Magnesium Reduces Blood-Brain Barrier Permeability and Regulates Amyloid-β Transcytosis

Poor Mg status is a risk factor for Alzheimer’s disease (AD), and the underlying mechanisms remain elusive. Here, we provided the first evidence that elevated Mg levels significantly reduced the blood-brain barrier (BBB) permeability and regulated its function in vitro. Transient receptor potential melastatin 7 (TRPM7) and magnesium transporter subtype 1 (MagT1) were two major cellular receptors mediating entry of extracellular Mg²⁺ into the cells. Elevated Mg levels also induced an accelerated clearance of amyloid-β peptide (Aβ) from the brain to the blood side via BBB transcytosis through low-density lipoprotein receptor-related protein (LRP) and phosphatidylinositol binding clathrin assembly protein (PICALM), while reduced the influx of Aβ from the blood to the brain side involving receptor for advanced glycation end products (RAGE) and caveolae. Mg enhanced BBB barrier properties and overall expression of LRP1 and PICALM whereas reduced that of RAGE and caveolin-1. Apical-to-basolateral and vice versa steady-state Aβ flux achieved an equilibrium of 18 and 0.27 fmol/min/cm², respectively, about 30 min after the initial addition of physiological levels of free Aβ. Knockdown of caveolin-1 or disruption of caveolae membrane microdomains reduced RAGE-mediated influx significantly, but not LRP1-mediated efflux of Aβ. Stimulating endothelial cells with vascular endothelial growth factor (VEGF) enhanced caveolin-1 phosphorylation and RAGE expression. Co-immunoprecipitation demonstrated that RAGE, but not LRP1, was physically associated with caveolin-1. Thus, Mg can reduce BBB permeability and promote BBB clearance of Aβ from the brain by increasing the expression of LRP1 and PICALM while reducing the level of RAGE and caveolin-1.     

Is Lamprey Metamorphosis Regulated by Thyroid Hormones?

Lampreys are one of just a few fishes which have a true (firstor first type) of metamorphosis in their life cycle. In thesea lamprey (Petromyzon marinus), spontaneous metamorphosisis initiated when the size (length and weight), condition factor,and lipid stores reach appropriate levels and coincide withthe postwinter rise in water temperature. The serum levels ofthe thyroid hormones, thyroxine (T₄) and triiodothyronine (T₃),drop dramatically at the onset of metamorphosis and metamorphosiscan be induced with treatment of animals with the goitrogen,KCIO₄, which also results in a decline in serum levels of thyroidhormones. The fact that thyroid hormone treatment can blockspontaneous and induced metamorphosis is support for the viewthat thyroid hormones, particularly T₃, operates like a juvenilehormone in lamprey metamorphosis; this view is counter to therole of thyroid hormones in metamorphosis of other vertebrates.The monodeiodinase pathways, whereby T₄ is converted to T₃ orto the biologically inactive reverse T₃, and even further degradationof T₃, may be a significant mechanism directing metamorphicchange. Lamprey metamorphosis is facultative in that it is initiatedor inhibited depending upon the coordination of a complex integrationof environmental, metabolic and hormonal cues. Thyroid hormonesdo not regulate lamprey metamorphosis in the sense observedin other vertebrate metamorphoses but they are important tothe developmental process. Some of the features of the involvementof thyroid hormones in lamprey metamorphosis may be relatedto the presence of the endostyle in larvae which in turn reflectsthe ancient origins of this vertebrate and perhaps the conservationof an ancient method of induction of metamorphosis. Some cluefor other factors which initiate lamprey metamorphosis may comethrough the examination of inducers of metamorphosis in lowerchordates     

Is Cell Elongation Regulated by Extracellular Auxin?

Experiments with isolated epidermal strips of maize coleoptiles, pretreated with auxin and further incubated on sucrose agar containing different concentrations of auxin (indole-3-acetic acid, IAA or naphthalene-1-acetic acid, NAA) and/or naphthylphthalamic acid (NPA), are described. Preincubation for 2h with 2 . 10^?4M IAA or 10^?5M NAA in buffer, followed by 30 min wash in buffer results in measurable cell elongation during a subsequent incubation for 6 h on sucrose agar. Addition of 10^?4M NPA inhibited the response to auxin and this inhibition could be reversed by providing IAA in addition to NPA. Inner tissue fragments (without outer epidermis) did not respond to external IAA. These results lead to the conclusion that auxin secretion at the outer epidermis may be an essential step in auxin-regulated coleoptile growth.     

