Stroke induces histamine accumulation and mast cell degranulation in the neonatal rat brain

Brain Maturation as a Fundamental Factor in Immune-Neurovascular Interactions in Stroke

Injuries in the developing brain cause significant long-term neurological deficits. Emerging clinical and preclinical data have demonstrated that the pathophysiology of neonatal and childhood stroke share similar mechanisms that regulate brain damage, but also have distinct molecular signatures and cellular pathways. The focus of this review is on two different diseases-neonatal and childhood stroke-with emphasis on similarities and distinctions identified thus far in rodent models of these diseases. This includes the susceptibility of distinct cell types to brain injury with particular emphasis on the role of resident and peripheral immune populations in modulating stroke outcome. Furthermore, we discuss some of the most recent and relevant findings in relation to the immune-neurovascular crosstalk and how the influence of inflammatory mediators is dependent on specific brain maturation stages. Finally, we comment on the current state of treatments geared toward inducing neuroprotection and promoting brain repair after injury and highlight that future prophylactic and therapeutic strategies for stroke should be age-specific and consider gender differences in order to achieve optimal translational success.

NMR based Serum metabolomics revealed metabolic signatures associated with oxidative stress and mitochondrial damage in brain stroke

Brain stroke (BS, also known as a cerebrovascular accident), represents a serious global health crisis. It has been a leading cause of permanent disability and unfortunately, frequent fatalities due to lack of timely medical intervention. While progress has been made in prevention and management, the complexities and consequences of stroke continue to pose significant challenges, especially, its impact on patient's quality of life and independence. During stroke, there is a substantial decrease in oxygen supply to the brain leading to alteration of cellular metabolic pathways, including those involved in mitochondrial-damage, leading to mitochondrial-dysfunction. The present proof-of-the-concept metabolomics study has been performed to gain insights into the metabolic pathways altered following a brain stroke and discover new potential targets for timely interventions to mitigate the effects of cellular and mitochondrial damage in BS. The serum metabolic profiles of 108 BS-patients were measured using 800 MHz NMR spectroscopy and compared with 60 age and sex matched normal control (NC) subjects. Compared to NC, the serum levels of glutamate, TCA-cycle intermediates (such as citrate, succinate, etc.), and membrane metabolites (betaine, choline, etc.) were found to be decreased BS patients, whereas those of methionine, mannose, mannitol, phenylalanine, urea, creatine and organic acids (such as 3-hydroxybutyrate and acetone) were found to be elevated in BS patients. These metabolic changes hinted towards hypoxia mediated mitochondrial dysfunction in BS-patients. Further, the area under receiver operating characteristic curve (ROC) values for five metabolic features (methionine, mannitol, phenylalanine, mannose and urea) found to be more than 0.9 suggesting their high sensitivity and specificity for differentiating BS from NC subjects.

Immune-Neurovascular Interactions in Experimental Perinatal and Childhood Arterial Ischemic Stroke

Emerging clinical and preclinical data have demonstrated that the pathophysiology of arterial ischemic stroke in the adult, neonates, and children share similar mechanisms that regulate brain damage but also have distinct molecular signatures and involved cellular pathways due to the maturational stage of the central nervous system and the immune system at the time of the insult. In this review, we discuss similarities and differences identified thus far in rodent models of 2 different diseases-neonatal (perinatal) and childhood arterial ischemic stroke. In particular, we review acquired knowledge of the role of resident and peripheral immune populations in modulating outcomes in models of perinatal and childhood arterial ischemic stroke and the most recent and relevant findings in relation to the immune-neurovascular crosstalk, and how the influence of inflammatory mediators is dependent on specific brain maturation stages. Finally, we discuss the current state of treatments geared toward age-appropriate therapies that signal via the immune-neurovascular interaction and consider sex differences to achieve successful translation.

Stabilizing histamine release in gut mast cells mitigates peripheral and central inflammation after stroke

Stroke is the most common cause of long-term disability and places a high economic burden on the global healthcare system. Functional outcomes from stroke are largely determined by the extent of ischemic injury, however, there is growing recognition that systemic inflammatory responses also contribute to outcomes. Mast cells (MCs) rapidly respond to injury and release histamine (HA), a pro-inflammatory neurotransmitter that enhances inflammation. The gut serves as a major reservoir of HA. We hypothesized that cromolyn, a mast cell stabilizer that prevents the release of inflammatory mediators, would decrease peripheral and central inflammation, reduce MC trafficking to the brain, and improve stroke outcomes. We used the transient middle cerebral artery occlusion (MCAO) model of ischemic stroke in aged (18 mo) male mice to investigate the role of MC in neuroinflammation post-stroke. After MCAO we treated mice with 25 mg/kg body weight of cromolyn (MC stabilizer) by oral gavage. Cromolyn was administered at 3 h, 10 h, 24 h and every 24 h for 3 days post-stroke. Three control groups were used. One group underwent a sham surgery and was treated with cromolyn, one received sham surgery with PBS vehicle and the third underwent MCAO with PBS vehicle. Mice were euthanized at 24 h and 3 days post-stroke. Cromolyn administration significantly reduced MC numbers in the brain at both 24 h and 3 days post-stroke. Infarct volume was not significantly different between groups, however improved functional outcomes were seen at 3 days post-stroke in mice that received cromolyn. Treatment with cromolyn reduced plasma histamine and IL-6 levels in both the 24-h and 3-day cohorts. Gut MCs numbers were significantly reduced after cromolyn treatment at 24 h and 3 days after stroke. To determine if MC trafficking from the gut to the brain occurred after injury, GFP+MCs were adoptively transferred to c-kit-/- MC knock-out animals prior to MCAO. 24 h after stroke, elevated MC recruitment was seen in the ischemic brain. Preventing MC histamine release by cromolyn improved gut barrier integrity and an improvement in stroke-induced dysbiosis was seen with treatment. Our results show that preventing MC histamine release possesses prevents post-stroke neuroinflammation and improves neurological and functional outcomes.

Mast cell-mediated immune regulation in health and disease

Mast cells are important components of the immune system, and they perform pro-inflammatory as well as anti-inflammatory roles in the complex process of immune regulation in health and disease. Because of their strategic perivascular localization, sensitivity and adaptability to the microenvironment, and ability to release a variety of preformed and newly synthesized effector molecules, mast cells perform unique functions in almost all organs. Additionally, Mast cells express a wide range of surface and cytoplasmic receptors which enable them to respond to a variety of cytokines, chemicals, and pathogens. The mast cell's role as a cellular interface between external and internal environments as well as between vasculature and tissues is critical for protection and repair. Mast cell interactions with different immune and nonimmune cells through secreted inflammatory mediators may also turn in favor of disease promoting agents. First and forefront, mast cells are well recognized for their multifaceted functions in allergic diseases. Reciprocal communication between mast cells and endothelial cells in the presence of bacterial toxins in chronic/sub-clinical infections induce persistent vascular inflammation. We have shown that mast cell proteases and histamine induce endothelial inflammatory responses that are synergistically amplified by bacterial toxins. Mast cells have been shown to exacerbate vascular changes in normal states as well as in chronic or subclinical infections, particularly among cigarette smokers. Furthermore, a potential role of mast cells in SARS-CoV-2-induced dysfunction of the capillary-alveolar interface adds to the growing understanding of mast cells in viral infections. The interaction between mast cells and microglial cells in the brain further highlights their significance in neuroinflammation. This review highlights the significant role of mast cells as the interface that acts as sensor and early responder through interactions with cells in systemic organs and the nervous system.

