Air-liquid interface cultures enhance the oxygen supply and trigger the structural and functional differentiation of intestinal porcine epithelial cells (IPEC)

Fabrication of 3D engineered intestinal tissue producing abundant mucus by air-liquid interface culture using paper-based dual-layer scaffold

Fabrication of engineered intestinal tissues with the structures and functions as humans is crucial and promising as the tools for developing drugs and functional foods. The aim of this study is to fabricate an engineered intestinal tissue from Caco-2 cells by air-liquid interface culture using a paper-based dual-layer scaffold and analyze its structure and functions. Just by simply placing on a folded paper soaked in the medium, the electrospun gelatin microfiber mesh as the upper cell adhesion layer of the dual-layer scaffold was exposed to the air, while the lower paper layer worked to preserve and supply the cell culture medium to achieve stable culture over several weeks. Unlike the flat tissue produced using the conventional commercial cultureware, Transwell, the engineered intestinal tissue fabricated in this study formed three-dimensional villous architectures. Microvilli and tight junction structures characteristic of epithelial tissue were also formed at the apical side. Furthermore, compared to the tissue prepared by Transwell, mucus production was significantly larger, and the enzymatic activities of drug metabolism and digestion were almost equivalent. In conclusion, the air-liquid interface culture using the paper-based dual-layer scaffold developed in this study was simple but effective in fabricating the engineered intestinal tissue with superior structures and functions.

Oxygen levels affect oviduct epithelium functions in air-liquid interface culture

Key reproductive events such as fertilization and early embryonic development occur in the lumen of the oviduct. Since investigating these processes in vivo is both technically challenging and ethically sensitive, cell culture models have been established to reproduce the oviductal microenvironment. Compartmentalized culture systems, particularly air-liquid interface cultures (ALI; cells access the culture medium only from the basolateral cell side), result in highly differentiated oviduct epithelial cell cultures. The oxygen (O2) tension within the oviduct is 4-10% across species, and its reduced O2 content is presumed to be important for early reproductive processes. However, cell culture models of the oviduct are typically cultivated without O2 regulation and therefore at about 18% O2. To investigate the impact of O2 levels on oviduct epithelium functions in vitro, we cultured porcine oviduct epithelial cells (POEC) at the ALI using both physiological (5%) and supraphysiological (18%) O2 levels and two different media regimes. Epithelium architecture, barrier function, secretion of oviduct fluid surrogate (OFS), and marker gene expression were comparatively assessed. Under all culture conditions, ALI-POEC formed polarized, ciliated monolayers with appropriate barrier function. Exposure to 18% O2 accelerated epithelial differentiation and significantly increased the apical OFS volume and total protein content. Expression of oviduct genes and the abundance of OVGP1 (oviduct-specific glycoprotein 1) in the OFS were influenced by both O2 tension and medium choice. In conclusion, oviduct epithelial cells can adapt to a supraphysiological O2 environment. This adaptation, however, may alter their capability to replicate in vivo tissue characteristics.

Deoxynivalenol triggers the expression of IL-8-related signaling cascades and decreases protein biosynthesis in primary monocyte-derived cells

Humans and their immune system are confronted with mold-contaminated food and/or mold-contaminated air in daily life and indoor activities. This results in metabolic stress and unspecific disease symptoms. Other studies provided evidence that exposure to mold is associated with the etiology of allergies. Deoxynivalenol (DON) is of great concern due to its frequent occurrence in toxically relevant concentrations. The exposure to this toxin is a permanent health risk for both humans and farm animals because DON cannot be significantly removed during standard milling and processing procedures. However, the direct effect on immunity or hematology is poorly defined because most investigations could not separate the effect of DON-contaminated feed intake. Due to the widespread distribution of DON after rapid absorption, it is not surprising that DON is known to affect the immune system. The immune system of the organism has one important function, to defend against the invasion of unknown substances/organisms. This study shows for the first time a synergistic effect of both-low physiological DON-doses in combination with low LPS-doses with the focus on the IL-8 expression on protein and RNA level. Both doses were found in vivo. IL-8 together with other anorectic cytokines like IL-1β can affect the food intake and anorexia. We could also show that a calcium-response is not involved in the increased IL-8 production after acute DON stimulation with high or low concentrations.

A Conformable Organic Electronic Device for Monitoring Epithelial Integrity at the Air Liquid Interface

Air liquid interfaced (ALI) epithelial barriers are essential for homeostatic functions such as nutrient transport and immunological protection. Dysfunction of such barriers are implicated in a variety of autoimmune and inflammatory disorders and, as such, sensors capable of monitoring barrier health are integral for disease modelling, diagnostics and drug screening applications. To date, gold-standard electrical methods for detecting barrier resistance require rigid electrodes bathed in an electrolyte, which limits compatibility with biological architectures and is non-physiological for ALI. This work presents a flexible all-planar electronic device capable of monitoring barrier formation and perturbations in human respiratory and intestinal cells at ALI. By interrogating patient samples with electrochemical impedance spectroscopy and simple equivalent circuit models, disease-specific and patient-specific signatures are uncovered. Device readouts are validated against commercially available chopstick electrodes and show greater conformability, sensitivity and biocompatibility. The effect of electrode size on sensing efficiency is investigated and a cut-off sensing area is established, which is one order of magnitude smaller than previously reported. This work provides the first steps in creating a physiologically relevant sensor capable of mapping local and real-time changes of epithelial barrier function at ALI, which will have broad applications in toxicology and drug screening applications.

Contactless mechanical stimulation of tissue engineered constructs: Development and validation of an air-pulse device

OBJECTIVE

Tissue engineering (TE) is the study and development of biological substitutes to restore, maintain or improve tissue function. Tissue engineered constructs (TECs) still present differences in mechanical and biological properties compared to native tissue. Mechanotransduction is the process through which mechanical stimulation triggers proliferation, apoptosis, and extracellular matrix synthesis, among other cell activities. Regarding that aspect, the effect of in vitro stimulations such as compression, stretching, bending or fluid shear stress loading modalities have been extensively studied. A fluid flow used to produce contactless mechanical stimulation induced by an air pulse could be easily achieved in vivo without altering the tissue integrity.

METHODS

A new air-pulse device for contactless and controlled mechanical simulation of a TECs was developed and validated in this study conducted in the following three phases: 1) conception of the controlled air-pulse device combined with a 3D printed bioreactor; 2) experimental and numerical mechanical characterization of the air-pulse impact by digital image correlation; and 3) achieving sterility and noncytotoxicity of the air-pulse and of the 3D printed bioreactor using a novel dedicated sterilization process.

RESULTS

We demonstrated that the treated PLA (polylactic acid) was noncytotoxic and did not influence cell proliferation. An ethanol/autoclaved sterilization protocol for 3D printed objects in PLA has been developed in this study, enabling the use of 3D printing in cell culture. A numerical twin of the device was developed and experimentally characterized by digital image correlation. It showed a coefficient of determination R² = 0.98 between the numerical and averaged experimental surface displacement profiles of the TEC substitute.

CONCLUSION

The results of the study assessed the noncytotoxicity of PLA for prototyping by 3D printing the homemade bioreactor. A novel sterilization process for PLA was developed in this study based on a thermochemical process. A numerical twin using fluid-structure interaction method has been developed to investigate the micromechanical effects of air pulses inside the TEC, which cannot all be measured experimentally, for instance, wave propagation generated during the air-pulse impact. The device could be used to study the cell response to contactless cyclic mechanical stimulation, particularly in TEC with fibroblasts, stromal cells and mesenchymal stem cells, which have been shown to be sensitive to the frequency and strain level at the air-liquid interface.

