USING RECOMBINANT HUMAN CARBAMOYL PHOSPHATE SYNTHETASE 1 (CPS1) FOR STUDYING THIS ENZYME'S FUNCTION, REGULATION, PATHOLOGY AND STRUCTURE

Tesis por compendio[EN] Carbamoyl phosphate synthetase 1 (CPS1), a 1462-residue mitochondrial enzyme, catalyzes the entry of ammonia into the urea cycle, which converts ammonia, the neurotoxic waste product of protein catabolism, into barely toxic urea. The urea cycle inborn error and rare disease CPS1 deficiency (CPS1D) is inherited with mendelian autosomal recessive inheritance, being due to CPS1 gene mutations (>200 mutations reported), and causing life-threatening hyperammonemia. We have produced recombinantly human CPS1 (hCPS1) in a baculovirus/insect cell expression system, isolating the enzyme in active and highly purified form, in massive amounts. This has allowed enzyme crystallization for structural studies by X-ray diffraction (an off-shoot of the present studies). This hCPS1 production system allows site-directed mutagenesis and enzyme characterization as catalyst (activity, kinetics) and as protein (stability, aggregation state, domain composition). We have revealed previously unexplored traits of hCPS1 such as its domain composition, the ability of glycerol to replace the natural and essential CPS1 activator N-acetyl-L-glutamate (NAG), and the hCPS1 protection (chemical chaperoning) by NAG and by its pharmacological analog N-carbamyl-L-glutamate (NCG). We have exploited this system to explore the effects on the activity, kinetic parameters and stability/folding of the enzyme, and to test the disease-causing nature, of mutations identified in patients with CPS1 deficiency (CPS1D). These results, supplemented with those obtained with other non-clinical mutations, have provided novel information on the functions of three non-catalytic domains of CPS1. We have introduced three CPS1D-associated mutations and one trivial polymorphism in the glutaminase-like domain of CPS1, supporting a stabilizing and an activity-enhancing function of this non-catalytic domain. Two mutations introduced into the bicarbonate phosphorylation domain have shed light on bicarbonate binding and have directly confirmed the importance of this domain for NAG binding to the distant (in the sequence) C-terminal CPS1 domain. The introduction of 18 CPS1D-associated missense mutations mapping in a clinically highly eloquent central non-catalytic domain have proven the disease-causing nature of most of these mutations while showing that in most of the cases they trigger enzyme misfolding and/or destabilization. These results, by proving an important role of this domain in the structural integration of the multidomain CPS1 protein, have led us to call this domain the Integrating Domain. Finally, we have examined the effects of eight CPS1D-associated mutations, of one trivial polymorphism and of five non-clinical mutations, all of them mapping in the C-terminal domain of the enzyme where NAG binds, whereas we have re-analyzed prior results with another four clinical and five non-clinical mutations affecting this domain. We have largely confirmed the pathogenic nature of the clinical mutations, predominantly because of decreased activity, in many cases due to hampered NAG binding. A few mutations had substantial negative effects on CPS1 stability/folding. Our analysis reveals that NAG activation begins with a movement of the final part of the ß4-¿4 loop of the NAG site. Transmission of the activating signal to the phosphorylation domains involves helix ¿4 from this domain and is possibly transmitted by the mutually homologous loops 1313-1332 and 778-787 (figures are residue numbers) belonging, respectively, to the carbamate and bicarbonate phosphorylation domains. These two homologous loops are called from here on Signal Transmission Loops.