Protein metabolism in health and diabetes

Insulin is a major protein anabolic hormone. It promotes dietary amino acid storage in the fed state and possesses anticatabolic properties in the basal state and during critical illness. The mechanisms of insulin action on protein metabolism are complex. They involve not only the activation of insulin and mTOR signaling in the target tissues, but also rely on amino acid availability and insulin-induced vasodilation. Since insulin is secreted during feeding, it is difficult to isolate its effect from the effects of increased nutrient and energy availability. Methodological issues further complicate the precise measurement of the effects of insulin on protein turnover. The effects of insulin are tissue-specific, increasing protein synthesis in some tissues and reducing protein breakdown in others. Insulin's effects can also be protein-specific. Specific pathophysiologic conditions, such as exercise, diabetes, aging, or critical illness can magnify or blunt insulin's effect on protein metabolism.