Differential Expression of Profibrotic and Growth Factors in Chronic Allograft Nephropathy

The role of CD47 in pathogenesis and treatment of renal ischemia reperfusion injury

Ischemia reperfusion (IR) injury is a process defined by the temporary loss of blood flow and tissue perfusion followed later by restoration of the same. Brief periods of IR can be tolerated with little permanent deficit, but sensitivity varies for different target cells and tissues. Ischemia reperfusion injuries have multiple causes including peripheral vascular disease and surgical interventions that disrupt soft tissue and organ perfusion as occurs in general and reconstructive surgery. Ischemia reperfusion injury is especially prominent in organ transplantation where substantial effort has been focused on protecting the transplanted organ from the consequences of IR. A number of factors mediate IR injury including the production of reactive oxygen species and inflammatory cell infiltration and activation. In the kidney, IR injury is a major cause of acute injury and secondary loss of renal function. Transplant-initiated renal IR is also a stimulus for innate and adaptive immune-mediated transplant dysfunction. The cell surface molecule CD47 negatively modulates cell and tissue responses to stress through limitation of specific homeostatic pathways and initiation of cell death pathways. Herein, a summary of the maladaptive activities of renal CD47 will be considered as well as the possible therapeutic benefit of interfering with CD47 to limit renal IR.

Interstitial fibrosis scored on whole-slide digital imaging of kidney biopsies is a predictor of outcome in proteinuric glomerulopathies

Background

Interstitial fibrosis (IF), tubular atrophy (TA) and interstitial inflammation (II) are known determinants of progression of renal disease. Standardized quantification of these features could add value to current classification of glomerulopathies.

Methods

We studied 315 participants in the Nephrotic Syndrome Study Network (NEPTUNE) study, including biopsy-proven minimal change disease (MCD = 98), focal segmental glomerulosclerosis (FSGS = 121), membranous nephropathy (MN = 59) and IgA nephropathy (IgAN = 37). Cortical IF, TA and II were quantified (%) on digitized whole-slide biopsy images, by five pathologists with high inter-reader agreement (intra-class correlation coefficient >0.8). Tubulointerstitial messenger RNA expression was measured in a subset of patients. Multivariable Cox proportional hazards models were fit to assess association of IF with the composite of 40% decline in estimated glomerular filtration rate (eGFR) and end-stage renal disease (ESRD) and separately as well, and with complete remission (CR) of proteinuria.

Results

IF was highly correlated with TA (P < 0.001) and II (P < 0.001). Median IF varied by diagnosis: FSGS 17, IgAN 21, MN 7, MCD 1 (P < 0.001). IF was strongly correlated with baseline eGFR (P < 0.001) and proteinuria (P = 0.002). After adjusting for clinical pathologic diagnosis, age, race, global glomerulosclerosis, baseline proteinuria, eGFR and medications, each 10% increase in IF was associated with a hazard ratio of 1.29 (P < 0.03) for ESRD/40% eGFR decline, but was not significantly associated with CR. A total of 981 genes were significantly correlated with IF (|r| > 0.4, false discovery rate (FDR) < 0.01), including upstream regulators such as tumor necrosis factor, interferon gamma (IFN-gamma), and transforming growth factor beta 1 (TGF-B1), and signaling pathways for antigen presentation and hepatic fibrosis.

Conclusions

The degree of IF is associated with risk of eGFR decline across different types of proteinuric glomerulopathy, correlates with inflammatory and fibrotic gene expression, and may have predictive value in assessing risk of progression.

Biomarkers of Chronic Renal Tubulointerstitial Injury

Progression of renal parenchyma injury is characterized by increasing interstitial fibrosis and tubular atrophy, irrespective of the cause. Histopathologic assessment of renal tissue obtained by biopsy remains the gold standard for determining the presence and extent of tubulointerstitial scarring. Discovery of robust non-invasive means for capturing a snapshot and for longitudinal monitoring of parenchymal deterioration has been the focus of intense multimodal effort by investigators within the renal community and beyond. Research in this field has included the use of in vitro and in vivo experimental models and has fostered the development and evaluation of tissue and biofluid assays for novel analytes with potential translation to the diagnosis and prognosis of kidney disease. Here, we examine recent advances in the search of "biomarkers" for detection of renal tubulointerstitial scarring and prediction of renal outcome in human renal disease.

