Striatal Cell Death Research Articles

Reduced mitochondrial complex II activity enhances cell death via intracellular reactive oxygen species in STHdhQ111 striatal neurons with mutant huntingtin

Huntington's disease (HD) is an inherited neurodegenerative disorder caused by CAG repeat expansion in the huntingtin (HTT) gene. Here, we examined the effects of antioxidants on 3-nitropropionic acid (3-NP; a mitochondrial complex II inhibitor)-induced mitochondrial dysfunction and cell death in STHdhQ111 striatal cells carrying homozygous mutant HTT with extended CAG repeats compared with those in STHdhQ7 striatal cells. 3-NP reduced cell viability and increased cell death both in STHdhQ111 and STHdhQ7, and the cytotoxicity was markedly attenuated by antioxidants (N-acetyl-l-cysteine and edaravone). Furthermore, 3-NP increased intracellular reactive oxygen species (ROS) production in both cell lines, and this increase was inhibited by antioxidants. Mitochondrial ROS was also increased by 3-NP in STHdhQ111 but not in STHdhQ7, and this increase was significantly inhibited by edaravone. Mitochondrial membrane potential (MMP) was lower in STHdhQ111 than that in STHdhQ7, and antioxidants prevented 3-NP-induced MMP decrease in STHdhQ111.3-NP enhanced oligomerization of dynamin-related protein 1 (Drp1), a protein that promotes mitochondrial fission in both cells, and both antioxidants prevented the increase in oligomerization. These results suggest that reduced mitochondrial complex II activity enhances cell death via intracellular ROS production and Drp1 oligomerization in striatal cells with mutant HTT and antioxidants may reduce striatal cell death.

Dysfunction of X-linked inhibitor of apoptosis protein (XIAP) triggers neuropathological processes via altered p53 activity in Huntington's disease.

Mitochondrial dysfunction is associated with neuronal damage in Huntington's disease (HD), but the precise mechanism of mitochondria-dependent pathogenesis is not understood yet. Herein, we found that colocalization of XIAP and p53 was prominent in the cytosolic compartments of normal subjects but reduced in HD patients and HD transgenic animal models. Overexpression of mutant Huntingtin (mHTT) reduced XIAP levels and elevated mitochondrial localization of p53 in striatal cells in vitro and in vivo. Interestingly, XIAP interacted directly with the C-terminal domain of p53 and decreased its stability via autophagy. Overexpression of XIAP prevented mitochondrially targeted-p53 (Mito-p53)-induced mitochondrial oxidative stress and striatal cell death, whereas, knockdown of XIAP exacerbated Mito-p53-induced neuronal damage in vitro. In vivo transduction of AAV-shRNA XIAP in the dorsal striatum induced rapid onset of disease and reduced the lifespan of HD transgenic (N171-82Q) mice compared to WT littermate mice. XIAP dysfunction led to ultrastructural changes of the mitochondrial cristae and nucleus morphology in striatal cells. Knockdown of XIAP exacerbated neuropathology and motor dysfunctions in N171-82Q mice. In contrast, XIAP overexpression improved neuropathology and motor behaviors in both AAV-mHTT-transduced mice and N171-82Q mice. Our data provides a molecular and pathological mechanism that deregulation of XIAP triggers mitochondria dysfunction and other neuropathological processes via the neurotoxic effect of p53 in HD. Together, the XIAP-p53 pathway is a novel pathological marker and can be a therapeutic target for improving the symptoms in HD.

Impact of hypoxia-ischemia and dopamine treatment on dopamine receptor binding density in the preterm fetal sheep brain.

