Cortical expression of endothelin receptor subtypes A and B following middle cerebral artery occlusion in rats

Ubiquitin C-terminal hydrolase-L1 expression in non-small-cell lung cancer and its association with clinicopathological features and prognosis

UbiquitinC-terminal hydrolase-L1 (UCH-L1) is a cysteine hydrolase. It functions as a ubiquitin hydrolase, stabilizes the ubiquitin monomer, and affects cell division through cell cycle protein deubiquitination. Abnormal UCH-L1 expression is closely related to the occurrence and development of several tumors. Although some in vitro studies have demonstrated the significance of UCH-L1 in non-small-cell lung cancer (NSCLC), only few clinical studies have focused on the UCH-L1 expression in NSCLC, and the results are controversial and non-uniform. We investigated the UCH-L1 expression in 401 cases of surgically resected NSCLC, including 286 cases of adenocarcinoma (ADC) and 65 cases of squamous cell carcinoma. The associations between the UCH-L1 expression and clinicopathological features, programmed cell death-ligand 1 (PD-L1) expression, and prognostic significance were analyzed. For NSCLC, the UCH-L1 expression is associated with sex, smoking history, tumor size (>3 cm), lymphocyte infiltration, advanced pathological stages, and shortened overall survival (OS; 89.72 vs. 114.55 months; P = 0.005), but not PD-L1 expression. The UCH-L1 expression in ADC is associated with advanced pathological stages, pleural invasion, and shortened OS (90.38 vs. 118.55 months; P = 0.010). Multivariate analysis confirmed that UCH-L1 expression was an independent poor prognostic factor for NSCLC (OS: hazard ratio [HR], 1.854; 95% confidence interval [CI], 1.132-3.038; P = 0.014). Our results suggest that the UCH-L1 expression differs across tumors with different clinicopathological features, and it is related to poor prognosis.

Apelin-13 attenuates injury following ischemic stroke by targeting matrix metalloproteinases (MMP), endothelin- B receptor, occludin/claudin-5 and oxidative stress

Oxidative stress, an adverse consequence of brain ischemia-reperfusion injury (IRI), activates matrix metalloproteinase enzymes which cause to destruction of extracellular matrix and tight junction proteins. Oxidative stress during stroke increases serum endothelin-1 and endothelin B receptor (ETBR) expression. Apelin-13, an endogenous peptide, is expressed in numerous tissues that regulate diverse physiological and pathological processes. This study aimed to investigate the effect of intravenous (IV) injection of apelin-13 on cerebral vasogenic edema due to brain IRI. Animals were divided into sham, ischemia, and treat groups. IRI model was induced by middle cerebral artery occlusion (MCAO) for 60 min followed by 23 h reperfusion. Apelin-13 was injected into the tail vein 5 min before reperfusion. Neurological defects were evaluated with longa test. Brain water content and BBB permeability were assessed according to cerebral dry-wet weight and brain Evans blue extraction. Malondialdehyde (MDA), superoxide dismutase (SOD), and catalase (CAT) were measured using the colorimetric method. Expression of occludin and claudin-5, matrix metalloproteinase- 2 and 9 (MMP-2 & 9) and, ETBR were evaluated using Western blot. Brain IRI was associated with BBB breakdowns and vasogenic edema. Apelin-13 significantly reduced BBB permeability and vasogenic edema. Apelin-13 significantly attenuated IRI-related oxidative stress. Apelin-13 decreased expression of mmp-2, 9 and ETBR, prevented from decrement of occludin and claudin-5 expersion, which protected BBB integrity and reduced vasogenic edema. In conclusion, our results have suggested that an IV injection of apelin-13 could somehow reduce vasogenic edema via targeting oxidative stress and ETBR expression.

Diabetes-related sex differences in the brain endothelin system following ischemia in vivo and in human brain endothelial cells in vitro

The endothelin (ET) system has been implicated to contribute to the pathophysiology of cognitive impairment and stroke in experimental diabetes. Our goals were to test the hypotheses that (1) circulating and (or) periinfarct ET-1 levels are elevated after stroke in both sexes and this increase is greater in diabetes, (2) ET receptors are differentially regulated in the diabetic brain, (3) brain microvascular endothelial cells (BMVEC) of female and male origin express the ETA receptor subtype, and (4) diabetes- and stroke-mimicking conditions increase ET-1 levels in BMVECs of both sexes. Control and diabetic rats were randomized to sham or stroke surgery. BMVECs of male (hBEC5i) and female (hCMEC/D3) origin, cultured under normal and diabetes-mimicking conditions, were exposed to normoxia or hypoxia. Circulating ET-1 levels were higher in diabetic animals and this was more pronounced in the male cohort. Stroke did not further increase plasma ET-1. Tissue ET-1 levels were increased after stroke only in males, whereas periinfarct ET-1 increased in both control and diabetic females. Male BMVECs secreted more ET-1 than female cells and hypoxia increased ET-1 levels in both cell types. There was sexually dimorphic regulation of ET receptors in both tissue and cell culture samples. There are sex differences in the stroke- and diabetes-mediated changes in the brain ET system at the endothelial and tissue levels.

