Regulation of neuronal energy metabolism by calcium: role of MCU and aralar/malate-aspartate shuttle

Calcium is a major regulator of cellular metabolism. Calcium controls mitochondrial respiration, and calcium signaling is used to meet cellular energetic demands through energy production in the organelle. Although it has been widely assumed that Ca2+-actions require its uptake by mitochondrial calcium uniporter (MCU), alternative pathways modulated by cytosolic Ca2+ have been recently proposed. Recent findings have indicated a role for cytosolic Ca2+ signals acting on mitochondrial NADH shuttles in the control of cellular metabolism in neurons using glucose as fuel. It has been demonstrated that AGC1/Aralar, the component of the malate/aspartate shuttle (MAS) regulated by cytosolic Ca2+, participates in the maintenance of basal respiration exerted through Ca2+-fluxes between ER and mitochondria, whereas mitochondrial Ca2+-uptake by MCU does not contribute. Aralar/MAS pathway, activated by small cytosolic Ca2+ signals, provides in fact substrates, redox equivalents and pyruvate, fueling respiration. Upon activation and increases in workload, neurons upregulate OxPhos, cytosolic pyruvate production and glycolysis, together with glucose uptake, in a Ca2+-dependent way, and part of this upregulation is via Ca2+ signaling. Both MCU and Aralar/MAS contribute to OxPhos upregulation, Aralar/MAS playing a major role, especially at small and submaximal workloads. Ca2+ activation of Aralar/MAS, by increasing cytosolic NAD+/NADH provides Ca2+-dependent increases in glycolysis and cytosolic pyruvate production priming respiration as a feed-forward mechanism in response to workload. Thus, except for glucose uptake, these processes are dependent on Aralar/MAS, whereas MCU is the relevant target for Ca2+ signaling when MAS is bypassed, by using pyruvate or β-hydroxybutyrate as substrate

Regulation of mitochondrial respiration in astrocytes: role of Ca2+, ATP demand and pyruvate production

Tesis doctoral inédita leída en la Universidad Autónoma de Madrid, Facultad de Ciencias, Departamento de Biología Molecular. Fecha de lectura: 23-01-2019Esta tesis tiene embargado el acceso al texto completo hasta el 23-07-202

The impact of a minimum wage increase on labour market outcomes: evidence from the northern Mexican border

Treball fi de màster de: Master's Degree in Specialized Economic Analysis: Economics of Public Policy Program. Curs 2022-2023Tutors: Ada Ferrer i Carbonell i Joan LlullA large informal sector and a low minimum wage have contributed to persistently high rates of inequality and poverty across Mexico. In particular, the development of cities located along the Mexico-US border has lagged behind in recent decades. The Northern Border Free Zone was implemented to counter this stagnation through economically stimulating policies, including a doubling of the minimum wage. This paper applies a Difference-in-Differences approach to estimate the impact of the minimum wage increase on low-wage workers. We find that the minimum wage significantly increased the wages of low-wage workers in both the formal and informal sector. Whilst we do not find any evidence of disemployment effects in either sector, we do find that the policy caused low-wage workers to work significantly less hours per week.Altas tasas de informalidad y salarios bajos han contribuido al aumento de la pobreza y desigualdad en todo México. En particular, el desarrollo de las ciudades ubicadas a lo largo de la frontera entre México y Estados Unidos se ha visto comprometido por esta problemática. La Zona Libre de la Frontera Norte se implementó para contrarrestar este estancamiento mediante políticas de estímulo económico, incluida la duplicación del salario mínimo. En esta investigación se emplea el método de diferencias en diferencias para estimar el impacto del aumento del salario mínimo en los trabajadores con salarios bajos. Los resultados sugieren que esta política aumentó significativamente los salarios de los trabajadores con salarios bajos tanto en el sector formal como en el informal. Si bien no encontramos ninguna evidencia de efectos negativos sobre el empleo en ninguno de los sectores, sí encontramos que la política provocó que los trabajadores con salarios bajos trabajaran significativamente menos horas por semana

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

A Ca 2+ -Dependent Mechanism Boosting Glycolysis and OXPHOS by Activating Aralar-Malate-Aspartate Shuttle, upon Neuronal Stimulation

International audienceCalcium is an important second messenger regulating a bioenergetic response to the workloads triggered by neuronal activation. In embryonic mouse cortical neurons using glucose as only fuel, activation by NMDA elicits a strong workload (ATP demand)-dependent on Na + and Ca 2+ entry, and stimulates glucose uptake, glycolysis, pyruvate and lactate production, and oxidative phosphorylation (OXPHOS) in a Ca 2+ -dependent way. We find that Ca 2+ upregulation of glycolysis, pyruvate levels, and respiration, but not glucose uptake, all depend on Aralar/AGC1/Slc25a12, the mitochondrial aspartate-glutamate carrier, component of the malate-aspartate shuttle (MAS). MAS activation increases glycolysis, pyruvate production, and respiration, a process inhibited in the presence of BAPTA-AM, suggesting that the Ca 2+ binding motifs in Aralar may be involved in the activation. Mitochondrial calcium uniporter (MCU) silencing had no effect, indicating that none of these processes required MCU-dependent mitochondrial Ca 2+ uptake. The neuronal respiratory response to carbachol was also dependent on Aralar, but not on MCU. We find that mouse cortical neurons are endowed with a constitutive ER-to-mitochondria Ca 2+ flow maintaining basal cell bioenergetics in which ryanodine receptors, RyR2, rather than InsP 3 R, are responsible for Ca 2+ release, and in which MCU does not participate. The results reveal that, in neurons using glucose, MCU does not participate in OXPHOS regulation under basal or stimulated conditions, while Aralar-MAS appears as the major Ca 2+ -dependent pathway tuning simultaneously glycolysis and OXPHOS to neuronal activation. SIGNIFICANCE STATEMENT Neuronal activation increases cell workload to restore ion gradients altered by activation. Ca 2+ is involved in matching increased workload with ATP production, but the mechanisms are still unknown. We find that glycolysis, pyruvate production, and neuronal respiration are stimulated on neuronal activation in a Ca 2+ -dependent way, independently of effects of Ca 2+ as workload inducer. Mitochondrial calcium uniporter (MCU) does not play a relevant role in Ca 2+ stimulated pyruvate production and oxygen consumption as both are unchanged in MCU silenced neurons. However, Ca 2+ stimulation is blunt in the absence of Aralar, a Ca 2+ -binding mitochondrial carrier component of Malate-Aspartate Shuttle (MAS). The results suggest that Ca 2+ -regulated Aralar-MAS activation upregulates glycolysis and pyruvate production, which fuels mitochondrial respiration, through regulation of cytosolic NAD + /NADH ratio