Hypoxia-induced iNOS expression in microglia is regulated by the PI3-kinase/Akt/mTOR signaling pathway and activation of hypoxia inducible factor-1α

The role of mTOR signaling pathway in spinal cord injury

The mammalian target of rapamycin (mTOR) signaling pathway plays an important role in multiple cellular functions, such as cell metabolism, proliferation and survival. Many previous studies have shown that mTOR regulates both neuroprotective and neuroregenerative functions in trauma and various diseases in the central nervous system (CNS). Recently, we reported that inhibition of mTOR using rapamycin reduces neural tissue damage and locomotor impairment after spinal cord injury (SCI) in mice. Our results demonstrated that the administration of rapamycin at four hours after injury significantly increases the activity of autophagy and reduces neuronal loss and cell death in the injured spinal cord. Furthermore, rapamycin-treated mice show significantly better locomotor function in the hindlimbs following SCI than vehicle-treated mice. These findings indicate that the inhibition of mTOR signaling using rapamycin during the acute phase of SCI produces neuroprotective effects and reduces secondary damage at lesion sites. However, the role of mTOR signaling in injured spinal cords has not yet been fully elucidated. Various functions are regulated by mTOR signaling in the CNS, and multiple pathophysiological processes occur following SCI. Here, we discuss several unresolved issues and review the evidence from related articles regarding the role and mechanisms of the mTOR signaling pathway in neuroprotection and neuroregeneration after SCI.

Psychostimulant abuse and neuroinflammation: emerging evidence of their interconnection

During the past two decades, there has been a tremendous expansion of knowledge regarding the neurobiological effects of substance abuse and how these effects impact behavior. At the same time, there has been a profound change in our understanding of the way in which the central nervous system responds to noxious stimuli. Most often referred to as the innate immune response (IIR), this defense mechanism is activated by a number of agents (toxic, microbial, ischemic) and has been implicated in the progression of a number of neurodegenerative diseases. We review evidence that psychostimulants of abuse (cocaine, methamphetamine, ecstasy) are associated with activation of the IIR. We first present background on what is currently known about the IIR including some of the cellular elements involved (microglia, astrocytes, vascular endothelial cells), key receptor pathways, and primary inflammatory cytokines (IL-1β, IL-6, TNF-α). We then present a variety of protein and gene expression data taken from animal studies that show increased expression of various components of the IIR following acute or repeated psychostimulant administration. Collectively the data indicate an association of psychostimulant use with IIR activation in the brain even at exposures not traditionally associated with neurotoxicity. Thus, the gradually escalating deleterious effects of psychostimulant use could in part involve neuroinflammatory mechanisms. Finally, we offer one hypothesis of a possible mechanism by which psychostimulants result in IIR activation and discuss the potential therapeutic implications of these findings for treatment of the recovering addict.

Multifaceted effects of rapamycin on functional recovery after spinal cord injury in rats through autophagy promotion, anti-inflammation, and neuroprotection

BACKGROUND

Spinal cord injuries (SCIs) are serious and debilitating health problems that lead to severe and permanent neurological deficits resulting from the primary mechanical impact followed by secondary tissue injury. During the acute stage after an SCI, the expression of autophagy and inflammatory responses contribute to the development of secondary injury. In the present study, we examined the multifaceted effects of rapamycin on outcomes of rats after an SCI.

MATERIALS AND METHODS

We used 72 female Sprague-Dawley rats for this study. In the SCI group, we performed a laminectomy at T10, followed by impact-contusion of the spinal cord. In the control group, we performed only a laminectomy without contusion. We evaluated the effects of rapamycin using the Basso, Beattie, and Bresnahan scale for functional outcomes, Western blot analyses for analyzing LC3-II, tumor necrosis factor expression, and p70S6K phosphorylation, and an immunostaining technique for localization and enumeration of microglial and neuronal cells.

RESULTS

Basso, Beattie, and Bresnahan scores after injury significantly improved in the rapamycin-treated group compared with the vehicle group (on Day 28 after the SCI; P < .05). The Western blot analysis demonstrated that rapamycin enhanced LC3-II expression and decreased p70S6K phosphorylation compared with the vehicle (P < .01), which implies promotion of autophagy through mammalian target of rapamycin inhibition. Furthermore, rapamycin treatment significantly attenuated tumor necrosis factor production and microglial expression (P < .05). Immunohistochemistry of NeuN (antibodies specific to neurons) showed remarkable neuronal cell preservation in the rapamycin-treated group compared with the vehicle-treated group (P < .05), which suggests a neuroprotective effect of rapamycin.

CONCLUSIONS

Rapamycin is a novel neuroprotectant with multifaceted effects on the rat spinal cord after injury. Use of such a clinically established drug could facilitate early clinical trials in selected cases of human SCIs.

Resveratrol inhibits inflammatory responses via the mammalian target of rapamycin signaling pathway in cultured LPS-stimulated microglial cells

BACKGROUND

Resveratrol have been known to possess many pharmacological properties including antioxidant, cardioprotective and anticancer effects. Although current studies indicate that resveratrol produces neuroprotection against neurological disorders, the precise mechanisms for its beneficial effects are still not fully understood. We investigate the effect of anti-inflammatory and mechamisms of resveratrol by using lipopolysaccharide (LPS)-stimulated murine microglial BV-2 cells.

