Pre-conditioning induces the precocious differentiation of neonatal astrocytes to enhance their neuroprotective properties

Serum vascular endothelial growth factor is a potential biomarker for acute mountain sickness

Background: Acute mountain sickness (AMS) is the most common disease caused by hypobaric hypoxia (HH) in high-altitude (HA) associated with high mortality when progressing to high-altitude pulmonary edema (HAPE) and/or high-altitude cerebral edema (HACE). There is evidence for a role of pro- and anti-inflammatory cytokines in development of AMS, but biological pathways and molecular mechanisms underlying AMS remain elusive. We aimed to measure changes in blood cytokine levels and their possible association with the development of AMS.

Method: 15 healthy mountaineers were included into this prospective clinical trial. All participants underwent baseline normoxic testing with venous EDTA blood sampling at the Bangor University in United Kingdom (69 m). The participants started from Beni at an altitude of 869 m and trekked same routes in four groups the Dhaulagiri circuit in the Nepali Himalaya. Trekking a 14-day route, the mountaineers reached the final HA of 5,050 m at the Hidden Valley Base Camp (HVBC). Venous EDTA blood sampling was performed after active ascent to HA the following morning after arrival at 5,050 m (HVBC). A panel of 21 cytokines, chemokines and growth factors were assessed using Luminex system (IL-1β, IL-2, IL-4, IL-6, IL-8, IL-10, IL-12p40, IL-1ra, sIL-2Rα, IFN-γ, TNF-α, MCP-1, MIP-1α, MIP-1β, IP-10, G-CSF, GM-CSF, EGF, FGF-2, VEGF, and TGF-β1).

Results: There was a significant main effect for the gradual ascent from sea-level (SL) to HA on nearly all cytokines. Serum levels for TNF-α, sIL-2Rα, G-CSF, VEGF, EGF, TGF-β1, IL-8, MCP-1, MIP-1β, and IP-10 were significantly increased at HA compared to SL, whereas levels for IFN-γ and MIP-1α were significantly decreased. Serum VEGF was higher in AMS susceptible versus AMS resistant subjects (p < 0.027, main effect of AMS) and increased after ascent to HA in both AMS groups (p < 0.011, main effect of HA). Serum VEGF increased more from SL values in the AMS susceptible group than in the AMS resistant group (p < 0.049, interaction effect).

Conclusion: Cytokine concentrations are significantly altered in HA. Within short interval after ascent, cytokine concentrations in HH normalize to values at SL. VEGF is significantly increased in mountaineers suffering from AMS, indicating its potential role as a biomarker for AMS.

Intranasal Leukemia Inhibitory Factor Attenuates Gliosis and Axonal Injury and Improves Sensorimotor Function After a Mild Pediatric Traumatic Brain Injury

Leukemia inhibitory factor (LIF) is a neuroprotective cytokine that is essential for appropriate glial responses, remyelination, and preservation of neuronal conductance after injury. The intranasal route for delivery of therapeutics to the central nervous system is of particular interest given that it bypasses the blood-brain barrier and peripheral clearance systems. We explored the possibility that LIF might improve neurological function when administered intranasally during the acute phase in a pediatric model of mild traumatic brain injury (mTBI). We tested two doses of LIF and evaluated behavioral outcomes. Here, we show that acute 40-ng intranasal LIF treatment twice a day for 3 days attenuates astrogliosis and microgliosis, protects against axonal damage, significantly improves sensorimotor function, and is well tolerated without detrimental effects on growth. Altogether, our studies provide pre-clinical evidence for the use of acute intranasal LIF treatment as a viable therapeutic for pediatric cases of mTBIs.

Acute Mountain Sickness Following Incremental Trekking to High Altitude: Correlation With Plasma Vascular Endothelial Growth Factor Levels and the Possible Effects of Dexamethasone and Acclimatization Following Re-exposure

Purpose: The recognition and treatment of high-altitude illness (HAI) is increasingly important in global emergency medicine. High altitude related hypobaric hypoxia can lead to acute mountain sickness (AMS), which may relate to increased expression of vascular endothelial growth factor (VEGF), and subsequent blood-brain barrier (BBB) compromise. This study aimed to establish the relationship between AMS and changes in plasma VEGF levels during a high-altitude ascent. VEGF level changes with dexamethasone, a commonly used AMS medication, may provide additional insight into AMS.

Methods: Twelve healthy volunteers ascended Mt Fuji (3,700 m) and blood samples were obtained at distinct altitudes for VEGF analysis. Oxygen saturation (SPO2) measurements were also documented at the same time-point. Six out of the 12 study participants were prescribed dexamethasone for a second ascent performed 48 h later, and blood was again collected to establish VEGF levels.

Results: Four key VEGF observations could be made based on the data collected: (i) the baseline VEGF levels between the two ascents trended upwards; (ii) those deemed to have AMS in the first ascent had increased VEGF levels (23.8–30.3 pg/ml), which decreased otherwise (23.8–30.3 pg/ml); (iii) first ascent AMS participants had higher VEGF level variability for the second ascent, and similar to those not treated with dexamethasone; and (iv) for the second ascent dexamethasone participants had similar VEGF levels to non-AMS first ascent participants, and the variability was lower than for first ascent AMS and non-dexamethasone participants. SPO2 changes were unremarkable, other than reducing by around 5% irrespective of whether measurement was taken for the first or second ascent.

