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The Long Pentraxin Ptx3 Is Synthesized in IgA Glomerulonephritis and Activates Mesangial Cells ¹

Benedetta Bussolati^*, Giuseppe Peri, Gennaro Salvidio, Daniela Verzola, Alberto Mantovani and Giovanni Camussi^2,*

^* Cattedra di Nefrologia, Dipartimento di Medicina Interna, Università di Torino and Centro Ricerca Medicina Sperimentale, Ospedale S. Giovanni Battista, Torino, Italy; Dipartimento di Immunologia e Biologia Cellulare, Istituto di Ricerche Farmacologiche Mario Negri, Milan, Italy; and Cattedra di Nefrologia, Dipartimento di Medicina Interna, Università di Genova, Genova, Italy

	Abstract

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The long pentraxin PTX3 has been recently involved in amplification of the inflammatory reactions and regulation of innate immunity. In the present study we evaluated the expression and role of PTX3 in glomerular inflammation. PTX3 expression was investigated in the IgA, type I membranoproliferative, and diffuse proliferative lupus glomerulonephritis, which are characterized by inflammatory and proliferative lesions mainly driven by resident mesangial cells, and in the membranous glomerulonephritis and the focal segmental glomerular sclerosis, where signs of glomerular inflammation are usually absent. We found an intense staining for PTX3 in the expanded mesangial areas of renal biopsies obtained from patients with IgA glomerulonephritis. The pattern of staining was on glomerular mesangial and endothelial cells. Scattered PTX3-positive cells were also detected in glomeruli of type I membranoproliferative glomerulonephritis. The concomitant expression of CD14 suggests an inflammatory origin of these cells. Normal renal tissue and biopsies from patients with the other glomerular nephropathies studied were mainly negative for PTX3 expression in glomeruli. However, PTX3-positive cells were detected in the interstitium of nephropathies showing inflammatory interstitial injury. In vitro, cultured human mesangial cells synthesized PTX3 when stimulated with TNF- and IgA and exhibited specific binding for recombinant PTX3. Moreover, stimulation with exogenous PTX3 promoted mesangial cell contraction and synthesis of the proinflammatory lipid mediator platelet-activating factor. In conclusion, we provide the first evidence that mesangial cells may both produce and be a target for PTX3. The detection of this long pentraxin in the renal tissue of patients with glomerulonephritis suggests its potential role in the modulation of glomerular and tubular injury.

	Introduction

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Primary IgA nephropathy is the most common type of glomerulonephritis (GN)³ and is a principal cause of renal failure worldwide. Typical clinical features include hematuria and proteinuria. IgA GN is defined by granular deposition of IgA and C3 in the glomerular mesangial areas, and it is considered an immune complex-mediated GN. IgA GN is characterized by proliferative changes in the glomerular mesangial cells (MC) and increases in the mesangial matrices. The activation of MC by IgA immune complexes or Abs is considered the initiating event in the pathogenesis of IgA GN (1). In vitro, IgA immune complexes stimulate MC production of proinflammatory mediators, such as chemokines, cytokines, and platelet-activating factor (PAF) (2). These mediators may, in turn, affect MC functions by stimulating cell contraction, proliferation, or matrix production (3), leading to glomerular injury.

Pentraxins are a family of proteins considered to be markers of the acute phase of inflammation, usually characterized by cyclic pentameric structure (4, 5, 6). Short pentraxins are produced in the liver in response to inflammatory mediators (7), and their function includes amplification of innate resistance against microbes, regulation of inflammation, and complement activation (6). PTX3 is the first cloned long pentraxin, structurally related to, but distinct from, C-reactive protein and serum amyloid P component. PTX3 was cloned as an IL-1-inducible gene in endothelial cells and as a TNF-inducible gene in fibroblasts (8). Inflammatory cytokines induce PTX3 expression in a variety of cell types, mainly endothelial cells and mononuclear phagocytes (8, 9, 10, 11, 12). Studies in transgenic mice and gene-targeted mice suggest an important role for PTX3 in the regulation of inflammatory reactions and innate immunity (13, 14, 15) (A. Mantovani, unpublished observations). This is supported by studies showing the ability of PTX3 to bind to the C1q component of the complement cascade (12) and to participate in the clearance of apoptotic cells (16). Moreover, PTX3 is elevated in critically ill patients, with a gradient from systemic inflammatory response syndrome to septic shock (17), and in several other diseases, such as myocardial infarction (18), rheumatoid arthritis (19), atherosclerosis (20), and small vessel vasculitis (21).

