SARS-CoV-2 productively infects human gut enterocytes

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) can cause coronavirus disease 2019 (COVID-19), an influenza-like disease that is primarily thought to infect the lungs with transmission through the respiratory route. However, clinical evidence suggests that the intestine may present another viral target organ. Indeed, the SARS-CoV-2 receptor angiotensin-converting enzyme 2 (ACE2) is highly expressed on differentiated enterocytes. In human small intestinal organoids (hSIOs), enterocytes were readily infected by SARS-CoV and SARS-CoV-2, as demonstrated by confocal and electron microscopy. Enterocytes produced infectious viral particles, whereas messenger RNA expression analysis of hSIOs revealed induction of a generic viral response program. Therefore, the intestinal epithelium supports SARS-CoV-2 replication, and hSIOs serve as an experimental model for coronavirus infection and biology.

TMPRSS2 and TMPRSS4 promote SARS-CoV-2 infection of human small intestinal enterocytes

Gastrointestinal symptoms and fecal shedding of SARS-CoV-2 RNA are frequently observed in COVID-19 patients. However, it is unclear whether SARS-CoV-2 replicates in the human intestine and contributes to possible fecal-oral transmission. Here, we report productive infection of SARS-CoV-2 in ACE2+ mature enterocytes in human small intestinal enteroids. Expression of two mucosa-specific serine proteases, TMPRSS2 and TMPRSS4, facilitated SARS-CoV-2 spike fusogenic activity and promoted virus entry into host cells. We also demonstrate that viruses released into the intestinal lumen were inactivated by simulated human colonic fluid, and infectious virus was not recovered from the stool specimens of COVID-19 patients. Our results highlight the intestine as a potential site of SARS-CoV-2 replication, which may contribute to local and systemic illness and overall disease progression.

Host response to translocated microbial products predicts outcomes of patients with HBV or HCV infection

BACKGROUND & AIMS

Chronic infection with hepatitis B or C virus (HBV or HCV) is a leading cause of cirrhosis by unknown mechanisms of pathogenesis. Translocation of gut microbial products into the systemic circulation might increase because of increased intestinal permeability, bacterial overgrowth, or impaired clearance of microbial products by Kupffer cells. We investigated whether the extent and progression of liver disease in patients with chronic HBV or HCV infection are associated with microbial translocation and subsequent activation of monocytes.

METHODS

In a retrospective study, we analyzed data from 16 patients with minimal fibrosis, 68 with cirrhosis, and 67 uninfected volunteers. We analyzed plasma levels of soluble CD14 (sCD14), intestinal fatty acid binding protein, and interleukin-6 by enzyme-linked immunosorbent assay, and lipopolysaccharide (LPS) by the limulus amebocyte lysate assay, at presentation and after antiviral treatment.

RESULTS

Compared with uninfected individuals, HCV- and HBV-infected individuals had higher plasma levels of LPS, intestinal fatty acid binding protein (indicating enterocyte death), sCD14 (produced upon LPS activation of monocytes), and interleukin-6. Portal hypertension, indicated by low platelet counts, was associated with enterocyte death (P=.045 at presentation, P<.0001 after therapy). Levels of sCD14 correlated with markers of hepatic inflammation (P=.02 for aspartate aminotransferase, P=.002 for ferritin) and fibrosis (P<.0001 for γ-glutamyl transpeptidase, P=.01 for alkaline phosphatase, P<.0001 for α-fetoprotein). Compared to subjects with minimal fibrosis, subjects with severe fibrosis at presentation had higher plasma levels of sCD14 (P=.01) and more hepatic CD14+ cells (P=.0002); each increased risk for disease progression (P=.0009 and P=.005, respectively).

CONCLUSIONS

LPS-induced local and systemic inflammation is associated with cirrhosis and predicts progression to end-stage liver disease in patients with HBV or HCV infection.