The Brain Response to Peripheral Insulin Declines with Age: A Contribution of the Blood-Brain Barrier?

ObjectivesIt is a matter of debate whether impaired insulin action originates from a defect at the neural level or impaired transport of the hormone into the brain. In this study, we aimed to investigate the effect of aging on insulin concentrations in the periphery and the central nervous system as well as its impact on insulin-dependent brain activity.MethodsInsulin, glucose and albumin concentrations were determined in 160 paired human serum and cerebrospinal fluid (CSF) samples. Additionally, insulin was applied in young and aged mice by subcutaneous injection or intracerebroventricularly to circumvent the blood-brain barrier. Insulin action and cortical activity were assessed by Western blotting and electrocorticography radiotelemetric measurements.ResultsIn humans, CSF glucose and insulin concentrations were tightly correlated with the respective serum/plasma concentrations. The CSF/serum ratio for insulin was reduced in older subjects while the CSF/serum ratio for albumin increased with age like for most other proteins. Western blot analysis in murine whole brain lysates revealed impaired phosphorylation of AKT (P-AKT) in aged mice following peripheral insulin stimulation whereas P-AKT was comparable to levels in young mice after intracerebroventricular insulin application. As readout for insulin action in the brain, insulin-mediated cortical brain activity instantly increased in young mice subcutaneously injected with insulin but was significantly reduced and delayed in aged mice during the treatment period. When insulin was applied intracerebroventricularly into aged animals, brain activity was readily improved.ConclusionsThis study discloses age-dependent changes in insulin CSF/serum ratios in humans. In the elderly, cerebral insulin resistance might be partially attributed to an impaired transport of insulin into the central nervous system.     

Blood–Brain Barrier Permeability to Sodium. Modification by Glucose or Insulin?

In order to explore the pathogenetic mechanism underlying the changes in blood-brain barrier sodium transport in experimental diabetes, the effects of hyperglycemia and of hypoinsulinemia were studied in nondiabetic rats. In untreated diabetes, the neocortical blood-brain barrier permeability for sodium decreased by 20% (5.6 +/- 0.7 versus 7.0 +/- 0.8 X 10(5) ml/g/s) as compared to controls. Intravenous infusion of 50% glucose for 2 h was associated with a decrease in the blood-brain barrier permeability to sodium (5.4 +/- 1.2 X 10(5) ml/g/s), whereas rats treated with an inhibitor of insulin-secretion (SMS 201-995, a somatostatin-analogue) had normal sodium permeability (7.3 +/- 2.0 X 10(5) ml/g/s). Acute insulin treatment of diabetic rats normalized the sodium permeability within a few hours as compared to a separate control group (7.7 +/- 1.1 versus 6.9 +/- 1.4 X 10(5) ml/g/s). To elucidate whether the abnormal blood-brain barrier passage is caused by a metabolic effect of glucose or by the concomitant hyperosmolality, rats were made hyperosmolar by intravenous injection of 50% mannitol. Although not statistically significant, blood-brain barrier sodium permeability increased in hyperosmolar rats as compared to the control rats (8.3 +/- 1.0 and 7.0 +/- 1.9 X 10(5) ml/g/s, respectively). It is concluded that either hyperglycemia per se or a glucose metabolite is responsible for the blood-brain barrier abnormality which occurs in diabetes. Further, we suggest that the specific decrease of sodium permeability could be the result of glucose-mediated inhibition of the Na+K+-ATPase localized at the blood-brain barrier.     

