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1 Department of Human Biology and Nutritional Sciences, University of Guelph, Ontario N1G 2W1; and 2 Department of Kinesiology, University of Waterloo, Ontario, Canada N2L 3G1
We have previously reported that
chronic leptin administration (2 wk) increases fatty acid (FA)
oxidation and triacylglycerol hydrolysis in rodent soleus muscle. Acute
stimulation of AMP-activated protein kinase (AMPK) results in a
repartitioning of FA toward oxidation and away from esterification in
rodent soleus muscle and has recently been shown to be responsible, at
least in part, for the acute stimulatory effect of leptin on FA
oxidation. Therefore, we hypothesized that the effects of chronic
leptin treatment on muscle FA metabolism are mediated in part through
an increased expression and/or activation of AMPK and a subsequent
phosphorylation of acetyl-CoA carboxylase and a decrease in malonyl-CoA
content. Female Sprague-Dawley rats were infused for 2 wk with leptin
(0.5 mg · kg
1 · day1)
using subcutaneously implanted mini-osmotic pumps. Control and pair-fed
animals received saline-filled implants. Leptin levels were elevated
approximately fourfold (P < 0.001) in treated animals, relative to controls. Chronic leptin treatment resulted in an ~2- to
3-fold greater protein expression of AMPK catalytic (
2) and regulatory (
2) units as well as a 1.5- to 2-fold
increase in Thr172 phosphorylation of AMPK in both soleus
and white gastrocnemius muscles. The increased
expression/phosphorylation of AMPK was not the result of an altered
energy status of the muscle. Correspondingly, there was also a 1.5- to
2-fold increase in acetyl-CoA carboxylase (ACC) phosphorylation after
leptin treatment in soleus and white gastrocnemius. In spite of the
measured increase in ACC phosphorylation after leptin treatment, we
were unable to detect a decrease in resting malonyl-CoA content in
either muscle. However, taken as a whole, our data support recent
evidence in rodent muscle that leptin stimulates FA oxidation through
stimulation of AMPK and a subsequent downregulation of ACC activity.
osmotic mini-pumps; fat oxidation; acetyl-coenzyme A carboxylase; adenosine monophosphate-activated protein kinase
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