Identification of Differentially Expressed microRNAs Associated with Ischemic Stroke by Integrated Bioinformatics Approaches

Ischemic stroke (IS) is one of the leading causes of disability and mortality worldwide. This study aims to find the crucial exosomal miRNAs associated with IS by using bioinformatics methods, reveal potential biomarkers for IS, and investigate the association between the identified biomarker and immune cell pattern in the peripheral blood of IS patients. In this study, 3 up-regulated miRNAs (hsa-miR-15b-5p, hsa-miR-184, and hsa-miR-16-5p) miRNAs in the serum exosomes between IS patients and healthy controls from GEO database (GSE199942) and 25 down-regulated genes of peripheral blood mononuclear cells of IS patients from GSE22255 were obtained with the help of the R software. GO annotation and KEGG pathway enrichment analysis showed that the 25 down-regulated genes were associated with coenzyme metabolic process and were mainly enriched in the N-glycan biosynthesis pathway. Furthermore, we performed the LASSO algorithm to narrow down the above 25 intersected genes, and identified 8 key genes which had a good diagnostic value in discriminating IS patients from the healthy controls analyzed with ROC curve. CIBERSORT algorithm indicated that the abundance of M0 macrophages and resting mast cells was significantly lower than that of the control group. The spearman correlation analysis showed that STT3A was negatively correlated with the proportion of follicular helper T cells, activated NK cells and resting dendritic cells. Finally, GSE117064 showed that has-miR-16-5p was more advantageous for diagnosing stroke. In conclusion, hsa-miR-15b-5p, hsa-miR-184, and hsa-miR-16-5p are identified as specific related exosomal miRNAs for IS patients. These genes may provide new targets for the early identification of IS.

Potential Role of Intracranial Mast Cells in Neuroinflammation and Neuropathology Associated with Food Allergy

Mast cells (MCs) are the major effector cells of allergic responses and reside throughout the body, including in the brain and meninges. Previously, we showed in a mouse model of subclinical cow's milk allergy that brain MC numbers were elevated in sensitized mice. However, the neurophysiological consequences of intracranial MC accumulation and activation are unclear. We hypothesized that centrally recruited MCs in sensitized mice could be activated by the allergen via the IgE/FcεRI mechanism and increase the blood-brain barrier (BBB) permeability to promote neuroinflammation. Furthermore, we suspected that repeated allergen exposure could sustain MC activation. To investigate our hypothesis, we sensitized C57BL6/J mice to a bovine whey allergen, β-lactoglobulin (BLG), and subsequently placed them on a whey-containing diet for two weeks. MC activity and associated changes in the brain were examined. BLG-sensitized mice showed mobility changes and depression-like behavior with significantly increased MC numbers and histamine levels in select brain regions. IgG extravasation and perivascular astrogliosis were also evident. Importantly, myelin staining revealed cortical demyelination in the BLG-sensitized mice, suggesting a potential neural substrate for their behavioral changes. Our findings support the ability of brain MCs to release histamine and other mediators to increase BBB permeability and facilitate neuroinflammatory responses in the brain.

Histamine in the Crosstalk Between Innate Immune Cells and Neurons: Relevance for Brain Homeostasis and Disease

Histamine is a biogenic amine playing a central role in allergy and peripheral inflammatory reactions and acts as a neurotransmitter and neuromodulator in the brain. In the adult, histamine is produced mainly by mast cells and hypothalamic neurons, which project their axons throughout the brain. Thus, histamine exerts a range of functions, including wakefulness control, learning and memory, neurogenesis, and regulation of glial activity. Histamine is also known to modulate innate immune responses induced by brain-resident microglia cells and peripheral circulating monocytes, and monocyte-derived cells (macrophages and dendritic cells). In physiological conditions, histamine per se causes mainly a pro-inflammatory phenotype while counteracting lipopolysaccharide-induced inflammation both in microglia, monocytes, and monocyte-derived cells. In turn, the activation of the innate immune system can profoundly affect neuronal survival and function, which plays a critical role in the onset and development of brain disorders. Therefore, the dual role of histamine/antihistamines in microglia and monocytes/macrophages is relevant for identifying novel putative therapeutic strategies for brain diseases. This review focuses on the effects of histamine in innate immune responses and the impact on neuronal survival, function, and differentiation/maturation, both in physiological and acute (ischemic stroke) and chronic neurodegenerative conditions (Parkinson's disease).

Systemic mastocytosis: The roles of histamine and its receptors in the central nervous system disorders

Mastocytosis is a rare disease of clonal hematological disorders characterized by a pathological accumulation of Mast Cells (MCs) in different tissues, with variable symptomatology and prognosis. Signs and symptoms of Systemic Mastocytosis (SM) are due to pathological infiltration of MCs and to the release of chemical mediators, mainly histamine. Patients with SM may also present with neurological symptoms or complications. The pathophysiology of these neurological disorders remains uncertain to this day, but it can be associated with the infiltration of tissue mastocytes, release of mastocytes' mediators or both. Moreover, there is a lot to understand about the role of neurological symptoms in SM and knowing, for example, what is the real frequency of neurological disorders in SM and if is present a relation between other SM subtypes, because it has been noted that the alteration of the histamine expression may be an initiating factor for susceptibility, gravity and progression of the epigenetic disease. In this review we explain the possible pathophysiological mechanism about neurological symptomatology found in some patients affected by SM, describing the role of histamine and its receptors in the nervous system and, in light of the results, what the future prospects may be for a more specific course of treatment.

Mast Cell and Astrocyte Hemichannels and Their Role in Alzheimer's Disease, ALS, and Harmful Stress Conditions

Considered relevant during allergy responses, numerous observations have also identified mast cells (MCs) as critical effectors during the progression and modulation of several neuroinflammatory conditions, including Alzheimer’s disease (AD) and amyotrophic lateral sclerosis (ALS). MC granules contain a plethora of constituents, including growth factors, cytokines, chemokines, and mitogen factors. The release of these bioactive substances from MCs occurs through distinct pathways that are initiated by the activation of specific plasma membrane receptors/channels. Here, we focus on hemichannels (HCs) formed by connexins (Cxs) and pannexins (Panxs) proteins, and we described their contribution to MC degranulation in AD, ALS, and harmful stress conditions. Cx/Panx HCs are also expressed by astrocytes and are likely involved in the release of critical toxic amounts of soluble factors—such as glutamate, adenosine triphosphate (ATP), complement component 3 derivate C3a, tumor necrosis factor (TNFα), apoliprotein E (ApoE), and certain miRNAs—known to play a role in the pathogenesis of AD, ALS, and other neurodegenerative disorders. We propose that blocking HCs on MCs and glial cells offers a promising novel strategy for ameliorating the progression of neurodegenerative diseases by reducing the release of cytokines and other pro-inflammatory compounds.

Therapeutic hypothermia reduces inflammation and oxidative stress in the liver after asphyxial cardiac arrest in rats

BACKGROUND

Few studies have evaluated the effects of hypothermia on cardiac arrest (CA)-induced liver damage. This study aimed to investigate the effects of hypothermic therapy on the liver in a rat model of asphyxial cardiac arrest (ACA).

METHODS

Rats were subjected to 5-minute ACA followed by return of spontaneous circulation (RoSC). Body temperature was controlled at 33°C±0.5°C or 37°C±0.5°C for 4 hours after RoSC in the hypothermia group and normothermia group, respectively. Liver tissues in each group were collected at 6 hours, 12 hours, 1 day, and 2 days after RoSC. To examine hepatic inflammation, mast cells were stained with toluidine blue. Superoxide anion radical production was evaluated using dihydroethidium fluorescence straining and expression of endogenous antioxidants (superoxide dismutase 1 [SOD1] and SOD2) was examined using immunohistochemistry.

RESULTS

There were significantly more mast cells in the livers of the normothermia group with ACA than in the hypothermia group with ACA. Gradual increase in superoxide anion radical production was found with time in the normothermia group with ACA, but production was significantly suppressed in the hypothermia group with ACA relative to the normothermia group with ACA. SOD1 and SOD2 levels were higher in the hypothermia group with ACA than in the normothermia group with ACA.

