Role of Phosphatidylethanolamine Biosynthesis in Herpes Simplex Virus 1-Infected Cells in Progeny Virus Morphogenesis in the Cytoplasm and in Viral Pathogenicity In Vivo

Mitochondrial bioenergetics stimulates autophagy for pathological MAPT/Tau clearance in tauopathy neurons

Hyperphosphorylation and aggregation of MAPT (microtubule-associated protein tau) is a pathogenic hallmark of tauopathies and a defining feature of Alzheimer disease (AD). Pathological MAPT/tau is targeted by macroautophagy/autophagy for clearance after being sequestered within autophagosomes, but autophagy dysfunction is indicated in tauopathy. While mitochondrial bioenergetic deficits have been shown to precede MAPT/tau pathology in tauopathy brains, it is unclear whether energy metabolism deficiency is involved in the pathogenesis of autophagy defects. Here, we reveal that stimulation of anaplerotic metabolism restores defective oxidative phosphorylation (OXPHOS) in tauopathy neurons which, strikingly, leads to pronounced MAPT/tau clearance by boosting autophagy functionality through enhancements of mitochondrial biosynthesis and supply of phosphatidylethanolamine for autophagosome biogenesis. Furthermore, early anaplerotic stimulation of OXPHOS elevates autophagy activity and attenuates MAPT/tau pathology, thereby counteracting memory impairment in tauopathy mice. Taken together, our study sheds light on a pivotal role of mitochondrial bioenergetic deficiency in tauopathy-related autophagy defects and suggests a new therapeutic strategy to prevent the buildup of pathological MAPT/tau in AD and other tauopathy diseases.Abbreviation: AA: antimycin A; AD, Alzheimer disease; ATP, adenosine triphosphate; AV, autophagosome/autophagic vacuole; AZ, active zone; Baf-A1: bafilomycin A1; CHX, cycloheximide; COX, cytochrome c oxidase; DIV, days in vitro; DRG, dorsal root ganglion; ETN, ethanolamine; FRET, Förster/fluorescence resonance energy transfer; FTD, frontotemporal dementia; Gln, glutamine; HA: hydroxylamine; HsMAPT/Tau, human MAPT; IMM, inner mitochondrial membrane; LAMP1, lysosomal-associated membrane protein 1; LIs, lysosomal inhibitors; MDAV, mitochondria-derived autophagic vacuole; MmMAPT/Tau, murine MAPT; NFT, neurofibrillary tangle; OCR, oxygen consumption rate; Omy: oligomycin; OXPHOS, oxidative phosphorylation; PPARGC1A/PGC-1alpha: peroxisome proliferative activated receptor, gamma, coactivator 1 alpha; PE, phosphatidylethanolamine; phospho-MAPT/tau, hyperphosphorylated MAPT; PS, phosphatidylserine; PISD, phosphatidylserine decarboxylase;SQSTM1/p62, sequestosome 1; STX1, syntaxin 1; SYP, synaptophysin; Tg, transgenic; TCA, tricarboxylic acid; TEM, transmission electron microscopy.

Alphaherpesvirus manipulates retinoic acid metabolism for optimal replication

Retinoic acid (RA), derived from retinol (ROL), is integral to cell growth, differentiation, and organogenesis. It is known that RA can inhibit herpes simplex virus (HSV) replication, but the interactions between alphaherpesviruses and RA metabolism are unclear. Our present study revealed that alphaherpesvirus (HSV-1 and Pseudorabies virus, PRV) infections suppressed RA synthesis from ROL by activating P53, which increased retinol reductase 3 (DHRS3) expression-an enzyme that converts retinaldehyde back to ROL. This process depended on the virus-triggered DNA damage response, the degradation of class I histone deacetylases, and the subsequent hyperacetylation of histones H3 and H4. Counteracting DHRS3 or P53 enabled higher RA synthesis and reduced viral growth. RA enhanced antiviral defenses by promoting ABCA1- and ABCG1-mediated lipid efflux. Treatment with the retinoic acid receptor (RAR) agonist palovarotene protected mice from HSV-1 infection, thus providing a potential therapeutic strategy against viral infections.