Endothelin-1 (ET-1) promotes a proinflammatory microglia phenotype in diabetic conditions

Diabetes increases the risk and severity of cognitive impairment, especially after ischemic stroke. It is also known that the activation of the endothelin (ET) system is associated with cognitive impairment and microglia around the periinfarct area produce ET-1. However, little is known about the effect of ET-1 on microglial polarization, especially under diabetic conditions. We hypothesized that (i) ET-1 activates microglia to the proinflammatory M-1-like phenotype and (ii) hypoxia/ lipopolysaccharide (LPS) activates the microglial ET system and promotes microglial activation towards the M-1 phenotype in diabetic conditions. Microglial cells (C8B4) cultured under normal-glucose (25 mmol/L) conditions and diabetes-mimicking high-glucose (50 mmol/L) conditions for 48 h were stimulated with ET-1, cobalt chloride (200 μmol/L), or LPS (100 ng/mL) for 24 h. PPET-1, ET receptor subtypes, and M1/M2 marker gene mRNA expression were measured by RT-PCR. Secreted ET-1 was measured by ELISA. A high dose of ET-1 (1 μmol/L) increases the mRNA levels of ET receptors and activates the microglia towards the M1 phenotype. Hypoxia or LPS activates the ET system in microglial cells and shifts the microglia towards the M1 phenotype in diabetic conditions. These in vitro observations warrant further investigation into the role of ET-1-mediated activation of proinflammatory microglia in post-stroke cognitive impairment in diabetes.

Effects of Bu Shen Yi sui capsule on NogoA/NgR and its signaling pathways RhoA/ROCK in mice with experimental autoimmune encephalomyelitis

Background

Axon growth inhibitory factors NogoA/Nogo receptor (NgR) and its signaling pathways RhoA/Rho kinase (ROCK) play a critical role in the repair of nerve damage in multiple sclerosis (MS). Bu Shen Yi Sui Capsule (BSYSC) is an effective Chinese formula utilized to treat MS in clinical setting and noted for its potent neuroprotective effects. In this study, we focus on the effects of BSYSC on promoting nerve repair and the underlying mechanisms in mice with experimental autoimmune encephalomyelitis (EAE), an animal model of MS.

Methods

The EAE mouse model was induced by injecting subcutaneously with myelin oligodendrocyte glycoprotein (MOG) _35–55 supplemented with pertussis toxin. BSYSC was orally administrated at dose of 3.0 g/kg once a day for 40 days. The levels of protein gene product (PGP) 9.5, p-Tau, growth associated protein (GAP) -43, KI67 and Nestin in the brain or spinal cord on 20 and 40 day post-induction (dpi) were detected via immunofluorescence and Western blot analysis. Furthermore, NogoA/NgR and RhoA/ROCK signaling molecules were studied by qRT-PCR and Western blot analysis.

Results

Twenty or 40 days of treatment with BSYSC increased markedly PGP9.5 and GAP-43 levels, reduced p-Tau in the brain or spinal cord of mice with EAE. In addition, BSYSC elevated significantly the expression of KI67 and Nestin in the spinal cord 40 dpi. Further study showed that the activation of NogoA/NgR and RhoA/ROCK were suppressed by the presence of BSYSC.

Conclusions

BSYSC could attenuate axonal injury and promote repair of axonal damage in EAE mice in part through the down-regulation of NogoA/NgR and RhoA/ROCK signaling pathways.