Dopamine is often used to treat hypotension in preterm infants who are at risk of hypoxic-ischemic (HI) brain injury due to cerebral hypoperfusion and impaired autoregulation. There is evidence that systemically administered dopamine crosses the preterm blood-brain barrier. However, the effects of exogenous dopamine and cerebral HI on dopaminergic signaling in the immature brain are unknown. We determined the effect of HI and dopamine on D1 and D2 receptor binding and expressions of dopamine transporter (DAT) and tyrosine hydroxylase (TH) in the striatum of the preterm fetal sheep. Fetal sheep (99 days of gestation, term = 147days) were unoperated controls (n = 6) or exposed to severe HI using umbilical cord occlusion and saline infusion (UCO + saline, n = 8) or to HI with dopamine infusion (UCO + dopamine, 10 µg/kg/min, n = 7) for 74 h. D1 and D2 receptor densities were measured by autoradiography in vitro. DAT, TH, and cell death were measured using immunohistochemistry. HI resulted in cell death in the caudate nucleus and putamen, and dopamine infusion started before HI did not exacerbate or ameliorate these effects. HI led to reduced D1 and D2 receptor densities in the caudate nucleus and reduction in DAT protein expression in the caudate and putamen. Fetal brains exposed to dopamine in addition to HI were not different from those exposed to HI alone in these changes in dopaminergic parameters. We conclude that dopamine infusion does not alter the striatal cell death or the reductions in D1 and D2 receptor densities and DAT protein expression induced by HI in the preterm brain.NEW & NOTEWORTHY This is the first study on the effects of hypoxia-ischemia and dopamine treatment on the dopaminergic pathway in the preterm brain. In the striatum of fetal sheep (equivalent to ∼26-28 wk of human gestation), we demonstrate that hypoxia-ischemia leads to cell death, reduces D1 and D2 receptors, and reduces dopamine transporter. Intravenous dopamine infusion at clinical dosage used in preterm human infants does not alter the striatal cell death, D1 and D2 receptor density levels, and DAT protein expressions after hypoxia-ischemia in the preterm brain.

Increased TRPC5 glutathionylation contributes to striatal neuron loss in Huntington's disease.

Aberrant glutathione or Ca(2+) homeostasis due to oxidative stress is associated with the pathogenesis of neurodegenerative disorders. The Ca(2+)-permeable transient receptor potential cation (TRPC) channel is predominantly expressed in the brain, which is sensitive to oxidative stress. However, the role of the TRPC channel in neurodegeneration is not known. Here, we report a mechanism of TRPC5 activation by oxidants and the effect of glutathionylated TRPC5 on striatal neurons in Huntington's disease. Intracellular oxidized glutathione leads to TRPC5 activation via TRPC5 S-glutathionylation at Cys176/Cys178 residues. The oxidized glutathione-activated TRPC5-like current results in a sustained increase in cytosolic Ca(2+), activated calmodulin-dependent protein kinase and the calpain-caspase pathway, ultimately inducing striatal neuronal cell death. We observed an abnormal glutathione pool indicative of an oxidized state in the striatum of Huntington's disease transgenic (YAC128) mice. Increased levels of endogenous TRPC5 S-glutathionylation were observed in the striatum in both transgenic mice and patients with Huntington's disease. Both knockdown and inhibition of TRPC5 significantly attenuated oxidation-induced striatal neuronal cell death. Moreover, a TRPC5 blocker improved rearing behaviour in Huntington's disease transgenic mice and motor behavioural symptoms in littermate control mice by increasing striatal neuron survival. Notably, low levels of TRPC1 increased the formation of TRPC5 homotetramer, a highly Ca(2+)-permeable channel, and stimulated Ca(2+)-dependent apoptosis in Huntington's disease cells (STHdh(Q111/111)). Taken together, these novel findings indicate that increased TRPC5 S-glutathionylation by oxidative stress and decreased TRPC1 expression contribute to neuronal damage in the striatum and may underlie neurodegeneration in Huntington's disease.

Sulforaphane Ameliorates 3-Nitropropionic Acid-Induced Striatal Toxicity by Activating the Keap1-Nrf2-ARE Pathway and Inhibiting the MAPKs and NF-κB Pathways.

