Targeting mast cell as a neuroprotective strategy

Interactions between the Autonomic Nervous System and the Immune System after Stroke

Acute stroke is one of the leading causes of morbidity and mortality worldwide. Stroke-induced immune-inflammatory response occurs in the perilesion areas and the periphery. Although stroke-induced immunosuppression may alleviate brain injury, it hinders brain repair as the immune-inflammatory response plays a bidirectional role after acute stroke. Furthermore, suppression of the systemic immune-inflammatory response increases the risk of life-threatening systemic bacterial infections after acute stroke. Therefore, it is essential to explore the mechanisms that underlie the stroke-induced immune-inflammatory response. Autonomic nervous system (ANS) activation is critical for regulating the local and systemic immune-inflammatory responses and may influence the prognosis of acute stroke. We review the changes in the sympathetic and parasympathetic nervous systems and their influence on the immune-inflammatory response after stroke. Importantly, this article summarizes the mechanisms on how ANS regulates the immune-inflammatory response through neurotransmitters and their receptors in immunocytes and immune organs after stroke. To facilitate translational research, we also discuss the promising therapeutic approaches modulating the activation of the ANS or the immune-inflammatory response to promote neurologic recovery after stroke. © 2022 American Physiological Society. Compr Physiol 12:3665-3704, 2022.

The association between hematologic parameters and intracranial injuries in pediatric patients with traumatic brain injury

OBJECTIVE

Analyzing the association between hematologic parameters and abnormal cranial computerized tomography (CT) findings after head trauma.

MATERIAL AND METHODS

A total of 287 children with isolated traumatic brain injury (TBI) were divided into the 'normal' (NG), 'linear fracture' (LFG) and 'intraparenchymal injury' groups (IPG) based on head CT findings. Demographical/clinical data and laboratory results were obtained from medical records.

RESULTS

The neutrophil-lymphocyte ratio was markedly higher in the LFG (p = 0.010 and p = 0.016, respectively) and IPG (p = 0.004 and p < 0.001, respectively) compared with NG. Lower lymphocyte-monocyte ratio (p = 0.044) and higher red cell distribution width-platelet ratio (RPR) (p = 0.030) were associated with intraparenchymal injuries. Patients requiring neurosurgical intervention had higher neutrophil-lymphocyte ratio (p = 0.026) and RPR values (p = 0.031) and lower platelet counts (p = 0.035). Lower levels of erythrocytes (p = 0.005), hemoglobin (p = 0.003) and hematocrit (p = 0.002) were associated with severe TBI and unfavorable outcome (p = 0.012, p = 0.004 and p = 0.006, respectively).

CONCLUSIONS

Hematologic parameters are useful in predicting the presence of abnormal cranial CT findings in children with TBI in association with injury severity; surgery need and clinical outcome.

Laparotomy-Induced Peripheral Inflammation Activates NR2B Receptors on the Brain Mast Cells and Results in Neuroinflammation in a Vagus Nerve-Dependent Manner

Background: The pathophysiological mechanisms underlying postoperative cognitive dysfunction (POCD) remain unclear over the years. Neuroinflammation caused by surgery has been recognized as an important element in the development of POCD. Many studies also suggest that the vagus nerve plays an important role in transmitting peripheral injury signals to the central nervous system (CNS) and the resultant neuroinflammation. Previously, we have demonstrated that brain mast cells (BMCs), as the “first responders”, play a vital role in neuroinflammation and POCD. However, how the vagus nerve communicates with BMCs in POCD has not yet been clarified.

Methods: In the current study, we highlighted the role of the vagus nerve as a conduction highway in surgery-induced neuroinflammation for the first time. In our model, we tested if mice underwent unilateral cervical vagotomy (VGX) had less neuroinflammation compared to the shams after laparotomy (LP) at an early stage. To further investigate the roles of mast cells and glutamate in the process, we employed Kit^W-sh mice and primary bone marrow-derived MCs to verify the glutamate-NR2B axis on MCs once again.

