2-(2-Benzofuranyl)-2-Imidazoline Attenuates the Disruption of the Blood-Brain Barrier in EAE via NMDAR

Blood-brain barrier (BBB) disruption has been recognized as an early hallmark of multiple sclerosis (MS) pathology. Our previous studies have shown that 2-(2-Benzofuranyl)-2-imidazoline (2-BFI) protected against experimental autoimmune encephalomyelitis (EAE), a classic animal model of MS. However, the potential effects of 2-BFI on BBB permeability have not yet been evaluated in the context of EAE. Herein, we aimed to investigate the effect of 2-BFI on BBB permeability in both an animal model and an in vitro BBB model using TNF-α to imitate the inflammatory damage to the BBB in MS. In the animal model, 2-BFI reduced neurological deficits and BBB permeability in EAE mice compared with saline treatment. The Western blot results indicated that 2-BFI not only alleviated the loss of the tight junction protein occludin caused by EAE but also inhibited the activation of the NR1-ERK signaling pathway. In an in vitro BBB model, 2-BFI (100 μM) alleviated the TNF-α-induced increase in permeability and reduction in expression of occludin in monolayer bEnd.3 cells. Similar protective effects were also observed after treatment with the NMDAR antagonist MK801. The Western blot results showed that the TNF-α-induced BBB breakdown and increase in NMDAR subunit 1 (NR1) levels and ERK phosphorylation could be blocked by pretreatment with 2-BFI or MK801. However, no additional effect was observed on BBB permeability or the expression of occludin and p-ERK after pretreatment with both 2-BFI and MK801. Our study indicates that 2-BFI alleviates the disruption of BBB in the context of inflammatory injury similar to that of MS by targeting NMDAR1, as well as by likely activating the subsequent ERK signaling pathway. These results provide further evidence for 2-BFI as a potential drug for the treatment of MS.

Quercetin protects against cerebral ischemia/reperfusion and oxygen glucose deprivation/reoxygenation neurotoxicity

Beyond nutrition effect, quercetin is applied as a complement or an alternative for promoting human health and treating diseases. However, its complicated neuroprotective mechanisms have not yet been fully elucidated. This study provides evidence of an alternative target for quercetin, and sheds light on the mechanisms of its neuroprotection against cerebral ischemia/reperfusion (I/R) injury in Sprague-Dawley rats. Oral pretreatment using quercetin has alleviated cerebral I/R-induced neurological deficits, brain infarction, blood-brain barrier disruption, oxidative stress, TNF-α and IL-1β mRNA expression, along with apoptotic caspase 3 activity. The neuroprotective, anti-oxidative, anti-inflammatory, and anti-apoptotic effects of quercetin were replicated in rat hippocampal slice cultures and neuron/glia cultures which suffered from oxygen-glucose deprivation and reoxygenation (OGDR). Biochemical studies revealed a reduction of extracellular signal-regulated kinase (ERK) and Akt phosphorylation, along with an increase in protein tyrosine and serine/threonine phosphatase activity in cerebral I/R rat cortical tissues and OGDR hippocampal slice and neuron/glia cultures. Quercetin alleviated the changes in ERK/Akt phosphorylation and protein phosphatase activities. Inhibition of ERK or Akt alone was enough to cause apoptotic cell death and cytotoxicity in hippocampal slice cultures and neuron/glia cultures, while activators of ERK or Akt alleviated OGDR-induced cytotoxicity. Taken together, our results demonstrate that quercetin alleviated the increment of protein tyrosine and serine/threonine phosphatase activity, along with the reduction of ERK and Akt phosphorylation, which may play pivotal roles in the expansion of brain injury after cerebral I/R.

Cyclosporine exacerbates ketamine toxicity in zebrafish: Mechanistic studies on drug-drug interaction

Cyclosporine A (CsA) is an immunosuppressive drug commonly used in organ transplant patients to prevent allograft rejections. Ketamine is a pediatric anesthetic that noncompetitively inhibits the calcium-permeable N-methyl-d-aspartic acid receptors. Adverse drug-drug interaction effects between ketamine and CsA have been reported in mammals and humans. However, the mechanism of such drug-drug interaction is unclear. We have previously reported adverse effects of combination drugs, such as verapamil/ketamine and shown the mechanism through intervention by other drugs in zebrafish embryos. Here, we show that ketamine and CsA in combination produce developmental toxicity even leading to lethality in zebrafish larvae when exposure began at 24 h post-fertilization (hpf), whereas CsA did not cause any toxicity on its own. We also demonstrate that acetyl l-carnitine (ALCAR) completely reversed the adverse effects. Both ketamine and CsA are CYP3A4 substrates. Although ketamine and CsA independently altered the expression of the hepatic marker CYP3A65, a zebrafish ortholog of human CYP3A4, both drugs together induced further increase in CYP3A65 expression. In the presence of ALCAR, however, CYP3A65 expression was normalized. ALCAR has been shown to prevent ketamine toxicity in mammal and zebrafish. In conclusion, CsA exacerbated ketamine toxicity and ALCAR reversed the effects. These results, providing evidence for the first time on the reversal of the adverse effects of CsA/ketamine interaction by ALCAR, would prove useful in addressing potential occurrences of such toxicities in humans. Published 2017. This article is a U.S. Government work and is in the public domain in the USA.

