Suppression subtraction hybridization and northern analysis reveal upregulation of heat shock, trkB, and sodium calcium exchanger genes following global cerebral ischemia in the rat

Molecular Mechanisms of Neuroprotection after the Intermittent Exposures of Hypercapnic Hypoxia

The review introduces the stages of formation and experimental confirmation of the hypothesis regarding the mutual potentiation of neuroprotective effects of hypoxia and hypercapnia during their combined influence (hypercapnic hypoxia). The main focus is on the mechanisms and signaling pathways involved in the formation of ischemic tolerance in the brain during intermittent hypercapnic hypoxia. Importantly, the combined effect of hypoxia and hypercapnia exerts a more pronounced neuroprotective effect compared to their separate application. Some signaling systems are associated with the predominance of the hypoxic stimulus (HIF-1α, A1 receptors), while others (NF-κB, antioxidant activity, inhibition of apoptosis, maintenance of selective blood-brain barrier permeability) are mainly modulated by hypercapnia. Most of the molecular and cellular mechanisms involved in the formation of brain tolerance to ischemia are due to the contribution of both excess carbon dioxide and oxygen deficiency (ATP-dependent potassium channels, chaperones, endoplasmic reticulum stress, mitochondrial metabolism reprogramming). Overall, experimental studies indicate the dominance of hypercapnia in the neuroprotective effect of its combined action with hypoxia. Recent clinical studies have demonstrated the effectiveness of hypercapnic-hypoxic training in the treatment of childhood cerebral palsy and diabetic polyneuropathy in children. Combining hypercapnic hypoxia with pharmacological modulators of neuro/cardio/cytoprotection signaling pathways is likely to be promising for translating experimental research into clinical medicine.

Long-term artificial sweetener acesulfame potassium treatment alters neurometabolic functions in C57BL/6J mice

With the prevalence of obesity, artificial, non-nutritive sweeteners have been widely used as dietary supplements that provide sweet taste without excessive caloric load. In order to better understand the overall actions of artificial sweeteners, especially when they are chronically used, we investigated the peripheral and central nervous system effects of protracted exposure to a widely used artificial sweetener, acesulfame K (ACK). We found that extended ACK exposure (40 weeks) in normal C57BL/6J mice demonstrated a moderate and limited influence on metabolic homeostasis, including altering fasting insulin and leptin levels, pancreatic islet size and lipid levels, without affecting insulin sensitivity and bodyweight. Interestingly, impaired cognitive memory functions (evaluated by Morris Water Maze and Novel Objective Preference tests) were found in ACK-treated C57BL/6J mice, while no differences in motor function and anxiety levels were detected. The generation of an ACK-induced neurological phenotype was associated with metabolic dysregulation (glycolysis inhibition and functional ATP depletion) and neurosynaptic abnormalities (dysregulation of TrkB-mediated BDNF and Akt/Erk-mediated cell growth/survival pathway) in hippocampal neurons. Our data suggest that chronic use of ACK could affect cognitive functions, potentially via altering neuro-metabolic functions in male C57BL/6J mice.

Neuroprotective action of lithium in disorders of the central nervous system

Substantial in vitro and in vivo evidence of neurotrophic and neuroprotective effects of lithium suggests that it may also have considerable potential for the treatment of neurodegenerative conditions. Lithium's main mechanisms of action appear to stem from its ability to inhibit glycogen synthase kinase-3 activity and also to induce signaling mediated by brain-derived neurotrophic factor. This in turn alters a wide variety of downstream effectors, with the ultimate effect of enhancing pathways to cell survival. In addition, lithium contributes to calcium homeostasis. By inhibiting N-methyl-D-aspartate receptor-mediated calcium influx, for instance, it suppresses the calcium-dependent activation of pro-apoptotic signaling pathways. By inhibiting the activity of phosphoinositol phosphatases, it decreases levels of inositol 1,4,5-trisphosphate, a process recently identified as a novel mechanism for inducing autophagy. These mechanisms allow therapeutic doses of lithium to protect neuronal cells from diverse insults that would otherwise lead to massive cell death. Lithium, moreover, has been shown to improve behavioral and cognitive deficits in animal models of neurodegenerative diseases, including stroke, amyotrophic lateral sclerosis, fragile X syndrome, and Huntington's, Alzheimer's, and Parkinson's diseases. Since lithium is already FDA-approved for the treatment of bipolar disorder, our conclusions support the notion that its clinical relevance can be expanded to include the treatment of several neurological and neurodegenerative-related diseases.

