p38 MAP-kinase regulates function of gap and tight junctions during regeneration of rat hepatocytes

Tight Junction Proteins as Therapeutic Targets to Treat Liver Fibrosis and Hepatocellular Carcinoma

In the last decade tight junction proteins exposed at the surface of liver or cancer cells have been uncovered as mediators of liver disease biology: Claudin-1 and Occludin are host factors for hepatitis C virus entry and Claudin-1 has been identified as a driver for liver fibrosis and hepatocellular carcinoma (HCC). Moreover, Claudins have emerged as therapeutic targets for liver disease and HCC. CLDN1 expression is upregulated in liver fibrosis and HCC. Monoclonal antibodies (mAbs) targeting Claudin-1 have completed preclinical proof-of-concept studies for treatment of liver fibrosis and HCC and are currently in clinical development for advanced liver fibrosis. Claudin-6 overexpression is associated with an HCC aggressive phenotype and treatment resistance. Claudin-6 mAbs or chimeric antigen receptor-T cells therapies are currently being clinically investigated for Claudin-6 overexpressing tumors. In conclusion, targeting Claudin proteins offers a novel clinical opportunity for the treatment of patients with advanced liver fibrosis and HCC.

The Pivotal Mediating Role of Adenosine Monophosphate-Activated Protein Kinase (AMPK) in Liver Tight Junctions and Liver Regeneration of a Partial-Hepatectomy Mouse Model

PURPOSE

This study aims to explore the pivotal mediating role of adenosine monophosphate-activated protein kinase (AMPK) in liver tight junctions and liver regeneration of a partial hepatectomy (PH) mouse model.

METHODS

A 70% PH mouse model was used. Firstly, mice were randomly divided into sham, 70% PH, AMPK-activated, and AMPK-inhibited groups. Then serum levels of alanine aminotransferase, aspartate transaminase, total bilirubin, direct bilirubin, albumin, and prealbumin were tested on postoperative days 1, 2 and 3. Furthermore, the expression of tight junction proteins like occludin, claudin-3, and ZO-1, together with bile salt export pump (BSEP), which reflects liver function, and AMPK were measured by Western blot and quantitative real-time polymerase chain reaction. Moreover, the expression of tight junction proteins, BSEP, and Ki-67 were examined by immunohistochemistry.

RESULTS

After 70% PH, without intervention, the changes in expression of hepatic tight junction proteins (occludin, claudin-3, and ZO-1) were consistent with that of BSEP, which could reflect liver function. After treatment with AMPK activator, the high expression status of tight junction proteins occurred in advance and was maintained stably and for a longer time. It was beneficial to liver function and liver regeneration was promoted at early periods and enhanced continuously after PH.

CONCLUSIONS

Activation of AMPK could effectively enhance the expression of hepatic tight junction proteins after PH. Therefore, it could speed up the recovery of liver function and promote liver regeneration especially early after PH.

Downregulation of p38 MAPK signaling pathway ameliorates tissue engineered corneal epithelium

Tissue engineered corneal epithelium transplantation is effective treatment for severe limbal stem cell deficiency (LSCD), while epithelial terminal differentiation, tans-differentiation and insufficient stem cell during construction affects the quality of tissue engineered corneal epithelium. In this study, we applied SB203580 in the culture medium to downregulate the P38 MAPK signaling pathway during construction of tissue engineered corneal epithelium. With application of SB203580, tissue engineered corneal epithelium showed enhanced strength and condensed structure. The expression of progenitor cell markers ABCG2, P63, K14, Wnt7a was increased, differentiation markers K12, Pax6, K10, K13, and trans-differentiation markers α-SMA and Snail1 was decreased, while cell junction markers Claudin-1 and E-cadherin was increased in the tissue engineered corneal epithelium. The wnt/β-catenin signaling pathway was upregulated in the epithelium after p38 MAPK inhibition. Transplantation of tissue engineered corneal epithelium treated with SB203580 to rabbit LSCD model showed faster wound healing and improved epithelial quality. We conclude that downregulation of p38 MAPK signaling pathway helps maintain the stemness, prevent terminal differentiation and abnormal differentiation of corneal epithelial cells during epithelium construction process, thus can improve the quality of tissue engineered corneal epithelium.

Protective Effects of Natural Polysaccharides on Intestinal Barrier Injury: A Review

Owing to their minimal side effects and effective protection from oxidative stress, inflammation, and malignant growth, natural polysaccharides (NPs) are a potential adjuvant therapy for several diseases caused by intestinal barrier injury (IBI). More studies are accumulating on the protective effects of NPs with respect to IBI, but the underlying mechanisms remain unclear. Thus, this review aims to represent current studies that investigate the protective effects of NPs on IBI by directly maintaining intestinal epithelial barrier integrity (inhibiting oxidative stress, regulating inflammatory cytokine expression, and increasing tight junction protein expression) and indirectly regulating intestinal immunity and microbiota. Furthermore, the mechanisms underlying IBI development are briefly introduced, and the structure-activity relationships of polysaccharides with intestinal barrier protection effects are discussed. Potential developments and challenges associated with NPs exhibiting protective effects against IBI have also been highlighted to guide the application of NPs in the treatment of intestinal diseases caused by IBI.

Probiotic-mediated p38 MAPK immune signaling prolongs the survival of Caenorhabditis elegans exposed to pathogenic bacteria

The host-microbiota cross-talk represents an important factor contributing to innate immune response and host resistance during infection. It has been shown that probiotic lactobacilli exhibit the ability to modulate innate immunity and enhance pathogen elimination. Here we showed that heat-inactivated probiotic strain Lactobacillus curvatus BGMK2-41 stimulates immune response and resistance of the Caenorhabditis elegans against Staphylococcus aureus and Pseudomonas aeruginosa. By employing qRT-PCR and western blot analysis we showed that heat-inactivated BGMK2-41 activated PMK-1/p38 MAPK immunity pathway which prolongs the survival of C. elegans exposed to pathogenic bacteria in nematode killing assays. The C. elegans pmk-1 mutant was used to demonstrate a mechanistic basis for the antimicrobial potential of BGMK2-41, showing that BGMK2-41 upregulated PMK-1/p38 MAPK dependent transcription of C-type lectins, lysozymes and tight junction protein CLC-1. Overall, this study suggests that PMK-1/p38 MAPK-dependent immune regulation by BGMK2-41 is essential for probiotic-mediated C. elegans protection against gram-positive and gram-negative bacteria and could be further explored for development of probiotics with the potential to increase resistance of the host towards pathogens.

