SARS-CoV-2 ORF7a blocked autophagy flux by intervening in the fusion between autophagosome and lysosome to promote viral infection and pathogenesis

The role of Bcl‑2 in controlling the transition between autophagy and apoptosis (Review)

The Bcl‑2 protein family serves a key role in maintaining cellular homeostasis by regulating the balance between autophagy and apoptosis. The present review aimed to summarize interactions of Bcl‑2 with key proteins, including Beclin 1, Bax and Bcl‑2 homologous antagonist/killer, as well as its influence on cellular processes such as mitophagy, nutrient sensing and endoplasmic reticulum stress response. The impact of post‑translational modifications of Bcl‑2, including phosphorylation, ubiquitination and sumoylation, is discussed with respect to their regulatory roles under stress. In pathological states, Bcl‑2 upregulation in cancer suppresses apoptosis and autophagy, thereby facilitating tumor survival and resistance to chemotherapy. Conversely, in neurodegenerative diseases, impaired autophagy and increased apoptosis contribute to neuronal loss. Therapeutic strategies targeting Bcl‑2 (for example inhibitors such as venetoclax, navitoclax, obatoclax and combination therapies involving autophagy modulators) were evaluated for their potential efficacy. There is lack of understanding of tissue‑specific functions of Bcl‑2 and its interactions with non‑coding RNAs. Future research should prioritize these areas and leverage advanced single‑cell technologies to elucidate the real‑time dynamics of Bcl‑2 in cell processes. The present review highlights the key role of Bcl‑2 in cell fate determination and highlights its potential as a therapeutic target, offering insight for the development of innovative treatments for cancer, neurodegenerative disorder and age‑related diseases.

ELV-N34, RvD6-Isomer, or NPD1 Halt Replication of SARS-CoV-2 Omicron BA.5 Virus in Human Lung and Nasal Cells

Current vaccines rely on the sequence of Spike (S) protein to induce immunity against the severe acute respiratory coronavirus-2 (SARS-CoV-2) virus. Because of the high mutation rate of the viral S protein, new mutant strains are developed to generate new infectivity profiles. Bioactive lipid mediators (LMs) derived from docosahexaenoic acid (DHA) are synthesized on demand to sustain homeostasis. The purpose of this study was to determine the action of selected LMs in the viral replication of SARS-CoV-2 Omicron BA.5 variant in human lung and nasal epithelial cells. Cells from healthy donors were infected with Omicron BA.5 for one hour and treated with 500 nM Elovanoid (ELV)-N32, ELV-N34, Resolvin D6 isomer (RvD6i), Neuroprotection D1 (NPD1), or vehicle before and after infection. Impedance was recorded to determine cell death by infectivity. Cells were then immunostained for nucleocapsid (N) protein, microtubule-associated protein 1B-light chain 3 (LC3B), and autophagic proteins. N and S RNA were measured to assess the synthesis of viral components. The addition of ELV-N34 or RvD6i decreased the synthesis of N RNA by 76.7% and 96.9%, respectively, in lung primary culture, while NPD1 exerted the same effect in nasal epithelial cells (61.7% reduction). In lung cells, transcription of autophagy-related gene-3 (ATG3) and Sequestosome 1 (SQSTM1/p62), components of the autophagy initiation process, decreased compared to the non-treated infected cells. The results suggest that specific LMs prevent viral autophagy machinery hijacking, leading to a decrease in BA.5 replication. This novel effect of the bioactive LMs as antivirals, regardless of the protein sequence, would potentially complement vaccination and other prevention and treatment therapeutics.

The hidden impact of producer cells on virion composition and infectivity

The cells infected by a virus in vivo are critical determinants of infection and disease. These same susceptible cells can also provide a wide range of options for viral propagation. The type of cell used to produce a virus, i.e. the producer cell type, can change the macromolecular composition of viruses and other factors associated with viral inoculum independent of genetic selection. Changes in the post-translational modifications of viral proteins, virion protein and lipid composition, and the types of viral structures released from different producer cells have been observed for several virus families. These producer cell-dependent changes can have wide ranging consequences on subsequent infection by altering viral tropism, antigenicity, and overall infectious capacity. The changes imparted by the producer cell impact experimental outcomes and influence viral spread and disease in vivo. In this review, we discuss the literature documenting the effects that producer cell type has on the macromolecular composition and infectious properties of virions and viral inoculum. We discuss the evidence of producer cell-dependent changes on the outcome of infection and antigenicity from diverse viral families. These observations highlight the need to better understand the impact producer cell type has on viral infections and disease.

