogenic and non-oncogenic viruses depend on host cell glycolysis for their survival and pathogenesis. Recent studies have shown that the rate of glycolysis plays an important role in oncolysis as well by oncolytic therapeutic viruses. During infection, viral proteins interact with various cellular glycolytic enzymes, and this interaction enhances the catalytic framework of the enzymes subsequently the glycolytic rate of the cell. Increased activity of glycolytic enzymes following their interaction with viral proteins is vital for replication and to counteract the inhibition of glycolysis caused by immune response. In this review, the importance of host cell glycolysis and the modulation of glycolysis by various viruses such as oncogenic, non-oncogenic and oncolytic viruses are presented.

Associations between human cytomegalovirus infection and type 2 diabetes mellitus: a systematic review and meta-analysis

OBJECTIVE

Multiple studies have reported a potential contribution of human cytomegalovirus (HCMV) to the pathogenesis of type 1 diabetes and post-transplantation diabetes. However, the association between HCMV and type 2 diabetes mellitus (T2DM) remains unclear. In this paper, we employ the meta-analysis approach to investigate the potential correlation between HCMV infection and T2DM.

METHOD

The data of our study were collected from PubMed, Embase, Web of Science, Cochrane Library, China National Knowledge Infrastructure and WAN FANG databases from inception to November 2022. Using the Review Manager V.5.4 software, the meta-analysis was performed.

RESULTS

A total of 18 139 patients from 22 studies were included in our analysis. In the Asian subgroup, the patients with T2DM group had a significantly higher frequency of HCMV infection and older age compared with the healthy group. In the European, the frequency of HCMV infection in the T2DM was lower than the healthy group, although this difference was not statistically significant. After adjusting for demographic factors, the adjusted OR of T2DM for risk of by HCMV status was not found to be significant (adjusted OR=1.19, 95% CI=0.88 to 1.62, p>0.05). Additionally, T2DM with vasculopathy had a significantly higher rate of HCMV infection compared with those without vasculopathy (OR=1.87, 95% CI=1.24 to 2.83, p<0.05). Among T2DM with HCMV infection, there were significant increases in fasting blood glucose levels and the proportion of CD8+ T lymphocytes. Conversely, fasting blood insulin levels, the proportion of CD4+ T lymphocyte and the CD4+/CD8+ ratio were significantly decreased compared with the healthy group.

CONCLUSION

At present, the available evidence does not provide a clear understanding of whether there is a significant association between T2DM and HCMV infection. Additionally, T2DM with HCMV infection exhibited significantly worse blood glucose regulation and immune markers, as well as a higher frequency of vasculopathy.

PROSPERO REGISTRATION NUMBER

CRD42022342066.

Defects in intratumoral arginine metabolism attenuate the replication and therapeutic efficacy of oncolytic myxoma virus

BACKGROUND

Arginine (Arg) is a semiessential amino acid whose bioavailability is required for the in vitro replication of several oncolytic viruses. In vivo, Arg bioavailability is regulated by a combination of dietary intake, protein catabolism, and limited biosynthesis through portions of the urea cycle. Interestingly, despite the importance of bioavailable Arg to support cellular proliferation, many forms of cancer are functionally auxotrophic for this amino acid due to the epigenetic silencing of argininosuccinate synthetase 1 (ASS1), an enzyme responsible for the conversion of citrulline and aspartate into the Arg precursor argininosuccinate. The impact of this silencing on oncolytic virotherapy (OV), however, has never been examined.

METHODS

To address this gap in knowledge, we generated tumor cells lacking ASS1 and examined how loss of this enzyme impacted the in vivo replication and therapeutic efficacy of oncolytic myxoma virus (MYXV). We also generated a series of recombinant MYXV constructs expressing exogenous ASS1 to evaluate the therapeutic benefit of virally reconstituting Arg biosynthesis in ASS1^-/- tumors.

RESULTS

Our results show that the in vitro replication of oncolytic MYXV is dependent on the presence of bioavailable Arg. This dependence can be overcome by the addition of the metabolic precursor citrulline, however, this rescue requires expression of ASS1. Because of this, tumors formed from functionally ASS1^-/- cells display significantly reduced MYXV replication as well as poorer therapeutic responses. Critically, both defects could be partially rescued by expressing exogenous ASS1 from recombinant oncolytic MYXVs.

CONCLUSIONS

These results demonstrate that intratumoral defects to Arg metabolism can serve as a novel barrier to virally induced immunotherapy and that the exogenous expression of ASS1 can improve the efficacy of OV in Arg-auxotrophic tumors.

Changes in Gene Expression of Whiteflies, Bemisia tabaci MED Feeding on Tomato Plants Infected by One of the Criniviruses, Tomato Chlorosis Virus through Transcriptome Analysis

Tomato chlorosis virus (ToCV), transmitted by the whitefly, Bemisia tabaci (Gennadius; Hemiptera: Aleyrodidae) has been continuously emerging on tomato plants and causing a significant economic loss throughout China. In the current study, RNA-Seq analysis was used to explore the gene expression profiles of B. tabaci Mediterranean (MED) that fed on both ToCV-infected and -uninfected tomato plants for 6, 12, 24, and 48 hours, respectively. The results revealed that dynamic changes occurred in the gene expressions of whiteflies at different time intervals after they acquired the virus. A total of 1709, 461, 4548, and 1748 differentially expressed genes (DEGs) were identified after a 6, 12, 24, and 48 hours feeding interval for the viral acquisition, respectively. The least number of expressed genes appeared in whiteflies with the 12 hours feeding treatment, and the largest numbers of those found in those with 24 hours feeding treatment. Kyoto Encyclopedia of Genes and Genomes pathway analysis revealed that B. tabaci MED responded to ToCV acquisition through altering its nerve system development, fertility, detoxification, glucose metabolism, and immune function before it lost its ability to transmit the virus. The number of DEGs, degree of differential gene expressions, expression level of the same gene, involved biological processes, and metabolic functions in whiteflies post the 12 hours feeding, and viral acquisition were different from those from other three feeding treatments, which could be a significant finding suggesting an effective control of B. tabaci MED should be done less than 12 hours after whiteflies started feeding on ToCV-infected tomatoes. Our results further provided a clarified understanding in how B. tabaci was protected from viral acquisitions through comparison of the differential profile of gene expressions in whiteflies feeding on plants that were infected by semipersistent viruses.

