Interleukin-13 modulates collagen homeostasis in human skin and keloid fibroblasts

Interleukin (IL)-13 has been implicated in the pathogenesis of various diseases characterized by fibrosis. We describe the effects of IL-13 on collagen homeostasis from normal (NF) and keloid (KF) fibroblasts and compare these effects with those of IL-4 and transforming growth factor (TGF)-beta(1). Total collagen generation was up-regulated in NF after 48 h of stimulation by IL-13; in KF, IL-13 stimulated a more rapid collagen response. The kinetics and magnitude of collagen generation induced by IL-13 were equivalent to those induced by similar concentrations of IL-4 and TGF-beta(1). Collagen type I production paralleled total collagen generation from both NF and KF; however, IL-4-induced collagen type I and total collagen production from KF was more transient than that induced by either IL-13 or TGF-beta(1). Procollagen 1alpha1 gene expression was induced in KF by stimulation with IL-13 for 24 h. Moreover, IL-13 was unique among these three cytokines in its ability to induce gene expression for procollagen 3alpha1. Finally, IL-13 inhibited IL-1beta-induced matrix metalloproteinase (MMP)-1 and MMP-3 production and enhanced tissue inhibitor of metalloproteinase (TIMP)-1 generation from NF; although similar effects were observed with IL-4, TGF-beta(1) transiently enhanced MMP-1 and MMP-3 generation without effecting TIMP-1. In KF, IL-13 and IL-4 inhibited MMP-3, whereas TGF-beta(1) enhanced MMP-3; TIMP-1 was unaffected by any of the three cytokines. These data demonstrate both the profibrotic effects of IL-13 on collagen homeostasis and the potential differential regulation of collagen homeostasis in fibroblast subtypes by IL-13.     

螺内酯对肝星状细胞表达基质金属蛋白酶及其抑制剂的影响

目的研究螺内酯干预肝星状细胞（HSCs）后基质金属蛋白酶2（MMP-2）、MMP-9、MMP-13和其组织抑制剂1（TIMP-1）的变化。探讨螺内酯对胶原代谢影响的机制。方法应用不同浓度螺内酯（1×10^-4）mol／L-（1×10^-7）mol／L干预HSCs 48小时,采用反转录-聚合酶链反应（RT-PCR）方法检测MMP-2、MMP-9、MMP-13 mRNA和TIMP-1 mRNA的表达。结果①螺内酯组的MMP-13基因表达强度上调,螺内酯（1×10^-4）mol／L-（1×10^-5）mol／L浓度组MMP-13基因表达强度（0．91±0．13、0．80±0．01、0．67±0．15）均明显高于对照组（0．53±0．10）（P〈0．01）。1×10^-4mol／L浓度组MMP-13基因表达强度接近对照组的2倍。②螺内酯干预HSCs48小时后,TIMP-1基因表达减少,螺内酯（1×10^-4）mol／L-（1×10^-6）mol／L浓度组（0．15±0．05、0．28±0．15、0．37±0．03）明显低于对照组（0．47±0．04）（P〈0．01或〈0．05）。③螺内酯不同浓度干预HSCs 48小时后,HSCs MMP-2、MMP-9基因表达无明显变化（P〉0．05）。结论螺内酯可抑制HSCs TIMP-1基因的表达,增加间质胶原酶MMP-13 mRNA的含量。螺内酯可能通过对MMPs及TIMP-1影响而促进胶原降解。     

A farnesoid x receptor-small heterodimer partner regulatory cascade modulates tissue metalloproteinase inhibitor-1 and matrix metalloprotease expression in hepatic stellate cells and promotes resolution of liver fibrosis

