AMP kinase signals the insulin-like growth factor system whether adequate nutrient is present to support an anabolic response.

摘要

Insulin-like growth factor-I is a peptide growth factor that stimulates balanced growth among all tissues and organs. In adult life IGF-I is an important anabolic factor and plays a key role in maintaining normal skeletal muscle mass. These anabolic actions also require an adequate nutrient supply, and IGF-I serves as in intermediary link that communicates a chemical signal to cells indicating that adequate protein and energy are available for anabolism. Caloric or protein restriction lowers serum IGF-I concentrations. Additionally, cells and tissues are preprogrammed to be resistant to IGF-Fs proanabolic effects in the presence of an inadequate nutrient supply, and intracel-lular factors are present that mediate this response. One such factor is AMP kinase. This enzyme serves as an important energy sensing mechanism that regulates fatty acid oxidation. The principle variable controlling the induction of AMPK is the AMP to ATP ratio.3 Thus, when glycolysis is reduced and ATP levels fall, AMP kinase is activated. Since under these circumstances it would be deleterious for the cell to undertake new protein synthesis that signaling mechanisms exist to counteract the anabolic response.