The alpha2 and alpha3 integrins are required for morphologic differentiation of an intestinal epithelial cell line

Purified fish skin collagen hydrolysate attenuates TNF-α induced barrier dysfunction in-vitro and DSS induced colitis in-vivo model

Inflammatory mediators are key components in establishing pathogenesis in inflammatory bowel disease. Balanced expression of anti-inflammatory and pro-inflammatory cytokines is an important cue in maintaining gut native and adaptive immunity. In the present study, purified hydrolysate fraction of fish skin collagen from Clarias batrachus and Pangasius pangasius was evaluated as a treatment agent against TNF-α induced barrier dysfunction in Caco-2 cell line model and DSS induced colitis in mice model. Cell adhesion on purified hydrolysate fraction coated surfaces was found to be enhanced with increasing concentration in both Clarias batrachus and Pangasius pangasius. Alkaline phosphatase activity was enhanced in a concentration-dependent manner. The paracellular permeability assay demonstrated that Pangasius pangasius purified hydrolysate fraction had countered TNF-α induced barrier dysfunction. Analysis of the tight junction proteins (occludin, zonulae occluden, and claudin) by RT PCR, immunofluorescence, and western blot, further confirmed the effectiveness of Pangasius pangasius purified hydrolysate fraction against TNF-α. The Pangasius pangasius purified hydrolysate fraction was further evaluated for efficacy in DSS-induced colitis mice model. Two concentration of Pangasius pangasius purified hydrolysate was chosen based on in-vitro experiments, 80 μg/kg and 200 μg/kg BW of Balb/C male mice administered through intra-rectal route along with fish skin collagen 80 μg/kg BW. Pangasius pangasius purified hydrolysate fraction treatment improved the clinical signs of colitis such as body weight, rectal bleeding, colon length, and stool consistency caused by DSS administration. Immunofluorescence of colon tissue section showed that Pangasius pangasius purified hydrolysate fraction enhanced the expression of occludin protein. This study hints at the use of Pangasius pangasius purified hydrolysate fraction as a potential nutraceutical or treatment agent in healing ulcers of the mucosa.

The role of integrins in inflammation and angiogenesis

Integrins are heterodimeric transmembrane cell adhesion molecules made up of alpha (α) and beta (β) subunits arranged in numerous dimeric pairings. These complexes have varying affinities to extracellular ligands. Integrins regulate cellular growth, proliferation, migration, signaling, and cytokine activation and release and thereby play important roles in cell proliferation and migration, apoptosis, tissue repair, as well as in all processes critical to inflammation, infection, and angiogenesis. This review presents current evidence from human and animal studies on integrin structure and molecular signaling, with particular emphasis on signal transduction in infants. We have included evidence from our own laboratory studies and from an extensive literature search in databases PubMed, EMBASE, Scopus, and the electronic archives of abstracts presented at the annual meetings of the Pediatric Academic Societies. To avoid bias in identification of existing studies, key words were short-listed prior to the actual search both from anecdotal experience and from PubMed's Medical Subject Heading (MeSH) thesaurus. IMPACT: Integrins are a family of ubiquitous αβ heterodimeric receptors that interact with numerous ligands in physiology and disease. Integrins play a key role in cell proliferation, tissue repair, inflammation, infection, and angiogenesis. This review summarizes current evidence from human and animal studies on integrin structure and molecular signaling and promising role in diseases of inflammation, infection, and angiogenesis in infants. This review shows that integrin receptors and ligands are novel therapeutic targets of clinical interest and hold promise as novel therapeutic targets in the management of several neonatal diseases.

A Simple Method to Test Mechanical Strain on Epithelial Cell Monolayers Using a 3D-Printed Stretcher