Air-liquid interface cultures trigger a metabolic shift in intestinal epithelial cells (IPEC-1)

An improved oxygen availability in air-liquid interface (ALI) cultures of enterocytes of the small intestine seems to be primarily responsible for morphological, metabolic, and functional changes. Intestinal porcine epithelial cells 1 (IPEC-1) are less investigated and are rarely used as model for intestinal barrier but showed a profound change of cell shape during ALI cultivation. We aim to answer the following question: Are the observed morphological effects accompanied by changes in metabolic function? A microarray analysis of submerged culture (SMC) and ALI cultures identified 830 significantly regulated genes. Subsequent functional clustering revealed alterations in 31 pathways, with the highest number of regulated genes in metabolic pathways, carbon metabolism, glycolysis, and hypoxia-inducible factor (HIF) signaling. Furthermore, HIF-1α as a mediator of a metabolic switch between glycolysis and oxidative phosphorylation showed a trend of increased mRNA levels in ALI in contrast to a reduced nuclear HIF-1α content in the nucleus. Candidate genes of oxidative phosphorylation such as a mitochondrial marker exhibited enhanced mRNA levels, which was confirmed by western blot analysis. Cytochrome C oxidase (COX) subunit 5B protein was decreased in ALI, although mRNA level was increased. The oxidation of ferrocytochrome C to ferricytochrome C was used for detection of cytochrome C oxidase activity of isolated mitochondria and resulted in a trend of higher activity in ALI. Furthermore, quantification of glucose and lactate concentrations in cell culture medium revealed significantly reduced glucose levels and decreased lactate production in ALI. To evaluate energy metabolism, we measured cellular adenosine triphosphate (ATP) aggregation in homogenized cell suspensions showing similar levels. However, application of the uncoupling agent FCCP reduced ATP levels in ALI but not in SMC. In contrast, blocking with 2-desoxy-D-glucose (2DG) significantly reduced ATP content in ALI and SMC. These results indicate a metabolic shift in IPEC-1 cultured under ALI conditions enhancing oxidative phosphorylation and suppressing glycolysis.

Intestinal organoids as advanced modeling platforms to study the role of host-microbiome interaction in homeostasis and disease

After birth, animals are colonized by a diverse community of microorganisms. The digestive tract is known to contain the largest number of microbiome in the body. With emergence of the gut-brain axis, the importance of gut microbiome and its metabolites in host health has been extensively studied in recent years. The establishment of organoid culture systems has contributed to studying intestinal pathophysiology by replacing current limited models. Owing to their architectural and functional complexity similar to a real organ, co-culture of intestinal organoids with gut microbiome can provide mechanistic insights into the detrimental role of pathobiont and the homeostatic function of commensal symbiont. Here organoid-based bacterial co-culture techniques for modeling host-microbe interactions are reviewed. This review also summarizes representative studies that explore impact of enteric microorganisms on intestinal organoids to provide a better understanding of host-microbe interaction in the context of homeostasis and disease. [BMB Reports 2023; 56(1): 15-23].

Cell Cultures at the Air-Liquid Interface and Their Application in Cancer Research

Air-liquid interface (ALI) cell cultures are considered a valid tool for the replacement of animals in biomedical research. By mimicking crucial features of the human in vivo epithelial barriers (e.g., lung, intestine, and skin), ALI cell cultures enable proper structural architectures and differentiated functions of normal and diseased tissue barriers. Thereby, ALI models realistically resemble tissue conditions and provide in vivo-like responses. Since their implementation, they are routinely used in several applications, from toxicity testing to cancer research, receiving an appreciable level of acceptance (in some cases a regulatory acceptance) as attractive testing alternatives to animals. In this chapter, an overview of the ALI cell cultures will be presented together with their application in cancer cell culture, highlighting the potential advantages and disadvantages of the model.

Establishment of an In Vitro Co-Culture Model of the Piglet Gut to Study Inflammatory Response and Barrier Integrity

In intensive farming, piglets are exposed to various challenges that activate intestinal inflammatory processes, negatively affecting animal health and leading to economic losses. To study the role of the inflammatory response on epithelial barrier integrity, co-culture systems that mimic in vivo complexity are more and more preferred over cell monocultures. In this study, an in vitro gut co-culture model consisting of intestinal porcine epithelial cells and porcine peripheral blood mononuclear cells was established. The model provides an appropriate tool to study the role of the inflammatory response on epithelial barrier integrity and to screen for feed and food components, exerting beneficial effects on gut health. In the established model, inflammation-like reactions and damage of the epithelial barrier, indicated by a decrease of transepithelial electrical resistance, were elicited by activation of peripheral blood mononuclear cells via one of 3 stimuli: lipopolysaccharide, lipoteichoic acid, or concanavalin A. Two phytogenic substances that are commonly used as feed additives, licorice extract and oregano oil, have been shown to counteract the drop in transepithelial electrical resistance values in the gut co-culture model. The established co-culture model provides a powerful in vitro tool to study the role of intestinal inflammation on epithelial barrier integrity. As it consists of porcine epithelial and porcine blood cells it perfectly mimics in vivo conditions and imitates the inter-organ communication of the piglet gut. The developed model is useful to screen for nutritional components or drugs, having the potential to balance intestinal inflammation and strengthen the epithelial barrier integrity in piglets.

From the Dish to the Real World: Modeling Interactions between the Gut and Microorganisms in Gut Organoids by Tailoring the Gut Milieu

The advent of human intestinal organoid systems has revolutionized the way we understand the interactions between the human gut and microorganisms given the host tropism of human microorganisms. The gut microorganisms have regionality (i.e., small versus large intestine) and the expression of various virulence factors in pathogens is influenced by the gut milieu. However, the culture conditions, optimized for human intestinal organoids, often do not fully support the proliferation and functionality of gut microorganisms. In addition, the regional identity of human intestinal organoids has not been considered to study specific microorganisms with regional preference. In this review we provide an overview of current efforts to understand the role of microorganisms in human intestinal organoids. Specifically, we will emphasize the importance of matching the regional preference of microorganisms in the gut and tailoring the appropriate luminal environmental conditions (i.e., oxygen, pH, and biochemical levels) for modeling real interactions between the gut and the microorganisms with human intestinal organoids.

Escherichia coli Nissle 1917 Enhances Efficacy of Oral Attenuated Human Rotavirus Vaccine in a Gnotobiotic Piglet Model

Human rotavirus (HRV) infection is a major cause of viral gastroenteritis in young children worldwide. Current oral vaccines perform poorly in developing countries where efficacious vaccines are needed the most. Therefore, an alternative affordable strategy to enhance efficacy of the current RV vaccines is necessary. This study evaluated the effects of colonization of neonatal gnotobiotic (Gn) pigs with Escherichia coli Nissle (EcN) 1917 and Lacticaseibacillus rhamnosus GG (LGG) probiotics on immunogenicity and protective efficacy of oral attenuated (Att) HRV vaccine. EcN-colonized pigs had reduced virulent HRV (VirHRV) shedding and decreased diarrhea severity compared with the LGG-colonized group. They also had enhanced HRV-specific IgA antibody titers in serum and antibody secreting cell numbers in tissues pre/post VirHRV challenge, HRV-specific IgA antibody titers in intestinal contents, and B-cell subpopulations in tissues post VirHRV challenge. EcN colonization also enhanced T-cell immune response, promoted dendritic cells and NK cell function, reduced production of proinflammatory cytokines/Toll like receptor (TLR), and increased production of immunoregulatory cytokines/TLR expression in various tissues pre/post VirHRV challenge. Thus, EcN probiotic adjuvant with AttHRV vaccine enhances the immunogenicity and protective efficacy of AttHRV to a greater extent than LGG and it can be used as a safe and economical oral vaccine adjuvant.

Characterization of increased mucus production of HT29-MTX-E12 cells grown under Semi-Wet interface with Mechanical Stimulation

The intestinal mucus layer plays a crucial role in human health. To study intestinal mucus function and structure in vitro, the mucus-producing intestinal cell line HT29-MTX-E12 has been commonly used. However, this cell line produces only low amounts of the intestine-specific MUC2. It has been shown previously that HT29-MTX-E12 cells cultured under Semi-Wet interface with Mechanical Stimulation (SWMS) produced higher amounts of MUC2, concomitant with a thicker mucus layer, compared to cells cultured conventionally. However, it remains unknown which underlying pathways are involved. Therefore, we aimed to further explore the cellular processes underlying the increased MUC2 production by HT29-MTX-E12 cells grown under SWMS conditions. Cells grown on Transwell membranes for 14 days under static and SWMS conditions (after cell seeding and attachment) were subjected to transcriptome analysis to investigate underlying molecular pathways at gene expression level. Caco-2 and LS174T cell lines were included as references. We characterized how SWMS conditions affected HT29-MTX-E12 cells in terms of epithelial barrier integrity, by measuring transepithelial electrical resistance, and cell metabolism, by monitoring pH and lactate production per molecule glucose of the conditioned medium. We confirmed higher MUC2 production under SWMS conditions at gene and protein level and demonstrated that this culturing method primarily stimulated cell growth. In addition, we also found evidence for a more aerobic cell metabolism under SWMS, as shown previously for similar models. In summary, we suggest different mechanisms by which MUC2 production is enhanced under SWMS and propose potential applications of this model in future studies.

