MEK1/2 inhibition attenuates vascular ETA and ETB receptor alterations after cerebral ischaemia

Pre-ischemic exercise prevents inflammation and apoptosis by inhibiting MAPK pathway in ischemic stroke

Introduction

Mitogen-activated protein kinase (MAPK) pathway is a major mechanism of acute brain damage in ischemic stroke. Pre-ischemic exercise is an effective method to reduce ischemic injury. However, the regulation by pre-ischemic exercise of MAPK pathway and associated mechanisms in animal models remains unclear.

Materials and methods

In this study, Male SD rats were randomly divided into sham group, middle cerebral artery occlusion (MCAO) group, and exercise plus MCAO (EX + MCAO) group for 21 days, and then was established by MCAO. Longa score was used to measure neurological deficits at 0, 1, 2, and 3 days after MCAO. Hematoxylin and eosin staining was used to observe the brain injury. The expression of MAPK pathway was quantified by western blot. The M1 microglia protein was quantified by western blot and immunofluorescence, and the level of inflammatory factor was measured by enzyme-linked immunosorbent assay. TUNEL staining and western blot were used to measure apoptosis.

Results

In the current study, we observed that pre-ischemic exercise effectively decreased infarct volume, neurological deficit score and brain injury in MCAO rats through suppressing the activation of p-JNK and p-ERK1/2. Further investigation revealed that pre-ischemic exercise decreased M1 microglia activation and the serum level of TNF-α and IL-1β. In addition, the increased number of TUNEL-positive cells and Bax/Bcl-2 ratio also were reversed by pre-ischemic exercise.

Conclusions

Pre-ischemic exercise can alleviate inflammatory response and apoptosis by inhibiting the MAPK pathway in MCAO rats.

MicroRNA152-3p Protects Against Ischemia/Reperfusion-Induced Bbb Destruction Possibly Targeting the MAP3K2/JNK/c-Jun Pathway

In the current study, we reported that overexpression of miR-152-3p effectively ameliorated neurological deficits and protected blood-brain barrier(BBB) integrity in middle cerebral artery occlusion (MCAO) rats. In an in vitro model, the level of miR-152-3p was significantly decreased in bEnd.3 cells after oxygen–glucose deprivation/reperfusion (OGD/R) insult. miR-152-3p overexpressing bEnd.3 cell monolayers were protected from OGD/R-induced microvascular hyperpermeability. The miR-152-3p-mediated protective effect was associated with lower apoptosis of endothelia by negatively modulating the MAP3K2/JNK/c-Jun pathway.

The MEK Inhibitor Trametinib Improves Outcomes following Subarachnoid Haemorrhage in Female Rats

Aneurysmal subarachnoid haemorrhage (SAH) is a haemorrhagic stroke that causes approximately 5% of all stroke incidents. We have been working on a treatment strategy that targets changes in cerebrovascular contractile receptors, by blocking the MEK/ERK1/2 signalling pathway. Recently, a positive effect of trametinib was found in male rats, but investigations of both sexes in pre-clinical studies are an important necessity. In the current study, a SAH was induced in female rats, by autologous blood-injection into the pre-chiasmatic cistern. This produces a dramatic, transient increase in intracranial pressure (ICP) and an acute and prolonged decrease in cerebral blood flow. Rats were then treated with either vehicle or three doses of 0.5 mg/kg trametinib (specific MEK/ERK1/2 inhibitor) intraperitoneally at 3, 9, and 24 h after the SAH. The outcome was assessed by a panel of tests, including intracranial pressure (ICP), sensorimotor tests, a neurological outcome score, and myography. We observed a significant difference in arterial contractility and a reduction in subacute increases in ICP when the rats were treated with trametinib. The sensory motor and neurological outcomes in trametinib-treated rats were significantly improved, suggesting that the improved outcome in females is similar to that of males treated with trametinib.

Changes in P2Y6 receptor-mediated vasoreactivity following focal and global ischemia

Ischemia, both in the form of focal thromboembolic stroke and following subarachnoid hemorrhage (SAH), causes upregulation of vasoconstrictive receptor systems within the cerebral vasculature. Descriptions regarding changes in purinergic signaling following ischemia are lacking, especially when the importance of purinergic signaling in regulating vascular tone is taken into consideration. This prompted us to evaluate changes in P2Y₆ -mediated vasomotor reactivity in two different stroke models in rat. We used wire myography to measure changes in cerebral vasoreactivity to the P2Y₆ agonist UDP-β-S following either experimental SAH or transient middle cerebral artery occlusion. Changes in receptor localization or receptor expression were evaluated using immunohistochemistry and quantitative flow cytometry. Transient middle cerebral artery occlusion caused an increase in Emax when compared to sham (233.6 [206.1-258.5]% vs. 161.1 [147.1-242.6]%, p = 0.0365). No such change was seen following SAH. Both stroke models were associated with increased levels of P2Y₆ receptor expression in the vascular smooth muscle cells (90.94 [86.99-99.15]% and 93.79 [89.96-96.39]% vs. 80.31 [70.80-80.86]%, p = 0.021) and p = 0.039 respectively. There was no change in receptor localization in either of the stroke models. Based on these findings, we conclude that focal ischemic stroke increases vascular sensitivity to UDP-β-S by upregulating P2Y₆ receptors on vascular smooth muscle cells while experimental SAH did not induce changes in vasoreactivity in spite of increased P2Y₆ receptor expression.

Ovariectomy Reduces Vasocontractile Responses of Rat Middle Cerebral Arteries After Focal Cerebral Ischemia

ABSTRACT

Effects of sex hormones on stroke outcome are not fully understood. A deleterious consequence of cerebral ischemia is upregulation of vasoconstrictor receptors in cerebral arteries that exacerbate stroke injury. Here, we tested the hypothesis that female sex hormones alter vasocontractile responses after experimental stroke in vivo or after organ culture in vitro, a model of vasocontractile receptor upregulation. Female rats with intact ovaries and ovariectomized (OVX) females treated with 17β-estradiol, progesterone, or placebo were subjected to transient, unilateral middle cerebral artery occlusion followed by reperfusion (I/R). The maximum contractile response, measured my wire myography, in response to the endothelin B receptor agonist sarafotoxin 6c was increased in female arteries after I/R, but the maximum response was significantly lower in arteries from OVX females. Maximum contraction mediated by the serotonin agonist 5-carboxamidotryptamine was diminished after I/R, with arteries from OVX females showing a greater decrease in maximum contractile response. Contraction elicited by angiotensin II was similar in all arteries. Neither estrogen nor progesterone treatment of OVX females affected I/R-induced changes in endothelin B- and 5-carboxamidotryptamine-induced vasocontraction. These findings suggest that sex hormones do not directly influence vasocontractile alterations that occur after ischemic stroke; however, loss of ovarian function does impact this process.

ETA receptors are involved in the febrile response induced by high dose of bacterial endotoxin

Previous studies have demonstrated that endothelin-1 (ET-1) is involved in the febrile response induced by lipopolysaccharide (LPS) in male and female rats. This peptide induces fever acting on ET_B receptors in the central nervous system. However, during sepsis, endothelinergic ET_A receptors in the brain also exert an important role reducing the mortality of the animals. The present study evaluated the participation of ET_A receptors in the febrile response induced by different doses LPS in rats. Male Wistar rats were treated with the ET_A receptor antagonist BQ123 before or after the injection of a low dose (10 μg/kg) or a high dose (200 μg/kg) of LPS intraperitoneally. The febrile response was evaluated. The treatment with BQ123, in both protocols did not change the febrile response induced by the lower dose of LPS. The pre-treatment with BQ123 also did not significantly change the febrile response induced by a higher dose of LPS but the post-treatment with the antagonist abolished the febrile response induced by this dose of LPS. These results suggest that even though ET_A receptors are not recruited in the febrile response induced by lower doses of LPS, they are involved in the febrile response induced by high doses of this stimulus.

Secondhand cigarette smoke induces increased expression of contractile endothelin receptors in rat coronary arteries via a MEK1/2 sensitive mechanism

OBJECTIVES

Cigarette smoke, a strong risk factor for cardiovascular diseases, upregulates contractile endothelin (ET) receptors in coronary arteries. The present study examined the effects of second hand cigarette smoke exposure on the contractile endothelin receptors and the role of the MEK1/2 pathway in rat coronary arteries. Design: Rats were exposed to secondhand smoke (SHS) for 8 weeks followed by intraperitoneal injection of a MEK1/2 inhibitor, U0126 daily for another 4 weeks. Contractile responses of isolated coronary arteries were recorded by a sensitive wire myograph. The receptor protein expression levels were examined by Western blotting. Results: The results showed that SHS in vivo caused increased expression of ET receptors ET_A and ET_B, and that the MEK1/2 blocker U0126 significantly reversed SHS exposure-increased ET_A-mediated contractile responses and protein levels. Similar alterations were observed in ET_B receptors. U0126 showed dose-dependent effects on SHS-induced response on contractile property and protein levels of the ET_B receptor. However, only the higher dose U0126 (15 mg/kg) had inhibitory effects on the ET_A receptor. Conclusions: Taken together, our data show that SHS increases contractile ET receptors and MEK1/2 pathway inhibitor offsets SHS exposure-induced ET_A and ET_B receptor upregulation in rat coronary arteries.