The aim of the present study was to investigate whether PTX3 is involved in glomerular inflammation. In particular, we investigated PTX3 expression in two different conditions: GN characterized by inflammatory and proliferative lesions driven by resident MC and/or by infiltrating leukocytes, such as IgA GN, membranoproliferative GN (MPGN), and diffuse proliferative lupus GN, and nonproliferative GN without signs of glomerular inflammation, such as membranous GN and focal segmental glomerular sclerosis (FSGS). Moreover, we investigated the possible effects of recombinant PTX3 on the function of cultured human MC with particular regard to cell contraction, proliferation and synthesis of the proinflammatory lipid mediator PAF.

	Materials and Methods

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Materials

Polymyxin B and BSA fraction V (tested for <1 ng of endotoxin/mg), human factor VIII antiserum, anti-smooth muscle cell myosin mAb, anti-cytokeratin mAb, anti-desmin, and anti-actin mAb were purchased from Sigma-Aldrich (St. Louis, MO). Anti-CD14 IOM2 and Leu M3 mAb were, respectively, from Immunotech (Marseilles, France) and BD Biosciences (Mountain View, CA). Human recombinant TNF-, IL-10, IL-1, human monomeric IgA, and LPS from Escherichia coli (0111:B4) were purchased from Sigma-Aldrich. IL-12 was a gift from G. Trinchieri. Synthetic PAF (1-hexadecyl-2-acetyl-sn-glyceryl-3-phosphorylcholine) was obtained from Bachem Feinchemikalien (Bubendorf, Switzerland). Human PTX3 was purified from CHO cells stably and constitutively expressing the protein as previously described (12).

Subjects

The study included 25 patients presenting IgA GN, 15 patients presenting membranous GN, 8 patients with FSGS. None of the patients had evidence of systemic disease on a clinical or laboratory basis. In addition, biopsies from nine patients with proliferative diffuse GN due to systemic lupus erythematosus (World Health Organization classes IVa and IVb) and from six patients with type I MPGN were studied. The presence of these diseases was confirmed by pathologic evaluation of renal biopsy specimens, such as light microscopy, electron microscopy, and immunofluorescence staining. No patients received steroids or immunosuppressive drugs before renal biopsy. In each instance informed consent was obtained from the donors for the use of tissue samples for experimental purposes. Normal kidney tissue was obtained from an intact pole of kidney removed for a circumscribed tumor (n = 5). These patients were selected for absence of proteinuria and lack of glomerular abnormalities detected by light and immunofluorescence microscopy. For all patients the protein content of 24-h urinary samples was measured by the Pyrogallol Red method. The creatinine concentration in plasma was analyzed by the kinetic Jaffé method with a Synchron CX3 (Beckman, Palo Alto, CA).

Immunofluorescence studies

Immunofluorescence studies were performed on kidney biopsies from the patients described above. The tissues were rapidly frozen in liquid nitrogen, and 2-µm-thick cryostat sections were fixed in 3.5% paraformaldehyde for 15 min and washed in PBS. To block the nonspecific binding, sections were preincubated with human serum (1/10 dilution) for 30 min. The sections were then incubated with anti-PTX3 rat mAbs (MNB4 and MNB6) at a concentration of 1 µg/ml or with the irrelevant rat control serum for 2 h at room temperature, washed in PBS, and incubated with FITC-conjugated sheep anti-rat IgG. The slides were washed, mounted with Vectashield mounting medium (Vector Laboratories, Burlingame, CA), and examined. Control experiments included incubation of sections with nonimmune control Abs or the omission of primary Abs followed by the appropriate labeled secondary Abs. The specificity of anti-PTX Ab was tested by preadsorption of the Ab (10 µg/ml) with purified recombinant PTX3 (30 µg/ml). The number of glomeruli available on each section for analysis of PTX3 expression ranged from three to seven. Three nonsequential sections were examined for each specimen. Fluorescence intensity was evaluated in nonsequential sections to observe at least six glomeruli, and the amount and extent of fluorescence were graded on a scale from 0–3.