Assessing Intestinal Health. In Vitro and Ex vivo Gut Barrier Models of Farm Animals: Benefits and Limitations

Animal performance is determined by the functionality and health of the gastrointestinal tract (GIT). Complex mechanisms and interactions are involved in the regulation of GIT functionality and health. The understanding of these relationships could be crucial for developing strategies to improve animal production yields. The concept of "gut health" is not well defined, but this concept has begun to play a very important role in the field of animal science. However, a clear definition of GIT health and the means by which to measure it are lacking. In vitro and ex vivo models can facilitate these studies, creating well-controlled and repeatable conditions to understand how to improve animal gut health. Over the years, several models have been developed and used to study the beneficial or pathogenic relationships between the GIT and the external environment. This review aims to describe the most commonly used animals' in vitro or ex vivo models and techniques that are useful for better understanding the intestinal health of production animals, elucidating their benefits and limitations.

Vitamin K Vitamers Differently Affect Energy Metabolism in IPEC-J2 Cells

The fat-soluble vitamin K (VK) has long been known as a requirement for blood coagulation, but like other vitamins, has been recently recognized to play further physiological roles, particularly in cell development and homeostasis. Vertebrates cannot de novo synthesize VK, which is essential, and it can only be obtained from the diet or by the activity of the gut microbiota. The IPEC-J2 cell line, obtained from porcine small intestine, which shows strong similarities to the human one, represents an excellent functional model to in vitro study the effect of compounds at the intestinal level. The acute VK treatments on the bioenergetic features of IPEC-J2 cells were evaluated by Seahorse XP Agilent technology. VK exists in different structurally related forms (vitamers), all featured by a naphtoquinone moiety, but with distinct effects on IPEC-J2 energy metabolism. The VK1, which has a long hydrocarbon chain, at both concentrations (5 and 10 μM), increases the cellular ATP production due to oxidative phosphorylation (OXPHOS) by 5% and by 30% through glycolysis. The VK2 at 5 μM only stimulates ATP production by OXPHOS. Conversely, 10 μM VK3, which lacks the long side chain, inhibits OXPHOS by 30% and glycolysis by 45%. However, even if IPEC-J2 cells mainly prefer OXPHOS to glycolysis to produce ATP, the OXPHOS/glycolysis ratio significantly decreases in VK1-treated cells, is unaffected by VK2, and only significantly increased by 10 μM VK3. VK1, at the two concentrations tested, does not affect the mitochondrial bioenergetic parameters, while 5 μM VK2 increases and 5 μM VK3 reduces the mitochondrial respiration (i.e., maximal respiration and spare respiratory capacity). Moreover, 10 μM VK3 impairs OXPHOS, as shown by the increase in the proton leak, namely the proton backward entry to the matrix space, thus pointing out mitochondrial toxicity. Furthermore, in the presence of both VK1 and VK2 concentrations, the glycolytic parameters, namely the glycolytic capacity and the glycolytic reserve, are unaltered. In contrast, the inhibition of glycoATP production by VK3 is linked to the 80% inhibition of glycolysis, resulting in a reduced glycolytic capacity and reserve. These data, which demonstrate the VK ability to differently modulate IPEC-J2 cell energy metabolism according to the different structural features of the vitamers, can mirror VK modulatory effects on the cell membrane features and, as a cascade, on the epithelial cell properties and gut functions: balance of salt and water, macromolecule cleavage, detoxification of harmful compounds, and nitrogen recycling.

Escherichia coli Nissle 1917 administered as a dextranomar microsphere biofilm enhances immune responses against human rotavirus in a neonatal malnourished pig model colonized with human infant fecal microbiota

Human rotavirus (HRV) is a leading cause of diarrhea in children. It causes significant morbidity and mortality, especially in low- and middle-income countries (LMICs), where HRV vaccine efficacy is low. The probiotic Escherichia coli Nissle (EcN) 1917 has been widely used in the treatment of enteric diseases in humans. However, repeated doses of EcN are required to achieve maximum beneficial effects. Administration of EcN on a microsphere biofilm could increase probiotic stability and persistence, thus maximizing health benefits without repeated administrations. Our aim was to investigate immune enhancement by the probiotic EcN adhered to a dextranomar microsphere biofilm (EcN biofilm) in a neonatal, malnourished piglet model transplanted with human infant fecal microbiota (HIFM) and infected with rotavirus. To create malnourishment, pigs were fed a reduced amount of bovine milk. Decreased HRV fecal shedding and protection from diarrhea were evident in the EcN biofilm treated piglets compared with EcN suspension and control groups. Moreover, EcN biofilm treatment enhanced natural killer cell activity in blood mononuclear cells (MNCs). Increased frequencies of activated plasmacytoid dendritic cells (pDC) in systemic and intestinal tissues and activated conventional dendritic cells (cDC) in blood and duodenum were also observed in EcN biofilm as compared with EcN suspension treated pigs. Furthermore, EcN biofilm treated pigs had increased frequencies of systemic activated and resting/memory antibody forming B cells and IgA+ B cells in the systemic tissues. Similarly, the mean numbers of systemic and intestinal HRV-specific IgA antibody secreting cells (ASCs), as well as HRV-specific IgA antibody titers in serum and small intestinal contents, were increased in the EcN biofilm treated group. In summary EcN biofilm enhanced innate and B cell immune responses after HRV infection and ameliorated diarrhea following HRV challenge in a malnourished, HIFM pig model.

Tissue-on-a-Chip: Microphysiometry With Human 3D Models on Transwell Inserts

Microphysiometry has proved to be a useful tool for monitoring the energy metabolism of living cells and their interactions with other cells. The technique has mainly been used for monitoring two-dimensional (2D) monolayers of cells. Recently, our group showed that it is also possible to monitor the extracellular acidification rate and transepithelial electrical resistance (TEER) of 3D skin constructs in an automated assay maintaining an air–liquid interface (ALI) with a BioChip extended by 3D-printed encapsulation. In this work, we present an optimized multichannel intestine-on-a-chip for monitoring the TEER of the commercially available 3D small intestinal tissue model (EpiIntestinal^TM from MatTek). Experiments are performed for 1 day, during which a 60 min cycle is repeated periodically. Each cycle consists of three parts: (1) maintain ALI; (2) application of the measurement medium or test substance; and (3) the rinse cycle. A cytotoxic and barrier-disrupting benchmark chemical (0.2% sodium dodecyl sulfate) was applied after 8 h of initial equilibration. This caused time-dependent reduction of the TEER, which could not be observed with typical cytotoxicity measurement methods. This work represents a proof-of-principle of multichannel time-resolved TEER monitoring of a 3D intestine model using an automated ALI. Reconstructed human tissue combined with the Intelligent Mobile Lab for In vitro Diagnostic technology represents a promising research tool for use in toxicology, cellular metabolism studies, and drug absorption research.

Human 3D Gastrointestinal Microtissue Barrier Function As a Predictor of Drug-Induced Diarrhea

Drug-induced gastrointestinal toxicities (GITs) rank among the most common clinical side effects. Preclinical efforts to reduce incidence are limited by inadequate predictivity of in vitro assays. Recent breakthroughs in in vitro culture methods support intestinal stem cell maintenance and continual differentiation into the epithelial cell types resident in the intestine. These diverse cells self-assemble into microtissues with in vivo-like architecture. Here, we evaluate human GI microtissues grown in transwell plates that allow apical and/or basolateral drug treatment and 96-well throughput. Evaluation of assay utility focused on predictivity for diarrhea because this adverse effect correlates with intestinal barrier dysfunction which can be measured in GI microtissues using transepithelial electrical resistance (TEER). A validation set of widely prescribed drugs was assembled and tested for effects on TEER. When the resulting TEER inhibition potencies were adjusted for clinical exposure, a threshold was identified that distinguished drugs that induced clinical diarrhea from those that lack this liability. Microtissue TEER assay predictivity was further challenged with a smaller set of drugs whose clinical development was limited by diarrhea that was unexpected based on 1-month animal studies. Microtissue TEER accurately predicted diarrhea for each of these drugs. The label-free nature of TEER enabled repeated quantitation with sufficient precision to develop a mathematical model describing the temporal dynamics of barrier damage and recovery. This human 3D GI microtissue is the first in vitro assay with validated predictivity for diarrhea-inducing drugs. It should provide a platform for lead optimization and offers potential for dose schedule exploration.