Endothelin: 30 Years From Discovery to Therapy

Discovered in 1987 as a potent endothelial cell-derived vasoconstrictor peptide, endothelin-1 (ET-1), the predominant member of the endothelin peptide family, is now recognized as a multifunctional peptide with cytokine-like activity contributing to almost all aspects of physiology and cell function. More than 30 000 scientific articles on endothelin were published over the past 3 decades, leading to the development and subsequent regulatory approval of a new class of therapeutics-the endothelin receptor antagonists (ERAs). This article reviews the history of the discovery of endothelin and its role in genetics, physiology, and disease. Here, we summarize the main clinical trials using ERAs and discuss the role of endothelin in cardiovascular diseases such as arterial hypertension, preecclampsia, coronary atherosclerosis, myocardial infarction in the absence of obstructive coronary artery disease (MINOCA) caused by spontaneous coronary artery dissection (SCAD), Takotsubo syndrome, and heart failure. We also discuss how endothelins contributes to diabetic kidney disease and focal segmental glomerulosclerosis, pulmonary arterial hypertension, as well as cancer, immune disorders, and allograft rejection (which all involve ET_A autoantibodies), and neurological diseases. The application of ERAs, dual endothelin receptor/angiotensin receptor antagonists (DARAs), selective ET_B agonists, novel biologics such as receptor-targeting antibodies, or immunization against ET_A receptors holds the potential to slow the progression or even reverse chronic noncommunicable diseases. Future clinical studies will show whether targeting endothelin receptors can prevent or reduce disability from disease and improve clinical outcome, quality of life, and survival in patients.

Enhanced Endothelin A and B Receptor Expression and Receptor-Mediated Vasoconstriction in Rat Mesenteric arteries after Lipopolysaccharide Challenge

During organ culture of intact vessels, endothelin receptors (ETRs) were upregulated in vascular smooth muscle cells (VSMCs) by various stimuli, but whether inflammation alters ETR expression in vivo remains unclear. We aimed to explore the effects of lipopolysaccharide (LPS) challenge on ETR expression in the VSMC in vivo. Male Sprague-Dawley rats received a single intraperitoneal injection of LPS (5 mg/kg body weight) or normal saline (NS) for 6 hrs. The function and expression of ETR type A (ET_A) and type B (ET_B) were evaluated in the mesenteric arteries without endothelium, by using myograph system, real-time quantitative PCR, Western blot, and immunohistochemical staining, respectively. Serum tumor necrosis factor-α (TNF-α) level was assessed by using enzyme-linked immunosorbent assay. The results showed that, compared to control (NS) group, LPS treatment potently enhanced the vasoconstriction mediated by ET_A or ET_B in rat mesenteric artery, with elevated maximum effects. ET_A and ET_B expressions in the VSMC were increased at both mRNA and protein levels after LPS treatment, paralleled with activation of the NF-κB pathway and augmented serum TNF-α level. Conclusively, in the rat model of immediate systemic inflammation induced by LPS, ET_A and ET_B expressions were increased in the mesenteric arterial VSMC, paralleled with enhanced receptor-mediated vasoconstriction and activation of the NF-κB pathway. Our data has for the first time demonstrated the upregulation of ETRs in VSMCs by LPS-induced immediate inflammation in vivo.

S1PR2 antagonist alleviates oxidative stress-enhanced brain endothelial permeability by attenuating p38 and Erk1/2-dependent cPLA2 phosphorylation

Both sphingosine-1-phosphate receptor-2 (S1PR2) and cytosolic phospholipase A₂ (cPLA₂) are implicated in the disruption of cerebrovascular integrity in experimental stroke. However, the role of S1PR2 in induction of cPLA₂ phosphorylation during cerebral ischemia-induced endothelial dysfunction remains unknown. This study investigated the effect of S1PR2 blockade on oxidative stress-induced cerebrovascular endothelial barrier impairment and explored the possible mechanisms. In bEnd3 cells, cPLA₂ inhibitor CAY10502 as well as S1PR2 antagonist JTE013 profoundly suppressed hydrogen peroxide (H₂O₂)-induced changes of paracellular permeability and ZO-1 localization. Besides p38, extracellular signal-regulated kinase (Erk) 1/2 is required for H₂O₂-increased cPLA₂ phosphorylation and endothelial permeability. Pharmacological and genetic inhibition of S1PR2 significantly suppressed their phosphorylation in response to H₂O₂. Especially lentivirus-mediated knockdown of S1PR2 inhibited H₂O₂-induced ZO-1 redistribution and paracellular hyperpermeability. Using the permanent middle cerebral artery occlusion (pMCAO) mouse model, we found JTE013 pretreatment markedly reduced Evans blue dye (EBD) extravasation and reversed the decrease in VE-cadherin, occludin, claudin-5 and CD31 expression in infarcted hemisphere. Lentivirus-mediated S1PR2 knockdown also attenuated EBD extravasation. Furthermore, JTE013 pretreatment attenuated neurological deficit, brain edema and infarction volume. Therefore, our findings suggest the protective effect of JTE013 on brain endothelial barrier integrity is likely mediated by suppressing p38 and Erk1/2-dependent cPLA₂ phosphorylation under oxidative stress.

Inhibiting of GRASP65 Phosphorylation by DL-3-N-Butylphthalide Protects against Cerebral Ischemia-Reperfusion Injury via ERK Signaling

Background and Purpose

The aim of this study was to explore the role of DL-3-n-butylphthalide (NBP) in cerebral ischemia-reperfusion injury (CIRI) mice model. The involvement of extracellular signal-regulated kinase (ERK) signaling pathway was also investigated.

Methods

All mice were divided into five groups: sham-operated group, CIRI group, NBP pretreatment group, NBP treatment group, and NBP pretreatment + treatment group. The CIRI mice model was established by the use of the Pulsinelli four-vessel occlusion method. Pretreatment mice received NBP (90 mg/kg/d) three times a day within four days before reperfusion by gavage. Treatment mice received NBP (90 mg/kg/d) three times a day within five days after reperfusion by gavage. We detected the infarction area, the neurological severity, and the superoxide dismutase and malondialdehyde levels. Furthermore, we observed the expressions of GRASP65, phosphorylation of GRASP65 (pGRASP65), ERK, and phosphorylation of ERK (pERK) by the use of Western blotting.

Results

The result showed that the ERK pathway was activated in response to CIRI. NBP decreases the expressions of pERK and pGRASP65 following CIRI. Additionally, NBP could decrease MDA and increase SOD level in brain tissues. Decreased infarct volume was also observed in the NBP group. Thereby, NBP inhibited the activation of the ERK pathway induced by CIRI and reduced the GRASP65 phosphorylation.

Conclusions

The current finding suggested that NBP protected the cerebrum from CIRI mediated by inhibiting the ERK signaling pathway and subsequently reducing GRASP65 phosphorylation.

Inhibition of mitogen-activated protein kinase 1/2 in the acute phase of stroke improves long-term neurological outcome and promotes recovery processes in rats

AIM

Extracellular signal-regulated kinase (ERK) 1/2 is activated during acute phase of stroke and contributes to stroke pathology. We have found that acute treatment with MEK1/2 inhibitors decreases infarct size and neurological deficits 2 days after experimental stroke. However, it is not known whether benefits of this inhibition persist long-term. Therefore, the aim of this study was to assess neurological function, infarct size and recovery processes 14 days after stroke in male rats to determine long-term outcome following acute treatment with the MEK1/2 inhibitor U0126.

METHODS

Transient middle cerebral artery occlusion was induced in male rats. U0126 or vehicle was given at 0 and 24 h of reperfusion. Neurological function was assessed by staircase, 6-point and 28-point neuroscore tests up to 14 days after induction of stroke. At day 14, infarct volumes were determined and recovery processes were evaluated by measuring protein expression of the tyrosine kinase receptor Tie-2 and nestin. Levels of p-ERK1/2 protein were determined.

RESULTS

Acute treatment with U0126 significantly improved long-term functional recovery, reduced infarct size, and enhanced Tie-2 and nestin protein expression at 14 days post-stroke. There was no residual blockade of p-ERK1/2 at this time point.

CONCLUSION

It is demonstrated that benefits of early treatment with U0126 persist beyond subacute phase of ischaemic stroke in male rats. Prevention of ERK1/2 activation in the acute phase results in improved long-term functional outcome and enhances later-stage recovery processes. These results expand our understanding of the benefits and promise of using MEK1/2 inhibitors in stroke recovery.

Enriched Environment Enhances Poststroke Neurological Function Recovery on Rat: Involvement of p-ERK1/2

BACKGROUND

Increasing evidence shows that exposure to an enriched environment (EE) after cerebral ischemia or reperfusion injury is neuroprotective in animal models, including that EE enhances functional recovery after ischemic stroke. However, the mechanism underlying this effect remains unclear. To clarify this critical issue, the current study investigated the effects of EE on the role of extracellular signal-regulated kinase (ERK) after cerebral ischemia or reperfusion injury of rat.