Pathogenesis of a genogroup II human norovirus in gnotobiotic pigs

We evaluated the gnotobiotic (Gn) pig as a model to study the pathogenesis of human norovirus (HuNoV) and to determine the target cells for viral replication. Sixty-five Gn pigs were inoculated with fecal filtrates of the NoV/GII/4/HS66/2001/US strain or with pig-passaged intestinal contents (IC) and euthanized acutely (n = 43) or after convalescence (n = 22). Age-matched Gn piglets (n = 14) served as mock-inoculated controls. Seventy-four percent (48/65) of the inoculated animals developed mild diarrhea compared to 0 of 14 controls. Pigs from postinoculation days (PID) 1 to 4 tested positive for HuNoV by reverse transcription-PCR of rectal swab fluids (29/65) and IC (9/43) and by antigen (Ag) enzyme-linked immunosorbent assay (ELISA) using antiserum to virus-like particles of HuNoV GII/4. No control pigs were positive. Histopathologic examination showed mild lesions in the proximal small intestine of only one pig (1/7). Seroconversion after PID 21 was detected by antibody ELISA in 13 of 22 virus-inoculated pigs (titers, 1:20 to 1:200) but not in controls. Immunofluorescent microscopy using a monoclonal antibody to HuNoV GII capsid revealed patchy infection of duodenal and jejunal enterocytes of 18 of 31 HuNoV-inoculated pigs with a few stained cells in the ileum and no immunofluorescence (IF) in mock-inoculated controls. Immunofluorescent detection of the viral nonstructural N-terminal protein antigen in enterocytes confirmed translation. Transmission electron microscopy of intestines from HuNoV-inoculated pigs showed disrupted enterocytes, with cytoplasmic membrane vesicles containing calicivirus-like particles of 25 to 40 nm in diameter. In summary, serial passage of HuNoV in pigs, with occurrence of mild diarrhea and shedding, and immunofluorescent detection of the HuNoV structural and nonstructural proteins in enterocytes confirm HuNoV replication in Gn pigs.

Tropism for tuft cells determines immune promotion of norovirus pathogenesis

Complex interactions between host immunity and the microbiome regulate norovirus infection. However, the mechanism of host immune promotion of enteric virus infection remains obscure. The cellular tropism of noroviruses is also unknown. Recently, we identified CD300lf as a murine norovirus (MNoV) receptor. In this study, we have shown that tuft cells, a rare type of intestinal epithelial cell, express CD300lf and are the target cell for MNoV in the mouse intestine. We found that type 2 cytokines, which induce tuft cell proliferation, promote MNoV infection in vivo. These cytokines can replace the effect of commensal microbiota in promoting virus infection. Our work thus provides insight into how the immune system and microbes can coordinately promote enteric viral infection.

Loss of mucosal CD103+ DCs and IL-17+ and IL-22+ lymphocytes is associated with mucosal damage in SIV infection

Human immunodeficiency virus (HIV) and Simian immunodeficiency virus (SIV) disease progression is associated with multifocal damage to the gastrointestinal tract epithelial barrier that correlates with microbial translocation and persistent pathological immune activation, but the underlying mechanisms remain unclear. Investigating alterations in mucosal immunity during SIV infection, we found that damage to the colonic epithelial barrier was associated with loss of multiple lineages of interleukin (IL)-17-producing lymphocytes, cells that microarray analysis showed expressed genes important for enterocyte homeostasis, including IL-22. IL-22-producing lymphocytes were also lost after SIV infection. Potentially explaining coordinate loss of these distinct populations, we also observed loss of CD103+ dendritic cells (DCs) after SIV infection, which associated with the loss of IL-17- and IL-22-producing lymphocytes. CD103+ DCs expressed genes associated with promotion of IL-17/IL-22+ cells, and coculture of CD103+ DCs and naïve T cells led to increased IL17A and RORc expression in differentiating T cells. These results reveal complex interactions between mucosal immune cell subsets providing potential mechanistic insights into mechanisms of mucosal immune dysregulation during HIV/SIV infection, and offer hints for development of novel therapeutic strategies to address this aspect of AIDS virus pathogenesis.

