The blood brain barrier: Insights from development and ageing

Extracellular vesicles from mouse trophoblast cells: Effects on neural progenitor cells and potential participants in the placenta-brain axis†

The fetal brain of the mouse is thought to be dependent upon the placenta as a source of serotonin (5-hydroxytryptamine; 5-HT) and other factors. How factors reach the developing brain remains uncertain but are postulated here to be part of the cargo carried by placental extracellular vesicles (EV). We have analyzed the protein, catecholamine, and small RNA content of EV from mouse trophoblast stem cells (TSC) and TSC differentiated into parietal trophoblast giant cells (pTGC), potential primary purveyors of 5-HT. Current studies examined how exposure of mouse neural progenitor cells (NPC) to EV from either TSC or pTGC affect their transcriptome profiles. The EV from trophoblast cells contained relatively high amounts of 5-HT, as well as dopamine and norepinephrine, but there were no significant differences between EV derived from pTGC and from TSC. Content of miRNA and small nucleolar (sno)RNA, however, did differ according to EV source, and snoRNA were upregulated in EV from pTGC. The primary inferred targets of the microRNA (miRNA) from both pTGC and TSC were mRNA enriched in the fetal brain. NPC readily internalized EV, leading to changes in their transcriptome profiles. Transcripts regulated were mainly ones enriched in neural tissues. The transcripts in EV-treated NPC that demonstrated a likely complementarity with miRNA in EV were mainly up- rather than downregulated, with functions linked to neuronal processes. Our results are consistent with placenta-derived EV providing direct support for fetal brain development and being an integral part of the placenta-brain axis.

Blood-brain barrier dysfunction in multiple sclerosis: causes, consequences, and potential effects of therapies

Established by brain endothelial cells, the blood-brain barrier (BBB) regulates the trafficking of molecules, restricts immune cell entry into the CNS, and has an active role in neurovascular coupling (the regulation of cerebral blood flow to support neuronal activity). In the early stages of multiple sclerosis, around the time of symptom onset, inflammatory BBB damage is accompanied by pathogenic immune cell infiltration into the CNS. In the later stages of multiple sclerosis, dysregulation of neurovascular coupling is associated with grey matter atrophy. Genetic and environmental factors associated with multiple sclerosis, including dietary habits, the gut microbiome, and vitamin D concentrations, might contribute directly and indirectly to brain endothelial cell dysfunction. Damage to brain endothelial cells leads to an influx of deleterious molecules into the CNS, accelerating leakage across the BBB. Potential future therapeutic approaches might help to prevent BBB damage (eg, monoclonal antibodies targeting cell adhesion molecules and fibrinogen) and help to repair BBB dysfunction (eg, mesenchymal stromal cells) in people with multiple sclerosis.

Effect of thymosin β4 on lipopolysaccharide‑stimulated brain microvascular endothelial cell remodeling: A possible role in blood‑brain barrier injury

War veterans, in particular, are more prone to mental illness as they are more likely to have encountered multiple traumatic brain injuries (TBIs) whilst serving on active duty in war zone areas. A TBI is known to cause mortality or serious neurological disabilities among survivors and elicits a number of pathological processes, including neuroinflammation and blood brain barrier (BBB) disruption, leading to secondary brain damage and subsequent impairment of the neurovascular unit. Although several drugs exhibit promising effects for TBI, the repertoire of currently available therapeutic strategies remains limited. Thymosin 4 (Tβ4) is a 43-amino acid G-acting sequestering peptide that confers neuroprotective potential in TBI models. However, its role in BBB function remains unclear. Further research into the mechanism of BBB disruption induced by TBI and its specific role in neurovascular pathophysiology is necessary. In the present study, the protective effects of Tβ4 in lipopolysaccharide (LPS)-stimulated gene expression of several tight junction proteins, inflammatory genes, apoptotic genes, and adhesion genes in human brain microvascular endothelial cells (hBMVECs), one of the pivotal cell types in the BBB, were reported. The results suggested that pretreatment with Tβ4 reversed the LPS-induced damage of BBB components in hBMVECs. Furthermore, these results identified neuregulin 1 as a possible target for Tβ4. Therefore, it is proposed that Tβ4-mediated cellular signaling in hBMVEC may be vital for understanding the association between the BBB and TBI pathophysiology, which warrants further investigation.

