Journal of Molecular Cell Biology

Palatine tonsil (hereinafter referred to as "tonsil") plays role in the immune systems first line of defense against foreign pathogens. Coronavirus disease 2019 (COVID-19), caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), has become a worldwide pandemic since the infection was first reported in China in December 2019. The aim of this study was to establish tonsil epithelial cell-derived organoids and to examine their feasibility as an ex vivo model for SARS-CoV-2 infection. Using an optimized protocol, we achieved 3D tonsil organoid culture from human tonsil tissue that reflects the distinctive characteristics of the tonsil epithelium, such as its cellular composition, histologic properties, and molecular biological features. Notably, we verified that SARS-CoV-2 can infect tonsil organoids with a robust replication efficiency. Furthermore, treatment with remdesivir, an antiviral agent, effectively protected them from viral infection. Therefore, tonsil organoids could be available for investigation of SARS-CoV-2 infection-mediated pathology and for preclinical screening of novel antiviral drug candidates. One-sentence SummaryThis study established tonsil epithelial cell-derived organoids and demonstrated their feasibility as an ex vivo model for SARS-CoV-2 infection.

Emerging evidence has manifested that long non-coding RNAs (lncRNAs) played critical roles in diabetes. The present research aimed to investigate the role and mechanism of XIST on proliferation, migration and apoptosis in diabetic cataract (DC). In the present study, lens epithelial cells (SRA01/04) were treated by high glucose (HG). The levels of XIST, miR-34a and SMAD2 were examined by RT-qPCR. MTT, transwell, wound healing and TUNEL assays were employed to examine cell proliferation, invasion, migration and apoptosis. The interaction between miR-34a and XIST or SMAD2 was verified by luciferase reporter assay. It was found that XIST expression was increased and miR-34a level was decreased in DC tissues and HG-induced SRA01/04 cells. XIST knockdown or miR-34a addition attenuated cell proliferation and migration, and induced apoptosis in SRA01/04 cells under HG. XIST targeted miR-34a and regulated DC progression via miR-34a. SMAD2 was a target gene of miR-34a and was positively modulated by XIST. SMAD2 addition accelerated cell proliferation, migration and inhibited the apoptosis in HG-stimulated SRA01/04 cells, which were abrogated by XIST depletion. In conclusion, XIST facilitated the proliferation, migration and invasion, and inhibited the apoptosis via miR-34a/SMAD2 axis in DC.

Calciphylaxis, also known as calcific uremic arteriolopathy (CUA), is an orphan disease without proven therapies, we rescued it with human amnion-derived mesenchymal stem cells (hAMSCs). In a discovery cohort of 10 uremic patients and 3 CUA patients, plasma proteomic analysis showed core differentially expressed proteins (DEPs) Thrombospondin 1 (THBS1) and Latent transforming growth factor (TGF)-{beta} binding protein 1 (LTBP1) decreased significantly after 3 days of hAMSC treatment. Single-cell transcriptome sequencing of peripheral blood mononuclear cells (PBMCs) indicated megakaryocytes were the source of THBS1 in CUA patient. Same as the discovery cohort, plasma THBS1 and TGF-{beta}1 levels were increased in seven CUA patients compared to the uremic group (n=20), as measured by enzyme-linked immunosorbent assay (ELISA) in the validation cohort. They can be inhibited after hAMSC treatment and increased as the frequency of therapy decreased. THBS1 and its receptor, CD47, were increased in the CUA skin. THBS1 and TGF-{beta}1 are biomarker candidates for calciphylaxis.