Molecular actions and therapeutic potential of lithium in preclinical and clinical studies of CNS disorders

Lithium has been used clinically to treat bipolar disorder for over half a century, and remains a fundamental pharmacological therapy for patients with this illness. Although lithium's therapeutic mechanisms are not fully understood, substantial in vitro and in vivo evidence suggests that it has neuroprotective/neurotrophic properties against various insults, and considerable clinical potential for the treatment of several neurodegenerative conditions. Evidence from pharmacological and gene manipulation studies support the notion that glycogen synthase kinase-3 inhibition and induction of brain-derived neurotrophic factor-mediated signaling are lithium's main mechanisms of action, leading to enhanced cell survival pathways and alteration of a wide variety of downstream effectors. By inhibiting N-methyl-D-aspartate receptor-mediated calcium influx, lithium also contributes to calcium homeostasis and suppresses calcium-dependent activation of pro-apoptotic signaling pathways. In addition, lithium decreases inositol 1,4,5-trisphosphate by inhibiting phosphoinositol phosphatases, a process recently identified as a novel mechanism for inducing autophagy. Through these mechanisms, therapeutic doses of lithium have been demonstrated to defend neuronal cells against diverse forms of death insults and to improve behavioral as well as cognitive deficits in various animal models of neurodegenerative diseases, including stroke, amyotrophic lateral sclerosis, fragile X syndrome, as well as Huntington's, Alzheimer's, and Parkinson's diseases, among others. Several clinical trials are also underway to assess the therapeutic effects of lithium for treating these disorders. This article reviews the most recent findings regarding the potential targets involved in lithium's neuroprotective effects, and the implication of these findings for the treatment of a variety of diseases.

Semax and Pro-Gly-Pro activate the transcription of neurotrophins and their receptor genes after cerebral ischemia

Consisting of a fragment of ACTH(4-7) and C-terminal PGP tripeptide, the polypeptide Semax is successfully used for acute stroke therapy. Previous experiments showed rapid induction of Bdnf, Ngf, and TrkB expression in intact rat hippocampus following Semax treatment. To investigate the mRNA expression of neurotrophins and their receptors after treatment with either Semax or PGP, the rat brains were analyzed at three time points following a permanent middle cerebral artery occlusion (pMCAO). We have shown for the first time that both Semax and PGP activate the transcription of neurotrophins and their receptors in the cortex of rats subjected to pMCAO. The profiles of transcription alteration under PGP and Semax treatment were partially overlapped. Semax enhanced the transcription of Bdnf, TrkC, and TrkA 3 h after occlusion, Nt-3 and Ngf 24 h after occlusion, and Ngf 72 h after occlusion. PGP enhanced the transcription of Bdnf and TrkC 3 h after pMCAO and Ngf, TrkB, TrkC, and TrkA 24 h after pMCAO. The analysis of the transcription alterations under PGP and Semax treatment in the cortex of rats without surgery, sham-operated rats and rats subjected to pMCAO revealed that Semax selectively affected the transcription of neurotrophins and their receptors in the ischemic rat cortex, whereas the influence of PGP was mainly unspecific.

Synergistic effects of prostaglandin E1 and lithium in a rat model of cerebral ischemia

AIM

Heat shock proteins (HSPs) are important regulators of cellular survival and exert neuroprotective effects against cerebral ischemia. Both prostaglandin E1 (PGE1) and lithium have been reported to protect neurons against ischemic injury. The present study was undertaken to examine if lithium could potentiate the neuroprotection of PGE1 against cerebral ischemia, and if the synergetic effects take place at the level of HSPs.

