Regulation of claudin/zonula occludens-1 complexes by hetero-claudin interactions

Metabotropic glutamate receptor 5 promotes blood-brain barrier recovery after traumatic brain injury

Blood-brain barrier (BBB) impairment and glutamate release are two pathophysiological features of traumatic brain injury (TBI), contributing to secondary brain damage and neuroinflammation. However, our knowledge of BBB integrity damage and dysfunction are still limited due to the diverse and fluctuating expression of glutamate receptors after trauma. Here, we confirmed the downregulation of metabotropic glutamate receptor 5 (mGluR5) on microvascular endothelial cell within the acute phase of TBI, and the recovered mGluR5 levels on BBB was positively associated with blood perfusion and neurological recovery. In whole body mGluR5-knockout mice, BBB dysfunction and neurological deficiency were exacerbated after TBI compared with wild type mice. In terms of mechanism, the amino acid sequence 201-259 of cytoskeletal protein Alpha-actinin-1 (ACTN1) interacted with mGluR5, facilitating mGluR5 translocation from cytoplasmic compartment to plasma membrane in endothelial cells. Activation of plasma membrane mGluR5 triggers the PLC/PKCμ/c-Jun signaling pathway, leading to increased expression of the tight junction-actin cytoskeleton connecting protein zonula occludens-1 (ZO-1). Our findings uncover a novel mechanism mediated by membrane and cytoplasmic mGluR5 in endothelial cell integrity maintenance and repair, providing the potential therapeutic target for TBI treatment targeting at mGluR5 and mGluR5/ACTN1 complex in BBB.

CLDN5: From structure and regulation to roles in tumors and other diseases beyond CNS disorders

Claudin-5 (CLDN5) is an essential component of tight junctions (TJs) and is critical for the integrity of the blood-brain barrier (BBB), ensuring homeostasis and protection from damage to the central nervous system (CNS). Currently, many researchers have summarized the role and mechanisms of CLDN5 in CNS diseases. However, it is noteworthy that CLDN5 also plays a significant role in tumor growth and metastasis. In addition, abnormal CLDN5 expression is involved in the development of respiratory diseases, intestinal diseases, cardiac diseases, and diabetic ocular complications. This paper aims to review the structure, expression, and regulation of CLDN5, focusing on its role in tumors, including its expression and regulation, effects on malignant phenotypes, and clinical significance. Furthermore, this paper will provide an overview of the role and mechanisms of CLDN5 in respiratory diseases, intestinal diseases, cardiac diseases, and diabetic ocular complications.

Effects of fetal growth restriction on the perinatal neurovascular unit and possible treatment targets

The neurovascular unit (NVU) within the brain is a multicellular unit that synergistically acts to maintain blood-brain barrier function and meet cerebral metabolic demand. Recent studies have indicated disruption to the NVU is associated with neuropathology in the perinatal brain. Infants with fetal growth restriction (FGR) are known to be at increased risk of neurodevelopmental conditions including motor, learning, and behavioural deficits. There are currently no neuroprotective treatments for these conditions. In this review, we analyse large animal studies examining the effects of FGR on the perinatal NVU. These studies show altered vascularity in the FGR brain as well as blood-brain barrier dysfunction due to underlying cellular changes, mediated by neuroinflammation. Neuroinflammation is a key mechanism associated with pathological effects in the FGR brain. Hence, targeting inflammation may be key to preserving the multicellular NVU and providing neuroprotection in FGR. A number of maternal and postnatal therapies with anti-inflammatory components have been investigated in FGR animal models examining targets for amelioration of NVU disruption. Each therapy showed promise by uniquely ameliorating the adverse effects of FGR on multiple aspects of the NVU. The successful implementation of a clinically viable neuroprotective treatment has the potential to improve outcomes for neonates affected by FGR. IMPACT: Disruption to the neurovascular unit is associated with neuropathology in fetal growth restriction. Inflammation is a key mechanism associated with neurovascular unit disruption in the growth-restricted brain. Anti-inflammatory treatments ameliorate adverse effects on the neurovascular unit and may provide neuroprotection.

Chronic alcohol use primes bronchial cells for altered inflammatory response and barrier dysfunction during SARS-CoV-2 infection

Alcohol use disorder (AUD) is a significant public health concern and people with AUD are more likely to develop severe acute respiratory distress syndrome (ARDS) in response to respiratory infections. To examine whether AUD was a risk factor for more severe outcome in response to severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection, we examined early responses to infection using cultured differentiated bronchial epithelial cells derived from brushings obtained from people with AUD or without AUD. RNA-seq analysis of uninfected cells determined that AUD cells were enriched for expression of epidermal genes as compared with non-AUD cells. Bronchial epithelial cells from patients with AUD showed a significant decrease in barrier function 72 h postinfection, as determined by transepithelial electrical resistance. In contrast, barrier function of non-AUD cells was enhanced 72 h after SARS-CoV-2 infection. AUD cells showed claudin-7 that did not colocalize with zonula occludens-1 (ZO-1), indicative of disorganized tight junctions. However, both AUD and non-AUD cells showed decreased β-catenin expression following SARS-CoV-2 infection. To determine the impact of AUD on the inflammatory response to SARS-CoV-2 infection, cytokine secretion was measured by multiplex analysis. SARS-CoV-2-infected AUD bronchial cells had enhanced secretion of multiple proinflammatory cytokines including TNFα, IL-1β, and IFNγ as opposed to non-AUD cells. In contrast, secretion of the barrier-protective cytokines epidermal growth factor (EGF) and granulocyte macrophage-colony stimulating factor (GM-CSF) was enhanced for non-AUD bronchial cells. Taken together, these data support the hypothesis that AUD is a risk factor for COVID-19, where alcohol primes airway epithelial cells for increased inflammation and increased barrier dysfunction and increased inflammation in response to infection by SARS-CoV-2.NEW & NOTEWORTHY Alcohol use disorder (AUD) is a significant risk factor for severe acute respiratory distress syndrome. We found that AUD causes a phenotypic shift in gene expression in human bronchial epithelial cells, enhancing expression of epidermal genes. AUD cells infected with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) had higher levels of proinflammatory cytokine secretion and barrier dysfunction not present in infected non-AUD cells, consistent with increased early COVID-19 severity due to AUD.

Human peritoneal tight junction, transporter and channel expression in health and kidney failure, and associated solute transport

Next to the skin, the peritoneum is the largest human organ, essentially involved in abdominal health and disease states, but information on peritoneal paracellular tight junctions and transcellular channels and transporters relative to peritoneal transmembrane transport is scant. We studied their peritoneal localization and quantity by immunohistochemistry and confocal microscopy in health, in chronic kidney disease (CKD) and on peritoneal dialysis (PD), with the latter allowing for functional characterizations, in a total of 93 individuals (0-75 years). Claudin-1 to -5, and -15, zonula occludens-1, occludin and tricellulin, SGLT1, PiT1/SLC20A1 and ENaC were consistently detected in mesothelial and arteriolar endothelial cells, with age dependent differences for mesothelial claudin-1 and arteriolar claudin-2/3. In CKD mesothelial claudin-1 and arteriolar claudin-2 and -3 were more abundant. Peritonea from PD patients exhibited increased mesothelial and arteriolar claudin-1 and mesothelial claudin-2 abundance and reduced mesothelial and arteriolar claudin-3 and arteriolar ENaC. Transperitoneal creatinine and glucose transport correlated with pore forming arteriolar claudin-2 and mesothelial claudin-4/-15, and creatinine transport with mesothelial sodium/phosphate cotransporter PiT1/SLC20A1. In multivariable analysis, claudin-2 independently predicted the peritoneal transport rates. In conclusion, tight junction, transcellular transporter and channel proteins are consistently expressed in peritoneal mesothelial and endothelial cells with minor variations across age groups, specific modifications by CKD and PD and distinct associations with transperitoneal creatinine and glucose transport rates. The latter deserve experimental studies to demonstrate mechanistic links.Clinical Trial registration: The study was performed according to the Declaration of Helsinki and is registered at www.clinicaltrials.gov (NCT01893710).

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

Claudin family tight junction proteins form charge- and size-selective paracellular channels that regulate epithelial barrier function. In the gastrointestinal tract, barrier heterogeneity is attributed to differential claudin expression. Here, we show that claudin-23 (CLDN23) is enriched in luminal intestinal epithelial cells where it strengthens the epithelial barrier. Complementary approaches reveal that CLDN23 regulates paracellular ion and macromolecule permeability by associating with CLDN3 and CLDN4 and regulating their distribution in tight junctions. Computational modeling suggests that CLDN23 forms heteromeric and heterotypic complexes with CLDN3 and CLDN4 that have unique pore architecture and overall net charge. These computational simulation analyses further suggest that pore properties are interaction-dependent, since differently organized complexes with the same claudin stoichiometry form pores with unique architecture. Our findings provide insight into tight junction organization and propose a model whereby different claudins combine to form multiple distinct complexes that modify epithelial barrier function by altering tight junction structure.