Air-liquid interface cell culture: From airway epithelium to the female reproductive tract

The air-liquid interface (ALI) approach is primarily used to mimic respiratory tract epithelia in vitro. It is also known to support excellent differentiation of 3D multilayered skin models. To establish an ALI culture, epithelial cells are seeded into compartmentalized culture systems on porous filter supports or gel substrata. After an initial propagation period, the culture medium is removed from the apical side of the epithelium, exposing the cells to the surrounding air. Therefore, nutritive supply to the cells is warranted only by the basolateral cell pole. Under these conditions, the epithelial cells differentiate and regain full baso-apical polarity. Some types of epithelia even generate in vivo-like apical fluid or mucus. Interestingly, the ALI culture approach has also been shown to support morphological and functional differentiation of epithelial cells that are not normally exposed to ambient air in vivo. This review aims at giving a brief overview on the characteristics of ALI cultures in general and ALI models of female reproductive tract epithelia in particular. We discuss the applicability of ALI models for the investigation of the early embryonic microenvironment and for its implications in assisted reproductive technologies.

Dynamic spatiotemporal expression pattern of limbal stem cell putative biomarkers during mouse development

Limbal stem cells (LSCs), a subpopulation of limbal epithelial basal cells, are crucial to the homeostasis and wound healing of corneal epithelium. The identification and isolation of LSCs remains a challenge due to lack of specific LSCs biomarkers. In this study, Haematoxylin-eosin (HE), 4', 6-diamidino-2-phenylindole (DAPI), and immunohistochemistry (IHC) stains were performed on the pre- and post-natal limbus tissues of mice which has the advantage of more controllable in term of sampling age relative to human origin. By morphological analysis, we supported that there is an absence of the Palisades of Vogt (POV) in the mouse. The development of prenatal and neonatal cornea was dominated by its stroma, whereas after eyelids opened at P14, the corneal epithelial cells (CECs) quickly go stratification in response to the liquid-air interface. Based on IHC staining, we found that the expression of LSCs putative biomarkers in limbal epithelial basal cells appeared in chronological order as follows: Vim = p63 > CK14 > CK15 (where = represents same time; > represents earlier), and in corneal epithelial basal cells were weakened in chronological order as follows: Vim > p63 > CK15 > CK14, which might also represent the stemness degree. Furthermore, the dynamic spatial expression of the examined LSCs putative biomarkers during mouse development also implied a temporal restriction. The expression of Vim in epithelial cells of mouse ocular surface occurred during E12-E19 only. The expression of CK15 was completely undetectable in CECs after P14, whereas the others putative molecular markers of LSCs, such as p63 and CK14, still remained weak expression, suggesting that CK15 was suitable to serve as the mouse LSCs biomarkers after P14. In this study, our data demonstrated the dynamic spatiotemporal expression pattern of LSCs putative biomarkers in mouse was age-related and revealed the time spectrum of the expression of LSCs in mouse, which adds in our knowledge by understanding the dynamic expression pattern of biomarkers of stem cells relate to maintenance of their stemness.

In Vitro Culture of Cryptosporidium parvum Using Stem Cell-Derived Intestinal Epithelial Monolayers

Cryptosporidium parvum has a complex life cycle consisting of asexual and sexual phases that culminate in oocyst formation in vivo. The most widely used cell culture platforms to study C. parvum only support a few days of growth and do not allow the parasite to proceed past the sexual stages to complete oocyst formation. Additionally, these cell culture platforms are mostly adenocarcinoma cell lines, which do not adequately model the parasite's natural environment in the small intestine. We describe here a method to create primary intestinal epithelial cell monolayers that support long-term C. parvum growth. Monolayers were derived from mouse intestinal stem cells grown as spheroids and plated onto transwells, allowing for separate apical and basolateral compartments. In the apical chamber, the cell growth medium was removed to create an "air-liquid interface" that enhanced host cell differentiation and supported long-term C. parvum growth. The use of primary intestinal cells to grow C. parvum in vitro will be a valuable tool for studying host-parasite interactions using a convenient in vitro model that more closely resembles the natural niche in the intestine.

The Role of C-X-C Chemokine Receptor Type 4 (CXCR4) in Cell Adherence and Spheroid Formation of Human Ewing's Sarcoma Cells under Simulated Microgravity

We studied the behavior of Ewing's Sarcoma cells of the line A673 under simulated microgravity (s-µg). These cells express two prominent markers-the oncogene EWS/FLI1 and the chemokine receptor CXCR4, which is used as a target of treatment in several types of cancer. The cells were exposed to s-µg in a random-positioning machine (RPM) for 24 h in the absence and presence of the CXCR4 inhibitor AMD3100. Then, their morphology and cytoskeleton were examined. The expression of selected mutually interacting genes was measured by qRT-PCR and protein accumulation was determined by western blotting. After 24 h incubation on the RPM, a splitting of the A673 cell population in adherent and spheroid cells was observed. Compared to 1 g control cells, EWS/FLI1 was significantly upregulated in the adherent cells and in the spheroids, while CXCR4 and CD44 expression were significantly enhanced in spheroids only. Transcription of CAV-1 was upregulated and DKK2 and VEGF-A were down-regulated in both, adherent in spheroid cells, respectively. Regarding, protein accumulation EWS/FLI1 was enhanced in adherent cells only, but CD44 decreased in spheroids and adherent cells. Inhibition of CXCR4 did not change spheroid count, or structure. Under s-µg, the tumor marker EWS/FLI1 is intensified, while targeting CXCR4, which influences adhesion proteins, did not affect spheroid formation.

Intestine-on-chip device increases ECM remodeling inducing faster epithelial cell differentiation

An intestine-on-chip has been developed to study intestinal physiology and pathophysiology as well as intestinal transport absorption and toxicity studies in a controlled and human similar environment. Here, we report that dynamic culture of an intestine-on-chip enhances extracellular matrix (ECM) remodeling of the stroma, basement membrane production and speeds up epithelial differentiation. We developed a three-dimensional human intestinal stromal equivalent composed of human intestinal subepithelial myofibroblasts embedded in their own ECM. Then, we cultured human colon carcinoma-derived cells in both static and dynamic conditions in the opportunely designed microfluidic system until the formation of a well-oriented epithelium. This low cost and handy microfluidic device allows to qualitatively and quantitatively detect epithelial polarization and mucus production as well as monitor barrier function and ECM remodeling after nutraceutical treatment.

Apoptosis Induction and Alteration of Cell Adherence in Human Lung Cancer Cells under Simulated Microgravity

BACKGROUND

Lung cancer cells are known to change proliferation and migration under simulated microgravity. In this study, we sought to evaluate cell adherence, apoptosis, cytoskeleton arrangement, and gene expression under simulated microgravity.

METHODS

Human lung cancer cells were exposed to simulated microgravity in a random-positioning machine (RPM). Cell morphology and adherence were observed under phase-contrast microscopy, cytoskeleton staining was performed, apoptosis rate was determined, and changes in gene and protein expression were detected by real-time PCR with western blot confirmation.

RESULTS

Three-dimensional (3D)-spheroid formation was observed under simulated microgravity. Cell viability was not impaired. Actin filaments showed a shift in alignment from longitudinal to spherical. Apoptosis rate was significantly increased in the spheroids compared to the control. TP53, CDKN2A, PTEN, and RB1 gene expression was significantly upregulated in the adherent cells under simulated microgravity with an increase in corresponding protein production for p14 and RB1. SOX2 expression was significantly upregulated in the adherent cells, but protein was not. Gene expressions of AKT3, PIK3CA, and NFE2L2 remained unaltered.

