Viruses and the Diversity of Cell Death

FUNDC1-mediated mitophagy regulates photodamage independently of the PINK1/Parkin-dependent pathway

BACKGROUND

Ultraviolet B(UVB) triggers a pro-survival response through mitophagy, but the role of FUNDC1-mediated mitophagy in photodamaged skin remains unexplored.

OBJECTIVES

To clarify the function of mitophagy in UVB-induced photodamaged skin.

METHODS

To investigate the role of FUNDC1-mediated mitophagy in UVB-induced mitochondrial damage and cell apoptosis, FUNDC1 knockdown in C57BL/6 mice was performed using adeno-associated virus. Additionally, FUNDC1 overexpression and knockdown in HaCaT cells were conducted using lentivirus. A comprehensive analysis was conducted on a panel of human sun-exposed skin samples, alongside control samples, to assess the expression levels of FUNDC1.

RESULTS

In UVB-induced C57BL/6 mice, the dorsal skin showed photodamage including erythema, scaling, erosion, and scabs. The expression levels of PINK1, Parkin, and BNIP3 did not show significant changes, while FUNDC1 expression consistently declined along with LC3B. Cytochrome C, Bax, and cleaved-caspase3 were upregulated, while Bcl2 was downregulated. UVB-induced HaCaT cells showed mitochondrial damage, accompanied by FUNDC1 downregulation and BNIP3 upregulation, while PINK1 and Parkin showed no significant changes. FUNDC1 overexpression led to an increase in mtROS and a decrease in mitochondrial membrane potential and ATP levels, indicating complete mitochondrial clearance and exacerbated cell death. FUNDC1 knockdown protected against UVB-induced photodamage in mice and mitigated mitochondrial damage and apoptosis in HaCaT cells by activating compensatory PINK1/Parkin-dependent mitophagy, which was evidenced by upregulation of PINK1 and Bcl2 and downregulation of Bax. In human sun-exposed skin samples, there was a decrease in the number of FUNDC1+ cells compared with non-sun-exposed controls.

CONCLUSIONS

FUNDC1-mediated mitophagy regulates skin photodamage and provides a novel mechanism for resisting photodamage, presenting a potential target for future therapeutic interventions.

Unveiling the Antiviral Potential of Minocycline: Modulation of Nuclear Export of Viral Ribonuclear Proteins during Influenza Virus Infection

Influenza A virus (IAV) poses a global threat worldwide causing pandemics, epidemics, and seasonal outbreaks. Annual modification of vaccines is costly due to continual shifts in circulating genotypes, leading to inadequate coverage in low- and middle-income countries like India. Additionally, IAVs are evolving resistance to approved antivirals, necessitating a search for alternative treatments. In this study, the antiviral role of the FDA-approved antibiotic minocycline against IAV strains was evaluated in vitro and in vivo by quantifying viral gene expression by qRT-PCR, viral protein levels by Western blotting, and viral titers. Our findings demonstrate that minocycline at a non-toxic dose effectively inhibits IAV replication, regardless of viral strain or cell line. Its antiviral mechanism operates independently of interferon signaling by targeting the MEK/ERK signaling pathway, which is crucial for the export of viral ribonucleoproteins (vRNPs). Minocycline prevents the assembly and release of infectious viral particles by causing the accumulation of vRNPs within the nucleus. Moreover, minocycline also inhibits IAV-induced late-stage apoptosis, further suppressing viral propagation. The antiviral activity of minocycline against IAVs could offer a promising solution amidst the challenges posed by influenza and the limitations of current treatments.

Wogonin Inhibits Apoptosis and Necroptosis Induced by Nephropathogenic Infectious Bronchitis Virus in Chicken Renal Tubular Epithelial Cells

NIBV is an acute and highly contagious virus that has a major impact on the poultry industry. Wogonin, as a flavonoid drug, has antiviral effects, but there have been no reports indicating its role in renal injury caused by NIBV infection. The aim of this study is to investigate the antiviral effect of wogonin against NIBV. Renal tubular epithelial cells were isolated and cultured, and divided into four groups: Con, Con+Wog, NIBV and NIBV+Wog. We found that wogonin significantly inhibited the copy number of NIBV and significantly alleviated NIBV-induced cell apoptosis and necrosis. Moreover, wogonin inhibited the reduction in mitochondrial membrane potential and the aberrant opening of mPTP caused by NIBV. In conclusion, wogonin can protect renal tubular epithelial cells from damage by inhibiting the replication of NIBV and preventing mitochondrial apoptosis and necroptosis induced by NIBV.

PA-824 inhibits porcine epidemic diarrhea virus infection in vivo and in vitro by inhibiting p53 activation

Porcine epidemic diarrhea virus (PEDV) is a type A coronavirus that causes severe watery diarrhea in piglets, resulting in severe economic losses worldwide. Therefore, new approaches to control PEDV infection are essential for a robust and sustainable pig industry. We screened 314 small-molecule drug libraries provided by Selleck and found that four drugs had obviously inhibitory effects on PEDV in Vero cells. PA-824, which had the highest SI index and the most reliable clinical safety, was selected for in vivo experiments. Animal attack tests showed that PA-824 effectively alleviated the clinical signs, intestinal pathological changes, and inflammatory responses in lactating piglets after PEDV infection. To further investigate the antiviral mechanism of PA-824, we measured the inhibitory effect of PA-824 on PEDV proliferation in a dose-dependent manner. By exploring the effect of PA-824 on the PEDV life cycle, we found that PA-824 acted directly on viral particles and hindered the adsorption, internalization, and replication phases of the virus, followed by molecular docking analysis to predict the interaction between PA-824 and PEDV non-structural proteins. Finally, we found that PA-824 could inhibit the apoptotic signaling pathway by suppressing PEDV-induced p53 activation. These results suggest that PA-824 could be protective against PEDV infection in piglets and could be developed as a drug or a feed additive to prevent and control PEDV diseases.IMPORTANCEPEDV is a highly contagious enteric coronavirus that widely spread worldwide, causing serious economic losses. There is no drug or vaccine to effectively control PEDV. In this study, we found that PA-824, a compound of mycobacteria causing pulmonary diseases, inhibited PEDV proliferation in both in vitro and in vivo. We also found that PA-824 directly acted on viral particles and hindered the adsorption, internalization, and replication stages of the virus. In addition, we found that PA-824 could inhibit the apoptotic signaling pathway by inhibiting PEDV-induced p53 activation. In conclusion, it is expected to be developed as a drug or a feed additive to prevent and control PEDV diseases.

TRIM7 ubiquitinates SARS-CoV-2 membrane protein to limit apoptosis and viral replication

SARS-CoV-2 is a highly transmissible virus that causes COVID-19 disease. Mechanisms of viral pathogenesis include excessive inflammation and viral-induced cell death, resulting in tissue damage. We identified the host E3-ubiquitin ligase TRIM7 as an inhibitor of apoptosis and SARS-CoV-2 replication via ubiquitination of the viral membrane (M) protein. Trim7 -/- mice exhibited increased pathology and virus titers associated with epithelial apoptosis and dysregulated immune responses. Mechanistically, TRIM7 ubiquitinates M on K14, which protects cells from cell death. Longitudinal SARS-CoV-2 sequence analysis from infected patients revealed that mutations on M-K14 appeared in circulating variants during the pandemic. The relevance of these mutations was tested in a mouse model. A recombinant M-K14/K15R virus showed reduced viral replication, consistent with the role of K15 in virus assembly, and increased levels of apoptosis associated with the loss of ubiquitination on K14. TRIM7 antiviral activity requires caspase-6 inhibition, linking apoptosis with viral replication and pathology.

Delineating organizational principles of the endogenous L-A virus by cryo-EM and computational analysis of native cell extracts

The high abundance of most viruses in infected host cells benefits their structural characterization. However, endogenous viruses are present in low copy numbers and are therefore challenging to investigate. Here, we retrieve cell extracts enriched with an endogenous virus, the yeast L-A virus. The determined cryo-EM structure discloses capsid-stabilizing cation-π stacking, widespread across viruses and within the Totiviridae, and an interplay of non-covalent interactions from ten distinct capsomere interfaces. The capsid-embedded mRNA decapping active site trench is supported by a constricting movement of two flexible opposite-facing loops. tRNA-loaded polysomes and other biomacromolecules, presumably mRNA, are found in virus proximity within the cell extract. Mature viruses participate in larger viral communities resembling their rare in-cell equivalents in terms of size, composition, and inter-virus distances. Our results collectively describe a 3D-architecture of a viral milieu, opening the door to cell-extract-based high-resolution structural virology.

