Skip to main content
. 2014 Aug 19;64(2):353–359. doi: 10.2337/db14-0582

Figure 1.

Figure 1

CD36 regulates AMPK phosphorylation and FA oxidation. A: CD36 depletion increases AMPK phosphorylation in myotubes. C2C12 myotubes were transfected with CD36-targeted siRNA (siCD36–1 and siCD36–2) or with a nonspecific siRNA (siCont). Knockdown efficiency relative to siCont: 85% ± 0.74, n = 4, P < 0.01 for siCD36–1; and 66% ± 2.9, n = 4, P < 0.01 for siCD36–2. Cells were serum starved for 16 h in DMEM buffer A containing 5 mmol/L glucose (see Research Design and Methods). Levels of CD36, pAMPK (T172), AMPK, and GAPDH were measured in cell lysates by immunoblotting. Graph shows the quantification by densitometry of pAMPK (T172)/AMPK as a fold change of siCont. Data are reported as the mean ± SE from four experiments. *P < 0.05, **P < 0.01, relative to siCont. B: CD36 is required for FA-induced AMPK activation. C2C12 myotubes treated with siCont or siCD36 were serum starved for 16 h in DMEM buffer A, incubated with 300 μmol/L PA (2:1 with BSA) or BSA (0 min) for the indicated times, and cell lysates were probed for CD36, pAMPK (T172), AMPK, and GAPDH. Graph shows the quantification of pAMPK (T172)/AMPK in cells treated with PA for 15 min as the fold change of levels in siCont. Data are reported as the mean ± SE from three experiments. ***P < 0.001, relative to siCont. C: CD36 depletion increases FA oxidation. C2C12 myotubes were starved for 16 h and processed for FA oxidation (see Research Design and Methods). Plots show PA-supported oxygen consumption (nmol/106 cells/15 min) for intact or Dig-permeabilized myotubes (siCont or CD36 depleted). Data are reported as the mean ± SE from five experiments. **P < 0.01, *P < 0.05 relative to the corresponding siCont. D: CD36 deletion increases AMPK phosphorylation in vivo. Skeletal muscle (gastrocnemius) and hearts, isolated from WT or CD36−/− mice fasted for 18 h were lysed and probed for CD36, pAMPK (T172), AMPK, and GAPDH for skeletal muscle or β-actin for heart (label omitted for clarity). Graph shows the quantification of pAMPK/AMPK levels in gastrocnemius muscle (n = 6 mice) and heart (n = 4 mice). Data are reported as the mean ± SE. ***P < 0.001, *P < 0.05 relative to WT mice. E: CD36 deletion increases FA oxidation in vivo. RQs were measured by indirect calorimetry for WT and CD36−/− mice under ad libitum feeding (18 h) and then during 18 h of fasting. Averaged RQs of fed or fasted WT and CD36−/− mice are shown. Data are reported as the mean ± SE. Significance reflects comparisons to fed WT mice (**P < 0.01) or fasted WT mice (#P < 0.01; n = 6 per group). F: Endogenous TG stores are depleted in CD36-deficient muscle. Left panel: Quadriceps TG content in WT and CD36−/− mice that had been fed or fasted for 18 h. *P < 0.05 compared with fasted WT mice (n = 6 per group). Right panel: Myocardial TG content in WT and CD36−/− mice fed or fasted for 18 h. Comparisons are to fed WT mice (**P < 0.01) or fasted WT mice (#P < 0.01; n = 5 per group). All data are reported as the mean ± SE.