Over-activation Of Astrocytes Research Articles

Fingolimod (FTY720) enhances hippocampal synaptic plasticity and memory in Huntington's disease by preventing p75NTR up-regulation and astrocyte-mediated inflammation.

Huntington's disease (HD) is a hereditary neurodegenerative disorder characterized by motor and cognitive impairments, involving striatum, cortex and hippocampus. Synaptic and memory dysfunction in HD mouse models have been related to low levels of brain-derived neurotrophic factor (BDNF) and imbalance between TrkB and p75(NTR) receptors. In addition, astrocyte over-activation has also been suggested to contribute to HD cognitive deficits. Fingolimod (FTY720), a modulator of sphingosine-1 phosphate (S1P) receptors, has been shown to increase BDNF levels and to reduce astrogliosis, proving its potential to regulate trophic support and inflammatory response. In this view, we have investigated whether FTY720 improves synaptic plasticity and memory in the R6/1 mouse model of HD, through regulation of BDNF signaling and astroglial reactivity. Chronic administration of FTY720 from pre-symptomatic stages ameliorated long-term memory deficits and dendritic spine loss in CA1 hippocampal neurons from R6/1 mice. Furthermore, FTY720 delivery prevented astrogliosis and over-activation of nuclear factor kappa beta (NF-κB) signaling in the R6/1 hippocampus, reducing tumor necrosis factor alpha (TNFα) and induced nitric oxide synthase (iNOS) levels. TNFα decrease correlated with the normalization of p75(NTR) expression in the hippocampus of FTY720-treated R6/1 mice, thus preventing p75(NTR)/TrkB imbalance. In addition, FTY720 increased cAMP levels and promoted phosphorylation of CREB and RhoA in the hippocampus of R6/1 mice, further supporting its role in the enhancement of synaptic plasticity. Our findings provide new insights into the mechanism of action of FTY720 and reveal a novel therapeutic strategy to treat memory deficits in HD.

Paeoniflorin, a Monoterpene Glycoside, Protects the Brain from Cerebral Ischemic Injury via Inhibition of Apoptosis.

Paeoniflorin (PF) is a principal bioactive component, which exhibits many pharmacological effects, including protection against ischemic injury. This paper aimed to investigate the protective effect of PF both in vivo and in vitro. Middle cerebral artery occlusion (MCAO) was performed on male Sprague-Dawley (SD) rat for 2 h, and different doses of PF or vehicle were administered 2 h after reperfusion. Rats were sacrificed after 7 days treatment of PF/vehicle. PF treatment for 7 days ameliorated MCAO-induced neurological deficit and decreased the infarct area. Further study demonstrated that PF inhibited the over-activation of astrocytes and apoptosis of neurons, and PF promoted up-regulation of neuronal specific marker neuron-specific nuclear (NeuN) and microtubule-associated protein 2 (MAP-2) in brain. Moreover, NMDA-induced neuron apoptosis was employed. The in vitro study revealed that PF treatment protected against NMDA-induced cell apoptosis and neuronal loss via up-regulation of neuronal specific marker NeuN, MAP-2 and Bcl-2 and the down-regulation Bax. Taken together, the present study demonstrates that PF produces its protective effect by inhibiting the over-activation of astrocytes, apoptosis of neurons and up-regulation of neuronal specific marker NeuN, MAP-2, and B-cell lymphoma-2 (Bcl-2), and down-regulation Bax. Our study reveals that PF may be a potential neuroprotective agent for stroke and can provide basic data for clinical use.