Results: Our results demonstrated that there were higher levels of glutamate and BMCs activation as early as 4 h after LP. Meanwhile, vagotomy could partially block the increases and reduce neuroinflammation caused by peripheral inflammation during the acute phase. Excitingly, inhibition of NR2B receptor and knockout of mast cells can attenuateneuroinflammation induced by glutamate.

Conclusion: Taken together, our findings indicate that the vagus is a high-speed pathway in the transmission of peripheral inflammation to the CNS. Activation of BMCs triggered a neuroinflammatory cascade. Inhibition of NR2B receptor on BMCs can reduce glutamate-induced BMCs activation, neuroinflammation, and memory impairment, suggesting a novel treatment strategy for POCD.

Mast cells and histamine are involved in the neuronal damage observed in a quinolinic acid-induced model of Huntington's disease

Huntington´s disease (HD) is a pathological condition that can be studied in mice by the administration of quinolinic acid (QUIN), an agonist of the N-methyl-d-aspartate receptor (NMDAR) that induces NMDAR-mediated cytotoxicity and neuroinflammation. Mast cells (MCs) participate in numerous inflammatory processes through the release of important amounts of histamine (HA). In this study, we aimed to characterize the participation of MCs and HA in the establishment of neural and oxidative damage in the QUIN-induced model of HD. C57BL6/J mice (WT), MC-deficient c-Kit^W-sh/W-sh (Wsh) mice and Wsh mice reconstituted by intracerebroventricular (i.c.v.) injection of 5 × 10⁵ bone marrow-derived mast cells (BMMCs), or i.c.v. administered with HA (5 µg) were used. All groups of animals were intrastriatally injected with 1 µL QUIN (30 nmol/µL) and 3 days later, apomorphine-induced circling behavior, striatal GABA levels and the number of Fluoro-Jade positive cells, as indicators of neuronal damage, were determined. Also, lipid peroxidation (LP) and reactive oxygen species production (ROS), as markers of oxidative damage, were analyzed. Wsh mice showed less QUIN-induced neuronal and oxidative damage than WT and Wsh-MC reconstituted animals. Histamine administration restored the QUIN-induced neuronal and oxidative damage in the non-reconstituted Wsh mice to levels equivalent or superior to those observed in WT mice. Our results demonstrate that MCs and HA participate in the neuronal and oxidative damages observed in mice subjected to the QUIN -induced model of Huntington's disease.

Inhibition of PAR-2 Attenuates Neuroinflammation and Improves Short-Term Neurocognitive Functions Via ERK1/2 Signaling Following Asphyxia-Induced Cardiac Arrest in Rats

OBJECTIVE

Global cerebral ischemia-induced neuroinflammation causes neurofunctional impairment following cardiac arrest. Previous studies have demonstrated that the activation of protease-activated receptor-2 (PAR-2) contributes to neuroinflammation. In the present study, we aimed to determine the potential treatment effect of PAR-2 inhibition against neuroinflammation in the setting of asphyxial CA (ACA) in rats.

METHODS

A total of 116 adult, male Sprague-Dawley rats were randomly divided into Sham (n = 18) and ACA (n = 98) groups. Time course, short-term outcome, and mechanism studies were conducted. All drugs were delivered intranasally. The effect of PAR-2 inhibitor FSLLRY-NH2 on neurocognitive functions was assessed by neurologic deficit score, number of seizures, and T-maze test, while hippocampal neuronal degeneration was evaluated by Fluoro-Jade C staining after ACA. Western blotting was performed for the mechanism study at 24 h following ACA. Selective PAR-2 agonist (AC55541) and ERK1/2 inhibitor (PD98059) were used for intervention.

RESULTS

Inhibition of PAR-2 decreased neuroinflammation, reduced the number of degenerating hippocampal neurons and improved neurocognitive functions following ACA. PAR-2 activator alone exerted opposite effects to PAR-2 inhibitor. PAR-2 mediated the augmented brain levels of proinflammatory cytokines by promoting the phosphorylation of ERK1/2.

CONCLUSIONS

PAR-2 inhibition diminished neuroinflammation and thereby reduced hippocampal neuronal degeneration and neurocognitive impairment following ACA. This effect was at least partly mediated via the PAR-2/ERK1/2 signaling.

