bOHB protective pathways in Aralar-Ko neurons and brain: An alternative to ketogenic diet

Aralar/AGC1/Slc25a12, the mitochondrial aspartate-glutamate carrier expressed in neurons, is the regulatory component of the NADH malate-aspartate shuttle. AGC1 deficiency is a neuropediatric rare disease characterized by hypomyelination, hypotonia, developmental arrest, and epilepsy. We have investigated whether b-hydroxybutyrate (bOHB), the main ketone body (KB) produced in ketogenic diet (KD), is neuroprotective in aralar-knock-out (KO) neurons and mice. We report that bOHB efficiently recovers aralar-KO neurons from deficits in basal-stimulated and glutamate-stimulated respiration, effects requiring bOHB entry into the neuron, and protects from glutamate excitotoxicity. Aralar-deficient mice were fed a KD to investigate its therapeutic potential early in development, but this approach was unfeasible. Therefore, aralar-KO pups were treated without distinction of gender with daily intraperitoneal injections of bOHB during 5d. This treatment resulted in a recovery of striatal markers of the dopaminergic system including dopamine (DA), 3,4-dihydroxyphenylacetic acid (DOPAC)/DA ratio, and vesicular monoamine transporter 2 (VMAT2) protein. Regarding postnatal myelination, myelin basic protein (MBP) and myelin-associated glycoprotein (MAG) myelin proteins were markedly increased in the cortices of bOHB-treated aralar-KO mice. Although brain Asp and NAA levels did not change by bOHB administration, a 4-d bOHB treatment to aralar-KO, but not to control, neurons led to a substantial increase in Asp (3-fold) and NAA (4-fold) levels. These results suggest that the lack of increase in brain Asp and NAA is possibly because of its active utilization by the aralar-KO brain and the likely involvement of neuronal NAA in postnatal myelination in these mice. The effectiveness of bOHB as a therapeutic treatment in AGC1 deficiency deserves further investigationThis work was supported by Ministerio de Economía Grants SAF2014-56929R (to J.S. and B.P.) and SAF2017-82560R (AEI/FEDER, UE; to B.P.); the Centro de Investigación Biomédica en Red de Enfermedades Raras, an initiative of the Instituto de Salud Carlos III (ISCIII); a grant from the Fundación Ramon Areces (J.S.); the Irycis Chromatographic Services and Nervous System Markers Unit, UCS (2018/0135; to M.J.C.); and an institutional grant from the Fundación Ramon Areces to the Centro de Biología Molecular Severo Ochoa. I.P.-L. is the recipient of Contrato Predoctoral de Formación de Personal Investigador (FPI MINECO). We thank Dr. Antonio S. Herranz for his inputs as an expert in amino acid analysis by HPLC-UV, Dr. Araceli del Arco for critical reading of the manuscript, and Isabel Manso and Barbara Sesé for technical support. All experiments were conducted in compliance with the ARRIVE guideline

Mitochondrial ATP-Mg/pi carrier SCaMC-3/Slc25a23 counteracts PARP-1-dependent fall in mitochondrial ATP caused by excitotoxic insults in neurons

Glutamate excitotoxicity is caused by sustained activation of neuronal NMDA receptors causing a large Ca2+and Na+ influx, activation of poly(ADP ribose) polymerase-1 (PARP-1), and delayed Ca2+ deregulation. Mitochondria undergo early changes in membrane potential during excitotoxicity, but their precise role in these events is still controversial. Using primary cortical neurons derived from mice, we show that NMDA exposure results in a rapid fall in mitochondrial ATP in neurons deficient in SCaMC-3/Slc25a23, a Ca2+-regulated mitochondrial ATP-Mg/Pi carrier. This fall is associated with blunted increases in respiration and a delayed decrease in cytosolic ATP levels, which are prevented by PARP-1 inhibitors or by SCaMC-3 activity promoting adenine nucleotide uptake into mitochondria. SCaMC-3 KO neurons show an earlier delayed Ca2+ deregulation, and SCaMC-3-deficient mitochondria incubated with ADP or ATP-Mg had reduced Ca2+retention capacity, suggesting a failure to maintain matrix adenine nucleotides as a cause for premature delayed Ca2+ deregulation. SCaMC-3 KO neurons have higher vulnerability to in vitro excitotoxicity, and SCaMC-3 KO mice are more susceptible to kainate-induced seizures, showing that early PARP-1-dependent fall in mitochondrial ATP levels, counteracted by SCaMC-3, is an early step in the excitotoxic cascade.This work was supported by Ministerio de Economía Grant BFU2011-30456, by Centro de Investigación Biomédica en Red de Enfermedades Raras [an initiative of the Instituto de Salud Carlos III (ISCIII)], by Comunidad de Madrid Grant S2010/BMD-2402 MITOLAB-CM (to J.S.), by ISCIII Grant PI080610 (to A.d.A.), and by an institutional grant from the Fundación Ramón Areces to the Centro de Biología Molecular Severo Ochoa. C.B.R. is the recipient of an Formacion Personal Universitario fellowship from the Ministerio de Educación y Ciencia. P.G.-S. is a recipient of a Formacion Personal Investigador-UAM fellowship from Universidad Autónoma de Madrid.Peer Reviewe