Contribution of carbohydrate-related metabolism in Herpesvirus infections

Human herpesviruses are enveloped viruses with double-stranded linear DNA genomes highly prevalent in the human population. These viruses are subdivided into three subfamilies, namely alphaherpesvirinae (herpes simplex virus type 1, HSV-1; herpes simplex virus type 2, HSV-2; and varicella-zoster virus, VZV), betaherpesvirinae (human cytomegalovirus, HCMV; human herpesvirus 6, HHV-6; and human herpesvirus 7, HHV-7) and gammaherpesvirinae (Epstein-Barr virus, EBV; and Kaposi's sarcoma-associated herpesvirus, KSHV). Besides encoding numerous molecular determinants to evade the host antiviral responses, these viruses also modulate cellular metabolic processes to promote their replication. Here, we review and discuss existing studies describing an interplay between carbohydrate metabolism and the replication cycle of herpesviruses, altogether highlighting potentially new molecular targets based on these interactions that could be used to block herpesvirus infections.

Targeting the Host Mitochondria as a Novel Human Cytomegalovirus Antiviral Strategy

Human cytomegalovirus (HCMV) exploits host mitochondrial function to promote viral replication. HCMV gene products have been described to directly interact and alter functional or structural aspects of host mitochondria. Current antivirals against HCMV, such as ganciclovir and letermovir, are designed against viral targets. Concerns with the current antivirals include toxicity and viral resistance. Targeting host mitochondrial function is a promising alternative or complimentary antiviral approach as (1) drugs targeting host mitochondrial function interact with host targets, minimizing viral resistance, and (2) host mitochondrial metabolism plays key roles in HCMV replication. This review describes how HCMV alters mitochondrial function and highlights pharmacological targets that can be exploited for novel antiviral development.

Glucose transporter 4: Insulin response mastermind, glycolysis catalyst and treatment direction for cancer progression

The glucose transporter family (GLUT) consists of fourteen members. It is responsible for glucose homeostasis and glucose transport from the extracellular space to the cell cytoplasm to further cascade catalysis. GLUT proteins are encoded by the solute carrier family 2 (SLC2) genes and are members of the major facilitator superfamily of membrane transporters. Moreover, different GLUTs also have their transporter kinetics and distribution, so each GLUT member has its uniqueness and importance to play essential roles in human physiology. Evidence from many studies in the field of diabetes showed that GLUT4 travels between the plasma membrane and intracellular vesicles (GLUT4-storage vesicles, GSVs) and that the PI3K/Akt pathway regulates this activity in an insulin-dependent manner or by the AMPK pathway in response to muscle contraction. Moreover, some published results also pointed out that GLUT4 mediates insulin-dependent glucose uptake. Thus, dysfunction of GLUT4 can induce insulin resistance, metabolic reprogramming in diverse chronic diseases, inflammation, and cancer. In addition to the relationship between GLUT4 and insulin response, recent studies also referred to the potential upstream transcription factors that can bind to the promoter region of GLUT4 to regulating downstream signals. Combined all of the evidence, we conclude that GLUT4 has shown valuable unknown functions and is of clinical significance in cancers, which deserves our in-depth discussion and design compounds by structure basis to achieve therapeutic effects. Thus, we intend to write up a most updated review manuscript to include the most recent and critical research findings elucidating how and why GLUT4 plays an essential role in carcinogenesis, which may have broad interests and impacts on this field.

Innate sensing and cellular metabolism: role in fine tuning antiviral immune responses

Several studies over the last decade have identified intimate links between cellular metabolism and macrophage function. Metabolism has been shown to both drive and regulate macrophage function by producing bioenergetic and biosynthetic precursors as well as metabolites (and other bioactive molecules) that regulate gene expression and signal transduction. Many studies have focused on lipopolysaccharide-induced reprogramming, assuming that it is representative of most inflammatory responses. However, emerging evidence suggests that diverse pathogen-associated molecular patterns (PAMPs) are associated with unique metabolic profiles, which may drive pathogen specific immune responses. Further, these metabolic pathways and processes may act as a rheostat to regulate the magnitude of an inflammatory response based on the biochemical features of the local microenvironment. In this review, we will discuss recent work examining the relationship between cellular metabolism and macrophage responses to viral PAMPs and describe how these processes differ from lipopolysaccharide-associated responses. We will also discuss how an improved understanding of the specificity of these processes may offer new insights to fine-tune macrophage function during viral infections or when using viral PAMPs as therapeutics.

Abnormal glucose metabolism in virus associated sepsis

Sepsis is identified as a potentially lethal organ impairment triggered by an inadequate host reaction to infection (Sepsis-3). Viral sepsis is a potentially deadly organ impairment state caused by the host's inappropriate reaction to a viral infection. However, when a viral infection occurs, the metabolism of the infected cell undergoes a variety of changes that cause the host to respond to the infection. But, until now, little has been known about the challenges faced by cellular metabolic alterations that occur during viral infection and how these changes modulate infection. This study concentrates on the alterations in glucose metabolism during viral sepsis and their impact on viral infection, with a view to exploring new potential therapeutic targets for viral sepsis.

Coxsackievirus B3 infection induces glycolysis to facilitate viral replication

Coxsackievirus B3 (CVB3) is a leading cause of viral myocarditis, but no effective treatment strategy against CVB3 is available. Viruses lack an inherent metabolic system and thus depend on host cellular metabolism for their benefit. In this study, we observed that CVB3 enhanced glycolysis in H9c2 rat cardiomyocytes and HL-1 mouse cardiomyocytes. Therefore, three key glycolytic enzymes, namely, hexokinase 2 (HK2), muscle phosphofructokinase (PFKM), and pyruvate kinase M2 (PKM2), were measured in CVB3-infected H9c2 and HL-1 cells. Expression levels of HK2 and PFKM, but not PKM2, were increased in CVB3-infected H9c2 cells. All three key glycolytic enzymes showed elevated expression in CVB3-infected HL-1 cells. To further investigate this, we used 2 deoxyglucose, sodium citrate, and shikonin as glycolysis inhibitors for HK2, PFKM, and PKM2, respectively. Glycolysis inhibitors significantly reduced CVB3 replication, while the glycolysis enhancer dramatically promoted it. In addition, glycolysis inhibitors decreased autophagy and accelerated autophagosome degradation. The autophagy inducer eliminated partial inhibition effects of glycolysis inhibitors on CVB3 replication. These results demonstrate that CVB3 infection enhances glycolysis and thus benefits viral replication.

