Differential regulation of PAI-1 gene expression in human fibroblasts predisposed to a fibrotic phenotype

Association of plasminogen activator inhibitor-1 and vitamin D receptor expression with the risk of keloid disease in a Chinese population

Keloid disease (KD) is a benign fibroproliferative scarring condition of unknown etiopathogenesis. Plasminogen activator inhibitor-1 (PAI-1) and vitamin D receptor (VDR) have been shown to play important roles in the progression of tissue fibrosis; therefore, both these genes are potential susceptibility genes for KD. We aimed to determine whether the gene expression levels of PAI-1 and VDR are altered in Chinese KD patients. We measured the expression of PAI and VDR in human peripheral blood lymphocytes in 236 patients with keloid and 219 age- and sex-matched healthy controls by quantitative real-time polymerase chain reaction. We found that PAI-1 expression in peripheral blood lymphocytes was significantly higher in patients with KD than in control individuals (p < 0.0001), while VDR expression was significantly lower in KD patients than in control individuals (p < 0.0001). High levels of PAI-1 and low levels of VDR expression were significantly associated with an increased risk for KD. PAI-1 and VDR might play important roles in keloid development. Gene expression levels of PAI-1 and VDR may, therefore, be used as potential markers for the prediction of keloid development after scarring.

Thrombospondin-1 Affects Bovine Luteal Function via Transforming Growth Factor-Beta1-Dependent and Independent Actions

Thrombospondin-1 (THBS1) and transforming growth factor-beta1 (TGFB1) are specifically up-regulated by prostaglandin F2alpha in mature corpus luteum (CL). This study examined the relationship between the expression of THBS1 and TGFB1 and the underlying mechanisms of their actions in luteal endothelial cells (ECs). TGFB1 stimulated SMAD2 phosphorylation and SERPINE1 levels in dose- and time-dependent manners in luteal EC. THBS1 also elevated SERPINE1; this effect was abolished by TGFB1 receptor-1 kinase inhibitor (SB431542). The findings here further imply that THBS1 activates TGFB1 in luteal ECs: THBS1 increased the effects of latent TGFB1 on phosphorylated SMAD (phospho-SMAD) 2 and SERPINE1. THBS1 silencing significantly decreased SERPINE1 and levels of phospho-SMAD2. Lastly, THBS1 actions on SERPINE1 were inhibited by LSKL peptide (TGFB1 activation inhibitor); LSKL also counteracted latent TGFB1-induced phospho-SMAD2. We found that TGFB1 up-regulated its own mRNA levels and those of THBS1. Both compounds generated apoptosis, but THBS1 was significantly more effective (2.5-fold). Notably, this effect of THBS1 was not mediated by TGFB1. THBS1 and TGFB1 also differed in their activation of p38 mitogen-activated protein kinase. Whereas TGFB1 rapidly induced phospho-p38, THBS1 had a delayed effect. Inhibition of p38 pathway by SB203580 did not modulate TGFB1 effect on cell viability, but it amplified THBS1 actions. THBS1-stimulated caspase-3 activation coincided with p38 phosphorylation, suggesting that caspase-induced DNA damage initiated p38 phosphorylation. The in vitro data suggest that a feed-forward loop exists between THBS1, TGFB1, and SERPINE1. Indeed all these three genes were similarly induced in the regressing CL. Their gene products can promote vascular instability, apoptosis, and matrix remodeling during luteolysis.

Site-specific keloid fibroblasts alter the behaviour of normal skin and normal scar fibroblasts through paracrine signalling

Keloid disease (KD) is an abnormal cutaneous fibroproliferative disorder of unknown aetiopathogenesis. Keloid fibroblasts (KF) are implicated as mediators of elevated extracellular matrix deposition. Aberrant secretory behaviour by KF relative to normal skin fibroblasts (NF) may influence the disease state. To date, no previous reports exist on the ability of site-specific KF to induce fibrotic-like phenotypic changes in NF or normal scar fibroblasts (NS) by paracrine mechanisms. Therefore, the aim of this study was to investigate the influence of conditioned media from site-specific KF on the cellular and molecular behaviour of both NF and NS enabled by paracrine mechanisms. Conditioned media was collected from cultured primary fibroblasts during a proliferative log phase of growth including: NF, NS, peri-lesional keloid fibroblasts (PKF) and intra-lesional keloid fibroblasts (IKF). Conditioned media was used to grow NF, NS, PKF and IKF cells over 240 hrs. Cellular behavior was monitored through real time cell analysis (RTCA), proliferation rates and migration in a scratch wound assay. Fibrosis-associated marker expression was determined at both protein and gene level. PKF conditioned media treatment of both NF and NS elicited enhanced cell proliferation, spreading and viability as measured in real time over 240 hrs versus control conditioned media. Following PKF and IKF media treatments up to 240 hrs, both NF and NS showed significantly elevated proliferation rates (p<0.03) and migration in a scratch wound assay (p<0.04). Concomitant up-regulation of collagen I, fibronectin, α-SMA, PAI-1, TGF-β and CTGF (p<0.03) protein expression were also observed. Corresponding qRT-PCR analysis supported these findings (P<0.03). In all cases, conditioned media from growing marginal PKF elicited the strongest effects. In conclusion, primary NF and NS cells treated with PKF or IKF conditioned media exhibit enhanced expression of fibrosis-associated molecular markers and increased cellular activity as a result of keloid fibroblast-derived paracrine factors.

