Lipid droplets are beneficial for rabies virus replication by facilitating viral budding

The many faces of DGAT1

Acyl-CoA:diacylglycerol acyltransferase 1 (DGAT1) is a multifaced enzyme with a wide spectrum of substrates, from lipids through waxes to retinoids, which makes it an interesting therapeutic target. DGAT1 inhibitors are currently at various stages of preclinical and clinical trials, mostly related to metabolic diseases. Interestingly, in recent years, a growing amount of research has shown the influence of DGAT1 on immune cell metabolism and functions, highlighting its important role during infections and tumorigenesis. In this review, we aim to elucidate the potential immunomodulatory effect of DGAT1 in physiological and pathological conditions.

Neuroinvasive virus utilizes a lipid droplet surface protein, perilipin2, to restrict apoptosis by decreasing Bcl-2 ubiquitination

Lipid droplets (LDs) can interact with other organelles to regulate cell death, and it has also been reported to play an important role in virus replication. However, the interplay among LDs, cell death, and viral replication remains unclear. Neuroinvasive viruses, such as Japanese encephalitis virus (JEV), rabies virus (RABV), and encephalomyocarditis virus (EMCV) still threaten global public health and raise intensive concerns. Here, we reveal that neuroinvasive virus infection enhances cellular triglyceride biosynthesis by upregulating the expression of diacylglycerol O-acyltransferase 2 (DGAT2) to promote LD formation and increase the expression of Perilipin 2 (PLIN2), an LD surface protein, which consequently facilitates neuroinvasive virus replication. Furthermore, PLIN2 could reduce mitochondrial damage and suppress apoptosis by restoring mitochondrial potential and interacting with anti-apoptotic protein Bcl-2, specifically the 136-209 amino acid region, to interrupt the BAX-Cytc-caspase-3 apoptotic pathway by decreasing the K48-linked ubiquitination of Bcl-2 at the 17th lysine. Together, we elucidate that neuroinvasive virus utilizes an LD surface protein to restrict the apoptosis of infected cells, providing a fresh insight into the pathogenesis and antiviral therapeutics development of neuroinvasive viruses.

IMPORTANCE

The neuroinvasive virus is a kind of pathogen that is capable of infiltrating and infecting the central nervous system to potentially induce severe neurological damage and disorders, which pose a significant threat to public health. Here, we found that neuroinvasive viruses can utilize an LD surface protein PLIN2 to facilitate viral replication. Notably, PLIN2 could reduce mitochondrial damage and suppress apoptosis by restoring mitochondrial potential and interacting with anti-apoptotic protein Bcl-2, specifically the 136-209 amino acid region, to interrupt the BAX-Cytc-caspase-3 apoptotic pathway by decreasing the K48-linked ubiquitination of Bcl-2 at the 17th lysine. This study reveals a common strategy for neuroinvasive viruses to avoid apoptosis of infected cells by employing LDs, which extends the important role of LDs in viral pathogenesis and may inspire further research in this field.

Z-Ligustilide restricts rabies virus replication by inducing ferroptosis through the ACSL4-LPCAT3-POR pathway

Rabies, induced by rabies virus (RABV), still threaten global health all over the world, and no effective therapy is available for rabies currently. Recently, a series of natural plant components have been found to inhibit virus production. In this study, Z-Ligustilide, a natural component of Ligusticum chuanxiong Hort, was found to inhibit RABV replication. Initially, the concentration of cytotoxicity 50 % (CC50) of Z-Ligustilide in N2a and BSR cells were 429.9 μM and 335.5 μM, respectively, which both significantly restrict RABV production in a concentration-dependent manner. Moreover, Z-Ligustilide was found to mainly inhibit the replication stage of RABV. Specifically, Z-Ligustilide can suppress lipid droplet (LD) formation via directly inhibiting diacylglycerol acyltransferase 1/2 (DGAT1/2) expression, which can further promote cellular lipid peroxidation, Fe2+ concentration, reactive oxygen species (ROS), and induce ferroptosis ultimately. Furthermore, Z-Ligustilide was demonstrated to increase ferroptosis via Acyl-CoA synthetase long-chain family member 4 (ACSL4)- Lysophosphatidylcholine Acyltransferase 3 (LPCAT3)- Cytochrome P450 Oxidoreductase (POR) pathway. Above all, this study explored the antiviral function of Z-Ligustilide, which provides a novel insight for developing anti-RABV drugs.