Involvement of Mast Cells in the Pathophysiology of Pain

Mast cells (MCs) are immune cells and are widely distributed throughout the body. MCs are not only classically viewed as effector cells of some allergic diseases but also participate in host defense, innate and acquired immunity, homeostatic responses, and immunoregulation. Mounting evidence indicates that activation of MCs releasing numerous vasoactive and inflammatory mediators has effects on the nervous system and has been involved in different pain conditions. Here, we review the latest advances made about the implication of MCs in pain. Possible cellular and molecular mechanisms regarding the crosstalk between MC and the nervous system in the initiation and maintenance of pain are also discussed.

Molecular Hydrogen Application in Stroke: Bench to Bedside

Stroke is a major cause of mortality and morbidity worldwide. Effective treatments are limited. Molecular hydrogen is emerging as a novel medical gas with therapeutic potential for various neurological diseases, including stroke. We reviewed the experimental and clinical findings of the effects of molecular hydrogen therapy in stroke patients and models. The underlying neuroprotective mechanisms against stroke pathology were also discussed.

LJ529 attenuates mast cell-related inflammation via A3R-PKCε-ALDH2 pathway after subarachnoid hemorrhage in rats

BACKGROUND AND PURPOSE

Mast cells (MCs) has been recognized as an effector of inflammation or a trigger of inflammatory factors during stroke. LJ529 was reported to attenuate inflammation through a Gi protein-coupled Adenosine A3 receptor (A₃R) after ischemia. Here, we aim to study the protective effect and its mechanism of LJ529 in subarachnoid hemorrhage (SAH) rat model for mast cell-related inflammation.

METHODS

155 Sprague-Dawley adult male rats were used in experiments. Endovascular perforation was used for SAH model. Intraperitoneal LJ529 was performed 1 h after SAH. Neurological scores were measured 24 h after SAH. Rotarod and morris water maze tests were evaluated for 21 days after SAH. Mast cell degranulation was assessed with Toluidine blue staining and Chymase/Typtase protein expressions. Mast cell-related inflammation was evaluated using IL-6, TNF-α and MCP-1 protein expressions. MRS1523, inhibitor of GPR18 and ε-V1-2, inhibitor of PKCε were respectively given intraperitoneally (i.p.) 1 h and 30 min before SAH for mechanism studies. Pathway related proteins were investigated with western blot and immunofluorescence staining.

RESULTS

Expression of A₃R, PKCε increased after SAH. LJ529 treatment attenuated mast cell degranulation and inflammation. Meanwhile, both short-term and long-term neurological functions were improved after LJ529 treatment. Administration of LJ529 resulted in increased expressions of A₃R, PKCε, ALDH2 proteins and decreased expressions of Chymase, Typtase, IL-6, TNF-α and MCP-1 proteins. MRS1523 abolished the treatment effects of LJ529 on neurobehavior and protein levels. ε-V1-2 also reversed the outcomes of LJ529 administration through reduction in protein expressions downstream of PKCε.

CONCLUSIONS

LJ529 attenuated mast cell-related inflammation through inhibiting degranulation via A3R-PKCε-ALDH2 pathway after SAH. LJ529 may serve as a potential treatment strategy to relieve post-SAH brain injury.

Potential Therapies for Cerebral Edema After Ischemic Stroke: A Mini Review

Stroke is the leading cause of global mortality and disability. Cerebral edema and intracranial hypertension are common complications of cerebral infarction and the major causes of mortality. The formation of cerebral edema includes three stages (cytotoxic edema, ionic edema, and vasogenic edema), which involve multiple proteins and ion channels. A range of therapeutic agents that successfully target cerebral edema have been developed in animal studies, some of which have been assessed in clinical trials. Herein, we review the mechanisms of cerebral edema and the research progress of anti-edema therapies for use after ischemic stroke.