Cardiac fibroblast-dependent extracellular matrix accumulation is associated with diastolic stiffness in type 2 diabetes

Cardiovascular complications are a leading cause of death in patients with type 2 diabetes mellitus (T2DM). Diastolic dysfunction is one of the earliest manifestations of diabetes-induced changes in left ventricular (LV) function, and results from a reduced rate of relaxation and increased stiffness. The mechanisms responsible for increased stiffness are not completely understood. Chronic hyperglycemia, advanced glycation endproducts (AGEs), and increased levels of proinflammatory and profibrotic cytokines are molecular pathways known to be involved in regulating extracellular matrix (ECM) synthesis and accumulation resulting in increased LV diastolic stiffness. Experiments were conducted using a genetically-induced mouse model of T2DM generated by a point mutation in the leptin receptor resulting in nonfunctional leptin receptors (db/db murine model). This study correlated changes in LV ECM and stiffness with alterations in basal activation of signaling cascades and expression of profibrotic markers within primary cultures of cardiac fibroblasts from diabetic (db/db) mice with nondiabetic (db/wt) littermates as controls. Primary cultures of cardiac fibrobroblasts were maintained in 25 mM glucose (hyperglycemic-HG; diabetic db/db) media or 5 mM glucose (normoglycemic-NG, nondiabetic db/wt) media. The cells then underwent a 24-hour exposure to their opposite (NG; diabetic db/db) media or 5 mM glucose (HG, nondiabetic db/wt) media. Protein analysis demonstrated significantly increased expression of type I collagen, TIMP-2, TGF-β, PAI-1 and RAGE in diabetic db/db cells as compared to nondiabetic db/wt, independent of glucose media concentration. This pattern of protein expression was associated with increased LV collagen accumulation, myocardial stiffness and LV diastolic dysfunction. Isolated diabetic db/db fibroblasts were phenotypically distinct from nondiabetic db/wt fibroblasts and exhibited a profibrotic phenotype in normoglycemic conditions.

PAI-1 in tissue fibrosis

Fibrosis is defined as a fibroproliferative or abnormal fibroblast activation-related disease. Deregulation of wound healing leads to hyperactivation of fibroblasts and excessive accumulation of extracellular matrix (ECM) proteins in the wound area, the pathological manifestation of fibrosis. The accumulation of excessive levels of collagen in the ECM depends on two factors: an increased rate of collagen synthesis and or decreased rate of collagen degradation by cellular proteolytic activities. The urokinase/tissue type plasminogen activator (uPA/tPA) and plasmin play significant roles in the cellular proteolytic degradation of ECM proteins and the maintenance of tissue homeostasis. The activities of uPA/tPA/plasmin and plasmin-dependent MMPs rely mostly on the activity of a potent inhibitor of uPA/tPA, plasminogen activator inhibitor-1 (PAI-1). Under normal physiologic conditions, PAI-1 controls the activities of uPA/tPA/plasmin/MMP proteolytic activities and thus maintains the tissue homeostasis. During wound healing, elevated levels of PAI-1 inhibit uPA/tPA/plasmin and plasmin-dependent MMP activities, and, thus, help expedite wound healing. In contrast to this scenario, under pathologic conditions, excessive PAI-1 contributes to excessive accumulation of collagen and other ECM protein in the wound area, and thus preserves scarring. While the level of PAI-1 is significantly elevated in fibrotic tissues, lack of PAI-1 protects different organs from fibrosis in response to injury-related profibrotic signals. Thus, PAI-1 is implicated in the pathology of fibrosis in different organs including the heart, lung, kidney, liver, and skin. Paradoxically, PAI-1 deficiency promotes spontaneous cardiac-selective fibrosis. In this review, we discuss the significance of PAI-1 in the pathogenesis of fibrosis in multiple organs.

Cellular senescence: molecular mechanisms, in vivo significance, and redox considerations

Cellular senescence is recognized as a critical cellular response to prolonged rounds of replication and environmental stresses. Its defining characteristics are arrested cell-cycle progression and the development of aberrant gene expression with proinflammatory behavior. Whereas the mechanistic events associated with senescence are generally well understood at the molecular level, the impact of senescence in vivo remains to be fully determined. In addition to the role of senescence as an antitumor mechanism, this review examines cellular senescence as a factor in organismal aging and age-related diseases, with particular emphasis on aberrant gene expression and abnormal paracrine signaling. Senescence as an emerging factor in tissue remodeling, wound repair, and infection is considered. In addition, the role of oxidative stress as a major mediator of senescence and the role of NAD(P)H oxidases and changes to intracellular GSH/GSSG status are reviewed. Recent findings indicate that senescence and the behavior of senescent cells are amenable to therapeutic intervention. As the in vivo significance of senescence becomes clearer, the challenge will be to modulate the adverse effects of senescence without increasing the risks of other diseases, such as cancer. The uncoupled relation between cell-cycle arrest and the senescent phenotype suggests that this is an achievable outcome.