Human cytomegalovirus induces neuronal enolase to support virally mediated metabolic remodeling

Viruses depend on cellular metabolic resources to supply the energy and biomolecular building blocks necessary for their replication. Human cytomegalovirus (HCMV), a leading cause of birth defects and morbidity in immunosuppressed individuals, induces numerous metabolic activities that are important for productive infection. However, many of the mechanisms through which these metabolic activities are induced and how they contribute to infection are unclear. We find that HCMV infection of fibroblasts induces a neuronal gene signature as well as the expression of several metabolic enzyme isoforms that are typically expressed in other tissue types. Of these, the most substantially induced glycolytic gene was the neuron-specific isoform of enolase 2 (ENO2). Induction of ENO2 expression is important for HCMV-mediated glycolytic activation as well as for the virally induced remodeling of pyrimidine-sugar metabolism, which provides the glycosyl subunits necessary for protein glycosylation. Inhibition of ENO2 expression or activity reduced uridine diphosphate (UDP)-sugar pools, attenuated the accumulation of viral glycoproteins, and induced the accumulation of noninfectious viral particles. In addition, our data indicate that the induction of ENO2 expression depends on the HCMV U_L38 protein. Collectively, our data indicate that HCMV infection induces a tissue atypical neuronal glycolytic enzyme to activate glycolysis and UDP-sugar metabolism, increase the accumulation of glycosyl building blocks, and enable the expression of an essential viral glycoprotein and the production of infectious virions.

Integrative transcriptome analysis of SARS-CoV-2 human-infected cells combined with deep learning algorithms identifies two potential cellular targets for the treatment of coronavirus disease

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) quickly spread worldwide, leading coronavirus disease 2019 (COVID-19) to hit pandemic level less than 4 months after the first official cases. Hence, the search for drugs and vaccines that could prevent or treat infections by SARS-CoV-2 began, intending to reduce a possible collapse of health systems. After 2 years, efforts to find therapies to treat COVID-19 continue. However, there is still much to be understood about the virus' pathology. Tools such as transcriptomics have been used to understand the impact of SARS-CoV-2 on different cells isolated from various tissues, leaving datasets in the databases that integrate genes and differentially expressed pathways during SARS-CoV-2 infection. After retrieving transcriptome datasets from different human cells infected with SARS-CoV-2 available in the database, we performed an integrative analysis associated with deep learning algorithms to determine differentially expressed targets mainly after infection. The targets found represented a fructose transporter (GLUT5) and a component of proteasome 26s. These targets were then molecularly modeled, followed by molecular docking that identified potential inhibitors for both structures. Once the inhibition of structures that have the expression increased by the virus can represent a strategy for reducing the viral replication by selecting infected cells, associating these bioinformatics tools, therefore, can be helpful in the screening of molecules being tested for new uses, saving financial resources, time, and making a personalized screening for each infectious disease.

Interplay between cellular metabolism and DNA viruses

Viruses as intracellular pathogens take over the host metabolism and reprogram to facilitate optimal virus production. DNA viruses can cause alterations in several metabolic pathways, including aerobic glycolysis also known as the Warburg effect, pentose phosphate pathway activation, and amino acid catabolism such as glutaminolysis, nucleotide biosynthesis, lipid metabolism, and amino acid biosynthesis. The available energy for productive infection can be increased in infected cells via modification of different carbon source utilization. This review discusses the metabolic alterations of the DNA viruses that will be the basis for future novel therapeutic approaches.

The Antiviral Effects of 2-Deoxy-D-glucose (2-DG), a Dual D-Glucose and D-Mannose Mimetic, against SARS-CoV-2 and Other Highly Pathogenic Viruses

Viral infection almost invariably causes metabolic changes in the infected cell and several types of host cells that respond to the infection. Among metabolic changes, the most prominent is the upregulated glycolysis process as the main pathway of glucose utilization. Glycolysis activation is a common mechanism of cell adaptation to several viral infections, including noroviruses, rhinoviruses, influenza virus, Zika virus, cytomegalovirus, coronaviruses and others. Such metabolic changes provide potential targets for therapeutic approaches that could reduce the impact of infection. Glycolysis inhibitors, especially 2-deoxy-D-glucose (2-DG), have been intensively studied as antiviral agents. However, 2-DG's poor pharmacokinetic properties limit its wide clinical application. Herein, we discuss the potential of 2-DG and its novel analogs as potent promising antiviral drugs with special emphasis on targeted intracellular processes.

Metabolic management of microenvironment acidity in glioblastoma

Glioblastoma (GBM), similar to most cancers, is dependent on fermentation metabolism for the synthesis of biomass and energy (ATP) regardless of the cellular or genetic heterogeneity seen within the tumor. The transition from respiration to fermentation arises from the documented defects in the number, the structure, and the function of mitochondria and mitochondrial-associated membranes in GBM tissue. Glucose and glutamine are the major fermentable fuels that drive GBM growth. The major waste products of GBM cell fermentation (lactic acid, glutamic acid, and succinic acid) will acidify the microenvironment and are largely responsible for drug resistance, enhanced invasion, immunosuppression, and metastasis. Besides surgical debulking, therapies used for GBM management (radiation, chemotherapy, and steroids) enhance microenvironment acidification and, although often providing a time-limited disease control, will thus favor tumor recurrence and complications. The simultaneous restriction of glucose and glutamine, while elevating non-fermentable, anti-inflammatory ketone bodies, can help restore the pH balance of the microenvironment while, at the same time, providing a non-toxic therapeutic strategy for killing most of the neoplastic cells.

An overview of possible pivotal mechanisms of Genistein as a potential phytochemical against SARS-CoV-2 infection: A hypothesis

The Coronavirus Disease 2019 (COVID‐19) pandemic has been caused by severe acute respiratory syndrome coronavirus 2 (SARS‐CoV‐2). It is a global problem that humanity has not yet found a definitive solution for it. In this regard, a global effort has been done to find effective or potential adjuvant therapies in order to fight this infection. Genistein is a small, biologically active phytoestrogen flavonoid that is found in high amounts in soy and plants of the Fabaceae family. This important compound is known due to its anti‐cancer, anti‐inflammatory, and antioxidant effects. Additionally, protective effects of genistein have been reported in different pathological conditions through modulating intracellular pathways such as PI3K, Akt, mTOR, NF‐κB, PPARγ, AMPK, and Nrf2. Scientific evidence suggests that genistein could have a potential role to treat COVID‐19 through its anti‐inflammatory and anti‐oxidant effects. Furthermore, it appears to interfere with intracellular pathways involved in viral entry into the cell. This review provides a basis for further research and development of clinical applications of genistein as a potential alternative therapy to decrease inflammation and oxidative stress in COVID‐19 patients.