Mitochondria-mediated Ferroptosis in Diseases Therapy: From Molecular Mechanisms to Implications

Ferroptosis, a type of cell death involving iron and lipid peroxidation, has been found to be closely associated with the development of many diseases. Mitochondria are vital components of eukaryotic cells, serving important functions in energy production, cellular metabolism, and apoptosis regulation. Presently, the precise relationship between mitochondria and ferroptosis remains unclear. In this study, we aim to systematically elucidate the mechanisms via which mitochondria regulate ferroptosis from multiple perspectives to provide novel insights into mitochondrial functions in ferroptosis. Additionally, we present a comprehensive overview of how mitochondria contribute to ferroptosis in different conditions, including cancer, cardiovascular disease, inflammatory disease, mitochondrial DNA depletion syndrome, and novel coronavirus pneumonia. Gaining a comprehensive understanding of the involvement of mitochondria in ferroptosis could lead to more effective approaches for both basic cell biology studies and medical treatments.

Brain Pathology in COVID-19: Clinical Manifestations and Potential Mechanisms

Neurological manifestations of coronavirus disease 2019 (COVID-19) are less noticeable than the respiratory symptoms, but they may be associated with disability and mortality in COVID-19. Even though Omicron caused less severe disease than Delta, the incidence of neurological manifestations is similar. More than 30% of patients experienced "brain fog", delirium, stroke, and cognitive impairment, and over half of these patients presented abnormal neuroimaging outcomes. In this review, we summarize current advances in the clinical findings of neurological manifestations in COVID-19 patients and compare them with those in patients with influenza infection. We also illustrate the structure and cellular invasion mechanisms of SARS-CoV-2 and describe the pathway for central SARS-CoV-2 invasion. In addition, we discuss direct damage and other pathological conditions caused by SARS-CoV-2, such as an aberrant interferon response, cytokine storm, lymphopenia, and hypercoagulation, to provide treatment ideas. This review may offer new insights into preventing or treating brain damage in COVID-19.

Circulating nucleosomes as potential biomarkers for cancer diagnosis and treatment monitoring

Nucleosomes play a crucial role in regulating gene expression through their composition and post-translational modifications. When cells die, intracellular endonucleases are activated and cleave chromatin into oligo- and mono-nucleosomes, which are then released into the body fluids. Studies have shown that the levels of nucleosomes are increased in serum and plasma in various cancer types, suggesting that analysis of circulating nucleosomes can provide an initial assessment of carcinogenesis. However, it should be noted that elevated serum nucleosome levels may not accurately diagnose certain tumor types, as increased cell death may occur in different pathological conditions. Nevertheless, detection of circulating nucleosomes and their histone modifications, along with specific tumor markers, can help diagnose certain types of cancer. Furthermore, monitoring changes in circulating nucleosome levels during chemotherapy or radiotherapy in patients with malignancies can provide valuable insights into clinical outcomes and therapeutic efficacy. The utilization of circulating nucleosomes as biomarkers is an exciting and emerging area of research, with the potential for early detection of various diseases and monitoring of treatment response. Integrating nucleosome-based biomarkers with existing ones may improve the specificity and sensitivity of current assays, offering the possibility of personalized precision medical treatment for patients.

Flow cytometry: Aspects and application in plant and biological science

Flow cytometry is a potent method that enables the quick and concurrent investigation of several characteristics of single cells in solution. Photodiodes or photomultiplier tubes are employed to detect the dispersed and fluorescent light signals that are produced by the laser beam as it passes through the cells. Photodetectors transform the light signals produced by the laser into electrical impulses. A computer then analyses these electrical impulses to identify and measure the various cell populations depending on their fluorescence or light scattering characteristics. Based on their fluorescence or light scattering properties, cell populations can be examined and/or isolated. This review covers the basic principle, components, working and specific biological applications of flow cytometry, including studies on plant, cell and molecular biology and methods employed for data processing and interpretation as well as the potential future relevance of this methodology in light of retrospective analysis and recent advancements in flow cytometry.

Isolation and Identification of a Tibetan Pig Porcine Epidemic Diarrhoea Virus Strain and Its Biological Effects on IPEC-J2 Cells

Porcine epidemic diarrhoea virus (PEDV) is a coronavirus that can cause severe watery diarrhoea in piglets, with high morbidity and mortality rates, seriously hindering the healthy development of the global swine industry. In this study, we isolated a strain of PEDV from Tibetan pigs and named it CH/GS/2022. Subsequently, we screened the apoptosis signals of PEDV-infected IPEC-J2 cells and studied the correlation between apoptosis signals and cell apoptosis. The results showed that different infections of PEDV induced different degrees of apoptosis in cells, and PEDV-induced cell apoptosis was dose-dependent. We then detected the expression of the p53, p38, JNK, Bax, and Bcl-2 genes in the apoptosis signal pathway. The results showed that 24 h after PEDV infection, the expression of the p53, p38, JNK, and Bax genes in IPEC-J2 cells increased significantly, while the expression of the Bcl-2 gene decreased significantly (p < 0.05). Subsequently, we used Western blot to detect the protein levels of these five genes, and the results showed that PEDV infection upregulated the expression of p53, p38, JNK, and Bax proteins (p < 0.05) while downregulating the expression of Bcl-2 protein (p < 0.05). Thus, it was initially inferred that PEDV infection could regulate cell apoptosis by activating the p53, p38, and JNK signalling pathways. Finally, we further investigated the apoptosis of the cells through the use of inhibitors. The results indicated that the p53 inhibitor Pifithrin-α has a significant inhibitory effect on the expression of the p53 protein after PEDV infection and can reverse the expression levels of Bax and Bcl-2 proteins. This suggested that p53 is involved in PEDV-induced cell apoptosis. Similarly, the p38 MAPK inhibitor SB203580 has an inhibitory effect on the expression of the p38 protein and can reverse the expression levels of Bax and Bcl-2 proteins. This suggested that p38 is also involved in PEDV-induced cell apoptosis. On the other hand, the JNK inhibitor SP600125 has no inhibitory effect on the expression of the JNK protein after PEDV infection, but the expression levels of Bax and Bcl-2 proteins have changed. Furthermore, it is noteworthy that SP600125 can inhibit the activity of apoptotic proteins but not their levels, resulting in reduced cell apoptosis. These preliminary results indicated that JNK may be involved in PEDV-induced IPEC-J2 cell apoptosis.

Age-related STAT3 signaling regulates severity of respiratory syncytial viral infection in human bronchial epithelial cells

Respiratory syncytial virus (RSV) can cause severe disease especially in infants; however, mechanisms of age-associated disease severity remain elusive. Here, employing human bronchial epithelium models generated from tracheal aspirate-derived basal stem cells of neonates and adults, we investigated whether age regulates RSV-epithelium interaction to determine disease severity. We show that following RSV infection, only neonatal epithelium model exhibited cytopathy and mucus hyperplasia, and neonatal epithelium had more robust viral spread and inflammatory responses than adult epithelium. Mechanistically, RSV-infected neonatal ciliated cells displayed age-related impairment of STAT3 activation, rendering susceptibility to apoptosis, which facilitated viral spread. In contrast, SARS-CoV-2 infection of ciliated cells had no effect on STAT3 activation and was not affected by age. Taken together, our findings identify an age-related and RSV-specific interaction with neonatal bronchial epithelium that critically contributes to severity of infection, and STAT3 activation offers a potential strategy to battle severe RSV disease in infants.

The Diagnostic, Prognostic, and Therapeutic Potential of Cell-Free DNA with a Special Focus on COVID-19 and Other Viral Infections

Cell-free DNA (cfDNA) in human blood serum, urine, and other body fluids recently became a commonly used diagnostic marker associated with various pathologies. This is because cfDNA enables a much higher sensitivity than standard biochemical parameters. The presence of and/or increased level of cfDNA has been reported for various diseases, including viral infections, including COVID-19. Here, we review cfDNA in general, how it has been identified, where it can derive from, its molecular features, and mechanisms of release and clearance. General suitability of cfDNA for diagnostic questions, possible shortcomings and future directions are discussed, with a special focus on coronavirus infection.