[ES] La carbamil fosfato sintetasa 1 (CPS1), una enzima mitocondrial, cataliza la entrada del amonio en el ciclo de la urea, que convierte esta neurotoxina derivada del catabolismo de las proteínas en urea, mucho menos tóxica. El déficit de CPS1 (CPS1D) es un error innato del ciclo de la urea, una enfermedad rara autosómica recesiva, que se debe a mutaciones en el gen CPS1 (>200 mutaciones descritas) y que cursa con hiperamonemia. Hemos producido CPS1 humana recombinante (hCPS1) en un sistema de expresión de células de insecto y baculovirus, y la hemos aislado en forma activa, muy pura y en cantidad elevada. Este sistema de producción de hCPS1 permite la realización de mutagénesis dirigida y la caracterización de la enzima como catalizador (actividad, cinética) y como proteína (estabilidad, estado de agregación y composición de dominios). Hemos revelado características de la hCPS1 antes no exploradas como es la composición de dominios, la capacidad que tiene el glicerol para reemplazar al activador natural y esencial de la CPS1, N-acetil-L-glutamato (NAG), y la protección de la hCPS1 por NAG y por su análogo farmacológico N-carbamil-L-glutamato (NCG) (chaperonas químicas). Hemos utilizado este sistema para explorar los efectos en actividad, parámetros cinéticos y estabilidad/plegamiento de la enzima, y para comprobar la naturaleza patogénica de mutaciones identificadas en pacientes con CPS1D. Estos resultados, junto con los obtenidos con otras mutaciones no clínicas, han aportado información novedosa sobre tres de los dominios no catalíticos de CPS1. Las observaciones realizadas tras introducir en el dominio de tipo glutaminasa de la enzima tres mutaciones asociadas a CPS1D y un polimorfismo trivial, apoyan la contribución de este dominio no catalítico a la estabilidad y a aumentar la actividad de la enzima. Dos mutaciones introducidas en el dominio de fosforilación de bicarbonato han arrojado luz sobre el modo de unión del bicarbonato (un sustrato). Los resultados de estas mutaciones también han confirmado la contribución de este dominio para la unión de NAG, cuyo sitio de unión se encuentra en el dominio C-terminal de CPS1, bastante alejado (en la secuencia) del dominio de fosforilación de bicarbonato. Además, hemos introducido 18 mutaciones de cambio de sentido asociadas a CPS1D, las cuales están localizadas en un dominio no catalítico, central y de elevada elocuencia clínica. Estos resultados han demostrado la naturaleza patogénica de estas mutaciones, ya que en la mayoría de los casos estas mutaciones producen un mal plegamiento o/y desestabilización de la enzima. Debido a que estos resultados han puesto de manifiesto el importante papel de este dominio en la integración estructural de la proteína multidominio CPS1, lo hemos llamado Dominio Integrador. Finalmente, hemos examinado los efectos de 8 mutaciones asociadas a CPS1D, de un polimorfismo trivial y de 5 mutaciones no clínicas, todas localizadas en el dominio C-terminal de la enzima, donde se une NAG. Además, hemos reanalizado resultados anteriores con otras 4 mutaciones clínicas y 5 no clínicas afectando a este dominio. Hemos confirmado el carácter patogénico de las mutaciones clínicas, las cuales predominantemente causan una disminución en la actividad enzimática, en muchos casos debida a que la unión de NAG se encuentra obstaculizada. Unas pocas mutaciones mostraron efectos negativos en la estabilidad/plegamiento de CPS1. Nuestros análisis revelan que la activación por el NAG empieza con un movimiento de la parte final del bucle ß4-¿4 del sitio de NAG. La transmisión de la señal activadora a los dominios de fosforilación implica a la hélice ¿4 de este dominio y posiblemente se transmite a través de los bucles homólogos 1313-1332 y 778-787 (numeración de residuos) pertenecientes, respectivamente, a los dominios de fosforilación de carbamato y bicarbonato. Por ello, hemos llamado a ambos bucles Bucles de[CA] La carbamil fosfat sintetasa 1 (CPS1), un enzim mitocondrial, catalitza l'entrada d'amoni en el cicle de la urea, que convertix l'amoni, producte neurotòxic del catabolisme de