With the realization that mechanical forces mediate many biological processes and contribute to disease progression, researchers are focusing on developing new methods to understand the role of mechanotransduction in biological systems. Despite recent advances in stretching devices that analyze the effects of mechanical strain in vitro, there are still possibilities to develop new equipment. For example, many of these devices tend be expensive, whereas few have been designed to assess the effects of mechanical strain driven by the extracellular matrix (ECM) to epithelial cell monolayers and to cell-cell adhesion. In this chapter, we introduce a cost-efficient, user-friendly, 3D-printed stretching device that can be used to test the effects of mechanical strain on cultured epithelial cells. Evaluation of the device using speckle-tracking shows homogeneous strain distribution along the horizontal plane of membranes at 2.5% and 5% strains, supporting the reliability of the device. Since cell-cell junctions are mechanosensitive protein complexes, we hereby used this device to examine effects on cell-cell adhesion. For this, we used colon epithelial Caco2 cell monolayers that well-differentiate in culture and form mature adherens junctions. Subjecting Caco2 cells to 2.5% and 5% strain using our device resulted in significant reduction in the localization of the core adherens junction component E-cadherin at areas of cell-cell contact and its increased translocation to the cytoplasm, which in agreement with other methodologies showing that increased ECM-driven strain negatively affects cell-cell adhesion. In summary, we here present a new, cost-effective, homemade device that can be reliably used to examine effects of mechanical strain on epithelial cell monolayers and cell-cell adhesion, in vitro.

KRAS and BRAF mutations induce anoikis resistance and characteristic 3D phenotypes in Caco‑2 cells

In a number of types of cancer, anoikis, a form of apoptosis induced by loss of extracellular matrix (ECM) attachment, is disturbed. Anoikis resistance is essential in the formation of metastases. A recent study identified carcinoma cell subpopulations surviving without ECM contact in pathological specimens of colorectal cancer. The occurrence of these subpopulations indicated anoikis resistance. In the present study, it is demonstrated that KRAS and BRAF mutations induce anoikis resistance in colon cancer (Caco-2) cells. In 3D cultures, Caco-2 cells transfected with mutated KRAS or BRAF formed multicellular structures analogous to anoikis-resistant subpopulations in actual carcinomas, and serve as an in vitro model for anoikis resistance. Caco-2 cell lines were constructed, with KRAS or BRAF mutations, using retroviral delivery. The current study investigated anoikis resistance using an Annexin V apoptosis test from suspension cultures. 3D in vitro cultures, which were generated in collagen-matrigel mixtures, were assessed using confocal microscopy. 3D cultures embedded in paraffin were analyzed using conventional histopathology. In suspension cultures, Caco-2 cells with KRAS or BRAF mutations indicated a significantly lower proportion of Annexin positivity than the native Caco-2 cells, indicating that these mutations induce anoikis resistance in Caco-2 cells. 3D cultures displayed native Caco-2 cells forming polarized cysts with a single layer thick epithelium, whereas Caco-2 cells with KRAS or BRAF mutations formed partially filled cystic structures or solid round structures where only the outermost layer was in contact with the ECM. Additionally, KRAS mutations induced reversed polarity to Caco-2 cells along with the emergence of solid growth. The present study demonstrated that KRAS and BRAF mutations induce anoikis resistance in Caco-2 colorectal cancer cells. The growth patterns generated from the KRAS and BRAF mutated cells in 3D cultures revealed a resemblance to the putative anoikis-resistant subpopulations in actual carcinomas, including micropapillary structures and solid tumor cell islands. Additionally, KRAS mutation induced the emergence of inverted polarity. In conclusion, 3D cultures with modified Caco-2 cells serve as a valid in vitro model for anoikis resistance and inverted polarity.

Centrosomal ALIX regulates mitotic spindle orientation by modulating astral microtubule dynamics

The orientation of the mitotic spindle (MS) is tightly regulated, but the molecular mechanisms are incompletely understood. Here we report a novel role for the multifunctional adaptor protein ALG-2-interacting protein X (ALIX) in regulating MS orientation in addition to its well-established role in cytokinesis. We show that ALIX is recruited to the pericentriolar material (PCM) of the centrosomes and promotes correct orientation of the MS in asymmetrically dividing Drosophila stem cells and epithelial cells, and symmetrically dividing Drosophila and human epithelial cells. ALIX-deprived cells display defective formation of astral microtubules (MTs), which results in abnormal MS orientation. Specifically, ALIX is recruited to the PCM via Drosophila Spindle defective 2 (DSpd-2)/Cep192, where ALIX promotes accumulation of γ-tubulin and thus facilitates efficient nucleation of astral MTs. In addition, ALIX promotes MT stability by recruiting microtubule-associated protein 1S (MAP1S), which stabilizes newly formed MTs. Altogether, our results demonstrate a novel evolutionarily conserved role of ALIX in providing robustness to the orientation of the MS by promoting astral MT formation during asymmetric and symmetric cell division.