METHODOLOGY/PRINCIPAL FINDINGS

BV-2 cells were treated with resveratrol (25, 50, and 100 µM) and/or LPS (1 µg/ml). Nitric oxide (NO) and prostaglandin E2 (PGE2) were measured by Griess reagent and ELISA. The mRNA and protein levels of proinflammatory proteins and cytokines were analysed by RT-PCR and double immunofluorescence labeling, respectively. Phosphorylation levels of PTEN (phosphatase and tensin homolog deleted on chromosome 10), Akt, mammalian target of rapamycin (mTOR), mitogen-activated protein kinases (MAPKs) cascades, inhibitor κB-α (IκB-α) and cyclic AMP-responsive element-binding protein (CREB) were measured by western blot. Resveratrol significantly attenuated the LPS-induced expression of NO, PGE2, inducible nitric oxide synthase (iNOS), cyclooxygenase-2 (COX-2), tumor necrosis factor-α (TNF-α), interleukin-1β (IL-1β) and nuclear factor-κB (NF-κB) in BV-2 cells. Resveratrol increased PTEN, Akt and mTOR phosphorylation in a dose-dependent manner or a time-dependent manner. Rapamycin (10 nM), a specific mTOR inhibitor, blocked the effects of resveratrol on LPS-induced microglial activation. In addition, mTOR inhibition partially abolished the inhibitory effect of resveratrol on the phosphorylation of IκB-α, CREB, extracellular signal-regulated kinase 1/2 (ERK1/2), c-Jun N-terminal protein kinase (JNK), and p38 mitogen-activated protein kinase (p38 MAPK).

CONCLUSION AND IMPLICATIONS

This study indicates that resveratrol inhibited LPS-induced proinflammatory enzymes and proinflammatory cytokines via down-regulation phosphorylation of NF-κB, CREB and MAPKs family in a mTOR-dependent manner. These findings reveal, in part, the molecular basis underlying the anti-inflammatory properties of resveratrol.

A forward loop between glioma and microglia: glioma-derived extracellular matrix-activated microglia secrete IL-18 to enhance the migration of glioma cells

The mediators and cellular effectors of inflammation are important constituents of the local environment of tumors. In some occasions, oncogenic changes induce an inflammatory microenvironment that promotes the progression of tumors. In gliomas, the presence of microglia may represent tumor-related inflammation and microglia activation, and subsequent inflammatory responses may influence tumor growth and metastasis. Here, we found that C6 glioma--but not primary astrocyte-derived extracellular matrix (ECM) could activate microglia, including primary microglia and BV-2 cell line, and activated microglia-secreted interleukin (IL)-18, a potent inflammatory cytokine of the IL-1 family, to promote C6 migration. In addition, by coating purified ECM components, it was found that secretion of IL-18 by activated microglia was enhanced when microglia encountered with fibronectin and vitronectin. Furthermore, IL-18-induced C6 migration and microfilament disassembly were antagonized by iNOS inhibitor, guanylate cyclase inhibitor, and protein kinase G inhibitor. Taken together, these results indicate that IL-18 secreted by microglia, which was activated by C6 glioma-derived ECM, enhanced migration of C6 glioma through NO/cGMP pathway.

Pharmacological inhibition of Akt and downstream pathways modulates the expression of COX-2 and mPGES-1 in activated microglia

Background

Microglia are considered a major target for modulating neuroinflammatory and neurodegenerative disease processes. Upon activation, microglia secrete inflammatory mediators that contribute to the resolution or to further enhancement of damage in the central nervous system (CNS). Therefore, it is important to study the intracellular pathways that are involved in the expression of the inflammatory mediators. Particularly, the role of the phosphatidylinositol 3-kinase (PI3K)/Akt/mammalian target of rapamycin (mTOR) and glycogen synthase kinase-3 (GSK-3) pathways in activated microglia is unclear. Thus, in the present study we investigated the role of Akt and its downstream pathways, GSK-3 and mTOR, in lipopolysaccharide (LPS)-activated primary rat microglia by pharmacological inhibition of these pathways in regard to the expression of cyclooxygenase (COX)-2 and microsomal prostaglandin E synthase-1 (mPGES-1) and to the production of prostaglandin (PG) E₂ and PGD₂.

Findings

We show that inhibition of Akt by the Akt inhibitor X enhanced the production of PGE₂ and PGD₂ without affecting the expression of COX-2, mPGES-1, mPGES-2 and cytosolic prostaglandin E synthase (cPGES). Moreover, inhibition of GSK-3 reduced the expression of both COX-2 and mPGES-1. In contrast, the mTOR inhibitor rapamycin enhanced both COX-2 and mPGES-1 immunoreactivity and the release of PGE₂ and PGD₂. Interestingly, NVP-BEZ235, a dual PI3K/mTOR inhibitor, enhanced COX-2 and reduced mPGES-1 immunoreactivity, albeit PGE₂ and PGD₂ levels were enhanced in LPS-stimulated microglia. However, this compound also increased PGE₂ in non-stimulated microglia.

Conclusion

Taken together, we demonstrate that blockade of mTOR and/or PI3K/Akt enhances prostanoid production and that PI3K/Akt, GSK-3 and mTOR differently regulate the expression of mPGES-1 and COX-2 in activated primary microglia. Therefore, these pathways are potential targets for the development of novel strategies to modulate neuroinflammation.