Neuroimmune connections between corticotropin-releasing hormone and mast cells: novel strategies for the treatment of neurodegenerative diseases

Corticotropin-releasing hormone is a critical component of the hypothalamic–pituitary–adrenal axis, which plays a major role in the body’s immune response to stress. Mast cells are both sensors and effectors in the interaction between the nervous and immune systems. As first responders to stress, mast cells can initiate, amplify and prolong neuroimmune responses upon activation. Corticotropin-releasing hormone plays a pivotal role in triggering stress responses and related diseases by acting on its receptors in mast cells. Corticotropin-releasing hormone can stimulate mast cell activation, influence the activation of immune cells by peripheral nerves and modulate neuroimmune interactions. The latest evidence shows that the release of corticotropin-releasing hormone induces the degranulation of mast cells under stress conditions, leading to disruption of the blood-brain barrier, which plays an important role in neurological diseases, such as Alzheimer’s disease, Parkinson’s disease, multiple sclerosis, autism spectrum disorder and amyotrophic lateral sclerosis. Recent studies suggest that stress increases intestinal permeability and disrupts the blood-brain barrier through corticotropin-releasing hormone-mediated activation of mast cells, providing new insight into the complex interplay between the brain and gastrointestinal tract. The neuroimmune target of mast cells is the site at which the corticotropin-releasing hormone directly participates in the inflammatory responses of nerve terminals. In this review, we focus on the neuroimmune connections between corticotropin-releasing hormone and mast cells, with the aim of providing novel potential therapeutic targets for inflammatory, autoimmune and nervous system diseases.

Acute Traumatic Brain Injury-Induced Neuroinflammatory Response and Neurovascular Disorders in the Brain

Acute traumatic brain injury (TBI) leads to neuroinflammation, neurodegeneration, cognitive decline, psychological disorders, increased blood-brain barrier (BBB) permeability, and microvascular damage in the brain. Inflammatory mediators secreted from activated glial cells, neurons, and mast cells are implicated in the pathogenesis of TBI through secondary brain damage. Abnormalities or damage to the neurovascular unit is the indication of secondary injuries in the brain after TBI. However, the precise mechanisms of molecular and ultrastructural neurovascular alterations involved in the pathogenesis of acute TBI are not yet clearly understood. Moreover, currently, there are no precision-targeted effective treatment options to prevent the sequelae of TBI. In this study, mice were subjected to closed head weight-drop-induced acute TBI and evaluated neuroinflammatory and neurovascular alterations in the brain by immunofluorescence staining or quantitation by enzyme-linked immunosorbent assay (ELISA) procedure. Mast cell stabilizer drug cromolyn was administered to inhibit the neuroinflammatory response of TBI. Results indicate decreased level of pericyte marker platelet-derived growth factor receptor-beta (PDGFR-β) and BBB-associated tight junction proteins junctional adhesion molecule-A (JAM-A) and zonula occludens-1 (ZO-1) in the brains 7 days after weight-drop-induced acute TBI as compared with the brains from sham control mice indicating acute TBI-associated BBB/tight junction protein disruption. Further, the administration of cromolyn drug significantly inhibited acute TBI-associated decrease of PDGFR-β, JAM-A, and ZO-1 in the brain. These findings suggest that acute TBI causes BBB/tight junction damage and that cromolyn administration could protect this acute TBI-induced brain damage as well as its long-time consequences.

Mast Cell Activation, Neuroinflammation, and Tight Junction Protein Derangement in Acute Traumatic Brain Injury

Traumatic brain injury (TBI) is one of the major health problems worldwide that causes death or permanent disability through primary and secondary damages in the brain. TBI causes primary brain damage and activates glial cells and immune and inflammatory cells, including mast cells in the brain associated with neuroinflammatory responses that cause secondary brain damage. Though the survival rate and the neurological deficiencies have shown significant improvement in many TBI patients with newer therapeutic options, the underlying pathophysiology of TBI-mediated neuroinflammation, neurodegeneration, and cognitive dysfunctions is understudied. In this study, we analyzed mast cells and neuroinflammation in weight drop-induced TBI. We analyzed mast cell activation by toluidine blue staining, serum chemokine C-C motif ligand 2 (CCL2) level by enzyme-linked immunosorbent assay (ELISA), and proteinase-activated receptor-2 (PAR-2), a mast cell and inflammation-associated protein, vascular endothelial growth factor receptor 2 (VEGFR2), and blood-brain barrier tight junction-associated claudin 5 and Zonula occludens-1 (ZO-1) protein expression in the brains of TBI mice. Mast cell activation and its numbers increased in the brains of 24 h and 72 h TBI when compared with sham control brains without TBI. Mouse brains after TBI show increased CCL2, PAR-2, and VEGFR2 expression and derangement of claudin 5 and ZO-1 expression as compared with sham control brains. TBI can cause mast cell activation, neuroinflammation, and derangement of tight junction proteins associated with increased BBB permeability. We suggest that inhibition of mast cell activation can suppress neuroimmune responses and glial cell activation-associated neuroinflammation and neurodegeneration in TBI.

