Relationship between plasminogen activator inhibitor-1 gene alterations and fibrosis in peritoneal dialysis patients

Peritoneal fibrosis (PF) is a pathological change that occurs mostly long-term peritoneal dialysis (PD) patients, as a result of triggering the inflammatory response. Plasminogen activator inhibitor-1 (PAI-1) is an important molecule featured in the development of fibrosis. It has been shown in literature that PAI-1 gene alterations are associated with fibrosis in many tissues and organs. However, PAI-1 gene alterations in long-term PD patients have not yet been investigated. In this study, PAI-1 4G/5G polymorphism was examined by reverse hybridization, and all coding exons of the PAI-1 gene were examined by sequence analysis to provide treatment modification in patients with predisposition before fibrosis develops. The patients were divided into two groups according to ultrafiltration failure test and duration of PD treatment: those with suspected PF or a high probability of developing PF (36%) and those with a low probability of developing PF (64%). There was no significant difference between the two groups in findings such as peritoneal equilibration test (PET), Kt/V, the content of the PD solution used, peritonitis, and PAI-1 4G/5G polymorphism (P > .05). A total of eight gene alterations (rs2227660, rs2227668, rs2854233, rs41281004, rs61553169, rs368413856, rs2227684) were detected by sequence analysis, one of which was exonic (rs6092). When the genotype distributions of these variants were examined, no significant difference was found between the two groups. PAI-1 gene changes were not detected in patients with the probability of developing PF. There is a need for further studies involving other molecules responsible for predisposing to PF with larger patient populations in patients undergoing long-term PD treatment.

Plasminogen activator inhibitor-1 in kidney pathology (Review)

Plasminogen activator inhibitor type-1 (PAI-1) inhibits tissue plasminogen activator (tPA) and urokinase plasminogen activator (uPA), which convert plasminogen to plasmin, a strong proteolytic enzyme. Thus, PAI-1 is a primary and negative regulator of plasmin-driven proteolysis. In addition to its main role as an inhibitor of fibrinolysis, PAI‑1 has been implicated as a mediator in other processes, including fibrosis, rheumatoid arthritis, atherosclerosis, tumor angiogenesis and bacterial infections. It also significantly modulates cellular adhesion or migration, wound healing, angiogenesis and tumor cell metastasis. However, in the present study, we have reviewed the literature in relation to different kidney diseases where PAI-1 regulates fibrinolysis and acts independently of proteolysis. PAI-1 is normally produced in trace amounts in healthy kidneys but is synthesized in a wide variety of both acute and chronic diseased kidneys. We reviewed the role of PAI-1 in diabetic kidney nephropathy, chronic kidney disease, hemodialysis, peritoneal dialysis and in kidney transplantation. Increased PAI-1 expression results in accumulation of extracellular matrix (ECM) leading to numerous kidney diseases. Predisposition to some diseases is due to the genetic role of PAI-1 in their development. A number of studies demonstrated that the inhibition of PAI-1 activity or therapy with a mutant PAI-1 increases matrix turnover and reduces glomerulosclerosis by competing with endogenous PAI-1. This strongly suggests that PAI-1 is a valid target in the treatment of fibrotic renal disease. However, net proteolytic activity depends on the delicate balance between its negative regulation by PAI-1 and activation by uPA and tPA. Also, plasmin activated by its inhibitors upregulates activity of other enzymes. Thus, assessment of prognosis for the diseased kidney should include a variety of proteolysis regulators and enzymes.

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.

PAI-1 secretion and matrix deposition in human peritoneal mesothelial cell cultures: transcriptional regulation by TGF-beta 1

BACKGROUND

Plasminogen activator inhibitor-1 (PAI-1), the main inhibitor of plasminogen activators in plasma and in peritoneum, impairs plasmin formation that is essential for the repair processes of the mesothelium damaged by peritoneal dialysis fluids and peritonitis. The fibrogenetic cytokine transforming growth factor-beta (TGF-beta) displays variable effects on extracellular matrix remodeling enzymes and their inhibitors depending on tissues and cell lines. We previously found an unexpected stimulating effect of TGF-beta 1 on matrix metalloproteinase-9 in peritoneal mesothelial cells. In this study, we analyzed the effects of TGF-beta 1 on PAI-1 production and deposition in extracellular matrix.

METHODS

We used primary cultured mesothelial cells and a recently established human peritoneal mesothelial cell line (HMrSV5). Cell-associated and secreted plasminogen activators and their inhibitors were detected and characterized by substrate gel zymography. PAI-1 was identified by reverse zymography and by Western blotting, and total PAI-1 was measured by ELISA. Secreted and cell-associated PA activity was measured by its ability to activate plasminogen into plasmin, that is, by the release of paranitroaniline from the plasmin synthetic substrate S-2251. PAI-1 mRNA accumulation was assessed by Northern blot. In vitro nuclear run-on assays were carried out to determine whether TGF-beta 1 had transcriptional effects on PAI-1 expression. Finally, the subcellular distribution of PAI-1 was analyzed by immunofluorescence and by immunogold silver staining.

RESULTS

TGF-beta 1 increased PAI-1 antigen in the conditioned media of HMrSV5 cells, in a time- and concentration-dependent manner. This induced a dramatic decrease of free tPA in the cell medium and of membrane-bound uPA, and a parallel increase of high molecular weight PA-PAI complexes. Consequently, secreted and cell-associated plasminogen activator activities were considerably reduced. In primary cultured peritoneal mesothelial cells, TGF-beta 1 also induced PAI-1 secretion and the shift of tPA toward high molecular weight complexes. TGF-beta 1 increased PAI-1 mRNA in a time- and concentration-dependent manner. This effect was at least in part transcriptional since an approximately threefold increase in the rate of PAI-1 gene transcription was observed in nuclei sampled after a four-hour cell exposure to 5 ng/ml TGF-beta 1. Finally, TGF-beta 1 substantially increased the amount of intracellular and matrix-associated PAI-1.

CONCLUSIONS

These results suggest that excessive TGF-beta 1 stimulated PAI-1 could prevent appropriate peritoneal healing by impairing the degradation of fibrin and of unorganized matrix components, and by interfering with cell migration.