Current therapeutic strategies to mitigate the eNOS dysfunction in ischaemic stroke

Impairment of endothelial nitric oxide synthase (eNOS) activity is implicated in the pathogenesis of endothelial dysfunction in many diseases including ischaemic stroke. The modulation of eNOS during and/or following ischaemic injury often represents a futile compensatory mechanism due to a significant decrease in nitric oxide (NO) bioavailability coupled with dramatic increases in the levels of reactive oxygen species that further neutralise NO. However, applications of a number of therapeutic agents alone or in combination have been shown to augment eNOS activity under a variety of pathological conditions by potentiating the expression and/or activity of Akt/eNOS/NO pathway components. The list of these therapeutic agents include NO donors, statins, angiotensin-converting enzyme inhibitors, calcium channel blockers, phosphodiesterase-3 inhibitors, aspirin, dipyridamole and ellagic acid. While most of these compounds exhibit anti-platelet properties and are able to up-regulate eNOS expression in endothelial cells and platelets, others suppress eNOS uncoupling and tetrahydrobiopterin (an eNOS stabiliser) oxidation. As the number of therapeutic molecules that modulate the expression and activity of eNOS increases, further detailed research is required to reveal their mode of action in preventing and/or reversing the endothelial dysfunction.

Ischemic postconditioning attenuates liver warm ischemia-reperfusion injury through Akt-eNOS-NO-HIF pathway

BACKGROUND

Ischemic postconditioning (IPO) has been demonstrated to attenuate ischemia/reperfusion (I/R) injury in the heart and brain, its roles to liver remain to be defined. The study was undertaken to determine if IPO would attenuate liver warm I/R injury and its protective mechanism.

METHODS

Mice were divided into sham, I/R, IPO+I/R (occlusing the porta hepatis for 60 min, then treated for three cycles of 10 sec brief reperfusion consecutively, followed by a persistent reperfusion); L-NAME+ sham (L-NAME, 16 mg/kg, i.v., 5 min before repefusion); L-NAME+I/R; and L-NAME+ IPO. Blood flow of caudate and left lobe of the liver was blocked. Functional and morphologic changes of livers were evaluated. Contents of nitric oxide, eNOS and iNOS in serum were assayed. Concentration of eNOS, iNOS, malondialdehyde (MDA) and activity of superoxide dismutase (SOD) in hepatic tissue were also measured. Expressions of Akt, p-Akt and HIF-1α protein were determined by western blot. Expressions of TNF-α and ICAM-1 were measured by immunohistochemistry and RT-PCR.

RESULTS

IPO attenuated the dramatically functional and morphological injuries. The levels of ALT was significantly reduced in IPO+I/R group (p < 0.05). Contents of nitric oxide and eNOS in serum were increased in the IPO+I/R group (p < 0.05). IPO also up-regulated the concentration of eNOS, activity of SOD in hepatic tissue (p < 0.05), while reduced the concentration of MDA (p < 0.05). Moreover, protein expressions of HIF-1α and p-Akt were markedly enhanced in IPO+I/R group. Protein and mRNA expression of TNF-α and ICAM-1 were markedly suppressed by IPO (p < 0.05). These protective effects of IPO could be abolished by L-NAME.

CONCLUSIONS

We found that IPO increased the content of NO and attenuated the overproduction of ROS and I/R-induced inflammation. Increased NO contents may contribute to increasing HIF-1α level, and HIF-1α and NO would simultaneously protect liver from I/R injury. These findings suggested IPO may have the therapeutic potential through Akt-eNOS-NO-HIF pathway for the better management of liver I/R injury.

Calorie restriction and stroke

Stroke, a major cause of disability and mortality in the elderly, occurs when a cerebral blood vessel is occluded or ruptured, resulting in ischemic damage and death of brain cells. The injury mechanism involves metabolic and oxidative stress, excitotoxicity, apoptosis and inflammatory processes, including activation of glial cells and infiltration of leukocytes. In animal models, dietary energy restriction, by daily calorie reduction (CR) or intermittent fasting (IF), extends lifespan and decreases the development of age-related diseases. Dietary energy restriction may also benefit neurons, as suggested by experimental evidence showing that CR and IF protect neurons against degeneration in animal models. Recent findings by our group and others suggest the possibility that dietary energy restriction may protect against stroke induced brain injury, in part by inducing the expression of neurotrophic factors, such as brain-derived neurotrophic factor (BDNF) and basic fibroblast growth factor (bFGF); protein chaperones, including heat shock protein 70 (Hsp70) and glucose regulated protein 78 (GRP78); antioxidant enzymes, such as superoxide dismutases (SOD) and heme oxygenase-1 (HO-1), silent information regulator T1 (SIRT1), uncoupling proteins and anti-inflammatory cytokines. This article discusses the protective mechanisms activated by dietary energy restriction in ischemic stroke.

Rb1 postconditioning attenuates liver warm ischemia-reperfusion injury through ROS-NO-HIF pathway

AIMS

Ginsenoside Rb1 could prevent ischemic neuronal death and focal cerebral ischemia, but its roles to liver warm I/R injury remain to be defined. We determined if Rb1 would attenuate warm I/R injury in mice.

MAIN METHODS

Mice were divided into sham, I/R, Rb1+I/R (Rb1 postconditioning, 20mg/kg, i.p. after ischemia), sham+L-NAME, I/R+L-NAME, and Rb1+I/R+L-NAME groups using 60min of the liver median and left lateral lobes ischemia. Serum levels of alanine aminotransferase (ALT) were measured and morphology changes of livers were evaluated. Contents of nitric oxide (NO) and nitric oxide synthase (NOS), malondialdehye (MDA) and activity of superoxide dismutase (SOD) were measured. Expressions of Akt, p-Akt, iNOS, HIF-1alpha, tumor necrosis factor-a (TNF-α) and intercellular adhesion molecule-1 (ICAM-1) were also determined by western blot or immunohistochemistry.

