Behavioral Characterization ofGCLM-Knockout Mice, a Model for Enhanced Susceptibility to Oxidative Stress

Abstract

Glutathione (GSH) is a major player in cellular defense against oxidative stress. Deletion of the modifier subunit of glutamate cysteine ligase (GCLM), the first and the rate-limiting enzyme in the synthesis of GSH, leads to significantly lower GSH levels in all tissues including the brain. GCLM-knockout (Gclm−/−) mice may thus represent a model for compromised response to oxidative stress amenable to in vitro and in vivo investigations. In order to determine whether the diminished GSH content would by itself cause behavioral alterations, a series of behavioral tests were carried out comparing young adult Gclm−/− with wild-type mice. Tests included the rotarod, acoustic startle reflex and prepulse inhibition of the startle reflex, open field behavior, and the platform reversal variant of the Morris Water Maze. Results showed no differences between Gclm−/− and wild-type mice in any of the neurobehavioral tests. However, more subtle alterations, or changes which may appear as animals age, cannot be excluded.

Functional significance of glutamate–cysteine ligase modifier for erythrocyte survival in vitro and in vivo

“…4 Although massively depleted of glutathione, the major antioxidant in most tissues, gclm À / À mice are seemingly healthy and normal. [3][4][5] In line with previous reports, we found that the glutathione concentration of erythrocytes from gclm À / À mice was o10% of the concentration of erythrocytes from gclm þ / þ mice.…”

“…4 Although massively depleted of glutathione, the major antioxidant in most tissues, gclm À / À mice are seemingly healthy and normal. [3][4][5] In line with previous reports, we found that the glutathione concentration of erythrocytes from gclm À / À mice was o10% of the concentration of erythrocytes from gclm þ / þ mice. 3,5 Glutathione is a major antioxidant of erythrocytes and reduces their considerable oxidative burden, which arises from their role as O 2 -transporting cells.…”

“…3 Each subunit is coded by a separate gene, and even in the absence of GCLM, GCLC is still catalytically active. 4 However, GCLM lowers the K M value for the substrate glutamate and raises the K i value for GSH, thereby optimizing the conditions for glutathione synthesis. 4 Whereas GCLC deficiency is embryonic lethal in mice, gclm À / À mice do not have an obvious phenotype under resting conditions, despite the fact that glutathione levels in many of their tissues are only B10-20% of those in wild-type mice.…”

“…4 However, GCLM lowers the K M value for the substrate glutamate and raises the K i value for GSH, thereby optimizing the conditions for glutathione synthesis. 4 Whereas GCLC deficiency is embryonic lethal in mice, gclm À / À mice do not have an obvious phenotype under resting conditions, despite the fact that glutathione levels in many of their tissues are only B10-20% of those in wild-type mice. 3,5 In men, a common GCLM gene polymorphism that is associated with lower GCLM expression has been shown to increase the risk of myocardial infarction 6 or may be linked to schizophrenia, 7 although this association is discussed controversially.…”

“…8 Gclm À / À mice are a valuable model to study conditions of low glutathione similar to those that are the consequence of genetic polymorphisms. 4 Erythrocytes are devoid of organelles but certain stressors, among them ROS, can trigger their programmed death. [9][10][11] ROS activates cation channels in the erythrocyte membrane, thereby allowing Ca 2 þ to enter the cell.…”