Mechanisms of Post-hemorrhagic Hydrocephalus after Germinal Matrix Hemorrhage

The inherently fragile vasculature of the germinal matrix is susceptible to rupture, possibly as a result of hemodynamic and cardiorespiratory instability associated with prematurity. Germinal matrix hemorrhage is a leading cause of morbidity and mortality in preterm and/or very low birthweight infants, and post-hemorrhagic hydrocephalus is major consequence of severe grade hemorrhages. Chronic post-hemorrhagic hydrocephalus treatment involves surgical insertion of shunts, which are costly and prone to complications. Thus, a safe non-invasive therapeutic approach towards post-hemorrhagic hydrocephalus clinical management would significantly improve the quality of life for this patient population. Thrombin, cerebroventricular blood clots, and iron have been identified as causative factors of hydrocephalus formation. Thrombin stimulates proteinase-activated receptors, leading to subsequent mTOR activation and extracellular matrix protein proliferation, which possibly obstruct the cerebroventricular system. Blood clots may directly impair cerebrospinal fluid circulation and absorption. PPARγ stimulation enhances micgroglial/macrophage phagocytosis of erythrocytes via CD36 scavenger receptor, augmenting clot resolution and improving outcomes after adult cerebral hemorrhage. Additionally, lysed erythrocytes and metabolized hemoglobin release iron, which is associated with brain injury after adult cerebral hemorrhage and contribute to post-hemorrhagic hydrocephalus development. The central aim of this proposal is to determine the role of activated thrombin/PAR-1/mTOR pathway as well as the role of hematoma resolution by PPARγ/CD36 and iron chelation by Deferoxamine in hydrocephalus development after germinal matrix hemorrhage. Direct thrombin inhibition reduced short-term mTOR activation and ameliorated long-term post-hemorrhagic hydrocephalus development, neurocogntive deficits, and extracellular matrix protein proliferation, although PAR-1 inhibition alone did not achieve the same therapeutic benefits. PPARγ stimulation improved short-term hematoma resolution, which was reversed by PPARγ antagonism and CD36 knockdown. PPARγ stimulation attenuated long-term neurocognitive deficits and post-hemorrhagic hydrocephalus, which was reversed by PPARγ antagonism. Acute and delayed iron chelation also reduced long-term post-hemorrhagic hydrocephalus development, neurocognitive deficits, and extracellular matrix protein proliferation. Thus, thrombin/PAR/mTOR pathway inhibition, enhanced PPARγ/CD36 mediated hematoma resolution, and iron chelation significantly ameliorated short and long-term brain sequelae after germinal matrix hemorrhage and are clinically viable therapeutic targets warranting further investigation

Regulatory T Cell in Stroke: A New Paradigm for Immune Regulation

Stroke is a common, debilitating trauma that has an incompletely elucidated pathophysiology and lacks an effective therapy. FoxP3+CD25+CD4+ regulatory T cells (Tregs) suppress a variety of normal physiological and pathological immune responses via several pathways, such as inhibitory cytokine secretion, direct cytolysis induction, and antigen-presenting cell functional modulation. FoxP3+CD25+CD4+ Tregs are involved in a variety of central nervous system diseases and injuries, including axonal injury, neurodegenerative diseases, and stroke. Specifically, FoxP3+CD25+CD4+ Tregs exert neuroprotective effects in acute experimental stroke models. These beneficial effects, however, are difficult to elucidate. In this review, we summarized evidence of FoxP3+CD25+CD4+ Tregs as potentially important immunomodulators in stroke pathogenesis and highlight further investigations for possible immunotherapeutic strategies by modulating the quantity and/or functional effects of FoxP3+CD25+CD4+ Tregs in stroke patients

Estrogen Treatment Reverses Prematurity-Induced Disruption in Cortical Interneuron Population

