Rho kinase inhibition maintains intestinal and vascular barrier function by upregulation of occludin in experimental necrotizing enterocolitis

Protective Effects of Lactobacillus reuteri on Intestinal Barrier Function in a Mouse Model of Neonatal Necrotizing Enterocolitis

OBJECTIVE

The intestinal mucosal and immune barriers play considerable roles in the pathogenesis of necrotizing enterocolitis (NEC). The present research was designed to assess the protective effects of Lactobacillus reuteri (LR) DSM 17938 (LR 17938) on the intestinal barriers and its beneficial effects on inflammation in a neonatal mouse model of NEC.

STUDY DESIGN

Overall, 7-day-old 75 C57BL/6 neonatal mice were separated into three groups (n = 25) as follows: (1) control, (2) NEC, and (3) NEC + LR17938 (LR group). NEC mice were administered a hypertonic feeding formula and subjected to asphyxia and hypothermia. Hematoxylin and eosin (HE) staining and pathological scores were used to assess the pathological changes in the intestine. Oxidative stress was evaluated based on the levels of superoxide dismutase (SOD) and malondialdehyde (MDA). Tumor necrosis factor (TNF)-α and interleukin (IL)-1β levels were detected to assess inflammation. Gut permeability levels, bacterial translocation, and the levels of secretory idioglobulin A (sIgA), β-defensin, and tight junction (TJ) proteins were detected to evaluate gut mucosal and immune barrier function, and gut microbial diversity was detected to assess the composition of the gut flora.

RESULTS

LR 17938 administration decreased the NEC-induced increase in intestinal scores, mortality rate, gut damage, the MDA level, and TNF-α and IL-1β expressions. Besides, LR 17938 improved the survival rate of NEC mice. Moreover, LR 17938 administration improved gut permeability levels, SOD activity and the bacterial translocation, ameliorated the expression of TJ proteins, and improved the gut microbiota compared with those of NEC mice.

CONCLUSION

LR 17938 reduced intestinal inflammation and played a protective role in a neonatal animal model of NEC, possibly by regulating oxidative stress and exerting a protective effect on the gut mucosal and immune barriers.

KEY POINTS

· Our research indicated a protective effect of LR 17938 on gut barrier function in NEC mice.. · LR 17938may affect the diversity of gut flora, which are known to target beneficial bacteria.. · LR 17938 protected gut barrier function in the NEC pups by improving gut permeability..

Occludin: a gatekeeper of brain Infection by HIV-1

Compromised structure and function of the blood-brain barrier (BBB) is one of the pathological hallmarks of brain infection by HIV-1. BBB damage during HIV-1 infection has been associated with modified expression of tight junction (TJ) proteins, including occludin. Recent evidence indicated occludin as a redox-sensitive, multifunctional protein that can act as both an NADH oxidase and influence cellular metabolism through AMPK kinase. One of the newly identified functions of occludin is its involvement in regulating HIV-1 infection. Studies suggest that occludin expression levels and the rate of HIV-1 infection share a reverse, bidirectional relationship; however, the mechanisms of this relationship are unclear. In this review, we describe the pathways involved in the regulation of HIV-1 infection by occludin. We propose that occludin may serve as a potential therapeutic target to control HIV-1 infection and to improve the lives of people living with HIV-1.

What animal model should I use to study necrotizing enterocolitis?

Unfortunately, we are all too familiar with the statement: "Necrotizing enterocolitis remains the leading cause of gastrointestinal surgical emergency in preterm neonates". It's been five decades since the first animal models of necrotizing enterocolitis (NEC) were described. There remains much investigative work to be done on identifying various aspects of NEC, ranging from the underlying mechanisms to treatment modalities. Experimental NEC is mainly focused on a rat, mouse, and piglet models. Our aim is to not only highlight the pros and cons of these three main models, but to also present some of the less-used animal models that have contributed to the body of knowledge about NEC. Choosing an appropriate model is essential to conducting effective research and answering the questions asked. As such, this paper reviews some of the variations that come with each model.

