Cerebral endothelial cells are a major source of adrenomedullin

Blood-brain Barrier and Neurovascular Unit Dysfunction in Parkinson's Disease: From Clinical Insights to Pathogenic Mechanisms and Novel Therapeutic Approaches

The blood-brain barrier (BBB) plays a crucial role in the central nervous system by tightly regulating the influx and efflux of biological substances between the brain parenchyma and peripheral circulation. Its restrictive nature acts as an obstacle to protect the brain from potentially noxious substances such as blood-borne toxins, immune cells, and pathogens. Thus, the maintenance of its structural and functional integrity is vital in the preservation of neuronal function and cellular homeostasis in the brain microenvironment. However, the barrier's foundation can become compromised during neurological or pathological conditions, which can result in dysregulated ionic homeostasis, impaired transport of nutrients, and accumulation of neurotoxins that eventually lead to irreversible neuronal loss. Initially, the BBB is thought to remain intact during neurodegenerative diseases, but accumulating evidence as of late has suggested the possible association of BBB dysfunction with Parkinson's disease (PD) pathology. The neurodegeneration occurring in PD is believed to stem from a myriad of pathogenic mechanisms, including tight junction alterations, abnormal angiogenesis, and dysfunctional BBB transporter mechanism, which ultimately causes altered BBB permeability. In this review, the major elements of the neurovascular unit (NVU) comprising the BBB are discussed, along with their role in the maintenance of barrier integrity and PD pathogenesis. We also elaborated on how the neuroendocrine system can influence the regulation of BBB function and PD pathogenesis. Several novel therapeutic approaches targeting the NVU components are explored to provide a fresh outlook on treatment options for PD.

Single-cell analysis of shared signatures and transcriptional diversity during zebrafish development

During development, animals generate distinct cell populations with specific identities, functions, and morphologies. We mapped transcriptionally distinct populations across 489,686 cells from 62 stages during wild-type zebrafish embryogenesis and early larval development (3-120 h post-fertilization). Using these data, we identified the limited catalog of gene expression programs reused across multiple tissues and their cell-type-specific adaptations. We also determined the duration each transcriptional state is present during development and identify unexpected long-term cycling populations. Focused clustering and transcriptional trajectory analyses of non-skeletal muscle and endoderm identified transcriptional profiles and candidate transcriptional regulators of understudied cell types and subpopulations, including the pneumatic duct, individual intestinal smooth muscle layers, spatially distinct pericyte subpopulations, and recently discovered best4+ cells. To enable additional discoveries, we make this comprehensive transcriptional atlas of early zebrafish development available through our website, Daniocell.

Molecular biomarkers for vascular cognitive impairment and dementia

As disease-specific interventions for dementia are being developed, the ability to identify the underlying pathology and dementia subtypes is increasingly important. Vascular cognitive impairment and dementia (VCID) is the second most common cause of dementia after Alzheimer disease, but progress in identifying molecular biomarkers for accurate diagnosis of VCID has been relatively limited. In this Review, we examine the roles of large and small vessel disease in VCID, considering the underlying pathophysiological processes that lead to vascular brain injury, including atherosclerosis, arteriolosclerosis, ischaemic injury, haemorrhage, hypoperfusion, endothelial dysfunction, blood-brain barrier breakdown, inflammation, oxidative stress, hypoxia, and neuronal and glial degeneration. We consider the key molecules in these processes, including proteins and peptides, metabolites, lipids and circulating RNA, and consider their potential as molecular biomarkers alone and in combination. We also discuss the challenges in translating the promise of these biomarkers into clinical application.

Future targets for migraine treatment beyond CGRP

BACKGROUND

Migraine is a disabling and chronic neurovascular headache disorder. Trigeminal vascular activation and release of calcitonin gene-related peptide (CGRP) play a pivotal role in the pathogenesis of migraine. This knowledge has led to the development of CGRP(-receptor) therapies. Yet, a substantial proportion of patients do not respond to these treatments. Therefore, alternative targets for future therapies are warranted. The current narrative review provides a comprehensive overview of the pathophysiological role of these possible non-CGRP targets in migraine.

FINDINGS

We covered targets of the metabotropic receptors (pituitary adenylate cyclase-activating polypeptide (PACAP), vasoactive intestinal peptide (VIP), amylin, and adrenomedullin), intracellular targets (nitric oxide (NO), phosphodiesterase-3 (PDE3) and -5 (PDE5)), and ion channels (potassium, calcium, transient receptor potential (TRP), and acid-sensing ion channels (ASIC)). The majority of non-CGRP targets were able to induce migraine-like attacks, except for (i) calcium channels, as it is not yet possible to directly target channels to elucidate their precise involvement in migraine; (ii) TRP channels, activation of which can induce non-migraine headache; and (iii) ASICs, as their potential in inducing migraine attacks has not been investigated thus far. Drugs that target its receptors exist for PACAP, NO, and the potassium, TRP, and ASIC channels. No selective drugs exist for the other targets, however, some existing (migraine) treatments appear to indirectly antagonize responses to amylin, adrenomedullin, and calcium channels. Drugs against PACAP, NO, potassium channels, TRP channels, and only a PAC₁ antibody have been tested for migraine treatment, albeit with ambiguous results.

CONCLUSION

While current research on these non-CGRP drug targets has not yet led to the development of efficacious therapies, human provocation studies using these targets have provided valuable insight into underlying mechanisms of migraine headaches and auras. Further studies are needed on these alternative therapies in non-responders of CGRP(-receptor) targeted therapies with the ultimate aim to pave the way towards a headache-free future for all migraine patients.

Single-cell analysis of shared signatures and transcriptional diversity during zebrafish development

During development, animals generate distinct cell populations with specific identities, functions, and morphologies. We mapped transcriptionally distinct populations across 489,686 cells from 62 stages during wild-type zebrafish embryogenesis and early larval development (3-120 hours post-fertilization). Using these data, we identified the limited catalog of gene expression programs reused across multiple tissues and their cell-type-specific adaptations. We also determined the duration each transcriptional state is present during development and suggest new long-term cycling populations. Focused analyses of non-skeletal muscle and the endoderm identified transcriptional profiles of understudied cell types and subpopulations, including the pneumatic duct, individual intestinal smooth muscle layers, spatially distinct pericyte subpopulations, and homologs of recently discovered human best4+ enterocytes. The transcriptional regulators of these populations remain unknown, so we reconstructed gene expression trajectories to suggest candidates. To enable additional discoveries, we make this comprehensive transcriptional atlas of early zebrafish development available through our website, Daniocell.

Diphenylarsinic acid induced activation of MAP kinases, transcription factors, and oxidative stress-responsive factors and hypersecretion of cytokines in cultured normal human cerebellar astrocytes

Diphenylarsinic acid (DPAA) is a non-natural pentavalent organic arsenic and was detected in well water in Kamisu, Ibaraki, Japan in 2003. Individuals that had consumed this arsenic-contaminated water developed cerebellar symptoms such as myoclonus. We previously revealed that DPAA exposure in rats in vitro and in vivo specifically affected astrocytes rather than neurons among cerebellar cells. Here, we evaluated adverse effects of DPAA in cultured normal human cerebellar astrocytes (NHA), which were compared with those in normal rat cerebellar astrocytes (NRA) exposed to DPAA at 10 μM for 96 h, focusing on aberrant activation of astrocytes; increase in cell viability, activation of MAP kinases (ERK1/2, p38MAPK, and SAPK/JNK) and transcription factors (CREB, c-Jun, and c-Fos), upregulation of oxidative stress-responsive factors (Nrf2, HO-1, and Hsp70), and also hypersecretion of brain cytokines (MCP-1, adrenomedullin, FGF-2, CXCL1, and IL-6) as reported in NRA. While DPAA exposure at 10 μM for 96 h had little effect on NHA, a higher concentration (50 μM for 96 h) and longer exposure (10 μM for 288 h) induced similar aberrant activation. Moreover, exposure to DPAA at 50 μM for 96 h or 10 μM for 288 h in NHA induced hypersecretion of cytokines induced in DPAA-exposed NRA (MCP-1, adrenomedullin, FGF-2, CXCL1, and IL-6), and IL-8 besides into culture medium. These results suggested that aberrantly activated human astrocytes by DPAA exposure might play a pivotal role in the pathogenesis of cerebellar symptoms, affecting adjacent neurons, microglia, brain blood vessels, or astrocyte itself through these brain cytokines in human.