Cell-cell junctions: structure and regulation in physiology and pathology

Epithelial and endothelial cell-cell contacts are established and maintained by several intercellular junctional complexes. These structurally and biochemically differentiated regions on the plasma membrane primarily include tight junctions (TJs), and anchoring junctions. While the adherens junctions (AJs) provide essential adhesive and mechanical properties, TJs hold the cells together and form a near leak-proof intercellular seal by the fusion of adjacent cell membranes. AJs and TJs play essential roles in vascular permeability. Considering their involvement in several key cellular functions such as barrier formation, proliferation, migration, survival, and differentiation, further research is warranted on the composition and signaling pathways regulating cell-cell junctions to develop novel therapeutics for diseases such as organ injuries. The current review article presents our current state of knowledge on various cell-cell junctions, their molecular composition, and mechanisms regulating their expression and function in endothelial and epithelial cells.

GDF11 impairs liver regeneration in mice after partial hepatectomy

Growth differentiation factor 11 (GDF11) is a member of the transforming growth factor (TGF)-β superfamily. The rejuvenative effect of GDF11 has been called into question recently, and its role in liver regeneration is unclear. Here, we investigated the pathophysiologic role of GDF11, as well as its plausible signaling mechanisms in a mouse model of partial hepatectomy (PH). We demonstrated that both serum and hepatic GDF11 protein expression increased following PH. Treatment with adeno-associated viruses-GDF11 and recombinant GDF11 protein severely impaired liver regeneration, whereas inhibition of GDF11 activity with neutralizing antibodies significantly improved liver regeneration after PH. In vitro, GDF11 treatment significantly delayed cell proliferation and induced cell-cycle arrest in α mouse liver 12 (AML12) cells. Moreover, GDF11 activated TGF-β-SMAD2/3 signaling pathway. Inhibition of GDF11-induced SMAD2/3 activity significantly blocked GDF11-mediated reduction in cell proliferation both in vivo and in vitro. In the clinical setting, GDF11 levels were significantly elevated in patients after hepatectomy. Collectively, these results indicate that rather than a ‘rejuvenating’ agent, GDF11 impairs liver regeneration after PH. Suppression of cell-cycle progression via TGF-β-SMAD2/3 signaling pathway may be a key mechanism by which GDF11 inhibits liver regeneration.

How does Helicobacter pylori cause gastric cancer through connexins: An opinion review

Helicobacter pylori (H. pylori) is a Gram-negative bacterium with a number of virulence factors, such as cytotoxin-associated gene A, vacuolating cytotoxin A, its pathogenicity island, and lipopolysaccharide, which cause gastrointestinal diseases. Connexins function in gap junctional homeostasis, and their downregulation is closely related to gastric carcinogenesis. Investigations into H. pylori infection and the fine-tuning of connexins in cells or tissues have been reported in previous studies. Therefore, in this review, the potential mechanisms of H. pylori-induced gastric cancer through connexins are summarized in detail.

Rumen-derived lipopolysaccharide induced ruminal epithelium barrier damage in goats fed a high-concentrate diet

This study aimed to investigate the mechanism of lipopolysaccharide (LPS) released in the rumen on epithelium barrier function of goats fed a HC diet. Twelve Boer goats were randomly divided into two groups: low-concentrate(LC) diet and high-concentrate(HC) diet treatment. We found that the pH of rumen fluid in the HC group was lower than in the LC group (P < 0.05). The mRNA and protein expression levels of p38 mitogen-activated protein kinase (MAPK), extracellular regulated protein kinases (ERK), and c-Jun N-terminal kinase (JNK) in the rumen epithelium were lower in the LC group than the HC group (P < 0.05). Gene expression and protein levels of the tight junction proteins claudin-1, claudin-4, occludin, and Zona occludin-1 were all greater in the LC group than the HC group (P < 0.05). Staining of claudin-1, occludin and ZO-1 was became irregular. In conclusion, high concentrate diet feeding can impair rumen epithelium function and decrease tight junction protein expression through MAPK signaling pathway.

Replacement of grains with soybean hulls ameliorates SARA-induced impairment of the colonic epithelium barrier function of goats

BACKGROUND

The effect of soybean hull feeding on the disruption of colonic epithelium barrier function was investigated in goats fed a high-concentrate diet. Twenty-one Boer goats (live weight, 32.57 ± 2.26 kg; age, 1 year) were randomly divided into three groups: low-concentrate diet (LC), high-concentrate diet (HC), and high-concentrate diet with soybean hulls (SH).

RESULTS

We found that the rumen fluid in the LC and SH group shown a higher pH value compared with the HC group. The mRNA and protein expression levels of extracellular regulated protein kinase (ERK), c-Jun N-terminal kinase (JNK), and p38 mitogen-activated protein kinase (MAPK) in the colonic epithelium were significantly decreased in the SH group than in the HC group. Moreover, in goats fed the HC diet, SH treatment promoted gene expression and protein abundance of claudin-1, claudin-4, occludin, and ZO-1 in the colonic epithelium. Additionally, the injury to the colonic epithelium barrier caused by the HC diet was reversed by SH treatment.

CONCLUSIONS

Our results indicated that supplemental SH feeding reverses the damage to colonic epithelium tight junctions by inhibiting the MAPK signalling pathway and has a protective effect on the colonic epithelium during SARA.

Iranian crack induces hepatic injury through mitogen-activated protein kinase pathway in the liver of Wistar rat

Objectives

Iranian crack (IC) is a heroin-based substance manifesting various pathologic side effects. Herein, we aimed to investigate the mechanism of IC-induced liver injuries in Wistar rats.

Materials and Methods

Twenty male Wistar rats were randomly divided into two groups: control, and IC (0.9 mg/kg/day/IP, for 30 days). Mitochondrial reactive oxygen species (ROS) production was measured by DCF fluorescence staining. The expression of tumor necrosis factor-alpha (TNF-α), interleukin 1β (IL-1β), and phosphorylation of p38 mitogen-activated protein kinase (p38 MAPK) and c-Jun N-terminal kinase (c-JNK) were assessed by immunoblotting assay. The intensity of collagen fiber in the liver was also determined by Trichrome-Masson staining. Furthermore, serum levels of alanine aminotransferase (ALT), aspartate aminotransferase (AST), and alkaline phosphatase (ALP) activities were measured using colorimetric methods.

