Primary Mixed Cortical Cultures Research Articles

Abstract 3653: Akt3 Offers Stronger Protection than Akt1 Against Brain Injury by Differentially Promoting Mtor Protein Levels In Both In Vitro and In Vivo Stroke Models

Background and Objective: Akt is a serine-threonine kinase that plays critical role in promoting cell survival. Akt consists of three isoforms (Akt1, 2, 3), with Akt3 predominantly expressed in the brain. Although Akt pathway has been shown to mediate neuronal survival in cerebral ischemic injury, it is unclear how these Akt isoforms contribute to neuronal protection, and whether exogenous Akt can protect the brain against ischemic injury or not. In this study, we over-expressed Akt isoforms and its downstream signaling proteins such as FKHR and PRAS40 to investigate the role of the Akt pathway along with its potential relationship with the mTOR pathway in stroke. Methods: Sprauge Dawley rats (250∼280g) were used for all studies. A lentiviral vector consists of a CMV promoter driving IRES-eGFP was used to clone an active Akt 1 and 3 (cAKt 1 and 3), dominant-negative Akt (AktDN), active FKHR (AAA FKHR), and PRAS40. Lentivirus expressing these genes were added to primary mixed cortical cultures for two days prior to oxygen glucose deprivation (OGD) (MOI=1:5). Neuronal survival was measured by LDH release. Lentivirus were stereotaxically injected into the cortex, and rats were subjected to focal ischemia induced by distal MCA occlusion combined with bilateral CCA occlusion. Western blotting and immunofluorescent confocal microscopy were used to detect the expression of Akt isoforms and other proteins in both the Akt and mTOR pathways. Results: Western blotting analysis showed that both endogenous Akt1 and 3 proteins degraded as early as 1 h after stroke, while Akt2 protein remained unchanged until 24 h after stroke. In vitro studies showed that over-expression of both constitutively active cAkt1 and cAkt3 decreased LDH release after OGD, while AktDN worsened neuronal death ( P <0.05). In vivo over-expression of cAkt1, cAkt3 and PRAS40 reduced infarct size after stroke ( P <0.01). Gene transfer of cAkt1 and 3 also promoted protein levels of pAkt (phosphorylated Akt), pPRAS40, pFKHR, pPTEN, pmTOR, but not pGSK3β. Both in vitro and in vivo studies showed that over-expression of cAkt3 resulted in a stronger protection than cAkt1 ( P <0.05). Interestingly, cAkt3 gene transfer preserved both endogenous protein levels of Akt1 and 3, whereas cAkt1 gene transfer only preserved endogenous Akt1. Furthermore, cAkt3 promoted higher pmTOR levels than cAkt1. Treatment of rapamycin, an mTOR inhibitor, blocked the protective effects of both cAkt1 and cAkt3 both in vitro and in vivo. Conclusion: Lentiviral-mediated overexpression of cAkt3 confers stronger protection than that of cAkt1, by maintaining both endogenous Akt1 and Akt3, as well as promoting higher mTOR activities after stroke.

Esculetin inhibitsN-methyl-D-aspartate neurotoxicity via glutathione preservation in primary cortical cultures

