Impaired mitochondrial dynamics and Nrf2 signaling contribute to compromised responses to oxidative stress in striatal cells expressing full-length mutant huntingtin

A small-molecule Nrf1 and Nrf2 activator mitigates polyglutamine toxicity in spinal and bulbar muscular atrophy

Spinal and bulbar muscular atrophy (SBMA, also known as Kennedy's disease) is one of nine neurodegenerative disorders that are caused by expansion of polyglutamine-encoding CAG repeats. Intracellular accumulation of abnormal proteins in these diseases, a pathological hallmark, is associated with defects in protein homeostasis. Enhancement of the cellular proteostasis capacity with small molecules has therefore emerged as a promising approach to treatment. Here, we characterize a novel curcumin analog, ASC-JM17, as an activator of central pathways controlling protein folding, degradation and oxidative stress resistance. ASC-JM17 acts on Nrf1, Nrf2 and Hsf1 to increase the expression of proteasome subunits, antioxidant enzymes and molecular chaperones. We show that ASC-JM17 ameliorates toxicity of the mutant androgen receptor (AR) responsible for SBMA in cell, fly and mouse models. Knockdown of the Drosophila Nrf1 and Nrf2 ortholog cap 'n' collar isoform-C, but not Hsf1, blocks the protective effect of ASC-JM17 on mutant AR-induced eye degeneration in flies. Our observations indicate that activation of the Nrf1/Nrf2 pathway is a viable option for pharmacological intervention in SBMA and potentially other polyglutamine diseases.

Phycocyanin prevents methylglyoxal-induced mitochondrial-dependent apoptosis in INS-1 cells by Nrf2

Phycocyanin prevents mitochondrial-dependent apoptosis in methylgiyoxal-induced INS-1 cells by activating Nrf2.

Dysregulation of Glutamate Cycling Mediates Methylmercury-Induced Neurotoxicity

To examine the toxicological implications of glutamate, this chapter will focus specifically on its impact in the brain. More explicitly, it will illustrate the role glutamate plays in mediating methylmercury (MeHg)-induced neurotoxicity. In this chapter, one intends to highlight the processes that occur prior to glutamate-stimulated excitotoxicity and subsequent neurodegeneration. As such, it will emphasize three main routes by which MeHg alters glutamate homeostasis. It is essential to recognize that these effects are not mutually exclusive, and that they synergistically influence glutamate dysregulation. Furthermore, the consequences of MeHg exposure will be presented here as a direct pathway; however, it must be noted these effects occur simultaneously. First, glutamate uptake will be reviewed emphasizing the function of astrocytes. Next, the induction of oxidative stress by MeHg exposure will be discussed. This process has a two-fold effect on glutamate homeostasis by (1) inhibiting extracellular glutamate uptake and (2) altering transcription of genes vital to glutamate cycling. Finally, the impact glutamate dysregulation has on glutathione synthesis will be examined. Although this chapter centers on the link between glutamate and MeHg toxicity, it is imperative that the reader acknowledges the processes discussed here can be extended to any pro-oxidant.

Untargeted metabolic profiling identifies interactions between Huntington's disease and neuronal manganese status

