Search

Mitochondrial reactive oxygen species (mROS) have been generally considered harmful byproducts wanted to clear when elevated to avoid brain damage. However, the abundance of mROS in astrocytes is very high -about one order of magnitude above that in neurons-, despite they are essential to preserve cell metabolism and animal behavior. Here, we have focused on this apparent ambiguity by discussing (i) the intrinsic mechanisms accounting for the higher production of mROS by the mitochondrial respiratory chain in astrocytes than in neurons, (ii) the specific molecular targets of astrocytic beneficial mROS, and (iii) how decreased astrocytic mROS causes excess neuronal mROS leading to cellular and organismal damage. We hope that this mini-review serves to clarifying the apparent controversy on the beneficial versus deleterious faces of ROS in the brain from molecular to higher-order organismal levels.

Having direct access to brain vasculature, astrocytes can take up available blood nutrients and metabolize them to fulfil their own energy needs and deliver metabolic intermediates to local synapses. These glial cells should be, therefore, metabolically adaptable to swap different substrates. However, in vitro and in vivo studies consistently show that astrocytes are primarily glycolytic, suggesting glucose is their main metabolic precursor. Notably, transcriptomic data and in vitro studies reveal that mouse astrocytes are capable of mitochondrially oxidizing fatty acids and that they can detoxify excess neuronal-derived fatty acids in disease models. Still, the factual metabolic advantage of fatty acid use by astrocytes and its physiological impact on higher-order cerebral functions remain unknown. Here, we show that knockout of carnitine-palmitoyl transferase-1A (CPT1A)—a key enzyme of mitochondrial fatty acid oxidation—in adult mouse astrocytes causes cognitive impairment. Mechanistically, decreased fatty acid oxidation rewired astrocytic pyruvate metabolism to facilitate electron flux through a super-assembled mitochondrial respiratory chain, resulting in attenuation of reactive oxygen species formation. Thus, astrocytes naturally metabolize fatty acids to preserve the mitochondrial respiratory chain in an energetically inefficient disassembled conformation that secures signalling reactive oxygen species and sustains cognitive performance.

Astrocytes show unique anatomical, morphological, and metabolic features to take up substrates from the blood and metabolize them for local delivery to active synapses to sustain neuron function. In the present review, we specifically focus on key molecular aspects of energy and redox metabolism that facilitate this astrocyte-neuronal coupling in a controlled manner. Basal glycolysis is co-ordinated by the anaphase-promoting complex/cyclosome (APC/C)-Cdh1, a ubiquitin ligase that targets the proglycolytic enzyme 6-phosphofructokinase-2, 6-bisphosphastate-3 (PFKFB3) for degradation. APC/C-Cdh1 activity is more robust in neurons than in astrocytes, which determine that PFKFB3 abundance and glycolytic rate are weaker in neurons. The low PFKFB3 activity in neurons facilitates glucose-6-phosphate oxidation via the pentose-phosphate pathway, which promotes antioxidant protection. Conversely, the high PFKFB3 activity in astrocytes allows the production and release of glycolytic lactate, which is taken up by neurons that use it as an oxidizable substrate. Importantly, the mitochondrial respiratory chain is tighter assembled in neurons than in astrocytes, thus the bioenergetic efficiency of mitochondria is higher in neurons. Because of this, the production of reactive oxygen species (mROS) by mitochondrial complex I is very low in neurons and very high in astrocytes. Such a naturally occurring high abundance of mROS in astrocytes physiologically determines a specific transcriptional fingerprint that contributes to sustaining cognitive performance. We conclude that the energy and redox metabolism of astrocytes must complementarily match that of neurons to regulate brain function and animal welfare.