Recently, loss of endogenous glutathione during N-methyl-D-aspartate (NMDA) receptor-mediated excitotoxic injury, and the resultant overproduction of reactive oxygen species (ROS) through an arachidonic acid cascade process in brain, have been implicated in neuronal damage in various neurodegenerative diseases. Glutathione depletion induced by L-buthionine-(S,R)-sulfoximine (BSO), an inhibitor of glutathione synthesis, is known to cause arachidonic acid-mediated excitotoxicity in primary mixed cortical cultures. The aim of this study was to investigate whether esculetin (6,7-dihydroxycoumarin), an inhibitor of lipoxygenase, protects against neurotoxicity induced by NMDA or BSO. We observed that neurotoxicity induced by NMDA but not kainic acid was attenuated by esculetin. At the same concentration (100 µM), esculetin attenuated the 45Ca2+ uptake elevation induced by NMDA. Free radical-mediated neuronal injury induced by H2O2 and xanthine/xanthine oxidase was concentration-dependently blocked by esculetin. Esculetin (1-30 µM) dose-dependently inhibited BSO-induced neuronal injury. In addition, arachidonate-induced neurotoxicity was completely blocked by esculetin. BSO also reduced glutathione peroxidase (GPx) activity, but did not change glutathione reductase (GR) activity 24 h after treatment. Esculetin dose-dependently increased GR activity, but did not alter GPx activity. These findings suggest that esculetin can contribute to the rescue of neuronal cells from NMDA neurotoxicity and that this protective effect occurs partly through NMDA receptor modulation and the sparing of glutathione depletion.

Use of high content image analysis to detect chemical-induced changes in synaptogenesis in vitro

Synaptogenesis is a critical process in nervous system development whereby neurons establish specialized contact sites which facilitate neurotransmission. Early life exposure to chemicals can result in persistent deficits in nervous system function at later life stages. These effects are often the result of abnormal development of synapses. Given the large number of chemicals in commerce with unknown potential to result in developmental neurotoxicity (DNT), the need exists for assays that can efficiently characterize and quantify chemical effects on brain development including synaptogenesis. The present study describes the application of automated high content image analysis (HCA) technology for examining synapse formation in rodent primary mixed cortical cultures. During the first 15 days in vitro (DIV) cortical neurons developed a network of polarized neurites (i.e., axons and dendrites) and expression of the pre-synaptic protein synapsin increased over time. The localization of punctate synapsin protein in close apposition to dendrites also increased, indicating an increase in synapse formation. Results demonstrated that: (1) punctate synapsin protein with a spatial orientation consistent with synaptic contact sites could be selectively measured, (2) the critical period for synaptogenesis in cortical cultures was consistent with previous reports, (3) chemicals known to inhibit synapse formation decreased automated measurements of synapse number and (4) parallel evaluation of neuron density, dendrite length and synapse number could distinguish frank cytotoxicity from specific effects on synapse formation or neuronal morphology. Collectively, these data demonstrate that automated image analysis can be used to efficiently assess synapse formation in primary cultures and that the resultant data is comparable to results obtained using lower throughput methods.

The individual and combined neuroprotective effects of propofol and ketamine on rat mixed cortical cultures exposed to oxygen-glucose deprivation-reperfusion injury

Propofol and ketamine are have been known to have neuroprotective effects. However, the effect of combined therapy with these 2 drugs is not well known with in vitro model. This study was conducted to determine whether combined administration of propofol and ketamine could have additive effects in protecting cortical neurons from the oxygen-glucose deprivation (ischemia) - reoxygenation (reperfusion) injury. Methods: Thirteen-day-old primary mixed cortical cultures were exposed to a 5-min combined oxygen-glucose deprivation (OGD, in vitro ischemia model), followed by 2 hr of reperfusion. Propofol (1, 10, 25, 50, 100μM) and ketamine (1, 2.5, 5, 10, 50μM) were added as alone or combination from the initiation of the OGD injury to the end of the reperfusion periods. The survived cells were counted using trypan-blue staining. The data were converted to the cell death rate. Statistical analysis was done by oneway-ANOVA tests and Bonferroni's test. P ＜ 0.05 was considered as statistically significant. Results: OGD-reperfusion demonstrated about a 70% cell death rate. 5−50μM of ketamine decreased the cell death rate compared with the no drug treated group (P ＜ 0.05). 10−100μM of propofol decreased the cell death rate compared with the no drug treated group (P ＜ 0.05). Combined administration of ketamine 2.5μM + propofol 50, 100μM, ketamine 10μM + propofol 100μM and propofol 1, 10μM + ketamine 5, 10μM decreased cell death rate compared with the same dosage of propofol or ketamine alone treated group (P ＜ 0.05). Conclusions: Propofol or ketamine demonstrated neuroprotective effects. And, combined administration ofpropofol and ketamine demonstrated additive neuroprotective effects against OGD-reperfusion injury.

