mRNA expression of urokinase and plasminogen activator inhibitor-1 in human crescentic glomerulonephritis

Identification of an unrecognized circRNA associated with development of renal fibrosis

Backgroud: Renal fibrosis is the common characteristic of chronic kidney disease. Circular RNA plays an essential role in the occurrence and development of Renal fibrosis, but its regulative mechanism remains elusive. Methods: The animal and cell model of Renal fibrosis was established, and RNA-sequencing and real-time polymerase chain reaction (qRT-PCR) experiments were implemented. Subsequently, experiments for detecting apoptosis and proliferation of cell, were carried out, and the isobaric tags for relative and absolute quantification proteomics analyses were performed accordingly. Results: It was found that a newly discovered Circular RNA (circRNA_0002158), is highly expressed in kidneys or cells with fibrosis, implying that this Circular RNA might be associated with the occurrence and development of Renal fibrosis. Subsequently, the overexpression and knockdown of circRNA_0002158 were conducted in the human kidney epithelial cell line (HK-2) cells, and the results indicated that the circRNA_0002158 could inhibit apoptosis, and promote proliferation of cells. The kidney injury-related factors, including Fibronectin and plasminogen activator inhibitor-1 (PAI-1), were decreased in HK-2 cells with overexpression of circRNA_0002158, while the results were reversed in cells with knockdown of circRNA_0002158. Finally, to explore the regulative mechanism of circRNA_0002158, the iTRAQ proteomics analyses were implemented for the cell samples with OE of circRNA_0002158 and its control, it showed that multiple genes and functional pathways were associated with the occurrence and development of Renal fibrosis. Conclusion: CircRNA_0002158 is associated with regulating Renal fibrosis, and may contribute to ameliorating the progression of Renal fibrosis in the future.

Glomerular endothelial cell senescence drives age-related kidney disease through PAI-1

The mechanisms underlying the development of glomerular lesions during aging are largely unknown. It has been suggested that senescence might play a role, but the pathophysiological link between senescence and lesion development remains unexplained. Here, we uncovered an unexpected role for glomerular endothelial cells during aging. In fact, we discovered a detrimental cross-talk between senescent endothelial cells and podocytes, through PAI-1. In vivo, selective inactivation of PAI-1 in endothelial cells protected glomeruli from lesion development and podocyte loss in aged mice. In vitro, blocking PAI-1 in supernatants from senescent endothelial cells prevented podocyte apoptosis. Consistently, depletion of senescent cells prevented podocyte loss in old p16 INK-ATTAC transgenic mice. Importantly, these experimental findings are relevant to humans. We showed that glomerular PAI-1 expression was predictive of poor outcomes in transplanted kidneys from elderly donors. In addition, we observed that in elderly patients, urinary PAI-1 was associated with age-related chronic kidney disease. Altogether, these results uncover a novel mechanism of kidney disease and identify PAI-1 as a promising biomarker of kidney dysfunction in allografts from elderly donors.

Fibroblast-specific plasminogen activator inhibitor-1 depletion ameliorates renal interstitial fibrosis after unilateral ureteral obstruction

BACKGROUND

Plasminogen activator inhibitor-1 (PAI-1) expression increases extracellular matrix deposition and contributes to interstitial fibrosis in the kidney after injury. While PAI-1 is ubiquitously expressed in the kidney, we hypothesized that interstitial fibrosis is strongly dependent on fibroblast-specific PAI-1 (fbPAI-1).

METHODS

Tenascin C Cre (TNC Cre) and fbPAI-1 knockdown (KD) mice with green fluorescent protein (GFP) expressed within the TNC construct underwent unilateral ureteral obstruction and were sacrificed 10 days later.

RESULTS

GFP+ cells in fbPAI-1 KD mice showed significantly reduced PAI-1 expression. Interstitial fibrosis, measured by Sirius red staining and collagen I western blot, was significantly decreased in fbPAI-1 KD compared with TNC Cre mice. There was no significant difference in transforming growth factor β (TGF-β) expression or its activation between the two groups. However, GFP+ cells from fbPAI-1 KD mice had lower TGF β and connective tissue growth factor (CTGF) expression. The number of fibroblasts was decreased in fbPAI-1 KD compared with TNC Cre mice, correlating with decreased alpha smooth muscle actin (α-SMA) expression and less fibroblast cell proliferation. TNC Cre mice had decreased E-cadherin, a marker of differentiated tubular epithelium, in contrast to preserved expression in fbPAI-1 KD. F4/80-expressing cells, mostly CD11c+/F4/80+ cells, were increased while M1 macrophage markers were decreased in fbPAI-1 KD compared with TNC Cre mice.

