Leptin Increases Axonal Growth Cone Size in Developing Mouse Cortical Neurons by Convergent Signals Inactivating Glycogen Synthase Kinase-3β

Enzo Nisoli,Valentina Ghisi,Alessandra Valerio,Antonio Giordano,Andrea Frontini,Cristina Tonello,Michele O. Carruba,Marina Ferrario,Marta Dossena,PierFranco Spano,Marina Pizzi

doi:10.1074/jbc.m508691200

Abstract

We examined the effects of the adipose hormone leptin on the development of mouse cortical neurons. Treatment of neonatal and adult mice with intraperitoneal leptin (5 mg/kg) induced extracellular signal-regulated kinase (ERK) 1/2 phosphorylation in pyriform and entorhinal cortex neurons. Stimulation of cultured embryonic cortical neurons with leptin evoked Janus kinase 2 and ERK1/2 phosphorylation and activated the downstream effector 90-kDa ribosomal protein S6 kinase. Moreover, leptin elicited the phosphorylation of the phosphatidylinositol 3-kinase effector Akt and evoked Ser-9 phosphorylation of glycogen synthase kinase-3beta (GSK3beta), an event inactivating this kinase. Leptin-mediated GSK3beta phosphorylation was prevented by the MEK/ERK inhibitor PD98059, the phosphatidylinositol 3-kinase inhibitor LY294002, or the protein kinase C inhibitor GF109203X. Exposure of cortical neurons to leptin also induced Ser-41 phosphorylation of the neuronal growth-associated protein GAP-43, an effect prevented by LY294002 and GF109203X but not by PD98059. Ser-41-GAP-43 phosphorylation is usually high in expanding axonal growth cones. Neurons exposed to 100 ng/ml leptin for 72 h displayed reduced rate of growth cone collapse, a shift of growth cone size distribution toward higher values, and a 4-fold increase in mean growth cone surface area compared with control cultures. The leptin-induced growth cone spreading was hampered in cortical neurons from Lepr(db/db) mice lacking functional leptin receptors; it was associated with localized Ser-9-GSK3beta phosphorylation and mimicked by the GSK3beta inhibitor SB216763. At concentrations preventing GSK3beta phosphorylation, PD98059, LY294002, or GF109203X reversed the leptin-induced growth cone surface enlargement. We concluded that the leptin-mediated regulation of growth cone morphogenesis in cortical neurons relies on upstream regulators of GSK3beta activity.

Highlights

The adipocyte-derived hormone leptin acts as satiety signal in hypothalamic nuclei to regulate energy homeostasis [1, 2]
We investigated the role of leptin in the development of mouse cerebral cortex neurons, and we discovered that the hormone acts as a trophic factor in the elaboration of cortical growth cones by modulating MEK/extracellular signal-regulated kinase (ERK), phosphatidylinositol 3-kinase (PI3K)/Akt, and PKC signaling pathways that converge in the inhibition of glycogen synthase kinase-3␤ (GSK3␤)
We found that developing mouse cortical neurons express LEPRb, which gradually increases during the process of in vitro neuronal maturation

Summary

Introduction

The adipocyte-derived hormone leptin acts as satiety signal in hypothalamic nuclei to regulate energy homeostasis [1, 2]. Leptin increases neurite extension in the arcuate nucleus during mouse perinatal development, playing an early trophic role within those circuits that will be the target of leptin physiological actions in adult life [14] These studies did not clarify whether the trophic effects of leptin are directly exerted on arcuate nucleus neurons, nor did the studies investigate the intracellular signals activated by leptin in the developmental and plastic changes described so far. We investigated the role of leptin in the development of mouse cerebral cortex neurons, and we discovered that the hormone acts as a trophic factor in the elaboration of cortical growth cones by modulating MEK/ERK, PI3K/Akt, and PKC signaling pathways that converge in the inhibition of glycogen synthase kinase-3␤ (GSK3␤)

Methods

Results

Conclusion