Cortistatin deficiency reveals a dysfunctional brain endothelium with impaired gene pathways, exacerbated immune activation, and disrupted barrier integrity

BACKGROUND

Brain activity governing cognition and behaviour depends on the fine-tuned microenvironment provided by a tightly controlled blood-brain barrier (BBB). Brain endothelium dysfunction is a hallmark of BBB breakdown in most neurodegenerative/neuroinflammatory disorders. Therefore, the identification of new endogenous molecules involved in endothelial cell disruption is essential to better understand BBB dynamics. Cortistatin is a neuroimmune mediator with anti-inflammatory and neuroprotective properties that exerts beneficial effects on the peripheral endothelium. However, its role in the healthy and injured brain endothelium remains to be evaluated. Herein, this study aimed to investigate the potential function of endogenous and therapeutic cortistatin in regulating brain endothelium dysfunction in a neuroinflammatory/neurodegenerative environment.

METHODS

Wild-type and cortistatin-deficient murine brain endothelium and human cells were used for an in vitro barrier model, where a simulated ischemia-like environment was mimicked. Endothelial permeability, junction integrity, and immune response in the presence and absence of cortistatin were evaluated using different size tracers, immunofluorescence labelling, qPCR, and ELISA. Cortistatin molecular mechanisms underlying brain endothelium dynamics were assessed by RNA-sequencing analysis. Cortistatin role in BBB leakage was evaluated in adult mice injected with LPS.

RESULTS

The endogenous lack of cortistatin predisposes endothelium weakening with increased permeability, tight-junctions breakdown, and dysregulated immune activity. We demonstrated that both damaged and uninjured brain endothelial cells isolated from cortistatin-deficient mice, present a dysregulated and/or deactivated genetic programming. These pathways, related to basic physiology but also crucial for the repair after damage (e.g., extracellular matrix remodelling, angiogenesis, response to oxygen, signalling, and metabolites transport), are dysfunctional and make brain endothelial barrier lacking cortistatin non-responsive to any further injury. Treatment with cortistatin reversed in vitro hyperpermeability, tight-junctions disruption, inflammatory response, and reduced in vivo BBB leakage.

CONCLUSIONS

The neuropeptide cortistatin has a key role in the physiology of the cerebral microvasculature and its presence is crucial to develop a canonical balanced response to damage. The reparative effects of cortistatin in the brain endothelium were accompanied by the modulation of the immune function and the rescue of barrier integrity. Cortistatin-based therapies could emerge as a novel pleiotropic strategy to ameliorate neuroinflammatory/neurodegenerative disorders with disrupted BBB.

Bezafibrate attenuates acute lung injury by preserving mitochondrial dynamics equilibrium in pulmonary epithelial cells

Acute lung injury (ALI) serves as a common life-threatening clinical syndrome with high mortality rates, which is characterized by disturbed mitochondrial dynamics in pulmonary epithelial barrier. Peroxisome proliferator-activated receptor-γ (PPAR-γ) is one of the critical nuclear receptors, exerting important roles in preserving mitochondrial dynamics equilibrium. Previous studies have suggested that bezafibrate (BEZ), a PPAR-γ agonist, could improve obesity and insulin resistance. In the present study, we explored whether bezafibrate could attenuate lipopolysaccharide (LPS)-induced ALI in vivo and in vitro. Using C57BL/6 mice exposed to LPS, we observed that BEZ pretreatment (100 mg/kg) for 7 days decreased lung pathologic injury, reduced oxidative stress, suppressed inflammation and apoptosis, accompanied by shifting the dynamic course of mitochondria from fission into fusion. Meanwhile, we observed that BEZ could reverse the inhibition of PPAR-γ in lung tissues from LPS-treated mice. In vitro experiments also disclosed that BEZ could improve cell viability in primary pulmonary epithelial cells in a concentration-dependent manner. And BEZ (80 μM) treatment could not only inhibit oxidative stress but also preserve mitochondrial dynamics equilibrium in primary pulmonary epithelial cells. However, PPAR-γ knockdown partially abolished BEZ-mediated antioxidation and completely offset its regulatory effects on mitochondrial dynamics in primary pulmonary epithelial cells. In PPAR-γ-deficient mice, BEZ lost its pulmonary protection including anti-inflammatory and antioxidative effects in mice with ALI. Taken together, BEZ could attenuate ALI by preserving mitochondrial dynamics equilibrium in pulmonary epithelial cells in a PPAR-γ-dependent manner.

20 kDa isoform of connexin-43 augments spatial reorganization of the brain endothelial junctional complex and lesion leakage in cerebral cavernous malformation type-3

Cerebral cavernous malformation type-3 (CCM3) is a type of brain vascular malformation caused by mutations in programmed cell death protein-10 (PDCD10). It is characterized by early life occurrence of hemorrhagic stroke and profound blood-brain barrier defects. The pathogenic mechanisms responsible for microvascular hyperpermeability and lesion progression in CCM3 are still largely unknown. The current study examined brain endothelial barrier structural defects formed in the absence of CCM3 in vivo and in vitro that may lead to CCM3 lesion leakage. We found significant upregulation of a 20 kDa isoform of connexin 43 (GJA1-20 k) in brain endothelial cells (BEC) in both non-leaky and leaky lesions, as well as in an in vitro CCM3 knockdown model (CCM3KD-BEC). Morphological, biochemical, FRET, and FRAP analyses of CCM3KD-BEC found GJA1-20 k regulates full-length GJA1 biogenesis, prompting uncontrolled gap junction growth. Furthermore, by binding to a tight junction scaffolding protein, ZO-1, GJA1-20 k interferes with Cx43/ZO-1 interactions and gap junction/tight junction crosstalk, promoting ZO-1 dissociation from tight junction complexes and diminishing claudin-5/ZO-1 interaction. As a consequence, the tight junction complex is destabilized, allowing "replacement" of tight junctions with gap junctions leading to increased brain endothelial barrier permeability. Modifying cellular levels of GJA1-20 k rescued brain endothelial barrier integrity re-establishing the spatial organization of gap and tight junctional complexes. This study highlights generation of potential defects at the CCM3-affected brain endothelial barrier which may underlie prolonged vascular leakiness.

Optical blood-brain-tumor barrier modulation expands therapeutic options for glioblastoma treatment

The treatment of glioblastoma has limited clinical progress over the past decade, partly due to the lack of effective drug delivery strategies across the blood-brain-tumor barrier. Moreover, discrepancies between preclinical and clinical outcomes demand a reliable translational platform that can precisely recapitulate the characteristics of human glioblastoma. Here we analyze the intratumoral blood-brain-tumor barrier heterogeneity in human glioblastoma and characterize two genetically engineered models in female mice that recapitulate two important glioma phenotypes, including the diffusely infiltrative tumor margin and angiogenic core. We show that pulsed laser excitation of vascular-targeted gold nanoparticles non-invasively and reversibly modulates the blood-brain-tumor barrier permeability (optoBBTB) and enhances the delivery of paclitaxel in these two models. The treatment reduces the tumor volume by 6 and 2.4-fold and prolongs the survival by 50% and 33%, respectively. Since paclitaxel does not penetrate the blood-brain-tumor barrier and is abandoned for glioblastoma treatment following its failure in early-phase clinical trials, our results raise the possibility of reevaluating a number of potent anticancer drugs by combining them with strategies to increase blood-brain-tumor barrier permeability. Our study reveals that optoBBTB significantly improves therapeutic delivery and has the potential to facilitate future drug evaluation for cancers in the central nervous system.

Storming the gate: New approaches for targeting the dynamic tight junction for improved drug delivery

As biologics used in the clinic outpace the number of new small molecule drugs, an important challenge for their efficacy and widespread use has emerged, namely tissue penetrance. Macromolecular drugs - bulky, high-molecular weight, hydrophilic agents - exhibit low permeability across biological barriers. Epithelial and endothelial layers, for example within the gastrointestinal tract or at the blood-brain barrier, present the most significant obstacle to drug transport. Within epithelium, two subcellular structures are responsible for limiting absorption: cell membranes and intercellular tight junctions. Previously considered impenetrable to macromolecular drugs, tight junctions control paracellular flux and dictate drug transport between cells. Recent work, however, has shown tight junctions to be dynamic, anisotropic structures that can be targeted for delivery. This review aims to summarize new approaches for targeting tight junctions, both directly and indirectly, and to highlight how manipulation of tight junction interactions may help usher in a new era of precision drug delivery.

Effects of sevoflurane on lung epithelial permeability in experimental models of acute respiratory distress syndrome

BACKGROUND

Preclinical studies in acute respiratory distress syndrome (ARDS) have suggested that inhaled sevoflurane may have lung-protective effects and clinical trials are ongoing to assess its impact on major clinical outcomes in patients with ARDS. However, the underlying mechanisms of these potential benefits are largely unknown. This investigation focused on the effects of sevoflurane on lung permeability changes after sterile injury and the possible associated mechanisms.