Development of cortical interneurons continues until the end of human pregnancy. Premature birth deprives the newborns from the supply of maternal estrogen and a secure intrauterine environment. Indeed, preterm infants suffer from neurobehavioral disorders. This can result from both preterm birth and associated postnatal complications, which might disrupt recruitment and maturation of cortical interneurons. We hypothesized that interneuron subtypes, including parvalbumin-positive (PV(+)), somatostatin-positive (SST(+)), calretinin-positive (CalR(+)), and neuropeptide Y-positive (NPY(+)) interneurons, were recruited in the upper and lower cortical layers in a distinct manner with advancing gestational age. In addition, preterm birth would disrupt the heterogeneity of cortical interneurons, which might be reversed by estrogen treatment. These hypotheses were tested by analyzing autopsy samples from premature infants and evaluating the effect of estrogen supplementation in prematurely delivered rabbits. The PV(+) and CalR(+) neurons were abundant, whereas SST(+) and NPY(+) neurons were few in cortical layers of preterm human infants. Premature birth of infants reduced the density of PV(+) or GAD67(+) neurons and increased SST(+) interneurons in the upper cortical layers. Importantly, 17 beta-estradiol treatment in preterm rabbits increased the number of PV(+) neurons in the upper cortical layers relative to controls at postnatal day 14 (P14) and P21 and transiently reduced SST population at P14. Moreover, protein and mRNA levels of Arx, a key regulator of cortical interneuron maturation and migration, were higher in estrogen-treated rabbits relative to controls. Therefore, deficits in PV(+) and excess of SST(+) neurons in premature newborns are ameliorated by estrogen replacement, which can be attributed to elevated Arx levels. Estrogen replacement might enhance neurodevelopmental outcomes in extremely preterm infants.SIGNIFICANCE STATEMENT Premature birth often leads to neurodevelopmental delays and behavioral disorders, which may be ascribed to disturbances in the development and maturation of cortical interneurons. Here, we show that preterm birth in humans is associated with reduced population of parvalbumin-positive (PV(+)) neurons and an excess of somatostatin-expressing interneurons in the cerebral cortex. More importantly, 17 beta-estradiol treatment increased the number of PV(+) neurons in preterm-born rabbits, which appears to be mediated by an elevation in the expression of Arx transcription factor. Hence the present study highlights prematurity-induced reduction in PV(+) neurons in human infants and reversal in their population by estrogen replacement in preterm rabbits. Because preterm birth drops plasma estrogen level 100-fold, estrogen replacement in extremely preterm infants might improve their developmental outcome and minimize neurobehavioral disorders

Adhesion molecules in CNS disorders: biomarker and therapeutic targets

Mounting evidence has been provided regarding the crucial role of leukocyte extravasation and subsequent inflammatory response in several central nervous system (CNS) disorders. The infiltrated leukocytes release proinflammatory mediators and activate resident cells, leading to tissue injury. Leukocyte-endothelia interaction is critical for leukocyte extravasation and migration from the intravascular space into the tissue during inflammation. The basic physiology of leukocyte-endothelia interaction has been investigated extensively. Traditionally, three kinds of adhesion molecules, selectin, integrin, and immunoglobulin families, are responsible for this multiple-step interaction. Furthermore, blocking adhesion molecule function by genetic knockout, antagonizing antibodies, or inhibitory pharmacological drugs provides neuroprotection, which is associated with a reduction in leukocyte accumulation within the tissue. Detection of the soluble form of adhesion molecules has also been proven to predict outcomes in CNS disorders. Lately, vascular adhesion protein-1, a novel adhesion molecule and endothelial cell surface enzyme, has been implicated as a brake in the rolling step of the adhesion cascade, and also a regulator of leukocyte transmigration step. In this review, we summarize the functions of traditional adhesion molecules as well as vascular adhesion protein-1in the leukocyte adhesion cascade. We also discuss the diagnostic and therapeutic potential of adhesion molecules in CNS disorders

Role of P2X purinoceptor 7 in neurogenic pulmonary edema after subarachnoid hemorrhage in rats.

