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

• Autores: Inés Juaristi Santos
• Directores de la Tesis: Jorgina Satrústegui Gil-Delgado (dir. tes.), Araceli del Arco Martínez (dir. tes.)
• Lectura: En la Universidad Autónoma de Madrid ( España ) en 2019
• Idioma: inglés
• Número de páginas: 133
• Programa de doctorado: Programa de Doctorado en Biociencias Moleculares por la Universidad Autónoma de Madrid
• Materias:
  • Ciencias de la vida
    • Biología molecular
• Enlaces
  • Tesis en acceso abierto en: Biblos-e Archivo
• Resumen

  • ARALAR, Ca2+-regulated aspartate-glutamate mitochondrial carrier, is an important component of the NADH malate aspartate shuttle (MAS). ARALAR-deficiency is a rare disease causing a severe phenotype (OMIM ID #612949). The animal model, ARALAR-KO mouse, recapitulates the major findings in humans. The aim of the work was understanding the impact of ARALAR-deficiency in brain lactate levels; finding that lactate production upon mitochondrial blockade depends on upregulation 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.

    Astrocytes are central in regulation of synaptic signaling and neurotransmitter recycling, which are energy consuming processes. The aim of the work was to address the role of respiration and calcium regulation of respiration as part of the astrocyte response to these workloads, particularly to those caused by extracellular ATP and glutamate, two neurotransmitters produced by neurons and astrocytes. Extracellular ATP (100 .M-1 mM) caused a Ca2+-dependent workload and fell of the cytosolic ATP/ADP ratio, which acutely increased astrocytes respiration. Part of this increase is related to a Ca2+- dependent upregulation of cytosolic pyruvate production. Conversely, L-glutamate (200 .M) caused a Na+, but not Ca2+, dependent workload even though glutamate-induced Ca2+ signals readily reached mitochondria. This workload is due to Na+-dependent glutamate transport activity and triggers a rapid fall in the cytosolic ATP/ADP ratio and stimulation of respiration. D-aspartate produced similar effects. Glutamate-induced increase in respiration is linked to a rapid increase in glycolytic pyruvate production, exceeding that caused by extracellular ATP. The results suggest that both signaling molecules cause an increase in astrocyte respiration fueled by workload-induced increase in glycolysis and pyruvate production. As stimulation of respiration by ATP and glutamate are similar and pyruvate production was smaller than in the first case, the results suggest that the metabolic response to extracellular ATP is a Ca2+-dependent upregulation of respiration added to upregulation of glycolysis. The global contribution of these astrocyte respiratory responses to brain oxygen consumption is an open question.

    A mouse model with mutations in Ca2+ binding domains of ARALAR, but with intact transporter domain (4mut-ARALAR) has been studied. Surprisingly, 4mut- ARALAR protein levels were mostly absent in brain mitochondria whereas mRNA levels were the same as WT. An analysis of the possible causes of 4mutAralar protein degradation is presented.