Manganese (Mn) is an essential micronutrient for development and function of the nervous system. Deficiencies in Mn transport have been implicated in the pathogenesis of Huntington's disease (HD), an autosomal dominant neurodegenerative disorder characterized by loss of medium spiny neurons of the striatum. Brain Mn levels are highest in striatum and other basal ganglia structures, the most sensitive brain regions to Mn neurotoxicity. Mouse models of HD exhibit decreased striatal Mn accumulation and HD striatal neuron models are resistant to Mn cytotoxicity. We hypothesized that the observed modulation of Mn cellular transport is associated with compensatory metabolic responses to HD pathology. Here we use an untargeted metabolomics approach by performing ultraperformance liquid chromatography-ion mobility-mass spectrometry (UPLC-IM-MS) on control and HD immortalized mouse striatal neurons to identify metabolic disruptions under three Mn exposure conditions, low (vehicle), moderate (non-cytotoxic) and high (cytotoxic). Our analysis revealed lower metabolite levels of pantothenic acid, and glutathione (GSH) in HD striatal cells relative to control cells. HD striatal cells also exhibited lower abundance and impaired induction of isobutyryl carnitine in response to increasing Mn exposure. In addition, we observed induction of metabolites in the pentose shunt pathway in HD striatal cells after high Mn exposure. These findings provide metabolic evidence of an interaction between the HD genotype and biologically relevant levels of Mn in a striatal cell model with known HD by Mn exposure interactions. The metabolic phenotypes detected support existing hypotheses that changes in energetic processes underlie the pathobiology of both HD and Mn neurotoxicity.

Protective effects of 3-alkyl luteolin derivatives are mediated by Nrf2 transcriptional activity and decreased oxidative stress in Huntington's disease mouse striatal cells

Huntington's disease (HD) is a polyglutamine-expansion neurodegenerative disorder caused by increased number of CAG repeats in the HTT gene, encoding for the huntingtin protein. The mutation is linked to several intracellular mechanisms, including oxidative stress. Flavones are compounds with a protective role in neurodegenerative pathologies. In the present study we analyzed the protective effect of luteolin (Lut, 3',4',5,7-tetrahydroxyflavone) and four luteolin derivatives bearing 3-alkyl chains of 1, 4, 6 and 10 carbons (Lut-C1, Lut-C4, Lut-C6, Lut-C10) in striatal cells derived from HD knock-in mice expressing mutant Htt (STHdh(Q111/Q111)) versus wild-type striatal cells (STHdh(Q7/Q7)). HD cells showed increased caspase-3-like activity and intracellular reactive oxygen species (ROS), which were significantly decreased following treatment with Lut-C4 and Lut-C6 under concentrations that enhanced cell viability. Interestingly, Lut-C4 and Lut-C6 rose the nuclear levels of phospho(Ser40)-nuclear factor (erythroid-derived-2)-like 2 (Nrf2) and Nrf2/ARE transcriptional activity. Concordantly with increased Nrf2/ARE transcription, Lut-C6 enhanced superoxide dismutase 1 (SOD1) mRNA and SOD activity and glutamate-cysteine ligase catalytic subunit (GCLc) mRNA and protein levels, while Lut-C4 induced mRNA levels of GCLc only in mutant striatal cells. Data suggest that Lut-C6 luteolin derivative (in particular) might be relevant for the development of antioxidant strategies in HD.

Bcl-2/adenovirus E1B 19-kDa interacting protein (BNip3) has a key role in the mitochondrial dysfunction induced by mutant huntingtin

Huntington's disease (HD) is a neurodegenerative disorder caused by the expansion of a CAG repeat in the IT15 gene that encodes the protein huntingtin (htt). Evidence shows that mutant htt causes mitochondrial depolarization and fragmentation, but the underlying molecular mechanism has yet to be clarified. Bax/Bak and BNip3 are pro-apoptotic members of the Bcl-2 family protein whose activation triggers mitochondrial depolarization and fragmentation inducing cell death. Evidence suggests that Bax/Bak and BNip3 undergo activation upon mutant htt expression but whether these proteins are required for mitochondrial depolarization and fragmentation induced by mutant htt is unclear. Our results show that BNip3 knock-out cells are protected from mitochondrial damage and cell death induced by mutant htt whereas Bax/Bak knock-out cells are not. Moreover, deletion of BNip3 C-terminal transmembrane domain, required for mitochondrial targeting, suppresses mitochondrial depolarization and fragmentation in a cell culture model of HD. Hence, our results suggest that changes in mitochondrial morphology and transmembrane potential, induced by mutant htt protein, are dependent and linked to BNip3 and not to Bax/Bak activation. These results provide new compelling evidence that underlies the molecular mechanisms by which mutant htt causes mitochondrial dysfunction and cell death, suggesting BNip3 as a potential target for HD therapy.