Tissue and cellular tropism of the coronavirus associated with severe acute respiratory syndrome: an in-situ hybridization study of fatal cases

Severe acute respiratory syndrome (SARS) is a new human infectious disease with significant morbidity and mortality. The disease has been shown to be associated with a new coronavirus (SARS‐CoV). The clinical and epidemiological aspects of SARS have been described. Moreover, the viral genome of SARS‐CoV has been fully sequenced. However, much of the biological behaviour of the virus is not known and data on the tissue and cellular tropism of SARS‐CoV are limited. In this study, six fatal cases of SARS were investigated for the tissue and cellular tropism of SARS‐CoV using an in‐situ hybridization (ISH) technique. Among all the tissues studied, positive signals were seen in pneumocytes in the lungs and surface enterocytes in the small bowel. Infected pneumocytes were further confirmed by immunofluorescence–fluorescence in‐situ hybridization (FISH) analysis. These results provide important information concerning the tissue tropism of SARS‐CoV, which is distinct from previously identified human coronaviruses, and suggest the possible involvement of novel receptors in this infection. Whereas the lung pathology was dominated by diffuse alveolar damage, the gut was relatively intact. These findings indicated that tissue responses to SARS‐CoV infection are distinct in different organs. Copyright © 2004 John Wiley & Sons, Ltd.

Enteric adenovirus infection in pediatric small bowel transplant recipients

Three of 70 small bowel transplant recipients were diagnosed with adenovirus enteritis. The biopsies were performed for surveillance in one patient at 2.7 years after transplantation and in two symptomatic children 1.5 years and 4.5 months after transplantation. In all three patients the characteristic epithelial changes were not noted by the primary observers. Two biopsies had been called "suggestive of acute rejection" and both patients had been so treated. One biopsy had been diagnosed as "regenerative". Once the epithelial changes were recognized as being viral, confirmation was possible by stool culture in one patient, immunohistochemistry in two patients, or by lift technique of the H&E sections for electron microscopy. The immune suppression was reduced and none of the patients developed disseminated infection. As in other transplanted organs, such as lung and liver, adenovirus infection may be limited largely to the allograft but can be destructive. Early recognition of the characteristic changes that are illustrated can lead to confirmation of the virus and appropriate reduction of immune suppression. A mistaken diagnosis of rejection and augmentation of immune suppression can lead to viral dissemination and potential fatality.

Bacteria and bacterial envelope components enhance mammalian reovirus thermostability

Enteric viruses encounter diverse environments as they migrate through the gastrointestinal tract to infect their hosts. The interaction of eukaryotic viruses with members of the host microbiota can greatly impact various aspects of virus biology, including the efficiency with which viruses can infect their hosts. Mammalian orthoreovirus, a human enteric virus that infects most humans during childhood, is negatively affected by antibiotic treatment prior to infection. However, it is not known how components of the host microbiota affect reovirus infectivity. In this study, we show that reovirus virions directly interact with Gram positive and Gram negative bacteria. Reovirus interaction with bacterial cells conveys enhanced virion thermostability that translates into enhanced attachment and infection of cells following an environmental insult. Enhanced virion thermostability was also conveyed by bacterial envelope components lipopolysaccharide (LPS) and peptidoglycan (PG). Lipoteichoic acid and N-acetylglucosamine-containing polysaccharides enhanced virion stability in a serotype-dependent manner. LPS and PG also enhanced the thermostability of an intermediate reovirus particle (ISVP) that is associated with primary infection in the gut. Although LPS and PG alter reovirus thermostability, these bacterial envelope components did not affect reovirus utilization of its proteinaceous cellular receptor junctional adhesion molecule-A or cell entry kinetics. LPS and PG also did not affect the overall number of reovirus capsid proteins σ1 and σ3, suggesting their effect on virion thermostability is not mediated through altering the overall number of major capsid proteins on the virus. Incubation of reovirus with LPS and PG did not significantly affect the neutralizing efficiency of reovirus-specific antibodies. These data suggest that bacteria enhance reovirus infection of the intestinal tract by enhancing the thermal stability of the reovirus particle at a variety of temperatures through interactions between the viral particle and bacterial envelope components.