CONCLUSION

These findings indicate that fbPAI-1 depletion ameliorates interstitial fibrosis by decreasing fibroblast proliferation in the renal interstitium, with resulting decreased collagen I. This is linked to decreased M1 macrophages and preserved tubular epithelium.

Apolipoprotein E and plasminogen activator inhibitor 1 gene polymorphism in children with chronic renal insufficiency associated with cardiovascular disease

Background

Cardiovascular disease (CVD) is considered a major cause of death in renal insufficiency (RI). Contributing genetic factors is a recent focus of research. This study aims to elucidate apolipoprotein E (APO-E) and plasminogen activator inhibitor 1 (PAI-1) gene polymorphisms in RI children associated with CVD.

Methods

We studied 50 cases with chronic kidney disease (CKD) associated with CVD, and 30 healthy controls. Study sample was grouped as one on conservative treatment, the second on hemodialysis and the third was posttransplant. PAI-1 and APO-E gene polymorphisms were investigated using allele-specific polymerase chain reaction (AS-PCR) and polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) respectively.

Results

4G4G and 4G5G were the most common PAI-1 polymorphism denoting high association of 4 G allele in renal insufficiency associated with CVD with absent link to dyslipidemia, echocardiography changes or thrombosis. E3E3 was the most common among APO-E polymorphism without relation to dyslipidemia or thrombosis. Dyslipidemia was significantly linked to thrombosis. The study confirmed the role of dyslipidemia and hemodialysis in promoting thrombosis.

Conclusion

Although PAI 4G Genotyping did not show significant association with echocardiography severity or thrombotic severity, yet genetic expression for high levels of PAI in plasma is expected in response to CRI factors known to trigger its release, in addition to those related to dialysis. APO-E3E3 genotyping showed a significant association with echocardiography severity as it enhances APO-A which contributes to CVD. The current study confirmed a significant association between dyslipidemia and CVD; however, the prevalent patterns 4G and E3E3 did not show a significant association with dyslipidemia. The genetic role for APO-A, B, O, or even other isomers for APO-E should be further studied as well.

An additive effect of anti-PAI-1 antibody to ACE inhibitor on slowing the progression of diabetic kidney disease

While angiotensin II blockade slows the progression of diabetic nephropathy, current data suggest that it alone cannot stop the disease process. New therapies or drug combinations will be required to further slow or halt disease progression. Inhibition of plasminogen activator inhibitor type 1 (PAI-1) aimed at enhancing ECM degradation has shown therapeutic potential in diabetic nephropathy. Here, using a mouse model of type diabetes, the maximally therapeutic dose of the PAI-1-neutralizing mouse monoclonal antibody (MEDI-579) was determined and compared with the maximally effective dose of enalapril. We then examined whether addition of MEDI-579 to enalapril would enhance the efficacy in slowing the progression of diabetic nephropathy. Untreated uninephrectomized diabetic db/db mice developed progressive albuminuria and glomerulosclerosis associated with increased expression of transforming growth factor (TGF)-β1, PAI-1, type IV collagen, and fibronectin from weeks 18 to 22, which were reduced by MEDI-579 at 3 mg/kg body wt, similar to enalapril given alone from weeks 12 to 22 Adding MEDI-579 to enalapril from weeks 18 to 22 resulted in further reduction in albuminuria and markers of renal fibrosis. Renal plasmin generation was dramatically reduced by 57% in diabetic mice, a decrease that was partially reversed by MEDI-579 or enalapril given alone but was further restored by these two treatments given in combination. Our results suggest that MEDI-579 is effective in slowing the progression of diabetic nephropathy in db/db mice and that the effect is additive to ACEI. While enalapril is renal protective, the add-on PAI-1 antibody may offer additional renoprotection in progressive diabetic nephropathy via enhancing ECM turnover.