Results

Our results showed that ROS production, p38 MAPK, c-JNK phosphorylation levels, and expression of TNF-α and IL-1β were significantly elevated in the liver tissue of IC group as compared to the control group. Moreover, collagen fiber and ALT activity were increased in the liver tissue of IC group compared to the control group. However, there was no statistically significant difference in the levels of ALP between two groups. In addition, there was a positive correlation between the intensity of collagen fiber and the ALT activity, and the levels of TNF-α and IL-1β and liver enzymes activities including ALP, ALT, and AST.

Conclusion

Our findings revealed that IC-induced liver cells injury is partially mediated by MAPK stress kinases. Therefore, regular liver examination in substance abuse is strongly recommended.

Liver Regeneration After Major Liver Resection for Hepatocellular Carcinoma in the Elderly

Background: With an aging population, more elderly patients are being considered for hepatic resection for hepatocellular carcinoma (HCC). This study aimed to evaluate postoperative outcomes including liver regeneration after major hepatectomy for HCC in the elderly.Methods: We assessed 41 patients who underwent major hepatectomy (≥3 segments) at our institute between 2000 and 2013. Patients were divided into two age groups, elderly group (age ≥70 years, n = 23) and younger group (age <70 years, n = 18). Clinicopathological data and outcomes were retrospectively compared. To evaluate the effect of aging on liver regeneration, we measured liver volumes preoperatively and at 1 and 6 months after liver resection using a 3D simulation imaging system.Results: Overall and major complications after hepatectomy were not different between elderly and younger groups, and no case of mortality was recorded. Moreover, recurrence-free and overall survivals were similar in both groups. With regard to liver regeneration, no differences were observed between elderly and younger groups at 1 and 6 months after liver resection. Baseline liver functions were comparable between the groups. Furthermore, the only factor associated with liver regeneration was resected liver volume (R² = 0.631, p < 0.001). Age was not correlated with liver regeneration rate (R² = 0.00537, p = 0.695).Conclusions: Liver regeneration after major hepatectomy for HCC was not affected by age and that resected liver volume is an important factor for liver regeneration. Short- and long-term outcomes after major hepatectomy were similar in elderly and younger patients.

Sodium Butyrate Improves High-Concentrate-Diet-Induced Impairment of Ruminal Epithelium Barrier Function in Goats

We investigated the effect of sodium butyrate feeding on the disruption of ruminal epithelium barrier function in goats fed a high-concentrate diet. A total of 18 male Boer goats (live weight of 31.75 ± 1.35 kg, aged 1 year) were randomly assigned to three groups, which were fed a low-concentrate diet (LC), a high-concentrate diet (HC), or a high-concentrate diet with 1% sodium butyrate by weight (SH) for 9 weeks. We found that the pH of rumen fluid in the SH and LC groups was higher than that in the HC group. The activity of protein kinase C (PKC) kinase in the rumen epithelium was higher in the HC group than that in the LC and SH groups. The mRNA expression and phosphorylated protein levels of mitogen-activated protein kinases (MAPKs) in the rumen epithelium were lower in the SH and LC groups than those in the HC group. The DNA methylation rate of occludin was higher in the HC group than that in the SH and LC groups. The mRNA and protein expression of claudin-1, claudin-4, occludin, and zona occludin-1 was greater in the SH and LC groups than that in the HC group. In addition, sodium butyrate mitigated damage to the rumen epithelium caused by the HC diet. Together, our results suggest that the supply of sodium butyrate reverses the damage of rumen epithelium tight junction by inhibiting PKC and MAPK signaling pathways and is protective to the rumen epithelium during subacute rumen acidosis.

Potential roles of AMP-activated protein kinase in liver regeneration in mice with acute liver injury

Liver regeneration post severe liver injury is crucial for the recovery of hepatic structure and function. The energy sensor AMP‑activated protein kinase (AMPK) has a crucial role in the regulation of nutrition metabolism in addition to other energy‑intensive physiological and pathophysiological processes. Cellular proliferation requires intensive energy and nutrition support, therefore the present study investigated whether AMPK is involved in liver regeneration post carbon tetrachloride (CCl4)‑induced acute hepatic injury. The experimental data indicated that phosphorylation level of AMPK increased 48 h post‑CCl4 exposure, which was accompanied with upregulation of proliferating cell nuclear antigen (PCNA) and recovery of alanine aminotransferase (ALT) level. Pretreatment with the AMPK inhibitor compound C had no obvious effects on ALT elevation in plasma and histological abnormalities in liver 24 h post CCl4 exposure. However, treatment with compound C 24 h post CCl4 exposure significantly suppressed CCl4‑induced AMPK phosphorylation, PCNA expression and ALT recovery. These data suggest that endogenous AMPK was primarily activated at the regeneration stage in mice with CCl4‑induced acute liver injury and may function as a positive regulator in liver regeneration.

Connexin 32 and connexin 43 are involved in lineage restriction of hepatic progenitor cells to hepatocytes

BACKGROUND

Bi-potential hepatic progenitor cells can give rise to both hepatocytes and cholangiocytes, which is the last phase and critical juncture in terms of sequentially hepatic lineage restriction from any kind of stem cells. If their differentiation can be controlled, it might access to functional hepatocytes to develop pharmaceutical and biotechnology industries as well as cell therapies for end-stage liver diseases.

METHODS

In this study, we investigated the influence of Cx32 and Cx43 on hepatocyte differentiation of WB-F344 cells by in vitro gain and loss of function analyses. An inhibitor of Cx32 was also used to make further clarification. To reveal p38 MAPK pathway is closely related to Cxs, rats with 70% partial hepatectomy were injected intraperitoneally with a p38 inhibitor, SB203580. Besides, the effects of p38 MAPK pathway on differentiation of hepatoblasts isolated from fetal rat livers were evaluated by addition of SB203580 in culture medium.

RESULTS

In vitro gain and loss of function analyses showed overexpression of Connexin 32 and knockdown of Connexin 43 promoted hepatocytes differentiation from hepatic progenitor cells. In addition, in vitro and ex vivo research revealed inhibition of p38 mitogen-activated protein kinase pathway can improve hepatocytes differentiation correlating with upregulation of Connexin 32 expression and downregulation of Connexin 43 expression.