Brain Renin-Angiotensin System: From Physiology to Pathology in Neuronal Complications Induced by SARS-CoV-2

Angiotensin-converting enzyme 2 (ACE2), a key enzyme in the renin-angiotensin system (RAS), is expressed in various tissues and organs, including the central nervous system (CNS). The spike protein of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), the virus responsible for coronavirus disease-2019 (COVID-19), binds to ACE2, which raises concerns about the potential for viral infection in the CNS. There are numerous reports suggesting a link between SARS-CoV-2 infection and neurological manifestations. This study aimed to present an updated review of the role of brain RAS components, especially ACE2, in neurological complications induced by SARS-CoV-2 infection. Several routes of SARS-CoV-2 entry into the brain have been proposed. Because an anosmia condition appeared broadly in COVID-19 patients, the olfactory nerve route was suggested as an early pathway for SARS-CoV-2 entry into the brain. In addition, a hematogenous route via disintegrations in the blood-brain barrier following an increase in systemic cytokine and chemokine levels and retrograde axonal transport, especially via the vagus nerve innervating lungs, have been described. Common nonspecific neurological symptoms in COVID-19 patients are myalgia, headache, anosmia, and dysgeusia. However, more severe outcomes include cerebrovascular diseases, cognitive impairment, anxiety, encephalopathy, and stroke. Alterations in brain RAS components such as angiotensin II (Ang II) and ACE2 mediate neurological manifestations of SARS-CoV-2 infection, at least in part. Downregulation of ACE2 due to SARS-CoV-2 infection, followed by an increase in Ang II levels, leads to hyperinflammation and oxidative stress, which in turn accelerates neurodegeneration in the brain. Furthermore, ACE2 downregulation in the hypothalamus induces stress and anxiety responses by increasing corticotropin-releasing hormone. SARS-CoV-2 infection may also dysregulate the CNS neurotransmission, leading to neurological complications observed in severe cases of COVID-19. It can be concluded that the neurological manifestations of COVID-19 may be partially associated with changes in brain RAS components.

Unmasking BACE1 in aging and age-related diseases

The beta-site amyloid precursor protein (APP)-cleaving enzyme 1 (BACE1) has long been considered a conventional target for Alzheimer's disease (AD). Unfortunately, AD clinical trials of most BACE1 inhibitors were discontinued due to ineffective cognitive improvement or safety challenges. Recent studies investigating the involvement of BACE1 in metabolic, vascular, and immune functions have indicated a role in aging, diabetes, hypertension, and cancer. These novel BACE1 functions have helped to identify new 'druggable' targets for BACE1 against aging comorbidities. In this review, we discuss BACE1 regulation during aging, and then provide recent insights into its enzymatic and nonenzymatic involvement in aging and age-related diseases. Our study not only proposes the perspective of BACE1's actions in various systems, but also provides new directions for using BACE1 inhibitors and modulators to delay aging and to treat age-related diseases.

Blood-Brain Barrier Disruption and Its Involvement in Neurodevelopmental and Neurodegenerative Disorders

The blood-brain barrier (BBB) is a highly specialized and dynamic compartment which regulates the uptake of molecules and solutes from the blood. The relevance of the maintenance of a healthy BBB underpinning disease prevention as well as the main pathomechanisms affecting BBB function will be detailed in this review. Barrier disruption is a common aspect in both neurodegenerative diseases, such as amyotrophic lateral sclerosis, and neurodevelopmental diseases, including autism spectrum disorders. Throughout this review, conditions altering the BBB during the earliest and latest stages of life will be discussed, revealing common factors involved. Due to the barrier's role in protecting the brain from exogenous components and xenobiotics, drug delivery across the BBB is challenging. Potential therapies based on the BBB properties as molecular Trojan horses, among others, will be reviewed, as well as innovative treatments such as stem cell therapies. Additionally, due to the microbiome influence on the normal function of the brain, microflora modulation strategies will be discussed. Finally, future research directions are highlighted to address the current gaps in the literature, emphasizing the idea that common therapies for both neurodevelopmental and neurodegenerative pathologies exist.