METHODS

To investigate whether sevoflurane could decrease lung alveolar epithelial permeability through the Ras homolog family member A (RhoA)/phospho-Myosin Light Chain 2 (Ser19) (pMLC)/filamentous (F)-actin pathway and whether the receptor for advanced glycation end-products (RAGE) may mediate these effects. Lung permeability was assessed in RAGE^-/- and littermate wild-type C57BL/6JRj mice on days 0, 1, 2, and 4 after acid injury, alone or followed by exposure at 1% sevoflurane. Cell permeability of mouse lung epithelial cells was assessed after treatment with cytomix (a mixture of TNFɑ, IL-1β, and IFNγ) and/or RAGE antagonist peptide (RAP), alone or followed by exposure at 1% sevoflurane. Levels of zonula occludens-1, E-cadherin, and pMLC were quantified, along with F-actin immunostaining, in both models. RhoA activity was assessed in vitro.

RESULTS

In mice after acid injury, sevoflurane was associated with better arterial oxygenation, decreased alveolar inflammation and histological damage, and non-significantly attenuated the increase in lung permeability. Preserved protein expression of zonula occludens-1 and less increase of pMLC and actin cytoskeletal rearrangement were observed in injured mice treated with sevoflurane. In vitro, sevoflurane markedly decreased electrical resistance and cytokine release of MLE-12 cells, which was associated with higher protein expression of zonula occludens-1. Improved oxygenation levels and attenuated increase in lung permeability and inflammatory response were observed in RAGE^-/- mice compared to wild-type mice, but RAGE deletion did not influence the effects of sevoflurane on permeability indices after injury. However, the beneficial effect of sevoflurane previously observed in wild-type mice on day 1 after injury in terms of higher PaO₂/FiO₂ and decreased alveolar levels of cytokines was not found in RAGE^-/- mice. In vitro, RAP alleviated some of the beneficial effects of sevoflurane on electrical resistance and cytoskeletal rearrangement, which was associated with decreased cytomix-induced RhoA activity.

CONCLUSIONS

Sevoflurane decreased injury and restored epithelial barrier function in two in vivo and in vitro models of sterile lung injury, which was associated with increased expression of junction proteins and decreased actin cytoskeletal rearrangement. In vitro findings suggest that sevoflurane may decrease lung epithelial permeability through the RhoA/pMLC/F-actin pathway.

Microglia and the Blood-Brain Barrier: An External Player in Acute and Chronic Neuroinflammatory Conditions

Microglia are the resident immune cells of the central nervous system that guarantee immune surveillance and exert also a modulating role on neuronal synaptic development and function. Upon injury, microglia get activated and modify their morphology acquiring an ameboid phenotype and pro- or anti-inflammatory features. The active role of microglia in blood-brain barrier (BBB) function and their interaction with different cellular components of the BBB-endothelial cells, astrocytes and pericytes-are described. Here, we report the specific crosstalk of microglia with all the BBB cell types focusing in particular on the involvement of microglia in the modulation of BBB function in neuroinflammatory conditions that occur in conjunction with an acute event, such as a stroke, or in a slow neurodegenerative disease, such as Alzheimer's disease. The potential of microglia to exert a dual role, either protective or detrimental, depending on disease stages and environmental conditioning factors is also discussed.

Programmed cell death 10 increased blood-brain barrier permeability through HMGB1/TLR4 mediated downregulation of endothelial ZO-1 in glioblastoma

Dysfunction of blood brain barrier (BBB) contributes to the development of peritumoral edema (PTE) and GBM progression. Programmed cell death 10 (PDCD10) exerts various influence on cancers, especially in glioblastoma (GBM). We previously found that PDCD10 expression was positively correlated with PTE extent in GBM. Thus, the present study aims to investigate the emerging role of PDCD10 in regulating BBB permeability in GBM. Here we found that in vitro indirect co-culture of ECs with Pdcd10-overexpressed GL261 cells resulted in a significant increase of FITC-Dextran (MW, 4000) leakage by reducing endothelial zonula occluden-1 (ZO-1) and Claudin-5 expression in ECs respectively. Overexpression of Pdcd10 in GBM cells (GL261) triggered an increase of soluble high mobility group box 1 (HMGB1) release, which in turn activated endothelial toll like receptor 4 (TLR4) and downstream NF-κB, Erk1/2 and Akt signaling in ECs through a paracrine manner. Moreover, Pdcd10-overexpressed GL261 cells facilitated a formation of abnormal vasculature and increased the BBB permeability in vivo. Our present study demonstrates that upregulation of PDCD10 in GBM triggered HMGB1/TLR4 signaling in ECs and significantly decreased endothelial ZO-1 expression, which in turn dominantly increased BBB permeability and contributed to tumor progression in GBM.

Dopamine D1 receptor agonist alleviates acute lung injury via modulating inflammatory responses in macrophages and barrier function in airway epithelial cells

Acute lung injury (ALI) or its severe form, acute respiratory distress syndrome (ARDS) is a life-threatening illness without effective therapeutic interventions currently. Multiple lines of evidence indicated that overwhelming inflammatory responses and impaired epithelial barrier contributed to the pathogenesis of ALI/ARDS. Recently, dopamine (DA) system was identified to participate in various pulmonary diseases. Here, we discovered that dopamine D1-like receptors mainly expressed in macrophages and airway epithelial cells (AECs), which were downregulated by lipopolysaccharide (LPS) challenge in ALI mouse lung. SKF38393 (SKF) is a selective agonist for D1-like receptors and was demonstrated to inhibit excessive inflammatory responses and oxidative stress in THP-1 cell-derived macrophages and Beas-2B cells, as well as improve airway epithelial barrier dysfunction induced by LPS stimulation. Moreover, SKF administration could effectively decrease pulmonary inflammation, ameliorate tissue damage in the LPS-triggered ALI mice. The broad protective actions of SKF might be attributed to the activation of Nrf2 antioxidative system by use of the specific inhibitor, ML385. This study offers evidence of potent immunoregulatory activity of SKF in macrophages, AECs as well as ALI mouse model, which opens novel therapeutic avenues for the intervention of ALI/ARDS.

Pharmacological reversal of post-transcriptional alterations implicated in alcohol-induced alveolar macrophage dysfunction

Alcohol use disorders (AUD) cause alveolar macrophage (AM) immune dysfunction and increase risk of lung infections. Excessive alcohol use causes AM oxidative stress, which impairs AM phagocytosis and pathogen clearance from the alveolar space. Alcohol induces expression of NADPH oxidases (Noxes), primary sources of oxidative stress in AM. In contrast, alcohol decreases AM peroxisome proliferator-activated receptor gamma (PPARγ), a critical regulator of AM immune function. To explore the underlying molecular mechanisms for these effects of alcohol, we hypothesized that ethanol promotes CCAAT/enhancer-binding protein beta (C/EBPβ)-mediated suppression of Nox-related microRNAs (miRs), in turn enhancing AM Nox expression, oxidative stress, and phagocytic dysfunction. We also hypothesized that PPARγ activation with pioglitazone (PIO) would reverse alcohol-induced C/EBPβ expression and attenuate AM oxidative stress and phagocytic dysfunction. Cells from the mouse AM cell line (MH-S) were exposed to ethanol in vitro or primary AM were isolated from mice fed ethanol in vivo. Ethanol enhanced C/EBPβ expression, decreased Nox 1-related miR-1264 and Nox 2-related miR-107 levels, and increased Nox1, Nox2, and Nox 4 expression in MH-S cells in vitro and mouse AM in vivo. These alcohol-induced AM derangements were abrogated by loss of C/EBPβ, overexpression of miRs-1264 or -107, or PIO treatment. These findings identify C/EBPβ and Nox-related miRs as novel therapeutic targets for PPARγ ligands, which could provide a translatable strategy to mitigate susceptibility to lung infections in people with a history of AUD. These studies further clarify the molecular underpinnings for a previous clinical trial using short-term PIO treatment to improve AM immunity in AUD individuals.

Cellular Distribution Pattern of tjp1 (ZO-1) in Xenopus laevis Oocytes Heterologously Expressing Claudins

Epithelial barriers constitute a fundamental requirement in every organism, as they allow the separation of different environments and set boundaries against noxious and other adverse effectors. In many inflammatory and degenerative diseases, epithelial barrier function is impaired because of a disturbance of the paracellular seal. Recently, the Xenopus laevis oocyte has been established as a heterologous expression model for the analysis of transmembrane tight junction protein interactions and is currently considered to be a suitable screening model for barrier effectors. A prerequisite for this application is a physiological anchoring of claudins to the cytoskeleton via the major scaffolding protein tjp1 (tight junction protein 1, ZO-1). We have analyzed the oocyte model with regard to the interaction of heterologously expressed claudins and tjp1. Our experiments have revealed endogenous tjp1 expression in protein and mRNA analyses of unfertilized Xenopus laevis oocytes expressing human claudin 1 (CLDN1) to claudin 5 (CLDN5). The amphibian cell model can therefore be used for the analysis of claudin interactions.

Steen solution protects pulmonary microvascular endothelial cells and preserves endothelial barrier after lipopolysaccharide-induced injury

OBJECTIVES

Acute respiratory distress syndrome represents the devastating result of acute lung injury, with high mortality. Limited methods are available for rehabilitation of lungs affected by acute respiratory distress syndrome. Our laboratory has demonstrated rehabilitation of sepsis-injured lungs via normothermic ex vivo and in vivo perfusion with Steen solution (Steen). However, mechanisms responsible for the protective effects of Steen remain unclear. This study tests the hypothesis that Steen directly attenuates pulmonary endothelial barrier dysfunction and inflammation induced by lipopolysaccharide.