les proteïnes, en urea, una molècula molt poc tòxica. El dèficit de CPS1 (CPS1D) és un error innat del cicle de la urea, una malaltia rara autosòmica recessiva, que es deu a mutacions en el gen CPS1 (>200 mutacions descrites) i que cursa amb hiperamonièmia. Hem produït CPS1 humana recombinant (hCPS1) en un sistema d'expressió de cèl·lules d'insecte i baculovirus, i l'hem aïllada en forma activa, molt pura i en gran quantitat. Això ha permés la cristal·lització de l'enzim per a estudis estructurals amb difracció de raios-X (treball no inclòs en esta tesi Aquest sistema de producció de hCPS1 permet la realització de mutagènesi dirigida i la caracterització de l'enzim com a catalitzador (activitat, cinètica) i com a proteïna (estabilitat, estat d'agregació i composició de dominis). Hem revelat característiques de la hCPS1 no explorades abans com és la composició de dominis, la capacitat que té el glicerol per a reemplaçar l'activador natural i essencial de CPS1, N-acetil-L-glutamat (NAG), i la protecció de la hCPS1 per NAG i pel seu anàleg farmacològic N-carbamil-L-glutamat (NCG) (xaperones químiques) . Hem utilitzat aquest sistema per a explorar els efectes en l'activitat, els paràmetres cinètics i l'estabilitat/plegament de l'enzim, i per a comprovar la naturalesa patogènica de mutacions identificades en pacients amb CPS1D. Aquestos resultats, junt amb els obtinguts amb altres mutacions no clíniques, han aportat informació nova sobre tres dels dominis no catalítics de la CPS1. Les observacions, després d'introduir tres mutacions associades a CPS1D i un polimorfisme trivial en el domini tipus glutaminasa de CPS1, recolzen la contribució d'aquest domini no catalític a l'estabilitat i a l'optimització de l'activitat enzimàtica. Dues mutacions introduïdes en el domini de fosforilació de bicarbonat han esclarit el mode d'unió de bicarbonat. Els resultats d'aquestes mutacions també han confirmat la contribució d'aquest domini per a la unió de NAG, el lloc d'unió de la qual es troba en el domini C-terminal de CPS1, prou allunyat (en la seqüència) del domini de fosforilació de bicarbonat. A més, hem introduït 18 mutacions de canvi de sentit associades a CPS1D, les quals estan localitzades en un domini no catalític, central i d'elevada eloqüència clínica. Aquestos resultats han demostrat la naturalesa patogènica d'aquestes mutacions, ja que, en la majoria dels casos produïxen un mal plegament o/i desestabilització de l'enzim. Pel fet que aquestos resultats han posat de manifest l'important paper d'aquest domini en la integració estructural de la proteïna multidomini CPS1, l'hem anomenat Domini Integrador. Finalment, hem examinat els efectes de huit mutacions associades a CPS1D, un polimorfisme trivial i cinc mutacions no clíniques, totes elles localitzades en el domini C-terminal de l'enzim, on s'unix NAG. A més, hem reanalitzat resultats anteriors amb altres quatre mutacions clíniques i cinc no clíniques que afecten aquest domini. Hem confirmat el caràcter patogènic de les mutacions clíniques, les quals predominantment causen una disminució en l'activitat enzimàtica, en molts casos pel fet que la unió de NAG es troba obstaculitzada. Unes poques mutacions van mostrar efectes negatius substancials en l'estabilitat/plegament de CPS1. Les nostres anàlisis revelen que l'activació de NAG comença amb un moviment de la part final del bucle ß4-¿4 del lloc de NAG. La transmissió del senyal activadora als dominis de fosforilació involucra l'hèlix ¿4 d'aquest domini i es transmet, possiblement, a través dels bucles homòlegs 1313-1332 i 778-787 (numeració dels residus), pertanyents, respectivament, als dominis de fosforilació de carbamato i bicarbonat. Per això, hem anomenat a ambdDíez Fernández, C. (2015). USING RECOMBINANT HUMAN CARBAMOYL PHOSPHATE SYNTHETASE 1 (CPS1) FOR STUDYING THIS ENZYME'S FUNCTION, REGULATION, PATHOLOGY AND STRUCTURE [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/52855TESISCompendi