Backgroud & AimsCurrently, the COVID-19 pandemic, caused by SARS-CoV-2 infection, represents a serious public health problem worldwide. Although it has been shown that ACE2 serves as the main receptor for SARS-CoV-2 entry into host cells, studies have shown that ACE2 is expressed at extremely low levels in various tissues, especially in some organs where virus particles have been found, such as the heart and liver. Therefore, these organs potentially express additional SARS-CoV-2 receptors that have not yet been discovered. Methods & ResultsHere, by a genome-wide CRISPR-Cas9 activation library screening, we found that ASGR1 promoted SARS-CoV-2 infection of 293T cells. In Huh-7 and HepG2 cell lines, simultaneous knock out of ACE2 and ASGR1 prevented SARS-CoV-2 pseudovirus infection. In the immortalized THLE-2 hepatocyte cell line and primary liver parenchymal cells, both of which hardly express ACE2, SARS-CoV-2 could successfully establish an infection. After treatment with ASGR1 antibody, the infection rate significantly reduced. This suggests that SARS-CoV-2 infects liver cells mainly through an ASGR1-dependent mechanism. Finally, we also found that the soluble ASGR1 could not only prevent the SARS-CoV-2 pseudovirus, which binds to the ASGR1 receptors, from infecting host liver cells, but also had a protective effect on those expressing ACE2, indicating that administration of soluble ASGR1 protein may represent a new treatment approach. ConclusionsColletively, these findings indicate that ASGR1 is a candidate receptor for SARS-CoV-2 that promotes infection of liver cells. Lay SummaryWe show that ASGR1 is a candidate receptor for SARS-CoV-2 to infect liver cells.

Since the infection of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) in several somatic cells, little is known about the infection of SASRS-CoV-2 and its related pangolin coronavirus (GX_P2V). Here we present for the first time that SARS-CoV-2 pseudovirus and GX_P2V could infect lung progenitor and even anterior foregut endoderm cells causing these cells death, which differentiated from human embryonic stem cells (hESCs). The infection and replication of SARS-CoV-2 and GX_P2V were inhibited when treated with whey protein of breastmilk and Remdesivir, confirming that these two viruses could infect lung progenitor and even anterior foregut endoderm. Moreover, we found that SARS-CoV-2 pseudovirus could infect endoderm and ectoderm. We found that whey protein blocked SARS-CoV-2 infecting these cells. In line with the SARS-CoV-2 results, GX_P2V could also infected endoderm and ectoderm, and also was inhibited by Remdesivir treatment. Although expressing coronavirus related receptor such as ACE2 and TMPRSS2, mesoderm cells are not permissive for SARS-CoV-2 and GX_P2V infection, which needed further to study the mechanisms. Interestingly, we also found that hESCs, which also express ACE2 and TMPRSS2 markers, are permissive for GX_P2V but not SARS-CoV-2 pseudovirus infection and replication, indicating the widespread cell types for GX_P2V infection. Heparin treatment blocked efficiently viral infection. These results provided insight that these stem cells maybe provided a stable repository of coronavirus function or genome. The potential consequence of SARS-CoV-2 and animal coronavirus such as GX_P2V infection in hESCs, germ layer and induced progenitors should be closely monitored.

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is the virus that causes coronavirus disease 2019 (COVID-19), the respiratory illness responsible for the COVID-19 pandemic. SARS-CoV-2 is a positive-stranded RNA virus belongs to Coronaviridae family. The viral genome of SARS-CoV-2 contains around 29.8 kilobase with a 5'-cap structure and 3'-poly-A tail, and shows 79.2% nucleotide identity with human SARS-CoV-1, which caused the 2002-2004 SARS outbreak. As the successor to SARS-CoV-1, SARS-CoV-2 now has circulated across the globe. There is a growing understanding of SARS-CoV-2 in virology, epidemiology, and clinical management strategies. In this study, we verified the existence of two 18-22 nt small viral RNAs (svRNAs) derived from the same precursor in human specimens infected with SARS-CoV-2, including nasopharyngeal swabs and formalin-fixed paraffin-embedded (FFPE) explanted lungs from lung transplantation of COVID-19 patients. We then simulated and confirmed the formation of these two SARS-CoV-2-Encoded small RNAs in human lung epithelial cells. And the potential pro-inflammatory effects of the splicing and maturation process of these two svRNAs in human lung epithelial cells were also explored. By screening cytokine storm genes and the characteristic expression profiling of COVID-19 in the explanted lung tissues and the svRNAs precursor transfected human lung epithelial cells, we found that the maturation of these two small viral RNAs contributed significantly to the infection associated lung inflammation, mainly via the activation of the CXCL8, CXCL11 and type I interferon signaling pathway. Taken together, we discovered two SARS-CoV-2-Encoded small RNAs and investigated the pro-inflammatory effects during their maturation in human lung epithelial cells, which might provide new insight into the pathogenesis and possible treatment options for COVID-19.