Conclusion: First ascent findings suggest a hallmark of AMS could be elevated VEGF levels. The lack of an exercise-induced VEGF level change strengthened the notion that elevated plasma VEGF was brain-derived, and related to AMS.

Dynamic expression of homeostatic ion channels in differentiated cortical astrocytes in vitro

The capacity of astrocytes to adapt their biochemical and functional features upon physiological and pathological stimuli is a fundamental property at the basis of their ability to regulate the homeostasis of the central nervous system (CNS). It is well known that in primary cultured astrocytes, the expression of plasma membrane ion channels and transporters involved in homeostatic tasks does not closely reflect the pattern observed in vivo. The individuation of culture conditions that promote the expression of the ion channel array found in vivo is crucial when aiming at investigating the mechanisms underlying their dynamics upon various physiological and pathological stimuli. A chemically defined medium containing growth factors and hormones (G5) was previously shown to induce the growth, differentiation, and maturation of primary cultured astrocytes. Here we report that under these culture conditions, rat cortical astrocytes undergo robust morphological changes acquiring a multi-branched phenotype, which develops gradually during the 2-week period of culturing. The shape changes were paralleled by variations in passive membrane properties and background conductance owing to the differential temporal development of inwardly rectifying chloride (Cl⁻) and potassium (K⁺) currents. Confocal and immunoblot analyses showed that morphologically differentiated astrocytes displayed a large increase in the expression of the inward rectifier Cl⁻ and K⁺ channels ClC-2 and Kir4.1, respectively, which are relevant ion channels in vivo. Finally, they exhibited a large diminution of the intermediate filaments glial fibrillary acidic protein (GFAP) and vimentin which are upregulated in reactive astrocytes in vivo. Taken together the data indicate that long-term culturing of cortical astrocytes in this chemical-defined medium promotes a quiescent functional phenotype. This culture model could aid to address the regulation of ion channel expression involved in CNS homeostasis in response to physiological and pathological challenges.

Involvement of monocarboxylate transporters in the cross-tolerance between epilepsy and cerebral infarction: A promising choice towards new treatments

Noxious stimuli applied at doses close to but below the threshold of cell injury induce adaptative responses that provide a defense against additional stress from the same (tolerance) or other (cross-tolerance) stimuli. Such endogenous modulators mediate the tolerance induced by numerous sublethal physical and chemical stress factors, of which epileptic preconditioning (EPC) and mild global ischemia are two most important mutually protective actions. However, the evidence for the complicated underlying mechanisms involved in this neuroprotective effects are lacking. During hypoxia/ischemia (H/I) and intense neural activity, lactate released from astrocytes is taken up by neurons and is stored for energy, a process mediated by monocarboxylate transporters (MCTs) in central nervous system (CNS). The present study investigated whether ischemic preconditioning (IPC) or EPC can provide protection to CNS against epilepsy or cerebral infarction respectively through regulation of MCTs expression in vivo. Rats were subjected to transitory middle cerebral artery occlusion (MCAO) or kainic acid (KA) preconditioning protocol respectively, followed by KA induced epilepsy or lethal MCAO as well as lactate transportation inhibitor injection, with a subsequent evaluation of behavior and infarct volume as well as MCTs expression in rats brain. IPC reduced the severity of status epilepticus induced by KA injection and EPC reduce infarct volume resulted from lethal MCAO. However, lactate transport blocking attenuated this neuroprotective effect and MCTs expression followed the same variation trends. These findings demonstrate that MCTs dependent mechanism is involved in the cross-tolerance between epilepsy and cerebral infarction, provide a potential basis for the clinical treatment of patients with brain diseases characterized by epilepsy and H/I.

Astrocytes Do Not Forfeit Their Neuroprotective Roles After Surviving Intense Oxidative Stress

In order to fulfill their evolutionary role as support cells, astrocytes have to tolerate intense oxidative stress under conditions of brain injury and disease. It is well known that astrocytes exposed to mild oxidative stress are preconditioned against subsequent stress exposure in dual hit models. However, it is unclear whether severe oxidative stress leads to stress tolerance, stress exacerbation, or no change in stress resistance in astrocytes. Furthermore, it is not known whether reactive astrocytes surviving intense oxidative stress can still support nearby neurons. The data in this Brief Report suggest that primary cortical astrocytes surviving high concentrations of the oxidative toxicant paraquat are completely resistant against subsequent oxidative challenges of the same intensity. Inhibitors of multiple endogenous defenses (e.g., glutathione, heme oxygenase 1, ERK1/2, Akt) failed to abolish or even reduce their stress resistance. Stress-reactive cortical astrocytes surviving intense oxidative stress still managed to protect primary cortical neurons against subsequent oxidative injuries in neuron/astrocyte co-cultures, even at concentrations of paraquat that otherwise led to more than 80% neuron loss. Although our previous work demonstrated a lack of stress tolerance in primary neurons exposed to dual paraquat hits, here we show that intensely stressed primary neurons can resist a second hit of hydrogen peroxide. These collective findings suggest that stress-reactive astroglia are not necessarily neurotoxic, and that severe oxidative stress does not invariably lead to stress exacerbation in either glia or neurons. Therefore, interference with the natural functions of stress-reactive astrocytes might have the unintended consequence of accelerating neurodegeneration.

