From apoplexy to stroke: historical perspectives and new research frontiers

Loss of Ribosomal RACK1 (Receptor for Activated Protein Kinase C 1) Induced by Phosphorylation at T50 Alleviates Cerebral Ischemia-Reperfusion Injury in Rats

Background and Purpose- RACK1 (receptor for activated protein kinase C 1) is an integral component of ribosomes with neuroprotective functions. The goal of this study was to determine the role of RACK1 in cerebral ischemia-reperfusion (I/R) injury and the underlying mechanisms. Methods- A middle cerebral artery occlusion/reperfusion model in adult male Sprague Dawley rats (250-280 g) was established, and cultured neurons were exposed to oxygen-glucose deprivation/reoxygenation to mimic I/R injury in vitro. Expression vectors encoding wild-type RACK1 and RACK1 with T50A mutation (T50A) were constructed and administered to rats by intracerebroventricular injection. Results- The potential role of RACK1 in cerebral I/R injury was confirmed by the decreased protein levels of RACK1 within penumbra tissue, especially of neurons. Second, there was an increase in the phosphorylation ratio of RACK1 at the threonine/serine residues at 1.5 hours after middle cerebral artery occlusion onset. Third, based on site-specific mutagenesis, we identified T50 as a key site for RACK1 phosphorylation during I/R. Fourth, wild-type RACK1 overexpression reduced infarct size, neuronal death, neuronal tissue loss, and neurobehavioral dysfunction, while RACK1 (T50A) overexpression exerted opposite effects. Finally, we found that RACK1 phosphorylation at T50 induced a loss of ribosomal RACK1, which switched RACK1 from beclin-1 translation inhibition to autophagy induction following I/R. Conclusions- RACK1 phosphorylation may be a potential intervention target for neurons during I/R; thus, exogenous supplementation of RACK1 may be a novel approach for ameliorating I/R injury.

Identification of two phosphorylation sites essential for annexin A1 in blood-brain barrier protection after experimental intracerebral hemorrhage in rats

Annexin A1 has been reported to exert a blood-brain barrier protection. This study was designed to examine the role of annexin A1 in intracerebral hemorrhage-induced blood-brain barrier dysfunction. A collagenase intracerebral hemorrhage model was performed in adult male Sprague Dawley rats. First, a possible relationship between annexin A1 and intracerebral hemorrhage pathology was confirmed by a loss of annexin A1 in the cerebrovascular endothelium and serum of intracerebral hemorrhage rats, and the rescue effects of i.v. administration of human recombinant annexin A1 in vivo and annexin A1 overexpression in vitro on the barrier function of brain microvascular endothelial cells exposed to intracerebral hemorrhage stimulus. Second, we found that intracerebral hemorrhage significantly increased the phosphorylation ratio of annexin A1 at the serine/threonine residues. Finally, based on site-specific mutagenesis, we identified two phosphorylation sites (a) annexin A1 phosphorylation at threonine 24 is required for its interaction with actin cytoskeleton, and (b) phosphorylation at serine27 is essential for annexin A1 secretion, both of which were essential for maintaining cytoskeleton integrity and paracellular permeability. In conclusion, annexin A1 prevents intracerebral hemorrhage-induced blood-brain barrier dysfunction in threonine 24 and serine27 phosphorylation-dependent manners. Annexin A1 phosphorylation may be a self-help strategy in brain microvascular endothelial cells after intracerebral hemorrhage; however, that was almost completely abolished by the intracerebral hemorrhage-induced loss of annexin A1.

18F-positron-emitting/fluorescent labeled erythrocytes allow imaging of internal hemorrhage in a murine intracranial hemorrhage model

An agent for visualizing cells by positron emission tomography is described and used to label red blood cells. The labeled red blood cells are injected systemically so that intracranial hemorrhage can be visualized by positron emission tomography (PET). Red blood cells are labeled with 0.3 µg of a positron-emitting, fluorescent multimodal imaging probe, and used to non-invasively image cryolesion induced intracranial hemorrhage in a murine model (BALB/c, 2.36 × 10⁸ cells, 100 µCi, <4 mm hemorrhage). Intracranial hemorrhage is confirmed by histology, fluorescence, bright-field, and PET ex vivo imaging. The low required activity, minimal mass, and high resolution of this technique make this strategy an attractive alternative for imaging intracranial hemorrhage. PET is one solution to a spectrum of issues that complicate single photon emission computed tomography (SPECT). For this reason, this application serves as a PET alternative to [^99mTc]-agents, and SPECT technology that is used in 2 million annual medical procedures. PET contrast is also superior to gadolinium and iodide contrast angiography for its lack of clinical contraindications.

