Metabolic, hormonal and environmental regulation of plasminogen activator inhibitor-1 (PAI-1) expression: lessons from the liver.

Plasminogen activator inhibitor-1 (PAI-1) controls the regulation of the fibrinolytic system in blood by inhibiting both urokinase-type and tissue-type plasminogen activators. Enhanced levels of PAI-1 are found in patients with type 2 diabetes mellitus which is associated with a dysbalance in glucose and lipid homeostasis. Especially a defective insulin response in the liver contributes to the development of hyperglycemia, dyslipidemia and peripheral insulin resistance and may contribute to hepatic over-expression of PAI-1 in diabetes type 2. Furthermore, a substantial upregulation of PAI-1 expression has also been shown in a variety of liver injury models. Thus, the liver appears to be not only a major site of PAI-1 synthesis in response to hormonal changes, but also in response to a variety of other pathological events. PAI-1 expression in liver largely depends on activation of signalling pathways and transcriptional regulators which may be the basis for a new level of cross-talk between different signalling pathways and thus may represent attractive therapeutic candidates. This article will primarily focus on the regulation of PAI-1 expression in liver cells and discuss potential cross-talks between metabolic, hormonal and environmental signals.