Adenoviral overexpression and small interfering RNA suppression demonstrate that plasminogen activator inhibitor-1 produces elevated collagen accumulation in normal and keloid fibroblasts

Keloids are tumor-like skin scars that grow as a result of the aberrant healing of skin injuries, with no effective treatment. We provide new evidence that both overexpression of plasminogen activator inhibitor-1 (PAI-1) and elevated collagen accumulation are intrinsic features of keloid fibroblasts and that these characteristics are causally linked. Using seven strains each of early passage normal and keloid fibroblasts, the keloid strains exhibited inherently elevated collagen accumulation and PAI-1 expression in serum-free, 0.1% ITS+ culture; larger increases in these parameters occurred when cells were cultured in 3% serum. To demonstrate a causal relationship between PAI-1 overexpression and collagen accumulation, normal fibroblasts were infected with PAI-1-expressing adenovirus. Such cells exhibited a two- to fourfold increase in the accumulation of newly synthesized collagen in a viral dose-dependent fashion in both monolayers and fibrin gel, provisional matrix-like cultures. Three different PAI-1-targeted small interfering RNAs, alone or in combination, produced greater than an 80% PAI-1 knockdown and reduced collagen accumulation in PAI-1-overexpressing normal or keloid fibroblasts. A vitronectin-binding mutant of PAI-1 was equipotent with wild-type PAI-1 in inducing collagen accumulation, whereas a complete protease inhibitor mutant retained approximately 50% activity. Thus, PAI-1 may use more than its protease inhibitory activity to control keloid collagen accumulation. PAI-1-targeted interventions, such as small interfering RNA and lentiviral short hairpin RNA-containing microRNA sequence suppression reported here, may have therapeutic utility in the prevention of keloid scarring.

SERPINE1 (PAI-1) is deposited into keratinocyte migration "trails" and required for optimal monolayer wound repair

Cutaneous tissue injury, both in vivo and in vitro, initiates activation of a "wound repair" transcriptional program. One such highly induced gene encodes plasminogen activator inhibitor type-1 (PAI-1, SERPINE1). PAI-1-GFP, expressed as a fusion protein under inducible control of +800 bp of the wound-activated PAI-1 promoter, prominently "marked" keratinocyte migration trails during the real-time of monolayer scrape-injury repair. Addition of active recombinant PAI-1 to wounded wild-type keratinocyte monolayers as well as to PAI-1(-/-) MEFs and PAI-1(-/-) keratinocytes significantly stimulated directional motility above basal levels in all cell types. PAI-1 expression knockdown or antibody-mediated functional inhibition, in contrast, effectively attenuated injury repair. The defect in wound-associated migratory activity as a consequence of antisense-mediated PAI-1 down-regulation was effectively reversed by addition of recombinant PAI-1 immediately after scrape injury. One possible mechanism underlying the PAI-1-dependent motile response may involve fine control of the keratinocyte substrate detachment/re-attachment process. Exogenous PAI-1 significantly enhanced keratinocyte spread cell "footprint" area while PAI-1 neutralizing antibodies, but not control non-immune IgG, effectively inhibited spreading with apoptotic hallmarks evident within 24 h. Importantly, PAI-1 not only stimulated keratinocyte adhesion and wound-initiated planar migration but also rescued keratinocytes from plasminogen-induced substrate detachment/anoikis. The early transcriptional response of the PAI-1 gene to monolayer trauma and its prominence in the injury repair genetic signature are consistent with its function as both a survival factor and regulator of the time course of epithelial migration as part of the cutaneous injury response program.

WRN polymorphisms affect expression levels of plasminogen activator inhibitor type 1 in cultured fibroblasts

BACKGROUND

Recessive mutations in WRN gene eliminate WRN protein function (helicase) and cause Werner syndrome. One of the most important clinical features of Werner syndrome patients are the premature onset and accelerated atherosclerosis process. Studies carried out on polymorphic WRN locus have shown that the alleles 1367R and 1074L confer protection for cardiovascular disease. Given that the levels of plasminogen activator inhibitor type 1 (PAI-1) were found to be significantly increased in Werner syndrome patients, is quiet possible that PAI-1 expression could be under regulation of WRN helicase. Therefore the purpose of this work was to evaluate the role of WRN polymorphism in modulating the expression of PAI-1.

METHODS

In order to accomplish our aim, an array of primary cultured fibroblasts from normal adult donors was genotyped for polymorphisms of both the WRN and PAI-1 loci. In addition, steady state levels of WRN and PAI-1 were measured by semi-quantitative RT-PCR assays in such cultures. To search for the potential relationship between the lack of WRN protein and PAI-1 expression, heterozygous cultures of fibroblasts (1367RC/1074LF; WRN genotype) were treated with a molecule of interference RNA against WRN messenger RNA (mRNA).

RESULTS

We found that, carriers of 1367R and 1074L alleles of WRN shown to have low amounts of PAI-1 in plasma (7.56 +/- 5.02), as compared with carriers of 1367C and 1074F alleles (16.09 +/- 6.03). Moreover, fibroblasts from carriers with these alleles had low expression levels of PAI-1 mRNA. The treatment of heterozygous primary fibroblast cultures (1367RC/1074LF; WRN genotype) with iRNA against WRN mRNA caused PAI-1 overexpression. Treatment with normal PAI-1 inducers (TGFbeta, TNFalpha, or insulin) in these cultures and from those with genotypes 1367CC/1074FF and 1367RR/1074FL resulted in a genotype-dependent PAI-1 expression level.

CONCLUSION

Our results suggest that polymorphisms in the WRN gene might have a significant role regulating PAI-1 levels in healthy individuals and "normal states" as well as acute or chronic stress, obesity, aging, acute inflammation, among others, where characteristic high levels of insulin, TNF alpha and TGFbeta, could favor PAI-1 high levels in carriers with polymorphic variants (C and F alleles), beyond the levels reached by carriers with other alleles (R and L alleles).

