Concept: Tight junction protein 1
Dysfunction of cell-cell tight junction (TJ) adhesions is a major feature in the pathogenesis of various diseases. Liver TJs preserve cellular polarity by delimiting functional bile-canalicular structures, forming the blood-biliary barrier. In acetaminophen-hepatotoxicity, the mechanism by which tissue cohesion and polarity are affected remains unclear. Here, we demonstrate that acetaminophen, even at low-dose, disrupts the integrity of TJ and cell-matrix adhesions, with indicators of cellular stress with liver injury in the human hepatic HepaRG cell line, and primary hepatocytes. In mouse liver, at human-equivalence (therapeutic) doses, dose-dependent loss of intercellular hepatic TJ-associated ZO-1 protein expression was evident with progressive clinical signs of liver injury. Temporal, dose-dependent and specific disruption of the TJ-associated ZO-1 and cytoskeletal-F-actin proteins, correlated with modulation of hepatic ultrastructure. Real-time impedance biosensing verified in vitro early, dose-dependent quantitative decreases in TJ and cell-substrate adhesions. Whereas treatment with NAPQI, the reactive metabolite of acetaminophen, or the PKCα-activator and TJ-disruptor phorbol-12-myristate-13-acetate, similarly reduced TJ integrity, which may implicate oxidative stress and the PKC pathway in TJ destabilization. These findings are relevant to the clinical presentation of acetaminophen-hepatotoxicity and may inform future mechanistic studies to identify specific molecular targets and pathways that may be altered in acetaminophen-induced hepatic depolarization.
Propolis has abundant polyphenolic constituents and is used widely as a health/functional food. Here, we investigated the effects of polyphenol-rich propolis extracts (PPE) on intestinal barrier function in human intestinal epithelial Caco-2 cells, as well as in rats. In Caco-2 cells, PPE increased transepithelial electrical resistance and decreased lucifer yellow flux. PPE-treated cells showed increased expression of the tight junction (TJ) loci occludin and zona occludens (ZO)-1. Confocal microscopy showed organized expressions in proteins related to TJ assembly, i.e., occludin and ZO-1, in response to PPE. Furthermore, PPE led to the activation of AMPK, ERK1/2, p38, and Akt. Using selective inhibitors, we found that the positive effects of PPE on barrier function were abolished in cells in which AMPK and ERK1/2 signaling were inhibited. Moreover, rats fed a diet supplemented with PPE (0.3% in the diet) exhibited increased colonic epithelium ZO-1 expression. Overall, these data suggest that PPE strengthens intestinal barrier function by activating AMPK and ERK signaling and provide novel insights into the potential application of propolis for human gut health.
Mosapride is known to affect gastric motility, however whether mosapride has anti-ulcergenic effects in gastric mucosal injury is unclear. The aim of the present study was to investigate the effects of mosapride on aspirin-induced gastric injuries. GES-1 cells were cultured and divided into 5 groups: Control group, aspirin injury group (treated with 18.2 mmol/l aspirin) and mosapride pretreatment groups (treated with 0.4, 0.5, or 0.6 µmol/l mosapride). Cell proliferation was evaluated via MTT assay and cell apoptosis was investigated via flow cytometry. The expression of occludin was determined by western blot analysis. A total of 40 male Sprague-Dawley rats were randomized into five groups: Control group, aspirin injury group (150 mg/kg) and mosapride pretreatment groups (0.25, 0.50 or 0.75 mg/kg). Gastric mucosal lesions were induced by administering 200 mg/kg aspirin daily for 4 days. Rats in the mosapride groups were pretreated with mosapride 1 h prior to aspirin administration. Histological changes were evaluated under a light microscope and gastric epithelial TJs were observed via transmission electron microscopy. The results revealed that cell apoptosis was significantly increased in the aspirin injury group compared with the control (P<0.05), whereas apoptosis was significantly decreased in the mosapride pretreatment groups compared with the aspirin group (P<0.05). Cell viability was significantly increased in the mosapride pretreatment groups compared with the aspirin injury group (P<0.05), and that of the aspirin injury group was significantly decreased compared with the control group (P<0.05). Compared with the aspirin injury group, occludin expression was significantly increased in the three mosapride pre-treatment groups (all P<0.05). It was also demonstrated that gastric damage was significantly attenuated in the mosapride pretreatment groups compared with the aspirin injury group (P<0.05). Impaired TJ integrity was observed in aspirin injury group, whereas TJs in the mosapride groups were almost intact. In conclusion, the results of the present study suggest that mosapride exerts a gastroprotective action on aspirin-induced gastric mucosal injury at least in part via attenuating cell apoptosis and increasing occludin expression.
Claudin-2, ZO-1, and occludin are major components of tight junctions (TJs) in the proximal tubule. However, their roles in maintaining paracellular permeability as leaky epithelia have yet to be defined.
