Examination of DNA-binding activity of neuronal transcription factors by electrophoretical mobility shift assay

Na(+)-K (+)-2Cl (-) cotransport inhibitor attenuates cerebral edema following experimental stroke via the perivascular pool of aquaporin-4

INTRODUCTION

The Na(+)-K(+)-2Cl(-) cotransporter localized in the brain vascular endothelium has been shown to be important in the evolution of cerebral edema following experimental stroke. Previous in vivo studies have demonstrated that bumetanide, a selective Na(+)-K(+)-2Cl(-) cotransport inhibitor, attenuates ischemia-evoked cerebral edema. Recently, bumetanide has been shown to also inhibit water permeability via aquaporin-4 (AQP4) expressed in Xenopus laevis oocytes. We tested the hypothesis that the perivascular pool of AQP4 plays a significant role in the anti-edema effect of bumetanide by utilizing wild-type (WT) mice as well as mice with targeted disruption of alpha-syntrophin (alpha-Syn(-/-)) that lack the perivascular pool of AQP4.

METHODS

Isoflurane-anesthetized adult male WT C57Bl6 and alpha-Syn(-/-) mice were subjected to 90 min middle cerebral artery occlusion (MCAO) followed by 24 or 48 h of reperfusion. Adequacy of MCAO and reperfusion was monitored with laser-Doppler flowmetry over the ipsilateral parietal cortex. Infarct volume (tetrazolium staining), cerebral edema (wet-to-dry ratios), and AQP4 protein expression (immunoblotting) were determined in different treatment groups in separate sets of experiments.

RESULTS

Bumetanide significantly attenuated infarct volume and decreased ipsilateral hemispheric water content in WT mice compared to vehicle treatment. In alpha-Syn(-/-) mice, bumetanide treatment had no effect on infarct volume or ischemia-evoked cerebral edema. Bumetanide-treated WT mice had a significant attenuation of AQP4 protein expression at 48 h post-MCAO compared to vehicle-treated WT mice.

CONCLUSIONS

These data suggest that bumetanide exerts its neuroprotective and anti-edema effects partly via blockade of the perivascular pool of AQP4 and may have therapeutic potential for ischemic stroke in the clinical setting.

Colitis affects the smooth muscle and neural response to motilin in the rabbit antrum

BACKGROUND AND PURPOSE

The underlying mechanisms of gastric dysfunction during or after an episode of intestinal inflammation are poorly understood. This study investigated the effects of colitis on the contractile effects of motilin, an important endocrine regulator of gastric motility, in the antrum.

EXPERIMENTAL APPROACH

Myeloperoxidase (MPO) activity, NF-kappaB activity and motilin receptor density were determined in the antrum of rabbits 5 days after the induction of 2,4,6-trinitrobenzenesulphonic acid colitis. Smooth muscle and neural responses to motilin were studied in antral smooth muscle strips in vitro.

KEY RESULTS

Colitis did not affect MPO activity, but increased NF-kappaB activity in the antrum. Motilin receptor density in the antrum was not affected. Under control conditions, motilin induced a slowly developing tonic smooth muscle contraction. Five days post-inflammation, tonic contractions to motilin were reduced and preceded by a rapid initial contraction. Other kinases were recruited for the phosphorylation of myosin light chain (MLC) (a multi-functional MLC kinase), and for the inhibition of MLC phosphatase (Rho kinase in addition to protein kinase C) to mediate the motilin-induced contractions during inflammation. Colitis potentiated the cholinergic neural on-contractions in the antrum. This was associated with a hyper-reactivity to motilin and an increased muscle response to ACh.

CONCLUSIONS AND IMPLICATIONS

Colitis altered the course of the motilin-induced smooth muscle contraction in the antrum. This involved changes in the kinases phosphorylating MLC. Increased cholinergic excitability to motilin in the antrum may play a role in the pathogenesis of inflammation-associated gastric motility disorders.