Peptide and small molecule inhibitors of the Keap1-Nrf2 protein-protein interaction

The transcription factor nuclear factor erythroid-2-related factor 2 (Nrf2) up-regulates the expression of a range of cytoprotective enzymes with antioxidant response elements in their promoter regions and thus can protect cells against oxidative damage. Increasing Nrf2 activity has been proposed as a therapeutic intervention in a range of chronic neurodegenerative conditions and cancer chemoprevention. One of the main mechanisms by which Nrf2 is negatively regulated involves an interaction with the ubiquitination facilitator protein, Kelch-like ECH-associated protein 1 (Keap1) that facilitates degradation of Nrf2. Inhibition of this process underlies the mode of action of a broad group of compounds that increase Nrf2 activity. A number of natural products, including the isothiocyanate sulforaphane, up-regulate Nrf2 by interacting with Keap1 in a covalent manner to stall its activity. Recently, a number of peptide and small molecule inhibitors of the protein-protein interaction (PPI) between Keap1 and Nrf2 have been described. These classes of compound have contrasting modes of action at the molecular level and there is emerging evidence that their biological activities have similarities and differences. This review describes the various classes of PPI inhibitor that have been described in the literature and the biological evaluations that have been performed.

An Overview of Potential Targets for Treating Amyotrophic Lateral Sclerosis and Huntington's Disease

Neurodegenerative diseases affect millions of people worldwide. Progressive damage or loss of neurons, neurodegeneration, has severe consequences on the mental and physical health of a patient. Despite all efforts by scientific community, there is currently no cure or manner to slow degeneration progression. We review some treatments that attempt to prevent the progress of some of major neurodegenerative diseases: Amyotrophic Lateral Sclerosis and Huntington's disease.

Cdk5-mediated mitochondrial fission: A key player in dopaminergic toxicity in Huntington's disease

The molecular mechanisms underlying striatal vulnerability in Huntington's disease (HD) are still unknown. However, growing evidence suggest that mitochondrial dysfunction could play a major role. In searching for a potential link between striatal neurodegeneration and mitochondrial defects we focused on cyclin-dependent kinase 5 (Cdk5). Here, we demonstrate that increased mitochondrial fission in mutant huntingtin striatal cells can be a consequence of Cdk5-mediated alterations in Drp1 subcellular distribution and activity since pharmacological or genetic inhibition of Cdk5 normalizes Drp1 function ameliorating mitochondrial fragmentation. Interestingly, mitochondrial defects in mutant huntingtin striatal cells can be worsened by D1 receptor activation a process also mediated by Cdk5 as down-regulation of Cdk5 activity abrogates the increase in mitochondrial fission, the translocation of Drp1 to the mitochondria and the raise of Drp1 activity induced by dopaminergic stimulation. In sum, we have demonstrated a new role for Cdk5 in HD pathology by mediating dopaminergic neurotoxicity through modulation of Drp1-induced mitochondrial fragmentation, which underscores the relevance for pharmacologic interference of Cdk5 signaling to prevent or ameliorate striatal neurodegeneration in HD.

The biology of proteostasis in aging and disease

Loss of protein homeostasis (proteostasis) is a common feature of aging and disease that is characterized by the appearance of nonnative protein aggregates in various tissues. Protein aggregation is routinely suppressed by the proteostasis network (PN), a collection of macromolecular machines that operate in diverse ways to maintain proteome integrity across subcellular compartments and between tissues to ensure a healthy life span. Here, we review the composition, function, and organizational properties of the PN in the context of individual cells and entire organisms and discuss the mechanisms by which disruption of the PN, and related stress response pathways, contributes to the initiation and progression of disease. We explore emerging evidence that disease susceptibility arises from early changes in the composition and activity of the PN and propose that a more complete understanding of the temporal and spatial properties of the PN will enhance our ability to develop effective treatments for protein conformational diseases.