Transepithelial transport of HIV-1 by M cells is receptor-mediated

Human colon carcinoma Caco-2 cell monolayers undergo conversion into cells that share morphological and functional features of M cells when allowed to interact with B lymphocytes. A lymphotropic (X4) HIV-1 strain crosses M cell monolayers and infects underlying CD4(+) target cells. Transport requires both lactosyl cerebroside and CXCR4 receptors, which are expressed on the apical surface of Caco-2 and M cells. Antibodies specific for each receptor block transport. In contrast, a monotropic (R5) HIV-1 strain is unable to cross M cell monolayers and infect underlying monocytes, despite efficient transport of latex beads. Caco-2 and M cells do not express CCR5, but transfection of these cells with CCR5 cDNA restores transport of R5 virus, which demonstrates that HIV-1 transport across M cells is receptor-mediated. The follicle-associated epithelium covering human gut lymphoid follicles expresses CCR5, but not CXCR4, and lactosyl cerebroside, suggesting that HIV-1 infection may occur through M cells and enterocytes at these sites.

Coronavirus Disease (COVID-19) Caused by (SARS-CoV-2) Infections: A Real Challenge for Human Gut Microbiota

The current COVID-19 pandemic is a great challenge for worldwide researchers in the human microbiota area because the mechanisms and long-term effects of the infection at the GI level are not yet deeply understood. In the current review, scientific literature including original research articles, clinical studies, epidemiological reports, and review-type articles concerning human intestinal infection with SARS-CoV-2 and the possible consequences on the microbiota were reviewed. Moreover, the following aspects pertaining to COVID-19 have also been discussed: transmission, resistance in the human body, the impact of nutritional status in relation to the intestinal microbiota, and the impact of comorbid metabolic disorders such as inflammatory bowel disease (IBS), obesity, and type two diabetes (T2D). The articles investigated show that health, age, and nutritional status are associated with specific communities of bacterial species in the gut, which could influence the clinical course of COVID-19 infection. Fecal microbiota alterations were associated with fecal concentrations of SARS-CoV-2 and COVID-19 severity. Patients suffering from metabolic and gastrointestinal (GI) disorders are thought to be at a moderate-to-high risk of infection with SARS-CoV-2, indicating the direct implication of gut dysbiosis in COVID-19 severity. However, additional efforts are required to identify the initial GI symptoms of COVID-19 for possible early intervention.

Epithelial response to IFN-γ promotes SARS-CoV-2 infection

SARS-CoV-2, the agent that causes COVID-19, invades epithelial cells, including those of the respiratory and gastrointestinal mucosa, using angiotensin-converting enzyme-2 (ACE2) as a receptor. Subsequent inflammation can promote rapid virus clearance, but severe cases of COVID-19 are characterized by an inefficient immune response that fails to clear the infection. Using primary epithelial organoids from human colon, we explored how the central antiviral mediator IFN-γ, which is elevated in COVID-19, affects epithelial cell differentiation, ACE2 expression, and susceptibility to infection with SARS-CoV-2. In mouse and human colon, ACE2 is mainly expressed by surface enterocytes. Inducing enterocyte differentiation in organoid culture resulted in increased ACE2 production. IFN-γ treatment promoted differentiation into mature KRT20+ enterocytes expressing high levels of ACE2, increased susceptibility to SARS-CoV-2 infection, and resulted in enhanced virus production in infected cells. Similarly, infection-induced epithelial interferon signaling promoted enterocyte maturation and enhanced ACE2 expression. We here reveal a mechanism by which IFN-γ-driven inflammatory responses induce a vulnerable epithelial state with robust replication of SARS-CoV-2, which may have an impact on disease outcome and virus transmission.

Relative Abundance of SARS-CoV-2 Entry Genes in the Enterocytes of the Lower Gastrointestinal Tract

There is increasing evidence of gastrointestinal (GI) infection by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). We surveyed the co-expression of SARS-CoV-2 entry genes ACE2 and TMPRSS2 throughout the GI tract to assess potential sites of infection. Publicly available and in-house single-cell RNA-sequencing datasets from the GI tract were queried. Enterocytes from the small intestine and colonocytes showed the highest proportions of cells co-expressing ACE2 and TMPRSS2. Therefore, the lower GI tract represents the most likely site of SARS-CoV-2 entry leading to GI infection.

