Elevated Cortical Extracellular Fluid Glutamate in Transgenic Mice Expressing Human Mutant (G93A) Cu/Zn Superoxide Dismutase

Abstract

Transgenic mice expressing a mutated (G93A) human Cu/Zn superoxide dismutase (SOD1) develop motor neuron pathology and clinical symptoms similar to those seen in patients with amyotrophic lateral sclerosis. Loss of motor neurons is most prominent in lumbar, followed by cervical cord and then brainstem. No significant cell death has been reported in motor cortex. The integrity of the cortical glutamate reuptake systems was evaluated using intracerebral microdialysis and western immunoblot assays for the glutamate transporters GLT-1, GLAST, and EAAC1. The basal extracellular fluid levels of aspartate, glutamate, glutamine, 3,4-dihydroxyphenylacetic acid, and 5-hydroxyindole-3-acetic acid were evaluated by HPLC. The extraction fraction of L-[ 3 H]glutamate, corrected with [ 14 C]mannitol, was also evaluated. GLT-1, EAAC1, and GLAST protein levels were determined by semiquantitative chemiluminescence immunoblot of proteins from membrane-enriched fractions. The relative optical density of film was translated into relative protein level by comparison with a standard control mouse. The SOD1 mutant mice demonstrated a significant ( p Ͻ 0.05) increase in basal levels of extracellular aspartate and glutamate. In addition, when the glutamate extraction fraction was challenged with exogenous unlabeled glutamate (500 M) by reversed microdialysis, the glutamate extraction fraction in the mutant SOD1 mice was decreased significantly from control levels. The SOD1 mutant mice demonstrated no difference in the cortical protein levels of the glutamate transporter subtypes. This study demonstrates that in areas of no visible pathology and no loss of glutamate transporter proteins, SOD1 mutant mice have elevated extracellular fluid aspartate and glutamate levels and a decreased capacity to clear glutamate from the extracellular space. Key Words: Glutamate-Reuptake-Transporter-SOD1-Amyotrophic lateral sclerosis-Mice -Microdialysis.

Intrathecal infusion of a Ca2+-permeable AMPA channel blocker slows loss of both motor neurons and of the astrocyte glutamate transporter, GLT-1 in a mutant SOD1 rat model of ALS

“…Previous reports have indicated progressive reactive astrogliosis, nitrotyrosine labeling and loss of astrocytic glutamate transport in SOD1 mutant rodent models of ALS (Alexander et al, 2000;Ferrante et al, 1997;Tu et al, 1996), and a specific decrease of the GLT-1 glutamate transporter has been reported in ventral horn of the G93A rats that are the subject of this study (Howland et al, 2002). Consistent with these prior studies we see a dramatic increase in astrogliosis, as indicated by GFAP labeling, most prominent initially in ventral horn, and extending throughout the gray matter of the spinal cord by the onset of symptoms (Fig 2A, 3).…”

Activation of the Nrf2–ARE pathway in muscle and spinal cord during ALS-like pathology in mice expressing mutant SOD1

“…These mice replicate much of the human ALS phenotype. They develop eventual paralysis of their hindlimbs at approximately 120 days of age subsequent to mitochondrial damage, an accumulation of extracellular glutamate and intracellular filamentous inclusions, motor neuron (MN) cell death, and loss of axons innervating the muscle [(Gurney et al 1994;Klivenyi et al 1999;Alexander et al 2000;Fischer et al 2004)]. …”

Presymptomatic motor neuron loss and reactive astrocytosis in the SOD1 mouse model of amyotrophic lateral sclerosis

“…Kong and Xu 16 proposed two likely scenarios for the loss of motor neurons: (1) there may be an extended period of gradual presymptomatic motor neuron loss, or (2) there may be an abrupt loss of motor neurons coinciding with symptom onset. So far, studies using mice with a short disease course have shown a gradual loss of motor neurons beginning at the onset of clinical symptoms, with no prior loss in the presymptomatic stage.…”