High plasminogen activator inhibitor type 2 expression is a hallmark of scleroderma fibroblasts in vitro

Cardiovascular-renal complications and the possible role of plasminogen activator inhibitor: a review

Since angiotensin increases the expression of plasminogen activator inhibitor (PAI), mechanisms associated with an actively functioning renin–angiotensin–aldosterone system can be expected to be associated with increased PAI-1 expression. These mechanisms are present not only in common conditions resulting in glomerulosclerosis associated with aging, diabetes or genetic mutations, but also in autoimmune disease (like scleroderma and lupus), radiation injury, cyclosporine toxicity, allograft nephropathy and ureteral obstruction. While the renin–angiotensin–aldosterone system and growth factors, such as transforming growth factor-beta (TGF-β), are almost always part of the process, there are rare experimental observations of PAI-1 expression without their interaction. Here we review the literature on PAI-1 and its role in vascular, fibrotic and oxidative injury as well as work suggesting potential areas of intervention in the pathogenesis of multiple disorders.

SerpinB2 Deficiency Results in a Stratum Corneum Defect and Increased Sensitivity to Topically Applied Inflammatory Agents

SerpinB2 (plasminogen activator inhibitor type 2) is constitutively expressed at high levels by differentiating keratinocytes in mice and humans; however, the physiological function of keratinocyte SerpinB2 remains unclear. Herein, we show that SerpinB2(-/-) mice are more susceptible to contact dermatitis after topical application of dinitrofluorobenzene, and show enhanced inflammatory lesions after topical applications of phorbol ester. Untreated SerpinB2(-/-) mice showed no overt changes in epithelial structure, and we were unable to find evidence for a role for keratinocyte SerpinB2 in regulating immunity, apoptosis, IL-1β production, proteasomal activity, or wound healing. Instead, the phenotype was associated with impaired skin barrier function and a defective stratum corneum, with SerpinB2(-/-) mice showing increased transepidermal water loss, increased overt loss of stratum corneum in inflammatory lesions, and impaired stratum corneum thickening after phorbol ester treatment. Immunoblotting suggested that SerpinB2 (cross-linked into the cornified envelope) is present in the stratum corneum and retains the ability to form covalent inhibitory complexes with urokinase. Data suggest that the function of keratinocyte SerpinB2 is protection of the stratum corneum from proteolysis via inhibition of urokinase, thereby maintaining the integrity and barrier function of the stratum corneum, particularly during times of skin inflammation. Implications for studies involving genetically modified mice treated with topical agents and human dermatological conditions, such as contact dermatitis, are discussed.

Culture medium and cell density impact gene expression in normal skin and abnormal scar-derived fibroblasts

Fibroblasts, the main cell type of the dermis, are responsible for production and remodeling of extracellular matrix during wound healing. Disruption of either production or degradation of extracellular matrix can lead to abnormal scarring, resulting in hypertrophic scar or keloid scar. Aberrations in proliferation and gene expression have been observed in fibroblasts isolated from abnormal scars, but differences observed may be related to biologic responses to growth conditions and media formulations. This study examined gene expression in primary human fibroblasts from normal skin or abnormal scar in two culture media formulations and three relative cell densities. In general, higher expression of collagen type 1 alpha-1 (COL1A1) and alpha-2 (COL1A2) and matrix metalloproteinase 3 (MMP3) and lower levels of MMP1 were observed in all cell strains cultured in standard medium containing 10% fetal bovine serum compared with cells cultured in medium optimized for proliferation. Normal and scar-derived fibroblasts exhibited differences in gene expression in specific response to media formulations and cell density. COL1A1 and COL1A2 were increased, and MMP1 and MMP3 were decreased, in keloid cells compared with normal fibroblasts under most conditions analyzed. However, expression of plasminogen activator inhibitor 1 in keloid fibroblasts, which was significantly different than in normal fibroblasts, was either increased or decreased in response to the medium formulation and relative cell density. A related gene, plasminogen activator inhibitor 2, was shown for the first time to be significantly increased in keloid fibroblasts compared with normal fibroblasts, in both media formulations and at all three cell densities. The results emphasize the critical role of culture conditions in interpretation of cell behavior and expression data and for comparison of cells representing normal and fibrotic phenotypes.

Fibrosis and immune dysregulation in systemic sclerosis

Autoimmune and inflammatory phenomena are characteristically present in systemic sclerosis (SSc) and impact on dysregulated fibroblast extracellular matrix deposition, hallmark of the disease in conjunction with fibroproliferative vasculopathy. Oligoclonal T helper 2-like cells are present in the skin and peripheral blood in early diffuse disease. Type 2 cytokines synergize with profibrotic cytokines including transforming growth factor beta, favoring collagen deposition and metalloproteinase inhibition by fibroblasts. Furthermore, chemokine with pro-fibrotic and pro-angiogenic properties are preferentially produced by fibroblasts under the influence of Th2-like cells. The profibrotic monocyte chemotactic protein 1 is also produced by fibroblasts, partially in response to Toll-like receptor 4 (TLR4) recognition, when autoantibodies (autoAb) bind to fibroblast surface. In addition, immune-complex formed by autoAb and ubiquitous antigens including topoisomerase-1 favor the production of interferon-alpha (IFN-α) possibly by interacting with intravesicular TLRs. Consistent with this findings, unbiased gene screening has revealed that SSc peripheral blood cells express genes induced by IFN-α, a characteristic shared with systemic lupus erythematosus and other autoimmune disorders. These findings highlight the complex relationship between adaptive and acquired immune responses, which may participate to the pathogenesis of SSc in manners until now unsuspected, which may help in identifying novel therapeutic targets.