Research advances on structure and biological functions of integrins

Integrins are an important family of adhesion molecules that were first discovered two decades ago. Integrins are transmembrane heterodimeric glycoprotein receptors consisting of α and β subunits, and are comprised of an extracellular domain, a transmembrane domain, and a cytoplasmic tail. Therein, integrin cytoplasmic domains may associate directly with numerous cytoskeletal proteins and intracellular signaling molecules, which are crucial for modulating fundamental cell processes and functions including cell adhesion, proliferation, migration, and survival. The purpose of this review is to describe the unique structure of each integrin subunit, primary cytoplasmic association proteins, and transduction signaling pathway of integrins, with an emphasis on their biological functions.

Endothelium-derived Netrin-4 supports pancreatic epithelial cell adhesion and differentiation through integrins α2β1 and α3β1

BACKGROUND

Netrins have been extensively studied in the developing central nervous system as pathfinding guidance cues, and more recently in non-neural tissues where they mediate cell adhesion, migration and differentiation. Netrin-4, a distant relative of Netrins 1-3, has been proposed to affect cell fate determination in developing epithelia, though receptors mediating these functions have yet to be identified.

METHODOLOGY/PRINCIPAL FINDINGS

Using human embryonic pancreatic cells as a model of developing epithelium, here we report that Netrin-4 is abundantly expressed in vascular endothelial cells and pancreatic ductal cells, and supports epithelial cell adhesion through integrins α2β1 and α3β1. Interestingly, we find that Netrin-4 recognition by embryonic pancreatic cells through integrins α2β1 and α3β1 promotes insulin and glucagon gene expression. In addition, full genome microarray analysis revealed that fetal pancreatic cell adhesion to Netrin-4 causes a prominent down-regulation of cyclins and up-regulation of negative regulators of the cell cycle. Consistent with these results, a number of other genes whose activities have been linked to developmental decisions and/or cellular differentiation are up-regulated.

CONCLUSIONS/SIGNIFICANCE

Given the recognized function of blood vessels in epithelial tissue morphogenesis, our results provide a mechanism by which endothelial-derived Netrin-4 may function as a pro-differentiation cue for adjacent developing pancreatic cell populations expressing adhesion receptors α2β1 and α3β1 integrins.

Fibrillar collagen type I stimulation of apolipoprotein B secretion in Caco-2 cells is mediated by beta1 integrin

Caco-2 cells spontaneously differentiate into enterocyte-like cells and secrete apolipoprotein B (apoB) lipoproteins. We evaluated the effect of different extracellular matrix proteins on lipoprotein secretion by these cells. Caco-2 cells grown on human amnion connective tissue (HACT) secreted twice as much apoB as control cells on Transwells, but secreted similar amounts of apoA1. Cells cultured on fibrillar collagen type I secreted increased amounts of apoB similar to the cells cultured on HACT, but cells cultured on non-fibrillar collagen type I, type IV collagen or laminin-1 did not. The increased secretion was nullified by a function inhibiting anti-integrin beta1 monoclonal antibody. Therefore, interactions between type I collagen and beta1 integrins augment apoB secretion by Caco-2 cells. Cells on HACT formed a more uniform columnar epithelium with lipid droplets polarized to the basolateral membrane. We also studied the effect of extracellular matrix proteins on transepithelial resistance (TER) of differentiated Caco-2 cells. TER in cells cultured on HACT was similar to that on Transwells, but cells on laminin-1 and collagen IV exhibited higher TER. Thus, various extracellular matrix proteins regulate apoB secretion and TER differently. This new observation that extracellular matrix proteins can enhance apoB secretion in Caco-2 cells could be useful to explore the modulation of lipid transport by these proteins.

Cdc42 controls spindle orientation to position the apical surface during epithelial morphogenesis

The establishment of apical–basal polarity within a single cell and throughout a growing tissue is a key feature of epithelial morphogenesis. To examine the underlying mechanisms, the human intestinal epithelial cell line Caco-2 was grown in a three-dimensional matrix to generate a cystlike structure, where the apical surface of each epithelial cell faces a fluid-filled central lumen. A discrete apical domain is established as early as the first cell division and between the two daughter cells. During subsequent cell divisions, the apical domain of each daughter cell is maintained at the center of the growing structure through a combination of mitotic spindle orientation and asymmetric abscission. Depletion of Cdc42 does not prevent the establishment of apical–basal polarity in individual cells but rather disrupts spindle orientation, leading to inappropriate positioning of apical surfaces within the cyst. We conclude that Cdc42 regulates epithelial tissue morphogenesis by controlling spindle orientation during cell division.