Bamboo Shoot and Artemisia capillaris Extract Mixture Ameliorates Dextran Sodium Sulfate-Induced Colitis

Inflammatory bowel disease (IBD) is a chronic inflammatory disease of the gastrointestinal tract and is characterized by recurrent chronic inflammation and mucosal damage of the gastrointestinal tract. Recent studies have demonstrated that bamboo shoot (BS) and Artemisia capillaris (AC) extracts enhance anti-inflammatory effects in various disease models. However, it is uncertain whether there is a synergistic protective effect of BS and AC in dextran sodium sulfate (DSS)-induced colitis. In the current study, we tested the combined effects of BS and AC extracts (BA) on colitis using in vivo and in vitro models. Compared with control mice, oral administration of DSS exacerbated colon length and increased the disease activity index (DAI) and histological damage. In DSS-induced colitis, treatment with BA significantly alleviated DSS-induced symptoms such as colon shortening, DAI, histological damage, and colonic pro-inflammatory marker expression compared to single extracts (BS or AC) treatment. Furthermore, we found BA treatment attenuated the ROS generation, F-actin formation, and RhoA activity compared with the single extract (BS or AC) treatment in DSS-treated cell lines. Collectively, these findings suggest that BA treatment has a positive synergistic protective effect on colonic inflammation compared with single extracts, it may be a highly effective complementary natural extract mixture for the prevention or treatment of IBD.

Understanding the development and function of the gut microbiota in health and inflammation

The gut microbiota is known to play an important role in maintaining gut health through a symbiotic relationship with the host. Altered gut microbiota is a common feature of several diseases of the gastrointestinal tract; however, the causal relationship between microbiota and disease pathogenesis is poorly understood. Necrotising enterocolitis (NEC) and inflammatory bowel disease (IBD) are both severe inflammatory diseases affecting the gastrointestinal tract. Although they affect very different patient populations, with NEC primarily being a disease of prematurity and IBD predominantly affecting adults although children can be affected, they both demonstrate common features of gut microbial dysbiosis and a dysregulated host immune response. By comparing and contrasting the changes in gut microbiota, host immune response and function, we aim to highlight common features in diseases that may seem clinically unrelated. Key areas of interest are the role of pattern recognition receptors in altered recognition and responses to the gut microbiota by the host immune system and the associated dysfunctional gut epithelial barrier. The challenge of identifying causal relationships between microbiota and disease is ever-present; however, considering a disease-agnostic approach may help to identify mechanistic pathways shared across several clinical diseases.

Tight junctions: from molecules to gastrointestinal diseases

Intestinal epithelium functions as a tissue barrier to prevent interaction between the internal compartment and the external milieu. Intestinal barrier function also determines epithelial polarity for the absorption of nutrients and the secretion of waste products. These vital functions require strong integrity of tight junction proteins. In fact, intestinal tight junctions that seal the paracellular space can restrict mucosal-to-serosal transport of hostile luminal contents. Tight junctions can form both an absolute barrier and a paracellular ion channel. Although defective tight junctions potentially lead to compromised intestinal barrier and the development and progression of gastrointestinal (GI) diseases, no FDA-approved therapies that recover the epithelial tight junction barrier are currently available in clinical practice. Here, we discuss the impacts and regulatory mechanisms of tight junction disruption in the gut and related diseases. We also provide an overview of potential therapeutic targets to restore the epithelial tight junction barrier in the GI tract.

Effects of acute and chronic oxidative stress on the blood-brain barrier in 2D and 3D in vitro models

Oxidative stress is a shared pathology of neurodegenerative disease and brain injuries, and is derived from perturbations to normal cell processes by aging or environmental factors such as UV exposure and air pollution. As oxidative cues are often present in systemic circulation, the blood-brain barrier (BBB) plays a key role in mediating the effect of these cues on brain dysfunction. Therefore, oxidative damage and disruption of the BBB is an emergent focus of neurodegenerative disease etiology and progression. We assessed barrier dysfunction in response to chronic and acute oxidative stress in 2D and 3D in vitro models of the BBB with human iPSC-derived brain microvascular endothelial-like cells (iBMECs). We first established doses of hydrogen peroxide to induce chronic damage (modeling aging and neurodegenerative disease) and acute damage (modeling the response to traumatic brain injury) by assessing barrier function via transendothelial electrical resistance in 2D iBMEC monolayers and permeability and monolayer integrity in 3D tissue-engineered iBMEC microvessels. Following application of these chronic and acute doses in our in vitro models, we found local, discrete structural changes were the most prevalent responses (rather than global barrier loss). Additionally, we validated unique functional changes in response to oxidative stress, including dysfunctional cell turnover dynamics and immune cell adhesion that were consistent with changes in gene expression.