KEY FINDINGS

Rb1 postconditioning attenuated the dramatically functional and morphological injuries. The levels of ALT were significantly reduced in Rb1 group (p<0.05). Rb1 upregulated the concentrations of NO, iNOS in serum, iNOS, and activity of SOD in hepatic tissues (p<0.05), while it dramatically reduced the concentration of MDA (p<0.05). Protein expressions of p-Akt, iNOS and HIF-1alpha were markedly enhanced in Rb1 group. Protein and mRNA expressions of TNF-α and ICAM-1 were markedly suppressed by Rb1 (p<0.05).

SIGNIFICANCE

We found that Rb1 postconditioning could protect liver from I/R injury by upregulating the content of NO and NOS, and also HIF-1alpha protein expression. These protective effects could be abolished by L-NAME. These findings suggested Rb1 may have the therapeutic potential through ROS-NO-HIF pathway for management of liver warm I/R injury.

Inflammation and brain injury: acute cerebral ischaemia, peripheral and central inflammation

Inflammation is a classical host defence response to infection and injury that has many beneficial effects. However, inappropriate (in time, place and magnitude) inflammation is increasingly implicated in diverse disease states, now including cancer, diabetes, obesity, atherosclerosis, heart disease and, most relevant here, CNS disease. A growing literature shows strong correlations between inflammatory status and the risk of cerebral ischaemia (CI, most commonly stroke), as well as with outcome from an ischaemic event. Intervention studies to demonstrate a causal link between inflammation and CI (or its consequences) are limited but are beginning to emerge, while experimental studies of CI have provided direct evidence that key inflammatory mediators (cytokines, chemokines and inflammatory cells) contribute directly to ischaemic brain injury. However, it remains to be determined what the relative importance of systemic (largely peripheral) versus CNS inflammation is in CI. Animal models in which CI is driven by a CNS intervention may not accurately reflect the clinical condition; stroke being typically induced by atherosclerosis or cardiac dysfunction, and hence current experimental paradigms may underestimate the contribution of peripheral inflammation. Experimental studies have already identified a number of potential anti-inflammatory therapeutic interventions that may limit ischaemic brain damage, some of which have been tested in early clinical trials with potentially promising results. However, a greater understanding of the contribution of inflammation to CI is still required, and this review highlights some of the key mechanism that may offer future therapeutic targets.

Hypoxia induces BMP-2 expression via ILK, Akt, mTOR, and HIF-1 pathways in osteoblasts

It has been shown that hypoxia stimulation regulates bone formation, maintenance, and repair. Bone morphogenetic protein (BMP) plays important roles in osteoblastic differentiation and bone formation. However, the effects of hypoxia exposure on BMP-2 expression in cultured osteoblasts are largely unknown. Here we found that hypoxia stimulation increased mRNA and protein levels of BMP-2 by qPCR, Western blot and ELISA assay in osteoblastic cells MG-63, hFOB and bone marrow stromal cells M2-10B4. Integrin-linked kinase (ILK) inhibitor (KP-392), Akt inhibitor (1L-6-hydroxymethyl-chiro-inositol-2-[(R)-2-O-methyl-3-O-octadecylcarbonate]) or mammalian target of rapamycin (mTOR) inhibitor (rapamycin) inhibited the potentiating action of hypoxia. Exposure to hypoxia increased the kinase activity of ILK and phosphorylation of Akt and mTOR. Furthermore, hypoxia also increased the stability and activity of HIF-1 protein. The binding of HIF-1alpha to the HRE elements after exposure to hypoxia was measured by EMSA assay. Moreover, the use of pharmacological inhibitors or genetic inhibition revealed that both ILK/Akt and mTOR signaling pathway were potentially required for hypoxia-induced HIF-1alpha activation and subsequent BMP-2 up-regulation. Taken together, our results provide evidence that hypoxia enhances BMP-2 expression in osteoblasts by an HIF-1alpha-dependent mechanism involving the activation of ILK/Akt and mTOR pathways.

Placental metabolic reprogramming: do changes in the mix of energy-generating substrates modulate fetal growth?

Insufficient oxygen leads to the cessation of growth in favor of cellular survival. Our unique model of high-altitude human pregnancy indicates that hypoxia-induced reductions in fetal growth occur at higher levels of oxygen than previously described. Fetal PO(2) is surprisingly high and fetal oxygen consumption unaffected by high altitude, whereas fetal glucose delivery and consumption decrease. Placental delivery of energy-generating substrates to the fetus is thus altered by mild hypoxia, resulting in maintained fetal oxygenation but a relative fetal hypoglycemia. Our data point to this altered mix of substrates as a potential initiating factor in reduced fetal growth, since oxygen delivery is adequate. These data support the existence, in the placenta, of metabolic reprogramming mechanisms, previously documented in tumor cells, whereby HIF-1 stimulates reductions in mitochondrial oxygen consumption at the cost of increased glucose consumption. Decreased oxygen consumption is not due to substrate (oxygen) limitation but rather results from active inhibition of mitochondrial oxygen utilization. We suggest that under hypoxic conditions, metabolic reprogramming in the placenta decreases mitochondrial oxygen consumption and increases anerobic glucose consumption, altering the mix of energy-generating substrates available for transfer to the fetus. Increased oxygen is available to support the fetus, but at the cost of less glucose availability, leading to a hypoglycemia-mediated decrease in fetal growth. Our data suggest that metabolic reprogramming may be an initiating step in the progression to more severe forms of fetal growth restriction and points to the placenta as the pivotal source of fetal programming in response to an adverse intrauterine environment.