METHODS

Primary pulmonary microvascular endothelial cells were exposed to lipopolysaccharide for 4 hours and then recovered for 8 hours in complete media (Media), Steen, or Steen followed by complete media (Steen/Media). Oxidative stress, chemokines, permeability, interendothelial junction proteins, and toll-like receptor 4-mediated pathways were assessed in pulmonary microvascular endothelial cells using standard methods.

RESULTS

Lipopolysaccharide treatment of pulmonary microvascular endothelial cells and recovery in Media significantly induced reactive oxygen species, lipid peroxidation, expression of chemokines (eg, chemokine [C-X-C motif] ligand 1 and C-C motif chemokine ligand 2) and cell adhesion molecules (P-selectin, E-selectin, and vascular cell adhesion molecule 1), permeability, neutrophil transmigration, p38 mitogen-activated protein kinase and nuclear factor kappa B signaling, and decreased expression of tight and adherens junction proteins (zonula occludens-1, zonula occludens-2, and vascular endothelial-cadherin). All of these inflammatory pathways were significantly attenuated after recovery of pulmonary microvascular endothelial cells in Steen or Steen/Media.

CONCLUSIONS

Steen solution preserves pulmonary endothelial barrier function after lipopolysaccharide exposure by promoting an anti-inflammatory environment via attenuation of oxidative stress, toll-like receptor 4-mediated signaling, and conservation of interendothelial junctions. These protective mechanisms offer insight into the advancement of methods for in vivo lung perfusion with Steen for the treatment of severe acute respiratory distress syndrome.

Microbial-derived metabolites induce actin cytoskeletal rearrangement and protect blood-brain barrier function

The gut microbiota influences host brain function, but the underlying gut-brain axis connections and molecular processes remain unclear. One pathway along this bidirectional communication system involves circulating microbially derived metabolites, such as short-chain fatty acids (SCFAs), which include butyrate and propionate. Brain endothelium is the main interface of communication between circulating signals and the brain, and it constitutes the main component of the blood-brain barrier (BBB). Here, we used a well-established in vitro BBB model treated with physiologically relevant concentrations of butyrate and propionate with and without lipopolysaccharide (LPS) to examine the effects of SCFAs on the actin cytoskeleton and tight junction protein structure. Both SCFAs induced distinct alterations to filamentous actin directionality. SCFAs also increased tight junction protein spikes and protected from LPS-induced tight-junction mis-localization, improved BBB integrity, and modulated mitochondrial network dynamics. These findings identify the actin cytoskeletal dynamics as another target further illuminating how SCFAs can influence BBB physiology.

Advanced development and mechanism of sepsis-related acute respiratory distress syndrome

The introduction of the Sepsis 3.0 guidelines in 2016 improved our understanding of sepsis diagnosis and therapy. Personalized treatment strategies and nursing methods for sepsis patients are recommended in the "Save Sepsis Campaign" in 2021. However, mortality in sepsis patients remains high. Patients with sepsis-related acute respiratory distress syndrome account for around 30% of them, with fatality rates ranging from 30 to 40%. Pathological specimens from individuals with sepsis-related ARDS frequently demonstrate widespread alveolar damage, and investigations have revealed that pulmonary epithelial and pulmonary endothelial injury is the underlying cause. As a result, the purpose of this work is to evaluate the mechanism and research progress of pulmonary epithelial and pulmonary endothelial damage in sepsis-related ARDS, which may provide new directions for future research, diagnosis, and therapy.

New insights into the mechanism of alcohol-mediated organ damage via its impact on immunity, metabolism, and repair pathways: A summary of the 2021 Alcohol and Immunology Research Interest Group (AIRIG) meeting

On November 19th, 2021, the annual Alcohol and Immunology Research Interest Group (AIRIG) meeting was held at Loyola University Chicago Health Sciences Campus in Maywood, Illinois. The 2021 meeting focused on how alcohol misuse is linked to immune system derangements, leading to tissue and organ damage, and how this research can be translated into improving treatment of alcohol-related disease. This meeting was divided into three plenary sessions: the first session focused on how alcohol misuse affects different parts of the immune system, the second session presented research on mechanisms of organ damage from alcohol misuse, and the final session highlighted research on potential therapeutic targets for treating alcohol-mediated tissue damage. Diverse areas of alcohol research were covered during the meeting, from alcohol's effect on pulmonary systems and neuroinflammation to epigenetic changes, senescence markers, and microvesicle particles. These presentations yielded a thoughtful discussion on how the findings can lead to therapeutic treatments for people suffering from alcohol-related diseases.

Nanoscale segregation of channel and barrier claudins enables paracellular ion flux

The paracellular passage of ions and small molecules across epithelia is controlled by tight junctions, complex meshworks of claudin polymers that form tight seals between neighboring cells. How the nanoscale architecture of tight junction meshworks enables paracellular passage of specific ions or small molecules without compromising barrier function is unknown. Here we combine super-resolution stimulated emission depletion microscopy in live and fixed cells and tissues, multivariate classification of super-resolution images and fluorescence resonance energy transfer to reveal the nanoscale organization of tight junctions formed by mammalian claudins. We show that only a subset of claudins can assemble into characteristic homotypic meshworks, whereas tight junctions formed by multiple claudins display nanoscale organization principles of intermixing, integration, induction, segregation, and exclusion of strand assemblies. Interestingly, channel-forming claudins are spatially segregated from barrier-forming claudins via determinants mainly encoded in their extracellular domains also known to harbor mutations leading to human diseases. Electrophysiological analysis of claudins in epithelial cells suggests that nanoscale segregation of distinct channel-forming claudins enables barrier function combined with specific paracellular ion flux across tight junctions.

Meshworks of claudin polymers control the paracellular transport and barrier properties of epithelial tight junctions. Here, the authors show different claudin nanoscale organization principles, finding that claudin segregation enables barrier formation and paracellular ion flux across tight junctions.

Natural Herbal Remedy Wumei Decoction Ameliorates Intestinal Mucosal Inflammation by Inhibiting Th1/Th17 Cell Differentiation and Maintaining Microbial Homeostasis

BACKGROUND

Evidence has shown that the traditional Chinese herbal medicine Wumei decoction (WMD) has a protective effect on ulcerative colitis. Here, we studied the anti-inflammatory effects and potential mechanisms of WMD on chronic colitis in mice.

METHODS

A dextran sulfate sodium (DSS)-induced chronic colitis model and CD45RBhighCD4+ T cell transfer model were established in mice. Body weight, Disease Activity Index, and colon length were assessed, and histopathology was confirmed by hematoxylin and eosin staining. Colon tissue samples were collected to detect the frequencies of various immune cells, expression of cytokines, and tight junction-related proteins using flow cytometry, quantitative real-time polymerase chain reaction, and enzyme-linked immunosorbent assay, respectively. 16S ribosomal DNA sequencing was performed to distinguish differential microbiota of fecal samples.

RESULTS

Severe chronic colitis was observed in mice after DSS exposure and in Rag1-/- mice reconstituted with CD45RBhighCD4+ T cells, as manifested by weight loss, hematochezia, and shortening and thickening of the colon, which were reversed by WMD treatment. WMD markedly suppressed intestinal mucosal CD4+ T cell differentiation and the secretion of proinflammatory cytokines (eg, tumor necrosis factor α, interleukin-1β, interferon γ, and IL-17A) by flow cytometry, quantitative real-time polymerase chain reaction, and enzyme-linked immunosorbent assay, respectively. Moreover, WMD promoted the expression of occludin, zonula occludens-1, and E-cadherin, thereby maintaining the epithelial barrier function. Additionally, 16S ribosomal DNA sequencing revealed that WMD regulated the dysbiosis of gut microbiota in CD45RBhighCD4+ T cell-reconstituted Rag1-/- mice, evidenced by an increase of Allobaculum and Bacteroides and a decrease of Ileibacterium.

CONCLUSIONS

WMD ameliorates chronic colitis in mice induced by DSS or reconstituted with CD45RBhighCD4+ T cells through suppressing Th1/Th17 cell differentiation and the secretion of proinflammatory cytokines, maintaining epithelial barrier function, and improving the dysbiosis.