Virologs, viral mimicry, and virocell metabolism: the expanding scale of cellular functions encoded in the complex genomes of giant viruses

The phylum Nucleocytoviricota includes the largest and most complex viruses known. These "giant viruses" have a long evolutionary history that dates back to the early diversification of eukaryotes, and over time they have evolved elaborate strategies for manipulating the physiology of their hosts during infection. One of the most captivating of these mechanisms involves the use of genes acquired from the host-referred to here as viral homologs or "virologs"-as a means of promoting viral propagation. The best-known examples of these are involved in mimicry, in which viral machinery "imitates" immunomodulatory elements in the vertebrate defense system. But recent findings have highlighted a vast and rapidly expanding array of other virologs that include many genes not typically found in viruses, such as those involved in translation, central carbon metabolism, cytoskeletal structure, nutrient transport, vesicular trafficking, and light harvesting. Unraveling the roles of virologs during infection as well as the evolutionary pathways through which complex functional repertoires are acquired by viruses are important frontiers at the forefront of giant virus research.

Transcriptomic analysis reveals upregulated host metabolisms and downregulated immune responses or cell death induced by acute African swine fever virus infection

The African swine fever virus is a virulent and communicable viral disease that can be transmitted by infected swine, contaminated pork products, or soft tick vectors. Nonstructural proteins encoded by ASFV regulate viral replication, transcription, and evasion. However, the mechanisms underlying the host response to ASFV infection remain incompletely understood. In order to enhance comprehension of the biology and molecular mechanisms at distinct time intervals (6, 12, 24 h) post infection, transcriptome analyses were executed to discern differentially expressed genes (DEGs) between ASFV and mock-infected PAMs. The transcriptomic analysis unveiled a total of 1,677, 2,122, and 2,945 upregulated DEGs and 933, 1,148, and 1,422 downregulated DEGs in ASFV- and mock-infected groups at 6, 12, and 24 h.p.i.. The results of the transcriptomic analysis demonstrated that the infection of ASFV significantly stimulated host metabolism pathways while concurrently inhibiting the expression of various immune responses and cell death pathways. Our study offers crucial mechanistic insights into the comprehension of ASFV viral pathogenesis and the multifaceted host immune responses. The genes that were dysregulated may serve as potential candidates for further exploration of anti-ASFV strategies.

SARS-CoV-2 E protein-induced THP-1 pyroptosis is reversed by Ruscogenin

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), an emerging pathogenic coronavirus, has been reported to cause excessive inflammation and dysfunction in multiple cells and organs, but the underlying mechanisms remain largely unknown. Here we showed exogenous addition of SARS-CoV-2 envelop protein (E protein) potently induced cell death in cultured cell lines, including THP-1 monocytic leukemia cells, endothelial cells, and bronchial epithelial cells, in a time- and concentration-dependent manner. SARS-CoV-2 E protein caused pyroptosis-like cell death in THP-1 and led to GSDMD cleavage. In addition, SARS-CoV-2 E protein upregulated the expression of multiple pro-inflammatory cytokines that may be attributed to activation of NF-κB, JNK and p38 signal pathways. Notably, we identified a natural compound, Ruscogenin, effectively reversed E protein-induced THP-1 death via inhibition of NLRP3 activation and GSDMD cleavage. In conclusion, these findings suggested that Ruscogenin may have beneficial effects on preventing SARS-CoV-2 E protein-induced cell death and might be a promising treatment for the complications of COVID-19.

Dabie bandavirus infection induces macrophagic pyroptosis and this process is attenuated by platelets

Severe fever with thrombocytopenia syndrome (SFTS) is an emerging tick-borne infection with a high mortality rate in humans, which is caused by Dabie bandavirus (DBV), formerly known as SFTS virus. Clinical manifestations of SFTS are characterized by high fever, thrombocytopenia, leukopenia, hemorrhage, gastrointestinal symptoms, myalgia and local lymph node enlargement with up to 30% case fatality rates in human. Macrophage depletion in secondary lymphoid organs have important roles in the pathogenic process of fatal SFTS, but its exact cell death mechanism remains largely unknown. Here, we showed for the first time that DBV infection induced macrophagic pyroptosis, as evidenced by swollen cells, pore-forming structures, accumulation of gasdermin D N-terminal (GSDMD-NT) as well as the release of lactate dehydrogenase (LDH) and IL-1β in human macrophages. In addition to the upregulation of pyronecrosis genes, the expressions of pyroptosis-related proteins (GSDMD, caspase-1 and IL-1β) were also elevated. To be noted, platelets were found to play a protective role in DBV-derived pyroptosis. Transcriptome analysis and in vitro studies demonstrated that platelets significantly reduced the gene expressions and protein production of pro-pyroptotic markers and inflammatory cytokines in macrophages, whereas platelets conferred a propagation advantage for DBV. Collectively, this study demonstrates a novel mechanism by which DBV invasion triggers pyroptosis as a host defense to remove replication niches in human macrophages and platelets provide an additional layer to reduce cellular death. These findings may have important implications to the pathogenesis of lethal DBV, and provide new ideas for developing novel therapeutics to combat its infection.

MARCO Inhibits Porcine Reproductive and Respiratory Syndrome Virus Infection through Intensifying Viral GP5-Induced Apoptosis

Studying viral glycoprotein-host membrane protein interactions contributes to the discovery of novel cell receptors or entry facilitators for viruses. Glycoprotein 5 (GP5), which is a major envelope protein of porcine reproductive and respiratory syndrome virus (PRRSV) virions, is a key target for the control of the virus. Here, the macrophage receptor with collagenous structure (MARCO), which is a member of the scavenger receptor family, was identified as one of the host interactors of GP5 through a DUALmembrane yeast two-hybrid screening. MARCO was specifically expressed on porcine alveolar macrophages (PAMs), and PRRSV infection downregulated MARCO expression both in vitro and in vivo. MARCO was not involved in viral adsorption and internalization processes, indicating that MARCO may not be a PRRSV-entry facilitator. Contrarily, MARCO served as a host restriction factor for PRRSV. The knockdown of MARCO in PAMs enhanced PRRSV proliferation, whereas overexpression suppressed viral proliferation. The N-terminal cytoplasmic region of MARCO was responsible for its inhibitory effect on PRRSV. Further, we found that MARCO was a proapoptotic factor in PRRSV-infected PAMs. MARCO knockdown weakened virus-induced apoptosis, whereas overexpression aggravated apoptosis. MARCO aggravated GP5-induced apoptosis, which may result in its proapoptotic function in PAMs. The interaction between MARCO and GP5 may contribute to the intensified apoptosis induced by GP5. Additionally, the inhibition of apoptosis during PRRSV infection weakened the antiviral function of MARCO, suggesting that MARCO inhibits PRRSV through the regulation of apoptosis. Taken together, the results of this study reveal a novel antiviral mechanism of MARCO and suggest a molecular basis for the potential development of therapeutics against PRRSV. IMPORTANCE Porcine reproductive and respiratory syndrome virus (PRRSV) has been one of the most serious threats to the global swine industry. Glycoprotein 5 (GP5) exposed on the surface of PRRSV virions is a major glycoprotein, and it is involved in viral entry into host cells. A macrophage receptor with collagenous structure (MARCO), which is a member of the scavenger receptor family, was identified to interact with PRRSV GP5 in a DUALmembrane yeast two-hybrid screening. Further investigation demonstrated that MARCO may not serve as a potential receptor to mediate PRRSV entry. Instead, MARCO was a host restriction factor for the virus, and the N-terminal cytoplasmic region of MARCO was responsible for its anti-PRRSV effect. Mechanistically, MARCO inhibited PRRSV infection through intensifying virus-induced apoptosis in PAMs. The interaction between MARCO and GP5 may contribute to GP5-induced apoptosis. Our work reveals a novel antiviral mechanism of MARCO and advances the development of control strategies for the virus.