METHODS

Brain ischemia was induced by a permanent middle cerebral artery occlusion (pMCAO) in rats. Rats were pretreated with subcutaneous injection of lithium for 2 d and a single intravenous administration of PGE1 immediately after ischemic insult. Cerebrocortical blood flow of each group was closely monitored prior to onset of ischemia, 5 min, 15 min, 30 min and 60 min after surgical operation. Body temperature was measured before, 5 min, 2 h and 24 h after the onset of pMCAO. The infarct volume, brain edema and motor behavior deficits were analyzed 24 h after ischemic insult. Cytoprotective HSP70 and heme oxygenase-1 (HO-1) in the striatum of the ipsilateral hemisphere were detected by immunoblotting. Brain sections from the striatum of the ipsilateral hemisphere were double-labeled with the anti-HSP70 antibody and 4,6-diamidino-2-phenylindole (DAPI).

RESULTS

Treatment with PGE1 (8 and 16 microg/kg, iv) or lithium (0.5 mEq/kg, sc) alone reduced infarct volume, neurological deficits and brain edema induced by focal cerebral ischemia in rats. Moreover, a greater neuroprotection was observed when PGE1 and lithium were given together. Co-administration of PGE1 and lithium significantly upregulated cytoprotective HSP70 and HO-1 protein levels.

CONCLUSION

Lithium and PGE1 may exert synergistic effects in treatment of cerebral ischemia and thus may have potential clinical value for the treatment of stroke.

Molecular physiology of preconditioning-induced brain tolerance to ischemia

Ischemic tolerance describes the adaptive biological response of cells and organs that is initiated by preconditioning (i.e., exposure to stressor of mild severity) and the associated period during which their resistance to ischemia is markedly increased. This topic is attracting much attention because preconditioning-induced ischemic tolerance is an effective experimental probe to understand how the brain protects itself. This review is focused on the molecular and related functional changes that are associated with, and may contribute to, brain ischemic tolerance. When the tolerant brain is subjected to ischemia, the resulting insult severity (i.e., residual blood flow, disruption of cellular transmembrane gradients) appears to be the same as in the naive brain, but the ensuing lesion is substantially reduced. This suggests that the adaptive changes in the tolerant brain may be primarily directed against postischemic and delayed processes that contribute to ischemic damage, but adaptive changes that are beneficial during the subsequent test insult cannot be ruled out. It has become clear that multiple effectors contribute to ischemic tolerance, including: 1) activation of fundamental cellular defense mechanisms such as antioxidant systems, heat shock proteins, and cell death/survival determinants; 2) responses at tissue level, especially reduced inflammatory responsiveness; and 3) a shift of the neuronal excitatory/inhibitory balance toward inhibition. Accordingly, an improved knowledge of preconditioning/ischemic tolerance should help us to identify neuroprotective strategies that are similar in nature to combination therapy, hence potentially capable of suppressing the multiple, parallel pathophysiological events that cause ischemic brain damage.

Na+/Ca2+ exchanger subtype (NCX1, NCX2, NCX3) protein expression in the rat hippocampus following 3 min and 8 min durations of global cerebral ischemia

There is increasing evidence that the sodium-calcium exchanger (NCX) subtypes, NCX1, NCX2 and NCX3 play an important role in intracellular calcium homeostasis/dysregulation following cerebral ischemia. In the present study we examined NCX1, NCX2 and NCX3 protein levels in the rat hippocampus at 3, 6, 12, 18, 24 and 48 h following a 3 min and 8 min duration of global cerebral ischemia. We observed that NCX1 protein levels were significantly increased by 22.3% and 20.6% at the 6 and 12 h respective time points following a 3 min duration of global ischemia, while NCX2 and NCX3 protein levels remained relatively constant. Following a 8 min duration of global ischemia, NCX1 protein levels remained relatively constant, while NCX2 protein levels were down-regulated by 6.9%, 10.8%, 14.4% and 10.3% at the 6, 18, 24 and 48 h respective time points, and NCX3 protein levels were up-regulated by 22.1% at the 18 h time point. Taken together, our results show that NCX subtype protein expression is sensitive to cerebral ischemia, and indicates that changes in NCX activity may be playing an important role in calcium maintenance and neuronal outcome following ischemia.