The Possible Role of Glucose-6-Phosphate Dehydrogenase in the SARS-CoV-2 Infection

Glucose-6-phosphate dehydrogenase (G6PD) is the second rate-limiting enzyme of the pentose phosphate pathway. This enzyme is present in the cytoplasm of all mammalian cells, and its activity is essential for an adequate functioning of the antioxidant system and for the response of innate immunity. It is responsible for the production of nicotinamide adenine dinucleotide phosphate (NADPH), the first redox equivalent, in the pentose phosphate pathway. Viral infections such as SARS-CoV-2 may induce the Warburg effect with an increase in anaerobic glycolysis and production of lactate. This condition ensures the success of viral replication and production of the virion. Therefore, the activity of G6PD may be increased in COVID-19 patients raising the level of the NADPH, which is needed for the enzymatic and non-enzymatic antioxidant systems that counteract the oxidative stress caused by the cytokine storm. G6PD deficiency affects approximately 350–400 million people worldwide; therefore, it is one of the most prevalent diseases related to enzymatic deficiency worldwide. In G6PD-deficient patients exposed to SARS-CoV-2, the amount of NADPH is reduced, increasing the susceptibility for viral infection. There is loss of the redox homeostasis in them, resulting in severe pneumonia and fatal outcomes.

Characterization of phosphofructokinase (PFK) from mud crab Scylla paramamosain and its role in mud crab dicistrovirus-1 proliferation

Phosphofructokinase (PFK), the key enzyme of glycolysis, can catalyze the irreversible transphosphorylation of fructose-6-phosphate forming fructose-1, 6-biphosphate. In the present study, a PFK gene from the mud crab Scylla paramamosain, named SpPFK, was cloned and characterized. The full length of SpPFK contained a 5'untranslated region (UTR) of 249 bp, an open reading frame of 2,859 bp, and a 3'UTR of 1,248 bp. The mRNA of SpPFK was highly expressed in the gill, followed by the hemocytes and muscle. The expression of SpPFK was significantly up-regulated after mud crab dicistrovirus-1 (MCDV-1) infection. Knocking down SpPFK in vivo by RNA interference significantly reduced the expression of lactate dehydrogenase after MCDV-1 infection. Furthermore, silencing of SpPFK in vivo increased the survival rate of mud crabs and decreased the MCDV-1 copies in the gill and hepatopancreas after MCDV-1 infection. All these results suggested that SpPFK could play an important role in the process of MCDV-1 proliferation in mud crab.

IFI16 Impacts Metabolic Reprogramming during Human Cytomegalovirus Infection

Cellular lipid metabolism plays a pivotal role in human cytomegalovirus (HCMV) infection, as increased lipogenesis in HCMV-infected cells favors the envelopment of newly synthesized viral particles. As all cells are equipped with restriction factors (RFs) able to exert a protective effect against invading pathogens, we asked whether a similar defense mechanism would also be in place to preserve the metabolic compartment from HCMV infection. Here, we show that gamma interferon (IFN-γ)-inducible protein 16 (IFI16), an RF able to block HCMV DNA synthesis, can also counteract HCMV-mediated metabolic reprogramming in infected primary human foreskin fibroblasts (HFFs), thereby limiting virion infectivity. Specifically, we find that IFI16 downregulates the transcriptional activation of the glucose transporter 4 (GLUT4) through cooperation with the carbohydrate-response element-binding protein (ChREBP), thereby reducing HCMV-induced transcription of lipogenic enzymes. The resulting decrease in glucose uptake and consumption leads to diminished lipid synthesis, which ultimately curbs the de novo formation of enveloped viral particles in infected HFFs. Consistently, untargeted lipidomic analysis shows enhanced cholesteryl ester levels in IFI16 KO versus wild-type (WT) HFFs. Overall, our data unveil a new role of IFI16 in the regulation of glucose and lipid metabolism upon HCMV replication and uncover new potential targets for the development of novel antiviral therapies.

Hyperglycemia and Loss of Redox Homeostasis in COVID-19 Patients

The infection with SARS-CoV-2 impairs the glucose−insulin axis and this contributes to oxidative (OS) and nitrosative (NSS) stress. Here, we evaluated changes in glucose metabolism that could promote the loss of redox homeostasis in COVID-19 patients. This was comparative cohort and analytical study that compared COVID-19 patients and healthy subjects. The study population consisted of 61 COVID-19 patients with and without comorbidities and 25 healthy subjects (HS). In all subjects the plasma glucose, insulin, 8-isoprostane, Vitamin D, H2S and 3-nitrotyrosine were determined by ELISA. The nitrites (NO2−), lipid-peroxidation (LPO), total-antioxidant-capacity (TAC), thiols, glutathione (GSH) and selenium (Se) were determined by spectrophotometry. The glucose, insulin and HOMA-IR (p < 0.001), 8-isoprostanes, 3-nitrotyrosine (p < 0.001) and LPO were increased (p = 0.02) while Vitamin D (p = 0.01), H2S, thiols, TAC, GSH and Se (p < 0.001) decreased in COVID-19 patients in comparison to HS. The SARS-CoV-2 infection resulted in alterations in the glucose−insulin axis that led to hyperglycemia, hyperinsulinemia and IR in patients with and without comorbidities. These alterations increase OS and NSS reflected in increases or decreases in some oxidative markers in plasma with major impact or fatal consequences in patients that course with metabolic syndrome. Moreover, subjects without comorbidities could have long-term alterations in the redox homeostasis after infection.

Virus-host protein interactions as footprints of human cytomegalovirus replication

Human cytomegalovirus (HCMV) is a pervasive β-herpesvirus that causes lifelong infection. The lytic replication cycle of HCMV is characterized by global organelle remodeling and dynamic virus-host interactions, both of which are necessary for productive HCMV replication. With the advent of new technologies for investigating protein-protein and protein-nucleic acid interactions, numerous critical interfaces between HCMV and host cells have been identified. Here, we review temporal and spatial virus-host interactions that support different stages of the HCMV replication cycle. Understanding how HCMV interacts with host cells during entry, replication, and assembly, as well as how it interfaces with host cell metabolism and immune responses promises to illuminate processes that underlie the biology of infection and the resulting pathologies.

Metabolomic Profiling Reveals New Insight of Fowl Adenovirus Serotype 4 Infection

Highly pathogenic fowl adenovirus serotype 4 (FAdV-4) is the causative agent of hydropericardium syndrome (HPS), which is characterized by pericardial effusion and hepatitis, and is one of the foremost causes of economic losses to the poultry industry over the last 30 years. However, the metabolic changes in cells in response to FAdV-4 infection remain unclear. In order to understand the metabolic interactions between the host cell and virus, we utilized ultra-high-performance liquid chromatography/quadrupole time-of-flight tandem mass spectrometry to analyze the metabolic profiles with hepatocellular carcinoma cell line (LMH) infected with FAdV-4. The results showed that FAdV-4 could restore metabolic networks in LMH cells and tricarboxylic acid cycle, glycolysis, and metabolism of purines, pyrimidines, alanine, aspartate, glutamate, and amino sugar and nucleotide sugar moieties. Moreover, FAdV-4 production was significantly reduced in LMH cells cultured in glucose or glutamine-deficient medium. These observations highlighted the importance of host cell metabolism in virus replication. Therefore, similarities and disparities in FAdV-4-regulation of the metabolism of host cells could help improve targeted drug and reduce infection.

