A Combined Pathway and Regional Heritability Analysis Indicates NETRIN1 Pathway is Associated with Major Depressive Disorder

AbstractBackgroundGenome-wide association studies (GWASs) of major depressive disorder (MDD) have identified few significant associations. Testing the aggregation of genetic variants, in particular biological pathways, may be more powerful. Regional heritability analysis can be used to detect genomic regions that contribute to disease risk.MethodsWe integrated pathway analysis and multilevel regional heritability analyses in a pipeline designed to identify MDD-associated pathways. The pipeline was applied to two independent GWAS samples [Generation Scotland: The Scottish Family Health Study (GS:SFHS, N = 6455) and Psychiatric Genomics Consortium (PGC:MDD) (N = 18,759)]. A polygenic risk score (PRS) composed of single nucleotide polymorphisms from the pathway most consistently associated with MDD was created, and its accuracy to predict MDD, using area under the curve, logistic regression, and linear mixed model analyses, was tested.ResultsIn GS:SFHS, four pathways were significantly associated with MDD, and two of these explained a significant amount of pathway-level regional heritability. In PGC:MDD, one pathway was significantly associated with MDD. Pathway-level regional heritability was significant in this pathway in one subset of PGC:MDD. For both samples the regional heritabilities were further localized to the gene and subregion levels. The NETRIN1 signaling pathway showed the most consistent association with MDD across the two samples. PRSs from this pathway showed competitive predictive accuracy compared with the whole-genome PRSs when using area under the curve statistics, logistic regression, and linear mixed model.ConclusionsThese post-GWAS analyses highlight the value of combining multiple methods on multiple GWAS data for the identification of risk pathways for MDD. The NETRIN1 signaling pathway is identified as a candidate pathway for MDD and should be explored in further large population studies

Desarrollo de un modelo experimental de estrés oxidativo in vivo

Memoria presentada por Seila Fernández Fernández para optar al Título de Doctor Europaeus, que ha sido realizada en el Departamento de Bioquímica y Biología Molecular y en el Instituto de Biología Funcional y Genómica, de la Universidad de Salamanca.The deleterious effects of reactive oxygen species (ROS) occur during adulthood, and it has been suggested that excess ROS -oxidative stress- may be a contributing factor in neurodegenerative processes. Glutathione (GSH) is one of the most abundant antioxidants and, in neurological diseases such as Parkinson's disease or mental disorders, GSH deficiency is the earliest known biochemical indicator of neuronal degeneration.This observation has led to the suggestion that oxidative stress may be behind the causes of neuronal dysfunction associated with these neurological disorders. Unfortunately, due to the lack of a sufficiently robust tool, the specific effect of GSH deficiency in the pathogenesis of neurological diseases has never been shown in vivo, thus the actual role of GSH loss-mediated oxidative stress in these disorders still remains elusive. Glutathione is a tripeptide (g-glutamylcysteinilglycine) synthesized by two consecutive ATP-dependent reactions. Glutamate-cysteine ligase (GCL or g-glutamylcysteine synthetase; EC 6.3.2.2) catalyzes the first -and rate-limiting- step, forming g-glutamylcysteine from glutamate and cysteine. This is followed by the glutathione synthetase (EC 6.3.2.3)-catalyzed reaction, which binds glycine to g-glutamylcysteine, forming glutathione. GCL is a heterodimeric enzyme composed of a catalytic (heavy; 73 kDa) and a modulatory (light; 27.7 kDa) subunit. Studies performed with purified GCL have shown that the active site resides at the catalytic subunit, whereas the modulatory subunit increases the affinity of the catalytic subunit for glutamate and decreases the sensitivity to feedback inhibition by GSH . In the brain, where -to the best of our knowledge- the enzyme has never been purified, GCL activity is very weak, although it is higher in astrocytes when compared with neurons.This contributes to the higher resistance of astrocytes, when compared with neurons, against oxidative stress. Astrocytes co-operate with neurons for neuronal antioxidant GSH biosynthesis by supplying GSH precursors. Thus, limiting either the supply of precursors, or the ability of neurons to use them, triggers oxidative stress in neurons leading to neurodegeneration, at least in culture. This has led us to hypothesize that neuronal-specific and temporally-controlled knockdown of GCL in vivo may lead to spontaneous neurological dysfunction, thus possibly mimicking the neurological problems associated with Parkinson's or mental diseases and potentially useful for the identification of novel redox-sensitive proteins involved in neurological disorders.The existing in vivo models for studying GCL, catalytic subunit, deficiency in the brain are scarce and failed. Homozygous knockout mice against GCL, catalytic subunit, are not viable beyond embryonic day 8th, and the heterozygous ones display compensation mechanisms such as increased ascorbate biosynthesis. In addition, this available genetic system does not knockout GCL tissue specifically or temporally controlled, thus being unsuitable to investigate the role of oxidative stress in central nervous system during adulthood. We had previously identified a small hairpin RNA (shRNA) targeted against GCL, catalytic subunit that, in cultured neurons, triggered spontaneous oxidative stress. We have implemented RNAi strategy in vivo to produce a double-conditional mouse expressing the GCL shRNA in the cells of the central nervous system, particularly hippocampal neurons, to recreate oxidative stress in vivo t tissue specific and inducible way. We used Cre-LoxP technology to create mice expressing shGCL in neurons in vivo, and they were characterized biochemically, immuno-histologically and behaviorally. We found a decrease in GCL, and an increase in oxidative markers. We also found sex-dependent effects in behavioural characterization for anxiety, motor ability and memory tasks.In conclusion, here we describe a novel strategy for studying oxidative stress in vivo in a tissue specific and time-controlled manner. This model may open new possibilities to study the involvement of elevated ROS in mental illnesses, such as Alzheimer's disease or anxiety, which are intrinsic to a number of psychiatric disorders including depression, panic attacks, phobias, obsessive-compulsive disorder and post-traumatic stress; however, these diseases currently lack of appropriate in vivo models for research on new therapeutic strategies. Furthermore, since we designed the genetic tool with two unique restriction sites flanking the shRNA sequence, new transgenic mice models could be straightforward generated to knockdown any other protein tissue-specifically in vivo. We believe that the transgenic mouse model herein described may be useful for a better understanding of the consequences of oxidative stress in specific cells in vivo, as well as for assessing novel pharmacological approaches.Gracias a la financiación del gobierno español bajo todas y cada una de sus cambiantes y caóticas denominaciones: MEC, MECyD, MECPSyD y el prometedor MICIIN finalmente reducido a una simple secretaría de estado de investigación en el MINECO. Gracias por las diferentes becas que he disfrutado durante toda mi formación, y en especial por el Programa Nacional de Formación de Profesorado Universitario (PNFPU), del que he sido beneficiaria, así como diversos contratos de investigación. Gracias también a la organización EMBO, por financiar mi estancia en el extranjero.Peer reviewe