Experimental Modeling of Necrotizing Enterocolitis in Human Infant Intestinal Enteroids

METHODS

There are several limitations when using a single cell culture to recapitulate the findings in a complex organism and results often vary between species, when proxy animal models are studied.

RESULTS

Human enteroids have allowed for study of human disease in complex multicellular culture systems. Here we present the novel use of human infant enteroids generated from premature infant intestine to study necrotizing enterocolitis (NEC), which is a devastating intestinal disorder that affects our most vulnerable pediatric population.

CONCLUSIONS

We demonstrate that NEC can be induced in premature human enteroids as supported by corresponding alterations in inflammation, apoptosis, tight junction expression, and permeability by treatment with lipopolysaccharide.

Design and development of novel fasudil derivatives as potent antibreast cancer agent that improves intestinal flora and intestinal barrier function in rats

This study was conducted to develop novel fasudil derivatives after incorporation of substituted thiazoles as potent anti-breast cancer (BC) agents. The compounds were developed using a facile synthetic route in excellent yields. The entire set of developed compounds was tested for inhibitory activity against rho-associated coiled-coil kinase (ROCK; ROCK1 and ROCK2) kinase, where they exhibit potent and selective inhibition of ROCK1 as compared to ROCK2. The most potent ROCK2 inhibitor, compound 6h significantly inhibited the viability of BC cells (MCF-7). It also causes inhibition of migration and invasion of MCF-7 cells. Moreover, the anti-BC activity of compound 6h was studied in 7,12 dimethyl Benz(a)anthracene (DMBA)-induced BC in female Sprague Dawley rats. Results suggest that it causes significant improvement in the bodyweight of the animals with a reduction in oxidative stress in the liver and mammary tissues of rats. It showed improvement in the intestinal barrier function of rats by restoring the level of Diamine oxidase, d-lactate, and endotoxin. In western blot analysis, it showed improvement in (ZO-1), occludin, and claudin-1 in the colon tissue of the rat as compared to the DMBA group. Our study demonstrated the development of the novel class of fasudil derivatives potent anti-BC agent that improves intestinal flora and intestinal barrier function in rats.

DRG1 Maintains Intestinal Epithelial Cell Junctions and Barrier Function by Regulating RAC1 Activity in Necrotizing Enterocolitis

BACKGROUND

An immature intestine is a high-risk factor for necrotizing enterocolitis (NEC), which is a serious intestinal disease in newborns. The regulation of developmentally regulated GTP-binding protein 1 (DRG1) during organ development suggests a potential role of DRG1 in the maturation process of the intestine.

AIM

To illustrate the function of DRG1 during the pathogenesis of NEC.

METHODS

DRG1 expression in the intestine was measured using immunohistochemistry and q-PCR. Immunoprecipitation coupled with mass spectrometry was used to identify the interacting proteins of DRG1. The biological functions of the potential interactors were annotated with the Database for Annotation, Visualization and Integrated Discovery. Caco2 and FHs74Int cells with stable DRG1 silencing or overexpression were used to investigate the influence of DRG1 on cell junctions and intestinal barrier permeability and to elucidate the downstream mechanism.

RESULTS

DRG1 was constitutively expressed during the intestinal maturation process but significantly decreased in the ileum in the context of NEC. Protein interaction analysis revealed that DRG1 was closely correlated with cell junctions. DRG1 deficiency destabilized the E-cadherin and occludin proteins near the cell membrane and increased the permeability of the epithelial cell monolayer, while DRG1 overexpression prevented lipopolysaccharide-induced disruption of E-cadherin and occludin expression and cell monolayer integrity. Further investigation suggested that DRG1 maintained cell junctions, especially adherens junctions, by regulating RAC1 activity, and RAC1 inhibition with NSC23766 attenuated intestinal injury and led to improved barrier integrity in experimental NEC.

