Abstract
During growth on fermentable substrates, such as glucose, pyruvate, which is the end-product of glycolysis, can be used to generate acetyl-CoA in the cytosol via acetaldehyde and acetate, or in mitochondria by direct oxidative decarboxylation. In the latter case, the mitochondrial pyruvate carrier (MPC) is responsible for pyruvate transport into mitochondrial matrix space. During chronological aging, yeast cells which lack the major structural subunit Mpc1 display a reduced lifespan accompanied by an age-dependent loss of autophagy. Here, we show that the impairment of pyruvate import into mitochondria linked to Mpc1 loss is compensated by a flux redirection of TCA cycle intermediates through the malic enzyme-dependent alternative route. In such a way, the TCA cycle operates in a “branched” fashion to generate pyruvate and is depleted of intermediates. Mutant cells cope with this depletion by increasing the activity of glyoxylate cycle and of the pathway which provides the nucleocytosolic acetyl-CoA. Moreover, cellular respiration decreases and ROS accumulate in the mitochondria which, in turn, undergo severe damage. These acquired traits in concert with the reduced autophagy restrict cell survival of the mpc1∆ mutant during chronological aging. Conversely, the activation of the carnitine shuttle by supplying acetyl-CoA to the mitochondria is sufficient to abrogate the short-lived phenotype of the mutant.
Highlights
Aging of postmitotic quiescent mammalian cells has been modelled in the yeast Saccharomyces cerevisiae by its chronological lifespan (CLS) [1, 2]
We show that the impairment of pyruvate import into mitochondria linked to Mpc1 loss is compensated by a flux redirection of TCA cycle intermediates through the malic enzyme-dependent alternative route
Lack of Mpc1 is accompanied by an increase of aldehyde dehydrogenase (Ald) enzymatic activities Since an impairment in the import of pyruvate into mitochondria linked to MPC1 deletion significantly restricted CLS (Fig. 2A) [8], we decided to analyze in more detail the metabolic changes underlying this short-lived phenotype
Summary
Aging of postmitotic quiescent mammalian cells has been modelled in the yeast Saccharomyces cerevisiae by its chronological lifespan (CLS) [1, 2]. We found that mpc1∆ cells make up for their impairment in mitochondrial pyruvate with a metabolic rewiring which involves several intermediates of the mitochondrially localized TCA cycle and the cytosolic glyoxylate shunt but results in a proaging process.
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