Greater stress protein expression enhanced by combined prostaglandin A1 and lithium in a rat model of focal ischemia

AIM

To investigate the effects of lithium (Li) and prostaglandin A1 (PGA1) on the expression of heat shock factor 1 (HSF-1), heat shock proteins (HSP), and apoptosis protease activating factor-1 (Apaf-1) induced by permanent focal ischemia in rats.

METHODS

The rats were pretreated with a subcutaneous (sc) injection of Li for 2 d or a single intracerebral ventricle (icv) administration of PGA1 for 15 min before ischemic insult, or a combination of Li (sc, 1 mEq/kg, 2 d) and PGA1 (icv, 15 min prior to ischemic insult). Brain ischemia was induced by the permanent middle cerebral artery occlusion (pMCAO). Twenty-four hours after the occlusion, the expression of HSF-1, HSP, and Apaf-1 in the ischemic striatum were examined with Western blot analysis.

RESULTS

The expression of HSF-1, heme oxygenase-1 (HO-1), HSP90alpha, and Apaf-1 were significantly increased, but the expression of HSP90beta was significantly decreased 24 h after the pMCAO. PGA1 and Li and their combination significantly enhanced the ischemia-induced elevation in the levels of HSF-1, HO-1, and HSP90alpha, and recovered HSP90beta expression, but decreased Apaf-1 levels in the ischemic striatum.

CONCLUSION

The present study demonstrates that PGA1 and Li have synergistic effects on the enhancement of the expression of HSP, suggesting that the synergistic effects of PGA1 and Li in the rat model of permanent focal cerebral ischemia may be mediated by the enhancement expression of HSP expression and the downregulation of Apaf-1. Our studies suggest that combined PGA1 and Li may have potential clinical value for the treatment of stroke.

Evidence that intracellular cyclophilin A and cyclophilin A/CD147 receptor-mediated ERK1/2 signalling can protect neurons against in vitro oxidative and ischemic injury

We previously reported that cyclophilin A protein is up-regulated in cortical neuronal cultures following several preconditioning treatments. In the present study, we have demonstrated that adenoviral-mediated over-expression of cyclophilin A in rat cortical neuronal cultures can protect neurons from oxidative stress (induced by cumene hydroperoxide) and in vitro ischemia (induced by oxygen glucose deprivation). We subsequently demonstrated that cultured neurons, but not astrocytes, express the recently identified putative cyclophilin A receptor, CD147 (also called neurothelin, basigin and EMMPRIN), and that administration of purified cyclophilin A protein to neuronal cultures induces a rapid but transient phosphorylation of the extracellular signal-regulated kinase (ERK) 1/2. Furthermore, administration of purified cyclophilin A protein to neuronal cultures protects neurons from oxidative stress and in vitro ischemia. Interestingly, we detected up-regulation of cyclophilin A mRNA, but not protein in the hippocampus following a 3-min period of sublethal global cerebral ischemia in the rat. Despite our in vivo findings, our in vitro data show that cyclophilin A has both intracellular- and extracellular-mediated neuroprotective mechanisms. To this end, we propose cyclophilin A's extracellular-mediated neuroprotection occurs via CD147 receptor signalling, possibly by activation of ERK1/2 pro-survival pathways. Further characterization of cyclophilin A's neuroprotective mechanisms may aid the development of a neuroprotective therapy.

Selective alteration of expression of Na+/Ca2+ exchanger isoforms after transient focal cerebral ischemia in rats