Mitochondrial bioenergetics stimulates autophagy for pathological tau clearance in tauopathy neurons

Hyperphosphorylation and aggregation of microtubule-associated tau is a pathogenic hallmark of tauopathies and a defining feature of Alzheimer's disease (AD). Pathological tau is targeted by autophagy for clearance, but autophagy dysfunction is indicated in tauopathy. While mitochondrial bioenergetic failure has been shown to precede the development of tau pathology, it is unclear whether energy metabolism deficiency is involved in tauopathy-related autophagy defects. Here, we reveal that stimulation of anaplerotic metabolism restores defective oxidative phosphorylation (OXPHOS) in tauopathy which, strikingly, leads to enhanced autophagy and pronounced tau clearance. OXPHOS-induced autophagy is attributed to increased ATP-dependent phosphatidylethanolamine biosynthesis in mitochondria. Excitingly, early bioenergetic stimulation boosts autophagy activity and reduces tau pathology, thereby counteracting memory impairment in tauopathy mice. Taken together, our study sheds light on a pivotal role of bioenergetic dysfunction in tauopathy-linked autophagy defects and suggests a new therapeutic strategy to prevent toxic tau buildup in AD and other tauopathies.

Lipid alternations in the plasma of COVID-19 patients with various clinical presentations

Background

COVID-19 is a highly infectious respiratory disease that can manifest in various clinical presentations. Although many studies have reported the lipidomic signature of COVID-19, the molecular changes in asymptomatic severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2)-infected individuals remain elusive.

Methods

This study combined a comprehensive lipidomic analysis of 220 plasma samples from 166 subjects: 62 healthy controls, 16 asymptomatic infections, and 88 COVID-19 patients. We quantified 732 lipids separately in this cohort. We performed a difference analysis, validated with machine learning models, and also performed GO and KEGG pathway enrichment analysis using differential lipids from different control groups.

Results

We found 175 differentially expressed lipids associated with SASR-CoV-2 infection, disease severity, and viral persistence in patients with COVID-19. PC (O-20:1/20:1), PC (O-20:1/20:0), and PC (O-18:0/18:1) better distinguished asymptomatic infected individuals from normal individuals. Furthermore, some patients tested positive for SARS-CoV-2 nucleic acid by RT-PCR but did not become negative for a longer period of time (≥60 days, designated here as long-term nucleic acid test positive, LTNP), whereas other patients became negative for viral nucleic acid in a shorter period of time (≤45 days, designated as short-term nucleic acid test positive, STNP). We have found that TG (14:1/14:1/18:2) and FFA (4:0) were differentially expressed in LTNP and STNP.

Conclusion

In summary, the integration of lipid information can help us discover novel biomarkers to identify asymptomatic individuals and further deepen our understanding of the molecular pathogenesis of COVID-19.

Rewiring of the Host Cell Metabolome and Lipidome during Lytic Gammaherpesvirus Infection Is Essential for Infectious-Virus Production

Oncogenic virus infections are estimated to cause ~15% of all cancers. Two prevalent human oncogenic viruses are members of the gammaherpesvirus family: Epstein-Barr virus (EBV) and Kaposi's sarcoma herpesvirus (KSHV). We use murine herpesvirus 68 (MHV-68), which shares significant homology with KSHV and EBV, as a model system to study gammaherpesvirus lytic replication. Viruses implement distinct metabolic programs to support their life cycle, such as increasing the supply of lipids, amino acids, and nucleotide materials necessary to replicate. Our data define the global changes in the host cell metabolome and lipidome during gammaherpesvirus lytic replication. Our metabolomics analysis found that MHV-68 lytic infection induces glycolysis, glutaminolysis, lipid metabolism, and nucleotide metabolism. We additionally observed an increase in glutamine consumption and glutamine dehydrogenase protein expression. While both glucose and glutamine starvation of host cells decreased viral titers, glutamine starvation led to a greater loss in virion production. Our lipidomics analysis revealed a peak in triacylglycerides early during infection and an increase in free fatty acids and diacylglyceride later in the viral life cycle. Furthermore, we observed an increase in the protein expression of multiple lipogenic enzymes during infection. Interestingly, pharmacological inhibitors of glycolysis or lipogenesis resulted in decreased infectious virus production. Taken together, these results illustrate the global alterations in host cell metabolism during lytic gammaherpesvirus infection, establish essential pathways for viral production, and recommend targeted mechanisms to block viral spread and treat viral induced tumors. IMPORTANCE Viruses are intracellular parasites which lack their own metabolism, so they must hijack host cell metabolic machinery in order to increase the production of energy, proteins, fats, and genetic material necessary to replicate. Using murine herpesvirus 68 (MHV-68) as a model system to understand how similar human gammaherpesviruses cause cancer, we profiled the metabolic changes that occur during lytic MHV-68 infection and replication. We found that MHV-68 infection of host cells increases glucose, glutamine, lipid, and nucleotide metabolic pathways. We also showed inhibition or starvation of glucose, glutamine, or lipid metabolic pathways results in an inhibition of virus production. Ultimately, targeting changes in host cell metabolism due to viral infection can be used to treat gammaherpesvirus-induced cancers and infections in humans.

