Leptin Induces Endothelial Cell Migration Through Akt, Which Is Inhibited by PPARγ-Ligands

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Abstract
Migration of endothelial cells (EC) is a key event in angiogenesis that contributes to neovascularization in diabetic vasculopathy. Leptin induces angiogenesis and is elevated in obesity and hyperinsulinemia. The antidiabetic thiazolidinediones (TZD) inhibit leptin gene expression and vascular smooth muscle cell migration through activation of the peroxisome proliferator–activated receptor-γ (PPARγ). This study investigates the role of leptin in EC migration, the chemotactic signaling pathways involved, and the effects of the TZD-PPARγ ligands troglitazone (TRO) and ciglitazone (CIG) on EC migration. We demonstrate that leptin induces EC migration. Because activation of two signaling pathways, the phosphatidylinositol-3 kinase (PI3K)→Akt→eNOS and the ERK1/2 MAPK pathway, is known to be involved in cell migration, we used the pharmacological inhibitors wortmannin and PD98059 to determine if chemotactic signaling by leptin involves Akt or ERK1/2, respectively. Both wortmannin and PD98059 significantly inhibited leptin-induced migration. Treatment with the TZD-PPARγ-ligands TRO and CIG significantly inhibited the chemotactic response toward leptin. Both PPARγ-ligands inhibited leptin-stimulated Akt and eNOS phosphorylation, but neither attenuated ERK 1/2 activation in response to leptin. The inhibition of Akt-phosphorylation was accompanied by a PPARγ-ligand–mediated upregulation of PTEN, a phosphatase that functions as a negative regulator of PI3K→Akt signaling. These experiments provide the first evidence that activation of Akt and ERK 1/2 are crucial events in leptin-mediated signal transduction leading to EC migration. Moreover, inhibition of leptin-directed migration by the PPARγ-ligands TRO and CIG through inhibition of Akt underscores their potential in the prevention of diabetes-associated complications.

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