CONCLUSIONS

Experimental hypothermic treatment after ACA significantly inhibited inflammation and superoxide anion radical production in the rat liver, indicating that this treatment enhanced or maintained expression of antioxidants. Our findings suggest that hypothermic therapy after CA can reduce mast cell-mediated inflammation through regulation of oxidative stress and the expression of antioxidants in the liver.

Preventive Effects of Neuroprotective Agents in a Neonatal Rat of Photothrombotic Stroke Model

Neonatal ischemic stroke has a higher incidence than childhood stroke. Seizures are the first sign for the need for clinical assessment in neonates, but many questions remain regarding treatments and follow-up modalities. In the absence of a known pathophysiological mechanism, only supportive care is currently provided. Stroke-induced microglia activation and neuroinflammation are believed to play a central role in the pathological progression of neonatal ischemic stroke. We induced a photothrombotic infarction with Rose Bengal in neonatal rats to investigate the effects of pre- and post-treatment with Aspirin (ASA), Clopidogrel (Clop), and Coenzyme Q10 (CoQ10), which are known for their neuroprotective effects in adult stroke. Pre-stroke medication ameliorates cerebral ischemic injury and reduces infarct volume by reducing microglia activation, cellular reactive oxygen species (ROS) production, and cytokine release. Post-stroke administration of ASA, Clop, and CoQ10 increased motor function and reduced the volume of infarction, and the statistical evidence was stronger than that seen in the pre-stroke treatment. In this study, we demonstrated that ASA, Clop, and CoQ10 treatment before and after the stroke reduced the scope of stroke lesions and increased behavioral activity. It suggests that ASA, Clop, and CoQ10 medication could significantly have neuroprotective effects in the neonates who have suffered strokes.

Age-dependent involvement of gut mast cells and histamine in post-stroke inflammation

BACKGROUND

Risk of stroke-related morbidity and mortality increases significantly with age. Aging is associated with chronic, low-grade inflammation, which is thought to contribute to the poorer outcomes after stroke seen in the elderly. Histamine (HA) is a major molecular mediator of inflammation, and mast cells residing in the gut are a primary source of histamine.

METHODS

Stroke was induced in male C57BL/6 J mice at 3 months (young) and 20 months (aged) of age. Role of histamine after stroke was examined using young (Yg) and aged (Ag) mice; mice underwent MCAO surgery and were euthanized at 6 h, 24 h, and 7 days post-ischemia; sham mice received the same surgery but no MCAO. In this work, we evaluated whether worsened outcomes after experimental stroke in aged mice were associated with age-related changes in mast cells, histamine levels, and histamine receptor expression in the gut, brain, and plasma.

RESULTS

We found increased numbers of mast cells in the gut and the brain with aging. Using the middle cerebral artery occlusion (MCAO) model of ischemic stroke, we demonstrate that stroke leads to increased numbers of gut mast cells and gut histamine receptor expression levels. These gut-centric changes are associated with elevated levels of HA and other pro-inflammatory cytokines including IL-6, G-CSF, TNF-α, and IFN-γ in the peripheral circulation. Our data also shows that post-stroke gut inflammation led to a significant reduction of mucin-producing goblet cells and a loss of gut barrier integrity. Lastly, gut inflammation after stroke is associated with changes in the composition of the gut microbiota as early as 24-h post-stroke.

CONCLUSION

An important theme emerging from our results is that acute inflammatory events following ischemic insults in the brain persist longer in the aged mice when compared to younger animals. Taken together, our findings implicate mast cell activation and histamine signaling as a part of peripheral inflammatory response after ischemic stroke, which are profound in aged animals. Interfering with histamine signaling orally might provide translational value to improve stroke outcome.

An Update of Palmitoylethanolamide and Luteolin Effects in Preclinical and Clinical Studies of Neuroinflammatory Events

The inflammation process represents of a dynamic series of phenomena that manifest themselves with an intense vascular reaction. Neuroinflammation is a reply from the central nervous system (CNS) and the peripheral nervous system (PNS) to a changed homeostasis. There are two cell systems that mediate this process: the glia of the CNS and the lymphocites, monocytes, and macrophages of the hematopoietic system. In both the peripheral and central nervous systems, neuroinflammation plays an important role in the pathogenesis of neurodegenerative diseases, such as Parkinson’s and Alzheimer’s diseases, and in neuropsychiatric illnesses, such as depression and autism spectrum disorders. The resolution of neuroinflammation is a process that allows for inflamed tissues to return to homeostasis. In this process the important players are represented by lipid mediators. Among the naturally occurring lipid signaling molecules, a prominent role is played by the N-acylethanolamines, namely N-arachidonoylethanolamine and its congener N-palmitoylethanolamine, which is also named palmitoylethanolamide or PEA. PEA possesses a powerful neuroprotective and anti-inflammatory power but has no antioxidant effects per se. For this reason, its co-ultramicronization with the flavonoid luteolin is more efficacious than either molecule alone. Inhibiting or modulating the enzymatic breakdown of PEA represents a complementary therapeutic approach to treating neuroinflammation. The aim of this review is to discuss the role of ultramicronized PEA and co-ultramicronized PEA with luteolin in several neurological diseases using preclinical and clinical approaches.

Histamine Induces Microglia Activation and the Release of Proinflammatory Mediators in Rat Brain Via H1R or H4R

Histamine is a major peripheral inflammatory mediator and a neurotransmitter in the central nervous system. We have reported that histamine induces microglia activation and releases proinflammatory factors in primary cultured microglia. Whether histamine has similar effects in vivo is unknown. In the present study, we aimed to investigate the role of histamine and its receptors in the release of inflammatory mediators and activation of microglia in rat brain. We site-directed injected histamine, histamine receptor agonists or histamine receptor antagonists in the rat lateral ventricle using stereotaxic techniques. Flow cytometry was employed to determine histamine receptor expression in rat microglia. Microglia activation was assessed by Iba1 immunohistochemistry. The levels of tumour necrosis factor-alpha (TNF-α), interleukin-1beta (IL-1β) and interleukin-10 (IL-10) were measured with commercial enzyme-linked immunosorbent assay (ELISA) kits, TNF-α, IL-1β and IL-10 mRNA expressions were determined with Quantitative Real-Time Polymerase Chain Reaction (qRT-PCR). We found that all four types of histamine receptors were expressed in rat brain microglia. Histamine was able to induce microglia activation and subsequent production of the inflammatory factors TNF-α, IL-1β and IL-10, and these effects were partially abolished by H₁R and H₄R antagonists. However, H₂R and H₃R antagonists significantly increased production of TNF-α and IL-1β, and decreased IL-10 levels. The H₁R or H₄R agonists stimulated the production of TNF-α and IL-1β, while the H₂R or H₃R agonists increased IL-10 release. Our results demonstrate that histamine induces microglia activation and the release of both proinflammatory and anti-inflammatory factors in rat brain, thus contributing to the development of inflammation in the brain. Graphical Abstract Histamine induces microglia activation and the release of both proinflammatory (TNF-α and IL-1β) and anti-inflammatory factors (IL-10) in rat brain, thus contributing to the development of inflammation in the brain.

The Role of Mast Cells in Intracerebral Hemorrhage

Mast cells are first responders to intracerebral hemorrhage. They release potent mediators that can disrupt the blood-brain barrier promoting injury, vasogenic edema formation, and hematoma exacerbation. Also, mast cells recruit other inflammatory cells that maintain and amplify brain damage. Given their early role in the cascade of events in intracerebral hemorrhage, mast cells may offer an alternative target for antichemotactic interventions.