Development and Characterization of a Macaque Model of Focal Internal Capsular Infarcts

Several studies have used macaque monkeys with lesions induced in the primary motor cortex (M1) to investigate the recovery of motor function after brain damage. However, in human stroke patients, the severity and outcome of motor impairments depend on the degree of damage to the white matter, especially that in the posterior internal capsule, which carries corticospinal tracts. To bridge the gap between results obtained in M1-lesioned macaques and the development of clinical intervention strategies, we established a method of inducing focal infarcts at the posterior internal capsule of macaque monkeys by injecting endothelin-1 (ET-1), a vasoconstrictor peptide. The infarcts expanded between 3 days and 1 week after ET-1 injection. The infarct volume in each macaque was negatively correlated with precision grip performance 3 days and 1 week after injection, suggesting that the degree of infarct expansion may have been a cause of the impairment in hand movements during the early stage. Although the infarct volume decreased and gross movement improved, impairment of dexterous hand movements remained until the end of the behavioral and imaging experiments at 3 months after ET-1 injection. A decrease in the abundance of large neurons in M1, from which the descending motor tracts originate, was associated with this later-stage impairment. The present model is useful not only for studying neurological changes underlying deficits and recovery but also for testing therapeutic interventions after white matter infarcts in primates.

Selective astrocytic endothelin-1 overexpression contributes to dementia associated with ischemic stroke by exaggerating astrocyte-derived amyloid secretion

Endothelin-1 (ET-1) is synthesized by endothelial cells and astrocytes in stroke and in brains of Alzheimer's disease patients. Our transgenic mice with ET-1 overexpression in the endothelial cells (TET-1) showed more severe blood-brain barrier (BBB) breakdown, neuronal apoptosis, and glial reactivity after 2-hour transient middle cerebral artery occlusion (tMCAO) with 22-hour reperfusion and more severe cognitive deficits after 30 minutes tMCAO with 5 months reperfusion. However, the role of astrocytic ET-1 in contributing to poststroke cognitive deficits after tMCAO is largely unknown. Therefore, GET-1 mice were challenged with tMCAO to determine its effect on neurologic and cognitive deficit. The GET-1 mice transiently displayed a sensorimotor deficit after reperfusion that recovered shortly, then more severe deficit in spatial learning and memory was observed at 3 months after ischemia compared with that of the controls. Upregulation of TNF-α, cleaved caspase-3, and Thioflavin-S-positive aggregates was observed in the ipsilateral hemispheres of the GET-1 brains as early as 3 days after ischemia. In an in vitro study, ET-1 overexpressing astrocytic cells showed amyloid secretion after hypoxia/ischemia insult, which activated endothelin A (ETA) and endothelin B (ETB) receptors in a PI3K/AKT-dependent manner, suggesting role of astrocytic ET-1 in dementia associated with stroke by astrocyte-derived amyloid production.

Stimulation of endothelin B receptors by IRL-1620 decreases the progression of Alzheimer's disease

Alzheimer's disease (AD) is a progressive neurodegenerative disorder characterized by severe cognitive impairment that ultimately leads to death. Endothelin (ET) and its receptors have been considered as therapeutic targets for AD. Recent studies in our lab have shown that stimulation of ETB receptors provide significant neuroprotection following Aβ1-40 administration. It is possible that IRL-1620 may be neuroprotective due to angiogenesis. However, the effect of IRL-1620 on neurovascular remodeling following Aβ1-40 administration has not been established. The purpose of this study was to determine the effect of stimulation of ETB receptors by IRL-1620 on vascular and neuronal growth factors after Aβ1-40 administration. Rats were treated with Aβ1-40 (day 1, 7 and 14) in the lateral cerebral ventricles using stereotaxically implanted cannula and received three intravenous injections of IRL-1620 (an ETB agonist), and/or BQ788 (an ETB antagonist) at 2-h interval on day 8; experiments were performed on day 15. Rats were sacrificed for estimation of brain ETB receptors, vascular endothelial growth factor (VEGF) and nerve growth factor (NGF) expression using immunofluorescence and Western blot. In the Morris swim task, amyloid-β (Aβ)-treated rats showed a significant (p<0.0001) impairment in spatial memory. Rats treated with IRL-1620 significantly (p<0.001) reduced the cognitive impairment induced by Aβ. BQ788 treatment completely blocked IRL-1620-induced improvement in cognitive impairment. IRL-1620 treatment enhanced the number of blood vessels labeled with VEGF compared to vehicle treatment. Additionally, cells showed increased (p<0.001) positive staining for NGF in IRL-1620-treated animals. ETB, VEGF and NGF protein expression significantly (p<0.001) increased in the brain of IRL-1620-treated rats as compared to vehicle. Pretreatment with BQ788 blocked the effects of IRL-1620, thus confirming the role of ETB receptors in the neurovascular remodeling actions of IRL-1620. Results of the present study demonstrate that IRL-1620 improves both acquisition (learning) and retention (memory) on the water maze task and enhances angiogenic and neurogenic remodeling. These findings indicate that the ETB receptor may be a novel therapeutic target for AD and other neurovascular degenerative disorders.