Hydrogen sulfide functions as a neuromodulator to regulate striatal neurotransmission in a mouse model of Parkinson's disease

Hydrogen sulfide (H2S), a novel endogenous gasotransmitter, has been considered a neuromodulator to enhance hippocampal long-term potentiation and exerts neuroprotective effects against neurotoxin-induced neurodegeneration in rodent models of Parkinson's disease (PD). However, whether H2S can function as a neuromodulator to regulate the levels of nigrostriatal neurotransmitters and then impact the vulnerability of dopaminergic (DA) neurons in response to neurotoxins remains unknown. For this study, we prepared a 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine plus probenecid (MPTP/p)-induced mouse subacute model of PD to explore the modulatory effect of H2S on monoamine and amino acid neurotransmitters in the striatum of MPTP-treated mice. This study shows that NaHS (an H2S donor, 5.6 mg/kg/day, i.p.) administration improves the survival rate and significantly ameliorates the weight loss of MPTP-treated mice. NaHS treatment attenuated MPTP-induced neuronal damage, restored the diminution of DA neurons, and suppressed the overactivation of astrocytes in the mouse striatum. Additionally, NaHS upregulated striatal serotonin levels and modulated the balance of excitatory glutamate and the inhibitory γ-aminobutyric acid system in response to MPTP challenge. The current study indicates that H2S may function as an effective neuromodulator to regulate striatal neurotransmission and provides insight into the potential of H2S for PD therapy.

Neuroprotective effects of Gualou Guizhi decoction in vivo and in vitro

Ethnopharmacological relevanceGualou Guizhi decoction (GLGZD) prescribed in traditional Chinese medicine has been reported to have protective effects on ischemic stroke. The present study is to investigate the therapeutic effect of GLGZD on ischemic stroke and explore its mode of action. Materials and methodsGLGZD was studied on transient middle cerebral artery occlusion (MCAO) followed by reperfusion in vivo, as well as on hippocampal primary neuron cultures in vitro. ResultsIn vivo, it was shown that GLGZD treatment for 7 days could ameliorate transient middle cerebral artery occlusion (MCAO)-induced neurological deficit, histopathology changes and decrease infarct area. Further study demonstrated that GLGZD inhibited over-activation of astrocytes and apoptosis of neurons and GLGZD promoted up-regulation of neuronal specific marker neuron-specific nuclear (NeuN) and microtubule-associated protein 2 (MAP-2) in brain. Moreover, the in vitro study revealed that GLGZD treatment protected against NMDA-induced cell apoptosis and neuronal loss, and promoted up-regulation of neuronal specific marker NeuN. ConclusionsTaken together, the present study demonstrates that GLGZD produces a protection in the MCAO model rats via inhibiting over-activation of astrocytes, apoptosis of neurons and up-regulation of neuronal specific marker NeuN and MAP-2. Our study reveals that GLGZD might be a potential neuroprotective agent for stroke and can provide basic data for clinical use.

Uncoupling protein 2 deficiency aggravates astrocytic endoplasmic reticulum stress and nod-like receptor protein 3 inflammasome activation

Astrocytes play crucial roles in determining the susceptibility to oxidative stress in the brain, and uncoupling protein 2 (UCP2) has been demonstrated to regulate reactive oxygen species (ROS) production. However, it is unclear whether UCP2 is expressed in astrocytes, and whether it participates in the regulation of astrocytic functions. Here we show that UCP2 knockout exacerbated dopaminergic neuron loss in a murine model of 1,2,3,6-methyl-phenyl-tetrahydropyridine (MPTP)–induced Parkinson's disease (PD), accompanied by overactivation of astrocytes. We further detected expression of UCP2 in primary cultures of mesencephalic astrocytes. UCP2 knockout increased intracellular ROS production and induced oxidative stress in response to l-methyl-4-phenylpyridinium (MPP+) treatment. Subsequently, UCP2 deficiency exacerbated endoplasmic reticulum (ER) stress, as evidenced by the upregulations of C/EBP homologous protein (CHOP), cleavage of caspase-12, and aggravated neuroinflammation via the activation of nod-like receptor protein 3 (NLRP3) inflammasomes in astrocytes. Collectively, our study indicates that UCP2 expressed in astrocytes modulates ER stress and neuroinflammation, and is crucial for the survival of dopaminergic neuron in the pathogenesis of PD. These findings gives us insights into the potential of UCP2 as a novel therapeutic avenue for PD treatment.