Pressure to evade cell-autonomous innate sensing reveals interplay between mitophagy, IFN signaling, and SARS-CoV-2 evolution

SARS-CoV-2 emerged, and continues to evolve, to efficiently infect humans worldwide. SARS-CoV-2 evades early innate recognition, interferon signaling occurring only in bystander cells. How the virus continues to evolve in the face of innate responses has important consequences, but the pathways involved are incompletely understood. Here, we find that autophagy genes regulate innate immune signaling, impacting the basal set point of interferons and, thus, permissivity to infection. Mechanistically, autophagy (mitophagy) genes negatively regulate MAVS, and this low basal level of MAVS is efficiently antagonized by SARS-CoV-2 ORF9b, blocking interferon activation in infected cells. However, loss of autophagy increased MAVS and overcomes ORF9b-mediated antagonism. This has driven the evolution of SARS-CoV-2 to express more ORF9b, allowing SARS-CoV-2 to replicate under conditions of increased MAVS signaling. Altogether, we find a critical role of mitophagy in the regulation of innate immunity and uncover an evolutionary trajectory of SARS-CoV-2 ORF9b to overcome host defenses.

Recognizing SARS-CoV-2 infection of nasopharyngeal tissue at the single-cell level by machine learning method

SARS-CoV-2 has posed serious global health challenges not only because of the high degree of virus transmissibility but also due to its severe effects on the respiratory system, such as inducing changes in multiple organs through the ACE2 receptor. This virus makes changes to gene expression at the single-cell level and thus to cellular functions and immune responses in a variety of cell types. Previous studies have not been able to resolve these mechanisms fully, and so our study tries to bridge knowledge gaps about the cellular responses under conditions of infection. We performed single-cell RNA-sequencing of nasopharyngeal swabs from COVID-19 patients and healthy controls. We assembled a dataset of 32,588 cells for 58 subjects for analysis. The data were sorted into eight cell types: ciliated, basal, deuterosomal, goblet, myeloid, secretory, squamous, and T cells. Using machine learning, including nine feature ranking algorithms and two classification algorithms, we classified the infection status of single cells and analyzed gene expression to pinpoint critical markers of SARS-CoV-2 infection. Our findings show distinct gene expression profiles between infected and uninfected cells across diverse cell types, with key indicators such as FKBP4, IFITM1, SLC35E1, CD200R1, MT-ATP6, KRT13, RBM15, and FTH1 illuminating unique immune responses and potential pathways for viral spread and immune evasion. The machine learning methods effectively differentiated between infected and non-infected cells, shedding light on the cellular heterogeneity of SARS-CoV-2 infection. The findings will improve our knowledge of the cellular dynamics of SARS-CoV-2.

Is Autophagy a Friend or Foe in SARS-CoV-2 Infection?

As obligate parasites, viruses need to hijack resources from infected cells to complete their lifecycle. The interaction between the virus and host determines the viral infection process, including viral propagation and the disease's outcome. Understanding the interaction between the virus and host factors is a basis for unraveling the intricate biological processes in the infected cells and thereby developing more efficient and targeted antivirals. Among the various fundamental virus-host interactions, autophagy plays vital and also complicated roles by directly engaging in the viral lifecycle and functioning as an anti- and/or pro-viral factor. Autophagy thus becomes a promising target against virus infection. Since the COVID-19 pandemic, there has been an accumulation of studies aiming to investigate the roles of autophagy in SARS-CoV-2 infection by using different models and from distinct angles, providing valuable information for systematically and comprehensively dissecting the interplay between autophagy and SARS-CoV-2. In this review, we summarize the advancements in the studies of the interaction between SARS-CoV-2 and autophagy, as well as detailed molecular mechanisms. We also update the current knowledge on the pharmacological strategies used to suppress SARS-CoV-2 replication through remodeling autophagy. These extensive studies on SARS-CoV-2 and autophagy can advance our understanding of virus-autophagy interaction and provide insights into developing efficient antiviral therapeutics by regulating autophagy.

The role of SARS-CoV-2 ORF7a in autophagy flux disruption: implications for viral infection and pathogenesis

Although alterations in the autophagy-lysosome pathway have been observed in the SARS-CoV-2 infection and invasion process since the outbreak of the coronavirus disease in 2019, the in-depth mechanism of autophagic and lysosomal reprogramming by SARS-CoV-2 has yet to be well identified. Our recent study unveiled a pivotal role played by the open reading frame 7a (ORF7a) protein in the SARS-CoV-2 genome, particularly in the modulation of macroautophagy/autophagy flux and function during viral infection and pathogenesis. Our study elucidated the underlying molecular mechanisms by which SARS-CoV-2 ORF7a intercepts autophagic flux, evades host autophagy-lysosome degradation, and accelerates viral infection and progeny germination. Furthermore, our study highlights that ORF7a can be a therapeutic target, and glecaprevir may hold potential as a drug against SARS-CoV-2 by targeting ORF7a. The key observations revealed in this study also contribute to a growing understanding of the function of SARS-CoV-2 ORF7a and the mechanisms underlying COVID-2019 treatment.