Remodeling of the Neurovascular Unit Following Cerebral Ischemia and Hemorrhage

Formulated as a group effort of the stroke community, the transforming concept of the neurovascular unit (NVU) depicts the structural and functional relationship between brain cells and the vascular structure. Composed of both neural and vascular elements, the NVU forms the blood-brain barrier that regulates cerebral blood flow to meet the oxygen demand of the brain in normal physiology and maintain brain homeostasis. Conversely, the dysregulation and dysfunction of the NVU is an essential pathological feature that underlies neurological disorders spanning from chronic neurodegeneration to acute cerebrovascular events such as ischemic stroke and cerebral hemorrhage, which were the focus of this review. We also discussed how common vascular risk factors of stroke predispose the NVU to pathological changes. We synthesized existing literature and first provided an overview of the basic structure and function of NVU, followed by knowledge of how these components remodel in response to ischemic stroke and brain hemorrhage. A greater understanding of the NVU dysfunction and remodeling will enable the design of targeted therapies and provide a valuable foundation for relevant research in this area.

Diffusion-weighted image analysis along the perivascular space (DWI-ALPS) for evaluating interstitial fluid status: age dependence in normal subjects

PURPOSE

The purpose of this study was to evaluate the interstitial fluid status in a wide range of age groups using diffusion-weighted image analysis along the perivascular space (DWI-ALPS) method, which is a simplified variation of diffusion tensor image analysis along the perivascular space (DTI-ALPS).

MATERIALS AND METHODS

This retrospective study included data from 128 patients who underwent clinical magnetic resonance imaging (MRI) studies, including DWI, and were found to have no abnormal findings in the brain on MRI. Three motion-probing gradients of the DWI were applied in an orthogonal direction to the imaging plane. Apparent diffusion coefficient images in the x-, y-, and z-axes were retrospectively generated, and composite color images were created to locate the projection and association fiber area on the slice including the body of the lateral ventricle. ALPS indices were calculated, and correlations with age were evaluated using linear and second-degree regression analysis. Linear regression analysis was also performed for a subgroup of patients older than 40 years. In addition, an analysis of variance (ANOVA) test among the generations was performed.

RESULTS

The linear regression analysis between age and the ALPS index showed a correlation coefficient of -0.20 for all age group and -0.51 for the subgroup older than 40 years. The second-degree regression analysis showed a correlation coefficient of 0.39. ANOVA showed that the 40's generation showed a statistically significant higher value of ALPS index compared to all other generations except for the 30's generation. While, the 70's generation showed a statistically significant lower value of the ALPS index compared to all other generations.

CONCLUSIONS

The analysis of the DWI-APLS method showed a correlation between age and the ALPS index in second-degree distribution which peaked in the 40's generation. This finding in normal subjects may be fundamental in the analysis of disease cases. We tried to evaluate the glymphatic system status in a wide range of age groups using diffusion-weighted image analysis along the perivascular space (DWI-ALPS) method, and the results showed a correlation between age and the ALPS index in second-degree distribution which peaked in the 40's generation.

Development of the Blood-Brain Barrier in Ducks

The blood-brain barrier (BBB) is an important internal barrier. Herein, the electron microscope examination of duck BBB was performed during the brain development. Meanwhile, the genes/proteins of tight junctions (TJs) including zonula occludens-1, occludin, and claudin-5 in the duck brain were detected by Q-PCR and immunohistochemistry. The results showed the density of capillaries in the brain gradually increased during the embryonic period. The generation of the BBB and the specialization of its components occurred mainly in the embryonic stage. During this period, the endothelial cells (ECs) became thinner and pinocytic vesicles decreased; the TJs between EC membranes became longer and more electron-dense; the basement membrane surrounding ECs and pericytes gradually thickened; and the astrocyte foot processes appeared to wrap around the vessels. By the day of hatching (P1), the whole set of duck BBB structures was completely assembled and gradually improved in the subsequent growth process. Interestingly, compared with the cerebrum and cerebellum, the maturity level of the midbrain BBB was earlier seen during the embryonic stage. The expression of TJs increased during the embryonic period and remained stable by post-hatching. The study systematically investigated the histochemical and ultrastructural features of duck BBB during development and explored the corresponding relationship between structure and function.

