Claudin-23 reshapes epithelial tight junction architecture to regulate barrier function

Inhibition of the STAT3-EPHX2 axis promotes regression of ulcerative colitis by treatment with novel porphyrin derivative

LD4, a novel porphyrin derivative, has attracted much attention for its excellent anti-inflammatory properties. It can promote the healing of colonic mucosa, reduce inflammatory response, regulate oxidative stress, and thus improve ulcerative colitis (UC) symptoms. However, the specific signaling pathways of LD4-PDT involved in UC have not been explored. The present study aimed to elucidate the effects of LD4 on UC and to investigate the underlying mechanisms both in vivo and in vitro. We classified and screened the LD4-PDT proteomic data to obtain key targets. Proteomic data revealed that EPHX2 and STAT3 are key targets of LD4-PDT for UC. Moreover, transcription factor STAT3 positively regulates the expression of EPHX2. Inhibiting EPHX2 can prevent the activation of NF-κB signaling pathway. Next, through pharmacological inhibition experiments, we confirmed that LD4-PDT can reduce intestinal inflammation by inhibiting STAT3-EPHX2 axis. However, by treating normal intestinal epithelial cells and colon cancer cells with TPPU and Stattic, our data confirmed that the STAT3-EPHX2 axis does not exist in colon cancer. In this study, we demonstrated that the transcription factor STAT3 can positively regulate the expression of EPHX2 in normal colon. LD4 can alleviate UC by inhibiting the STAT3-EPHX2 axis, but this axis does not exist in colon cancer. LD4-PDT may become a new and effective method for treating UC.

Nanostructure-Mediated Transport of Therapeutics through Epithelial Barriers

The ability to precisely treat human disease is facilitated by the sophisticated design of pharmacologic agents. Nanotechnology has emerged as a valuable approach to creating vehicles that can specifically target organ systems, effectively traverse epithelial barriers, and protect agents from premature degradation. In this review, we discuss the molecular basis for epithelial barrier function, focusing on tight junctions, and describe different pathways that drugs can use to cross barrier-forming tissue, including the paracellular route and transcytosis. Unique features of drug delivery applied to different organ systems are addressed: transdermal, ocular, pulmonary, and oral delivery. We also discuss how design elements of different nanoscale systems, such as composition and nanostructured architecture, can be used to specifically enhance transepithelial delivery. The ability to tailor nanoscale drug delivery vehicles to leverage epithelial barrier biology is an emerging theme in the pursuit of facilitating the efficacious delivery of pharmacologic agents.

Analysis of the key genes of Lactobacillus reuteri strains involved in the protection against alcohol-induced intestinal barrier damage

Gastrointestinal inflammation and intestinal barrier function have important effects on human health. Alcohol, an important foodborne hazard factor, damages the intestinal barrier, increasing the risk of disease. Lactobacillus reuteri strains have been reported to reduce gastrointestinal inflammation and strengthen the intestinal barrier. In this study, we selected three anti-inflammatory L. reuteri strains to evaluate their role in the protection of the intestinal barrier and their immunomodulatory activity in a mouse model of gradient alcohol intake. Among the three strains tested (FSCDJY33M3, FGSZY33L6, and FCQHCL8L6), L. reuteri FSCDJY33M3 was found to protect the intestinal barrier most effectively, possibly due to its ability to reduce the expression of interleukin (IL)-1β, IL-6, and tumor necrosis factor-alpha (TNF-α) and increase the expression of tight junction proteins (occludin, claudin-3). Genomic analysis suggested that the protective effects of L. reuteri FSCDJY33M3 may be related to functional genes and glycoside hydrolases associated with energy production and conversion, amino acid transport and metabolism, carbohydrate transport and metabolism, and DNA replication, recombination, and repair. These genes include COG2856, COG1804, COG2071, and COG1061, which encode adenine deaminase, acyl-CoA transferases, glutamine amidotransferase, RNA helicase, and glycoside hydrolases, including GH13_20, GH53, and GH70. Our results identified functional genes that may be related to protection against alcohol-induced intestinal barrier damage, which might be useful for screening lactic acid bacterial strains that can protect the intestinal barrier.