METHODS

Adult rats were subjected to ischemia induced by middle cerebral artery occlusion (MCAO) followed by reperfusion. Ladder walking task and limb-use asymmetry task were used to test the recovery of rat behavior on postoperative days 1, 3, 5, 7, 14 and days 3, 7, 14, respectively. On the eighth day after MCAO, infarct volume was assessed by 2,3,5-triphenyltetrazolium chloride staining. Expressions of phosphorylated ERK1/2 (p-ERK1/2) and total ERK1/2 were examined by western blot, and electron microscopy was used to evaluate the astrocytes morphology surround in the perivascular 14 days after MCAO.

RESULTS

EE improves the recovery of coordination and integration of motor movements on rats after cerebral ischemia or reperfusion injury. EE downregulates the level of p-ERK1/2 in the rat cortex after cerebral ischemia or reperfusion injury. Furthermore, EE reduces astrocytic swelling and injury.

CONCLUSIONS

These findings suggest that EE could promote rehabilitation after ischemia via regulation of p-ERK1/2 expression, which may provide a therapeutic approach for cerebral ischemia or reperfusion injury. The suppression of postischemic astrocytic swelling in the brain of the ischemic rats through the intervention of EE would be one of the underlying mechanisms in the protective effect of cerebral ischemia.

Picroside II Inhibits the MEK-ERK1/2-COX2 Signal Pathway to Prevent Cerebral Ischemic Injury in Rats

The objective of this study is to explore the neuroprotective effect and mechanism of picroside II on ERK1/2-COX2 signal transduction pathway after cerebral ischemic injury in rats. Focal cerebral ischemic models were established by inserting monofilament threads into the middle cerebral artery in 200 Wistar rats. Twenty four rats were randomly selected into control group, while the other rats were randomly divided into six groups: model group, picroside group, lipopolysaccharide (LPS) with picroside group, U0126 with picroside group, LPS group, and U0126 group with each group containing three subgroups with ischemia at 6, 12, and 24 h. Neurobehavioral function in the rats was evaluated by modified neurological severity score points (mNSS) test; structure of neurons was observed using hematoxylin-eosin (HE) staining; apoptotic cells were counted using terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) assay; expressions of phosphorylated mitogen/extracellular signal-regulated kinase kinas1/2 (pMEK1/2), phosphorylated extracellular signal-regulated protein kinase1/2 (pERK1/2), and cyclooxygenase (COX2) in the cortex were determined using immunohistochemistry (IHC) and Western blot (WB); and real-time PCR was used to determine the level of COX2 mRNA. The neurological behavioral malfunction appeared in all rats with middle cerebral artery occlusion (MCAO). In the model group, neuron damage was extensive, while the neurobehavioral function score, apoptotic cell index, expression of pMEK1/2, pERK1/2, and COX2 and the level of COX2 mRNA increased significantly when compared to the control group. The peak COX2 mRNA level was in ischemia 12 h, prior to the peak in COX2 protein expression. In the picroside and U0126 groups, the neurological behavioral function was improved, and the number of apoptotic cells and the expression of pMEK1/2, pERK1/2, and COX2 decreased significantly when compared to the model group. In the LPS with picroside group, at ischemia 6 h neuron damage was extensive, and pMEK1/2, pERK1/2, and COX2 expression were much higher than in the model group. But at ischemia 12 and 24 h, the expression of pMEK1/2, pERK1/2, and COX2 decreased slightly, and the neurobehavioral function also improved slightly. In LPS group, neuron damage was extensive, pMEK1/2, pERK1/2, and COX2 expression was still at a high level, and COX2 mRNA peak arrived at ischemic 12 h. Picroside II downregulates COX2 expression after MCAO by inhibiting MEK-ERK1/2 in rats to protect neurons from apoptosis and inflammation.

U0126 attenuates cerebral vasoconstriction and improves long-term neurologic outcome after stroke in female rats

Sex differences are well known in cerebral ischemia and may impact the effect of stroke treatments. In male rats, the MEK1/2 inhibitor U0126 reduces ischemia-induced endothelin type B (ETB) receptor upregulation, infarct size and improves acute neurologic function after experimental stroke. However, responses to this treatment in females and long-term effects on outcome are not known. Initial experiments used in vitro organ culture of cerebral arteries, confirming ERK1/2 activation and increased ETB receptor-mediated vasoconstriction in female cerebral arteries. Transient middle cerebral artery occlusion (tMCAO, 120 minutes) was induced in female Wistar rats, with U0126 (30 mg/kg intraperitoneally) or vehicle administered at 0 and 24 hours of reperfusion, or with no treatment. Infarct volumes were determined and neurologic function was assessed by 6-point and 28-point neuroscores. ETB receptor-mediated contraction was studied with myograph and protein expression with immunohistochemistry. In vitro organ culture and tMCAO resulted in vascular ETB receptor upregulation and activation of ERK1/2 that was prevented by U0126. Although no effect on infarct size, U0126 improved the long-term neurologic function after experimental stroke in female rats. In conclusion, early prevention of the ERK1/2 activation and ETB receptor-mediated vasoconstriction in the cerebral vasculature after ischemic stroke in female rats improves the long-term neurologic outcome.

Cerebrospinal fluid from patients with subarachnoid haemorrhage and vasospasm enhances endothelin contraction in rat cerebral arteries

INTRODUCTION

Previous studies have suggested that cerebrospinal fluid from patients with subarachnoid hemorrhage (SAH) leads to pronounced vasoconstriction in isolated arteries. We hypothesized that only cerebrospinal fluid from SAH patients with vasospasm would produce an enhanced contractile response to endothelin-1 in rat cerebral arteries, involving both endothelin ETA and ETB receptors.

METHODS

Intact rat basilar arteries were incubated for 24 hours with cerebrospinal fluid from 1) SAH patients with vasospasm, 2) SAH patients without vasospasm, and 3) control patients. Arterial segments with and without endothelium were mounted in myographs and concentration-response curves for endothelin-1 were constructed in the absence and presence of selective and combined ETA and ETB receptor antagonists. Endothelin concentrations in culture medium and receptor expression were measured.

RESULTS

Compared to the other groups, the following was observed in arteries exposed to cerebrospinal fluid from patients with vasospasm: 1) larger contractions at lower endothelin concentrations (p<0.05); 2) the increased endothelin contraction was absent in arteries without endothelium; 3) higher levels of endothelin secretion in the culture medium (p<0.05); 4) there was expression of ETA receptors and new expression of ETB receptors was apparent; 5) reduction in the enhanced response to endothelin after ETB blockade in the low range and after ETA blockade in the high range of endothelin concentrations; 6) after combined ETA and ETB blockade a complete inhibition of endothelin contraction was observed.

CONCLUSIONS

Our experimental findings showed that in intact rat basilar arteries exposed to cerebrospinal fluid from patients with vasospasm endothelin contraction was enhanced in an endothelium-dependent manner and was blocked by combined ETA and ETB receptor antagonism. Therefore we suggest that combined blockade of both receptors may play a role in counteracting vasospasm in patients with SAH.

Lipopolysaccharide enhanced renal vascular response to endothelin-1 through ETA overexpression in portal hypertensive rats

BACKGROUND AND AIM

Hypo-perfusion resulting from intense renal vasoconstriction is traditionally contributed to renal dysfunction in advanced liver disease, although cumulative studies demonstrated renal vasodilatation with impaired vascular contractility to endogenous vasoconstrictors in portal hypertension and compensated liver cirrhosis. The pathophysiology of altered renal hemodynamics remains unclear. This study, using a rat model of portal hypertension with superimposed endotoxemia, was designed to delineate the evolution of renal vascular reactivity and vaso-regulatory gene expression during liver disease progression.

METHODS

Rats were randomized into sham surgery (SHAM) or partial portal vein ligation (PVL). Endotoxemia was induced by intraperitoneal injection of lipopolysaccharide (LPS) on the seventh day following surgery. Isolated kidney perfusion was performed at 0.5 h or 5 h after LPS to evaluate renal vascular response to endothelin-1.

RESULTS

In contrast to impaired vascular contractility of SHAM rats, PVL rats displayed enhanced renal vascular reactivity to endothelin-1 at 5 h following endotoxemia. There were extensive upregulations of inducible nitric oxide synthase in kidney tissues of endotoxemic rats. The changes of renal endothelin receptor type A (ETA ) level paralleled with the changes of renal vascular reactivity in LPS-treated rats. Compared with SHAM rats, PVL rats showed increased renal ETA and phosphorylated extracellular-signal-regulated kinases 1/2 (p-ERK1/2) at 5 h after LPS.

CONCLUSION

LPS-induced systemic hypotension induces a paradoxical change of renal vascular response to endothelin-1 between SHAM and PVL rats. LPS-induced renal vascular hyperreactivity in PVL rats was associated with upregulation of renal ETA and subsequent activation of ERK1/2 signaling.

CaMKII and MEK1/2 inhibition time-dependently modify inflammatory signaling in rat cerebral arteries during organ culture

BACKGROUND

Cerebral ischemia induces transcriptional upregulation of inflammatory genes in the brain parenchyma and in cerebral arteries, thereby contributing to the infarct development. The present study was designed to evaluate the involvement of calcium-calmodulin-dependent protein kinase (CaMKII) II and extracellular signal-regulated kinase1/2 (ERK1/2) on inflammatory mediators in rat cerebral arteries using organ culture as a method for inducing ischemic-like vascular wall changes.