Desensitizing Mitochondrial Permeability Transition by ERK-Cyclophilin D Axis Contributes to the Neuroprotective Effect of Gallic Acid against Cerebral Ischemia/Reperfusion Injury

Ischemic stroke is a devastating disease with complex pathophysiology. Much evidence confirms that opening of the mitochondrial permeability transition pore (MPTP) is related with mitochondrial dysfunction to apoptosis in ischemic stroke, thus elucidating its signaling mechanism and screening novel MPTP inhibitor is therefore of paramount importance. Our earlier studies identified that gallic acid (GA), a naturally occurring plant phenol, endows with effect on inhibition of mitochondrial dysfunction, which has significant neuroprotective effect in cerebral ischemia/reperfusion injury. However, its molecular mechanisms regulating mitochondrial dysfunction remain elusive. Here, we uncover a role of GA in protecting mitochondria via MPTP inhibition. In addition to inhibit CypD binding to adenine nucleotide translocator, GA potentiates extracellular signal-regulated kinases (ERK) phosphorylation, leading to a decrease in cyclophilin D (CypD) expression, resulting in a desensitization to induction of MPTP, thus inhibiting caspase activation and ultimately giving rise to cellular survival. Our study firstly identifies ERK-CypD axis is one of the cornerstones of the cell death pathways following ischemic stroke, and confirms GA is a novel inhibitor of MPTP, which inhibits apoptosis depending on regulating the ERK-CypD axis.

Systemic revealing pharmacological signalling pathway networks in the hippocampus of ischaemia-reperfusion mice treated with baicalin

Background. Baicalin (BA) exhibits ill understood neuroprotective, anti-inflammatory, and antioxidative effects in brain injury. Objective. To identify the differential network pathways associated with BA-related biological effects. Methods. MCAO-induced mice received BA 5 mg/Kg (BA group). Controls received vehicle only. Following ischaemia-reperfusion, ArrayTrack analysed the whole genome microarray of hippocampal genes, and MetaCore analysed differentially expressed genes. Results. Four reversing pathways were common to BA and controls, but only 6 were in the top 10 for BA. Three of the top 5 signalling pathways in controls were not observed in BA. BA treatment made absent 3 pathways of the top 5 signalling pathways from the top 5 in controls. There were 2 reversing pathways between controls and BA that showed altered gene expression. Controls had 6 networks associated with cerebral ischaemia. After BA treatment, 9 networks were associated with cerebral ischaemia. Enrichment analysis identified 10 significant biological processes in BA and controls. Of the 10 most significant molecular functions, 7 were common to BA and controls, and only 3 occurred in BA. BA and controls had 7 significant cellular components. Conclusions. This study showed that the clinical effectiveness of BA was based on the complementary effects of multiple pathways and networks.

Ceramide from sphingomyelin hydrolysis differentially mediates mitogen-activated protein kinases (MAPKs) activation following cerebral ischemia in rat hippocampal CA1 subregion

Objective

To explore the role that ceramide plays in the activation of mitogen-activated protein kinases (MAPKs) during cerebral ischemia and reperfusion.

Methods

Rats were subjected to ischemia by the four-vessel occlusion (4-VO) method. The sphingomyelinase inhibitor TPCK was administered to the CA1 subregion of the rat hippocampus before inducing ischemia. Western blot was used to examine the activity of extracellular-signal regulated kinase (ERK) and c-Jun N-terminal protein kinase (JNK) using antibodies against ERK, JNK and diphosphorylated ERK and JNK.

Results

At 1h reperfusion post-ischemia, JNK reached its peak activity while ERK was undergoing a sharp inactivation (P < 0.05). The level of diphosphorylated JNK was significantly reduced but the sharp inactivation of ERK was visibly reversed (P < 0.05) by the sphingomyelinase inhibitor.