Global Lipidome Profiling Revealed Multifaceted Role of Lipid Species in Hepatitis C Virus Replication, Assembly, and Host Antiviral Response

Hepatitis C virus (HCV) is a major human pathogen that requires a better understanding of its interaction with host cells. There is a close association of HCV life cycle with host lipid metabolism. Lipid droplets (LDs) have been found to be crucial organelles that support HCV replication and virion assembly. In addition to their role in replication, LDs also have protein-mediated antiviral properties that are activated during HCV infection. Studies have shown that HCV replicates well in cholesterol and sphingolipid-rich membranes, but the ways in which HCV alters host cell lipid dynamics are not yet known. In this study, we performed a kinetic study to check the enrichment of LDs at different time points of HCV infection. Based on the LD enrichment results, we selected early and later time points of HCV infection for global lipidomic study. Early infection represents the window period for HCV sensing and host immune response while later infection represents the establishment of viral RNA replication, virion assembly, and egress. We identified the dynamic profile of lipid species at early and later time points of HCV infection by global lipidomic study using mass spectrometry. At early HCV infection, phosphatidylinositol phospholipids (PIPs), lysophosphatidic acid (LPA), triacyl glycerols (TAG), phosphatidylcholine (PC), and trihexosylceramides (Hex3Cer) were observed to be enriched. Similarly, free fatty acids (FFA), phosphatidylethanolamine (PE), N-acylphosphatidylethanolamines (NAPE), and tri acylglycerols were enriched at later time points of HCV infection. Lipids enriched at early time of infection may have role in HCV sensing, viral attachment, and immune response as LPA and PIPs are important for immune response and viral attachment, respectively. Moreover, lipid species observed at later infection may contribute to HCV replication and virion assembly as PE, FFA, and triacylglycerols are known for the similar function. In conclusion, we identified lipid species that exhibited dynamic profile across early and later time points of HCV infection compared to mock cells, which could be therapeutically relevant in the design of more specific and effective anti-viral therapies.

ATF1 Restricts Human Herpesvirus 6A Replication via Beta Interferon Induction

The stimulus-induced cAMP response element (CRE)-binding protein (CREB) family of transcription factors bind to CREs to regulate diverse cellular responses, including proliferation, survival, and differentiation. Human herpesvirus 6A (HHV-6A), which belongs to the Betaherpesvirinae subfamily, is a lymphotropic herpesvirus frequently found in patients with neuroinflammatory diseases. Previous reports implicated the importance of CREs in the HHV-6A life cycle, although the effects of the binding of transcription factors to CREs in viral replication have not been fully elucidated. In this study, we analyzed the role of the CREB family of transcription factors during HHV-6A replication. We found that HHV-6A infection enhanced phosphorylation of the CREB family members CREB1 and activating transcription factor 1 (ATF1). Knockout (KO) of CREB1 or ATF1 enhanced viral gene expression and viral replication. The increase in viral yields in supernatants from ATF1-KO cells was greater than that in supernatants from CREB1-KO cells. Transcriptome sequencing (RNA-seq) analysis showed that sensors of the innate immune system were downregulated in ATF1-KO cells, and mRNAs of beta interferon (IFN-β) and IFN-regulated genes were reduced in these cells infected with HHV-6A. IFN-β treatment of ATF1-KO cells reduced progeny viral yields significantly, suggesting that the enhancement of viral replication was caused by a reduction of IFN-β. Taken together, our results suggest that ATF1 is activated during HHV-6A infection and restricts viral replication via IFN-β induction. IMPORTANCE Human herpesvirus 6A (HHV-6A) is a ubiquitous herpesvirus implicated in Alzheimer's disease, although its role in its pathogenesis has not been confirmed. Here, we showed that the transcription factor ATF1 restricts HHV-6A replication, mediated by IFN-β induction. Our study provides new insights into the role of ATF1 in innate viral immunity and reveals the importance of IFN-β for regulation of HHV-6A replication, which possibly impairs HHV-6A pathogenesis.