Metabolic Reprogramming of Glioblastoma Cells during HCMV Infection Induces Secretome-Mediated Paracrine Effects in the Microenvironment

Glioblastoma (GBM) is an aggressive primary central nervous system neoplasia with limited therapeutic options and poor prognosis. Following reports of cytomegalovirus (HCMV) in GBM tumors, the anti-viral drug Valganciclovir was administered and found to significantly increase the longevity of GBM patients. While these findings suggest a role for HCMV in GBM, the relationship between them is not clear and remains controversial. Treatment with anti-viral drugs may prove clinically useful; however, their results do not explain the underlying mechanism between HCMV infection and GBM progression. We hypothesized that HCMV infection would metabolically reprogram GBM cells and that these changes would allow for increased tumor progression. We infected LN-18 GBM cells and employed a Seahorse Bioanalyzer to characterize cellular metabolism. Increased mitochondrial respiration and glycolytic rates were observed following infection. These changes were accompanied by elevated production of reactive oxygen species and lactate. Due to lactate’s numerous tumor-promoting effects, we examined the impact of paracrine signaling of HCMV-infected GBM cells on uninfected stromal cells. Our results indicated that, independent of viral transmission, the secretome of HCMV-infected GBM cells was able to alter the expression of key metabolic proteins and epigenetic markers. This suggests a mechanism of action where reprogramming of GBM cells alters the surrounding tumor microenvironment to be permissive to tumor progression in a manner akin to the Reverse-Warburg Effect. Overall, this suggests a potential oncomodulatory role for HCMV in the context of GBM.

Adaptive homeostasis and the p53 isoform network

All living organisms have developed processes to sense and address environmental changes to maintain a stable internal state (homeostasis). When activated, the p53 tumour suppressor maintains cell and organ integrity and functions in response to homeostasis disruptors (stresses) such as infection, metabolic alterations and cellular damage. Thus, p53 plays a fundamental physiological role in maintaining organismal homeostasis. The TP53 gene encodes a network of proteins (p53 isoforms) with similar and distinct biochemical functions. The p53 network carries out multiple biological activities enabling cooperation between individual cells required for long‐term survival of multicellular organisms (animals) in response to an ever‐changing environment caused by mutation, infection, metabolic alteration or damage. In this review, we suggest that the p53 network has evolved as an adaptive response to pathogen infections and other environmental selection pressures.

Inhibiting cytomegalovirus replication through targeting the host electron transport chain

Human cytomegalovirus (HCMV) is a near ubiquitous herpesvirus that relies on host cell metabolism for efficient replication. Although it has been shown that HCMV requires functional host cell mitochondria for efficient replication, it is unknown whether mitochondrial targeted pharmacological agents can be repurposed as antivirals. Here we report that treatment with drugs targeting the electron transport chain (ETC) complexes inhibit HCMV replication. Addition of rotenone, oligomycin, antimycin and metformin resulted in decreased HCMV titers in vitro, independent of HCMV strain. This further illustrates the dependence of HCMV replication on functional mitochondria. Metformin, an FDA approved drug, delays HCMV replication kinetics resulting in a reduction of viral titers. Repurposing metformin as an antiviral is advantageous as its safety profile and epidemiological data are well accepted. Our findings provide new insight into the potential for targeting HCMV infection through host cell metabolism and how these pharmacological interventions function.

The human cytomegalovirus protein pUL13 targets mitochondrial cristae architecture to increase cellular respiration during infection

Viruses modulate mitochondrial processes during infection to increase biosynthetic precursors and energy output, fueling virus replication. In a surprising fashion, although it triggers mitochondrial fragmentation, the prevalent pathogen human cytomegalovirus (HCMV) increases mitochondrial metabolism through a yet-unknown mechanism. Here, we integrate molecular virology, metabolic assays, quantitative proteomics, and superresolution confocal microscopy to define this mechanism. We establish that the previously uncharacterized viral protein pUL13 is required for productive HCMV replication, targets the mitochondria, and functions to increase oxidative phosphorylation during infection. We demonstrate that pUL13 forms temporally tuned interactions with the mitochondrial contact site and cristae organizing system (MICOS) complex, a critical regulator of cristae architecture and electron transport chain (ETC) function. Stimulated emission depletion superresolution microscopy shows that expression of pUL13 alters cristae architecture. Indeed, using live-cell Seahorse assays, we establish that pUL13 alone is sufficient to increase cellular respiration, not requiring the presence of other viral proteins. Our findings address the outstanding question of how HCMV targets mitochondria to increase bioenergetic output and expands the knowledge of the intricate connection between mitochondrial architecture and ETC function.

Blood glucose regulation in context of infection

The immune and endocrine systems collectively control homeostasis in the body. The endocrine system ensures that values of essential factors and nutrients such as glucose, electrolytes and vitamins are maintained within threshold values. The immune system resolves local disruptions in tissue homeostasis, caused by pathogens or malfunctioning cells. The immediate goals of these two systems do not always align. The immune system benefits from optimal access to nutrients for itself and restriction of nutrient availability to all other organs to limit pathogen replication. The endocrine system aims to ensure optimal nutrient access for all organs, limited only by the nutrients stores that the body has available. The actual state of homeostatic parameters such as blood glucose levels represents a careful balance based on regulatory signals from the immune and endocrine systems. This state is not static but continuously adjusted in response to changes in the current metabolic needs of the body, the amount of resources it has available and the level of threats it encounters. This balance is maintained by the ability of the immune and endocrine systems to interact and co-regulate systemic metabolism. In context of metabolic disease, this system is disrupted, which impairs functionality of both systems. The failure of the endocrine system to retain levels of nutrients such as glucose within threshold values impairs functionality of the immune system. In addition, metabolic stress of organs in context of obesity is perceived by the immune system as a disruption in local homeostasis, which it tries to resolve by the excretion of factors which further disrupt normal metabolic control. In this chapter, we will discuss how the immune and endocrine systems interact under homeostatic conditions and during infection with a focus on blood glucose regulation. In addition, we will discuss how this system fails in the context of metabolic disease.