SARS-CoV-2 ORF3a sensitizes cells to ferroptosis via Keap1-NRF2 axis

Viral infection-induced cell death has long been considered as a double-edged sword in the inhibition or exacerbation of viral infections. Patients with severe Coronavirus Disease 2019 (COVID-19) are characterized by multiple organ dysfunction syndrome and cytokine storm, which may result from SARS-CoV-2-induced cell death. Previous studies have observed enhanced ROS level and signs of ferroptosis in SARS-CoV-2 infected cells or specimens of patients with COVID-19, but the exact mechanism is not clear yet. Here, we find SARS-CoV-2 ORF3a sensitizes cells to ferroptosis via Keap1-NRF2 axis. SARS-CoV-2 ORF3a promotes the degradation of NRF2 through recruiting Keap1, thereby attenuating cellular resistance to oxidative stress and facilitated cells to ferroptotic cell death. Our study uncovers that SARS-CoV-2 ORF3a functions as a positive regulator of ferroptosis, which might explain SARS-CoV-2-induced damage in multiple organs in COVID-19 patients and imply the potential of ferroptosis inhibition in COVID-19 treatment.

Transcriptome analysis reveals the host immune response upon LMBV infection in largemouth bass (Micropterus salmoides)

Largemouth bass (Micropterus salmoides) is one of the important economical freshwater aquaculture species in China. However, the outbreak of viral diseases always caused great economic losses in the largemouth bass aquaculture industry. Largemouth bass virus (LMBV), a double-stranded DNA (dsDNA) virus belonging to genus Ranavirus, family Iridoviridae causes high mortality in cultivated largemouth bass. However, host responses, especially the molecular events involved in LMBV infection still remained largely uncertain. Here, we established an in vivo model of LMBV infection, and systematically investigated the mRNA expression profiles of host genes in liver and spleen from infected largemouth bass using RNA sequencing (RNA-seq). Histopathological analysis indicated that necrotic cells and the formed necrotic focus were present in spleen, while numerous basophilic cells, hepatocytes volume shrinkage, nucleus pyknosis, and the disappeared boundary of hepatocytes were observed in the liver of infected largemouth bass. Transcriptomic analysis showed that transcription levels of 5128 genes (2804 up-regulated genes and 2324 down-regulated) in liver and 7008 genes (2603 up-regulated and 4405 down-regulated) in spleen were altered significantly. Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis indicated that numerous co-regulated differentially expressed genes (DEGs) in liver and spleen were enriched in the pathways related to cell death and immune signaling, such as apoptosis, necroptosis, cytokine-cytokine receptor interaction and JAK-STAT signaling. Moreover, the DEGs specially regulated by LMBV infection in liver were significantly enriched in the KEGG pathways related to metabolism and cell death, while those in spleen were enriched in the immune related pathways. In addition, the expression changes of several randomly selected genes, such as SOCS1, IL-6, CXCL2, CASP8, CYC and TNF from qPCR were consistent with the transcriptomic data. Taken together, our findings will provide new insights into the fundamental patterns of molecular responses induced by LMBV in vivo, but also contribute greatly to understanding the host defense mechanisms against iridoviral pathogens.

Phospholipid analysis of two influenza A virus-infected cell lines differing in their viral replication kinetics

Fluctuations in phospholipid composition in infected cells during influenza A virus replication were analyzed using two different susceptible host cell lines: H292 cells, exhibiting a rapid cytopathic effect, and A549 cells, exhibiting a retarded cytopathic effect. Microarray analysis demonstrated that A549 cells recognized influenza A virus invasion, expression of pathogen recognition genes was affected, and antiviral genes were activated. On the other hand, H292 cells did not display such an antiviral state, and in these cells, rapid virus amplification and a rapid cytopathic effect were observed. Levels of ceramide, diacylglycerol, and lysolipids were higher in virus-infected cells than in the corresponding mock-infected cells at the later stages of infection. The accumulation of these lipids in IAV-infected cells occurred together with viral replication. The relationship between the characteristic features of ceramide, diacylglycerol, and lysolipid in the plasma membrane, where enveloped viruses are released, and their role in viral envelope formation are discussed. Our results indicate that viral replication disturbs cellular lipid metabolism, with consequences for viral replication kinetics.

Mitochondrial control of inflammation

Numerous mitochondrial constituents and metabolic products can function as damage-associated molecular patterns (DAMPs) and promote inflammation when released into the cytosol or extracellular milieu. Several safeguards are normally in place to prevent mitochondria from eliciting detrimental inflammatory reactions, including the autophagic disposal of permeabilized mitochondria. However, when the homeostatic capacity of such systems is exceeded or when such systems are defective, inflammatory reactions elicited by mitochondria can become pathogenic and contribute to the aetiology of human disorders linked to autoreactivity. In addition, inefficient inflammatory pathways induced by mitochondrial DAMPs can be pathogenic as they enable the establishment or progression of infectious and neoplastic disorders. Here we discuss the molecular mechanisms through which mitochondria control inflammatory responses, the cellular pathways that are in place to control mitochondria-driven inflammation and the pathological consequences of dysregulated inflammatory reactions elicited by mitochondrial DAMPs.

Apoptosis or Antiapoptosis? Interrupted Regulated Cell Death of Host Cells by Ascovirus Infection In Vitro

Ascoviruses are insect-specific viruses thought to utilize the cellular apoptotic processes of host larvae to produce numerous virion-containing vesicles. In this study, we first determined the biochemical characteristics of ascovirus-infected, in vitro-cultured insect cells and the possible antiapoptotic capacity of ascovirus-infected insect cells. The results indicated that the ascovirus infection in the first 24 h was different from the infection from 48 h to the later infection stages. In the early infection stage, the Spodoptera exigua host cells had high membrane permeability and cleaved gasdermin D (GSDMD) but uncleaved Casp-6 (SeCasp-6). In contrast, the later infection stage had no such increased membrane permeability and had cleaved SeCasp-6. Four different chemicals were used to induce apoptosis at different stages of ascovirus infection: hydrogen peroxide (H₂O₂) and actinomycin D (ActD) had similar effects on the ascovirus-infected cells, whereas cMYC inhibitors and tumor necrosis factor alpha (TNF-α) plus SM-164 apoptosis inducers (T/S) had similar effects on infected cells. The former two inducers inhibited viral DNA replication in most situations, while the latter two inducers inhibited viral DNA replication in the early stage of infection but promoted viral DNA replication in the later infection stage. Furthermore, immunoblotting assays verified that T/S treatment could increase the expression levels of viral major capsid protein (MCP) and the host inhibitor of apoptosis protein (SeIAP). Coimmunoprecipitation assays revealed interaction between SeIAP and SeCasps, but this interaction was disturbed in ascovirus-infected cells. This study details the in vitro infection process of ascovirus, indicating the utilization of pyroptosis for antiapoptosis cytopathology. IMPORTANCE Clarifying the relationship between different types of viral infections and host regulation of cell death (RCD) can provide insights into the interaction between viruses and host cells. Ascoviruses are insect-specific viruses with apoptosis-utilizing-like infection cytopathology. However, RCD does not only include apoptosis, and while in our previous transmission electron microscopic observations, ascovirus-infected cells did not show typical apoptotic characteristics (unpublished data), in this study, they did show increased membrane permeability. These results indicate that the cytopathology of ascovirus infection is a complex process in which the virus manipulates host RCD. The RCD of insect cells is quite different from that of mammals, and studies on the former are many fewer than those on the latter, especially in the case of RCD in lepidopteran insects. Our results will lay a foundation for understanding the RCD of lepidopteran insects and its function in the process of insect virus infection.