Conclusion

The ceramide signaling pathway is up-regulated through sphingomyelin hydrolysis in brain ischemia, promoting JNK activation and suppressing ERK activation, culminating in the ischemic lesion.

PI3K/Akt-independent negative regulation of JNK signaling by MKP-7 after cerebral ischemia in rat hippocampus

Background

The inactivation of c-Jun N-terminal kinase (JNK) is associated with anti-apoptotic and anti-inflammatory effects in cerebral ischemia, which can be induced by an imbalance between upstream phosphatases and kinases.

Result

Mitogen-activated protein kinase phosphatase 7 (MKP-7) was upregulated significantly at 4 h of reperfusion postischemia in rat hippocampi. By administration of cycloheximide or siRNA against mitogen-activated protein kinase phosphatase 7 (MKP-7) in a rat model of ischemia/reperfusion, an obvious enhancement of JNK activity was observed in 4 h of reperfusion following ischemia, suggesting MKP-7 was involved in JNK inactivation after ischemia. The subcellular localization of MKP-7 altered after ischemia, and the inhibition of MKP-7 nuclear export by Leptomycin B up-regulated JNK activity. Although PI3K/Akt inhibition could block downregulation of JNK activity through SEK1 and MKK-7 activation, PI3K/Akt activity was not associated with the regulation of JNK by MKP-7.

Conclusions

MKP-7, independently of PI3K/Akt pathway, played a key role in downregulation of JNK activity after ischemia in the rat hippocampus, and the export of MKP-7 from the nucleus was involved in downregulation of cytoplasmic JNK activity in response to ischemic stimuli.

Ras family small GTPase-mediated neuroprotective signaling in stroke

Selective neuronal cell death is one of the major causes of neuronal damage following stroke, and cerebral cells naturally mobilize diverse survival signaling pathways to protect against ischemia. Importantly, therapeutic strategies designed to improve endogenous anti-apoptotic signaling appear to hold great promise in stroke treatment. While a variety of complex mechanisms have been implicated in the pathogenesis of stroke, the overall mechanisms governing the balance between cell survival and death are not well-defined. Ras family small GTPases are activated following ischemic insults, and in turn, serve as intrinsic switches to regulate neuronal survival and regeneration. Their ability to integrate diverse intracellular signal transduction pathways makes them critical regulators and potential therapeutic targets for neuronal recovery after stroke. This article highlights the contribution of Ras family GTPases to neuroprotective signaling cascades, including mitogen-activated protein kinase (MAPK) family protein kinase- and AKT/PKB-dependent signaling pathways as well as the regulation of cAMP response element binding (CREB), Forkhead box O (FoxO) and hypoxiainducible factor 1(HIF1) transcription factors, in stroke.

Effects of estrogen on beta-amyloid-induced cholinergic cell death in the nucleus basalis magnocellularis

Alzheimer disease is characterized by accumulation of β-amyloid (Aβ) and cognitive dysfunctions linked to early loss of cholinergic neurons. As estrogen-based hormone replacement therapy has beneficial effects on cognition of demented patients, and it may prevent memory impairments, we investigated the effect of estrogen-pretreatment on Aβ-induced cholinergic neurodegeneration in the nucleus basalis magnocellularis (NBM). We tested which Aβ species induces the more pronounced cholinotoxic effect in vivo. We injected different Aβ assemblies in the NBM of mice, and measured cholinergic cell and cortical fiber loss. Spherical Aβ oligomers had the most toxic effect. Pretreatment of ovariectomized mice with estrogen before Aβ injection decreased cholinergic neuron loss and partly prevented fiber degeneration. By using proteomics, we searched for proteins involved in estrogen-mediated protection and in Aβ toxicity 24 h following injection. The change in expression of, e.g., DJ-1, NADH ubiquinone oxidoreductase, ATP synthase, phosphatidylethanolamine-binding protein 1, protein phosphatase 2A and dimethylarginine dimethylaminohydrolase 1 support our hypothesis that Aβ induces mitochondrial dysfunction, decreases MAPK signaling, and increases NOS activation in NBM. On the other hand, altered expression of, e.g., MAP kinase kinase 1 and 2, protein phosphatase 1 and 2A by Aβ might increase MAPK suppression and NOS signaling in the cortical target area. Estrogen pretreatment reversed most of the changes in the proteome in both areas. Our experiments suggest that regulation of the MAPK pathway, mitochondrial pH and NO production may all contribute to Aβ toxicity, and their regulation can be prevented partly by estrogen pretreatment.