METHODS

Rat basilar arteries were cultured in serum-free medium for 0, 3, 6 or 24 hours in the presence or absence of the CaMKII inhibitor KN93 or the MEK1/2 inhibitor U0126. Protein expression of activated CaMKII, ERK1/2, and inflammatory-associated protein kinases and mediators were examined with western blot and immunohistochemistry. Caspase-3 mRNA levels in basilar arteries were studied with real-time PCR.

RESULTS

Western blot evaluation showed that organ culture induced a significant increase in phosphorylated ERK1/2 at 3, 6 and 24 hours, while CaMKII was found to be already activated in fresh non-incubated arteries and to decrease with incubation time. The addition of U0126 or KN93 decreased levels of phosphorylated c-Jun N-terminal kinase and p-p38, as evaluated by immunohistochemistry. KN93 affected the increase in caspase-3 mRNA expression only when given at the start of incubation, while U0126 had an inhibitory effect when given up to six hours later. Tumor necrosis factor receptor 1 was elevated after organ culture. This inflammatory marker was reduced by both of the two different protein kinase inhibitors.

CONCLUSIONS

The novel findings of the present study are that the cross-talk between the two protein kinases and the inhibition of CaMKII or MEK1/2 in a time-dependent manner attenuates inflammatory-associated protein kinases and mediators, suggesting that they play a role in cerebrovascular inflammation.

Early MEK1/2 inhibition after global cerebral ischemia in rats reduces brain damage and improves outcome by preventing delayed vasoconstrictor receptor upregulation

Background

Global cerebral ischemia following cardiac arrest is associated with increased cerebral vasoconstriction and decreased cerebral blood flow, contributing to delayed neuronal cell death and neurological detriments in affected patients. We hypothesize that upregulation of contractile ET_B and 5-HT_1B receptors, previously demonstrated in cerebral arteries after experimental global ischemia, are a key mechanism behind insufficient perfusion of the post-ischemic brain, proposing blockade of this receptor upregulation as a novel target for prevention of cerebral hypoperfusion and delayed neuronal cell death after global cerebral ischemia. The aim was to characterize the time-course of receptor upregulation and associated neuronal damage after global ischemia and investigate whether treatment with the MEK1/2 inhibitor U0126 can prevent cerebrovascular receptor upregulation and thereby improve functional outcome after global cerebral ischemia. Incomplete global cerebral ischemia was induced in Wistar rats and the time-course of enhanced contractile responses and the effect of U0126 in cerebral arteries were studied by wire myography and the neuronal cell death by TUNEL. The expression of ET_B and 5-HT_1B receptors was determined by immunofluorescence.

Results

Enhanced vasoconstriction peaked in fore- and midbrain arteries 3 days after ischemia. Neuronal cell death appeared initially in the hippocampus 3 days after ischemia and gradually increased until 7 days post-ischemia. Treatment with U0126 normalised cerebrovascular ET_B and 5-HT_1B receptor expression and contractile function, reduced hippocampal cell death and improved survival rate compared to vehicle treated animals.

Conclusions

Excessive cerebrovascular expression of contractile ET_B and 5-HT_1B receptors is a delayed response to global cerebral ischemia peaking 3 days after the insult, which likely contributes to the development of delayed neuronal damage. The enhanced cerebrovascular contractility can be prevented by treatment with the MEK1/2 inhibitor U0126, diminishes neuronal damage and improves survival rate, suggesting MEK1/2 inhibition as a novel strategy for early treatment of neurological consequences following global cerebral ischemia.

ERK inhibition with PD184161 mitigates brain damage in a mouse model of stroke

Ischemic stroke is a leading cause of death. It has previously been shown that blocking activation of extracellular signal-regulated kinase (ERK) with the MEK inhibitor U0126 mitigates brain damage in rodent models of ischemic stroke. Here we show that the newer MEK inhibitor PD184161 reduces cell death and altered gene expression in cultured neurons and mice undergoing excitotoxicity, and has similar protective effects in a mouse model of stroke. This further supports ERK inhibition as a potential treatment for stroke.

Neuroprotective effects of prior exposure to enriched environment on cerebral ischemia/reperfusion injury in rats: the possible molecular mechanism

Increasing evidence shows that exposure to an enriched environment (EE) after cerebral ischemia/reperfusion injury is neuroprotective in animal models. Recent studies have demonstrated that animals housed in an enriched environment condition after an experimental stroke obtained a better functional outcome than those housed in a standard condition. However, little is known about the underlying mechanisms of neuroprotective effects of enriched environment exposure prior to injury. The current study examined the neuroprotective effects of prior enriched environment exposure after transient middle cerebral artery occlusion (MCAO) in rats. Male Sprague Dawley (SD) rats, weighing 55-65g at the beginning of the experiment, were randomly assigned to a pre-ischemic enriched environment (PIEE) or pre-ischemic standard condition (PISC) group for 1 month. They were weighed on days1, 7, 18, and 28, and their locomotor activity was tracked during the period between 9:00am and 3:00pm daily. After 1 month, ischemia was induced by occluding the middle cerebral artery for 90min, followed by reperfusion. After approximately 24h of the operation, functional outcomes were assessed using the beam-walking test and a neurological evaluation scale in all rats. We measured the expression of extracellular signal regulated protein kinases1/2 (ERK1/2) by western blotting and gene expression levels of neuronal nitric oxide synthase (nNOS) and inducible nitric oxide synthasen (iNOS) by Real-Time PCR in the cortical area affected by ischemia. Finally, we measured the level of malondialdehyde (MDA) content, which is a biomarker of oxidative stress. The results showed that rats in the PIEE group had lighter weight than those in the PISC group. The functional outcomes of rats in the PIEE group were better than those in the PISC group, and substances associated with inflammation, such as MDA, nNOS, iNOS, and phospho-ERK1/2, were lower in the PIEE group compared with the PISC group. These results indicate that enriched environment may provide neuroprotection via ischemic preconditioning and enhance resilience to cerebral ischemia.

tPA-S(481)A prevents impairment of cerebrovascular autoregulation by endogenous tPA after traumatic brain injury by upregulating p38 MAPK and inhibiting ET-1

Traumatic brain injury (TBI) is associated with loss of cerebrovascular autoregulation, which leads to cerebral hypoperfusion. Mitogen activated protein kinase (MAPK) isoforms ERK, p38, and JNK and endothelin-1 (ET-1) are mediators of impaired cerebral hemodynamics after TBI. Excessive tissue plasminogen activator (tPA) released after TBI may cause loss of cerebrovascular autoregulation either by over-activating N-methyl-D-aspartate receptors (NMDA-Rs) or by predisposing to intracranial hemorrhage. Our recent work shows that a catalytically inactive tPA variant (tPA-S(481)A) that competes with endogenous wild type (wt) tPA for binding to NMDA-R through its receptor docking site but that cannot activate it, prevents activation of ERK by wt tPA and impairment of autoregulation when administered 30 min after fluid percussion injury (FPI). We investigated the ability of variants that lack proteolytic activity but bind/block activation of NMDA-Rs by wt tPA (tPA-S(481)A), do not bind/block activation of NMDA-Rs but are proteolytic (tPA-A(296-299)), or neither bind/block NMDA-Rs nor are proteolytic (tPA-A(296-299)S(481)A) to prevent impairment of autoregulation after TBI and the role of MAPK and ET-1 in such effects. Results show that tPA-S(481)A given 3 h post-TBI, but not tPA-A(296-299) or tPA-A(296-299)S(481)A prevents impaired autoregulation by upregulating p38 and inhibiting ET-1, suggesting that tPA-S(481)A has a realistic therapeutic window and focuses intervention on NMDA-Rs to improve outcome.

Male-female differences in upregulation of vasoconstrictor responses in human cerebral arteries

BACKGROUND AND PURPOSE

Male-female differences may significantly impact stroke prevention and treatment in men and women, however underlying mechanisms for sexual dimorphism in stroke are not understood. We previously found in males that cerebral ischemia upregulates contractile receptors in cerebral arteries, which is associated with lower blood flow. The present study investigates if cerebral arteries from men and women differ in cerebrovascular receptor upregulation.

EXPERIMENTAL APPROACH

Freshly obtained human cerebral arteries were placed in organ culture, an established model for studying receptor upregulation. 5-hydroxtryptamine type 1B (5-HT1B), angiotensin II type 1 (AT1) and endothelin-1 type A and B (ETA and ETB) receptors were evaluated using wire myograph for contractile responses, real-time PCR for mRNA and immunohistochemistry for receptor expression.

KEY RESULTS

Vascular sensitivity to angiotensin II and endothelin-1 was markedly lower in cultured cerebral arteries from women as compared to men. ETB receptor-mediated contraction occurred in male but not female arteries. Interestingly, there were similar upregulation in mRNA and expression of 5-HT1B, AT1, and ETB receptors and in local expression of Ang II after organ culture.