CONCLUSION

Simulated microgravity induces alteration in cell adherence, increases apoptosis rate, and leads to upregulation of tumor suppressor genes in human lung cancer cells.

Development and characterization of swine primary respiratory epithelial cells and their susceptibility to infection by four influenza virus types

Influenza viruses are a group of respiratory pathogens that have evolved into four different types: A, B, C, and D. A common feature is that all four types are capable of replicating and transmitting among pigs. Here, we describe the development of isogenous cell culture system from the swine respiratory tract to study influenza viruses. Phenotypic characterization of swine primary nasal turbinate, trachea and lung cells revealed high expression of cytokeratin and demonstrated tissue site dependent expression of tight junction proteins. Furthermore, lectin binding assay on these cells demonstrated higher levels of Sia2-6Gal than Sia2-3Gal receptors and supported the replication of influenza A, B, C, and D viruses to appreciable levels at both 33 and 37 °C, but replication competence was dependent on virus type or temperature used. Overall, these swine primary respiratory cells showed epithelial phenotype, which is suitable for studying the comparative biology and pathobiology of influenza viruses.

Modeling Host-Pathogen Interactions in the Context of the Microenvironment: Three-Dimensional Cell Culture Comes of Age

Tissues and organs provide the structural and biochemical landscapes upon which microbial pathogens and commensals function to regulate health and disease. While flat two-dimensional (2-D) monolayers composed of a single cell type have provided important insight into understanding host-pathogen interactions and infectious disease mechanisms, these reductionist models lack many essential features present in the native host microenvironment that are known to regulate infection, including three-dimensional (3-D) architecture, multicellular complexity, commensal microbiota, gas exchange and nutrient gradients, and physiologically relevant biomechanical forces (e.g., fluid shear, stretch, compression). A major challenge in tissue engineering for infectious disease research is recreating this dynamic 3-D microenvironment (biological, chemical, and physical/mechanical) to more accurately model the initiation and progression of host-pathogen interactions in the laboratory. Here we review selected 3-D models of human intestinal mucosa, which represent a major portal of entry for infectious pathogens and an important niche for commensal microbiota. We highlight seminal studies that have used these models to interrogate host-pathogen interactions and infectious disease mechanisms, and we present this literature in the appropriate historical context. Models discussed include 3-D organotypic cultures engineered in the rotating wall vessel (RWV) bioreactor, extracellular matrix (ECM)-embedded/organoid models, and organ-on-a-chip (OAC) models. Collectively, these technologies provide a more physiologically relevant and predictive framework for investigating infectious disease mechanisms and antimicrobial therapies at the intersection of the host, microbe, and their local microenvironments.

Preclinical models for the study of Barrett's carcinogenesis

Barrett's esophagus (BE) is clinically significant, as it is the only known precursor lesion for esophageal adenocarcinoma. To develop improved therapies for the treatment of BE, a greater understanding of the disease process at the molecular genetic level is needed. However, achieving a greater understanding will require improved preclinical models so that the disease process can be more closely studied and novel therapies can be tested. Our concise review highlights progress in the development of preclinical models for the study of BE and identifies the most suitable model in which to test novel therapies.

In vitro study of intestinal epithelial interaction with engineered oil in water nanoemulsions conveying curcumin

The development of innovative nano-bio-encapsulation systems continues to be an area of intense activity as the demand of improved delivery systems is constantly increasing in several fields including nanomedicine. For this purpose, an important goal is carrying out appropriate engineering of the surface of these nanocarriers to satisfy the organ target features for an effective in situ release and elucidate the mechanism of action which most of the time is neglected. Here, an oil-in-water (O/W) nanoemulsion coated with a polysaccharide layer film - i.e. a glycol chitosan modified with a thiol moiety - was used as nanocarrier to convey a promising poorly water-soluble nature based drug, curcumin. The final nanocarrier was completely bio-compatible and bio-stable. We investigated the enhancement of the effect of curcumin loaded in our system across monolayers of intestinal epithelial cells CaCo-2 in Transwell culture. Such in vitro platform resulted suitable to evaluate the functionality of the proposed nanocarrier and its adhesion towards the mucosal epithelial layer and, as applicative example, to investigate the anti-inflammatory effects exerted by the encapsulation of curcumin.

Effects of deoxynivalenol (DON) and its microbial biotransformation product deepoxy-deoxynivalenol (DOM-1) on a trout, pig, mouse, and human cell line

Deoxynivalenol (DON), a trichothecene produced by various Fusarium species, is one of the most prevalent food- and feed-associated mycotoxins. The effects of DON and deepoxy-deoxynivalenol (DOM-1) were assessed in five different cell lines from different tissues and species starting from the first line of defense, the trout gill (RTgill-W1) and pig intestinal cells (IPEC-1 and IPEC-J2) over immune cells, as second line of defense (mouse macrophages RAW 264.7) to human liver cells (HepG2). Viability was assessed with a WST-1 assay, except for RTgill-W1, where a neutral red (NR) and sulforhodamine B (SRB) assay was performed. Additionally, more sensitive parameters, such as interleukin-, nitric oxide (NO)-, and albumin-release were determined. Viability was affected by DON at concentrations starting at 10 μmol/L (RTgill-W1), 0.9 μmol/L (IPEC-1), 3.5 μmol/L (IPEC-J2), and 0.9 μmol/L (HepG2), whereas DOM-1 did not have such an effect. Additionally, NO was decreased (0.84 μmol/L DON), whereas interleukin (IL)-6 was increased (0.42 μmol/L DON) in lipopolysaccharide (LPS)-stimulated DON-, but not DOM-1-treated RAW cells. Tumor necrosis factor (TNF)-α release, however, was not affected. Interestingly, albumin secretion of HepG2 cells was decreased by both DON and DOM-1 but at a much higher concentration for DOM-1 (228 versus 0.9 μmol/L for DON). 98.9% of DOM-1 was retrieved by liquid chromatography tandem mass spectrometry at the end of the experiment, proving its stability. In this study, IL-6 was the most sensitive parameter, followed by NO and albumin release and viability for HepG2 and IPEC-1.

Protein Malnutrition Modifies Innate Immunity and Gene Expression by Intestinal Epithelial Cells and Human Rotavirus Infection in Neonatal Gnotobiotic Pigs

Malnutrition and rotavirus infection, prevalent in developing countries, individually and in combination, affect the health of millions of children, compromising their immunity and increasing the rates of death from infectious diseases. However, the interactions between the two and their combined effects on immune and intestinal functions are poorly understood. We have established the first human infant microbiota-transplanted neonatal pig model of childhood malnutrition that reproduced the impaired immune, intestinal, and other physiological functions seen in malnourished children. This model can be used to evaluate relevant dietary and other health-promoting interventions. Our findings provide an explanation of why adequate nutrition alone may lack efficacy in malnourished children.

Malnutrition affects millions of children in developing countries, compromising immunity and contributing to increased rates of death from infectious diseases. Rotavirus is a major etiological agent of childhood diarrhea in developing countries, where malnutrition is prevalent. However, the interactions between the two and their combined effects on immune and intestinal functions are poorly understood. In this study, we used neonatal gnotobiotic (Gn) pigs transplanted with the fecal microbiota of a healthy 2-month-old infant (HIFM) and fed protein-deficient or -sufficient bovine milk diets. Protein deficiency induced hypoproteinemia, hypoalbuminemia, hypoglycemia, stunting, and generalized edema in Gn pigs, as observed in protein-malnourished children. Irrespective of the diet, human rotavirus (HRV) infection early, at HIFM posttransplantation day 3 (PTD3), resulted in adverse health effects and higher mortality rates (45 to 75%) than later HRV infection (PTD10). Protein malnutrition exacerbated HRV infection and affected the morphology and function of the small intestinal epithelial barrier. In pigs infected with HRV at PTD10, there was a uniform decrease in the function and/or frequencies of natural killer cells, plasmacytoid dendritic cells, and CD103⁺ and apoptotic mononuclear cells and altered gene expression profiles of intestinal epithelial cells (chromogranin A, mucin 2, proliferating cell nuclear antigen, SRY-Box 9, and villin). Thus, we have established the first HIFM-transplanted neonatal pig model that recapitulates major aspects of protein malnutrition in children and can be used to evaluate physiologically relevant interventions. Our findings provide an explanation of why nutrient-rich diets alone may lack efficacy in malnourished children.