Elimination of donor CD47 protects against vascularized allograft rejection in mice

CD47 is a ubiquitously expressed transmembrane glycoprotein that plays a complex role in regulation of cell survival and function. We have previously shown that the interspecies incompatibility of CD47 plays an important role in triggering rejection of cellular xenografts by macrophages. However, the role of CD47 in solid organ transplantation remains undetermined. Here, we explored this question in mouse models of heart allotransplantation. We observed that the lack of CD47 in donor hearts had no deleterious effect on graft survival in syngeneic or single MHC class I-mismatched recipients, in which both wild-type (WT) and CD47 knockout (CD47 KO) mouse hearts survived long term with no sign of rejection. Paradoxically, elimination of donor CD47 was beneficial for graft survival in signal MHC class II- and class I- plus class II-mismatched combinations, in which CD47 KO donor hearts showed significantly improved survival compared to WT donor hearts. Similarly, CD47 KO donor hearts were more resistant than WT hearts to humoral rejection in α1,3-galactosyltransferase-deficient mice. Moreover, a significant prolongation of WT allografts was observed in recipient mice treated with antibodies against a CD47 ligand thrombospondin-1 (TSP1) or with TSP1 deficiency, indicating that TSP1-CD47 signaling may stimulate vascularized allograft rejection. Thus, unlike cellular transplantation, donor CD47 expression may accelerate the rejection of vascularized allografts.

The Use of Genomics and Pathway Analysis in Our Understanding and Prediction of Clinical Renal Transplant Injury

The development and application of high-throughput molecular profiling have transformed the study of human diseases. The problem of handling large, complex data sets has been facilitated by advances in complex computational analysis. In this review, the recent literature regarding the application of transcriptional genomic information to renal transplantation, with specific reference to acute rejection, acute kidney injury in allografts, chronic allograft injury, and tolerance is discussed, as is the current published data regarding other "omics" strategies-proteomics, metabolomics, and the microRNA transcriptome. These data have shed new light on our understanding of the pathogenesis of specific disease conditions after renal transplantation, but their utility as a biomarker of disease has been hampered by study design and sample size. This review aims to highlight the opportunities and obstacles that exist with genomics and other related technologies to better understand and predict renal allograft outcome.

Kidney Fibrosis: Origins and Interventions

All causes of renal allograft injury, when severe and/or sustained, can result in chronic histological damage of which interstitial fibrosis and tubular atrophy are dominant features. Unless a specific disease process can be identified, what drives interstitial fibrosis and tubular atrophy progression in individual patients is often unclear. In general, clinicopathological factors known to predict and drive allograft fibrosis include graft quality, inflammation (whether "nonspecific" or related to a specific diagnosis), infections, such as polyomavirus-associated nephropathy, calcineurin inhibitors (CNI), and genetic factors. The incidence and severity of chronic histological damage have decreased substantially over the last 3 decades, but it is difficult to disentangle what effects individual innovations (eg, better matching and preservation techniques, lower CNI dosing, BK viremia screening) may have had. There is little evidence that CNI-sparing/minimization strategies, steroid minimization or renin-angiotensin-aldosterone system blockade result in better preservation of intermediate-term histology. Treatment of subclinical rejections has only proven beneficial to histological and functional outcome in studies in which the rate of subclinical rejection in the first 3 months was greater than 10% to 15%. Potential novel antifibrotic strategies include antagonists of transforming growth factor-β, connective tissue growth factor, several tyrosine kinase ligands (epidermal growth factor, platelet-derived growth factor, vascular endothelial growth factor), endothelin and inhibitors of chemotaxis. Although many of these drugs are mainly being developed and marketed for oncological indications and diseases, such as idiopathic pulmonary fibrosis, a number may hold promise in the treatment of diabetic nephropathy, which could eventually lead to applications in renal transplantation.

