mTORC1 Activates SREBP-1c and Uncouples Lipogenesis From Gluconeogenesis

Abstract

Insulin resistance, which is defined as the inability of insulin to promote efficient glucose uptake by peripheral tissues, is a metabolic condition associated with obesity, type 2 diabetes, dyslipidemia, and cardiovascular diseases. Although important advances in our understanding of the molecular mechanisms involved in the development of insulin resistance have been made during the last decades ( 1), many questions remain. One of these questions relates to the fact that, in the liver of many insulin-resistant mouse models, insulin fails to suppress glucose production (gluconeogenesis) but continues to promote lipid synthesis (lipogenesis) ( 2). This selective hepatic insulin resistance contributes to hyperglycemia and hyperlipidemia and suggests that the insulin-signaling pathway must bifurcate upstream of lipogenesis and gluconeogenesis. In this issue of PNAS, Li et al. ( 3) identify a bifurcation point in the insulin-signaling pathway that could help resolve this important paradox.