Ontogeny of endothelin receptors in the brain, heart, and kidneys of neonatal rats

BACKGROUND

Endothelin (ET) plays an important role in many physiological functions. It has been demonstrated that endogenous ET-1 concentration in the central nervous system (CNS) changes with age; however the ontogeny of ETA and ETB receptors in the brain, heart, and kidneys during postnatal development has not been studied.

METHODS

Brains, hearts and kidneys of rats at postnatal days 1, 7, 14 and 28 were evaluated for the expression of ETA and ETB receptors via Western blot. ETB receptors within the developing brain were further accessed via immunofluorescence.

RESULTS

The mean organ and body weights increased proportionally with advancing age demonstrating normal growth. The expression of ETA receptors in the brain, heart, and kidneys and ETB receptor expression in the heart and kidneys was similar in these rats at postnatal ages 1, 7, 14 and 28days. However, brain ETB receptor expression significantly (P<0.001) decreased by 72% on day 28 compared to the levels on postnatal day 1. Upon immunofluorescent analysis, the intensity of ETB staining in the cerebral cortex and subventricular zones of the developing rat brain decreased significantly from day 1 to day 7 (P<0.001) and from day 7 to day 14 (P<0.0001). There was no further decrease in ETB intensity noted in the cerebral cortex and subventricular zones between day 14 and day 28 of postnatal age. The intensity of ETB receptor staining within the cerebrovasculature, on the other hand, increased significantly (P<0.05) from days 1 and 7 to day 14.

CONCLUSIONS

These results demonstrate that expression of ETA receptors does not change with postnatal development. On the other hand ETB receptors in the cerebral cortex and subventricular zones of the brain decrease with age, while ETB receptors in the cerebrovasculature increase with age, implicating ETB receptor involvement in the structural maturity and development of the CNS.

Cardiac autonomic nerve distribution and arrhythmia

OBJECTIVE:

To analyze the distribution characteristics of cardiac autonomic nerves and to explore the correlation between cardiac autonomic nerve distribution and arrhythmia.

DATA RETRIEVAL:

A computer-based retrieval was performed for papers examining the distribution of cardiac autonomic nerves, using heart, autonomic nerve, sympathetic nerve, vagus nerve, nerve distribution, rhythm and atrial fibrillation as the key words.

SELECTION CRITERIA:

A total of 165 studies examining the distribution of cardiac autonomic nerve were screened, and 46 of them were eventually included.

MAIN OUTCOME MEASURES:

The distribution and characteristics of cardiac autonomic nerves were observed, and immunohistochemical staining was applied to determine the levels of tyrosine hydroxylase and acetylcholine transferase (main markers of cardiac autonomic nerve distribution). In addition, the correlation between cardiac autonomic nerve distribution and cardiac arrhythmia was investigated.

RESULTS:

Cardiac autonomic nerves were reported to exhibit a disordered distribution in different sites, mainly at the surface of the cardiac atrium and pulmonary vein, forming a ganglia plexus. The distribution of the pulmonary vein autonomic nerve was prominent at the proximal end rather than the distal end, at the upper left rather than the lower right, at the epicardial membrane rather than the endocardial membrane, at the left atrium rather than the right atrium, and at the posterior wall rather than the anterior wall. The main markers used for cardiac autonomic nerves were tyrosine hydroxylase and acetylcholine transferase. Protein gene product 9.5 was used to label the immunoreactive nerve distribution, and the distribution density of autonomic nerves was determined using a computer-aided morphometric analysis system.

CONCLUSION:

The uneven distribution of the cardiac autonomic nerves is the leading cause of the occurrence of arrhythmia, and the cardiac autonomic nerves play an important role in the occurrence, maintenance, and symptoms of arrhythmia.

Spatial alterations in endothelin receptor expression are temporally associated with the altered microcirculation after brain trauma

OBJECTIVES

To study the cellular distribution of endothelin receptors A and B (ETrA and ETrB) in the post-traumatic sensorimotor cortex and hippocampus.

MATERIALS AND METHODS

We inflicted closed head trauma to male Sprague-Dawley rats and visualized ETrA and ETrB immunoreactivity with 3,3'-diaminobenzidine.

RESULTS

ETrA immunolabeling was the most prominent in pyramidal neurons 24 and 48 hours post-trauma, while it reached its peak in the microvasculature at hour 4. ETrB immunolabeling was observed in endothelial cells, perivascular neurons, smooth muscle cells (SM) and pericytes, the expression being the most pronounced 24 hours post-trauma.

