Alcohol impairs skeletal muscle protein synthesis and mTOR signaling in a time-dependent manner following electrically stimulated muscle contraction

Abstract

Alcohol (EtOH) decreases protein synthesis and mammalian target of rapamycin (mTOR)-mediated signaling and blunts the anabolic response to growth factors in skeletal muscle. The purpose of the current investigation was to determine whether acute EtOH intoxication antagonizes the contraction-induced increase in protein synthesis and mTOR signaling in skeletal muscle. Fasted male mice were injected intraperitoneally with 3 g/kg EtOH or saline (control), and the right hindlimb was electrically stimulated (10 sets of 6 contractions). The gastrocnemius muscle complex was collected 30 min, 4 h, or 12 h after stimulation. EtOH decreased in vivo basal protein synthesis (PS) in the nonstimulated muscle compared with time-matched Controls at 30 min, 4 h, and 12 h. In Control, but not EtOH, PS was decreased 15% after 30 min. In contrast, PS was increased in Control 4 h poststimulation but remained unchanged in EtOH. Last, stimulation increased PS 10% in Control and EtOH at 12 h, even though the absolute rate remained reduced by EtOH. The stimulation-induced increase in the phosphorylation of S6K1 Thr(421)/Ser(424) (20-52%), S6K1 Thr(389) (45-57%), and its substrate rpS6 Ser(240/244) (37-72%) was blunted by EtOH at 30 min, 4 h, and 12 h. Phosphorylation of 4E-BP1 Ser(65) was also attenuated by EtOH (61%) at 4 h. Conversely, phosphorylation of extracellular signal-regulated kinase Thr(202)/Tyr(204) was increased by stimulation in Control and EtOH mice at 30 min but only in Control at 4 h. Our data indicate that acute EtOH intoxication suppresses muscle protein synthesis for at least 12 h and greatly impairs contraction-induced changes in synthesis and mTOR signaling.

Sepsis Attenuates the Anabolic Response to Skeletal Muscle Contraction

“…Approximately 18–24 h after the induction of sepsis, mice were anesthetized via isoflurane (3–4% in O 2 with 2% maintenance) and prepared for the muscle contraction protocol that was performed exactly as described previously (11). Briefly, a small incision was made through the skin and muscle to expose the sciatic nerve.…”

“…Needle electrodes were placed over the nerve and maximal muscular contractions were evoked using a current stimulator (Model A365, World Precision Instruments, Sarasota, Fl) interfaced with Powerlab 4/35 and LabChart software (ADI Instruments, Colorado Springs, CO). The stimulation protocol included 10 sets of 6 contractions (each lasting 3 s) with 10 s rest between each contraction and 60 s rest after each set of 6 contractions (11). To ensure maximal contractions were induced the current was set to 1 milliamperes (mA) with a pulse height of 6 volts (V).…”

“…Both frozen tissue and plasma were stored at −80°C until analysis. The experimental time point of 2 h post electrically stimulated muscle contraction was chosen based on a previous investigation showing induction of S6K1 Thr 389 phosphorylation by 30 min (11) and to stay within a 24 h time period following CLP surgery.…”

“…High performance liquid chromatography (HPLC) was used for the measurement of specific radioactivity of plasma Phe levels in the supernatant from trichloroacetic acid (TCA) treated plasma extracts. The global rate of [ 3 H]Phe incorporation into protein within the muscle was assessed as previously described by our laboratory (11). …”

Nutrition and Alcoholic Liver Disease

“…One of the mediators of the liver muscle axis is hyperammonemia that occurs due to impaired hepatic ureagenesis 42,53-55 . The effects of ethanol include lower skeletal muscle protein synthesis 56-59 , increased autophagy 60 , and mitochondrial dysfunction caused by ethanol or its metabolites including acetaldehyde 61,62 . In alcoholic cirrhosis and liver disease, both hyperammonemia and ethanol contribute to muscle loss that can explain more severe muscle loss in these patients.…”