Inhibition of mast cell tryptase attenuates neuroinflammation via PAR-2/p38/NFκB pathway following asphyxial cardiac arrest in rats

Background

Cardiac arrest survivors suffer from neurological dysfunction including cognitive impairment. Cerebral mast cells, the key regulators of neuroinflammation contribute to neuroinflammation-associated cognitive dysfunction. Mast cell tryptase was demonstrated to have a proinflammatory effect on microglia via the activation of microglial protease-activated receptor-2 (PAR-2). This study investigated the potential anti-neuroinflammatory effect of mast cell tryptase inhibition and the underlying mechanism of PAR-2/p-p38/NFκB signaling following asphyxia-induced cardiac arrest in rats.

Methods

Adult male Sprague-Dawley rats resuscitated from 10 min of asphyxia-induced cardiac arrest were randomized to four separate experiments including time-course, short-term outcomes, long-term outcomes and mechanism studies. The effect of mast cell tryptase inhibition on asphyxial cardiac arrest outcomes was examined after intranasal administration of selective mast cell tryptase inhibitor (APC366; 50 μg/rat or 150 μg/rat). AC55541 (selective PAR-2 activator; 30 μg/rat) and SB203580 (selective p38 inhibitor; 300 μg/rat) were used for intervention. Short-term neurocognitive functions were evaluated using the neurological deficit score, number of seizures, adhesive tape removal test, and T-maze test, while long-term cognitive functions were evaluated using the Morris water maze test. Hippocampal neuronal degeneration was evaluated by Fluoro-Jade C staining.

Results

Mast cell tryptase and PAR-2 were dramatically increased in the brain following asphyxia-induced cardiac arrest. The inhibition of mast cell tryptase by APC366 improved both short- and long-term neurological outcomes in resuscitated rats. Such behavioral benefits were associated with reduced expressions of PAR-2, p-p38, NFκB, TNF-α, and IL-6 in the brain as well as less hippocampal neuronal degeneration. The anti-neuroinflammatory effect of APC366 was abolished by AC55541, which when used alone, indeed further exacerbated neuroinflammation, hippocampal neuronal degeneration, and neurologic deficits following cardiac arrest. The deleterious effects aggregated by AC55541 were minimized by p38 inhibitor.

Conclusions

The inhibition of mast cell tryptase attenuated neuroinflammation, led to less hippocampal neuronal death and improved neurological deficits following cardiac arrest. This effect was at least partly mediated via inhibiting the PAR-2/p-p38/NFκB signaling pathway. Thus, mast cell tryptase might be a novel therapeutic target in the management of neurological impairment following cardiac arrest.

Clinical Prognosis for SAH Consistent with Redox Imbalance and Lipid Peroxidation