CONCLUSIONS AND IMPLICATIONS

In spite of receptor upregulation after organ culture in both sexes, cerebral arteries from women were significantly less responsive to vasoconstrictors angiotensin II and endothelin-1 as compared to arteries from men. This suggests receptor coupling and/or signal transduction mechanisms involved in cerebrovascular contractility may be suppressed in females. This is the first study to demonstrate sex differences in the vascular function of human brain arteries.

MAPK signaling pathway regulates cerebrovascular receptor expression in human cerebral arteries

BACKGROUND

Cerebral ischemia results in enhanced expression of contractile cerebrovascular receptors, such as endothelin type B (ET(B)), 5-hydroxytryptamine type 1B (5-HT(1B)), angiotensin II type 1 (AT(1)) and thromboxane (TP) receptors in the cerebral arteries within the ischemic area. The receptor upregulation occurs via activation of the mitogen-activated protein kinases (MAPK) pathway. Previous studies have shown that inhibitors of the MAPK pathway diminished the ischemic area and contractile cerebrovascular receptors after experimental cerebral ischemia. The aim of this study was to examine if the upregulation of contractile cerebrovascular receptors after 48 h of organ culture of human cerebral arteries involves MAPK pathways and if it can be prevented by a MEK1/2 inhibitor. Human cerebral arteries were obtained from patients undergoing intracranial tumor surgery. The vessels were divided into ring segments and incubated for 48 h in the presence or absence of the specific MEK1/2 inhibitor U0126. The vessels were then examined by using in vitro pharmacological methods and protein immunohistochemistry.

RESULTS

After organ culture of the cerebral arteries the contractile responses to endothelin (ET)-1, angiotensin (Ang) II and thromboxane (TP) were enhanced in comparison with fresh human arteries. However, 5-carboxamidotryptamine (5-CT) induced decreased contractile responses after organ culture as compared to fresh arteries. Incubation with U0126 diminished the maximum contraction elicited by application of ET-1, Ang II and U46619 in human cerebral arteries. In addition, the MEK1/2 inhibitor decreased the contractile response to 5-CT. Immunohistochemistry revealed that organ culture resulted in increased expression of endothelin ET(A), endothelin ET(B) angiotensin AT(2), 5-hydroxytryptamine 5-HT(1B) and thromboxane A2 receptors, and elevated levels of activated pERK1/2, all localized to the smooth muscle cells of the cerebral arteries. Co-incubation with U0126 normalized these proteins.

CONCLUSION

The study demonstrated that there is a clear association between human cerebrovascular receptor upregulation via transcription involving activation of the MAPK pathway after organ culture. Inhibition of the MAPK pathways attenuated the vasoconstriction mediated by ET, AT and TP receptors in human cerebral arteries and the enhanced expression of their receptors. The results indicate that MAPK inhibition might be a novel target for treatment of cerebrovascular disorders.

Expressional changes in cerebrovascular receptors after experimental transient forebrain ischemia

BACKGROUND

Global ischemic stroke is one of the most prominent consequences of cardiac arrest, since the diminished blood flow to the brain results in cell damage and sometimes permanently impaired neurological function. The post-arrest period is often characterised by cerebral hypoperfusion due to subacute hemodynamic disturbances, the pathophysiology of which are poorly understood. In two other types of stroke, focal ischemic stroke and subarachnoid hemorrhage, it has earlier been demonstrated that the expression of certain vasoconstrictor receptors is increased in cerebral arteries several days after the insult, a phenomenon that leads to increased contraction of cerebral arteries, reduced perfusion of the affected area and worsened ischemic damage. Based on these findings, the aim of the present study was to investigate if transient global cerebral ischemia is associated with upregulation of vasoconstrictive endothelin and 5-hydroxytryptamine receptors in cerebral arteries. Experimental transient forebrain ischemia of varying durations was induced in male wistar rats, followed by reperfusion for 48 hours. Neurological function was assessed daily by three different tests and cerebrovascular expression and contractile function of endothelin and 5-hydroxytryptamine receptors were evaluated by wire myography, immunohistochemistry and western blotting.

RESULTS

Transient forebrain ischemia induced neurological deficits as well as functional upregulation of vasoconstrictive ET(B) and 5-HT(1B) receptors in cerebral arteries supplying mid- and forebrain regions. No receptor upregulation was seen in arteries supplying the hindbrain. Immunohistochemical stainings and western blotting demonstrated expressional upregulation of these receptor subtypes in the mid- and forebrain arteries and confirmed that the receptors were located in the smooth muscle layer of the cerebral arteries.

CONCLUSIONS

This study reveals a new pathophysiological aspect of global ischemic stroke, namely expressional upregulation of vasoconstrictor receptors in cerebral arteries two days after the insult, which might contribute to cerebral hypoperfusion and delayed neuronal damage after cardiac arrest.

In vivo experimental stroke and in vitro organ culture induce similar changes in vasoconstrictor receptors and intracellular calcium handling in rat cerebral arteries

Cerebral arteries subjected to different types of experimental stroke upregulate their expression of certain G-protein-coupled vasoconstrictor receptors, a phenomenon that worsens the ischemic brain damage. Upregulation of contractile endothelin B (ET(B)) and 5-hydroxytryptamine 1B (5-HT(1B)) receptors has been demonstrated after subarachnoid hemorrhage and global ischemic stroke, but the situation is less clear after focal ischemic stroke. Changes in smooth muscle calcium handling have been implicated in different vascular diseases but have not hitherto been investigated in cerebral arteries after stroke. Here, we evaluate changes of ET(B) and 5-HT(1B) receptors, intracellular calcium levels, and calcium channel expression in rat middle cerebral artery (MCA) after focal cerebral ischemia and in vitro organ culture, a proposed model of vasoconstrictor receptor changes after stroke. Rats were subjected to 2 h MCA occlusion followed by reperfusion for 1 or 24 h. Alternatively, MCAs from naïve rats were cultured for 1 or 24 h. ET(B) and 5-HT(1B) receptor-mediated contractions were evaluated by wire myography. Receptor and channel expressions were measured by real-time PCR and immunohistochemistry. Intracellular calcium was measured by FURA-2. Expression and contractile functions of ET(B) and 5-HT(1B) receptors were strongly upregulated and slightly downregulated, respectively, 24 h after experimental stroke or organ culture. ET(B) receptor-mediated contraction was mediated by calcium from intracellular and extracellular sources, whereas 5-HT(1B) receptor-mediated contraction was solely dependent on extracellular calcium. Organ culture and stroke increased basal intracellular calcium levels in MCA smooth muscle cells and decreased the expression of inositol triphosphate receptor and transient receptor potential canonical calcium channels, but not voltage-operated calcium channels.

Cigarette smoke upregulates rat coronary artery endothelin receptors in vivo

BACKGROUND

Cigarette smoking is a strong cardiovascular risk factor and endothelin (ET) receptors are related to coronary artery diseases. The present study established an in vivo secondhand smoke (SHS) exposure model and investigated the hypothesis that cigarette smoke induces ET receptor upregulation in rat coronary arteries and its possible underlying mechanisms.

METHODOLOGY/PRINCIPAL FINDINGS

Rats were exposed to SHS for 200 min daily for 8 weeks. The coronary arteries were isolated and examined. The vasoconstriction was studied by a sensitive myograph. The expression of mRNA and protein for receptors was examined by real-time PCR, Western blot and immunofluorescence. Compared to fresh air exposure, SHS increased contractile responses mediated by endothelin type A (ET(A)) and type B (ET(B)) receptors in coronary arteries. In parallel, the expression of mRNA and protein for ET(A) and ET(B) receptors of smoke exposed rats were higher than that of animals exposed to fresh air, suggesting that SHS upregulates ET(A) and ET(B) receptors in coronary arteries in vivo. Immunofluorescence staining showed that the enhanced receptor expression was localized to the smooth muscle cells of coronary arteries. The protein levels of phosphorylated (p)-Raf-1 and p-ERK1/2 in smoke exposed rats were significantly higher than in control rats, demonstrating that SHS induces the activation of the Raf/ERK/MAPK pathway. Treatment with Raf-1 inhibitor GW5074 suppressed SHS-induced enhanced contraction mediated by ET(A) receptors, and inhibited the elevated mRNA and protein levels of ET(A) and ET(B) receptors caused by SHS. The results of correlation and regression analysis showed that phosphorylation of Raf and ERK1/2 were independent determinants to affect protein expression of ET(B) and ET(A) receptors.

CONCLUSIONS/SIGNIFICANCE

Cigarette smoke upregulates ET(B) and ET(A) receptors in rat coronary artery, which is associated with the activation of the Raf/ERK/MAPK pathway.

Oestrogen signalling and neuroprotection in cerebral ischaemia

17β-Oestradiol (E(2)) is an important hormone signal that regulates multiple tissues and functions in the body. This review focuses on the neuroprotective actions of E(2) in the brain against cerebral ischaemia and the potential underlying mechanisms. A particular focus of the review will be on the role of E(2) to attenuate NADPH oxidase activation, superoxide and reactive oxygen species generation and reduce oxidative stress in the ischaemic brain as a potentially key neuroprotective mechanism. Evidence of a potential novel role of extranuclear oestrogen receptors in mediating E(2) signalling and neuroprotective actions is also discussed. An additional subject is the growing evidence indicating that periods of long-term oestrogen deprivation, such as those occurring after menopause or surgical menopause, may lead to loss or attenuation of E(2) signalling and neuroprotective actions in the brain, as well as enhanced sensitivity of the hippocampus to ischaemic stress damage. These findings have important implications with respect to the 'critical period hypothesis', which proposes that oestrogen replacement must be initiated at peri-menopause in humans to exert its beneficial cardiovascular and neural effects. The insights gained from these various studies will prove valuable for guiding future directions in the field.