The potential neuroprotective value of sulforaphane (SFN) in Huntington's disease (HD) has not been established yet. We investigated whether SFN prevents and improves the neurological impairment and striatal cell death in a 3-nitropropionic acid (3-NP)-induced mouse model of HD. SFN (2.5 and 5.0 mg/kg/day, i.p.) was given daily 30 min before 3-NP treatment (pretreatment) and from onset/progression/peak points of the neurological scores. Pretreatment with SFN (5.0 mg/kg/day) produced the best neuroprotective effect with respect to the neurological scores and lethality among other conditions. The protective effects due to pretreatment with SFN were associated with the following: suppression of the formation of a lesion area, neuronal death, succinate dehydrogenase activity, apoptosis, microglial activation, and mRNA or protein expression of inflammatory mediators, including tumor necrosis factor-alpha, interleukin (IL)-1β, IL-6, inducible nitric oxide synthase, and cyclooxygenase-2 in the striatum after 3-NP treatment. Also, pretreatment with SFN activated the Kelch-like ECH-associated protein 1 (Keap1)-nuclear factor erythroid 2-related factor 2 (Nrf2)-antioxidant response element (ARE) pathway and inhibited the mitogen-activated protein kinases (MAPKs) and nuclear factor-kappa B (NF-κB) pathways in the striatum after 3-NP treatment. As expected, the pretreatment with activators (dimethyl fumarate and antioxidant response element inducer-3) of the Keap1-Nrf2-ARE pathway decreased the neurological impairment and lethality after 3-NP treatment. Our findings suggest that SFN may effectively attenuate 3-NP-induced striatal toxicity by activating the Keap1-Nrf2-ARE pathway and inhibiting the MAPKs and NF-κB pathways and that SFN has a wide therapeutic time-window for HD-like symptoms.

Disruption of the nuclear membrane by perinuclear inclusions of mutant huntingtin causes cell-cycle re-entry and striatal cell death in mouse and cell models of Huntington's disease.

Accumulation of N-terminal fragments of mutant huntingtin (mHTT) in the cytoplasm, nuclei and axons of neurons is a hallmark of Huntington's disease (HD), although how these fragments negatively impact neurons remains unclear. We followed the distribution of mHTT in the striata of transgenic R6/2-J2 HD mice as their motor function declined. The fraction of cells with diffuse, perinuclear or intranuclear mHTT changed in parallel with decreasing motor function. In transgenic mice, medium spiny neurons (MSNs) that exhibited perinuclear inclusions expressed cell-cycle markers typically not seen in the striata of normal mice, and these cells are preferentially lost as disease progresses. Electron microscopy reveals that perinuclear inclusions disrupt the nuclear envelope. The progression of perinuclear inclusions being accompanied by cell-cycle activation and culminating in cell death was also observed in 1° cortical neurons. These observations provide a strong correlation between the subcellular location of mHTT, disruption of the nucleus, re-entry into the cell-cycle and eventual neuronal death. They also highlight the fact that the subcellular distribution of mHTT is highly dynamic such that the distribution of mHTT observed depends greatly on the stage of the disease being examined.

Geldanamycin attenuates 3‑nitropropionic acid‑induced apoptosis and JNK activation through the expression of HSP 70 in striatal cells.

