title: Porcine leptin inhibits protein breakdown and stimulates fatty acid oxidation in C2C12 myotubes.
abstract: This study evaluated the potential mechanism(s) by which leptin treatment inhibits loss of muscle mass with fasting. Cultures of C2C12 myoblasts were differentiated into myotubes with 5% (vol/vol) horse serum in Dulbecco's modified Eagle's medium/F12. These myotubes were used to assess 3H-tyrosine incorporation and release following incubation with recombinant porcine leptin (0 to 500 ng/mL). Protein synthesis in myotubes, as measured by 3H-tyrosine incorporation, was not affected by leptin treatment (P > 0.05). Protein breakdown in C2C12 myotubes, as measured by 3H-tyrosine release, was inhibited by leptin treatment. A leptin concentration of 0.5 ng/mL was sufficient to inhibit 3H-tyrosine release by 3.5% (P < 0.05); 50 ng/mL produced a maximal inhibition of 10.2% (P < 0.05). Dexamethasone (1 microM) was used to maximally stimulate protein breakdown. Leptin (50 ng/mL leptin) decreased dexamethasone-induced 3H-tyrosine release by 32% (P < 0.05). The inhibition of 3H-tyrosine release in C2C12 myotubes suggests that leptin produces a protein-sparing effect in vitro by inhibiting protein breakdown. Fatty acid metabolism also was investigated because fatty acids are a major energy source for muscle during periods of reduced intake, as occurs with leptin treatment. Acute (4 h) and chronic (24 h) exposures to porcine leptin (0 to 500 ng/mL) were used to evaluate 14C-palmitate oxidation. Acute leptin treatment had no effect (P > 0.05) on palmitate metabolism. Chronic leptin exposure resulted in up to a 26% increase in palmitate oxidation (P < 0.05). The stimulation of fatty acid oxidation with chronic leptin treatment suggests that leptin spares other energy sources in muscle from oxidation during periods of a leptin-induced decrease in feed intake.
authors.affiliation: Growth Biology Laboratory, USDA-ARS, Beltsville, MD 20705, USA. tramsay@anri.barc.usda.gov
authors.forename: T G
authors.initials: TG
authors.lastname: Ramsay
mesh_terms: D000818:Animals; D002460:Cell Line; D003907:Dexamethasone / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D005947:Glucose / Q000378:metabolism; D006003:Glycogen / Q000378:metabolism; D020738:Leptin / Q000494:pharmacology*; D051379:Mice; D018485:Muscle Fibers, Skeletal / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D010084:Oxidation-Reduction / Q000187:drug effects; D010168:Palmitates / Q000378:metabolism*; D011506:Proteins / Q000187:drug effects / Q000378:metabolism*; D011897:Random Allocation; D013552:Swine; D014443:Tyrosine / Q000378:metabolism*
chemical_list: D020738:Leptin; D010168:Palmitates; D011506:Proteins; D014443:Tyrosine; D003907:Dexamethasone; D006003:Glycogen; D005947:Glucose