Culture of human MC

Human glomeruli were isolated from surgical specimens of kidneys using the method described by Striker et al. (22). The separated cortex was sliced and forced through a graded series of stainless steel meshes, and isolated uncapsulated glomeruli were recovered. MC were obtained from collagenase-treated isolated glomeruli to remove the epithelial cell component. The cells used were characterized by the following criteria (22): 1) morphologic appearance of stellate cells growing in interwoven bundles, 2) uniform fluorescence with FITC-labeled phalloidin specific for filamentous actin, 3) immunofluorescence staining for smooth muscle-type myosin, 4) immunofluorescence staining of extracellular matrix for type IV collagen and fibronectin using monospecific antisera, and 5) negative immunofluorescence staining for HLA-DR and leukocyte common Ag (CD-45) and human factor VIII Ags. In parallel experiments cell viability was monitored by trypan blue and ranged between 88 and 95%. Cells were used between the second and fourth culture passages.

PTX3 assay

Recombinant PTX3 was purified from stably transfected CHO cells as previously described (12). The levels of PTX3 in plasma or culture supernatant were measured by ELISA, based on mAb MNB4 and rabbit antiserum, as previously described (18). For cell culture experiments cells were grown to confluence in 24-well plates, serum-starved overnight, and then stimulated using DMEM containing 0.25% BSA. After 24 h cell supernatants were centrifuged and immediately frozen at -20°C.

Binding of PTX3 to MC

The binding of biotinylated PTX3 to MC was evaluated by cytofluorometric analysis as previously described (16). Cells were challenged with biotinylated PTX3 (range tested, 0.1–500 µg/ml) for 30 min at room temperature. The procedure of biotinylation did not influence the structural or functional integrity of the molecule (16). Cell-bound PTX3 was revealed by flow cytometry after addition of PE-conjugated streptavidin (Pierce, Rockford, IL). The fluorescence background was calculated with PE-conjugated streptavidin only. The specificity of the binding was verified incubating apoptotic cells with biotinylated PTX3 (1 µg/ml) in the presence of the native protein (10- to 1000-fold the biotinylated PTX3).

Purification and quantification of PAF

The effect of PTX3 on PAF production from MC was studied. Cells were equilibrated for 15 min in Tris-buffered Tyrode containing 0.25% delipidized BSA (fraction V) as previously described (23) and then were incubated at 37°C for the indicated time with PTX3 (100 ng/ml). The supernatants and cell pellets were extracted according to a modification of the Bligh and Dyer procedure (24), with formic acid added to lower the pH of the aqueous phase to 3.0. PAF was quantified after extraction and purification by TLC (silica gel plates 60 F254, Merck, Darmstadt, Germany) and HPLC (µPorasil column; Millipore Chromatographic Division, Waters Corp., Milford, MA) by aggregation of washed rabbit platelets as previously reported (23, 25).

