Fibrin-Induced Skin Fibrosis in Mice Deficient in Tissue Plasminogen Activator

Abstract

The deposition of fibrin is an integral part of the tissue repair process, but its persistence is also associated with a number of fibrotic conditions. This study addressed the hypothesis that reduced fibrinolysis and fibrin persistence are associated with an enhanced accumulation of collagen and the development of skin fibrosis. Decreased fibrinolysis was confirmed in fibrin gel cultures that contained human dermal fibroblasts plus the specific plasmin inhibitor ␣ 2 -antiplasmin or dermal fibroblasts isolated from plasminogen activator (PA)-deficient mice. Collagen accumulation was significantly increased in the presence of inhibitor and in tPA-deficient, but not uPAdeficient, fibroblasts compared with controls. These findings were also confirmed using a skin fibrosis model in which multiple injections of fibrin were given subcutaneously to PA-deficient mice. Injection sites from tPA-deficient mice displayed significantly increased collagen levels compared with uPA-deficient mice and wild-type controls. Up-regulation of fibroblast procollagen gene expression and reduced activation of pro-MMP-1 appeared to mediate the increase in collagen by human dermal fibroblasts in the presence of ␣2-antiplasmin. These findings suggest that persistent fibrin is associated with enhanced collagen accumulation that may result in the development of fibrotic skin disorders in which reduced fibrinolysis is a feature.

Adenoviral Overexpression and Small Interfering RNA Suppression Demonstrate That Plasminogen Activator Inhibitor-1 Produces Elevated Collagen Accumulation in Normal and Keloid Fibroblasts

“…Cell monolayers were used in the current study to bypass the influence of fibrin matrix 44 and test directly the link between PAI-1 expression and collagen accumulation. In addition, cell monolayers can be readily varied in size, permit rapid verification of experimental manipulations and retention of cells, and avoid the loss of cells from fibrin gels cultured under serum-free conditions.…”

“…The principal role of PAI-1 is to balance the uPA/tissue type plasminogen activatordependent generation of plasmin from plasminogen. 25 Excess PAI-1 inhibits plasminogen activators and prevents plasmin generation and its activation of matrix metalloproteinases, including collagenases, as well as its proteolysis of matrix proteins, including fibrin 44 and Fn. 40 Thus, in the presence of PAI-1, even normal matrix synthesis would yield higher levels of matrix because of the lack of plasmin activity and its attendant matrix turnover.…”

An acidic microenvironment sets the humoral pattern recognition molecule PTX3 in a tissue repair mode

“…Results presented here on the interaction of PTX3 with fibrin and plasminogen suggest that defective pericellular fibrinolysis of remodeling cells associated to PTX3 deficiency is responsible for these defects. Along the same line, in arterial thrombosis, PTX3 deficiency was associated to increased thrombus repair in different models, including skin wound healing and liver and lung injury (Carmeliet et al, 1994;Romer et al, 1996;Pohl et al, 2001;Idell, 2003;de Giorgio-Miller et al, 2005;Calvaruso et al, 2008). Thus, PTX3 acts as a molecular scaffold Fibrin and other provisional ECM proteins are transiently deposited after tissue injury and their subsequent degradation heralds tissue remodeling and scar formation.…”

Adenosine Potentiates Human Lung Mast Cell Tissue Plasminogen Activator Activity

“…Studies involving tPA-deficient mice highlighted the protective role of tPA against pulmonary and skin fibrosis (20,21), although it promoted kidney fibrosis (40). In addition, aerosolized tPA greatly improved the clearance of obstructed airways following acute lung injury (48) and airway hyperresponsiveness (49).…”

“…These effects may be mediated, in part, by the ability of tPA to activate myofibroblasts and prevent myofibroblast apoptosis (18,19). However, in some systems, tPA protects against fibrosis (20,21), and so its biology with respect to fibrosis and remodeling is undoubtedly complex. The vascular endothelium is considered to be the major site of synthesis and release of tPA (22).…”