Pathology of astrovirus associated diarrhoea in a paediatric bone marrow transplant recipient

Human astrovirus infection often causes outbreaks of self limiting diarrhoea, but may also infect patients who are immunodeficient or immunocompromised. Although there are previous publications relating to various aspects of astroviruses, there is a minimal amount of literature on the histopathological features of gastrointestinal astrovirus infection in humans. We report the histopathological findings, including immunohistochemical and electron microscopic features, of astrovirus infection in a bone marrow transplant recipient aged 4 years with diarrhoea. The appearance of a small intestinal biopsy did not suggest graft versus host disease, but demonstrated villous blunting, irregularity of surface epithelial cells, and an increase in lamina propria inflammatory cell density. Immunohistochemical staining with a murine astrovirus group specific monoclonal antibody demonstrated progressively more extensive staining in the duodenal and jejunal biopsies, predominantly restricted to the luminal surface and cytoplasm of surface epithelial cells, most marked at the villus tips. Electron microscopic examination demonstrated viral particles within the cytoplasm of enterocytes, focally forming paracrystalline arrays.

Coronaviral hypothetical and structural proteins were found in the intestinal surface enterocytes and pneumocytes of severe acute respiratory syndrome (SARS)

Severe acute respiratory syndrome (SARS) is a newly emerging infectious disease that haunted the world from November 2002 to July 2003. Little is known about the biology and pathophysiology of the novel coronavirus that causes SARS. The tissue and cellular distributions of coronaviral hypothetical and structural proteins in SARS were investigated. Antibodies against the hypothetical (SARS 3a, 3b, 6, 7a and 9b) and structural proteins (envelope, membrane, nucleocapsid and spike) of the coronavirus were generated from predicted antigenic epitopes of each protein. The presence of these proteins were first verified in coronavirus-infected Vero E6 tissue culture model. Immunohistochemical studies on different human tissues, including a cohort of nine autopsies, two liver biopsies and intestinal biopsies of SARS patients, further confirmed the existence of coronaviral hypothetical and structural proteins in the cytoplasm of pneumocytes and small intestinal surface enterocytes in SARS patients. With this vast array of antibodies, no signal was observed in other cell types including those organs in which reverse transcriptase-polymerase chain reactions were reported to be positive. Structural proteins and the functionally undefined hypothetical proteins were expressed in coronavirus-infected cells with distinct expression pattern in different organs in SARS patients. These antipeptide antibodies can be useful for the diagnosis of SARS at the tissue level.

Primary murine small intestinal epithelial cells, maintained in long-term culture, are susceptible to rotavirus infection

We describe a method for long-term culture of primary small intestinal epithelial cells (IEC) from suckling mice. IEC were digested from intestinal fragments as small intact units of epithelium (organoids) by using collagenase and dispase. IEC proliferated from organoids on a basement-membrane-coated culture surface and remained viable for 3 weeks. Cultured IEC had the morphologic and functional characteristics of immature enterocytes, notably sustained expression of cytokeratin and alkaline phosphatase. Few mesenchymal cells were present in the IEC cultures. IEC were also cultured from adult BALB/c mice and expressed major histocompatibility complex (MHC) class II antigens for at least 48 h in vitro. Primary IEC supported the growth of rhesus rotavirus (RRV) to a greater extent than a murine small intestinal cell line, m-IC(cl2). Cell-culture-adapted murine rotavirus strain EDIM infected primary IEC and m-IC(cl2) cells to a lesser extent than RRV. Wild-type EDIM did not infect either cell type. Long-term culture of primary murine small intestinal epithelial cells provides a method to study (i) virus-cell interactions, (ii) the capacity of IEC to act as antigen-presenting cells using a wide variety of MHC haplotypes, and (iii) IEC biology.

Rotavirus infection induces cytoskeleton disorganization in human intestinal epithelial cells: implication of an increase in intracellular calcium concentration

Rotavirus infection is the most common cause of severe infantile gastroenteritis worldwide. In vivo, rotavirus exhibits a marked tropism for the differentiated enterocytes of the intestinal epithelium. In vitro, differentiated and undifferentiated intestinal cells can be infected. We observed that rotavirus infection of the human intestinal epithelial Caco-2 cells induces cytoskeleton alterations as a function of cell differentiation. The vimentin network disorganization detected in undifferentiated Caco-2 cells was not found in fully differentiated cells. In contrast, differentiated Caco-2 cells presented Ca(2+)-dependent microtubule disassembly and Ca(2+)-independent cytokeratin 18 rearrangement, which both require viral replication. We propose that these structural alterations could represent the first manifestations of rotavirus-infected enterocyte injury leading to functional perturbations and then to diarrhea.

