The underrated gut microbiota helminths, bacteriophages, fungi, and archaea

The microbiota inhabits the gastrointestinal tract, providing essential capacities to the host. The microbiota is a crucial factor in intestinal health and regulates intestinal physiology. However, microbiota disturbances, named dysbiosis, can disrupt intestinal homeostasis, leading to the development of diseases. Classically, the microbiota has been referred to as bacteria, though other organisms form this complex group, including viruses, archaea, and eukaryotes such as fungi and protozoa. This review aims to clarify the role of helminths, bacteriophages, fungi, and archaea in intestinal homeostasis and diseases, their interaction with bacteria, and their use as therapeutic targets in intestinal maladies

Enteric Species F Human Adenoviruses use Laminin-Binding Integrins as Co-Receptors for Infection of Ht-29 Cells

The enteric species F human adenovirus types 40 and 41 (HAdV-40 and -41) are the third most common cause of infantile gastroenteritis in the world. Knowledge about HAdV-40 and -41 cellular infection is assumed to be fundamentally different from that of other HAdVs since HAdV-40 and -41 penton bases lack the aV-integrin-interacting RGD motif. This motif is used by other HAdVs mainly for internalization and endosomal escape. We hypothesised that the penton bases of HAdV-40 and -41 interact with integrins independently of the RGD motif. HAdV-41 transduction of a library of rodent cells expressing specific human integrin subunits pointed to the use of laminin-binding alpha 2-, alpha 3- and alpha 6- containing integrins as well as other integrins as candidate co-receptors. Specific laminins prevented internalisation and infection, and recombinant, soluble HAdV-41 penton base proteins prevented infection of human intestinal HT-29 cells. Surface plasmon resonance analysis demonstrated that HAdV-40 and -41 penton base proteins bind to alpha 6-containing integrins with an affinity similar to that of previously characterised penton base:integrin interactions. With these results, we propose that laminin-binding integrins are co-receptors for HAdV-40 and -41

Capsid protein functions of enteric human adenoviruses

Human adenoviruses (HAdVs) cause respiratory illnesses, epidemic conjunctivitis and infantile gastroenteritis. HAdV types 40 and 41 cause enteric infections in infants worldwide. HAdVs use various receptors for attachment onto different host cells. Coxsackievirus and adenovirus receptor, CD46, sialic acid, coagulation factors IX and X, lactoferrin and heparan sulfate are some receptors and molecules which the hexon and fiber proteins (components of the capsid) bind for direct or indirect cellular attachment. The penton base protein (another component of the capsid) is responsible for the internalization of the virus into the host cell. An arginine-glycine-aspartic acid amino acid motif is present in most but not all adenovirus penton base proteins and mediates interaction with αv integrins, resulting in internalization. The enteric HAdVs are unique since they do not have this arginine-glycine-aspartic acid motif on their penton base. Using a library of hamster cells expressing specific human integrins, along with recombinant soluble penton base from HAdV type 41 and commercially available soluble laminins, we identified laminin-binding integrins as co-receptors for entry and infection of human intestinal HT-29 cells by the enteric HAdVs. HAdV types 40, 41 and 52 are the only three HAdVs that have two different fiber proteins, one long and one short. By performing cell binding and infection experiments, we have found that the receptor for the short fiber of HAdV-52 is sialic acid-containing glycans and the long fiber receptor is CAR although most of the binding was dependent on sialic acid-containing glycans. We also observed that the short fiber of HAdV type 40 interacts with soluble heparin or cell surface heparan sulfate. Further investigation pointed out that the specific sulfate groups on heparin/heparan sulfate (sulfated glycosaminoglycans) are important for this binding. Also, we identified that the interaction and utilization of these glycosaminoglycans as receptors is dependent on exposure to low pH. We also studied the potential mechanism behind the symptoms caused by these enteric HAdVs in enteroendocrine cells called enterochromaffin cells. We could show that the short fiber and the hexon of HAdV type 41 stimulated release of serotonin from the enterochromaffin cells, which can be a cause of vomiting and diarrhea. These studies have given us insight into the role of enteric HAdV capsid proteins as ligands to hitherto unidentified receptors and co-receptors. We also show that these molecules play important functions in the virus’ infectious cycle and probably also in their disease mechanism of host cells