Diacylglycerol O-acyltransferase 2, a Novel Target of Flavivirus NS2B3 Protease, Promotes Zika Virus Replication by Regulating Lipid Droplet Formation

Various lipid metabolism-related factors are essential for Zika virus (ZIKV) replication. In this study, we revealed a crucial role of diacylglycerol O-acyltransferase 2 (DGAT2) in ZIKV replication using a short hairpin RNA-based gene knockdown technique. The replication of ZIKV was significantly inhibited by DGAT2 depletion in multiple cell lines and restored by trans-complementation with DGAT2. Mechanistically, DGAT2 is recruited in the viral replication complex by interacting with non-structural (NS) proteins. Among them, both human and murine DGAT2s can be cleaved by NS2B3 at the 122R-R-S124 site. Interestingly, the cleavage product of DGAT2 becomes more stable and is sufficient to promote the lipid droplet (LD) formation independent of its enzymatic activity. This work identifies DGAT2 as a novel target of the viral protease NS2B3 and elucidates that DGAT2 is recruited by viral proteins into the replication complex, thereby playing a proviral role by promoting LD formation, which advances our understanding of host-flavivirus interaction.

ACADM inhibits AMPK activation to modulate PEDV-induced lipophagy and β-oxidation for impairing viral replication

Porcine epidemic diarrhea virus (PEDV) belongs to the Alphacoronavirus genus within the Coronavirus family, causing severe watery diarrhea in piglets and resulting in significant economic losses. Medium-chain acyl-CoA dehydrogenase (ACADM) is an enzyme participating in lipid metabolism associated with metabolic diseases and pathogen infections. Nonetheless, the precise role of ACADM in regulating PEDV replication remains uncertain. In this study, we identified ACADM as the host binding partner of NSP4 via immunoprecipitation-mass spectrometry analysis. The interaction between ACADM and NSP4 was subsequently corroborated through coimmunoprecipitation and laser confocal microscopy. Following this, a notable upsurge in ACADM expression was observed during PEDV infection. ACADM overexpression effectively inhibited virus replication, whereas ACADM knockdown facilitated virus replication, suggesting ACADM has negative regulation effect on PEDV infection. Furthermore, we demonstrated fatty acid β-oxidation affected PEDV replication for the first time, inhibition of fatty acid β-oxidation reduced PEDV replication. ACADM decreased PEDV-induced β-oxidation to suppress PEDV replication. Mechanistically, ACADM reduced cellular free fatty acid levels and subsequent β-oxidation by hindering AMPK-mediated lipophagy. In summary, our results reveal that ACADM plays a negative regulatory role in PEDV replication by regulating lipid metabolism. The present study introduces a novel approach for the prevention and control of PEDV infection.

Lyssavirus matrix protein inhibits NLRP3 inflammasome assembly by binding to NLRP3

Lyssavirus is a kind of neurotropic pathogen that needs to evade peripheral host immunity to enter the central nervous system to accomplish infection. NLRP3 inflammasome activation is essential for the host to defend against pathogen invasion. This study demonstrates that the matrix protein (M) of lyssavirus can inhibit both the priming step and the activation step of NLRP3 inflammasome activation. Specifically, M of lyssavirus can compete with NEK7 for binding to NLRP3, which restricts downstream apoptosis-associated speck-like protein containing a CARD (ASC) oligomerization. The serine amino acid at the 158th site of M among lyssavirus is critical for restricting ASC oligomerization. Moreover, recombinant lab-attenuated lyssavirus rabies (rabies lyssavirus [RABV]) with G158S mutation at M decreases interleukin-1β (IL-1β) production in bone-marrow-derived dendritic cells (BMDCs) to facilitate lyssavirus invasion into the brain thereby elevating pathogenicity in mice. Taken together, this study reveals a common mechanism by which lyssavirus inhibits NLRP3 inflammasome activation to evade host defenses.

Identification of proteins related to SIS3 by iTRAQ and PRM-based comparative proteomic analysis in cisplatin-induced acute kidney injury

Background

Cisplatin is a commonly used nephrotoxic drug and can cause acute kidney injury (AKI). In the present study, isobaric tags for relative and absolute quantification (iTRAQ) and parallel reaction monitoring (PRM)-based comparative proteomics were used to analyze differentially expressed proteins (DEPs) to determine the key molecular mechanism in mice with cisplatin-induced AKI in the presence or absence of SIS3, a specific p-smad3 inhibitor, intervention.