The Role of Endothelial Dysfunction in the Pathophysiology and Cerebrovascular Effects of Migraine: A Narrative Review

Background and Purpose

Migraine is a complex neurovascular disorder whose triggers are not entirely understood. Endothelial dysfunction might play a role in migraine, and there have been numerous reports on endothelium dysfunction and migraine pathophysiology, but their reciprocal cause–effect relationship remains unclear. This review reports the current evidence on endothelium dysfunction, its link with migraine, and its possible consequences for cerebral hemodynamics.

Methods

We performed a systematic literature search of PubMed up to March 2020. We included 115 articles in a narrative review.

Results

Several studies have demonstrated that endothelium dysfunction may play an important role in migraine. Despite the lack of specific biomarkers, there is evidence of oxidative stress and inflammation—two of the primary causes of endothelial damage—in migraine. The main consequences of endothelial dysfunction are increased vascular tone, thrombosis, inflammation, and increased vascular permeability. As a consequence of oxidative stress, the activity of endothelin-1 is not counterbalanced by nitric oxide (NO), whose levels decrease to lead to vasoconstriction and a possible contribution to cortical spreading depression. NO is involved in pain perception via the cyclic guanosine monophosphate (cGMP) pathway and the induction of calcitonin gene-related peptide. Oxidative stress may induce a hypercoagulable state that mainly affects platelet function through different mechanisms. Endothelial dysfunction seems to be particularly pronounced in migraine with aura (MA). Endothelial dysfunction in migraine particularly involves intracranial vessels, since flow-mediated dilation cannot detect overt peripheral vascular dysfunction.

Conclusions

Endothelial dysfunction is a vascular risk marker. How it impacts migraine, and particularly MA, needs to be understood better by defining its possible role in increasing the stroke risk in migraine patients.

Effect of Adrenomedullin on Migraine-Like Attacks in Patients With Migraine: A Randomized Crossover Study

OBJECTIVE

To determine whether the IV infusion of adrenomedullin, a potent vasodilator belonging to calcitonin family of peptides, provokes attacks of migraine in patients.

METHODS

Twenty patients with migraine without aura participated in a placebo-controlled and double-blind clinical study. In a randomized crossover design, the patients received an IV infusion of human adrenomedullin (19.9 pmol/kg/min) or placebo (saline) administrated via an automated IV pump (20 minutes). The patients participated in 2 study days with a washout period of minimum of 7 days. The primary outcome of the study was predefined as a difference in migraine incidence (0-12 hours), and the secondary outcomes were the area under curve (AUC_0-12 hours) for the headache intensity score and AUC_{0-90 minutes} for mean arterial blood pressure (MAP), flushing, and heart rate (HR).

RESULTS

Eleven patients with migraine without aura (55%) fulfilled migraine attacks criteria after adrenomedullin infusion compared to only 3 patients who reported attack (15%) after placebo (p = 0.039). We found that patients reported in a period of 0 to 12 hours stronger headache intensity after adrenomedullin compared to placebo infusion (p = 0.035). AUC_{0-90 minutes} value for HR and flushing (p < 0.05) was significant and for MAP (p = 0.502) remained unchanged. Common reported adverse events were facial flushing, heat sensation, and palpitation (p < 0.001).

CONCLUSION

Our data implicate adrenomedullin in migraine pathogenesis. This suggests that adrenomedullin or its receptors are novel therapeutic targets for the treatment of migraine. However, we cannot discount the possibility that adrenomedullin may be acting through the canonical calcitonin gene-related peptide receptor.

TRIAL REGISTRATION INFORMATION

ClinicalTrials.gov Identifier: NCT04111484.

Diagnostic and prognostic blood biomarkers in vascular dementia: From the viewpoint of ischemic stroke

Reliable quantitative blood biomarkers are important in vascular dementia (VaD) because early diagnosis and therapeutic intervention are effective in preventing progression of dementia. Although many blood biomarkers for acute ischemic stroke (AIS) or VaD have been reported, there are few reliable blood biomarkers. VaD and AIS have similar pathological conditions that are associated with small vessel disease (SVD) such as oxidative stress, inflammation, endothelial dysfunction, and neuronal injury. Therefore, it may be possible to find superior blood biomarkers of VaD among AIS blood biomarkers. Owing to recent developments, noncoding RNAs such as microRNA and long noncoding RNA, which can be analyzed using a single drop of blood, are also particularly reliable VaD markers because they stably reflect brain tissue damage. A multimarker combining several blood biomarkers or artificial intelligence technology may also be beneficial to compensate for insufficiencies of a single blood biomarker. This review describes the blood biomarkers of VaD and how they are related to blood biomarkers of AIS.

Adrenomedullin: A vasoactive agent for sporadic and hereditary vascular cognitive impairment

Adrenomedullin (AM) is an endogenous peptide mainly secreted from endothelial cells, which has multiple physiological actions such as anti-inflammation, vasodilation, vascular permeability regulation and angiogenesis. Blood AM levels are upregulated in a variety of pathological states including sepsis, severe COVID-19, acute ischemic stroke and vascular cognitive impairment with white matter changes, likely serving as a compensatory biological defense response against infection and ischemia. AM is currently being tested in clinical trials for ulcerative colitis, Crohn's disease, severe COVID-19 for its anti-inflammatory properties and in ischemic stroke for its additional angiogenic action. AM has been proposed as a therapeutic option for vascular cognitive impairment as its arteriogenic and angiogenic properties are thought to contribute to a slowing of cognitive decline in mice after chronic cerebral hypoperfusion. As AM promotes differentiation of oligodendrocyte precursor cells into mature oligodendrocytes under hypoxic conditions, AM could also be used in the treatment of CADASIL, where reduced oxygen delivery is thought to lead to the death of hypoxia-prone oligodendrocytes. AM therefore holds potential as an innovative therapeutic drug, which may regenerate blood vessels, while controlling inflammation in cerebrovascular diseases.

The neuronal oxygen-sensing pathway controls postnatal vascularization of the murine brain

The contribution of neurons to growth and refinement of the microvasculature during postnatal brain development is only partially understood. Tissue hypoxia is the physiologic stimulus for angiogenesis by enhancing angiogenic mediators partly through activation of hypoxia-inducible factors (HIFs). Hence, we investigated the HIF oxygen-sensing pathway in postmitotic neurons for physiologic angiogenesis in the murine forebrain during postnatal development by using mice lacking the HIF suppressing enzyme prolyl-4-hydroxylase domain (PHD)2 and/or HIF-1/2α in postmitotic neurons. Perinatal activation or inactivation of the HIF pathway in neurons inversely modulated brain vascularization, including endothelial cell number and proliferation, density of total and perfused microvessels, and vascular branching. Accordingly, several angiogenesis-related genes were up-regulated in vivo and in primary neurons derived from PHD2-deficient mice. Among them, only VEGF and adrenomedullin (Adm) promoted angiogenic sprouting of brain endothelial cells. VEGF and Adm additively enhanced endothelial sprouting through activation of multiple pathways. PHD2 deficiency in neurons caused HIF-α stabilization and increased VEGF mRNA levels not only in neurons but unexpectedly also in astrocytes, suggesting a new mechanism of neuron-to-astrocyte signaling. Collectively, our results identify the PHD-HIF pathway in neurons as an important determinant for vascularization of the brain during postnatal development.-Nasyrov, E., Nolan, K. A., Wenger, R. H., Marti, H. H., Kunze, R. The neuronal oxygen-sensing pathway controls postnatal vascularization of the murine brain.

The blood-brain barrier as an endocrine tissue

The blood-brain barrier (BBB) was first noted for its ability to prevent the unregulated exchange of substances between the blood and the central nervous system (CNS). Over time, its characterization as an interface that enables regulated exchanges between the CNS and substances that are carried in the blood in a hormone-like fashion have emerged. Therefore, communication between the CNS, BBB and peripheral tissues has many endocrine-like properties. In this Review, I examine the various ways in which the BBB exhibits endocrine-related properties. The BBB is a target for hormones, such as leptin and insulin, that affect many of its functions. The BBB is also a secretory body, releasing substances either into the blood or the interstitial fluid of the brain. The BBB selectively allows classical and non-classical hormones entry to and exit from the CNS, thus allowing the CNS to be both an endocrine target and a secretory tissue. The BBB is affected by endocrine diseases such as diabetes mellitus and can cause or participate in endocrine diseases, including those related to thyroid hormones and obesity. The endocrine-like mechanisms of the BBB can extend the definition of endocrine disease to include neurodegenerative conditions, including Alzheimer disease, and of hormones to include cytokines, triglycerides and fatty acids.

