Knockdown of Cytosolic Glutaredoxin 1 Leads to Loss of Mitochondrial Membrane Potential: Implication in Neurodegenerative Diseases

Mitochondrial dysfunction including that caused by oxidative stress has been implicated in the pathogenesis of neurodegenerative diseases. Glutaredoxin 1 (Grx1), a cytosolic thiol disulfide oxido-reductase, reduces glutathionylated proteins to protein thiols and helps maintain redox status of proteins during oxidative stress. Grx1 downregulation aggravates mitochondrial dysfunction in animal models of neurodegenerative diseases, such as Parkinson's and motor neuron disease. We examined the mechanism underlying the regulation of mitochondrial function by Grx1. Downregulation of Grx1 by shRNA results in loss of mitochondrial membrane potential (MMP), which is prevented by the thiol antioxidant, α-lipoic acid, or by cyclosporine A, an inhibitor of mitochondrial permeability transition. The thiol groups of voltage dependent anion channel (VDAC), an outer membrane protein in mitochondria but not adenosine nucleotide translocase (ANT), an inner membrane protein, are oxidized when Grx1 is downregulated. We then examined the effect of β-N-oxalyl amino-L-alanine (L-BOAA), an excitatory amino acid implicated in neurolathyrism (a type of motor neuron disease), that causes mitochondrial dysfunction. Exposure of cells to L-BOAA resulted in loss of MMP, which was prevented by overexpression of Grx1. Grx1 expression is regulated by estrogen in the CNS and treatment of SH-SY5Y cells with estrogen upregulated Grx1 and protected from L-BOAA mediated MMP loss. Our studies demonstrate that Grx1, a cytosolic oxido-reductase, helps maintain mitochondrial integrity and prevents MMP loss caused by oxidative insult. Further, downregulation of Grx1 leads to mitochondrial dysfunction through oxidative modification of the outer membrane protein, VDAC, providing support for the critical role of Grx1 in maintenance of MMP

Dopaminergic D1 receptor signalling is necessary, but not sufficient for cued fear memory destabilisation

Rationale. Pharmacological targeting of memory reconsolidation is a promising therapeutic strategy for the treatment of fear memory-related disorders. However, the success of reconsolidation-based approaches depends upon the effective destabilisation of the fear memory by memory reactivation. Objectives. Here, we aimed to determine the functional involvement of dopamine D1 receptors in cued fear memory destabilisation, using systemic drug administration. Results. We observed that direct D1 receptor agonism was not sufficient to stimulate tone fear memory destabilisation to facilitate reconsolidation disruption by the glucocorticoid receptor antagonist mifepristone. Instead, administration of the nootropic nefiracetam did facilitate mifepristone-induced amnesia, in a manner that was dependent upon dopamine D1 receptor activation, although. Finally, while the combined treatment with nefiracetam and mifepristone did not confer fear-reducing effects under conditions of extinction learning, there was some evidence that mifepristone reduces fear expression irrespective of memory reactivation parameters. Conclusions. The use of combination pharmacological treatment to stimulate memory destabilisation and impair reconsolidation has potential therapeutic benefits, without risking a maladaptive increase of fear

The 'Arctic' APP mutation (E693G) causes Alzheimer's disease by enhanced Abeta protofibril formation.

Several pathogenic Alzheimer's disease (AD) mutations have been described, all of which cause increased amyloid beta-protein (Abeta) levels. Here we present studies of a pathogenic amyloid precursor protein (APP) mutation, located within the Abeta sequence at codon 693 (E693G), that causes AD in a Swedish family. Carriers of this 'Arctic' mutation showed decreased Abeta42 and Abeta40 levels in plasma. Additionally, low levels of Abeta42 were detected in conditioned media from cells transfected with APPE693G. Fibrillization studies demonstrated no difference in fibrillization rate, but Abeta with the Arctic mutation formed protofibrils at a much higher rate and in larger quantities than wild-type (wt) Abeta. The finding of increased protofibril formation and decreased Abeta plasma levels in the Arctic AD may reflect an alternative pathogenic mechanism for AD involving rapid Abeta protofibril formation leading to accelerated buildup of insoluble Abeta intra- and/or extracellularly

The 'Arctic' APP mutation (E693G) causes Alzheimer's disease by enhanced Abeta protofibril formation.

