High affinity [3H]glutamate uptake systems in normal and audiogenic seizure-susceptible mice

Cordero, Mayra L.; Ortíz, José G.; Santiago, Glysette

doi:10.1016/0165-3806(94)90007-8

Cited by 6 publications

(5 citation statements)

References 16 publications

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“…We suspect that the paradoxical increase in glutamate transport in the knockout synaptosomes reflects a compensatory response of the neurons either to the presence of small-molecule peptide inhibitors with L-isoaspartyl linkages or to a covalently damaged intracellular protein. For example, increased glutamate uptake into synaptosomes prepared from the seizure-prone C57BL͞10 SPS͞sps mice is thought to represent a compensatory reaction to a decreased seizure threshold (45).…”

Section: Discussionmentioning

confidence: 99%

“…We observed a 30% increase in glutamate uptake into synaptosomes prepared from 4-to 5-week-old knockout mice (n ϭ 4), compared with heterozygous and wild-type littermate controls (n ϭ 4) (1,296 Ϯ 48 vs. 1,020 Ϯ 24 pmol per mg of protein per min, P Ͻ 0.01). Although we do not fully understand the mechanism for this paradoxical increase, it may represent a compensatory response in Pcmt-1 knockout mice to a decreased seizure threshold (45).…”

Section: Fig 4 (A)mentioning

confidence: 99%

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Deficiency of a protein-repair enzyme results in the accumulation of altered proteins, retardation of growth, and fatal seizures in mice

Kim

Lowenson

MacLaren

et al. 1997

Proc. Natl. Acad. Sci. U.S.A.

270

316

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L-Asparaginyl and L-aspartyl residues in proteins are subject to spontaneous degradation reactions that generate isomerized and racemized aspartyl derivatives. Proteins containing L-isoaspartyl and D-aspartyl residues can have altered structures and diminished biological activity. These residues are recognized by a highly conserved cytosolic enzyme, the protein L-isoaspartate(D-aspartate) O-methyltransferase (EC 2.1.1.77). The enzymatic methyl esterification of these abnormal residues in vitro can lead to their conversion (i.e., repair) to normal L-aspartyl residues and should therefore prevent the accumulation of potentially dysfunctional proteins in vivo as cells and tissues age. Particularly high levels of the repair methyltransferase are present in the brain, although enyzme activity is present in all vertebrate tissues. To define the physiological relevance of this protein-repair pathway and to determine whether deficient protein repair would cause central nervous system dysfunction, we used gene targeting in mouse embryonic stem cells to generate protein L-isoaspartate(D-aspartate) O-methyltransferase-deficient mice. Analyses of tissues from methyltransferase knockout mice revealed a striking accumulation of protein substrates for this enzyme in the cytosolic fraction of brain, heart, liver, and erythrocytes. The knockout mice showed significant growth retardation and succumbed to fatal seizures at an average of 42 days after birth. These results suggest that the ability of mice to repair L-isoaspartyl-and D-aspartylcontaining proteins is essential for normal growth and for normal central nervous system function.The success of an aging organism depends on its ability to maintain the integrity of its unstable macromolecular machinery over time (1, 2). We have been particularly interested in the consequences of protein damage on aging. Proteins are subject to a variety of spontaneous degradation processes, including oxidation, glycation, deamidation, isomerization, and racemization (1, 3-9). These nonenzymatic modifications can produce functionally damaged species that reflect the action of aging at the molecular level (5, 10).L-Asparagine and L-aspartate are among the most unstable residues in proteins, being particularly susceptible to linked deamidation, isomerization, and racemization reactions (6, 11-13). The initial event in these nonenzymatic reactions at neutral pH is generally the nucleophilic attack of the side-chain carbonyl carbon by the peptide-bond nitrogen to yield an unstable five-membered L-succinimidyl ring (Fig. 1). The spontaneous hydrolysis of the succinimide produces either an L-isoaspartyl residue (in which the peptide backbone is redirected through the ␤-carboxyl group) or a normal L-aspartyl residue. In addition, the ␣-carbon of the succinimidyl residue is racemization-prone, and D-aspartyl and D-isoaspartyl residues can also form, although in lower yields (6,14). Under physiological conditions, succinimide-linked deamidation of asparagine can occur with half-times as short a...

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Section: Discussionmentioning

confidence: 99%

Section: Fig 4 (A)mentioning

confidence: 99%

Deficiency of a protein-repair enzyme results in the accumulation of altered proteins, retardation of growth, and fatal seizures in mice

Kim

Lowenson

MacLaren

et al. 1997

Proc. Natl. Acad. Sci. U.S.A.

270

316

View full text Add to dashboard Cite

show abstract

“…To date, no studies have specifically examined the effects of HICs on glutamate uptake, although others have reported that glutamate uptake is impacted by seizures (Lallement et al 1991;Cordero et al 1994). Increased extracellular glutamate levels are also Fig.…”

Section: Discussionmentioning

confidence: 96%

“…The glutamate uptake assays were accomplished using a technique modified from Cordero et al (1994). Preliminary experiments were performed to determine the optimal conditions for the assay, including incubation time and the concentrations of protein and ligands (data not shown).…”

Section: Synaptosomal L-[ 3 H]glutamate Uptakementioning

confidence: 99%

“…Following a subcutaneous injection of the convulsant soman (an acetylcholinesterase inhibitor), rats show an increase in extracellular glutamate levels in the CA1 of the hippocampus, as measured by in vivo microdialysis as well as an increase in L-[ 3 H]glutamate uptake in hippocampal homogenates (Lallement et al 1991). Cordero et al (1994), on the other hand, reported that genetically bred, seizure-prone C57BL/10Bg SPS /sps mice have significantly less hippocampal synaptosomal [ 3 H]glutamate uptake as compared to their seizureresistant counterparts. These mice exhibit a susceptibility to absence seizures resulting from audiogenic stimulation (Maxson et al 1983).…”

Section: Introductionmentioning

confidence: 99%

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