Neuroimmune responses in the developing brain following traumatic brain injury

Traumatic brain injury (TBI) is one of the leading causes of both acute and long-term morbidity in the pediatric population, leading to a substantial, long-term socioeconomic burden. Despite the increase in the amount of pre-clinical and clinical research, treatment options for TBI rely heavily on supportive care with very limited targeted interventions that improve the acute and chronic sequelae of TBI. Other than injury prevention, not much can be done to limit the primary injury, which consists of tissue damage and cellular destruction. Secondary injury is the result of the ongoing complex inflammatory pathways that further exacerbate tissue damage, resulting in the devastating chronic outcomes of TBI. On the other hand, some level of inflammation is essential for neuronal regeneration and tissue repair. In this review article we discuss the various stages of the neuroimmune response in the immature, pediatric brain in the context of normal maturation and development of the immune system. The developing brain has unique features that distinguish it from the adult brain, and the immune system plays an integral role in CNS development. Those features could potentially make the developing brain more susceptible to worse outcomes, both acutely and in the long-term. The neuroinflammatory reaction which is triggered by TBI can be described as a highly intricate interaction between the cells of the innate and the adaptive immune systems. The innate immune system is triggered by non-specific danger signals that are released from damaged cells and tissues, which in turn leads to neutrophil infiltration, activation of microglia and astrocytes, complement release, as well as histamine release by mast cells. The adaptive immune response is subsequently activated leading to the more chronic effects of neuroinflammation. We will also discuss current attempts at modulating the TBI-induced neuroinflammatory response. A better understanding of the role of the immune system in normal brain development and how immune function changes with age is crucial for designing therapies to appropriately target the immune responses following TBI in order to enhance repair and plasticity.

The Role of Mast Cells in Stroke

Mast cells (MCs) are densely granulated perivascular resident cells of hematopoietic origin. Through the release of preformed mediators stored in their granules and newly synthesized molecules, they are able to initiate, modulate, and prolong the immune response upon activation. Their presence in the central nervous system (CNS) has been documented for more than a century. Over the years, MCs have been associated with various neuroinflammatory conditions of CNS, including stroke. They can exacerbate CNS damage in models of ischemic and hemorrhagic stroke by amplifying the inflammatory responses and promoting brain–blood barrier disruption, brain edema, extravasation, and hemorrhage. Here, we review the role of these peculiar cells in the pathophysiology of stroke, in both immature and adult brain. Further, we discuss the role of MCs as potential targets for the treatment of stroke and the compounds potentially active as MCs modulators.

Meningeal Mast Cells as Key Effectors of Stroke Pathology

Stroke is the leading cause of adult disability in the United States. Because post-stroke inflammation is a critical determinant of damage and recovery after stroke, understanding the interplay between the immune system and the brain after stroke holds much promise for therapeutic intervention. An understudied, but important aspect of this interplay is the role of meninges that surround the brain. All blood vessels travel through the meningeal space before entering the brain parenchyma, making the meninges ideally located to act as an immune gatekeeper for the underlying parenchyma. Emerging evidence suggests that the actions of immune cells resident in the meninges are essential for executing this gatekeeper function. Mast cells (MCs), best known as proinflammatory effector cells, are one of the long-term resident immune cells in the meninges. Here, we discuss recent findings in the literature regarding the role of MCs located in the meningeal space and stroke pathology. We review the latest advances in mouse models to investigate the roles of MCs and MC-derived products in vivo, and the importance of using these mouse models. We examine the concept of the meninges playing a critical role in brain and immune interactions, reevaluate the perspectives on the key effectors of stroke pathology, and discuss the opportunities and challenges for therapeutic development.

Mast cell disorders: From infancy to maturity

Mast cells are typically linked to immediate hypersensitivity and anaphylaxis. This review looks beyond this narrow role, focusing on how these cells have evolved and diversified via natural selection promoting serine protease gene duplication, augmenting their innate host defense function against helminths and snake envenomation. Plasticity of mast cell genes has come at a price. Somatic activating mutations in the mast cell growth factor KIT gene cause cutaneous mastocytosis in young children and systemic mastocytosis with a more guarded prognosis in adults who may also harbor other gene mutations with oncogenic potential as they age. Allelic TPSAB1 gene duplication associated with higher basal mast cell tryptase is possibly one of the commonest autosomal dominantly inherited multi-system diseases affecting the skin, gastrointestinal tract, circulation and musculoskeletal system. Mast cells are also establishing a new-found importance in severe asthma, and in remodeling of blood vessels in cancer and atherosclerotic vascular disease. Furthermore, recent evidence suggests that mast cells sense changes in oxygen tension, particularly in neonates, and that subsequent degranulation may contribute to common lung, eye, and brain diseases of prematurity classically associated with hypoxic insults. One hundred and forty years since Paul Ehrlich's initial description of "mastzellen," this review collates and highlights the complex and diverse roles that mast cells play in health and disease.

Perinatal arterial ischemic stroke

Perinatal arterial ischemic stroke is a relatively common and serious neurologic disorder that can affect the fetus, the preterm, and the term-born infant. It carries significant long-term disabilities. Herein we describe the current understanding of its etiology, pathophysiology and classification, different presentations, and optimal early management. We discuss the role of different brain imaging modalities in defining the extent of lesions and the impact this has on the prediction of outcomes. In recent years there has been progress in treatments, making early diagnosis and the understanding of likely morbidities imperative. An overview is given of the range of possible outcomes and optimal approaches to follow-up and support for the child and their family in the light of present knowledge.

A Model of Perinatal Ischemic Stroke in the Rat: 20 Years Already and What Lessons?

Neonatal hypoxia-ischemia (HI) and ischemia are a common cause of neonatal brain injury resulting in cerebral palsy with subsequent learning disabilities and epilepsy. Recent data suggest a higher incidence of focal ischemia-reperfusion located in the middle cerebral artery (MCA) territory in near-term and newborn babies. Pre-clinical studies in the field of cerebral palsy research used, and still today, the classical HI model in the P7 rat originally described by Rice et al. (1). At the end of the 90s, we designed a new model of focal ischemia in the P7 rat to explore the short and long-term pathophysiology of neonatal arterial ischemic stroke, particularly the phenomenon of reperfusion injury and its sequelae (reported in 1998). Cerebral blood-flow and cell death/damage correlates have been fully characterized. Pharmacologic manipulations have been applied to the model to test therapeutic targets. The model has proven useful for the study of seizure occurrence, a clinical hallmark for neonatal ischemia in babies. Main pre-clinical findings obtained within these 20 last years are discussed associated to clinical pattern of neonatal brain damage.

Oral sensitization to whey proteins induces age- and sex-dependent behavioral abnormality and neuroinflammatory responses in a mouse model of food allergy: a potential role of mast cells

BACKGROUND

Growing evidence has strengthened the association of food allergy with neuropsychiatric symptoms such as depression, anxiety, and autism. However, underlying mechanisms by which peripheral allergic responses lead to behavioral dysfunction are yet to be determined. Allergen-activated mast cells may serve as mediators by releasing histamine and other inflammatory factors that could adversely affect brain function. We hypothesized that eliciting food allergy in experimental animals would result in behavioral changes accompanied by mast cell accumulation in the brain. Our hypothesis was tested in a mouse model of milk allergy using bovine milk whey proteins (WP) as the allergen.

METHODS

Male and female C57BL/6 mice at 4 weeks (young) and 10 months (old) of age underwent 5-week WP sensitization with weekly intragastric administration of 20 mg WP and 10 μg cholera toxin as an adjuvant. Age-matched sham animals were given the vehicle containing only the adjuvant. All animals were orally challenged with 50 mg WP in week 6 and their intrinsic digging behavior was assessed the next day. Animals were sacrificed 3 days after the challenge, and WP-specific serum IgE, intestinal and brain mast cells, glial activation, and epigenetic DNA modification in the brain were examined.