DISCUSSION

The results suggest that the vasoconstrictor effect of endothelin-1 (ET-1) is mediated primarily by ETrA. The dual effects of ETrB are reflected in its vasoconstrictor role at the vascular bed and conversely, in the attenuation of ET-1 availability and synthesis. We conclude that both receptors play a role in the disturbed microvascular autoregulation and in the sustained reduction of blood flow following trauma to the brain.

The effect of endothelin receptor A antagonism on basilar artery endothelium-dependent relaxation after ischemic stroke

AIMS

Endothelin (ET) receptor A antagonism decreases neuronal damage in experimental models of stroke. Since large arteries like basilar artery contribute significantly to total cerebrovascular resistance and are major determinants of microvascular pressure, dysregulation of basilar artery function may worsen stroke injury. ET-1 is involved in the regulation of basilar constriction. However, whether stroke influences vasoreactivity of basilar artery and to what extent ET-1 contributes to basilar vascular dysfunction after stroke remained unknown. The goal of this study was to test the hypothesis that ET-1 impairs basilar artery vasorelaxation after ischemia/reperfusion (I/R) injury via activation of ET(A) receptor.

MAIN METHODS

Male Wistar rats were subjected to 3h middle cerebral artery occlusion (MCAO) and 21 h reperfusion. One group received ET(A) receptor antagonist atrasentan (5 mg/kg, i.p.) at reperfusion. At 24h, basilar arteries were isolated from control non-stroked, stroked and stroked+atrasentan-treated animals for vascular reactivity measurements using pressurized arteriograph.

KEY FINDINGS

Acetylcholine (Ach)-induced maximum relaxation (R(max)) was decreased in stroked animals as compared to non-stroked group and ET(A) antagonism partially restored it. There was also a trend for decreased EC(50) value for the antagonist treatment group indicating improved Ach sensitivity.

SIGNIFICANCE

These findings suggest that I/R not only affects vessels distal to the occlusion but also impairs relaxation of proximal large vessels. ET-1-mediated basilar artery dysfunction may contribute to neurovascular damage after stroke and early restoration of vascular function by ET receptor antagonism after I/R injury may offer a therapeutic strategy.

Endothelin-1 plasma concentrations in patients with retinitis pigmentosa

PURPOSE

The aim of this study was to investigate the behaviour of plasma endothelin-1 (ET-1) levels in patients affected by retinitis pigmentosa (RP) and syndromic RP.

METHODS

Blood samples were obtained from a group of 40 consecutive patients with RP matched with 35 healthy subjects (HS) as control. We carried out a complete ophthalmological examination. The study group included 26 patients with RP and 14 patients with syndromic RP. Plasma ET-1 levels were determined in duplicate with a specific radioimmunoassay method.

RESULTS

In the HS plasma ET-1 levels were 7.48+/-2.58 pg/mL. The mean of plasma ET-1 concentrations in all patients with RP ( 16.2+/-5.6 pg/mL) was significantly (P<0.01) higher than that of HS. Moreover, in the syndromic RP patients, plasma ET-1 levels (18.9+/-6.8 pg/mL) were higher than those of HS and RP patients (P<0.01).

CONCLUSION

The increase of plasma ET-1 levels in RP patients suggests that ET-1 may play a role in the pathophysiology of the diseases involving retinal pigment epithelial cells and the retinal vascular system such as RP.

Endothelin promotes neurite elongation by a mechanism dependent on c-Jun N-terminal kinase

Endothelin (ET), which is known as a vasoconstrictive peptide, is associated with a lot of biological functions. Although endothelin receptors are expressed in the central nervous system (CNS), little is known about the effects of endothelin on neuronal function. In this study, we reported that endothelins elongate cortical neurites via the endothelin A receptor. All the endothelin isoforms tested, endothelin-1, endothelin-2, and endothelin-3, promoted neurite elongation. ET-1-induced neurite elongation was specifically inhibited by treatment with BQ123, an antagonist for the endothelin A receptor. In addition, inhibition of ET-1-induced c-Jun N-terminal kinase (JNK) activation by treatment with SP600125, a JNK inhibitor, also prevented the ET-1-mediated promotion of neurite elongation. Thus, endothelin induces cortical neurite elongation through the endothelin A receptor by a mechanism dependent on JNK.