Porcine sapovirus-induced RIPK1-dependent necroptosis is proviral in LLC-PK cells

Sapoviruses belonging to the genus Sapovirus within the family Caliciviridae are commonly responsible for severe acute gastroenteritis in both humans and animals. Caliciviruses are known to induce intrinsic apoptosis in vitro and in vivo, however, calicivirus-induced necroptosis remains to be fully elucidated. Here, we demonstrate that infection of porcine kidney LLC-PK cells with porcine sapovirus (PSaV) Cowden strain as a representative of caliciviruses induces receptor-interacting protein kinase 1 (RIPK1)-dependent necroptosis and acts as proviral compared to the antiviral function of PSaV-induced apoptosis. Infection of LLC-PK cells with PSaV Cowden strain showed that the interaction of phosphorylated RIPK1 (pRIPK1) with RIPK3 (pRIPK3), mixed lineage kinase domain-like protein (pMLKL) increased in a time-dependent manner, indicating induction of PSaV-induced RIPK1-dependent necroptosis. Interfering of PSaV-infected cells with each necroptotic molecule (RIPK1, RIPK3, or MLKL) by treatment with each specific chemical inhibitor or knockdown with each specific siRNA significantly reduced replication of PSaV but increased apoptosis and cell viability, implying proviral action of PSaV-induced necroptosis. In contrast, treatment of PSaV-infected cells with pan-caspase inhibitor Z-VAD-FMK increased PSaV replication and necroptosis, indicating an antiviral action of PSaV-induced apoptosis. These results suggest that PSaV-induced RIPK1-dependent necroptosis and apoptosis‒which have proviral and antiviral effects, respectively‒counterbalanced each other in virus-infected cells. Our study contributes to understanding the nature of PSaV-induced necroptosis and apoptosis and will aid in developing efficient and affordable therapies against PSaV and other calicivirus infections.

Oncolytic viruses as emerging therapy against cancers including Oncovirus-induced cancers

There are several human viruses with known potential for causing cancers including, Hepatitis B virus, Hepatitis C virus, Epstein-Barr virus, Kaposi's sarcoma herpesvirus, Human T-cell lymphotropic virus, Human papillomavirus, and Merkel cell polyomavirus. Cancer is the second leading cause of death that affects humans worldwide, especially in developing countries. Surgery, chemotherapy, and radiotherapy can cure about 60% of humans with cancer but recurrent and metastatic diseases remain a major reason for death. In recent years, understanding the molecular characteristics of cancer cells has led to the improvement of therapeutic strategies using novel emerging therapies. Oncolytic viruses with the potential of lysing cancer cells defined the field of oncolytic virology, hence becoming a biotechnology tool rather than just a cause of disease. This study mainly focused on targeting cell proliferation and death pathways in human tumor-inducing viruses by developing innovative therapies for cancer patients based on the natural oncolytic properties of reovirus. To kill tumor cells efficiently and reduce the chance of recurrence both the direct ability of reovirus infection to lyse the tumor cells and the stimulation of a potent host immune response are applied. Hence, bioengineered stem cells can be used as smart carriers to improve the efficacy of oncolytic reovirus and safety profiles.

Risk Factors of Severe COVID-19: A Review of Host, Viral and Environmental Factors

The clinical course and outcome of COVID-19 are highly variable, ranging from asymptomatic infections to severe disease and death. Understanding the risk factors of severe COVID-19 is relevant both in the clinical setting and at the epidemiological level. Here, we provide an overview of host, viral and environmental factors that have been shown or (in some cases) hypothesized to be associated with severe clinical outcomes. The factors considered in detail include the age and frailty, genetic polymorphisms, biological sex (and pregnancy), co- and superinfections, non-communicable comorbidities, immunological history, microbiota, and lifestyle of the patient; viral genetic variation and infecting dose; socioeconomic factors; and air pollution. For each category, we compile (sometimes conflicting) evidence for the association of the factor with COVID-19 outcomes (including the strength of the effect) and outline possible action mechanisms. We also discuss the complex interactions between the various risk factors.

Transcriptomic reveals the ferroptosis features of host response in a mouse model of Zika virus infection

Zika virus (ZIKV) is a neurotropic flavivirus. The outbreak of ZIKV in 2016 created a global health emergency. However, the underlying pathogenic mechanisms remain elusive. We investigated the host response features of in vivo replication in a mouse model of ZIKV infection, by performing a series of transcriptomic and bioinformatic analyses of ZIKV and mock-infected brain tissue. Tissue damage, inflammatory cells infiltration and high viral replication were observed in the brain tissue of ZIKV infected mice. RNA-Seq of the brain indicated the activation of ferroptosis pathways. Enrichment analysis of ferroptosis regulators revealed their involvement in pathways such as mineral absorption, fatty acid biosynthesis, fatty acid degradation, PPAR signaling pathway, peroxidase, and adipokinesine signalling pathway. We then identified 12 interacted hub ferroptosis regulators (CYBB, HMOX1, CP, SAT1, TF, SLC39A14, FTL, LPCAT3, FTH1, SLC3A2, TP53, and SLC40A1) that were related to the differential expression of CD8⁺ T cells, microglia and monocytes. CYBB, HMOX1, SALT, and SLAC40A1 were selected as potential biomarkers of ZIKV infection. Finally, we validated our results using RT-qPCR and outside available datasets. For the first time, we proposed a possible mechanism of ferroptosis in brain tissue infected by ZIKV in mice and identified the four key ferroptosis regulators.

Characterization of the Second Apoptosis Inhibitor Encoded by Guinea Pig Cytomegalovirus

Despite the usefulness of guinea pig cytomegalovirus (GPCMV) for studies on congenital CMV infection, its viral mechanisms for the evasion of host defense strategies have not been fully elucidated. We reported previously that GPCMV gp38.1 functions as a viral mitochondria-localized inhibitor of apoptosis-like function, and its weak activity suggested the presence of an additional inhibitory molecule(s). Here, we identified gp38.3-2, a 42-amino-acid (aa) reading frame embedded within the gp38.3 gene that encodes a positional homolog of murine CMV (MCMV) m41. Characterization of gp38.3-2 resulted in the following findings: (i) the aa sequence of gp38.3-2 shows some similarity to that of MCMV m41.1, a viral inhibitor of oligomerization of a member of Bcl-2 family protein BAK, but there is no correspondence in their predicted secondary structures; (ii) gp38.3-2, but not gp38.3, showed inhibitory activities against staurosporine-induced apoptosis; (iii) three-dimensional protein complex prediction suggests that the N-terminal α-helix of gp38.3-2 interacts with residues in the BH3 and BH1 motifs of BAK, and analysis of gp38.3-2 and BAK mutants supported this model; (iv) guinea pig fibroblast cells infected with gp38.3-2-deficient GPCMV strain Δ38.3-2 died earlier than cells infected with rescued strain r38.3-2, resulting in lower yields of Δ38.3-2; (v) Δ38.3-2 exhibited a partial but significant decrease in monocyte and macrophage infection in comparison with r38.3-2; and, however, (vi) little difference in the viral infection of guinea pigs was observed between these two strains. Therefore, we hypothesize that gp38.3-2 contributes little to the evasion of host defense mechanisms under the experimental conditions used. IMPORTANCE Although GPCMV provides a useful animal model for studies on the pathogenesis of congenital CMV infection and the development of CMV vaccine strategies, our understanding of the viral mechanisms by which it evades apoptosis of infected cells has been limited in comparison with those of murine and human CMVs. Here, we report a second GPCMV apoptosis inhibitor (42 amino acids in length) that interacts with BAK, a Bcl-2 family proapoptotic protein. Three-dimensional structural prediction indicated a unique BAK recognition by gp38.3-2 via the BH3 and BH1 motif sequences. Our findings suggest the potential development of BH3 mimetics that can regulate inhibition or induction of apoptosis based on short ~40-amino-acid peptide molecules as with GPCMV.

Larval-Transcriptome Dynamics of Ectropis grisescens Reveals Differences in Virulence Mechanism between Two EcobNPV Strains

The biological insecticide, Ectropis obliqua nucleopolyhedrovirus (EcobNPV), has been applied to control the major tea-pest Ectropis grisescens. Previously, the virus strain EcobNPV-QF4 showed higher a mortality rate (58.2% vs. 88.2%) and shorter median lethal-time (13.9 d vs. 15.4 d) on E. grisescens than the strain EcobNPV-QV. However, the mechanism of the difference in virulence between the two strains remains unclear. Using the leaf-disc method, we detected the virulence of the two strains on 3^rd-instar larvae, and found that median lethal-dose (LD₅₀) of EcobNPV-QF4 is 55-fold higher than that of EcobNPV-QV (4.35 × 10⁸ vs. 7.89 × 10⁶). Furthermore, fourteen larva transcriptomes of E. grisescens were subsequently sequenced at seven time-points after ingestion of the two virus strains, yielding 410.72 Gb of raw reads. Differential gene-expression analysis shows that 595, 87, 27, 108, 0, 12, and 290 genes were up-regulated in EcobNPV-QF4 at 0, 2, 6, 12, 24, 36 h and 48 h post ingestion (hpi), while 744, 68, 152, 8, 1, 0, 225 were down-regulated. KEGG enrichment showed that when the virus first invades (eats the leaf-discs), EcobNPV-QF4 mainly affects pathways such as ribosome (p-value = 2.47 × 10^-29), and at 48 hpi EcobNPV-QF4, causes dramatic changes in the amino-acid-synthesis pathway and ribosome pathway (p-value = 6.94 × 10^-13) in E. grisescens. Among these, thirteen key genes related to immunity were screened. The present study provides the first ever comprehensive analysis of transcriptional changes in E. grisescens after ingestion of the two strains of EcobNPV.