A plasminogen activator inhibitor type 1 mutant retards diabetic nephropathy in db/db mice by protecting podocytes

A mutant non-inhibiting plasminogen activator inhibitor type 1 (PAI-1), termed PAI-1R, which reduces endogenous PAI-1 activity, has been shown to inhibit albuminuria and reduce glomerulosclerosis in experimental diabetes. The mechanism of the reduction of albuminuria is unclear. This study sought to determine whether the administration of PAI-1R protected podocytes from injury directly, thereby reducing albuminuria in the db/db mouse, a model of type 2 diabetes. Untreated uninephrectomized db/db mice developed significant mesangial matrix expansion and albuminuria at week 22 of age, associated with segmental podocyte foot-process effacement, reduction of renal nephrin, podocin and zonula occludin-1 production and induction of renal desmin and B7-1 generation. In contrast, treatment with PAI-1R at 0.5 mg (kg body weight)(-1) i.p., twice daily from week 20 to 22, reduced glomerular matrix accumulation, fibronectin and collagen production and albuminuria by 36, 62, 65 and 31%, respectively (P < 0.05), without affecting blood glucose level or body weight. Podocyte morphology and protein markers were also significantly attenuated by PAI-1R administration. Importantly, recombinant PAI-1 downregulated nephrin and zonula occludin-1 but increased desmin and B7-1 mRNA expression and protein production by podocytes in vitro, similar to the effects of transforming growth factor-β1. These observations provide evidence that PAI-1, in a manner similar to transforming growth factor-β1, directly induces podocyte injury, particularly in the setting of diabetes, where elevated PAI-1 may contribute to the progression of albuminuria. Reducing the increased PAI-1 activity by administration of PAI-1R, in fact, reduces podocyte injury, thereby reducing albuminuria. Therefore, PAI-1R provides an additional therapeutic effect in slowing the progression of diabetic nephropathy via the protection of podocytes.

Loss of heparin-binding protein prevents necrotizing glomerulonephritis: first clues hint at plasminogen activator inhibitor-1

The orchestration of acute inflammatory kidney injury is subject to widespread influences and involves cytokines as well as chemokines released by resident as well as infiltrating cells. Although intense research efforts have been made in the field, it still unravels yet novel key molecules involved in the pathogenesis of this kidney disease. A heparin-binding growth factor denoted midkine is expressed by various cell types following stress of tissue damage. Specific functions relate to orchestration of reparative and inflammatory processes by promoting migration of leucocytes and release of chemokines with ensuing angiogenesis. Midkine appears as a double-edged sword with beneficial or harmful effects in injured tissues. Here, we discuss a recent publication that provides evidence for the beneficial role of midkine in progressive glomerulonephritis, most likely due to blockade of plasminogen activator inhibitor-1 release.

Obesity-related glomerulopathy and podocyte injury: a mini review

Obesity-related glomerulopathy (ORG) is morphologically defined as focal segmental glomerulosclerosis and glomerulomegaly. Podocyte hypertrophy and reduced density are related to proteinuria which in a portion of patients is in the nephrotic range and evolvs towards renal failure. This article reviews the pathogenetic mechanisms of podocyte injury or dysfunction and lists new possible antiproteinuric strategies based on pharmaceutical targeting of the reported pathogenetic mechanisms. The pathogenetic mechnisms discussed include: renin angiotensin system, plasminogen activation inhibitor-1 (PAI-1), lipid metabolism, adiponectin, macrophages and proinflammatory cytokines, oxidative stress. The proposed antiproteinuric strategies include: AT2 receptor blockers; adipokine complement C19 TNF-related protein-1 blocker; selective PAI-1 inhibitor; farnesoid x receptor activation; increase of circulating adiponectin; selective antiinflammatory drugs; more potent antioxidants (Heme oxigenase, NOX4 inhibitors). However, because ORG is a rare disease, the need for a long term pharmaceutical approach in obese proteinuric patients should be carefully evaluated and limited to the cases with progressive loss of renal function.

