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Am J Physiol Endocrinol Metab 296: E862-E868, 2009. First published February 3, 2009; doi:10.1152/ajpendo.90651.2008
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Amino acid-sensing mTOR signaling is involved in modulation of lipolysis by chronic insulin treatment in adipocytes

Chongben Zhang, Mee-Sup Yoon, and Jie Chen

Department of Cell and Developmental Biology, University of Illinois at Urbana-Champaign, Urbana, Illinois

Submitted 2 August 2008 ; accepted in final form 28 January 2009

Chronically high insulin levels and increased circulating free fatty acids released from adipose tissue through lipolysis are two features associated with insulin resistance. The relationship between chronic insulin exposure and adipocyte lipolysis has been unclear. In the present study we found that chronic insulin exposure in 3T3-L1 adipocytes, as well as in mouse primary adipocytes, increased basal lipolysis rates. This effect of insulin on lipolysis was only observed when the mammalian target of rapamycin (mTOR) pathway was inhibited by rapamycin in the adipocytes. In addition, amino acid deprivation in adipocytes phenocopied the effect of rapamycin in permitting the stimulation of lipolysis by chronic insulin exposure. The phosphatidylinositol 3-kinase-Akt pathway does not appear to be involved in this insulin effect. Furthermore, we found that triacylglycerol hydrolase (TGH) activity was required for the stimulation of lipolysis by combined exposure to insulin and rapamycin. Therefore, we propose that nutrient sufficiency, mediated by an mTOR pathway, suppresses TGH-dependent lipolysis stimulated by chronic insulin exposure in adipocytes.

mammalian target of rapamycin; insulin resistance; 3T3-L1 cells; nutrient sufficiency; triacylglycerol hydrolase


Address for reprint requests and other correspondence: C. Zhang, Univ. of Virginia school of medicine, 409 Lane Rd., MR4-6051A, Charlottesville, VA 22908 (e-mail: chongben.zhang{at}virginia.edu)






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