CONCLUSIONS

Our findings illustrate the mechanism underlying the effect of DRG1 deficiency on epithelial cell permeability regulation and provide evidence supporting the application of RAC1 inhibitors for protection against NEC.

Low doses of imidacloprid induce disruption of intercellular adhesion and initiate proinflammatory changes in Caco-2 cells

Imidacloprid is the most widely used pesticide of the neonicotinoid class. Neonicotinoid toxicities against various insects are well known. Nevertheless, there are rising evidences that neonicotinoids exert cytotoxic effects on different non-target organisms including mammals, fish, birds etc. Besides, depending on pesticide application, the exposed plants absorb some part of used neonicotinoids and their residues are detected in agricultural products worldwide. Thus, the continuous consumption of fruits and vegetables contaminated with neonicotinoids is a high risk factor for humans despite the low doses. Intestine epithelial cells are the first targets of the neonicotinoid cytotoxicity in humans because of its direct way of administration. The epithelial cells provide the barrier function of the intestinal system via specialized intercellular adhesion. The effects of imidacloprid on the intestine barrier function and inflammatory cytokines production are still unknown. In the present study, we exposed the human Caucasian colon adenocarcinoma (Caco-2) epithelial cells to low doses (0.10–0.75 µg/mL) of imidacloprid in order to assess the expression of tight and adherens junctions proteins, occludin and E-cadherin, and production of proinflammatory cytokine TNF α and iNOS. Imidacloprid induced dose-dependent decline in both occludin and E-cadherin levels. By contrast, TNF-α and iNOS contents were upregulated in imidacloprid-exposed Caco-2 cells. Decrease in tight and adherens junctions proteins indicates that the barrier function of intestine epithelial cells could be damaged by imidacloprid administration. In addition, TNF-α and iNOS upregulation indicates that imidacloprid is potent to activate proinflammatory response in enterocytes. Thus, imidacloprid can affect intestine barrier function through the increase of proinflammatory cytokine production and decrease in adhesiveness of enterocytes. The further assessment of the role of adhesion proteins and inflammatory cytokines in neonicotinoid pesticide cytotoxicity as it affects enterocyte barrier function is required to highlight the risk factor of use of neonicotinoids.

Small-molecule modulators of INAVA cytosolic condensate and cell-cell junction assemblies

Epithelial cells lining mucosal surfaces distinctively express the inflammatory bowel disease risk gene INAVA. We previously found that INAVA has dual and competing functions: one at lateral membranes where it affects mucosal barrier function and the other in the cytosol where INAVA enhances IL-1β signal transduction and protein ubiquitination and forms puncta. We now find that IL-1β–induced INAVA puncta are biomolecular condensates that rapidly assemble and physiologically resolve. The condensates contain ubiquitin and the E3 ligase βTrCP2, and their formation correlates with amplified ubiquitination, suggesting function in regulation of cellular proteostasis. Accordingly, a small-molecule screen identified ROS inducers, proteasome inhibitors, and inhibitors of the protein folding chaperone HSP90 as potent agonists for INAVA condensate formation. Notably, inhibitors of the p38α and mTOR pathways enhanced resolution of the condensates, and inhibitors of the Rho–ROCK pathway induced INAVA’s competing function by recruiting INAVA to newly assembled intercellular junctions in cells where none existed before.

Necrotizing Enterocolitis: Overview on In Vitro Models

Necrotizing enterocolitis (NEC) is a gut inflammatory disorder which constitutes one of the leading causes of morbidity and mortality for preterm infants. The pathophysiology of NEC is yet to be fully understood; several observational studies have led to the identification of multiple factors involved in the pathophysiology of the disease, including gut immaturity and dysbiosis of the intestinal microbiome. Given the complex interactions between microbiota, enterocytes, and immune cells, and the limited access to fetal human tissues for experimental studies, animal models have long been essential to describe NEC mechanisms. However, at present there is no animal model perfectly mimicking human NEC; furthermore, the disease mechanisms appear too complex to be studied in single-cell cultures. Thus, researchers have developed new approaches in which intestinal epithelial cells are exposed to a combination of environmental and microbial factors which can potentially trigger NEC. In addition, organoids have gained increasing attention as promising models for studying NEC development. Currently, several in vitro models have been proposed and have contributed to describe the disease in deeper detail. In this paper, we will provide an updated review of available in vitro models of NEC and an overview of current knowledge regarding its molecular underpinnings.