AGC1-malate aspartate shuttle activity is critical for dopaminehandling in the nigrostriatal pathway

This is the pre-peer reviewed version of the following article: Llorente-Folch, I. et al. "AGC1-malate aspartate shuttle activity is critical for dopaminehandling in the nigrostriatal pathway". Journal of Neurochemistry 124.3 (2013): 347-362, which has been published in final form at http://dx.doi.org/10.1111/jnc.12096This study was supported by grants from the Ministerio deEducacion y Ciencia BFU2008-04084/BMC (to JS), and Ciencia eInnovacion (SAF2010-16427 to MD), Comunidad de Madrid S-GEN-0269-2006 MITOLAB-CM (to JS), European Union GrantLSHM-CT-2006-518153 (to J.S.), and CureFXS E-Rare. EU/FISPS09102673, Spanish Ministry of Health (PI 082038 to MD),Marato TV3, Jerome Lejeune (JMLM/AC /08-044) to MD, Fundac-ion Medica Mutua Madrile~na (to BP), and by an institutional grantfrom the Fundacion Ramon Areces to the CBMSO. CIBERER is aninitiative of the ISCI

New roles of aralar, the brain aspartate-glutamate carrier, in dopamine handling, glutamate excitotoxicity and regulation of mitochondrial respiration

Tesis doctoral inédita. Universidad Autónoma de Madrid, Facultad de Ciencias, Departamento de Biología Molecular. Fecha de lectura: 06-06-201

L-lactate-mediated neuroprotection against glutamate- induced excitotoxicity requires ARALAR/AGC1

ARALAR/AGC1/Slc25a12, the aspartate-glutamate carrier from brain mitochondria, is the regulatory step in the malate-aspartate NADH shuttle, MAS. MAS is used to oxidize cytosolic NADH in mitochondria, a process required to maintain oxidative glucose utilization. The role of ARALAR was analyzed in two paradigms of glutamate-induced excitotoxicity in cortical neurons: glucose deprivation and acute glutamate stimulation. ARALAR deficiency did not aggravate glutamate-induced neuronal death in vitro, although glutamate-stimulated respiration was impaired. In contrast, the presence of L-lactate as an additional source protected against glutamate-induced neuronal death in control, but not ARALAR-deficient neurons. L-Lactate supplementation increased glutamate-stimulated respiration partially prevented the decrease in the cytosolic ATP/ADP ratio induced by glutamate and substantially diminished mitochondrial accumulation of 8-oxoguanosine, a marker of reactive oxygen species production, only in the presence, but not the absence, of ARALAR. In addition, L-lactate potentiated glutamate-induced increase in cytosolic Ca, in a way independent of the presence of ARALAR. Interestingly, in vivo, the loss of half-a-dose of ARALAR inaralar mice enhanced kainic acid-induced seizures and neuronal damage with respect to control animals, in a model of excitotoxicity in which increased L-lactate levels and L-lactate consumption have been previously proven. These results suggest that, in vivo, an inefficient operation of the shuttle in the aralar hemizygous mice prevents the protective role of L-lactate on glutamate excitotoxiciy and that the entry and oxidation of L-lactate through ARALAR-MAS pathway is required for its neuroprotective function. SIGNIFICANCE STATEMENT Lactate now stands as a metabolite necessary for multiple functions in the brain and is an alternative energy source during excitotoxic brain injury. Here we find that the absence of a functional malate-aspartate NADH shuttle caused by aralar/AGC1 disruption causes a block in lactate utilization by neurons, which prevents the protective role of lactate on excitotoxicity, but not glutamate excitotoxicity itself. Thus, failure to use lactate is detrimental and is possibly responsible for the exacerbated in vivo excitotoxicity in aralar mice.Peer Reviewe

BCL2 and BCL(X)L selective inhibitors decrease mitochondrial ATP production in breast cancer cells and are synthetically lethal when combined with 2-deoxy-D-glucose.