Urokinase induces survival or pro-apoptotic signals in human mesangial cells depending on the apoptotic stimulus

Deregulated apoptosis of MCs (mesangial cells) is associated with a number of kidney diseases including end-stage diabetic nephropathy. Cell death by apoptosis is a tightly orchestrated event, whose mechanisms are not completely defined. In the present study we show that the uPA (urokinase-type plasminogen activator)/uPAR (uPA receptor) system can initiate both cell survival and pro-apoptotic signals in human MCs in response to different apoptotic stimuli. uPA abrogated MC apoptosis induced by serum withdrawal conditions and enhanced apoptosis initiated in MCs by high glucose. Effects of uPA were independent of its proteolytic activity and required uPAR for both pro- and anti-apoptotic effects. Studies on the uPAR interactome provide evidence that the opposing effects of uPA were directed via different uPAR-interacting transmembrane partners. Exposure of MCs to RGD (Arg-Gly-Asp) peptide led to abrogation of the anti-apoptotic effect of uPA, which implies involvement of integrins in this process. A pro-apoptotic effect of uPA under high-glucose conditions was mediated via association of uPAR and the cation-independent M6P (mannose-6-phosphate)/IGF2R (insulin-like growth factor 2 receptor). Both receptors were co-precipitated and co-localized in MCs. Studies on the underlying signalling indicate that the ERK1/2 (extracellular-signal-regulated kinase 1/2), Akt and BAD (Bcl-2/Bcl-X(L)-antagonist, causing cell death) protein were involved in regulation of apoptosis by uPA in MCs. M6P/IGF2R mediated BAD perinuclear localization during apoptosis initiated by uPA and high glucose. In conclusion, we provide evidence that, in MCs, the uPA/uPAR system regulates survival/apoptosis processes in a stimulus-specific fashion via a mitochondria-dependent mechanism and that BAD protein serves as a downstream molecule.

TGF-beta type II receptor deficiency prevents renal injury via decrease in ERK activity in crescentic glomerulonephritis

The role of transforming growth factor-beta (TGF-beta) receptor complex in the pathogenesis of crescentic glomerulonephritis (GN) is not clear. To test the hypothesis that TGF-beta signaling plays a crucial role in the development and progression of crescentic GN by inducing the activation of extracellular signal-regulated kinase (ERK) and expression of its target genes, anti-glomerular basement membrane (GBM) GN was induced in TGF-beta type II receptor (TGF-betaIIR) gene heterozygous (TGF-betaIIR(+/-)) C57BL/6J mice and wild-type animals. GN was initiated in preimmunized mice by administration of rabbit anti-mouse GBM serum. TGF-betaIIR deficiency was significantly associated with decreased renal damage at days 14, 21, and 28 after induction of GN: renal function impairment, proteinuria, proportion of crescents, glomerular accumulation of periodic acid-Schiff-positive material, relative cortical interstitial volume, as well as renal cortical phosphorylation of ERK and plasminogen activator inhibitor type I (PAI-1) and alpha2(I) collagen mRNA levels were significantly decreased in TGF-betaIIR(+/-) mice compared with wild-type animals. These results provide the first direct evidence that TGF-betaIIR deficiency protects against renal injury in crescentic GN, possibly by inhibiting the sustained activation of ERK and PAI-1 and alpha2(I) collagen gene expression. Thus, TGF-beta signaling appears to play an important role in the development and progression of crescentic GN by inducing the ERK activity, and PAI-1 and alpha2(I) mRNA expression.

Oxidized LDL activates PAI-1 transcription through autocrine activation of TGF-beta signaling in mesangial cells

BACKGROUND

Lipid abnormalities and oxidative stress may be involved in the development of glomerulosclerosis. Plasminogen activator inhibitor-1 (PAI-1) is a component of extracellular matrix (ECM) and target gene of transforming growth factor-beta (TGF-beta). Smad proteins play a key role in TGF-beta signaling, and Smad binding CAGA boxes are present in the PAI-1 promoter. This study examined whether oxidized low-density lipoprotein (Ox-LDL) activates PAI-1 transcription in human mesangial cells, mediated by increased Smad/DNA interactions.

METHODS

Quiescent HMC were incubated with 50 microg/mL of Cu(++)-catalyzed Ox-LDL for 15 minutes to 4 hours, and the effects of Ox-LDL on TGF-beta1 and PAI-1 mRNA expression, PAI-1 promoter activity, and DNA binding activity of Smad proteins were examined.