CONCLUSIONS

Here we demonstrate that Connexins play crucial roles in facilitating differentiation of hepatic progenitors. Our work further implicates that regulators of Connexins and their related pathways might provide new insights to improve lineage restriction of stem cells to mature hepatocytes.

Connexin 32-mediated cell-cell communication is essential for hepatic differentiation from human embryonic stem cells

Gap junction-mediated cell-cell interactions are highly conserved and play essential roles in cell survival, proliferation, differentiation and patterning. We report that Connexin 32 (Cx32)-mediated gap junctional intercellular communication (GJIC) is necessary for human embryonic stem cell-derived hepatocytes (hESC-Heps) during step-wise hepatic lineage restriction and maturation. Vitamin K2, previously shown to promote Cx32 expression in mature hepatocytes, up-regulated Cx32 expression and GJIC activation during hepatic differentiation and maturation, resulting in significant increases of hepatic markers expression and hepatocyte functions. In contrast, negative Cx32 regulator 2-aminoethoxydiphenyl borate blocked hESC-to-hepatocyte maturation and muted hepatocyte functions through disruption of GJIC activities. Dynamic gap junction organization and internalization are phosphorylation-dependent and the p38 mitogen-activated protein kinases pathway (MAPK) can negatively regulate Cxs through phosphorylation-dependent degradation of Cxs. We found that p38 MAPK inhibitor SB203580 improved maturation of hESC-Heps correlating with up-regulation of Cx32; by contrast, the p38 MAPK activator, anisomycin, blocked hESC-Heps maturation correlating with down-regulation of Cx32. These results suggested that Cx32 is essential for cell-cell interactions that facilitate driving hESCs through hepatic-lineage maturation. Regulators of both Cx32 and other members of its pathways maybe used as a promising approach on regulating hepatic lineage restriction of pluripotent stem cells and optimizing their functional maturation.

Model Predicts That MKP1 and TAB1 Regulate p38α Nuclear Pulse and Its Basal Activity through Positive and Negative Feedback Loops in Response to IL-1

Interleukin-1 mediates inflammation and stress response through nuclear activity of p38α. Although IL-1 receptor is not degraded, p38α activation is transient. IL-1 also causes cell migration and EMT by modulating cell-cell junctions. Although molecules involved in p38 activation are known, mechanism of the transient nuclear response and its basal activity remains unknown. By mathematical modeling of IL1/p38 signaling network, we show that IL-1 induces robust p38α activation both in the nucleus and in the cytoplasm/membrane. While nuclear response consists of an acute phase, membrane response resembles a step change. Following stimulation, p38α activity returns to a basal level in absence of receptor degradation. While nuclear pulse is controlled by MKP1 through a negative feedback to pp38, its basal activity is controlled by both TAB1 and MKP1 through a positive feedback loop. Our model provides insight into the mechanism of p38α activation, reason for its transient nuclear response, and explanation of the basal activity of MKK3/6 and p38α, which has been experimentally observed by other groups.

Connexin32 deficiency exacerbates carbon tetrachloride-induced hepatocellular injury and liver fibrosis in mice

OBJECTIVE

Liver fibrosis results from the perpetuation of the normal wound healing response to several types of injury. Despite the wealth of knowledge regarding the involvement of intracellular and extracellular signaling pathways in liver fibrogenesis, information about the role of intercellular communication mediated by gap junctions is scarce.

METHODS

In this study, liver fibrosis was chemically induced by carbon tetrachloride in mice lacking connexin32, the major liver gap junction constituent. The manifestation of liver fibrosis was evaluated based on a series of read-outs, including collagen morphometric and mRNA analysis, oxidative stress, apoptotic, proliferative and inflammatory markers.

RESULTS

More pronounced liver damage and enhanced collagen deposition were observed in connexin32 knockout mice compared to wild-type animals in experimentally triggered induced liver fibrosis. No differences between both groups were noticed in apoptotic signaling nor in inflammation markers. However, connexin32 deficient mice displayed decreased catalase activity and increased malondialdehyde levels.

CONCLUSION

These findings could suggest that connexin32-based signaling mediates tissue resistance against liver damage by the modulation of the antioxidant capacity. In turn, this could point to a role for connexin32 signaling as a therapeutic target in the treatment of liver fibrosis.

Inhibition of wild-type p53-induced phosphatase 1 promotes liver regeneration in mice by direct activation of mammalian target of rapamycin

The liver possesses extraordinary regenerative capacity in response to injury. However, liver regeneration (LR) is often impaired in disease conditions. Wild-type p53-induced phosphatase 1 (Wip1) is known as a tumor promoter and enhances cell proliferation, mainly by deactivating antioncogenes. However, in this work, we identified an unexpected role of Wip1 in LR. In contrast to its known role in promoting cell proliferation in extrahepatic tissue, we found that Wip1 suppressed hepatocyte proliferation after partial hepatectomy (PHx). Deletion of Wip1 increased the rate of LR after PHx. Enhanced LR in Wip1-deficient mice was a result of the activation of the mammalian target of rapamycin (mTOR) complex 1 (mTORC1) pathway. Furthermore, we showed that Wip1 physically interacted with and dephosphorylated mTOR. Interestingly, inhibition of Wip1 also activated the p53 pathway during LR. Disruption of the p53 pathway further enhanced LR in Wip1-deficient mice. Therefore, inhibition of Wip1 has a dual role in LR, i.e., promoting hepatocyte proliferation through activation of the mTORC1 pathway, meanwhile suppressing LR through activation of the p53 pathway. However, the proregenerative role of mTORC1 overwhelms the antiproliferative role of p53. Furthermore, CCT007093, a Wip1 inhibitor, enhanced LR and increased the survival rate of mice after major hepatectomy.

CONCLUSION

mTOR is a new direct target of Wip1. Wip1 inhibition can activate the mTORC1 pathway and enhance hepatocyte proliferation after hepatectomy. These findings have clinical applications in cases where LR is critical, including acute liver failure, cirrhosis, or small-for-size liver transplantations.