RESULTS

WP-sensitized males showed significantly less digging activity than the sham males in both age groups while no apparent difference was observed in females. Mast cells and their activities were evident in the intestines in an age- and sex-dependent manner. Brain mast cells were predominantly located in the region between the lateral midbrain and medial hippocampus, and their number increased in the WP-sensitized young, but not old, male brains. Noticeable differences in for 5-hydroxymethylcytosine immunoreactivity were observed in WP mice of both age groups in the amygdala, suggesting epigenetic regulation. Increased microglial Iba1 immunoreactivity and perivascular astrocytes hypertrophy were also observed in the WP-sensitized old male mice.

CONCLUSIONS

Our results demonstrated that food allergy induced behavioral abnormality, increases in the number of mast cells, epigenetic DNA modification in the brain, microgliosis, and astrocyte hypertrophy in a sex- and age-dependent manner, providing a potential mechanism by which peripheral allergic responses evoke behavioral dysfunction.

An Inflammation-Centric View of Neurological Disease: Beyond the Neuron

Inflammation is a complex biological response fundamental to how the body deals with injury and infection to eliminate the initial cause of cell injury and effect repair. Unlike a normally beneficial acute inflammatory response, chronic inflammation can lead to tissue damage and ultimately its destruction, and often results from an inappropriate immune response. Inflammation in the nervous system (“neuroinflammation”), especially when prolonged, can be particularly injurious. While inflammation per se may not cause disease, it contributes importantly to disease pathogenesis across both the peripheral (neuropathic pain, fibromyalgia) and central [e.g., Alzheimer disease, Parkinson disease, multiple sclerosis, motor neuron disease, ischemia and traumatic brain injury, depression, and autism spectrum disorder] nervous systems. The existence of extensive lines of communication between the nervous system and immune system represents a fundamental principle underlying neuroinflammation. Immune cell-derived inflammatory molecules are critical for regulation of host responses to inflammation. Although these mediators can originate from various non-neuronal cells, important sources in the above neuropathologies appear to be microglia and mast cells, together with astrocytes and possibly also oligodendrocytes. Understanding neuroinflammation also requires an appreciation that non-neuronal cell—cell interactions, between both glia and mast cells and glia themselves, are an integral part of the inflammation process. Within this context the mast cell occupies a key niche in orchestrating the inflammatory process, from initiation to prolongation. This review will describe the current state of knowledge concerning the biology of neuroinflammation, emphasizing mast cell-glia and glia-glia interactions, then conclude with a consideration of how a cell's endogenous mechanisms might be leveraged to provide a therapeutic strategy to target neuroinflammation.

Mast Cell Activation in Brain Injury, Stress, and Post-traumatic Stress Disorder and Alzheimer's Disease Pathogenesis

Mast cells are localized throughout the body and mediate allergic, immune, and inflammatory reactions. They are heterogeneous, tissue-resident, long-lived, and granulated cells. Mast cells increase their numbers in specific site in the body by proliferation, increased recruitment, increased survival, and increased rate of maturation from its progenitors. Mast cells are implicated in brain injuries, neuropsychiatric disorders, stress, neuroinflammation, and neurodegeneration. Brain mast cells are the first responders before microglia in the brain injuries since mast cells can release prestored mediators. Mast cells also can detect amyloid plaque formation during Alzheimer's disease (AD) pathogenesis. Stress conditions activate mast cells to release prestored and newly synthesized inflammatory mediators and induce increased blood-brain barrier permeability, recruitment of immune and inflammatory cells into the brain and neuroinflammation. Stress induces the release of corticotropin-releasing hormone (CRH) from paraventricular nucleus of hypothalamus and mast cells. CRH activates glial cells and mast cells through CRH receptors and releases neuroinflammatory mediators. Stress also increases proinflammatory mediator release in the peripheral systems that can induce and augment neuroinflammation. Post-traumatic stress disorder (PTSD) is a traumatic-chronic stress related mental dysfunction. Currently there is no specific therapy to treat PTSD since its disease mechanisms are not yet clearly understood. Moreover, recent reports indicate that PTSD could induce and augment neuroinflammation and neurodegeneration in the pathogenesis of neurodegenerative diseases. Mast cells play a crucial role in the peripheral inflammation as well as in neuroinflammation due to brain injuries, stress, depression, and PTSD. Therefore, mast cells activation in brain injury, stress, and PTSD may accelerate the pathogenesis of neuroinflammatory and neurodegenerative diseases including AD. This review focusses on how mast cells in brain injuries, stress, and PTSD may promote the pathogenesis of AD. We suggest that inhibition of mast cells activation and brain cells associated inflammatory pathways in the brain injuries, stress, and PTSD can be explored as a new therapeutic target to delay or prevent the pathogenesis and severity of AD.

Impact of Inflammation on the Blood-Neural Barrier and Blood-Nerve Interface: From Review to Therapeutic Preview

A number of nervous system disorders are characterized by a state of inflammation (neuroinflammation) in which members of the innate immune system, most notably mast cells and microglia-acting as single entities and in unison-produce inflammatory molecules that play major roles. A neuroinflammatory environment can weaken not only blood-nerve and blood-brain barrier (BBB) integrity but also that of the blood-spinal cord barrier. Mast cells, with their distribution in peripheral nerves and the central nervous system, are positioned to influence blood-nerve barrier characteristics. Being close also to the perivasculature and on the brain side of the BBB, the mast cell is well positioned to disrupt BBB function. Interestingly, tissue damage and/or stress activates homeostatic mechanisms/molecules expressed by mast cells and microglia, and includes N-acylethanolamines. Among the latter, N-palmitoylethanolamine has distinguished itself as a key component in supporting homeostasis of the organism against external stressors capable of provoking inflammation. This review will discuss the pathobiology of neuroinflammation with emphasis on mast cells and microglia, their roles in BBB health, and novel therapeutic opportunities, including nanoscale delivery for targeting these immune cells with a view to maintain the BBB.

Immune responses in perinatal brain injury

The perinatal period has often been described as immune deficient. However, it has become clear that immune responses in the neonate following exposure to microbes or as a result of tissue injury may be substantial and play a role in perinatal brain injury. In this article we will review the immune cell composition under normal physiological conditions in the perinatal period, both in the human and rodent. We will summarize evidence of the inflammatory responses to stimuli and discuss how neonatal immune activation, both in the central nervous system and in the periphery, may contribute to perinatal hypoxic-ischemic brain injury.

S1P receptor 1-Mediated Anti-Renin-Angiotensin System Cardioprotection: Pivotal Role of Mast Cell Aldehyde Dehydrogenase Type 2

In the ischemic-reperfused (I/R) heart, renin-containing mast cells (MC) release enzymatically active renin, activating a local renin-angiotensin system (RAS), causing excessive norepinephrine release and arrhythmic dysfunction. Activation of G_i-receptors on MC and/or ischemic preconditioning (IPC) prevent renin release, thus providing anti-RAS cardioprotection. We questioned whether sphingosine-1-phosphate (S1P), a sphingolipid produced in the I/R heart, might afford anti-RAS cardioprotection by activating G_i-coupled S1P₁ receptors (S1P₁R) on MC. We report that activation of G_i-coupled S1P₁R in cardiac MC confers IPC-like anti-RAS cardioprotection due to S1P₁R-mediated inhibition of I/R-induced cardiac MC degranulation and renin release. This results from an initial translocation of protein kinase C subtype-ε and subsequent activation of aldehyde dehydrogenase type 2 (ALDH2), culminating in the elimination of the MC-degranulating effects of acetaldehyde and other toxic species produced during I/R. Inhibition of toxic aldehydes-induced MC-renin release prevents local RAS activation, reduces infarct size, and alleviates arrhythmias. Notably, these cardioprotective effects are lacking in hearts and MC from gene-targeted knock-in mice (ALDH2*2) in which ALDH2 enzymatic activity is maximally reduced. Thus, ALDH2 appears to play a pivotal role in this protective process. Our findings suggest that MC S1P₁R may represent a new pharmacologic and therapeutic target for the direct alleviation of RAS-induced cardiac dysfunctions, including ischemic heart disease and congestive heart failure.