CLN7 neuronal ceroid lipofuscinosis is an inherited lysosomal storage neurodegenerative disease highly prevalent in children. CLN7/MFSD8 gene encodes a lysosomal membrane glycoprotein, but the biochemical processes affected by CLN7-loss of function are unexplored thus preventing development of potential treatments. Here, we found, in the Cln7∆ex2 mouse model of CLN7 disease, that failure in autophagy causes accumulation of structurally and bioenergetically impaired neuronal mitochondria. In vivo genetic approach reveals elevated mitochondrial reactive oxygen species (mROS) in Cln7∆ex2 neurons that mediates glycolytic enzyme PFKFB3 activation and contributes to CLN7 pathogenesis. Mechanistically, mROS sustains a signaling cascade leading to protein stabilization of PFKFB3, normally unstable in healthy neurons. Administration of the highly selective PFKFB3 inhibitor AZ67 in Cln7∆ex2 mouse brain in vivo and in CLN7 patients-derived cells rectifies key disease hallmarks. Thus, aberrant upregulation of the glycolytic enzyme PFKFB3 in neurons may contribute to CLN7 pathogenesis and targeting PFKFB3 could alleviate this and other lysosomal storage diseases.

[ES] Aleph es un sistema de ayuda a la decisión médica web desarrollado en Django, el cual ofrece herramientas de manejo de enfermedades, apoyo a la toma de decisiones clínicas y apoyo al tratamiento. Para mejorar dicho sistema queremos evaluar su usabilidad y la experiencia del usuario. Para llevar a cabo este trabajo hemos diseñado y desarrollado Alf, un chatbot que realiza un test usabilidad y la experiencia de usuario de Aleph de manera interactiva, en el que se adaptan dos de los cuestionarios más usados para evaluar dichas cualidades junto con tres tareas sencillas para familiarizar al usuario con Aleph. Los cuestionarios que hemos adaptado son el System Usabity Scale (SUS) y el User Experience Questionnaire (UEQ-S). Adicionalmente en las tareas evaluamos su dificultad, el tiempo empleado, su eficacia y la satisfacción del usuario. Este chatbot está compuesto de dos módulos, un Frontend, desarrollado en Django, y un Backend compuesto por una API de REST, una Object-Relational Mapping (ORM), una base de datos y una máquina de estados creada en Python 3., [EN] Aleph is a web-based medical decision support system developed in Django, which offers disease management tools, clinical decision support, and treatment support. To improve this system we want to evaluate its usability and user experience. To carry out this work we have designed and developed Alf, a chatbot that performs a usability test and the Aleph user experience in an interactive way, in which two of the most used questionnaires are adapted to evaluate these qualities together with three simple tasks to familiarize the user with Aleph. The questionnaires that we have adapted are the System Usabity Scale (SUS) and the User Experience Questionnaire (UEQ-S). Additionally, in the tasks we evaluate their difficulty, the time spent, their effectiveness and user satisfaction. This chatbot is made up of two modules, a Frontend, developed in Django, and a Backend made up of a REST API, an Object-Relational Mapping (ORM), a database, and a state machine created in Python 3., [CA] Aleph és un sistema d’ajuda a la decisió mèdica web desenvolupat en Django, el qual ofereix eines de maneig de malalties, suport a la presa de decisions clíniques i suport al tractament. Per a millorar aquest sistema volem avaluar la seua usabilitat i l’experiència d’usuari. Per dur a terme aquest treball hem dissenyat i desenvolupat Alf, un xatbot que realitza un test usabilitat i l’experiència d’usuari d’Aleph de manera interactiva al que s’adapten dos dels qüestionaris més usats per avaluar aquestes qualitats juntament amb tres tasques senzilles per familiaritzar l’usuari amb Aleph. Els qüestionaris que hem adaptat són el System Usabity Scale (SUS) i el User Experience Questionnaire (UEQ-S). A més en les tasques avaluem la seua dificultat, el temps emprat, la seua eficàcia i la satisfacció de l’usuari. Aquest xatbot està compost per dos mòduls, un Frontend desenvolupat en Django, un Backend compost per una API de REST, un Object-Relational Mapping (ORM), una base de dades i una màquina d’estats creada en Python 3.