Quantitative Studies of Amyloidogenic Protein Residue Interaction Networks and Abnormal Ammonia Metabolism in Neurotoxicity and Disease

Investigating similarities among neurological diseases can provide insight into disease processes. Two prominent commonalities of neurological diseases are the formation of amyloid deposits and altered ammonia and glutamate metabolism. Computational techniques were used to explore these processes in several neurological diseases. Residue interaction networks (RINs) abstract protein structure into a series of nodes (representing residues) and edges (representing connections between residues likely to interact). Analyzing the RINs of monomeric forms of amyloidogenic proteins for common network features revealed similarities not previously known. First, amyloidogenic variants of lysozyme were used to demonstrate the usefulness of RINs to the study of amyloidogenic proteins. Next, I compared RINs of amyloidogenic proteins with randomized control networks and a group of real protein controls and found similarities in network structures unique to amyloidogenic proteins. The use of 3D structure data and network structure data of amyloid-beta (1-42) (Abeta42) in a hydrophobic, membrane-mimicking solvent led to the identification of an interaction between Val24 and Ile31 as potentially involved in preventing Abeta aggregation. Since Abeta causes oxidative damage, since the ammonia metabolism enzyme glutamine synthetase is particularly susceptible to oxidative damage, and since glutamate plays a central role in neuronal function, I expanded my research to include the study of ammonia and glutamate metabolism in neurological diseases. A computational model of the effects of the interactions between the amount of dietary protein and the activities of ammonia metabolism enzymes on blood and brain ammonia levels supports potentially important roles for these enzymes in the protection of neural function. Next, I reviewed the role of amino acid catabolism in Alzheimer’s disease (AD). Common tissue pathology and the ability of memantine, an NMDA receptor antagonist, to relieve symptoms in patients and animal models of AD, major depressive disorder (MDD), and type 2 diabetes (T2D) further support a role for ammonia and glutamate metabolism in disease. Lastly, I found that single nucleotide polymorphisms (SNPs) in select ammonia metabolism genes are associated with these three diseases. The results presented in this dissertation demonstrate that investigating neurological diseases using computational approaches can provide great insight into the common underlying pathologies

Quantitative Studies of Amyloidogenic Protein Residue Interaction Networks and Abnormal Ammonia Metabolism in Neurotoxicity and Disease

Investigating similarities among neurological diseases can provide insight into disease processes. Two prominent commonalities of neurological diseases are the formation of amyloid deposits and altered ammonia and glutamate metabolism. Computational techniques were used to explore these processes in several neurological diseases. Residue interaction networks (RINs) abstract protein structure into a series of nodes (representing residues) and edges (representing connections between residues likely to interact). Analyzing the RINs of monomeric forms of amyloidogenic proteins for common network features revealed similarities not previously known. First, amyloidogenic variants of lysozyme were used to demonstrate the usefulness of RINs to the study of amyloidogenic proteins. Next, I compared RINs of amyloidogenic proteins with randomized control networks and a group of real protein controls and found similarities in network structures unique to amyloidogenic proteins. The use of 3D structure data and network structure data of amyloid-beta (1-42) (Abeta42) in a hydrophobic, membrane-mimicking solvent led to the identification of an interaction between Val24 and Ile31 as potentially involved in preventing Abeta aggregation. Since Abeta causes oxidative damage, since the ammonia metabolism enzyme glutamine synthetase is particularly susceptible to oxidative damage, and since glutamate plays a central role in neuronal function, I expanded my research to include the study of ammonia and glutamate metabolism in neurological diseases. A computational model of the effects of the interactions between the amount of dietary protein and the activities of ammonia metabolism enzymes on blood and brain ammonia levels supports potentially important roles for these enzymes in the protection of neural function. Next, I reviewed the role of amino acid catabolism in Alzheimer’s disease (AD). Common tissue pathology and the ability of memantine, an NMDA receptor antagonist, to relieve symptoms in patients and animal models of AD, major depressive disorder (MDD), and type 2 diabetes (T2D) further support a role for ammonia and glutamate metabolism in disease. Lastly, I found that single nucleotide polymorphisms (SNPs) in select ammonia metabolism genes are associated with these three diseases. The results presented in this dissertation demonstrate that investigating neurological diseases using computational approaches can provide great insight into the common underlying pathologies

Glutathione in Cancer Cell Death

Glutathione (L-γ-glutamyl-L-cysteinyl-glycine; GSH) in cancer cells is particularly relevant in the regulation of carcinogenic mechanisms; sensitivity against cytotoxic drugs, ionizing radiations, and some cytokines; DNA synthesis; and cell proliferation and death. The intracellular thiol redox state (controlled by GSH) is one of the endogenous effectors involved in regulating the mitochondrial permeability transition pore complex and, in consequence, thiol oxidation can be a causal factor in the mitochondrion-based mechanism that leads to cell death. Nevertheless GSH depletion is a common feature not only of apoptosis but also of other types of cell death. Indeed rates of GSH synthesis and fluxes regulate its levels in cellular compartments, and potentially influence switches among different mechanisms of death. How changes in gene expression, post-translational modifications of proteins, and signaling cascades are implicated will be discussed. Furthermore, this review will finally analyze whether GSH depletion may facilitate cancer cell death under in vivo conditions, and how this can be applied to cancer therapy