Endothelial endothelin-1 over-expression using receptor tyrosine kinase tie-1 promoter leads to more severe vascular permeability and blood brain barrier breakdown after transient middle cerebral artery occlusion

Endothelin-1 (ET-1) is up-regulated in the endothelial cells and astrocytes under ischemia. Transgenic mice with astrocytic ET-1 over-expression (GET-1) showed more severe neurological deficit and larger infarct after transient middle cerebral artery occlusion (MCAO). Here, the significance of endothelial ET-1 in ischemic brain injury was investigated using transgenic mice with the endothelial ET-1 over-expression (TET-1). Increased ET-1 level was observed in the TET-1 brain infarct core after transient MCAO. ET(A) receptor expression was induced in the penumbra and ET(A) antagonist (A-147627) partially normalized the infarct volume and neurological deficit. In the infarct core of TET-1 brain, superoxide, nitrotyrosine, and gp91(phox) levels were increased. TET-1 brain displayed increased matrix metalloproteinase-2 expression, water content, immunoglobulin leakage and decreased occludin level in the ipsilateral hemisphere indicative of BBB breakdown and hemispheric edema. Interestingly, AQP-4 expression was increased in the penumbra of TET-1 brain following transient MCAO leading to the water accumulation. Taken together, endothelial ET-1 over-expression and ETA receptor activation contributes to the increased oxidative stress, water accumulation and BBB breakdown after transient MCAO leading to more severe neurological deficit and increased infarct.

Regulation of glial inflammatory mediators synthesis: possible role of endothelins

Endothelins are well known as modulators of inflammation in the periphery, but little is known about their possible role in brain inflammation. Stimulation of astrocyte prostaglandin, an inflammatory mediator, synthesis was shown so far only by endothelin 3 (ET-3). By contrast, several studies showed no change or slight decrease of basal nitric oxide synthesis after treatment of astrocytes with endothelin 1 (ET-1) and ET-3. However, a significant increase in astrocytic and microglial nitric oxide synthase (NOS) was observed after exposure to ET-1 and ET-3 in a model of forebrain ischaemia. Here we demonstrate that all three endothelins (ET-1, ET-2, ET-3) significantly enhanced the synthesis of prostaglandin E(2) and nitric oxide in glial cells. Each of the selective antagonists for ETA and ETB receptors (BQ123 and BQ788 respectively), significantly inhibited endothelins-induced production of both nitric oxide and prostaglandin E(2). These results suggest a regulatory mechanism of endothelins, interacting with both endothelin receptors, on glial inflammation. Therefore, inhibition of endothelin receptors may have a therapeutic potential in pathological conditions of the brain, when an uncontrolled inflammatory response is involved.

Role of endothelins as mediators of injury-induced alterations of glial glutamate turnover

Astroglia terminate glutamatergic neurotransmission and prevent excitotoxic extracellular glutamate concentration by clearing synaptically released glutamate through the high-affinity, sodium-dependent glutamate transporters GLT-1 and GLAST. Many brain injures are associated with the disturbed expression of glial glutamate transporters and a subsequent increase of extracellular glutamate to neurotoxic levels. We have now followed up initial hints pointing to endothelins, a family of injury-regulated peptides, as mediators of this injury-induced loss of glial glutamate transporter expression. We observed that, in line with such a role, endothelins not only act as potent inhibitors of basal and exogenously (dbcAMP)-induced expression of GLT-1 in cortical astrocytes as shown before, but likewise inhibit expression of GLT-1 or GLAST in astrocytes cultured from the diencephalon, mesencephalon, cerebellum, and spinal cord. We further demonstrate that endothelins equally inhibit GLT-1 expression in cortical slice cultures, a culture system closely resembling the in vivo situation. Although brain injuries are usually associated with an increase in the expression of the glutamate-converting enzyme glutamine synthetase, cultured cortical astrocytes maintained with endothelins showed an almost complete loss of glutamine synthetase. Interestingly, the inhibitory effects of endothelins on the expression of glutamine synthetase, but not of glutamate transporters, was overridden by high extracellular glutamate, indicating that the primarily inhibitory action of endothelins on the various components of glial glutamate turnover dissociates in the injured brain.

Gap junctional control of glial glutamate transporter expression

The uptake of glutamate into astroglia is the predominant mechanism to terminate glutamatergic neurotransmission and to prevent neurotoxic extracellular glutamate concentrations. Here, we show that uncoupling cultured cortical astrocytes with the gap junction blocker, propofol, or the Cx43 mimetic peptide, Gap27, inhibits the expression of GLT-1, the major glutamate transporter subtype in the cortex. The dependence of GLT-1 expression on gap junctions was further confirmed by the use of astrocytes in which either the expression of Cx43, the major astrocytic gap junction protein, was inhibited by RNA interference or which were derived from animals carrying an astrocyte-specific deletion of the Cx43 gene. In both cases, reduced astrocytic coupling was associated with a pronounced decline in GLT-1 expression. Finally, a luciferase reporter gene assay demonstrated that blockade of gap junctions/connexins suppressed transcriptional activity of GLT-1 promoter. These observations unravel a previously unrecognized role of gap junctions in the control of glial glutamate transport.

