Raffaella Monno

MONOCYTE CHEMOTACTIC PEPTIDE-1 EXPRESSION AND MONOCYTE INFILTRATION IN ACUTE RENAL TRANSPLANT REJECTION

Mononuclear cell infiltration is a common histopathological feature of acute renal transplant rejection, in which it seems to play a key role in the pathogenesis of tubulointerstitial lesions. Monocyte chemotactic peptide-1 (MCP-1) is a specific chemotactic and activating factor for monocytes. Thus, the present study was aimed at evaluating MCP-1 gene and protein expression in renal biopsies of kidney transplant recipients with acute deterioration of graft function, and to correlate it with the extent of monocyte infiltration. We studied 20 kidney transplant recipients with acute graft dysfunction (13 with acute rejection, seven with acute tubular damage). MCP-1 gene and protein expression were analyzed by in situ hybridization and immunohistochemistry, respectively. CD68-positive cells were identified as monocytes. CD68-positive cell number and MCP-1 expression were quantified by a computerized image analysis system. MCP-1 gene expression, undetectable in normal human kidneys, was strikingly increased in patients with acute rejection. The chemokine localized mainly to the proximal tubular cells and to mononuclear-infiltrating cells. In patients with acute tubular damage, the MCP-1 expression, even if higher than in controls, was significantly lower than in acute rejection. The expression of the chemokine strictly correlated with the number of infiltrating monocytes (r=0.87, P<0.05). Moreover, we measured MCP-1 urinary excretion by ELISA, in eight normal subjects (36+/-16 pg/mg urine creatinine), in 13 clinically stable transplant recipients (33+/-9 pg/mg, ns vs. normal patients), in 12 transplant recipients with acute rejection (250+/-46 pg/mg, P<0.01 vs. normal patients), and in five transplant recipients with acute tubular damage (97+/-33 pg/mg, P<0.05 vs. controls and patients with acute rejection). Urinary MCP-1 excretion directly correlated with renal MCP-1 gene expression (r=0.65, P=0.05). Finally, we observed a significant reduction in MCP-1 urine levels in patients with acute rejection, who responded to the antirejection treatment. In conclusion, our data suggest that MCP-1 may play a critical role in modulating monocyte influx and consequent tubulointerstitial damage in acute rejection. Therefore, an increase in urinary MCP-1 excretion may represent an early signal of ongoing acute graft rejection.

Protease-Activated Receptor-2 Expression in IgA Nephropathy: A Potential Role in the Pathogenesis of Interstitial Fibrosis

An increasing body of evidence suggests that proteases may play a key role in the pathogenesis of tissue fibrosis. Protease-activated receptor-2 (PAR-2) is cleaved and activated by trypsin-like proteolytic enzymes, including tryptase and activated coagulation factor X (FXa). Both these soluble mediators have been demonstrated, directly or indirectly, at the interstitial level in progressive renal diseases, including IgA nephropathy (IgAN). PAR-2 mRNA and protein levels were investigated by RT-PCR and immunohistochemistry, respectively, in 17 biopsies from IgAN patients and 10 normal kidneys. PAR-2 expression was also evaluated, by RT-PCR and western blotting, in cultured human mesangial and proximal tubular cells. Finally, gene expression of plasminogen activator inhibitor-1 (PAI-1) and TGF-beta, two powerful fibrogenic factors, was evaluated in FXa-, trypsin-, and PAR-2 activating peptide-stimulated human proximal tubular cells by Northern blot. In normal kidneys, PAR-2 gene expression was barely detectable, whereas in IgAN biopsies the mRNA levels for this protease receptor were strikingly increased and directly correlated with the extent of interstitial fibrosis. Immunohistochemical staining demonstrated that PAR-2 protein expression in IgAN biopsies was mainly localized in the proximal tubuli and within the interstitial infiltrate. Proximal tubular cells in culture expressed PAR-2. Activation of this receptor by FXa in tubular cells induced a striking increase in intracellular calcium concentration. In addition, incubation of both cell lines with trypsin, FXa, or PAR-2 activating peptide caused a marked upregulation of PAI-1 gene expression that was not counterbalanced by an increased expression of plasminogen activators. Finally, PAR-2 activation induced a significant upregulation of TGF-beta gene and protein expression in both mesangial and tubular cells. On the basis of our data, we can suggest that PAR-2 expressed by renal resident cells and activated by either mast cell tryptase or FXa may induce extracellular matrix deposition modifying the PAI-1/PA balance and inducing TGF-beta expression. These molecular mechanisms may underlie interstitial fibrosis in IgAN.