Rho GTPases as Key Molecular Players within Intestinal Mucosa and GI Diseases

Rho proteins operate as key regulators of the cytoskeleton, cell morphology and trafficking. Acting as molecular switches, the function of Rho GTPases is determined by guanosine triphosphate (GTP)/guanosine diphosphate (GDP) exchange and their lipidation via prenylation, allowing their binding to cellular membranes and the interaction with downstream effector proteins in close proximity to the membrane. A plethora of in vitro studies demonstrate the indispensable function of Rho proteins for cytoskeleton dynamics within different cell types. However, only in the last decades we have got access to genetically modified mouse models to decipher the intricate regulation between members of the Rho family within specific cell types in the complex in vivo situation. Translationally, alterations of the expression and/or function of Rho GTPases have been associated with several pathological conditions, such as inflammation and cancer. In the context of the GI tract, the continuous crosstalk between the host and the intestinal microbiota requires a tight regulation of the complex interaction between cellular components within the intestinal tissue. Recent studies demonstrate that Rho GTPases play important roles for the maintenance of tissue homeostasis in the gut. We will summarize the current knowledge on Rho protein function within individual cell types in the intestinal mucosa in vivo, with special focus on intestinal epithelial cells and T cells.

Targeting desmosomal adhesion and signalling for intestinal barrier stabilization in inflammatory bowel diseases-Lessons from experimental models and patients

Inflammatory bowel diseases (IBD) such as Crohn's disease (CD) and Ulcerative colitis (UC) have a complex and multifactorial pathogenesis which is incompletely understood. A typical feature closely associated with clinical symptoms is impaired intestinal epithelial barrier function. Mounting evidence suggests that desmosomes, which together with tight junctions (TJ) and adherens junctions (AJ) form the intestinal epithelial barrier, play a distinct role in IBD pathogenesis. This is based on the finding that desmoglein (Dsg) 2, a cadherin-type adhesion molecule of desmosomes, is required for maintenance of intestinal barrier properties both in vitro and in vivo, presumably via Dsg2-mediated regulation of TJ. Mice deficient for intestinal Dsg2 show increased basal permeability and are highly susceptible to experimental colitis. In several cohorts of IBD patients, intestinal protein levels of Dsg2 are reduced and desmosome ultrastructure is altered suggesting that Dsg2 is involved in IBD pathogenesis. In addition to its adhesive function, Dsg2 contributes to enterocyte cohesion and intestinal barrier function. Dsg2 is also involved in enterocyte proliferation, barrier differentiation and induction of apoptosis, in part by regulation of p38MAPK and EGFR signalling. In IBD, the function of Dsg2 appears to be compromised via p38MAPK activation, which is a critical pathway for regulation of desmosomes and is associated with keratin phosphorylation in IBD patients. In this review, the current findings on the role of Dsg2 as a novel promising target to prevent loss of intestinal barrier function in IBD patients are discussed.

New directions in necrotizing enterocolitis with early-stage investigators

The 2019 Necrotizing Enterocolitis (NEC) Symposium expanded upon the NEC Society's goals of bringing stakeholders together to discuss cutting-edge science, potential therapeutics and preventative measures, as well as the patient-family perspectives of NEC. The Symposium facilitated discussions and shared knowledge with the overarching goal of creating "A World Without NEC." To accomplish this goal, new research to advance the state of the science is necessary. Over the last decade, several established investigators have significantly improved our understanding of the pathophysiology of NEC and they have paved the way for the next generation of clinician-scientists funded to perform NEC research. This article will serve to highlight the contributions of these young clinician-scientists that seek to elucidate how immune, microbial and nervous system dysregulation contributes to the pathophysiology of NEC.