Neuron-specific oxidative stress using a novel RNAi strategy in vivo causes cognitive impairment and carbonylation of key dendrite proteins

Resumen del póster presentado al XXXVI Congreso de la Sociedad Española de Bioquímica y Biología Molecular celebrado en Madrid del 3 al 6 de septiembre de 2013.Excess reactive oxygen species is behind the causes of neurological disorders, but the lack of tissue-specific experimental models of oxidative stress has complicated in vivo demonstration of proof-of-concept and mechanisms. Here, we designed and constructed a DNA vector with two unique restriction sites ready to insert any small hairpin RNA (shRNA) sequence in the opposite strand orientation, flanked by LoxP and Lox2272 sites, and governed by the polymerase III (H1) promoter. This DNA construct, after insertion of any shRNA, is suitable to trigger protein knockdown-mediated loss-of-function after tissue specific Cre-mediated recombination in vitro or in vivo. Using this strategy, we inserted a previously validated shRNA sequence targeted against glutamate-cysteine ligase catalytic subunit (GCL), the rate-limiting step in glutathione biosynthesis, into the above-mentioned DNA vector. With this shGCLfloxed DNA construct, we generated several transgenic mice founders, one of which harbored a unique insertion site and showed no apparent biochemical or phenotypic alterations. This shGCLfloxed mouse was crossed with mice harboring Cre recombinase governed by the neuron-specific CaMKIIα promoter (CaMKIIα-Cre), which is active after two postnatal weeks. The resulting CaMKIIα-shGCL mouse showed decreased GCL protein levels and increased signs of oxidative stress in hippocampal neurons during adulthood in vivo, as well as cognitive impairment. Oxy-proteome analysis of this region revealed a 3-fold increase in carbonylation of several proteins, of which at least one is involved in dendrite formation. To the best of our knowledge, this is the first evidence showing that neuron-specific oxidative stress in vivo oxidizes a key protein involved in memory formation leading to signs of dementia.Peer Reviewe

Hippocampal neurons require a large pool of glutathione to sustain dendrite integrity and cognitive function