Association between cytotoxic T-lymphocyte-associated antigen 4 +49A/G polymorphism and persistent hepatitis B virus infection in the Asian population: evidence from the current studies

AIMS

A number of studies assessed the association between cytotoxic T-lymphocyte-associated antigen 4 (CTLA-4) +49A/G polymorphism and persistent hepatitis B virus (HBV) infection risk. However, the results are quite contradictory. In order to obtain a more precise estimation of the relationship, a meta-analysis was performed.

METHODS

Pubmed, ISI Web of Knowledge, HuGE Navigator, Wanfang Database, and China National Knowledge Infrastructure were searched. Crude odds ratios (ORs) with 95% confidence intervals (95% CIs) were calculated to estimate the strength of this association.

RESULTS

Six publications were included in the final meta-analysis with 1075 cases and 1321 controls for CTLA-4 +49A/G polymorphism according to our inclusion and exclusion criteria. We observed that the CTLA-4 +49A/G polymorphism was significantly correlated with chronic HBV infection risk (the homozygote codominant model: OR 1.67, 95% CI 1.30-2.15; the dominant model: OR 1.34, 95% CI 1.01-1.78; the recessive model: OR 1.56, 95% CI 1.24-1.96; the allele contrast model: OR 1.32, 95% CI 1.10-1.59). No publication bias was observed in this study according to Begg's funnel plot and Egger's test.

CONCLUSION

CTLA-4 +49A/G polymorphism is assumed to confer a higher risk for persistent HBV infection in the Asian population.

Side-stream smoking reduces intestinal inflammation and increases expression of tight junction proteins

AIM: To investigate the effect of side-stream smoking on gut microflora composition, intestinal inflammation and expression of tight junction proteins.

METHODS: C57BL/6 mice were exposed to side-stream cigarette smoking for one hour daily over eight weeks. Cecal contents were collected for microbial composition analysis. Large intestine was collected for immunoblotting and quantitative reverse transcriptase polymerase chain reaction analyses of the inflammatory pathway and tight junction proteins.

RESULTS: Side-stream smoking induced significant changes in the gut microbiota with increased mouse intestinal bacteria, Clostridium but decreased Fermicutes (Lactoccoci and Ruminococcus), Enterobacteriaceae family and Segmented filamentous baceteria compared to the control mice. Meanwhile, side-stream smoking inhibited the nuclear factor-κB pathway with reduced phosphorylation of p65 and IκBα, accompanied with unchanged mRNA expression of tumor necrosis factor-α or interleukin-6. The contents of tight junction proteins, claudin3 and ZO2 were up-regulated in the large intestine of mice exposed side-stream smoking. In addition, side-stream smoking increased c-Jun N-terminal kinase and p38 MAPK kinase signaling, while inhibiting AMP-activated protein kinase in the large intestine.

CONCLUSION: Side-stream smoking altered gut microflora composition and reduced the inflammatory response, which was associated with increased expression of tight junction proteins.

Effects of n-3 polyunsaturated fatty acids on rat livers after partial hepatectomy via LKB1-AMPK signaling pathway

OBJECTIVE

n-3 polyunsaturated fatty acid (n-3 PUFA) are considered to be associated with liver regeneration. We investigated the effects of n-3 PUFA on hepatic tight junction (TJs) and liver regeneration after 70% partial hepatectomy (PH) in rats.

METHODS

Male Sprague-Dawley rats were divided into four groups: sham group; control group, fish oil (FO; 1 mL/kg), and the FO (2 mL/kg) group. We examined changes in expression of hepatic TJs by at confocal microscopy in liver regeneration by routine clinical chemistry methods for hepatic function, and in activation of liver kinase B1-adenosine monophosphate-activated protein kinase (AMPK) signaling pathway. Using Western blot analysis.

RESULTS

After PH survival was higher in the FO than the control group. We observed treatment with n-3 PUFA to activated the LKB1-AMPK signaling pathway as well as to earlier, stronger and prolonged of the expression of Occludin, Claudin-3, zonula occludens-1, and proliferating cell nuclear antigen proteins. In addition, hepatic TJ structures and the level of liver function were protected after n-3 PUFA treatment.

CONCLUSIONS

After PH in rats, n-3 PUFA enhanced expression and protected the structure of hepatic TJs via the LKB1-AMPK signaling pathway. Moreover, it may promote liver regeneration partly via the LKB1-AMPK signaling pathway. It protected postoperative hepatic function and may be a liver protective agent against liver failure.

Injury of the hepatic barrier and intestinal barrier in patients with small-for-size graft syndrome after partial liver transplantation: mechanisms and protective measures

The intestinal barrier can resist the invasion of pathogens and prevent harmful substances from going into blood circulation to maintain the stability of internal environment, while the hepatic barrier is a vital structure that can protect liver function and prevent endotoxin and virus from entering the liver to damage hepatocytes. Both the two barrier structures are most vulnerable to damage after partial liver transplantation due to the occurrence of postoperative 'small-for-size graft syndrome'. The pathogenesis of 'small-for-size graft syndrome' is associated with postoperative portal hypertension and hyperperfusion. How to effectively control the occurrence of 'small-for-size graft syndrome' and to protect the intestinal barrier and hepatic barrier postoperatively are key to the maintenance of intestinal and hepatic functions. The primary aim of this paper is to review the mechanisms underlying the development of injury of the hepatic barrier and intestinal barrier in patients with small-for-size graft syndrome after partial liver transplantation and to propose the corresponding protective measures.

Effect of ω-3 polyunsaturated fatty acids on hepatic tight junctions and liver regeneration in rats after partial hepatectomy

AIM: To investigate the effect of ω-3 polyunsaturated fatty acids (PUFAs) on hepatic tight junctions and liver regeneration in rats after partial hepatectomy (PH)

METHODS: A rat model of 70% PH was used in this study. Eighty male SD rats were randomly divided into sham operation group, PH group, PH + low-dose ω-3 PUFA (1 mL/kg) group and PH + high-dose ω-3 PUFA (2 mL/kg) group. Serum samples were collected to measure the levels of total bile acids, total bilirubin, alanine aminotransferase (ALT) and albumin on days 1, 2, 3 and 5 after PH. Tissue samples were collected for detecting the expression of hepatic tight junction proteins (Occludin, Claudin-3 and ZO-1) and PCNA (a parameter reflecting liver regeneration) by Western blot. Tissue samples were also collected for observation of structural changes in hepatic tight junctions by confocal microscopy.

