Implication of the Phosphatidylinositol-3 Kinase/Protein Kinase
B Signaling Pathway in the Neuroprotective Effect of Estradiol
in the Striatum of 1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine
Myreille D’Astous, Pablo Mendez, Marc Morissette, Luis Miguel Garcia-Segura, and
Th´ er` ese Di Paolo
Molecular Endocrinology and Oncology Research Center, Laval University Medical Center, CHUL, and Faculty of Pharmacy,
Laval University, Quebec City, Quebec, Canada (M.D., M.M., T.D.P.); and Instituto Cajal, Consejo Superior de Investigaciones
Cientificas, Madrid, Spain (P.M., L.M.G.-S.)
Received September 4, 2005; accepted January 24, 2006
The present experiments sought to determine the implication of
estrogen receptors (ER? and ER?) and their interaction with
insulin-like growth factor receptor (IGF-IR) signaling pathways
in neuroprotection by estradiol against 1-methyl-4-phenyl-
1,2,3,6-tetrahydropyridine (MPTP) toxicity. C57BL/6 male mice
were pretreated for 5 days with 17?-estradiol, an estrogen
receptor ? (ER?) agonist, 4,4?,4?-(4-propyl-[1H]-pyrazole-1,3,5-
triyl)tris-phenol (PPT), or an estrogen receptor ? (ER?) agonist,
5-androsten-3?, 17?-diol (?5-diol). On day 5, mice received
MPTP (9 mg/kg) or saline injections, and estrogenic treatments
were continued for 5 more days. MPTP decreased striatal
dopamine, measured by high-performance liquid chromatog-
raphy, to 59% of control values; 17?-estradiol and PPT but not
?5-diol protected against this depletion. MPTP increased
IGF-IR measured by Western blot, which was prevented by
PPT. The phosphorylation of protein kinase B (Akt) (at serine
473), an essential mediator of IGF-I neuroprotective actions,
increased after 17?-estradiol and tended to increase with PPT
but not with ?5-diol treatments in MPTP mice. Glycogen syn-
thase kinase 3? (GSK3?) phosphorylation (at serine 9) was
greatly reduced in MPTP mice; this was completely prevented
by PPT, whereas 17?-estradiol and ?5-diol treatments were
less effective. The ratio between the levels of striatal Bcl-2 and
BAD proteins, two apoptotic regulators, decreased after MPTP
treatment. This effect was effectively prevented only in the
animals treated with PPT. In nonlesioned mice, 17?-estradiol
and PPT increased phosphorylation of striatal Akt and GSK3?,
whereas the other markers measured remained unchanged.
?5-Diol increased GSK3? phosphorylation less than the PPT
treatment. These results suggest that a pretreatment with es-
tradiol promoted dopamine neuron survival by activating ER?
and increasing Akt and GSK3? phosphorylation.
Many studies have demonstrated the neuroprotective ef-
fects of estradiol in vivo against neurotoxins of the nigrostri-
atal dopaminergic system (Callier et al., 2000; Dluzen and
McDermott, 2000; D’Astous et al., 2004). The molecular
mechanisms implicated in the neuroprotection have yet to be
described. The aim of the present experiment was to inves-
tigate the possible implication of the insulin-like growth fac-
tor (IGF-I) signaling pathway in the neuroprotective effects
of estradiol because there is a great interdependence between
the actions of estradiol, IGF-I, and their respective receptors.
Indeed, these molecules interact with one another, via their
receptors, and are involved in cross-talking through different
signaling pathways (Kahlert et al., 2000). These molecules
interact to positively affect neuronal differentiation, neuro-
genesis, synaptic plasticity, neuroendocrine regulation, and
neuroprotection (Cardona-Gomez et al., 2001; Garcia-Segura
et al., 2001).
Intracellular signaling of IGF-I receptors (IGF-IR) is me-
This research was supported by grants from the Canadian Institutes of
Health Research (CIHR) (to T.D.P.) and from Ministerio de Ciencia y Tecno-
logı ´a, Spain (SAF 2002-00652) (to L.M.G.-S.). M.D. held a CIHR studentship.
M.D.A. and P.M. contributed equally to this work.
Article, publication date, and citation information can be found at
ABBREVIATIONS: IGF-I, insulin growth factor I; ER, estrogen receptor; IGF-IR, insulin growth factor receptor; MPTP, 1-methyl-4-phenyl-1,2,3,6-
tetrahydropyridine; PPT, 4,4?,4?-(4-propyl-[1H]-pyrazole-1,3,5-triyl)tris-phenol; ?5-diol, 5-androsten-3?, 17?-diol; PI3K, phosphatidylinositol-3
kinase; Akt, protein kinase B; GSK3?, glycogen synthase kinase 3?; DOPAC, 3,4-dihydroxyphenylacetic acid; pAkt or pSer473Akt, phosphory-
lated protein kinase B at serine 473; pGSK3 or pSer9GSK3?, phosphorylated glycogen synthase kinase 3? at serine 9; ANOVA, analysis of
Copyright © 2006 The American Society for Pharmacology and Experimental Therapeutics
Mol Pharmacol 69:1492–1498, 2006
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Address correspondence to: Dr. The ´re `se Di Paolo, Molecular Endocrinology
and Oncology Research Center, Laval University Medical Center, CHUL, 2705
Laurier Boulevard, Quebec City, Quebec, Canada G1V 4G2. E-mail: therese.
D’Astous et al.