Subarachnoid hemorrhage (SAH) accounts for 3% of all strokes. As more and more data indicates the role of oxidative stress in acute brain damage caused by SAH, an attempt was made to correlate the clinical status of patients with systemic level of antioxidants and lipid peroxidation products. The hemorrhage was diagnosed with brain computed tomography (CT) and aneurysm with angio-CT and angiography, while the vasospasm was monitored with transcranial Doppler. Plasma glutathione peroxidase activity (GSH-Px) and vitamin A, E, and C levels were determined spectrophotometrically and by HPLC, respectively. The levels of polyunsaturated fatty acids (PUFAs) cyclization products were determined by GC–MS, while F₂-isoprostanes and neuroprostanes (NP) were determined by LC–MS. SAH was accompanied by changes in antioxidant capacity in blood plasma, including initially (day 1) an increase in GSH-Px activity, followed by its decrease and a progressive decrease in glutathione (GSH) levels and vitamins A, E, and C. On the other hand, levels of PUFAs cyclization products, F₂-isoprostanes, and neuroprostanes were highest on day 1 (two and eight times higher, respectively) and decreased over time. The levels of 4-HNE (4-hydroxynonenal), 4-ONE (4-oxononenal), and MDA (malondialdehyde) changed similarly. In contrast, the 4-HHE (4-hydroxyhexenal) level reduced after SAH increased significantly after a week. It was found that the deterioration of the overall clinical and neurological condition of SAH patients due to cerebral edema, intracranial hemorrhage, or vasoconstriction corresponded to reduced antioxidant defense and, as a consequence, increased lipid peroxidation and slower observed changes in regression. It can be concluded that monitoring the level of lipid peroxidation products (neuroprostanes, 4-ONE, and MDA) can support the monitoring of the clinical status of patients, especially with regard to the assessment of vasospasm.

Brain Injury-Mediated Neuroinflammatory Response and Alzheimer's Disease

Traumatic brain injury (TBI) is a major health problem in the United States, which affects about 1.7 million people each year. Glial cells, T-cells, and mast cells perform specific protective functions in different regions of the brain for the recovery of cognitive and motor functions after central nervous system (CNS) injuries including TBI. Chronic neuroinflammatory responses resulting in neuronal death and the accompanying stress following brain injury predisposes or accelerates the onset and progression of Alzheimer's disease (AD) in high-risk individuals. About 5.7 million Americans are currently living with AD. Immediately following brain injury, mast cells respond by releasing prestored and preactivated mediators and recruit immune cells to the CNS. Blood-brain barrier (BBB), tight junction and adherens junction proteins, neurovascular and gliovascular microstructural rearrangements, and dysfunction associated with increased trafficking of inflammatory mediators and inflammatory cells from the periphery across the BBB leads to increase in the chronic neuroinflammatory reactions following brain injury. In this review, we advance the hypothesis that neuroinflammatory responses resulting from mast cell activation along with the accompanying risk factors such as age, gender, food habits, emotional status, stress, allergic tendency, chronic inflammatory diseases, and certain drugs can accelerate brain injury-associated neuroinflammation, neurodegeneration, and AD pathogenesis.

Calming Down Mast Cells with Ketotifen: A Potential Strategy for Multiple Sclerosis Therapy?

Multiple sclerosis (MS) is a chronic autoimmune disease of the central nervous system (CNS) characterized by extensive inflammation, demyelination, axonal loss and gliosis. Evidence indicates that mast cells contribute to immunopathogenesis of both MS and experimental autoimmune encephalomyelitis (EAE), which is the most employed animal model to study this disease. Considering the inflammatory potential of mast cells, their presence at the CNS and their stabilization by certain drugs, we investigated the effect of ketotifen fumarate (Ket) on EAE development. EAE was induced in C57BL/6 mice by immunization with MOG35-55 and the animals were injected daily with Ket from the seventh to the 17th day after disease induction. This early intervention with Ket significantly reduced disease prevalence and severity. The protective effect was concomitant with less NLRP3 inflammasome activation, rebalanced oxidative stress and also reduced T cell infiltration at the CNS. Even though Ket administration did not alter mast cell percentage at the CNS, it decreased the local CPA3 and CMA1 mRNA expression that are enzymes typically produced by these cells. Evaluation of the CNS-barrier permeability indicated that Ket clearly restored the permeability levels of this barrier. Ket also triggered an evident lymphadenomegaly due to accumulation of T cells that produced higher levels of encephalitogenic cytokines in response to in vitro stimulation with MOG. Altogether these findings reinforce the concept that mast cells are particularly relevant in MS immunopathogenesis and that Ket, a known stabilizer of their activity, has the potential to be used in MS control.

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.

