Aged xCT-Deficient Mice Are Less Susceptible for Lactacystin-, but Not 1-Methyl-4-Phenyl-1,2,3,6- Tetrahydropyridine-, Induced Degeneration of the Nigrostriatal Pathway

Abstract

The astrocytic cystine/glutamate antiporter system xc– (with xCT as the specific subunit) imports cystine in exchange for glutamate and has been shown to interact with multiple pathways in the brain that are dysregulated in age-related neurological disorders, including glutamate homeostasis, redox balance, and neuroinflammation. In the current study, we investigated the effect of genetic xCT deletion on lactacystin (LAC)- and 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-induced degeneration of the nigrostriatal pathway, as models for Parkinson’s disease (PD). Dopaminergic neurons of adult xCT knock-out mice (xCT–/–) demonstrated an equal susceptibility to intranigral injection of the proteasome inhibitor LAC, as their wild-type (xCT+/+) littermates. Contrary to adult mice, aged xCT–/– mice showed a significant decrease in LAC-induced degeneration of nigral dopaminergic neurons, depletion of striatal dopamine (DA) and neuroinflammatory reaction, compared to age-matched xCT+/+ littermates. Given this age-related protection, we further investigated the sensitivity of aged xCT–/– mice to chronic and progressive MPTP treatment. However, in accordance with our previous observations in adult mice (Bentea et al., 2015a), xCT deletion did not confer protection against MPTP-induced nigrostriatal degeneration in aged mice. We observed an increased loss of nigral dopaminergic neurons, but equal striatal DA denervation, in MPTP-treated aged xCT–/– mice when compared to age-matched xCT+/+ littermates. To conclude, we reveal age-related protection against proteasome inhibition-induced nigrostriatal degeneration in xCT–/– mice, while xCT deletion failed to protect nigral dopaminergic neurons of aged mice against MPTP-induced toxicity. Our findings thereby provide new insights into the role of system xc– in mechanisms of dopaminergic cell loss and its interaction with aging.

Astrocytic Glutamatergic Transmission and Its Implications in Neurodegenerative Disorders

“…In a recent study, xCT deletion did not show any effect over 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) induced neurodegeneration [ 146 ]. On the other hand, xCT deletion conferred protection over Lactacystin-induced neurodegeneration in aged but not young mice [ 148 ]. Lactacystin is a proteasome inhibitor and induces PD differently compared with the other neurotoxins such as MPTP.…”

“…The levels of xCT were found to be similar in both young and aged mice; however, deletion of xCT showed a protective effect against Lactacystin-induced neurodegeneration in old mice only. Altogether, these studies indicate a possible age-dependent association of xCT with proteasome degradation and neurotoxicity in PD [ 148 ].…”

Glial Glutamate Transporter-Mediated Plasticity: System xc-/xCT/SLC7A11 and EAAT1/2 in Brain Diseases

“…When nigrostriatal lesions in mice were induced through the application of the proteasome inhibitor lactacystin, treatment with the anticonvulsant zonisamide ameliorated this phenotype without any modulation of system x c − [135], implicating that system x c − is neglectable in some cases of anti-neurodegenerative therapy. With age, system x c − deficient mice were less prone to this lactacystin-induced nigrostriatal degeneration [136].…”

Effects of lactate, super-GDF9, and low oxygen tension during bi-phasic in vitro maturation on the bioenergetic profiles of mouse cumulus–oocyte complex

“…Then, 5-15 COCs (one biological replicate) were transferred per assay well together with 20 μl XF assay medium (final assay volume per well is 180 μl), and the plate was placed into the CO 2 -free incubator at 37 • C to de-gas for 1 h. Final concentrations (per well) for Mito Stress Test Kit reagents oligomycin, FCCP (carbonyl cyanide p-trifluoro-methoxyphenyl hydrazone), and Rot/AA (rotenone/antimycin A) were 1, 2.5, and 2.5 μM, respectively [48]. Upon completing the runs with the Seahorse, the contents of each well were lysed using 75 μl extraction buffer (2% sodium dodecyl sulfate, 60 nM Tris, 100 mM DTT, protease and phosphatase inhibitor cocktails) [49]. Supernatants were collected after incubating the samples at 37 • C for 30 min followed by centrifuging at 4 • C at 10 000 rpm for 15 min.…”