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The N-terminal tripeptide of IGF-I (GPE) stimulates the proliferation of 3T3 mouse embryo astrocytes

Cristina Almengló; Tamara González-Mosquera,;Pablo Devesa; Jesús Devesa;Víctor M. Arce


INTRODUCTION
Insulin like growth factor-I (IGF-I) is a well-known regulator of multiple neural functions, including the stimulation of the proliferation and survival of neural cells. In addition, IGF-I has been also shown to be cleaved in neurons resulting in an N-terminal tripeptide (GPE) which has been shown to exert some neuroprotective effects both in vitro and in vivo. However, little is known about both the effect of GPE on neural cells and its mechanism of action. In this study, we have investigated the effects of GPE in a model of immortalized mouse embryo astrocytes (MEAs).

MATERIALS AND METHODS
Primary MEAs were obtained from brains of 13.5 day old mice embyos (strain 126BL/6) and grown at 37ºC and 5% CO2 in DMEM supplemented with 10% FBS. MEAs were immortalized with the 3T3 protocol and 15-passage cells were used to perform a wound healing assay. Briefly, cells were seeded on a glass plate and serum starved for 48 h in the presence of 100 µM GPE or 500 ng/ml GH or saline. All treatments were administered every 24 h. Cell proliferation was investigating after immunostaining with antibodies against Ki67 or BrdU. Activation of PI3K/Akt or MEK/ERK pathways was investigated by western blot.

RESULTS
Both GPE or GH treatment induced a significant increase MEAs proliferation, as compared with saline-treated cells. This effect was even greater when GPE and GH were administered together. Immortalized MEAs showed a clearcut activation of Akt phosphorylation even under basal conditions, that was unchanged by any treatment. In constrast, basal ERK phosphorylation was absent and significantly increased after either GPE or GH treatment.

CONCLUSIONS
Both GPE and GH stimulate the proliferation of a immortalized line of MEAs through a mechanism that may involve the activation of ERK phosphorylation. In contrast, neither GPE nor GH modify Akt phosphorylation in these cells, probably due to its high basal levels.

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