Differential induction of heme oxygenase and other stress proteins in cultured hippocampal astrocytes and neurons by inorganic lead.
We examined the effects of exposure to inorganic lead (Pb2+) on the induction of stress proteins in cultured hippocampal neurons and astrocytes, with particular emphasis on the induction of heme oxygenase-1 (HO-1). In radiolabeled neuronal cultures, Pb2+ exposure had no significant effect on the synthesis of any protein at any concentration (up to 250 microM) or duration of exposure (up to 4 days). In radiolabeled astrocyte cultures, however, Pb2+ exposure (100 nM to 100 microM; 1-4 days) increased synthesis of proteins with approximate molecular weights of 23, 32, 45, 57, 72, and 90 kDa. Immunoblot experiments showed that Pb2+ exposure (100 nM to 10 microM, 1-14 days) induces HO-1 synthesis in astrocytes, but not in neurons; this is probably the 32-kDa protein. The other heme oxygenase isoform, HO-2, is present in both neurons and astrocytes, but is not inducible by Pb2+ at concentrations up to 100 microM. HO-1 can be induced by a variety of stimuli. We found that HO-1 induction in astrocytes is increased by combined exposure to Pb2+ and many other stresses, including heat, nitric oxide, H2O2, and superoxide. One of the stimuli that may induce HO-1 is oxidative stress. Lead exposure causes oxidative stress in many cell types, including astrocytes. Induction of HO-1 by Pb2+ is reduced by the hydroxyl radical scavengers dimethylthiourea (DMTU) and mannitol, but not by inhibitors of calmodulin, calmodulin-dependent protein kinases, protein kinase C, or extracellular signal-regulated kinases (ERK). Therefore, we conclude that oxidative stress is an important mechanism by which Pb2+ induces HO-1 synthesis in astrocytes.
Cabell
Leigh
L
Biology Department, University of Colorado at Denver, Denver, CO 80217-3364, USA.
Ferguson
Charles
C
Luginbill
Deana
D
Kern
Marcey
M
Weingart
Adam
A
Audesirk
Gerald
G
D000818:Animals; D001253:Astrocytes / Q000187:drug effects* / Q000201:enzymology / Q000473:pathology; D002478:Cells, Cultured; D004305:Dose-Response Relationship, Drug; D004790:Enzyme Induction; D004791:Enzyme Inhibitors / Q000494:pharmacology; D016166:Free Radical Scavengers / Q000494:pharmacology; D006360:Heat-Shock Proteins / Q000096:biosynthesis*; D006419:Heme Oxygenase (Decyclizing) / Q000037:antagonists & inhibitors / Q000096:biosynthesis*; D051547:Heme Oxygenase-1; D006624:Hippocampus / Q000166:cytology* / Q000196:embryology; D015151:Immunoblotting; D007854:Lead / Q000633:toxicity*; D009474:Neurons / Q000187:drug effects* / Q000201:enzymology / Q000473:pathology; D018384:Oxidative Stress / Q000502:physiology; D051381:Rats; D017207:Rats, Sprague-Dawley; D013890:Thiourea / Q000031:analogs & derivatives* / Q000494:pharmacology
D004791:Enzyme Inhibitors; D016166:Free Radical Scavengers; D006360:Heat-Shock Proteins; D007854:Lead; C038983:1,3-dimethylthiourea; D006419:Heme Oxygenase (Decyclizing); D051547:Heme Oxygenase-1; D013890:Thiourea