Cancer cells display differences regarding their engagement of glycolytic vs. mitochondrial oxidative phosphorylation (OXPHOS) pathway. Triple negative breast cancer, an aggressive form of breast cancer, is characterized by elevated glycolysis, while estrogen receptor positive breast cancer cells rely predominantly on OXPHOS. BCL2 proteins control the process of mitochondrial outer membrane permeabilization during apoptosis, but also regulate cellular bioenergetics. Because BCL2 proteins are overexpressed in breast cancer and targetable by selective antagonists, we here analysed the effect of BCL2 and BCL(X)L selective inhibitors, Venetoclax and WEHI-539, on mitochondrial bioenergetics and cell death. Employing single cell imaging using a FRET-based mitochondrial ATP sensor, we found that MCF7 breast cancer cells supplied with mitochondrial substrates reduced their mitochondrial ATP production when treated with Venetoclax or WEHI-539 at concentrations that per se did not induce cell death. Treatments with lower concentrations of both inhibitors also reduced the length of the mitochondrial network and the dynamics, as evaluated by quantitative confocal microscopy. We next tested the hypothesis that mitochondrial ATP production inhibition with BCL2 or BCL(X)L antagonists was synthetically lethal when combined with glycolysis inhibition. Treatment with 2-deoxy-D-glucose in combination with Venetoclax or WEHI-539 synergistically reduced the cellular bioenergetics of ER+ and TNBC breast cancer cells and abolished their clonogenic potential. Synthetic lethality was also observed when cultures were grown in 3D spheres. Our findings demonstrate that BCL2 antagonists exert potent effects on cancer metabolism independent of cell death-inducing effects, and demonstrate a synthetic lethality when these are applied in combination with glycolysis inhibitors.</p

ARALAR/AGC1 deficiency, a neurodevelopmental disorder with severe impairment of neuronal mitochondrial respiration, does not produce a primary increase in brain lactate.

ARALAR/AGC1 (aspartate-glutamate mitochondrial carrier 1) is an important component of the NADH malate-aspartate shuttle (MAS). AGC1-deficiency is a rare disease causing global cerebral hypomyelination, developmental arrest, hypotonia, and epilepsy (OMIM ID #612949); the aralar-KO mouse recapitulates the major findings in humans. This study was aimed at understanding the impact of ARALAR-deficiency in brain lactate levels as a biomarker. We report that lactate was equally abundant in wild-type and aralar-KO mouse brain in vivo at postnatal day 17. We find that lactate production upon mitochondrial blockade depends on up-regulation of lactate formation in astrocytes rather than in neurons. However, ARALAR-deficiency decreased cell respiration in neurons, not astrocytes, which maintained unchanged respiration and lactate production. As the primary site of ARALAR-deficiency is neuronal, this explains the lack of accumulation of brain lactate in ARALAR-deficiency in humans and mice. On the other hand, we find that the cytosolic and mitochondrial components of the glycerol phosphate shuttle are present in astrocytes with similar activities. This suggests that glycerol phosphate shuttle is the main NADH shuttle in astrocytes and explains the absence of effects of ARALAR-deficiency in these cells

Altered postnatal development of cortico-hippocampal neuronal electric activity in mice deficient for the mitochondrial aspartate-glutamate transporter