Our group is interested in understanding the mechanisms that contribute to the metabolic and redox coupling between astrocytes and neurons, as well as their implication in cognitive and motor functions. Neurons show a high dependence on mitochondrial oxidative phosphorylation for survival, whereas astrocytes resist to almost complete inhibition of mitochondrial respiration. A key factor in this process is PFKFB3, an enzyme that promotes glycolysis by activating its regulatory enzyme PFK1. We previously demonstrated that PFKFB3 is a substrate of the E3 ubiquitin ligase APC/C-Cdh1. By degrading PFKFB3, APC/C-Cdh1 ac- tivity shifts the equilibrium of glucose consumption from glycolysis towards pentose-phosphate pathway (PPP), thus regulating the redox status and survival of neurons. Conversely, APC/C-Cdh1 activity in astrocytes is very low, which accounts for the elevated PFKFB3 protein levels and glycolytic phenotype of these cells. However, the impact of PFKFB3 modulation in specific brain cells on cognitive and motor functions have not yet been explored. To address this, wgenerated a Cre recombinase inducible ROSA26-floxed knock-in mouse harboring the full-length PFKFB3 cDNA (PFKFB3LoxP/+) to specifically assess the impact of PFKFB3 expression in neurons in vivo. PFKFB3LoxP/+ mice were crossed with mice expressing Cre recombinase under the neuronal CAMKIIa promoter (CAMKIIa-Cre). We found that the resulting PFKFB3LoxP/+; CAMKIIa-Cre mice showed increased PFKFB3 protein levels in neurons in vivo and symptoms of cognitive decline and motor discoordination as from the 3 months of age. Interestingly, this PFKFB3-induced phenotype was rescued by in vivo coexpressing mitoCatalase (mCAT), i.e. the antioxidant enzyme catalase confined to neuronal mitochondria. These results indicate that aberrant enhancement of glycolysis in neurons causes behavioral impairment in mouse through a mitochondrial redox stress-mediated mechanism.

Cells naturally produce mitochondrial reactive oxygen species (mROS), but the in vivo pathophysiological significance has long remained controversial. Within the brain, astrocyte-derived mROS physiologically regulate behaviour and are produced at one order of magnitude faster than in neurons. However, whether neuronal mROS abundance differentially impacts on behaviour is unknown. To address this, we engineered genetically modified mice to down modulate mROS levels in neurons in vivo. Whilst no alterations in motor coordination were observed by down modulating mROS in neurons under healthy conditions, it prevented the motor discoordination caused by the pro-oxidant neurotoxin, 3-nitropropionic acid (3-NP). In contrast, abrogation of mROS in astrocytes showed no beneficial effect against the 3-NP insult. These data indicate that the impact of modifying mROS production on mouse behaviour critically depends on the specific cell-type where they are generated.

CLN7 neuronal ceroid lipofuscinosis is an inherited lysosomal storage neurodegenerative disease highly prevalent in children. CLN7/MFSD8 gene encodes a lysosomal membrane glycoprotein, but the biochemical processes affected by CLN7-loss of function are unexplored thus preventing development of potential treatments. Here, we found, in the Cln7∆ex2 mouse model of CLN7 disease, that failure in the autophagy-lysosomal pathway causes accumulation of structurally and bioenergetically impaired neuronal mi- tochondria. In vivo genetic approach revealed elevated mitochondrial reactive oxygen species (mROS) in Cln7∆ex2 neurons that mediates glycolysis activation and contributes to CLN7 pathogenesis. Mechanistically, mROS sustains a signaling cascade leading to protein stabilization of PFK- FB3, a glycolytic-promoting enzyme normally unstable in healthy neurons. Pharmacological inhibition of PFKFB3 in Cln7∆ex2 mouse brain in vivo and in CLN7 patients-derived cells rectified key disease hallmarks. Thus, aberrant upregulation of neuronal glycolysis contributes to CLN7 patho-genesis and targeting PFKFB3 may alleviate this and other lysosomal storage diseases