RESULTS: In comparison with the PH group on day 1, the levels of total bile acids (181.2 ± 63.9, 166.7 ± 68.9 vs 228.9 ± 37.7), total bilirubin (13.5 ± 8.8, 7.6 ± 0.1 vs 25.9 ± 15.3) and ALT (1042.2 ± 179.7, 901.4 ± 182.3 vs 2703.9 ± 130.0) decreased significantly in the low- and high-dose ω-3 PUFA groups (all P < 0.05), whereas no marked changes in the level of albumin (27.2 ± 1.1, 29.8 ± 0.9 vs 30.5 ± 1.2) were observed. Compared to the PH group on day 2, a significant decrease in the levels of total bilirubin (6.8 ± 9.2, 6.1 ± 2.0 vs 17.7 ± 1.1) and ALT (452.8 ± 258.5, 499.8 ± 155.9 vs 1 466.5 ± 30.2) was noted in the low- and high-dose ω-3 PUFA groups (all P < 0.05), whereas no marked changes in the level of albumin (26.8 ± 0.4, 27.7 ± 1.0 vs 25.7 ± 0.6) were observed. The expression of hepatic tight junction proteins (Occludin, Claudin-3 and ZO-1) increased significantly on days 1, 2 and 5 after PH (all P < 0.05), and liver regeneration was enhanced significantly on days 1, 2, 3 and 5 after PH (all P < 0.05). Treatment with ω-3 PUFAs promoted structural restoration of hepatic tight junctions.

CONCLUSION: ω-3 PUFAs not only promote the expression of tight junction proteins and protect the structure of hepatic tight junctions but also promote liver regeneration and protect liver function in rats after PH.

The growth pattern of transplanted normal and nodular hepatocytes

Overt neoplasia is often the end result of a long biological process beginning with the appearance of focal lesions of altered tissue morphology. While the putative clonal nature of focal lesions has often been emphasized, increasing attention is being devoted to the possible role of an altered growth pattern in the evolution of carcinogenesis. Here we compare the growth patterns of normal and nodular hepatocytes in a transplantation system that allows their selective clonal proliferation in vivo. Rats were pre-treated with retrorsine, which blocks the growth of resident hepatocytes, and were then transplanted with hepatocytes isolated from either normal liver or hepatocyte nodules. Both cell types were able to proliferate extensively in the recipient liver, as expected. However, their growth pattern was remarkably different. Clusters of normal hepatocytes integrated in the host liver, displaying a normal histology; however, transplanted nodular hepatocytes formed new hepatocyte nodules, with altered morphology and sharp demarcation from surrounding host liver. Both the expression and distribution of proteins involved in cell polarity, cell communication, and cell adhesion, including connexin 32, E-cadherin, and matrix metalloproteinase-2, were altered in clusters of nodular hepatocytes. Furthermore, we were able to show that down-regulation of connexin 32 and E-cadherin in nodular hepatocyte clusters was independent of growth rate. These results support the concept that a dominant pathway towards neoplastic disease in several organs involves defect(s) in tissue pattern formation.

Expression and function of claudins in hepatocytes

Tight junctions of hepatocytes play crucial roles in the barrier to keep bile in bile canaliculi away from the blood circulation, which we call the blood-biliary barrier. Tight junction proteins of hepatocytes are regulated by various cytokines and growth factors via distinct signal transduction pathways. To investigate changes in expression and function of tight junction proteins including claudins via signal transduction pathways in hepatocytes during EMT induced by TGF-β, we examined effects of TGF-β on expression and localization of the integral tight junction proteins, claudin-1, -2, and occludin, as well as the fence function by using primary cultures of adult rat hepatocytes.

Connexins: sensors and regulators of cell cycling

It is nowadays well established that gap junctions are critical gatekeepers of cell proliferation, by controlling the intercellular exchange of essential growth regulators. In recent years, however, it has become clear that the picture is not as simple as originally anticipated, as structural precursors of gap junctions can affect cell cycling by performing actions not related to gap junctional intercellular communication. Indeed, connexin hemichannels also foresee a pathway for cell growth communication, albeit between the intracellular compartment and the extracellular environment, while connexin proteins as such can directly or indirectly influence the production of cell cycle regulators independently of their channel activities. Furthermore, a novel set of connexin-like proteins, the pannexins, have lately joined in as regulators of the cell proliferation process, which they can affect as either single units or as channel entities. In the current paper, these multifaceted aspects of connexin-related signalling in cell cycling are reviewed.

Inactivation of p38 MAPK during liver regeneration

There is increasing evidence that p38 MAPK, which is classified as a stress-activated kinase, also participates in cell cycle regulation, functioning as a suppressor of cell proliferation and tumorigenesis. We conducted a study of p38 MAPK phosphorylation during liver regeneration in mice to determine whether p38 MAPK activation or inactivation may correlate with events that lead to DNA replication after partial hepatectomy (PH), and whether p38 MAPK activation may be required for hepatocyte DNA replication in vivo and in culture. We report that active p38 (Pi-p38 MAPK) is present in normal liver, is rapidly inactivated starting 30 min after PH, and is re-activated by 12h. Although levels of Pi-MKK 3/6, the upstream kinases that activate p38 MAPK increase after PH, the expression of the dual protein phosphatase 1 is also elevated, and may be responsible for Pi-p38 MAPK dephosphorylation after PH. Inactivation and re-activation of p38 MAPK inversely correlates with the stimulation of protein synthesis and translation pathways, as indicated by activation of p70S6 kinase, increases in the phosphorylation of initiation factor elF-4E and translational repressor, 4E-BP. The activity of a p38 MAPK downstream substrate, MAPKAPK2 (MK2), did not reflect the changing levels of Pi-p38 MAPK during liver regeneration. Pi-p38 MAPK may be involved in TNF-stimulated DNA replication of murine hepatocytes in culture, but is not necessary for hepatocyte DNA replication after PH. Our results suggest that p38 MAPK inactivation plays a permissible role in DNA replication during liver regeneration and is consistent with a role for p38 MAPK in the maintenance of hepatocyte cell cycle arrest in adult liver.