Because of its insensitive to existing radiotherapy, chemotherapy and targeted treatments, Triple-negative breast cancer (TNBC) remains a great challenge to overcome. More and more evidence has indicated abnormal wnt/{beta}-catenin pathway activation in TNBC but not luminal or her2+ breast cancer, and lncRNAs play a key role in a variety of cancers. Through lncRNA microarray profiling between Activated and inactivated Wnt/{beta}-catenin pathway of TNBC tissues, lnc-WAL (Wnt/{beta}-catenin associated lncRNA; WAL) was selected as the top up-regulated lncRNA in Wnt/{beta}-catenin pathway activation compared with the inactivation group. RIP-seq was analyzed between {beta}-catenin and IgG groups of, where lnc-WAL could interact with {beta}-catenin. Clinically, increased lnc-WAL in the TNBC tumor tissue was associated with shorter survival. lnc-WAL promoted the EMT, the ability of breast cancer stem cells (BCSC), proliferation, migration and invasion of TNBC cells. Mechanistically, lnc-WAL inhibited {beta}-catenin protein degradation via Axin-mediated phosphorylation at serine 45. Subsequently, {beta}-catenin was accumulated in nuclear and activated the target genes. Importantly, Wnt/{beta}-catenin pathway activation stimulated the transcription of lnc-WAL. These results pointed to a master regulatory role of lnc-WAL/Axin/{beta}-catenin in the malignant progression of TNBC. Our findings provide important clinical translational evidence that lnc-WAL maybe as potential therapeutic target against TNBC.

The recently emerged severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), the causative agent of the ongoing global pandemic of COVID-19, may trigger immunosuppression in the early stage and a cytokine storm in the late stage of infection, however, the underlying mechanisms are not well understood. Here we demonstrated that the SARS-CoV-2 nucleocapsid (N) protein dually regulated innate immune responses, i.e., the low-dose N protein suppressed type I interferon (IFN-I) signaling and inflammatory cytokines, whereas high-dose N protein promoted IFN-I signaling and inflammatory cytokines. Mechanistically, the SARS-CoV-2 N protein interacted with the tripartite motif protein 25 (TRIM25), thereby dually regulating the phosphorylation and nuclear translocation of IRF3, STAT1 and STAT2. Additionally, low-dose N protein combined with TRIM25 could suppress retinoic acid-inducible gene I (RIG-I) ubiquitination and activation. Our findings revealed a regulatory mechanism of innate immune responses by the SARS-CoV-2 N protein, which would contribute to understanding the pathogenesis of SARS-CoV-2 and other SARS-like coronaviruses, and development of more effective strategies for controlling COVID-19.

