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First published online on April 27, 2006.
 Copyright © 2006 by The Physiological Society
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Received February 9, 2006
Revised March 2, 2006
Accepted after revision April 24, 2006

Fatty acids stimulate AMP-activated protein kinase and enhance fatty acid oxidation in L6 myotubes

Matthew J Watt1*, Greg Steinberg1, Zhi-Ping Chen1, Bruce Kemp1, and Mark A. Febbraio2

1 St. Vincent's Institute of Medical Research
2 RMIT University

* To whom correspondence should be addressed. E-mail: mwatt{at}svi.edu.au.

We investigated the role of fatty acid availability on AMPK signalling and fatty acid oxidation in skeletal muscle. Incubating L6 skeletal muscle myotubes with palmitate (saturated fatty acid) or linoleate (polyunsaturated fatty acid) increased AMPK activity by 56 and 38%, respectively, compared with untreated cells. Consistent with these changes, AMPK Thr172 and acetyl CoA carboxylase {beta} Ser218 phosphorylation were increased in fatty acid treated cells. Pre- incubating cells with palmitate or linoleate increased subsequent fatty acid oxidation by 86 and 92%, respectively. The enhanced AMPK signalling occurred in the absence of detectable changes in free AMP and glycogen content. The activity of the upstream kinase LKB1 was decreased by fatty acid treatment indicating that AMPK activation was not a consequence of LKB1 activation. Instead, fatty acids enhanced LKB1 phosphorylation of AMPK. Fatty acids did not alter LKB1 activity when either synthetic peptide or AMPK {alpha} (1-312) catalytic fragment was used as substrate indicating that the {beta}{gamma} subunits were required for the fatty acid activation. Infection of cells with a dominant-negative AMPK adenovirus reduced basal fatty acid oxidation and inhibited the stimulatory effects of fatty acid pre-treatment on fatty acid oxidation. These results indicate that increasing fatty acid availability increases AMPK activity independent of changes in the cellular energy charge and support the view that fatty acids may modulate AMPK allosterically, making it a better substrate for LKB1.


Key words: Fatty acids • Metabolic regulation • Skeletal muscle




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