IMPORTANCE Malnutrition and rotavirus infection, prevalent in developing countries, individually and in combination, affect the health of millions of children, compromising their immunity and increasing the rates of death from infectious diseases. However, the interactions between the two and their combined effects on immune and intestinal functions are poorly understood. We have established the first human infant microbiota-transplanted neonatal pig model of childhood malnutrition that reproduced the impaired immune, intestinal, and other physiological functions seen in malnourished children. This model can be used to evaluate relevant dietary and other health-promoting interventions. Our findings provide an explanation of why adequate nutrition alone may lack efficacy in malnourished children.

Air-liquid interface enhances oxidative phosphorylation in intestinal epithelial cell line IPEC-J2

The intestinal porcine epithelial cell line IPEC-J2, cultured under the air-liquid interface (ALI) conditions, develops remarkable morphological characteristics close to intestinal epithelial cells in vivo. Improved oxygen availability has been hypothesised to be the leading cause of this morphological differentiation. We assessed oxygen availability in ALI cultures and examined the influence of this cell culture method on glycolysis and oxidative phosphorylation in IPEC-J2 using the submerged membrane culture (SMC) and ALI cultures. Furthermore, the role of HIF-1 as mediator of oxygen availability was analysed. Measurements of oxygen tension confirmed increased oxygen availability at the medium-cell interface and demonstrated reduced oxygen extraction at the basal compartment in ALI. Microarray analysis to determine changes in the genetic profile of IPEC-J2 in ALI identified 2751 modified transcripts. Further examinations of candidate genes revealed reduced levels of glycolytic enzymes hexokinase II and GAPDH, as well as lactate transporting monocarboxylate transporter 1 in ALI, whereas expression of the glucose transporter GLUT1 remained unchanged. Cytochrome c oxidase (COX) subunit 5B protein analysis was increased in ALI, although mRNA level remained at constant level. COX activity was assessed using photometric quantification and a three-fold increase was found in ALI. Quantification of glucose and lactate concentrations in cell culture medium revealed significantly reduced glucose levels and decreased lactate production in ALI. In order to evaluate energy metabolism, we measured cellular adenosine triphosphate (ATP) aggregation in homogenised cell suspensions showing similar levels. However, application of the uncoupling agent FCCP reduced ATP levels in ALI but not in SMC. In addition, HIF showed reduced mRNA levels in ALI. Furthermore, HIF-1α protein was reduced in the nuclear compartment of ALI when compared to SCM as confirmed by confocal microscopy. These results indicate a metabolic switch in IPEC-J2 cultured under ALI conditions enhancing oxidative phosphorylation and suppressing glycolysis. ALI-induced improvement of oxygen supply reduced nuclear HIF-1α, demonstrating a major change in the transcriptional response.

Effects of Escherichia coli Nissle 1917 and Ciprofloxacin on small intestinal epithelial cell mRNA expression in the neonatal piglet model of human rotavirus infection

We evaluated the effects of the probiotic Escherichia coli Nissle 1917 (EcN) and the antibiotic Ciprofloxacin (Cipro) on mRNA expression of intestinal epithelial cells (IEC) in gnotobiotic (Gn) piglets colonized with a defined commensal microflora (DMF) and inoculated with human rotavirus (HRV) that infects IECs. We analyzed mRNA levels of IEC genes for enteroendocrine cells [chromogranin A (CgA)], goblet cells [mucin 2 (MUC2)], transient amplifying progenitor cell [proliferating cell nuclear antigen (PCNA)], intestinal epithelial stem cell (SOX9) and enterocytes (villin). Cipro treatment enhanced HRV diarrhea and decreased the mRNA levels of MUC2 and villin but increased PCNA. These results suggest that Cipro alters the epithelial barrier, potentially decreasing the numbers of mature enterocytes (villin) and goblet cells secreting protective mucin (MUC2). These alterations may induce increased IEC proliferation (PCNA expression) to restore the integrity of the epithelial layer. Coincidental with decreased diarrhea severity in EcN treated groups, the expression of CgA and villin was increased, while SOX9 expression was decreased representing higher epithelial integrity indicative of inhibition of cellular proliferation. Thus, EcN protects the intestinal epithelium from damage by increasing the gene expression of enterocytes and enteroendocrine cells, maintaining the absorptive function and, consequently, decreasing the severity of diarrhea in HRV infection.

Deoxynivalenol and its metabolite deepoxy-deoxynivalenol: multi-parameter analysis for the evaluation of cytotoxicity and cellular effects

The mycotoxin deoxynivalenol (DON) contaminates agricultural commodities worldwide, posing health threats to humans and animals. Associated with DON are derivatives, such as deepoxy-deoxynivalenol (DOM-1), produced by enzymatic transformation of certain intestinal bacteria, which are naturally occurring or applied as feed additives. Using differentiated porcine intestinal epithelial cells (IPEC-J2), we provide the first multi-parameter comparative cytotoxicity analysis of DON and DOM-1, based on the parallel evaluation of lysosomal activity, total protein content, membrane integrity, mitochondrial metabolism and ATP synthesis. The study investigated the ability of DON and—for the first time of its metabolite DOM-1—to induce apoptosis, mitogen-activated protein kinase (MAPK) signalling, oxidative events and alterations of mitochondrial structure in porcine intestinal epithelial cells (IECs). The degree of DON toxicity strongly varied, depending on the cytotoxicity parameter evaluated. DON compromised viability according to the parameters of lysosomal activity, total protein content and membrane integrity, but increased viability according to assays based on mitochondrial metabolism and ATP synthesis. DON induced expression of cleaved caspase-3 (maximum induction 3.9-fold) and MAPK p38 and p42/p44 (maximum induction 2.51- and 2.30-fold, respectively). DON altered mitochondrial morphology, but did not increase intracellular ROS. DOM-1-treated IPEC-J2 remained unaffected at equimolar concentrations in all assays, thereby confirming the safety of feed additives using DON- to DOM-1-transforming bacteria. The study additionally highlights that an extensive multi-parameter analysis significantly contributes to the quality of in vitro data.

Early Activation of MAPK p44/42 Is Partially Involved in DON-Induced Disruption of the Intestinal Barrier Function and Tight Junction Network

Deoxynivalenol (DON), produced by the plant pathogens Fusarium graminearum and Fusarium culmorum, is one of the most common mycotoxins, contaminating cereal and cereal-derived products. Although worldwide contamination of food and feed poses health threats to humans and animals, pigs are particularly susceptible to this mycotoxin. DON derivatives, such as deepoxy-deoxynivalenol (DOM-1), are produced by bacterial transformation of certain intestinal bacteria, which are naturally occurring or applied as feed additives. Intestinal epithelial cells are the initial barrier against these food- and feed-borne toxins. The present study confirms DON-induced activation of MAPK p44/42 and inhibition of p44/42 by MAPK-inhibitor U0126 monoethanolate. Influence of DON and DOM-1 on transepithelial electrical resistance (TEER), viability and expression of seven tight junction proteins (TJ), as well as the potential of U0126 to counteract DON-induced effects, was assessed. While DOM-1 showed no effect, DON significantly reduced TEER of differentiated IPEC-J2 and decreased expression of claudin-1 and -3, while leaving claudin-4; ZO-1, -2, and -3 and occludin unaffected. Inhibition of p44/42 counteracted DON-induced TEER decrease and restored claudin-3, but not claudin-1 expression. Therefore, effects of DON on TEER and claudin-3 are at least partially p44/42 mediated, while effects on viability and claudin-1 are likely mediated via alternative pathways.