Loss of brain glutathione has been associated with cognitive decline and neuronal death during aging and neurodegenerative diseases. However, whether decreased glutathione precedes or follows neuronal dysfunction has not been unambiguously elucidated. Previous attempts to address this issue were approached by fully eliminating glutathione, a strategy causing abrupt lethality or premature neuronal death that led to multiple interpretations. To overcome this drawback, here we aimed to moderately decrease glutathione content by genetically knocking down the rate-limiting enzyme of glutathione biosynthesis in mouse neurons in vivo. Biochemical and morphological analyses of the brain revealed a modest glutathione decrease and redox stress throughout the hippocampus, although neuronal dendrite disruption and glial activation was confined to the hippocampal CA1 layer. Furthermore, the behavioral characterization exhibited signs consistent with cognitive impairment. These results indicate that the hippocampal neurons require a large pool of glutathione to sustain dendrite integrity and cognitive function. Keywords: Neurons, Glutamate-cysteine ligase, Glutathione, In vivo knockdown, Dendrite disruption, Memory impairmen

ARMS/Kidins220 temporally coordinates neurotrophin-mediated differentiation and -regulated BDNF secretion

Resumen del trabajo presentado al XXXXVIII Congreso de la Sociedad Española de Bioquímica y Biología Molecular (SEBBM), celebrado en Valencia del 7 al 10 de septiembre de 2015.During nervous system development secretion must be tightly controlled meanwhile neurons differentiate projecting axons and dendrites to their specific targets. Neurotrophins regulate, among other functions, differentiation and regulated secretion in the nervous system. However, the molecular mechanisms underlying the temporal coordination of differentiation and secretion by neurotrophins are unknown. Here we describe the involvement of ARMS/Kidins220, a downstream protein of Trk neurotrophin receptors, acting through Synembryn-B and Trio in the regulated secretion mediated by neurotrophins. We observed that PC12 differentiation and regulated secretion are temporally controlled since non-differentiated or differentiated neurons display a poor or strong regulated secretion in response to neurotrophins, respectively. Interestingly, high levels of ARMS/Kidins220 and Synembryn-B are required for differentiation, when regulated secretion is minimal, whereas a strong downregulation of both proteins occurred once the cells are differentiated, when regulated secretion is maximal. Overexpression or downregulation of ARMS/Kidins220 and Synembryn-B levels in non-differentiated PC12 cells blocks or potentiates NGF-mediated secretion, respectively. Similarly, secretion of BDNF in cortical neurons in response to NT-3 or NT-4 augments with a concomitant downregulation of ARMS/Kidins220 and Synembryn-B protein levels. In addition, knockdown of ARMS/Kidins220 and Synembryn-B potentiated further BDNF evoked secretion. Finally, downregulation of ARMS/Kidins220 protein in vivo enhanced BDNF secretion from cortex in response to depolarization, NT-3 or NT-4 and a signifi cant accumulation of BDNF in the striatum coming from the cortex and hippocampus.Peer reviewe

Regulation of BDNF release by ARMS/Kidins220 through modulation of synaptotagmin-IV levels

BDNF is a growth factor with important roles in the nervous system in both physiological and pathological conditions, but the mechanisms controlling its secretion are not completely understood. Here, we show that ARMS/Kidins220 negatively regulates BDNF secretion in neurons from the CNS and PNS. Downregulation of the ARMS/Kidins220 protein in the adult mouse brain increases regulated BDNF secretion, leading to its accumulation in the striatum. Interestingly, two mouse models of Huntington's disease (HD) showed increased levels of ARMS/Kidins220 in the hippocampus and regulated BDNF secretion deficits. Importantly, reduction of ARMS/Kidins220 in hippocampal slices from HD mice reversed the impaired regulated BDNF release. Moreover, there are increased levels of ARMS/Kidins220 in the hippocampus and PFC of patients with HD. ARMS/Kidins220 regulates Synaptotagmin-IV levels, which has been previously observed to modulate BDNF secretion. These data indicate that ARMS/Kidins220 controls the regulated secretion of BDNF and might play a crucial role in the pathogenesis of HD.This work was supported by MINECO BFU2011-22898, BFU2014-51846-R, and BFU2017-82667-R to J.C.A. and SAF2013-41177-RtoJ.P.B., andthe EU 7th Framework Program(Marie Curie IRG and PAINCAGE)toJ.C.A. S.L.-B.was supported by Consejería de Educacio´n Junta de Castilla y Leo´n and the European Social Fund. M.E.P. and L.T. were supported by the National Institutes of Health Intramural Research Program, Center for Cancer Research, National Cancer Institute.Peer reviewe