The influence of propofol administration time on oxygen-glucose deprivation-reperfusion injury in rat mixed cortical cultures focused on N-Methyl-D-Aspartate (NMDA) receptors

Background: Propofol has been shown to have neuroprotective properties. However, the effect of propofol administration time on neuroprotection is not well understood. This study was conducted to determine if propofol administration time would influence its neuroprotective effects on an in vitro ischemia-reperfusion model, with special attention directed toward NMDA-induced calcium influx. Methods: Primary mixed cortical cultures of thirteen-day-old rats were exposed to 5 min of oxygen-glucose deprivation (OGD), followed by 2 hr of reperfusion. Propofol (1−100μM) was administered before OGD or administered from the time of OGD to the end of the reperfusion period. In the blank and full kill groups, no drug or NMDA 500μM treatment was given. The surviving cells were counted using trypan-blue staining, and cell death rate (CDR) was determined. To measure the maximum Ca2+ influx, 50μM propofol was pre-treated or co-treated with 100μM NMDA. In the control and NMDA 100μM groups, no drug or NMDA 100μM was given. A P ＜ 0.05 was considered statistically significant. Results: Cells pre-treated with propofol (10−100μM) or co-treated (50−100μM) at the time of OGD injury had a decreased CDR compared to the blank group. Cells pre-treated (2,713 nA) or co-treated (3,626 nA) with propofol had a decreased maximum Ca2+ influx compared to the 100μM NMDA group (4,075 nA). Cells pre-treated with propofol had a decreased maximum Ca2+ influx compared to co-treated rats. Conclusions: Propofol demonstrated neuroprotective effects at lower concentrations when administered prior to OGD injury. This may be partially attributable to the reduction of Ca2+ influx against NMDA receptor activation.

Differential effects of chemokines on oligodendrocyte precursor proliferation and myelin formation in vitro

Chemokines have recently been postulated to have important functions in the central nervous system (CNS) in addition to their principal role of directional migration of leukocytes. In particular, it has been shown that chemokines may play a role in the regulation of oligodendrocyte biology. Here, we have chosen to study the role of certain chemokines in regulating myelination. We have used the murine oligodendrocyte precursor-like cell line, Oli- neu, and primary mixed cortical cultures as experimental systems to assess their activities on oligodendrocyte precursor proliferation and developmental in vitro myelination. GRO-α, IL-8, SDF-1α and RANTES dose-dependently increased proliferation of this mouse A2B5 precursor-like cell line, while MCP-1 did not. Furthermore, the CXC chemokines GRO-α, IL-8 and SDF-1α stimulated myelin basic protein synthesis in a dose-dependent manner in primary myelinating cultures and enhanced myelin segment formation in this system, while the CC chemokines MCP-1 and RANTES did not. We also demonstrate that the receptor for SDF-1α, CXCR4, is expressed in mixed cortical cultures by PDGFαR positive oligodendrocyte precursors (OLPs) as well as by Oli- neu cells. SDF-1α induced proliferation in primary mixed cultures and the Oli- neu cell line was mediated through this receptor. We propose, therefore, that CXC chemokines and in particular SDF-1α regulates CNS myelination via their effects on cells of the oligodendrocyte lineage, specifically stimulation of OLP proliferation.