Gene Expression Profile Analysis of Human Epidermal Keratinocytes Expressing Human Papillomavirus Type 8 E7

Background: Human papillomavirus type 8 (HPV8) has been implicated in the progress of non-melanoma skin cancers and their precursor lesions. The HPV8 E7 oncoprotein plays a key role in the tumorigenesis of HPV-associated cutaneous tumors. However, the exact role of HPV8 E7 in human epidermal carcinogenesis has not been fully elucidated.

Methods: To investigate the potential carcinogenic effects of HPV8 E7 on epithelial cells, we used RNA-sequencing technology to analyze the gene expression profile of HPV8 E7-overexpressed normal human epidermal keratinocytes (NHEKs).

Results: RNA-sequencing revealed 831 differentially expressed genes (DEGs) between HPV8 E7-expressing NHEKs and control cells, among which, 631 genes were significantly upregulated, and 200 were downregulated. Gene ontology annotation enrichment analysis showed that HPV8 E7 mainly affected the expression of genes associated with protein heterodimerization activity, DNA binding, nucleosomes, and nucleosome assembly. Kyoto Encyclopedia of Genes and Genomes pathway enrichment analysis revealed that overexpression of HPV8 E7 affected the expression of gene clusters associated with viral carcinogenesis and transcriptional misregulation in cancer and necroptosis signaling pathways that reportedly play crucial roles in HPV infection promotion and cancer progression. We also found the DEGs, such as HKDC1 and TNFAIP3, were associated with epigenetic modifications, immune regulation, and metabolic pathways.

Conclusion: Our results demonstrate that the pro-carcinogenic effect of HPV8 expression in epithelial cells may be attributed to the regulatory effect of oncogene E7 on gene expression associated with epigenetic modifications and immune and metabolic status-associated gene expression. Although our data are based on an in vitro experiment, it provides the theoretical evidence that the development of squamous cell carcinoma can be caused by HPV.

UV-LED irradiation reduces the infectivity of herpes simplex virus type 1 by targeting different viral components depending on the peak wavelength

Herpes simplex virus type 1 (HSV-1) is an enveloped virus that mainly infects humans. Given its high global prevalence, disinfection is critical for reducing the risk of infection. Ultraviolet-light-emitting diodes (UV-LEDs) are eco-friendly irradiating modules with different peak wavelengths, but the molecules degraded by UV-LED irradiation have not been clarified. To identify the target viral molecules of UV-LEDs, we exposed HSV-1 suspensions to UV-LED irradiation at wavelengths of 260-, 280-, 310-, and 365-nm and measured viral DNA, protein, and lipid damage and infectivity in host cells. All UV-LEDs substantially reduced by inhibiting host cell transcription, but 260- and 280-nm UV-LEDs had significantly stronger virucidal efficiency than 310- and 365-nm UV-LEDs. Meanwhile, 260- and 280-nm UV-LEDs induced the formation of viral DNA photoproducts and the degradation of viral proteins and some phosphoglycerolipid species. Unlike 260- and 280-nm UV-LEDs, 310- and 365-nm UV-LEDs decreased the viral protein levels, but they did not drastically change the levels of viral DNA photoproducts and lipophilic metabolites. These results suggest that UV-LEDs reduce the infectivity of HSV-1 by targeting different viral molecules based on the peak wavelength. These findings could facilitate the optimization of UV-LED irradiation for viral inactivation.