Although selective striatal cell death is a characteristic hallmark in the pathogenesis of Huntington’s disease (HD), the underlying mechanism of striatal susceptibility remains to be clarified. Heat shock proteins (HSPs) have been reported to suppress the aggregate formation of mutant huntingtin and concurrent striatal cell death. In a previous study, we observed that heat shock transcription factor 1 (HSF1), a major transcription factor of HSPs, significantly attenuated 3-nitropropionic acid (3NP)-induced reactive oxygen species (ROS) production and apoptosis through the expression of HSP 70 in striatal cells. To investigate the differential roles of HSPs in 3NP-induced striatal cell death, the effect of geldanamycin (GA), an HSP 90 inhibitor, was examined in 3NP-stimulated striatal cells. GA significantly attenuated 3NP-induced striatal apoptosis and ROS production with an increased expression of HSP 70. Triptolide (TL), an HSP 70 inhibitor, abolished GA-mediated protective effects in 3NP-stimulated striatal cells. To understand the underlying mechanism by which GA-mediated HSP 70 protects striatal cells against 3NP stimulation, the involvement of various signaling pathways was examined. GA significantly attenuated 3NP-induced c-Jun N-terminal kinase (JNK) phosphorylation and subsequent c-Jun phosphorylation in striatal cells. Taken together, the present study demonstrated that GA exhibits protective properties against 3NP-induced apoptosis and JNK activation via the induction of HSP 70 in striatal cells, suggesting that expression of HSP 70 may be a valuable therapeutic target in the treatment of HD.

ER Stress-Induced eIF2-alpha Phosphorylation Underlies Sensitivity of Striatal Neurons to Pathogenic Huntingtin

A hallmark of Huntington’s disease is the pronounced sensitivity of striatal neurons to polyglutamine-expanded huntingtin expression. Here we show that cultured striatal cells and murine brain striatum have remarkably low levels of phosphorylation of translation initiation factor eIF2α, a stress-induced process that interferes with general protein synthesis and also induces differential translation of pro-apoptotic factors. EIF2α phosphorylation was elevated in a striatal cell line stably expressing pathogenic huntingtin, as well as in brain sections of Huntington’s disease model mice. Pathogenic huntingtin caused endoplasmic reticulum (ER) stress and increased eIF2α phosphorylation by increasing the activity of PKR-like ER-localized eIF2α kinase (PERK). Importantly, striatal neurons exhibited special sensitivity to ER stress-inducing agents, which was potentiated by pathogenic huntingtin. We could strongly reduce huntingtin toxicity by inhibiting PERK. Therefore, alteration of protein homeostasis and eIF2α phosphorylation status by pathogenic huntingtin appears to be an important cause of striatal cell death. A dephosphorylated state of eIF2α has been linked to cognition, which suggests that the effect of pathogenic huntingtin might also be a source of the early cognitive impairment seen in patients.

Apoptosis signal-regulating kinase-1 aggravates ROS-mediated striatal degeneration in 3-nitropropionic acid-infused mice

Apoptosis signal-regulating kinase-1 (ASK1), an early signaling element in the cell death pathway, has been suggested to participate in the pathology of neurodegenerative diseases, which may be associated with environmental factors that impact the diseases. Although it is not entirely elucidated, 3-nitropropionic acid (3-NP) provokes mitochondrial dysfunction and selectively forms striatal lesions similar to those found in Huntington’s disease. The current study investigated whether ASK1 is involved in striatal pathology following chronic systemic infusion of 3-NP. The results show that ASK1 acts as a primary mediator of there active oxygen species (ROS) cell death signal cascade in the 3-NP-damaged striatal region by disrupting the positive feedback cycle. In 3-NP-infused striatal lesions, ROS increased ASK1. Superoxide dismutase transgenic (SOD-tg) mice reduced ASK1by scavenging ROS, and reduction of ASK1leads to a reduction in cell death. However, ASK1 down-regulation in 3-NP infusion mice also decreased striatal cell death without scavenging ROS. In contrast decreasing cell death by si-ASK1 treatment along with 3-NP in both SOD tg and wild-type mice (wt), cell death rebounded when ASK1 peptide was added to SOD tg mice. The present study suggests that ROS-inducing ASK1 may be an important step in the pathogenesis of 3-NP infused striatal lesions in murine brains.