Intronic locus determines SHROOM3 expression and potentiates renal allograft fibrosis

Fibrosis underlies the loss of renal function in patients with chronic kidney disease (CKD) and in kidney transplant recipients with chronic allograft nephropathy (CAN). Here, we studied the effect of an intronic SNP in SHROOM3, which has previously been linked to CKD, on the development of CAN in a prospective cohort of renal allograft recipients. The presence of the rs17319721 allele at the SHROOM3 locus in the donor correlated with increased SHROOM3 expression in the allograft. In vitro, we determined that the sequence containing the risk allele at rs17319721 is a transcription factor 7-like 2-dependent (TCF7L2-dependent) enhancer element that functions to increase SHROOM3 transcription. In renal tubular cells, TGF-β1 administration upregulated SHROOM3 expression in a β-catenin/TCF7L2-mediated manner, while SHROOM3 in turn facilitated canonical TGF-β1 signaling and increased α1 collagen (COL1A1) expression. Inducible and tubular cell-specific knockdown of Shroom3 markedly abrogated interstitial fibrosis in mice with unilateral ureteric obstruction. Moreover, SHROOM3 expression in allografts at 3 months after transplant and the presence of the SHROOM3 risk allele in the donor correlated with increased allograft fibrosis and with reduced estimated glomerular filtration rate at 12 months after transplant. Our findings suggest that rs17319721 functions as a cis-acting expression quantitative trait locus of SHROOM3 that facilitates TGF-β1 signaling and contributes to allograft injury.

Long-term gene therapy with thrombospondin 2 inhibits TGF-β activation, inflammation and angiogenesis in chronic allograft nephropathy

We recently identified Thrombospondin-2 (TSP-2) as a regulator of matrix remodelling and inflammation in experimental kidney disease by using TSP-2 null mice and successfully proved TSP-2 overexpression as a therapeutic concept in a short term glomerulonephritis model in the rat. In this current study, we investigated if long-term TSP-2 overexpression is also capable to ameliorate the progression of chronic kidney disease in the setting of the chronic allograft nephropathy F344-Lewis model in the rat. Two weeks after renal transplantation, two rat thigh muscles were transfected once only with either a TSP-2 overexpressing plasmid (n = 8) or a luciferase-expressing plasmid as control (n = 8). Rats were monitored for renal function, histological changes and gene expression in the graft for up to 30 weeks after transplantation. Unexpectedly, only in the TSP-2 treated group 2 rats died before the end of the experiment and renal function tended to be worsened in the TSP-2 group compared to the luciferase-treated controls. In addition, glomerular sclerosis and tubular interstitial injury as well as cortical fibronectin deposition was significantly increased in the TSP-2 treated kidneys despite reduced TGF-β activation and marked anti-inflammatory (macrophages, T-cells and B-cells) effects in this group. Long-term TSP-2 therapy impaired repair of renal endothelium, as demonstrated by significant higher glomerular and peritubular endothelial rarefaction and reduced endothelial cell proliferation in the transplanted kidneys from TSP-2 treated rats compared to controls. This TSP-2 effect was associated with decreased levels of renal VEGF but not VEGF1 receptor. In conclusion, despite its anti-inflammatory and TGF-β activation blocking effects, TSP-2 gene therapy did not ameliorate but rather worsened experimental chronic allograft nephropathy most likely via its anti-angiogenic properties on the renal microvasculature.