Meclizine Inhibits Pseudorabies Virus Replication by Interfering With Virus Entry and Release

Pseudorabies virus (PRV) is a pathogen that causes substantial economic losses to the swine industry. With the emergence and widespread of PRV variants since 2011 in China, current commercial vaccines cannot provide complete protection against PRV infection. Therefore, antiviral drugs may work as an alternative way to control and prevent PRV. In this study, the inhibitory effects and underlying molecular mechanisms of meclizine against PRV were studied. Meclizine displayed a significant inhibitory effect against PRV when it was added before, simultaneously with, or after virus infection. The inhibitory effect of meclizine occurred during viral entry and cell-to-cell spreading but not at viral attachment into PK-15 cells. Meclizine also inhibited viral particle release at the late stage of infection. The antiviral effect of meclizine was tested in mice, and the results showed that meclizine reduced the severity of clinical symptoms and the viral loads in tissues, and delayed the death, after PRV challenge. The above results indicated that meclizine had an inhibitory effect on PRV. Our findings will contribute to the development of potential therapeutic drugs against PRV infection.

Human Herpesvirus 6A Tegument Protein U14 Induces NF-κB Signaling by Interacting with p65

Viral infection induces host cells to mount a variety of immune responses, which may either limit viral propagation or create conditions conducive to virus replication in some instances. In this regard, activation of the NF-κB transcription factor is known to modulate virus replication. Human herpesvirus 6A (HHV-6A), which belongs to the Betaherpesvirinae subfamily, is frequently found in patients with neuroinflammatory diseases, although its role in disease pathogenesis has not been elucidated. In this study, we found that the HHV-6A-encoded U14 protein activates NF-κB signaling following interaction with the NF-κB complex protein, p65. Through induction of nuclear translocation of p65, U14 increases the expression of interleukin-6 (IL-6), IL-8, and monocyte chemoattractant protein 1 transcripts. We also demonstrated that activation of NF-κB signaling is important for HHV-6A replication, since inhibition of this pathway reduced virus protein accumulation and viral genome copy number. Taken together, our results suggest that HHV-6A infection activates the NF-κB pathway and promotes viral gene expression via late gene products, including U14. IMPORTANCE Human herpesvirus 6A (HHV-6A) is frequently found in patients with neuro-inflammation, although its role in the pathogenesis of this disease has not been elucidated. Most viral infections activate the NF-κB pathway, which causes the transactivation of various genes, including those encoding proinflammatory cytokines. Our results indicate that HHV-6A U14 activates the NF-κB pathway, leading to upregulation of proinflammatory cytokines. We also found that activation of the NF-κB transcription factor is important for efficient viral replication. This study provides new insight into HHV-6A U14 function in host cell signaling and identifies potential cellular targets involved in HHV-6A pathogenesis and replication.

Biosynthetic Mechanisms and Biological Significance of Glycerol Phosphate-Containing Glycan in Mammals

Bacteria contain glycerol phosphate (GroP)-containing glycans, which are important constituents of cell-surface glycopolymers such as the teichoic acids of Gram-positive bacterial cell walls. These glycopolymers comprising GroP play crucial roles in bacterial physiology and virulence. Recently, the first identification of a GroP-containing glycan in mammals was reported as a variant form of O-mannosyl glycan on α-dystroglycan (α-DG). However, the biological significance of such GroP modification remains largely unknown. In this review, we provide an overview of this new discovery of GroP-containing glycan in mammals and then outline the recent progress in elucidating the biosynthetic mechanisms of GroP-containing glycans on α-DG. In addition, we discuss the potential biological role of GroP modification along with the challenges and prospects for further research. The progress in this newly identified glycan modification will provide insights into the phylogenetic implications of glycan.

Host and Viral Factors Involved in Nuclear Egress of Herpes Simplex Virus 1

Herpes simplex virus 1 (HSV-1) replicates its genome and packages it into capsids within the nucleus. HSV-1 has evolved a complex mechanism of nuclear egress whereby nascent capsids bud on the inner nuclear membrane to form perinuclear virions that subsequently fuse with the outer nuclear membrane, releasing capsids into the cytosol. The viral-encoded nuclear egress complex (NEC) plays a crucial role in this vesicle-mediated nucleocytoplasmic transport. Nevertheless, similar system mediates the movement of other cellular macromolecular complexes in normal cells. Therefore, HSV-1 may utilize viral proteins to hijack the cellular machinery in order to facilitate capsid transport. However, little is known about the molecular mechanisms underlying this phenomenon. This review summarizes our current understanding of the cellular and viral factors involved in the nuclear egress of HSV-1 capsids.