Mechanisms of immune effector cell-associated neurotoxicity syndrome after CAR-T treatment

Chimeric antigen receptor T-cell (CAR-T) treatment has revolutionized the landscape of cancer therapy with significant efficacy on hematologic malignancy, especially in relapsed and refractory B cell malignancies. However, unexpected serious toxicities such as cytokine release syndrome (CRS) and immune effector cell-associated neurotoxicity syndrome (ICANS) still hamper its broad application. Clinical trials using CAR-T cells targeting specific antigens on tumor cell surface have provided valuable information about the characteristics of ICANS. With unclear mechanism of ICANS after CAR-T treatment, unremitting efforts have been devoted to further exploration. Clinical findings from patients with ICANS strongly indicated existence of overactivated peripheral immune response followed by endothelial activation-induced blood-brain barrier (BBB) dysfunction, which triggers subsequent central nervous system (CNS) inflammation and neurotoxicity. Several animal models have been built but failed to fully replicate the whole spectrum of ICANS in human. Hopefully, novel and powerful technologies like single-cell analysis may help decipher the precise cellular response within CNS from a different perspective when ICANS happens. Moreover, multidisciplinary cooperation among the subjects of immunology, hematology, and neurology will facilitate better understanding about the complex immune interaction between the peripheral, protective barriers, and CNS in ICANS. This review elaborates recent findings about ICANS after CAR-T treatment from bed to bench, and discusses the potential cellular and molecular mechanisms that may promote effective management in the future. This article is categorized under: Cancer > Biomedical Engineering Immune System Diseases > Molecular and Cellular Physiology Neurological Diseases > Molecular and Cellular Physiology.

Immune gene network of neurological diseases: Multiple sclerosis (MS), Alzheimer's disease (AD), Parkinson's disease (PD) and Huntington's disease (HD)

Neurological diseases, such as MS, AD, PD and HD, are a major health concern of the elderly population, but still therapeutic options are limited. Recent advances in genomic sequencing and bioinformatics, present an opportunity to understand mechanisms of these diseases for identification of therapeutic targets. Several studies have shown association of immune dysfunction with immune system mediated neurological disease, MS, as well as neurodegenerative diseases (AD, PD and HD). However, similarities and differences in role of the immune system, immune pathways and immune cell types in these diseases remains unknown. In this study, immune cell type signature genes in gene networks associated with neurological diseases, MS, AD, PD and HD was investigated using meta-analysis and bioinformatics methods. Application of Weighted Gene Co-expression Network Analysis (WGCNA) on publicly available gene expression datasets (microarray and RNA-seq) revealed a ModArray_04 module (microarray) or ModRNAseq_06 module (RNA-seq), significantly associated with MS, AD, PD and HD. Hypergeometric enrichment test revealed significant enrichment of immune cell type genes in these neurological disease modules. This study demonstrates that immune system mediated neurological disease, MS and neurodegenerative diseases (AD, PD and HD), share a common gene network characterized by immune cell type signature genes (microglia, monocytes and macrophages) and are probable targets for therapeutic intervention. In summary, this work shows a connection between MS, a disease where the role of the immune system and inflammation is established, and neurodegenerative diseases (AD, PD and HD) where the role of inflammation is still a hypothesis.

BBB-crossing adeno-associated virus vector: An excellent gene delivery tool for CNS disease treatment

The presence of the blood-brain barrier (BBB) remains a challenge in the treatment of central nervous system (CNS) diseases, as it hinders the infiltration of many therapeutic drugs into the brain parenchyma. Therefore, developing efficacious pharmacological agents that can traverse the BBB is crucial for optimal treatment of diseases of the CNS such as neurodegenerative conditions and brain tumors. Adeno-associated virus (AAV), one of the most promising gene therapy vectors, has been shown to cross the BBB safely and is non-pathogenic in nature and therefore has been utilized for numerous diseases of the CNS. Along with the development of protein engineering techniques such as directed evolution including DNA shuffling, a great number of BBB-crossing AAVs have been developed, that could be systemically injected for therapeutic benefit. In this review, we discuss several feasible approaches to improve transportation of therapeutic agents to the CNS. We also discuss the advantages of using BBB-crossing AAVs, their role as a gene delivery agent and highlight the different types of BBB-AAV vectors that have been developed in order to provide a greater insight into how they can be used in diseases of the CNS.