Estrogen neuroprotection and the critical period hypothesis

17β-Estradiol (estradiol or E2) is implicated as a neuroprotective factor in a variety of neurodegenerative disorders. This review focuses on the mechanisms underlying E2 neuroprotection in cerebral ischemia, as well as emerging evidence from basic science and clinical studies, which suggests that there is a "critical period" for estradiol's beneficial effect in the brain. Potential mechanisms underlying the critical period are discussed, as are the neurological consequences of long-term E2 deprivation (LTED) in animals and in humans after natural menopause or surgical menopause. We also summarize the major clinical trials concerning postmenopausal hormone therapy (HT), comparing their outcomes with respect to cardiovascular and neurological disease and discussing their relevance to the critical period hypothesis. Finally, potential caveats, controversies and future directions for the field are highlighted and discussed throughout the review.

Secondhand smoke exposure induces Raf/ERK/MAPK-mediated upregulation of cerebrovascular endothelin ETA receptors

BACKGROUND

Cigarette smoking enhances the risk of stroke. However, the underlying molecular mechanisms are largely unknown. The present study established an in vivo rat secondhand cigarette smoking (SHS) model and examined the hypothesis that SHS upregulates endothelin receptors with increased cerebrovascular contraction via the Raf/extracellular signal-regulated kinase (ERK)/mitogen-activated protein kinases (MAPK) pathway.

RESULTS

Rats were exposed to SHS for up to 8 weeks. The cerebral artery vasoconstriction was recorded by a sensitive myograph. The mRNA and protein expressions for endothelin receptors in cerebral arteries were studied by real-time PCR and Western blot. Compared to fresh air exposed rats, cerebral arteries from SHS rats exhibited stronger contractile responses (P < 0.05) mediated by endothelin type A (ETA) receptors. The expressions of mRNA and protein for ETA receptors in the cerebral arteries from SHS rats were higher (P < 0.05) than that in control. SHS did not affect endothelin type B (ETB) receptor-mediated contractions, mRNA or protein levels. The results suggest that SHS upregulates ETA, but not ETB receptors in vivo. After SHS exposure, the mRNA levels of Raf-1 and ERK1/2, the protein expression of phosphorylated (p)-Raf-1 and p-ERK1/2 were increased (P < 0.05). Raf-1 inhibitor, GW5074 suppressed the enhanced ETA receptor-mediated contraction, mRNA and protein levels induced by SHS. In addition, GW5074 inhibited the SHS-caused increased mRNA and phosphorylated protein levels of Raf-1 and ERK1/2, suggesting that SHS induces activation of the Raf/ERK/MAPK pathway.

CONCLUSIONS

SHS upregulates cerebrovascular ETA receptors via the Raf/ERK/MAPK pathway, which provides novel understanding of mechanisms involved in SHS-associated stroke.

Inhibition of cerebrovascular raf activation attenuates cerebral blood flow and prevents upregulation of contractile receptors after subarachnoid hemorrhage

BACKGROUND

Late cerebral ischemia carries high morbidity and mortality after subarachnoid hemorrhage (SAH) due to reduced cerebral blood flow (CBF) and the subsequent cerebral ischemia which is associated with upregulation of contractile receptors in the vascular smooth muscle cells (SMC) via activation of mitogen-activated protein kinase (MAPK) of the extracellular signal-regulated kinase (ERK)1/2 signal pathway. We hypothesize that SAH initiates cerebrovascular ERK1/2 activation, resulting in receptor upregulation. The raf inhibitor will inhibit the molecular events upstream ERK1/2 and may provide a therapeutic window for treatment of cerebral ischemia after SAH.

RESULTS

Here we demonstrate that SAH increases the phosphorylation level of ERK1/2 in cerebral vessels and reduces the neurology score in rats in additional with the CBF measured by an autoradiographic method. The intracisternal administration of SB-386023-b, a specific inhibitor of raf, given 6 h after SAH, aborts the receptor changes and protects the brain from the development of late cerebral ischemia at 48 h. This is accompanied by reduced phosphorylation of ERK1/2 in cerebrovascular SMC. SAH per se enhances contractile responses to endothelin-1 (ET-1), 5-carboxamidotryptamine (5-CT) and angiotensin II (Ang II), upregulates ETB, 5-HT1B and AT1 receptor mRNA and protein levels. Treatment with SB-386023-b given as late as at 6 h but not at 12 h after the SAH significantly decreased the receptor upregulation, the reduction in CBF and the neurology score.

CONCLUSION

These results provide evidence for a role of the ERK1/2 pathway in regulation of expression of cerebrovascular SMC receptors. It is suggested that raf inhibition may reduce late cerebral ischemia after SAH and provides a realistic time window for therapy.

Vascular plasticity in cerebrovascular disorders

Cerebral ischemia remains a major cause of morbidity and mortality with little advancement in subacute treatment options. This review aims to cover and discuss novel insight obtained during the last decade into plastic changes in the vasoconstrictor receptor profiles of cerebral arteries and microvessels that takes place after different types of stroke. Receptors like the endothelin type B, angiotensin type 1, and 5-hydroxytryptamine type 1B/1D receptors are upregulated in the smooth muscle layer of cerebral arteries after different types of ischemic stroke as well as after subarachnoid hemorrhage, yielding rather dramatic changes in the contractility of the vessels. Some of the signal transduction processes mediating this receptor upregulation have been elucidated. In particular the extracellular regulated kinase 1/2 pathway, which is activated early in the process, has proven to be a promising therapeutic target for prevention of vasoconstrictor receptor upregulation after stroke. Together, those findings provide new perspectives on the pathophysiology of ischemic stroke and point toward a novel way of reducing vasoconstriction, neuronal cell death, and thus neurologic deficits after stroke.

P2 receptor antagonists prevent synaptic failure and extracellular signal-regulated kinase 1/2 activation induced by oxygen and glucose deprivation in rat CA1 hippocampus in vitro

To investigate the role of purinergic P2 receptors under ischemia, we studied the effect of P2 receptor antagonists on synaptic transmission and mitogen-activated protein kinase (MAPK) activation under oxygen and glucose deprivation (OGD) in rat hippocampal slices. The effect of the P2 antagonists pyridoxalphosphate-6-azophenyl-2',4'-disulfonate (PPADS, unselective, 30 μm), N( 6) -methyl-2'-deoxyadenosine-3',5'-bisphosphate (MRS2179, selective for P2Y(1) receptor, 10 μm), Brilliant Blue G (BBG, selective for P2X(7) receptor, 1 μm), and 5-[[[(3-phenoxyphenyl)methyl][(1S)-1,2,3,4-tetrahydro-1-naphthalenyl]amino]carbonyl]-1,2,4-benzenetricarboxylic acid (A-317491, selective for P2X(3) receptor, 10 μm), and of the newly synthesized P2X(3) receptor antagonists 2-amino-9-(5-iodo-2-isopropyl-4-methoxybenzyl)adenine (PX21, 1 μm) and 2-amino-9-(5-iodo-2-isopropyl-4-methoxybenzyl)-N( 6)-methyladenine (PX24, 1 μm), on the depression of field excitatory postsynaptic potentials (fEPSPs) and anoxic depolarization (AD) elicited by 7 min of OGD were evaluated. All antagonists significantly prevented these effects. The extent of CA1 cell injury was assessed 3 h after the end of 7 min of OGD by propidium iodide staining. Substantial CA1 pyramidal neuronal damage, detected in untreated slices exposed to OGD injury, was significantly prevented by PPADS (30 μm), MRS2179 (10 μm), and BBG (1 μm). Western blot analysis showed that, 10 min after the end of the 7 min of OGD, extracellular signal-regulated kinase (ERK)1/2 MAPK activation was significantly increased. MRS2179, BBG, PPADS and A-317491 significantly counteracted ERK1/2 activation. Hippocampal slices incubated with the ERK1/2 inhibitors 1,4-diamino-2,3-dicyano-1,4-bis(2-aminophenylthio)butadiene (U0126, 10 μm) and α-[amino[(4-aminophenyl)thio]methylene]-2-(trifluoromethyl) benzeneacetonitrile (SL327, 10 μm) showed significant fEPSP recovery after OGD and delayed AD, supporting the involvement of ERK1/2 in neuronal damage induced by OGD. These results indicate that subtypes of hippocampal P2 purinergic receptors have a harmful effect on neurotransmission in the CA1 hippocampus by participating in AD appearance and activation of ERK1/2.