Astrocytes and Circadian Rhythms: An Emerging Astrocyte-Neuron Synergy in the Timekeeping System

Animals have an internal timekeeping system to anticipate daily changes associated with the transition of day to night, which is deeply involved in the regulation and maintenance of behavioral and physiological processes. Prevailing knowledge associated the control of circadian clocks to a network of neurons in the central pacemaker, the suprachiasmatic nucleus (SCN), but astrocytes are rapidly emerging as key cellular contributors to the timekeeping system. However, how these glial cells impact the neuronal clock to modulate rhythmic neurobehavioral outputs just begin to be investigated. Astrocyte-neuron cocultures are an excellent exploratory method to further characterize the critical role of circadian communication between nerve cells, as well as to address the role of astrocytes as modulators and targets of neuronal rhythmic behaviors. Here, we describe a robust method to study astrocyte rhythmic interactions with neurons by coculturing them with primary neurons in physically separated layers. This simple coculture system provides hints on in vivo signaling processes. Moreover, it allows investigating cell-type specific effects separately as well as the identification of extracellular astrocytic or neuronal factors involved in rhythm generation in both cell types.

Prevention of neuronal apoptosis by astrocytes through thiol-mediated stress response modulation and accelerated recovery from proteotoxic stress

The development of drugs directly interfering with neurodegeneration has proven to be astonishingly difficult. Alternative therapeutic approaches could result from a better understanding of the supportive function of glial cells for stressed neurons. Therefore, here, we investigated the mechanisms involved in the endogenous neuro-defensive activity of astrocytes. A well-established model of postmitotic human dopaminergic neurons (LUHMES cells) was used in the absence ('LUHMES' mono-culture) or presence ('co-culture') of astrocytes. Inhibition of the LUHMES proteasome led to proteotoxic (protein aggregates; ATF-4 induction) and oxidative (GSH-depletion; NRF-2 induction) stress, followed by neuronal apoptosis. The presence of astrocytes attenuated the neuronal stress response, and drastically reduced neurodegeneration. A similar difference between LUHMES mono- and co-cultures was observed, when proteotoxic and oxidative stress was triggered indirectly by inhibitors of mitochondrial function (rotenone, MPP+). Human and murine astrocytes continuously released glutathione (GSH) into the medium, and transfer of glia-conditioned medium was sufficient to rescue LUHMES, unless it was depleted for GSH. Also, direct addition of GSH to LUHMES rescued the neurons from inhibition of the proteasome. Both astrocytes and GSH blunted the neuronal ATF-4 response and similarly upregulated NRF-1/NFE2L1, a transcription factor counter-regulating neuronal proteotoxic stress. Astrocyte co-culture also helped to recover the neurons' ability to degrade aggregated poly-ubiquitinated proteins. Overexpression of NRF-1 attenuated the toxicity of proteasome inhibition, while knockdown increased toxicity. Thus, astrocytic thiol supply increased neuronal resilience to various proteotoxic stressors by simultaneously attenuating cell death-related stress responses, and enhancing the recovery from proteotoxic stress through upregulation of NRF-1.

Dibutyryl Cyclic Adenosine Monophosphate Rescues the Neurons From Degeneration in Stab Wound and Excitotoxic Injury Models

Dibutyryl cyclic adenosine monophosphate (dBcAMP), a cell-permeable synthetic analog of cAMP, has been shown to induce astrogliosis in culture. However, the exact mechanism underlying how dBcAMP exerts its function in situ is not clear. The objective of this study was to examine the effects of dBcAMP on astrogliosis and survival of neurons in stab wound and kainic acid models of brain injury. Stab wound was done in cerebral cortex of BALB/c male mice. Kainic acid lesion was induced in hippocampus by injecting 1μl kainic acid into the lateral ventricle. Animals in both models of injury were divided into L+dBcAMP and L+PBS groups and treated with dBcAMP or PBS for 3, 5, and 7 days respectively. The brain sections were stained for Cresyl violet and Fluro jade-B to assess the degenerating neurons. Immunostaining for GFAP and Iba-1 was done for assessing the astrogliosis and microglial response respectively. Expression of GFAP and BDNF levels in the tissue were estimated by Western blotting and ELISA respectively. The results showed a gradual increase in the number of both astrocytes and microglia in both injuries with a significant increase in dBcAMP-treated groups. The number of degenerating neurons significantly decreased in dBcAMP treated groups. In addition, it was found that dBcAMP stimulated the expression of GFAP and BDNF in both stab wound and kainic acid injuries. Treatment with BDNF receptor inhibitor AZ-23, showed an increase in the degenerating neurons suggesting the role of BDNF in neuroprotection. This study indicates that dBcAMP protects neurons from degeneration by enhancing the production of BDNF and may be considered for use as therapeutic agent for treatment of brain injuries.