Molecular studies of CGRP and the CGRP family of peptides in the central nervous system

BACKGROUND

Calcitonin gene-related peptide is an important target for migraine and other painful neurovascular conditions. Understanding the normal biological functions of calcitonin gene-related peptide is critical to understand the mechanisms of calcitonin gene-related peptide-blocking therapies as well as engineering improvements to these medications. Calcitonin gene-related peptide is closely related to other peptides in the calcitonin gene-related peptide family of peptides, including amylin. Relatedness in peptide sequence and in receptor biology makes it difficult to tease apart the contributions that each peptide and receptor makes to physiological processes and to disorders.

SUMMARY

The focus of this review is the expression of calcitonin gene-related peptide, related peptides and their receptors in the central nervous system. Calcitonin gene-related peptide is expressed throughout the nervous system, whereas amylin and adrenomedullin have only limited expression at discrete sites in the brain. The components of two receptors that respond to calcitonin gene-related peptide, the calcitonin gene-related peptide receptor (calcitonin receptor-like receptor with receptor activity-modifying protein 1) and the AMY₁ receptor (calcitonin receptor with receptor activity-modifying protein 1), are expressed throughout the nervous system. Understanding expression of the peptides and their receptors lays the foundation for more deeply understanding their physiology, pathophysiology and therapeutic use.

Physical insights into the blood-brain barrier translocation mechanisms

The number of individuals suffering from diseases of the central nervous system (CNS) is growing with an aging population. While candidate drugs for many of these diseases are available, most of these pharmaceutical agents cannot reach the brain rendering most of the drug therapies that target the CNS inefficient. The reason is the blood-brain barrier (BBB), a complex and dynamic interface that controls the influx and efflux of substances through a number of different translocation mechanisms. Here, we present these mechanisms providing, also, the necessary background related to the morphology and various characteristics of the BBB. Moreover, we discuss various numerical and simulation approaches used to study the BBB, and possible future directions based on multi-scale methods. We anticipate that this review will motivate multi-disciplinary research on the BBB aiming at the design of effective drug therapies.

From blood-brain barrier to blood-brain interface: new opportunities for CNS drug delivery

One of the biggest challenges in the development of therapeutics for central nervous system (CNS) disorders is achieving sufficient blood-brain barrier (BBB) penetration. Research in the past few decades has revealed that the BBB is not only a substantial barrier for drug delivery to the CNS but also a complex, dynamic interface that adapts to the needs of the CNS, responds to physiological changes, and is affected by and can even promote disease. This complexity confounds simple strategies for drug delivery to the CNS, but provides a wealth of opportunities and approaches for drug development. Here, I review some of the most important areas that have recently redefined the BBB and discuss how they can be applied to the development of CNS therapeutics.

Blood-Brain Barrier Deterioration and Hippocampal Gene Expression in Polymicrobial Sepsis: An Evaluation of Endothelial MyD88 and the Vagus Nerve

Systemic infection can initiate or exacerbate central nervous system (CNS) pathology, even in the absence of overt invasion of bacteria into the CNS. Recent epidemiological studies have demonstrated that human survivors of sepsis have an increased risk of long-term neurocognitive decline. There is thus a need for improved understanding of the physiological mechanisms whereby acute sepsis affects the CNS. In particular, MyD88-dependent activation of brain microvascular endothelial cells and a resulting loss of blood-brain barrier integrity have been proposed to play an important role in the effects of systemic inflammation on the CNS. Signaling through the vagus nerve has also been considered to be an important component of CNS responses to systemic infection. Here, we demonstrate that blood-brain barrier permeabilization and hippocampal transcriptional responses during polymicrobial sepsis occur even in the absence of MyD88-dependent signaling in cerebrovascular endothelial cells. We further demonstrate that these transcriptional responses can occur without vagus nerve input. These results suggest that redundant signals mediate CNS responses in sepsis. Either endothelial or vagus nerve activation may be individually sufficient to transmit systemic inflammation to the central nervous system. Transcriptional activation in the forebrain in sepsis may be mediated by MyD88-independent endothelial mechanisms or by non-vagal neuronal pathways.

Calcitonin gene-related peptide (CGRP) receptors are important to maintain cerebrovascular reactivity in chronic hypertension

Cerebral blood flow autoregulation (CA) shifts to higher blood pressures in chronic hypertensive patients, which increases their risk for brain damage. Although cerebral vascular smooth muscle cells express the potent vasodilatatory peptides calcitonin gene-related peptide (CGRP) and adrenomedullin (AM) and their receptors (calcitonin receptor-like receptor (Calclr), receptor-modifying proteins (RAMP) 1 and 2), their contribution to CA during chronic hypertension is poorly understood. Here we report that chronic (10 weeks) hypertensive (one-kidney-one-clip-method) mice overexpressing the Calclr in smooth muscle cells (CLR-tg), which increases the natural sensitivity of the brain vasculature to CGRP and AM show significantly better blood pressure drop-induced cerebrovascular reactivity than wt controls. Compared to sham mice, this was paralleled by increased cerebral CGRP-binding sites (receptor autoradiography), significantly in CLR-tg but not wt mice. AM-binding sites remained unchanged. Whereas hypertension did not alter RAMP-1 expression (droplet digital (dd) PCR) in either mouse line, RAMP-2 expression dropped significantly in both mouse lines by about 65%. Moreover, in wt only Calclr expression was reduced by about 70% parallel to an increase of smooth muscle actin (Acta2) expression. Thus, chronic hypertension induces a stoichiometric shift between CGRP and AM receptors in favor of the CGRP receptor. However, the parallel reduction of Calclr expression observed in wt mice but not CLR-tg mice appears to be a key mechanism in chronic hypertension impairing cerebrovascular reactivity.

Involvement of calcitonin gene-related peptide and receptor component protein in experimental autoimmune encephalomyelitis

Calcitonin Gene-Related Peptide (CGRP) inhibits microglia inflammatory activation in vitro. We here analyzed the involvement of CGRP and Receptor Component Protein (RCP) in experimental autoimmune encephalomyelitis (EAE). Alpha-CGRP deficiency increased EAE scores which followed the scale alpha-CGRP null>heterozygote>wild type. In wild type mice, CGRP delivery into the cerebrospinal fluid (CSF) 1) reduced chronic EAE (C-EAE) signs, 2) inhibited microglia activation (revealed by quantitative shape analysis), and 3) did not alter GFAP expression, cell density, lymphocyte infiltration, and peripheral lymphocyte production of IFN-gamma, TNF-alpha, IL-17, IL-2, and IL-4. RCP (probe for receptor involvement) was expressed in white matter microglia, astrocytes, oligodendrocytes, and vascular-endothelial cells: in EAE, also in infiltrating lymphocytes. In relapsing-remitting EAE (R-EAE) RCP increased during relapse, without correlation with lymphocyte density. RCP nuclear localization (stimulated by CGRP in vitro) was I) increased in microglia and decreased in astrocytes (R-EAE), and II) increased in microglia by CGRP CSF delivery (C-EAE). Calcitonin like receptor was rarely localized in nuclei of control and relapse mice. CGRP increased in motoneurons. In conclusion, CGRP can inhibit microglia activation in vivo in EAE. CGRP and its receptor may represent novel protective factors in EAE, apparently acting through the differential cell-specific intracellular translocation of RCP.

Modelling the endothelial blood-CNS barriers: a method for the production of robust in vitro models of the rat blood-brain barrier and blood-spinal cord barrier

Background

Modelling the blood-CNS barriers of the brain and spinal cord in vitro continues to provide a considerable challenge for research studying the passage of large and small molecules in and out of the central nervous system, both within the context of basic biology and for pharmaceutical drug discovery. Although there has been considerable success over the previous two decades in establishing useful in vitro primary endothelial cell cultures from the blood-CNS barriers, no model fully mimics the high electrical resistance, low paracellular permeability and selective influx/efflux characteristics of the in vivo situation. Furthermore, such primary-derived cultures are typically labour-intensive and generate low yields of cells, limiting scope for experimental work. We thus aimed to establish protocols for the high yield isolation and culture of endothelial cells from both rat brain and spinal cord. Our aim was to optimise in vitro conditions for inducing phenotypic characteristics in these cells that were reminiscent of the in vivo situation, such that they developed into tight endothelial barriers suitable for performing investigative biology and permeability studies.

