Submitted on June 26, 2007
Accepted on December 12, 2007
Effect of weight loss on lactate transporter expression in skeletal muscle of obese subjects
Lore L. Metz1, Jacques Mercier1, Angelo Tremblay2, Natalie Almeras3, and Denis R. Joanisse4*
1 Physiologie, Laboratoire de physiologie des interactions, Montpellier, France
2 Laval University, Ste-Foy, Canada
3 Laval Hospital Research Centre, Quebec, Canada
4 Department of Social and Preventive Medicine, Laval University, Quebec, Canada; Department of Social and Preventive Medicine, Laval University, Division of Kinesiology, Faculty of Medicine, Ste-Foy, Quebec, G1K 7P4, Canada
* To whom correspondence should be addressed. E-mail: denis.joanisse{at}kin.msp.ulaval.ca.
The effects of weight loss on skeletal muscle lactate transporter (MCT) expression in obese subjects were investigated in order to better understand how lactate transporters metabolism is regulated in insulin resistant states. Ten obese subjects underwent non-macronutrient-specific energy restriction for 15 weeks. Anthropometric measurements and a needle biopsy of the vastus lateralis muscle before and after the weight loss program were performed. Enzymatic activity, fibre type distribution and skeletal muscle MCT protein expression were measured. Muscle from non-obese control subjects was used for comparison of MCT levels. The program induced a weight loss of 9.2±1.6 kg. Compared to controls, muscle from obese subjects showed a strong tendency (p = 0.06) for elevated MCT4 expression (+69%) before the weight loss program. MCT4 expression decreased (-7%) following weight loss, to reach levels that were not statistically different from control levels. There were no differences in MCT1 expression between controls and obese subjects before and after weight loss. A highly predictive regression model (R2=0.93) including waist circumference, citrate synthase activity and % of type 1 fibres was found to explain the highly variable MCT1 response to weight loss in the obese group. Therefore, in obesity, MCT1 expression appears linked both to changes in oxidative parameters and to changes in visceral adipose tissue content. The strong tendency for elevated expression of muscle MCT4 could reflect the need to release greater amounts of muscle lactate in the obese state, a situation that would be normalized with weight loss as indicated by decreased MCT4 levels.