Ser129D mutant alpha-synuclein induces earlier motor dysfunction while S129A results in distinctive pathology in a rat model of Parkinson's disease

Alpha-synuclein phosphorylated at serine 129 (S129) is highly elevated in Parkinson's disease patients where it mainly accumulates in the Lewy bodies. Several groups have studied the role of phosphorylation at the S129 in α-synuclein in a rat model for Parkinson's disease using recombinant adeno-associated viral (rAAV) vectors. The results obtained are inconsistent and accordingly the role of S129 phosphorylation in α-synuclein toxicity remains unclear. This prompted us to re-examine the neuropathological and behavioral effects of the S129 modified α-synuclein species in vivo. For this purpose, we used two mutated forms of human α-synuclein in which the S129 was replaced either with an alanine (S129A), to block phosphorylation, or with an aspartate (S129D), to mimic phosphorylation, and compared them with the wild type α-synuclein. This approach was similar in design to previous studies, however our investigation of dopaminergic degeneration also included performing a detailed study of the α-synuclein induced pathology in the striatum and the analysis of motor deficits. Our results showed that overexpressing S129D or wild type α-synuclein resulted in an accelerated dopaminergic fiber loss as compared with S129A α-synuclein. Furthermore, the motor deficit seen in the group treated with the mutant S129D α-synuclein appeared earlier than the other two forms of α-synuclein. Conversely, S129A α-synuclein showed significantly larger pathological α-synuclein-positive inclusions, and slower dopaminergic fiber loss, when compared to the other two forms of α-synuclein, suggesting a neuroprotective effect of the mutation. When examined at long-term, all three α-synuclein forms resulted in pathological accumulations of α-synuclein in striatal fibers and dopaminergic cell death in the substantia nigra. Our data show that changes in the S129 residue of α-synuclein influence the rate of pathology and neurodegeneration, with an overall deleterious effect of exchanging S129 to a residue mimicking its phosphorylated state.

Imbalance of p75NTR/TrkB protein expression in Huntington’s disease: implication for neuroprotective therapies

Neuroprotective therapies based on brain-derived neurotrophic factor (BDNF) administration have been proposed for Huntington's disease (HD) treatment. However, our group has recently reported reduced levels of TrkB in HD mouse models and HD human brain suggesting that besides a decrease on BDNF levels a reduction of TrkB expression could also contribute to diminished neurotrophic support in HD. BDNF can also bind to p75 neurotrophin receptor (p75NTR) modulating TrkB signaling. Therefore, in this study we have analyzed the levels of p75NTR in several HD models, as well as in HD human brain. Our data demonstrates a p75NTR/TrkB imbalance in the striatum of two different HD mouse models, HdhQ111/111 homozygous knockin mice and R6/1 mice that was also manifested in the putamen of HD patients. The imbalance between TrkB and p75NTR levels in a HD cellular model did not affect BDNF-mediated TrkB activation of prosurvival pathways but induced activation of apoptotic cascades as demonstrated by increased JNK phosphorylation. Moreover, BDNF failed to protect mutant huntingtin striatal cells transfected with p75NTR against NMDA-mediated excitotoxicity, which was associated with decreased Akt phosphorylation. Interestingly, lack of Akt activation following BDNF and NMDA treatment correlated with increased PP1 levels. Accordingly, pharmacological inhibition of PP1 by okadaic acid (OA) prevented mutant huntingtin striatal cell death induced by NMDA and BDNF. Altogether, our findings demonstrate that the p75NTR/TrkB imbalance induced by mutant huntingtin in striatal cells associated with the aberrant activity of PP1 disturbs BDNF neuroprotection likely contributing to increasing striatal vulnerability in HD. On the basis of this data we hypothesize that normalization of p75NTR and/or TrkB expression or their signaling will improve BDNF neuroprotective therapies in HD.