Sulfisoxazole, an endothelin receptor antagonist, protects retinal neurones from insults of ischemia/reperfusion or lipopolysaccharide

Endothelins exert pathological effects in the eye and much interest centres on their role in causing retinal neuronal death in ischemic diseases like glaucoma. In the present study the influence of the non-selective endothelin antagonist, sulfisoxazole on raised intraocular pressure-induced ischemia to the rat retina was investigated. Moreover, in vitro studies on primary rat retinal cultures were undertaken to see whether sulfisoxazole is able to blunt the toxic effect of lipopolysaccharide (LPS) to retinal neurones. In order to determine whether sulfisoxazole provides protection to the retina the a- and b-wave amplitudes of the electroretinogram (ERG), the localisation of retinal choline acetyltransferase (ChAT), nitric oxide synthase (nNOS) and Thy-1 and the retinal mRNA levels of Thy-1 and FGF-2 were deduced in retinas subjected to ischemia in the absence or presence of sulfisoxazole. The results showed that the ischemia-induced changes to the a- and b-wave amplitudes of the ERG and changes associated with the localisation of ChAT, nNOS and Thy-1 to be significantly blunted by sulfisoxazole. However, while the ischemia-induced changes to Thy-1 and FGF-2 mRNAs were reduced by sulfisoxazole, the reduction was non-significant. The in vitro studies provided support for the protective effect of sulfisoxazole. Here, it was clearly shown that sulfisoxazole attenuated the elevation of nitric oxide (deduced by measuring nitrite) and the reduction in numbers of GABA-containing neurones caused by LPS. The present study provides evidence for the first time that endothelin antagonist can protect the retina from ischemic-like insults as occurs in glaucoma.

Endothelin-1 and endothelin receptors in light-induced retinal degeneration

We have studied the distribution of endothelinergic molecules: prepro-endothelin-1 (PPET-1), endothelin-1 (ET-1), and receptors A and B (ET-A) and (ET-B) in the retina of mice. The localization of these molecules in normal mice was compared to their localization in retinas from animals submitted to continuous illumination during 1, 6, 9 or 18 days. We also evaluated the distribution of smooth muscle actin (SMA) and glial markers, glial fibrillary acidic protein (GFAP) and glutamine synthase (GS). PPET-1 immunoreactivity mainly appeared in retinal pigment epithelium (RPE) and cells of the ganglion cell layer (GCL), whereas ET-1 immunoreactivity was present in the RPE, outer plexiform layer (OPL) and astrocytes. Astrocytes exhibited the strongest immunostaining in the retina. ET-A immunoreactivity was observed in endothelium, RPE, OPL and cells of the GCL. By contrast, ET-B immunoreactivity could be detected in endothelial cells, horizontal cells and astrocytes. Astrocytes of the optic nerve also exhibited ET-1, ET-A, and ET-B immunoreactivities. After light-induced degeneration, there was an increase of RPE immunostaining. Degeneration of photoreceptors was accompanied by disappearance of immunoreactivity in the OPL. However, ET-A immunoreactivity appeared in the amacrine sublayer of the INL. There was an enormous increase in astrocytes and its cell processes. The increase of astrocytic immunoreactivities for ET-1 and ET-B was confirmed by quantitative image analysis. Growth of astrocytic cell processes was most marked around retinal blood vessels. Our findings indicate that there are at least three endothelinergic pathways in the normal retina: (1) between the RPE and choriocapillaris, (2) at the OPL, and (3) between blood vessels, astrocytes and cells of the GCL. After light-induced degeneration of photoreceptors, endothelinergic molecules were overexpressed at the RPE and astrocytes, but mostly disappeared from the OPL.