Methods

Brain and spinal cord tissue was taken from the same rats and used to specifically isolate endothelial cells to reconstitute as in vitro blood-CNS barrier models. Isolated endothelial cells were cultured to expand the cellular yield and then passaged onto cell culture inserts for further investigation. Cell culture conditions were optimised using commercially available reagents and the resulting barrier-forming endothelial monolayers were characterised by functional permeability experiments and in vitro phenotyping by immunocytochemistry and western blotting.

Results

Using a combination of modified handling techniques and cell culture conditions, we have established and optimised a protocol for the in vitro culture of brain and, for the first time in rat, spinal cord endothelial cells. High yields of both CNS endothelial cell types can be obtained, and these can be passaged onto large numbers of cell culture inserts for in vitro permeability studies. The passaged brain and spinal cord endothelial cells are pure and express endothelial markers, tight junction proteins and intracellular transport machinery. Further, both models exhibit tight, functional barrier characteristics that are discriminating against large and small molecules in permeability assays and show functional expression of the pharmaceutically important P-gp efflux transporter.

Conclusions

Our techniques allow the provision of high yields of robust sister cultures of endothelial cells that accurately model the blood-CNS barriers in vitro. These models are ideally suited for use in studying the biology of the blood-brain barrier and blood-spinal cord barrier in vitro and for pre-clinical drug discovery.

Pharmacological inhibition of mitochondrial carbonic anhydrases protects mouse cerebral pericytes from high glucose-induced oxidative stress and apoptosis

Diabetes-associated complications in the microvasculature of the brain are caused by oxidative stress, generated by overproduction of reactive oxygen species from hyperglycemia-induced accelerated oxidative metabolism of glucose. Pericytes, essential for the viability of the microvasculature, are especially susceptible to oxidative stress. Mitochondrial carbonic anhydrases, regulators of the oxidative metabolism of glucose, determine the rate of reactive oxygen species production and inhibition of mitochondrial carbonic anhydrases rescues glucose-induced pericyte loss in the diabetic mouse brain. We hypothesized that high glucose induces intracellular oxidative stress and pericyte apoptosis and that inhibition of mitochondrial carbonic anhydrases protects pericytes from oxidative stress-induced apoptosis. To validate our hypothesis, conditionally immortalized cerebral pericyte (IPC) cultures were established from Immortomice to investigate the effect of high glucose on oxidative stress and pericyte apoptosis. The IPCs expressed pericyte markers and induced high transendothelial electrical resistance and low permeability in brain endothelial cell monolayers comparable with pericytes in primary cultures. The IPCs also secreted cytokines constitutively and in response to lipopolysaccharide similar to pericytes. High glucose caused oxidative stress and apoptosis of these cells, with both oxidative stress and apoptosis significantly reduced after mitochondrial carbonic anhydrase inhibition. These results provide the first evidence that pharmacological inhibition of mitochondrial carbonic anhydrases attenuates pericyte apoptosis caused by high glucose-induced oxidative stress. Carbonic anhydrase inhibitors have a long history of safe clinical use and can be immediately evaluated for this new indication in translational research. Thus, mitochondrial carbonic anhydrases may provide a new therapeutic target for oxidative stress-related illnesses of the brain.

Protection against recurrent stroke with resveratrol: endothelial protection

Despite increased risk of a recurrent stroke following a minor stroke, information is minimal regarding the interaction between injurious mild cerebral ischemic episodes and the possible treatments which might be effective. The aim of the current study was to investigate recurrent ischemic stroke and whether resveratrol, a nutritive polyphenol with promising cardio- and neuro- protective properties, could ameliorate the associated brain damage. Experiments in adult rats demonstrated that a mild ischemic stroke followed by a second mild cerebral ischemia exacerbated brain damage, and, daily oral resveratrol treatment after the first ischemic insult reduced ischemic cell death with the recurrent insult (P<0.002). Further investigation demonstrated reduction of both inflammatory changes and markers of oxidative stress in resveratrol treated animals. The protection observed with resveratrol treatment could not be explained by systemic effects of resveratrol treatment including effects either on blood pressure or body temperature measured telemetrically. Investigation of resveratrol effects on the blood-brain barrier in vivo demonstrated that resveratrol treatment reduced blood-brain barrier disruption and edema following recurrent stroke without affecting regional cerebral blood flow. Investigation of the mechanism in primary cell culture studies demonstrated that resveratrol treatment significantly protected endothelial cells against an in vitro ‘ischemia’ resulting in improved viability against oxygen and glucose deprivation (39.6±6.6% and 81.3±9.5% in vehicle and resveratrol treated cells, respectively). An inhibition of nitric oxide synthesis did not prevent the improved cell viability following oxygen glucose deprivation but SIRT-1 inhibition with sirtinol partially blocked the protection (P<0.001) suggesting endothelial protection is to some extent SIRT-1 dependent. Collectively, the results support that oral resveratrol treatment provides a low risk strategy to protect the brain from enhanced damage produced by recurrent stroke which is mediated in part by a protective effect of resveratrol on the endothelium of the cerebrovasculature.

Adrenomedullin as a growth and cell fate regulatory factor for adult neural stem cells

The use of stem cells as a strategy for tissue repair and regeneration is one of the biomedical research areas that has attracted more interest in the past few years. Despite the classic belief that the central nervous system (CNS) was immutable, now it is well known that cell turnover occurs in the mature CNS. Postnatal neurogenesis is subjected to tight regulation by many growth factors, cell signals, and transcription factors. An emerging molecule involved in this process is adrenomedullin (AM). AM, a 52-amino acid peptide which exerts a plethora of physiological functions, acts as a growth and cell fate regulatory factor for adult neural stem and progenitor cells. AM regulates the proliferation rate and the differentiation into neurons, astrocytes, and oligodendrocytes of stem/progenitor cells, probably through the PI3K/Akt pathway. The active peptides derived from the AM gene are able to regulate the cytoskeleton dynamics, which is extremely important for mature neural cell morphogenesis. In addition, a defective cytoskeleton may impair cell cycle and migration, so AM may contribute to neural stem cell growth regulation by allowing cells to pass through mitosis. Regulation of AM levels may contribute to program stem cells for their use in medical therapies.

Brain meets body: the blood-brain barrier as an endocrine interface

The blood-brain barrier (BBB) separates the central nervous system (CNS) from the peripheral tissues. However, this does not prevent hormones from entering the brain, but shifts the main control of entry to the BBB. In general, steroid hormones cross the BBB by transmembrane diffusion, a nonsaturable process resulting in brain levels that reflect blood levels, whereas thyroid hormones and many peptides and regulatory proteins cross using transporters, a saturable process resulting in brain levels that reflect blood levels and transporter characteristics. Protein binding, brain-to-blood transport, and pharmacokinetics modulate BBB penetration. Some hormones have the opposite effect within the CNS than they do in the periphery, suggesting that these hormones cross the BBB to act as their own counterregulators. The cells making up the BBB are also endocrine like, both responding to circulating substances and secreting substances into the circulation and CNS. By dividing a hormone's receptors into central and peripheral pools, the former of which may not be part of the hormone's negative feed back loop, the BBB fosters the development of variable hormone resistance syndromes, as exemplified by evidence that altered insulin action in the CNS can contribute to Alzheimer's disease. In summary, the BBB acts as a regulatory interface in an endocrine-like, humoral-based communication between the CNS and peripheral tissues.

Adrenomedullin receptors on human T cells are glucocorticoid-sensitive

Adrenomedullin (AM) is a novel vasodilatatory peptide which acts primarily through the calcitonin receptor-like receptor (CLR) in combination with either receptor-activity-modifying-protein (RAMP) 2 or 3 (forming receptors, AM(1) and AM(2) respectively). AM plays an important role during inflammation, with its expression increasing following cytokine treatment, promoting macrophage action in situ and high expression by T cells during hypoxic conditions. Examination of T cell AM receptor expression has previously been incomplete, hence we here consider the presentation of AM receptors and their responsiveness to AM and glucocorticoids (GC). AM receptor expression was examined by PCR and flow cytometry in primary human T cells, revealing that RAMP2, 3 and CLR are physiologically expressed in unstimulated T cells, both intracellularly and on the cell surface. PHA stimulation decreased receptor proteins, significantly so for CLR and RAMP3. Incubation with AM elicited limited receptor alterations however, GC treatment (10(-6) M; 24 h) markedly affected cell surface expression, significantly increasing receptor components in unstimulated cells and significantly decreasing the same in stimulated T cells. Our findings indicate that human T cells utilize both AM(1) and AM(2) receptors, which are GC-sensitive in an activation-state dependent manner.