Protease-activated receptor 1 and plasminogen activator inhibitor 1 expression in chronic allograft nephropathy : The role of coagulation and fibrinolysis in renal graft fibrosis

BACKGROUND Chronic allograft nephropathy (CAN), the major cause of renal graft failure, frequently displays extensive interstitial fibrin deposition. Little is known in regard to the cause of the altered coagulation/fibrinolysis balance and its relevance in the pathogenesis of CAN. Thrombin, present within the fibrin clots, can interact with a specific receptor, protease-activated receptor 1 (PAR-1), and modulate a variety of cell functions. On the other hand, the derangement of the fibrinolytic system may directly affect extracellular matrix (ECM) degradation. METHODS In the present study, we investigated, by in situ hybridization, PAR-1 gene expression and the mRNA levels for tissue factor and plasminogen activator inhibitor 1 (PAI-1), two key regulatory molecules of coagulation and fibrinolysis, in 16 CAN biopsies and in 10 normal human kidney grafts. The thrombin-induced transforming growth factor beta (TGF-beta) gene and protein expression in proximal tubular cells (PTC) was investigated by Northern blotting and ELISA, respectively. RESULTS Fibrin deposits, absent in normal grafts, were observed in the interstitial space and arterial wall of CAN. Tissue factor gene expression was not increased either at the vascular or at the interstitial level in CAN. On the contrary, PAI-1 gene expression, barely detectable in control tissue, was strikingly increased in CAN, with a distribution resembling the pattern of fibrin deposition. Note that PAI-1 gene expression was directly correlated with the degree of interstitial fibrosis. In addition, fibrin deposits were strictly associated with a marked increase of PAR-1 gene expression in endothelial cells and PTC. The tubular expression of PAR-1 was significantly higher in Banff grade II-III than in grade I. In vitro, incubation of PTC with thrombin caused a significant up-regulation of TGF-beta gene expression, followed by an increased TGF-beta release into the supernatant. Interestingly, urine from CAN patients contained significantly higher levels of TGF-beta. CONCLUSIONS Fibrin deposits in CAN may result from the increased expression of PAI-1 and the subsequent inhibition of fibrinolysis. The reduced fibrinolysis may cause, in turn, a decreased ECM turnover. Finally, thrombin, preserved in the active form within the fibrin clots, may interact with PAR-1 highly expressed on PTC and induce an up-regulation of ECM deposition in a TGF-beta-dependent manner.

Tissue factor, plasminogen activator inhibitor-1, and thrombin receptor expression in human crescentic glomerulonephritis

Glomerular fibrin deposition is a common histological feature of crescentic glomerulonephritis (CGN). Tissue factor (TF) is the most powerful activator of the coagulation system, whereas plasminogen activator inhibitor (PAI)-1 is a key modulator of the fibrinolytic pathway. Thrombin, released locally as the final step of the coagulation cascade and trapped within the fibrin clots, can induce the activation of glomerular cells, through the interaction with a specific receptor. To investigate the mechanisms underlying coagulation cascade activation and fibrin deposition and the role of this phenomenon in the pathogenesis of human CGN, TF, PAI-1, and thrombin receptor expression were studied in CGN biopsy specimens. Glomerular TF gene and protein expression were strikingly increased in CGN, in particular within the crescents and in the mesangial area, with the same distribution of fibrin deposits. Interestingly, very few infiltrating mononuclear cells were stained in TF immunohistochemistry. To better evaluate the involvement of monocytes in TF expression, TF mRNA and CD68 protein were studied by an in situ hybridization/immunohistochemistry combined technique. Only 16% of the cells expressing TF mRNA were CD68 positive. However, most of the TF signal was localized in the proximity of monocytes, suggesting that soluble mediator(s) released by these cells could induce TF expression. Indeed, interleukin-1 (IL-1), one of the main monocyte-derived cytokines, upregulated TF mRNA levels in cultured human mesangial cells in a time-dependent manner. Moreover, a striking increase in IL-1 expression was present within the cellular crescents in CGN biopsy specimens. Finally, we observed a marked upregulation of both PAI-1 and thrombin receptor mRNA levels in CGN with a pattern resembling TF and fibrin distribution. Surprisingly, thrombin receptor protein expression was strikingly downregulated in CGN, suggesting its continuous activation and degradation. In conclusion, we can hypothesize that TF and PAI-1, mainly expressed by resident cells, may play a pivotal role in the development and preservation of fibrin deposits in CGN. In addition, thrombin, released locally and accumulated within the fibrin clots, may represent a pathogenetic mediator of crescentic lesions.