An update on promising therapies for CNS conditions

In this special edition, we present five articles that explore various neurovascular and neurodegenerative diseases and update the readers on promising therapies. We discuss where the current focus of research on central nervous conditions is heading. The topics range from discussing different brain injury models simulate human physiology, to analyzing outcomes following subdural hematoma evacuation. In addition, this special issue discusses new therapeutic targets during the acute phase of brain injury. The ideas and expert analysis regarding different neurological topics set up readers to explore future research on the subject matter.

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.

Thyroid Hormone, Thyroid Hormone Metabolites and Mast Cells: A Less Explored Issue

Mast cells are primary players in immune and inflammatory diseases. In the brain, mast cells are located at the brain side of the blood brain barrier (BBB) exerting a crucial role in protecting the brain from xenobiotic invasion. Furthermore, recent advances in neuroscience indicate mast cells may play an important role in glial cell-neuron communication through the release of mediators, including histamine. Interestingly, brain mast cells contain not only 50% of the brain histamine but also hormones, proteases and lipids or amine mediators; and cell degranulation may be triggered by different stimuli activating membrane bound receptors including the four types of histaminergic receptors. Among hormones, mast cells can store thyroid hormone (T3) and express membrane-bound thyroid stimulating hormone receptors (TSHRs), thus suggesting from one side that thyroid function may affect mast cells function, from the other that mast cell degranulation may impact on thyroid function. In this respect, the research on hormones in mast cells is scarce. Recent pharmacological evidence indicates the existence of a non-genomic portion of the thyroid secretion including thyroid hormone metabolites. Among which the 3,5 diiodothyronine (3,5-T2), 3-iodothyroanamine (T1AM) and 3-iodothyroacetic acid (TA1) are the most studied. All these compounds are endogenously occurring and found to be increased in inflammatory-based diseases involving mast cells. T1AM and TA1 induce, as T3, neuroprotective effects and itch but also hyperalgesia in rodents with a mechanism largely unknown but mediated by the release of histamine. Due to the rapid onset of their effectiveness they may trigger histamine release from a cell where it is “ready-to-be released,” i.e., mast cells. Following a very thin path which passes through old experimental and clinical evidence, at the light of novel acquisitions on endogenous T3 metabolites, we aim to stimulate the attention on the possibility that mast cell histamine may be the connector of a novel (neuro) endocrine pathway linking the thyroid with mast cells.

Mast Cells in Stress, Pain, Blood-Brain Barrier, Neuroinflammation and Alzheimer's Disease

Mast cell activation plays an important role in stress-mediated disease pathogenesis. Chronic stress cause or exacerbate aging and age-dependent neurodegenerative diseases. The severity of inflammatory diseases is worsened by the stress. Mast cell activation-dependent inflammatory mediators augment stress associated pain and neuroinflammation. Stress is the second most common trigger of headache due to mast cell activation. Alzheimer's disease (AD) is a progressive irreversible neurodegenerative disease that affects more women than men and woman's increased susceptibility to chronic stress could increase the risk for AD. Modern life-related stress, social stress, isolation stress, restraint stress, early life stress are associated with an increased level of neurotoxic beta amyloid (Aβ) peptide. Stress increases cognitive dysfunction, generates amyloid precursor protein (APP), hyperphosphorylated tau, neurofibrillary tangles (NFTs), and amyloid plaques (APs) in the brain. Stress-induced Aβ persists for years and generates APs even several years after the stress exposure. Stress activates hypothalamic-pituitary adrenal (HPA) axis and releases corticotropin-releasing hormone (CRH) from hypothalamus and in peripheral system, which increases the formation of Aβ, tau hyperphosphorylation, and blood-brain barrier (BBB) disruption in the brain. Mast cells are implicated in nociception and pain. Mast cells are the source and target of CRH and other neuropeptides that mediate neuroinflammation. Microglia express receptor for CRH that mediate neurodegeneration in AD. However, the exact mechanisms of how stress-mediated mast cell activation contribute to the pathogenesis of AD remains elusive. This mini-review highlights the possible role of stress and mast cell activation in neuroinflammation, BBB, and tight junction disruption and AD pathogenesis.