Sequential Involvement of Distinct Glutamate Receptors in Domoic Acid-Induced Neurotoxicity in Rat Mixed Cortical Cultures: Effect of Multiple Dose/Duration Paradigms, Chronological Age, and Repeated Exposure

The increasing occurrence of poisoning accidents in marine animals caused by the amnesic shellfish toxin, domoic acid (DOM), necessitates a better understanding of the factors contributing to DOM neurotoxicity. Here we evaluated the contribution and temporal involvement of NMDA, non-NMDA- and metabotropic-type glutamate receptors (GluRs) in DOM-induced neuronal death using rat primary mixed cortical cultures. Co-application of antagonists for AMPA/kainate- (NBQX) and NMDA-type GluRs (D-AP5) but not for metabotropic GluRs reduced DOM toxicity induced by either of three EC50 dose/duration exposure paradigms. Maximal protection offered by D-AP5 and NBQX either extended or not to the 30- to 60-min period after DOM exposure, respectively. Antagonists were ineffective if applied with a 2-h delay, indicating the presence of a critical time window for neuronal protection after DOM exposure. Early effects correlated with neuronal swelling was seen as early as 10 min post-DOM, which has been linked to non-NMDAR-mediated depolarization and release of endogenous glutamate. That DOM toxicity is dictated by iGluRs is supported by the finding that increased efficacy and potency of DOM with in vitro neuronal maturation are positively correlated with elevated protein levels of iGluR subunits, including NR1, GluR1, GluR2/3, GluR5, and GluR6/7. We determined the time course of DOM excitotoxicity. At >10 microM maximal neuronal death occurs within 2 h, while doses < or = 10 microM continue to produce death during the subsequent 22-h washout period, indicating a quicker progression of the neuronal death cascade with high DOM concentrations. Accordingly, NBQX applied 30 min post-DOM afforded better protection against low dose/prolonged duration (3 microM/24 h) than against high dose/brief duration exposure (50 microM/10 min). Interestingly, prior exposure to subthreshold DOM dose-dependently aggravated toxicity produced by a subsequent exposure to DOM. These findings provide greater insight into the complex properties underlying DOM toxicity, including the sequential involvement of multiple GluRs, greater potency with increasing neuronal maturation and protein levels of iGluRs, varying efficacy depending on dose, duration, and prior history of DOM exposure.

Mechanisms and Structural Determinants of HIV-1 Coat Protein, gp41-Induced Neurotoxicity

Of the individuals with human immunodeficiency virus type 1 (HIV-1) infection, 20-30% will develop the neurological complication of HIV-associated dementia (HAD). The mechanisms underlying HAD are unknown; however, indirect immunologically mediated mechanisms are theorized to play a role. Recently, the HIV-1 coat protein gp41 has been implicated as a major mediator of HAD through induction of neurocytokines and subsequent neuronal cell death. Using primary mixed cortical cultures from neuronal nitric oxide synthase (NOS) null (nNOS-/-) mice and immunological NOS null (iNOS-/-) mice, we establish iNOS-derived NO as a major mediator of gp41 neurotoxicity. Neurotoxicity elicited by gp41 is markedly attenuated in iNOS-/- cultures compared with wild-type and nNOS-/- cultures. The NOS inhibitor L-nitroarginine methyl ester is neuroprotective in wild-type and nNOS-/- cultures, confirming the role of iNOS-derived NO in gp41 neurotoxicity. Confirming that iNOS-/- cultures lack iNOS, gp41 did not induce iNOS in iNOS-/- cultures, but it markedly induced iNOS in wild-type and nNOS-/- cultures. We elucidate the region of gp41 that is critical for iNOS induction and neuronal cell death by monitoring iNOS induction with overlapping peptides spanning gp41. We show that the N-terminal region of gp41, which we designate as the neurotoxic domain, induces iNOS protein activity and iNOS-dependent neurotoxicity at picomolar concentrations in a manner similar to recombinant gp41 protein. Our experiments suggest that gp41 is eliciting the induction of iNOS through potential cell surface receptors or binding sites because the induction of iNOS is dose dependent and saturable and occurs at physiologically relevant concentrations. These data confirm that the induction of iNOS by gp41 and the production of NO are primary mediators of neuronal damage and identify a neurotoxic domain of gp41 that may play an important role in HAD.