Methods

The cisplatin-induced AKI mouse model was established and treated with SIS3. We used iTRAQ to search for DEPs, PRM to verify key DEPs and combined Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) for bioinformatics analysis. We then assessed lipid deposition, malondialdehyde (MDA) and reactive oxygen species (ROS) and detected the expression of SREBF1, SCD1, CPT1A, PPARα and NDRG1 in vitro.

Results

Proteomic analysis showed that the identified DEPs were mainly enriched in energy metabolism pathways, especially in lipid metabolism. When SIS3 was applied to inhibit the phosphorylation of Smad3, the expression of NDRG1 and fatty acid oxidation key proteins CPT1A and PPARα increased, the expression of lipid synthesis related proteins SREBF1 and SCD1 decreased and the production of lipid droplets, MDA and ROS decreased.

Conclusion

SIS3 alleviates oxidative stress, reduces lipid accumulation and promotes fatty acid oxidation through NDRG1 in cisplatin-induced AKI. Our study provides a new candidate protein for elucidating the molecular mechanisms of fatty acid metabolism disorders in cisplatin-induced acute kidney injury.

Neuroinvasive virus facilitates viral replication by employing lipid droplets to reduce arachidonic acid-induced ferroptosis

Lipids have been previously implicated in the lifecycle of neuroinvasive viruses. However, the role of lipids in programmed cell death and the relationship between programmed cell death and lipid droplets (LDs) in neuroinvasive virus infection remains unclear. Here, we found that the infection of neuroinvasive virus, such as rabies virus and encephalomyocarditis virus could enhance the LD formation in N2a cells, and decreasing LDs production by targeting diacylglycerol acyltransferase could suppress viral replication. The lipidomics analysis revealed that arachidonic acid (AA) was significantly increased after reducing LD formation by restricting diacylglycerol acyltransferase, and AA was further demonstrated to induce ferroptosis to inhibit neuroinvasive virus replication. Moreover, lipid peroxidation and viral replication inhibition could be significantly alleviated by a ferroptosis inhibitor, ferrostatin-1, indicating that AA affected neuroinvasive virus replication mainly through inducing ferroptosis. Furthermore, AA was demonstrated to activate the acyl-CoA synthetase long-chain family member 4-lysophosphatidylcholine acyltransferase 3-cytochrome P450 oxidoreductase axis to induce ferroptosis. Our findings highlight novel cross-talks among viral infection, LDs, and ferroptosis for the first time, providing a potential target for antiviral drug development.

Lipid Droplets: Formation, Degradation, and Their Role in Cellular Responses to Flavivirus Infections

Lipid droplets (LDs) are cellular organelles derived from the endoplasmic reticulum (ER), serving as lipid storage sites crucial for maintaining cellular lipid homeostasis. Recent attention has been drawn to their roles in viral replication and their interactions with viruses. However, the precise biological functions of LDs in viral replication and pathogenesis remain incompletely understood. To elucidate the interaction between LDs and viruses, it is imperative to comprehend the biogenesis of LDs and their dynamic interactions with other organelles. In this review, we explore the intricate pathways involved in LD biogenies within the cytoplasm, encompassing the uptake of fatty acid from nutrients facilitated by CD36-mediated membranous protein (FABP/FATP)-FA complexes, and FA synthesis via glycolysis in the cytoplasm and the TCL cycle in mitochondria. While LD biogenesis primarily occurs in the ER, matured LDs are intricately linked to multiple organelles. Viral infections can lead to diverse consequences in terms of LD status within cells post-infection, potentially involving the breakdown of LDs through the activation of lipophagy. However, the exact mechanisms underlying LD destruction or accumulation by viruses remain elusive. The significance of LDs in viral replication renders them effective targets for developing broad-spectrum antivirals. Moreover, considering that reducing neutral lipids in LDs is a strategy for anti-obesity treatment, LD depletion may not pose harm to cells. This presents LDs as promising antiviral targets for developing therapeutics that are minimally or non-toxic to the host.