Lack of sex-linked differences in cerebral edema and aquaporin-4 expression after experimental stroke

Aquaporin-4 (AQP4) has been shown to be important in the evolution of stroke-associated cerebral edema. However, the role of AQP4 in stroke-associated cerebral edema as it pertains to sex has not been previously studied. The perivascular pool of AQP4 is important in the influx and efflux of water during focal cerebral ischemia. We used mice with targeted disruption of the gene encoding alpha-syntrophin (alpha-Syn(-/-)) that lack the perivascular AQP4 pool but retain the endothelial pool of this protein. Infarct volume at 72 h after transient focal ischemia (90 mins) in isoflurane-anesthetized mice was attenuated in both sexes with alpha-Syn deletion as compared with their wild-type (WT) counterparts. There were no sex differences in hemispheric water content in WT and alpha-Syn(-/-) mice or regional AQP4 expression in WT mice. In neither sex did alpha-Syn deletion lead to alterations in end-ischemic regional cerebral blood flow (rCBF). These data suggest that after experimental stroke: (1) there is no difference in stroke-associated cerebral edema based on sex, (2) AQP4 does not involve in sex-based differences in stroke volume, and (3) perivascular pool of AQP4 has no significant role in end-ischemic rCBF.

A Key role for cyclic AMP-responsive element binding protein in hypoxia-mediated activation of the angiogenesis factor CCN1 (CYR61) in Tumor cells

Hypoxia is a prominent feature of solid tumors known to contribute to malignant progression and therapeutic resistance. Cancer cells adapt to hypoxia using various pathways, allowing tumors to thrive in a low oxygen state. Induction of new blood vessel formation via the secretion of proangiogenic factors is one of the main adaptive responses engaged by tumor cells under hypoxic conditions. Hypoxia-inducible factor 1 (HIF-1) is a transcription factor that plays a pivotal role in mediating such responses. In addition, several other transcription factors have also been implicated in hypoxic gene regulation, either independently or in cooperation with HIF-1. In this work, we show that the expression of the angiogenesis-related, immediate early gene CCN1 (formerly known as CYR61), considered to be involved in tumor growth and invasiveness, is enhanced upon hypoxia stress primarily in a protein kinase A and cyclic AMP-responsive element binding protein (CREB) and CRE-dependent manner in various cell lines. The hypoxia-mediated activation of the CCN1 promoter is independent of HIF-1 and HIF-2, as shown by small interfering RNA knockdown. We identify the cis element in the mouse CCN1 promoter responsible for CREB binding to be one of two partial CRE sites present in the promoter. Moreover, we report for the first time that CREB-mediated CCN1 transcription is enhanced in hypoxic regions of tumors in vivo. Identifying and characterizing the molecular mechanisms that govern the response of tumors to hypoxia may be instrumental to identify the tumors that will respond favorably to inhibition of angiogenesis and thus lead to the development of treatments that could complement hypoxia-inducing treatment modalities.

Gender-specific response to isoflurane preconditioning in focal cerebral ischemia

Inhalation anesthetics are effective chemical preconditioning agents in experimental cerebral ischemia. However, previous work has been performed exclusively in male animals. We determined if there is a gender difference in ischemic outcome after isoflurane preconditioning (IsoPC), and if this sex-specific response is linked to differences in Akt phosphorylation or expression of neuronal inducible cell-death putative kinase (NIPK), a negative modulator of Akt activation. Young and middle-aged male and female mice were preconditioned for 4 h with air (sham PC) or 1.0% IsoPC and recovered for 24 h. Cortices were subdissected from preconditioned young male and female mice for measurement of Akt phosphorylation (Western blot) and NIPK mRNA (quantitative polymerase chain reaction). Additional cohorts underwent 2 h of reversible middle cerebral artery occlusion. Lastly, male and female Akt1(+/+) and Akt1(-/-) mice were studied to determine if gender differences in ischemic outcome after IsoPC is Akt1-dependent. Infarction volume was determined at 22 h reperfusion (2,3,5-triphenyltetrazolium chloride). As expected, IsoPC decreased ischemic damage as compared with sham PC in young and middle-aged male mice. In contrast, IsoPC markedly increased infarction in young female mice and had no effect in middle-aged female mice. Cortical phospho-Akt was increased by IsoPC versus sham PC only in male mice. No increase was observed in IsoPC female mice. NIPK mRNA was higher in female mice than in male mice regardless of preconditioning status. Male IsoPC neuroprotection was lost in Akt1-deficient male mice. We conclude that IsoPC is beneficial only in ischemic male brain and that sex differences in IsoPC are mediated through Akt activation and basal NIPK expression.