Activated CD47 regulates multiple vascular and stress responses: implications for acute kidney injury and its management

Ischemia-reperfusion injury (IRI) remains a significant source of early and delayed renal transplant failure. Therapeutic interventions have yet to resolve this ongoing clinical challenge although the reasons for this remain unclear. The cell surface receptor CD47 is widely expressed on vascular cells and in tissues. It has one known soluble ligand, the stress-released matricellular protein thrombospondin-1 (TSP1). The TSP1-CD47 ligand receptor axis controls a number of important cellular processes, inhibiting survival factors such as nitric oxide, cGMP, cAMP, and VEGF, while activating injurious pathways such as production of reactive oxygen species. A role of CD47 in renal IRI was recently revealed by the finding that the TSP1-CD47 axis is induced in renal tubular epithelial cells (RTEC) under hypoxia and following IRI. The absence of CD47 in knockout mice increases survival, mitigates RTEC damage, and prevents subsequent kidney failure. Conversely, therapeutic blockade of TSP1-CD47 signaling provides these same advantages to wild-type animals. Together, these findings suggest an important role for CD47 in renal IRI as a proximate promoter of injury and as a novel therapeutic target.

Discovery and validation of a molecular signature for the noninvasive diagnosis of human renal allograft fibrosis

BACKGROUND

Tubulointerstitial fibrosis (fibrosis), a histologic feature associated with a failing kidney allograft, is diagnosed using the invasive allograft biopsy. A noninvasive diagnostic test for fibrosis may help improve allograft outcome.

METHODS

We obtained 114 urine specimens from 114 renal allograft recipients: 48 from 48 recipients with fibrosis in their biopsy results and 66 from 66 recipients with normal biopsy results. Levels of messenger RNAs (mRNAs) in urinary cells were measured using kinetic, quantitative polymerase chain reaction assays, and the levels were related to allograft diagnosis. A discovery set of 76 recipients (32 with allograft fibrosis and 44 with normal biopsy results) was used to develop a diagnostic signature, and an independent validation set of 38 recipients (16 with allograft fibrosis and 22 with normal biopsy results) was used to validate the signature.

RESULTS

In the discovery set, urinary cell levels of the following mRNAs were significantly associated with the presence of allograft fibrosis: vimentin (P<0.0001, logistic regression model), hepatocyte growth factor (P<0.0001), α-smooth muscle actin (P<0.0001), fibronectin 1 (P<0.0001), perforin (P=0.0002), plasminogen activator inhibitor 1 (P=0.0002), transforming growth factor β1 (P=0.0004), tissue inhibitor of metalloproteinase 1 (P=0.0009), granzyme B (P=0.0009), fibroblast-specific protein 1 (P=0.006), CD103 (P=0.02), and collagen 1A1 (P=0.04). A four-gene model composed of the levels of mRNA for vimentin, NKCC2, and E-cadherin and of 18S ribosomal RNA provided the most accurate, parsimonious diagnostic model of allograft fibrosis with a sensitivity of 93.8% and a specificity of 84.1% (P<0.0001). In the independent validation set, this same model predicted the presence of allograft fibrosis with a sensitivity of 77.3% and a specificity of 87.5% (P<0.0001).

CONCLUSIONS

Measurement of mRNAs in urinary cells may offer a noninvasive means of diagnosing fibrosis in human renal allografts.

The PDGF family in renal fibrosis

The platelet-derived growth factor (PDGF) family plays an important role in embryonic development, malignancy, wound healing, atherosclerosis, and fibrosis in multiple organs. It belongs to the best-characterized growth factor systems in normal and diseased kidneys, and there is accumulating evidence that members of the PDGF family are key players in the development of renal fibrosis independent of the underlying kidney disease. All components of the PDGF system, consisting of four isoforms (PDGF-A, -B, -C, -D) and two receptor chains (PDGFR-α and -β), are constitutively or inducibly expressed in most renal cells. They regulate multiple pathophysiologic events, ranging from cell proliferation and migration, extracellular matrix accumulation and production of pro- and anti-inflammatory mediators, to tissue permeability and hemodynamics. This review focuses on advances in defining the roles of different PDGF isoforms in the development of glomerulosclerosis and tubulointerstitial fibrosis. The recent identification of endogenous PDGF inhibitors offers additional novel therapeutic strategies.