The farnesoid X receptor (FXR) is expressed by and regulates hepatic stellate cells (HSCs). In the present study, we investigated whether 6-ethyl chenodeoxycholic acid (6-ECDCA or INT-747), a semisynthetic derivative of chenodeoxycholic acid (CDCA), modulates tissue metalloproteinase inhibitor (TIMP)-1 and matrix metalloprotease (MMP)-2 expression/activity in HSCs and in the liver of rats rendered cirrhotic by 4-week administration of CCl(4). Exposure of HSCs to FXR ligands increases small heterodimer partner (SHP) mRNA by 3-fold and reduces basal and thrombin-stimulated expression of alpha1(I)collagen, alpha-smooth muscle actin (alpha-SMA), TIMP-1, and TIMP-2 by approximately 60 to 70%, whereas it increased matrix metalloprotease (MMP)-2 activity by 2-fold. In coimmunoprecipitation, electromobility shift, and transactivation experiments, FXR activation/overexpression caused a SHP-dependent inhibition of JunD binding to its consensus element in the TIMP-1 promoter. Inhibition of TIMP-1 expression by SHP overexpression enhanced the sensitivity of HSCs to proapoptogenic stimuli. Administration of 3 mg/kg 6-ECDCA, but not 15 mg/kg ursodeoxycholic acid, resulted in early (3-5-day) induction of SHP and prevention of early up-regulation of TIMP-1 mRNA induced by CCl(4). In the prevention protocol, 4-week administration of 6-ECDCA reduced alpha1(I)collagen, alpha-SMA, and TIMP-1 mRNA by 60 to 80%, whereas it increased MMP-2 activity by 5-fold. In the resolution protocol, administration of 3 mg/kg 6-ECDCA promoted liver fibrosis resolution and increased the apoptosis of nonparenchyma liver cells. By demonstrating that a FXR-SHP regulatory cascade promotes the development of a quiescent phenotype and increases apoptosis of HSCs, this study establishes that FXR ligands may be beneficial in treatment of liver fibrosis.     

Myocardial fibrosis in transforming growth factor-beta(1) (TGF-beta(1)) transgenic mice is associated with inhibition of interstitial collagenase

BACKGROUND: TGF-beta(1) mediates effects on fibroblast proliferation and collagen synthesis in the myocardium. The extracellular matrix remodeling depends on the fibrillar collagen degrading matrix metalloproteinases (MMPs) and their inhibitors (TIMPs). The in vivo effects of TGF-beta(1) on the MMP/TIMP system in TGF-beta(1) overexpressing transgenic mice were studied. METHODS: Male Alb/TGF-beta(1)(cys(223,225)ser) transgenic mice (TG) and nontransgenic controls (C; 8 weeks) were examined. Protein expression of collagen type I, -III, interstitial collagenase (Int Coll), MMP-2, -9, TIMP-1, -2, -4 and TGF-beta(1) as well as enzyme activity (MMP-2, -9) were measured (Western blots, zymographic assays). mRNA expression of the interstitial collagenase and MMP-9 was studied with the Light-Cycler based real-time PCR. RESULTS: Overexpression of TGF-beta(1) resulted in a 10-fold increase in plasma and a seven-fold increase in myocardial TGF-beta(1) concentrations. Relative heart weights increased (mg g(-1): 7.8 +/- 0.4 vs. 4.8 +/- 0.6, n = 6; P < 0.01) in TG compared to C. Collagen type I and III increased in TG (1.9-fold and 1.7-fold) compared to controls. Interstitial collagenase protein activity (- 91%) and mRNA expression (-75%) in TG were reduced (P < 0.05-P < 0.001). Gelatinase (MMP-2, MMP-9) expression and activity were not significantly alterated. MMP-inhibitors were increased 2.5-fold (TIMP-1, -4) and 6-fold (TIMP-2) in TG. CONCLUSIONS: TGF-beta(1) produces myocardial fibrosis in vivo. This effect is not only produced by a stimulation of matrix protein formation: a complex regulation of MMP and TIMP interaction, namely decrease of expression and activity of interstitial collagenase and an enhanced inhibition by increased levels of TIMPs, are involved. These mechanisms are optional targets for therapeutic interventions in myocardial diseases.     

α2-Macroglobulin reduces paracrine- and autocrine-stimulated matrix synthesis of cultured rat hepatic stellate cells