Animal models are essential for understanding the pathogenesis of SARS-CoV-2 and for developing therapeutic strategies. Replicon delivery particles (RDPs) were a component of trans-complementary systems for SARS-CoV-2, which is a safe and convenient tool in researching SARS-CoV-2 in animal biosafety level-II laboratory (ABSL-2). Here, we constructed a mouse model that conditional expressing SARS-CoV-2 N on the background of the K18-hACE2 KI mice. The SARS-CoV-2 N with flanked loxP-stop-loxP sequence was under the CAG promoter, and this cassette was knocked into the Tiger locus of mouse by CRISPR-Cas9 (K18-hACE2-N KI). By mating K18-hACE2-N KI mice with Cre tool mice, the offspring can express SARS-CoV-2 N (Cre-N-hACE2 KI) systemically and in a tissue-specific manner. Cre-N-hACE2 KI exhibited susceptibility to the SARS-CoV-2 {Delta}N-GFP/HBiT infection. The viral loads in lung exhibited a mountain-like trend, peaking at 4 days post-infection, and lung injuries can be observed. Overall, we demonstrated a mouse model infection for SARS-CoV-2 {Delta}N-GFP/HBiT to understand SARS-CoV-2 pathogenesis.

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is the virus responsible for the coronavirus disease 2019 pandemic. ORF6 is known to antagonize the interferon signaling by inhibiting the nuclear translocation of STAT1. Here we show that ORF6 acts as a virulence factor through two distinct strategies. First, ORF6 directly interacts with STAT1 in an IFN-independent manner to inhibit its nuclear translocation. Second, ORF6 directly binds to importin 1, which is a nuclear transport factor encoded by KPNA2, leading to a significant suppression of importin 1-mediated nuclear transport. Furthermore, we found that KPNA2 knockout enhances the viral replication, suggesting that importin 1 suppresses the viral propagation. Additionally, the analyses of gene expression data revealed that importin 1 levels decreased significantly in the lungs of older individuals. Taken together, SARS-CoV-2 ORF6 disrupts the nucleocytoplasmic trafficking to accelerate the viral replication, resulting in the disease progression, especially in older individuals.

Single-cell RNA profiling of ACE2, the SARS-CoV-2 receptor, had proposed multiple tissue cells as the potential targets of SARS-CoV-2, the novel coronavirus causing the COVID-19 pandemic. However, most were not echoed by the patients clinical manifestations, largely due to the lack of protein expression information of ACE2 and co-factors. Here, we incorporated the protein information to analyse the expression of ACE2, together with TMPRSS2 and Furin, two proteases assisting SARS-CoV-2 infection, at single cell level in situ, which we called protein-proofed single-cell RNA (pscRNA) profiling. Systemic analysis across 36 tissues revealed a rank list of candidate cells potentially vulnerable to SARS-CoV-2. The top targets are lung AT2 cells and macrophages, then cardiomyocytes and adrenal gland stromal cells, followed by stromal cells in testis, ovary and thyroid. Whereas, the polarized kidney proximal tubule cells, liver cholangiocytes and intestinal enterocytes are less likely to be the primary SARS-CoV-2 targets as ACE2 localizes at the apical region of cells, where the viruses may not readily reach. Actually, the stomach may constitute a physical barrier against SARS-CoV-2 as the acidic environment in normal stomach (pH < 2.0) could completely inactivate SARS-CoV-2 pseudo-viruses. These findings are in concert with the clinical characteristics of prominent lung symptoms, frequent heart injury, and uncommon intestinal symptoms and acute kidney injury. Together, we provide a comprehensive view on the potential SARS-CoV-2 targets by pscRNA profiling, and propose that, in addition to acute respiratory distress syndrome, attentions should also be paid to the potential injuries in cardiovascular, endocrine and reproductive systems during the treatment of COVID-19 patients.

T cell invigoration is an essential step for eliminating pathogens and cancer cells. Co-stimulatory molecules, such as CD80, CD86, and ICOSLG reinforce TCR stimuli for T cell activations. Despite identifying multiple co-stimulatory molecules, the differences of those in downstream signaling have remained unclear. Here, we unravel the differences in avidity of co-stimulatory molecules with T cells cause distinct T cell fates. Specially, CD80 + TCR stimulus promotes induction of multiple T cell effector genes based on prolonged and magnified activation of ERK and AKT compared with other combined stimuli. Long-term and robust activation of these signaling pathways leads to T cell impairment by induction of PD1, and exhausted T cells are vulnerable to disrupt effector functions by interactions with PDL1. Collectively, we reveal the quantitative differences in binding activities of co-stimulatory molecules to T cells cause qualitative differences in downstream signals and gene expressions, thereby branching T cell fates.