Human cerebrovascular contractile receptors are upregulated via a B-Raf/MEK/ERK-sensitive signaling pathway

Background

Cerebral ischemia results in a rapid increase in contractile cerebrovascular receptors, such as the 5-hydroxytryptamine type 1B (5-HT_1B), angiotensin II type 1 (AT₁), and endothelin type B (ET_B) receptors, in the vessel walls within the ischemic region, which further impairs local blood flow and aggravates tissue damage. This receptor upregulation occurs via activation of the mitogen-activated protein kinase pathway. We therefore hypothesized an important role for B-Raf, the first signaling molecule in the pathway. To test our hypothesis, human cerebral arteries were incubated at 37°C for 48 h in the absence or presence of a B-Raf inhibitor: SB-386023 or SB-590885. Contractile properties were evaluated in a myograph and protein expression of the individual receptors and activated phosphorylated B-Raf (p-B-Raf) was evaluated immunohistochemically.

Results

5-HT_1B, AT₁, and ET_B receptor-mediated contractions were significantly reduced by application of SB-590885, and to a smaller extent by SB-386023. A marked reduction in AT₁ receptor immunoreactivity was observed after treatment with SB-590885. Treatment with SB-590885 and SB-386023 diminished the culture-induced increase of p-B-Raf immunoreactivity.

Conclusions

B-Raf signaling has a key function in the altered expression of vascular contractile receptors observed after organ culture. Therefore, specific targeting of B-Raf might be a novel approach to reduce tissue damage after cerebral ischemia by preventing the previously observed upregulation of contractile receptors in smooth muscle cells.

Blockade of the MEK/ERK pathway with a raf inhibitor prevents activation of pro-inflammatory mediators in cerebral arteries and reduction in cerebral blood flow after subarachnoid hemorrhage in a rat model

Cerebral ischemia that develops after subarachnoid hemorrhage (SAH) carries high morbidity and mortality. Inflammatory mediators are involved in the development of cerebral ischemia through activation of the mitogen-activated protein kinase pathway. We hypothesized that blockade of the MAPkinase/ERK (MEK)/extracellular signal-regulated kinase (ERK) pathway upstream with a specific raf inhibitor would prevent SAH-induced activation of the cerebrovascular inflammatory response. The raf inhibitor SB-386023-b was injected intracisternally in our rat model at 0, 6, or 12 hours after the SAH. After 48 hours, cerebral arteries were harvested, and iNOS, interleukin (IL)-6, IL-1β, matrix metalloproteinase (MMP)-9, tissue inhibitors of metalloproteinase (TIMP)-1, and phosphorylated ERK1/2 were investigated by immunofluorescence, real-time polymerase chain reaction (PCR), and Western blot analysis. Cerebral blood flow (CBF) was measured using autoradiography. Protein levels of MMP-9, TIMP-1, iNOS, IL-6, and IL-1β were increased after SAH, as were mRNA levels of IL-6, MMP-9, and TIMP-1. After SAH, pERK1/2 was increased, but CBF was reduced. Treatment with SB-386023-b at 0 or 6 hours after SAH normalized CBF and prevented SAH-induced upregulation of MMPs, pro-inflammatory cytokines, and pERK1/2 proteins. These results suggested that inhibition of MEK/ERK signal transduction by a specific raf inhibitor administered up to 6 hours after SAH normalized the expression of pro-inflammatory mediators and extracellular matrix-related genes.

Derangements of post-ischemic cerebral blood flow by protein kinase C delta

Cerebral ischemia causes blood flow derangements characterized by hyperemia (increased cerebral blood flow, CBF) and subsequent hypoperfusion (decreased CBF). We previously demonstrated that protein kinase C delta (δPKC) plays an important role in hippocampal neuronal death after ischemia. However, whether part of this protection is due to the role of δPKC on CBF following cerebral ischemia remains poorly understood. We hypothesized that δPKC exacerbates hyperemia and subsequent hypoperfusion resulting in CBF derangements following ischemia. Sprague-Dawley (SD) rats pretreated with a δPKC specific inhibitor (δV1-1, 0.5 mg/kg) exhibited attenuation of hyperemia and latent hypoperfusion characterized by vasoconstriction followed by vasodilation of microvessels after 2-vessel occlusion plus hypotension measured by 2-photon microscopy. In an asphyxial cardiac arrest model (ACA), SD rats treated with δV1-1 (pre- and post-ischemia) exhibited improved perfusion after 24 h and less hippocampal CA1 neuronal death 7 days after ACA. These results suggest possible therapeutic potential of δPKC in modulating CBF and neuronal damage after cerebral ischemia.

Comparison of MEK/ERK pathway inhibitors on the upregulation of vascular G-protein coupled receptors in rat cerebral arteries

Organ culture is an in vitro method for investigating cellular mechanisms involved in upregulation of vasocontractile G-protein coupled receptors. We hypothesize that mitogen-activated-protein kinase (MEK) and/or extracellular-signal-regulated kinase (ERK) specific inhibitors will attenuate the G-protein coupled receptor expression following organ culture. Rat cerebral arteries were incubated 48h in the presence of MEK/ERK specific inhibitors U0126, PD98059, SL327, or AG126 for different time periods. Contractile responses by activation of endothelin receptor type A and type B, serotonin receptor 5-HT(1B), prostanoid TP receptor, and angiotensin II receptor type 1 and type 2 were investigated. Results were verified by measurement of mRNA with real time PCR and by protein immunohistochemistry. Organ culture induced transcriptional upregulation of endothelin ET(B) receptor and of serotonin 5-HT(1B) receptor on translational level and increased respective contractions. The prostanoid TP receptor mediated contraction curve was left-wards shifted by organ culture. Organ culture was associated with elevated pERK1/2 in the vascular smooth muscle cells: the MEK1/2 inhibitor U0126 attenuated the endothelin ET(B) receptor mediated contraction at post-translational level or by changing the receptor affinities. The serotonin 5-HT(1B) receptor and prostanoid TP receptor mediated contractions were abolished by U0126. Administration of U0126 6h after start of incubation blocked the receptor upregulation. In conclusion, MEK specific inhibitor U0126 is a potent inhibitor of G-protein coupled receptor alteration seen during organ culture. Given the ability to inhibit G-protein coupled receptor alteration at the clinically relevant time-point 6h post incubation makes it an attractive therapeutic agent for in vivo studies.

Cerebral ischemia induces microvascular pro-inflammatory cytokine expression via the MEK/ERK pathway

BACKGROUND

Cerebral ischemia from middle cerebral artery wall (MCA) occlusion results in increased expression of cerebrovascular endothelin and angiotensin receptors and activation of the mitogen-activated protein kinase (MAPK) pathway, as well as reduced local cerebral blood flow and increased levels of pro-inflammatory mediators in the infarct region. In this study, we hypothesised that inhibition of the cerebrovascular inflammatory reaction with a specific MEK1/2 inhibitor (U0126) to block transcription or a combined receptor blockade would reduce infarct size and improve neurological score.

METHODS

Rats were subjected to a 2-hours middle cerebral artery occlusion (MCAO) followed by reperfusion for 48 hours. Two groups of treated animals were studied; (i) one group received intraperitoneal administration of a specific MEK1/2 inhibitor (U0126) starting at 0, 6, or 12 hours after the occlusion, and (ii) a second group received two specific receptor antagonists (a combination of the angiotensin AT1 receptor inhibitor Candesartan and the endothelin ETA receptor antagonist ZD1611), given immediately after occlusion. The middle cerebral arteries, microvessels and brain tissue were harvested; and the expressions of tumor necrosis factor-alpha (TNF-alpha), interleukin-1ss (IL-1ss), interleukin-6 (IL-6), inducible nitric oxide synthase (iNOS) and phosphorylated ERK1/2, p38 and JNK were analysed using immunohistochemistry.

RESULTS

We observed an infarct volume of 25 +/- 2% of total brain volume, and reduced neurological function 2 days after MCAO followed by 48 hours of recirculation. Immunohistochemistry revealed enhanced expression of TNF-alpha, IL-1ss, IL-6 and iNOS, as well as elevated levels of phosphorylated ERK1/2 in smooth muscle cells of ischemic MCA and in associated intracerebral microvessels. U0126, given intraperitoneal at zero or 6 hours after the ischemic event, but not at 12 hours, reduced the infarct volume (11.7 +/- 2% and 15 +/- 3%, respectively), normalized pERK1/2, and prevented elevation of the expressions of TNF-alpha IL-1ss, IL-6 and iNOS. Combined inhibition of angiotensin AT1 and endothelin ETA receptors decreased the volume of brain damaged (12.3 +/- 3; P < 0.05) but only slightly reduced MCAO-induced enhanced expression of iNOS and cytokines

CONCLUSION

The present study shows elevated microvascular expression of TNF-alpha, IL-1ss, IL-6 and iNOS following focal ischemia, and shows that this expression is transcriptionally regulated via the MEK/ERK pathway.

Enhanced cerebrovascular expression of matrix metalloproteinase-9 and tissue inhibitor of metalloproteinase-1 via the MEK/ERK pathway during cerebral ischemia in the rat

Background

Cerebral ischemia is usually characterized by a reduction in local blood flow and metabolism and by disruption of the blood-brain barrier in the infarct region. The formation of oedema and opening of the blood-brain barrier in stroke is associated with enhanced expression of metalloproteinase-9 (MMP-9) and tissue inhibitor of metalloproteinase-1 (TIMP-1).