Modelling and genetic correction of liver genetic diseases

The urea cycle is a set of biochemical reactions that converts highly toxic ammonia into urea for excretion. Deficiencies in any of the genes of the cycle can be life-threatening, with liver transplantation currently being the only definitive treatment. However, the scarcity of donor organs dictates the investigation of alternative treatments, which requires appropriate disease models, in vitro and in vivo, that faithfully recapitulate the disease pathology. Recent advancements in the field of genome engineering make interventions in the genetic code less challenging, thereby assisting in the generation of such tools, as well as raising the potential for genetic correction of these conditions. The research conducted in this thesis centres around two broad aims: the investigation of disease models and genetic correction of inherited liver disorders. Induced pluripotent stem cells (iPSC) hold great potential both for disease modelling and as a source of cells for cell therapy. However, their generation through cell reprogramming is sometimes challenging and inefficient. Therefore, in PAPER I we sought to optimize the reprogramming procedure by introducing modifications to the currently existing protocols, and managed to increase the reprogramming efficiency. IPSC could theoretically differentiate into any cell type, including hepatocytes. In order to assess the level of differentiation of the hepatocyte-like cells (HLC) generated from stem cell sources, comparisons with authentic primary liver tissues are necessary. To this end, in PAPER II we created gene expression profiles of fetal and mature (post-natal) liver tissues from a significant number of individuals. The dataset can serve as an accurate and simple assessment tool to evaluate and compare HLC, generated in different laboratories, to authentic human liver tissues. If HLC resemble the functions observed in mature primary hepatocytes, they could be used as in vitro disease models. In addition, programmable nucleases can be applied to either correct or introduce disease-causing of interest in the genome. In PAPER III, we generated iPSC from a patient with a pathogenic variant in the ornithine transcarbamylase (OTC) gene, the most common UCD, corrected the genetic defect and differentiated the cells into HLC. The correction was molecularly, as well as phenotypically confirmed by the restoration of urea cycle function. The thesis also focuses on the investigation of in vivo disease models of UCD. Specifically, in PAPERS IV and V we created liver-humanized mice with hepatocytes from patients with UCD, OTC deficiency (OTCD) or carbamoyl phosphate synthetase 1 deficiency (CPS1D). Highly repopulated animals faithfully recapitulated the clinical manifestations of the disease observed in patients, including hyperammonemia which is considered a hallmark of these UCD. Furthermore, in PAPER V, we investigated the efficacy and safety of ex vivo gene editing of primary OTCD hepatocytes. Ureagenesis was restored in vitro in edited cells, as well as in vivo as mice liver-repopulated with genetically engineered cells partially or completely reversed all markers of the disease investigated. Finally, extensive gene expression and deep sequencing analysis revealed no unspecific mutagenesis effected by the programmable nucleases, pointing out the safety of the application. In conclusion, the research work conducted in this thesis demonstrates the prospects that iPSC and humanized mice possess for the generation of models of liver genetic diseases, in vitro and in vivo. Furthermore, the emergence of genome editing technologies further enhances the aforementioned potentials, as well as raises possibilities for the treatment of liver genetic defects through genome manipulation

New insights on ammonia metabolism in endothelial cells of the blood brain barrier

