Hepatoviruses promote very-long-chain fatty acid and sphingolipid synthesis for viral RNA replication and quasi-enveloped virus release

PINLYP-mediated phospholipid metabolism reprogramming contributes to chronic herpesvirus infection

Many viruses alter the phospholipid metabolism to benefit their own life cycles. It is unclear whether the host or the virus is driving phospholipid metabolism reprogramming, and how virus infections are affected by the metabolic status. Here we report that phospholipase A2 inhibitor and LY6/PLAUR domain-containing protein (PINLYP) inhibits Kaposi's sarcoma-associated herpesvirus (KSHV) lytic reactivation by remodeling phospholipid metabolism and especially triacylglycerol (TAG) biosynthesis. PINLYP deficiency led to increased phospholipase cPLA2α activity, cPLA2α-mediated AKT phosphorylation, and KSHV lytic reactivation. Analyses of RNA-seq and lipidomics reveal that PINLYP regulates long-chain fatty acid CoA ligase ACSL5 expression and TAG production. The inhibition of ACSL5 activity or TAG biosynthesis suppresses AKT phosphorylation and KSHV lytic reactivation, restoring the phenotype of PINLYP deficiency. This finding underscores the pivotal role of PINLYP in remodeling phospholipid metabolism and promoting viral latency, which sheds new light on how phospholipid metabolism is regulated by herpesvirus and provides a potential target for controlling chronic herpesvirus infection.

Human Cytomegalovirus Infection Reduces an Endogenous Antiviral Fatty Acid by Promoting Host Metabolism

Some viruses, including human cytomegalovirus (HCMV), induce the synthesis of fatty acids and lipids to ensure that the lipid environment of infected cells supports virus replication. HCMV infection broadly reprograms metabolism to ensure central carbon metabolism provides the metabolites required for anabolic synthesis of nucleotides, proteins, and lipids while also meeting the energy demands placed on the infected cells. While HCMV infection increases the levels of most very long chain fatty acids (VLCFA), we found that the levels of erucic acid (EA), a C22:1 monounsaturated VLCFA, are reduced. Treating infected cells with EA disrupted a late step in virus replication, resulting in the release of virions with reduced infectivity. Moreover, we used lipidomics to determine that EA-treated cells had elevated levels of lipids containing a combination of a C22:1 tail and a VLC polyunsaturated fatty acid tail (VLC-PUFA). We demonstrate that fatty acid elongase 5 (ELOVL5) mediated production of VLC-PUFAs is stimulated by HCMV infection. ELOVL5 aided the increase in lipids with C22:1 plus VLC-PUFA tails following EA treatment and reduced the overall level of C22:1 in HCMV-infected cells. Moreover, we found that ELOVL5 mollified EA inhibition of HCMV replication, suggesting ELOVL5 plays a critical role in reducing the level of an endogenous FA with antiviral properties. Our study provides insight into how infection may increase the synthesis of an antiviral metabolite or FA and how the virus may evade their antiviral effect by promoting their metabolism.

Dengue virus is particularly sensitive to interference with long-chain fatty acid elongation and desaturation

Orthoflaviviruses are emerging arthropod-borne pathogens whose replication cycle is tightly linked to host lipid metabolism. Previous lipidomic studies demonstrated that infection with the closely related hepatitis C virus (HCV) changes the fatty acid (FA) profile of several lipid classes. Lipids in HCV-infected cells had more very long-chain and desaturated FAs and viral replication relied on functional FA elongation and desaturation. Here, we systematically analyzed the role of FA elongases and desaturases in infection models of the most prevalent pathogenic orthoflaviviruses, dengue (DENV), Zika (ZIKV), West Nile (WNV), yellow fever (YFV), and tick-borne encephalitis virus (TBEV). Knockdown of desaturases and elongases in Huh7 cells only marginally affected ZIKV, WNV, YFV, and TBEV replication, while DENV titers were strongly reduced. This was most prominent for enzymes involved in very long-chain fatty acid synthesis. In detail, knockdown of the FA elongase ELOVL4, which catalyzes ultra-long-chain FA synthesis, significantly reduced DENV titers, decreased the formation of replication intermediates, and lowered viral protein levels in DENV-infected hepatoma cells, suggesting a function of ELOVL4 in DENV RNA replication. In contrast, the activity of FA desaturase FADS2, rate-limiting in poly-unsaturated FA biosynthesis, is not involved in viral RNA replication or translation, but is essentially required for the formation of infectious DENV particles. Further, in immunocompetent immortalized microglial cells, FADS2 deletion additionally limits viral replication through increased expression of interferon-stimulated genes in response to DENV infection. Taken together, enzymes involved in very long-chain FA synthesis are critical for different steps of DENV replication.

Inhibiting UGCG prevents PRV infection by decreasing lysosome-associated autophage