An overview of the molecular mechanisms and novel roles of Nrf2 in neurodegenerative disorders

Recently, growing evidence has demonstrated that nuclear factor erythroid 2-related factor 2 (Nrf2) is a pivotal regulator of endogenous defense systems that function via the activation of a set of protective genes, and this is particularly clear in the central nervous system (CNS). Therefore, it is highly useful to summarize the current literature on the molecular mechanisms and role of Nrf2 in the CNS. In this review, we first briefly introduce the molecular features of Nrf2. We then discuss the regulation, cerebral actions, upstream modulators and downstream targets of Nrf2 pathway. Following this background, we expand our discussion to the role of Nrf2 in several major neurodegenerative disorders (NDDs) such as Alzheimer's disease, Parkinson's disease, Huntington's disease, multiple sclerosis and amyotrophic lateral sclerosis. Lastly, we discuss some potential future directions. The information reviewed here may be significant in the design of further experimental research and increase the potential of Nrf2 as a therapeutic target in the future.

Insulin and IGF-1 improve mitochondrial function in a PI-3K/Akt-dependent manner and reduce mitochondrial generation of reactive oxygen species in Huntington's disease knock-in striatal cells

Oxidative stress and mitochondrial dysfunction have been described in Huntington's disease, a disorder caused by expression of mutant huntingtin (mHtt). IGF-1 was previously shown to protect HD cells, whereas insulin prevented neuronal oxidative stress. In this work we analyzed the role of insulin and IGF-1 in striatal cells derived from HD knock-in mice on mitochondrial production of reactive oxygen species (ROS) and related antioxidant and signaling pathways influencing mitochondrial function. Insulin and IGF-1 decreased mitochondrial ROS induced by mHtt and normalized mitochondrial SOD activity, without affecting intracellular glutathione levels. IGF-1 and insulin promoted Akt phosphorylation without changing the nuclear levels of phosphorylated Nrf2 or Nrf2/ARE activity. Insulin and IGF-1 treatment also decreased mitochondrial Drp1 phosphorylation, suggesting reduced mitochondrial fragmentation, and ameliorated mitochondrial function in HD cells in a PI-3K/Akt-dependent manner. This was accompanied by increased total and phosphorylated Akt, Tfam, and mitochondrial-encoded cytochrome c oxidase II, as well as Tom20 and Tom40 in mitochondria of insulin- and IGF-1-treated mutant striatal cells. Concomitantly, insulin/IGF-1-treated mutant cells showed reduced apoptotic features. Hence, insulin and IGF-1 improve mitochondrial function and reduce mitochondrial ROS caused by mHtt by activating the PI-3K/Akt signaling pathway, in a process independent of Nrf2 transcriptional activity, but involving enhanced mitochondrial levels of Akt and mitochondrial-encoded complex IV subunit.

Aqueous extract of Glycyrrhiza inflata inhibits aggregation by upregulating PPARGC1A and NFE2L2-ARE pathways in cell models of spinocerebellar ataxia 3