Ischemic Conditioning and neonatal hypoxic ischemic encephalopathy: a literature review

Hypoxic Ischemic Encephalopathy (HIE) is the result of severe anoxic brain injury during the neonatal period and causes life-long morbidity and premature mortality. Currently, therapeutic hypothermia immediately after birth is the standard of care for clinically relevant HIE. However, therapeutic hypothermia alone does not provide complete neuroprotection and there is an urgent need for adjunctive therapies. Ischemic conditioning is an adaptive process of endogenous protection in which small doses of sub-lethal ischemia can provide a protection against a lethal ischemic event. Remote Ischemic Post-conditioning (RIPC), a form of ischemic conditioning, is highly translatable for HIE diagnosed immediately after birth as the conditioned ischemic stimulus is applied at the limb after the lethal ischemic episode. A number of studies in neonatal rats have demonstrated that RIPC is effective at reducing injury in focal cerebral ischemia models and improves neurological outcomes. In this review, we focus on the available data on HIE and its current treatment, models in HIE studies, ischemic conditioning/RIPC and its mechanism. We discuss in particular the effect of RIPC on neonatal brain with HIE. We postulate that combining RIPC with standard therapeutic hypothermia can be an attractive therapeutic approach for HIE.

No influence of ischemic preconditioning on running economy

PURPOSE

Many of the potential performance-enhancing properties of ischemic preconditioning suggest that the oxygen cost for a given endurance exercise workload will be reduced, thereby improving the economy of locomotion. The aim of this study was to identify whether ischemic preconditioning improves exercise economy in recreational runners.

METHODS

A randomized sham-controlled crossover study was employed in which 18 adults (age 27 ± 7 years; BMI 24.6 ± 3 kg/m²) completed two, incremental submaximal (65-85% VO_2max) treadmill running protocols (3 × 5 min stages from 7.2-14.5 km/h) coupled with indirect calorimetry to assess running economy following ischemic preconditioning (3 × 5 min bilateral upper thigh ischemia) and sham control. Running economy was expressed as mlO₂/kg/km and as the energy in kilocalories required to cover 1 km of horizontal distance (kcal/kg/km).

RESULTS

Ischemic preconditioning did not influence steady-state heart rate, oxygen consumption, minute ventilation, respiratory exchange ratio, energy expenditure, and blood lactate. Likewise, running economy was similar (P = 0.647) between the sham (from 201.6 ± 17.7 to 204.0 ± 16.1 mlO₂/kg/km) and ischemic preconditioning trials (from 202.8 ± 16.2 to 203.1 ± 15.6 mlO₂/kg/km). There was no influence (P = 0.21) of ischemic preconditioning on running economy expressed as the caloric unit cost (from 0.96 ± 0.12 to 1.01 ± 0.11 kcal/kg/km) compared with sham (from 1.00 ± 0.10 to 1.00 ± 0.08 kcal/kg/km).

CONCLUSIONS

The properties of ischemic preconditioning thought to affect exercise performance at vigorous to severe exercise intensities, which generate more extensive physiological challenge, are ineffective at submaximal workloads and, therefore, do not change running economy.

Astrocytes Surviving Severe Stress Can Still Protect Neighboring Neurons from Proteotoxic Injury

Astrocytes are one of the major cell types to combat cellular stress and protect neighboring neurons from injury. In order to fulfill this important role, astrocytes must sense and respond to toxic stimuli, perhaps including stimuli that are severely stressful and kill some of the astrocytes. The present study demonstrates that primary astrocytes that managed to survive severe proteotoxic stress were protected against subsequent challenges. These findings suggest that the phenomenon of preconditioning or tolerance can be extended from mild to severe stress for this cell type. Astrocytic stress adaptation lasted at least 96 h, the longest interval tested. Heat shock protein 70 (Hsp70) was raised in stressed astrocytes, but inhibition of neither Hsp70 nor Hsp32 activity abolished their resistance against a second proteotoxic challenge. Only inhibition of glutathione synthesis abolished astrocytic stress adaptation, consistent with our previous report. Primary neurons were plated upon previously stressed astrocytes, and the cocultures were then exposed to another proteotoxic challenge. Severely stressed astrocytes were still able to protect neighboring neurons against this injury, and the protection was unexpectedly independent of glutathione synthesis. Stressed astrocytes were even able to protect neurons after simultaneous application of proteasome and Hsp70 inhibitors, which otherwise elicited synergistic, severe loss of neurons when applied together. Astrocyte-induced neuroprotection against proteotoxicity was not elicited with astrocyte-conditioned media, suggesting that physical cell-to-cell contacts may be essential. These findings suggest that astrocytes may adapt to severe stress so that they can continue to protect neighboring cell types from profound injury.