Neuroinflammation, Mast Cells, and Glia: Dangerous Liaisons

The perspective of neuroinflammation as an epiphenomenon following neuron damage is being replaced by the awareness of glia and their importance in neural functions and disorders. Systemic inflammation generates signals that communicate with the brain and leads to changes in metabolism and behavior, with microglia assuming a pro-inflammatory phenotype. Identification of potential peripheral-to-central cellular links is thus a critical step in designing effective therapeutics. Mast cells may fulfill such a role. These resident immune cells are found close to and within peripheral nerves and in brain parenchyma/meninges, where they exercise a key role in orchestrating the inflammatory process from initiation through chronic activation. Mast cells and glia engage in crosstalk that contributes to accelerate disease progression; such interactions become exaggerated with aging and increased cell sensitivity to stress. Emerging evidence for oligodendrocytes, independent of myelin and support of axonal integrity, points to their having strong immune functions, innate immune receptor expression, and production/response to chemokines and cytokines that modulate immune responses in the central nervous system while engaging in crosstalk with microglia and astrocytes. In this review, we summarize the findings related to our understanding of the biology and cellular signaling mechanisms of neuroinflammation, with emphasis on mast cell-glia interactions.

Contribution of mast cells to injury mechanisms in a mouse model of pediatric traumatic brain injury

The cognitive and behavioral deficits caused by traumatic brain injury (TBI) to the immature brain are more severe and persistent than injuries to the adult brain. Understanding this developmental sensitivity is critical because children under 4 years of age of sustain TBI more frequently than any other age group. One of the first events after TBI is the infiltration and degranulation of mast cells (MCs) in the brain, releasing a range of immunomodulatory substances; inhibition of these cells is neuroprotective in other types of neonatal brain injury. This study investigates for the first time the role of MCs in mediating injury in a P7 mouse model of pediatric contusion-induced TBI. We show that various neural cell types express histamine receptors and that histamine exacerbates excitotoxic cell death in primary cultured neurons. Cromoglycate, an inhibitor of MC degranulation, altered the inflammatory phenotype of microglia activated by TBI, reversing several changes but accentuating others, when administered before TBI. However, without regard to the time of cromoglycate administration, inhibiting MC degranulation did not affect cell loss, as evaluated by ventricular dilatation or cleaved caspase-3 labeling, or the density of activated microglia, neurons, or myelin. In double-heterozygous cKit mutant mice lacking MCs, this overall lack of effect was confirmed. These results suggest that the role of MCs in this model of pediatric TBI is restricted to subtle effects and that they are unlikely to be viable neurotherapeutic targets. © 2016 Wiley Periodicals, Inc.

Dexmedetomidine alleviates the spinal cord ischemia-reperfusion injury through blocking mast cell degranulation

OBJECTIVE

To investigate the neuro-protective effects of dexmedetomidine (dex) on I/R-induced spinal injury and potential mechanisms.

METHODS

sprague-Dawley rats in the treatment group received intraperitoneal injections of 25 mg/kg dexmedetomidine, MC stabilizer cromolyn (100 mg/kg), MCs stimuliser compound 48/80 (80 mg/kg), PBS at 24 h befor IR. Underwent 5 minutes of aortic occlusion via median sternotomy, functional scores were recorded at 12, 24, 36 and 48 hours after reperfusion. Additionally, 3 mice underwent sham surgery with sternotomy and dissection of the aorta and subclavian artery with no occlusion. Spinal cords were examined for protein kinase B (AKT), CREB, and brain-derived neurotrophic factor (BDNF) following treatment alone or ischemia-reperfusion surgery. Collected the serum to observe the expression of pro-inflammation cytokines (TNF-α, INF-γ and IL-1β) and anti-inflammation cytokines (TGF-β, IL-10 and IL-6). Then the MCs were harvested to test the expression surface molecular of FcεR and MCs' degranulation.

RESULTS

Pretreated the rats with dexmedetomidine has higher neurologic function at all time points after I/R injury. We collected the serum of rats then detected the pro-inflammation cytokines TNF-α, INF-γ and IL-1β levels and anti-inflammation cytokinses TGF-β, IL-10 and IL-6 levels, found that the pro-inflammation cytokines of dexmedetomidine group was decreased whereas the anti-inflammation cytokinses was increased. At the same time the protect protein of AKT, CREB and mRNA BDNF were increased. They had the same results with cromolyn group, and opposite with the compound 48/80 group. We pretreated MCs with dexmedetomidine in vitro, and found that the activity surface molecular of MCs was down-regulation, and MCs degranulation was decreased.

CONCLUSION

We thus demonstrate a possible mechanism by which dexmedetomidine alleviates spinal cord I/R injury through blocking the MCs degranulation.

Neonatal encephalopathy: pre-clinical studies in neuroprotection

Neonatal encephalopathy resulting from HI (hypoxia-ischaemia) continues to be a significant cause of mortality and morbidity in infants and children, affecting 1-2/1000 live term births and up to 60% of pre-term births. In order to understand the pathophysiology of this insult, as well as design therapeutic interventions, it is important to establish a relevant animal model for pre-clinical studies. One of the most frequently used models of HI-induced brain damage in immature animals is the unilateral carotid ligation/hypoxia model, initially developed in our laboratory more than 30 years ago. The original model employed the postnatal day 7 rat, whose brain is representative of that of a late gestation, pre-term [32-36 weeks GA (gestational age)] human infant. We, and others, have employed this model to characterize the pathophysiological, biochemical/energetic and neuropathological events following HI, as well as the determination of the unique characteristics of the immature brain that define its vulnerability to, and outcome from, HI. In defining the cascade of events following HI, it has become possible to identify potential targets for intervention and neuroprotection. Currently, the only available therapeutic intervention for neonatal encephalopathy in the term asphyxiated infant is therapeutic hypothermia, although this must be initiated within 6 h of birth and is at best partially effective in moderately injured infants. Ongoing pre-clinical studies are necessary to determine the basis for the partial protection afforded by hypothermia as well as the design of adjunct therapies to improve the outcome. The present review highlights the importance of using a well-characterized and relevant animal model to continue to pursue translational research in neuroprotection for the infant brain.

Evidence that meningeal mast cells can worsen stroke pathology in mice

Stroke is the leading cause of adult disability and the fourth most common cause of death in the United States. Inflammation is thought to play an important role in stroke pathology, but the factors that promote inflammation in this setting remain to be fully defined. An understudied but important factor is the role of meningeal-located immune cells in modulating brain pathology. Although different immune cells traffic through meningeal vessels en route to the brain, mature mast cells do not circulate but are resident in the meninges. With the use of genetic and cell transfer approaches in mice, we identified evidence that meningeal mast cells can importantly contribute to the key features of stroke pathology, including infiltration of granulocytes and activated macrophages, brain swelling, and infarct size. We also obtained evidence that two mast cell-derived products, interleukin-6 and, to a lesser extent, chemokine (C-C motif) ligand 7, can contribute to stroke pathology. These findings indicate a novel role for mast cells in the meninges, the membranes that envelop the brain, as potential gatekeepers for modulating brain inflammation and pathology after stroke.

The role of inflammation in perinatal brain injury

Inflammation is increasingly recognized as being a critical contributor to both normal development and injury outcome in the immature brain. The focus of this Review is to highlight important differences in innate and adaptive immunity in immature versus adult brain, which support the notion that the consequences of inflammation will be entirely different depending on context and stage of CNS development. Perinatal brain injury can result from neonatal encephalopathy and perinatal arterial ischaemic stroke, usually at term, but also in preterm infants. Inflammation occurs before, during and after brain injury at term, and modulates vulnerability to and development of brain injury. Preterm birth, on the other hand, is often a result of exposure to inflammation at a very early developmental phase, which affects the brain not only during fetal life, but also over a protracted period of postnatal life in a neonatal intensive care setting, influencing critical phases of myelination and cortical plasticity. Neuroinflammation during the perinatal period can increase the risk of neurological and neuropsychiatric disease throughout childhood and adulthood, and is, therefore, of concern to the broader group of physicians who care for these individuals.