Postoperative intraperitoneal adhesion pathophysiology

Aside from the normal 'ad integrum' peritoneal regeneration, the postoperative intraperitoneal adhesion formation process may be considered as the pathological part of peritoneal healing following any injury, particularly a surgical one. Despite a large body of clinical and experimental studies, its pathophysiology remains controversial. Moreover, a better understanding of the pathophysiological events and of the medical and surgical factors involved in the adhesion formation process is pivotal in any attempt to control this very frequent phenomenon and its serious consequences.

Transforming growth factor-beta3 affects plasminogen activator inhibitor-1 expression in fetal mice and modulates fibroblast-mediated collagen gel contraction

For over two decades, the precise role of transforming growth factor-beta (TGF-beta) isoforms in scarless healing of mammalian fetal skin wounds has generated much interest. Although their exact role remains to be established, it has been suggested that high TGF-beta3 activity may correlate with a scarless phenotype. Previously, we showed that plasminogen activator inhibitor-1 (PAI-1), a known TGF-beta downstream molecule and marker of fibrosis, is also developmentally regulated during fetal skin development. In this study, the relationship between TGF-beta3 and PAI-1 was investigated using embryonic day 14.5 TGF-beta3 knockout (ko) mice. The results showed increased PAI-1 expression in the epidermis and dermis of ko mice, using an ex vivo limb-wounding study. Furthermore, increased PAI-1 expression and activity was seen in embryo extracts and conditioned media of ko dermal fibroblasts. When TGF-beta3 knockout fibroblasts were placed into three-dimensional collagen matrices, they were found to have decreased collagen gel contraction, suggesting altered cell-matrix interaction. These findings provide a further avenue for the interactive role of TGF-beta3 and PAI-1 during fetal scarless repair.

PAI-1 transcriptional regulation during the G0 --> G1 transition in human epidermal keratinocytes

Plasminogen activator inhibitor type-1 (PAI-1) is the major negative regulator of the plasmin-dependent pericellular proteolytic cascade. PAI-1 gene expression is normally growth state regulated but frequently elevated in chronic fibroproliferative and neoplastic diseases affecting both stromal restructuring and cellular migratory activities. Kinetic modeling of cell cycle transit in synchronized human keratinocytes (HaCaT cells) indicated that PAI-1 transcription occurred early after serum stimulation of quiescent (G0) cells and prior to entry into a cycling G1 condition. PAI-1 repression (in G0) was associated with upstream stimulatory factor-1 (USF-1) occupancy of two consensus E box motifs (5'-CACGTG-3') at the PE1 and PE2 domains in the PF1 region (nucleotides -794 to -532) of the PAI-1 promoter. Chromatin immunoprecipitation (ChIP) analysis established that the PE1 and PE2 site E boxes were occupied by USF-1 in quiescent cells and by USF-2 in serum-activated, PAI-1-expressing keratinocytes. This reciprocal and growth state-dependent residence of USF family members (USF-1 vs. USF-2) at PE1/PE2 region chromatin characterized the G0 --> G1 transition period and the transcriptional status of the PAI-1 gene. A consensus E box motif was required for USF/E box interactions, as a CG --> AT substitution at the two central nucleotides inhibited formation of USF/probe complexes. The 5' flanking sites (AAT or AGAC) in the PE2 segment were not necessary for USF binding. USF recognition of the PE1/PE2 region E box sites required phosphorylation with several potential involved residues, including T153, maping to the USF-specific region (USR). A T153A substitution in USF-1 did not repress serum-induced PAI-1 expression whereas the T153D mutant was an effective suppressor. As anticipated from the ChIP results, transfection of wild-type USF-2 failed to inhibit PAI-1 induction. Collectively, these data suggest that USF family members are important regulators of PAI-1 gene control during serum-stimulated recruitment of quiescent human epithelial cells into the growth cycle.

N-acetyl-L-cysteine abrogates fibrogenic properties of fibroblasts isolated from Dupuytren's disease by blunting TGF-beta signalling

Dupuytren's disease, a benign fibroproliferative disorder of the palmar fascia, represents an ideal model to study tissue fibrosis. Transforming growth factor-β₁ (TGF-β₁) and its downstream Smad signalling system is well established as a key player during fibrogenesis. Thus, targeting this basic pathomechanism seems suitable to establish new treatment strategies. One such promising treatment involves the substance N-acetyl-L-cysteine (NAC), shown to have antifibrotic properties in hepatic stellate cells and rat fibroblasts. In order to investigate antifibrotic effects of N-acetyl-L-cysteine (NAC), fibroblasts were isolated from surgically resected fibrotic palmar tissues (Dupuytren fibroblasts, DF) and exposed to different concentrations of NAC and recombinant TGF-β₁. Fibroblasts isolated from tendon pulleys served as controls (control fibroblasts, CF). Smad signalling was investigated by a Smad binding element driven reporter gene analysis. Both cell types express TGF-β₁, indicating autocrine signalling in DF and CF. This was confirmed by comparing reporter gene activity from LacZ and Smad7 adenovirus infected cells. NAC treatment resulted in abrogation of Smad mediated signalling comparable to ectopically overexpressed Smad7, even when the cells were stimulated with recombinant TGF-β₁ or ectopically expressed a constitutively active TGF-β receptor type I. Additionally, NAC dose-dependently decreased expression of three major indicators of impaired fibrotic matrix turnover, namely alpha-smooth muscle actin (α-SMA), α 1 type I procollagen (CollA1), and plasminogen activator inhibitor-type I (PAI-1). Our results suggest that TGF-β signalling and subsequent expression of fibrogenesis related proteins in Dupuytren's disease is abrogated by NAC thus providing a basis for a therapeutic strategy in Dupuytren's disease and other fibroproliferative disorders.