Severe acute respiratory syndrome coronavirus 2 infection reaches the human nervous system: How?

Without protective and/or therapeutic agents the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection known as coronavirus disease 2019 is quickly spreading worldwide. It has surprising transmissibility potential, since it could infect all ages, gender, and human sectors. It attacks respiratory, gastrointestinal, urinary, hepatic, and endovascular systems and can reach the peripheral nervous system (PNS) and central nervous system (CNS) through known and unknown mechanisms. The reports on the neurological manifestations and complications of the SARS-CoV-2 infection are increasing exponentially. Herein, we enumerate seven candidate routes, which the mature or immature SARS-CoV-2 components could use to reach the CNS and PNS, utilizing the within-body cross talk between organs. The majority of SARS-CoV-2-infected patients suffer from some neurological manifestations (e.g., confusion, anosmia, and ageusia). It seems that although the mature virus did not reach the CNS or PNS of the majority of patients, its unassembled components and/or the accompanying immune-mediated responses may be responsible for the observed neurological symptoms. The viral particles and/or its components have been specifically documented in endothelial cells of lung, kidney, skin, and CNS. This means that the blood-endothelial barrier may be considered as the main route for SARS-CoV-2 entry into the nervous system, with the barrier disruption being more logical than barrier permeability, as evidenced by postmortem analyses.

Role of non-coding RNAs in age-related vascular cognitive impairment: An overview on diagnostic/prognostic value in Vascular Dementia and Vascular Parkinsonism

Age is the pivotal risk factor for different common medical conditions such as cardiovascular diseases, cancer and dementia. Among age-related disorders, cardiovascular and cerebrovascular diseases, represent the leading causes of premature mortality strictly related to vascular ageing, a pathological condition characterized by endothelial dysfunction, atherosclerosis, hypertension, heart disease and stroke. These features negatively impact on the brain, owing to altered cerebral blood flow, neurovascular coupling and impaired endothelial permeability leading to cerebrovascular diseases (CVDs) as Vascular Dementia (VD) and Parkinsonism (VP). It is an increasing opinion that neurodegenerative disorders and cerebrovascular diseases are associated from a pathogenetic point of view, and in this review, we discuss how cerebrovascular dysfunctions, due to epigenetic alterations, are linked with neuronal degeneration/dysfunction that lead to cognitive impairment. The relation between neurodegenerative and cerebrovascular diseases are reviewed with a focus on role of ncRNAs in age-related vascular diseases impairing the endothelium in the blood-brain barrier with consequent dysfunction of cerebral blood flow. In this review we dissert about different regulatory mechanisms of gene expression implemented by ncRNAs in the pathogenesis of age-related neurovascular impairment, aiming to highlight the potential use of ncRNAs as biomarkers for diagnostic/prognostic purposes as well as novel therapeutic targets.

Structural and Functional Remodeling of the Brain Vasculature Following Stroke

Maintenance of cerebral blood vessel integrity and regulation of cerebral blood flow ensure proper brain function. The adult human brain represents only a small portion of the body mass, yet about a quarter of the cardiac output is dedicated to energy consumption by brain cells at rest. Due to a low capacity to store energy, brain health is heavily reliant on a steady supply of oxygen and nutrients from the bloodstream, and is thus particularly vulnerable to stroke. Stroke is a leading cause of disability and mortality worldwide. By transiently or permanently limiting tissue perfusion, stroke alters vascular integrity and function, compromising brain homeostasis and leading to widespread consequences from early-onset motor deficits to long-term cognitive decline. While numerous lines of investigation have been undertaken to develop new pharmacological therapies for stroke, only few advances have been made and most clinical trials have failed. Overall, our understanding of the acute and chronic vascular responses to stroke is insufficient, yet a better comprehension of cerebrovascular remodeling following stroke is an essential prerequisite for developing novel therapeutic options. In this review, we present a comprehensive update on post-stroke cerebrovascular remodeling, an important and growing field in neuroscience, by discussing cellular and molecular mechanisms involved, sex differences, limitations of preclinical research design and future directions.