A Claudin-9–Based Ion Permeability Barrier Is Essential for Hearing

Hereditary hearing loss is one of the most common birth defects, yet the majority of genes required for audition is thought to remain unidentified. Ethylnitrosourea (ENU)–mutagenesis has been a valuable approach for generating new animal models of deafness and discovering previously unrecognized gene functions. Here we report on the characterization of a new ENU–induced mouse mutant (nmf329) that exhibits recessively inherited deafness. We found a widespread loss of sensory hair cells in the hearing organs of nmf329 mice after the second week of life. Positional cloning revealed that the nmf329 strain carries a missense mutation in the claudin-9 gene, which encodes a tight junction protein with unknown biological function. In an epithelial cell line, heterologous expression of wild-type claudin-9 reduced the paracellular permeability to Na⁺ and K⁺, and the nmf329 mutation eliminated this ion barrier function without affecting the plasma membrane localization of claudin-9. In the nmf329 mouse line, the perilymphatic K⁺ concentration was found to be elevated, suggesting that the cochlear tight junctions were dysfunctional. Furthermore, the hair-cell loss in the claudin-9–defective cochlea was rescued in vitro when the explanted hearing organs were cultured in a low-K⁺ milieu and in vivo when the endocochlear K⁺-driving force was diminished by deletion of the pou3f4 gene. Overall, our data indicate that claudin-9 is required for the preservation of sensory cells in the hearing organ because claudin-9–defective tight junctions fail to shield the basolateral side of hair cells from the K⁺-rich endolymph. In the tight-junction complexes of hair cells, claudin-9 is localized specifically to a subdomain that is underneath more apical tight-junction strands formed by other claudins. Thus, the analysis of claudin-9 mutant mice suggests that even the deeper (subapical) tight-junction strands have biologically important ion barrier function.     

Interleukin-25 Expressed by Brain Capillary Endothelial Cells Maintains Blood-Brain Barrier Function in a Protein Kinase C?-dependent Manner

Interleukin (IL)-25, a member of the IL-17 family of cytokines, is expressed in the brains of normal mice. However, the cellular source of IL-25 and its function in the brain remain to be elucidated. Here, we show that IL-25 plays an important role in preventing infiltration of the inflammatory cells into the central nervous system. Brain capillary endothelial cells (BCECs) express IL-25. However, it is down-regulated by inflammatory cytokines, including tumor necrosis factor (TNF)-α, IL-17, interferon-γ, IL-1β, and IL-6 in vitro, and is also reduced in active multiple sclerosis (MS) lesions and in the inflamed spinal cord of experimental autoimmune encephalomyelitis, an animal model of MS. Furthermore, IL-25 restores the reduced expression of tight junction proteins, occludin, junction adhesion molecule, and claudin-5, induced by TNF-α in BCECs and consequently repairs TNF-α-induced blood-brain barrier (BBB) permeability. IL-25 induces protein kinase Cϵ (PKCϵ) phosphorylation, and up-regulation of claudin-5 is suppressed by PKCϵ inhibitor peptide in the IL-25-stimulated BCECs. These results suggest that IL-25 is produced by BCECs and protects against inflammatory cytokine-induced excessive BBB collapse through a PKCϵ-dependent pathway. These novel functions of IL-25 in maintaining BBB integrity may help us understand the pathophysiology of inflammatory brain diseases such as MS.     

Is the Testis a Chemo-Privileged Site? Is There a Blood-Testis Barrier?

The incidence of testicular cancer, primarily seminoma, has been increasing in many countries, including the United States. The testis is often the site of residual cancer after adequate treatment with systemic chemotherapy. The blood-testis barrier is commonly cited as the explanation for residual tumor within the gonad after chemotherapy and as the indication for delayed orchiectomy. Conversely, complete eradication of viable tumor from the primary site is common and argues against the testis as a "tumor sanctuary." Residual tumor is also demonstrated within metastatic foci, and the disparity between the histopathologic response of the primary tumor and metastatic sites may be best explained by tumor heterogeneity and multiple tumor clones. Regardless of the scientific and academic arguments, delayed radical orchiectomy remains an important part of treatment for patients undergoing primary chemotherapy.     

The Nuclear Localization of γ-Tubulin Is Regulated by SadB-mediated Phosphorylation

γ-Tubulin is an important cell division regulator that arranges microtubule assembly and mitotic spindle formation. Cytosolic γ-tubulin nucleates α- and β-tubulin in a growing microtubule by forming the ring-shaped protein complex γTuRC. Nuclear γ-tubulin also regulates S-phase progression by moderating the activities of E2 promoter-binding factors. The mechanism that regulates localization of γ-tubulin is currently unknown. Here, we demonstrate that the human Ser/Thr kinase SadB short localizes to chromatin and centrosomes. We found that SadB-mediated phosphorylation of γ-tubulin on Ser³⁸⁵ formed chromatin-associated γ-tubulin complexes that moderate gene expression. In this way, the C-terminal region of γ-tubulin regulates S-phase progression. In addition, chromatin levels of γ-tubulin were decreased by the reduction of SadB levels or expression of a non-phosphorylatable Ala³⁸⁵-γ-tubulin but were enhanced by expression of SadB, wild-type γ-tubulin, or a phosphomimetic Asp³⁸⁵-γ-tubulin mutant. Our results demonstrate that SadB kinases regulate the cellular localization of γ-tubulin and thereby control S-phase progression.     