Novel functions of intracellular IL-1ra in human dermal fibroblasts: implications in the pathogenesis of fibrosis

Intracellular IL-1 receptor antagonist (icIL-1ra) is reportedly involved in functions independent of blocking IL-1 receptor signaling. Fibroblasts derived from the involved skin of patients with systemic sclerosis (SSc) are predominantly of the myofibroblast phenotype, with higher levels of icIL-1ra compared to normal skin fibroblasts. We examined the effect of overexpression of icIL-1ra on the phenotype and function of normal fibroblasts with respect to the expression of alpha smooth muscle actin (alpha-SMA), a specific marker for myofibroblasts, and plasminogen activator inhibitor (PAI), a protein involved in fibrogenesis and expressed at higher levels in myofibroblasts, and the production of collagenase (matrix metalloproteinase-1 (MMP-1)), the major enzyme involved in the degradation of native collagen in the skin. Normal human foreskin fibroblasts overexpressing icIL-1ra showed higher levels of alpha-SMA and PAI and had lower levels of collagenase and MMP-1 mRNA induced by inflammatory cytokines. By contrast, levels of mRNA for tissue inhibitor of metalloproteinase-1 in the transfected cells were not different from the control cells. Pretreatment of the ic-IL-1ra-transfected cells with antisense oligonucleotide directed against the mRNA of icIL-1ra restored MMP-1 expression induced by stimulation with IL-1beta. Our data indicate novel functions for icIL-1ra, which might be relevant to the genesis of fibrotic diseases such as SSc.

Plasminogen activator inhibitor-I–related regulation of procollagen I (α1 and α2) by antitransforming growth factor-β1 treatment during radiation-impaired wound healing

PURPOSE

Plasminogen activator inhibitor (PAI)-1 mediates transforming growth factor-beta1 (TGF-beta1)-related signaling by stimulating collagen Type I synthesis in radiation-impaired wound healing. The regulation of alpha(I)-procollagen is contradictory in fibroblasts of different fibrotic lesions. It is not known whether anti-TGF-beta1 treatment specifically inhibits alpha(I)-procollagen synthesis. We used an experimental wound healing study to address anti-TGF-beta1-associated influence on alpha(I)-procollagen synthesis.

METHODS AND MATERIALS

A free flap was transplanted into the preirradiated (40 Gy) or nonirradiated neck region of Wistar rats: Group 1 (n = 8) surgery alone; Group 2 (n = 14) irradiation and surgery; Group 3 (n = 8) irradiation and surgery and anti-TGF-beta1 treatment. On the 14th postoperative day, skin samples were processed for fibroblast culture, in situ hybridization for TGF-beta1, immunohistochemistry, and immunoblotting for PAI-1, alpha1/alpha2(I)-procollagen.

RESULTS

Anti-TGF-beta1 significantly reduced TGF-beta1 mRNA (p < 0.05) and PAI-1 expression (p < 0.05). Anti-TGF-beta1 treatment in vivo significantly reduced alpha1(I)-procollagen protein (p < 0.05) and the number of expressing cells (p < 0.05) in contrast to significantly increased (p < 0.05) alpha2(I)-procollagen expression.

CONCLUSION

These results emphasize anti-TGF-beta1 treatment to reduce radiation-induced fibrosis by decreasing alpha1(I)-procollagen synthesis in vivo. alpha1(I)-procollagen and alpha2(I)-procollagen might be differentially regulated by anti-TGF-beta1 treatment. Increased TGF-beta signaling in irradiated skin fibroblasts seemed to be reversible, as shown by a reduction in PAI-1 expression after anti-TGF-beta1 treatment.

Plasminogen activator inhibitor-1 is elevated, but not essential, in the development of bleomycin-induced murine scleroderma

Accumulative data have demonstrated that plasminogen activator inhibitor-1 (PAI-1) plays an important role in the extracellular matrix metabolism; however, the involvement of PAI-1 in scleroderma has not been fully elucidated. In this study, we investigated the role of PAI-1 in bleomycin-induced murine scleroderma. 100 microg of bleomycin was injected subcutaneously to the back skin of C3H/HeJ mice on alternate day for 4 weeks. Histopathological findings revealed that PAI-1 was positive in macrophage-like cells and fibroblastic cells in the dermis, in parallel with the induction of dermal sclerosis. PAI-1 mRNA expression in the whole skin was up-regulated at 1 and 4 weeks. The production of active PAI-1 protein in the lesional skin was significantly increased 3 and 4 weeks after bleomycin treatment. Next, we examined whether dermal sclerosis is induced by bleomycin in PAI-1-deficient (PAI-1-/-) mice. 10 microg of bleomycin was subcutaneously injected to PAI-1-/- and wild type (WT) mice 5 days per week for 4 weeks. Histological examination revealed that dermal sclerosis was similarly induced even in PAI-1-/- as well as WT mice. Dermal thickness and collagen contents in the skin were significantly increased by bleomycin injection in both PAI-1-/- and WT mice, and the rate of increase was similar. These data suggest that PAI-1 plays an important role, possibly via TGF-beta pathway activation. However, the fact that PAI-1 deficiency did not ameliorate skin sclerosis suggest that PAI-1 is not the essential factor in the development of bleomycin-induced scleroderma, and more complex biochemical effects other than PA/plasmin system are greatly suspected.

