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

Switching Off Vascular MAPK Signaling: A Novel Strategy to Prevent Delayed Cerebral Ischemia Following Subarachnoid Hemorrhage

Patients who initially survive the rupture and repair of a brain aneurysm often take a devastating turn for the worse some days later and die or suffer permanent neurologic deficits. This catastrophic sequela is attributed to a delayed phase of global cerebral ischemia (DCI) following aneurysmal subarachnoid hemorrhage (aSAH), but we lack effective treatment. Here we present our view, based on 20 years of research, that the initial drop in blood flow at the time of rupture triggers genomic responses throughout the brain vasculature that manifest days later as increased vasoconstriction and decreased cerebral blood flow. We propose a novel treatment strategy to prevent DCI by early inhibition of the vascular mitogen-activated protein kinase (MAPK) pathway that triggers expression of vasoconstrictor and inflammatory mediators. We summarize evidence from experimental SAH models showing early treatment with MAPK inhibitors "switches off" these detrimental responses, maintains flow, and improves neurological outcome. This promising therapy is currently being evaluated in clinical trials.

Chronic real-time particulate matter exposure causes rat pulmonary arteriole hyperresponsiveness and remodeling: The role of ETBR-ERK1/2 signaling

Exposure to air pollution is associated with the incidence of respiratory diseases. The present study evaluated the pulmonary vascular system injury by chronic real-time particulate matter (PM₁₀) exposure and investigated the underlying mechanisms. Rats were exposed to PM₁₀ or filtered air for 2 to 4 months using a whole body exposure system, and intraperitoneally injected with the MEK1/2 inhibitor U0126. Right heart catheterization and myography were performed to detect lung function and pulmonary vascular reactivity, respectively. Western blotting, qRT-PCR, enzyme-linked immunosorbent assay and histological analyses were used to detect the effects and mechanisms by which PM₁₀ exposure-induced pulmonary vascular dysfunction. Functional experiment results showed that PM₁₀ exposure increased the pulmonary artery pressure of rats and caused endothelin B receptor (ET_BR)-mediated pulmonary arteriole hyperreactivity. U0126 significantly rescued these pathological changes. PM₁₀ exposure upregulated the contractile ET_BR of pulmonary arteriolar smooth muscle, and damaged pulmonary artery endothelial cells to induce the release of more endothelin 1 (ET-1). The upregulated ET_BR bound to increased ET-1 induced pulmonary arteriolar hyperresponsiveness and remodeling. U0126 inhibited the PM₁₀ exposure-induced upregulation of ET_BR in pulmonary arteriole, ET_BR-mediated pulmonary arterial hyperresponsiveness and vascular remodeling. In conclusion, chronic real-time particulate matter exposure can activate the ERK1/2 signaling, thereby inducing the upregulation of contractile ET_BR in pulmonary arteriole, which may be involved in pulmonary arteriole hyperresponsiveness and remodeling in rats. These findings provide new mechanistic evidence of PM₁₀ exposure-induced respiratory diseases, and a new possible target for treatment.

Paeonol alleviates primary dysmenorrhea in mice via activating CB2R in the uterus

BACKGROUND AND PURPOSE

Primary dysmenorrhea is the most common gynaecologic problem in menstruating women and is characterized by spasmodic uterine contraction and pain symptoms associated with inflammatory disturbances. Paeonol is an active phytochemical component that has shown anti-inflammatory and analgesic effects in several animal models. The aim of this study was to explore whether paeonol is effective against dysmenorrhea and to investigate the potential mechanism of cannabinoid receptor signalling.

EXPERIMENTAL APPROACH

Dysmenorrhea was established by injecting oestradiol benzoate into female mice. The effects of paeonol on writhing time and latency, uterine pathology and inflammatory mediators were explored. Isolated uterine smooth muscle was used to evaluate the direct effect of paeonol on uterine contraction.