Iptakalim, an ATP-sensitive potassium channel opener, confers neuroprotection against cerebral ischemia/reperfusion injury in rats by protecting neurovascular unit cells

OBJECTIVE

To investigate the role of iptakalim, an ATP-sensitive potassium channel opener, in transient cerebral ischemia/reperfusion (I/R) injury and its involved mechanisms.

METHODS

Intraluminal occlusion of middle cerebral artery (MCAO) in a rat model was used to investigate the effect of iptakalim at different time points. Infarct volume was measured by staining with 2,3,5-triphenyltetrazolium chloride, and immunohistochemistry was used to evaluate the expressions of Bcl-2 and Bax. In vitro, neurovascular unit (NVU) cells, including rat primary cortical neurons, astrocytes, and cerebral microvascular endothelial cells, were cultured and underwent oxygen-glucose deprivation (OGD). The protective effect of iptakalim on NVU cells was investigated by cell viability and injury assessments, which were measured by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide and release of lactate dehydrogenase. Caspase-3, Bcl-2 and Bax mRNA expressions were evaluated by real-time polymerase chain reaction (PCR).

RESULTS

Administration of iptakalim 0 or 1 h after reperfusion significantly reduced infarct volumes, improved neurological scores, and attenuated brain edema after cerebral I/R injury. Iptakalim treatment (0 h after reperfusion) also reduced caspase-3 expression and increased the ratio of Bcl-2 to Bax by immunohistochemistry. Iptakalim inhibited OGD-induced cell death in cultured neurons and astrocytes, and lactate dehydrogenase release from cerebral microvascular endothelial cells. Iptakalim reduced mRNA expression of caspase-3 and increased the ratio of Bcl-2 to Bax in NVU cells.

CONCLUSIONS

Iptakalim confers neuroprotection against cerebral I/R injury by protecting NVU cells via inhibiting of apoptosis.

Shared and separate functions of the RAMP-based adrenomedullin receptors

Adrenomedullin (AM) is a novel hypotensive peptide that exerts a variety of strongly protective effects against multiorgan damage. AM-specific receptors were first identified as heterodimers composed of calcitonin-receptor-like receptor (CLR), a G protein coupled receptor, and one of two receptor activity-modifying proteins (RAMP2 or RAMP3), which are accessory proteins containing a single transmembrane domain. RAMPs are required for the surface delivery of CLR and the determination of its phenotype. CLR/RAMP2 (AM₁ receptor) is more highly AM-specific than CLR/RAMP3 (AM₂ receptor). Although there have been no reports showing differences in intracellular signaling via the two AM receptors, in vitro studies have shed light on their distinct trafficking and functionality. In addition, the tissue distributions of RAMP2 and RAMP3 differ, and their gene expression is differentially altered under pathophysiological conditions, which is suggestive of the separate roles played by AM₁ and AM₂ receptors in vivo. Both AM and the AM₁ receptor, but not the AM₂ receptor, are crucial for the development of the fetal cardiovascular system and are able to effectively protect against various vascular diseases. However, AM₂ receptors reportedly play an important role in maintaining a normal body weight in old age and may be involved in immune function. In this review article, we focus on the shared and separate functions of the AM receptor subtypes and also discuss the potential for related drug discovery. In addition, we mention their possible function as receptors for AM2 (or intermedin), an AM-related peptide whose biological functions are similar to those of AM.

Cyclosporin A induces hyperpermeability of the blood-brain barrier by inhibiting autocrine adrenomedullin-mediated up-regulation of endothelial barrier function

Cyclosporin A, a potent immunosuppressant, can often produce neurotoxicity in patients, although its penetration into the brain is restricted by the blood-brain barrier (BBB). Brain pericytes and astrocytes, which are periendothelial accessory structures of the BBB, can be involved in cyclosporin A-induced BBB disruption. However, the mechanism by which cyclosporin A causes BBB dysfunction remains unknown. Here, we show that in rodent brain endothelial cells, cyclosporin A decreased transendothelial electrical resistance (TEER) by inhibiting intracellular signal transduction downstream of adrenomedullin, an autocrine regulator of BBB function. Cyclosporin A stimulated adrenomedullin release from brain endothelial cells, but did not affect binding of adrenomedullin to its receptors. This cyclosporin A-induced decrease in TEER was attenuated by exogenous addition of adrenomedullin. Cyclosporin A dose-dependently decreased the total cAMP concentration in brain endothelial cells. A combination of cyclosporin A (1microM) with an adenylyl cyclase inhibitor, 9-(tetrahydro-2-furanyl)-9H-purin-6-amine (SQ22536; 10microM), or a protein kinase A (PKA) inhibitor, N-[2-(p-bromocinnamylamino)ethyl]-5-isoquinolinesulfonamide dihydrochloride (H89; 1microM), markedly increased sodium fluorescein permeability in brain endothelial cells, whereas each drug alone had no effect. Thus, these data suggest that cyclosporin A inhibits the adenylyl cyclase/cyclic AMP/PKA signaling pathway activated by adrenomedullin, leading to impairment of brain endothelial barrier function.

Effect of Adrenomedullin on the Cerebral Circulation: Relevance to Primary Headache Disorders

Adrenomedullin (ADM) is closely related to calcitonin gene-related peptide, which has a known causative role in migraine. Animal studies have strongly suggested that ADM has a vasodilatory effect within the cerebral circulation. For these reasons, ADM is also likely to be involved in migraine. However, the hypothetical migraine-inducing property and effect on human cerebral circulation of ADM have not previously been investigated. Human ADM (0.08 µg kg−1 min−1) or placebo (saline 0.9%) was administered as a 20-min intravenous infusion to 12 patients suffering from migraine without aura in a crossover double-blind study. The occurrence of headache and associated symptoms were registered regularly 24 h post infusion. Cerebral blood flow (CBF) was measured by 133Xenon single-photon emission computed tomography, mean blood flow velocity in the middle cerebral artery (VMCA) by transcranial Doppler and the diameter of peripheral arteries by transdermal ultrasound (C-scan). ADM did not induce significantly more headache or migraine compared with placebo ( P = 0.58). CBF was unaffected by ADM infusion (global CBF, P = 0.32 and rCBFMCA, P = 0.38) and the same applied for the VMCA ( P = 0.18). The superficial temporal artery dilated compared with placebo ( P < 0.001), and facial flushing was seen after ADM administration ( P = 0.001). In conclusion, intravenous ADM is not a mediator of migraine headache and does not dilate intracranial arteries.

Adrenomedullin-induced relaxation of rat brain pericytes is related to the reduced phosphorylation of myosin light chain through the cAMP/PKA signaling pathway

Brain pericytes are known to embrace the abluminal endothelial surfaces of cerebral microvessels. The rich expression of contractile proteins in these cells suggests pericytal regulation of cerebral blood flow. Here, we investigated the molecular mechanisms by which an endothelium-derived relaxing factor, adrenomedullin, was able to induce the relaxation of rat primary cultured brain pericytes. Adrenomedullin increased the relative proportion of pericytes that were relaxed, as shown by an increased cell surface area. A smaller fragment of adrenomedullin (adrenomedullin(22-52)) blocked the adrenomedullin-induced relaxation. Adrenomedullin increased intracellular cAMP concentrations and decreased the phosphorylation of myosin light chain (MLC). H89 (a PKA inhibitor) inhibited the adrenomedullin-induced increase in the number of relaxed pericytes, and returned the level of phosphorylation of MLC to the control level. The results of the present study suggest that adrenomedullin-induced relaxation of brain pericytes is related to the reduced phosphorylation of MLC through cAMP/PKA.