Advances in the Modulation of Cutaneous Wound Healing and Scarring

Cutaneous wounds inevitably heal with scars, which can be disfiguring and compromise function. In general, the greater the insult, the worse the scarring, although genetic make up, regional variations and age can influence the final result. Excessive scarring manifests as hypertrophic and keloid scars. At the other end of the spectrum are poorly healing chronic wounds, such as foot ulcers in diabetic patients and pressure sores. Current therapies to minimize scarring and accelerate wound healing rely on the optimization of systemic conditions, early wound coverage and closure of lacerations, and surgical incisions with minimal trauma to the surrounding skin. The possible benefits of topical therapies have also been assessed. Further major improvements in wound healing and scarring require an understanding of the molecular basis of this process. Promising strategies for modulating healing include the local administration of platelet derived growth factor (PDGF)-BB to accelerate the healing of chronic ulcers, and increasing the relative ratio of transforming growth factor (TGF)beta-3 to TGFbeta-1 and TGFbeta-2 in order to minimize scarring.

Elevated vascular endothelial growth factor in keloids: relevance to tissue fibrosis

Excessive scar or keloid shares common features of a benign dermal growth. Yet, in contrast to malignant tumor, a keloid does not expand beyond the dermis. What triggers the continuing growth of a benign lesion? Deficient or overabundant levels of vascular endothelial growth factor have been reported to contribute to impaired or excessive wound healing. Although numerous studies have examined the pathophysiology of impaired wounds, little information has been provided on mechanisms of exuberant healing. The molecular basis of keloid formation is governed by the interplay of cellular signaling pathways, specific target gene activation, and the nature of the microenvironment. Recent works have demonstrated an accumulation of hypoxia-inducible factor-1alpha protein in freshly biopsied keloid tissues, thus providing first evidence that a local state of hypoxia exists in keloids. Our findings and the findings of others support at least two plausible mechanisms implicated in the development of fibrotic wounds, a state of ongoing fibroplasia or inflammation and an excessive accumulation of extracellular matrix. This article will review recent works examining the potential role of vascular endothelial growth factor in keloid pathogenesis with particular focus on its involvement in the two proposed pathological processes, a prolonged inflammation and an altered balance in extracellular matrix metabolism.

PAI-1 expression is required for epithelial cell migration in two distinct phases of in vitro wound repair

Several proteases and their specific inhibitors modulate the interdependent processes of cell migration and matrix proteolysis as part of the global program of trauma repair. Expression of plasminogen activator inhibitor type-1 (PAI-1), a serine protease inhibitor (SERPIN) important in the control of barrier proteolysis and cell-to-matrix adhesion, for example, is spatially-temporally regulated following epithelial denudation injury in vitro as well as in vivo. PAI-1 mRNA/protein synthesis was induced early after epidermal monolayer scraping and restricted to keratinocytes comprising the motile cohort closely recapitulating, thereby, similar events during cutaneous healing. The time course of PAI-1 promoter-driven PAI-1-GFP fusion "reporter" expression in wound-juxtaposed cells approximated that of the endogenous PAI-1 gene confirming the location-specificity of gene regulation in this model. ERK activation was evident within 5 min after injury and particularly prominent in cells residing at the scrape-edge (suggesting a possible role in PAI-1 induction and/or the motile response) as was myosin light chain (MLC) phosphorylation. Indeed, MEK blockade with PD98059 or U0126 attenuated keratinocyte migration (by > or =60%), as did transient transfection of a dominant-negative ERK1 construct (40% decrease in monolayer repair), and completely inhibited PAI-1 transcript expression. Anti-sense down-regulation of PAI-1 synthesis (by 80-85%), or addition of PAI-1 neutralizing antibodies also inhibited injury site closure over a 24 h period establishing that PAI-1 was required for efficient long-term planar motility in this system. PAI-1 anti-sense transfection or actinomycin D transcriptional blockade, in contrast, did not affect the initial migratory response suggesting that residual PAI-1 protein levels (at least in transfectant cells and actinomycin D-treated cultures) may be sufficient to support early cell movement. Pharmacologic inhibition of keratinocyte MEK signaling effectively ablated scrape-induced PAI-1 mRNA expression but failed to attenuate wound-associated increases in cellular PAI-1 protein levels soon after monolayer injury. Collectively, these data suggest that basal PAI-1 transcripts may be mobilized for initial PAI-1 synthesis and, perhaps, the early motile response while maintenance of the normal rate of migration requires the prolonged PAI-1 expression that typically accompanies the repair response. To assess this possibility, scrape site closure studies were designed using keratinocytes isolated from PAI-1-/- mice. PAI-1-/- keratinocytes, in fact, had a significant wound healing defect evident even within the first 6 h following monolayer denudation injury. Addition of active PAI-1 protein to PAI-/- keratinocytes rescued the migratory phenotype that that approximating wild-type cells. These findings validate use of the present keratinocyte model to investigate injury-related controls on PAI-1 gene regulation and, collectively, implicate participation of PAI-1 in two distinct phases of epidermal wound repair.