INTRODUCTION: Neurogenic pulmonary edema (NPE) is an acute and serious complication after subarachnoid hemorrhage (SAH) with high mortality. The present study aimed to test the therapeutic potential of brilliant blue G (BBG), a selective P2X purinoceptor 7 (P2X7R) antagonist, on NPE in a rat SAH model. METHODS: SAH was induced by endovascular perforation. 86 Sprague-Dawley rats were randomly divided into sham, vehicle-, or BBG-treatment groups. Mortality, body weight, SAH grading, neurological deficits, NPE clinical symptoms, and pulmonary index were measured at 24 hours following SAH. Western blot, gelatin zymography, lung histopathology, and immunofluorescence staining were performed in the left lung lobe to explore the underlying mechanisms at 24 hours post-surgery. RESULTS: The incidence of clinical symptoms was correlated with pulmonary index. P2X7R and the marker of alveolar type I epithelial cells (the mucin-type glycoprotein T1-α) immunoreactivities were generally co-localized. BBG administration decreased mature interleukin-1β, myeloperoxidase, and matrix metallopeptidase-9 activation, but increased tight junction proteins, such as ZO-1 and occludin, which ameliorated pulmonary edema via anti-inflammation and improved neurological deficits. CONCLUSION: P2X7R inhibition prevented NPE after SAH by attenuating inflammation. Thus, BBG is a potential therapeutic application for NPE after SAH and warrants further research

Role of SCH79797 in maintaining vascular integrity in rat model of subarachnoid hemorrhage

BACKGROUND AND PURPOSE: Plasma thrombin concentration is increased after subarachnoid hemorrhage (SAH). However, the role of thrombin receptor (protease-activated receptor-1 [PAR-1]) in endothelial barrier disruption has not been studied. The aims of this study were to investigate the role of PAR-1 in orchestrating vascular permeability and to assess the potential therapeutics of a PAR-1 antagonist, SCH79797, through maintaining vascular integrity. METHODS: SCH79797 was injected intraperitoneally into male Sprauge-Dawley rats undergoing SAH by endovascular perforation. Assessment was conducted at 24 hours after SAH for brain water content, Evans blue content, and neurobehavioral testing. To explore the role of PAR-1 activation and the specific mechanism of SCH79797\u27s effect after SAH, Western blot, immunoprecipitation, and immunofluorescence of hippocampus tissue were performed. A p21-activated kinase-1 (PAK1) inhibitor, IPA-3, was used to explore the underlying protective mechanism of SCH79797. RESULTS: At 24 hours after SAH, animals treated with SCH79797 demonstrated a reduction in brain water content, Evans blue content, and neurobehavioral deficits. SCH79797 also attenuated PAR-1 expression and maintained the level of vascular endothelial-cadherin, an important component of adherens junctions. Downstream to PAR-1, c-Src-dependent activation of p21-activated kinase-1 led to an increased serine/threonine phosphorylation of vascular endothelial-cadherin; immunoprecipitation results revealed an enhanced binding of phosphorylated vascular endothelial-cadherin with endocytosis orchestrator β-arrestin-2. These pathological states were suppressed after SCH79797 treatment. CONCLUSIONS: PAR-1 activation after SAH increases microvascular permeability, at least, partly through a PAR-1-c-Src-p21-activated kinase-1-vascular endothelial-cadherin phosphorylation pathway. Through suppressing PAR-1 activity, SCH79797 plays a protective role in maintaining microvascular integrity after SAH

An Experimental Model of Vasovagal Syncope Induces Cerebral Hypoperfusion and Fainting-Like Behavior in Awake Rats

