Regulation of apolipoprotein E secretion in rat primary hippocampal astrocyte cultures.
Apolipoprotein E isoforms may have differential effects on a number of pathological processes underlying Alzheimer's disease. Recent studies suggest that the amount, rather than the type, of apolipoprotein E may also be an important determinant for Alzheimer's disease. Therefore, understanding the regulated synthesis of apolipoprotein E is important for determining its role in Alzheimer's disease. We show here that in rat primary hippocampal astrocyte cultures, dibutyryl-cAMP increased apolipoprotein E secretion with time in a dose-dependent manner (to 177% at 48 h) and that retinoic acid potentiated this effect (to 298% at 48 h). Dibutyryl-cAMP also gave a rapid, albeit transient, increase of apolipoprotein E mRNA expression (to 200% at 1 h). In contrast, the protein kinase C activator phorbol 12-myristate 13-acetate decreased both apolipoprotein E secretion (to 59% at 48 h) and mRNA expression (to 22% at 1 h). Phorbol 12-myristate 13-acetate also reversed the effects of dibutyryl-cAMP. Apolipoprotein E secretion was also modulated by receptor agonists for the adenylyl cyclase/cAMP pathway. Isoproterenol (50 nM, a beta-adrenoceptor agonist) enhanced, while clonidine (250 nM, an alpha2-adrenoceptor agonist) decreased, secreted apolipoprotein E. We also analysed the effects of agonists for the phospholipase C/protein kinase C pathway. Arterenol (1 microM, an alpha1-adrenoceptor agonist) and serotonin (2.5 microM) enhanced, whereas carbachol (10 microM, an acetylcholine muscarinic receptor agonist) decreased secreted apolipoprotein E. The effects of these non-selective receptor agonists were modest, probably due to effects on different signalling pathways. Arterenol also potentiated the isoproterenol-mediated increase. We also show that phorbol 12-myristate 13-acetate and dibutyryl-cAMP have opposite effects on nerve growth factor, as compared to apolipoprotein E, secretion, suggesting that the results obtained were unlikely to be due to a general effect on protein synthesis. We conclude that astrocyte apolipoprotein E production can be regulated by factors that affect cAMP intracellular concentration or activate protein kinase C. Alterations in these signalling pathways in Alzheimer's disease brain may have consequences for apolipoprotein E secretion in this disorder.
Cedazo-Mínguez
A
A
Karolinska Institutet, NEUROTEC, Section for Experimental Genetics, Huddinge, Sweden.
Hamker
U
U
Meske
V
V
Veh
R W
RW
Hellweg
R
R
Jacobi
C
C
Albert
F
F
Cowburn
R F
RF
Ohm
T G
TG
D000544:Alzheimer Disease / Q000378:metabolism* / Q000503:physiopathology; D000818:Animals; D000831:Animals, Newborn; D001057:Apolipoproteins E / Q000187:drug effects / Q000235:genetics / Q000378:metabolism*; D001253:Astrocytes / Q000187:drug effects / Q000378:metabolism*; D003994:Bucladesine / Q000494:pharmacology; D002217:Carbachol / Q000494:pharmacology; D002470:Cell Survival / Q000187:drug effects / Q000502:physiology; D002478:Cells, Cultured / Q000187:drug effects / Q000378:metabolism*; D003000:Clonidine / Q000494:pharmacology; D000242:Cyclic AMP / Q000378:metabolism*; D004347:Drug Interactions; D006624:Hippocampus / Q000187:drug effects / Q000378:metabolism* / Q000503:physiopathology; D007150:Immunohistochemistry; D007545:Isoproterenol / Q000494:pharmacology; D020932:Nerve Growth Factor / Q000187:drug effects / Q000378:metabolism; D009638:Norepinephrine / Q000494:pharmacology; D011493:Protein Kinase C / Q000187:drug effects / Q000378:metabolism*; D012333:RNA, Messenger / Q000187:drug effects / Q000378:metabolism; D051381:Rats; D017208:Rats, Wistar; D012701:Serotonin / Q000494:pharmacology; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology; D014212:Tretinoin / Q000494:pharmacology
D001057:Apolipoproteins E; D012333:RNA, Messenger; D012701:Serotonin; D014212:Tretinoin; D003994:Bucladesine; D002217:Carbachol; D020932:Nerve Growth Factor; D000242:Cyclic AMP; D011493:Protein Kinase C; D007545:Isoproterenol; D003000:Clonidine; D013755:Tetradecanoylphorbol Acetate; D009638:Norepinephrine