Glucosylceramide synthase (UGCG) is a key enzyme that catalyzes the initial glycosylation step in the biosynthesis of glycosphingolipids (GSLs) derived from glucosylceramide. UGCG is closely associated with various cellular processes, including the cell cycle, angiogenesis, multidrug resistance, and pathogen invasion. In this study, a short hairpin RNA (shRNA) library designed to target key genes involved in the sphingolipid metabolic pathway was utilized to elucidate their roles in Pseudorabies Virus (PRV). Those findings confirm a significant association between sphingolipid metabolism and PRV infection. In addition, this study demonstrated that the knockdown UGCG expression or inhibition of its activity significantly suppresses PRV infection. This suppression is accompanied by reduced expression of autophagy-related proteins that are induced by PRV infection, blockade of autophagic flux, and significant activation of the STING signaling pathway induced by PRV infection. Through extensive investigation, this research revealed that inhibition of UGCG affects the expression of lysosome-associated proteins, alters the lysosomal pH, disrupts lysosomal homeostasis, and impedes autophagolysosomal degradation. Additionally, UGCG inhibition influences the conversion of light chain 3-II (LC3-II) and the formation of LC3-STING complexes, negatively regulates the autophagic degradation of STING, and ensures sustained activation of the PRV-induced STING signaling pathway, thereby achieving resistance against PRV infection. Finally, through in vivo evaluation, this study revealed that UGCG inhibitors, Eliglustat hemitartrate and Ibiglustat, hold promise as potential therapeutics for the treatment of PRV infection. In summary, this study preliminarily elucidates the impact of UGCG on PRV infection and its associated molecular mechanisms, suggesting UGCG could serve as a potential novel target for the prevention and treatment of viral diseases such as PRV.

Drugs Targeting Sirtuin 2 Exhibit Broad-Spectrum Anti-Infective Activity

Direct-acting anti-infective drugs target pathogen-coded gene products and are a highly successful therapeutic paradigm. However, they generally target a single pathogen or family of pathogens, and the targeted organisms can readily evolve resistance. Host-targeted agents can overcome these limitations. One family of host-targeted, anti-infective agents modulate human sirtuin 2 (SIRT2) enzyme activity. SIRT2 is one of seven human sirtuins, a family of NAD+-dependent protein deacylases. It is the only sirtuin that is found predominantly in the cytoplasm. Multiple, structurally distinct SIRT2-targeted, small molecules have been shown to inhibit the replication of both RNA and DNA viruses, as well as intracellular bacterial pathogens, in cell culture and in animal models of disease. Biochemical and X-ray structural studies indicate that most, and probably all, of these compounds act as allosteric modulators. These compounds appear to impact the replication cycles of intracellular pathogens at multiple levels to antagonize their replication and spread. Here, we review SIRT2 modulators reported to exhibit anti-infective activity, exploring their pharmacological action as anti-infectives and identifying questions in need of additional study as this family of anti-infective agents advances to the clinic.

Virus infection and sphingolipid metabolism

Cellular sphingolipids have vital roles in human virus replication and spread as they are exploited by viruses for cell entry, membrane fusion, genome replication, assembly, budding, and propagation. Intracellular sphingolipid biosynthesis triggers conformational changes in viral receptors and facilitates endosomal escape. However, our current understanding of how sphingolipids precisely regulate viral replication is limited, and further research is required to comprehensively understand the relationships between viral replication and endogenous sphingolipid species. Emerging evidence now suggests that targeting and manipulating sphingolipid metabolism enzymes in host cells is a promising strategy to effectively combat viral infections. Additionally, serum sphingolipid species and concentrations could function as potential serum biomarkers to help monitor viral infection status in different patients. In this work, we comprehensively review the literature to clarify how viruses exploit host sphingolipid metabolism to accommodate viral replication and disrupt host innate immune responses. We also provide valuable insights on the development and use of antiviral drugs in this area.

Lipidomics reveals the significance and mechanism of the cellular ceramide metabolism for rotavirus replication

As one of the most important causative agents of severe gastroenteritis in children, piglets, and other young animals, species A rotaviruses have adversely impacted both human health and the global swine industry. Vaccines against rotaviruses (RVs) are insufficiently effective, and no specific treatment is available. To understand the relationships between porcine RV (PoRV) infection and enterocytes in terms of the cellular lipid metabolism, we performed an untargeted liquid chromatography mass spectrometry (LC-MS) lipidomics analysis of PoRV-infected IPEC-J2 cells. Herein, a total of 451 lipids (263 upregulated lipids and 188 downregulated lipids), spanning sphingolipid, glycerolipid, and glycerophospholipids, were significantly altered compared with the mock-infected group. Interestingly, almost all the ceramides among these lipids were upregulated during PoRV infection. LC-MS analysis was used to validated the lipidomics data and demonstrated that PoRV replication increased the levels of long-chain ceramides (C16-ceramide, C18-ceramide, and C24-ceramide) in cells. Furthermore, we found that these long-chain ceramides markedly inhibited PoRV infection and that their antiviral actions were exerted in the replication stage of PoRV infection. Moreover, downregulation of endogenous ceramides with the ceramide metabolic inhibitors enhanced PoRV propagation. Increasing the levels of ceramides by the addition of C6-ceramide strikingly suppressed the replication of diverse RV strains. We further found that the treatment with an apoptotic inhibitor could reverse the antiviral activity of ceramide against PoRV replication, demonstrating that ceramide restricted RV infection by inducing apoptosis. Altogether, this study revealed that ceramides played an antiviral role against RV infection, providing potential approaches for the development of antiviral therapies.IMPORTANCERotaviruses (RVs) are among the most important zoonosis viruses, which mainly infected enterocytes of the intestinal epithelium causing diarrhea in children and the young of many mammalian and avian species. Lipids play an essential role in viral infection. A comprehensive understanding of the interaction between RV and lipid metabolism in the enterocytes will be helpful to control RV infection. Here, we mapped changes in enterocyte lipids following porcine RV (PoRV) infection using an untargeted lipidomics approach. We found that PoRV infection altered the metabolism of various lipid species, especially ceramides (derivatives of the sphingosine). We further demonstrated that PoRV infection increased the accumulation of ceramides and that ceramides exerted antiviral effects on RV replication by inducing apoptosis. Our findings fill a gap in understanding the alterations of lipid metabolism in RV-infected enterocytes and highlight the antiviral effects of ceramides on RV infection, suggesting potential approaches to control RV infection.