KEY RESULTS

The oral administration of paeonol reduced dysmenorrhea pain and PGE2 and TNF-α expression in the uterine tissues of mice, and paeonol was found to be distributed in lesions of the uterus. Paeonol almost completely inhibited oxytocin-, high potassium- and Ca²⁺-induced contractions in isolated uteri. Antagonists of CB2R (AM630) and the MAPK pathway (U0126), but not of CB1R (AM251), reversed the inhibitory effect of paeonol on uterine contraction. Paeonol significantly blocked L-type Ca²⁺ channels and calcium influx in uterine smooth muscle cells via CB2R. Molecular docking results showed that paeonol fits well with the binding site of CB2R.

CONCLUSIONS AND IMPLICATIONS

Paeonol partially acts through CB2R to restrain calcium influx and uterine contraction to alleviate dysmenorrhea in mice. These results suggest that paeonol has therapeutic potential for the treatment of dysmenorrhea.

Pre-clinical effects of highly potent MEK1/2 inhibitors on rat cerebral vasculature after organ culture and subarachnoid haemorrhage

Background: Aneurysmal subarachnoid haemorrhage (SAH) is a variant of haemorrhagic stroke with a striking 50% mortality rate. In addition to the initial insult, secondary delayed brain injury may occur days after the initial ischemic insult and is associated with vasospasms leading to delayed cerebral ischemia. We have previously shown that the MEK1/2 inhibitor U0126 improves neurological assessment after SAH in rats. Aim: The purpose of the present study was to analyse the impact of a broad selection of high potency MEK1/2 inhibitors in an organ culture model and use the IC50 values obtained from the organ culture to select highly potent inhibitors for pre-clinical in vivo studies. Results: Nine highly potent mitogen activated protein kinase kinase (MEK1/2) inhibitors were screened and the two most potent inhibitors from the organ culture screening, trametinib and PD0325901, were tested in an in vivo experimental rat SAH model with intrathecal injections. Subsequently, the successful inhibitor trametinib was administered intraperitoneally in a second in vivo study. In both regimens, trametinib treatment caused significant reductions in the endothelin-1 induced contractility after SAH, which is believed to be associated with endothelin B receptor up-regulation. Trametinib treated rats showed improved neurological scores, evaluated by the ability to traverse a rotating pole, after induced SAH. Conclusion: The PD0325901 treatment did not improve the neurological score after SAH, nor showed any beneficial therapeutic effect on the contractility, contrasting with the reduction in neurological deficits seen after trametinib treatment. These data show that trametinib might be a potential candidate for treatment of SAH.

MEK1/2 inhibitor U0126, but not nimodipine, reduces upregulation of cerebrovascular contractile receptors after subarachnoid haemorrhage in rats

Vascular pathophysiological changes after haemorrhagic stroke, such as phenotypic modulation of the cerebral arteries and cerebral vasospasms, are associated with delayed cerebral ischemia (DCI) and poor outcome. The only currently approved drug treatment shown to reduce the risk of DCI and improve neurologic outcome after aneurysmal subarachnoid haemorrhage (SAH) is nimodipine, a dihydropyridine L-type voltage-gated Ca2+ channel blocker. MEK1/2 mediated transcriptional upregulation of contractile receptors, including endothelin-1 (ET-1) receptors, has previously been shown to be a factor in the pathology of SAH. The aim of the study was to compare intrathecal and subcutaneous treatment regimens of nimodipine and intrathecal treatment regimens of U0126, a MEK1/2 inhibitor, in a single injection experimental rat SAH model with post 48 h endpoints consisting of wire myography of cerebral arteries, flow cytometry of cerebral arterial tissue and behavioural evaluation. Following ET-1 concentration-response curves, U0126 exposed arteries had a significantly lower ET-1max than vehicle arteries. Arteries from both the intrathecal- and subcutaneous nimodipine treated animals had significantly higher ET-1max contractions than the U0126 arteries. Furthermore, Ca2+ concentration response curves (precontracted with ET-1 and in the presence of nimodipine) showed that nimodipine treatment could result in larger nimodipine insensitive contractions compared to U0126. Flow cytometry showed decreased protein expression of the ETB receptor in U0126 treated cerebral vascular smooth muscle cells compared to vehicle. Only U0126 treatment lowered ET-1max contractions and ETB receptor levels, as well as decreased the contractions involving nimodipine-insensitive Ca2+ channels, when compared to both intrathecal and subcutaneous nimodipine treatment. This indicate that targeting gene expression might be a better strategy than blocking specific receptors or ion channels in future treatments of SAH.