Angiotensin-converting enzyme 2 (ACE2) has been suggested as a receptor for severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) entry to cause coronavirus disease 2019 (COVID-19). However, no ACE2 inhibitors have shown definite beneficiaries for COVID-19 patients, applying the presence of another receptor for SARS-CoV-2 entry. Here we show that ACE2 knockout dose not completely block virus entry, while TfR directly interacts with virus Spike protein to mediate virus entry and SARS-CoV-2 can infect mice with over-expressed humanized transferrin receptor (TfR) and without humanized ACE2. TfR-virus co-localization is found both on the membranes and in the cytoplasma, suggesting SARS-CoV-2 transporting by TfR, the iron-transporting receptor shuttling between cell membranes and cytoplasma. Interfering TfR-Spike interaction blocks virus entry to exert significant anti-viral effects. Anti-TfR antibody (EC50 ~16.6 nM) shows promising anti-viral effects in mouse model. Collectively, this report indicates that TfR is another receptor for SARS-CoV-2 entry and a promising anti-COVID-19 target.

Melanoma differentiation-associated gene-5 (MDA5) acts as a cytoplasmic RNA sensor to detect viral dsRNA and mediates type I interferon (IFN) signaling and antiviral innate immune responses to infection by RNA viruses. Upon recognition of viral dsRNA, MDA5 is activated with K63-linked polyubiquitination and then triggers the recruitment of MAVS and activation of TBK1 and IKK, subsequently leading to IRF3 and NF-{kappa}B phosphorylation. Great numbers of symptomatic and severe infections of SARS-CoV-2 are spreading worldwide, and the poor efficacy of treatment with type I interferon and antiviral agents indicates that SARS-CoV-2 escapes from antiviral immune responses via an unknown mechanism. Here, we report that SARS-CoV-2 nonstructural protein 8 (NSP8) acts as an innate immune suppressor and inhibits type I IFN signaling to promote infection of RNA viruses. It downregulates the expression of type I IFNs, IFN-stimulated genes and proinflammatory cytokines by binding to MDA5 and impairing its K63-linked polyubiquitination. Our findings reveal that NSP8 mediates innate immune evasion during SARS-CoV-2 infection and may serve as a potential target for future therapeutics for SARS-CoV-2 infectious diseases. ImportanceThe large-scale spread of COVID-19 is causing mass casualties worldwide, and the failure of antiviral immune treatment suggests immune evasion. It has been reported that several nonstructural proteins of severe coronaviruses suppress antiviral immune responses; however, the immune suppression mechanism of SARS-CoV-2 remains unknown. Here, we revealed that NSP8 protein of SARS-CoV-2 directly blocks the activation of the cytosolic viral dsRNA sensor MDA5 and significantly downregulates antiviral immune responses. Our study contributes to our understanding of the direct immune evasion mechanism of SARS-CoV-2 by showing that NSP8 suppresses the most upstream sensor of innate immune responses involved in the recognition of viral dsRNA.