Shape change of MC

MC, seeded in small petri dishes (35 mm in diameter) coated with dimethylpolyxiloxane at subconfluent density, in DMEM with 0.25% BSA were kept in an attached, hermetically sealed, NP-2 incubator (Nikon, Melville, NY) at 37°C. Cells were stimulated with PTX3 (100 ng/ml), and cell shape change was studied over a 2-h period under a Nikon Diaphot inverted microscope with a x20 phase-contrast objective as previously described (25). Cell shape change was recorded using a JVC-1CCD video camera. Image analysis was performed with a MicroImage analysis system (Cast Imaging, Venice Italy) and an IBM-compatible system equipped with a video card (Targa 2000; Truevision, Santa Clara, CA). Image analysis was performed by digital saving and comparing of the images before stimulation and then at 5-min intervals for 2 h. The cell planar surface was calculated using MicroImage software (Cast Imaging, Venice, Italy). A reduction of the planar cell surface by >15% was used as a parameter of cell shape change compatible with a cell contraction. Both the number of contracted cells and the mean cell contraction were indicated. Between 10 and 25 cells were analyzed for each experimental condition, and each experiment was repeated at least four times. Values are given as the mean ± SE.

	Results

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Glomerular expression of PTX3

PTX3 expression was investigated by immunofluorescence using two different rat anti-human PTX3 Abs on renal biopsies from patients with IgA (n = 25), type I MPGN (n = 6), diffuse proliferative lupus GN (n = 9), and membranous (n = 15) and FSGS (n = 8) GN. Five normal human renal tissues obtained from kidney nephrectomized for polar renal carcinoma were used as controls. PTX3 was detected (Table I and Fig. 1, A and B) in the mesangium of 22 of 25 IgA GN patients. In some glomeruli the pattern of PTX3 staining was concomitantly endothelial and mesangial (Fig. 1A). In others, a typical intracytoplasmatic mesangial pattern was observed (Fig. 1B). Moreover, PTX3 was expressed on inflammatory cells infiltrating the renal interstitium and on peritubular capillaries (Fig. 1, C and D). Double immunofluorescence staining with anti-CD14 Ab indicated that several of the PTX3-positive cells present in the interstitium were monocytes/macrophages (Fig. 1D, inset), whereas glomerular PTX3-positive cells were negative. In contrast, absence of staining was observed on tubular cells (Fig. 1). The staining pattern obtained with the two different rat anti-PTX3 mAbs used, MNB4 and MNB6, was superimposable. Control normal renal tissue showed only scattered positive cells in glomeruli and negative interstitium (Fig. 1E). In four of six MPGN, several PTX3-positive cells were detected in glomeruli (Table I and Fig. 2A). The majority of these cells were also positive for CD14 staining (Fig. 2B), suggesting their inflammatory origin. In diffuse proliferative lupus GN, PTX3-positive cells were mainly absent in glomeruli despite the intense proliferative and inflammatory reaction. In contrast, both MPGN and diffuse proliferative lupus GN showed an intense infiltration of PTX3-positive cells in the interstitium (Table I). In membranous GN and FSGS, glomeruli were mainly negative, with only rare positive cells detected in the mesangial areas of some glomeruli (Table I). The membranous GN and, in particular, FSGS that exhibited a chronic tubulo-interstitial injury showed intense infiltration of PTX3-positive cells (Table I and Fig. 1F). In contrast, membranous GN and FSGS that did not exhibit tubulo-interstitial damage showed only a few scattered PTX3-positive cells in the interstitium (Table I). Replacement of the primary Ab with an irrelevant rat Ab or preabsorption of the anti-PTX3 Abs with recombinant PTX3 (1 µg/ml) abrogated the staining observed on both glomeruli and interstitium in IgA GN (Fig. 1, G and H).

View larger version (105K): [in this window] [in a new window]   FIGURE 1. Micrographs showing PTX3 expression in renal biopsies. A and B, PTX3 staining is detectable in the glomerular mesangium of IgA GN. Both endothelial (A, arrows) and mesangial (B) patterns of staining were observed. C and D, Inflammatory cells infiltrating the interstitium (C) and peritubular capillaries (D, arrows) were positive for PTX3 in IgA GN, whereas the tubular epithelial cells were negative. Double immunofluorescence staining with PE-labeled anti-CD14 Ab (inset) and with FITC-labeled anti-PTX3 Ab (D, arrowheads) shows cells positive for both CD14 and PTX3. E, Glomerular and tubular structures of normal tissue showed only rare PTX3-positive cells. F, Intense positive staining for PTX3 in the interstitium of a FSGS with tubulo-interstitial damage. The glomerulus was negative. G and H, Preadsorption of the anti-PTX3 Abs with the recombinant protein abolished glomerular (G) and peritubular (H) staining in IgA GN. Magnification: A–D, G, and H, x400; E and F, x150.