Cell-specific metabolomic responses to injury: novel insights into blood-brain barrier modulation

On one hand blood-brain barrier (BBB) disturbance aggravates disease progression, on the other it prevents drug access and impedes therapeutic efficacy. Effective ways to modulate barrier function and resolve these issues are sorely needed. Convinced that better understanding of cell-oriented BBB responses could provide valuable insight, and the fact that metabolic dysregulation is prominent in many vascular-related pathological processes associated with BBB disturbance, we hypothesized that differential cell-specific metabolic adaptation majorly influences physiological and pathological barrier functionality. Untargeted liquid chromatography-mass spectrometry (LC-MS) metabolomic profiling was used to obtain individual biochemical fingerprints of primary astrocytes (AC) and brain endothelial cells (EC) during normoxic conditions and increasing hypoxic/ischemic injury and thus a functional readout of cell status. Bioinformatic analyses showed each cell had a distinct metabolic signature. Corroborating their roles in BBB and CNS protection, AC showed an innate ability to dynamically alter their metabolome depending on the insult. Surprisingly, in complete contrast, EC largely maintained their normoxic characteristics in injury situations and their profiles diverged from those of non-brain origin. Tissue specificity/origin is clearly important when considering EC responses. Focusing on energy capacity and utilization we discuss how cell-specific metabolic adaptive capabilities could influence vascular stability and the possibility that altering metabolite levels may be an effective way to modulate brain EC function. Overall this work novel insight into cell-associated metabolic changes, and provides a powerful resource for understanding BBB changes during different injury scenarios.

Transitions in metabolic and immune systems from pre-menopause to post-menopause: implications for age-associated neurodegenerative diseases

The brain undergoes two aging programs: chronological and endocrinological. This is particularly evident in the female brain, which undergoes programs of aging associated with reproductive competency. Comprehensive understanding of the dynamic metabolic and neuroinflammatory aging process in the female brain can illuminate windows of opportunities to promote healthy brain aging. Bioenergetic crisis and chronic low-grade inflammation are hallmarks of brain aging and menopause and have been implicated as a unifying factor causally connecting genetic risk factors for Alzheimer's disease and other neurodegenerative diseases. In this review, we discuss metabolic phenotypes of pre-menopausal, peri-menopausal, and post-menopausal aging and their consequent impact on the neuroinflammatory profile during each transition state. A critical aspect of the aging process is the dynamic metabolic neuro-inflammatory profiles that emerge during chronological and endocrinological aging. These dynamic systems of biology are relevant to multiple age-associated neurodegenerative diseases and provide a therapeutic framework for prevention and delay of neurodegenerative diseases of aging. While these findings are based on investigations of the female brain, they have a broader fundamental systems of biology strategy for investigating the aging male brain. Molecular characterization of alterations in fuel utilization and neuroinflammatory mechanisms during these neuro-endocrine transition states can inform therapeutic strategies to mitigate the risk of Alzheimer's disease in women. We further discuss a precision hormone replacement therapy approach to target symptom profiles during endocrine and chronological aging to reduce risk for age-related neurodegenerative diseases.

Microvascular Dysfunction in the Critically Ill

Microvascular dysfunction is a frequent complication of many chronic and acute conditions, especially in the critically ill. Moreover, the severity of microvascular alterations is associated with development of organ dysfunction and poor outcome. The complexities and heterogeneity of critical illness, especially in the elderly patient, requires more mechanistically oriented clinical trials that monitor the effectiveness of existing therapies and of those to come. Recent advances in the ability to obtain physiologically based assessments of microcirculatory function at the bedside will make microcirculatory-guided resuscitation a point of care reality.

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.