Heat shock transcription factor-1 suppresses apoptotic cell death and ROS generation in 3-nitropropionic acid-stimulated striatal cells

Striatal neuronal cell death is one of the pathological features of Huntington's disease (HD). Overexpression of some heat shock proteins (HSPs) has been reported to suppress the aggregate formation of mutant huntingtin and concurrent cell death. Heat shock transcription factor-1 (HSF 1), a major transcription factor of HSPs, has also been reported to be increased in HD models. However, the exact role of HSF 1 in the pathogenesis of HD has not been clearly elucidated. 3-Nitropropionic acid (3NP), an irreversible inhibitor of the mitochondrial complex II, induces selective damage to the striatum in animals and produces clinical features of HD. To investigate roles of HSF 1 on 3NP-induced oxidative stress, HSF 1 was transiently overexpressed in striatal cells. Expression of HSF 1 significantly attenuated 3NP-induced apoptotic striatal cell death and resulted in increased expression of HSP 70. Furthermore, expression of HSF 1 significantly attenuated 3NP-induced intracellular reactive oxygen species (ROS) generation. Taken together, the present study clearly demonstrates that HSF 1 attenuates 3NP-induced apoptotic striatal cell death and ROS generation, possibly through HSP70 expression, suggesting that HSF 1 might be a valuable therapeutic target in the treatment of HD.

Inflammatory Pathways in Parkinson’s Disease; A BNE Microarray Study

The aetiology of Parkinson's disease (PD) is yet to be fully understood but it is becoming more and more evident that neuronal cell death may be multifactorial in essence. The main focus of PD research is to better understand substantia nigra homeostasis disruption, particularly in relation to the wide-spread deposition of the aberrant protein α-synuclein. Microarray technology contributed towards PD research with several studies to date and one gene, ALDH1A1 (Aldehyde dehydrogenase 1 family, member A1), consistently reappeared across studies including the present study, highlighting dopamine (DA) metabolism dysfunction resulting in oxidative stress and most probably leading to neuronal cell death. Neuronal cell death leads to increased inflammation through the activation of astrocytes and microglia. Using our dataset, we aimed to isolate some of these pathways so to offer potential novel neuroprotective therapeutic avenues. To that effect our study has focused on the upregulation of P2X7 (purinergic receptor P2X, ligand-gated ion channel, 7) receptor pathway (microglial activation) and on the NOS3 (nitric oxide synthase 3) pathway (angiogenesis). In summary, although the exact initiator of striatal DA neuronal cell death remains to be determined, based on our analysis, this event does not remain without consequence. Extracellular ATP and reactive astrocytes appear to be responsible for the activation of microglia which in turn release proinflammatory cytokines contributing further to the parkinsonian condition. In addition to tackling oxidative stress pathways we also suggest to reduce microglial and endothelial activation to support neuronal outgrowth.

Age-Dependent Resistance to Excitotoxicity in Htt CAG140 Mice and the Effect of Strain Background

Mouse strain background can influence vulnerability to excitotoxic neuronal cell death and potentially modulate phenotypes in transgenic mouse models of human disease. Evidence supports a contribution of excitotoxicity to the selective death of medium spiny neurons in Huntington's disease (HD). Here, we assess whether strain differences in excitotoxic vulnerability influence striatal cell death in a knock-in mouse model of HD. Previous studies that evaluated resistance to excitotoxic lesions in several mouse models of HD had variable outcomes. In the present study, we directly compare one model on two different background strains to test the contribution of strain to excitotoxicity-mediated neurodegeneration. Mice of the FVB/N strain, which are highly vulnerable to excitotoxicity, become extremely resistant to quinolinic acid-induced striatal neurodegeneration with age, when carrying a huntingtin (Htt) allele expressing a HD transgene (CAG140). The resistance is much greater than the age-dependent resistance that has been previously reported in YAC128 mice. By 12 months of age, both heterozygous and homozygous FVB.CAG140 mice displayed virtually complete resistance to quinolinic acid-induced striatal neurodegeneration. A similar resistance develops in CAG140 mice on a C57BL/6N background although the effect size is smaller because C57BL/6N mice are already resistant due to genetic background. In a direct comparison with the YAC128 mice, FVB.CAG140 mice have greater resistance. FVB.CAG140 mice are also resistant to neurodegeneration following kainic acid-induced status epilepticus suggesting the existence of a common cellular mechanism that provides protection against multiple types of excitotoxic insult. These findings establish FVB.CAG140 mice as a useful model to investigate the cellular and molecular mechanisms that confer neuroprotection against excitotoxicity.

