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Mitochondrial lactate metabolism is involved in antioxidative defense in human astrocytoma cells.

Significance Statement

Energy-intensive organs like the brain and heart utilize a variety of carbon sources to fuel their energetic needs. These metabolites must be readily accessible to the mitochondrion as this organelle is the primary generator of ATP mediated by a process known as oxidative phosphorylation. The latter utilizes such reducing factors as NADH and FADH2 to form ATP in the presence of oxygen. However, the formation of toxic reactive oxygen species (ROS) is a major drawback that has to be controlled if this ATP-producing machine is to work effectively. Hence, it is not surprising that mitochondria have evolved an intricate ROS-combating apparatus. In healthy cells, the presence of lactate dehydrogenase (LDH) in this organelle supplies readily-accessible ingredients like NADH and pyruvate to propel this ATP machine. However, during oxidative stress, pyruvate is essentially directed towards the elimination of ROS while oxidative phosphorylation and ATP synthesis are sharply reduced.  Meanwhile, the pyruvate-catalyzed detoxification of ROS generates acetate that is converted into fats. Thus, lactate and LDH, biomolecules whose roles have usually been relegated to the realm of anaerobic respiration and as the harbingers of various maladies are actually critical players responsible for the proper functioning of high-energy requiring organs like the brain. It may not be unlikely that this duo is also recruited to perform other intriguing tasks in humans and various biological systems. Indeed, this ancient tandem may orchestrate other cellular feats that still need to be unearthed, underscoring the significance of functional metabolic studies in this endeavor.

 

 

Mitochondrial lactate metabolism is involved in antioxidative defense in human astrocytoma cells

Journal Reference

Lemire J, Auger C, Mailloux R, Appanna VD.

J Neurosci Res. 2014 Apr;92(4):464-75.

Department of Chemistry and Biochemistry, Laurentian University, Sudbury, Ontario, Canada.

 

 

Abstract

 

Although lactate has traditionally been known to be an end product of anaerobic metabolism, recent studies have revealed its disparate biological functions. Oxidative energy production and cell signaling are two important roles assigned to this monocarboxylic acid. Here we demonstrate that mitochondrial lactate metabolism to pyruvate mediated by lactate dehydrogenase (LDH) in a human astrocytic cell line is involved in antioxidative defense. The pooling of this {Alpha}-ketoacid helps to detoxify reactive oxygen species, with the concomitant formation of acetate. In-gel activity assays following blue native PAGE electrophoresis were utilized to demonstrate the increase inmitochondrial LDH activity coupled to the decrease in pyruvate dehydrogenase activity in the cells challenged by oxidative stress. The enhanced production of pyruvate with the concomitant formation of acetate in astrocytoma cells was monitored by high-performance liquid chromatography. The ability of pyruvate to fend off oxidative stress was visualized by fluorescence microscopy with the aid of the dye 2′,7′-dichlorodihydrofluorescein diacetate. Immunoblotting helped confirm the presence of elevated levels of LDH in cells exposed to oxidative stress, and recovery experiments were performed with pyruvate to diminish the oxidative burden on the astrocytoma. The acetate, generated as a consequence of the antioxidative attribute of pyruvate, was subsequently channeled toward the production of lipids, a process facilitated by the upregulation in activity of acetyl-CoA synthetase and acetyl-CoA carboxylase, as demonstrated by in-gel activity assays. The  mitochondrial lactate metabolism mediated by LDH appears to play an important role in antioxidative defence in this astrocytic system.

Copyright © 2014 Wiley Periodicals, Inc.

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