Author Summary: The tight control of cellular metabolism and energy production plays a crucial role during embryonic development, cancer and neurodegenerative disorders. We show that mitochondrial pyruvate carrier deficiency in mice causes metabolic alterations that result in lactic acidosis, neurotransmitter imbalance, energy deficit, brain damage and embryonic lethality. Feeding the pregnant dams a ketogenic diet allowed the survival of affected embryos until birth. Our results demonstrate the importance of the mitochondrial pyruvate carrier in maintaining the metabolic program necessary to sustain normal mammalian development.
Impressive at least. Both on the wet/dry front.
But allow me to laser-beam (yeap, just used it as a verb!) on the off-target metabolomics approach.
Sounds interesting. Wish more papers about keto had that kind of willingness to search likewise.
Quoting straight from ze paper:
“ MPC deficiency alters the metabolic and neurotransmitter balance in the embryonic brainIn an attempt to understand the metabolic changes that could explain the survival ofMPC1gt/gt embryos until the end of gestation, we performed non-targeted metabolomic analyses on telencenphalic brain extracts from E13.5 embryos maintained on a normal or a ketogenic diet. Upon processing and annotation, a total of 222 metabolite ions could be detected (S3 Table). A principal component analysis of these data revealed that the most prominent metabolic changes were specific to the MPC1gt/gt brain samples from animals maintained on normal diet, while MPC1gt/gt ketogenic diet samples clustered with theMPC1+/+ samples (Fig 6A). Moreover, the predominant changes were all indicative of abnormal TCA cycle activity (Fig 6B).”
“A ketogenic diet is commonly used to treat the lactic acidosis resulting from PDH deficiency in humans [26,27], and has been shown to have similar effects in experiments with zebrafish ♥ embryos [34].
Used therapeutically, the ketogenic diet reduces lactic acidosis probably by decreasing glucose uptake and aerobic glycolysis, the main pathway induced in mammalian cells to compensate for a deficiency in OXPHOS.
The beneficial effects of the ketogenic diet may be:
immediate, through fueling the TCA cycle with acetyl-CoA, or
delayed, through an epigenetic regulation of gene expression [35] in the embryos.
In addition, the beneficial effects of the ketogenic diet may also be mediated through changes in the maternal metabolism thus changing the supply of metabolites and/or growth factors to the embryo.
In our experiments, maintaining the pregnant dams on a ketogenic diet from E8.5 onwards reduced lactate accumulation allowing the MPC1gt/gt embryos to complete normal gestation (Fig 5).
We suggest that this is because the diet is able to sustain efficient oxidative metabolism, which is required during the later stages of embryogenesis for cell and tissue differentiation [1,3,4].
In agreement with this is the fact that the ketogenic diet rescued the energy deficit observed in vivo in the brains of E13.5 MPC1gt/gt embryos (S3 Fig).
Moreover, in addition to the effects on lactic acid and energy balance, we observed that the ketogenic diet also normalized other metabolic parameters in the brain, including:
glutaminolysis which seemed abnormally elevated in untreated MPC1gt/gt embryos as evidenced by reduced glutamine and glutamate levels (Fig 6C and 6D).
Under the ketogenic diet,
levels were increased compared to untreated MPC1gt/gt embryos (Fig 6C and 6D) whereas the level of NAAG was decreased (Fig 6C).
It was recently shown that GABAergic transmission in neonatal mice is essential for cortical neuron development and the establishment of a proper balance between excitation and inhibition in the adult cortex [36].
Together our results allow us to hypothesize that during embryogenesis, MPC activity is required not only for adapting energy metabolism to the needs of the developing embryo, but also in maintaining a balanced pool of major neurotransmitters and ensuring normal brain development.
It is already established that pyruvate dehydrogenase (PDH) deficiency is associated with severe neurological phenotypes such as :
the latter being caused by impaired energetic status and abnormal neurotransmitter metabolism [26].
Despite the ability of the ketogenic diet to restore normal metabolism and gestation of theMPC1gt/gt embryos (Figs 5 and 6 and S2 Fig), the newborn pups survive for only a few minutes post-delivery. This suggests that without nutritional support from the dam, which provides a continuous source of glucose and ketone bodies, MPC1gt/gt pups were not able independently to meet their energetic needs during the post-natal starvation state. Loss of pyruvate oxidation and ketogenic supply in the MPC1gt/gt pups may be further exacerbated by the fact that
autophagy-driven gluconeogenesis,
an important source of energy during the post-natal period [37], is probably impaired in these newborn animals.
Indeed, recent reports indicate that liver-specific ablation of MPC activity diminishes the gluconeogenic flux because of the relatively low efficiency of compensatory pathways such as:
pyruvate/alanine cycling in liver [18,19].
Our results show that global loss of MPC activity is incompatible with embryonic development and neonatal survival in mammals.”
Non-carbohydrate substrates for gluconeonenesis pathways: amino acids (sans pyruvate, that is)
Change in neurotransmitters levels and/or ratios
Readily available Acetyl-Coa from ketone bodies
Pyruvate is a pivotal component in intermediary metabolism, lying at the crossroads between (←♥!) cytosolic and mitochondrial metabolism.
The main intracellular source of pyruvate is glycolysis in the cytosol, which generates two molecules of pyruvate per molecule of glucose.
Glycolysis-derived pyruvate then follows one of two major routes for energy production: conversion into lactate by lactate dehydrogenase (LDH) in a reaction that replenishes the cytosolic NAD+ cofactor pool, allowing maintenance of the glycolytic flux;
cytosolic pyruvate can enter the mitochondria to be oxidized to acetyl-CoA by the pyruvate dehydrogenase complex (PDH), fueling the TCA cycle and oxidative phosphorylation (OXPHOS).
mitochondrial pyruvate can be used in an
through conversion to oxaloacetate by pyruvate carboxylase.
In most differentiated cells, decarboxylation of pyruvate by PDH is used in order to meet the high energetic demands associated with specialized cellular processes such as the transmission of neuronal signals or muscle contraction [1].
In contrast, the strong anabolic requirements of proliferating cells are better met by (←♥ ) high glycolytic rates, since several intermediates in this pathway serve as precursors for biomass production, <!--aka: fast depletion-->
including nucleotides and proteins synthesis [1,2].
This marked reliance on high glycolytic flux is a hallmark of highly proliferating cells, including many cancer cells in which a shift from oxidative phosphorylation to aerobic glycolysis (the Warburg effect) is frequently observed [2]. ”
“In order to fuel the TCA cycle and drive oxidative phosphorylation, glucose-derived pyruvate must enter the mitochondrial matrix.
To do so, it is believed to
diffuse non-specifically through the outer mitochondrial membrane via porins [5],
before being taken up by a specific carrier to cross the impermeable inner mitochondrial membrane.
The existence of a specific transporter has been postulated since the 1970s [6], and its biochemical properties have been extensively studied, including its specific inhibition by chemical compounds [7,8].
However, the molecular and genetic identity of the mitochondrial pyruvate carrier (MPC) were revealed only recently by us and by others [9,10].”
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