A single high dose of methamphetamine induces apoptotic and necrotic striatal cell loss lasting up to 3 months in mice

Methamphetamine (METH) is an addictive agent that poses a public health problem due to its toxic effects on neural tissue. We have shown that METH induces striatal lesions (cell loss) within 24 h of administration. Because cell proliferation has been found to follow excitotoxic and other types of lesions in adult brain, we tested the hypothesis that cell proliferation would follow METH-induced striatal cell death. To that end, METH (30 mg/kg i.p.) was injected into adult male mice followed by a single injection of the proliferation marker 5-bromo-2'-deoxyuridine (BrdU, 100 mg/kg i.p.) at various times post-METH up to 12 weeks. Immunohistochemical analysis of striatal tissue showed that METH-treated animals incorporated BrdU between 24-48 h post-METH. To determine the survival of the newly generated cells, a subgroup of animals received BrdU 36 h after METH and were sacrificed at various times up to 12 weeks post-METH. Morphological analysis of striatal tissue from these animals showed that by 12 weeks post-METH, approximately 42% and 30% of the newly generated cells showed pyknotic or necrotic morphology, respectively. Thus, approximately 30% of the newly generated cells survive up to 12 weeks post-METH. Striatal volume was increased by METH and normalized to control levels by 12 weeks after METH. The data demonstrate that a single bolus injection of METH induces cellular changes and responses that persist for months after exposure to METH.

Cystamine and ethyl-eicosapentaenoic acid treatment fail to prevent malonate-induced striatal toxicity in mice

Cystamine has demonstrated neuroprotective activity in a variety of studies, and is currently being evaluated in a human clinical trial in Huntington's disease (HD). Cystamine treatment of various genetic models of HD demonstrated protection against neurodegeneration and/or improvement in behavior. Given the need for a rapid screening tool for HD therapeutics, we assessed the potential therapeutic benefits of cystamine in a short-term acute toxicity murine model of striatal cell death. Cystamine did not provide neuroprotection against bilateral intrastriatal malonate injections in mice as measured by lesion size, loss of striatal volume, or decreased striatal neuronal counts. Similar results were obtained for treatment with another potential therapeutic agent that was protective in genetic mouse models of HD, the essential fatty acid ethyl-eicosapentaenoic acid. Our findings suggest that this toxic model is not reflective or predictive of findings in genetic mouse models, and may not be useful as a preclinical screen for HD therapeutics.

Proneural transcription factors Dlx2 and Pax6 are altered in adult SVZ neural precursor cells following striatal cell loss

Compensatory replacement of neurons by endogenous subventricular zone (SVZ)-derived neural precursor cells has been demonstrated in the adult brain following striatal cell loss. Such cell replacement is associated with increased SVZ cell proliferation and neuroblast expansion in the rostral migratory stream (RMS). SVZ-derived neural precursor cells co-express multiple transcription factors involved in lineage restriction and cell fate determination. We propose that compensatory neurogenesis in response to striatal cell loss will alter the temporal expression of transcription factors in discrete populations of SVZ-derived neural precursor cells. We therefore examined the expression of Mash1, Dlx2, Pax6 and Olig2 in SVZ-derived neural precursor cell populations across a range of times following quinolinic acid (QA) induced striatal cell death. We have identified a heterogeneous population of SVZ-derived neural precursor cells that respond independently to striatal cell loss. In both the anterior SVZ (aSVZ) and RMS we observed an increase in a sub-population of Dlx2+ transit amplifying precursor (TAP) cells and neuroblasts following QA lesioning when compared to controls. Subsequently, the number of Pax6+ TAPs and neuroblasts in the QA lesioned aSVZ and RMS was also increased. Olig2 expression was not however altered in response to QA-induced cell loss. Our results suggest Dlx2 and Pax6 may play a prominent role in directing neural precursor cell proliferation and neuroblast generation following striatal cell loss. Selective alteration of specific transcription factors in the SVZ and during migration through the RMS in response to cell loss may predetermine the subsequent generation of specific neuronal subclasses for endogenous replacement.