Ramipril Inhibits in vitro Human Mesangial Cell Proliferation and Platelet-Derived Growth Factor Expression

Angiotensin-converting enzyme (ACE) inhibitors are antihypertensive drugs that have been shown to reduce proteinuria and to slow down the progression of renal function deterioration in different models of chronic glomerular disease. Major pathogenetic features of progressive glomerular injury leading to glomerulosclerosis are mesangial cell proliferation and platelet-derived growth factor (PDGF) expression. The aim of the present study was to evaluate the effect of ramipril, an ACE inhibitor, on these two potential therapeutic targets. Thus, the effect of ramipril on DNA synthesis, cell proliferation and PDGF A and B chain gene expression in fetal calf serum (FCS)-activated cultured human glomerular mesangial cells was investigated. DNA synthesis was evaluated by tritiated thymidine incorporation, cell proliferation by direct cell counting and cell viability by 3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyltetrazolium bromide (MTT). PDGF A and B chain gene expressions were studied by Northern blot and RT-PCR, respectively. In a dose-dependent manner ramipril inhibited the FCS-induced DNA synthesis and cell proliferation. This effect was not dependent upon a toxic effect as demonstrated by MTT. The antiproliferative effect of ramipril was most likely independent of its ability to inhibit ACE present in the FCS and/or expressed by the cells, since a synthetic peptide that specifically inhibits ACE, at the same molar concentrations, did not inhibit FCS-stimulated DNA synthesis. Moreover, ramipril significantly reduced FCS-induced PDGF A and B chain gene expression. Finally, ramipril completely abolished the PDGF A and B chain gene expression induced by phorbol 12-myristate 13-acetate, a specific protein kinase C activator, suggesting a site of action downstream of this enzyme in the mitogenic signal transduction pathway. Our study would suggest that the modulatory action of ramipril on activated mesangial cell proliferation and PDGF expression is independent of its ability to inhibit ACE and could represent an additional mechanism in the renal protective effects of this drug.

Cytokine, chemokine and growth factor expression in the pathogenesis of progressive renal damage

Summary: Chronic renal diseases are untreatable conditions characterized by a final phase of progressive impairment of renal function, leading to end‐stage renal failure (ESRF). Once the primary injury has damaged a part of the nephron, the remainder undergo a number of adaptative changes leading to glomerulosclerosis, interstitial fibrosis and, consequently, end‐stage kidney disease. Glomerular lesions, mainly represented by mesangial cell proliferation, mononuclear cell infiltration and extracellular matrix deposition, have always been considered as the key factors in the progression of renal damage. However, in this context, it is now clear that the degree of tubulointerstitial damage is a better prognostic marker than the extent of glomerular lesions. Tubulointerstitial involvement is characterized by monocyte and neutrophil infiltration, tubular atrophy, proliferation of interstitial fibroblasts, that acquire a myofibroblast‐like phenotype and, finally, extracellular matrix deposition. the pathogenesis of these histological changes is largely unknown, but there is an increasing body of evidence suggesting the possible involvement of some soluble factors produced and released locally, such as cytokines, chemokines and growth factors. Aiming to elucidate the pathogenetic mechanisms underlying glomerular and tubulointerstitial damage in progressive renal diseases, we investigated the renal gene and protein expression of some of these soluble factors. On the basis of the histopathological lesions, we decided to focus our attention on monocyte chemotactic peptide‐1 (MCP‐1), a specific chemotactic and activating factor for monocytes, on complement C3, a powerful activator of neutrophils, on epidermal growth factor (EGF), the physiological modulator of tubular cell growth, on platelet‐derived growth factor (PDGF), the most powerful mitogenic and activating peptide for mesenchymal cells and on transforming growth factor‐β (TGF‐β), the main regulator of extracellular matrix synthesis and degradation.