Spinocerebellar ataxia (SCA) types 1, 2, 3, 6, 7, and 17 and dentatorubropallidoluysian atrophy, as well as Huntington disease, are a group of neurodegenerative disorders caused by a CAG triplet-repeat expansion encoding a long polyglutamine (polyQ) tract in the respective mutant proteins. The cytoplasmic and nuclear aggregate formation, a pathological hallmark of polyQ diseases, is probably the initial process triggering the subsequent pathological events. Compromised oxidative stress defense capacity and mitochondrial dysfunction have emerged as contributing factors to the pathogenesis of polyQ diseases. The roots of licorice (Glycyrrhiza species) have long been used as an herbal medicine. In this study, we demonstrate the aggregate-inhibitory effect of Glycyrrhiza inflata herb extract and its constituents licochalcone A and ammonium glycyrrhizinate (AMGZ) in both 293 and SH-SY5Y ATXN3/Q75 cells, SCA3 cell models. The reporter assay showed that G. inflata herb extract, licochalcone A, and AMGZ could enhance the promoter activity of peroxisome proliferator-activated receptor γ, coactivator 1α (PPARGC1A), a known regulator of mitochondrial biogenesis and antioxidative response genes. G. inflata extract, licochalcone A, and AMGZ upregulated PPARGC1A expression and its downstream target genes, SOD2 and CYCS, in the 293 ATXN3/Q75 cell model. The expression of nuclear factor erythroid 2-related factor 2 (NFE2L2), the principal transcription factor that binds to antioxidant-responsive elements (AREs) to promote ARE-dependent gene expression when the cells respond to oxidative stress, and its downstream genes, HMOX1, NQO1, GCLC, and GSTP1, was also increased by G. inflata herb extract, licochalcone A, and AMGZ. Knockdown of PPARGC1A increased aggregates in ATXN3/Q75 cells and also attenuated the aggregate-inhibiting effect of the tested compounds. G. inflata extract and its constituents significantly elevated GSH/GSSG ratio and reduced reactive oxidative species in ATXN3/Q75 cells. The study results suggest that the tested agents activate PPARGC1A activity and NFE2L2-ARE signaling to increase mitochondrial biogenesis, decrease oxidative stress, and reduce aggregate formation in SCA3 cellular models.

Aluminium induced endoplasmic reticulum stress mediated cell death in SH-SY5Y neuroblastoma cell line is independent of p53

Aluminium (Al) is the third most abundant element in the earth’s crust and its compounds are used in the form of house hold utensils, medicines and in antiperspirant etc. Increasing number of evidences suggest the involvement of Al⁺³ ions in a variety of neurodegenerative disorders including Alzheimer’s disease. Here, we have attempted to investigate the role of Al in endoplasmic reticulum stress and the regulation of p53 during neuronal apoptosis using neuroblastoma cell line. We observed that Al caused oxidative stress by increasing ROS production and intracellular calcium levels together with depletion of intracellular GSH levels. We also studied modulation of key pro- and anti-apoptotic proteins and found significant alterations in the levels of Nrf2, NQO1, pAKT, p21, Bax, Bcl2, Aβ1-40 and Cyt c together with increase in endoplasmic reticulum (ER) stress related proteins like CHOP and caspase 12. However, with respect to the role of p53, we observed downregulation of its transcript as well as protein levels while analysis of its ubiquitination status revealed no significant changes. Not only did Al increase the activities of caspase 9, caspase 12 and caspase 3, but, by the use of peptide inhibitors of specific and pan-caspases, we observed significant protection against neuronal cell death upon inhibition of caspase 12, demonstrating the prominent role of endoplasmic reticulum stress generated responses in Al toxicity. Overall our findings suggest that Al induces ER stress and ROS generation which compromises the antioxidant defenses of neuronal cells thereby promoting neuronal apoptosis in p53 independent pathway.

Deficits in bioenergetics and impaired immune response in granulocytes from children with autism

Despite the emerging role of mitochondria in immunity, a link between bioenergetics and the immune response in autism has not been explored. Mitochondrial outcomes and phorbol 12-myristate 13-acetate (PMA)-induced oxidative burst were evaluated in granulocytes from age-, race-, and gender-matched children with autism with severity scores of ≥7 (n = 10) and in typically developing (TD) children (n = 10). The oxidative phosphorylation capacity of granulocytes was 3-fold lower in children with autism than in TD children, with multiple deficits encompassing ≥1 Complexes. Higher oxidative stress in cells of children with autism was evidenced by higher rates of mitochondrial reactive oxygen species production (1.6-fold), higher mitochondrial DNA copy number per cell (1.5-fold), and increased deletions. Mitochondrial dysfunction in children with autism was accompanied by a lower (26% of TD children) oxidative burst by PMA-stimulated reduced nicotinamide-adenine dinucleotide phosphate (NADPH) oxidase and by a lower gene expression (45% of TD children's mean values) of the nuclear factor erythroid 2-related factor 2 transcription factor involved in the antioxidant response. Given that the majority of granulocytes of children with autism exhibited defects in oxidative phosphorylation, immune response, and antioxidant defense, our results support the concept that immunity and response to oxidative stress may be regulated by basic mitochondrial functions as part of an integrated metabolic network.