L'encéphalopathie hépatique (HE) est un syndrome neuropsychiatrique complexe, une complication majeure de la maladie du foie. L'œdème cytotoxique est une complication grave de l'encéphalopathie hépatique, connu comme étant le résultat d'un gonflement des astrocytes. Les facteurs pathogéniques dérivés du sang tels que l'ammoniaque (NH4+) et le stress oxydatif (SO) sont connus pour être synergiquement impliqués. Les cellules endothéliales (CE) de la barrière hémato-encéphalique (BHE), régulant le passage vers le cerveau, sont les premières cellules à entrer en contact avec les molécules circulantes. L'effet de l'ammoniaque et du SO sur le transport et le métabolisme des CE n'a jamais été complètement exploré. Par conséquent, notre objectif était d'évaluer les effets de NH4+ et des espèces réactives de l'oxygène (ROS) sur les CE de la BHE en utilisant des systèmes de modèles in vivo et in vitro. Il a été démontré que le cotransporteur Na-K-2Cl (NKCC1) était impliqué dans la pathogenèse de l'œdème cérébral dans de nombreuses affections neurologiques. Le NKCC1 peut transporter NH4+ vers le cerveau et est régulé par les ROS. Par conséquent, l'expression de NKCC1 a été évaluée dans des CE primaires soumises à différentes concentrations de ROS et de NH4+ ainsi que dans des microvaisseaux cérébraux (MVC) isolés chez le rat BDL (bile-duct ligated), un modèle d'EH induit par une maladie hépatique chronique. Aucune régulation à la hausse de NKCC n'était présente chez les CE traitées ou les MVC. La glutamine synthétase (GS) est une enzyme qui joue un rôle compensatoire important dans la détoxification du NH4+ au cours de la maladie du foie. La GS est exprimée dans le muscle et le cerveau (astrocytes), mais n'a jamais été totalement explorée dans les CE de la BHE. L'expression et l'activité de la protéine GS ont été trouvées dans les CE de la BHE in vitro (CE primaires) et in vivo (MVC isolés de rats naïfs). Dans le modèle BDL, l'expression de GS dans les MVC n'était pas significativement différente des témoins (SHAM). Par ailleurs, nous avons traité des CE avec du milieu conditionné à partir de plasma de rats BDL et avons trouvé une diminution de l’expression de la protéine GS et de l'activité par rapport aux SHAM. De plus, les CE traitées avec NH4+ augmentaient en activité de GS tandis que les traitements avec SO avec et sans NH4+ diminuent l'activité de GS. Globalement, ces résultats démontrent pour la première fois que la GS est présente dans les CE, à la fois in vivo et in vitro. La GS est régulée à la baisse dans les CE traitées avec du plasma de BDL (mais pas dans les MVC de BDL). Il est intéressant de noter que le NH4+ stimule l'activité de GS dans les CE, alors que le SO inhibe l'activité de GS, ce qui justifie possiblement les résultats de nos études avec les milieux conditionnés. Nous supposons que le SO empêche la régulation à la hausse de GS de la BHE, en diminuant la capacité des CE à détoxifier l'ammoniaque et à limiter l'entrée d'ammoniaque dans le cerveau. Nous envisageons qu'une régulation à la hausse de GS dans les CE de la BHE pourrait devenir une nouvelle cible thérapeutique de l'EH.Hepatic encephalopathy (HE) is a complex neuropsychiatric syndrome, which is a major complication of liver disease. Cytotoxic edema is a serious complication of HE, known to be the result of astrocyte swelling. Blood derived pathogenic factors such as ammonia (NH4+) and oxidative stress’ (OS) are known to be synergistically implicated. Endothelial cells (EC) of the blood brain barrier (BBB) are the first cells regulating passage into the brain and to contact blood-derived molecules. The effect of ammonia and oxidative stress on EC transport and metabolism has never been thoroughly explored. Therefore, our aim was to evaluate the effects of NH4+ and reactive oxygen species (ROS) on EC of the BBB using in vivo and in vitro models systems. The Na–K–2Cl cotransporter (NKCC1) has been demonstrated to be involved in the pathogenesis of brain edema in numerous neurological conditions. NKCC1 can transport NH4+ into the brain and is regulated by ROS. Therefore, the expression of NKCC1 was evaluated in primary EC submitted to different concentrations of ROS and NH4+ as well as in cerebral microvessels (CMV) isolated from the bile-duct ligated (BDL) rat, a model HE induced by chronic liver disease. No upregulation of NKCC1 was present in either the treated EC or CMV. Glutamine synthetase (GS) is an enzyme with an important compensatory role in NH4+ detoxification during liver disease. GS is expressed in muscle and brain (astrocytes) but has never been thoroughly explored in ECs of the BBB. GS protein expression and activity was found in EC of the BBB in vitro (primary EC) and in vivo (CMV isolated from naive rats). In the BDL model, GS expression in CMVs was not significantly different from SHAM-operated controls. In addition, we treated ECs with conditioned medium from plasma of BDL rats and found a decrease in GS protein and activity when compared to SHAM. Furthermore, EC treated with NH4+ increased GS activity while treatments with ROS with and without NH4+ decreased GS activity. Overall these results demonstrate for the first time that GS is present in EC both in vivo and in vitro. GS is downregulated in EC treated with BDL plasma (but not in BDL CMV). Interestingly, NH4+ stimulates GS activity in ECs, while ROS inhibits GS activity, possibly justifying the results found from the conditioned medium studies. We speculate that ROS prevents the upregulation of GS in the BBB, decreasing the capacity of the EC to detoxify ammonia and to limit ammonia entry into the brain. We foresee that upregulating GS in ECs of the BBB could become a new therapeutic target for HE