Involvement of mTOR kinase in cytokine-dependent microglial activation and cell proliferation

Neuroinflammation plays a prominent role in the pathophysiology of several neurodegenerative disorders, including Multiple Sclerosis. Reactive microglial cells are always found in areas of active demyelination as well as in normal-appearing white matter. Microglia contribute to initiating and maintaining brain inflammation, and once activated release pro-inflammatory mediators potentially cytotoxic, like nitric oxide (NO). It is now evident that the mTOR signaling pathway regulates different functions in the innate immune system, contributing to macrophage activation. More recently, mTOR has been found to enhance the survival of EOC2 microglia during oxygen-glucose deprivation and increase NO synthase 2 (NOS2) expression during hypoxia in BV2 microglial cell line, thus suggesting an involvement in microglial pro-inflammatory activation. In the present study, we detected mTOR activation in response to two different stimuli, namely LPS and a mixture of cytokines, in primary cultures of rat cortical microglia. Moreover, mTOR inhibitors reduced NOS activity and NOS2 expression induced by cytokines, but not those induced by LPS. The mTOR inhibitor RAD001, in combination with cytokines, also reduced microglial proliferation and the intracellular levels of cyclooxygenase. Under basal conditions mTOR inhibition significantly reduced microglial viability. Interestingly, mTOR inhibitors did not display any relevant effect on astrocyte NOS2 activity or cell viability. In conclusion, mTOR selectively controls microglial activation in response to pro-inflammatory cytokines and appears to play a crucial role in microglial viability; thus these drugs may be a useful pharmacological tool to reduce neuroinflammation.

Baicalein suppresses hypoxia-induced HIF-1alpha protein accumulation and activation through inhibition of reactive oxygen species and PI 3-kinase/Akt pathway in BV2 murine microglial cells

Hypoxia induces an inflammatory activation of microglia during cerebral ischemia. The transcription factor of hypoxia-inducible genes hypoxia-inducible factor-1 (HIF-1) is known to be involved in inflammation and immune response. Although baicalein (BE), a flavonoid, is shown to have anti-inflammatory effects and attenuate ischemic injury, its action mechanism is not understood well. Thus, we examined effect of BE on hypoxia-induced HIF-1 activation and its signaling mechanism in BV2 microglial cells. BE inhibited hypoxia-induced HIF-1alpha protein accumulation and HIF-1 transcriptional activation. Consistently, BE suppressed hypoxia-induced expression of hypoxia responsive genes, iNOS, COX-2, and VEGF. We then showed that BE inhibited hypoxia-induced phosphorylation of Akt but not that of ERK and p38. Moreover, BE inhibited hypoxia-induced PI 3-kinase activation. Finally, we showed that BE inhibited hypoxia-induced ROS generation, and an antioxidant N-acetylcysteine reduced hypoxia-induced HIF-1alpha and iNOS protein expression and PI 3-kinase/Akt activation in BV2 microglia. Taken together, these results suggest that BE suppresses hypoxia-induced HIF-1alpha protein and activation as well as expression of hypoxia responsive genes by inhibiting ROS and PI 3-kinase/Akt pathway in BV2 microglia.

Effects of marginal iron overload on iron homeostasis and immune function in alveolar macrophages isolated from pregnant and normal rats

The effects of changes in macrophage iron status, induced by single or multiple iron injections, iron depletion or pregnancy, on both immune function and mRNA expression of genes involved in iron influx and egress have been evaluated. Macrophages isolated from iron deficient rats, or pregnant rats at day 21 of gestation, either supplemented with a single dose of iron dextran, 10 mg, at the commencement of pregnancy, or not, showed significant increases of macrophage ferroportin mRNA expression, which was paralleled by significant decreases in hepatic Hamp mRNA expression. IRP activity in macrophages was not significantly altered by iron status or the inducement of pregnancy +/- a single iron supplement. Macrophage immune function was significantly altered by iron supplementation and pregnancy. Iron supplementation, alone or combined with pregnancy, increased the activities of both NADPH oxidase and nuclear factor kappa B (NFkappaB). In contrast, the imposition of pregnancy reduced the ability of these parameters to respond to an inflammatory stimuli. Increasing iron status, if only marginally, will reduce the ability of macrophages to mount a sustained response to inflammation as well as altering iron homeostatic mechanisms.

Rapamycin prevents mesenteric neo-angiogenesis and reduces splanchnic blood flow in portal hypertensive mice

AIM

Increased angiogenesis in the mesenteric microvasculature of portal hypertensive animals may contribute to the development of splanchnic vasodilation associated with portal hypertension (PHT). Experimental data suggest that rapamycin may reduce angiogenesis and tumour growth by inhibiting the vascular endothelial growth factor (VEGF) pathway. This study determines whether rapamycin can prevent the neoangiogenesis in the mesentery of portal hypertensive mice and may influence the splanchnic vasodilation.

METHODS

PHT was induced by partial portal vein ligation (PPVL). PPVL and Sham mice were treated daily with rapamycin or placebo for 2 weeks. Protein expressions of VEGF, CD 31, Akt and p70S6 kinase (mTOR signalling pathway) were evaluated. Mesenteric blood flow (MBF) was measured by a perivascular flow probe.

