2023
Research News
Lactate: Ugly Duckling from Senescent Cells? Chinese Researchers Find Clue
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Carbohydrates account for about half the caloric intake in humans. Energy can derive from carbohydrates such as glucose through two processes, fermentation and respiration. Both processes begin with glucose catabolism via glycolysis into two molecules of pyruvate with associated production of two adenosine triphosphate (ATP) and two reduced nicotinamide adenine dinucleotide (NADH) molecules. During fermentation, the NADH is used to reduce pyruvate to lactate, a molecule that is perhaps the best-known metabolic waste product for years.
Recent studies showed that in mammals lactate also serves as a major circulating carbohydrate fuel. By providing both a convenient source and sink for carbon 3 (3C) compounds, circulating lactate enables the uncoupling of carbohydrate-driven mitochondrial energy generation from glycolysis in mammalian cells. The reconceptualization of lactate as a fuel-analogous to how Hans Christian Andersen’s ugly duckling is actually a beautiful swan-may reshape the field of energy metabolism.
However, the coin is now turned over again. In a study published in Nature Metabolism, the researchers from Shanghai Institute of Nutrition and Health of the Chinese Academy of Sciences, and East China University of Science and Technology conducted a study with human senescent cells, and disclosed that these cells are more prone to undergo aerobic glycolysis and produce a large amount of lactate. As senescent cells also sustain mitochondrial respiration, such a special form of metabolic reprogramming sharply differs from “Warburg effect”, a well-known metabolic pattern mostly observed in cancer cells.
"Metabolism plays an important role in regulating cellular senescence, the original driving force of natural aging process,” said Dr. SUN Yu, the leader of this study.
By metabolic profiling and functional assessments of glucose consumption, the researchers decoded the metabolic password of human senescent cells. They discovered that pyruvate dehydrogenase kinase 4 (PDK4), a glycolysis-promoting enzyme, indeed acts as a key regulator of biochemical activities to shape a unique form of metabolism, namely hypercatabolism, in these “aged” cells.
Besides, the researchers found that lactate promotes reactive oxygen species (ROS) production via NOX1 to drive the senescence-associated secretory phenotype (SASP), whereas PDK4 inhibition alleviates DNA damage and limits the SASP development. In preclinical trials, pharmacological suppression of PDK4 prevents physical dysfunction and ameliorates age-associated frailty.
Chronological age-associated cellular senescence in microenvironments bridges the gap between lactate overproduction, chronic inflammation and pathological events, while accumulation of lactate in solid organs is a pivotal and early event in various human disorders.
"Given that PDK4 expression rewires energy metabolism, has the potential for causing tissue homeostasis imbalance and overall physical dysfunction, the data raise the possibility that PDK4 is specifically targeted to delay natural aging and intervene multiple age-related pathologies which include but are not limited to various malignancies,” Dr. SUN said.
PDK4 mediates hypercatabolism and lactate production of senescent cells, together promoting chronological aging and age-related diseases. (Image by Dr. SUN Yu’s group)
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