Alveolar epithelial cells (AECs) maintain the pulmonary blood-gas barrier integrity with gasket like intercellular tight junctions (TJ) that are anchored internally to the actin cytoskeleton. We have previously shown that AEC monolayers stretched cyclically and equibiaxially undergo rapid magnitude- and frequency-dependent actin cytoskeletal remodeling to form perjunctional actin rings (PJARs). In this work, we show that even 10 min of stretch induced increases in the phosphorylation of Akt and LIMK, and decreases in cofilin phosphorylation, suggesting that the Rac1/Akt pathway is involved in these stretch-mediated changes. We confirmed that Rac1 inhibitors wortmannin or EHT-1864 decrease stretch-stimulated Akt and LIMK phosphorylation, and that Rac1 agonists PIP3 or PDGF increase phosphorylation of these proteins in unstretched cells. We also confirmed that Rac1 pathway inhibition during stretch modulated stretch-induced changes in occludin content and monolayer permeability, actin remodeling and PJAR formation, and cell death. As further validation, overexpression of Rac GTPase-activating protein β2-chimerin also preserved monolayer barrier properties in stretched monolayers. In summary, our data suggest that constitutive activity of Rac1, which is necessary for stretch-induced activation of the Rac1 downstream proteins, mediates stretch-induced increases in permeability and PJAR formation.

Claudins are a family of tight junction proteins regulating paracellular permeability and cell polarity with different patterns of expression in benign and malignant human tissues. There are approximately 27 members of the claudin family identified to date with varying cell and tissue-specific expression. Claudins-3, -4 and -7 represent the most highly differentially expressed claudins in ovarian cancer. While their exact role in ovarian tumors is still being elucidated, these proteins are thought to be critical for ovarian cancer cell invasion/dissemination and resistance to chemotherapy. Claudin-3 and claudin-4 are the natural receptors for the Clostridium perfringens enterotoxin (CPE), a potent cytolytic toxin. These surface proteins may therefore represent attractive targets for the detection and treatment of chemotherapy-resistant ovarian cancer and other aggressive solid tumors overexpressing claudin-3 and -4 using CPE-based theranostic agents.

Ischemic preconditioning has been reported to protect against spinal cord ischemia-reperfusion (I-R) injury, but the underlying mechanisms are not fully understood. To investigate this, Japanese white rabbits underwent I-R (30 min aortic occlusion followed by reperfusion), ischemic preconditioning (three cycles of 5 min aortic occlusion plus 5 min reperfusion) followed by I-R, or sham surgery. At 4 and 24 h following reperfusion, neurological function was assessed using Tarlov scores, blood spinal cord barrier permeability was measured by Evan's Blue extravasation, spinal cord edema was evaluated using the wet-dry method, and spinal cord expression of zonula occluden-1 (ZO-1), matrix metalloproteinase-9 (MMP-9), and tumor necrosis factor-α (TNF-α) were measured by Western blot and a real-time polymerase chain reaction. ZO-1 was also assessed using immunofluorescence. Spinal cord I-R injury reduced neurologic scores, and ischemic preconditioning treatment ameliorated this effect. Ischemic preconditioning inhibited I-R-induced increases in blood spinal cord barrier permeability and water content, increased ZO-1 mRNA and protein expression, and reduced MMP-9 and TNF-α mRNA and protein expression. These findings suggest that ischemic preconditioning attenuates the increase in blood spinal cord barrier permeability due to spinal cord I-R injury by preservation of tight junction protein ZO-1 and reducing MMP-9 and TNF-α expression.

Epidermal barrier acquisition during late murine gestation is accompanied by an increase in Akt kinase activity and cJun dephosphorlyation. The latter is directed by the Ppp2r2a regulatory subunit of the Pp2a phosphatase. This was accompanied by a change of Claudin-1 localisation to the cell surface and interaction between Occludin and Claudin-1 which are thought to be required for tight junction formation. The aim of this study was to determine the nature of the barrier defect caused by the loss of AKT/Ppp2r2a function. There was a paracellular barrier defect in rat epidermal keratinocytes expressing a Ppp2r2a siRNA. In Ppp2r2a knockdown cells, Claudin-1 was located to the cytoplasm and its expression was increased. Inhibiting cJun phosphorylation restored barrier function and plasma membrane localisation of Claudin-1. Expression of the Rab3 GTPase activating protein, Rab3Gap1, was restored in Ppp2r2a siRNA cells when cJun phosphorylation was inhibited. During normal mouse epidermal development, Claudin-1 plasma membrane localisation and Rab3Gap1 cell surface expression were co-incident with Akt activation in mouse epidermis, strongly suggesting a role of Rab3Gap1 in epidermal barrier acquisition. Supporting this hypothesis, siRNA knockdown of Rab3Gap1 prevented plasma membrane Claudin-1 expression and the formation of a barrier competent epithelium. Replacing Rab3Gap1 in Ppp2r2a knockdown cells was sufficient to rescue Claudin-1 transport to the cell surface. Therefore these data suggest Rab3Gap1 mediated exocytosis of Claudin-1 is an important component of epidermal barrier acquisition during epidermal development.

