Time course of upregulation of fibrogenic growth factors and cellular infiltration in a rodent model of chronic renal allograft rejection

Microarray Analysis Reveals Increased Expression of Matrix Metalloproteases and Cytokines of Interleukin-20 Subfamily in the Kidneys of Neonate Rats Underwent Unilateral Ureteral Obstruction: A Potential Role of IL-24 in the Regulation of Inflammation and Tissue Remodeling

BACKGROUND/AIMS

Congenital obstructive nephropathy (CON) is the main cause of pediatric chronic kidney diseases leading to renal fibrosis. High morbidity and limited treatment opportunities of CON urge the better understanding of the underlying molecular mechanisms.

METHODS

To identify the differentially expressed genes, microarray analysis was performed on the kidney samples of neonatal rats underwent unilateral ureteral obstruction (UUO). Microarray results were then validated by real-time RT-PCR and bioinformatics analysis was carried out to identify the relevant genes, functional groups and pathways involved in the pathomechanism of CON. Renal expression of matrix metalloproteinase (MMP)-12 and interleukin (IL)-24 were evaluated by real-time RT-PCR, flow cytometry and immunohistochemical analysis. Effect of the main profibrotic factors on the expression of MMP-12 and IL-24 was investigated on HK-2 and HEK-293 cell lines. Finally, the effect of IL-24 treatment on the expression of pro-inflammatory cytokines and MMPs were tested in vitro.

RESULTS

Microarray analysis revealed 880 transcripts showing >2.0-fold change following UUO, enriched mainly in immune response related processes. The most up-regulated genes were MMPs and members of IL-20 cytokine subfamily, including MMP-3, MMP-7, MMP-12, IL-19 and IL-24. We found that while TGF-β treatment inhibits the expression of MMP-12 and IL-24, H2O2 or PDGF-B treatment induce the epithelial expression of MMP-12. We demonstrated that IL-24 treatment decreases the expression of IL-6 and MMP-3 in the renal epithelial cells.

CONCLUSIONS

This study provides an extensive view of UUO induced changes in the gene expression profile of the developing kidney and describes novel molecules, which may play significant role in the pathomechanism of CON.

Molecular pathways involved in loss of graft function in kidney transplant recipients

Interstitial fibrosis (IF) and tubular atrophy (TA) are integral parts of chronic allograft dysfunction and represent in the new classification a separate entity with or without the identification of a specific etiology. Loss of kidney graft function with IF/TA is one of the causes of most kidney allograft losses. Despite progress in immunosuppression, chronic allograft dysfunction remains the main clinical challenge for improving long-term graft survival. The sustained damage to the allograft does not represent a single entity but the summated effects of tissue injury from several pathogenic insults, as well as the kidney's healing response, modified by alloimmunity and immunosuppression. A major challenge in the future of kidney transplantation includes the study of chronic allograft dysfunction pathogenesis to identify early markers of disease progression, as well as potential therapeutics pathways.

Sequential observations show upregulation of TGF-beta1 at the early phase of chronic small bowel rejection in rats

Although TGF-beta1 is related to chronic rejection in various solid organs, its role remains controversial in the setting of small bowel transplantation. The aim of this study is to investigate the distinct role of TGF-beta1 and its receptors in the setting of chronic small bowel rejection. Sequential protocol biopsies were performed every 2 weeks from week 2 till week 8 after transplantation and recipients were sacrificed at week 16 as the end point. Gene expression was evaluated by SYBR Green I real-time polymerase chain reaction and protein was determined by immunohistochemistry. The gene expressions of TGF-beta1 and Type I receptor were upregulated and attained statistical significance at 4, 6 and 8 weeks in allografts. Dynamic expressions of TGF-beta1 and Type I receptor mRNA shown by sequential protocol biopsies support the view that TGF-beta1 signaling is involved in the pathogenesis of chronic small bowel rejection, especially at the early phase.

Endothelial apoptosis and chronic transplant vasculopathy: recent results, novel mechanisms

Chronic transplant vasculopathy (CTV) is a progressive form of vascular obliteration affecting the arteries, arterioles and capillaries of solid organ transplants. It is characterized by intimal accumulation of mononuclear cells, vascular smooth muscle cells (VSMC), myofibroblasts and connective tissue. Mounting evidence, based on animal models and human biopsy results, suggests that acute and persistent rejection triggering apoptosis of endothelial cells (EC) plays a pivotal role in CTV. The precise mechanisms that underlie the induction of fibroproliferative changes in association with endothelial apoptosis have yet to be clearly delineated. Recent observations in the field of apoptosis research provide some important mechanistic clues. First, endothelial apoptosis creates a state of hyperadhesiveness for mononuclear cells, thus facilitating sustained leukocyte infiltration. Second, phosphatidylserine-dependent engulfment of apoptotic cells by infiltrating mononuclear leukocytes promotes transforming growth factor-beta1 production. Third, apoptosis of EC triggers extracellular matrix (ECM) proteolysis thus initiating the production of fibroproliferative/fibrogenic ECM fragments. The relative importance of these mechanisms in the pathophysiology of CTV will need to be addressed in vivo. Yet, these recent developments provide a new mechanistic framework that will help better define the importance of immune-mediated EC apoptosis in the regulation of vascular repair.

