Exercise training and calorie restriction increase SREBP-1 expression and intramuscular triglyceride in skeletal muscle

KJ Nadeau, LB Ehlers, LE Aguirre… - American Journal …, 2006 - journals.physiology.org
KJ Nadeau, LB Ehlers, LE Aguirre, RL Moore, KN Jew, HK Ortmeyer, BC Hansen…
American Journal of Physiology-Endocrinology and Metabolism, 2006journals.physiology.org
Intramuscular triglyceride (IMTG) deposition in skeletal muscle is associated with obesity
and type 2 diabetes (T2DM) and is thought to be related to insulin resistance (IR). Curiously,
despite enhanced skeletal muscle insulin sensitivity, highly trained athletes and calorie-
restricted (CR) monkeys also have increased IMTG. Sterol regulatory element-binding
proteins (SREBPs) are transcription factors that regulate the biosynthesis of cholesterol and
fatty acids. SREBP-1 is increased by insulin in skeletal muscle in vitro and in skeletal muscle …
Intramuscular triglyceride (IMTG) deposition in skeletal muscle is associated with obesity and type 2 diabetes (T2DM) and is thought to be related to insulin resistance (IR). Curiously, despite enhanced skeletal muscle insulin sensitivity, highly trained athletes and calorie-restricted (CR) monkeys also have increased IMTG. Sterol regulatory element-binding proteins (SREBPs) are transcription factors that regulate the biosynthesis of cholesterol and fatty acids. SREBP-1 is increased by insulin in skeletal muscle in vitro and in skeletal muscle of IR subjects, but SREBP-1 expression has not been examined in exercise training or calorie restriction. We examined the relationship between IMTG and SREBP-1 expression in animal models of exercise and calorie restriction. Gastrocnemius and soleus muscle biopsies were obtained from 38 Sprague-Dawley rats (18 control and 20 exercise trained). Triglyceride content was higher in the gastrocnemius and soleus muscles of the trained rats. SREBP-1c mRNA, SREBP-1 precursor and mature proteins, and fatty acid synthase (FAS) protein were increased with exercise training. Monkeys (Macaca mulatta) were CR for a mean of 10.4 years, preventing weight gain and IR. Vastus lateralis muscle was obtained from 12 monkeys (6 CR and 6 controls). SREBP-1 precursor and mature proteins and FAS protein were higher in the CR monkeys. In addition, phosphorylation of ERK1/ERK2 was increased in skeletal muscle of CR animals. In summary, SREBP-1 protein and SREBP-1c mRNA are increased in interventions that increase IMTG despite enhanced insulin sensitivity. CR and exercise-induced augmentation of SREBP-1 expression may be responsible for the increased IMTG seen in skeletal muscle of highly conditioned athletes.
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