Stem cell therapies in age-related neurodegenerative diseases and stroke

Aging, a complex process associated with various structural, functional and metabolic changes in the brain, is an important risk factor for neurodegenerative diseases and stroke. These diseases share similar neuropathological changes, such as the formation of misfolded proteins, oxidative stress, loss of neurons and synapses, dysfunction of the neurovascular unit (NVU), reduction of self-repair capacity, and motor and/or cognitive deficiencies. In addition to gray matter dysfunction, the plasticity and repair capacity of white matter also decrease with aging and contribute to neurodegenerative diseases. Aging not only renders patients more susceptible to these disorders, but also attenuates their self-repair capabilities. In addition, low drug responsiveness and intolerable side effects are major challenges in the prevention and treatment of senile diseases. Thus, stem cell therapies-characterized by cellular plasticity and the ability to self-renew-may be a promising strategy for aging-related brain disorders. Here, we review the common pathophysiological changes, treatments, and the promises and limitations of stem cell therapies in age-related neurodegenerative diseases and stroke.

Transient receptor potential channel 1/4 reduces subarachnoid hemorrhage-induced early brain injury in rats via calcineurin-mediated NMDAR and NFAT dephosphorylation

Transient receptor potential channel 1/4 (TRPC1/4) are considered to be related to subarachnoid hemorrhage (SAH)-induced cerebral vasospasm. In this study, a SAH rat model was employed to study the roles of TRPC1/4 in the early brain injury (EBI) after SAH. Primary cultured hippocampal neurons were exposed to oxyhemoglobin to mimic SAH in vitro. The protein levels of TRPC1/4 increased and peaked at 5 days after SAH in rats. Inhibition of TRPC1/4 by SKF96365 aggravated SAH-induced EBI, such as cortical cell death (by TUNEL staining) and degenerating (by FJB staining). In addition, TRPC1/4 overexpression could increase calcineurin activity, while increased calcineurin activity could promote the dephosphorylation of N-methyl-D-aspartate receptor (NMDAR). Calcineurin antagonist FK506 could weaken the neuroprotection and the dephosphorylation of NMDAR induced by TRPC1/4 overexpression. Contrarily, calcineurin agonist chlorogenic acid inhibited SAH-induced EBI, even when siRNA intervention of TRPC1/4 was performed. Moreover, calcineurin also could lead to the nuclear transfer of nuclear factor of activated T cells (NFAT), which is a transcription factor promoting the expressions of TRPC1/4. TRPC1/4 could inhibit SAH-induced EBI by supressing the phosphorylation of NMDAR via calcineurin. TRPC1/4-induced calcineurin activation also could promote the nuclear transfer of NFAT, suggesting a positive feedback regulation of TRPC1/4 expressions.

White matter injury in ischemic stroke

Stroke is one of the major causes of disability and mortality worldwide. It is well known that ischemic stroke can cause gray matter injury. However, stroke also elicits profound white matter injury, a risk factor for higher stroke incidence and poor neurological outcomes. The majority of damage caused by stroke is located in subcortical regions and, remarkably, white matter occupies nearly half of the average infarct volume. Indeed, white matter is exquisitely vulnerable to ischemia and is often injured more severely than gray matter. Clinical symptoms related to white matter injury include cognitive dysfunction, emotional disorders, sensorimotor impairments, as well as urinary incontinence and pain, all of which are closely associated with destruction and remodeling of white matter connectivity. White matter injury can be noninvasively detected by MRI, which provides a three-dimensional assessment of its morphology, metabolism, and function. There is an urgent need for novel white matter therapies, as currently available strategies are limited to preclinical animal studies. Optimal protection against ischemic stroke will need to encompass the fortification of both gray and white matter. In this review, we discuss white matter injury after ischemic stroke, focusing on clinical features and tools, such as imaging, manifestation, and potential treatments. We also briefly discuss the pathophysiology of WMI and future research directions.