Capsid protein functions of enteric human adenoviruses

Human adenoviruses (HAdVs) cause respiratory illnesses, epidemic conjunctivitis and infantile gastroenteritis. HAdV types 40 and 41 cause enteric infections in infants worldwide. HAdVs use various receptors for attachment onto different host cells. Coxsackievirus and adenovirus receptor, CD46, sialic acid, coagulation factors IX and X, lactoferrin and heparan sulfate are some receptors and molecules which the hexon and fiber proteins (components of the capsid) bind for direct or indirect cellular attachment. The penton base protein (another component of the capsid) is responsible for the internalization of the virus into the host cell. An arginine-glycine-aspartic acid amino acid motif is present in most but not all adenovirus penton base proteins and mediates interaction with αv integrins, resulting in internalization. The enteric HAdVs are unique since they do not have this arginine-glycine-aspartic acid motif on their penton base. Using a library of hamster cells expressing specific human integrins, along with recombinant soluble penton base from HAdV type 41 and commercially available soluble laminins, we identified laminin-binding integrins as co-receptors for entry and infection of human intestinal HT-29 cells by the enteric HAdVs. HAdV types 40, 41 and 52 are the only three HAdVs that have two different fiber proteins, one long and one short. By performing cell binding and infection experiments, we have found that the receptor for the short fiber of HAdV-52 is sialic acid-containing glycans and the long fiber receptor is CAR although most of the binding was dependent on sialic acid-containing glycans. We also observed that the short fiber of HAdV type 40 interacts with soluble heparin or cell surface heparan sulfate. Further investigation pointed out that the specific sulfate groups on heparin/heparan sulfate (sulfated glycosaminoglycans) are important for this binding. Also, we identified that the interaction and utilization of these glycosaminoglycans as receptors is dependent on exposure to low pH. We also studied the potential mechanism behind the symptoms caused by these enteric HAdVs in enteroendocrine cells called enterochromaffin cells. We could show that the short fiber and the hexon of HAdV type 41 stimulated release of serotonin from the enterochromaffin cells, which can be a cause of vomiting and diarrhea. These studies have given us insight into the role of enteric HAdV capsid proteins as ligands to hitherto unidentified receptors and co-receptors. We also show that these molecules play important functions in the virus’ infectious cycle and probably also in their disease mechanism of host cells

Capsid protein functions of enteric human adenoviruses

Human adenoviruses (HAdVs) cause respiratory illnesses, epidemic conjunctivitis and infantile gastroenteritis. HAdV types 40 and 41 cause enteric infections in infants worldwide. HAdVs use various receptors for attachment onto different host cells. Coxsackievirus and adenovirus receptor, CD46, sialic acid, coagulation factors IX and X, lactoferrin and heparan sulfate are some receptors and molecules which the hexon and fiber proteins (components of the capsid) bind for direct or indirect cellular attachment. The penton base protein (another component of the capsid) is responsible for the internalization of the virus into the host cell. An arginine-glycine-aspartic acid amino acid motif is present in most but not all adenovirus penton base proteins and mediates interaction with αv integrins, resulting in internalization. The enteric HAdVs are unique since they do not have this arginine-glycine-aspartic acid motif on their penton base. Using a library of hamster cells expressing specific human integrins, along with recombinant soluble penton base from HAdV type 41 and commercially available soluble laminins, we identified laminin-binding integrins as co-receptors for entry and infection of human intestinal HT-29 cells by the enteric HAdVs. HAdV types 40, 41 and 52 are the only three HAdVs that have two different fiber proteins, one long and one short. By performing cell binding and infection experiments, we have found that the receptor for the short fiber of HAdV-52 is sialic acid-containing glycans and the long fiber receptor is CAR although most of the binding was dependent on sialic acid-containing glycans. We also observed that the short fiber of HAdV type 40 interacts with soluble heparin or cell surface heparan sulfate. Further investigation pointed out that the specific sulfate groups on heparin/heparan sulfate (sulfated glycosaminoglycans) are important for this binding. Also, we identified that the interaction and utilization of these glycosaminoglycans as receptors is dependent on exposure to low pH. We also studied the potential mechanism behind the symptoms caused by these enteric HAdVs in enteroendocrine cells called enterochromaffin cells. We could show that the short fiber and the hexon of HAdV type 41 stimulated release of serotonin from the enterochromaffin cells, which can be a cause of vomiting and diarrhea. These studies have given us insight into the role of enteric HAdV capsid proteins as ligands to hitherto unidentified receptors and co-receptors. We also show that these molecules play important functions in the virus’ infectious cycle and probably also in their disease mechanism of host cells

