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The Journal of Neuroscience, January 15, 2000, 20(2):722-728
Insulin-Like Growth Factor-I Protects Axotomized Rat Retinal
Ganglion Cells from Secondary Death via PI3-K-Dependent Akt
Phosphorylation and Inhibition of Caspase-3 In Vivo
Pawel
Kermer,
Nikolaj
Klöcker,
Monika
Labes, and
Mathias
Bähr
Department of Neurology, Medical School, University of
Tübingen, 72076 Tübingen, Germany
Recently we have shown that the majority of retinal ganglion cells
(RGCs) dies via activation of caspase-3 after transection of the optic
nerve (ON) in the adult rat. In the present study we investigated
whether insulin-like growth factor-I (IGF-I), an important factor in
retinal development, prevents secondary death of RGCs after axotomy.
Moreover, we studied potential intracellular mechanisms of IGF-mediated
neuroprotection in more detail. Our results indicate that intraocular
application of IGF-I protects RGCs from death after ON transection in a
dose-dependent manner. We show reduced caspase-3 activity as one
possible neuroprotective mechanism of IGF-I treatment in
vivo. Caspase-3 mRNA expression remained unchanged. Because
caspase inhibition can be mediated by Akt in vitro, we
examined phosphorylation of Akt after axotomy and under IGF treatment.
Western blot analysis revealed decreased Akt phosphorylation after
axotomy without treatment and an increased phosphorylation of Akt under
treatment with IGF-I. This strong increase could be reduced by
simultaneous injection of wortmannin (WM), a potent inhibitor of
phosphatidylinositol 3-kinase (PI3-K). To prove the pathway
suggested by these experiments as relevant for the in
vivo situation, we assessed the number of RGCs 14 d after
ON transection under a combined treatment strategy of IGF-I and WM. As
expected, WM significantly reduced the neuroprotective effects of
IGF-I. In summary, we show for the first time in vivo that IGF is neuroprotective via PI3-K-dependent Akt phosphorylation and
by inhibition of caspase-3.
Key words:
insulin-like growth factor-I; retinal ganglion cells; neuroprotection; PKB/Akt; PI3-K; caspase-3; apoptosis
Copyright © 2000 Society for Neuroscience 0270-6474/00/202722-07$05.00/0
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