Re-exposure to the hypobaric hypoxic brain injury of high altitude: plasma S100B levels and the possible effect of acclimatisation on blood-brain barrier dysfunction

Hypobaric hypoxic brain injury results in elevated peripheral S100B levels which may relate to blood-brain barrier (BBB) dysfunction. A period of acclimatisation or dexamethasone prevents altitude-related illnesses and this may involve attenuation of BBB compromise. We hypothesised that both treatments would diminish the S100B response (a measure of BBB dysfunction) on re-ascent to the hypobaric hypoxia of high altitude, in comparison to an identical ascent completed 48 h earlier by the same group. Twelve healthy volunteers, six of which were prescribed dexamethasone, ascended Mt Fuji (summit 3700 m) and serial plasma S100B levels measured. The S100B values reduced from a baseline 0.183 µg/l (95 % CI 0.083-0.283) to 0.145 µg/l (95 % CI 0.088-0.202) at high altitude for the dexamethasone group (n = 6) and from 0.147 µg/l (95 % CI 0.022-0.272) to 0.133 µg/l (95 % CI 0.085-0.182) for the non-treated group (n = 6) [not statistically significant (p = 0.43 and p = 0.82) for the treated and non-treated groups respectively]. [These results contrasted with the statistically significant increase during the first ascent, S100B increasing from 0.108 µg/l (95 % CI 0.092-0.125) to 0.216 µg/l (95 % CI 0.165-0.267) at high altitude]. In conclusion, an increase in plasma S100B was not observed in the second ascent and this may relate to the effect of acclimatisation (or hypoxic pre-conditioning) on the BBB. An exercise stimulated elevation of plasma S100B levels was also not observed during the second ascent. The small sample size and wide confidence intervals, however, precludes any statistically significant conclusions and a larger study would be required to confirm these findings.

The "adaptive responses" of low concentrations of HBCD in L02 cells and the underlying molecular mechanisms

This study aimed to investigate the "adaptive responses" of hexabromocyclododecanes (HBCD) at environmentally relevant concentrations in human hepatocytes L02. L02 cells were pre-treated with low concentrations of HBCD (10(-13)-10(-11) M), followed by treatment with high concentrations of HBCD, α-hexachlorocyclohexane (α-HCH), polychlorinated biphenyls (PCBs), or polybrominated diphenyl ether-47 (BDE47). The results showed that the pre-treatment with low concentrations of HBCD induced "adaptive responses" to high concentrations of HBCD/α-HCH exposure (but not to PCBs and BDE47), as evidenced by attenuation of survival inhibition, reactive oxygen species (ROS) over-production, and deoxyribonucleic acid (DNA) damage induction. The "adaptive responses" induced by low concentrations of HBCD, which depended on the activation of the phosphatidylinositide 3-kinase/protein kinase B (PI3K/Akt) pathway, reduced the phosphorylation of adenosine monophosphate-activated kinase (AMPK) and enhanced the phosphorylation of p38 mitogen-activated protein kinases (p38 MAPK). The observations were further confirmed by the experiments with inhibitors. Moreover, the evaluation on the changes of metabolic enzymes revealed that HBCD and α-HCH shared a similar pattern of cytochrome P450 induction (CYP2B6), which was different from those of PCBs and BDE47 (CYP1A1 and CYP2B6). These results indicated that low concentrations of HBCD could induce "adaptive responses" to the subsequent treatment with high concentrations of HBCD/α-HCH in L02 cells, which was associated with the PI3K/Akt pathway, and AMPK and p38 MAPK signaling. The "adaptive responses" seemed to be dependent on the types of chemicals in terms of the metabolic patterns and chemical structures.

Leukemia Inhibitory Factor Haplodeficiency Desynchronizes Glial Reactivity and Exacerbates Damage and Functional Deficits after a Concussive Brain Injury

Reactions of both astrocytes and microglia to central nervous system injury can be beneficial or detrimental to recovery. To gain insights into the functional importance of gliosis, we developed a new model of adolescent closed-head injury (CHI) and interrogated the behavioral, physiological, and cellular outcomes after a concussive CHI in leukemia inhibitory factor (LIF) haplodeficient mice. These mice were chosen because LIF is important for astrocyte and microglial activation. Behaviorally, the LIF haplodeficient animals were equally impaired 4 h after the injury, but in the subsequent 2 weeks, the LIF haplodeficient mice acquired more severe motor and sensory deficits, compared with wild type mice. The prolonged accumulation of neurological impairment was accompanied by desynchronization of the gliotic response, increased cell death, axonal degeneration, diminished callosal compound action potential, and hypomyelination. Our results clearly show that LIF is an essential injury-induced cytokine that is required to prevent the propagation of secondary neurodegeneration.

A Cytotoxic, Co-operative Interaction Between Energy Deprivation and Glutamate Release From System xc- Mediates Aglycemic Neuronal Cell Death

The astrocyte cystine/glutamate antiporter (system xc(-)) contributes substantially to the excitotoxic neuronal cell death facilitated by glucose deprivation. The purpose of this study was to determine the mechanism by which this occurred. Using pure astrocyte cultures, as well as, mixed cortical cell cultures containing both neurons and astrocytes, we found that neither an enhancement in system xc(-) expression nor activity underlies the excitotoxic effects of aglycemia. In addition, using three separate bioassays, we demonstrate no change in the ability of glucose-deprived astrocytes--either cultured alone or with neurons--to remove glutamate from the extracellular space. Instead, we demonstrate that glucose-deprived cultures are 2 to 3 times more sensitive to the killing effects of glutamate or N-methyl-D-aspartate when compared with their glucose-containing controls. Hence, our results are consistent with the weak excitotoxic hypothesis such that a bioenergetic deficiency, which is measureable in our mixed but not astrocyte cultures, allows normally innocuous concentrations of glutamate to become excitotoxic. Adding to the burgeoning literature detailing the contribution of astrocytes to neuronal injury, we conclude that under our experimental paradigm, a cytotoxic, co-operative interaction between energy deprivation and glutamate release from astrocyte system xc(-) mediates aglycemic neuronal cell death.

