Hoffmann, R. A wiki for the life sciences where authorship matters. Nature Genetics (2008)

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Nadeau, K.J. et al.

Nadeau, Ehlers, Aguirre, Moore, Jew, Ortmeyer, Hansen, Reusch, Draznin,

Exercise training and calorie restriction increase SREBP-1 expression and intramuscular triglyceride 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.[1]

References

Exercise training and calorie restriction increase SREBP-1 expression and intramuscular triglyceride in skeletal muscle. Nadeau, K.J., Ehlers, L.B., Aguirre, L.E., Moore, R.L., Jew, K.N., Ortmeyer, H.K., Hansen, B.C., Reusch, J.E., Draznin, B. Am. J. Physiol. Endocrinol. Metab. (2006) [Pubmed]

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