Mitochondrial membrane fluidity is consistently increased in different models of Huntington disease: restorative effects of olesoxime

Huntington disease (HD) is a fatal neurodegenerative disorder caused by a CAG repeat expansion in exon 1 of the huntingtin gene (HTT). One prominent target of the mutant huntingtin protein (mhtt) is the mitochondrion, affecting its morphology, distribution, and function. Thus, mitochondria have been suggested as potential therapeutic targets for the treatment of HD. Olesoxime, a cholesterol-like compound, promotes motor neuron survival and neurite outgrowth in vitro, and its effects are presumed to occur via a direct interaction with mitochondrial membranes (MMs). We examined the properties of MMs isolated from cell and animal models of HD as well as the effects of olesoxime on MM fluidity and cholesterol levels. MMs isolated from brains of aged Hdh Q111/Q111 knock-in mice showed a significant decrease in 1,6-diphenyl-hexatriene (DPH) anisotropy, which is inversely correlated with membrane fluidity. Similar increases in MM fluidity were observed in striatal STHdh Q111/Q111 cells as well as in MMs isolated from brains of BACHD transgenic rats. Treatment of STHdh cells with olesoxime decreased the fluidity of isolated MMs. Decreased membrane fluidity was also measured in olesoxime-treated MMs isolated from brains of HD knock-in mice. In both models, treatment with olesoxime restored HD-specific changes in MMs. Accordingly, olesoxime significantly counteracted the mhtt-induced increase in MM fluidity of MMs isolated from brains of BACHD rats after 12 months of treatment in vivo, possibly by enhancing MM cholesterol levels. Thus, olesoxime may represent a novel pharmacological tool to treat mitochondrial dysfunction in HD.

HACE1 reduces oxidative stress and mutant Huntingtin toxicity by promoting the NRF2 response

Oxidative stress plays a key role in late onset diseases including cancer and neurodegenerative diseases such as Huntington disease. Therefore, uncovering regulators of the antioxidant stress responses is important for understanding the course of these diseases. Indeed, the nuclear factor erythroid 2-related factor 2 (NRF2), a master regulator of the cellular antioxidative stress response, is deregulated in both cancer and neurodegeneration. Similar to NRF2, the tumor suppressor Homologous to the E6-AP Carboxyl Terminus (HECT) domain and Ankyrin repeat containing E3 ubiquitin-protein ligase 1 (HACE1) plays a protective role against stress-induced tumorigenesis in mice, but its roles in the antioxidative stress response or its involvement in neurodegeneration have not been investigated. To this end we examined Hace1 WT and KO mice and found that Hace1 KO animals exhibited increased oxidative stress in brain and that the antioxidative stress response was impaired. Moreover, HACE1 was found to be essential for optimal NRF2 activation in cells challenged with oxidative stress, as HACE1 depletion resulted in reduced NRF2 activity, stability, and protein synthesis, leading to lower tolerance against oxidative stress triggers. Strikingly, we found a reduction of HACE1 levels in the striatum of Huntington disease patients, implicating HACE1 in the pathology of Huntington disease. Moreover, ectopic expression of HACE1 in striatal neuronal progenitor cells provided protection against mutant Huntingtin-induced redox imbalance and hypersensitivity to oxidative stress, by augmenting NRF2 functions. These findings reveal that the tumor suppressor HACE1 plays a role in the NRF2 antioxidative stress response pathway and in neurodegeneration.