BACKGROUND: Transforming growth factor beta1 (TGF-beta1) is considered to represent a major fibrogenic mediator in the liver. The aim of the present study was to investigate whether alpha2-macroglobulin (alpha2M) might reduce paracrine- and autocrine-stimulated matrix synthesis of cultured rat hepatic stellate cells (HSCs) by scavenging TGF-beta. METHODS AND RESULTS: Using native agarose electrophoresis, we demonstrated that alpha2M binds [125I]-TGF-beta1 within minutes. Preincubation of transiently acidified supernatants of cultured Kupffer cells, secondary cultured (activated) HSC and platelet lysate with, respectively, 500 and 2000 microg mL-1 alpha2M significantly reduced the concentration of active TGF-beta1 in these media. As a consequence of TGF-beta scavenging by alpha2M, paracrine-stimulated proteoglycan synthesis of primary cultured HSCs was reduced significantly. Furthermore, addition of 200 microg mL-1 alpha2M to passaged (activated) HSCs resulted in (a) a reduction in autocrine-stimulated extracellular matrix synthesis (proteoglycan -52%, fibronectin -55%) and (b) increased cell proliferation. A similar reduction in matrix synthesis was observed after the addition of 5 micromol L-1 TGF-beta1 antisense oligonucleotide to activated HSCs. CONCLUSION: We conclude that alpha2M reduces paracrine-and autocrine-stimulated extracellular matrix synthesis of cultured HSCs by scavenging TGF-beta. These mechanisms might restrict liver fibrogenesis.     

Effect of cyclosporin A on human gingival fibroblast collagen turnover in relation to the development of gingival overgrowth: an in vitro study.

In a significant number of cases (25-81%) immunosuppressant treatment with cyclosporin A (CsA) is associated with gingival overgrowth, seriously interfering with the functions of mastication and speech. In CsA-induced gingival enlargement, quantitative modifications of the extracellular matrix components occur, and collagen (COL) metabolism and matrix metalloproteinases (MMPs) have been suggested as being the main targets. Since the mechanisms at the basis of CsA-induced gingival overgrowth are not yet completely understood, our aim was to analyze the effect of CsA on COL turnover in cultured human gingival fibroblasts. Cultured human gingival fibroblasts from four healthy volunteers were incubated with CsA (800 ng/ml) or with its vehicle (VH) for variable intervals of time (24, 48, 72 h). Fibroblast morphology was studied by light and electron microscope. Collagen type I (COL-I), MMP-1, MMP-2, TIMP-1 and TGF-beta1 mRNA were determined by RT-PCR; COL-I and MMP-1 by dot blot, and MMP-2 by zymography. Our results evidenced an up-regulation of COL-I and TGF-beta1 gene expression 72 h after CsA treatment. MMP-1, MMP-2 and TIMP-1 mRNA levels are affected but not significantly. Protein analysis revealed COL-I increase at all the considered times and, 72 h after CsA treatment, reduced collagenolytic levels. Our data suggest that COL accumulation during CsA-induced gingival overgrowth may be mainly sustained by an altered COL-I degradation due to decreased MMP-1 activity. However, interindividual differences of collagenase levels after CsA treatment suggest that a genetic predisposition to develop gingival overgrowth may be relevant.     

NADPH oxidase signal transduces angiotensin II in hepatic stellate cells and is critical in hepatic fibrosis

Angiotensin II (Ang II) is a pro-oxidant and fibrogenic cytokine. We investigated the role of NADPH oxidase in Ang II-induced effects in hepatic stellate cells (HSCs), a fibrogenic cell type. Human HSCs express mRNAs of key components of nonphagocytic NADPH oxidase. Ang II phosphorylated p47phox, a regulatory subunit of NADPH oxidase, and induced reactive oxygen species formation via NADPH oxidase activity. Ang II phosphorylated AKT and MAPKs and increased AP-1 DNA binding in a redox-sensitive manner. Ang II stimulated DNA synthesis, cell migration, procollagen alpha1(I) mRNA expression, and secretion of TGF-beta1 and inflammatory cytokines. These effects were attenuated by N-acetylcysteine and diphenylene iodonium, an NADPH oxidase inhibitor. Moreover, Ang II induced upregulation of genes potentially involved in hepatic wound-healing response in a redox-sensitive manner, as assessed by microarray analysis. HSCs isolated from p47phox-/- mice displayed a blunted response to Ang II compared with WT cells. We also assessed the role of NADPH oxidase in experimental liver fibrosis. After bile duct ligation, p47phox-/- mice showed attenuated liver injury and fibrosis compared with WT counterparts. Moreover, expression of smooth muscle alpha-actin and expression of TGF-beta1 were reduced in p47phox-/- mice. Thus, NADPH oxidase mediates the actions of Ang II on HSCs and plays a critical role in liver fibrogenesis.     