P19 S-propargyl-cysteine (SPRC) attenuates cognitive impairment in APP/PS1 mice and protects neurons against glial overactivation induced by Aβ1−40 via modulation of cystathionine-β-synthase

Background Hydrogen sulfide (H2S) plays an important role in central nervous system (CNS). In CNS, H2S production is mainly related to cystathionine β-synthetase (CBS), which are enriched in astrocytes. Many reports have documented that CBS activity and hydrogen sulfide is significantly decreased in the brain of Alzheimer’s disease patients. Thus therapeutic strategies based on modulating CBS might be promising. In this study, we investigated possible neuroprotective effect and mechanisms of SPRC in astrocytes and APP/PS1 mice. Methods Double transgenic mice expressing mutant genes for amyloid precursor protein and presenilin1 (APP/PS1) were tested in Morris water maze (MWM) and novel object recognition (NOR) behavioral studies for cognitive evaluations. Forty-nine 12-month-old mice were divided into five groups: wild-type group, APP/PS1 group, APP/PS1 + 100 mg/kg or 200 mg/kg SPRC group, APP/PS1+ Donepezil group. Radioactive sulfur-35-labeled SPRC were administered by gavage to relatively quantify drug distributions in various brain areas. Immunocytochemistry (IHC) staining, Congo red stain and ELISA were performed for evaluating astrogliosis, Amyloid-β (Aβ) load and ratio of Aβ1−42/Aβ1−40. Transmission electron microscope (TEM) was applied to observe ultrastructure change of hippocampus. CBS enzymatic activity was determined by colorimetry and protein expressions were evaluated by Western blot assay. For in vitro study, purified primary astrocytes were stimulated with Aβ1−40 or were pretreated with SPRC before Aβ1−40 treatment. SRB assay, Griess reaction and enzyme linked immunosorbent assay (ELISA) were applied to measure cell viability, nitrites production and proinflammatory cytokines, respectively. CBS-small interfering RNA (CBS siRNA) and a CBS inhibitor amino-oxyacetic acid (AOAA) were applied to investigate possible role of CBS in neuroprotective actions of SPRC in inhibiting overactivated astrocytes. In addition, a glia/neuron co-culture system was used to investigate neuron’s behavior in the presence of differently pretreated astrocytes. Results Sulfur-35-labeled SPRC could enter blood–brain barrier and widely distributed in different brain areas with a relative high concentration in hippocampus and striatum. Compared to APP/PS1 group, mice treated with 100 mg/kg and 200 mg/kg SPRC showed improved cognitive performances both in MWM and NOR tests. Observations by TEM and IHC showed that less dark neurons, decreased lipofuscin deposition and astrogliosis were found in the hippocampus. Neuroinflammation was alleviated as phosphorylations of NF-B and MAPK pathways were suppressed in SPRC treated groups. SPRC could reduce ratio of Aβ1−42/Aβ1−40 of insoluble fraction but not that of soluble fraction. SPRC could also increased activity and expression of CBS, elevate concentration of hydrogen sulfide in the plasma and brain tissue of mice, suppress TNF-α and nitrite production of astrocytes activated by Aβ1−40 treatment. Co-culture assay showed that pretreatment of astrocytes with SPRC could significantly increase neuronal viability and inhibit synaptophysin degradation in neurons. These neuroprotective effects could be abolished by CBS siRNA or AOAA. Conclusions Our study demonstrated that SPRC could ameliorate cognitive performances of APP/PS1 mice, suppress overactivation of astrocytes and alleviate neuroinflammation at least partially via CBS/H2S pathway in the CNS. Therefore, we concluded that SPRC could serve as a CBS modulator in treating AD and might be a drug candidate in the future.