The structure of enteric human adenovirus 41 : A leading cause of diarrhea in children

Human adenovirus (HAdV) types F40 and F41 are a prominent cause of diarrhea and diarrhea-associated mortality in young children worldwide. These enteric HAdVs differ notably in tissue tropism and pathogenicity from respiratory and ocular adenoviruses, but the structural basis for this divergence has been unknown. Here, we present the first structure of an enteric HAdV-HAdV-F41-determined by cryo-electron microscopy to a resolution of 3.8 angstrom. The structure reveals extensive alterations to the virion exterior as compared to nonenteric HAdVs, including a unique arrangement of capsid protein IX. The structure also provides new insights into conserved aspects of HAdV architecture such as a proposed location of core protein V, which links the viral DNA to the capsid, and assembly-induced conformational changes in the penton base protein. Our findings provide the structural basis for adaptation of enteric HAdVs to a fundamentally different tissue tropism

Heparan Sulfate Is a Cellular Receptor for Enteric Human Adenoviruses.

Human adenovirus (HAdV)-F40 and -F41 are leading causes of diarrhea and diarrhea-associated mortality in children under the age of five, but the mechanisms by which they infect host cells are poorly understood. HAdVs initiate infection through interactions between the knob domain of the fiber capsid protein and host cell receptors. Unlike most other HAdVs, HAdV-F40 and -F41 possess two different fiber proteins-a long fiber and a short fiber. Whereas the long fiber binds to the Coxsackievirus and adenovirus receptor (CAR), no binding partners have been identified for the short fiber. In this study, we identified heparan sulfate (HS) as an interaction partner for the short fiber of enteric HAdVs. We demonstrate that exposure to acidic pH, which mimics the environment of the stomach, inactivates the interaction of enteric adenovirus with CAR. However, the short fiber:HS interaction is resistant to and even enhanced by acidic pH, which allows attachment to host cells. Our results suggest a switch in receptor usage of enteric HAdVs after exposure to acidic pH and add to the understanding of the function of the short fibers. These results may also be useful for antiviral drug development and the utilization of enteric HAdVs for clinical applications such as vaccine development

Interaction of Human Enterochromaffin Cells with Human Enteric Adenovirus 41 Leads to Serotonin Release and Subsequent Activation of Enteric Glia Cells