High-Dose Acetaminophen Alters the Integrity of the Blood-Brain Barrier and Leads to Increased CNS Uptake of Codeine in Rats

The consumption of acetaminophen (APAP) can induce neurological changes in human subjects; however, effects of APAP on blood-brain barrier (BBB) integrity are unknown. BBB changes by APAP can have profound consequences for brain delivery of co-administered drugs. To study APAP effects, female Sprague-Dawley rats (12-16 weeks old) were administered vehicle (i.e., 100% dimethyl sulfoxide (DMSO), intraperitoneally (i.p.)) or APAP (80 mg/kg or 500 mg/kg in DMSO, i.p.; equivalent to a 900 mg or 5600 mg daily dose for a 70 kg human subject). BBB permeability was measured via in situ brain perfusion using [¹⁴C]sucrose and [³H]codeine, an opioid analgesic drug that is co-administered with APAP (i.e., Tylenol #3). Localization and protein expression of tight junction proteins (i.e., claudin-5, occludin, ZO-1) were studied in rat brain microvessels using Western blot analysis and confocal microscopy, respectively. Paracellular [¹⁴C]sucrose "leak" and brain [³H]codeine accumulation were significantly enhanced in rats treated with 500 mg/kg APAP only. Additionally, claudin-5 localization and protein expression were altered in brain microvessels isolated from rats administered 500 mg/kg APAP. Our novel and translational data show that BBB integrity is altered following a single high APAP dose, results that are relevant to patients abusing or misusing APAP and/or APAP/opioid combination products.

The Impact of Alcohol Use Disorder on Tuberculosis: A Review of the Epidemiology and Potential Immunologic Mechanisms

Globally, an estimated 107 million people have an alcohol use disorder (AUD) leading to 2.8 million premature deaths each year. Tuberculosis (TB) is one of the leading causes of death globally and over 8% of global TB cases are estimated to be attributable to AUD. Social determinants of health such as poverty and undernutrition are often shared among those with AUD and TB and could explain the epidemiologic association between them. However, recent studies suggest that these shared risk factors do not fully account for the increased risk of TB in people with AUD. In fact, AUD has been shown to be an independent risk factor for TB, with a linear increase in the risk for TB with increasing alcohol consumption. While few studies have focused on potential biological mechanisms underlying the link between AUD and TB, substantial overlap exists between the effects of alcohol on lung immunity and the mechanisms exploited by Mycobacterium tuberculosis (Mtb) to establish infection. Alcohol misuse impairs the immune functions of the alveolar macrophage, the resident innate immune effector in the lung and the first line of defense against Mtb in the lower respiratory tract. Chronic alcohol ingestion also increases oxidative stress in the alveolar space, which could in turn facilitate Mtb growth. In this manuscript, we review the epidemiologic data that links AUD to TB. We discuss the existing literature on the potential mechanisms by which alcohol increases the risk of TB and review the known effects of alcohol ingestion on lung immunity to elucidate other mechanisms that Mtb may exploit. A more in-depth understanding of the link between AUD and TB will facilitate the development of dual-disease interventions and host-directed therapies to improve lung health and long-term outcomes of TB.

Microscopic Visualization of Cell-Cell Adhesion Complexes at Micro and Nanoscale

Considerable progress has been made in our knowledge of the morphological and functional varieties of anchoring junctions. Cell-cell adhesion contacts consist of discrete junctional structures responsible for the mechanical coupling of cytoskeletons and allow the transmission of mechanical signals across the cell collective. The three main adhesion complexes are adherens junctions, tight junctions, and desmosomes. Microscopy has played a fundamental role in understanding these adhesion complexes on different levels in both physiological and pathological conditions. In this review, we discuss the main light and electron microscopy techniques used to unravel the structure and composition of the three cell-cell contacts in epithelial and endothelial cells. It functions as a guide to pick the appropriate imaging technique(s) for the adhesion complexes of interest. We also point out the latest techniques that have emerged. At the end, we discuss the problems investigators encounter during their cell-cell adhesion research using microscopic techniques.

Aldehyde Trapping by ADX-102 Is Protective against Cigarette Smoke and Alcohol Mediated Lung Cell Injury

Most individuals diagnosed with alcohol use disorders smoke cigarettes. Large concentrations of malondialdehyde and acetaldehyde are found in lungs co-exposed to cigarette smoke and alcohol. Aldehydes directly injure lungs and form aldehyde protein adducts, impacting epithelial functions. Recently, 2-(3-Amino-6-chloroquinolin-2-yl)propan-2-ol (ADX-102) was developed as an aldehyde-trapping drug. We hypothesized that aldehyde-trapping compounds are protective against lung injury derived from cigarette smoke and alcohol co-exposure. To test this hypothesis, we pretreated mouse ciliated tracheal epithelial cells with 0-100 µM of ADX-102 followed by co-exposure to 5% cigarette smoke extract and 50 mM of ethanol. Pretreatment with ADX-102 dose-dependently protected against smoke and alcohol induced cilia-slowing, decreases in bronchial epithelial cell wound repair, decreases in epithelial monolayer resistance, and the formation of MAA adducts. ADX-102 concentrations up to 100 µM showed no cellular toxicity. As protein kinase C (PKC) activation is a known mechanism for slowing cilia and wound repair, we examined the effects of ADX-102 on smoke and alcohol induced PKC epsilon activity. ADX-102 prevented early (3 h) activation and late (24 h) autodownregulation of PKC epsilon in response to smoke and alcohol. These data suggest that reactive aldehydes generated from cigarette smoke and alcohol metabolism may be potential targets for therapeutic intervention to reduce lung injury.

Nano-scale architecture of blood-brain barrier tight-junctions

Tight junctions (TJs) between blood-brain barrier (BBB) endothelial cells construct a robust physical barrier, whose damage underlies BBB dysfunctions related to several neurodegenerative diseases. What makes these highly specialized BBB-TJs extremely restrictive remains unknown. Here, we use super-resolution microscopy (dSTORM) to uncover new structural and functional properties of BBB TJs. Focusing on three major components, Nano-scale resolution revealed sparse (occludin) vs. clustered (ZO1/claudin-5) molecular architecture. In mouse development, permeable TJs become first restrictive to large molecules, and only later to small molecules, with claudin-5 proteins arrangement compacting during this maturation process. Mechanistically, we reveal that ZO1 clustering is independent of claudin-5 in vivo. In contrast to accepted knowledge, we found that in the developmental context, total levels of claudin-5 inversely correlate with TJ functionality. Our super-resolution studies provide a unique perspective of BBB TJs and open new directions for understanding TJ functionality in biological barriers, ultimately enabling restoration in disease or modulation for drug delivery.

Xuebijing Injection Ameliorates H2S-Induced Acute Respiratory Distress Syndrome by Promoting Claudin-5 Expression

OBJECTIVE

To investigate the protective effects and underlying mechanisms of Xuebijing Injection (XBJ) on the lung endothelial barrier in hydrogen sulfide (H₂S)-induced acute respiratory distress syndrome (ARDS).

METHODS

Sprague-Dawley rats were exposed to H₂S (300 ppm) to establish ARDS model, while human pulmonary microvascular endothelial cells (HPMECs) were incubated with NaHS (a H₂S donor, 500 µmol/L) to establish cell model. H₂S and XBJ were concurrently administered to the rat and cell models. Lung hematoxylin and eosin staining, immunohistochemistry, transmission electron microscopy and wet/dry ratio measurement were used to confirm ARDS induced by H₂S in vivo. The expression levels of claudin-5, phosphorylated protein kinase B (p-AKT)/t-AKT and p-forkhead box transcription factor O1 (FoxO1)/t-FoxO1 in vivo and in vitro were also assessed. Paracellular permeability and transepithelial electrical resistance (TEER) were measured to evaluate endothelial barrier function in the cell model.

RESULTS

The morphological investigation showed that XBJ attenuated H₂S-induced ARDS in rats. XBJ significantly ameliorated both the reduction in TEER and the increased paracellular permeability observed in NaHS-treated HPMECs (P<0.05). The protective effects of XBJ were blocked by LY294002, a phosphatidylinositol 3-kinase (PI3K)/AKT/FoxO1 pathway antagonist (P<0.05). Furthermore, XBJ promoted the expression of claudin-5 and increased the levels of p-AKT and p-FoxO1 in vivo and in vitro (P<0.05).

CONCLUSIONS

XBJ ameliorated H₂S-induced ARDS by promoting claudin-5 expression via the PI3K/AKT/FoxO1 signaling pathway.

Claudin-5: A Pharmacological Target to Modify the Permeability of the Blood-Brain Barrier

Claudin-5 is the dominant tight junction protein in brain endothelial cells and exclusively limits the paracellular permeability of molecules larger than 400 Da across the blood-brain barrier (BBB). Its pathological impairment or sustained down-regulation has been shown to lead to the progression of psychiatric and neurological disorders, whereas its expression under physiological conditions prevents the passage of drugs across the BBB. While claudin-5 enhancers could potentially act as vascular stabilizers to treat neurological diseases, claudin-5 inhibitors could function as delivery systems to enhance the brain uptake of hydrophilic small-molecular-weight drugs. Therefore, the effects of claudin-5 manipulation on modulating the BBB in different neurological diseases requires further examination. To manipulate claudin-5 expression levels and function, several claudin-5 modulating molecules have been developed. In this review, we first describe the molecular, cellular and pathological aspects of claudin-5 to highlight the mechanisms of claudin-5 enhancers/inhibitors. We then discuss recently developed claudin-5 enhancers/inhibitors and new methods to discover these molecules.

