Mitochondrial electron transport chain complex III sustains hepatitis E virus replication and represents an antiviral target

Mitochondrial Oxidative Phosphorylation in Viral Infections

Mitochondria have been identified as the "powerhouse" of the cell, generating the cellular energy, ATP, for almost seven decades. Research over time has uncovered a multifaceted role of the mitochondrion in processes such as cellular stress signaling, generating precursor molecules, immune response, and apoptosis to name a few. Dysfunctional mitochondria resulting from a departure in homeostasis results in cellular degeneration. Viruses hijack host cell machinery to facilitate their own replication in the absence of a bonafide replication machinery. Replication being an energy intensive process necessitates regulation of the host cell oxidative phosphorylation occurring at the electron transport chain in the mitochondria to generate energy. Mitochondria, therefore, can be an attractive therapeutic target by limiting energy for viral replication. In this review we focus on the physiology of oxidative phosphorylation and on the limited studies highlighting the regulatory effects viruses induce on the electron transport chain.

Host mitochondria: more than an organelle in SARS-CoV-2 infection

Since December 2019, the world has been facing viral pandemic called COVID-19 (Coronavirus disease 2019) caused by a new beta-coronavirus named severe acute respiratory syndrome coronavirus-2, or SARS-CoV-2. COVID-19 patients may present with a wide range of symptoms, from asymptomatic to requiring intensive care support. The severe form of COVID-19 is often marked by an altered immune response and cytokine storm. Advanced age, age-related and underlying diseases, including metabolic syndromes, appear to contribute to increased COVID-19 severity and mortality suggesting a role for mitochondria in disease pathogenesis. Furthermore, since the immune system is associated with mitochondria and its damage-related molecular patterns (mtDAMPs), the host mitochondrial system may play an important role during viral infections. Viruses have evolved to modulate the immune system and mitochondrial function for survival and proliferation, which in turn could lead to cellular stress and contribute to disease progression. Recent studies have focused on the possible roles of mitochondria in SARS-CoV-2 infection. It has been suggested that mitochondrial hijacking by SARS-CoV-2 could be a key factor in COVID-19 pathogenesis. In this review, we discuss the roles of mitochondria in viral infections including SARS-CoV-2 infection based on past and present knowledge. Paying attention to the role of mitochondria in SARS-CoV-2 infection will help to better understand the pathophysiology of COVID-19 and to achieve effective methods of prevention, diagnosis, and treatment.

The Warburg effect modulates DHODH role in ferroptosis: a review

Ferroptosis is an iron-dependent regulated cell death that suppresses tumor growth. It is activated by extensive peroxidation of membrane phospholipids caused by oxidative stress. GPX4, an antioxidant enzyme, reduces these peroxidized membrane phospholipids thereby inhibiting ferroptosis. This enzyme has two distinct subcellular localization; the cytosol and mitochondria. Dihydroorotate dehydrogenase (DHODH) complements mitochondrial GPX4 in reducing peroxidized membrane phospholipids. It is the rate-limiting enzyme in de novo pyrimidine nucleotide biosynthesis. Its role in ferroptosis inhibition suggests that DHODH inhibitors could have two complementary mechanisms of action against tumors; inhibiting de novo pyrimidine nucleotide biosynthesis and enhancing ferroptosis. However, the link between mitochondrial function and ferroptosis, and the involvement of DHODH in the ETC suggests that its role in ferroptosis could be modulated by the Warburg effect. Therefore, we reviewed relevant literature to get an insight into the possible effect of this metabolic reprogramming on the role of DHODH in ferroptosis. Furthermore, an emerging link between DHODH and cellular GSH pool has also been highlighted. These insights could contribute to the rational design of ferroptosis-based anticancer drugs. Video Abstract.

Possible Pathogenesis and Prevention of Long COVID: SARS-CoV-2-Induced Mitochondrial Disorder

Patients who have recovered from coronavirus disease 2019 (COVID-19) infection may experience chronic fatigue when exercising, despite no obvious heart or lung abnormalities. The present lack of effective treatments makes managing long COVID a major challenge. One of the underlying mechanisms of long COVID may be mitochondrial dysfunction. Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infections can alter the mitochondria responsible for energy production in cells. This alteration leads to mitochondrial dysfunction which, in turn, increases oxidative stress. Ultimately, this results in a loss of mitochondrial integrity and cell death. Moreover, viral proteins can bind to mitochondrial complexes, disrupting mitochondrial function and causing the immune cells to over-react. This over-reaction leads to inflammation and potentially long COVID symptoms. It is important to note that the roles of mitochondrial damage and inflammatory responses caused by SARS-CoV-2 in the development of long COVID are still being elucidated. Targeting mitochondrial function may provide promising new clinical approaches for long-COVID patients; however, further studies are needed to evaluate the safety and efficacy of such approaches.