Biophysics of claudin proteins in tight junction architecture: Three decades of progress

Tight junctions are cell-cell adhesion complexes that act as gatekeepers of the paracellular space. Formed by several transmembrane proteins, the claudin family performs the primary gate-keeping function. The claudin proteins form charge and size-selective diffusion barriers to maintain homeostasis across endothelial and epithelial tissue. Of the 27 known claudins in mammals, some are known to seal the paracellular space, while others provide selective permeability. The differences in permeability arise due to the varying expression levels of claudins in each tissue. The tight junctions are observed as strands in freeze-fracture electron monographs; however, at the molecular level, tight junction strands form when multiple claudin proteins assemble laterally (cis assembly) within a cell and head-on (trans assembly) with claudins of the adjacent cell in a zipper-like architecture, closing the gap between the neighboring cells. The disruption of tight junctions caused by changing claudin expression levels or mutations can lead to diseases. Therefore, knowledge of the molecular architecture of the tight junctions and how that is tied to tissue-specific function is critical for fighting diseases. Here, we review the current understanding of the tight junctions accrued over the last three decades from experimental and computational biophysics perspectives.

Cadmium modulates intestinal Wnt/β-catenin signaling ensuing intestinal barrier disruption and systemic inflammation

The intricate architecture of the intestinal epithelium, crucial for nutrient absorption, is constantly threatened by environmental factors. The epithelium undergoes rapid turnover, which is essential for maintaining homeostasis, under the control of intestinal stem cells (ISCs). The central regulator, Wnt/β-catenin signaling plays a key role in intestinal integrity and turnover. Despite its significance, the impact of environmental factors on this pathway has been largely overlooked. This study, for the first time, investigates the influence of Cd on the intestinal Wnt signaling pathway using a mouse model. In this study, male BALB/c mice were administered an environmentally relevant Cd dose (0.98 mg/kg) through oral gavage to investigate the intestinal disruption and Wnt signaling pathway. Various studies, including histopathology, immunohistochemistry, RT-PCR, western blotting, ELISA, intestinal permeability assay, and flow cytometry, were conducted to study Cd-induced changes in the intestine. The canonical Wnt signaling pathway experienced significant downregulation as a result of sub-chronic Cd exposure, which caused extensive damage throughout the small intestine. Increased intestinal permeability and a skewed immune response were also observed. To confirm that Wnt signaling downregulation is the key driver of Cd-induced gastrointestinal toxicity, mice were co-exposed to LiCl (a recognized Wnt activator) and Cd. The results clearly showed that the harmful effects of Cd could be reversed, which is strong evidence that Cd mostly damages the intestine through the Wnt/β-catenin signalling axis. In conclusion, this research advances the current understanding of the role of Wnt/β catenin signaling in gastrointestinal toxicity caused by diverse environmental pollutants.

Type 1 diabetes human enteroid studies reveal major changes in the intestinal epithelial compartment

Lack of understanding of the pathophysiology of gastrointestinal (GI) complications in type 1 diabetes (T1D), including altered intestinal transcriptomes and protein expression represents a major gap in the management of these patients. Human enteroids have emerged as a physiologically relevant model of the intestinal epithelium but establishing enteroids from individuals with long-standing T1D has proven difficult. We successfully established duodenal enteroids using endoscopic biopsies from pediatric T1D patients and compared them with aged-matched enteroids from healthy subjects (HS) using bulk RNA sequencing (RNA-seq), and functional analyses of ion transport processes. RNA-seq analysis showed significant differences in genes and pathways associated with cell differentiation and proliferation, cell fate commitment, and brush border membrane. Further validation of these results showed higher expression of enteroendocrine cells, and the proliferating cell marker Ki-67, significantly lower expression of NHE3, lower epithelial barrier integrity, and higher fluid secretion in response to cAMP and elevated calcium in T1D enteroids. Enteroids established from pediatric T1D duodenum identify characteristics of an abnormal intestinal epithelium and are distinct from HS. Our data supports the use of pediatric enteroids as an ex-vivo model to advance studies of GI complications and drug discovery in T1D patients.

