Enhanced Fatty Acid Oxidation and FATP4 Protein Expression after Endurance Exercise Training in Human Skeletal Muscle

et al. (2012) Enhanced Fatty Acid Oxidation and FATP4 Protein Expression after Endurance Exercise Training in Human Skeletal Muscle. PLoS ONE 7(1): e29391. doi:10.1371/journal.pone.0029391 Enhanced Fatty Acid Oxidation and FATP4 Protein Expression after Endurance Exercise Training in Human Skeletal Muscle Jacob Jeppesen 0 Andreas B. Jordy 0 Kim A. Sjberg 0 Joachim Fu llekrug 0 Andreas Stahl 0 Lars Nybo 0 Bente Kiens 0 Thierry Alquier, Montreal Diabetes Research Center, Canada 0 1 Molecular Physiology Group, Department of Exercise and Sport Sciences, University of Copenhagen, Copenhagen, Denmark , 2 Integrated Physiology , Department of Exercise and Sport Sciences, University of Copenhagen , Copenhagen , Denmark , 3 Molecular Cell Biology Laboratory, Internal Medicine IV, University of Heidelberg , Heidelberg, Germany , 4 Department of Nutritional Sciences and Toxicology, University of California , Berkeley, California , United States of America FATP1 and FATP4 appear to be important for the cellular uptake and handling of long chain fatty acids (LCFA). These findings were obtained from loss- or gain of function models. However, reports on FATP1 and FATP4 in human skeletal muscle are limited. Aerobic training enhances lipid oxidation; however, it is not known whether this involves up-regulation of FATP1 and FATP4 protein. Therefore, the aim of this project was to investigate FATP1 and FATP4 protein expression in the vastus lateralis muscle from healthy human individuals and to what extent FATP1 and FATP4 protein expression were affected by an increased fuel demand induced by exercise training. Eight young healthy males were recruited to the study. All subjects were non smokers and did not participate in regular physical activity (,1 time per week for the past 6 months, VO2peak 3.460.1 l O2 min21). Subjects underwent an 8 week supervised aerobic training program. Training induced an increase in VO2peak from 3.460.1 to 3.960.1 l min21 and citrate synthase activity was increased from 53.762.5 to 80.863.7 mmol g21 min21. The protein content of FATP4 was increased by 33%, whereas FATP1 protein content was reduced by 20%. Interestingly, at the end of the training intervention a significant association (r2 = 0.74) between the observed increase in skeletal muscle FATP4 protein expression and lipid oxidation during a 120 min endurance exercise test was observed. In conclusion, based on the present findings it is suggested that FATP1 and FATP4 proteins perform different functional roles in handling LCFA in skeletal muscle with FATP4 apparently more important as a lipid transport protein directing lipids for lipid oxidation. - Funding: The financial support from the Integrated Project Grant LSHM-CT-2004-005272 funded by the European Commission, the Danish Agency of Science, Technology and Innovation and the Ministry of Food, Agriculture and Fisheries and The Novo Nordisk Foundation (Bente Kiens) are acknowledged. Also, this work was supported in part by the German research foundation DFG (FU 340/5-1 to Joachim Fu llekrug) and by NIH/NIDDK grants R56DK066336/R01DK066336 (Andreas Stahl). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. Competing Interests: The authors have declared that no competing interests exist. Skeletal muscle expresses several membrane bound lipid binding proteins such as the plasma membrane fatty acid binding protein (FABPpm) [1], fatty acid transport protein (FATP) 1 and 4 [2,3,4,5], fatty acid translocase CD36 (FAT/CD36) [6] and, in addition, two intracellular proteins, the cytosolic fatty acid binding protein (FABPc) [7] and the acyl-CoA binding protein (ACBP) [8], which have been shown to be important in cellular LCFA handling [9,10,11]. Furthermore, two small integral membrane proteins, Caveolin 1 and Caveolin 3, critical in the formation of caveolae in endothelia cells (Caveolin 1) [12] and skeletal muscle (Caveolin 3) [13], were recently shown to have an important role in regulation of LCFA metabolism [14,15]. Most of the lipid binding proteins have been identified in human skeletal muscle on the protein level [16,17,18,19,20,21]. However, whether protein, and not only mRNA, levels of FATP1 and FATP4, the major FATP isoforms expressed in rodent skeletal muscle [3,4,5,22], are expressed in human skeletal muscle, have yet to be addressed. The generation of genetic FATP1 and FATP4 loss-of-function models (i.e. FATP1 KO- and FATP4 heterozygote mice) revealed an important role in LCFA uptake in muscle cells [23] and enterocytes [2], respectively. However, the mechanism by which these proteins facilitate LCFA uptake in skeletal muscle cells is unclear. Detailed membrane topology analysis suggests that FATP1 protein has at least one transmembrane and multiple membrane associated domains [24]. FATP4 appears to share this transmembrane domain topology [25], and an overall sequence similarity [26] suggests it is common to all FATP family members [27]. Importantly, FATP1 and FATP4 were shown to possess long chain acyl CoA synthetase activity [28,29]. Taken together, the findings suggest that FATP1 and FATP4 induced activation of LCFA, by the formation of fatty acyl-CoA once LCFA is taken up by cells or released from the intramyocellular triacylglycerol (IMTG) pool, could be a major contributor to the regulation of LCFA metabolism in skeletal muscle. Under physiological conditions with increased cellular demand of LCFA for energy turnover, such as exercise training, FABPpm protein expression has consistently been shown to be increased in human skeletal muscle [16,19,20,21], whereas reports of the effect of exercise training on FAT/CD36 protein expression are contradictory [19,20,21,30]. Furthermore, FABPpm and FAT/ CD36 protein expression were increased in vastus lateralis muscle from human subjects after 47 weeks on an isocaloric high fat diet [31]. This could indicate that LCFA flux in human skeletal muscle is associated with an increased FABPpm and FAT/CD36 protein expression. In contrast, it is unknown how increased LCFA turnover affects FATP1 and/or FATP4 protein expression. Therefore the main purpose of this study was to identify if human skeletal muscle expresses FATP1 and FATP4 at the protein level and furthermore, whether these proteins were affected by an increased fuel demand induced by exercise training. We hypothesized that endurance exercise training, which is known to increase the potential for an enhanced systemic LCFA utilization [32,33,34,35] and skeletal muscle lipolytic capacity [36,37,38,39], will provide adaptations in FATP1 and FATP4 protein expression in order to increase the cellular capacity for FA handling to accompany the increased cellular LCFA flux. Subjects Eight healthy males (age 3061 yr; body weight 90.065.3 kg; body fat percentage 30.562.5; body mass index (BMI) 27.062.0) were recruited to the study (Table 1). These subjects were part of the in (...truncated)