Ischemic preconditioning reveals that GLT1/EAAT2 glutamate transporter is a novel PPARgamma target gene involved in neuroprotection.
Excessive levels of extracellular glutamate in the nervous system are excitotoxic and lead to neuronal death. Glutamate transport, mainly by glutamate transporter GLT1/EAAT2, is the only mechanism for maintaining extracellular glutamate concentrations below excitotoxic levels in the central nervous system. We recently showed that neuroprotection after experimental ischemic preconditioning (IPC) involves, at least partly, the upregulation of the GLT1/EAAT2 glutamate transporter in astrocytes, but the mechanisms were unknown. Thus, we decided to explore whether activation of the nuclear receptor peroxisome proliferator-activated receptor (PPAR) gamma, known for its antidiabetic and antiinflammatory properties, is involved in glutamate transport. First, we found that the PPARgamma antagonist T0070907 inhibits both IPC-induced tolerance and reduction of glutamate release after lethal oxygen-glucose deprivation (OGD) (70.1%+/-3.4% versus 97.7%+/-5.2% of OGD-induced lactate dehydrogenase (LDH) release and 61.8%+/-5.9% versus 85.9%+/-7.9% of OGD-induced glutamate release in IPC and IPC+T0070907 1 mumol/L, respectively, n=6 to 12, P<0.05), as well as IPC-induced astrocytic GLT-1 overexpression. IPC also caused an increase in nuclear PPARgamma transcriptional activity in neurons and astrocytes (122.1%+/-8.1% and 158.6%+/-22.6% of control PPARgamma transcriptional activity, n=6, P<0.05). Second, the PPARgamma agonist rosiglitazone increased both GLT-1/EAAT2 mRNA and protein expression and [(3)H]glutamate uptake, and reduced OGD-induced cell death and glutamate release (76.3%+/-7.9% and 65.5%+/-15.1% of OGD-induced LDH and glutamate release in rosiglitazone 1 mumol/l, respectively, n=6 to 12, P<0.05). Finally, we have identified six putative PPAR response elements (PPREs) in the GLT1/EAAT2 promoter and, consistently, rosiglitazone increased fourfold GLT1/EAAT2 promoter activity. All these data show that the GLT1/EAAT2 glutamate transporter is a target gene of PPARgamma leading to neuroprotection by increasing glutamate uptake.
Romera
Cristina
C
Departamento de Farmacología, Facultad de Medicina, Universidad Complutense de Madrid, Madrid, Spain.
Hurtado
Olivia
O
Mallolas
Judith
J
Pereira
Marta P
MP
Morales
Jesús R
JR
Romera
Alejandro
A
Serena
Joaquín
J
Vivancos
José
J
Nombela
Florentino
F
Lorenzo
Pedro
P
Lizasoain
Ignacio
I
Moro
Maria A
MA
D000818:Animals; D001253:Astrocytes / Q000187:drug effects / Q000378:metabolism / Q000473:pathology; D001549:Benzamides / Q000494:pharmacology; D015153:Blotting, Western; D001921:Brain / Q000098:blood supply / Q000187:drug effects / Q000378:metabolism*; D002478:Cells, Cultured; D002851:Chromatography, High Pressure Liquid; D018920:Coculture Techniques; D027342:Excitatory Amino Acid Transporter 2 / Q000235:genetics* / Q000378:metabolism*; D015870:Gene Expression; D018698:Glutamic Acid / Q000032:analysis / Q000378:metabolism; D007004:Hypoglycemic Agents / Q000494:pharmacology; D020244:Infarction, Middle Cerebral Artery / Q000378:metabolism / Q000473:pathology; D019194:Ischemic Preconditioning; D008297:Male; D009474:Neurons / Q000187:drug effects / Q000378:metabolism / Q000473:pathology; D047495:PPAR gamma / Q000378:metabolism*; D011401:Promoter Regions, Genetic; D011725:Pyridines / Q000494:pharmacology; D012333:RNA, Messenger / Q000032:analysis / Q000187:drug effects; D051381:Rats; D011916:Rats, Inbred F344; D017208:Rats, Wistar; D020218:Response Elements; D020133:Reverse Transcriptase Polymerase Chain Reaction; D000077154:Rosiglitazone; D045162:Thiazolidinediones / Q000494:pharmacology
D001549:Benzamides; D027342:Excitatory Amino Acid Transporter 2; D007004:Hypoglycemic Agents; D047495:PPAR gamma; D011725:Pyridines; D012333:RNA, Messenger; C458508:T 0070907; D045162:Thiazolidinediones; D000077154:Rosiglitazone; D018698:Glutamic Acid