Sphingomyelinase decreases transepithelial anion secretion in airway epithelial cells in part by inhibiting CFTR-mediated apical conductance

The cystic fibrosis transmembrane conductance regulator (CFTR) is an anion channel whose dysfunction causes cystic fibrosis (CF). The loss of CFTR function in pulmonary epithelial cells causes surface dehydration, mucus build-up, inflammation, and bacterial infections that lead to lung failure. Little has been done to evaluate the effects of lipid perturbation on CFTR activity, despite CFTR residing in the plasma membrane. This work focuses on the acute effects of sphingomyelinase (SMase), a bacterial virulence factor secreted by CF relevant airway bacteria which degrades sphingomyelin into ceramide and phosphocholine, on the electrical circuitry of pulmonary epithelial monolayers. We report that basolateral SMase decreases CFTR-mediated transepithelial anion secretion in both primary bronchial and tracheal epithelial cells from explant tissue, with current CFTR modulators unable to rescue this effect. Focusing on primary cells, we took a holistic ion homeostasis approach to determine a cause for reduced anion secretion following SMase treatment. Using impedance analysis, we determined that basolateral SMase inhibits apical and basolateral conductance in non-CF primary cells without affecting paracellular permeability. In CF primary airway cells, correction with clinically relevant CFTR modulators did not prevent SMase-mediated inhibition of CFTR currents. Furthermore, SMase was found to inhibit only apical conductance in these cells. Future work should determine the mechanism for SMase-mediated inhibition of CFTR currents, and further explore the clinical relevance of SMase and sphingolipid imbalances.

Exosomal delivery of therapeutic modulators through the blood-brain barrier; promise and pitfalls

Nowadays, a large population around the world, especially the elderly, suffers from neurological inflammatory and degenerative disorders/diseases. Current drug delivery strategies are facing different challenges because of the presence of the BBB, which limits the transport of various substances and cells to brain parenchyma. Additionally, the low rate of successful cell transplantation to the brain injury sites leads to efforts to find alternative therapies. Stem cell byproducts such as exosomes are touted as natural nano-drug carriers with 50-100 nm in diameter. These nano-sized particles could harbor and transfer a plethora of therapeutic agents and biological cargos to the brain. These nanoparticles would offer a solution to maintain paracrine cell-to-cell communications under healthy and inflammatory conditions. The main question is that the existence of the intact BBB could limit exosomal trafficking. Does BBB possess some molecular mechanisms that facilitate the exosomal delivery compared to the circulating cell? Although preliminary studies have shown that exosomes could cross the BBB, the exact molecular mechanism(s) beyond this phenomenon remains unclear. In this review, we tried to compile some facts about exosome delivery through the BBB and propose some mechanisms that regulate exosomal cross in pathological and physiological conditions.

Context-Dependent Roles of Claudins in Tumorigenesis

The barrier and fence functions of the claudin protein family are fundamental to tissue integrity and human health. Increasing evidence has linked claudins to signal transduction and tumorigenesis. The expression of claudins is frequently dysregulated in the context of neoplastic transformation. Studies have uncovered that claudins engage in nearly all aspects of tumor biology and steps of tumor development, suggesting their promise as targets for treatment or biomarkers for diagnosis and prognosis. However, claudins can be either tumor promoters or tumor suppressors depending on the context, which emphasizes the importance of taking various factors, including organ type, environmental context and genetic confounders, into account when studying the biological functions and targeting of claudins in cancer. This review discusses the complicated roles and intrinsic and extrinsic determinants of the context-specific effects of claudins in cancer.

Pioglitazone Reverses Alcohol-Induced Alveolar Macrophage Phagocytic Dysfunction

Alcohol use disorders (AUD) increase susceptibility to respiratory infections by 2- to 4-fold in part because of impaired alveolar macrophage (AM) immune function. Alcohol causes AM oxidative stress, diminishing AM phagocytic capacity and clearance of microbes from the alveolar space. Alcohol increases AM NADPH oxidases (Noxes), primary sources of AM oxidative stress, and reduces peroxisome proliferator-activated receptor γ (PPARγ) expression, a critical regulator of AM immune function. To investigate the underlying mechanisms of these alcohol-induced AM derangements, we hypothesized that alcohol stimulates CCAAT/enhancer-binding protein β (C/EBPβ) to suppress Nox-related microRNAs (miRs), thereby enhancing AM Nox expression, oxidative stress, and phagocytic dysfunction. Furthermore, we postulated that pharmacologic PPARγ activation with pioglitazone would inhibit C/EBPβ and attenuate alcohol-induced AM dysfunction. AM isolated from human AUD subjects or otherwise healthy control subjects were examined. Compared with control AM, alcohol activated AM C/EBPβ, decreased Nox1-related miR-1264 and Nox2-related miR-107, and increased Nox1, Nox2, and Nox4 expression and activity. These alcohol-induced AM derangements were abrogated by inhibition of C/EBPβ, overexpression of miR-1264 or miR-107, or pioglitazone treatment. These findings define novel molecular mechanisms of alcohol-induced AM dysfunction mediated by C/EBPβ and Nox-related miRs that are amenable to therapeutic targeting with PPARγ ligands. These results demonstrate that PPARγ ligands provide a novel and rapidly translatable strategy to mitigate susceptibility to respiratory infections and related morbidity in individuals with AUD.

Asymmetric distribution of dynamin-2 and β-catenin relative to tight junction spikes in alveolar epithelial cells

Tight junctions between lung alveolar epithelial cells maintain an air-liquid barrier necessary for healthy lung function. Previously, we found that rearrangement of tight junctions from a linear, cortical orientation into perpendicular protrusions (tight junction spikes) is associated with a decrease in alveolar barrier function, especially in alcoholic lung syndrome. Using quantitative super-resolution microscopy, we found that spikes in control cells were enriched for claudin-18 as compared with alcohol-exposed cells. Moreover, using an in situ method to measure barrier function, tight junction spikes were not associated with localized increases in permeability. This suggests that tight junction spikes have a regulatory role as opposed to causing a physical weakening of the epithelial barrier. We found that tight junction spikes form at cell-cell junctions oriented away from pools of β-catenin associated with actin filaments, suggesting that adherens junctions determine the directionality of tight junction spikes. Dynamin-2 was associated with junctional claudin-18 and ZO-1, but showed little localization with β-catenin and tight junction spikes. Treatment with Dynasore decreased the number of tight junction spikes/cell, increased tight junction spike length, and stimulated actin to redistribute to cortical tight junctions. By contrast, Dynole 34-2 and MiTMAB altered β-catenin localization, and reduced tight junction spike length. These data suggest a novel role for dynamin-2 in tight junction spike formation by reorienting junction-associated actin. Moreover, the greater spatial separation of adherens and tight junctions in squamous alveolar epithelial cells as compared with columnar epithelial cells facilitates analysis of molecular regulation of the apical junctional complex.

[A review on the effect of Claudin-18 on bronchopulmonary dysplasia in preterm infants]

Bronchopulmonary dysplasia (BPD) has the main manifestations of pulmonary edema in the early stage and characteristic alveolar obstruction and microvascular dysplasia in the late stage, which may be caused by structural and functional destruction of the lung epithelial barrier. The Claudin family is the main component of tight junction and plays an important role in regulating the permeability of paracellular ions and solutes. Claudin-18 is the only known tight junction protein solely expressed in the lung. The lack of Claudin-18 can lead to barrier dysfunction and impaired alveolar development, and the knockout of Claudin-18 can cause characteristic histopathological changes of BPD. This article elaborates on the important role of Claudin-18 in the development and progression of BPD from the aspects of lung epithelial permeability, alveolar development, and progenitor cell homeostasis, so as to provide new ideas for the pathogenesis and clinical treatment of BPD.

Target specific tight junction modulators

Intercellular tight junctions represent a formidable barrier against paracellular drug absorption at epithelia (e.g., nasal, intestinal) and the endothelium (e.g., blood-brain barrier). In order to enhance paracellular transport of drugs and increase their bioavailability and organ deposition, active excipients modulating tight junctions have been applied. First-generation of permeation enhancers (PEs) acted by unspecific interactions, while recently developed PEs address specific physiological mechanisms. Such target specific tight junction modulators (TJMs) have the advantage of a defined specific mechanism of action. To date, merely a few of these novel active excipients has entered into clinical trials, as their lack in safety and efficiency in vivo often impedes their commercialisation. A stronger focus on the development of such active excipients would result in an economic and therapeutic improvement of current and future drugs.

Plant Biology: New Insight into How Roots 'Mask Up'

Extra- and trans-cellular barriers are essential for root function under even mild stress. New research shows that establishing both the lignin and suberin barriers in the Arabidopsis endodermis requires phenylpropanoid biosynthesis by endodermal cells themselves.