CLDN1 knock out keratinocytes as a model to investigate multiple skin disorders

The transmembrane protein claudin-1 is critical for formation of the epidermal barrier structure called tight junctions (TJ) and has been shown to be important in multiple disease states. These include neonatal ichthyosis and sclerosing cholangitis syndrome, atopic dermatitis and various viral infections. To develop a model to investigate the role of claudin-1 in different disease settings, we used CRISPR/Cas9 to generate human immortalized keratinocyte (KC) lines lacking claudin-1 (CLDN1 KO). We then determined whether loss of claudin-1 expression affects epidermal barrier formation/function and KC differentiation/stratification. The absence of claudin-1 resulted in significantly reduced barrier function in both monolayer and organotypic cultures. CLDN1 KO cells demonstrated decreases in gene transcripts encoding the barrier protein filaggrin and the differentiation marker cytokeratin-10. Marked morphological differences were also observed in CLDN1 KO organotypic cultures including diminished stratification and reduced formation of the stratum granulosum. We also detected increased proliferative KC in the basale layer of CLDN1 KO organotypic cultures. These results further support the role of claudin-1 in epidermal barrier and suggest an additional role of this protein in appropriate stratification of the epidermis.

Claudins in Cancer: A Current and Future Therapeutic Target

Claudins are a family of 27 proteins that have an important role in the formation of tight junctions. They also have an important function in ion exchange, cell mobility, and the epithelial-to-mesenchymal transition, the latter being very important in cancer invasion and metastasis. Therapeutic targeting of claudins has been investigated to improve cancer outcomes. Recent evidence shows improved outcomes when combining monoclonal antibodies against claudin 18.2 with chemotherapy for patients with gastroesophageal junction cancer. Currently, chimeric antigen receptor T-cells targeting claudin 18 are under investigation. In this review, we will discuss the major functions of claudins, their distribution in the normal as well as cancerous tissues, and their effect in cancer metastasis, with a special focus on the therapeutic targeting of claudins to improve cancer outcomes.

Rome III Criteria Capture Higher Irritable Bowel Syndrome SNP-Heritability and Highlight a Novel Genetic Link With Cardiovascular Traits

BACKGROUND & AIMS

Irritable bowel syndrome (IBS) shows genetic predisposition, and large-scale genome-wide association studies (GWAS) are emerging, based on heterogeneous disease definitions. We investigated the genetic architecture of IBS defined according to gold standard Rome Criteria.

METHODS

We conducted GWAS meta-analyses of Rome III IBS and its subtypes in 24,735 IBS cases and 77,149 asymptomatic control subjects from 2 independent European cohorts (UK Biobank and Lifelines). Single-nucleotide polymorphism (SNP)-based heritability (h2SNP) and genetic correlations (rg) with other traits were calculated. IBS risk loci were functionally annotated to identify candidate genes. Sensitivity and conditional analyses were conducted to assess impact of confounders. Polygenic risk scores were computed and tested in independent datasets.

RESULTS

Rome III IBS showed significant SNP-heritability (up to 13%) and similar genetic architecture across subtypes, including those with manifestations at the opposite ends of the symptom spectrum (rg = 0.48 between IBS-D and IBS-C). Genetic correlations with other traits highlighted commonalities with family history of heart disease and hypertension, coronary artery disease, and angina pectoris (rg = 0.20-0.45), among others. Four independent GWAS signals (P < 5×10-8) were detected, including 2 novel loci for IBS (rs2035380) and IBS-mixed (rs2048419) that had been previously associated with hypertension and coronary artery disease. Functional annotation of GWAS risk loci revealed genes implicated in circadian rhythm (BMAL1), intestinal barrier (CLDN23), immunomodulation (MFHAS1), and the cyclic adenosine monophosphate pathway (ADCY2). Polygenic risk scores allowed the identification of individuals at increased risk of IBS (odds ratio, 1.34; P = 1.1×10-3).

CONCLUSIONS

Rome III Criteria capture higher SNP-heritability than previously estimated for IBS. The identified link between IBS and cardiovascular traits may contribute to the delineation of alternative therapeutic strategies, warranting further investigation.

Super-enhancers: Implications in gastric cancer

Gastric cancer (GC) is the fifth most prevalent malignancy and the third leading cause of cancer-related mortality globally. Despite intensive efforts to enhance the efficiencies of various therapeutics (chemotherapy, surgical interventions, molecular-targeted therapies, immunotherapies), the prognosis for patients with GC remains poor. This might be predominantly due to the limited understanding of the complicated etiology of GC. Importantly, epigenetic modifications and alterations are crucial during GC development. Super-enhancers (SEs) are a large cluster of adjacent enhancers that greatly activate transcription. SEs sustain cell-specific identity by enhancing the transcription of specific oncogenes. In this review, we systematically summarize how SEs are involved in GC development, including the SE landscape in GC, the SE target genes in GC, and the interventions related to SE functions for treating GC.