RESULTS

Ox-LDL induced TGF-beta1 and PAI-1 mRNA expression. Ox-LDL increased the transiently transfected PAI-1 promoter activity as compared with controls to 3.9-fold. Ox-LDL-treated cells increased Smad3 protein levels two times the control levels in the nuclei. Electrophoretic mobility shift assay (EMSA) performed using a CAGA sequence probe and nuclear extracts showed that Ox-LDL increased DNA/protein complexes. When nuclear extracts were preincubated with 100 molar excess of unlabeled CAGA oligonucleotide or SB-431542, an inhibitor of the TGF-beta type I receptor, the formation of complex was prevented. The DNA binding protein was shown to be Smad3 by antibody supershift. Transfection of phosphorothioate CAGA oligonucleotides, which compete with the CAGA-containing PAI-1 promoter for Smad3 binding, inhibited the Ox-LDL-induced PAI-1 mRNA expression. Cotransfection of phosphorothioate CAGA oligonucleotides with PAI-1 reporter vector also blocked the Ox-LDL-induced PAI-1 promoter activity.

CONCLUSION

These results suggest that Ox-LDL activates TGF-beta/Smad signaling to stimulate PAI-1 transcription in human mesangial cells. Thus, progression of glomerular disease may be promoted by PAI-1 up-regulation in human mesangial cells mediated by the Ox-LDL-induced TGF-beta/Smad signaling pathways.

Glomerular plasmin-like activity in relation to nephritis-associated plasmin receptor in acute poststreptococcal glomerulonephritis

A nephritogenic antigen for acute poststreptococcal glomerulonephritis (APSGN) was isolated recently from group A streptococcus and termed nephritis-associated plasmin receptor (NAPlr). In vitro experimental data indicate that the pathogenic role of NAPlr occurs through its ability to bind to plasmin and maintain its proteolytic activity. However, the mechanism whereby this antigen induces glomerular damage in vivo has not been fully elucidated. Renal biopsy tissues from 17 patients with APSGN, 8 patients with rapidly progressive glomerulonephritis, and 10 normal kidneys were analyzed in this study. Plasmin-like activity was assessed on cryostat sections by in situ zymography with a plasmin-sensitive synthetic substrate. Serial sections were simultaneously assessed for NAPlr deposition by immunofluorescence staining. Glomerular plasmin-like activity was absent or weak in normal controls and in patients with rapidly progressive glomerulonephritis, although tubulointerstitial activity was occasionally detected. Prominent glomerular plasmin-like activity was found in patients who had APSGN and in whom glomerular NAPlr was positive, whereas it was absent or weak in patients who had APSGN and in whom glomerular NAPlr was negative. The distribution of glomerular plasmin-like activity was identical to that of NAPlr deposition but was generally different from that of fibrin(ogen) deposition as assessed by double staining. The activity was abolished by the addition of aprotinin to the reaction mixture but was not altered by the addition of a matrix metalloprotease inhibitor, a cysteine protease inhibitor, or inhibitors of plasminogen activators. Thus, upregulated glomerular plasmin-like activity in relation to NAPlr deposition in APSGN was identified. This result supports the nephritogenic character of NAPlr and offers insight into the mechanism whereby this antigen induces nephritis.

Glycated albumin activates PAI-1 transcription through Smad DNA binding sites in mesangial cells

Amadori-modified glycated albumin stimulates extracellular matrix and transforming growth factor-β (TGF-β) expression in cultured mesangial cells. Smad proteins transduce the TGF-β-mediated signal, and Smad-binding CAGA sequences are present in the plasminogen activator inhibitor-1 (PAI-1) promoter. This study examined whether glycated albumin induces PAI-1 transcription in human mesangial cells (HMC) through Smad-binding sites in the PAI-1 promoter. Quiescent HMC were exposed to 200 μg/ml bovine serum albumin (BSA) or glycated BSA (Gly-BSA) for 12–72 h. At 24 h, Gly-BSA stimulated TGF-β1and PAI-1 mRNA expression in HMC to 1.8 and 3.2 times that in the BSA-treated control cells. Gly-BSA also activated the PAI-1 promoter luciferase activity 2.3-fold. Gly-BSA-treated cells enhanced Smad2 and Smad3 protein levels 2.5 times the control levels in the nuclei. An electrophoretic mobility shift assay performed using CAGA sequences as a probe showed that Gly-BSA increased DNA/protein complexes. When nuclear extracts were preincubated with 100-fold molar excess of unlabeled CAGA oligonucleotide, the formation of complex was prevented. The DNA-binding protein was shown to be Smad3 by antibody supershift. Transfection of phosphorothioate CAGA oligonucleotide, a CAGA antisense analog, inhibited Gly-BSA-induced PAI-1 mRNA expression. Cotransfection of phosphorothioate CAGA oligonucleotides with PAI-1 reporter vector also blocked Gly-BSA-induced PAI-1 promoter luciferase activity. These results indicate that Gly-BSA increases DNA binding activity of Smad3 and that it stimulates PAI-1 transcription through Smad-binding CAGA sequences in the PAI-1 promoter in HMC. Thus progression of diabetic nephropathy may be promoted by PAI-1 upregulation mediated by the glycated albumin-induced Smad/DNA interactions.