Signaling events during induction of plasminogen activator inhibitor-1 expression by sphingosylphosphorylcholine in cultured human dermal fibroblasts

Sphingosylphosphorylcholine (SPC) is a bioactive sphingolipid metabolite that can enhance wound healing. In a search for effectors downstream of SPC in the wound-healing process, we found that the expression of the gene for plasminogen activator inhibitor-1 (PAI-1) was significantly affected. ELISA and western blot analyses showed that SPC markedly induced PAI-1 production in human dermal fibroblasts cultured in vitro. Inhibition by pre-treatment with pertussis toxin (PTx), but not by tyrphostin A47 (a receptor tyrosine kinase inhibitor), indicated that PTx-sensitive G proteins were involved in SPC-induced PAI-1 expression. SPC elicited a rapid and transient increase in intracellular calcium levels ([Ca2+]i), measured using laser scanning confocal microscopy, which was partly mediated through PTx-sensitive G proteins. Pre-treatment with thapsigargin, but not with EGTA, abolished SPC-induced PAI-1 expression, indicating the importance of Ca2+ release from internal stores. Phorbol-12-myristate-13-acetate (PMA) induced the expression of PAI-1, and pre-treatment with Ro 31-8220 (a PKC inhibitor) markedly suppressed SPC-induced PAI-1 expression. SPC-induced PAI-1 expression was also significantly suppressed by PD98059 (a specific MAPK kinase 1/2 inhibitor). Consistent with this result, SPC stimulated the phosphorylation of p42/44 extracellular signal-regulated kinase (ERK). Together, these results suggest that SPC induces PAI-1 production through a G protein-coupled calcium increase and downstream kinase signaling events in cultured human dermal fibroblasts.

Crosstalk of hypoxia-mediated signaling pathways in upregulating plasminogen activator inhibitor-1 expression in keloid fibroblasts

Keloids are skin fibrotic conditions characterized by an excess accumulation of extracellular matrix (ECM) components secondary to trauma or surgical injuries. Previous studies have shown that plasminogen activator inhibitor-1 (PAI-1) can be upregulated by hypoxia and may contribute to keloid pathogenesis. In this study we investigate the signaling mechanisms involved in hypoxia-mediated PAI-1 expression in keloid fibroblasts. Using Northern and Western blot analysis, transient transfections, and pharmacological agents, we demonstrate that hypoxia-induced upregulation of PAI-1 expression is mainly controlled by hypoxia inducible factors-1alpha (HIF-1alpha) and that hypoxia leads to a rapid and transient activation of phosphatidylinositol-3-kinase/Akt (PI3-K/Akt) and extracellular signal-regulated kinases 1/2 (ERK1/2). Treatment of cells with PI-3K/Akt inhibitor (LY294002) and tyrosine protein kinase inhibitor (genistein) significantly attenuated hypoxia-induced PAI-1 mRNA and protein expression as well as promoter activation, apparently via an inhibition of the hypoxia-induced stabilization of HIF-1alpha protein, attenuation of the steady-state level of HIF-1alpha mRNA, and its DNA-binding activity. Even though disruption of ERK1/2 signaling pathway by PD98059 abolished hypoxia-induced PAI-1 promoter activation and mRNA/protein expression in keloid fibroblasts, it did not inhibit the hypoxia-mediated stabilization of HIF-1alpha protein and the steady-state level of HIF-1alpha mRNA nor its DNA binding activity. Our findings suggest that a combination of several signaling pathways, including ERK1/2, PI3-K/Akt, and protein tyrosine kinases (PTKs), may contribute to the hypoxia-mediated induction of PAI-1 expression via activation of HIF-1alpha in keloid fibroblasts.

Increased vascular endothelial growth factor may account for elevated level of plasminogen activator inhibitor-1 via activating ERK1/2 in keloid fibroblasts

Keloids are characterized as an "overexuberant" healing response in which disequilibrium between production and catabolism of extracellular matrix (ECM) occurs. Previous studies from our laboratory and others demonstrate an intrinsically higher level of plasminogen activator inhibitor-1 (PAI-1) expression in keloid tissues and cultured fibroblasts compared with normal bordering skin. These findings support the concept that an altered balance of activator and inhibitor activities in the plasminogen system, in particular, an overexpression of PAI-1, may partly contribute to keloid formation and tissue fibrosis. Vascular endothelial growth factor (VEGF) has been implicated as a critical factor in regulating angiogenesis and inflammation under both physiological and pathological conditions. This study was designed to assess whether VEGF plays a role in keloid fibrosis. We report that VEGF was expressed at higher levels in keloid tissues and their derived fibroblasts compared with their associated normal skin. We have further demonstrated that VEGF stimulated the expression of PAI-1, but not urokinase plasminogen activator (uPA), in keloid fibroblasts at both mRNA and protein levels, in a dose- and time-dependent manner. However, treatment of normal skin fibroblasts with VEGF exerted little effects on PAI-1 gene expression. Additionally, we have characterized for the first time that the extracellular signal-regulated kinase (ERK)1/2 signaling pathway is mainly involved in VEGF-induced PAI-1 expression and have demonstrated its potential as a target molecule for modulation of scar fibrosis. These findings suggest that VEGF may play an important role in keloid formation by altering ECM homeostasis toward a state of impaired degradation and excessive accumulation.

Mechanisms of Hypoxic Regulation of Plasminogen Activator Inhibitor-1 Gene Expression in Keloid Fibroblasts

Keloids are an excessive accumulation of extracellular matrix. Although numerous studies have shown elevated plasminogen activator inhibitor-1 (PAI-1) levels in keloid fibroblasts compared with those of normal skin. Their specific mechanisms involved in the differential expression of PAI-1 in these cell types. In this study, the upregulation of PAI-1 expression is demonstrated in keloid tissues and their derived dermal fibroblasts, attesting to the persistence, if any, of fundamental differences between in vivo and in vitro paradigms. We further examined the mechanisms involved in hypoxia-induced regulation of PAI-1 gene in dermal fibroblast derived from keloid lesions and associated clinically normal peripheral skins from the same patient. Primary cultures were exposed to an environmental hypoxia or desferroxamine. We found that the hypoxia-induced elevation of PAI-1 gene appears to be regulated at both transcriptional and post-transcriptional levels in keloid fibroblasts. Furthermore, our results showed a consistent elevation of HIF-1alpha protein level in keloid tissues compared with their normal peripheral skin controls, implying a potential role as a biomarker for local skin hypoxia. Treatment with antisense oligonucleotides against hypoxia-inducible factor 1alpha (HIF-1alpha) led to the downregulation of steady-state levels of PAI-1 mRNA under both normoxic and hypoxic conditions. Conceivably, our results suggest that HIF-1alpha may be a novel therapeutic target to modulate the scar fibrosis process.