Alveolar epithelial glycocalyx shedding aggravates the epithelial barrier and disrupts epithelial tight junctions in acute respiratory distress syndrome

The main pathophysiological mechanism of acute respiratory distress syndrome (ARDS) invovles the increase in alveolar barrier permeability that is primarily caused by epithelial glycocalyx and tight junction (TJ) protein destruction. This study was performed to explore the effects of the alveolar epithelial glycocalyx on the epithelial barrier, specifically on TJ proteins, in ARDS. We used C57BL/6 mice and human lung epithelial cell models of lipopolysaccharide (LPS)-induced ARDS. Changes in alveolar permeability were evaluated via pulmonary histopathology analysis and by measuring the wet/dry weight ratio of the lungs. Degradation of heparan sulfate (HS), an important component of the epithelial glycocalyx, and alterations in levels of the epithelial TJ proteins (occludin, zonula occludens 1, and claudin 4) were assessed via ELISA, immunofluorescence analysis, and western blotting analysis. Real-time quantitative polymerase chain reaction was used to detect the mRNA of the TJ protein. Changes in glycocalyx and TJ ultrastructures in alveolar epithelial cells were evaluated through electron microscopy. In vivo and in vitro, LPS increased the alveolar permeability and led to HS degradation and TJ damage. After LPS stimulation, the expression of the HS-degrading enzyme heparanase (HPA) in the alveolar epithelial cells was increased. The HPA inhibitor N-desulfated/re-N-acetylated heparin alleviated LPS-induced HS degradation and reduced TJ damage. In vitro, recombinant HPA reduced the expression of the TJ protein zonula occludens-1 (ZO-1) and inhibited its mRNA expression in the alveolar epithelial cells. Taken together, our results demonstrate that shedding of the alveolar epithelial glycocalyx aggravates the epithelial barrier and damages epithelial TJ proteins in ARDS, with the underlying mechanism involving the effect of HPA on ZO-1.

UPR modulation of host immunity by Pseudomonas aeruginosa in cystic fibrosis

Cystic fibrosis (CF) is a progressive multiorgan autosomal recessive disease with devastating impact on the lungs caused by derangements of the CF transmembrane conductance regulator (CFTR) gene. Morbidity and mortality are caused by the triad of impaired mucociliary clearance, microbial infections and chronic inflammation. Pseudomonas aeruginosa is the main respiratory pathogen in individuals with CF infecting most patients in later stages. Despite its recognized clinical impact, molecular mechanisms that underlie P. aeruginosa pathogenesis and the host response to P. aeruginosa infection remain incompletely understood. The nuclear hormone receptor peroxisome proliferator-activated receptor (PPAR) γ (PPARγ), has shown to be reduced in CF airways. In the present study, we sought to investigate the upstream mechanisms repressing PPARγ expression and its impact on airway epithelial host defense. Endoplasmic reticulum-stress (ER-stress) triggered unfolded protein response (UPR) activated by misfolded CFTR and P. aeruginosa infection contributed to attenuated expression of PPARγ. Specifically, the protein kinase RNA (PKR)-like ER kinase (PERK) signaling pathway led to the enhanced expression of the CCAAT-enhancer-binding-protein homologous protein (CHOP). CHOP induction led to the repression of PPARγ expression. Mechanistically, we showed that CHOP induction mediated PPARγ attenuation, impacted the innate immune function of normal and ∆F508 primary airway epithelial cells by reducing expression of antimicrobial peptide (AMP) and paraoxanse-2 (PON-2), as well as enhancing IL-8 expression. Furthermore, mitochondrial reactive oxygen species production (mt-ROS) and ER-stress positive feedforward loop also dysregulated mitochondrial bioenergetics. Additionally, our findings implicate that PPARγ agonist pioglitazone (PIO) has beneficial effect on the host at the multicellular level ranging from host defense to mitochondrial re-energization.

Structure, Function, and Regulation of the Blood-Brain Barrier Tight Junction in Central Nervous System Disorders

The blood-brain barrier (BBB) allows the brain to selectively import nutrients and energy critical to neuronal function while simultaneously excluding neurotoxic substances from the peripheral circulation. In contrast to the highly permeable vasculature present in most organs that reside outside of the central nervous system (CNS), the BBB exhibits a high transendothelial electrical resistance (TEER) along with a low rate of transcytosis and greatly restricted paracellular permeability. The property of low paracellular permeability is controlled by tight junction (TJ) protein complexes that seal the paracellular route between apposing brain microvascular endothelial cells. Although tight junction protein complexes are principal contributors to physical barrier properties, they are not static in nature. Rather, tight junction protein complexes are highly dynamic structures, where expression and/or localization of individual constituent proteins can be modified in response to pathophysiological stressors. These stressors induce modifications to tight junction protein complexes that involve de novo synthesis of new protein or discrete trafficking mechanisms. Such responsiveness of BBB tight junctions to diseases indicates that these protein complexes are critical for maintenance of CNS homeostasis. In fulfillment of this vital role, BBB tight junctions are also a major obstacle to therapeutic drug delivery to the brain. There is an opportunity to overcome this substantial obstacle and optimize neuropharmacology via acquisition of a detailed understanding of BBB tight junction structure, function, and regulation. In this review, we discuss physiological characteristics of tight junction protein complexes and how these properties regulate delivery of therapeutics to the CNS for treatment of neurological diseases. Specifically, we will discuss modulation of tight junction structure, function, and regulation both in the context of disease states and in the setting of pharmacotherapy. In particular, we will highlight how these properties can be potentially manipulated at the molecular level to increase CNS drug levels via paracellular transport to the brain.

Ruffles and spikes: Control of tight junction morphology and permeability by claudins

Epithelial barrier function is regulated by a family of transmembrane proteins known as claudins. Functional tight junctions are formed when claudins interact with other transmembrane proteins, cytosolic scaffold proteins and the actin cytoskeleton. The predominant scaffold protein, zonula occludens-1 (ZO-1), directly binds to most claudin C-terminal domains, crosslinking them to the actin cytoskeleton. When imaged by immunofluorescence microscopy, tight junctions most frequently are linear structures that form between tricellular junctions. However, tight junctions also adapt non-linear architectures exhibiting either a ruffled or spiked morphology, which both are responses to changes in claudin engagement of actin filaments. Other terms for ruffled tight junctions include wavy, tortuous, undulating, serpentine or zig-zag junctions. Ruffling is under the control of hypoxia induced factor (HIF) and integrin-mediated signaling, as well as direct mechanical stimulation. Tight junction ruffling is specifically enhanced by claudin-2, antagonized by claudin-1 and requires claudin binding to ZO-1. Tight junction spikes are sites of active vesicle budding and fusion that appear as perpendicular projections oriented towards the nucleus. Spikes share molecular features with focal adherens junctions and tubulobulbar complexes found in Sertoli cells. Lung epithelial cells under stress form spikes due to an increase in claudin-5 expression that directly disrupts claudin-18/ZO-1 interactions. Together this suggests that claudins are not simply passive cargoes controlled by scaffold proteins. We propose a model where claudins specifically influence tight junction scaffold proteins to control interactions with the cytoskeleton as a mechanism that regulates tight junction assembly and function.

Tight junction modulation at the blood-brain barrier: Current and future perspectives

The blood-brain barrier (BBB) is the one of the most robust physical barriers in the body, comprised of tight junction (TJ) proteins in brain microvascular endothelial cells. The need for drugs to treat central nervous systems diseases is ever increasing, however the presence of the BBB significantly hampers the uptake of drugs into the brain. To overcome or circumvent the barrier, many kinds of techniques are being developed. Modulating the paracellular route by disruption of the TJ complex has been proposed as a potential drug delivery system to treat brain diseases, however, it has several limitations and is still in a developmental stage. However, recent significant advance in medical equipment /tools such as targeted ultra-sound technologies may resolve these limitations. In this review, we introduce recent advances in site- or molecular size-selective BBB disruption/modulation technologies and we include details on pharmacological inhibitory molecules against intercellular TJ proteins to modulate the BBB.

Molecular architecture and assembly of the tight junction backbone

The functional and structural concept of tight junctions has developed after discovery of claudin and TAMP proteins. Many of these proteins contribute to epi- and endothelial barrier but some, in contrast, form paracellular channels. Claudins form the backbone of tight junction (TJ) strands whereas other proteins regulate TJ dynamics. The current joined double-row model of TJ strands and channels is crucially based on the linear alignment of claudin-15 in the crystal. Molecular dynamics simulations, protein docking, mutagenesis, cellular TJ reconstitution, and electron microscopy studies largely support stability and functionality of the model. Here, we summarize in silico and in vitro data about TJ strand assembly including comparison of claudin crystal structures and alternative models. Sequence comparisons, experimental and structural data substantiate differentiation of classic and non-classic claudins differing in motifs related to strand assembly. Classic claudins seem to share a similar mechanism of strand formation. Interface variations likely contribute to TJ strand flexibility. Combined in vitro/in silico studies are expected to elucidate mechanistic keys determining TJ regulation.

Super-Resolution Imaging of Tight and Adherens Junctions: Challenges and Open Questions

The tight junction (TJ) and the adherens junction (AJ) bridge the paracellular cleft of epithelial and endothelial cells. In addition to their role as protective barriers against bacteria and their toxins they maintain ion homeostasis, cell polarity, and mechano-sensing. Their functional loss leads to pathological changes such as tissue inflammation, ion imbalance, and cancer. To better understand the consequences of such malfunctions, the junctional nanoarchitecture is of great importance since it remains so far largely unresolved, mainly because of major difficulties in dynamically imaging these structures at sufficient resolution and with molecular precision. The rapid development of super-resolution imaging techniques ranging from structured illumination microscopy (SIM), stimulated emission depletion (STED) microscopy, and single molecule localization microscopy (SMLM) has now enabled molecular imaging of biological specimens from cells to tissues with nanometer resolution. Here we summarize these techniques and their application to the dissection of the nanoscale molecular architecture of TJs and AJs. We propose that super-resolution imaging together with advances in genome engineering and functional analyses approaches will create a leap in our understanding of the composition, assembly, and function of TJs and AJs at the nanoscale and, thereby, enable a mechanistic understanding of their dysfunction in disease.