Intrinsic disorder in the open reading frame 2 of hepatitis E virus: a protein with multiple functions beyond viral capsid

BACKGROUND

Hepatitis E virus (HEV) is the cause of a liver disease hepatitis E. The translation product of HEV ORF2 has recently been demonstrated as a protein involved in multiple functions besides performing its major role of a viral capsid. As intrinsically disordered regions (IDRs) are linked to various essential roles in the virus's life cycle, we analyzed the disorder pattern distribution of the retrieved ORF2 protein sequences by employing different online predictors. Our findings might provide some clues on the disorder-based functions of ORF2 protein that possibly help us in understanding its behavior other than as a HEV capsid protein.

RESULTS

The modeled three dimensional (3D) structures of ORF2 showed the predominance of random coils or unstructured regions in addition to major secondary structure components (alpha helix and beta strand). After initial scrutinization, the predictors VLXT and VSL2 predicted ORF2 as a highly disordered protein while the predictors VL3 and DISOPRED3 predicted ORF2 as a moderately disordered protein, thus categorizing HEV-ORF2 into IDP (intrinsically disordered protein) or IDPR (intrinsically disordered protein region) respectively. Thus, our initial predicted disorderness in ORF2 protein 3D structures was in excellent agreement with their predicted disorder distribution patterns (evaluated through different predictors). The abundance of MoRFs (disorder-based protein binding sites) in ORF2 was observed that signified their interaction with binding partners which might further assist in viral infection. As IDPs/IDPRs are targets of regulation, we carried out the phosphorylation analysis to reveal the presence of post-translationally modified sites. Prevalence of several disordered-based phosphorylation sites further signified the involvement of ORF2 in diverse and significant biological processes. Furthermore, ORF2 structure-associated functions revealed its involvement in several crucial functions and biological processes like binding and catalytic activities.

CONCLUSIONS

The results predicted ORF2 as a protein with multiple functions besides its role as a capsid protein. Moreover, the occurrence of IDPR/IDP in ORF2 protein suggests that its disordered region might serve as novel drug targets via functioning as potential interacting domains. Our data collectively might provide significant implication in HEV vaccine search as disorderness in viral proteins is related to mechanisms involved in immune evasion.

The Role and Mechanism of Action of Mitophagy in Various Liver Diseases

Significance: Liver disease is one of the biggest threats to public health, affecting as much as 5.5 million people worldwide. Mitochondrial dysfunction is associated with various acute and chronic liver diseases. Mitophagy, a selective form of autophagy for damaged/excessive mitochondria, plays a key role either in the pathogenesis or in maintaining hepatic homeostasis in response to various liver diseases. Recent Advances: Significant progress has been achieved to ascertain the causes of liver disease. The conserved pathways for mitochondrial degradation via mitophagy, the deregulation of mitophagy in liver diseases, and pharmacological or genetic maneuvers that alter the mitophagic flux for liver disease treatment have been widely studied but yet to be comprehensively reviewed. Critical Issues: Liver disease is considered a leading cause of mortality globally, causing the heavy burden of disability and the increased health care utilization that needs to be settled urgently. Mitophagy plays an important role in protecting liver from tissue damage to maintain hepatic homeostasis or in pathogenesis of liver disease. Elaborating mitophagy implicated in the pathogenesis of liver disease, as well as potential therapeutic regimens by targeting mitophagy is of great significance for the understanding and treatment of liver disease. Future Directions: This review comprehensively describes the distinct mitophagy signaling pathways and their interplay with various liver diseases. Given that mitophagy affects a wide array of physiological processes, a deeper understanding of how to modulate mitophagy could provide innovative avenues for precise therapy. Future studies based on pharmacologically or genetically targeting mitophagy-relevant factors will uncover the links between intact mitophagic responses and hepatic homeostasis in physiological and pathological settings. This will allow us to overcome obstacles of applying mitophagy as the therapeutic target in the clinic. Antioxid. Redox Signal. 38, 529-549.