RESULTS

Increased mesenteric angiogenesis and VEGF protein levels were observed in PPVL(placebo) mice compared to Sham(placebo) mice. Rapamycin treatment caused significant reduction in CD 31 positive endothelial cells and VEGF protein in the PPVL(rapamycine) group compared to the PPVL(placebo) group, to levels comparable with Sham(placebo) and Sham(rapamycine) groups. MBF was significantly higher in PPVL(placebo) mice compared to the Sham(placebo) mice. Rapamycin decreased significantly the MBF in PPVL(rapamycine) mice compared to PPVL(placebo) mice. Phospo-Akt and p70S6 kinase protein levels were increased in the mesenteric tissue of PPVL(placebo) mice compared to Sham(placebo) mice, which were also prevented by treatment with rapamycin.

CONCLUSIONS

An increased VEGF dependent neo-angiogenesis is present in the mesentery of portal hypertensive mice. Rapamycin prevents angiogenesis in the mesenteric tissue and decreases the mesenteric blood flow in portal hypertensive mice, at least in part through an anti-VEGF activity and influence on the mTOR signalling pathway.

Hypoxia enhances CXCR4 expression favoring microglia migration via HIF-1alpha activation

Migration toward pathological area is the first critical step in microglia engagement during the central nervous system (CNS) injury, although the molecular mechanisms underlying microglia mobilization have not been fully understood. Here, we report that hypoxia promotes stromal cell-derived factor-1alpha (SDF-1alpha) induced microglia migration by inducing the CXC chemokine receptor 4 (CXCR4) expression. Exposure to hypoxia significantly enhanced CXCR4 expression levels in N9 microglia cell. Then, cell migration induced by SDF-1, a CXCR4-specific ligand, was observed accelerated. Blockade of hypoxia inducible factor-1alpha (HIF-1alpha) activation by inhibitors of phosphoinositide-3-kinase (PI3K)/Akt signaling pathway abrogated both of hypoxia-induced CXCR4 up-regulation and cell-migration acceleration. These results point to a crucial role of Hypoxia-HIF-1alpha-CXCR4 pathway during microglia migration.

Immunosuppression after traumatic or ischemic CNS damage: it is neuroprotective and illuminates the role of microglial cells

Acute traumatic and ischemic events in the central nervous system (CNS) invariably result in activation of microglial cells as local representatives of the immune system. It is still under debate whether activated microglia promote neuronal survival, or whether they exacerbate the original extent of neuronal damage. Protagonists of the view that microglial cells cause secondary damage have proposed that inhibition of microglial activation by immunosuppression is beneficial after acute CNS damage. It is the aim of this review to analyse the effects of immunosuppressants on isolated microglial cells and neurons, and to scrutinize the effects of immunosuppression in different in vivo models of acute CNS trauma or ischemia. It is found that the immunosuppressants cytosine-arabinoside, different steroids, cyclosporin A, FK506, rapamycin, mycophenolate mofetil, and minocycline all have direct inhibitory effects on microglial cells. These effects are mainly exerted by inhibiting microglial proliferation or microglial secretion of neurotoxic substances such as proinflammatory cytokines and nitric oxide. Furthermore, immunosuppression after acute CNS trauma or ischemia results in improved structure preservation and, mostly, in enhanced function. However, all investigated immunosuppressants also have direct effects on neurons, and some immunosuppressants affect other glial cells such as astrocytes. In summary, it is safe to conclude that immunosuppression after acute CNS trauma or ischemia is neuroprotective. Furthermore, circumferential evidence indicates that microglial activation after traumatic or ischemic CNS damage is not beneficial to adjacent neurons in the immediate aftermath of such acute lesions. Further experiments with more specific agents or genetic approaches that specifically inhibit microglial cells are needed in order to fully answer the question of whether microglial activation is "good or bad".

Inducible nitric oxide synthase mediates hypoxia-induced hypoxia-inducible factor-1 alpha activation and vascular endothelial growth factor expression in oxygen-induced retinopathy

OBJECTIVE

Previous studies provided evidence that many factors contribute to retinal angiogenesis, including inducible nitric oxide synthase (iNOS), hypoxia-inducible factor-1 alpha (HIF-1 alpha) and vascular endothelial growth factor (VEGF). But the role of nitric oxide generated by iNOS in the regulation of expression of hypoxia-inducible genes in retinopathy of prematurity remains unclear. So we sought to better define the molecular basis of this iNOS-dependent regulation.

METHODS

In this study, using immunohistochemistry, real-time PCR and Western blotting technologies, we investigated the changes of iNOS, HIF-1 alpha, VEGF and phosphatidylinositol 3-kinase/Akt (PI3K/Akt) expressions.

RESULTS

Hypoxia- induced overexpression of iNOS, HIF-1 alpha, VEGF, PI3K/Akt and phosphorylated PI3K/Akt was observed in the untreated retinopathy of the prematurity group. Administration of the selective iNOS inhibitor aminoguanidine hemisulfate markedly decreased the expression of these genes.

CONCLUSIONS

These results indicate that iNOS mediates HIF-1 alpha activation and VEGF expression in retinal angiogenesis and that the PI3K/Akt signaling pathway may play a role in this process.