Increased mRNA Expression of Transforming Growth Factor Beta in the Arterial Wall of Chronically Rejected Renal Allografts in Humans

INTRODUCTION

Transforming growth factor beta (TGF-beta) has an established role in interstitial damage of renal transplants during chronic rejection (CR). However, its involvement in transplant vasculopathy is not clear. The aim of the study was to assess TGF-beta gene expression in the walls of large-caliber arteries within chronically rejecting renal allografts. We evaluated associations between gene expression of this factor and intimal thickness or clinical data.

MATERIAL AND METHODS

Renal artery samples of kidney allografts were obtained from 20 hemodialysis patients with end-stage renal graft disease due to CR, who were undergoing graftectomy. The control group included 32 hemodialysis patients with end-stage renal disease, undergoing nephrectomy due to autosomal dominant polycystic kidney disease (n = 12), chronic pyelonephritis (n = 13), or kidney limited tumor (n = 7). Gene expression of TGF-beta was measured using real-time PCR.

RESULTS

TGF-beta mRNA expression was 3.25-fold higher in CR than in control patients (P < .001). Expression of mRNA for this cytokine was not influenced by the following factors: intimal thickness; age; serum cholesterol, triglycerides and glucose; BMI; graft survival; time of dialysis before transplantation; total ischemic time; immunosuppressive regimen; incidence of acute rejection episode; panel reactive antibodies; and period of dialysis before graftectomy. TGF-beta is involved in neointimal formation in CR.

Chlamydia Pneumoniae Infection: An Additional Factor for Chronic Allograft Rejection

INTRODUCTION

Chronic rejection (CHR) of organ allografts, one of the most significant problems in modern transplantation, is not fully understood. This study sought to evaluate the influence of selected parameters on late kidney transplant function.

PATIENTS AND METHOD

The studied group consisted of eighty-six patients who received allogeneic transplants between 1988 and 1999 for leukocyte Chlamydia pneumoniae-DNA, immunoglobulin (Ig)A/IgG anti-C pneumoniae, blood lipids, ischemic damage in the donor and during organ preservation, HLA mismatch, and acute rejection episodes.

RESULTS

Eighty-six patients were segregated as 26 patients (30%) with histologically proven chronic graft rejection (CHR[+]) and 59 patients (70%) without (CHR[-]). The presence of C pneumoniae-DNA in peripheral blood leukocytes was significantly more frequent in CHR(+) than CHR(-) group (46% vs 20%). Patients with leukocytes positive for C pneumoniae-DNA more frequently (50%) had CHR than patients negative for C pneumoniae-DNA (22%). CHR(+) patients showed significantly lower HDL levels (47 mg/dL vs 58 mg/dL) and higher triglyceride levels (193 mg/dL vs 148 mg/dL). To study the cumulative effect of differences between the CHR(+) and CHR(-) groups, we applied a multiple binary logistic regression analysis. An econometric model enabled us to calculate the probability of CHR for a given patient taking into account covariates chosen by means of stepwise selection: the presence of C pneumoniae-DNA in blood leukocytes, the use of continuous pulsatile perfusion in hypothermia, myocardial infarction occurrence, and triglyceride concentrations.

CONCLUSION

The presence of C pneumoniae-DNA in peripheral blood leukocytes increased the risk of CHR, which may be predicted by a multifactor analysis of chosen parameters.

Distinctive role of Stat3 and Erk-1/2 activation in mediating interferon-gamma inhibition of TGF-beta1 action

Interferon-gamma (IFN-gamma) is a multifunctional cytokine that elicits antifibrotic activity in a variety of organs. In this study, we investigated the potential role and mechanism of IFN-gamma in modulating the fibrogenic action of transforming growth factor (TGF)-beta(1) in tubular epithelial cells. Incubation of human proximal tubular epithelial (HKC) cells with IFN-gamma inhibited TGF-beta(1)-mediated alpha-smooth muscle actin (alpha-SMA) expression. IFN-gamma also abolished TGF-beta(1)-induced fibronectin and plasminogen activator inhibitor-1 (PAI-1) expression. To explore the mechanisms by which INF-gamma inhibits TGF-beta(1) action, the signaling pathways that are critical for mediating the antifibrotic activity of IFN-gamma were studied. Stimulation of HKC cells with IFN-gamma triggered a sustained activation of Erk-1/2 and signal transducer and activator of transcription-3 (Stat3). Blockade of Erk-1/2 activation with an Mek1 inhibitor abolished the inhibitory effect of IFN-gamma on alpha-SMA expression, whereas inhibition of Stat3 activation had no influence. Constitutive activation of Erk-1/2 by ectopic expression of activated Mek1 mimicked IFN-gamma and suppressed TGF-beta(1)-mediated alpha-SMA expression. Interestingly, inhibition of Stat3 activation abolished the ability of IFN-gamma to attenuate TGF-beta(1)-mediated PAI-1 and fibronectin expression in HKC cells. These findings indicate that IFN-gamma is capable of antagonizing the fibrogenic actions of TGF-beta(1) in renal tubular epithelial cells. The antifibrotic action of IFN-gamma appears to be mediated through a coordinated activation of both Erk-1/2 and Stat3 signal pathways in a mutually independent fashion.