<div><p>Vasovagal syncope, a contributing factor to elderly falls, is the transient loss of consciousness caused by decreased cerebral perfusion. Vasovagal syncope is characterized by hypotension, bradycardia, and reduced cerebral blood flow, resulting in fatigue, altered coordination, and fainting. The purpose of this study is to develop an animal model which is similar to human vasovagal syncope and establish an awake animal model of vasovagal syncope. Male Sprague-Dawley rats were subjected to sinusoidal galvanic vestibular stimulation (sGVS). Blood pressure, heart rate, and cerebral blood flow were monitored before, during, and post-stimulation. sGVS resulted in hypotension, bradycardia, and decreased cerebral blood flow. One cohort of animals was subjected to sGVS while freely moving. sGVS in awake animals produced vasovagal syncope-like symptoms, including fatigue and uncoordinated movements; two animals experienced spontaneous falling. Another cohort of animals was preconditioned with isoflurane for several days before being subjected to sGVS. Isoflurane preconditioning before sGVS did not prevent sGVS-induced hypotension or bradycardia, yet isoflurane preconditioning attenuated sGVS-induced cerebral blood flow reduction. The sGVS rat model mimics elements of human vasovagal syncope pathophysiology (hypotension, bradycardia, and decreased cerebral perfusion), including behavioral symptoms such as fatigue and altered balance. This study indicates that the sGVS rat model is similar to human vasovagal syncope and that therapies directed at preventing cerebral hypoperfusion may decrease syncopal episodes and reduce injuries from syncopal falls.</p></div

Isoflurane Post-Treatment Ameliorates GMH-Induced Brain Injury in Neonatal Rats

Background and purposeThis study investigated whether isoflurane ameliorates neurological sequelae after germinal matrix hemorrhage (GMH) through activation of the cytoprotective sphingosine kinase/sphingosine-1-phosphate receptor/Akt pathway.MethodsGMH was induced in P7 rat pups by intraparenchymal infusion of bacterial collagenase (0.3 U) into the right hemispheric germinal matrix. GMH animals received 2% isoflurane either once 1 hour after surgery or every 12 hours for 3 days. Isoflurane treatment was then combined with sphingosine-1-phosphate receptor-1/2 antagonist VPC23019 or sphingosine kinase 1/2 antagonist N,N-dimethylsphingosine.ResultsBrain protein expression of sphingosine kinase-1 and phosphorylated Akt were significantly increased after isoflurane post-treatment, and cleaved caspase-3 was decreased at 24 hours after surgery, which was reversed by the antagonists. Isoflurane significantly reduced posthemorrhagic ventricular dilation and improved motor, but not cognitive, functions in GMH animals 3 weeks after surgery; no improvements were observed after VPC23019 administration.ConclusionsIsoflurane post-treatment improved the neurological sequelae after GMH possibly by activation of the sphingosine kinase/Akt pathway

Isoflurane Post-Treatment Ameliorates GMH-Induced Brain Injury in Neonatal Rats

BACKGROUND AND PURPOSE: This study investigated whether isoflurane ameliorates neurological sequelae after germinal matrix hemorrhage (GMH) through activation of the cytoprotective sphingosine kinase/sphingosine-1-phosphate receptor/Akt pathway. METHODS: GMH was induced in P7 rat pups by intraparenchymal infusion of bacterial collagenase (0.3U) into the right hemispheric germinal matrix. GMH animals received 2% isoflurane either once 1 hour after surgery, or every 12 hours for 3 days. Isoflurane treatment was then combined with sphingosine-1-phoshate receptor-1/2 antagonist VPC23019 or sphingosine kinase 1/2 antagonist N,N-dimethylsphingosine. RESULTS: Brain protein expression of sphingosine kinase-1 and phosphorylated Akt were significantly increased after isoflurane post-treatment, and cleaved capase-3 was decreased at 24 hours after surgery; which was reversed by the antagonists. Isoflurane significantly reduced post-hemorrhagic ventricular dilation and improved motor, but not cognitive, functions in GMH animals 3 weeks after surgery; no improvements were observed following VPC23019 administration. CONCLUSION: Isoflurane post-treatment improved the neurological sequelae after GMH possibly by activation of the sphingosine kinase/Akt pathway