Lipopolysaccharide induces hypoxia-inducible factor-1 alpha mRNA expression and activation via NADPH oxidase and Sp1-dependent pathway in BV2 murine microglial cells

Hypoxia-inducible factor-1 (HIF-1), the key transcription factor of hypoxia-inducible genes, is known to be involved in inflammation and immune response, but little is known about the regulation of HIF-1 during microglial activation. Thus, we examined effect of lipopolysaccharide (LPS) on HIF-1 activation and its signaling mechanism in BV2 microglial cells. LPS induced HIF-1alpha mRNA and protein expression as well as HIF-1 transcriptional activation. Moreover, HIF-1alpha knockdown by small interfering RNA (siRNA) decreased LPS-induced expression of hypoxia responsive genes, VEGF, iNOS, and COX-2. We then showed that LPS-induced HIF-1alpha mRNA expression was blocked by an antioxidant, NADPH oxidase inhibitors, and siRNA of gp91phox, a subunit of NADPH oxidase. In addition, we showed that specific pharmacological inhibitors of PI 3-kinase and protein kinase C decreased LPS-induced HIF-1alpha mRNA expression. Finally, we showed that inhibition of transcription factor Sp1 by mithramycin A or Sp1 siRNA decreased LPS-induced HIF-1alpha mRNA and protein expression. Consistently, LPS increased Sp1 DNA binding and its transcriptional activity. Taken together, these results suggest that LPS induces HIF-1alpha mRNA expression and activation via NADPH oxidase and Sp1 in BV2 microglia.

Leptin-induced IL-6 production is mediated by leptin receptor, insulin receptor substrate-1, phosphatidylinositol 3-kinase, Akt, NF-kappaB, and p300 pathway in microglia

Leptin, the adipocyte-secreted hormone that centrally regulates weight control, is known to function as an immunomodulatory regulator. We investigated the signaling pathway involved in IL-6 production caused by leptin in microglia. Microglia expressed the long (OBRl) and short (OBRs) isoforms of the leptin receptor. Leptin caused concentration- and time-dependent increases in IL-6 production. Leptin-mediated IL-6 production was attenuated by OBRl receptor antisense oligonucleotide, PI3K inhibitor (Ly294002 and wortmannin), Akt inhibitor (1L-6-hydroxymethyl-chiro-inositol-2-((R)-2-O-methyl-3-O-octadecylcarbonate)), NF-kappaB inhibitor (pyrrolidine dithiocarbamate), IkappaB protease inhibitor (L-1-tosylamido-2-phenylenylethyl chloromethyl ketone), IkappaBalpha phosphorylation inhibitor (Bay 117082), or NF-kappaB inhibitor peptide. Transfection with insulin receptor substrate (IRS)-1 small-interference RNA or the dominant-negative mutant of p85 and Akt also inhibited the potentiating action of leptin. Stimulation of microglia with leptin activated IkappaB kinase alpha/IkappaB kinase beta, IkappaBalpha phosphorylation, IkappaBalpha degradation, p65 phosphorylation at Ser(276), p65 and p50 translocation from the cytosol to the nucleus, and kappaB-luciferase activity. Leptin-mediated an increase of IkappaB kinase alpha/IkappaB kinase beta activity, kappaB-luciferase activity, and p65 and p50 binding to the NF-kappaB element was inhibited by wortmannin, Akt inhibitor, and IRS-1 small-interference RNA. The binding of p65 and p50 to the NF-kappaB elements, as well as the recruitment of p300 and the enhancement of histone H3 and H4 acetylation on the IL-6 promoter was enhanced by leptin. Our results suggest that leptin increased IL-6 production in microglia via the leptin receptor/IRS-1/PI3K/Akt/NF-kappaB and p300 signaling pathway.

Ultrasound Induces Hypoxia-inducible Factor-1 Activation and Inducible Nitric-oxide Synthase Expression through the Integrin/Integrin-linked Kinase/Akt/Mammalian Target of Rapamycin Pathway in Osteoblasts

It has been shown that ultrasound (US) stimulation accelerates fracture healing in the animal models and clinical studies. Nitric oxide (NO) is a crucial early mediator in mechanically induced bone formation. Here we found that US stimulation increased NO formation and the protein level of inducible nitric-oxide synthase (iNOS). US-mediated iNOS expression was attenuated by anti-integrin alpha5beta1 or beta1 antibodies but not anti-integrin alphavbeta3 or beta3 antibodies or focal adhesion kinase mutant. Integrin-linked kinase (ILK) inhibitor (KP-392), Akt inhibitor (1L-6-hydroxymethyl-chiro-inositol-2-[(R)-2-O-methyl-3-O-octadecylcarbonate]) or mammalian target of rapamycin (mTOR) inhibitor (rapamycin) also inhibited the potentiating action of US. US stimulation increased the kinase activity of ILK and phosphorylation of Akt and mTOR. Furthermore, US stimulation also increased the stability and activity of HIF-1 protein. The binding of HIF-1alpha to the HRE elements on the iNOS promoter was enhanced by US stimulation. Moreover, the use of pharmacological inhibitors or genetic inhibition revealed that both ILK/Akt and mTOR signaling pathway were potentially required for US-induced HIF-1alpha activation and subsequent iNOS up-regulation. Taken together, our results provide evidence that US stimulation up-regulates iNOS expression in osteoblasts by an HIF-1alpha-dependent mechanism involving the activation of ILK/Akt and mTOR pathways via integrin receptor.