Cerebromicrovascular endothelial cells are resistant to L-glutamate

Cerebral microvascular endothelial cells (CMVECs) have recently been implicated as targets of excitotoxic injury by l-glutamate (l-glut) or N-methyl-d-aspartate (NMDA) in vitro. However, high levels of l-glut do not compromise the function of the blood-brain barrier in vivo. We sought to determine whether primary cultures of rat and piglet CMVECs or cerebral microvascular pericytes (CMVPCs) are indeed sensitive to l-glut or NMDA. Viability was unaffected by 8-h exposure to 1-10 mM l-glut or NMDA in CMVECs or CMVPCs isolated from both species. Furthermore, neither 1 mM l-glut nor NMDA augmented cell death induced by 12-h oxygen-glucose deprivation in rat CMVECs or by 8-h medium withdrawal in CMVPCs. Additionally, transendothelial electrical resistance of rat CMVEC-astrocyte cocultures or piglet CMVEC cultures were not compromised by up to 24-h exposure to 1 mM l-glut or NMDA. The Ca(2+) ionophore calcimycin (5 microM), but not l-glut (1 mM), increased intracellular Ca(2+) levels in rat CMVECs and CMVPCs assessed with fluo-4 AM fluorescence and confocal microscopy. CMVEC-dependent pial arteriolar vasodilation to hypercapnia and bradykinin was unaffected by intracarotid infusion of l-glut in anesthetized piglets by closed cranial window/intravital microscopy. We conclude that cerebral microvascular cells are insensitive and resistant to glutamatergic stimuli in accordance with their in vivo role as regulators of potentially neurotoxic amino acids across the blood-brain barrier.

Effect of curcumin on the adhesion of platelets to brain microvascular endothelial cells in vitro

AIM

To determine whether curcumin prevents the adhesion of platelets to brain microvascular endothelial cells (BMECs) cultured in vitro.

METHODS

[3H]Adenine- labeled platelets were incubated with BMECs to investigate the role of curcumin in the adhesion of platelets to BMECs. The number of platelets adhering to the BMECs monolayer was determined by liquid scintillation spectroscopy. The thrombin-induced expression of platelets P-selectin, glycoprotein IIb (GPIIb), and glycoprotein IIIa (GPIIIa) on the cell surface, was measured by flow cytometry. P-selectin mRNA levels of BMECs were determined by RT-PCR. The TNF-alpha- induced expressions of P-selectin and E-selectin on the surface of BMECs were determined by Western blotting.

RESULTS

The adhesion between thrombin-activated platelets and normal BMECs, and that of TNF-alpha-activated BMECs and normal platelets were significantly increased, and this increase could be inhibited by curcumin (30-240 micromol/L) in a concentration-dependant manner. The platelets activated with thrombin and BMECs stimulated by TNF-alpha demonstrated an upregulated expressions of P-selectin and E-selectin, and this increase, when pretreated with curcumin for 30 min, could be restrained dose dependently. Curcumin also inhibited the increase of the GPIIb/GPIIIa expression of thrombinactivated platelets in a concentration-dependent manner.

CONCLUSION

Curcumin can inhibit the platelets to BMECs. This effect may be related to the decreased expressions of P-selectin, E-selectin, and GPIIb/GPIIIa on platelets and BMECs.

The epithelial membrane protein 1 is a novel tight junction protein of the blood-brain barrier

In the central nervous system, a constant microenvironment required for neuronal cell activity is maintained by the blood-brain barrier (BBB). The BBB is formed by the brain microvascular endothelial cells (BMEC), which are sealed by tight junctions (TJ). To identify genes that are differentially expressed in BMEC compared with peripheral endothelial cells, we constructed a subtractive cDNA library from porcine BMEC (pBMEC) and aortic endothelial cells (AOEC). Screening the library for differentially expressed genes yielded 26 BMEC-specific transcripts, such as solute carrier family 35 member F2 (SLC35F2), ADP-ribosylation factor-like 5B (ARL5B), TSC22 domain family member 1 (TSC22D1), integral membrane protein 2A (ITM2A), and epithelial membrane protein 1 (EMP1). In this study, we show that EMP1 transcript is enriched in pBMEC compared with brain tissue and that EMP1 protein colocalizes with the TJ protein occludin in mouse BMEC by coimmunoprecipitation and in rat brain vessels by immunohistochemistry. Epithelial membrane protein 1 expression was transiently induced in laser-capture microdissected rat brain vessels after a 20-min global cerebral ischemia, in parallel with the loss of occludin immunoreactivity. The study identifies EMP1 as a novel TJ-associated protein of the BBB and suggests its potential role in the regulation of the BBB function in cerebral ischemia.

The blood-brain barrier: connecting the gut and the brain

The BBB prevents the unrestricted exchange of substances between the central nervous system (CNS) and the blood. The blood-brain barrier (BBB) also conveys information between the CNS and the gastrointestinal (GI) tract through several mechanisms. Here, we review three of those mechanisms. First, the BBB selectively transports some peptides and regulatory proteins in the blood-to-brain or the brain-to-blood direction. The ability of GI hormones to affect functions of the BBB, as illustrated by the ability of insulin to alter the BBB transport of amino acids and drugs, represents a second mechanism. A third mechanism is the ability of GI hormones to affect the secretion by the BBB of substances that themselves affect feeding and appetite, such as nitric oxide and cytokines. By these and other mechanisms, the BBB regulates communications between the CNS and GI tract.

Nitric oxide isoenzymes regulate lipopolysaccharide-enhanced insulin transport across the blood-brain barrier

Insulin transported across the blood-brain barrier (BBB) has many effects within the central nervous system. Insulin transport is not static but altered by obesity and inflammation. Lipopolysaccharide (LPS), derived from the cell walls of Gram-negative bacteria, enhances insulin transport across the BBB but also releases nitric oxide (NO), which opposes LPS-enhanced insulin transport. Here we determined the role of NO synthase (NOS) in mediating the effects of LPS on insulin BBB transport. The activity of all three NOS isoenzymes was stimulated in vivo by LPS. Endothelial NOS and inducible NOS together mediated the LPS-enhanced transport of insulin, whereas neuronal NOS (nNOS) opposed LPS-enhanced insulin transport. This dual pattern of NOS action was found in most brain regions with the exception of the striatum, which did not respond to LPS, and the parietal cortex, hippocampus, and pons medulla, which did not respond to nNOS inhibition. In vitro studies of a brain endothelial cell (BEC) monolayer BBB model showed that LPS did not directly affect insulin transport, whereas NO inhibited insulin transport. This suggests that the stimulatory effect of LPS and NOS on insulin transport is mediated through cells of the neurovascular unit other than BECs. Protein and mRNA levels of the isoenzymes indicated that the effects of LPS are mainly posttranslational. In conclusion, LPS affects insulin transport across the BBB by modulating NOS isoenzyme activity. NO released by endothelial NOS and inducible NOS acts indirectly to stimulate insulin transport, whereas NO released by nNOS acts directly on BECs to inhibit insulin transport.

Intermedin (adrenomedullin-2): a novel counter-regulatory peptide in the cardiovascular and renal systems

Intermedin (IMD) is a novel peptide related to calcitonin gene-related peptide (CGRP) and adrenomedullin (AM). Proteolytic processing of a larger precursor yields a series of biologically active C-terminal fragments, IMD(1-53), IMD(1-47) and IMD(8-47). IMD shares a family of receptors with AM and CGRP composed of a calcitonin-receptor like receptor (CALCRL) associated with one of three receptor activity modifying proteins (RAMP). Compared to CGRP, IMD is less potent at CGRP(1) receptors but more potent at AM(1) receptors and AM(2) receptors; compared to AM, IMD is more potent at CGRP(1) receptors but less potent at AM(1) and AM(2) receptors. The cellular and tissue distribution of IMD overlaps in some aspects with that of CGRP and AM but is distinct from both. IMD is present in neonatal but absent or expressed sparsely, in adult heart and vasculature and present at low levels in plasma. The prominent localization of IMD in hypothalamus and pituitary and in kidney is consistent with a physiological role in the central and peripheral regulation of the circulation and water-electrolyte homeostasis. IMD is a potent systemic and pulmonary vasodilator, influences regional blood flow and augments cardiac contractility. IMD protects myocardium from the deleterious effects of oxidative stress associated with ischaemia-reperfusion injury and exerts an anti-growth effect directly on cardiomyocytes to oppose the influence of hypertrophic stimuli. The robust increase in expression of the peptide in hypertrophied and ischaemic myocardium indicates an important protective role for IMD as an endogenous counter-regulatory peptide in the heart.