View larger version (9K): [in this window] [in a new window]   FIGURE 2. Micrographs showing PTX3 and CD14 coexpression in type I MPGN. A, Detection of PTX3 in some cells within a glomerulus and interstitium by FITC-labeled anti-PTX3 Ab. B, Staining of the same section with PE-labeled anti-CD14 Ab. Magnification, x150.

The expression of PTX3 by MC in IgA GN prompted us to evaluate whether human cultured MC could release PTX3 in their supernatant. Basal PTX3 production, evaluated by ELISA in 12 different primary cell lines, showed a high variability among cell lines, with PTX3 levels ranging from <0.2 to 13.4 ng/5 x 10⁵ cells (mean ± SE, 2.1 ± 1.3; n = 12). No differences among cell passages were observed. TNF- (10 ng/ml) significantly increased PTX3 release (Fig. 3A) after 24-h incubation. Moreover, stimulation with IgA induced a dose-dependent PTX3 release from MC (Fig. 3, A and B). Other stimuli known to induce PTX3 in monocytes, such as LPS and IL-1 (11), were ineffective in inducing PTX3 from MC. Moreover, stimuli specific for MC activation, such as IL-10, IL-12, and angiotensin II (3), did not stimulate PTX3 synthesis (Fig. 3A).

View larger version (17K): [in this window] [in a new window]   FIGURE 3. A, PTX3 release in the supernatant of cultured human MC stimulated for 24 h with vehicle alone (DMEM + 0.25% BSA), TNF- (TNF; 10 ng/ml), IgA (1 µg/ml), LPS (100 ng/ml), IL-1 (40 ng/ml), angiotensin II (AT-II; 10 U/ml), IL-10 (20 ng/ml), and IL-12 (20 ng/ml). Data represent the mean ± SEM of at least three individual experiments performed in triplicate. B, PTX3 release in the supernatant of MC stimulated for 24 h with increasing doses of IgA. Data represent the mean ± SEM of three individual experiments performed in triplicate. ANOVA with Dunnett’s multicomparison test was performed between vehicle and treatment (*, p < 0.05).

To verify the possible role of PTX3 on MC, PTX3 was purified from CHO cells stably and constitutively expressing the protein, and binding to MC was revealed by flow cytometry. Biotinylated PTX3 efficiently bound MC (Fig. 4, A and C). The preincubation of MC with the native molecule (100-fold) inhibited the binding (Fig. 4B), demonstrating its specificity. A linear increase in binding was observed when increasing concentrations of biotinylated PTX3 were used, reaching a plateau at 100 µg/ml (Fig. 4C).

View larger version (12K): [in this window] [in a new window]   FIGURE 4. PTX3 binding to MC. A, MC were incubated with PTX3 (1 µg/ml) as described in Materials and Methods, and binding was revealed by addition of PE-streptavidin (dark line). The background fluorescence is indicated by the filled line. B, PTX3 (1 µg/ml) binding to MC (dark line) is significantly reduced by competitive experiments with recombinant PTX3 (1 mg/ml; filled line). Two experiments were carried out with similar results. In each individual experiment the Kolmogorov-Smirnov statistic analysis between biotinylated PTX3 and biotinylated PTX3 plus recombinant PTX3 was significant (p < 0.05). C, Increasing concentrations of biotinylated PTX3 were added to MC. Results are expressed as the mean fluorescence intensity. Data are representative of one experiment of three with comparable results.

PAF production by PTX3-stimulated MC

PTX3 induced the production of PAF from MC (Fig. 4). Heat inactivation of PTX3 significantly reduced the effect on PAF synthesis, indicating its specificity (Fig. 5). PAF production peaked 30 min after stimulation with 100 ng/ml of PTX3 and was mainly associated to the cell fraction (Fig. 5). Cell viability tested at the end of each experiment by trypan blue dye exclusion test was >90%.