Role of cocaine- and amphetamine-regulated transcript in estradiol-mediated neuroprotection

Estrogen reduces brain injury after experimental cerebral ischemia in part through a genomic mechanism of action. Using DNA microarrays, we analyzed the genomic response of the brain to estradiol, and we identified a transcript, cocaine- and amphetamine-regulated transcript (CART), that is highly induced in the cerebral cortex by estradiol under ischemic conditions. Using in vitro and in vivo models of neural injury, we confirmed and characterized CART mRNA and protein up-regulation by estradiol in surviving neurons, and we demonstrated that i.v. administration of a rat CART peptide is protective against ischemic brain injury in vivo. We further demonstrated binding of cAMP response element (CRE)-binding protein to a CART promoter CRE site in ischemic brain and rapid activation by CART of ERK in primary cultured cortical neurons. The findings suggest that CART is an important player in estrogen-mediated neuroprotection and a potential therapeutic agent for stroke and other neurodegenerative diseases.

The effects of dexamethasone on rat brain cortical nuclear factor kappa B (NF-kappaB) in endotoxic shock

To explore the molecular mechanism of brain tissue injury induced by lipopolysaccharide (LPS), we studied the effects of endotoxic shock on rat brain cortex NF-kappaB and the effects of dexamethasone on these changes. Rats were randomly divided into LPS, LPS + dexamethasone, and control groups. The DNA-binding activity of NF-kappaB was observed using electrophoretic mobility shift assay (EMSA). Protein expression in nuclear extracts was studied using Western blots, and nuclear translocation was observed using immunohistochemistry. These indices were assayed at 1 h and 4 h after intravenous injection of LPS (4 mg x kg(-1)). EMSA showed significantly increased NF-kappaB DNA-binding activity in nuclear extracts from the LPS group at both 1 h and 4 h after LPS injection, compared with the control group (P < 0.01). For the LPS group, the NF-kappaB DNA-binding activity was greater at 1 h than at 4 h (P < 0.05). The expression of p65 and p50 protein in the nuclear extracts was also increased, as compared with the control group. However, the expression of p65 and p50 protein from cytosolic extracts did not show any significant change. Dexamethasone down-regulated not only NF-kappaB DNA-binding activity but also the expression of p65 protein in the nuclear extracts. From these data, we have concluded that NF-kappaB activation and nuclear translocation of NF-kappaB play a key role in the molecular mechanism of brain tissue injury in endotoxic shock. Dexamethasone may alleviate brain injury by inhibiting NF-kappaB activation.

Caffeic acid phenethyl ester (CAPE) prevents inflammatory stress in organotypic hippocampal slice cultures

Caffeic acid phenethyl ester (CAPE) is an antioxidant component of propolis, a natural product secreted by honeybee. Recent literature shows that CAPE inhibits nuclear factor kappa B (NFkappaB) activation in cell lines. Since NFkappaB was shown to be a crucial factor in neuroinflammation and to be associated with some neuropathologies, CAPE might reduce these disorders in brain too and have therapeutic applications. To test this hypothesis we used a model of endotoxic insult (interferon-gamma, followed by lipopolysaccharide) on rat organotypic hippocampal cultures. Cerebral inflammatory responses were strongly inhibited by CAPE (100 microM): reductions of NFkappaB nuclear activity, tumor necrosis factor alpha and nitric oxide productions were observed. At the dose of maximal effects (100 microM), an increase of cAMP-responsive element binding protein (CREB) activity, which anti-inflammatory role is well known, was seen. We compared CAPE effects with those of other drugs: anti-inflammatory as acetyl-salicylate and dexamethasone (glucocorticoid), antioxidant as pyrrolidine dithiocarbamate, or selective permeant inhibitor of NFkappaB as SN 50 peptide. These studies lead us to conclude that CAPE presents an interesting and original neuropharmacological profile compared to these drugs and might be helpful in the prevention of neurotoxic events due to excessive inflammatory reaction in brain. CAPE interferes with several effectors of neuroinflammation that might have complementary and synergic effects and allows a rather durable control since an acute treatment at the time of endotoxin exposure allows to control inflammatory factors for over 48 h.

Characterization and identification of promoter elements in the mouse COX17 gene

Cox17p, essential for the assembly of functional cytochrome c oxidase (CCO) in Saccharomyces cerevisiae, has been believed to deliver copper ions to the mitochondrion for insertion into the enzyme. We have recently isolated an approximately 20 kb genomic fragment of the mouse COX17. Reporter assay experiments have shown that most of the promoter activity was restricted to a 0.85 kb fragment flanking the first exon. Further intensive deletion and detailed mutation analysis suggested that the minimal essential region for transactivation was located at bases -155 to -70. This 5'-flanking region did not possess a TATA box, but contained putative Sp1, NRF-1 and NRF-2 binding sites. COX17 basal promoter activity was abrogated by site-directed mutagenesis of Sp1, NRF-1 and NRF-2 binding sites. Electrophoretic mobility shift assays with AtT-20 and NIH3T3 cell nuclear extract revealed that this region binds both a Sp1-like protein and NRF-1 transcription factors. These results indicated that Sp1, NRF-1 and NRF-2 are involved in basal transcription of the COX17 gene, similar to the transcription mechanism of other CCO-related genes.