Microbiota-gut-brain axis and toll-like receptors in Alzheimer's disease

Alzheimer’s disease (AD) is a multifactorial disease which involves both the periphery and central nervous system (CNS). It has been recently recognized that gut microbiota interacts with the gut and brain (microbiota-gut-brain axis), contributing to the pathogenesis of neurodegenerative diseases, such as AD. Dysbiosis of gut microbiota can induce increased intestinal permeability and systemic inflammation, which may lead to the development of AD pathologies and cognitive impairment via the neural, immune, endocrine, and metabolic pathways. Toll-like receptors (TLRs) play an important role in the innate immune system via recognizing microbes-derived pathogens and initiating the inflammatory process. TLRs have also been found in the brain, especially in the microglia, and have been indicated in the development of AD. In this review, we summarized the relationship between microbiota-gut-brain axis and AD, as well as the complex role of TLRs in AD. Intervention of the gut microbiota or modulation of TLRs properly might emerge as promising preventive and therapeutic strategies for AD.

Thymosin β4 for the treatment of acute stroke: neurorestorative or neuroprotective?

INTRODUCTION

Thymosin β4 (Tβ4) is a 5K peptide which influences cellular migration by inhibiting organization of the actin-cytoskeleton. Treatment of acute stroke presently involves use of rt-PA and/or endovascular treatment with thrombectomy, both of which have time limitations. Therefore, development of a treatment beyond these times is necessary as most stroke patients present beyond these time limits. A drug which could be administered within 24 h from symptom onset would provide substantial benefit.

AREAS COVERED

This review summarizes the data and results of two in-vivo studies testing Tβ4 in an embolic stroke model of young and aged rats. In addition, we describe in-vitro investigations of the neurorestorative and neuroprotective properties of Tβ4 in a variety of neuroprogenitor and oligoprogenitor cell models.

EXPERT OPINION

Tβ4 acts as a neurorestorative agent when employed in a young male rat model of embolic stroke while in an aged model it acts a neuroprotectant. However evaluation of Tβ4 as a treatment of stroke requires further preclinical evaluation in females and in males and females with comorbidities such as, hypertension and diabetes in models of embolic stroke to further define the mechanism of action and potential as a treatment of stroke in humans.

Decline in Sirtuin-1 expression and activity plays a critical role in blood-brain barrier permeability in aging

Accumulating evidence suggest that cerebral microvascular disease increases with advancing age and is associated with lacunar stroke, leukoaraiosis, vascular dementia and Alzheimer disease. Increased blood brain barrier (BBB) permeability/leakage takes "center stage" in ongoing age-related vascular/brain parenchymal injury. Although significant effort has been made in defining the gene mutations and risk factors involved in microvascular alterations in vascular dementia and Alzheimer disease, the intra- and intercellular pathogenic mechanisms responsible for vascular hyperpermeability are still largely unknown. The present study aimed to reveal the ongoing senescence process in brain endothelial cells and its effect on BBB integrity in healthy/non-disease conditions. An analysis of BBB integrity during the life span of C56Bl6 mice (young, 2-6 months; middle-aged, 6-12, months; old, 16-22 months) showed increased BBB permeability for different molecular sized tracers (sodium fluorescein, inulin and 20 kDa dextran) in aged mice which was accompanied by modifications in tight junction (TJ) complex organization, manifested as altered TJ protein expression (particularly claudin-5). A gene screening analysis of aging associated markers in brain microvessels isolated from "aged" mice (C56Bl6, 18-20 months) and human brain samples showed a significant decline in sirtuin-1 expression (Sirt1; ~2.8-fold) confirmed at mRNA and protein levels and by activation assay. Experiments in Sirt1 transgenic mice and brain endothelial cell-specific Sirt1 knockout mice indicated that Sirt1 affects BBB integrity, with loss increasing permeability. Similarly, in vitro, overexpressing Sirt1 or increasing Sirt1 activity with an agonist (Sirt1720) protected against senescence-induced brain endothelial barrier hyperpermeability, stabilized claudin-5/ZO-1 interactions and rescued claudin-5 expression. These findings reveal a novel role of Sirt1 in modulating aging-associated BBB persistent leakage.

Building barriers

Formation of tissue barriers starts in early development where it is critical for normal cell fate selection, differentiation and organogenesis. Barrier maintenance is critical to the ongoing function of organs during adulthood and aging. Dysfunctional tissue barrier formation and function at any stage of the organismal life cycle underlies many disease states.