Noroviral p-particles as an in vitro model to assess the interactions of noroviruses with probiotics

Noroviruses (NoVs) are the main etiologic agents of acute epidemic gastroenteritis and probiotic bacteria have been reported to exert a positive effect on viral diarrhea. The protruding (P) domain from NoVs VP1 capsid protein has the ability to assemble into the so-called P-particles, which retain the binding ability to host receptors. We purified the P-domains from NoVs genotypes GI.1 and GII.4 as 6X(His)-tagged proteins and determined that, similar to native domains, they were structured into P-particles that were functional in the recognition of the specific glycoconjugated receptors, as established by surface plasmon resonance experiments. We showed that several lactic acid bacteria (probiotic and non-probiotic) and a Gram-negative probiotic strain have the ability to bind P-particles on their surfaces irrespective of their probiotic status. The binding of P-particles (GI.1) to HT-29 cells in the presence of selected strains showed that bacteria can inhibit P-particle attachment in competitive exclusion experiments. However, pre-treatment of cells with bacteria or adding bacteria to cells with already attached P-particles enhanced the retention of the particles. Although direct viral binding and blocking of viral receptors have been postulated as mechanisms of protection against viral infection by probiotic bacteria, these results highlight the need for a careful evaluation of this hypothesis. The work presented here investigates for the first time the probiotic-NoVs-host interactions and points up the NoVs P-particles as useful tools to overcome the absence of in vitro cellular models to propagate these viruses.

Pathology of Rotavirus Infection in Suckling Mice: A Study by Conventional Histology, Immunofluorescence, Ultrathin Sections, and Scanning Electron Microscopy

Pathologic changes induced in the small intestine of suckling mice by rotavirus infection were studied by conventional histology, immunofluorescence, scanning electron microscopy, and electron microscopy of ultrathin sections. Infection could be detected within 24 hours in a few mice, but after 2 days it was well established. Swollen, often vacuolated infected cells were found on the sides and tips of villi from which they rapidly became detached; microvilli showed variable irregularity. Immature enterocytes from crypts replaced lost infected cells. By the tenth day very few infected cells could still be found. Both tubular structures and spherical particles occurred in the infected cells. Only tubular structures were found in nuclei.

Differentiation-dependent redistribution of heparan sulfate in epithelial intestinal Caco-2 cells leads to basolateral entry of cytomegalovirus

Human cytomegalovirus (HCMV) causes a broad spectrum of clinical manifestations in immunocompromised patients, including infection of the gastrointestinal tract. To investigate the role of epithelial cells in the gastrointestinal HCMV disease, we used the intestinal epithelial cell line Caco-2, which is permissive for HCMV replication. In differentiated Caco-2 cells, we showed previously that HCMV infection proceeds preferentially from the basolateral membrane, suggesting that receptors for HCMV may be contained predominantly in the basolateral membrane (A. Esclatine et al., 2000, J. Virol. 74, 513-517). Therefore, we examined expression and localization in Caco-2 cells of heparan sulfate (HS) proteoglycan and annexin II, previously implicated in initial events of HCMV infection. We observed that annexin II is expressed in Caco-2 cells, but is not essential for entry of HCMV. We showed that, during the differentiation process, HS, initially present on the entire surface of the membrane of undifferentiated cells, ultimately became sequestered at the basolateral cell surface of fully differentiated cells. We established by biochemical assays that membrane-associated HS proteoglycan mediates both viral attachment to, and subsequent infection of, Caco-2 cells, regardless of the cell differentiation state. Thus, the redistribution of HS is implicated in the basolateral entry of HCMV into differentiated Caco-2 cells.