Hepatic tight junctions: From viral entry to cancer metastasis

The tight junction (TJ) is a critical cellular component for maintenance of tissue integrity, cellular interactions and cell-cell communications, and physiologically functions as the “great wall” against external agents and the surrounding hostile environment. During the host-pathogen evolution, viruses somehow found the key to unlock the gate for their entry into cells and to exploit and exhaust the host cells. In the liver, an array of TJ molecules is localized along the bile canaliculi forming the blood-biliary barrier, where they play pivotal roles in paracellular permeability, bile secretion, and cell polarity. In pathology, certain hepatic TJ molecules mediate virus entry causing hepatitis infection; deregulation and functional abnormality of the TJ have also been implicated in triggering liver cancer development and metastasis. All these findings shed new insights on the understanding of hepatic TJs in the development of liver disease and provide new clues for potential intervention.

Asymmetric dimethylarginine damages connexin43-mediated endothelial gap junction intercellular communication

Asymmetric dimethylarginine (ADMA), a major endogenous inhibitor of nitric oxide synthase, is recently defined as a novel atherogenic factor. Communication via gap junction (GJIC) is involved in the regulation of a variety of endothelial activities, such as cell differentiation and senescence. The aim of this study is to explore the effects of ADMA on connexin43 (Cx43) mediated endothelial GJIC. Lysophosphatidylcholine (LPC) caused the downregulation of Cx43 expression and GJIC dysfunction in cultured human umbilical vein endothelial cells (HUVECs), which were significantly ameliorated by decreasing ADMA accumulation. Furthermore, we found that ADMA (10 µmol·L–1, 24 h) markedly downregulated Cx43 expression and damaged GJIC function in HUVECs. ADMA also increased production of intracellular reactive oxygen species (ROS) and induced phosphorylation of p38 MAPK. Furthermore, the inhibitory effect of ADMA on Cx43-mediated GJIC could be attenuated by NADPH oxidase inhibitor diphenyleneiodonium and apocynin as well as p38 MAPK inhibitor SB203580, respectively. In conclusion, our present results suggest that ADMA inhibits endothelial GJIC function via downregulating Cx43 expression, which suggesting a novel mechanism linking between elevated ADMA level and progression of atherosclerosis.

Connexin32 is expressed in vascular endothelial cells and participates in gap-junction intercellular communication

Endothelial cells (ECs) play many roles in vascular biology, including control of blood pressure, blood clotting, atherosclerosis, angiogenesis, and inflammation. Gap junctions (GJs) are channel-like assemblies of connexin (Cx) family proteins that connect neighboring cells and modulate and synchronize their intracellular environments by the transfer of intracellular mediators. It has been reported that vascular ECs express Cx37, Cx40, and Cx43, but not Cx32. Here, we showed that Cx32 mRNA and protein are expressed in various cultured human ECs. We confirmed Cx32 expression in blood vessel ECs using wild-type and Cx32 knock-out mice. We observed that dye transfer between cultured ECs through gap junctions is suppressed by an anti-Cx32 monoclonal antibody. These findings suggest that vascular ECs express Cx32, which participates in endothelial gap-junction intercellular communication.

Knockdown of tight junction protein claudin-2 prevents bile canalicular formation in WIF-B9 cells

The polarization of hepatocytes involves formation of functionally distinct sinusoidal (basolateral) and bile canalicular (apical) plasma membrane domains that are separated by tight junctions. Although various molecular mechanisms and signaling cascades including polarity complex proteins may contribute to bile canalicular formation in hepatocytes, the role of tight junction proteins in bile canalicular formation remains unclear. To investigate the role of the integral tight junction protein claudin-2 in bile canalicular formation, we depleted claudin-2 expression by siRNA in the polarized hepatic cell line WIF-B9 after treatment with or without phenobarbital. When WIF-B9 cells were treated with phenobarbital, claudin-2 expression and tight junction strands were markedly increased together with induction of canalicular formation with a biliary secretion function. Knockdown of claudin-2 prevented bile canalicular formation after treatment with or without phenobarbital. Furthermore, knockdown of claudin-2 caused a change from a hepatic polarized phenotype to a simple polarized phenotype, together with upregulation of pLKB1, pMAPK, pAkt and pp38 MAPK, but not pMLC, PTEN or cdc42, and an increase of intracellular vacuoles, which were present before bile canalicular formation. These results suggest that claudin-2 may affect not only the bile canalicular seal but also bile canalicular formation.

Aspirin induces gastric epithelial barrier dysfunction by activating p38 MAPK via claudin-7

Tight junctions create a paracellular permeability barrier that is breached when nonsteroidal anti-inflammatory drugs cause gastrointestinal injury, including increased gastrointestinal permeability. However, the mechanism by which aspirin affects the function of gastric epithelial tight junctions is unknown. Thus, we examined the effect of aspirin on gastric mucosal barrier properties and tight junction organization using MKN28, a human gastric epithelial cell line that expresses claudin-3, claudin-4, claudin-7, zonula occludens (ZO)-1, and occludin, but not claudin-2 or claudin-5, as determined by immunoblot analysis and immunofluorescent staining. Aspirin (5 mM) treatment of MKN28 gastric epithelial monolayers significantly decreased transepithelial electrical resistance and increased dextran permeability. Both aspirin-mediated permeability and phosphorylation of p38 MAPK were significantly attenuated by SB-203580 (a p38 MAPK inhibitor) but not by U-0126 (a MEK1 inhibitor) or SP-600125 (a JNK inhibitor). Aspirin significantly decreased the quantity of claudin-7 protein produced by MKN28 cells but not the quantity of claudin-3, claudin-4, ZO-1, or occludin. The aspirin-induced decrease in claudin-7 protein was completely abolished by SB-203580 pretreatment. These results demonstrate, for the first time, that claudin-7 protein is important in aspirin-induced gastric barrier loss and that p38 MAPK activity mediates this epithelial barrier dysfunction.

Transforming growth factor-beta induces epithelial to mesenchymal transition by down-regulation of claudin-1 expression and the fence function in adult rat hepatocytes

BACKGROUND/AIMS

Transforming growth factor-beta (TGF-beta) initiates and maintains epithelial-mesenchymal transition (EMT), which causes disassembly of tight junctions and loss of epithelial cell polarity. In mature hepatocytes during EMT induced by TGF-beta, changes in the expression of tight junction proteins and the fence function indicated that epithelial cell polarity remains unclear.

