Insulin and Leptin Acutely Regulate Cholesterol Ester Metabolism in Macrophages by Novel Signaling Pathways

  1. Lisa O’Rourke1,
  2. Steven J. Yeaman2 and
  3. Peter R. Shepherd1
  1. 1Department of Biochemistry and Molecular Biology, University College London, London
  2. 2School of Biochemistry and Genetics, University of Newcastle-upon-Tyne, Newcastle-upon-Tyne, U.K.

    Abstract

    Leptin is produced in adipose tissue and acts in the hypothalamus to regulate food intake. However, recent evidence also indicates a potential for direct roles for leptin in peripheral tissues, including those of the immune system. In this study, we provide direct evidence that macrophages are a target tissue for leptin. We found that J774.2 macrophages express the functional long form of the leptin receptor (ObRb) and that this becomes tyrosine-phosphorylated after stimulation with low doses of leptin. Leptin also stimulates both phosphoinositide 3-kinase (PI 3-kinase) activity and tyrosine phosphorylation of JAK2 and STAT3 in these cells. We investigated the effects of leptin on hormone-sensitive lipase (HSL), which acts as a neutral cholesterol esterase in macrophages and is a rate-limiting step in cholesterol ester breakdown. Leptin significantly increased HSL activity in J774.2 macrophages, and these effects were additive with the effects of cAMP and were blocked by PI 3-kinase inhibitors. Conversely, insulin inhibited HSL in macrophages, but unlike adipocytes, this effect did not require PI 3-kinase. These results indicate that leptin and insulin regulate cholesterol-ester homeostasis in macrophages and, therefore, defects in this process caused by leptin and/or insulin resistance could contribute to the increased incidence of atherosclerosis found associated with obesity and type 2 diabetes.

    Footnotes

    • Address correspondence and reprint requests to Peter R. Shepherd, PhD, Department of Biochemistry and Molecular Biology, University College London, Gower Street, London, WC1E 6BT, U.K. E-mail: p.shepherd{at}biochem.ucl.ac.uk.

      Received for publication 22 August 2000 and accepted in revised form 14 December 2000.

      BSA, bovine serum albumin; CPT-cAMP, 8-(4-chlorophenylthio)-adenosine 3′:5′-cyclic monophosphate; DMEM, Dulbecco’s modified Eagle’s medium; HSL, hormone-sensitive lipase; nCE, neutral cholesterol esterase; PDE, phosphodiesterase; PI 3-kinase, phosphoinositide 3-kinase; PKA, protein kinase A; PKB, protein kinase B.

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