Mast cells promote blood brain barrier breakdown and neutrophil infiltration in a mouse model of focal cerebral ischemia

Blood brain barrier (BBB) breakdown and neuroinflammation are key events in ischemic stroke morbidity and mortality. The present study investigated the effects of mast cell deficiency and stabilization on BBB breakdown and neutrophil infiltration in mice after transient middle cerebral artery occlusion (tMCAo). Adult male C57BL6/J wild type (WT) and mast cell-deficient (C57BL6/J Kit(Wsh/Wsh) (Wsh)) mice underwent tMCAo and BBB breakdown, brain edema and neutrophil infiltration were examined after 4 hours of reperfusion. Blood brain barrier breakdown, brain edema, and neutrophil infiltration were significantly reduced in Wsh versus WT mice (P<0.05). These results were reproduced pharmacologically using mast cell stabilizer, cromoglycate. Wild-type mice administered cromoglycate intraventricularly exhibited reduced BBB breakdown, brain edema, and neutrophil infiltration versus vehicle (P<0.05). There was no effect of cromoglycate versus vehicle in Wsh mice, validating specificity of cromoglycate on brain mast cells. Proteomic analysis in Wsh versus WT indicated that effects may be via expression of endoglin, endothelin-1, and matrix metalloproteinase-9. Using an in vivo model of mast cell deficiency, this is the first study showing that mast cells promote BBB breakdown in focal ischemia in mice, and opens up future opportunities for using mice to identify specific mechanisms of mast cell-related BBB injury.

Preconditioning donor livers with cromolyn or compound 48/80 prolongs recipient survival in a rat orthotopic liver transplantation model

BACKGROUND

Acute rejection (AR) remains a challenge in organ transplantation. Preconditioning donor organs can reduce AR and prolong survival. Whether preconditioning with cromolyn (CRM), a mast cell (MC) stabilizer, or compound 48/80 (CMP 48/80), a MC degranulator, can alleviate AR and prolong survival has not been studied.

METHODS

We used the male-DA-to-female-Lewis-rat orthotopic liver transplantation (OLT) model. Donors were preconditioned with CRM in a MC stabilizing way (CRM group) or CMP 48/80 in a MC depleting way (CMP 48/80 group). Rats preconditioned with phosphate-buffered saline were used as controls (PBS group). After preconditioning, OLT surgeries were carried out. OLT male-Lewis-to-female-Lewis-rats were used as the syngeneic group (syngeneic group).

RESULTS

Rats in the PBS group developed AR rapidly and died at 7.40 ± 1.14 days. Rats in the CRM and CMP 48/80 groups had significantly slower rejections and died at day 17.40 ± 1.67 or 14.20 ± 2.28, respectively (P < .05). Rats in the syngeneic group survived more than 60 days. Rejection activity indexes (RAIs) and liver functions were all alleviated through CRM or CMP 48/80 preconditioning. Interferon-γ messenger RNA (mRNA) expressions were reduced and interleukin-10 mRNA levels were higher in allografts in the CRM and CMP 48/80 groups, compared with the PBS group. These were confirmed by testing serum interferon-γ and interlerkin-10.

CONCLUSION

Preconditioning donor livers with CRM or CMP 48/80 can reduce AR and prolong survival of recipients after OLT.

Blood-brain barrier dysfunction in disorders of the developing brain

Disorders of the developing brain represent a major health problem. The neurological manifestations of brain lesions can range from severe clinical deficits to more subtle neurological signs or behavioral problems and learning disabilities, which often become evident many years after the initial damage. These long-term sequelae are due at least in part to central nervous system immaturity at the time of the insult. The blood-brain barrier (BBB) protects the brain and maintains homeostasis. BBB alterations are observed during both acute and chronic brain insults. After an insult, excitatory amino acid neurotransmitters are released, causing reactive oxygen species (ROS)-dependent changes in BBB permeability that allow immune cells to enter and stimulate an inflammatory response. The cytokines, chemokines and other molecules released as well as peripheral and local immune cells can activate an inflammatory cascade in the brain, leading to secondary neurodegeneration that can continue for months or even years and finally contribute to post-insult neuronal deficits. The role of the BBB in perinatal disorders is poorly understood. The inflammatory response, which can be either acute (e.g., perinatal stroke, traumatic brain injury) or chronic (e.g., perinatal infectious diseases) actively modulates the pathophysiological processes underlying brain injury. We present an overview of current knowledge about BBB dysfunction in the developing brain during acute and chronic insults, along with clinical and experimental data.

Barrier mechanisms in neonatal stroke

Clinical data continue to reveal that the incidence of perinatal stroke is high, similar to that in the elderly. Perinatal stroke leads to significant morbidity and severe long-term neurological and cognitive deficits, including cerebral palsy. Experimental models of cerebral ischemia in neonatal rodents have shown that the pathophysiology of perinatal brain damage is multifactorial. Cerebral vasculature undergoes substantial structural and functional changes during early postnatal brain development. Thus, the state of the vasculature could affect susceptibility of the neonatal brain to cerebral ischemia. In this review, we discuss some of the most recent findings regarding the neurovascular responses of the immature brain to focal arterial stroke in relation to neuroinflammation. We also discuss a possible role of the neonatal blood-CSF barrier in modulating inflammation and the long-term effects of early neurovascular integrity after neonatal stroke on angiogenesis and neurogenesis.

E-NTPDase1/CD39 modulates renin release from heart mast cells during ischemia/reperfusion: a novel cardioprotective role

Ischemia/reperfusion (I/R) elicits renin release from cardiac mast cells (MC), thus activating a local renin-angiotensin system (RAS), culminating in ventricular fibrillation. We hypothesized that in I/R, neurogenic ATP could degranulate juxtaposed MC and that ecto-nucleoside triphosphate diphosphohydrolase 1/CD39 (CD39) on MC membrane could modulate ATP-induced renin release. We report that pharmacological inhibition of CD39 in a cultured human mastocytoma cell line (HMC-1) and murine bone marrow-derived MC with ARL67156 (100 µM) increased ATP-induced renin release (≥2-fold), whereas purinergic P2X7 receptors (P2X7R) blockade with A740003 (3 µM) prevented it. Likewise, CD39 RNA silencing in HMC-1 increased ATP-induced renin release (≥2-fold), whereas CD39 overexpression prevented it. Acetaldehyde, an I/R product (300 µM), elicited an 80% increase in ATP release from HMC-1, in turn, causing an autocrine 20% increase in renin release. This effect was inhibited or potentiated when CD39 was overexpressed or silenced, respectively. Moreover, P2X7R silencing prevented ATP- and acetaldehyde-induced renin release. I/R-induced RAS activation in ex vivo murine hearts, characterized by renin and norepinephrine overflow and ventricular fibrillation, was potentiated (∼2-fold) by CD39 inhibition, an effect prevented by P2X7R blockade. Our data indicate that by regulating ATP availability at the MC surface, CD39 modulates local renin release and thus, RAS activation, ultimately exerting a cardioprotective effect.

The role of mast cells in ischemia and reperfusion injury

INTRODUCTION

Ischemia and reperfusion (IR) injury is a challenging clinical problem that is triggered by ischemia in an organ followed by subsequent restoration of the blood supply. The effects of mast cell (MC) in IR injury are not totally clear.

