Loss of PDGF-B activity increases hepatic vascular permeability and enhances insulin sensitivity

Hepatic vasculature is not thought to pose a permeability barrier for diffusion of macromolecules from the bloodstream to hepatocytes. In contrast, in extrahepatic tissues, the microvasculature is critically important for insulin action, because transport of insulin across the endothelial cell layer is rate limiting for insulin-stimulated glucose disposal. However, very little is known concerning the role in this process of pericytes, the mural cells lining the basolateral membrane of endothelial cells. PDGF-B is a growth factor involved in the recruitment and function of pericytes. We studied insulin action in mice expressing PDGF-B lacking the proteoglycan binding domain, producing a protein with a partial loss of function (PDGF-B^ret/ret). Insulin action was assessed through measurements of insulin signaling and insulin and glucose tolerance tests. PDGF-B deficiency enhanced hepatic vascular transendothelial transport. One outcome of this change was an increase in hepatic insulin signaling. This correlated with enhanced whole body glucose homeostasis and increased insulin clearance from the circulation during an insulin tolerance test. In obese mice, PDGF-B deficiency was associated with an 80% reduction in fasting insulin and drastically reduced insulin secretion. These mice did not have significantly higher glucose levels, reflecting a dramatic increase in insulin action. Our findings show that, despite already having a high permeability, hepatic transendothelial transport can be further enhanced. To the best of our knowledge, this is the first study to connect PDGFB-induced changes in hepatic sinusoidal transport to changes in insulin action, demonstrating a link between PDGF-B signaling and insulin sensitivity.