Blockage of ceramide metabolism exacerbates palmitate inhibition of pro-insulin gene expression in pancreatic beta-cells

Chronic exposure to elevated levels of fatty acids (FAs) in conjunction with chronic hyperglycemia has been reported to contribute to the progressive deterioration of beta-cell function in patients with type 2 diabetes mellitus. The long-chain saturated free fatty acid (FFA) palmitate, unlike the unsaturated FFA oleate, is known to have an inhibitory effect on proinsulin gene expression through ceramide synthesis. This study was aimed at investigating whether this effect was exacerbated by the inhibition of ceramide degradation in pancreatic beta-cells and the molecular mechanism of intracellular ceramide-induced inhibition of proinsulin gene transcription in response to exposure to palmitate. We exposed insulin-secreting (INS-1) cells treated with low levels of palmitate to the ceramidase inhibitor n-oleoylethanolamine (NOE); this led to the generation of high levels of intracellular ceramide. We observed that the effects of ceramide accumulation in INS-1 cells were similar to the effects of the inhibition of this protein on proinsulin mRNA levels that are caused by the negative regulation of insulin promoter activity. In addition, we observed that ceramide accumulation induced by NOE leads to a significant decrease in the levels of activated extracellular signal-regulated kinase (ERK); the inactivation of the ERK cascade in response to palmitate stimuli is induced by protein phosphatase 2A (PP2A) activity. Based on these findings, we suggest that the aberrant accumulation of ceramide was caused by the inhibition of ceramide metabolism, which in turn leads to the inhibition of proinsulin gene expression; the inhibition of ERK cascades by PP2A serves as an important factor in the inhibitory effects of ceramide.

Src kinase up-regulates the ERK cascade through inactivation of protein phosphatase 2A following cerebral ischemia

BACKGROUND

The regulation of protein phosphorylation requires a balance in the activity of protein kinases and protein phosphatases. Our previous data indicates that Src can increase ERK activity through Raf kinase in response to ischemic stimuli. This study examined the molecular mechanisms by which Src activates ERK cascade through protein phosphatases following cerebral ischemia.

RESULTS

Ischemia-induced Src activation is followed by phosphorylation of PP2A at Tyr307 leading to its inhibition in the rat hippocampus. SU6656, a Src inhibitor, up-regulates PP2A activity, resulting in a significant decreased activity in ERK and its targets, CREB and ERalpha. In addition, the PP2A inhibitor, cantharidin, led to an up-regulation of ERK activity and was able to counteract Src inhibition during ischemia.

CONCLUSION

Src induces up-regulation of ERK activity and its target transcription factors, CREB and ERalpha, through attenuation of PP2A activity. Therefore, activation of ERK is the result of a crosstalk between two pathways, Raf-dependent positive regulators and PP2A-dependent negative regulators.

Tissue transglutaminase regulates matrix metalloproteinase-2 in ovarian cancer by modulating cAMP-response element-binding protein activity

Tissue transglutaminase 2 (TG2) is overexpressed in epithelial ovarian cancer (EOC) and promotes intraperitoneal metastasis. How TG2 facilitates the spread of EOC is unknown. Here, we show that TG2 regulates the expression and function of matrix metalloproteinase-2 (MMP-2), a critical mediator of tissue invasiveness. TG2 knockdown down-regulates MMP-2 protein and mRNA expression in SKOV3, IGROV-1, MDA-MB-436, and PC-3 cancer cells. TG2 knockdown or inhibition of TG2 activity using KCC009 decreases MMP-2 gelatinase activity in cancer cells. MMP-2 expression and function are regulated by TG2 at transcriptional level, as demonstrated by quantitative PCR and reporter assays. We used bioinformatics and chromatin immunoprecipitation to identify a CREB binding site in the MMP-2 promoter. Binding of CREB to the MMP-2 promoter was diminished in cells that expressed decreased TG2 levels. TG2 knockdown decreased CREB phosphorylation, and CREB knockdown decreased MMP-2 expression. The effect of TG2 on CREB activity and MMP-2 transcription is mediated by TG2-dependent degradation of protein phosphatase 2 (PP2A-alpha). We show that PP2A-alpha complexes with and is targeted for degradation by TG2. In addition to their related in vitro expression levels, TG2 and MMP-2 expression were significantly correlated in vivo, as shown by concordant immunostaining in peritoneal xenografts and in human ovarian tumors. The capacity of TG2 to regulate MMP-2 expression in vitro and in vivo identifies a mechanism that may facilitate tissue invasion and the spread of EOC. The demonstration that TG2 induced degradation of PP2A-alpha activates CREB, and thereby increases MMP-2 transcription, provides novel mechanistic insight into the pro- metastatic function of TG2.