A Dual Pharmacological Strategy against COVID-19: The Therapeutic Potential of Metformin and Atorvastatin

Metformin (MET) and atorvastatin (ATO) are promising treatments for COVID-19. This review explores the potential of MET and ATO, commonly prescribed for diabetes and dyslipidemia, respectively, as versatile medicines against SARS-CoV-2. Due to their immunomodulatory and antiviral capabilities, as well as their cost-effectiveness and ubiquitous availability, they are highly suitable options for treating the virus. MET's effect extends beyond managing blood sugar, impacting pathways that can potentially decrease the severity and fatality rates linked with COVID-19. It can partially block mitochondrial complex I and stimulate AMPK, which indicates that it can be used more widely in managing viral infections. ATO, however, impacts cholesterol metabolism, a crucial element of the viral replicative cycle, and demonstrates anti-inflammatory characteristics that could modulate intense immune reactions in individuals with COVID-19. Retrospective investigations and clinical trials show decreased hospitalizations, severity, and mortality rates in patients receiving these medications. Nevertheless, the journey from observing something to applying it in a therapeutic setting is intricate, and the inherent diversity of the data necessitates carefully executed, forward-looking clinical trials. This review highlights the requirement for efficacious, easily obtainable, and secure COVID-19 therapeutics and identifies MET and ATO as promising treatments in this worldwide health emergency.

Defensive-lipid droplets: Cellular organelles designed for antimicrobial immunity

Microbes have developed many strategies to subvert host organisms, which, in turn, evolved several innate immune responses. As major lipid storage organelles of eukaryotes, lipid droplets (LDs) are an attractive source of nutrients for invaders. Intracellular viruses, bacteria, and protozoan parasites induce and physically interact with LDs, and the current view is that they "hijack" LDs to draw on substrates for host colonization. This dogma has been challenged by the recent demonstration that LDs are endowed with a protein-mediated antibiotic activity, which is upregulated in response to danger signals and sepsis. Dependence on host nutrients could be a generic "Achilles' heel" of intracellular pathogens and LDs a suitable chokepoint harnessed by innate immunity to organize a front-line defense. Here, we will provide a brief overview of the state of the conflict and discuss potential mechanisms driving the formation of the 'defensive-LDs' functioning as hubs of innate immunity.

Porcine reproductive and respiratory syndrome virus regulates lipid droplet accumulation in lipid metabolic pathways to promote viral replication

Porcine reproductive and respiratory syndrome (PRRS) is a severe respiratory disease caused by porcine reproductive and respiratory syndrome virus (PRRSV) that can lead to the abortion of pregnant sows and decreased boar semen quality. However, the mechanisms of PRRSV replication in the host have not yet been fully elucidated. As lipid metabolism and lipid droplets (LDs) have been reported to play important roles in the replication of various viruses, we aimed to explore the mechanisms through which LDs affect PRRSV replication. Laser confocal and transmission electron microscopy revealed that PRRSV infection promoted intracellular LD accumulation, which was significantly reduced by treatment with the NF-κB signaling pathway inhibitors BAY11-7082 and metformin hydrochloride (MH). In addition, treatment with a DGAT1 inhibitor significantly reduced the protein expression of Phosphorylated NF-ΚB P65and PIκB and the transcription of IL-1β and IL-8 in the NF-κB signaling pathway. Furthermore, we showed that the reduction of the NF-κB signaling pathway and LDs significantly reduced PRRSV replication. Together, the findings of this study suggest a novel mechanism through which PRRSV regulates the NF-κB signaling pathway to increase LD accumulation and promote viral replication. Moreover, we demonstrated that both BAY11-7082 and MH can reduce PRRSV replication by reducing the NF-κB signaling pathway and LD accumulation. This study lays a theoretical foundation for research on the mechanism of PRRS prevention and control, as well as the research and development of antiviral drugs.

Multifaceted Nature of Lipid Droplets in Viral Interactions and Pathogenesis

Once regarded as inert organelles with limited and ill-defined roles, lipid droplets (LDs) have emerged as dynamic entities with multifaceted functions within the cell. Recent research has illuminated their pivotal role as primary energy reservoirs in the form of lipids, capable of being metabolized to meet cellular energy demands. Their high dynamism is underscored by their ability to interact with numerous cellular organelles, notably the endoplasmic reticulum (the site of LD genesis) and mitochondria, which utilize small LDs for energy production. Beyond their contribution to cellular bioenergetics, LDs have been associated with viral infections. Evidence suggests that viruses can co-opt LDs to facilitate their infection cycle. Furthermore, recent discoveries highlight the role of LDs in modulating the host's immune response. Observations of altered LD levels during viral infections suggest their involvement in disease pathophysiology, potentially through production of proinflammatory mediators using LD lipids as precursors. This review explores these intriguing aspects of LDs, shedding light on their multifaceted nature and implications in viral interactions and disease development.