The antiviral sirtuin 3 bridges protein acetylation to mitochondrial integrity and metabolism during human cytomegalovirus infection

Regulation of mitochondrial structure and function is a central component of infection with viruses, including human cytomegalovirus (HCMV), as a virus means to modulate cellular metabolism and immune responses. Here, we link the activity of the mitochondrial deacetylase SIRT3 and global mitochondrial acetylation status to host antiviral responses via regulation of both mitochondrial structural integrity and metabolism during HCMV infection. We establish that SIRT3 deacetylase activity is necessary for suppressing virus production, and that SIRT3 maintains mitochondrial pH and membrane potential during infection. By defining the temporal dynamics of SIRT3-substrate interactions during infection, and overlaying acetylome and proteome information, we find altered SIRT3 associations with the mitochondrial fusion factor OPA1 and acetyl-CoA acyltransferase 2 (ACAA2), concomitant with changes in their acetylation levels. Using mutagenesis, microscopy, and virology assays, we determine OPA1 regulates mitochondrial morphology of infected cells and inhibits HCMV production. OPA1 acetylation status modulates these functions, and we establish K834 as a site regulated by SIRT3. Control of SIRT3 protein levels or enzymatic activity is sufficient for regulating mitochondrial filamentous structure. Lastly, we establish a virus restriction function for ACAA2, an enzyme involved in fatty acid beta-oxidation. Altogether, we highlight SIRT3 activity as a regulatory hub for mitochondrial acetylation and morphology during HCMV infection and point to global acetylation as a reflection of mitochondrial health.

Given their functions in cellular metabolism and immune responses, mitochondria are targeted and disrupted by numerous prevalent viral pathogens, including human cytomegalovirus (HCMV). To characterize mechanisms underlying mitochondrial regulation during HCMV infection in human fibroblasts, this study integrates enzyme-substrate interaction studies, mass spectrometry quantification of protein abundance and acetylation, mutagenesis, microscopy, and virology assays. These analyses establish a link between the mitochondrial acetylation status and mitochondrial structure and metabolism during HCMV infection. We demonstrate that the mitochondrial deacetylase SIRT3 acts in host defense by modulating proteins that regulate mitochondrial structure and fatty acid oxidation. SIRT3 helps to maintain mitochondrial integrity through several mechanisms, including regulation of mitochondrial pH, membrane potential, and the balance between mitochondrial fission and fusion. As excess mitochondrial acetylation is detrimental to mitochondrial metabolism, the virus-induced alterations in SIRT3 functions and mitochondrial acetylation may be linked to known HCMV pathologies, such as the metabolic syndrome and cardiac hypertrophy.

Human Cytomegalovirus Induces the Expression of the AMPKa2 Subunit to Drive Glycolytic Activation and Support Productive Viral Infection

Human Cytomegalovirus (HCMV) infection modulates cellular metabolism to support viral replication. Calcium/calmodulin-dependent kinase kinase (CaMKK) and AMP-activated protein kinase (AMPK) regulate metabolic activation and have been found to be important for successful HCMV infection. Here, we explored the contributions that specific CaMKK isoforms and AMPK subunit isoforms make toward HCMV infection. Our results indicate that various CaMKK and AMPK isoforms contribute to infection in unique ways. For example, CaMKK1 is important for HCMV infection at a low multiplicity of infection, but is dispensable for AMPK activation at the earliest times of infection, which our data suggest is more reliant on CaMKK2. Our results also indicate that HCMV specifically induces the expression of the non-ubiquitous AMPKa2 catalytic subunit, found to be important for both HCMV-mediated glycolytic activation and high titer infection. Further, we find that AMPK-mediated glycolytic activation is important for infection, as overexpression of GLUT4, the high capacity glucose transporter, partially rescues viral replication in the face of AMPK inhibition. Collectively, our data indicate that HCMV infection selectively induces the expression of specific metabolic regulatory kinases, relying on their activity to support glycolytic activation and productive infection.IMPORTANCE Viruses are obligate parasites that depend on the host cell to provide the energy and molecular building blocks to mass produce infectious viral progeny. The processes that govern viral modulation of cellular resources have emerged as critical for successful infection. Here, we find that HCMV depends on two kinase isoforms to support infection, CaMKK1 and AMPKa2. We find that HCMV specifically induces expression of the AMPKa2 subunit to induce metabolic activation and drive robust viral replication. These results suggest that HCMV has evolved mechanisms to target specific metabolic regulatory kinase subunits to support productive infection, thereby providing insight into how HCMV hijacks cellular metabolism for its replication, and sheds light on potential viral therapeutic vulnerabilities.

Type 2 diabetes and viral infection; cause and effect of disease

The recent pandemic of COVID-19 has made abundantly clear that Type 2 diabetes (T2D) increases the risk of more frequent and more severe viral infections. At the same time, pro-inflammatory cytokines of an anti-viral Type-I profile promote insulin resistance and form a risk factor for development of T2D. What this illustrates is that there is a reciprocal, detrimental interaction between the immune and endocrine system in the context of T2D. Why these two systems would interact at all long remained unclear. Recent findings indicate that transient changes in systemic metabolism are induced by the immune system as a strategy against viral infection. In people with T2D, this system fails, thereby negatively impacting the antiviral immune response. In addition, immune-mediated changes in systemic metabolism upon infection may aggravate glycemic control in T2D. In this review, we will discuss recent literature that sheds more light on how T2D impairs immune responses to viral infection and how virus-induced activation of the immune system increases risk of development of T2D.

Nitric Oxide Circumvents Virus-Mediated Metabolic Regulation during Human Cytomegalovirus Infection

Nitric oxide is a versatile and critical effector molecule that can modulate many cellular functions. Although recognized as a regulator of infections, the inhibitory mechanism of nitric oxide against human cytomegalovirus (HCMV) replication remains elusive. We demonstrate that nitric oxide attenuates viral replication by interfering with HCMV-mediated modulation of several cellular processes. Nitric oxide exposure reduced HCMV genome synthesis and infectious viral progeny with cell-type-dependent differences observed. Mitochondrial respiration was severely reduced in both uninfected and HCMV-infected cells during exposure with little impact on ATP levels indicating changes in cellular metabolism. Metabolomics identified significantly altered small molecules in multiple pathways during nitric oxide exposure including nucleotide biosynthesis, tricarboxylic acid (TCA) cycle, and glutamine metabolism. Glutathione metabolites were increased coinciding with a reduction in the glutathione precursor glutamine. This shift was accompanied by increased antioxidant enzymes. Glutamine deprivation mimicked defects in HCMV replication and mitochondrial respiration observed during nitric oxide exposure. These data suggest that nitric oxide limits glutaminolysis by shuttling glutamine to glutathione synthesis. In addition, lipid intermediates were severely altered, which likely contributes to the observed increase in defective viral particles. Nitric oxide disrupts multiple cellular processes, and we had limited success in rescuing replication defects by supplementing with metabolic intermediates. Our studies indicate that nitric oxide attenuation of HCMV is multifactorial with interference in viral manipulation of cellular metabolism playing a central role.IMPORTANCE Human cytomegalovirus is a prevalent pathogen that can cause serious disease in patients with compromised immune systems, including transplant patients and during congenital infection. HCMV lytic replication likely occurs in localized sites of infection with immune cells infiltrating and releasing nitric oxide with other effector molecules. This nonspecific immune response results in both uninfected and infected cells exposed to high levels of nitric oxide. The absence of nitric oxide synthase has been associated with lethal HCMV infection. We demonstrate that nitric oxide inhibition of HCMV replication is multifactorial and cell type dependent. Our results indicate that nitric oxide controls replication by interfering with viral modulation of cellular metabolism while also affecting proliferation and mitochondrial respiration of neighboring uninfected cells. These studies identify the mechanism and contribution of nitric oxide during immune control of HCMV infection and provide insight into its role in other viral infections.