Inhibition of A2B Adenosine Receptor Attenuates Intestinal Injury in a Rat Model of Necrotizing Enterocolitis

Necrotizing enterocolitis (NEC) is a lethal gastrointestinal tract disease that occurs in premature infants. Adenosine receptor A_2B (A_2BR) regulates the inflammation cytokine secretion and immune cell infiltration in the colonic pathophysiology conditions. In the present study, we aim to determine the roles of A_2BR in the development of NEC. A NEC rat model was established and treated with A_2BR agonist-BAY60-6583 or A_2BR antagonist-PSB1115. Animals in the control group were free from any interventions. Our results showed that the inhibition of A_2BR PSB1115 improved intestinal injury and inflammation in newborn NEC rats. The expression levels of caspase-3 and the ratio of apoptotic cells were upregulated in NEC rats, and these indices were downregulated after treating with PSB1115 but further upregulated by BAY60-6583. Meanwhile, a similar trend was also witnessed in the changes of MPO activities and proinflammatory cytokines including IL-6, IFN-γ, and TNF-α. However, the anti-inflammatory cytokine IL-10 in the NECP group was significantly higher than that in the NEC and NECB groups (p < 0.05, respectively). Moreover, the expression of Ki67 was significantly increased in the NECP group as compared with those of the NEC and the NECB groups (p < 0.05, respectively). Collectively, our study suggested that the inhibition of A_2BR attenuates NEC in the neonatal rat, at least partially through the modulation of inflammation and the induction of epithelial cell proliferation.

ROCK1 inhibitor stabilizes E-cadherin and improves barrier function in experimental necrotizing enterocolitis

Necrotizing enterocolitis (NEC) is a devastating gastrointestinal disease of newborns. Although incompletely understood, NEC is associated with intestinal barrier dysfunction. E-cadherin, an adherens junction, is a protein complex integral in maintaining normal barrier homeostasis. Rho-associated protein kinase-1 (ROCK1) is a kinase that regulates the E-cadherin complex, and p120-catenin is a subunit of the E-cadherin complex that has been implicated in stabilizing the cadherin complex at the plasma membrane. We hypothesized that E-cadherin is decreased in NEC and that inhibition of ROCK1 would protect against adherens junction disruption. To investigate this, a multimodal approach was used: In vitro Caco-2 model of NEC (LPS/TNFα), rap pup model (hypoxia + bacteria-containing formula), and human intestinal samples. E-cadherin was decreased in NEC compared with controls, with relocalization from the cell border to an intracellular location. ROCK1 exhibited a time-dependent response to disease, with increased early expression in NEC and decreased expression at later time points and disease severity. Administration of ROCK1 inhibitor (RI) resulted in preservation of E-cadherin expression at the cell border, preservation of intestinal villi on histological examination, and decreased apoptosis. ROCK1 upregulation in NEC led to decreased association of E-cadherin to p120 and increased intestinal permeability. RI helped maintain the stability of the E-cadherin-p120 complex, leading to improved barrier integrity and protection from experimental NEC.NEW & NOTEWORTHY This paper is the first to describe the effect of ROCK1 on E-cadherin expression in the intestinal epithelium and the protective effects of ROCK inhibitor on E-cadherin stability in necrotizing enterocolitis.

Endothelial tight junctions and their regulatory signaling pathways in vascular homeostasis and disease

Endothelial tight junctions (TJs) regulate the transport of water, ions, and molecules through the paracellular pathway, serving as an important barrier in blood vessels and maintaining vascular homeostasis. In endothelial cells (ECs), TJs are highly dynamic structures that respond to multiple external stimuli and pathological conditions. Alterations in the expression, distribution, and structure of endothelial TJs may lead to many related vascular diseases and pathologies. In this review, we provide an overview of the assessment methods used to evaluate endothelial TJ barrier function both in vitro and in vivo and describe the composition of endothelial TJs in diverse vascular systems and ECs. More importantly, the direct phosphorylation and dephosphorylation of TJ proteins by intracellular kinases and phosphatases, as well as the signaling pathways involved in the regulation of TJs, including and the protein kinase C (PKC), PKA, PKG, Ras homolog gene family member A (RhoA), mitogen-activated protein kinase (MAPK), phosphatidylinositol 3-kinase (PI3K)/Akt, and Wnt/β-catenin pathways, are discussed. With great advances in this area, targeting endothelial TJs may provide novel treatment for TJ-related vascular pathologies.