View larger version (16K): [in this window] [in a new window]   FIGURE 5. A, PAF production from 1 x 106 MC stimulated with recombinant PTX3 (100 ng/ml) or heat-inactivated PTX3 (H-I PTX3; 100 ng/ml) for 30 min. ANOVA with Dunnett’s multicomparison test was performed between PTX3 and inactivated PTX3 (*, p < 0.05). B, Time course of PAF synthesis from 1 x 106 MC stimulated with 100 ng/ml PTX3. PAF was detected as cell associated (•) and released in the supernatant (). Data are the mean ± SEM of three individual experiments.

Shape change of MC, compatible with cell contraction, was evaluated as changes in planar surface area in response to different stimuli. PTX3 induced a reduction of the cell planar surface of >15% in 84% of MC (Fig. 6). Fig. 7 is representative of the MC shape change observed after stimulation with PTX3. The change in shape of individual cells occurred at different times (Fig. 7). Heat inactivation of PTX3 abolished its effect on cell shape, indicating its specific effect. The changes in cell shape of MC were reversed by replacement of the stimuli with fresh medium. No significant cell shape change was observed in MC stimulated with vehicle alone.

View larger version (14K): [in this window] [in a new window]   FIGURE 6. Kinetics of change of MC shape after stimulation with 100 ng/ml of PTX3 evaluated using a video-recording system as described in Materials and Methods. Cell retraction is expressed as the reduction of the planar surface evaluated before stimulation. Between 10 and 25 cells were analyzed for each experimental condition, and each experiment was repeated at least four times. Values are given as the mean ± SEM. ANOVA with Dunnett’s multicomparison test was performed between vehicle and PTX3 (*, p < 0.05).

View larger version (63K): [in this window] [in a new window]   FIGURE 7. Micrographs representative of MC, seeded in petri dishes coated with dimethylpolyxiloxane at subconfluent density, in DMEM with 0.25% BSA stimulated with PTX3. Cell shape change was studied over a 2-h period under a Nikon Diaphot inverted microscope with a x20 phase-contrast objective using a JVC-1CCD video camera. The figure shows the morphological changes in MC, consistent with a progressive cell contraction, observed every 30 min after stimulation with PTX3 (magnification, x200).

	Discussion

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PTX3, a recently cloned member of the pentraxin family, has been reported to be mainly expressed by activated endothelial cells and monocytes (8, 10). In vivo, PTX3 expression has been observed in diseased human vessels during small vessel vasculitis (21) and advanced atherosclerosis (20). In the present study we found intense staining of PTX3 in the mesangium of patients with IgA GN. PTX3 was expressed by both glomerular mesangial and endothelial cells. In patients with type I MPGN, several PTX3-positive cells were also detected in glomeruli. At variance with IgA GN, PTX3-positive cells coexpressed CD14, indicating their inflammatory origin. Normal renal tissue and biopsies from patients with other glomerular nephropathies, such as diffuse proliferative lupus GN, membranous GN, and FSGS, were mainly negative for PTX3 expression in glomeruli. These data indicate that mesangial and endothelial glomerular cells are activated to synthesize PTX3 in IgA GN. An increased level of acute phase proteins and, in particular, of C-reactive protein, has recently been reported in IgA GN (26). Indeed, it has been proposed that PTX3 may play the same function in the periphery as C-reactive protein does in the circulation (12, 21). We also found the expression of PTX3 in endothelial cells and in CD14-positive monocytes infiltrating the renal interstitium in IgA GN with tubulo-interstitial injury, indicating that the cells involved in the inflammatory process were activated to synthesize PTX3. However, a double immunofluorescence study suggests that cells other than monocytes and vascular endothelium may contribute to the interstitial expression of PTX3. As it has been shown that PTX3 is a TNF-inducible gene in fibroblasts (8), one can speculate that renal interstitial fibroblasts may synthesize PTX3 in the injured interstitium. The expression by inflammatory interstitial cells and peritubular capillaries was not specifically linked to IgA GN, as it was also detectable in all GN with tubulo-interstitial injury. Of interest is the absence of glomerular PTX3 expression in diffuse proliferative lupus GN despite the presence of inflammatory cells and of IgA-containing immune deposits in glomeruli.

