Mice with Genetic γ-Glutamyl Transpeptidase Deficiency Exhibit Glutathionuria, Severe Growth Failure, Reduced Life Spans, and Infertility

Abstract

A mouse mutant with glutathionuria was discovered by screening for amino acidurias in the progeny of ethylnitrosourea-mutagenized mice. Total glutathione concentration was increased in both blood and urine but decreased in liver homogenates from affected mice. Glutathionuric mice exhibited lethargy, severe growth failure, shortened life spans and infertility. ␥-Glutamyl transpeptidase activity was deficient in kidney homogenates of glutathionuric mice. The glutathionuric phenotype in these mice is inherited as an autosomal recessive trait. This mouse mutant will be a useful animal model for the study of ␥-glutamyl transpeptidase physiology and glutathione metabolism.GSH is the most abundant cellular thiol and functions as the principal reducing reagent in all cell types (1). A partial listing of the antioxidative functions of GSH include: protection against mitochondrial damage, protection against oxygen toxicity in the lung, protection against lipid peroxidation, detoxification of electrophilic compounds through conjugation, preservation of proper sulfide bonds in proteins, a postulated function in anticarcinogenesis, and a role in the immune system (2). GSH metabolism also provides a source of cysteine for cells (3). ␥-Glutamyl transpeptidase (␥-GT; EC 2.3.2.2) 1 catalyzes the initial step in the degradation of GSH (4). ␥-GT is a key step in the ␥-glutamyl cycle (5), a series of degradative and synthetic reactions that mediate cellular GSH metabolism. Several reviews of ␥-GT physiology and function have been published (4 -6), but despite intensive investigation, the exact role ␥-GT plays in GSH metabolism or its putative contribution to renal amino acid transport have not been definitively determined. Bound to secretory endothelial cell membranes in several organs but predominantly in proximal renal tubule cells, ␥-GT participates in the transmembrane transport of GSH and in interorgan GSH exchange ( Fig. 1) (7). Meister (8) proposed that ␥-GT also contributes to amino acid transport in the proximal renal tubule through transpeptidation of GSH and subsequent tubule cell uptake of ␥-glutamyl amino acids. In vivo model systems that have lost ␥-GT activity are an exquisitely powerful tool for the study of ␥-GT function and its relationship to GSH metabolism. Administration of chemical inhibitors of ␥-GT to animals results in both glutathionuria and glutathionemia (9), but chemically treated animal models are limited by several drawbacks including the temporary nature of inhibition and the difficulty of long-term continuous inhibitor administration. Also, the degree and specificity of enzyme inhibition in various tissues (particularly the brain) of these chemically treated animals is unknown. Genetic ␥-GT deficiency has been described in only five humans (6), and the effects of various different disease states or environmental influences upon ␥-GT deficient individuals cannot be adequately evaluated given the rarity of the disorder. A genetic animal model of total ␥-GT deficiency overcomes the limitations of previ...

Phenotypic Characterization of <i>Ggt1^dwg/dwg</i> Mice,a Mouse Model for Hereditary γ-GlutamylTransferase Deficiency

“…3). It should be noted that these results clearly contradicted the previous reports indicating that the survival rates of the Ggt1 −/− and Ggt1 enu1/enu1 mice at 25 weeks of age are about 10 and 50%, respectively [5,14].…”

“…Dwarfism, cataracts, infertility, and early death have been shown to be common phenotypes in these mice [5,10,14]. Glutathionemia, glutathionuria, deficiency of cellular GSH, and high susceptibility to oxidative stress have also been reported in these mice [1,5,14]. These abnormalities are reversed by administration of N-acetyl-L-cysteine (NAC), a precursor of GSH synthesis [2,11,12,14].…”

“…Mice with targeted disruption of the Ggt1 gene (Ggt1 tm1Zuk ) and those with chemically induced [Nethyl-N-nitrosourea (ENU)-induced] mutation, referred to as Ggt1 −/− mice and Ggt1 enu1/enu1 mice in this paper, respectively, have been developed. Dwarfism, cataracts, infertility, and early death have been shown to be common phenotypes in these mice [5,10,14]. Glutathionemia, glutathionuria, deficiency of cellular GSH, and high susceptibility to oxidative stress have also been reported in these mice [1,5,14].…”

Aγ-Glutamyl Transpeptidase-Independent Pathway of Glutathione Catabolism to Glutamate via 5-Oxoproline in Arabidopsis

“…The g-glutamyl cycle is responsible for reabsorbing the GSH by first triggering its breakdown and then, after reabsorption of the component amino acids, catalyzing their conversion back to GSH. This idea is supported in GGT knockout mice that showed glutathionuria, Cys deficiency, and growth and reproductive defects that can be reversed by feeding acetylcysteine (Lieberman et al, 1996;Harding et al, 1997;Kumar et al, 2000).…”

Up-regulation of γ-glutamyl transpeptidase activity following glutathione depletion has a compensatory rather than an inhibitory effect on mitochondrial complex I activity: implications for Parkinson's disease

“…Earlier studies in the GGT enu1 mouse demonstrated that GGT deficiency has a dramatic impact on glutathione homeostasis. Genetic GGT deficiency in the GGT enu1 mouse impairs intracellular glutathione metabolism and results in systemic glutathionemia and oxidant stress in the kidney [22]. Previous studies with lung epithelial cells also demonstrated that when cells were exposed to quinones as an oxidantinduced stress, GGT would be increased as part of the adaptation of cells to oxidative stress by enhancing the utilization of extracellular GSH [23].…”