G-CSF attenuates neuroinflammation and stabilizes the blood-brain barrier via the PI3K/Akt/GSK-3β signaling pathway following neonatal hypoxia-ischemia in rats

OBJECTIVE

Neonatal hypoxia occurs in approximately 60% of premature births and is associated with a multitude of neurological disorders. While various treatments have been developed, translating them from bench to bedside has been limited. We previously showed G-CSF administration was neuroprotective in a neonatal hypoxia-ischemia rat pup model, leading us to hypothesize that G-CSF inactivation of GSK-3β via the PI3K/Akt pathway may attenuate neuroinflammation and stabilize the blood-brain barrier (BBB).

METHODS

P10 Sprague-Dawley rat pups were subjected to unilateral carotid artery ligation followed by hypoxia for 2.5h. We assessed inflammation by measuring expression levels of IKKβ, NF-κB, TNF-α, IL-1β, IL-10, and IL-12 as well as neutrophil infiltration. BBB stabilization was evaluated by measuring Evans blue extravasation, and Western blot analysis of Claudin-3, Claudin-5, ICAM-1, and VCAM-1.

MEASUREMENTS AND MAIN RESULTS

First, the time course study showed that p-β-catenin/β-catenin, IKKβ, and NF-κB expression levels peaked at 48h post-HI. The knockdown of GSK-3β with siRNA prevented the HI-induced increase of p-β-catenin/β-catenin, IKKβ, and NF-κB expression levels 48h after HI. G-CSF treatment reduced brain water content and neuroinflammation by downregulating IKKβ, NF-κB, TNF-α, IL-1β, and IL-12 and upregulating IL-10, thereby reducing neutrophil infiltration. Additionally, G-CSF stabilizes the BBB by downregulating VCAM-1 and ICAM-1, as well as upregulating Claudins 3 and 5 in endothelial cells. G-CSFR knockdown by siRNA and Akt inhibition by Wortmannin reversed G-CSF's neuroprotective effects.

CONCLUSIONS

We demonstrate G-CSF plays a pivotal role in attenuating neuroinflammation and BBB disruption following HI by inactivating GSK-3β through the PI3K/Akt pathway.

Diffusion tensor imaging in hemorrhagic stroke

Diffusion tensor imaging (DTI) has evolved considerably over the last decade to now be knocking on the doors of wider clinical applications. There have been several efforts over the last decade to seek valuable and reliable application of DTI in different neurological disorders. The role of DTI in predicting outcomes in patients with brain tumors has been extensively studied and has become a fairly established clinical tool in this scenario. More recently DTI has been applied in mild traumatic brain injury to predict clinical outcomes based on DTI of the white matter tracts. The resolution of white matter fiber tractography based on DTI has improved over the years with increased magnet strength and better tractography post-processing. The role of DTI in hemorrhagic stroke has been studied preliminarily in the scientific literature. There is some evidence that DTI may be efficacious in predicting outcomes of motor function in animal models of intracranial hemorrhage. Only a handful of studies of DTI have been performed in subarachnoid hemorrhage or intraventricular hemorrhage scenarios. In this manuscript we will review the evolution of DTI, the existing evidence for its role in hemorrhagic stroke and discuss possible application of this non-invasive evaluation technique of human cerebral white matter tracts in the future.

The evolving roles of pericyte in early brain injury after subarachnoid hemorrhage

Despite accumulated understanding on the mechanisms of early brain injury and improved management of subarachnoid hemorrhage (SAH), it is still one of the serious and refractory health problems around the world. Traditionally, pericyte, served as capillary contraction handler, is recently considered as the main participant of microcirculation regulation in SAH pathophysiology. However, accumulate evidences indicate that pericyte is much more than we already know. Therefore, we briefly review the characteristics, regulation pathways and functions of pericyte, aim to summarize the evolving new pathophysiological roles of pericyte that are implicated in early brain injury after SAH and to improve our understanding in order to explore potential novel therapeutic options for patients with SAH. This article is part of a Special Issue entitled SI: Cell Interactions In Stroke.

MFGE8/Integrin β3 pathway alleviates apoptosis and inflammation in early brain injury after subarachnoid hemorrhage in rats

BACKGROUND

Milk fat globule-epidermal growth factor-factor 8(MFGE8)/Integrin β3 pathway was reported to be involved in reducing oxidative stress and early brain injury after subarachnoid hemorrhage (SAH). In the present study, the potential effects of MFGE8 and its receptor Integrin β3 in the inhibition of apoptosis and neuroinflammation in early brain injury after SAH were investigated.