Premises among SARS-CoV-2, dysbiosis and diarrhea: Walking through the ACE2/mTOR/autophagy route

Recently, a new coronavirus (SARS-CoV-2) was discovered in China. Due to its high level of contagion, it has already reached most countries, quickly becoming a pandemic. Although the most common symptoms are related to breathing problems, SARS-CoV-2 infections also affect the gastrointestinal tract culminating in inflammation and diarrhea. However, the mechanisms related to these enteric manifestations are still not well understood. Evidence shows that the SARS-CoV-2 binds to the angiotensin-converting enzyme receptor 2 (ACE2) in host cells as a viral invasion mechanism and can infect the lungs and the gut. Other viruses have already been linked to intestinal symptoms through binding to ACE2. In turn, this medical hypothesis article conjectures that the ACE2 downregulation caused by the SARS-CoV-2 internalization could lead to decreased activation of the mechanistic target of mTOR with increased autophagy and lead to intestinal dysbiosis, resulting in diarrhea. Besides that, dysbiosis can directly affect the respiratory system through the lungs. Although there are clues to other viruses that modulate the ACE2/gut/lungs axis, including the participation of autophagy and dysbiosis in the development of gastrointestinal symptoms, there is still no evidence of the ACE2/mTOR/autophagy pathway in SARS-CoV-2 infections. Thus, we propose that the new coronavirus causes a change in the intestinal microbiota, which culminates in a diarrheal process through the ACE2/mTOR/autophagy pathway into enterocytes. Our assumption is supported by premises that unregulated intestinal microbiota increases the susceptibility to other diseases and extra-intestinal manifestations, which can even cause remote damage in lungs. These putative connections lead us to suggest and encourage future studies aiming at assessing the aforementioned hypothesis and regulating dysbiosis caused by SARS-CoV-2 infection, in order to confirm the decrease in lung injuries and the improvement in the prognosis of the disease.

Cell-type specific regulation of gene expression by simian virus 40 T antigens

SV40 transforms cells through the action of two oncoproteins, large T antigen and small t antigen. Small t antigen targets phosphatase PP2A, while large T antigen stimulates cell proliferation and survival by action on multiple proteins, including the tumor suppressors Rb and p53. Large T antigen also binds components of the transcription initiation complex and several transcription factors. We examined global gene expression in SV40-transformed mouse embryo fibroblasts, and in enterocytes obtained from transgenic mice. SV40 transformation alters the expression of approximately 800 cellular genes in both systems. Much of this regulation is observed in both MEFs and enterocytes and is consistent with T antigen action on the Rb-E2F pathway. However, the regulation of many genes is cell-type specific, suggesting that unique signaling pathways are activated in different cell types upon transformation, and that the consequences of SV40 transformation depends on the type of cell targeted.

Infection of human enterocyte-like cells with rotavirus enhances invasiveness of Yersinia enterocolitica and Y. pseudotuberculosis

Mixed infection with rotavirus and either Yersinia enterocolitica or Y. pseudotuberculosis was analysed in Caco-2 cells, an enterocyte-like cell line highly susceptible to these pathogens. Results showed an increase of bacterial adhesion and internalisation in rotavirus-infected cells. Increased internalisation was also seen with Escherichia coli strain HB101 (pRI203), harbouring the inv gene from Y. pseudotuberculosis, which is involved in the invasion process of host cells. In contrast, the superinfection with bacteria of Caco-2 cells pre-infected with rotavirus resulted in decreased viral antigen synthesis. Transmission electron microscopy confirmed the dual infection of enterocytes. These data suggest that rotavirus infection enhances the early interaction between host cell surfaces and enteroinvasive Yersinia spp.

SARS-CoV-2 productively infects human gut enterocytes

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) can cause coronavirus disease 2019 (COVID-19), an influenza-like disease that is primarily thought to infect the lungs with transmission through the respiratory route. However, clinical evidence suggests that the intestine may present another viral target organ. Indeed, the SARS-CoV-2 receptor angiotensin-converting enzyme 2 (ACE2) is highly expressed on differentiated enterocytes. In human small intestinal organoids (hSIOs), enterocytes were readily infected by SARS-CoV and SARS-CoV-2, as demonstrated by confocal and electron microscopy. Enterocytes produced infectious viral particles, whereas messenger RNA expression analysis of hSIOs revealed induction of a generic viral response program. Therefore, the intestinal epithelium supports SARS-CoV-2 replication, and hSIOs serve as an experimental model for coronavirus infection and biology.