Proteomic Characterization of PAMs with PRRSV-ADE Infection

The antibody-dependent enhancement (ADE) effect of a PRRSV infection is that the preexisting sub- or non-neutralizing antibodies specific against PRRSV can facilitate the virus entry and replication, and it is likely to be a great obstacle for the selection of immune strategies and the development of high-efficiency PRRSV vaccines. However, the proteomic characterization of primary alveolar macrophages (PAMs) with a PRRSV-ADE infection has not yet been investigated so far. Therefore, we performed a tandem mass tag (TMT)-based quantitative proteomic analysis of PAMs with a PRRSV-ADE infection in this study. The results showed that a total of 3935 differentially expressed proteins (DEPs) were identified in the PAMs infected with PRRSV-ADE, including 2004 up-regulated proteins and 1931 down-regulated proteins. Further, the bioinformatics analysis for these DEPs revealed that a PRRSV-ADE infection might disturb the functions of ribosome, proteasome and mitochondria. Interestingly, we also found that the expression of the key molecules in the innate immune pathways and antiviral proteins were significantly down-regulated during a PRRSV-ADE infection. This study was the first attempt to analyze the proteomic characterization of PAMs with a PRRSV-ADE infection in vitro. Additionally, the findings will provide valuable information for a better understanding of the mechanism of virus-antibody-host interactions during a PRRSV-ADE infection.

Identification of two novel neutralizing nanobodies against swine hepatitis E virus

Hepatitis E virus (HEV) is thought to be a zoonotic pathogen that causes serious economic loss and threatens human health. However, there is a lack of efficient antiviral strategies. As a more promising tool for antiviral therapy, nanobodies (also named single-domain antibodies, sdAbs) exhibit higher specificity and affinity than traditional antibodies. In this study, nanobody anti-genotype four HEV open reading frame 2 (ORF2) was screened using phage display technology, and two nanobodies (nb14 and nb53) with high affinity were prokaryotically expressed. They were identified to block HEV ORF2 virus like particle (VLP) sp239 (aa 368-606) absorbing HepG2 cells in vitro. With the previously built animal model, the detection indicators of fecal shedding, viremia, seroconversion, alanine aminotransferase (ALT) levels, and liver lesions showed that nb14 could completely protect rabbits from swine HEV infection, and nb53 partially blocked swine HEV infection in rabbits. Collectively, these results revealed that nb14, with its anti-HEV neutralizing activity, may be developed as an antiviral drug for HEV.

Targeting the complex I and III of mitochondrial electron transport chain as a potentially viable option in liver cancer management

Liver cancer is one of the most common and lethal types of oncological disease in the world, with limited treatment options. New treatment modalities are desperately needed, but their development is hampered by a lack of insight into the underlying molecular mechanisms of disease. It is clear that metabolic reprogramming in mitochondrial function is intimately linked to the liver cancer process, prompting the possibility to explore mitochondrial biochemistry as a potential therapeutic target. Here we report that depletion of mitochondrial DNA, pharmacologic inhibition of mitochondrial electron transport chain (mETC) complex I/complex III, or genetic of mETC complex I restricts cancer cell growth and clonogenicity in various preclinical models of liver cancer, including cell lines, mouse liver organoids, and murine xenografts. The restriction is linked to the production of reactive oxygen species, apoptosis induction and reduced ATP generation. As a result, our findings suggest that the mETC compartment of mitochondria could be a potential therapeutic target in liver cancer.

Role of "dual-personality" fragments in HEV adaptation-analysis of Y-domain region

BACKGROUND

Hepatitis E is a liver disease caused by the pathogen hepatitis E virus (HEV). The largest polyprotein open reading frame 1 (ORF1) contains a nonstructural Y-domain region (YDR) whose activity in HEV adaptation remains uncharted. The specific role of disordered regions in several nonstructural proteins has been demonstrated to participate in the multiplication and multiple regulatory functions of the viruses. Thus, intrinsic disorder of YDR including its structural and functional annotation was comprehensively studied by exploiting computational methodologies to delineate its role in viral adaptation.