METHODS

Ninety-five (95) male Sprague-Dawley rats were used. The SAH model was induced by endovascular perforation. Recombinant human MFGE8 (rhMFGE8), MFGE8 small interfering RNA (siRNA) and Integrin β3 siRNA were injected intracerebroventricularly. SAH grade, neurologic scores, Western blots and immunofluorescence were employed to study the mechanisms of MFGE8 and its receptor Integrin β3, as well as neurological outcome.

RESULTS

SAH induced significant neuronal apoptosis and inflammation and exhibited neurological dysfunction in rats. Knockdown endogenous MFGE8 with siRNA significantly increased the protein levels of cleaved caspase 3 and IL-1β, accompanied with more neurological deficits. rhMFGE8 significantly reduced neural cell death in cortex, decreased cleaved caspase 3 and IL-1β expressions, and improved neurological functions 24h after SAH. The anti-apoptosis and anti-inflammation effects of rhMFGE8 were abolished by Integrin β3 siRNA.

CONCLUSION

MFGE8 could alleviate neurologic damage in early brain injury after SAH via anti-inflammation and anti-apoptosis effects. MFGE8 may serve as a promising therapeutic target for future management of SAH patients.

Sphingosine kinase 1 mediates neuroinflammation following cerebral ischemia

Sphingosine kinases (Sphks) are the rate-limiting kinases in the generation of sphingosine-1-phosphate, which is a well-established intracellular pro-survival lipid mediator. Sphk2 has been reported to be protective following experimental stroke. We investigated the role of Sphk1 in cerebral ischemia using a mouse middle cerebral artery occlusion (MCAO) model and an in vitro glucose-oxygen deprivation (OGD) model. Sphk expression and activity were assessed in the ischemic brain with quantitative PCR (qPCR), Western blot, immunohistochemistry and enzyme-linked immunosorbent assay (ELISA). Pharmacological and gene knockdown approaches were utilized to investigate the effects of Sphk1 on stroke outcomes. The expression of Sphk1 but not that of Sphk2 was rapidly induced in the cortical penumbra over 96h after MCAO, and the microglia were one of the major cellular sources of Sphk1 induction. Consistently, Sphk activity was enhanced in the cortical penumbra. In contrast to the protective role of Sphk2, pharmacological inhibition and cortical knockdown of Sphk1 reduced infarction at 24 and 96h after reperfusion. Additionally, the Sphk1 inhibitor improved the neurological deficits at 96h after reperfusion. Mechanistically, Sphk1 inhibition and knockdown significantly attenuated MCAO-induced expression of inflammatory mediators in the cortical penumbra. Moreover, using a conditioned medium transfer approach, we demonstrated that OGD-treated neurons induced the expression of Sphk1 and pro-inflammatory mediators in primary microglia, and the microglial induction of pro-inflammatory mediators by ischemic neurons was blunted by Sphk1 inhibition. Taken together, our results indicate that Sphk1 plays an essential role in mediating post-stroke neuroinflammation.

Venous system in acute brain injury: Mechanisms of pathophysiological change and function

Cerebral vascular injury is a major component of acute brain injury. Currently, neuroprotective strategies primarily focus on the recanalization of cerebral arteries and capillaries, and the protection of insulted neurons. Hitherto, the role of vein drainage in the pathophysiology of acute brain injury has been overlooked, due to an under appreciation of the magnitude of the impact of veins in circulation. In this review, we summarize the changes in the vein morphology and functions that are known, or likely to occur related to acute brain injury, and aim to advance the therapeutic management of acute brain injury by shifting the focus from reperfusion to another term: recirculation. Recent progress in the neurobiological understanding of the vascular neural network has demonstrated that cerebral venous systems are able to respond to acute brain injury by regulating the blood flow disharmony following brain edema, blood brain barrier disruption, ischemia, and hemorrhage. With the evidence presented in this review, future clinical management of acutely brain injured patients will expand to include the recirculation concept, establishing a harmony between arterial and venous systems, in addition to the established recanalization and reperfusion strategies.

Vascular neural network: the importance of vein drainage in stroke

This perspective commentary summarized the stroke pathophysiology evolution, especially the focus in the past on neuroprotection and neurovascular protection and highlighted the newer term for stroke pathophysiology: vascular neural network. Emphasis is on the role of venules and veins after an acute stroke and as potential treatment targets. Vein drainage may contribute to the acute phase of brain edema and the outcomes of stroke patients.