METHODS

In the present study, using primary cultures of adult rat hepatocytes at day 10 after plating, in which epithelial cell polarity is well maintained by tight junctions, we examined the effects of 0.01-20 ng/ml TGF-beta on the expression of the integral tight junction proteins, claudin-1, -2 and occludin, as well as the fence function.

RESULTS

In adult rat hepatocytes, TGF-beta induced EMT, which was indicated as upregulation of Smad-interacting protein-1 (SIP1) and Snail and down-regulation of E-cadherin. Down-regulation of claudin-1 and upregulation of occludin were observed beginning from a low dose of TGF-beta, whereas upregulation of claudin-2 was observed at a high dose of TGF-beta. Furthermore, treatment with TGF-beta caused disruption of the fence function, which was closely associated with the expression of claudin-1 via p38 mitogen-activated protein kinase (MAPK), phosphoinositide-3 kinase and protein kinase C but not MAPK signalling pathways.

CONCLUSION

These results suggest that in mature hepatocytes in vitro, TGF-beta induces EMT by down-regulation of claudin-1 and the fence function via distinct signalling pathways.

Multiple effects of acetaminophen and p38 inhibitors: towards pathway toxicology

The majority of drug-related toxicities are idiosyncratic, with little pathophysiological insight and mechanistic understanding. Pathway toxicology is an emerging field of toxicology in the post-genomic era that studies the molecular interactions between toxicants and biological pathways as a way to bridge this knowledge gap. Using two case studies--acetaminophen and p38 MAPK inhibitors--this review illustrates how a pathway-based perspective has advanced our understanding of compound and target-based toxicities. The advancement of pathway toxicology will be dependent on integrated applications of techniques from basic sciences and a fundamental understanding of the interdependence of multiple biological pathways in living organisms.

Roles of Gap Junctions and Connexins in Non-Neoplastic Pathological Processes in which Cell Proliferation Is Involved

Cell proliferation is an important process for reproduction, growth and renewal of living cells and occurs in several situations during life. Cell proliferation is present in all the steps of carcinogenesis, initiation, promotion and progression. Gap junctions are the only specialization of cell membranes that allows communication between adjacent cells. They are known to contribute to tissue homeostasis and are composed of transmembrane proteins called "connexins." These junctions are also known to be involved in cell proliferation control. The roles of gap junctions and connexins in cell proliferation are complex and still under investigation. Since pioneer studies by Loewenstein, it is known that neoplastic cells lack communicating junctions. They do not communicate with their neighbors or with non-neoplastic cells from the surrounding area. There are many studies and review articles dedicated to neoplastic tissues. The aim of this review is to present evidence on the roles of gap junctions and connexins in non-neoplastic processes in which cell proliferation is involved.

Oncostatin M induces upregulation of claudin-2 in rodent hepatocytes coinciding with changes in morphology and function of tight junctions

In rodent livers, integral tight junction (TJ) proteins claudin-1, -2, -3, -5 and -14 are detected and play crucial roles in the barrier to keep bile in bile canaculi away from the blood circulation. Claudin-2 shows a lobular gradient increasing from periportal to pericentral hepatocytes, whereas claudin-1 and -3 are expressed in the whole liver lobule. Although claudin-2 expression induces cation-selective channels in tight junctions of epithelial cells, the physiological functions and regulation of claudin-2 in hepatocytes remain unclear. Oncostatin M (OSM) is a multifunctional cytokine implicated in the differentiation of hepatocytes that induces formation of E-cadherin-based adherens junctions in fetal hepatocytes. In this study, we examined whether OSM could induce expression and function of claudin-2 in rodent hepatocytes, immortalized mouse and primary cultured proliferative rat hepatocytes. In the immortalized mouse and primary cultured proliferative rat hepatocytes, treatment with OSM markedly increased mRNA and protein of claudin-2 together with formation of developed networks of TJ strands. The increase of claudin-2 enhanced the paracellular barrier function which depended on molecular size. The increase of claudin-2 expression induced by OSM in rodent hepatocytes was regulated through distinct signaling pathways including PKC. These results suggest that expression of claudin-2 in rodent hepatocytes may play a specific role as controlling the size of paracellular permeability in the barrier to keep bile in bile canaculi.

EGF-induced inhibition of glucose transport is mediated by PKC and MAPK signal pathways in primary cultured chicken hepatocytes

EGF is a regulator of a wide variety of processes in various cell systems. Hepatocytes are important sites in the body's metabolism and function. Glucose transporter 2 (GLUT2) is a major transporter that is expressed strongly in hepatocytes. Therefore, this study examined the effect of EGF on GLUT2 and its related signal cascades in primary cultured chicken hepatocytes. EGF decreased [(3)H]deoxyglucose uptake in a dose- and time-dependent manner (>10 ng/ml, 2 h). AG-1478 (an EGF receptor antagonist) and genistein and herbimycin A (tyrosine kinase inhibitors) blocked the EGF-induced decrease in [(3)H]deoxyglucose uptake, which correlated with the GLUT2 expression level. In addition, the EGF-induced decrease in GLUT2 protein expression was inhibited by staurosporine, H-7, or bisindolylmaleimide I (PKC inhibitors), PD-98059 (a MEK inhibitor), SB-203580 (a p38 MAPK inhibitor), and SP-600125 (a JNK inhibitor), suggesting a role of both PKC and MAPKs (p44/42 MAPK, p38 MAPK, and JNK). In particular, EGF increased the translocation of PKC isoforms (PKC-alpha, -beta(1), -gamma, -delta, and -zeta) from the cytosol to the membrane fraction and increased the activation of p44/42 MAPK, p38 MAPK, and JNK. Moreover, PKC inhibitors blocked the EGF-induced phosphorylation of three MAPKs. In conclusion, EGF decreases the GLUT2 expression level via the PKC-MAPK signal cascade in chicken hepatocytes.

Pattern recognition receptors: a contemporary view on liver diseases

Pattern recognition receptors (PRRs) function as sensors of microbial danger signals enabling the vertebrate host to initiate an immune response. PRRs are present not only in immune cells but also in liver parenchymal cells and the complexity of the cell populations provide unique aspects to pathogen recognition and tissue damage in the liver. This review discusses the role of different PRRs in pathogen recognition in the liver, and focuses on the role of PRRs in hepatic inflammation, cholestasis, ischemia, repair and fibrosis. PRRs as novel therapeutic targets are evaluated.