Deoxynivalenol, but not E. coli lipopolysaccharide, changes the response pattern of intestinal porcine epithelial cells (IPEC-J2) according to its route of application

The porcine intestinal epithelium is a primary target for mycotoxin deoxynivalenol (DON) and lipopolysaccharides (LPS). Although epithelial cells are exposed to these toxins mainly from the luminal-chyme compartment an exposure from the blood side resulting from systemic absorption cannot be excluded. Thus, we investigated the effect of DON and LPS, alone or combined, on porcine intestinal epithelial cells IPEC-J2 on a transcriptional, translational and functional level when administered either from apical or basolateral. IPEC-J2 cells were cultured on 12-well inserts in complete medium at 5% CO2 and 39°C and subjected to following treatments: control (CON), 2000 ng/mL DON, 1 μg/mL LPS or DON+LPS for 72 h, either from apical or basolateral. Transepithelial electrical resistance (TEER), protein and IL-8 content were measured and microarray analysis, qRT-PCR (IL-8, zonula occludens-1 ZO-1, β-actin), Western Blot (ZO-1, β-actin) and immunofluorescence (ZO-1) were performed. Data of at least three independent experiments were analysed with ANOVA and Dunnett's post hoc test. Basolateral DON resulted in significantly lower cell counts (p<0.05) with larger cells (p<0.01), whereas apical DON reduced total (p<0.001) and specific protein content (IL-8 content CON vs. DON: 2378 pg/3 mL vs. 991 pg/3 mL; p<0.001). Transcripts of ß-actin and ZO-1 were significantly upregulated in response to DON, irrespective of direction, whereas IL-8 mRNA remained unaffected. However, ZO-1 spatial distribution in the tight junction and its function (TEER) were detrimentally affected by basolateral DON only. In conclusion, direction of DON exposure affected IPEC-J2 differently on a translational and functional level, but was mainly inconsequential on a transcriptional level.

Comparing Two Intestinal Porcine Epithelial Cell Lines (IPECs): Morphological Differentiation, Function and Metabolism

The pig shows genetical and physiological resemblance to human, which predestines it as an experimental animal model especially for mucosal physiology. Therefore, the intestinal epithelial cell lines 1 and J2 (IPEC-1, IPEC-J2) - spontaneously immortalised cell lines from the porcine intestine - are important tools for studying intestinal function. A microarray (GeneChip Porcine Genome Array) was performed to compare the genome wide gene expression of IPECs. Different significantly up-regulated pathways were identified, like “lysosome”, “pathways in cancer”, “regulation of actin cytoskeleton” and “oxidative phosphorylation” in IPEC-J2 in comparison to IPEC-1. On the other hand, “spliceosome”, “ribosome”, “RNA-degradation” and “tight junction” are significantly down-regulated pathways in IPEC-J2 in comparison to IPEC-1. Examined pathways were followed up by functional analyses. ATP-, oxygen, glucose and lactate-measurement provide evidence for up-regulation of oxidative phosphorylation in IPEC-J2. These cells seem to be more active in their metabolism than IPEC-1 cells due to a significant higher ATP-content as well as a higher O₂- and glucose-consumption. The down-regulated pathway “ribosome” was followed up by measurement of RNA- and protein content. In summary, IPEC-J2 is a morphologically and functionally more differentiated cell line in comparison to IPEC-1. In addition, IPEC-J2 cells are a preferential tool for in vitro studies with the focus on metabolism.

Topographically grooved gel inserts for aligning epithelial cells during air-liquid-interface culture

Epithelial tissues are a critical component of all tubular organs. Engineering artificial epithelium requires an understanding of the polarization of epithelia: both apicobasal and in a planar fashion. Air liquid interface (ALI) culture is typically used to generate apicobasal polarized airway epithelium in vitro; however, this approach does not provide any signalling cues to induce morphological planar polarization of the generated epithelial layer. Here we describe a microgrooved gelatin hydrogel insert that can induce alignment of confluent epithelial cell sheets under ALI conditions to induce both apicobasal and morphologically planar polarized epithelium. Microgrooves are imprinted into the surface of the gelatin insert using elastomeric stamps moulded from a diffraction grating film and gels are stabilized by crosslinking with glutaraldehyde. We show that microgrooved gelatin inserts produce alignment of 3T3 fibroblasts and a number of epithelial cell lines (ARPE-19, BEAS2B and IMCD3 cells). Furthermore, we show that BEAS2B apicobasally polarize and form a similar density of cilia on both gelatin inserts and standard transwell filters used for ALI culture but that as apicobasal polarization progresses cell alignment on the grooves is lost. Our method provides a simple strategy that can easily be adopted by labs without microfabrication expertise for manipulating epithelial organization in transwell culture and studying the interplay of various polarization forces.

Newborn pig trachea cell line cultured in air-liquid interface conditions allows a partial in vitro representation of the porcine upper airway tissue

Background

The domestic pig is an excellent animal model to study human microbial diseases due to its similarity to humans in terms of anatomy, physiology, and genetics. We assessed the suitability of an in vitro air-liquid interface (ALI) culture system for newborn pig trachea (NPTr) cells as a practical tool for analyzing the immune response of respiratory epithelial cells to aggressors. This cell line offers a wide microbial susceptibility spectrum to both viruses and bacteria. The purpose of our study was to evaluate and characterize diverse aspects of cell differentiation using different culture media. After the NPTr cells reached confluence, the apical medium was removed and the cells were fed by medium from the basal side.

Results

We assessed the cellular layer’s capacity to polarize and differentiate in ALI conditions. Using immunofluorescence and electronic microscopy we evaluated the presence of goblet and ciliated cells, the epithelial junction organization, and the transepithelial electrical resistance. We found that the cellular layer develops a variable density of mucus producing cells and acquires a transepithelial resistance. We also identified increased development of cellular junctions over the culture period. Finally, we observed variable expression of transcripts associated to proteins such as keratin 8, mucins (MUC1, MUC2, and MUC4), occludin, and villin 1.

Conclusions

The culture of NPTr cells in ALI conditions allows a partial in vitro representation of porcine upper airway tissue that could be used to investigate some aspects of host/respiratory pathogen interactions.

Improved cell line IPEC-J2, characterized as a model for porcine jejunal epithelium

Cell lines matching the source epithelium are indispensable for investigating porcine intestinal transport and barrier properties on a subcellular or molecular level and furthermore help to reduce animal usage. The porcine jejunal cell line IPEC-J2 is established as an in vitro model for porcine infection studies but exhibits atypically high transepithelial resistances (TER) and only low active transport rates so that the effect of nutritional factors cannot be reliably investigated. This study aimed to properly remodel IPEC-J2 and then to re-characterize these cells regarding epithelial architecture, expression of barrier-relevant tight junction (TJ) proteins, adequate TER and transport function, and reaction to secretagogues. For this, IPEC-J2 monolayers were cultured on permeable supports, either under conventional (fetal bovine serum, FBS) or species-specific (porcine serum, PS) conditions. Porcine jejunal mucosa was analyzed for comparison. Main results were that under PS conditions (IPEC-J2/PS), compared to conventional FBS culture (IPEC-J2/FBS), the cell height increased 6-fold while the cell diameter was reduced by 50%. The apical cell membrane of IPEC-J2/PS exhibited typical microvilli. Most importantly, PS caused a one order of magnitude reduction of TER and of trans- and paracellular resistance, and a 2-fold increase in secretory response to forskolin when compared to FBS condition. TJ ultrastructure and appearance of TJ proteins changed dramatically in IPEC-J2/PS. Most parameters measured under PS conditions were much closer to those of typical pig jejunocytes than ever reported since the cell line’s initial establishment in 1989. In conclusion, IPEC-J2, if cultured under defined species-specific conditions, forms a suitable model for investigating porcine paracellular intestinal barrier function.

Deoxynivalenol affects the composition of the basement membrane proteins and influences en route the migration of CD16(+) cells into the intestinal epithelium

The numerous pores in the basement membrane (BM) of the intestinal villi are essential for the communication of enterocytes with cells in the lamina propria, an important mechanism for the induction of intestinal immune responses. The intestinal epithelial barrier is affected by the mycotoxin deoxynivalenol (DON) from both the apical (luminal) and basolateral (serosal) side. The pig is the most susceptible species to the anorectic and immune-modulating effects of DON, which is most prevalent in crops. We analysed in pigs the effect of DON-contaminated feed on the composition and perforation of the BM and the presence of CD16⁺ cells or their dendrites in the epithelium. In addition to in vivo experiments, in vitro studies were carried out. Using microarray analyses, the effects of DON on IPEC-J2 cells were studied with the focus on the BM. Our in vivo results showed in the control pigs: (1) a significant increased pore number (p ≤ 0.001) in the jejunum in comparison to ileum, (2) no difference in the pore size, and (3) comparable frequency of intraepithelial CD16⁺ cells/dendrites in the jejunum and ileum. There was a marked trend that DON feeding increases: (1) the pore number in jejunum, and (2) the number of CD16⁺ cells/dendrites in the epithelium (Tukey–Kramer; p = 0.055 and p = 0.067, respectively). The in vivo results were extended with microarray analyses of epithelial cell (IPEC-J2 cells). The down-regulation of genes like syndecan, fibulin 6 and BM-40 was observed. These proteins are important factors in the BM composition and in formation of pores. Our results provide evidence that already low basolateral concentrations of DON (50 ng/mL) influence the production of the BM protein laminin by epithelial cells. Thus, DON affects the composition of the BM.

