FIGURE 1.

Glycerol metabolism: working model of the interplay between the liver and adipose tissue in fed and starved states in mouse. During fasted state, glucagon secretion is induced, TAG are hydrolyzed to glycerol and free fatty acids in adipocytes, and both AQP7 and AQP3 traffic to the plasma membrane and participate with AQP9 to glycerol efflux. AQP9 allows plasma glycerol entry in hepatocytes. Glycerol is then converted to glycerol-3-phosphate by glycerol kinase, and thereby participates to gluconeogenesis. During fed state inducing insulin secretion, glucose metabolites, glycerol-3-phosphate (obtained from glycerol by glycerol kinase enzymatic activity) and free fatty acids are used to produce TAG in both liver and adipose tissue. In response to insulin in adipocytes, AQP3 and AQP7 traffic from the plasma membrane to intracellular compartments. Glycerol most likely mainly enters adipocytes via AQP9. During lipogenesis, adipose glycerol uptake is likely low due to the weak activity of the glycerol kinase. In hepatocytes, glycerol likely enters via AQP7 and AQP9. ATGL, adipose triglyceride lipase; GK, glycerol kinase; Glut2, glucose transporter 2; Glut4, glucose transporter 4; G3P, glycerol-3-phosphate; FFA, free fatty acids; HSL, hormone sensitive lipase; TAG, triacylglycerols; broken arrows: trafficking.