Peptidyl alpha-keto amide inhibitor of calpain blocks excitotoxic damage without affecting signal transduction events

The cysteine protease calpain is activated by calcium and has a wide range of substrates. Calpain-mediated cellular damage is associated with many neuropathologies, and calpain also plays a role in signal transduction events that are essential for cell maintenance, including the activation of important kinases and transcription factors. In the present study, the hippocampal slice culture was used as a model of excitotoxicity to test whether the neuroprotection elicited by selective calpain inhibition is associated with changes in cell signaling. Peptidyl alpha-keto amide and alpha-keto acid inhibitors reduced both calpain-mediated cytoskeletal damage and the concomitant synaptic deterioration resulting from an N-methyl-D-aspartate exposure. The alpha-keto amide CX295 was protective when infused into slice cultures before or after the excitotoxic episode. The slices protected with CX295 exhibited normal activation levels of mitogen-activated protein kinase and the transcription factor nuclear factor-kappaB. Thus, selective inhibition of calpain provides neuroprotection without influencing critical signaling pathways.

Alterations of AP-1 and CREB protein DNA binding in rat supraoptic and paraventricular nuclei by acute and repeated hyperosmotic stress

Electrophoretic mobility shift assays were used to analyze Fos and CREB protein-DNA-interactions in the rat hypothalamic paraventricular (PVN) and supraoptic (SON) nuclei. After intraperitoneal administration of normal saline, PVN (but not SON) extracts exhibited a significant 183% increase in binding to the activational protein-1 (AP-1) canonical DNA binding sequence. Hypertonic saline treatment resulted in a approximately 2.5-fold increase in binding by tissue samples from both regions. AP-1 binding by SON extracts after two hypertonic saline injections caused a 307% increase in binding that was significantly greater than binding by PVN extracts (207%). Fos binding was equal in the SON after one and two hypertonic saline injections, but the PVN exhibited less of an increase after two injections. Binding to the canonical cyclic adenosine monophosphate regulatory element (CRE), and phosphorylated CREB (pCREB) supershift binding, indicated pCREB is constitutively expressed. Any experimental treatment (handling and an injection) caused an elevation in binding in the PVN. AP-1 protein complex DNA binding was increased after osmotic stimulation, and SON and PVN exhibit differences in AP-1 DNA binding kinetics, after repeated hypertonic saline stress. Changes in PVN tissue samples were subtle, and may reflect the fact that magnocellular and parvocellular neurons mediate, respectively, fluid homeostasis and stress responses.

Electrophoretic mobility shift assay for the detection of specific DNA-protein complex in nuclear extracts from the cultured cells and frozen autopsy human brain tissue

The electrophoretic mobility shift assay (EMSA) is generally used to study the interaction of transcription factors to specific DNA sequences. The preparation of high quality nuclear extracts is an important step before performing the assay. Here we describe a rapid method for the isolation of good-quality DNA-binding proteins from cultured cell lines and autopsy tissue samples from the human brain. The 'rapid method' (RM) utilizes the low salt/detergent lysis steps followed by high salt extraction of nuclei. To test and compare the activity of nuclear extracts prepared by the standard and 'rapid' methods for its ability to form the specific DNA-protein complex, EMSA was carried out with three different oligonucleotide probes: AP1, NF-kappaB and URE. A comparative study indicates that the capacity to form the specific DNA-protein complex with these oligonucleotide probes by standard and RM nuclear extracts was very similar. Each nuclear extract formed the corresponding DNA-protein complex, the specificity of which was checked by the competition experiment. In some cases unspecific bands were observed and which were present in nuclear extracts from both preparations. Thus the simplicity of the 'rapid method' permits the preparation of nuclear extracts from several cell lines and tissue samples at the same time at much shorter time than the 'standard' method without compromising the DNA-binding activity. The RM can be applied to determine the cell type or tissue specificity of transcription factors in an efficient, economical and consistent manner.