Isolation and Characterization of a Discrete Genetically Homogeneous Viral Subpopulation of Mumps Virus RS-12 Strain with Superior Oncolytic Potency Compared to Its Progenitor Virus

Background: Oncolytic virotherapy can serve as a novel therapeutic strategy in oncology. In this study, we aimed to evaluate the oncolytic activity of the mumps virus RS-12 strain after its adaptation to cancer cells via serial passaging. Methods: To adapt the RS-12 strain-based vaccine to cancer cells, it was passaged eight times in the HT1080 cell line and was isolated via two terminal endpoint dilutions. The genetic homogeneity of isolated cancer cell-adapted RS-12 variant was confirmed by direct sequencing of regions, encompassing four known heterogeneous genomic positions. The in vitro cytotoxic effects of viruses was assessed in two different cancer cell lines using the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay. The apoptosis-inducing effects of the cancer cell-adapted variant and its parental virus on cancer cells were quantified by flow cytometry. Results: According to the chromatograms, the RS-12 strain vaccine seed exhibited two peaks at the genomic nucleotide positions 1591, 2417, 3774, and 12977. On the contrary, cancer cell-adapted RS-12, isolated by terminal endpoint serial dilutions, contained no viral subpopulations in these positions. A significant improvement was observed in the oncolytic potency of our cancer cell-adapted variant compared to its parental virus vaccine seed in vitro. Besides, the variant efficiently induced apoptosis in the human fibrosarcoma and adenocarcinoma cell lines. Conclusions: Considering the increased oncolytic potency and apoptosis-inducing capacity of this variant in cancer cells, it can be a promising option for future experiments.

The intersection molecule MDA5 in Cancer and COVID-19

The connections between pattern recognition receptors (PRRs) and pathogen-associated molecular patterns (PAMPs) constitutes the crucial signaling pathways in the innate immune system. Cytoplasmic nucleic acid sensor melanoma differentiation-associated gene 5 (MDA5) serves as an important pattern recognition receptor in the innate immune system by recognizing viral RNA. MDA5 also plays a role in identifying the cytoplasmic RNA from damaged, dead cancer cells or autoimmune diseases. MDA5’s recognition of RNA triggers innate immune responses, induces interferon (IFN) response and a series of subsequent signaling pathways to produce immunomodulatory factors and inflammatory cytokines. Here we review the latest progress of MDA5 functions in triggering anti-tumor immunity by sensing cytoplasmic dsRNA, and recognizing SARS-CoV-2 virus infection for antiviral response, in which the virus utilizes multiple ways to evade the host defense mechanism.

Lipid balance remodelling by human positive-strand RNA viruses and the contribution of lysosomes

A marked reorganization of internal membranes occurs in the cytoplasm of cells infected by single stranded positive-sense RNA viruses. Most cell compartments change their asset to provide lipids for membrane rearrangement into replication organelles, where to concentrate viral proteins and enzymes while hiding from pathogen pattern recognition molecules. Because the endoplasmic reticulum is a central hub for lipid metabolism, when viruses hijack the organelle to form their replication organelles, a cascade of events change the intracellular environment. This results in a marked increase in lipid consumption, both by lipolysis and lipophagy of lipid droplets. In addition, lipids are used to produce energy for viral replication. At the same time, inflammation is started by signalling lipids, where lysosomal processing plays a relevant role. This review is aimed at providing an overview on what takes place after human class IV viruses have released their genome into the host cell and the consequences on lipid metabolism, including lysosomes.

Advances in cell death mechanisms involved in viral myocarditis

Viral myocarditis is an acute inflammatory disease of the myocardium. Although many etiopathogenic factors exist, coxsackievirus B3 is a the leading cause of viral myocarditis. Abnormal cardiomyocyte death is the underlying problem for most cardiovascular diseases and fatalities. Various types of cell death occur and are regulated to varying degrees. In this review, we discuss the different cell death mechanisms in viral myocarditis and the potential interactions between them. We also explore the role and mechanism of cardiomyocyte death with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection. Exploring the mechanisms may help in the early identification and the development of effective treatments, thus improving the quality of life of patients with viral myocarditis. We believe that the inhibition of cardiomyocyte death has immense therapeutic potential in increasing the longevity and health of the heart.

Ferroptosis in viral infection: the unexplored possibility

Virus-induced cell death has long been thought of as a double-edged sword in the inhibition or exacerbation of viral infections. The vital role of iron, an essential element for various enzymes in the maintenance of cellular physiology and efficient viral replication, places it at the crossroads and makes it a micronutrient of competition between the viruses and the host. Viruses can interrupt iron uptake and the antioxidant response system, while others can utilize iron transporter proteins as receptors. Interestingly, the unavailability of iron facilitates certain viral infections and causes cell death characterized by lipid peroxide accumulation and malfunction of the antioxidant system. In this review, we discuss how iron uptake, regulation and metabolism, including the redistribution of iron in the host defense system during viral infection, can induce ferroptosis. Fenton reactions, a central characteristic of ferroptosis, are caused by the increased iron content in the cell. Therefore, viral infections that increase cellular iron content or intestinal iron absorption are likely to cause ferroptosis. In addition, we discuss the hijacking of the iron regulatoy pathway and the antioxidant response, both of which are typical in viral infections. Understanding the potential signaling mechanisms of ferroptosis in viral infections will aid in the development of new therapeutic agents.

Largemouth Bass Virus Infection Induced Non-Apoptotic Cell Death in MsF Cells

Largemouth bass virus (LMBV), belonging to the genus Ranavirus, causes high mortality and heavy economic losses in largemouth bass aquaculture. In the present study, a novel cell line, designated as MsF, was established from the fin of largemouth bass (Micropterus salmoides), and applied to investigate the characteristics of cell death induced by LMBV. MsF cells showed susceptibility to LMBV, evidenced by the occurrence of a cytopathic effect (CPE), increased viral gene transcription, protein synthesis, and viral titers. In LMBV-infected MsF cells, two or more virus assembly sites were observed around the nucleus. Notably, no apoptotic bodies occurred in LMBV-infected MsF cells after nucleus staining, suggesting that cell death induced by LMBV in host cells was distinct from apoptosis. Consistently, DNA fragmentation was not detected in LMBV-infected MsF cells. Furthermore, only caspase-8 and caspase-3 were significantly activated in LMBV-infected MsF cells, suggesting that caspases were involved in non-apoptotic cell death induced by LMBV in host cells. In addition, the disruption of the mitochondrial membrane potential (ΔΨm) and reactive oxygen species (ROS) generation were detected in both LMBV-infected MsF cells and fathead minnow (FHM) cells. Combined with our previous study, we propose that cell death induced by LMBV infection was cell type dependent. Although LMBV-infected MsF cells showed the characteristics of non-apoptotic cell death, the signal pathways might crosstalk and interconnect between apoptosis and other PCD during LMBV infection. Together, our results not only established the in vitro LMBV infection model for the study of the interaction between LMBV and host cells but also shed new insights into the mechanisms of ranavirus pathogenesis.