The Crosstalk of Epigenetics and Metabolism in Herpesvirus Infection

Epigenetics is a versatile player in manipulating viral infection and a potential therapeutic target for the treatment of viral-induced diseases. Both epigenetics and metabolism are crucial in establishing a highly specific transcriptional network, which may promote or suppress virus infection. Human herpesvirus infection can induce a broad range of human malignancies and is largely dependent on the status of cellular epigenetics as well as its related metabolism. However, the crosstalk between epigenetics and metabolism during herpesvirus infection has not been fully explored. Here, we describe how epigenetic regulation of cellular metabolism affects herpesvirus infection and induces viral diseases. This further highlights the importance of epigenetics and metabolism during viral infection and provides novel insights into the development of targeted therapies.

The key role of Warburg effect in SARS-CoV-2 replication and associated inflammatory response

Current mortality due to the Covid-19 pandemic (approximately 1.2 million by November 2020) demonstrates the lack of an effective treatment. As replication of many viruses - including MERS-CoV - is supported by enhanced aerobic glycolysis, we hypothesized that SARS-CoV-2 replication in host cells (especially airway cells) is reliant upon altered glucose metabolism. This metabolism is similar to the Warburg effect well studied in cancer. Counteracting two main pathways (PI3K/AKT and MAPK/ERK signaling) sustaining aerobic glycolysis inhibits MERS-CoV replication and thus, very likely that of SARS-CoV-2, which shares many similarities with MERS-CoV. The Warburg effect appears to be involved in several steps of COVID-19 infection. Once induced by hypoxia, the Warburg effect becomes active in lung endothelial cells, particularly in the presence of atherosclerosis, thereby promoting vasoconstriction and micro thrombosis. Aerobic glycolysis also supports activation of pro-inflammatory cells such as neutrophils and M1 macrophages. As the anti-inflammatory response and reparative process is performed by M2 macrophages reliant on oxidative metabolism, we speculated that the switch to oxidative metabolism in M2 macrophages would not occur at the appropriate time due to an uncontrolled pro-inflammatory cascade. Aging, mitochondrial senescence and enzyme dysfunction, AMPK downregulation and p53 inactivation could all play a role in this key biochemical event. Understanding the role of the Warburg effect in COVID-19 can be essential to developing molecules reducing infectivity, arresting endothelial cells activation and the pro-inflammatory cascade.

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Enhanced aerobic glycolysis supports replication of many viruses including MERS-CoV.

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PI3K/AKT and MAPK/ERK inhibitors arrest MERS-CoV replication.

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This metabolism likely sustains SARS-CoV-2 replication in host cells, in particular airway cells .

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The Warburg effect also supports activation of endothelial cells and pro-inflammatory cells .

The constitutive activity of the viral-encoded G protein-coupled receptor US28 supports a complex signalling network contributing to cancer development

US28 is a viral G protein-coupled receptor (GPCR) encoded by the human cytomegalovirus (HCMV). This receptor, expressed both during lytic replication and viral latency, is required for latency. US28 is binding to a wide variety of chemokines but also exhibits a particularly high constitutive activity robustly modulating a wide network of cellular pathways altering the host cell environment to benefit HCMV infection. Several studies suggest that US28-mediated signalling may contribute to cancer progression. In this review, we discuss the unique structural characteristics that US28 acquired through evolution that confer a robust constitutive activity to this viral receptor. We also describe the wide downstream signalling network activated by this constitutive activation of US28 and discuss how these signalling pathways may promote and support important cellular aspects of cancer.

Another Consequence of the Warburg Effect? Metabolic Regulation of Na+/H+ Exchangers May Link Aerobic Glycolysis to Cell Growth

To adjust cell growth and proliferation to changing environmental conditions or developmental requirements, cells have evolved a remarkable network of signaling cascades that integrates cues from cellular metabolism, growth factor availability and a large variety of stresses. In these networks, cellular information flow is mostly mediated by posttranslational modifications, most notably phosphorylation, or signaling molecules such as GTPases. Yet, a large body of evidence also implicates cytosolic pH (pHc) as a highly conserved cellular signal driving cell growth and proliferation, suggesting that pH-dependent protonation of specific proteins also regulates cellular signaling. In mammalian cells, pHc is regulated by growth factor derived signals and responds to metabolic cues in response to glucose stimulation. Importantly, high pHc has also been identified as a hall mark of cancer, but mechanisms of pH regulation in cancer are only poorly understood. Here, we discuss potential mechanisms of pH regulation with emphasis on metabolic signals regulating pHc by Na⁺/H⁺-exchangers. We hypothesize that elevated NHE activity and pHc in cancer are a direct consequence of the metabolic adaptations in tumor cells including enhanced aerobic glycolysis, generally referred to as the Warburg effect. This hypothesis not only provides an explanation for the growth advantage conferred by a switch to aerobic glycolysis beyond providing precursors for accumulation of biomass, but also suggests that treatments targeting pH regulation as a potential anti-cancer therapy may effectively target the result of altered tumor cell metabolism.

Interplay Between Calcium and AMPK Signaling in Human Cytomegalovirus Infection

Calcium signaling and the AMP-activated protein kinase (AMPK) signaling networks broadly regulate numerous aspects of cell biology. Human Cytomegalovirus (HCMV) infection has been found to actively manipulate the calcium-AMPK signaling axis to support infection. Many HCMV genes have been linked to modulating calcium signaling, and HCMV infection has been found to be reliant on calcium signaling and AMPK activation. Here, we focus on the cell biology of calcium and AMPK signaling and what is currently known about how HCMV modulates these pathways to support HCMV infection and potentially contribute to oncomodulation.