Vascular pathology of large cerebral arteries in experimental subarachnoid hemorrhage: Vasoconstriction, functional CGRP depletion and maintained CGRP sensitivity

Subarachnoid hemorrhage (SAH) is associated with increased cerebral artery sensitivity to vasoconstrictors and release of the perivascular sensory vasodilator CGRP. In the current study the constrictive phenotype and the vasodilatory effects of exogenous and endogenous perivascular CGRP were characterized in detail applying myograph technology to cerebral artery segments isolated from experimental SAH and sham-operated rats. Following experimental SAH, cerebral arteries exhibited increased vasoconstriction to endothelin-1, 5-hydroxytryptamine and U46419. In addition, depolarization-induced vasoconstriction (60 mM potassium) was significantly increased, supporting a general SAH-associated vasoconstrictive phenotype. Using exogenous CGRP, we demonstrated that sensitivity of the arteries to CGRP-induced vasodilation was unchanged after SAH. However, vasodilation in response to capsaicin (100 nM), a sensory nerve activator used to release perivascular CGRP, was significantly reduced by SAH (P = 0.0079). Because CGRP-mediated dilation is an important counterbalance to increased arterial contractility, a reduction in CGRP release after SAH would exacerbate the vasospasms that occur after SAH. A similar finding was obtained with artery culture (24 h), an in vitro model of SAH-induced vascular dysfunction. The arterial segments maintained sensitivity to exogenous CGRP but showed reduced capsaicin-induced vasodilation. To test whether a metabolically stable CGRP analogue could be used to supplement the loss of perivascular CGRP release in SAH, SAX was systemically administered in our in vivo SAH model. SAX treatment, however, induced CGRP-desensitization and did not prevent the development of vasoconstriction in cerebral arteries after SAH.

Reduced Mechanical Stretch Induces Enhanced Endothelin B Receptor-Mediated Contractility via Activation of Focal Adhesion Kinase and Extracellular Regulated Kinase 1/2 in Cerebral Arteries from Rat

Cerebral ischaemia results in enhanced endothelin B (ETB ) receptor-mediated contraction and receptor protein expression in the affected cerebrovascular smooth muscle cells (SMC). Organ culture of cerebral arteries is a method to induce similar alterations in ETB receptor expression. We suggest that rapid and sustained reduction in wall tension/stretch is a possible trigger mechanism for this vascular remodelling. Isolated rat middle cerebral artery (MCA) segments were incubated in a wire myograph with or without mechanical stretch, prior to assessment of their contractile response to the selective ETB receptor agonist sarafotoxin 6c. The involvement of extracellular regulated kinase (ERK) 1/2 and focal adhesion kinase (FAK) was studied by their specific inhibitors U0126 and PF-228, respectively. Compared with their stretched counterparts, unstretched MCA segments showed a significantly increased ETB receptor-mediated contractile response after 12 hr of incubation, which was attenuated by either U0126 or PF-228. The functionally increased ETB -mediated contractility could be attributed to two different mechanisms: (i) a difference in ETB receptor localization from primarily endothelial expression to SMC expression and (ii) an increased calcium sensitivity of the SMCs due to an increased expression of the calcium channel transient receptor potential canonical 1. Collectively, our results present a possible mechanism linking lack of vessel wall stretch/tension to changes in ETB receptor-mediated contractility via triggering of an early mechanosensitive signalling pathway involving ERK1/2 and FAK signalling. A mechanism likely to be an initiating factor for the increased ETB receptor-mediated contractility found after cerebral ischaemia.