Cross-talk between farnesoid-X-receptor (FXR) and peroxisome proliferator-activated receptor gamma contributes to the antifibrotic activity of FXR ligands in rodent models of liver cirrhosis

The nuclear receptors farnesoid X receptor (FXR) and peroxisome proliferator-activated receptor (PPAR)gamma exert counter-regulatory effects on hepatic stellate cells (HSCs) and protect against liver fibrosis development in rodents. Here, we investigated whether FXR ligands regulate PPARgamma expression in HSCs and models of liver fibrosis induced in rats by porcine serum and carbon tetrachloride administration and bile duct ligation. Our results demonstrate that HSCs trans-differentiation associated with suppression of PPARgamma mRNA expression, whereas FXR mRNA was unchanged. Exposure of cells to natural and synthetic ligands of FXR, including 6-ethyl chenodeoxycholic acid (6-ECDCA), a synthetic derivative of chenodeoxycholic acid, reversed this effect and increased PPARgamma mRNA by approximately 40-fold. Submaximally effective concentrations of FXR and PPARgamma ligands were additive in inhibiting alpha1(I) collagen mRNA accumulation induced by transforming growth factor (TGF)beta1. Administration of 6-ECDCA in rats rendered cirrhotic by porcine serum and carbon tetrachloride administration or bile duct ligation reverted down-regulation of PPARgamma mRNA expression in HSCs. Cotreatment with 6-ECDCA potentiates the antifibrotic activity of rosiglitazone, a PPARgamma ligand, in the porcine serum model as measured by morphometric analysis of liver collagen content, hydroxyproline, and liver expression of alpha1(I) collagen mRNA, alpha-smooth muscle actin, fibronectin, TGFbeta1, and tissue inhibitor of metalloprotease 1 and 2, whereas it enhanced the expression of PPARgamma and uncoupling protein 2, a PPARgamma-regulated gene, by 2-fold. In conclusion, by using an in vitro and in vivo approach, we demonstrated that FXR ligands up-regulate PPARgamma mRNA in HSCs and in rodent models of liver fibrosis. A FXR-PPARgamma cascade exerts counter-regulatory effects in HSCs activation.     

丹参单体IH764-3对肝星状细胞胶原代谢的影响及其机制研究

目的 研究丹参单体IH764- 3对H2O2刺激的肝星状细胞(HSCs)胶原合成、膜型基质金属蛋白酶(MT1-MMP)、基质金属蛋白酶2(MMP- 2)及其组织抑制因子(TIMP-2)表达的影响,探讨丹参单体IH76 4-3在调控HSCs胶原代谢中的作用机制.方法 应用体外细胞培养技术,以不同剂量IH764-3干预过氧化氢(H2O2)刺激的HSCs,通过3H脯氨酸(3 H-Pro)掺入法检测HSCs总胶原和I型胶原合成能力,应用Western blot技术检测MT1MMP、MMP-2及TIMP-2蛋白的表达.结果 不同剂量IH764-3(10 μg/ml,20 μg/ml,30 μ/ml,40 μg/ml)作用于H2O2刺激的HSCs 24小时,与单纯H2O2组相比,30 μg/ml组和40 μg/ml组能显著抑制总胶原和I型胶原的合成(P＜0.05),而H2O2组、10 μg/ml组和20 μg/ml组之间差异无统计学意义(P＞0.05).IH764-3干预组与H2O2组相比,能够明显上调MT1-MMP和MMP-2的表达,下调TIMP-2表达,并呈剂量依赖性关系.结论 丹参单体IH764-3可能通过下调TIMP-2、上调MT1-MMP及MMP-2表达调控HSCs胶原代谢.     

