Regulation Of HiLo On AMPK/TSC2/mTOR Signaling Pathway In Skeletal Muscle

Objective:By acute hypoxia exposure, the variations of LKB1, AMP/ATP, AMPK and mTOR signals in skeletal muscle in a reoxygen period are observed and respective time course variation regularity is found. By observing the time course variations of AMPK/TSC2/mTOR signals during four-week HiLo, an action mechanism that hypoxia reduces protein synthesis in skeletal muscle via the signaling pathway is illustrated. At the same time, which way plays a leading role during the activation of AMPK by hypoxia via LKB1 and AMP/ATP ways is validated.Methods:As a research object, SD rats are employed in the present research and randomly divided into groups. An acute hypoxia test is divided into a sedentary group, hypoxia instant group, reoxygen 1h group, reoxygen 2h group, reoxygen 6h group and reoxygen 12h group. A four-week HiLo test is divided into four groups as follows:normoxia sedentary group, normoxia exercise group, hypoxia comparison group and HiLo group. The four groups are subdivided into one-day group, one-week group, two-week group and four-week group according to time course. A hypoxia exposure mode is defined as hypoxia exposure for 10 hours in a hypoxia room from 10 p.m. at night to 8 a.m. in the next day (oxygen concentration 13.6%, about 3500m). A normoxia exercise mode is defined as endurance exercise for 1 hour in a normoxia environment in the daytime (running platform gradient 5°, running speed 20m/min, continuous exercise time 1h/d,6d/w). The acute hypoxia test and the hypoxia exposure group employ the above-mentioned hypoxia exposure mode. The normoxia exercise group employs the normoxia exercise mode. The HiLo group performs hypoxia exposure in the hypoxia room at night after endurance exercise in the daytime, the exercise mode and the hypoxia exposure mode of which are respectively identical to that of the normoxia exercise group and the hypoxia exposure group. The normoxia sedentary group lives sedentarily in a normoxia environment. By using HPLC method, Bradford method, Western Blot method, etc., detected are AMP and ATP contents in extensor digitorum longus (EDL) of a rat, MHC protein expression, and the phosphorylation of the loci of LKB1 Ser428, AMPK Thr172, TSC2 Thr1462, mTOR Ser2448, p70S6K Thr389 and 4EBP1 Thr37/46. Results:(1) Immediately after hypoxia exposure, AMP content, AMP/ATP ratio and the phosphorylation of LKB1, AMPK and TSC2 in skeletal muscle increase remarkably (P<0.01), and meanwhile the phosphorylation of mTOR decreases remarkably (P<0.01), all of which restore to a sedentary level after reoxygen for 6h. (2) At each time point in four-week hypoxia exposure, hypoxia enables AMP content, AMP/ATP ratio and the phosphorylation of LKB1 and AMPK in skeletal muscle to remarkably increase, and remarkably inhibits the phosphorylation of MHC, mTOR and downstream signals thereof in skeletal muscle. (3) At each time point in four-week normoxia exercise, exercise remarkably facilitates the phosphorylation of MHC, LKB1, AMPK, mTOR and downstream signals thereof, and inhibits the expression of the phosphorylation of TSC2. (4) During the four-week HiLo training, exercise slows the inhibition of hypoxia on the phosphorylation of MHC, mTOR and downstream signals thereof in skeletal muscle.Conclusions:(1) Hypoxia can activate AMPK via AMP/ATP ratio and LKB1 ways, and reduce the activity of mTOR via AMPK/TSC2/mTOR pathways, and further inhibit protein synthesis. AMP/ATP ratio possibly activates AMPK via LKB1. (2) Hypoxia inhibits protein synthesis in skeletal muscle via AMPK/TSC2/mTOR pathways, but exercise facilitates the synthesis by amplifying mTOR signal. (3) The four-week HiLo training can weaken the inhibition effect of hypoxia on protein synthesis in skeletal muscle.论文随机验证编号:BT674012244090...