Ganglioside accumulation in activated glia in the developing brain: comparison between WT and GalNAcT KO mice

Our previous studies have shown accumulation of GM2 ganglioside during ethanol-induced neurodegeneration in the developing brain, and GM2 elevation has also been reported in other brain injuries and neurodegenerative diseases. Using GM2/GD2 synthase KO mice lacking GM2/GD2 and downstream gangliosides, the current study explored the significance of GM2 elevation in WT mice. Immunohistochemical studies indicated that ethanol-induced acute neurodegeneration in postnatal day 7 (P7) WT mice was associated with GM2 accumulation in the late endosomes/lysosomes of both phagocytic microglia and increased glial fibrillary acidic protein (GFAP)-positive astrocytes. However, in KO mice, although ethanol induced robust neurodegeneration and accumulation of GD3 and GM3 in the late endosomes/lysosomes of phagocytic microglia, it did not increase the number of GFAP-positive astrocytes, and the accumulation of GD3/GM3 in astrocytes was minimal. Not only ethanol, but also DMSO, induced GM2 elevation in activated microglia and astrocytes along with neurodegeneration in P7 WT mice, while lipopolysaccharide, which did not induce significant neurodegeneration, caused GM2 accumulation mainly in lysosomes of activated astrocytes. Thus, GM2 elevation is associated with activation of microglia and astrocytes in the injured developing brain, and GM2, GD2, or other downstream gangliosides may regulate astroglial responses in ethanol-induced neurodegeneration.

Hypoxic postconditioning reduces microglial activation, astrocyte and caspase activity, and inflammatory markers after hypoxia-ischemia in the neonatal rat brain

BACKGROUND

Postconditioning (PostC) with mild hypoxia shortly after a neonatal hypoxic-ischemic (HI) brain injury can reduce brain damage, however, the mechanisms underlying this protection are not known. We hypothesize that hypoxic PostC reduces brain markers of glial activity, inflammation, and apoptosis following HI injury.

METHODS

Sprague Dawley rat pups were exposed to right common carotid artery occlusion and hypoxia (7% oxygen, 3 h) on postnatal day 7 and 24 h later, pups were exposed to hypoxic PostC (8% O2 for 1 h/day for 5 d) or kept at ambient conditions for the same duration. HI+N pups demonstrated ~10% loss in ipsilateral brain tissue which was rescued with HI+PostC. To investigate the cellular responses, markers of astrocytes, microglia, inflammation, and caspase 3 activity were examined using immunohistochemistry and enzyme-linked immunosorbent assay.

RESULTS

PostC reduced the area of astrocyte staining compared to HI+N. There was also a shift in microglial morphology toward a primed state in both PostC groups. Protein levels of interleukin-1β and caspase 3 were elevated in HI+N brains and reduced by PostC.

CONCLUSION

This is the first demonstration that PostC can reduce glial activity, inflammatory mediators, and cell death after a neonatal HI brain injury.

Intermittent hypoxia preconditioning-induced epileptic tolerance by upregulation of monocarboxylate transporter 4 expression in rat hippocampal astrocytes

Noxious stimuli applied at doses close to but below the threshold of cell injury induce adaptive responses that provide a defense against additional stress. Epileptic preconditioning protects neurons against status epilepticus and ischemia; however, it is not known if the converse is true. During hypoxia/ischemia (H/I), lactate released from astrocytes is taken up by neurons and is stored for energy, a process mediated by monocarboxylate transporter 4 (MCT4) in astroglia. The present study investigated whether H/I preconditioning can provide protection to neurons against epilepsy through upregulation of MCT4 expression in astrocytes in vitro and in vivo. An oxygen/glucose deprivation protocol was used in primary astrocyte cultures, while rats were subjected to an intermittent hypoxia preconditioning (IHP) paradigm followed by lithium-pilocarpine-induced epilepsy as well as lactate transportation inhibitor injection, with a subsequent evaluation of protein expression as well as behavior. H/I induced an upregulation of MCT4 expression, while an IHP time course of 5 days provided the greatest protection against epileptic seizures, which was most apparent by 3 days after IHP. However, lactate transport function disturbances can block the protective effect induced by IHP. These findings provide a potential basis for the clinical treatment of epilepsy.

