Increased mitochondrial glycerol-3-phosphate acyltransferase protein and enzyme activity in rat epididymal fat upon cessation of wheel running.

Triacylglycerol synthesis in rat epididymal fat overshoots sedentary levels at 10, 29, and 53 h of physical inactivity after 21 days of wheel running. The purposes of the present study were to determine 1) whether this effect is also observed after an acute bout of physical activity and 2) what enzymatic changes might contribute to this effect. We show that more than one bout of physical activity, such as that which occurs with 21 days of wheel running, is necessary for palmitic acid incorporation into triacylglyceride (triglyceride synthesis) to overshoot sedentary values, which suggests that pretranslational mechanisms may be responsible for this overshoot effect. Ten hours after 21 days of wheel running, activity of the mitochondrial glycerol-3-phosphate acyltransferase-1 (mtGPAT1) isoform, a key regulator of triacylglycerol synthesis, overshot sedentary values by 48% and remained higher than sedentary values at 29 and 53 h of reduced physical activity. The overshoot in mtGPAT1 activity was accompanied by an increase in mtGPAT protein level. Cyclic AMP response element-binding protein-binding protein level was higher in sedentary 29 h after 21 days of wheel running. AMP kinase-alpha Thr(172) phosphorylation was increased immediately after treadmill running, but decreased to sedentary values by 5 h after activity. Casein kinase-2alpha protein level and activity were unchanged. We conclude that an increase in mtGPAT protein might contribute to the overshoot in triacylglycerol synthesis.