Methamphetamine Induces Striatal Cell Death Followed by the Generation of New Cells and a Second Round of Cell Death in Mice

Our laboratory has been investigating the impact of a neurotoxic exposure to methamphetamine (METH) on cellular components of the striatum post-synaptic to the dopaminergic terminals. A systemic bolus injection of METH (30 mg/kg, ip) induces the production of new cells in the striatum during a period lasting from 24-48 hours after METH. The newly generated cells arise from dormant striatal progenitors and not from the subventricular zone. The newly generated cells display glial phenotypes and begin to die 24 hours after birth, or 2.5 days post-METH. The protracted phase of cell death lasts for at least three months post-METH at which time the bulk of the newly generated cells have disappeared. The METH-induced production of new cells is associated with enlarged striatal volume (up to 50% larger than controls in some animals). As the newly generated cells die over a period of three months, the enlarged striatal volume normalizes. In conclusion, a neurotoxic dose of METH induces the generation of new cells in the striatum associated with enlarged striatal volume. The new cells die over three months post-METH and the enlarged striatal volume returns to control levels. This observation is significant because studies involving METH users show striatal enlargement and the normalization of striatal volume in METH users who have been abstinent for up to 20 months.

Necrostatin-1 ameliorates symptoms in R6/2 transgenic mouse model of Huntington's disease

Necrostatin-1 ameliorates symptoms in R6/2 transgenic mouse model of Huntington's disease

TRPM2 Cation Channels, Oxidative Stress and Neurological Diseases: Where Are We Now?

The Na+ and Ca(2+)-permeable melastatin related transient receptor potential 2 (TRPM2) channels can be gated either by ADP-ribose (ADPR) in concert with Ca(2+) or by hydrogen peroxide (H(2)O(2)), an experimental model for oxidative stress, binding to the channel's enzymatic Nudix domain. Since the mechanisms that lead to TRPM2 gating in response to ADPR and H(2)O(2) are not understood in neuronal cells, I summarized previous findings and important recent advances in the understanding of Ca(2+) influx via TRPM2 channels in different neuronal cell types and disease processes. Considering that TRPM2 is activated by oxidative stress, mediated cell death and inflammation, and is highly expressed in brain, the channel has been investigated in the context of central nervous system. TRPM2 plays a role in H(2)O(2) and amyloid β-peptide induced striatal cell death. Genetic variants of the TRPM2 gene confer a risk of developing Western Pacific amyotropic lateral sclerosis and parkinsonism-dementia complex and bipolar disorders. TRPM2 also contributes to traumatic brain injury processes such as oxidative stress, inflammation and neuronal death. There are a limited number of TRPM2 channel blockers and they seem to be cell specific. For example, ADPR-induced Ca(2+) influx in rat hippocampal cells was not blocked by N-(p-amylcinnomoyl)anthralic acid (ACA), the IP(3) receptor inhibitor 2-aminoethoxydiphenyl borate or PLC inhibitor flufenamic acid (FFA). However, the Ca(2+) entry in rat primary striatal cells was blocked by ACA and FFA. In conclusion TRPM2 channels in neuronal cells can be gated by either ADPR or H(2)O(2). It seems to that the exact relationship between TRPM2 channels activation and neuronal cell death still remains to be determined.