The ERK1/2 pathway participates in the upregulation of the expression of mesenteric artery α1 receptors by intravenous tail injections of mmLDL in mice

Minimally modified low density lipoprotein (mmLDL) is a risk factor for cardiovascular diseases. However, no studies examining the effect of mmLDL on vascular smooth muscle receptors have been released. The current study investigated the effect of mmLDL on the mesenteric artery α1 adrenoceptor and the molecular mechanisms. Mice were divided into the normal saline (NS), mmLDL, and mmLDL+U0126 groups. In the mmLDL+U0126 group, the animals were subjected to an intravenous tail injection of mmLDL and an intraperitoneal injection of U0126. Vascular tension caused by noradrenaline (NA) in mesenteric arteries was measured with a sensitive myograph system. The serum levels of oxLDL, TNF-α, and IL-1β were detected using enzyme-linked immunosorbent assays. The expressions of the α1 adrenoceptor, the α2 adrenoceptor, TNF-α, IL-1β, and pERK1/2 were detected using real-time polymerase chain reactions and Western blot analysis. Compared with the NS group, the mmLDL group exhibited a noticeably enhanced NA shrinkage dose-response curve and a significantly increased Emax value (P<0.01). Prazosin (α1 adrenoceptor antagonist) caused a noticeable right shift of the dose-response curve. U0126 inhibited the increases in the serum levels and vessel wall expression of IL-1β and TNF-α and enhanced the NA shrinkage dose-response curve caused by mmLDL, as observed by a significantly decreased Emax value (P<0.01). It inhibited the increased α1 adrenoceptor expression caused by mmLDL. The serum levels of IL-1β and TNF-α demonstrated a positive correlation with the NA-induced maximum shrinkage percentage. U0126 inhibited the mmLDL-induced increase in the pERK1/2 protein level in the vessel wall. In conclusion, mmLDL increased the serum levels of IL-1β and TNF-α in vivo by activating the ERK1/2 pathway, which resulted in α1 receptor-mediated vasoconstriction and an increase in the expression of α1 adrenoceptor. The results of this study may provide new ideas for the prevention and cure of cardiovascular diseases in the future.

Resveratrol prevents cardiovascular complications in the SHR/STZ rat by reductions in oxidative stress and inflammation

The cardioprotective effects of resveratrol are well established in animal models of metabolic disease but are yet to be investigated in a combined model of hypertension and diabetes. This study investigated the ability of resveratrol's antioxidant and anti-inflammatory effects to prevent cardiovascular complications in the spontaneously hypertensive streptozotocin-induced diabetic rat. Diabetes was induced in eight-week-old male spontaneously hypertensive rats via a single intravenous injection of streptozotocin. Following this, resveratrol was administered orally for an eight-week period until the animals were sixteen weeks of age. Upon completion of the treatment regime assessments of oxidative stress, lipid peroxidation, inflammation, and cardiovascular function were made. Resveratrol administration to hypertensive-diabetic animals did not impact upon blood glucose or haemodynamics but significantly reduced oxidative stress, lipid peroxidation, and inflammatory cytokines. Reductions in systemic levels of oxidative stress and inflammation conferred improvements in vascular reactivity and left ventricular pump function and electrophysiology. This study demonstrates that resveratrol administration to hypertensive diabetic animals can elicit cardioprotective properties via antioxidant and anti-inflammatory effects. The observed preservation of cardiovascular function was independent of changes in blood glucose concentration and haemodynamics, suggesting that oxidative stress and inflammation are key components within the pathological cascade associated with hypertension and diabetes.

Permanent distal occlusion of middle cerebral artery in rat causes local increased ETB, 5-HT₁B and AT₁ receptor-mediated contractility downstream of occlusion

BACKGROUND/AIMS

In response to experimental stroke, a characteristic functional and expressional upregulation of contractile G-protein-coupled receptors has been uncovered in the affected cerebral vasculature; however, the mechanism initiating this phenomenon remains unknown.

