Activin in glucose metabolism.

Activins, members of the TGF-β family, are multifunctional growth and differentiation factors. Activins regulate glucose/energy metabolism by promoting the differentiation of insulin-producing and -responsive cells, and regulating function of the differentiated cells. In the pancreas, activins stimulate the differentiation of β cells and secretion of insulin, which enables the cells to respond to glucose uptake efficiently. By contrast, in the liver, skeletal muscle and white adipose tissue, activins exert negative regulation on organogenesis, which leads to impaired insulin sensitivity. Activins induce the phenotypic switch of macrophages from the M1 to M2 phenotypes, which reduces inflammation. Since adipose inflammation is closely associated with insulin resistance and the onset of type 2 diabetes, activins may improve insulin resistance through their anti-inflammatory activity. Because activins modulate events involved in insulin sensitivity in a tissue-dependent manner, the activities of activins should be locally regulated to improve whole-body insulin responsiveness. Thus, activins or activin inhibitors may be effective as therapeutic agents for metabolic syndrome.