Sulforaphane enhances proteasomal and autophagic activities in mice and is a potential therapeutic reagent for Huntington's disease

The ubiquitin proteasome system (UPS) is impaired in Huntington's disease, a devastating neurodegenerative disorder. Sulforaphane, a naturally occurring compound, has been shown to stimulate UPS activity in cell cultures. To test whether sulforaphane enhances UPS function in vivo, we treated UPS function reporter mice ubiquitously expressing the green fluorescence protein (GFP) fused to a constitutive degradation signal that promotes its rapid degradation in the conditions of a healthy UPS. The modified GFP is termed GFP UPS reporter (GFPu). We found that both GFPu and ubiquitinated protein levels were significantly reduced and the three peptidase activities of the proteasome were increased in the brain and peripheral tissues of the mice. Interestingly, sulforaphane treatment also enhanced autophagy activity in the brain and the liver. To further examine whether sulforaphane promotes mutant huntingtin (mHtt) degradation, we treated Huntington's disease cells with sulforaphane and found that sulforaphane not only enhanced mHtt degradation but also reduced mHtt cytotoxicity. Sulforaphane-mediated mHtt degradation was mainly through the UPS pathway as the presence of a proteasome inhibitor abolished this effect. Taken together, these data indicate that sulforaphane activates protein degradation machineries in both the brain and peripheral tissues and may be a therapeutic reagent for Huntington's disease and other intractable disorders. Accumulation of mutant huntingtin (mHtt) protein causes Huntington's disease (HD). Sulforaphane (SFN), a naturally occurring compound, increased proteasome and autophagy activities in vivo and enhanced mHtt turnover and cell survival in HD cell models. SFN-mediated mHtt degradation is mainly through the proteasome pathway. These data suggest that SFN can be a therapeutic reagent for treating HD and other intractable disorders.

Mitochondrial permeability transition pore induces mitochondria injury in Huntington disease

Background

Mitochondrial impairment has been implicated in the pathogenesis of Huntington’s disease (HD). However, how mutant huntingtin impairs mitochondrial function and thus contributes to HD has not been fully elucidated. In this study, we used striatal cells expressing wild type (STHdh^Q7/Q7) or mutant (STHdh^Q111/Q111) huntingtin protein, and cortical neurons expressing the exon 1 of the huntingtin protein with physiological or pathological polyglutamine domains, to examine the interrelationship among specific mitochondrial functions.

Results

Depolarization induced by KCl resulted in similar changes in calcium levels without compromising mitochondrial function, both in wild type and mutant cells. However, treatment of mutant cells with thapsigargin (a SERCA antagonist that raises cytosolic calcium levels), resulted in a pronounced decrease in mitochondrial calcium uptake, increased production of reactive oxygen species (ROS), mitochondrial depolarization and fragmentation, and cell viability loss. The mitochondrial dysfunction in mutant cells was also observed in cortical neurons expressing exon 1 of the huntingtin protein with 104 Gln residues (Q104-GFP) when they were exposed to calcium stress. In addition, calcium overload induced opening of the mitochondrial permeability transition pore (mPTP) in mutant striatal cells. The mitochondrial impairment observed in mutant cells and cortical neurons expressing Q104-GFP was prevented by pre-treatment with cyclosporine A (CsA) but not by FK506 (an inhibitor of calcineurin), indicating a potential role for mPTP opening in the mitochondrial dysfunction induced by calcium stress in mutant huntingtin cells.

Conclusions

Expression of mutant huntingtin alters mitochondrial and cell viability through mPTP opening in striatal cells and cortical neurons.

Development of an ELISA assay for the quantification of soluble huntingtin in human blood cells

Background

Huntington’s disease (HD) is a monogenic disorder caused by an aberrant expansion of CAG repeats in the huntingtin gene (HTT). Pathogenesis is associated with expression of the mutant (mHTT) protein in the CNS, with its levels most likely related to disease progression and symptom severity. Since non-invasive methods to quantify HTT in the CNS do not exist, measuring amount of soluble HTT in peripheral cells represents an important step in development of disease-modifying interventions in HD.