Plasminogen activator/plasmin system: a major player in wound healing?

The role of the plasminogen activator/plasmin system in fibrinolysis has been well established. Indeed, clinicians worldwide have successfully utilized recombinant tissue-type plasminogen activator as first-line treatment of acute myocardial infarction for almost 2 decades. Outside the field of cardiology, there has been increasing excitement regarding the possible contribution of this system in many other important biological processes, including cell adhesion, cell migration, cell-cell signaling, tumor invasion and metastasis, ovulation, and wound healing. In this review, we present evidence in the current literature that the plasminogen activator/plasmin system does have a role in wound healing, looking at both normal and abnormal healing. Furthermore, the invaluable insights provided by numerous transgenic animal experiments are summarized.

Increased plasminogen activator inhibitor-1 in keloid fibroblasts may account for their elevated collagen accumulation in fibrin gel cultures

Proteolytic degradation of the provisional fibrin matrix and subsequent substitution by fibroblast-produced collagen are essential features of injury repair. Immunohistochemical studies revealed that although dermal fibroblasts of normal scars and keloids expressed both urokinase type plasminogen activator (uPA) and plasminogen activator inhibitor-1 (PAI-1), keloid fibroblasts had a much higher PAI-1 expression. In long-term three-dimensional fibrin gel cultures (the in vitro fibroplasia model), normal fibroblasts expressed moderate and modulated activity levels of uPA and PAI-1. In contrast, keloid fibroblasts expressed a persistently high level of PAI-1 and a low level of uPA. The high PAI-1 activity of keloid fibroblasts correlated with their elevated collagen accumulation in fibrin gel cultures. Substituting collagen for fibrin in the gel matrix resulted in increased uPA activity and reduced collagen accumulation of keloid fibroblasts. Furthermore, decreasing PAI-1 activity of keloid fibroblasts in fibrin gel cultures with anti-PAI-1-neutralizing antibodies also resulted in a reduction in collagen accumulation by keloid fibroblasts. Cumulatively, these results suggest that PAI-1 overexpression is a consistent feature of keloid fibroblasts both in vitro and in vivo, and PAI-1 may play a causative role in elevated collagen accumulation of keloid fibroblasts.

Plasminogen activator inhibitor-1 4G/5G genetic polymorphism does not affect peritoneal transport characteristic

There is evidence that type 1 plasminogen activator inhibitor (PAI-1) may have an important role in peritoneal function. We studied the effect of physiologically relevant PAI-1 promotor polymorphisms on peritoneal permeability. We performed a standard peritoneal equilibration test (PET) in 100 new continuous ambulatory peritoneal dialysis (CAPD) patients. We studied another 48 prevalent CAPD patients who had a baseline PET performed 2 years before; a standard PET was repeated on enrollment. The PAI-1 promotor polymorphism was examined. All patients then were followed up for 16.7 +/- 15.0 months. Prevalences of 4G/4G, 4G/5G, and 5G/5G genotypes were 31.8%, 46.6%, and 21.6%, respectively. Of the 100 new CAPD patients, there was no difference in net ultrafiltration (UF), dialysate-plasma (D/P) creatinine ratio at 4 hours, or mass transfer area coefficient (MTAC) of creatinine among the three genotype groups. D/P creatinine ratios at 4 hours were 0.595 +/- 0.133, 0.607 +/- 0.137, and 0.627 +/- 0.142 for the 4G/4G, 4G/5G, and 5G/5G groups, respectively (one way analysis of variance, P = 0.715). Of the 48 prevalent patients, PAI-1 genotype did not affect the longitudinal change in net UF, D/P creatinine ratio at 4 hours, or MTAC of creatinine. During follow-up, 16 patients developed peritonitis episodes that required Tenckhoff catheter removal. One patient died, 8 patients returned to long-term CAPD therapy after peritonitis resolved, and the other 7 patients developed peritoneal failure and were switched to long-term hemodialysis therapy. PAI-1 promotor genotype did not predict peritoneal failure after an episode of severe peritonitis (chi-square test, P = 0.328). We conclude that PAI-1 promotor polymorphism is not associated with peritoneal transport characteristics in stable peritoneal dialysis patients, longitudinal change in peritoneal transport, or development of peritoneal failure after an episode of severe peritonitis.

Idiopathic pulmonary fibrosis: an epithelial/fibroblastic cross-talk disorder

Idiopathic pulmonary fibrosis is a chronic and usually progressive lung disorder of unknown etiology. A growing body of evidence suggests that, in contrast to other interstitial lung diseases, IPF is a distinct entity in which inflammation is a secondary and non-relevant pathogenic partner. Evidence includes the presence of similar mild/moderate inflammation either in early or late disease, and the lack of response to potent anti-inflammatory therapy. Additionally, it is clear from experimental models and some human diseases that it is possible to have fibrosis without inflammation. An evolving hypothesis proposes that IPF may result from epithelial micro-injuries and abnormal wound healing.