title: Activation of the mitogen-activated protein kinase (ERK(1/2)) signaling pathway by cyclic AMP potentiates the neuroprotective effect of the neurotransmitter noradrenaline on dopaminergic neurons.
abstract: We have shown previously that low concentrations of noradrenaline (NA) confer long-term but partial protection to tyrosine hydroxylase (TH(+)) dopaminergic neurons by reducing spontaneously occurring oxidative stress. We demonstrate here that the effect of NA is strongly enhanced by cAMP-elevating agents, in particular forskolin (FK), through a mechanism that does not involve activation of adrenoceptors. FK also enhanced the neuroprotective action of antioxidants that mimic the trophic effects of NA, such as trolox and pyrocatechol, but was totally ineffective by itself, suggesting that inhibition of oxidative stress was a required step to reveal the cAMP-dependent mechanism. Neuroprotection afforded by FK was rapidly reversible, optimal when the treatment was initiated in the early phase of the culture and exquisitely specific to dopaminergic neurons. FK stimulated the phosphorylation of extracellular signal-activated kinases (ERK)(1/2) in a subpopulation of dopaminergic neurons, suggesting that the mitogen-activated protein kinase (MAPK) pathway was involved in the effects of cAMP-elevating agents. Accordingly, inhibition of the upstream kinases of ERK(1/2) by 2'-amino-3'-methoxyflavone (PD98059) not only suppressed MAPK activation caused by FK but also abolished the survival promoting activity that this compound exerts on TH(+) neurons. PD98059 did not reduce, however, the trophic effects provided by NA alone. Surprisingly, the archetypal cAMP-dependent protein kinase was apparently not responsible for ERK(1/2) activation. The data suggest that the MAPK signaling pathway plays a key role in the trophic effects that cAMP elevating agents and NA cooperatively exert on TH(+) neurons.
authors.affiliation: Institut National de la Santé et de la Recherche Médicale U289, Experimental Neurology and Therapeutics, Hôpital de la Salpêtrière, Paris, France.
authors.forename: Jean-Denis
authors.initials: JD
authors.lastname: Troadec
authors.forename: Marc
authors.initials: M
authors.lastname: Marien
authors.forename: Sophie
authors.initials: S
authors.lastname: Mourlevat
authors.forename: Thomas
authors.initials: T
authors.lastname: Debeir
authors.forename: Merle
authors.initials: M
authors.lastname: Ruberg
authors.forename: Francis
authors.initials: F
authors.lastname: Colpaert
authors.forename: Patrick P
authors.initials: PP
authors.lastname: Michel
mesh_terms: D000818:Animals; D002478:Cells, Cultured; D005576:Colforsin / Q000494:pharmacology; D000242:Cyclic AMP / Q000378:metabolism*; D017362:Cyclic AMP Response Element-Binding Protein / Q000378:metabolism; D017868:Cyclic AMP-Dependent Protein Kinases / Q000378:metabolism; D004298:Dopamine / Q000378:metabolism; D004347:Drug Interactions; D004357:Drug Synergism; D004622:Embryo, Mammalian / Q000166:cytology; D004789:Enzyme Activation; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism*; D008934:Mitogens / Q000494:pharmacology; D009474:Neurons / Q000187:drug effects* / Q000378:metabolism; D018696:Neuroprotective Agents / Q000494:pharmacology*; D009638:Norepinephrine / Q000494:pharmacology*; D051381:Rats; D017208:Rats, Wistar; D011943:Receptors, Adrenergic, beta / Q000378:metabolism; D011954:Receptors, Dopamine / Q000378:metabolism; D015398:Signal Transduction / Q000187:drug effects* / Q000502:physiology
chemical_list: D017362:Cyclic AMP Response Element-Binding Protein; D008934:Mitogens; D018696:Neuroprotective Agents; D011943:Receptors, Adrenergic, beta; D011954:Receptors, Dopamine; D005576:Colforsin; D000242:Cyclic AMP; D017868:Cyclic AMP-Dependent Protein Kinases; D020928:Mitogen-Activated Protein Kinases; D004298:Dopamine; D009638:Norepinephrine