Drosophila Immunity: Is Antigen Processing the First Step?

A new genetic study has shown that the phagocytic ability of Drosophila blood cells, the hemocytes, may be important for the further induction of an antibacterial response in other tissues.     

How Is Vaccine Effectiveness Scaled by the Transmission Dynamics of Interacting Pathogen Strains with Cross-Protective Immunity?

Background

Many novel vaccines can cover only a fraction of all antigenic types of a pathogen. Vaccine effectiveness (VE) in the presence of interactions between vaccine strains and others is complicated by the interacting transmission dynamics among all strains. The present study investigated how the VE estimates measured in the field, based on estimated odds ratio or relative risks, are scaled by vaccination coverage and the transmission dynamics in the presence of cross-protective immunity between two strains, i.e. vaccine and non-vaccine strains.

Methodology/Principal Findings

Two different types of epidemiological models, i.e. with and without re-infection by the same antigenic type, were investigated. We computed the relative risk of infection and the odds ratio of vaccination, the latter of which has been measured by indirect cohort method as applied to vaccine effectiveness study of Streptococcus pneumoniae. The VE based on the relative risk was less sensitive to epidemiological dynamics such as cross-protective immunity and vaccination coverage than the VE calculated from the odds ratio, and this was especially the case for the model without re-infection. Vaccine-induced (cross-protective) immunity against a non-vaccine strain appeared to yield the highest impact on the VE estimate calculated from the odds ratio of vaccination.

Conclusion

It is essential to understand the transmission dynamics of non-vaccine strains so that epidemiological methods can appropriately measure both the direct and indirect population impact of vaccination. For pathogens with interacting antigenic types, the most valid estimates of VE, that are unlikely to be biased by the transmission dynamics, may be obtained from longitudinal prospective studies that permit estimation of the VE based on the relative risk of infection among vaccinated compared to unvaccinated individuals.     

Endothelial Vesicles in the Blood–Brain Barrier: Are They Related to Permeability?

1. Macromolecules cross capillary walls via large vascular pores that are thought to be formed by plasmalemmal vesicles. Early hypotheses suggested that vesicles transferred plasma constituents across the endothelial wall either by a shuttle mechanism or by fusing to form transient patent channels for diffusion. Recent evidence shows that the transcytotic pathway involves both movement of vesicles within the cell and a series of fusions and fissions of the vesicular and cellular membranes.2. The transfer of macromolecules across the capillary wall is highly specific and is mediated by receptors incorporated into specific membrane domains. Therefore, despite their morphological similarity, endothelial vesicles form heterogeneous populations in which the predominant receptor proteins incorporated in their membranes define the functions of individual vesicles.3. Blood–brain barrier capillaries have very low permeabilities to most hydrophilic molecules. Their low permeability to macromolecules has been presumed to be due to an inhibition of the transcytotic mechanism, resulting in a low density of endothelial vesicles.4. A comparison of vesicular densities and protein permeabilities in a number of vascular beds shows only a very weak correlation, therefore vesicle numbers alone cannot be used to predict permeability to macromolecules.5. Blood–brain barrier capillaries are fully capable of transcytosing specific proteins, for example, insulin and transferrin, although the details are still somewhat controversial.6. It has recently been shown that the albumin binding protein gp60 (also known as albondin), which facilitates the transcytosis of native albumin in other vascular beds, is virtually absent in brain capillaries.7. It seems likely that the low blood–brain barrier permeability to macromolecules may be due to a low level of expression of specific receptors, rather than to an inhibition of the transcytosis mechanism.     

Are Structural Changes Induced by Lithium in the HIV Brain Accompanied by Changes in Functional Connectivity?