Recent Advances in Prevention and Therapies for Clinical or Experimental Necrotizing Enterocolitis

Necrotizing enterocolitis (NEC) is one of the most severe diseases of preterm neonates and has a high mortality rate. With the development of inspection techniques and new biomarkers, the diagnostic accuracy of NEC is constantly improving. The most recognized potential risk factors include prematurity, formula-feeding, infection, and microbial dysbiosis. With further understanding of the pathogenesis, more effective prevention and therapies will be applied to clinical or experimental NEC. At present, such new potential prevention and therapies for NEC are mainly focused on the Toll-like receptor 4 inflammatory signaling pathway, the repair of intestinal barrier function, probiotics, antioxidative stress, breast-feeding, and immunomodulatory agents. Many new studies have changed our understanding of the pathogenesis of NEC and improve our approaches for preventing and treating of NEC each year. This review provides an overview of the recent researches focused on clinical or experimental NEC and highlights the advances made within the past 5 years toward the development of new potential preventive approaches and therapies for this disease.

Caveolin 1 is Associated with Upregulated Claudin 2 in Necrotizing Enterocolitis

Necrotizing enterocolitis (NEC) is a devastating gastrointestinal emergency of neonates. Epithelial tight junction (TJ) proteins, such as claudins, are essential for regulation and function of the intestinal barrier. Rho kinase (ROCK) affects cellular permeability and TJ regulation. We hypothesized that TJ protein changes would correlate with increased permeability in experimental NEC, and ROCK inhibitors would be protective against NEC by regulation of key claudin proteins. We tested this hypothesis using an in vivo rat pup model, an in vitro model of experimental NEC, and human intestinal samples from patients with and without NEC. Experimental NEC was induced in rats via hypoxia and bacteria-containing formula, and in Caco-2 cells by media inoculated with LPS. The expression of claudins was measured by gene and protein analysis. Experimental NEC in rat pups and Caco-2 cells had increased permeability compared to controls. Gene and protein expression of claudin 2 was increased in experimental NEC. Sub-cellular fractionation localized increased claudin 2 protein to the cytoskeleton. ROCK inhibition was associated with normalization of these alterations and decreased severity of experimental NEC. Co-immunoprecipitation of caveolin-1 with claudin 2 suggests that caveolin-1 may act as a shuttle for the internalization of claudin 2 seen in experimental NEC. In conclusion, NEC is associated with intestinal permeability and increased expression of claudin 2, increased binding of caveolin-1 and claudin 2, and increased trafficking of claudin 2 to the cytoskeleton.

Effect of melatonin on EGF- and VEGF-induced monolayer permeability of HUVECs

Melatonin is a natural hormone involved in the regulation of circadian rhythm, immunity, and cardiovascular function. In the present study, we focused on the mechanism of melatonin in the regulation of vascular permeability. We found that melatonin could inhibit both VEGF- and EGF-induced monolayer permeability of human umbilical vein endothelial cells (HUVECs) and change the tyrosine phosphorylation of vascular-endothelial (VE-)cadherin, which was related to endothelial barrier function. In addition, phospho-AKT (Ser⁴⁷³) and phospho-ERK(1/2) played significant roles in the regulation of VE-cadherin phosphorylation. Both the phosphatidylinositol 3-kinase/AKT inhibitor LY49002 and MEK/ERK inhibitor U0126 could inhibit the permeability of HUVECs, but with different effects on tyrosine phosphorylation of VE-cadherin. Melatonin can influence the two growth factor-induced phosphorylation of AKT (Ser⁴⁷³) but not ERK(1/2). Our results show that melatonin can inhibit growth factor-induced monolayer permeability of HUVECs by influencing the phosphorylation of AKT and VE-cadherin. Melatonin can be a potential treatment for diseases associated with abnormal vascular permeability. NEW & NOTEWORTHY We found that melatonin could inhibit both EGF- and VEGF-induced monolayer permeability of human umbilical vein endothelial cells, which is related to phosphorylation of vascular-endothelial cadherin. Blockade of phosphatidylinositol 3-kinase/AKT and MEK/ERK pathways could inhibit the permeability of human umbilical vein endothelial cells, and phosphorylation of AKT (Ser⁴⁷³) might be a critical event in the changing of monolayer permeability and likely has cross-talk with the MEK/ERK pathway.