Intermedin: a skin peptide that is downregulated in atopic dermatitis

Intermedin (IMD), also called adrenomedullin-2, is a peptide that belongs to the calcitonin/calcitonin gene-related peptide/amylin peptide family. IMD exerts many effects on the cardiovascular system, gastrointestinal tract, and central nervous system. Here, we analyzed the expression of the IMD peptide in human skin of healthy controls, in biopsies from lesional and non-lesional areas of atopic dermatitis (AD) skin, in cultured human keratinocytes, and in the HaCaT keratinocyte cell line at the transcriptional (quantitative reverse transcription-PCR) and translational (immunohistochemistry) level. IMD messenger RNA (mRNA) and protein could be detected in keratinocytes and human skin. Keratinocytes, nerve fibers, periglandular cells, arterial/arteriolar smooth muscle cells, and pericytes of dermal microvessels were intensely IMD-immunoreactive. The IMD mRNA was, compared to healthy skin, significantly reduced in lesional and non-lesional areas of AD skin. This was accompanied by a reduction of IMD immunoreactivity in pericytes of the upper dermis indicating that skin from AD patients is generally affected, and downregulation of IMD in AD skin is not a secondary phenomenon caused by acute inflammation but is a general characteristic of AD skin. These data further point to a role of IMD expressed by pericytes in conferring higher susceptibility of the skin of AD patients to inflammatory stimuli.

The in vivo effect of adrenomedullin on rat dural and pial arteries

Adrenomedullin is related to the calcitonin gene-related peptide (CGRP) family and is present in cerebral blood vessels. It may be involved in migraine mechanisms. We measured the change in dural and pial artery diameter, mean arterial blood pressure and local cerebral blood flow flux (LCBF(Flux)) after intravenous (i.v.) infusion of adrenomedullin. The study was performed in the presence or absence of the CGRP1 (calcitonin-receptor-like-receptor (CALCRL)/receptor activity-modifying protein-1 (RAMP1)) receptor antagonists BIBN4096BS, CGRP-(8-37) and the adrenomedullin receptor antagonist adrenomedullin-(22-52). I.v. infusion of 15 mug kg(-1) adrenomedullin (n=8) induced dilatation of dural (32+/-7.5%) and pial (18+/-5.5%) arteries, a reduction in mean arterial blood pressure (19+/-3%) and an increase in LCBF(Flux) (16+/-8.4%). The duration of the responses was 25 min for the dural artery, while the response of the pial artery lasted for 15 min. The CGRP1-receptor antagonists BIBN4096BS and CGRP-(8-37) and the adrenomedullin receptor antagonist adrenomedullin-(22-52) significantly inhibited the effect of adrenomedullin (n=7, P<0.05 for both arteries) on dural and pial artery diameter and mean arterial blood pressure. No significant inhibition of LCBF(Flux) was found. The antagonist alone had no effect on mean arterial blood pressure or LCBF(Flux). In conclusion, we suggest that adrenomedullin in the rat cranial circulation dilates dural and pial arteries, reduces mean arterial blood pressure and increases LCBF(Flux), probably via a CGRP1-receptor.

Adrenomedullin improves the blood-brain barrier function through the expression of claudin-5

AIMS

Brain vascular endothelial cells secret Adrenomedullin (AM) has multifunctional biological properties. AM affects cerebral blood flow and blood-brain barrier (BBB) function. We studied the role of AM on the permeability and tight junction proteins of brain microvascular endothelial cells (BMEC).

METHODS

BMEC were isolated from rats and a BBB in vitro model was generated. The barrier functions were studied by measuring the transendothelial electrical resistance (TEER) and the permeability of sodium fluorescein and Evans' blue albumin. The expressions of tight junction proteins were analyzed using immunocytochemistry and immunoblotting.

RESULTS

AM increased TEER of BMEC monolayer dose-dependently. Immunocytochemistry revealed that AM enhanced the claudin-5 expression at a cell-cell contact site in a dose-dependent manner. Immunoblotting also showed an overexpression of claudin-5 in AM exposure.

CONCLUSIONS

AM therefore inhibits the paracellular transport in a BBB in vitro model through claudin-5 overexpression.

Adrenomedullin 2 protects rat cerebral endothelial cells from oxidative damage in vitro

Adrenomedullin 2 (AM2, intermedin) is a recently identified new member of the calcitonin gene-related peptide family. We examined whether AM2 can attenuate the increased blood-brain barrier permeability and cerebral endothelial cell (CEC) death induced by oxidative stress in vitro. Hydrogen peroxide (H(2)O(2), 0.5 mM) induced a continuous decrease of the transendothelial electrical resistance (TEER) and resulted in intercellular gap formations in rat CECs co-cultured with astrocytes. AM2 induced cAMP and nitric oxide production, increased TEER, enhanced peripheral localization of F-actin bands, and attenuated the increased permeability induced by H(2)O(2). AM2 treatment preserved mitochondrial membrane potential and improved CEC viability in H(2)O(2) treated cultures. These effects of AM2 were similar to those what were reported for adrenomedullin. These results suggest that AM2 protects CECs against oxidative injury in vitro.

Effects of LPS stimulation on the expression of prostaglandin carriers in the cells of the blood-brain and blood-cerebrospinal fluid barriers

Prostaglandins produced in cerebral endothelial cells (CECs) are the final signal transduction mediators from the periphery to the brain during fever response. However, prostaglandins are organic anions at physiological pH, and they enter cells poorly using simple diffusion. Several transporters have been described that specifically transport prostaglandins across cell membranes. We examined the expression of the two principal prostaglandin carriers, prostaglandin transporter (PGT), and multidrug resistance-associated protein 4 (MRP4) in cells of the blood-brain barrier and in choroid epithelial cells in vitro as well as in vivo in rat brain in control conditions and after lipopolysaccharide (LPS) challenge. We detected PGT in primary cultures of rat CECs, astrocytes, pericytes, and choroid epithelial cells. LPS stimulation had no effect on the expression level of PGT in these cells; however, after LPS stimulation the polarized, dominantly luminal, expression pattern of PGT significantly changed. MRP4 is also expressed in CECs, and its level was not influenced by LPS treatment. In rat brain, PGT was highly expressed in the supraoptic and paraventricular nuclei of the hypothalamus, in the ependymal cell layer of the third ventricle, and in the choroid plexus. LPS treatment increased the expression of PGT in the supraoptic and paraventricular nuclei. Our results suggest that PGT and MRP4 likely play a role in transporting prostaglandins through the blood-brain and blood-cerebrospinal fluid barriers and may be involved in the maintenance of prostaglandin homeostasis in the brain and in the initiation of fever response.

Postischemic infusion of adrenomedullin protects against ischemic stroke by inhibiting apoptosis and promoting angiogenesis

Adrenomedullin (AM) is a peptide hormone widely distributed in the central nervous system. Our previous study showed that AM gene delivery immediately after middle cerebral artery occlusion (MCAO) protected against cerebral ischemia/reperfusion (I/R) injury by promoting glial cell survival and migration. In the present study, we investigated the effect of delayed AM peptide infusion on ischemic brain injury at 24 h after MCAO. AM infusion significantly reduced neurological deficit scores at days 2, 4, and 8 after cerebral I/R. AM reduced cerebral infarct size at 8 and 15 days after surgery as determined by quantitative analysis. Double staining showed that AM infusion reduced TUNEL-positive apoptotic cells in both neurons and glial cells, as well as reduced caspase-3 activity in the ischemic area of the brain. In addition, AM treatment increased capillary density in the ischemic region at 15 days after I/R injury. Parallel studies revealed that AM treatment enhanced the proliferation of cultured endothelial cells as measured by both (3)H-thymidine incorporation and in situ BrdU labeling. Both in vitro and in vivo AM effects were blocked by calcitonin gene-related peptide (8-37), an AM receptor antagonist. Moreover, AM's effects were associated with increased cerebral nitric oxide (NO) levels, as well as decreased NAD(P)H oxidase activities and superoxide anion production. These results indicate that a continuous supply of exogenous AM peptide protects against I/R injury by improving the survival of neuronal and glial cells, and promoting angiogenesis through elevated NO formation and suppression of oxidative stress.

Autocrine peptide mediators of cerebral endothelial cells and their role in the regulation of blood-brain barrier

A unique feature of cerebral endothelial cells (CECs) is the formation of the blood-brain barrier (BBB), which contributes to the stability of the brain microenvironment. CECs are capable of producing several substances mediating endothelium-dependent vasorelaxation or vasoconstriction, regulating BBB permeability, and participating in the regulation of cell-cell interactions during inflammatory and immunological processes. The chemical nature of these mediators produced by CECs ranges from gaseous anorganic molecules (e.g. nitric oxide) through lipid mediators (e.g. prostaglandins) to peptides. Peptide mediators are a large and diverse family of bioactive molecules which can elicit multiple effects on cerebral endothelial functions. In this review, we summarize current knowledge of peptide mediators produced by CECs, such as adrenomedullin, angiotensin, endothelin and several others and their role in the regulation of BBB functions.