Several pathogenic Alzheimer's disease (AD) mutations have been described, all of which cause increased amyloid beta-protein (Abeta) levels. Here we present studies of a pathogenic amyloid precursor protein (APP) mutation, located within the Abeta sequence at codon 693 (E693G), that causes AD in a Swedish family. Carriers of this 'Arctic' mutation showed decreased Abeta42 and Abeta40 levels in plasma. Additionally, low levels of Abeta42 were detected in conditioned media from cells transfected with APPE693G. Fibrillization studies demonstrated no difference in fibrillization rate, but Abeta with the Arctic mutation formed protofibrils at a much higher rate and in larger quantities than wild-type (wt) Abeta. The finding of increased protofibril formation and decreased Abeta plasma levels in the Arctic AD may reflect an alternative pathogenic mechanism for AD involving rapid Abeta protofibril formation leading to accelerated buildup of insoluble Abeta intra- and/or extracellularly

Serotoninergics Attenuate Hyperlocomotor Activity in Rats. Potential New Therapeutic Strategy for Hyperactivity

Hyperactivity is thought to be associated with an alteration of dopamine (DA) neurochemistry in brain. This conventional view became solidified on the basis of observed hyperactivity in DA-lesioned animals and effectiveness of the dopaminomimetics such as amphetamine (AMP) in abating hyperactivity in humans and in animal models of hyperactivity. However, because AMPreleases serotonin (5-HT) as well as DA, we investigated the potential role of 5-HT in an animal model of hyperactivity. We found that a greater intensity of hyperactivity was produced in rats when both DA and 5-HT neurons were damaged at appropriate times in ontogeny. Therefore, previously we proposed this as an animal model of attention deficit hyperactivity disorder (ADHD) - induced by destruction of dopaminergic neurons with 6-hydroxydopamine (6-OHDA (neonatally) and serotoninergic neurons with 5,7-dihydroxytryptamine (5,7-DHT) (in adulthood). In this model effects similar to that of AMP(attenuation of hyperlocomotion) were produced by m-chlorophenylpiperazine (m-CPP) but not by 1-phenylbiguanide (1-PG), respective 5-HT2 and 5-HT3 agonists. The effect of m-CPP was shown to be replicated by desipramine, and was largely attenuated by the 5-HT2 antagonist mianserin. These findings implicate 5-HT neurochemistry as potentially important therapeutic targets for treating human hyperactivity and possibly childhood ADHD

Altered Corticostriatal Connectivity and Exploration/Exploitation Imbalance Emerge as Intermediate Phenotypes for a Neonatal Dopamine Dysfunction

Findings showing that neonatal lesions of the forebrain dopaminergic system in rodents lead to juvenile locomotor hyperactivity and learning deficits have been taken as evidence of face validity for the attention deficit hyperactivity disorder. However, the core cognitive and physiological intermediate phenotypes underlying this rodent syndrome remain unknown. Here we show that early postnatal dopaminergic lesions cause long-lasting deficits in exploitation of shelter, social and nutritional resources, and an imbalanced exploratory behavior, where nondirected local exploration is exacerbated, whereas sophisticated search behaviors involving sequences of goal directed actions are degraded. Importantly, some behavioral deficits do not diminish after adolescence but instead worsen or mutate, particularly those related to the exploration of wide and spatially complex environments. The in vivo electrophysiological recordings and morphological reconstructions of striatal medium spiny neurons reveal corticostriatal alterations associated to the behavioral phenotype. More specifically, an attenuation of corticostriatal functional connectivity, affecting medial prefrontal inputs more markedly than cingulate and motor inputs, is accompanied by a contraction of the dendritic arbor of striatal projection neurons in this animal model. Thus, dopaminergic neurons are essential during postnatal development for the functional and structural maturation of corticostriatal connections. From a bottom-up viewpoint, our findings suggest that neuropsychiatric conditions presumably linked to developmental alterations of the dopaminergic system should be evaluated for deficits in foraging decision making, alterations in the recruitment of corticostriatal circuits during foraging tasks, and structural disorganization of the frontostriatal connections.Fil: Braz, Bárbara Yael. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Fisiología y Biofísica Bernardo Houssay. Universidad de Buenos Aires. Facultad de Medicina. Instituto de Fisiología y Biofísica Bernardo Houssay; ArgentinaFil: Galiñanes, Gregorio Luis. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Fisiología y Biofísica Bernardo Houssay. Universidad de Buenos Aires. Facultad de Medicina. Instituto de Fisiología y Biofísica Bernardo Houssay; Argentina. Universidad de Ginebra; SuizaFil: Taravini, Irene Rita Eloisa. Universidad de Buenos Aires. Facultad de Farmacia y Bioquímica; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Belforte, Juan Emilio. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Fisiología y Biofísica Bernardo Houssay. Universidad de Buenos Aires. Facultad de Medicina. Instituto de Fisiología y Biofísica Bernardo Houssay; ArgentinaFil: Murer, Mario Gustavo. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Fisiología y Biofísica Bernardo Houssay. Universidad de Buenos Aires. Facultad de Medicina. Instituto de Fisiología y Biofísica Bernardo Houssay; Argentin