The Na+/Ca2+ exchanger (NCX) is an antiporter located in the plasma membrane of many cells, which can maintain the intracellular Ca(2+) homeostasis. Some studies have shown the close relationship of NCX and cerebral ischemia. But controversial results were obtained. Three NCX isoforms, NCX1, NCX2, and NCX3 were distributed selectively in central nervous system, which suggests that each isoform may have different function in cerebral ischemia. In this study we investigated the time-related alteration of gene and protein expressions of NCX1, NCX2, and NCX3 in rat brain cortex after 2 h of transient middle cerebral artery occlusion (tMCAO). Reverse transcription-polymerase chain reaction (RT-PCR) was used to investigate the mRNA levels of each NCX isoform at 2, 6, 12, and 24 h of reperfusion, respectively. Western blot was used to measure the protein expressions of each NCX isoform at 2, 12, and 24 h of reperfusion, respectively. The results showed that NCX1 mRNA level was reduced by 42.1% and 27.8%, respectively, at 2 and 6h of reperfusion and restored to normal level at 12 and 24 h of reperfusion. NCX1 protein was decreased by 36.6% at 2 h of reperfusion and recovered at 12 and 24 h of reperfusion. The mRNA and protein levels of NCX2 and NCX3 did not change significantly over time. These results suggest that NCX1 might play an important role in transient focal cerebral ischemia.

Na+/Ca2+ exchanger 1 alters in pyramidal cells and expresses in astrocytes of the gerbil hippocampal CA1 region after ischemia

Alterations of immunoreactivity and protein contents of Na(+)/Ca(2+) exchanger 1 (NCX1) were observed in the gerbil hippocampus proper after 5 min of transient forebrain ischemia. NCX1 immunoreactivity was significantly changed in the hippocampal CA1 region, but not in the CA2/3 region after ischemia/reperfusion. In the sham-operated group, NCX1 immunoreactivity was mainly detected in CA1 pyramidal cells. However, 30 min after ischemia/reperfusion, NCX1 immunoreactivity was significantly decreased and then increased at 1 day after ischemia. At this time, NCX1 immunoreactivity in CA1 pyramidal cells was similar to that of the sham-operated group. At 3 days after ischemia, NCX1 immunoreactivity was significantly reduced in the CA1 region compared to that of the sham-operated group and NCX1 immunoreactivity was significantly increased again 4 days after ischemia. Thereafter, NCX1 immunoreactivity was decreased time-dependently in ischemia groups. Between 15 min and 6 h post-ischemia, NCX1 immunoreactivity was expressed in astrocytes in the strata oriens and radiatum of the CA1 region. From 3 days post-ischemia, NCX1 immunoreactivity was expressed in astrocytes in the strata oriens and radiatum. Ischemia-induced changes in NCX1 protein contents in the hippocampus proper concurred with immunohistochemical data post-ischemia. Our results suggest that changes in NCX1 in CA1 pyramidal cells and astrocytes after ischemia are associated with intracellular Na(+) concentrations and that NCX1 may induce an intracellular calcium overload, which may be related to neuronal death.

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Overexpression of genes in the CA1 hippocampus region of adult rat following episodes of global ischemia

Ischemic stress is associated with marked changes in gene expression in the hippocampus--albeit little information exists on the activation of nonabundant genes. We have examined the expression of several known genes and identified novel ones in the adult rat hippocampus after a mild, transient, hypovolemic and hypotensive, global ischemic stress. An initial differential screening using a prototype array to assess gene expression after stress followed by a suppression subtractive hybridization protocol and cDNA microarray revealed 124 nonoverlapped transcripts predominantly expressed in the CA1 rat hippocampus region in response to ischemic stress. About 78% of these genes were not detected with nonsubtracted probes. Reverse transcription polymerase chain reaction (RT-PCR) and in situ hybridization on these 124 transcripts confirmed the differential expression of at least 83. Most robustly expressed were gene sequences NFI-B, ATP1B1, RHOGAP, PLA2G4A, BAX, CASP3, P53, MAO-A, FRA1, HSP70.2, and NR4A1 (NUR77), as well as sequence tags of unknown function. New stress-related genes of similar functional motifs were identified, reemphasizing the importance of functional grouping in the analysis of multiple gene expression profiles. These data indicate that ischemia elicits expression of an array of functional gene clusters that may be used as an index for stress severity and a template for target therapy design.