The mesangial detection of PTX3 in IgA GN suggest that MC may contribute, after an appropriate stimulation, to the synthesis of this pentraxin. We therefore investigated the ability of MC to synthesize PTX3 in vitro and the stimuli involved in its production. Human cultured MC synthesized PTX3 in basal conditions and increased PTX3 synthesis when stimulated with IgA or TNF-, a cytokine implicated in IgA GN. Other stimuli known to induce PTX3 synthesis in monocytes, such as IL-1 and LPS (11), as well as other mediators known to activate MC (3) were ineffective, indicating a specific stimulatory pathway for PTX3 synthesis by MC that could be relevant for the pathogenesis of IgA GN.

To further investigate the role of PTX3 in IgA GN, we studied whether PTX3 could bind and activate MC. In particular, we evaluated some cell functions relevant for mesangial physiopathology, such as contraction and synthesis of the proinflammatory mediator PAF. We found that PTX3 bound to MC in a dose-dependent and saturable way. Although we could not identify the receptor involved in PTX3 binding, its specificity was demonstrated by the displacement of biotinylated PTX3 by recombinant PTX3. The exact role of PTX3 in glomerulonephritis remains to be determined. Indeed, to date there has been little functional information about PTX3. We here demonstrated the PTX3 is involved in MC activation. In a time-lapse analysis, the microscopic observation of MC stimulated with PTX3 showed morphological changes in cell shape compatible with cell contraction. The alterations in MC shape observed are similar to those induced by PAF (27) and TNF- (28). The contraction of mesangium is relevant in glomerulonephritides, as it is responsible for a reduction in the glomerular filtration area and may therefore affect the coefficient of filtration (29). In addition, PTX3 enhanced the synthesis by MC of PAF, a mediator of glomerular inflammation and injury (30). PAF favors immune complex deposition in glomeruli and affects glomerular filtration and permeability in several experimental models (31). Indeed, several studies suggested that blockade of PAF receptor may improve renal injury and vascular inflammatory lesions (32, 33, 34). In humans, reduced PAF inactivation due to PAF acetylhydrolase gene mutation has been shown to worsen the course of IgA nephropathy (35).

Recently, PTX3 was shown to enhance tissue factor expression by endothelial cells, suggesting a role in thrombogenesis and ischemic vascular disease (36). Therefore, PTX3 in IgA GN could participate in the activation of both endothelial and MC, and contribute to glomerular inflammation by inducing the production of secondary mediators. A similar mechanism may be involved in tubular interstitial injury associated with different GN. In conclusion, we provide the first evidence that MC may both produce and be a target of PTX3. The detection of this long pentraxin in the renal tissue of patients with GN suggests its potential role in the modulation of glomerular and tubular injury.

	Footnotes

 
¹ This work was supported by the National Research Council (Target Project Biotechnology), Istituto Superiore di Sanità (Target Project AIDS), and MURST Cofin (2001 and ex60%).

² Address correspondence and reprint requests to Dr. Giovanni Camussi, Cattedra di Nefrologia, Dipartimento di Medicina Interna, Ospedale Maggiore S. Giovanni Battista, Corso Dogliotti 14, 10126, Torino, Italy. E-mail address: giovanni.camussi{at}unito.it

³ Abbreviations used in this paper: GN, glomerulonephritis; FSGS, focal segmental glomerular sclerosis; MC, mesangial cell; MPGN, membranoproliferative GN; PAF, platelet-activating factor; PTX3, long pentraxin.

Received for publication July 31, 2002. Accepted for publication November 19, 2002.

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