Human adenovirus 41 (HAdV-41) causes acute gastroenteritis in young children. The main characteristics of HAdV-41 infection are diarrhea and vomiting. Nevertheless, the precise mechanism of HAdV-41-induced diarrhea is unknown, as a suitable small-animal model has not been described. In this study, we used the human midgut carcinoid cell line GOT1 to investigate the effect of HAdV-41 infection and the individual HAdV-41 capsid proteins on serotonin release by enterochromaffin cells and on enteric glia cell (EGC) activation. We first determined that HAdV-41 could infect the enterochromaffin cells. Immunofluorescence staining revealed that the cells expressed HAdV-41-specific coxsackievirus and adenovirus receptor (CAR); flow cytometry analysis supported these findings. HAdV-41 infection of the enterochromaffin cells induced serotonin secretion dose dependently. In contrast, control infection with HAdV-5 did not induce serotonin secretion in the cells. Confocal microscopy studies of enterochromaffin cells infected with HAdV-41 revealed decreased serotonin immunofluorescence compared to that in uninfected cells. Incubation of the enterochromaffin cells with purified HAdV-41 short fiber knob and hexon proteins increased the serotonin levels in the harvested cell supernatant significantly. HAdV-41 infection could also activate EGCs, as shown in the significantly altered expression of glia fibrillary acidic protein (GFAP) in EGCs incubated with HAdV-41. The EGCs were also activated by serotonin alone, as shown in the significantly increased GFAP staining intensity. Likewise, EGCs were activated by the cell supernatant of HAdV-41-infected enterochromaffin cells. IMPORTANCE The nonenveloped human adenovirus 41 causes diarrhea, vomiting, dehydration, and low-grade fever mainly in children under 2 years of age. Even though acute gastroenteritis is well described, how human adenovirus 41 causes diarrhea is unknown. In our study, we analyzed the effect of human adenovirus 41 infection on human enterochromaffin cells and found it stimulates serotonin secretion in the cells, which is involved in regulation of intestinal secretion and gut motility and can also activate enteric glia cells, which are found in close proximity to enterochromaffin cells in vivo. This disruption of gut barrier homeostasis as maintained by these cells following human adenovirus 41 infection might be a mechanism in enteric adenovirus pathogenesis in humans and could indicate a possible serotonin-dependent cross talk between human adenovirus 41, enterochromaffin cells, and enteric glia cells.Funding Agencies|Swedish Research Council [320301, 2013-2753]; MIIC, Linkoping University</p

Enteric species F human adenoviruses use laminin-binding integrins as co-receptors for infection of Ht-29 cells

The enteric species F human adenovirus types 40 and 41 (HAdV-40 and -41) are the third most common cause of infantile gastroenteritis in the world. Knowledge about HAdV-40 and -41 cellular infection is assumed to be fundamentally different from that of other HAdVs since HAdV-40 and -41 penton bases lack the αV-integrin-interacting RGD motif. This motif is used by other HAdVs mainly for internalization and endosomal escape. We hypothesised that the penton bases of HAdV-40 and -41 interact with integrins independently of the RGD motif. HAdV-41 transduction of a library of rodent cells expressing specific human integrin subunits pointed to the use of laminin-binding α2-, α3- and α6-containing integrins as well as other integrins as candidate co-receptors. Specific laminins prevented internalisation and infection, and recombinant, soluble HAdV-41 penton base proteins prevented infection of human intestinal HT-29 cells. Surface plasmon resonance analysis demonstrated that HAdV-40 and -41 penton base proteins bind to α6-containing integrins with an affinity similar to that of previously characterised penton base:integrin interactions. With these results, we propose that laminin-binding integrins are co-receptors for HAdV-40 and -41.Originally included in thesis in manuscript form.</p

Virion composition and relative expression of CAR and sialic acid on human epithelial cells.

<p>A) Western blot analysis of HAdV-52 virion fiber content using a mouse mab (clone 4D2) recognizing an epitope (MKRARPSEDTFNPVYPY) conserved in the tail domain of all HAdVs. The experiment was performed three times (with three different virus preparations) and the figure shows one representative set of results. B) Flow cytometry analysis of CAR expression on A549 and human corneal epithelial (HCE) cells using an anti CAR mouse mab (clone E1-1). Data are shown as geometrical mean (geo mean) and the experiment was performed three times with duplicate samples in each experiment. Error bars represent means ± SD.</p