High doses of simvastatin upregulate dopamine D1 and D2 receptor expression in the rat prefrontal cortex: possible involvement of endothelial nitric oxide synthase

This study aims to investigate whether or not long-term statin treatment causes upregulation of D1 and D2 receptor gene expression with concomitant increase in endothelial nitric oxide synthase (eNOS) expression in Sprague-Dawley rats. Serum triglyceride levels were dose dependently reduced in the simvastatin-treated rats reaching statistical significance at the highest dose (49% reduction), while pravastatin caused similar effects (52%) at the same dose. Cholesterol levels remained unchanged in both groups at all doses. Simvastatin, 10 or 30 mg kg(-1) day(-1), increased D1 and D2 receptor expressions in the prefrontal cortex. Similar upregulation was observed neither with simvastatin in the striatum nor with pravastatin in both brain regions. Simvastatin (10 mg kg(-1) day(-1)) also increased eNOS expression in the prefrontal cortex but not neuronal NOS or inducible NOS. D1 receptor activation by chloro-APB (5 microM) increased cAMP levels in synaptosomes prepared from the prefrontal cortex of control and simvastatin-treated rats by 88 and 285%, respectively. This effect was markedly attenuated by the selective D1 antagonist SCH-23390 (25 microM). D2 receptor activation by quinpirole (5 microM) had no effect on the basal cAMP levels in synaptosomes prepared from the prefrontal cortex of control and simvastatin-treated rats, while the same concentration of quinpirole completely abolished the D1 receptor-mediated increase. These results suggest that lipophilic statins can alter dopaminergic functions in the prefrontal cortex possibly via a central mechanism. The possibility of a nitric oxide mechanism involving eNOS requires further investigation.

Simvastatin reverses the downregulation of dopamine D1 and D2 receptor expression in the prefrontal cortex of 6-hydroxydopamine-induced Parkinsonian rats

Sprague-Dawley rats with unilateral lesion of the medial forebrain bundle by 6-hydroxydopamine showed marked decrease in the expression of dopamine D1 and D2 receptors in the prefrontal cortex. Simvastatin (10 mg/kg/day for 4 weeks) restored receptor expression to control levels. Given the association of dopaminergic dysfunction in the prefrontal cortex and cognitive deficits in Parkinson's disease, these findings may have implication in the treatment of cognitive decline in advanced Parkinson's disease.

Endothelins negatively regulate glial glutamate transporter expression

Glutamate is the main excitatory neurotransmitter in the mammalian central nervous system which at high extracellular levels leads to neuronal over-stimulation and subsequent excitotoxic neuronal cell death. Both the termination of glutamatergic neurotransmission and the prevention of neurotoxic extracellular glutamate concentrations are predominantly achieved by the uptake of extracellular glutamate into astroglia through the high-affinity glutamate transporters, excitatory amino acid transporter-2/glutamate transporter-1 (EAAT-2/GLT-1) and EAAT-1/glutamate aspartate transporter (GLAST). Although several injury-induced growth factors such as epidermal growth factor (EGF) and transforming growth factor alpha (TGFalpha) potently stimulate the expression of glutamate transporters in cultured astroglia, GLT-1 and/or GLAST expression temporarily decreases during acute brain injuries eventually contributing to secondary neuronal cell death. We now demonstrate that the stimulatory influences of these injury-regulated growth factors are overridden by endothelins (ETs), a family of peptides also upregulated in the injured brain. Exposure of cultured cortical astroglia to ET-1, ET-2, and ET-3 resulted in a major loss of basal glutamate transporter expression after 72 hours and the complete prevention of the known stimulatory influences of dibutyryl cyclic (dbc)AMP, pituitary adenylate cyclase-activating polypeptide (PACAP), EGF, and TGFalpha on both GLT-1 and GLAST expression. With all ET isoforms, the inhibitory effects were detectable with similar low nanomolar concentrations and persisted in endothelin B-receptor deficient astroglia, suggesting that the inhibitory action is equally induced by endothelin A and B receptors. In astroglial cultures maintained with endothelins alone or in combination with PACAP, the inhibitory action was remarkably long-lasting and was still detectable after 7 days. In apparent contrast, glutamate transporter expression partially recovered between days 5 and 7 in cultures maintained with a combination of ETs and the injury-regulated growth factors EGF or TGFalpha. These findings point to ETs as major mediators of injury-dependent down-regulation of glial glutamate transporters and subsequent glutamate-induced brain damage.

Differential expression of endothelin receptors in regenerating spinal motor neurons in mice

On day 4 after sciatic nerve crush injury, expression and localization of endothelin receptors ET(A) and ET(B) in the lumbar spinal cord were examined. Immunohistochemical staining with antibodies to ET(A) and ET(B) receptors showed cytoplasmic distribution of ET(A) receptors in motor neurons, whereas ET(B) receptors were localized in the perinuclear region. On the injured side of the lumbar spinal cord, when compared to contralateral, results demonstrated an up-regulation of ET(B) and a down-regulation of ET(A) receptors expression at the level of both mRNA and protein. These results suggest that ET(B) receptors may play a role in the regeneration of axotomized motor neurons.