Results

Here, we found an infarct volume of 24.8 ± 2% and a reduced neurological function after two hours of middle cerebral artery occlusion (MCAO), followed by 48 hours of recirculation in rat. Immunocytochemistry and confocal microscopy revealed enhanced expression of MMP-9, TIMP-1, and phosphorylated ERK1/2 in the smooth muscle cells of the ischemic MCA and associated intracerebral microvessels. The specific MEK1/2 inhibitor U0126, given intraperitoneal zero or 6 hours after the ischemic event, reduced the infarct volume significantly (11.8 ± 2% and 14.6 ± 3%, respectively; P < 0.05), improved neurological function, normalized expression of phosphorylated ERK1/2, and reduced expression of MMP-9 and TIMP-1 in the vessel walls. Administration of U0126 12 hours after MCAO did not alter the expression of MMP-9. Immunocytochemistry showed no overlap in expression between MMP-9/TIMP-1 and the astrocyte/glial cell marker GFAP in the vessel walls.

Conclusion

These data are the first to show that the elevated vascular expression of MMP-9 and TIMP-1, associated with breakdown of the blood-brain barrier following focal ischemia, are transcriptionally regulated via the MEK/ERK pathway.

Activating deltaPKC antagonizes the protective effect of ERK1/2 inhibition against stroke in rats

Two pathways that have been shown to mediate cerebral ischemic damage are the MEK/ERK cascade and the pro-apoptotic deltaPKC pathway. We investigated the relationship between these pathways in a rat model of focal ischemia by observing and modifying the activation state of each pathway. The ERK1/2 inhibitor, U0126, injected at ischemia onset, attenuated the increase in phosphorylated ERK1/2 (P-ERK1/2) after reperfusion. The deltaPKC inhibitor, deltaV1-1, delivered at reperfusion, did not significantly change P-ERK1/2 levels. In contrast, the deltaPKC activator, psi deltaRACK, injected at reperfusion, reduced ERK1/2 phosphorylation measured 4 h after reperfusion. Additionally, U0126 pretreatment at ischemia onset reduced infarct size compared with vehicle, but U0126 injected at the onset of reperfusion had no protection. Finally, combination of U0126 injection at ischemia onset plus deltaV1-1 injection at reperfusion further reduced infarct size, while combination of U0126 delivered at ischemia onset with psi deltaRACK injected at reperfusion increased infarct size compared with U0126 alone. In conclusion, we find that inhibiting both the MEK/ERK and the deltaPKC pathways offers greater protection than either alone, indicating they likely act independently.

Enhanced expressions of microvascular smooth muscle receptors after focal cerebral ischemia occur via the MAPK MEK/ERK pathway

BACKGROUND

MEK1/2 is a serine/threonine protein that phosphorylates extracellular signal-regulated kinase (ERK1/2). Cerebral ischemia results in enhanced expression of cerebrovascular contractile receptors in the middle cerebral artery (MCA) leading to the ischemic region. Here we explored the role of the MEK/ERK pathway in receptor expression following ischemic brain injury using the specific MEK1 inhibitor U0126.

METHODS AND RESULT

Rats were subjected to a 2-h middle cerebral artery occlusion (MCAO) followed by reperfusion for 48-h and the ischemic area was calculated. The expression of phosphorylated ERK1/2 and Elk-1, and of endothelin ETA and ETB, angiotensin AT1, and 5-hydroxytryptamine 5-HT1B receptors were analyzed with immunohistochemistry using confocal microscopy in cerebral arteries, microvessels and in brain tissue. The expression of endothelin ETB receptor was analyzed by quantitative Western blot. We demonstrate that there is an increase in the number of contractile smooth muscle receptors in the MCA and in micro- vessels within the ischemic region. The enhanced expression occurs in the smooth muscle cells as verified by co-localization studies. This receptor upregulation is furthermore associated with enhanced expression of pERK1/2 and of transcription factor pElk-1 in the vascular smooth muscle cells. Blockade of transcription with the MEK1 inhibitor U0126, given at the onset of reperfusion or as late as 6 hours after the insult, reduced transcription (pERK1/2 and pElk-1), the enhanced vascular receptor expression, and attenuated the cerebral infarct and improved neurology score.

CONCLUSION

Our results show that MCAO results in upregulation of cerebrovascular ETB, AT1 and 5-HT1B receptors. Blockade of this event with a MEK1 inhibitor as late as 6 h after the insult reduced the enhanced vascular receptor expression and the associated cerebral infarction.

Cerebral ischemia induces transcription of inflammatory and extracellular-matrix-related genes in rat cerebral arteries

Cerebral ischemia results in a local inflammatory response that contributes to the size of the lesion, however, the involvement of the cerebral vasculature is unknown. We hypothesise that the expression of inflammatory genes (Il6, iNOS, cxcl2, TNF-alpha and Il-1beta) and extracellular-matrix-related genes (MMP9, MMP13) is induced in cerebral arteries following cerebral ischemia via activation of mitogen activated kinases (MAPKs). This hypothesis was tested in vivo by experimental subarachnoid haemorrhage (SAH) and temporal middle cerebral artery occlusion (MCAO), and by organ culture of isolated cerebral arteries with quantitative real time PCR (mRNA expression) and immunohistochemistry (localization of protein expression). The gene promoters were investigated in silica with computer analysis. The mRNA analysis revealed that the ischemic models, SAH and MCAO, as well as organ culture of isolated cerebral arteries resulted in transcriptional upregulation of the abovementioned genes. The protein expression involved phosphorylation of three different MAPKs signalling pathways (p38, ERK 1/2 and SAPK/JNK) and the downstream transcription factors (ATF-2, Elk-1, c-Jun) shown by immunohistochemistry and quantified by image analysis. All three models revealed the same pattern of activation in the cerebrovascular smooth muscle cells. The in silica analysis demonstrated binding sites for said transcription factors. The results suggest that cerebral ischemia and organ culture induce activation of p38, ERK 1/2 and SAPK/JNK in cerebral arteries which in turn activate the transcription factors ATF-2, Elk-1 and c-Jun and the expression of inflammatory and extracellular-matrix-related genes in the wall of cerebral arteries.

Cooperative effect of angiotensin AT1 and endothelin ETA receptor antagonism limits the brain damage after ischemic stroke in rat

Cerebral ischemia results in enhanced expression of smooth muscle cell endothelin and angiotensin receptors in cerebral arteries. We hypothesise that this phenomenon may be detrimental and that acute treatment with a combined non-hypotensive dose of the angiotensin AT(1) receptor inhibitor candesartan and the endothelin ET(A) receptor antagonist ZD1611 reduces the infarct in experimental ischemic stroke. Transient middle cerebral artery occlusion was induced in male Wistar rats by the intraluminal filament technique for 2 h followed by recirculation. The animals received systemic candesartan (0.05 mg/kg/day), ZD1611 (0.15 mg/kg/day), both combined or vehicle with start immediately after the occlusion. After 48 h the rats were sacrificed, the brains sliced and stained with 1% 2, 3, 5-triphenyltetrazolium chloride (TTC) and the volume of ischemic damage determined. The middle cerebral arteries were harvested for immunocytochemical studies of angiotensin AT(1) and endothelin ET(A) receptor expression. Candesartan or ZD1611 did alone not significantly decrease the brain damage or improve neurological scores as compared to vehicle controls. The combined inhibition of angiotensin AT(1) and endothelin ET(A) receptors however decreased the brain damage and improved the neurological scores (both P<0.05). The treatment did not change resting mean arterial blood pressure. In addition, there was an upregulation of angiotensin AT(1) receptors in the ischemic middle cerebral artery smooth muscle cells, which was normalised by the combined treatment. In conclusion, the present study shows that combined inhibition of angiotensin AT(1) and endothelin ET(A) receptors reduces the brain damage and improves the neurological outcome after ischemic stroke in rat.

Protein kinase C inhibition attenuates vascular ETB receptor upregulation and decreases brain damage after cerebral ischemia in rat

Background

Protein kinase C (PKC) is known to be involved in the pathophysiology of experimental cerebral ischemia. We have previously shown that after transient middle cerebral artery occlusion, there is an upregulation of endothelin receptors in the ipsilateral middle cerebral artery. The present study aimed to examine the effect of the PKC inhibitor Ro-32-0432 on endothelin receptor upregulation, infarct volume and neurology outcome after middle cerebral artery occlusion in rat.

Results

At 24 hours after transient middle cerebral artery occlusion (MCAO), the contractile endothelin B receptor mediated response and the endothelin B receptor protein expression were upregulated in the ipsilateral but not the contralateral middle cerebral artery. In Ro-32-0432 treated rats, the upregulated endothelin receptor response was attenuated. Furthermore, Ro-32-0432 treatment decreased the ischemic brain damage significantly and improved neurological scores. Immunohistochemistry showed fainter staining of endothelin B receptor protein in the smooth muscle cells of the ipsilateral middle cerebral artery of Ro-32-0432 treated rats compared to control.

Conclusion

The results suggest that treatment with Ro-32-0432 in ischemic stroke decreases the ischemic infarction area, neurological symptoms and associated endothelin B receptor upregulation. This provides a new perspective on possible mechanisms of actions of PKC inhibition in cerebral ischemia.