Adrenomedullin protects rat cerebral endothelial cells from oxidant damage in vitro

Increased permeability and reduced cerebral endothelial cell (CEC) viability induced by oxidative stress are the hallmarks of the blood-brain barrier disruption. In our experiments hydrogen peroxide (H2O2, 0.5 mM) induced a continuous decrease of the transendothelial electrical resistance (TEER) and resulted in intercellular gap formations in cultured rat CECs. Adrenomedullin (AM) increased TEER, enhanced peripheral localization of F-actin bands and attenuated the increased permeability induced by H2O2. Furthermore, AM treatment preserved mitochondrial membrane potential, attenuated cytochrome c release, and consequently improved CEC viability in H2O2 treated cultures. These results suggest that AM treatment protects CECs against oxidative injury.

Diazoxide preserves hypercapnia-induced arteriolar vasodilation after global cerebral ischemia in piglets

Diazoxide (Diaz), an activator of mitochondrial ATP-sensitive K+(mitoKATP) channels, is neuroprotective, but the mechanism of action is unclear. We tested whether Diaz preserves endothelium-dependent (hypercapnia) or -independent [iloprost (Ilo)] cerebrovascular dilator responses after ischemia-reperfusion (I/R) in newborn pigs and whether the effect of Diaz is sensitive to 5-hydroxydecanoate (5-HD), an inhibitor of mitoKATPchannels. Anesthetized, ventilated piglets ( n = 48) were equipped with closed cranial windows. Changes in diameter of pial arterioles were determined with intravital microscopy in response to graded hypercapnia (5–10% CO2-21% O2-balance N2, n = 25) or Ilo (0.1–1 μg/ml, n = 18) before and 1 h after 10 min of global I/R. Experimental groups were pretreated with vehicle, NS-398 (a selective cyclooxygenase-2 inhibitor, 1 mg/kg), Diaz (3 mg/kg), or 5-HD (20 mg/kg) + Diaz. Potential direct effects of Diaz and 5-HD on hypercapnic vasodilation were also tested in the absence of I/R ( n = 5). To confirm the direct effect of Diaz on mitochondria, mitochondrial membrane potential in cultured piglet cerebrovascular endothelial cells was monitored using Mito Tracker Red. Hypercapnia resulted in dose-dependent pial arteriolar vasodilation, which was attenuated by ∼70% after I/R in vehicle- and NS-398-treated animals. Diaz and 5-HD did not affect the CO2response. Diaz significantly preserved the postischemic vasodilation response to hypercapnia, but not to Ilo. Diaz depolarized mitochondria in cultured piglet cerebrovascular endothelial cells, and 5-HD completely abolished the protective effect of Diaz, both findings indicate a role for mitoKATPchannels. In summary, preservation of arteriolar dilator responsiveness by Diaz may contribute to neuroprotection.

Human immunodeficiency virus type 1 transport across the in vitro mouse brain endothelial cell monolayer

Human immunodeficiency virus type 1 (HIV-1) is associated with a neuroinflammatory dementia. Cognitive impairment remains a common complication of late-stage HIV-1 infection. Previous studies have shown that entry of HIV-1 into the central nervous system (CNS) occurs soon after infection. For these reasons, it is important to understand how HIV-1 crosses the BBB. We used primary mouse brain microvessel endothelial cell (MBEC) monolayer models to study interactions between brain endothelial cells and radioactively labeled HIV-1 CL4 (131I-HIV-1), which had been rendered noninfectious with aldithiol, and compared to radioactively labeled bovine serum albumin (131I-BSA or 125I-BSA) and detected HIV-1 on MBEC monolayer with electron microscopic analysis. The permeability of the monolayers to HIV-1 was measured by determining the percent material transported (PMT). Luminal to abluminal PMT of 131I-HIV-1 was 4.65 times greater than that of the much smaller 131I-BSA, showing that the MBEC monolayer is more permeable to HIV-1 than to BSA. Electron microscopy showed that HIV-1 was transported through a trans-cellular pathway from luminal side to basolateral space with some virus associated with the nucleus. Unlabeled HIV-1 did not affect the transport of 131I-HIV-1 or break down the MBEC monolayer. Wheatgerm agglutinin (WGA) increased 131I-HIV-1 penetration across the MBEC monolayer, consistent with absorptive endocytosis as the mechanism for HIV-1 penetration. The enhanced transport of HIV-1 was unidirectional, as the abluminal to luminal PMT of 131I-HIV-1 was not different from that of BSA nor enhanced by WGA. Characterization of the radioactivity transported from the luminal to abluminal chamber on Sepharose 4B-200 columns showed the transported radioactivity represented intact virus. MBEC monolayers preloaded from the luminal surface with 131I-HIV-1 showed most of the virus was retained by the endothelial cells, while the remainder was effluxed mainly to the luminal surface. MBEC monolayers preloaded from the abluminal surface with 131I-HIV-1 retained little virus and most of the virus was effluxed mainly to the abluminal surface. In conclusion, cell-free, intact 131I-HIV-1 crossed brain endothelial cell monolayers unidirectionally in the luminal to abluminal direction through an adsorptive endocytotic pathway. HIV-1 taken up from luminal side by monolayers of brain endothelial cells was mainly released to the luminal side. HIV-1 efflux mechanisms are different from influx mechanisms.

Effects of hypoxia on endothelial/pericytic co-culture model of the blood-brain barrier

The blood-brain barrier (BBB) is composed of endothelial cells, pericytes and astrocytic foot processes. Most research for the in vitro BBB is performed endothelial cells with or without astrocytes. Hypoxia damage to the BBB induces vasogenic brain edema. We have generated a new model of the BBB with brain endothelial cells and pericytes and have examined the effects of hypoxia using this model. Brain microvascular endothelial cells and pericytes were isolated from three-week-old male Wister rats using enzyme and mechanical homogenization. Three models (A: only endothelial monolayer, B: endothelial monolayer with pericytes non-contact condition, and C: contact condition) were made by culturing these cells using Transwell co-culture system and were exposed to hypoxic condition. We evaluated barrier function with transendothelial electrical resistance (TEER) and permeability of Evans blue-albumin and sodium fluorescein. The tightest barrier was observed in the endothelial/pericytic contact model. Despite hypoxia-induced disruption of the barrier in endothelial monolayer and non-contact co-culture models, a minimum of dysfunction was seen in the contact co-culture model. Therefore, it is considered that pericytes effect on the endothelia by secreting factors or through a gap junction. In short, pericytes induce endothelial maturation and a tighter barrier function, which supports the function against the hypoxic injury. Intercellular communication might be important to keep the BBB functional and stabilize in hypoxia.

Effects of a behaviorally active antibody on the brain uptake and clearance of amyloid beta proteins

Antibodies directed against amyloid beta protein (AssP) have been suggested to be effective in the treatment of Alzheimer's disease (AD). Here, we used in vivo and in vitro models to test some of the mechanisms by which antibodies may produce their effects. We found that the blood-to-brain uptake of murine AssP1-42 was significantly reduced when co-injected peripherally with an antibody known to reverse cognitive defects in the SAMP8, an mouse model of AD. This antibody was not effective when tested against the more slowly transported human AssP1-42. Antibody given by intracerebroventricular (icv) injection did not improve the clearance of murine AssP1-42 from the brains of young healthy mice, which already rapidly clear AssP by saturable and non-saturable mechanisms. Antibody given icv also did not improve the clearance of human AssP1-42 from the brains of aged SAMP8 mice, a combination in which the AssP is only poorly cleared from brain. IV antibody also did not affect retention of murine AssP in young mice. In vitro transwell studies with monolayers of mouse brain endothelial cells (MBEC) found no evidence that antibody in the vascular chamber would retard the reuptake of AssP which had been effluxed from the brain-side chamber. A statistical trend suggested that antibody might decrease the association of AssP with brain vasculature. In conclusion, we found that icv administration of antibody was not effective in aiding clearance of AssP already in brain, but that blood-borne antibody can inhibit the entry of AssP into brain and might prevent AssP from associating with the brain vasculature.