Glutathione: A Real "Knock-Out" for Mammalian Development

Michael Lieberman
Baylor College of Medicine

Background: Glutathione (GSH) is an essential intermediate in many physiologic reactions and functions involved in the metabolism of carcinogens and xenobiotics as well as protecting cells from free radical damage. Previous work has shown that newborn rats (but not adults) and guinea pigs which lack the ability to synthesize Vitamin C (ascorbate), another free radical scavenger, die with widespread intracellular damage when a GSH inhibitor is administered. This damage occurs in intracellular organelles called mitochondria that are the "power factories" of cells and are a major source of free radicals in the form of reactive oxygen. The role GSH plays in growth and development has been difficult to study because GSH inhibitors given to pregnant rodents do not always completely inhibit GSH production.

Advance: To further investigate the role of GSH in development, this team of investigators used molecular genetics techniques to create a "knock-out" mouse unable to produce a key enzyme required for GSH synthesis rendering its cells incapable of producing GSH. Embryos homozygous for the trait undergo arrested development and die prior to day 8.5 of gestation. Death results from program cell death or apoptosis but not from a lack of cell growth or division. In vitro studies performed on cells harvested from embryos earlier in development thrive if supplemented with GSH or dithiothreitol. However, these cells could not be rescued with any other reducing agents, or vitamin C or vitamin E.. Using electron microscopy, the investigators found no changes in the appearance of these cells' mitochondria.

Implication: These experiments demonstrate that GSH is required for mammalian development but that it is not necessary in cell culture. This is a stunning result since GSH is required for the breakdown of hydrogen peroxide by glutathione peroxide in the mitochondria. These results demonstrate that mitochondria must have other metabolic pathways for the break down of hydrogen peroxide, a normal by product of oxidative phosphorylation. According to the investigators, "The availability of these mutant cells deficient in GSH synthesis will allow further exploration of the role of cellular redox status in signal transduction, posttranslational regulation of proteins . . ., cell growth, differentiation, and cell death." [Area of Emphasis: New Approaches to Pathogenesis; GPRA Goal: Add to the body of knowledge about normal and abnormal biological functions and behavior (Molecular and Cellular Mechanisms)]

Citation: Shi ZZ, Osei-Frimpong J, Kala G, Kala SV, Barrios RJ, Habib GM, Lukin DJ, Danney CM, Matzuk MM, Lieberman MW: Glutathione synthesis is essential for mouse development but not for cell growth in culture. Proc. Natl. Acad. Sci. U S A. 97: 5101-5106, 2000.