The effects of oral glutamine supplementation on exercise induced gastrointestinal permeability and tight junction protein expression
- Journal of applied physiology (Bethesda, Md. : 1985)
- Published about 6 years ago
The purposes of this study are to assess whether 7 days of oral glutamine supplementation: (1) reduces exercise induced intestinal permeability; (2) prevents the pro-inflammatory response; and (3) to determine whether these changes are associated with the up-regulation of the heat shock response. On separate occasions, eight human subjects participated in baseline testing, glutamine (GLN), and placebo (PLA) trials followed by a 60-min treadmill run. Intestinal permeability was higher in the PLA trial compared to baseline and GLN (0.0604 ± 0.047 vs. 0.0218 ±0.008 and 0.0272 ± 0.007, respectively, p<0.05). PBMC IκBα expression was higher 240-min post-ex in GLN trial compared to PLA (1.411 ± 0.523 vs. 0.9839 ± 0.343, p<0.05). In vitro (Caco-2) we measured effects of glutamine supplementation (0 mM, 4 mM, and 6 mM) on heat-induced (37° or 41.8°C) HSP70, HSF-1, and occludin expression. HSF-1 and HSP70 levels increased in 6 mM 41ºC compared to 0 mM 41ºC (1.785 ± 0.495 vs. 0.6681 ± 0.290, and 1.973 ± 0.325 vs. 1.133 ± 0.129, respectively, p<0.05). Occludin levels increased after 4 mM 41ºC and 6 mM 41ºC compared to 0 mM 41ºC (1.236 ± 0.219 and 1.849 ± 0.564 vs. 0.7434 ± 0.027, p<0.001, respectively). Glutamine supplementation prevented exercise-induced permeability, possibly through HSF-1 activation.
The occludin and ZO-1 complex, defined by small angle X-ray scattering and NMR, has implications for modulating tight junction permeability.
- Proceedings of the National Academy of Sciences of the United States of America
- Published over 7 years ago
Tight junctions (TJs) are dynamic cellular structures that are critical for compartmentalizing environments within tissues and regulating transport of small molecules, ions, and fluids. Phosphorylation-dependent binding of the transmembrane protein occludin to the structural organizing protein ZO-1 contributes to the regulation of barrier properties; however, the details of their interaction are controversial. Using small angle X-ray scattering (SAXS), NMR chemical shift perturbation, cross-saturation, in vitro binding, and site-directed mutagenesis experiments. we define the interface between the ZO-1 PDZ3-SH3-U5-GuK (PSG) and occludin coiled-coil (CC) domains. The interface is comprised of basic residues in PSG and an acidic region in CC. Complex formation is blocked by a peptide (REESEEYM) that corresponds to CC residues 468-475 and includes a previously uncharacterized phosphosite, with the phosphorylated version having a larger effect. Furthermore, mutation of E470 and E472 reduces cell border localization of occludin. Together, these results localize the interaction to an acidic region in CC and a predominantly basic helix V within the ZO-1 GuK domain. This model has important implications for the phosphorylation-dependent regulation of the occludin:ZO-1 complex.
Epithelial barrier dysfunction and increased permeability may contribute to antigen sensitization and disease progression in asthma. Claudin-18.1 is the only known lung-specific tight junction protein, but its contribution to airway barrier function or asthma is unclear.
Epithelial-mesenchymal transition (EMT) is considered to play a critical role in cancer progression and metastasis. However, the impact of EMT on the prognosis of hepatocellular carcinoma (HCC) is still elusive. In this study, we examined the relationship between the expression of EMT markers and recurrence-free survival (RFS) and overall survival (OS) in HCC patients after hepatic resection.
Intestinal alkaline phosphatase (IAP) plays a pivotal role in maintaining gut health and well-being. Oral supplementation with IAP in mice improves gut barrier function and prevents luminal proinflammatory factors from gaining access to the circulation. In this study, we sought to explore the relationship between IAP and tight junction protein (TJP) expression and function.
Dietary amino acids provide various beneficial effects for our health. The aim of the present study was to assess the effects of tryptophan (Trp) supplementation on barrier function. Ninety-six healthy finishing pigs (initial body weight 51.49 ± 1.12 kg) were randomly allocated into 2 treatment groups, control group, and 0.2% Trp group. The control group was fed the basal diet, and 0.2% Trp group was fed basal diet plus 0.2% Trp. The trial period is 60 d. Compared with control group, the mRNA abundance of claudin-3 and zonula occluden-1 (ZO-1) in the jejunum in 0.2% Trp group (P < 0.05) was increased. According to immunohistochemistry and immunoblotting test, the expression of ZO-1 in jejunum in 0.2% Trp group was also significantly increased compared with the control group (P < 0.05). These results revealed that Trp enhanced the expression of tight junction protein ZO-1 in the intestine of pig model. Trp may be potential and beneficial dietary functional factor for regulating the intestinal development and inhibiting intestinal aging.