Endurance training increases skeletal muscle LKB1 and PGC-1α protein abundance: effects of time and intensity

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Abstract
Recent research suggests that LKB1 is the major AMP-activated protein kinase kinase (AMPKK). Peroxisome-proliferator-activated receptor-γ coactivator-1α (PGC-1α) is a master coordinator of mitochondrial biogenesis. Previously we reported that skeletal muscle LKB1 protein increases with endurance training. The purpose of this study was to determine whether training-induced increases in skeletal muscle LKB1 and PGC-1α protein exhibit a time course and intensity-dependent response similar to that of citrate synthase. Male Sprague-Dawley rats completed endurance- and interval-training protocols. For endurance training, rats trained for 4, 11, 25, or 53 days. Interval-training rats trained identically to endurance-trained rats, except that after 25 days interval training was combined with endurance training. Time course data were collected from endurance-trained red quadriceps (RQ) after each time point. Interval training data were collected from soleus, RQ, and white quadriceps (WQ) muscle after 53 days only. Mouse protein 25 (MO25) and PGC-1α protein increased significantly after 4 days. Increased citrate synthase activity, increased LKB1 protein, and decreased AMPKK activity were found after 11 days. Maximal increases occurred after 4 days for hexokinase II, 25 days for MO25, and 53 days for citrate synthase, LKB1, and PGC-1α. In WQ, but not RQ or soleus, interval training had an additive effect to endurance training and induced significant increases in all proteins measured. These results demonstrate that LKB1 and PGC-1α protein abundances increase with endurance and interval training similarly to citrate synthase. The increase in LKB1 and PGC-1α with endurance and interval training may function to maintain the training-induced increases in mitochondrial mass.