RESULTS

Based on our findings, it was evident that YDR contains significantly higher levels of ordered regions with less prevalence of disordered residues. Sequence-based analysis of YDR revealed it as a "dual personality" (DP) protein due to the presence of both structured and unstructured (intrinsically disordered) regions. The evolution of YDR was shaped by pressures that lead towards predominance of both disordered and regularly folded amino acids (Ala, Arg, Gly, Ile, Leu, Phe, Pro, Ser, Tyr, Val). Additionally, the predominance of characteristic DP residues (Thr, Arg, Gly, and Pro) further showed the order as well as disorder characteristic possessed by YDR. The intrinsic disorder propensity analysis of YDR revealed it as a moderately disordered protein. All the YDR sequences consisted of molecular recognition features (MoRFs), i.e., intrinsic disorder-based protein-protein interaction (PPI) sites, in addition to several nucleotide-binding sites. Thus, the presence of molecular recognition (PPI, RNA binding, and DNA binding) signifies the YDR's interaction with specific partners, host membranes leading to further viral infection. The presence of various disordered-based phosphorylation sites further signifies the role of YDR in various biological processes. Furthermore, functional annotation of YDR revealed it as a multifunctional-associated protein, due to its susceptibility in binding to a wide range of ligands and involvement in various catalytic activities.

CONCLUSIONS

As DP are targets for regulation, thus, YDR contributes to cellular signaling processes through PPIs. As YDR is incompletely understood, therefore, our data on disorder-based function could help in better understanding its associated functions. Collectively, our novel data from this comprehensive investigation is the first attempt to delineate YDR role in the regulation and pathogenesis of HEV.

Cellular Organelles Involved in Hepatitis E Virus Infection

Hepatitis E virus (HEV), a major cause of acute hepatitis worldwide, infects approximately 20 million individuals annually. HEV can infect a wide range of mammalian and avian species, and cause frequent zoonotic spillover, increasingly raising public health concerns. To establish a successful infection, HEV needs to usurp host machineries to accomplish its life cycle from initial attachment to egress. However, relatively little is known about the HEV life cycle, especially the functional role(s) of cellular organelles and their associated proteins at different stages of HEV infection. Here, we summarize current knowledge regarding the relation of HEV with the different cell organelles during HEV infection. Furthermore, we discuss the underlying mechanisms by which HEV infection is precisely regulated in infected cells and the modification of host cell organelles and their associated proteins upon HEV infection.

Mitochondrial changes associated with viral infectious diseases in the paediatric population

Infectious diseases occur worldwide with great frequency in both adults and children, causing 350,000 deaths in 2017, according to the latest World Health Organization reports. Both infections and their treatments trigger mitochondrial interactions at multiple levels: (i) incorporation of damaged or mutated proteins into the complexes of the electron transport chain; (ii) impact on mitochondrial genome (depletion, deletions and point mutations) and mitochondrial dynamics (fusion and fission); (iii) membrane potential impairment; (iv) apoptotic regulation; and (v) generation of reactive oxygen species, among others. Such alterations may result in serious adverse clinical events with considerable impact on the quality of life of the children and could even cause death. Herein, we use a systematic review to explore the association between mitochondrial alterations in paediatric infections including human immunodeficiency virus, cytomegalovirus, herpes viruses, various forms of hepatitis, adenovirus, T-cell lymphotropic virus and influenza. We analyse how these paediatric viral infectious processes may cause mitochondrial deterioration in this especially vulnerable population, with consideration for the principal aspects of research and diagnosis leading to improved disease understanding, management and surveillance.

The host cellular protein Ndufaf4 interacts with the vesicular stomatitis virus M protein and affects viral propagation

Vesicular stomatitis virus (VSV) is an archetypal member of Mononegavirales which causes important diseases in cattle, horses and pigs. The matrix protein (M) of VSV plays critical roles in the replication, assembly/budding and pathogenesis of VSV. To further investigate the role of M during viral growth, we used a two-hybrid system to screen for host factors that interact with the M protein. Here, NADH: ubiquinone oxidoreductase complex assembly factor 4 (Ndufaf4) was identified as an M-binding partner, and this interaction was confirmed by yeast cotransformation and GST pulldown assays. The globular domain of M was mapped and shown to be critical for the M-Ndufaf4 interaction. Two double mutations (E156A/H157A, D180A/E181A) in M impaired the M-Ndufaf4 interaction. Overexpression of Ndufaf4 inhibited VSV propagation, and knockdown of Ndufaf4 by short hairpin RNA (shRNA) markedly promoted VSV replication. Finally, we also demonstrate that the anti-VSV effect of Ndufaf4 is independent of activation of the type I IFN response. These results indicated that Ndufaf4 might exploit other mechanisms to affect VSV replication. In summary, we identify Ndufaf4 as a potential target for the inhibition of VSV propagation. These results provided further insight into the study of VSV pathogenesis.