Results

An ELISA assay using commercially available antibodies was developed to quantify HTT levels in complex matrices like mammalian cell cultures lysates and human samples. The immunoassay was optimized using a recombinant full-length HTT protein, and validated both on wild-type and mutant HTT species. The ability of the assay to detect significant variations of soluble HTT levels was evaluated using an HSP90 inhibitor that is known to enhance HTT degradation. Once optimized, the bioassay was applied to peripheral blood mononuclear cells (PBMCs) from HD patients, demonstrating good potential in tracking the disease course.

Conclusions

The method described here represents a validated, simple and rapid bio-molecular assay to evaluate soluble HTT levels in blood cells as useful tool in disease and pharmacodynamic marker identification for observational and clinical trials.

NRF2-regulation in brain health and disease: implication of cerebral inflammation

The nuclear factor erythroid 2 related factor 2 (NRF2) is a key regulator of endogenous inducible defense systems in the body. Under physiological conditions NRF2 is mainly located in the cytoplasm. However, in response to oxidative stress, NRF2 translocates to the nucleus and binds to specific DNA sites termed "anti-oxidant response elements" or "electrophile response elements" to initiate transcription of cytoprotective genes. Acute oxidative stress to the brain, such as stroke and traumatic brain injury is increased in animals that are deficient in NRF2. Insufficient NRF2 activation in humans has been linked to chronic diseases such as Parkinson's disease, Alzheimer's disease and amyotrophic lateral sclerosis. New findings have also linked activation of the NRF2 system to anti-inflammatory effects via interactions with NF-κB. Here we review literature on cellular mechanisms of NRF2 regulation, how to maintain and restore NRF2 function and the relationship between NRF2 regulation and brain damage. We bring forward the hypothesis that inflammation via prolonged activation of key kinases (p38 and GSK-3β) and activation of histone deacetylases gives rise to dysregulation of the NRF2 system in the brain, which contributes to oxidative stress and injury.

Oxidizing effects of exogenous stressors in Huntington's disease knock-in striatal cells--protective effect of cystamine and creatine

Huntington's disease (HD) is a polyglutamine-expansion disease associated to degeneration of striatal and cortical neurons. Previously, we showed that oxidative stress occurs in HD knock-in striatal cells, but little is known regarding cell antioxidant response against exogenous stimuli. Therefore, in the present study we analyzed cellular antioxidant profile following hydrogen peroxide (H2O2) and staurosporine (STS) exposure and tested the protective effect of cystamine and creatine in striatal cells expressing mutant huntingtin with 111 glutamines (STHdh (Q111/Q111); mutant cells) versus wild-type cells (STHdh (Q7/Q7)). Mutant cells displayed increased mitochondrial reactive oxygen species (ROS) and decreased NADPH oxidase and xanthine oxidase (XO) activities, reflecting lower superoxide cytosolic generation, along with increased superoxide dismutases (SODs) and components of glutathione redox cycle. Exposure to H2O2 and STS enhanced ROS in mutant cells and largely increased XO activity; STS further boosted the generation of mitochondrial ROS and caspase-3 activity. Both stimuli slightly increased SOD1 activity, without affecting SOD2 activity, and decreased glutathione reductase with a consequent rise in oxidized glutathione or glutathione disulfide in mutant cells, whereas H2O2 only increased glutathione peroxidase activity. Additionally, creatine and cystamine increased mutant cells viability and prevented ROS formation in HD cells subjected to H2O2 and STS. These results indicate that elevation of the antioxidant systems accompanies mitochondrial-driven ROS generation in mutant striatal cells and that exposure to noxious stimuli induces a higher susceptibility to oxidative stress by increasing XO activity and lowering the antioxidant response. Furthermore, creatine and cystamine are efficient in preventing H2O2- and STS-evoked ROS formation in HD striatal cells.