The macrophage is the predominant inflammatory cell in renal allograft intimal arteritis

BACKGROUND

Intimal arteritis defines acute vascular rejection in the Banff 97 schema. The arteritis is generally considered to be lymphocytic, although the cellular infiltrate in tubulitis is composed of both lymphocytes and macrophages. This study aimed to determine the extent of macrophage involvement in renal allograft intimal arteritis.

METHODS

We obtained archival biopsy material from 57 biopsies of 34 renal allografts transplanted between March 1999 and February 2002. All biopsies were diagnostic. We examined clinical and histological parameters. Biopsies were graded using the Banff 97 criteria. We identified macrophages and memory T cells using immunohistochemistry for CD68 and CD45RO, respectively.

RESULTS

In all, 24 biopsies showed borderline rejection, and 12 biopsies showed grade IA, 13 showed grade IB, and 8 showed grade II or III acute rejection. Both lymphocytes and macrophages were present in the tubulointerstitium in all grades of acute rejection. We identified intimal arteritis in 10 vessels in eight biopsies. The infiltrating cells invariably included CD68-positive cells; however, we saw intimal CD45RO-positive cells in only seven vessels. There were significantly more CD68-positive cells than CD45RO-positive cells (mean, 9.5 vs. 4.4 positive cells per vessel, P< 0.01). CD45RO cells were never the predominant component of the intimal inflammatory infiltrate.

CONCLUSIONS

In the intimal arteritis of biopsies graded as Banff II or III acute rejection, the infiltrating cells were predominantly macrophages. T cells were in the minority. This finding challenges the assumption that the mononuclear cells in intimal arteritis are predominantly lymphocytic.

The role of vascular endothelial growth factor (VEGF) in renal pathophysiology

Vascular endothelial growth factor (VEGF) is an endothelial-specific growth factor that promotes endothelial cell proliferation, differentiation and survival, mediates endothelium-dependent vasodilatation, induces microvascular hyperpermeability and participates in interstitial matrix remodeling. In the kidney, VEGF expression is most prominent in glomerular podocytes and in tubular epithelial cells, while VEGF receptors are mainly found on preglomerular, glomerular, and peritubular endothelial cells. The role of VEGF in normal renal physiology is essentially unknown. The absence of prominent effects of VEGF blockade in normal experimental animals suggests a limited function during homeostasis, although a role in the formation and maintenance of glomerular capillary endothelial fenestrations has been suggested. VEGF and its receptors are up-regulated in experimental animals and humans with type 1 and type 2 diabetes. Inhibition of VEGF has beneficial effects on diabetes-induced functional and structural alterations, suggesting a deleterious role for VEGF in the pathophysiology of diabetic nephropathy. VEGF is required for glomerular and tubular hypertrophy and proliferation in response to nephron reduction, and loss of VEGF is associated with the development of glomerulosclerosis and tubulointerstitial fibrosis in the remnant kidney. No firm conclusions on the role of VEGF in minimal change or membranous glomerulonephritis can be drawn. VEGF may be an essential mediator of glomerular recovery in proliferative glomerulonephritis. Glomerular and tubulointerstitial repair in thrombotic microangiopathy and cyclosporin nephrotoxicity may also be VEGF-dependent. In conclusion, VEGF is required for growth and proliferation of glomerular and peritubular endothelial cells. While deleterious in some, it may contribute to recovery in other forms of renal diseases.

The role of nitric oxide in renal transplantation

This review discusses the concept that nitric oxide synthase (NOS) may orchestrate both the inflammatory response to the renal allograft and anti-inflammatory defense in the graft itself. NO is produced by endothelial, epithelial, as well as inflammatory cells. In the setting of transplantation, the endothelium is the first lining to be subjected to the early response to injury. In turn, activated endothelial cells facilitate leukocyte recruitment, immune-mediated injury, and angiogenesis. On activation by inflammatory stimuli, endothelial cells up-regulate multiple vasoactive substances, oxygen radicals, cytokines, chemokines, and growth factors. Therefore, endothelial integrity, especially the expression of protecting vasoactive agents, such as NO, may be a key factor in resistance or sensitivity to transplantation-mediated injury. Thus, evaluating the mechanisms by which NO is involved in either protecting or injuring the transplanted allogeneic kidney is important for our understanding of renal allograft rejection. This review focuses on the role of NO in the inflammatory endothelial-leukocyte interactions, which are implicated in acute and chronic rejection of the transplanted kidney.