Differences and similarities between innate immune evasion strategies of human coronaviruses

So far, seven coronaviruses have emerged in humans. Four recurring endemic coronaviruses cause mild respiratory symptoms. Infections with epidemic Middle East respiratory syndrome-related coronavirus or severe acute respiratory syndrome coronavirus (SARS-CoV)-1 are associated with high mortality rates. SARS-CoV-2 is the causative agent of the coronavirus disease 2019 pandemic. To establish an infection, coronaviruses evade restriction by human innate immune defenses, such as the interferon system, autophagy and the inflammasome. Here, we review similar and distinct innate immune manipulation strategies employed by the seven human coronaviruses. We further discuss the impact on pathogenesis, zoonotic emergence and adaptation. Understanding the nature of the interplay between endemic/epidemic/pandemic coronaviruses and host defenses may help to better assess the pandemic potential of emerging coronaviruses.

Infectious bronchitis virus (IBV) triggers autophagy to enhance viral replication by activating the VPS34 complex

Autophagy plays an important role in the lifecycle of viruses. However, there is currently a lack of systematic research on the relationship between Infectious Bronchitis Virus (IBV) and autophagy. This study aims to investigate the impact of IBV on autophagy and the role of autophagy in viral replication. We observed that IBV infection increased the expression of microtubule-associated protein 1 light chain 3, a marker of autophagy, decreased the expression of sequestosome 1, and led to elevated intracellular LC3 puncta levels. These findings suggest that IBV infection activates the autophagic process in cells. To investigate the impact of autophagy on the replication of IBV, we utilized rapamycin as an autophagy activator and 3-methyladenine as an autophagy inhibitor. Our results indicate that IBV promotes viral replication by inducing autophagy. Further investigation revealed that IBV induces autophagosome formation by inhibiting the mTOR-ULK1 pathway and activating the activity of vacuolar protein sorting 34 (VPS34), autophagy-related gene 14, and the Beclin-1 complex. VPS34 plays a crucial role in this process, as inhibiting VPS34 protein activity enhances cell proliferation after IBV infection. Additionally, inhibiting VPS34 significantly improves the survival rate of IBV-infected chicks, suppresses IBV replication in the kidney, and alleviates tracheal, lung, and kidney damage caused by IBV infection. In summary, IBV infection can induce autophagy by modulating the mTOR/ULK1 signaling pathway and activating the VPS34 complex, while autophagy serves to promote virus replication.

NSP6 inhibits the production of ACE2-containing exosomes to promote SARS-CoV-2 infectivity

The emergence of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has triggered a global pandemic, which severely endangers public health. Our and others' works have shown that the angiotensin-converting enzyme 2 (ACE2)-containing exosomes (ACE2-exos) have superior antiviral efficacies, especially in response to emerging variants. However, the mechanisms of how the virus counteracts the host and regulates ACE2-exos remain unclear. Here, we identified that SARS-CoV-2 nonstructural protein 6 (NSP6) inhibits the production of ACE2-exos by affecting the protein level of ACE2 as well as tetraspanin-CD63 which is a key factor for exosome biogenesis. We further found that the protein stability of CD63 and ACE2 is maintained by the deubiquitination of proteasome 26S subunit, non-ATPase 12 (PSMD12). NSP6 interacts with PSMD12 and counteracts its function, consequently promoting the degradation of CD63 and ACE2. As a result, NSP6 diminishes the antiviral efficacy of ACE2-exos and facilitates the virus to infect healthy bystander cells. Overall, our study provides a valuable target for the discovery of promising drugs for the treatment of coronavirus disease 2019.

IMPORTANCE

The outbreak of coronavirus disease 2019 (COVID-19) severely endangers global public health. The efficacy of vaccines and antibodies declined with the rapid emergence of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) mutants. Angiotensin-converting enzyme 2-containing exosomes (ACE2-exos) therapy exhibits a broad neutralizing activity, which could be used against various viral mutations. Our study here revealed that SARS-CoV-2 nonstructural protein 6 inhibited the production of ACE2-exos, thereby promoting viral infection to the adjacent bystander cells. The identification of a new target for blocking SARS-CoV-2 depends on fully understanding the virus-host interaction networks. Our study sheds light on the mechanism by which the virus resists the host exosome defenses, which would facilitate the study and design of ACE2-exos-based therapeutics for COVID-19.