Expression of urokinase plasminogen activator and its receptor during acute renal allograft rejection

BACKGROUND

In inflammation, urokinase plasminogen activator (uPA) and its receptor (uPAR) play an important role in fibrinolysis and in activation and chemotaxis of neutrophils and lymphocytes. Moreover, the uPA/uPAR system is involved in processes that affect turnover of the extracellular matrix (ECM). The aim of this study was to determine the local and systemic release of uPAR, and the expression of uPA and uPAR in renal tissues during acute renal allograft rejection.

METHODS

Blood, urine, and tissue samples were collected from 33 patients diagnosed with acute allograft rejection and from 14 transplant patients without rejection. From 10 healthy volunteers, blood and urine were collected as a control. In urine and blood samples, the levels of uPAR were determined by enzyme-linked immunosorbent assay (ELISA). Immunostaining and in situ hybridization for uPA and uPAR were performed on renal biopsies.

RESULTS

uPAR was detectable at low levels in serum and urine of healthy volunteers and was increased in nonrejecting allograft recipients. Serum and urine levels of uPAR were higher in transplant recipients with rejection compared to nonrejectors. The urine and serum levels of uPAR correlated with the renal function. Immunostaining and in situ hybridization showed an up-regulation of both uPA and uPAR in rejection biopsies. Nonrejected grafts displayed no expression of uPA and uPAR by immunostaining, or of uPAR by in situ hybridization. uPA was detected in a limited number of tubular epithelial cells by in situ hybridization. During rejection, lymphocytes as well as tubular epithelial cells showed uPA and uPAR expression. In the vascular types of rejection, strong expression of uPA was also seen in the entire vessel wall, while uPAR was expressed by the endothelium.

CONCLUSION

This study shows that (1) uPA and uPAR are up-regulated during acute renal allograft rejection; (2) uPAR levels in urine and serum correlate with serum creatinine levels, and (3) uPA and uPAR are produced by inflammatory cells, tubular epithelium, and vascular endothelium during acute renal allograft rejection.

Biphasic regulation of plasminogen activator/inhibitor by LDL in mesangial cells

Lipid abnormalities and dysregulation of the plasminogen activator (PA)/plasmin system may be involved in the development of glomerulosclerosis. We investigated the effects of low-density lipoprotein (LDL) on PA inhibitor-1 (PAI-1), urokinase-type PA (uPA), and tissue-type PA (tPA) in relationship to protein kinase C (PKC) in cultured human mesangial cells (HMC). LDL (200 microg/ml) induced two peaks of PKC activation at hours 0.25 and 6, with translocation of PKC-alpha, -beta(1), and -delta from cytosol to the membrane. The second increase in PKC activity gradually decreased to the control value by hour 18. LDL downregulated 2.4-kb PAI-1, uPA, and tPA mRNA expression within 6 h of incubation with HMC. On the other hand, after 12-48 h, LDL-treated cells showed a significant increase in PAI-1, tPA, and uPA mRNA levels. LDL induced up to a twofold increase in PAI-1 antigen levels in the extracellular matrix of HMC after 24-48 h as well as increased PA inhibitory activity in the culture medium. Analysis of the adhesion plaques from cells incubated with LDL for 48 h by zymography showed increased intensity of lysis near molecular weights of approximately 55,000 and 100,000. LDL slightly increased tPA release at hours 24 and 48 but did not increase PA activity in culture medium. The stimulatory effects of LDL on PAI-1, tPA, and uPA gene regulation in HMC were blocked by the inhibition of PKC using GF-109203X 12 h after treatment with LDL or downregulation of PKC using phorbol myristate acetate. In summary, LDL regulates PAI-1, uPA, and tPA in biphasic patterns in HMC, and the upregulation of PAI-1, uPA, and tPA after long-term LDL exposure seems to be mediated by a delayed PKC activation associated with an increased PA inhibitory activity. These results suggest that LDL, after prolonged incubations with HMC, causes a PA/inhibitor imbalance favoring accumulation of matrix.