Discerning apical and basolateral properties of HT-29/B6 and IPEC-J2 cell layers by impedance spectroscopy, mathematical modeling and machine learning

Quantifying changes in partial resistances of epithelial barriers in vitro is a challenging and time-consuming task in physiology and pathophysiology. Here, we demonstrate that electrical properties of epithelial barriers can be estimated reliably by combining impedance spectroscopy measurements, mathematical modeling and machine learning algorithms. Conventional impedance spectroscopy is often used to estimate epithelial capacitance as well as epithelial and subepithelial resistance. Based on this, the more refined two-path impedance spectroscopy makes it possible to further distinguish transcellular and paracellular resistances. In a next step, transcellular properties may be further divided into their apical and basolateral components. The accuracy of these derived values, however, strongly depends on the accuracy of the initial estimates. To obtain adequate accuracy in estimating subepithelial and epithelial resistance, artificial neural networks were trained to estimate these parameters from model impedance spectra. Spectra that reflect behavior of either HT-29/B6 or IPEC-J2 cells as well as the data scatter intrinsic to the used experimental setup were created computationally. To prove the proposed approach, reliability of the estimations was assessed with both modeled and measured impedance spectra. Transcellular and paracellular resistances obtained by such neural network-enhanced two-path impedance spectroscopy are shown to be sufficiently reliable to derive the underlying apical and basolateral resistances and capacitances. As an exemplary perturbation of pathophysiological importance, the effect of forskolin on the apical resistance of HT-29/B6 cells was quantified.

Enterotoxigenic Escherichia coli CS21 pilus contributes to adhesion to intestinal cells and to pathogenesis under in vivo conditions

Colonization surface antigens (CSs) represent key virulence-associated factors of enterotoxigenic Escherichia coli (ETEC) strains. They are required for gut colonization, the first step of the diarrhoeal disease process induced by these bacteria. One of the most prevalent CSs is CS21, or longus, a type IV pili associated with bacterial self-aggregation, protection against environmental stresses, biofilm formation and adherence to epithelial cell lines. The objectives of this study were to assess the role of CS21 in adherence to primary intestinal epithelial cells and to determine if CS21 contributes to the pathogenesis of ETEC infection in vivo. We evaluated adherence of a CS21-expressing wild-type ETEC strain and an isogenic CS21-mutant strain to pig-derived intestinal cell lines. To determine the role of CS21 in pathogenesis we used the above ETEC strains in a neonatal mice challenge infection model to assess mortality. Quantitative adherence assays confirmed that ETEC adheres to primary intestinal epithelial cells lines in a CS21-dependent manner. In addition, the CS21-mediated ETEC adherence to cells was specific as purified LngA protein, the CS21 major subunit, competed for binding with the CS21-expressing ETEC while specific anti-LngA antibodies blocked adhesion to intestinal cells. Neonatal DBA/2 mice died after intra-stomach administration of CS21-expressing strains while lack of CS21 expression drastically reduced the virulence of the wild-type ETEC strain in this animal model. Collectively these results further support the role of CS21 during ETEC infection and add new evidence on its in vivo relevance in pathogenesis.

Air-liquid and liquid-liquid interfaces influence the formation of the urothelial permeability barrier in vitro

Optimizing culture conditions is known to be crucial for the differentiation of urothelial cell cultures and the formation of the permeability barrier. However, so far, no data exist to confirm if air-liquid (AL) and liquid-liquid (LL) interfaces are physiologically relevant during urothelial differentiation and barrier formation. To reveal the influence of interfaces on the proliferation, differentiation, and barrier formation of the urothelial cells (UCs) in vitro, we cultured UCs under four different conditions, i.e., at the AL or LL interfaces with physiological calcium concentration and without serum or without physiological calcium concentration and with serum. For each of the four models, the urothelial integrity was tested by measuring the transepithelial resistance (TER), and the differentiation stage was examined by immunolabeling of differentiation-related markers and ultrastructural analysis. We found that the UCs at a LL interface, regardless of the presence or absence of calcium or serum, form the urothelium with more cell layers and achieve a higher TER than UCs at an AL interface. However, UCs grown at an AL interface with physiological concentration of calcium in medium form only one- to two-layered urothelium of UCs, which are larger and express more differentiation-related proteins uroplakins than UCs in other models. These results demonstrate that the interface itself can play a major, although so-far neglected, role in urothelial physiology, particularly in the formation of the urothelial permeability barrier in vitro and the regulatory mechanisms related with urothelial differentiation. In the study, the culturing of UCs in three successive steps is proposed.

The necessity of identity assessment of animal intestinal cell lines: A case report

Eight intestinal cell lines, established from different animal species were submitted to DSMZ (German Collection of Microorganisms and Cell Cultures) in order to analyze their species of origin and their microbial contamination. Species identity was determined by PCR targeting mitochondrial genes and hence confirmed by sequencing the amplified PCR products. For three cell lines (CIEB, CLAB, PSI-1) we confirmed the species identity, whereas the species of origin of the three other cell lines (B6, B10XI and IPEC) was not the expected one: B6 and B10XI cells, which were supposed to be of chicken origin were identified as porcine cells. IPEC, allegedly a sub clone of the well-known porcine intestinal cell line IPEC-J2, was of bovine instead of porcine origin. However, two further IPEC-clones, namely IPEC-1 and IPEC-J2, provided by another source were shown to be derived from the correct species (i.e. pig). Furthermore, six out of these eight cell lines turned out to be highly contaminated with mycoplasma. Alerted by this high incidence of infected and false specified cell lines, we feel obliged to inform all those working with animal intestinal cell lines and we strongly recommend verifying the species identity before using them. Also, the presence of mycoplasma should be tested when taking the cells in culture for the first time, and this mycoplasma control should be repeated at regular time intervals (e.g. every 4 weeks).

Toxicokinetics as a key to the integrated toxicity risk assessment based primarily on non-animal approaches

Toxicokinetics (TK) is the endpoint that informs about the penetration into and fate within the body of a toxic substance, including the possible emergence of metabolites. Traditionally, the data needed to understand those phenomena have been obtained in vivo. Currently, with a drive towards non-animal testing approaches, TK has been identified as a key element to integrate the results from in silico, in vitro and already available in vivo studies. TK is needed to estimate the range of target organ doses that can be expected from realistic human external exposure scenarios. This information is crucial for determining the dose/concentration range that should be used for in vitro testing. Vice versa, TK is necessary to convert the in vitro results, generated at tissue/cell or sub-cellular level, into dose response or potency information relating to the entire target organism, i.e. the human body (in vitro-in vivo extrapolation, IVIVE). Physiologically based toxicokinetic modelling (PBTK) is currently regarded as the most adequate approach to simulate human TK and extrapolate between in vitro and in vivo contexts. The fact that PBTK models are mechanism-based which allows them to be 'generic' to a certain extent (various extrapolations possible) has been critical for their success so far. The need for high-quality in vitro and in silico data on absorption, distribution, metabolism as well as excretion (ADME) as input for PBTK models to predict human dose-response curves is currently a bottleneck for integrative risk assessment.

Recent progress in histochemistry and cell biology

Studies published in Histochemistry and Cell Biology in the year 2011 represent once more a manifest of established and newly sophisticated techniques being exploited to put tissue- and cell type-specific molecules into a functional context. The review is therefore the Histochemistry and Cell Biology's yearly intention to provide interested readers appropriate summaries of investigations touching the areas of tissue biology, developmental biology, the biology of the immune system, stem cell research, the biology of subcellular compartments, in order to put the message of such studies into natural scientific-/human- and also pathological-relevant correlations.