Ginsenoside Rh2 inhibits HeLa cell energy metabolism and induces apoptosis by upregulating voltage‑dependent anion channel 1

20(S)‑Ginsenoside Rh2 [20(S)‑GRh2], one of the main active components of Panax ginseng, induces apoptosis in a wide range of cancer cell types. The present study found that 20(S)‑GRh2 reduces mitochondrial membrane potential, decreases adenosine triphosphate generation and induces reactive oxygen species in HeLa cervical cancer cells. In addition, 20(S)‑GRh2 activated mitochondrion‑dependent apoptosis and inhibited both mitochondrial oxidative phosphorylation and glycolysis in HeLa cells. It was found that voltage‑dependent anion channel 1 (VDAC1) expression was significantly upregulated by 20(S)‑GRh2 treatment, while hexokinase 2 expression was downregulated and segregated from the mitochondria. Furthermore, 20(S)‑GRh2 promoted Bax transport from the cytoplasm to the mitochondria, and knockdown of VDAC1 inhibited Bax transport and apoptosis. These results suggest that VDAC1 is a novel target of 20(S)‑GRh2. The present study provides a better understanding of the mechanistic link between cervical cancer metabolism and growth control, and these results may facilitate the development of new treatments for cervical cancer.

Identification and pathogenicity of a novel genotype avian hepatitis E virus from silkie fowl (gallus gallus)

Hepatitis E virus (HEV) is a public health concern because of its zoonotic potential; however, the host species spectrum and the genetic diversity of HEV in many birds are unknown. In the present study, a novel genotype avian HEV was isolated from a bird, silkie fowl, and designated CHN-GS-aHEV (GenBank No. MN562265). The genome of CHN-GS-aHEV was analyzed in comparison with other avian HEVs' and the pathogenicity in silkie fowl was characterized. The results show that the CHN-GS-aHEV shares about 81 % identity with known avian HEV in chickens, ORF3 shares the highest identity (85.1 %-88.0 %) at the nucleotide level, while ORF2 shares the highest identity (96.5 %-98.0 %) at the amino acid level, indicating that the CHN-GS-aHEV belongs to a new genotype avian HEV. The pathogenicity study showed that silkie fowl experimentally infected with the CHN-GS-aHEV demonstrated seroconversion, viremia, fecal virus shedding, liver lesions, and increased ALT level. Furthermore, ultrastructural changes in hepatocyte cells by transmission electron microscopy were characterized by the loss of mitochondrial cristae and swollen mitochondria and endoplasmic reticulum in the infected birds, suggesting that these two organelles may play a significant role in HEV replication. Overall, this study reports the complete genome characterization of a novel avian HEV and successful experimental infection in silkie fowl, and may be serving as a prominent indicator for additional avian HEV detection in other species.

FDA-drug screening identifies deptropine inhibiting hepatitis E virus involving the NF-κB-RIPK1-caspase axis

Hepatitis E virus (HEV) infection is the leading cause of acute hepatitis worldwide and can develop into chronic infection in immunocompromised patients, promoting the development of effective antiviral therapies. In this study, we performed a screening of a library containing over 1000 FDA-approved drugs. We have identified deptropine, a classical histamine H1 receptor antagonist used to treat asthmatic symptoms, as a potent inhibitor of HEV replication. The anti-HEV activity of deptropine appears dispensable of the histamine pathway, but requires the inhibition on nuclear factor-κB (NF-κB) activity. This further activates caspase mediated by receptor-interacting protein kinase 1 (RIPK1) to restrict HEV replication. Given deptropine being widely used in the clinic, our results warrant further evaluation of its anti-HEV efficacy in future clinical studies. Importantly, the discovery that NF-κB-RIPK1-caspase pathway interferes with HEV infection reveals new insight of HEV-host interactions.

Mitochondria in the biology, pathogenesis, and treatment of hepatitis virus infections

Hepatitis virus infections affect a large proportion of the global population. The host responds rapidly to viral infection by orchestrating a variety of cellular machineries, in particular, the mitochondrial compartment. Mitochondria actively regulate viral infections through modulation of the cellular innate immunity and reprogramming of metabolism. In turn, hepatitis viruses are able to modulate the morphodynamics and functions of mitochondria, but the mode of actions are distinct with respect to different types of hepatitis viruses. The resulting mutual interactions between viruses and mitochondria partially explain the clinical presentation of viral hepatitis, influence the response to antiviral treatment, and offer rational avenues for novel therapy. In this review, we aim to consider in depth the multifaceted interactions of mitochondria with hepatitis virus infections and emphasize the implications for understanding pathogenesis and advancing therapeutic development.