Human herpesvirus 6A promotes glycolysis in infected T cells by activation of mTOR signaling

Human herpesvirus 6 (HHV-6) is an important immunosuppressive and immunomodulatory virus worldwide. However, whether and how HHV-6 infection influences the metabolic machinery of the host cell to provide the energy and biosynthetic resources for virus propagation remains unknown. In this study, we identified that HHV-6A infection promotes glucose metabolism in infected T cells, resulting in elevated glycolytic activity with an increase of glucose uptake, glucose consumption and lactate secretion. Furthermore, we explored the mechanisms involved in HHV-6A-mediated glycolytic activation in the infected T cells. We found increased expressions of the key glucose transporters and glycolytic enzymes in HHV-6A-infected T cells. In addition, HHV-6A infection dramatically activated AKT-mTORC1 signaling in the infected T cells and pharmacological inhibition of mTORC1 blocked HHV-6A-mediated glycolytic activation. We also found that direct inhibition of glycolysis by 2-Deoxy-D-glucose (2-DG) or inhibition of mTORC1 activity in HHV-6A-infected T cells effectively reduced HHV-6 DNA replication, protein synthesis and virion production. These results not only reveal the mechanism of how HHV-6 infection affects host cell metabolism, but also suggest that targeting the metabolic pathway could be a new avenue for HHV-6 therapy.

The interferon-inducible protein TDRD7 inhibits AMP-activated protein kinase and thereby restricts autophagy-independent virus replication

The interferon system is the first line of defense against virus infection. Recently, using a high-throughput genetic screen of a human interferon-stimulated gene short-hairpin RNA library, we identified a viral restriction factor, TDRD7 (Tudor domain-containing 7). TDRD7 inhibits the paramyxo-/pneumoviruses (e.g. Sendai virus and respiratory syncytial virus) by interfering with the virus-induced cellular autophagy pathway, which these viruses use for their replication. Here, we report that TDRD7 is a viral restriction factor against herpes simplex virus (HSV-1). Using knockdown, knockout, and ectopic expression systems, we demonstrate the anti-HSV-1 activity of TDRD7 in multiple human and mouse cell types. TDRD7 inhibited the virus-activated AMP-activated protein kinase (AMPK), which was essential for HSV-1 replication. Genetic ablation or chemical inhibition of AMPK activity suppressed HSV-1 replication in multiple human and mouse cells. Mechanistically, HSV-1 replication after viral entry depended on AMPK but not on its function in autophagy. The antiviral activity of TDRD7 depended on its ability to inhibit virus-activated AMPK. In summary, our results indicate that the newly identified viral restriction factor TDRD7 inhibits AMPK and thereby blocks HSV-1 replication independently of the autophagy pathway. These findings suggest that AMPK inhibition represents a potential strategy to manage HSV-1 infections.

Targeted Metabolic Reprogramming to Improve the Efficacy of Oncolytic Virus Therapy

Oncolytic viruses (OVs) represent a promising new class of cancer therapeutics and cause antitumor effects by two major mechanisms: (1) directly killing cancer cells in a process known as oncolysis, or (2) initiating a powerful antitumor immune response. Interestingly, energy metabolism, within either cancer cells or immune cells, plays a pivotal role in defining the outcome of OV-mediated antitumor effects. Following therapeutic administration, OVs must hijack host cell metabolic pathways to acquire building blocks such as nucleotides, lipids, and amino acids for the process of replication that is necessary for oncolysis. Additionally, OV-stimulated antitumor immune responses are highly dependent on the metabolic state within the tumor microenvironment. Thus, metabolic reprogramming strategies bear the potential to enhance the efficacy of both OV-mediated oncolysis and antitumor immune responses.

Metabolic Reprogramming of Host Cells in Response to Enteroviral Infection

Enterovirus 71 (EV71) infection is an endemic disease in Southeast Asia and China. We have previously shown that EV71 virus causes functional changes in mitochondria. It is speculative whether EV71 virus alters the host cell metabolism to its own benefit. Using a metabolomics approach, we demonstrate that EV71-infected Vero cells had significant changes in metabolism. Glutathione and its related metabolites, and several amino acids, such as glutamate and aspartate, changed significantly with the infectious dose of virus. Other pathways, including glycolysis and tricarboxylic acid cycle, were also altered. A change in glutamine/glutamate metabolism is critical to the viral infection. The presence of glutamine in culture medium was associated with an increase in viral replication. Dimethyl α-ketoglutarate treatment partially mimicked the effect of glutamine supplementation. In addition, the immunoblot analysis revealed that the expression of glutamate dehydrogenase (GDH) and trifunctional carbamoyl-phosphate synthetase 2, aspartate transcarbamylase, and dihydroorotase (CAD) increased during infection. Knockdown of expression of glutaminase (GLS), GDH and CAD drastically reduced the cytopathic effect (CPE) and viral replication. Furthermore, we found that CAD bound VP1 to promote the de novo pyrimidine synthesis. Our findings suggest that virus may induce metabolic reprogramming of host cells to promote its replication through interactions between viral and host cell proteins.

Human Cytomegalovirus Alters Host Cell Mitochondrial Function during Acute Infection

Human cytomegalovirus (HCMV) is a large DNA herpesvirus that is highly prevalent in the human population. HCMV can result in severe direct and indirect pathologies under immunosuppressed conditions and is the leading cause of birth defects related to infectious disease. Currently, the effect of HCMV infection on host cell metabolism as an increase in glycolysis during infection has been defined. We have observed that oxidative phosphorylation is also increased. We have identified morphological and functional changes to host mitochondria during HCMV infection. The mitochondrial network undergoes fission events after HCMV infection. Interestingly, the network does not undergo fusion. At the same time, mitochondrial mass and membrane potential increase. The electron transport chain (ETC) functions at an elevated rate, resulting in the release of increased reactive oxygen species. Surprisingly, despite the stress applied to the host mitochondria, the network is capable of responding to and meeting the increased bioenergetic and biosynthetic demands placed on it. When mitochondrial DNA is depleted from the cells, we observed severe impairment of viral replication. Mitochondrial DNA encodes many of the ETC components. These findings suggest that the host cell ETC is essential to HCMV replication. Our studies suggest the host cell mitochondria may be a therapeutic target.IMPORTANCE Human cytomegalovirus (HCMV) is a herpesvirus present in up to 85% of some populations. Like all herpesviruses, HCMV infection is for life. No vaccine is currently available, neutralizing antibody therapies are ineffective, and current antivirals have limited long-term efficacy due to side effects and potential for viral mutation and resistance. The significance of this research is in understanding how HCMV manipulates the host mitochondria to support bioenergetic and biosynthetic requirements for replication. Despite a large genome, HCMV relies exclusively on host cells for metabolic functions. By understanding the dependency of HCMV on the mitochondria, we could exploit these requirements and develop novel antivirals.