Biopolymers composed of a pH-responsive, hydrophilic poly(methacrylic acid-grafted-ethylene glycol) network polymerized in the presence of poly(methyl methacrylate) nanoparticles were designed for the oral delivery of chemotherapeutics for the treatment of colon cancer. An inulin-doxorubicin conjugate, designed to target the colon and improve doxorubicin efficacy, was loaded into these polymer carriers at an efficiency of 54%. Release studies indicated these polymer carriers minimized conjugate release in low pH conditions and released the conjugate at neutral pH conditions using a two-step pH experiment modeling the stomach and the small intestine. At lower concentration levels, the presence of the polymer carriers did not disrupt tight junctions as determined by transepithelial electrical resistance studies using Caco-2 and HT29-MTX cell lines which are an accurate model of the GI tract epithelia. Permeability values of unmodified doxorubicin and the inulin-doxorubicin conjugate in the presence of the polymer carriers were also determined using the same cell models and ranged from 1.87 to 3.80 × 10 (-6) cm/s.

We report the simultaneous measurement of conductance and thermopower of highly conducting single-molecule junctions using a scanning tunneling microscope-based break-junction setup. We start with molecular backbones (alkanes and oligophenyls) terminated with trimethyltin end groups that cleave off in situ, to create junctions where terminal carbons are covalently bonded to the Au electrodes. We apply a thermal gradient across these junctions and measure their conductance and thermopower. Due to the electronic properties of the highly-conducting Au-C links, the thermoelectric properties and power factor are very high. Our results show that the molecular thermopower increases non-linearly with the molecular length while conductance decreases exponentially with increasing molecular length. Density functional theory calculations show that a gateway state representing the Au-C covalent bond plays a key role in the conductance. With this as input, we analyze a series of simplified models and show that a tight-binding model that explicitly includes the gateway states and the molecular backbone states accurately captures the experimentally measured trends.

The aim of our study was to develop a model of high altitude cerebral edema (HACE) using an acute, hypobaric hypoxia environment combined with exhaustive exercise. Forty healthy male Sprague-Dawley rats were randomly divided into a plains control group (PC group) and a plateau altitude hypoxia group (AH group). After 2 days of treadmill adaptation under normoxic conditions, the AH group was housed in hypobaric conditions (simulating 4000m above sea level) for 2 days while performing exhaustive exercise. The simulated altitude was then increased to 8000m for 3 days of simple hypobaric hypoxia exposure. Compared with the PC group, the AH group showed significantly greater (P<0.01) water content and Evans blue staining in their brain tissue. Furthermore, the hippocampal formation was seriously damaged, and the number of pyramidal cells decreased. In addition, the brain structure was altered into a loose state with notable edema, which was demonstrated by the leakage of lanthanum nitrate particles from brain microvessels into the surrounding tissue through widened tight junctions. Some neurons and glial cell organelles were swollen and some nerve fibers were demyelinated as well. We have shown that acute hypobaric hypoxia exposure with exhaustive exercise increases the permeability of the blood-brain barrier and leads to cerebral edema, making this a valid animal model of HACE.