Respiratory syncytial virus (RSV) is a major pathogen that can cause acute respiratory infectious diseases of the upper and lower respiratory tract, especially in children, elderly individuals and immunocompromised people. Generally, following viral infection, respiratory epithelial cells secrete cytokines and chemokines to recruit immune cells and initiate innate and/or adaptive immune responses. However, whether chemokines affect viral replication in non-immune cells is rarely clear. In this study, we detect that chemokine CCL5 was highly expressed, while expression of its receptor, CCR1, was downregulated in respiratory epithelial cells after RSV infection. When we overexpressed CCR1 on respiratory epithelial cells in vivo/in vitro, viral load was significantly suppressed, which can be restored by the neutralizing antibody for CCR1. Interestingly, the antiviral effect of CCR1 was not related to type I interferon (IFN-I), apoptosis induction or viral adhesion or entry inhibition; in contrast, it was related to the preferential recruitment and activation of adaptor Gi, which promoted inositol 1,4,5-triphosphate receptor type 3 (ITPR3) expression, leading to inhibited STAT3 phosphorylation, explicitly, phosphorylated (p)-STAT3 was verified to be among the important factors regulating the activity of HSP90, which has been previously reported to be a chaperone of RSV RNA polymerase. In summary, we are the first to reveal that CCR1 on the surface of non-immune cells regulates RSV replication through a previously unknown mechanism that does not involve IFN-I induction.

BackgroundCalciphylaxis, which mostly affects individuals with end-stage kidney disease (ESKD), is also known as calcific uremic arteriolopathy (CUA). It is a rare and fatal disease that manifests with calcification and thrombosis of microvessels, ischemia, and necrosis in skin tissues(ORPHA:280062). Histopathological features of extracutaneous tissues of CUA patients undergoing human amnion-derived mesenchymal stem cell (hAMSC) treatment remain unknown. MethodsA female CUA patient, treated with hAMSCs for 20 months, passed away due to stroke. Histopathological features of her extracutaneous tissues were compared with those of ESKD patients (n = 7). Raman spectroscopy was applied to identify the composition of calcifications. The distribution of hAMSCs, derived from the amnion of a male fetus, in tissues of the CUA patient was determined by detecting the Y chromosome using reverse-transcription-polymerase chain reaction. ResultsMicrovessel lesions were more prevalent in the extracutaneous tissues of the CUA patient than in those of ESKD patients, although the regenerated skin showed normal histological characteristics. The CUA patient exhibited calcifications of microvessel media, including the microvessels in the lungs, kidneys, spleen, pancreas, and uterus. Her mitral valve and kidney displayed severe calcification, identified as calcium phosphate with some calcium carbonate. hAMSCs were not detected in the tissues of the CUA patient. ConclusionUnder the treatment strategy with hAMSCs, based on the effects of skin regeneration, microvascular lesions in the extracutaneous tissues of the CUA patient were more severe than those in ESKD patients. CUA should be considered a systemic disease when identifying treatment targets.

We firstly disclose single compound yields better therapeutic outcome than Remdesivir in COVID-19 hamster treatments as it is armed with direct inhibition viral replication and intrinsic suppression inflammatory cytokines expression. Crystal data reveals that Au (I), released from Au22Glutathione18 (GA), covalently binds thiolate of Cys145 of SARS-CoV-2 Mpro. GA directly decreases SARS-CoV-2 viral replication (EC50: ~0.24 M) and intrinsically down-regulates NF{kappa}B pathway therefore significantly inhibiting expression of inflammatory cytokines in cells. The lung viral load and inflammatory cytokines in GA-treated COVID-19 transgenic mice are found to be significantly lower than that of control mice. When COVID-19 golden hamsters are treated by GA, the lung inflammatory cytokines levels are significantly lower than that of Remdesivir while their lung viral load are decreased to same level. The pathological results show that GA treatment significantly reduce lung inflammatory injuries when compared to that of Remdesivir-treated COVID-19 golden hamsters. One Sentence SummaryWe found that gold cluster molecule directly inhibits SARS-CoV-2 replication and intrinsically suppresses inflammatory cytokines expression in COVID-19 transgenic mouse and golden hamster model, gold cluster providing a better lung injury protection than Remdesivir in COVID-19 golden hamsters via intranasally dropping administration.