The deficiency in the mitochondrial aspartate/glutamate transporter Aralar/AGC1 results in a loss of the malate-aspartate NADH shuttle in the brain neurons, hypomyelination, and additional defects in the brain metabolism. We studied the development of cortico/hippocampal local field potential (LFP) in Aralar/AGC1 knockout (KO) mice. Laminar profiles of LFP, evoked potentials, and unit activity were recorded under anesthesia in young (P15 to P22) Aralar-KO and control mice as well as control adults. While LFP power increased 3 to 7 times in both cortex and hippocampus of control animals during P15 to P22, the Aralar-KO specimens hardly progressed. The divergence was more pronounced in the CA3/hilus region. In parallel, spontaneous multiunit activity declined severely in KO mice. Postnatal growth of hippocampal-evoked potentials was delayed in KO mice, and indicated abnormal synaptic and spike electrogenesis and reduced output at P20 to P22. The lack of LFP development in KO mice was accompanied by the gradual appearance of epileptic activity in the CA3/hilus region that evolved to status epilepticus. Strikingly, CA3 bursts were poorly conducted to the CA1 field. We conclude that disturbed substrate supply to neuronal mitochondria impairs development of cortico-hippocampal LFPs. Aberrant neuronal electrogenesis and reduced neuron output may explain circuit dysfunction and phenotype deficiencies. © 2012 ISCBFM All rights reserved.Ministerio de Educación y Ciencia; BFU2007-66621/BFI; BFU2008-04084/BMC; Comunidad de Madrid, S-SEM-0255-2006 OLFACTOSENSE; S-GEN-0269-2006 MITOLAB-CM; Fundación Mutua Madrileña; Fundación Ramón Areces; CIBERERPeer Reviewe

Calcium-regulation of mitochondrial respiration maintains ATP homeostasis and requires ARALAR/AGC1-malate aspartate shuttle in intact cortical neurons

Neuronal respiration is controlled by ATP demand and Ca2++ but the roles played by each are unknown, as any Ca2++ signal also impacts on ATP demand. Ca2+can control mitochondrial function through Ca2++-regulated mitochondrial carriers, the aspartate-glutamate and ATP-Mg/Pi carriers, ARALAR/AGC1 and SCaMC-3, respectively, or in the matrix after Ca2++ transport through the Ca2++ uniporter. We have studied the role of Ca2++signaling in the regulation of mitochondrial respiration in intact mouse cortical neurons in basal conditions and in response to increased workload caused by increases in [Na+]cyt (veratridine, high-K+ depolarization) and/or [Ca2++]cyt (carbachol). Respiration in nonstimulated neurons on 2.5-5mM glucose depends on ARALAR-malate aspartate shuttle (MAS), with a 46% drop in aralar KO neurons. All stimulation conditions induced increased OCR (oxygen consumption rate) in the presence of Ca2++, which was prevented by BAPTA-AM loading (to preserve the workload), or in Ca2++-free medium (which also lowers cell workload). SCaMC-3 limits respiration only in response to high workloads and robust Ca2++ signals. In every condition tested Ca2++ activation of ARALAR-MAS was required to fully stimulate coupled respiration by promoting pyruvate entry into mitochondria. In aralar KO neurons, respiration was stimulated by veratridine, but not by KCl or carbachol, indicating that the Ca2++uniporter pathway played a role in the first, but not in the second condition, even though KCl caused an increase in [Ca2++]mit. The results suggest a requirement for ARALAR-MAS in priming pyruvate entry in mitochondria as a step needed to activate respiration by Ca2++ in response to moderate workloads. © 2013 the authors.Ministerio de Economía Grant BFU2011-30456; CIBERER; Comunidad de Madrid (S2010/BMD-2402 MITOLAB-CM); ISCIII PI080610; Fundacion Ramon ArecesPeer Reviewe

Brain glutamine synthesis requires neuronal-born aspartate as amino donor for glial glutamate formation

The glutamate–glutamine cycle faces a drain of glutamate by oxidation, which is balanced by the anaplerotic synthesis of glutamate and glutamine in astrocytes. De novo synthesis of glutamate by astrocytes requires an amino group whose origin is unknown. The deficiency in Aralar/AGC1, the main mitochondrial carrier for aspartate–glutamate expressed in brain, results in a drastic fall in brain glutamine production but a modest decrease in brain glutamate levels, which is not due to decreases in neuronal or synaptosomal glutamate content. In vivo 13C nuclear magnetic resonance labeling with 13C2acetate or (1-13C) glucose showed that the drop in brain glutamine is due to a failure in glial glutamate synthesis. Aralar deficiency induces a decrease in aspartate content, an increase in lactate production, and lactate-to-pyruvate ratio in cultured neurons but not in cultured astrocytes, indicating that Aralar is only functional in neurons. We find that aspartate, but not other amino acids, increases glutamate synthesis in both control and aralar-deficient astrocytes, mainly by serving as amino donor. These findings suggest the existence of a neuron-to-astrocyte aspartate transcellular pathway required for astrocyte glutamate synthesis and subsequent glutamine formation. This pathway may provide a mechanism to transfer neuronal-born redox equivalents to mitochondria in astrocytes