Mediators of ischemic preconditioning identified by microarray analysis of rat spinal cord

Spinal ischemia is a frequent cause of paralysis. Here we explore the biological basis of ischemic preconditioning (IPC), the phenomenon in which a brief period of ischemia can confer protection against subsequent longer and normally injurious ischemia, to identify mediators of endogenous neuroprotection. Using microarrays, we examined gene expression changes induced by brief spinal ischemia using a rat balloon occlusion model. Among the nearly 5000 genes assayed, relatively few showed two-fold changes, and three groups stood out prominently. The first group codes for heat shock protein 70, which is induced selectively and robustly at 30 min after brief ischemia, with increases up to 100-fold. A second group encodes metallothioneins 1 and 2. These mRNAs are increased at 6 and 12 h after ischemia, up to 12-fold. The third group codes for a group of immediate-early genes not previously associated with spinal ischemia: B-cell translocation gene 2 (BTG2), the transcription factors early growth response 1 (egr-1) and nerve growth factor inducible B (NGFI-B), and a mitogen-activated protein kinase phosphatase, ptpn16, an important cell signaling regulator. These mRNAs peak at 30 min and return to baseline or are decreased 6 h after ischemia. Several other potentially protective genes cluster with these induced mRNAs, including small heat shock proteins, and many have not been previously associated with IPC. These results provide both putative mediators of IPC and molecular targets for testing preconditioning therapies.

DNA microarray analysis of hippocampal gene expression measured twelve hours after hypoxia-ischemia in the mouse

Cell death from cerebral ischemia is a dynamic process. In the minutes to days after an ischemic insult, progressive changes in cellular morphology occur. Associated with these events is the regulation of competing programs of gene expression; some are protective against ischemic insult, and others contribute to delayed cell death. Many genes involved in these processes have been identified, but individually, these findings have provided only limited insight into the systems biology of cerebral ischemia. Attempts to characterize the coordinated expression of large numbers of genes in cerebral ischemia has only recently become possible. Today, DNA microarray technology provides a powerful tool for investigating parallel expression changes for thousands of genes at one time. In this study, adult mice were subjected to 30 minutes of hypoxia-ischemia (HI), and the hippocampus was examined 12 hours later for differential gene expression using a 15K high-density mouse EST array. The genomic response to HI is complex, affecting approximately 7% of the total number of ESTs examined. Assigning differentially expressed ESTs to molecular functional groups revealed that HI affects many pathways including the molecular chaperones, transcription factors, kinases, and calcium ion binding genes. A comprehensive list of regulated genes should prove valuable in advancing our understanding of the pathogenesis of cerebral ischemia.

cDNA suppression subtraction library for screening down-regulated genes in gastric carcinoma

AIM: To establish cDNA suppression subtraction library with a high subtraction efficiency by counterpart normal gastric mucosa mixture mRNA subtracting gastric cancer cells mixture mRNA for screening down-regulated genes in gastric carcinoma.

METHODS: RNA of gastric cancer tissues and counterpart normal gastric mucosa were respectively isolated in five patients with gastric cancer, and their mRNA was purified. cDNA suppression subtraction library was established by counterpart normal gastric mucosa mixture mRNA (tester) subtracting gastric cancer tissues mixture mRNA (driver) of five patients with gastric carcinoma. The library plasmids were transformed into competent bacteria DH5a after ligation of the library cDNA fragments with T vectors. Library plasmids were extracted after picking colonies and shaking bacteria overnight. Its subtraction efficiency was confirmed by PCR and reverse hybridization of a nylon filter onto which the colonies of bacteria were transfered with probes of reverse transcription products cDNA of gastric cancer tissues mRNA and counterpart normal gastric mucosa mRNA labeled with α-³²P dCTP.

RESULTS: mRNA purified from total RNA of gastric cancer tissues and counterpart normal gastric mucosa in five patients with gastric carcinoma revealed a good quality. cDNA suppression subtraction library constructed for screening down-regulated genes in gastric carcinoma represented a high subtraction efficiency. 86% of differential expression in down-regulated genes between counterpart normal gastric mucosa and gastric carcinoma was confirmed.

CONCLUSION: cDNA suppression subtraction library with a high subtraction efficiency for screening down-regulated genes in gastric carcinoma is successfully established.