Short term morphine exposure in vitro alters proliferation and differentiation of neural progenitor cells and promotes apoptosis via mu receptors

BACKGROUND

Chronic morphine treatment inhibits neural progenitor cell (NPC) progression and negatively effects hippocampal neurogenesis. However, the effect of acute opioid treatment on cell development and its influence on NPC differentiation and proliferation in vitro is unknown. We aim to investigate the effect of a single, short term exposure of morphine on the proliferation, differentiation and apoptosis of NPCs and the mechanism involved.

METHODS

Cell cultures from 14-day mouse embryos were exposed to different concentrations of morphine and its antagonist naloxone for 24 hours and proliferation, differentiation and apoptosis were studied. Proliferating cells were labeled with bromodeoxyuridine (BrdU) and cell fate was studied with immunocytochemistry.

RESULTS

Cells treated with morphine demonstrated decreased BrdU expression with increased morphine concentrations. Analysis of double-labeled cells showed a decrease in cells co-stained for BrdU with nestin and an increase in cells co-stained with BrdU and neuron-specific class III β-tubuline (TUJ1) in a dose dependent manner. Furthermore, a significant increase in caspase-3 activity was observed in the nestin- positive cells. Addition of naloxone to morphine-treated NPCs reversed the anti-proliferative and pro-apoptotic effects of morphine.

CONCLUSIONS

Short term morphine exposure induced inhibition of NPC proliferation and increased active caspase-3 expression in a dose dependent manner. Morphine induces neuronal and glial differentiation and decreases the expression of nestin- positive cells. These effects were reversed with the addition of the opioid antagonist naloxone. Our results demonstrate the effects of short term morphine administration on the proliferation and differentiation of NPCs and imply a mu-receptor mechanism in the regulation of NPC survival.

Hypoxic preconditioning differentially affects GABAergic and glutamatergic neuronal cells in the injured cerebellum of the neonatal rat

In this study we examined cerebellar alterations in a neonatal rat model of hypoxic-ischemic brain injury with or without hypoxic preconditioning (Pc). Between postnatal days 7 and 15, the cerebellum is still undergoing intense cellular proliferation, differentiation and migration, dendritogenesis and synaptogenesis. The expression of glutamate decarboxylase 1 (GAD67) and the differentiation factor NeuroD1 were examined as markers of Purkinje and granule cells, respectively. We applied quantitative immunohistochemistry to sagittal cerebellar slices, and Western blot analysis of whole cerebella obtained from control (C) rats and rats submitted to Pc, hypoxia-ischemia (L) and a combination of both treatments (PcL). We found that either hypoxia-ischemia or Pc perturbed the granule cells in the posterior lobes, affecting their migration and final placement in the internal granular layer. These effects were partially attenuated when the Pc was delivered prior to the hypoxia-ischemia. Interestingly, whole nuclear NeuroD1 levels in Pc animals were comparable to those in the C rats. However, a subset of Purkinje cells that were severely affected by the hypoxic-ischemic insult—showing signs of neuronal distress at the levels of the nucleus, cytoplasm and dendritic arborization—were not protected by Pc. A monoclonal antibody specific for GAD67 revealed a three-band pattern in cytoplasmic extracts from whole P15 cerebella. A ∼110 kDa band, interpreted as a potential homodimer of a truncated form of GAD67, was reduced in Pc and L groups while its levels were close to the control animals in PcL rats. Additionally we demonstrated differential glial responses depending on the treatment, including astrogliosis in hypoxiated cerebella and a selective effect of hypoxia-ischemia on the vimentin-immunolabeled intermediate filaments of the Bergmann glia. Thus, while both glutamatergic and GABAergic cerebellar neurons are compromised by the hypoxic-ischemic insult, the former are protected by a preconditioning hypoxia while the latter are not.

Hypoxic preconditioning protection is eliminated in HIF-1α knockout mice subjected to neonatal hypoxia-ischemia

BACKGROUND

Hypoxic preconditioning (HPc) protects the neonatal brain in the setting of hypoxia-ischemia (HI). The mechanisms of protection may depend on activation of hypoxia-inducible factor (HIF-1α). This study sought to clarify the role of HIF-1α after HPc and HI.

METHODS

To induce HPc, HIF-1α knockout and wild-type (WT) mice were exposed to hypoxia at postnatal day 6. At day 7, the mice underwent HI. Brain injury was determined by histology. HIF-1α, downstream targets, and markers of cell death were measured by western blot.

RESULTS

HPc protected the WT brain compared with WT without HPc, but did not protect the HIF-1α knockout brain. In WT, HIF-1α increased after hypoxia and after HI, but not with HPc. The HIF-1α knockout showed no change in HIF-1α after hypoxia, HI, or HPc/HI. After HI, spectrin 145/150 was higher in HIF-1α knockout, but after HPc/HI, it was higher in WT. Lysosome-associated membrane protein was higher in WT early after HI, but not later. After HPc/HI, lysosome-associated membrane protein was higher in HIF-1α knockout.

CONCLUSION

These results indicate that HIF-1α is necessary for HPc protection in the neonatal brain and may affect cell death after HI. Different death and repair mechanisms depend on the timing of HPc.