The Plasminogen Activator System in Fibroblasts from Systemic Sclerosis

Systemic sclerosis (SSc) is characterized by excessive fibrosis throughout the body. There are two major subsets of SSc, diffuse cutaneous Systemic sclerosis (dSSc) and limited cutaneous Systemic sclerosis (ISSc). Fibroblasts play a key role in SSc. The expression and function of the urokinase (uPA)-mediated plasminogen activation (PA) system, a well-characterized system of serine-proteases involved in several pathological processes, has been investigated in SSc fibroblasts. The expression of the components of the PA system, including uPA, its type-1 and type-2 inhibitors (PAI-1 and PAI-2) and its receptor (uPAR), was examined by Western blot in fibroblasts from patients affected by limited and diffuse forms of SSc. uPA and PAI-1 secretion increased only in fibroblasts from ISSc lesions compared to normal fibroblasts. PAI-2 levels were decreased in fibroblasts from both SSc forms. Interestingly, fibroblasts from areas not adjacent to the lesions (not-affected) of the diffuse form showed reduced levels of PAI-1 and increased uPAR expression. Adhesion experiments showed reduced adherence to VN of fibroblasts from ISSc lesions and from non-affected areas of the diffuse form, as compared to normal controls. These results suggest a role for uPA and PAI-1 in the ISSc form, likely related to the activation of latent forms of cytokines and to the accumulation of ECM components, whereas a role for uPAR can be hypothesized in the evolvement of the diffuse form, based on its up-regulation in the non-affected areas.

A physiological function of inflammation-associated SerpinB2 is regulation of adaptive immunity

SerpinB2 (plasminogen activator inhibitor-2) is widely described as an inhibitor of urokinase plasminogen activator; however, SerpinB2(-/-) mice show no detectable increase in urokinase plasminogen activator activity. In this study, we describe an unexpected immune phenotype in SerpinB2(-/-) mice. After immunization with OVA in CFA, SerpinB2(-/-) mice made approximately 6-fold more IgG2c and generated approximately 2.5-fold more OVA-specific IFN-gamma-secreting T cells than SerpinB2(+/+) littermate controls. In SerpinB2(+/+) mice, high inducible SerpinB2 expression was seen at the injection site and in macrophages low levels in draining lymph nodes and conventional dendritic cells, and no expression was seen in plasmacytoid dendritic, B, T, or NK cells. SerpinB2(-/-) macrophages promoted greater IFN-gamma secretion from wild-type T cells in vivo and in vitro and, when stimulated with anti-CD40/IFN-gamma or cultured with wild-type T cells in vitro, secreted more Th1-promoting cytokines than macrophages from littermate controls. Draining lymph node SerpinB2(-/-) myeloid APCs similarly secreted more Th1-promoting cytokines when cocultured with wild-type T cells. Regulation of Th1 responses thus appears to be a physiological function of inflammation-associated SerpinB2; an observation that may shed light on human inflammatory diseases like pre-eclampsia, lupus, asthma, scleroderma, and periodontitis, which are associated with SerpinB2 polymorphisms or dysregulated SerpinB2 expression.

Update on pathophysiology of scleroderma with special reference to immunoinflammatory events

Scleroderma or systemic sclerosis (SSc) is a complex disease in which the vasculopathy and the activation of the immune system with production of inflammatory mediators lead to dysregulated fibroblast activation. The resulting excessive deposition of collagens and other extracellular matrix proteins ends in fibrosis and organ dysfunction. The cause is unknown, but environmental factors are thought to play a role by triggering abnormal responses in genetically susceptible hosts. The recent past has witnessed important advances in the definition of mechanisms that underlie the persistent activation in fibroblasts of genes involved in uncontrolled fibrosis, a hallmark of SSc. These include the preferential production of type 2 T cell cytokines in target organs, the presence of autoantibodies with fibroblast-activating capacities, the production of vasoconstrictive mediators that impact on fibroblast biosynthetic properties, the transforming growth factor-beta-related metabolic signature, and the presence of altered signaling pathways in fibroblasts. Furthermore, while no animal models recapitulate all the features of SSc, they have been instrumental for assessing the relevance of specific processes to the development of fibrosis. More importantly, some of the research findings are leading to therapies that target altered processes with the potential of changing the prognosis of some dismal aspects of the disease.

Mechanical tension and integrin alpha 2 beta 1 regulate fibroblast functions

The extracellular matrix (ECM) environment in connective tissues provides fibroblasts with a structural scaffold and modulates cell shape, but it also profoundly influences the fibroblast phenotype. Here we studied fibroblasts cultured in a three-dimensional network of native collagen, which was either mechanically stressed or relaxed. Mechanical load induces fibroblasts that synthesize abundant ECM and a characteristic array of cytokines/chemokines. This phenotype is reminiscent of late granulation tissue or scleroderma fibroblasts. By contrast, relaxed fibroblasts are characterized by induction of proteases and a subset of cytokines that does not overlap with that of mechanically stimulated cells. Thus, the biochemical composition and physical nature of the ECM exert powerful control over the phenotypes of fibroblasts, ranging from "synthetic" to "inflammatory" phenotypes. Interactions between fibroblasts and collagen fibrils are mostly mediated by a subset of beta 1 integrin receptors. Fibroblasts utilize alpha 1 beta 1, alpha 2 beta 1, and alpha 11 beta 1 integrins for establishing collagen contacts and transducing signals. In vitro assays and mouse genetics have demonstrated individual tasks served by each receptor, but also functional redundancy. Unraveling the integrated functions of fibroblasts, collagen integrin receptors, collagen fibrils, and mechanical tension will be important to understand the molecular mechanisms underlying tissue repair and fibrosis.