血清基质金属蛋白酶13及其抑制因子在绝经后骨质疏松发病中的作用

目的检测基质金属蛋白酶13（MMP．13）和组织金属蛋白酶抑制因子1（TIMP-1）的血清含量,分析其在妇女绝经后骨质疏松发病中的作用。方法2009年3月-2012年9月选取武汉附近地区129例49～63岁绝经后妇女,根据双能x线吸收法检测的骨密度数值,分为正常组、低骨量组和骨质疏松组。采取酶联免疫吸附试验检测MMP-13、TIMP-1以及雌二醇（E2）、I型原胶原N端前肽（PINP）和I型胶原交联C末端肽（CTX）、骨保护蛋白（OPG）及其配体（OPGL）的含量,统计MMP-13／TIMP-1比值。结果①骨质疏松组中血清MMP-13水平[（44．254-1．21）肛班】高于正常组[（27．08±1．41）μg/L】（P〈0．05）;②骨质疏松组中血清MMP-13与骨密度、血清E2、OPGL水平存在明显负相关性（P〈0．05）,和OPG、PINP和CTX存在明显正相关性（P〈0．05）;③低骨量组中MMP．13略高于骨质疏松组,且两者差异无统计学意义（P〉0．05）,但是明显高于正常组（P〈0．05）,同时与骨密度和血清E2、OPG、OPGL、PINP和CTX存在明显相关性（P〈0．05）。结论血清MMP．13和MMP-13／TIMP-1比值与绝经后骨质疏松症妇女和绝经后低骨量组妇女骨代谢指标具有关联性。两者升高可能为绝经后妇女早期骨代谢尤其是胶原代谢过程增快的表现。     

The effect of stress-deprivation and cyclic loading on the TIMP/MMP ratio in tendon cells: An in vitro experimental study

Purpose. To determine the effect of stress deprivation and cyclic loading on TIMP-1/MMP-13 mRNA expression ratio in rat tail tendon (RTT) cells.

Method. Adult RTTs were stress-deprived for 0, 24, 48, or 72 hours in the presence or absence of a MMP inhibitor (ilomastat), or subjected to 1%, 3%, or 6% strain for 24 h under tissue culture conditions. TIMP-1 and MMP-13 (rat interstitial collagenase) mRNA expression were measured using quantitative PCR and TIMP/MMP ratios were calculated for each group.

Results. The ratio of TIMP-1 to MMP-13 in control RTTs was 3.73:1 ± 0.73. Stress deprivation for 24 h significantly decreased the TIMP-1/MMP-13 ratio (0.25:1 ± 0.04) and MMP-13 expression continued to increase significantly with time of stress deprivation. Inhibition of MMP-13 mRNA expression with ilomastat in stress-deprived samples did not alter TIMP-1 expression when compared to normal controls. Cyclic loading significantly increased TIMP-1/MMP-13 expression at all strain levels examined.

Conclusions. RTTs normally have a positive TIMP-1/MMP-13 expression ratio. While cyclic loading increased the TIMP-1/MMP-13 ratio, loss of cellular homeostatic tension inversed this ratio through a significant increase in MMP-13 mRNA expression rather than a decrease in TIMP expression. A negative TIMP/MMP ratio has been implicated in the pathogenesis of tendinopathy. Increasing the TIMP/MMP ratios in these patients through exercise may be beneficial in the management of tendinopathy.     

Dilinoleoylphosphatidylcholine decreases hepatic stellate cell activation

The prevention of cirrhosis in alcohol-fed baboons by the administration of a soybean extract-43% to 50% of which was dilinoleoyl-phosphatidylcholine (DLPC) and 24% of which was 1,palmitoyl 2,linoleoyl-phosphatidylcholine (PLPC)-was associated with a significant reduction in the number of stellate cells transformed to myofibroblast-like cells. To study whether these two major phospholipids affect the similar transformation that occurs by culturing stellate cells on uncoated plastic, we assessed their effects on proliferation (by (methyl-3H)-thymidine incorporation into DNA), expression of alpha-smooth muscle actin and type I procollagen (by densitometry of Western blots), and collagen synthesis (by incorporation of tritiated proline into collagenase-digestible proteins). These manifestations of stellate cell activation were decreased by 10 micromol/L DLPC but not by 10 micromol/L PLPC when compared with controls incubated either with 17 mmol/L ethanol (used as solvent for the phospholipids) or without addition. These agents did not affect cell viability, contamination with other cells, or the capacity of stellate cells to synthesize protein. Thus DLPC specifically decreases the in vitro activation of stellate cells, as judged by the decreases in proliferative activity, alpha-smooth muscle actin and procollagen I expressions, and collagen synthesis, whereas PLPC did not show such effects. alpha-Procollagen (type I) mRNA was not affected by DLPC, suggesting a post-translational effect. The reduction in the activation of hepatic stellate cells by DLPC may be responsible for, or at least contribute to, the prevention of fibrosis by the polyenylphosphatidylcholine mixture administered in vivo.     