Laminin-driven Epac/Rap1 regulation of epithelial barriers on decellularized matrix

Decellularized tissues offer a unique tool for developing regenerative biomaterials or in vitro platforms for the study of cell-extracellular matrix (ECM) interactions. One main challenge associated with decellularized lung tissue is that ECM components can be stripped away or altered by the detergents used to remove cellular debris. Without characterizing the composition of lung decellularized ECM (dECM) and the cellular response caused by the altered composition, it is difficult to utilize dECM for regeneration and specifically, engineering the complexities of the alveolar-capillary barrier. This study takes steps towards uncovering if dECM must be enhanced with lost ECM proteins to achieve proper epithelial barrier formation. To achieve this, the epithelial barrier function was assessed on dECM coatings with and without the systematic addition of several key basement membrane proteins. After comparing barrier function on collagen I, fibronectin, laminin, and dECM in varying combinations as an in vitro coating, the alveolar epithelium exhibited superior barrier function when dECM was supplemented with laminin as evidenced by trans-epithelial electrical resistance (TEER) and permeability assays. Increased barrier resistance with laminin addition was associated with upregulation of Claudin-18, E-cadherin, and junction adhesion molecule (JAM)-A, and stabilization of zonula occludens (ZO)-1 at junction complexes. The Epac/Rap1 pathway was observed to play a role in the ECM-mediated barrier function determined by protein expression and Epac inhibition. These findings revealed potential ECM coatings and molecular therapeutic targets for improved regeneration with decellularized scaffolds. STATEMENT OF SIGNIFICANCE: Efforts to produce a transplantable organ-scale biomaterial for lung regeneration has not been entirely successful to date, due to incomplete cell-cell junction formation, ultimately leading to severe edema in vivo. To fully understand the process of alveolar junction formation on ECM-derived biomaterials, this research has characterized and tailored decellularized ECM (dECM) to mitigate reductions in barrier strength or cell attachment caused by abnormal ECM compositions or detergent damage to dECM. These results indicate that laminin-driven Epac signaling plays a vital role in the stabilization of the alveolar barrier. Addition of laminin or Epac agonists during alveolar regeneration can reduce epithelial permeability within bioengineered lungs.

Lipopolysaccharide disrupts the cochlear blood-labyrinth barrier by activating perivascular resident macrophages and up-regulating MMP-9

OBJECTIVE

To determine the distribution of perivascularresident macrophages (PVMs) in BLB and their relationship with capillaries, and to explore the possible mechanisms responsible for lipopolysaccharide (LPS)-induced activation of PVMs and the breakdown of BLB.

METHODS

Adult Balb/c mice were either trans-tympanically injected with LPS, or mock-treated. Auditory brainstem response was tested before and 48 h after treatments. Distribution of pericytes, PVMs and capillaries was analyzed by immunohistochemical staining, and BLB permeability was estimated by FITC-dextran leakage assay. Ultrastructure of stria vascularis was examined by transmission electron microscope. Protein and mRNA level of matrix metallopeptidase 9 (MMP-9), zona occludens-1 (ZO-1), interleukin-33 (IL-33) and its receptor suppression of tumorigenicity 2 (ST2) was measured by IHC and qRT-PCR.

RESULTS

Unlike pericytes that surround one capillary, PVMs branched to connect with more than one capillary. LPS caused hearing loss in mice. Following LPS challenge, cochleae showed vascular leakage in stria vascularis, and PVMs presented morphological changes including reduced contact with capillaries. TEM revealed a reduced number of tight junction contact points between endothelial cells and a wider space between PVMs, pericytes and endothelial cells. The mRNA and protein levels of MMP-9 and ST2 in stria vascularis were up-regulated, while ZO-1 were down-regulated after exposure to LPS.

CONCLUSIONS

Our results suggest that PVMs may play a more significant role than pericytes in maintaining the integrity of BLB. Our findings also reveal a possible mechanism contributing to LPS-induced activation of PVMs, breakdown of BLB and hearing loss.

The Blood-Brain Barrier and Its Intercellular Junctions in Age-Related Brain Disorders

With age, our cognitive skills and abilities decline. Maybe starting as an annoyance, this decline can become a major impediment to normal daily life. Recent research shows that the neurodegenerative disorders responsible for age associated cognitive dysfunction are mechanistically linked to the state of the microvasculature in the brain. When the microvasculature does not function properly, ischemia, hypoxia, oxidative stress and related pathologic processes ensue, further damaging vascular and neural function. One of the most important and specialized functions of the brain microvasculature is the blood-brain barrier (BBB), which controls the movement of molecules between blood circulation and the brain parenchyma. In this review, we are focusing on tight junctions (TJs), the multiprotein complexes that play an important role in establishing and maintaining barrier function. After a short introduction of the cell types that modulate barrier function via intercellular communication, we examine how age, age related pathologies and the aging of the immune system affects TJs. Then, we review how the TJs are affected in age associated neurodegenerative disorders: Alzheimer's disease and Parkinson's disease. Lastly, we summarize the TJ aspects of Huntington's disease and schizophrenia. Barrier dysfunction appears to be a common denominator in neurological disorders, warranting detailed research into the molecular mechanisms behind it. Learning the commonalities and differences in the pathomechanism of the BBB injury in different neurological disorders will predictably lead to development of new therapeutics that improve our life as we age.

Alcohol-induced mitochondrial DNA damage promotes injurious crosstalk between alveolar epithelial cells and alveolar macrophages

Excessive alcohol users have a higher risk for developing respiratory infections compared to individuals who do not chronically misuse alcohol, due to impaired host immune defense. In the lung, alveolar epithelial cells play a critical role in host immune defense against invading pathogens in the lower respiratory tract due to their capacity to maintain barrier integrity, and alveolar macrophages play a key role in pulmonary innate immunity by phagocytizing and clearing infiltrating microbes. Chronic alcohol misuse induces mitochondrial damage that results in release of mitochondrial DNA (mtDNA) in exosomes. We hypothesized that alcohol-induced cellular damage leads to release of exosomes containing damaged mtDNA, which can mediate injurious crosstalk between lung epithelial cells and macrophages. The mouse alveolar epithelial cell line, MLE-12, and the mouse alveolar macrophage cell line, MH-S, were transfected with a damaged mtDNA overexpression plasmid or exposed to ethanol in vitro. Overexpression of damaged mtDNA impaired MLE-12 barrier function and MH-S phagocytic capacity. Ethanol induced damage of mtDNA in MLE-12 and MH-S cells, and promoted release of exosomes enriched with damaged mtDNA from these cells. Exosomes from ethanol-exposed MH-S cells caused mtDNA damage and barrier dysfunction in MLE-12 cells, and exosomes from ethanol-exposed MLE-12 cells caused mtDNA damage and phagocytic dysfunction in MH-S cells. Collectively, these data show that ethanol-induced mtDNA damage in MLE-12 and MH-S cells stimulates release of damaged mtDNA-enriched exosomes and contributes to injurious crosstalk between the alveolar epithelium and macrophages, potentially leading to impaired host immune defense against respiratory infections.

Effects of different routes of endotoxin injury on barrier function in alcoholic lung syndrome

In the lung, chronic alcohol consumption is a risk factor for acute respiratory distress syndrome (ARDS), a disorder that can be fatal due to airspace flooding. The severity of pulmonary edema is controlled by multiple barriers, and in particular the alveolar epithelial barrier and pulmonary microvasculature. However, to date, the effects of chronic alcohol ingestion on both of these barriers in the lung has not been directly and simultaneously measured. In addition the effects of alcohol on systemic, indirect lung injury versus direct injury have not been compared. In this study, we used tissue morphometry and Evans Blue permeability assays to assess the effects of alcohol and endotoxemia injury on pulmonary barrier function comparing intraperitoneal (IP) administration of lipopolysaccharide (LPS) to intratracheal (IT) administration. Consistent with previous reports, we found that in alcohol-fed mice, the alveolar barrier was impaired, allowing Evans Blue to permeate into the airspaces. Moreover, IT administered LPS caused a significant breach of both the alveolar epithelial and vascular barriers in alcohol-fed mice, whereas the endothelial barrier was less affected in response to IP administered LPS. The alveolar barrier of control mice remained intact for both IP and IT administered LPS. However, both injuries caused significant interstitial edema, independently of whether the mice were fed alcohol or not. These data suggest that in order to properly target pulmonary edema due to alcoholic lung syndrome, both the alveolar and endothelial barriers need to be considered as well as the nature of the "second hit" that initiates ARDS.