SARS-CoV-2 membrane protein causes the mitochondrial apoptosis and pulmonary edema via targeting BOK

Deaths caused by coronavirus disease 2019 (COVID-19) are largely due to the lungs edema resulting from the disruption of the lung alveolo-capillary barrier, induced by SARS-CoV-2-triggered pulmonary cell apoptosis. However, the molecular mechanism underlying the proapoptotic role of SARS-CoV-2 is still unclear. Here, we revealed that SARS-CoV-2 membrane (M) protein could induce lung epithelial cells mitochondrial apoptosis. Notably, M protein stabilized B-cell lymphoma 2 (BCL-2) ovarian killer (BOK) via inhibiting its ubiquitination and promoted BOK mitochondria translocation. The endodomain of M protein was required for its interaction with BOK. Knockout of BOK by CRISPR/Cas9 increased cellular resistance to M protein-induced apoptosis. BOK was rescued in the BOK-knockout cells, which led to apoptosis induced by M protein. M protein induced BOK to trigger apoptosis in the absence of BAX and BAK. Furthermore, the BH2 domain of BOK was required for interaction with M protein and proapoptosis. In vivo M protein recombinant lentivirus infection induced caspase-associated apoptosis and increased alveolar-capillary permeability in the mouse lungs. BOK knockdown improved the lung edema due to lentivirus-M protein infection. Overall, M protein activated the BOK-dependent apoptotic pathway and thus exacerbated SARS-CoV-2 associated lung injury in vivo. These findings proposed a proapoptotic role for M protein in SARS-CoV-2 pathogenesis, which may provide potential targets for COVID-19 treatments.

Revisiting Regulated Cell Death Responses in Viral Infections

The fate of a viral infection in the host begins with various types of cellular responses, such as abortive, productive, latent, and destructive infections. Apoptosis, necroptosis, and pyroptosis are the three major types of regulated cell death mechanisms that play critical roles in viral infection response. Cell shrinkage, nuclear condensation, bleb formation, and retained membrane integrity are all signs of osmotic imbalance-driven cytoplasmic swelling and early membrane damage in necroptosis and pyroptosis. Caspase-driven apoptotic cell demise is considered in many circumstances as an anti-inflammatory, and some pathogens hijack the cell death signaling routes to initiate a targeted attack against the host. In this review, the selected mechanisms by which viruses interfere with cell death were discussed in-depth and were illustrated by compiling the general principles and cellular signaling mechanisms of virus–host-specific molecule interactions.

Nanomaterials for virus sensing and tracking

The effect of the on-going COVID-19 pandemic on global healthcare systems has underlined the importance of timely and cost-effective point-of-care diagnosis of viruses. The need for ultrasensitive easy-to-use platforms has culminated in an increased interest for rapid response equipment-free alternatives to conventional diagnostic methods such as polymerase chain reaction, western-blot assay, etc. Furthermore, the poor stability and the bleaching behavior of several contemporary fluorescent reporters is a major obstacle in understanding the mechanism of viral infection thus retarding drug screening and development. Owing to their extraordinary surface-to-volume ratio as well as their quantum confinement and charge transfer properties, nanomaterials are desirable additives to sensing and imaging systems to amplify their signal response as well as temporal resolution. Their large surface area promotes biomolecular integration as well as efficacious signal transduction. Due to their hole mobility, photostability, resistance to photobleaching, and intense brightness, nanomaterials have a considerable edge over organic dyes for single virus tracking. This paper reviews the state-of-the-art of combining carbon-allotrope, inorganic and organic-based nanomaterials with virus sensing and tracking methods, starting with the impact of human pathogenic viruses on the society. We address how different nanomaterials can be used in various virus sensing platforms (e.g. lab-on-a-chip, paper, and smartphone-based point-of-care systems) as well as in virus tracking applications. We discuss the enormous potential for the use of nanomaterials as simple, versatile, and affordable tools for detecting and tracing viruses infectious to humans, animals, plants as well as bacteria. We present latest examples in this direction by emphasizing major advantages and limitations.

Therapy Targets SARS-CoV-2 Infection-Induced Cell Death

Coronavirus Disease 2019 (COVID-19) caused by SARS-CoV-2 has become a global health issue. The clinical presentation of COVID-19 is highly variable, ranging from asymptomatic and mild disease to severe. However, the mechanisms for the high mortality induced by SARS-CoV-2 infection are still not well understood. Recent studies have indicated that the cytokine storm might play an essential role in the disease progression in patients with COVID-19, which is characterized by the uncontrolled release of cytokines and chemokines leading to acute respiratory distress syndrome (ARDS), multi-organ failure, and even death. Cell death, especially, inflammatory cell death, might be the initiation of a cytokine storm caused by SARS-CoV-2 infection. This review summarizes the forms of cell death caused by SARS-CoV-2 in vivo or in vitro and elaborates on the dedication of apoptosis, necroptosis, NETosis, pyroptosis of syncytia, and even SARS-CoV-2 E proteins forming channel induced cell death, providing insights into targets on the cell death pathway for the treatment of COVID-19.

Reovirus Activated Cell Death Pathways

Mammalian orthoreoviruses (ReoV) are non-enveloped viruses with segmented double-stranded RNA genomes. In humans, ReoV are generally considered non-pathogenic, although members of this family have been proven to cause mild gastroenteritis in young children and may contribute to the development of inflammatory conditions, including Celiac disease. Because of its low pathogenic potential and its ability to efficiently infect and kill transformed cells, the ReoV strain Type 3 Dearing (T3D) is clinical trials as an oncolytic agent. ReoV manifests its oncolytic effects in large part by infecting tumor cells and activating programmed cell death pathways (PCDs). It was previously believed that apoptosis was the dominant PCD pathway triggered by ReoV infection. However, new studies suggest that ReoV also activates other PCD pathways, such as autophagy, pyroptosis, and necroptosis. Necroptosis is a caspase-independent form of PCD reliant on receptor-interacting serine/threonine-protein kinase 3 (RIPK3) and its substrate, the pseudokinase mixed-lineage kinase domain-like protein (MLKL). As necroptosis is highly inflammatory, ReoV-induced necroptosis may contribute to the oncolytic potential of this virus, not only by promoting necrotic lysis of the infected cell, but also by inflaming the surrounding tumor microenvironment and provoking beneficial anti-tumor immune responses. In this review, we summarize our current understanding of the ReoV replication cycle, the known and potential mechanisms by which ReoV induces PCD, and discuss the consequences of non-apoptotic cell death—particularly necroptosis—to ReoV pathogenesis and oncolysis.

Huaier Polysaccharide Interrupts PRV Infection via Reducing Virus Adsorption and Entry

A pseudorabies virus (PRV) novel virulent variant outbreak occurred in China in 2011. However, little is known about PRV prevention and treatment. Huaier polysaccharide has been used to treat some solid cancers, although its antiviral activity has not been reported. Our study confirmed that the polysaccharide can effectively inhibit infection of PRV XJ5 in PK15 cells. It acted in a dose-dependent manner when blocking virus adsorption and entry into PK15 cells. Moreover, it suppressed PRV replication in PK15 cells. In addition, the results suggest that Huaier polysaccharide plays a role in treating PRV XJ5 infection by directly inactivating PRV XJ5. In conclusion, Huaier polysaccharide might be a novel therapeutic agent for preventing and controlling PRV infection.

Acyl-Coenzyme A Synthetase Long-Chain Family Member 4 Is Involved in Viral Replication Organelle Formation and Facilitates Virus Replication via Ferroptosis

Enterovirus infections can cause severe complications, such as poliomyelitis, encephalitis, myocarditis, meningitis, neurological pulmonary edema, and even death. Here, we used genome-wide CRISPR screens to gain new insight into the mechanism by which enteroviruses co-opt host pathways to potentiate replication and propagation. We found that acyl-coenzyme A synthetase long-chain family member 4 (ACSL4) is involved in viral replication organelle formation. ACSL4 is a key component of ferroptosis, an iron-dependent, nonapoptotic programmed cell death. Our results indicated that enteroviruses and coronaviruses can induce ferroptosis via ACSL4. Most importantly, ferroptosis inhibitors, including two FDA-approved drugs, rosiglitazone (ROSI; ACSL4 inhibitor) and pioglitazone (PIO; ACSL4 inhibitor), decreased the viral load of human enteroviruses and coronaviruses, suggesting that ACSL4 is a target for counteracting viral infection. IMPORTANCE We provide the first evidence for the role of ACSL4 in enterovirus replication organelle formation. Moreover, both enteroviruses and coronaviruses induce ferroptosis via ACSL4. These findings establish a novel regulatory mechanism for viral replication. The inhibition of ACSL4 by ferroptosis inhibitors can reduce viral yields of enteroviruses and coronaviruses, including SARS-CoV-2, implying that ACSL4-mediated ferroptosis is a promising therapeutic target for viral diseases.