Neuroprotective Peptide Humanin Inhibits Inflammatory Response in Astrocytes Induced by Lipopolysaccharide

Humanin (HN) has been proved to be an extensive neuroprotective peptide against AD-related and unrelated insults, but little is know about the effect of HN in inflammation response. Current studies indicated the receptors of HN have a close relationship with immune system, which led us to hypothesize HN might have a role in inflammatory response. In this study, we used lipopolysaccharide (LPS) to induce astrocyte inflammation response. This model in vitro allowed us to study the effect of HN on the pure response of astrocyte without the exogenous influence between cells in vivo. Our results showed that 1.0μg/ml LPS induced a significant activation of astrocyte, shown as the marked increase in the glial fibrillary acidic protein (GFAP) expression, the cell viability and the number of 5-bromo-2'-deoxyuridine (BrdU)-positive living cells. Pretreatment with HN (5, 10, 20μM) led to a significant inhibition in astrocyte overactivation in a concentration dependent manner. We also found pretreatment with HN decreased the level of proinflammatory cytokines, interleukin (IL)-6, IL-1β and tumor necrosis factor α (TNFα) induced by LPS. Furthermore, we noticed HN couldn't completely reverse the above inflammatory injury. Our findings imply that HN partly antagonizes inflammation injury induced by LPS and the protective effect of HN on astrocyte is concentration-dependent.

Paeoniflorin Protects against Ischemia-Induced Brain Damages in Rats via Inhibiting MAPKs/NF-κB-Mediated Inflammatory Responses

Paeoniflorin (PF), the principal component of Paeoniae Radix prescribed in traditional Chinese medicine, has been reported to exhibit many pharmacological effects including protection against ischemic injury. However, the mechanisms underlying the protective effects of PF on cerebral ischemia are still under investigation. The present study showed that PF treatment for 14 days could significantly inhibit transient middle cerebral artery occlusion (MCAO)-induced over-activation of astrocytes and microglia, and prevented up-regulations of pro-inflamamtory mediators (TNFα, IL-1β, iNOS, COX2 and 5-LOX) in plasma and brain. Further study demonstrated that chronic treatment with PF suppressed the activations of JNK and p38 MAPK, but enhanced ERK activation. And PF could reverse ischemia-induced activation of NF-κB signaling pathway. Moreover, our in vitro study revealed that PF treatment protected against TNFα-induced cell apoptosis and neuronal loss. Taken together, the present study demonstrates that PF produces a delayed protection in the ischemia-injured rats via inhibiting MAPKs/NF-κB mediated peripheral and cerebral inflammatory response. Our study reveals that PF might be a potential neuroprotective agent for stroke.

Molecular basis of cognitive improvement of pioglitazone and rosiglitazone

Brain glucose uptake and metabolism are impaired in Alzheimer's disease (AD), and this impairment appears to contribute to the pathogenesis of the disease. Insulin sensitizers, which are widely used for increasing insulin sensitivity and glucose utilization in diabetes, have shown some improvement in memory in AD mouse models and in AD clinical trials in AD patients. The present study was aimed to understand the possible molecular mechanisms by which two of these insulin sensitizers, pioglitazone and rosiglitazone, might cause the improvement. Ten-month-old female 3xTg-AD mice and the wild type controls were orally administered with pioglitazone (20 mg/kg body weight/day) and rosiglitazone (5 mg /kg body weight/day) for four months. Spatial memory was tested by using Morris water maze before and after the treatments. At the end of treatments and behavioral tests, the mice were sacrificed and the brain tissue was analyzed both by Western blots and immunohistochemistry for the insulin-PI3K-AKT signaling pathway, phosphorylation and deposition of tau, Aβ accumulation, and glial activation. We observed that four-month treatments of 3xTg-AD mice with pioglitazone or rosiglitazone attenuated the deficits in spatial reference memory of the 3xTg-AD mice. These drug treatments also resulted in activation of protein kinase B (AKT) and inhibition of GSK-3β in the brain, suggesting activation of the insulin-PI3K-AKT signaling pathway. At the same time, hyperphosphorylation of tau at several sites, including Ser202, Thr217, Thr231, Ser404 and Ser422, Aβ accumulation, and astrocyte over-activation were found to be attenuated in the drug-treated mice. Our results suggest that pioglitazone and rosiglitazone probably improve the memory deficits through several pathways, including elevation of insulin-PI3K-AKT signaling and attenuation of tau hyperphosphorylation, Aβ accumulation, and inhibition of astrocyte over-activation. These findings suggest the potential usefulness of glitazones in the treatment for AD.