Comparison of primary and secondary rat astrocyte cultures regarding glucose and glutathione metabolism and the accumulation of iron oxide nanoparticles

Astrocyte-rich primary cultures (APCs) are frequently used as a model system for the investigation of properties of brain astrocytes. However, as APCs contain a substantial number of microglial and oligodendroglial cells, biochemical parameters determined for such cultures may at least in part reflect also the presence of the contaminating cell types. To lower the potential contributions of microglial and oligodendroglial cells on properties of the astrocytes in APCs we prepared rat astrocyte-rich secondary cultures (ASCs) by subculturing of APCs and compared these ASCs with APCs regarding basal metabolic parameters, specific enzyme activities and the accumulation of iron oxide nanoparticles. Immunocytochemical characterization revealed that ASCs contained only minute amounts of microglial and oligodendroglial cells. ASCs and APCs did not significantly differ in their specific glucose consumption and lactate production rates, in their specific iron and glutathione contents, in their specific activities of various enzymes involved in glucose and glutathione metabolism nor in their accumulation of iron oxide nanoparticles. Thus, the absence or presence of some contaminating microglial and oligodendroglial cells appears not to substantially modulate the investigated metabolic parameters of astrocyte cultures.

Astrocytes and glutamate homoeostasis in Alzheimer's disease: a decrease in glutamine synthetase, but not in glutamate transporter-1, in the prefrontal cortex

Astrocytes control tissue equilibrium and hence define the homoeostasis and function of the CNS (central nervous system). Being principal homoeostatic cells, astroglia are fundamental for various forms of neuropathology, including AD (Alzheimer's disease). AD is a progressive neurodegenerative disorder characterized by the loss of cognitive functions due to specific lesions in mnesic-associated regions, including the mPFC (medial prefrontal cortex). Here, we analyzed the expression of GS (glutamine synthetase) and GLT-1 (glutamate transporter-1) in astrocytes in the mPFC during the progression of AD in a triple-transgenic mouse model (3xTg-AD). GS is an astrocyte-specific enzyme, responsible for the intracellular conversion of glutamate into glutamine, whereas the removal of glutamate from the extracellular space is accomplished mainly by astroglia-specific GLT-1. We found a significant decrease in the numerical density (Nv, cells/mm³) of GS-positive astrocytes from early to middle ages (1–9 months; at the age of 1 month by 17%, 6 months by 27% and 9 months by 27% when compared with control animals) in parallel with a reduced expression of GS (determined by Western blots), which started at the age of 6 months and was sustained up to 12 months of age. We did not, however, find any changes in the expression of GLT-1, which implies an intact glutamate uptake mechanism. Our results indicate that the decrease in GS expression may underlie a gradual decline in the vital astrocyte-dependent glutamate–glutamine conversion pathway, which in turn may compromise glutamate homoeostasis, leading towards failures in synaptic connectivity with deficient cognition and memory.

Gold- and silver nanoparticles affect the growth characteristics of human embryonic neural precursor cells

Rapid development of nanotechnologies and their applications in clinical research have raised concerns about the adverse effects of nanoparticles (NPs) on human health and environment. NPs can be directly taken up by organs exposed, but also translocated to secondary organs, such as the central nervous system (CNS) after systemic- or subcutaneous administration, or via the olfactory system. The CNS is particularly vulnerable during development and recent reports describe transport of NPs across the placenta and even into brain tissue using in vitro and in vivo experimental systems. Here, we investigated whether well-characterized commercial 20 and 80 nm Au- and AgNPs have an effect on human embryonic neural precursor cell (HNPC) growth. After two weeks of NP exposure, uptake of NPs, morphological features and the amount of viable and dead cells, proliferative cells (Ki67 immunostaining) and apoptotic cells (TUNEL assay), respectively, were studied. We demonstrate uptake of both 20 and 80 nm Au- and AgNPs respectively, by HNPCs during proliferation. A significant effect on the sphere size- and morphology was found for all cultures exposed to Au- and AgNPs. AgNPs of both sizes caused a significant increase in numbers of proliferating and apoptotic HNPCs. In contrast, only the highest dose of 20 nm AuNPs significantly affected proliferation, whereas no effect was seen on apoptotic cell death. Our data demonstrates that both Au- and AgNPs interfere with the growth profile of HNPCs, indicating the need of further detailed studies on the adverse effects of NPs on the developing CNS.

Primary cultures of astrocytes: their value in understanding astrocytes in health and disease

During the past few decades of astrocyte research it has become increasingly clear that astrocytes have taken a central position in all central nervous system activities. Much of our new understanding of astrocytes has been derived from studies conducted with primary cultures of astrocytes. Such cultures have been an invaluable tool for studying roles of astrocytes in physiological and pathological states. Many central astrocytic functions in metabolism, amino acid neurotransmission and calcium signaling were discovered using this tissue culture preparation and most of these observations were subsequently found in vivo. Nevertheless, primary cultures of astrocytes are an in vitro model that does not fully mimic the complex events occurring in vivo. Here we present an overview of the numerous contributions generated by the use of primary astrocyte cultures to uncover the diverse functions of astrocytes. Many of these discoveries would not have been possible to achieve without the use of astrocyte cultures. Additionally, we address and discuss the concerns that have been raised regarding the use of primary cultures of astrocytes as an experimental model system.