The interplay between lipid droplets and virus infection

As an intracellular parasite, the virus usurps cellular machinery and modulates cellular metabolism pathways to replicate itself in cells. Lipid droplets (LDs) are universally conserved energy storage organelles that not only play vital roles in maintaining lipid homeostasis but are also involved in viral replication. Increasing evidence has demonstrated that viruses take advantage of cellular lipid metabolism by targeting the biogenesis, hydrolysis, and lipophagy of LD during viral infection. In this review, we summarize the current knowledge about the modulation of cellular LD by different viruses, with a special emphasis on the Hepatitis C virus, Dengue virus, and SARS-CoV-2.

Plasma-Like Culture Medium for the Study of Viruses

Viral infections attract more and more attention, especially after the emergence of novel zoonotic coronaviruses and the monkeypox virus over the last 2 decades. Research on viruses is based to a great extent on mammalian cell lines that are permissive to the respective viruses. These cell lines are usually cultivated according to the protocols established in the 1950s to 1970s, although it is clear that classical media have a significant imprint on cell growth, phenotype, and especially metabolism. So, recently in the field of biochemistry and metabolomics novel culture media have been developed that resemble human blood plasma. As perturbations in metabolic and redox pathways during infection are considered significant factors of viral pathogenesis, these novel medium formulations should be adapted by the virology field. So far, there are only scarce data available on viral propagation efficiencies in cells cultivated in plasma-like media. But several groups have presented convincing data on the use of such media for cultivation of uninfected cells. The aim of the present review is to summarize the current state of research in the field of plasma-resembling culture media and to point out the influence of media on various cellular processes in uninfected cells that may play important roles in viral replication and pathogenesis in order to sensitize virology research to the use of such media.

Host Desmin Interacts with RABV Matrix Protein and Facilitates Virus Propagation

Microfilaments and microtubules, two crucial structures of cytoskeletal networks, are usurped by various viruses for their entry, egress, and/or intracellular trafficking, including the Rabies virus (RABV). Intermediate filaments (IFs) are the third major component of cytoskeletal filaments; however, little is known about the role of IFs during the RABV infection. Here, we identified the IF protein desmin as a novel host interactor with the RABV matrix protein, and we show that this physical interaction has a functional impact on the virus lifecycle. We found that the overexpression of desmin facilitates the RABV infection by increasing the progeny virus yield, and the suppression of endogenous desmin inhibits virus replication. Furthermore, we used confocal microscopy to observe that the RABV-M co-localizes with desmin in IF bundles in the BHK-21 cells. Lastly, we found that mice challenged with RABV displayed an enhanced expression of desmin in the brains of infected animals. These findings reveal a desmin/RABV-M interaction that positively regulates the virus infection and suggests that the RABV may utilize cellular IFs as tracks for the intracellular transport of viral components and efficient budding.

Grass Carp Reovirus Induces Formation of Lipid Droplets as Sites for Its Replication and Assembly

Grass carp is an important commercial fish in China that is plagued by various diseases, especially the hemorrhagic disease induced by grass carp reovirus (GCRV). Nevertheless, the mechanism by which GCRV hijacks the host metabolism to complete its life cycle is unclear. In this study, we performed lipidomic analysis of grass carp liver samples collected before and after GCRV infection. GCRV infection altered host lipid metabolism and increased de novo fatty acid synthesis. Increased de novo fatty acid synthesis induced accumulation of lipid droplets (LDs). LDs are associated with GCRV viroplasms, as well as viral proteins and double-stranded RNA. Pharmacological inhibition of LD formation led to the disappearance of viroplasms, accompanied by decreased viral replication capacity. Moreover, transmission electron microscopy revealed LDs in close association with the viroplasms and mounted GCRV particles. Collectively, these data suggest that LDs are essential for viroplasm formation and are sites for GCRV replication and assembly. Our results revealed the detailed molecular events of GCRV hijacking host lipid metabolism to benefit its replication and assembly, which may provide new perspective for the prevention and control of GCRV. IMPORTANCE Grass carp reovirus (GCRV) is the most virulent pathogen in the genus Aquareovirus, which belongs to the family Reoviridae. GCRV-induced hemorrhagic disease is a major threat to the grass carp aquaculture industry. Viruses are obligate intracellular parasites that require host cell machinery to complete their life cycle; the mechanism by which GCRV hijacks the host metabolism to benefit viral replication and assembly remains unclear. Our study demonstrated that GCRV infection alters host lipid metabolism and increases de novo fatty acid synthesis. The increased de novo fatty acid synthesis induced accumulation of LDs, which act as sites or scaffolds for GCRV replication and assembly. Our findings illustrate a typical example of how the virus hijacks cellular organelles for replication and assembly and hence may provide new insights for the prevention and control of GCRV.

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.