Expression and response to angiotensin-converting enzyme inhibition of matrix metalloproteinases 2 and 9 in renal glomerular damage in young transgenic rats with renin-dependent hypertension

Extracellular matrix expansion in the glomerular mesangium contributes to the development of glomerulosclerosis and chronic renal disease in arterial hypertension. Transforming growth factor-beta1 (TGF-beta1), matrix metalloproteinases (MMPs), and tissue inhibitors of MMPs (TIMPs) are involved in this process. Conflicting data are reported on the effects of angiotensin II (Ang II) and the response to angiotensin-converting enzyme inhibition on MMPs and TIMPs in early stages of hypertensive glomerular damage. We therefore investigated the effects of Ang II-dependent hypertension on MMP-2, MMP-9, TIMP-1, and TIMP-2 in isolated glomeruli of 8-week-old homozygous male rats overexpressing the mouse Ren2 gene [TGR(mRen2)27]. At this age, systolic blood pressure was already significantly elevated in Ren2 compared with Sprague-Dawley (SD) rats (197 +/- 38 versus 125 +/- 16 mm Hg, p < 0.01). Ren2 exhibited renal damage as determined by increased urinary albumin excretion, focal glomerulosclerosis, mesangial matrix expansion, and alpha-smooth muscle actin deposition. Quantification of mRNA levels in isolated glomeruli by real-time polymerase chain reaction showed a significant increase of TGF-beta1, a 2.3- and a 2.6-fold increase of MMP-2 and TIMP-1 in Ren2 compared with SD (p < 0.01, respectively) and no strain differences for TIMP-2. In contrast, MMP-9 mRNA expression was markedly suppressed to 10% of control levels in Ren2 (p < 0.01). Early treatment with ramipril completely prevented renal damage in Ren2 and restored mRNA expression of TGF-beta1, MMP-2, and TIMP-1 to SD control levels. Interestingly, down-regulation of MMP-9 mRNA, protein, and activity was not affected by ramipril, indicating that the protective effect of this compound is not attributable to restoration of MMP-9 in the glomerulus.     

Thrombin suppresses matrix metalloproteinase 2 activity and increases tissue inhibitor of metalloproteinase 1 synthesis in cultured human peritoneal mesothelial cells.

OBJECTIVE: Recently, high levels of intraperitoneally generated thrombin were found in the effluent of patients treated with continuous ambulatory peritoneal dialysis (CAPD). The aim of the present study was to investigate in human peritoneal mesothelial cells (HMCs) the effect of thrombin on the activity and synthesis of matrix metalloproteinases (MMPs), which regulate the degradation of basement membrane collagen. METHODS: Cultured HMCs were isolated from omental tissue and used at confluence for the experiments. Conditioned media were obtained by incubating cells with serum-free M199 containing the relevant doses of thrombin. Activity of MMP-2 and MMP-9 were determined by an activity assay system. The antigen levels of MMPs and of the specific tissue inhibitor of metalloproteinases 1 (TIMP-1) were measured by ELISA. Northern blot analysis was applied to analyze mRNA expression of MMP-2 and TIMP-1. RESULTS: Incubation of HMCs with increasing doses of thrombin resulted in a concentration- and time-dependent suppression of MMP-2 activity. No changes in MMP-9 activity were seen. After a 48-hour stimulation period with thrombin (5 U/mL), MMP-2 activity decreased to 53% of that seen in control conditions. Antigen measurements revealed that this decrease was paralleled by a slight reduction in MMP-2 levels, which became significant at a thrombin dose of 5 U/mL [50.65 +/- 7.5 ng/10(5) cells (48 hours, 5 U/mL) vs 64.6 +/- 10.1 ng/10(5) cells (control)]. Under the same conditions, TIMP-1 levels were considerably increased [3.9 +/- 0.46 microg/10(5) cells (48 hours, 5 U/mL) vs 1.2 +/- 0.14 microg/10(5) cells (control)]. Hirudin (10 U/mL) completely inhibited the thrombin-induced effects on MMP-2 and TIMP-1 synthesis. These results were also reflected by Northern blot hybridization, where a slight decrease in MMP-2 and an increase in TIMP-1 mRNA expression were observed in response to thrombin. CONCLUSIONS: Our results suggest that high thrombin levels suppress MMP-2 activity through decreased MMP-2 and increased TIMP-1 synthesis. Thus, thrombin may promote the accumulation of basement membrane collagen. In addition to fibrin formation, this mechanism may represent a further contribution by thrombin to peritoneal thickening during CAPD.