METHODS

Using a model of permanent distal occlusion of rat middle cerebral arteries, we investigated whether there was a regional difference in receptor-mediated contractility of segments located upstream and downstream of the occlusion site. The contractile response to endothelin, angiotensin and 5-hydroxytryptamine receptor stimulation was studied by sensitive wire myograph.

RESULTS

Only downstream segments exhibited an augmented contractile response to stimulation with each of the three ligands, with the response towards sarafotoxin 6c being especially augmented compared to sham, upstream and contralateral controls. This functional increase did not seem to relate to ischemic tissue damage, inflammatory cell infiltration or the element of reperfusion. Interestingly, immunohistochemistry did not show any difference in the level of immunoreactivity towards endothelin B (ETB) receptors between groups.

CONCLUSION

Single artery occlusion without significant visible infarct resulted in locally increased ETB, angiotensin type 1 and 5-hydroxytryptamine 1B receptor-mediated contractile responses only in segments located downstream of the occlusion site. This suggests lack of wall stress as an initiating trigger leading to regulation of contractile response after cerebral stroke.

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.

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.

Vasoconstrictor 5-HT receptors in the smooth muscle of the rat middle cerebral artery

Serotonin (5-HT) can constrict cerebral arteries via activation of 5-HT(1B) and 5-HT(2A) receptors. Our goal was to reveal the importance and relative contribution of the two 5-HT receptor subtypes to the serotonin-induced vasoconstriction in the rat middle cerebral artery. The vasoconstrictor effects of 5-carboxamidotryptamine, sumatriptan and 5-HT were measured without and with pre-treatment with SB 216641 (5-HT(1B) antagonist), or ritanserin, (5-HT(2A) antagonist), in endothelium-denuded arteries, in vitro. All agonists caused vasoconstrictions. The order of potency (EC(50)) of the compounds was: 5-carboxamidotryptamine (14±3 nM)>5-HT (270±30 nM)>sumatriptan (5.8±1.9 μM). The concentration-response curve of 5-carboxamidotryptamine resembled the sum of two sigmoid curves (EC(50) 14±3 nM and 15±7 μM), and SB 216641 and ritanserin antagonized its low and high concentration components, respectively. Vasoconstrictions evoked by 5-HT at low and high concentrations were also fully antagonized by SB 216641 and ritanserin, respectively. Sumatriptan constricted the middle cerebral artery exclusively via 5-HT(1B) receptors. The efficacy of 5-carboxamidotryptamine and sumatriptan was low in comparison to the maximum contractile force elicited by 120 mmol/l KCl, reaching only 18-23% for 5-HT(1B) and 14% for 5-HT(2A) receptor activation. In conclusion, 5-HT produced small vasoconstrictions in the rat middle cerebral artery that were mediated by 5-HT(1B) receptors with high potency and by 5-HT(2A) receptors with low potency. Thus, 5-HT may have a minor physiological role in blood flow regulation via 5-HT(1B) receptor activation while 5-HT(2A) receptors seem to have a pathophysiological role in this vessel.

Endothelin-1 activation of ETB receptors leads to a reduced cellular proliferative rate and an increased cellular footprint

Endothelin-1 (ET-1) is a vasoactive peptide which signals through two G-protein coupled receptors, endothelin receptor A (ETA) and B (ETB). We determined that ET-1 activation of its ETB receptor in stably cDNA transfected CHO cells leads to a 55% reduction in cell number by end-point cell counting and a 35% decrease in cell growth by a real-time cell-substrate impedance-based assay after 24h of cell growth. When CHO ETB cells were synchronized in the late G1 cell cycle phase, ET-1 delayed their S phase progression compared to control by 30% as determined by [(3)H]-thymidine incorporation. On the other hand, no such delay was observed during late G2/M to G1 transit when cells were treated with ET-1 after release from mitotic arrest. Using the cell-substrate impedance-based assay, we observed that ET-1 induces opposing morphological changes in CHO ETA and CHO ETB cells with ETB causing an increase in the cell footprint and ETA a decrease. Likewise, in pulmonary artery smooth muscle cells, which express both ETA and ETB receptors, ET-1 induces an ETA-dependent contraction and an ETB dependent dilation. These results are shedding light on a possible beneficial role for ETB in diseases involving ET-1 dysfunction such as pulmonary hypertension.