Growth surface-induced gene and protein expression patterns in Caco-2 cells

The underlying matrix plays an important role in the adhesion, proliferation and differentiation processes of Caco-2 cells. When culturing these cells for pharmaceutical purposes it is essential to know the influence of different supports on morphological and functional cell parameters. The impact of polystyrene, Matrigel-coated polystyrene, glass and nanostructured Easy-To-Clean (ETC01) slides was investigated over time by real-time quantitative reverse transcription polymerase chain reaction, enzymatic assays and immunofluorescent staining techniques. Compared to polystyrene, ETC01 slides induced cellular activities towards functional differentiation after short cultivation times. Glass significantly accelerated the differentiation process up to day 10 in culture, while Matrigel-coating had no significant benefit. By day 21 postseeding, the phenotype had equalized as indicated by constant brush border enzyme activity and villin mRNA expression masking the initial differences between the supports. The accelerated differentiation on specific matrices could be advantageous as it may enable cultured monolayers to be used earlier, and has to be considered when interpreting and comparing results.

Influence of surface modification on vitality and differentiation of Caco-2 cells

It is widely accepted that the functional and morphological differentiation of cells is initiated and determined by the interaction of molecules of the extracellular matrix and adhesion molecules of the cell membrane. To assess the influence of the underlying matrix on the characteristics of cells, enterocyte-like Caco-2 cells were cultivated on substrates commonly used for cell culture as well as on glass coated with hydrophobic layers. Providing the same starting conditions for growth, the parameters investigated on preconfluent Caco-2 cells were the number of adhering cells, the proliferative activity and the degree of differentiation indicated by the expression of three brush border enzymes. Whereas tissue culture treated polystyrene elicited highest rates of adhesion, proliferation, and differentiation, even glass altered the pattern of brush border enzyme expression. The hydrophobic surfaces strongly decreased the adhesion and the proliferation but the surviving cells exhibited a pronounced higher degree of differentiation. Interestingly, each sub-type of hydrophobic matrix triggered a different pattern of brush border enzyme expression. Thus, the development of a certain phenotype of a cell can not only be triggered by certain components of the extracellular matrix but also by artificially prepared surface coatings of the underlying matrix. In the future it seems to be feasible that cells can be programmed by tailoring the surface of the underlying substrate.

Stem cell-derived Sca-1+ progenitors differentiate into smooth muscle cells, which is mediated by collagen IV-integrin alpha1/beta1/alphav and PDGF receptor pathways

Embryonic stem (ES) cells can differentiate into smooth muscle cells (SMCs) that can be used for tissue engineering and repair of damaged organs. However, little is known about the molecular mechanisms of differentiation in these cells. In the present study, we found collagen IV can promote ES cells to differentiate into stem cell antigen-1-positive (Sca-1(+)) progenitor cells and SMCs. Pretreatment of ES cells with antibodies against collagen IV significantly inhibited SMC marker expression. To further elucidate the effect of collagen IV on the induction and maintenance of SMC differentiation, Sca-1(+) progenitor cells were isolated with magnetic beads, placed in collagen-IV-coated flasks, and cultured in differentiation medium with or without platelet-derived growth factor (PDGF)-BB for 6-90 days. Both immunostaining and fluorescence-activated cell sorter analyses revealed that the majority of these cells were positive for SMC-specific markers. Pretreatment of Sca-1(+) progenitors with antibodies against integrin alpha(1), alpha(v), and beta(1), but not beta(3), inhibited focal adhesion kinase (FAK) and paxillin phosphorylation and resulted in a marked inhibition of SMC differentiation. Various tyrosine kinase inhibitors, and specific siRNA for phosphatidylinositol 3-kinase (PI 3-kinase) and PDGF receptor-beta significantly inhibited SMC marker expression. Taken together, we demonstrate for the first time that collagen IV plays a crucial role in the early stage of SMC differentiation and that integrin (alpha(1), beta(1), and alpha(v))-FAK-PI 3-kinase-mitogen-activated protein kinase and PDGF receptor-beta signaling pathways are involved in SMC differentiation.