Lithium therapy has been shown to affect imaging measures of brain function and microstructure in human immunodeficiency virus (HIV)-infected subjects with cognitive impairment. The aim of this proof-of-concept study was to explore whether changes in brain microstructure also entail changes in functional connectivity. Functional MRI data of seven cognitively impaired HIV infected individuals enrolled in an open-label lithium study were included in the connectivity analysis. Seven regions of interest (ROI) were defined based on previously observed lithium induced microstructural changes measured by Diffusion Tensor Imaging. Generalized partial directed coherence (gPDC), based on time-variant multivariate autoregressive models, was used to quantify the degree of connectivity between the selected ROIs. Statistical analyses using a linear mixed model showed significant differences in the average node strength between pre and post lithium therapy conditions. Specifically, we found that lithium treatment in this population induced changes suggestive of increased strength in functional connectivity. Therefore, by exploiting the information about the strength of functional interactions provided by gPDC we can quantify the connectivity changes observed in relation to a given intervention. Furthermore, in conditions where the intervention is associated with clinical changes, we suggest that this methodology could enable an interpretation of such changes in the context of disease or treatment induced modulations in functional networks.     

Is The Special Callose Wall of Microsporocytes an Impermeable Barrier?

During the course of cytochemical studies in sugar beet anthers(Beta vulgaris L.) to test the applicability of cerium methodsfor the ultrastructural localization of enzymatic activity inplant tissues, new evidence was obtained that questions theimpermeability of the special callose wall surrounding the tetradof microspores. Cerous ions, added to cytochemical media asa potential capture agent for enzymatically-produced hydrogenperoxide, showed binding to cell walls and plasma membranesexclusively in the zone of mechanical injury to the tissues,which may correspond to sites of hydrogen peroxide formationas a consequence of wounding. The cerium perhydroxide precipitateformed as a result of this reaction was localized within thecell walls of anther tissues, inside the callose surroundingtetrads of microspore and in the primexine layer of the microsporewall. The results of this study provide evidence for callosepermeability in in vivo conditions, for at least some substancessuch as cerous ions or cerium perhydroxide. Key words: Callose, cerous ions/cerium perhydroxide, permeability     

Is stunning prevented by ischemic preconditioning?

In a model of global ischemia in the isolated perfused rat heart, a 20-min ischemic period followed by 30 min of reperfusion induces a decrease in isovolumic developed pressure (LVDP) and +dP/dt_max to 61 ± 6% and 61 ± 7% of baseline, respectively. Left ventricular end-diastolic pressure (LVEDP) increases to 36 ± 4 mmHg at the end of the reperfusion period. No significant necrotic area as assessed by triphenyltetrazolium chloride (TTC) was detected at the end of the reperfusion period. By an immunohistochemical method using antiactin monoclonal antibodies 10.8 ± 1.9% of unstained cells were detected in the stunned hearts and 10.3 ± 1.2% in control hearts. Preceding the ischemic episode with a cycle of 5 min of ischemia followed by 10 min of reperfusion (ischemic preconditioning) protected contractile function. LVDP and +dP/dt_max now stabilized at 89 ± 5% and 94 ± 5% of baseline respectively. LVEDP was 20 ± 2 mmHg at the end of the reperfusion period. The protection of contractile dysfunction after 20 min of ischemia was achieved also by early reperfusion of low Ca²⁺-low pH perfusate. With this intervention LVDP stabilized at 87 ± 5% of baseline. LVEDP was 12 ± 2 mmHg at the end of the reperfusion period. A positive inotropic intervention induced by a modified postextrasystolic potentiation protocol at the end of the reperfusion period increases LVDP to levels higher than baseline in the stunned hearts. However, these values were less than those obtained in control hearts. Ischemic preconditioning significantly increased the maximal inotropic response. Therefore, ischemic preconditioning diminishes the contractile dysfunction of early stunning.     

Is infant immunization by breastfeeding possible?

Breastfeeding is known as the most efficient way to prevent infectious disease in early life. Maternal anti-microbial immunoglobulins transfer through milk confers passive immunity to the breastfed child while his immune system is maturing. Maternal milk also contains bioactive factors that will stimulate this maturation. From the literature on breastfeeding prevention of immune-mediated disease and more specifically from our experiments conducted in the field of allergic disease prevention, we propose that breastfeeding may also induce antigen-specific immune responses in the breastfed child. We found that early oral antigen exposure through breast milk leads to tolerance or immune priming depending on the nature of the antigen transferred and accompanying maternal milk cofactors. Here, we will discuss our data in the light of prevention of infectious disease and will propose that possible milk transfer of microbial antigen could affect actively the immune response in breastfed children and thereby their long-term susceptibility to infectious disease. Further research in this direction may lead to novel strategies of early life vaccination, taking advantage of the possibility to stimulate antigen-specific immune responses through breast milk.