Cells can sense invading viruses and trigger type I interferons (IFN-/{beta}) to evoke antiviral innate immune response. Induction of IFNs needs to be fine-tuned to achieve the antiviral consequence while avoiding severe disruption of host cell homeostasis. Here, we reported that NAT10, the acetyltransferase of histone and N4-acetylcytidine (ac4C) RNA modification, promotes infection of RNA viruses via regulation of type I IFN signaling. Depletion of NAT10 increased the expression of IFN-{beta} and interferon-stimulated genes (ISGs) upon stimulation of type I IFN antiviral signaling, while it impaired viral replication. NAT10 dynamically associated with the IFN-{beta} promotor and negatively regulated IRF3 through modulation of long non-coding RNAs (lncRNAs) that inhibit IRFs. Consistently, the small molecule inhibitor of NAT10, Remodelin, increased IFN-{beta} expression while inhibiting viral infections. Overall, our findings indicated that NAT10 is a negative regulator of type I IFN signaling, suggesting its potential as a target of antiviral treatment.

Adoptive chimeric antigen receptor (CAR)-modified T or NK cells (CAR-T/NK) have emerged as a novel form of disease treatment. Lentiviral vectors (LVs) are commonly employed to engineer T/NK cells for the efficient expression of CARs. This study reported for the first time the influence of single-promoter and dual-promoter LVs on the CAR expression and cytotoxicity of engineered NK cells. Our results demonstrated that the selected CAR exhibits both a higher expression level and a higher coexpression concordance with the GFP reporter in HEK-293T or NK92 cells by utilizing the optimized single-promoter pCDHsp rather than the original dual-promoter pCDHdp. After puromycin selection, the pCDHsp produces robust CAR expression and enhanced in vitro cytotoxicity of engineered NK cells. Therefore, infection with a single-promoter pCDHsp lentivector is recommended to prepare CAR-engineered cells. This research will help to optimize the production of CAR-NK cells and improve their functional activity, to provide CAR-NK cell products with better and more uniform quality.

ACE2 is a major receptor for cell entry of SARS-CoV-2. Despite advances in targeting ACE2 to inhibit SARS-CoV-2s binding, how to efficiently and flexibly control ACE2 levels for prevention of SARS-CoV-2 infection has not been explored. Here, we revealed Vitamin C (VitC) administration as an effective strategy to prevent SARS-CoV-2 infection. VitC reduced ACE2 protein levels in a dose-dependent manner, while partial reduction of ACE2 can greatly restrict SARS-CoV-2 infection. Further studies uncovered that USP50 is a crucial regulator of ACE2 protein levels, and VitC blocks the USP50-ACE2 interaction, thus promoting K48-linked polyubiquitination at Lys788 and degradation of ACE2, without disrupting ACE2 transcriptional expression. Importantly, VitC administration reduced host ACE2 and largely blocked SARS-CoV-2 infection in mice. This study identified an in vivo ACE2 balance controlled by both USP50 and an essential nutrient VitC, and revealed a critical role and application of VitC in daily protection from SARS-CoV-2 infection. HighlightsO_LIVitC reduces ACE2 protein levels in a dose-dependent manner C_LIO_LIVitC and USP50 regulate K48-linked ubiquitination at Lys788 of ACE2 C_LIO_LIVitC blocks the interaction between USP50 and ACE2 C_LIO_LIVitC administration lowers host ACE2 and prevents SARS-CoV-2 infection in vivo C_LI O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=151 SRC="FIGDIR/small/499651v1_ufig1.gif" ALT="Figure 1"> View larger version (60K): org.highwire.dtl.DTLVardef@196682borg.highwire.dtl.DTLVardef@190f14dorg.highwire.dtl.DTLVardef@d22b59org.highwire.dtl.DTLVardef@1c0faa_HPS_FORMAT_FIGEXP M_FIG C_FIG The deubiquitinase USP50 controls ACE2 protein stability and levels, while Vitamin C blocks the USP50-ACE2 interaction and therefore results in ACE2 degradation, offering a flexible and efficient approach to protection of the host from SARS-CoV-2 infection.