To investigate the role of claudin-11, a tight junction component of Sertoli cells, in spermatogenic dysfunction induced by oxidative stress in mice exposed to local radiation.We randomly allocated 48 male Kunming mice to a blank control group (A) and three radiation groups (B, C and D) of equal number, the latter three exposed to local radiation of the lower abdomen with 2 Gy, 6 Gy and 10 Gy of 60Co-gamma-ray, respectively, to induce oxidative stress. Four weeks later, we killed the animals, obtained their body and testis weights, observed the histological changes of the testis by HE staining, measured the levels of serum FSH, testosterone and LH by ELISA, and determined the mRNA levels of claudin-11 and inhibin beta B in Sertoli cells by real time quantitative PCR.After exposure to 60Co-gamma-ray radiation, the testis weights were (129.4 +/- 10.81), (87.5 +/- 16.83) and (56.1 +/- 12.36) mg in groups B, C and D, significantly decreased as compared with (182.9 +/- 8.43) mg in group A (P < 0.05); the testis indexes were (3.39 +/- 0.57), (2.46 +/- 0.46) and (1.63 +/- 0.44) mg/g in groups B, C and D, remarkably lower than (4.28 +/- 0.31) mg/g in group A (P < 0.01). Histological analysis revealed obviously decreased diameters of seminiferous tubules, reduced seminiferous epithelia and disarranged spermatogenic cells in the three radiation groups. The tubule differentiation indexes (TDI) were markedly lower in groups B, C and D than in A (P < 0.01). The levels of serum FSH were (6.74 +/- 1.95), (8.41 +/- 2.44) and (10.93 +/- 3.16) IU/L in groups B, C and D, 1.9 times higher in D than in A. With increased dose of radiation, the mRNA levels of inhibinbeta B in the testis tissue were descended, while the transcription levels of claudin-11 elevated, significantly higher in groups C and D than in A (P < 0.01).Local radiation-induced testicular oxidative stress can decrease the mRNA level of inhibinbeta B, increase serum FSH, damage Sertoli cells and elevate the expression of claudin-11 in the testis tissue. Increased claudin-11 and serum FSH may delay the cyclical restitution of hemotesticular barrier and reduce the number of meiotic spermatocytes in the seminiferous epithelium, which consequently leads to male infertility.

Claudin 3 is a protein component of the tight junction strands. Tight junctions between adjacent Claudin 3 is a protein component of the tight junction strands. Tight junctions between adjacent Sertoli cells form the blood-testis barrier (BTB). During spermatogenesis, seminiferous stage-specific expression of claudin 3 is believed to regulate the migration of preleptotene/leptotene spermatocytes across the BTB. Here, we determined the cell types expressing claudin 3 in adult mouse testis and investigated spermatogenesis after testis-specific in vivo knockdown of claudin 3. The results of in situ hybridization revealed that claudin 3 mRNA was predominantly expressed in germ cells near the basal lamina of seminiferous stage VI-IX tubules. Furthermore, claudin 3 protein was localized to not only the BTB but also the cell membrane of STRA8-expressing preleptotene/leptotene spermatocytes in the testis of adult ICR.Cg-Tg(Stra8-EGFP)1Ysa/YsaRbrc mice. Although claudin 3 knockdown did not affect BTB integrity, it caused a partial delay in spermatocyte migration across the BTB. Moreover, claudin 3 knockdown resulted in a prolonged period of the preleptotene phase during spermatogenesis. These data indicate that the seminiferous stage-specific expression and localization of claudin 3 during spermatogenesis regulate the progression of meiosis by promoting germ cell migration across the BTB.

Claudins constitute a family of tight junction transmembrane proteins whose first extracellular loop (ECL1) determines the paracellular permeability and ion selectivity in epithelia. There are two cysteines in the ECL1 that are conserved among all claudins. We hypothesized that these extracellular cysteines are linked by an intramolecular disulfide bond that is necessary for correct pore folding and function. To test this, we mutated C54 and C64 in claudin-2, either individually or together to alanine or serine, and generated stable MDCK I Tet-off cell lines. Immunoblotting showed a higher molecular weight band in the mutants with a single cysteine mutation, consistent with a claudin-2 dimer, suggesting that the two conserved cysteines normally form an intramolecular disulfide bond in wild-type claudin-2. By immunofluorescent staining, the alanine mutants were mislocalized intracellularly, while the serine mutants were expressed at the tight junction. Thus, dimerization of both C54A and C64A did not require tight junction expression, suggesting that C54 and C64 are located near an intermolecular interface involved in cis-interaction. The conductance and Na+ permeability of the serine mutants were markedly lower than the wild-type, but there was no difference between the single mutants and the double mutant. We conclude that the disulfide bond between the conserved extracellular cysteines in claudin-2 is necessary for pore formation, probably by stabilizing the ECL1 fold, but is not required for correct protein trafficking. We further speculate that this role is generalizable to other claudin family members.