Mitochondria and Viral Infection: Advances and Emerging Battlefronts

Mitochondria are dynamic organelles vital for energy production with now appreciated roles in immune defense. During microbial infection, mitochondria serve as signaling hubs to induce immune responses to counteract invading pathogens like viruses. Mitochondrial functions are central to a variety of antiviral responses including apoptosis and type I interferon signaling (IFN-I). While apoptosis and IFN-I mediated by mitochondrial antiviral signaling (MAVS) are well-established defenses, new dimensions of mitochondrial biology are emerging as battlefronts during viral infection. Increasingly, it has become apparent that mitochondria serve as reservoirs for distinct cues that trigger immune responses and that alterations in mitochondrial morphology may also tip infection outcomes. Furthermore, new data are foreshadowing pivotal roles for classic, homeostatic facets of this organelle as host-virus interfaces, namely, the tricarboxylic acid (TCA) cycle and electron transport chain (ETC) complexes like respiratory supercomplexes. Underscoring the importance of "housekeeping" mitochondrial activities in viral infection is the growing list of viral-encoded inhibitors including mimics derived from cellular genes that antagonize these functions. For example, virologs for ETC factors and several enzymes from the TCA cycle have been recently identified in DNA virus genomes and serve to pinpoint new vulnerabilities during infection. Here, we highlight recent advances for known antiviral functions associated with mitochondria as well as where the next battlegrounds may be based on viral effectors. Collectively, new methodology and mechanistic insights over the coming years will strengthen our understanding of how an ancient molecular truce continues to defend cells against viruses.

A genome-wide CRISPR screen identifies HuR as a regulator of apoptosis induced by dsRNA and virus

We performed an unbiased whole-genome CRISPR/Cas9 screen in A549 cells to identify potential regulators involved in cell death triggered by dsRNA. Of several top candidate genes, we identified the RNA binding protein ELAV like protein 1 (ELAVL1) that encodes Hu antigen R (HuR). Depletion of HuR led to less cell death induced by dsRNA. HuR is mainly involved in the apoptosis, and all of its RNA recognition motifs are essential for its proapoptotic function. We further showed that the HuR depletion had no influence on the mRNA level of an anti-apoptotic gene, BCL2, instead downregulated its translation in a cap-independent way. Polysome fractionation studies showed that HuR retarded the BCL2 mRNA in the non-translating pool of polysomes. Moreover, protection from dsRNA-induced apoptosis by HuR depletion required the presence of BCL2, indicating that the proapoptotic function of HuR is executed by suppressing BCL2. Consistently, HuR regulated apoptosis induced by infection of encephalomyocarditis or Semliki Forest virus. Collectively, our work identified a suite of proteins that regulate dsRNA-induced cell death, and elucidated the mechanism by which HuR acts as a pro-apoptotic factor.

Molecular Events Involved in Influenza A Virus-Induced Cell Death

Viral infection usually leads to cell death. Moderate cell death is a protective innate immune response. By contrast, excessive, uncontrolled cell death causes tissue destruction, cytokine storm, or even host death. Thus, the struggle between the host and virus determines whether the host survives. Influenza A virus (IAV) infection in humans can lead to unbridled hyper-inflammatory reactions and cause serious illnesses and even death. A full understanding of the molecular mechanisms and regulatory networks through which IAVs induce cell death could facilitate the development of more effective antiviral treatments. In this review, we discuss current progress in research on cell death induced by IAV infection and evaluate the role of cell death in IAV replication and disease prognosis.

The adaptation of SARS-CoV-2 to humans

The process of adaptation of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) to humans probably had started decades ago, when its ancestor diverged from the bat coronavirus. The adaptive process comprises strategies the virus uses to overcome the respiratory tract defense barriers and replicate and shed in the host cells. These strategies include the impairment of interferon production, hiding immunogenic motifs, avoiding viral RNA detection, manipulating cell autophagy, triggering host cell death, inducing lymphocyte exhaustion and depletion, and finally, mutation and escape from immunity. In addition, SARS-CoV-2 employs strategies to take advantage of host cell resources for its benefits, such as inhibiting the ubiquitin-proteasome system, hijacking mitochondria functions, and usage of enhancing antibodies. It may be anticipated that as the tradeoffs of adaptation progress, the virus destructive burden will gradually subside. Some evidence suggests that SARS-CoV-2 will become part of the human respiratory virome, as had occurred with other coronaviruses, and coevolve with its host.

Gastrointestinal cancer-associated fibroblasts expressing Junctional Adhesion Molecule-A are amenable to infection by oncolytic reovirus

Gastrointestinal (GI) cancers are characterized by extensive tumor stroma that both promotes tumor progression and acts as a physical barrier for adjacent tumor cells, limiting the effect of current treatment modalities. Oncolytic virotherapy is currently investigated in clinical trials as a novel therapeutic agent for different malignancies of the GI tract, but it is largely unknown whether these viruses can also target the tumor stroma. Here, we investigated the tropism of two commonly studied OVs, adenovirus and reovirus, towards primary GI fibroblasts from human oesophageal, gastric, duodenal and pancreatic carcinomas (N = 36). GI fibroblasts were susceptible to type 3 Dearing (T3D) strain R124 and bioselected mutant reovirus (jin-3) infection but not oncolytic adenovirus (Ad5-Δ24). Efficient infection and apoptosis of human and mouse GI cancer-derived fibroblasts by these reoviruses was partially dependent on the expression of the reovirus entry receptor, Junctional Adhesion Molecule-A (JAM-A). Moreover, human GI cancer organoid-fibroblast co-cultures showed higher overall infectivity when containing JAM-A expressing fibroblasts as compared to JAM-A negative fibroblasts, indicating a potential role of JAM-A expressing fibroblasts for viral dissemination. We further show that JAM-A is not only necessary for efficient reovirus infection of fibroblasts but also partially mediates reovirus-induced apoptosis, dependent on signaling through the C-terminal PDZ-domain of JAM-A. Altogether, our data show the presence of JAM-A expressing fibroblasts in both human and murine GI cancers that are amenable to infection and induction of apoptosis by reovirus, extending the potential anti-cancer actions of reovirus with stromal targeting.

The roles of cellular protease interactions in viral infections and programmed cell death: a lesson learned from the SARS-CoV-2 outbreak and COVID-19 pandemic

The unprecedented pandemic of SARS-CoV-2 (severe acute respiratory syndrome coronavirus 2), which leads to COVID-19, is threatening global health. Over the last 2 years, we have witnessed rapid progress in research focusing on developing new antiviral vaccines and drugs, as well as in academic and clinical efforts to understand the biology and pathology of COVID-19. The roles of proteases among master regulators of SARS-CoV-2 invasion and replication and their pivotal roles in host defence against this pathogen, including programmed cell death, have not been well established. Our understanding of protease function in health and disease has increased considerably over the last two decades, with caspases, matrix metalloproteases, and transmembrane serine proteases representing the most prominent examples. Therefore, during the COVID-19 pandemic, these enzymes have been investigated as potential molecular targets for therapeutic interventions. Proteases that are responsible for SARS-CoV-2 cell entry and replication, such as TMPRSS2, ACE2 or cathepsins, are screened with inhibitor libraries to discover lead structures for further drug design that would prevent virus multiplication. On the other hand, proteases that orchestrate programmed cell death can also be harnessed to enhance the desired demise of infected cells through apoptosis or to attenuate highly inflammatory lytic cell death that leads to undesired cytokine storms, a major hallmark of severe COVID-19. Given the prominent role of proteases in SARS-CoV-2-induced cell death, we discuss the individual roles of these enzymes and their catalytic interactions in the pathology of COVID-19 in this article. We provide a rationale for targeting proteases participating in cell death as potential COVID-19 treatments and identify knowledge gaps that might be investigated to better understand the mechanism underlying SARS-CoV-2-induced cell death.