Loss of expression of type IV collagen alpha5 and alpha6 chains in colorectal cancer associated with the hypermethylation of their promoter region

Type IV collagen, a major component of the basement membrane (BM), is composed of six genetically distinct alpha(IV) chains, alpha1(IV) to alpha6(IV). Their genes are paired on three different chromosomes in a head-to-head arrangement. The alpha5(IV) gene (COL4A5) and the alpha6(IV) gene (COL4A6) are on chromosome Xq22 and are regulated by a bidirectional promoter. Loss of the alpha5(IV)/alpha6(IV) chains in epithelial BM occur in the early stage of cancer invasion. However, the regulatory mechanism of the specific loss of the alpha5(IV)/alpha6(IV) chains during cancer cell invasion is still undetermined. In the present study, we examined the expression of the alpha5(IV)/alpha6(IV) chains and the methylation profiles of the bidirectional promoter region of COL4A5/COL4A6 in colon cancer cell lines and colorectal tumor tissues. The expression of the alpha5(IV)/alpha6(IV) chains was down-regulated in colorectal cancer, and the loss of expression of the alpha5(IV)/alpha6(IV) chains was associated with the hypermethylation of their promoter region. In conclusion, the hypermethylation of the bidirectional promoter region of COL4A5/COL4A6 is one of the events that is responsible for the loss of expression of the alpha5(IV)/alpha6(IV) chains and the remodeling of the epithelial BM during cancer cell invasion.

Interleukin-8/CXCL8 forms an autocrine loop in fetal intestinal mucosa

IL-8/CXC ligand (CXCL) 8 is ingested in high concentrations by the human fetus/neonate with amniotic fluid and human milk, and is also produced constitutively by intestinal epithelial cells (IEC). We have shown that recombinant human IL-8/CXCL8 (rhIL-8/CXCL8) protects cultured IEC against tumor necrosis factor (TNF)-alpha and cycloheximide-induced cytotoxicity. In view of its constitutive production, we hypothesized that IL-8/CXCL8 might play an autocrine role in fetal enterocyte maintenance. In this study, we measured IL-8/CXCL8 mRNA concentrations in fetal intestine (11-22 wk gestation), sought the presence of the protein by immunohistochemistry in fetal stomach and intestine (9-24 wk), measured IL-8/CXCL8 in neonatal gastric secretions, and studied constitutive and stimulated IL-8/CXCL8 expression in cultured IEC. We found that IL-8/CXCL8 is consistently transcribed and expressed in fetal intestinal tissue, in a developmentally regulated inverse relationship with gestational maturation. The cognate receptors for IL-8/CXCL8 are also expressed abundantly in the fetal intestine, and, therefore, we sought to determine whether the expressed IL-8/CXCL8 would complete an autocrine loop. Neutralization of IL-8/CXCL8 resulted in increased cell death in cultured IEC in the presence of TNF-alpha. This effect is specifically mediated through the CXCR2 receptors. We speculate that IL-8/CXCL8 secretion during cytotoxic stress reflects a cellular self-defense mechanism.

Physiological and Pathological Roles of α3β1 Integrin

Alpha3beta1 integrin has been considered to be a mysterious adhesion molecule due to the pleiotropy in its ligand-binding specificity. However, recent studies have identified laminin isoforms as high-affinity ligands for this integrin, and demonstrated that alpha3beta1 integrin plays a number of essential roles in development and differentiation, mainly by mediating the establishment and maintenance of epithelial tissues. Furthermore, alpha3beta1 integrin is also implicated in many other biological phenomena, including cell growth and apoptosis, angiogenesis and neural functions. This integrin receptor forms complexes with various other membrane proteins, such as the transmembrane-4 superfamily proteins (tetraspanins), cytoskeletal proteins and signaling molecules. Recently, lines of evidence have been reported showing that complex formation regulates integrin functions in cell adhesion and migration, signal transduction across cell membranes, and cytoskeletal organization. In addition to these roles in physiological processes, alpha3beta1 integrin performs crucial functions in various pathological processes, especially in wound healing, tumor invasion and metastasis, and infection by pathogenic microorganisms.