YC-1 attenuates LPS-induced proinflammatory responses and activation of nuclear factor-kappaB in microglia

BACKGROUND AND PURPOSE

An inflammatory response in the central nervous system mediated by the activation of microglia is a key event in the early stages of the development of neurodegenerative diseases. LPS has been reported to cause marked microglia activation. It is very important to develop drugs that can inhibit microglia activation and neuroinflammation. Here, we investigated the inhibitory effect of YC-1, a known activator of soluble guanylyl cyclase, against LPS-induced inflammatory responses in microglia.

EXPERIMENTAL APPROACH

To understand the inhibitory effects of YC-1 on LPS-induced neuroinflammation, primary cultures of rat microglia and the microglia cell line BV-2 were used. To examine the mechanism of action of YC-1, LPS-induced nitric oxide (NO) and prostaglandin E2 (PGE2) production, iNOS, COX-2 and cytokine expression were analyzed by Griess reaction, ELISA, Western blotting and RT-PCR, respectively. The effect of YC-1 on LPS-induced activation of nuclear factor kappa B (NF-kappaB) was studied by NF-kappaB reporter assay and immunofluorocytochemistry.

KEY RESULTS

YC-1 inhibited LPS-induced production of NO and PGE2 in a concentration-dependent manner. The protein and mRNA expression of iNOS and COX-2 in response to LPS application were also decreased by YC-1. In addition, YC-1 effectively reduced LPS-induced expression of the mRNA for the proinflammatory cytokines, TNF-alpha and IL-1beta. Furthermore, YC-1 inhibited LPS-induced NF-kappaB activation in microglia.

CONCLUSIONS AND IMPLICATIONS

YC-1 was able to inhibit LPS-induced iNOS and COX-2 expression and NF-kappaB activation, indicating that YC-1 may be developed as an anti-inflammatory neuroprotective agent.

Hyperbaric oxygen therapy might improve certain pathophysiological findings in autism

Autism is a neurodevelopmental disorder currently affecting as many as 1 out of 166 children in the United States. Numerous studies of autistic individuals have revealed evidence of cerebral hypoperfusion, neuroinflammation and gastrointestinal inflammation, immune dysregulation, oxidative stress, relative mitochondrial dysfunction, neurotransmitter abnormalities, impaired detoxification of toxins, dysbiosis, and impaired production of porphyrins. Many of these findings have been correlated with core autistic symptoms. For example, cerebral hypoperfusion in autistic children has been correlated with repetitive, self-stimulatory and stereotypical behaviors, and impairments in communication, sensory perception, and social interaction. Hyperbaric oxygen therapy (HBOT) might be able to improve each of these problems in autistic individuals. Specifically, HBOT has been used with clinical success in several cerebral hypoperfusion conditions and can compensate for decreased blood flow by increasing the oxygen content of plasma and body tissues. HBOT has been reported to possess strong anti-inflammatory properties and has been shown to improve immune function. There is evidence that oxidative stress can be reduced with HBOT through the upregulation of antioxidant enzymes. HBOT can also increase the function and production of mitochondria and improve neurotransmitter abnormalities. In addition, HBOT upregulates enzymes that can help with detoxification problems specifically found in autistic children. Dysbiosis is common in autistic children and HBOT can improve this. Impaired production of porphyrins in autistic children might affect the production of heme, and HBOT might help overcome the effects of this problem. Finally, HBOT has been shown to mobilize stem cells from the bone marrow to the systemic circulation. Recent studies in humans have shown that stem cells can enter the brain and form new neurons, astrocytes, and microglia. It is expected that amelioration of these underlying pathophysiological problems through the use of HBOT will lead to improvements in autistic symptoms. Several studies on the use of HBOT in autistic children are currently underway and early results are promising.

Minocycline modulates chemokine receptors but not interleukin-10 mRNA expression in hypoxic-ischemic neonatal rat brain

Hypoxic-ischemic (HI) brain injury in the perinatal period causes significant morbidity. Minocycline (MN) is a tetracycline derivative that has reduced brain injury in various animal models of neurodegeneration, including perinatal ischemia. To determine whether MN can modulate the expression of chemokine receptors and interleukin-10 (IL10) in a model of neonatal brain injury, we produced an HI insult to the right cerebral hemisphere (ipsilateral) of the 7-day-old rat (PD7) by right common carotid artery ligation and 2.25 hr of hypoxia in 8% oxygen. MN (45 mg/kg, i.p.) or vehicle (PBS) was injected twice: 2 days and immediately before the HI insult. At 0, 1, 3, and 24 hr and 14 days after HI, total RNA from the ipsilateral and contralateral (exposed to hypoxia only) hemispheres was extracted, reverse transcribed, and amplified with gene-specific primers using a semiquantitative RT-PCR for macrophage inflammatory protein-1alpha), interferon-inducible protein (IP-10), C-C chemokine receptor 5 (CCR5; MIP-1alpha receptor), C-X-C chemokine receptor 3 (CXCR3; IP-10 receptor), and IL10. We found that, in the ipsilateral hemisphere, a significant (P < 0.05) increase in MIP-1alpha, IP-10, CCR5, and CXCR3 mRNA levels was observed. MN treatment decreased mRNA levels for CCR5 and CXCR3. In contrast, the levels of antiinflammatory cytokine IL10 were markedly decreased as a result of HI insult. Treatment with MN, however, had no effect on IL10. We conclude that MN decreased proinflammatory chemokine receptor expression but had little or no influence on the expression of antiinflammatory cytokine IL10. These effects confirm the antiinflammatory effect of MN in neonatal HI brain injury.