Amino acid synthesis deficiencies

In recent years the number of disorders known to affect amino acid synthesis has grown rapidly. Nor is it just the number of disorders that has increased: the associated clinical phenotypes have also expanded spectacularly, primarily due to the advances of next generation sequencing diagnostics. In contrast to the "classical" inborn errors of metabolism in catabolic pathways, in which elevated levels of metabolites are easily detected in body fluids, synthesis defects present with low values of metabolites or, confusingly, even completely normal levels of amino acids. This makes the biochemical diagnosis of this relatively new group of metabolic diseases challenging. Defects in the synthesis pathways of serine metabolism, glutamine, proline and, recently, asparagine have all been reported. Although these amino acid synthesis defects are in unrelated metabolic pathways, they do share many clinical features. In children the central nervous system is primarily affected, giving rise to (congenital) microcephaly, early onset seizures and varying degrees of mental disability. The brain abnormalities are accompanied by skin disorders such as cutis laxa in defects of proline synthesis, collodion-like skin and ichthyosis in serine deficiency, and necrolytic erythema in glutamine deficiency. Hypomyelination with accompanying loss of brain volume and gyration defects can be observed on brain MRI in all synthesis disorders. In adults with defects in serine or proline synthesis, spastic paraplegia and several forms of polyneuropathy with or without intellectual disability appear to be the major symptoms in these late-presenting forms of amino acid disorders. This review provides a comprehensive overview of the disorders in amino acid synthesis

Targeting metabolism for resolving Non-Alcoholic Steatohepatitis.

Los capítulos 5.2 y 6 están sujetos a confidencialidad por el autor. 207 p.La presente tesis doctoral trata sobre la modulación del metabolismo para el tratamiento de laesteatohepatitis no alcohólica (EHNA). Esta patología se caracteriza por una acumulación de grasa en elhígado que da lugar a complicaciones derivadas como la muerte celular, la inflamación, hinchamientoo ydesarrollo de fibrosis. Para identificar las dianas terapéuticas presentadas nos hemos centrado enperturbaciones descritas en el transcurso de la EHNA o patologías más severas: el metabolismo delamonio y nitrógeno y la homeostasis de magnesio. En base a ello hemos identificado la glutaminasa 1(GLS1) y la ciclina M4 (CNNM4) como dianas potenciales a la hora de tratar la enfermedad. Se hacaracterizado una sobre-expresión de ambas proteínas en muestras de pacientes diagnosticados de EHNA,así como en modelos animales de ratón de la enfermedad. Se han realizado estudios pre-clínicos en losque se ha inducido la patología por dos dietas distintas y se ha silenciado específicamente la proteínamediante inyección por vena de la cola, inhibiendo así la expresión del enzima en el hígado. En ambosensayos pre-clínicos se ha observado una menor acumulación de lípidos intrahepáticos y una disminucióndel estrés oxidativo derivado. Además, a la hora de elucidar el mecanismo de acción mediante el cual laacumulación de grasa o esteatosis es reducida, se ha identificado que el silenciamiento específico de Gls1y Cnnm4 promueve la secreción de lípidos en forma de partículas de muy baja densidad (VLDL)