Hypoxia stabilizes type 2 deiodinase activity in rat astrocytes.
T(4) activation into T(3) is catalyzed by type 2 deiodinase (D2) in the brain. The rapid induction of D2 in astrocytes by transient brain ischemia has prompted us to explore the effects of hypoxia on D2 in cultures of astrocytes. Hypoxia (2.5% O(2)) of cultured astrocytes increased D2 activity, alone or in association with agents stimulating the cAMP pathway. Hypoxia had no effect on D2 mRNA accumulation. Cycloheximide did not block the effect of hypoxia on D2 activity and D2 half-life was enhanced under hypoxia demonstrating a posttranslational action of hypoxia. Furthermore, the D2 activity increase by hypoxia was not additive with the increase promoted by the proteasome inhibitor carbobenzoxy-L-leucyl-L-leucyl-L-leucinal (MG132). This strongly suggests that hypoxia leads to stabilization of D2 by slowing its degradation by the proteasome pathway. Hypoxia, in contrast to MG132, did not block the T(4)-induced D2 inactivation. A contribution of prolyl hydroxylase to the hypoxia effects on D2 was also suggested on the basis of increased D2 activity after addition of different prolyl hydroxylase inhibitors (cobalt chloride, desferrioxamine, dimethyloxalylglycine, dimethylsuccinate). Specific inhibitors of ERK, p38 MAPK, or phosphatidylinositol 3-kinase pathways were without any effect on hypoxia-increased D2 activity, eliminating their role in the effects of hypoxia. Interestingly, diphenyleneiodonium, an inhibitor of nicotinamide adenine dinucleotide phosphate oxidase inhibited the hypoxia-increased D2 indicating a role for some reactive oxygen species in the mechanism of D2 increase. Further studies are required to clarify the precise molecular mechanisms involved in the D2 stabilization by hypoxia.
Lamirand
Audrey
A
Institut National de la Santé et de la Recherche Médicale, UMR 854, and Université Paris-Sud 11, 80 Rue du Général Leclerc, 94276 Le Kremlin-Bicêtre, France.
Mercier
Gilles
G
Ramaugé
Martine
M
Pierre
Michel
M
Courtin
Françoise
F
D000818:Animals; D001253:Astrocytes / Q000201:enzymology* / Q000378:metabolism; D001921:Brain / Q000166:cytology; D002478:Cells, Cultured; D005947:Glucose / Q000172:deficiency; D000860:Hypoxia / Q000139:chemically induced / Q000201:enzymology*; D007453:Iodide Peroxidase / Q000235:genetics / Q000378:metabolism*; D007527:Isoenzymes / Q000235:genetics / Q000378:metabolism; D019255:NADPH Oxidases / Q000378:metabolism; D011494:Protein Kinases / Q000378:metabolism; D011499:Protein Processing, Post-Translational; D012333:RNA, Messenger / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley
D007527:Isoenzymes; D012333:RNA, Messenger; D007453:Iodide Peroxidase; D019255:NADPH Oxidases; D011494:Protein Kinases; D005947:Glucose