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.

DJ-1 upregulates tyrosine hydroxylase gene expression by activating its transcriptional factor Nurr1 via the ERK1/2 pathway

Loss-of-function DJ-1 mutations have been linked to autosomal recessive early-onset Parikinsonism. However, the putative function of DJ-1 is not completely understood. Previous studies indicate that DJ-1 overexpression results in upregulation of the tyrosine hydroxylase gene. The mechanism by which DJ-1 affects tyrosine hydroxylase expression remains elusive. In the present study, we show that DJ-1 overexpression induces ERK1/2 activation, along with increased tyrosine hydroxylase expression. The L166P DJ-1 mutant, which has been identified as being responsible for familial Parkinsonism, did not have this effect. Moreover, suppression of ERK1/2 phosphorylation by the pharmacological inhibitor U0126 partially abolished the regulating effect of DJ-1 on tyrosine hydroxylase. Nurr1, a transcriptional factor for tyrosine hydroxylase, can be phosphorylated by ERK1/2 and translocate to the nucleus, where it is activated. Thus, we measured nuclear translocation of Nurr1. Confocal microscopy and Western blotting revealed that Nurr1 translocated to the nucleus and was activated by overexpression of wild-type DJ-1, but not of its L166P mutant. Knockdown of Nurr1 gene expression abolished the effect on tyrosine hydroxylase induced by DJ-1. Taken together, these data suggest that DJ-1 upregulates tyrosine hydroxylase expression by activating its transcription factor Nurr1 via the ERK1/2 pathway.

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.

Alteration in contractile G-protein coupled receptor expression by moist snuff and nicotine in rat cerebral arteries

The cardiovascular risk for users of use of Swedish snus/American snuff (moist tobacco) has been debated for a long time. The present study was designed to examine the effects of water- or lipid-soluble (DMSO-soluble) snus and nicotine, the most important substance in tobacco, on the expression of vasocontractile G-protein coupled receptors (GPCR), such as endothelin ET(B), serotonin 5-HT(1B), and thromboxane A(2) TP receptors, in rat cerebral arteries. Studies show that these vasocontractile GPCR show alterations by lipid-soluble cigarette smoke particles via activation of mitogen-activated protein kinases (MAPK). However, the effects of moist tobacco on the expression of GPCR are less studied. Rat middle cerebral arteries were isolated and organ cultured in serum-free medium for 24h in the presence of water-soluble snus (WSS), DMSO-soluble snus (DSS), or nicotine. The dose of snus and nicotine was kept at plasma level of snus users (25ng nicotine/ml). A high dose (250ng nicotine/ml) was also included due to the previous results showing alteration in the GPCR expression by nicotine at this concentration. Contractile responses to the ET(B) receptor agonist sarafotoxin 6c, 5-HT(1B) receptor agonist 5-carboxamidotryptamine, and TP receptor agonist U46619 were investigated by a sensitive myograph. The expression of ET(B), 5-HT(1B), and TP receptors was studied at mRNA and protein levels using quantitative real-time PCR and immunohistochemistry, respectively. Organ culture with WSS or DSS (25ng nicotine/ml) lowered the 5-HT(1B) receptor-mediated contraction. Furthermore, DSS shifted the TP receptor-mediated contraction curve left-wards with a stronger contraction. High dose of nicotine (250ng nicotine/ml) increased the ET(B) receptor-mediated contraction. The combined 5-HT(1B) and 5-HT(2A) receptor-mediated contraction was increased, and both the 5-CT and TxA2 induced contractions were left-ward shifted by WSS, DSS, or nicotine (250ng nicotine/ml). Only the DSS group showed that the increase of 5-HT(1B) receptor-mediated contraction occurred at the transcriptional level, demonstrated by an increased mRNA expression for the receptor. Thus, snus and nicotine alter the GPCR expression in the cerebral arteries, which may be involved in cerebral vascular disease.