Plasminogen Activator Inhibitor Type‐1 as a Regulator of Fibrosis

Fibrosis is known as a frequent and irreversible pathological condition which is associated with organ failure. Tissue fibrosis is a central process in a variety of chronic progressive diseases such as diabetes, hypertension, and persistent inflammation. This state could contribute to chronic injury and the initiation of tissue repair. Fibrotic disorders represent abnormal wound healing with defective matrix turnover and clearance that lead to excessive accumulation of extracellular matrix components. A variety of identified growth factors, cytokines, and persistently activated myofibroblasts have critical roles in the pathogenesis of fibrosis. Irrespective of etiology, the transforming growth factor‐β pathway is the major driver of fibrotic response. Plasminogen activator inhibitor‐1 (PAI‐1) is a crucial downstream target of this pathway. Transforming growth factor‐β positively regulates PAI‐1 gene expression via two main pathways including Smad‐mediated canonical and non‐canonical pathways. Overexpression of PAI‐1 reduces extracellular matrix degradation via perturbing the plasminogen activation system. Indeed, elevated PAI‐1 levels inhibit proteolytic activity of tissue plasminogen activator and urokinase plasminogen activator which could contribute to a variety of inflammatory elements in the injury site and to excessive matrix deposition. This review summarizes the current knowledge of critical pathways that regulate PAI‐1 gene expression and suggests effective approaches for the treatment of fibrotic disease. J. Cell. Biochem. 119: 17–27, 2018. © 2017 Wiley Periodicals, Inc.