MATERIALS AND METHODS

We review the body of literature on the role of MCs in IR injury based on an unrestricted Pubmed search for the descriptors "mast cell", "ischemia" and "reperfusion injury", as well as discuss implications for treatment and future directions.

RESULTS

Shortly after IR, chemicals released by MC can trigger vasoactive substance formation, tissue leakage, upregulation of adhesive molecules followed by leukocyte recruitment and infiltration, and pronecrotic pathway activation, among other physiologic changes. In the long term, MCs may influence tissue remodeling and repair as well as blood restoration after IR. Consistent with these findings, methods and drugs that target MCs have been shown to attenuate IR injury.

CONCLUSION

It has been demonstrated that MCs play a role in IR injury, but the mechanisms are complex and need to be further studied.

Histamine H4-receptors inhibit mast cell renin release in ischemia/reperfusion via protein kinase C ε-dependent aldehyde dehydrogenase type-2 activation

Renin released by ischemia/reperfusion (I/R) from cardiac mast cells (MCs) activates a local renin-angiotensin system (RAS) causing arrhythmic dysfunction. Ischemic preconditioning (IPC) inhibits MC renin release and consequent activation of this local RAS. We postulated that MC histamine H4-receptors (H4Rs), being Gαi/o-coupled, might activate a protein kinase C isotype-ε (PKCε)-aldehyde dehydrogenase type-2 (ALDH2) cascade, ultimately eliminating MC-degranulating and renin-releasing effects of aldehydes formed in I/R and associated arrhythmias. We tested this hypothesis in ex vivo hearts, human mastocytoma cells, and bone marrow-derived MCs from wild-type and H4R knockout mice. We found that activation of MC H4Rs mimics the cardioprotective anti-RAS effects of IPC and that protection depends on the sequential activation of PKCε and ALDH2 in MCs, reducing aldehyde-induced MC degranulation and renin release and alleviating reperfusion arrhythmias. These cardioprotective effects are mimicked by selective H4R agonists and disappear when H4Rs are pharmacologically blocked or genetically deleted. Our results uncover a novel cardioprotective pathway in I/R, whereby activation of H4Rs on the MC membrane, possibly by MC-derived histamine, leads sequentially to PKCε and ALDH2 activation, reduction of toxic aldehyde-induced MC renin release, prevention of RAS activation, reduction of norepinephrine release, and ultimately to alleviation of reperfusion arrhythmias. This newly discovered protective pathway suggests that MC H4Rs may represent a new pharmacologic and therapeutic target for the direct alleviation of RAS-induced cardiac dysfunctions, including ischemic heart disease and congestive heart failure.

A focus on mast cells and pain

Mast cells (MCs) are immunocytes with secretory functions that act locally in peripheral tissues to modulate local hemodynamics, nociceptor activation and pain. They are also able to infiltrate the central nervous system (CNS), especially the spinal cord and the thalamus, but their cerebral function remains an enigma. A role in regulating the opening of the blood-brain barrier has been proposed. Paracrine-like action of MCs on synaptic transmission might also signal a modulation of the nervous system by the immune system. In this review, we examine the link between MCs and nociceptive process, at the periphery as well as in the CNS.

Mast cell degranulation promotes ischemia-reperfusion injury in rat liver

BACKGROUND

Mast cells (MCs) play a role in ischemia-reperfusion (I/R) injury in many organs. However, a recent study found that MCs are not involved in I/R injury in isolated rat livers that were perfused only for 1 h. The purpose of this study is to reevaluate the role of MCs in hepatic I/R injury in rat.

MATERIALS AND METHODS

A warm hepatic I/R injury model of 1 h ischemia followed by 24 h of reperfusion was used. MC modulation was induced via cromolyn injection or a method called MC depletion using compound 48/80. The effects of MC modulation were evaluated by toluidine blue staining and assessment of mast cell tryptase in sera. The role of MCs in I/R injury was evaluated by hematoxylin and eosin staining graded by Suzuki criteria, alanine aminotransferase and aspartate aminotransferase levels in sera, and malondialdehyde levels in liver homogenates.

RESULTS

First, MC degranulation peaked after 2 h of reperfusion and liver damage peaked after approximately 6 h of reperfusion. Second, a method called MC depletion previously used in the skin with repeated injections of compound 48/80 worked similarly in the hepatic setting. Third, stabilization of MCs with cromolyn or depletion of MCs with compound 48/80 each decreased hepatic I/R injury. The most noticeable effects of cromolyn and compound 48/80 treatment were observed after approximately 6 h of reperfusion.

CONCLUSIONS

MC degranulation promotes hepatic I/R injury in rats.

Glia and mast cells as targets for palmitoylethanolamide, an anti-inflammatory and neuroprotective lipid mediator

Glia are key players in a number of nervous system disorders. Besides releasing glial and neuronal signaling molecules directed to cellular homeostasis, glia respond also to pro-inflammatory signals released from immune-related cells, with the mast cell being of particular interest. A proposed mast cell-glia communication may open new perspectives for designing therapies to target neuroinflammation by differentially modulating activation of non-neuronal cells normally controlling neuronal sensitization-both peripherally and centrally. Mast cells and glia possess endogenous homeostatic mechanisms/molecules that can be upregulated as a result of tissue damage or stimulation of inflammatory responses. Such molecules include the N-acylethanolamines, whose principal family members are the endocannabinoid N-arachidonoylethanolamine (anandamide), and its congeners N-stearoylethanolamine, N-oleoylethanolamine, and N-palmitoylethanolamine (PEA). A key role of PEA may be to maintain cellular homeostasis when faced with external stressors provoking, for example, inflammation: PEA is produced and hydrolyzed by microglia, it downmodulates mast cell activation, it increases in glutamate-treated neocortical neurons ex vivo and in injured cortex, and PEA levels increase in the spinal cord of mice with chronic relapsing experimental allergic encephalomyelitis. Applied exogenously, PEA has proven efficacious in mast cell-mediated experimental models of acute and neurogenic inflammation. This fatty acid amide possesses also neuroprotective effects, for example, in a model of spinal cord trauma, in a delayed post-glutamate paradigm of excitotoxic death, and against amyloid β-peptide-induced learning and memory impairment in mice. These actions may be mediated by PEA acting through "receptor pleiotropism," i.e., both direct and indirect interactions of PEA with different receptor targets, e.g., cannabinoid CB2 and peroxisome proliferator-activated receptor-alpha.

The role of mast cells in neuroinflammation

Mast cells (MCs) are densely granulated perivascular resident cells of hematopoietic origin and well known for their pathogenetic role in allergic and anaphylactic reactions. In addition, they are also involved in processes of innate and adaptive immunity. MCs can be activated in response to a wide range of stimuli, resulting in the release of not only pro-inflammatory, but also anti-inflammatory mediators. The patterns of secreted mediators depend upon the given stimuli and microenvironmental conditions, accordingly MCs have the ability to promote or attenuate inflammatory processes. Their presence in the central nervous system (CNS) has been recognized for more than a century. Since then a participation of MCs in various pathological processes in the CNS has been well documented. They can aggravate CNS damage in models of brain ischemia and hemorrhage, namely through increased blood-brain barrier damage, brain edema and hemorrhage formation and promotion of inflammatory responses to such events. In contrast, recent evidence suggests that MCs may have a protective role following traumatic brain injury by degrading pro-inflammatory cytokines via specific proteases. In neuroinflammatory diseases such as multiple sclerosis, the role of MCs seems to be ambiguous. MCs have been shown to be damaging, neuroprotective, or even dispensable, depending on the experimental protocols used. The role of MCs in the formation and progression of CNS tumors such as gliomas is complex and both positive and negative relationships between MC activity and tumor progression have been reported. In summary, MCs and their secreted mediators modulate inflammatory processes in multiple CNS pathologies and can thereby either contribute to neurological damage or confer neuroprotection. This review intends to give a concise overview of the regulatory roles of MCs in brain disease.