Progressive histological damage in renal allografts is associated with expression of innate and adaptive immunity genes

The degree of progressive chronic histological damage is associated with long-term renal allograft survival. In order to identify promising molecular targets for timely intervention, we examined renal allograft protocol and indication biopsies from 120 low-risk pediatric and adolescent recipients by whole-genome microarray expression profiling. In data-driven analysis, we found a highly regulated pattern of adaptive and innate immune gene expression that correlated with established or ongoing histological chronic injury, and also with development of future chronic histological damage, even in histologically pristine kidneys. Hence, histologically unrecognized immunological injury at a molecular level sets the stage for the development of chronic tissue injury, while the same molecular response is accentuated during established and worsening chronic allograft damage. Irrespective of the hypothesized immune or nonimmune trigger for chronic allograft injury, a highly orchestrated regulation of innate and adaptive immune responses was found in the graft at the molecular level. This occurred months before histologic lesions appear, and quantitatively below the diagnostic threshold of classic T-cell or antibody-mediated rejection. Thus, measurement of specific immune gene expression in protocol biopsies may be warranted to predict the development of subsequent chronic injury in histologically quiescent grafts and as a means to titrate immunosuppressive therapy.

Identifying biomarkers as diagnostic tools in kidney transplantation

There is a critical need for biomarkers for early diagnosis, treatment response, and surrogate end point and outcome prediction in organ transplantation, leading to a tailored and individualized treatment. Genomic and proteomic platforms have provided multiple promising new biomarkers during the last few years. However, there is still no routine application of any of these markers in clinical transplantation. This article will discuss the existing gap between biomarker discovery and clinical application in the kidney transplant setting. Approaches to implementing biomarker monitoring into clinical practice will also be discussed.

Gene expression changes are associated with loss of kidney graft function and interstitial fibrosis and tubular atrophy: diagnosis versus prediction

BACKGROUND

Loss of kidney graft function due to interstitial fibrosis (IF) and tubular atrophy (TA) is the most common cause of kidney allograft loss.

METHODS

One hundred one allograft tissues (26 samples with IF/TA, 17 normal allografts, and an independent biopsy group collected at 3 month [n=34] posttransplantation) underwent microarray analysis to identify early detection/diagnostic biomarkers of IF/TA. Profiling of 24 allograft biopsies collected at or after 9-month posttransplantation (range 9-18 months) was used for validation. Three-month posttransplantation biopsies were classified as IF/TA nonprogressors (group 1) or progressors (group 2) using graft function and histology at 9-month posttransplantation.

RESULTS

We identified 2223 differentially expressed probe sets between IF/TA and normal allograft biopsies using a Bonferroni correction. Genes up-regulated in IF/TA were primarily involved in pathways related to T-cell activation, natural killer cell-mediated cytotoxicity, and programmed cell death. A least absolute shrinkage and selection operator model was derived from the differentially expressed probe sets, resulting in a final model that included 10 probe sets and had 100% training set accuracy. The N-fold crossvalidated error was 2.4% (sensitivity 95.8% and specificity 100%). When 3-month biopsies were tested using the model, all the samples were classified as normal. However, evaluating gene expression of the 3-month biopsies and fitting a new penalized model, 100% sensitivity was observed in classifying the samples as group1 or 2. This model was evaluated in the sample set collected at or after 9-month posttransplantation.

CONCLUSIONS

An IF/TA gene expression signature was identified, and it was useful for diagnosis but not prediction. However, gene expression profiles at 3 months might predict IF/TA progression.

Aristolochic acid I and ochratoxin A differentially regulate VEGF expression in porcine kidney epithelial cells--the involvement of SP-1 and HIFs transcription factors

Aristolochic acid I (AAI) and ochratoxin A (OTA) cause chronic kidney diseases. Recently, the contribution of hypoxic injuries and angiogenic disturbances to nephropathies has been suggested, but underlying mechanisms have not been fully clarified yet.

In porcine kidney epithelial cell line, LLC-PK1 cells, treatment with non-toxic doses of AAI increased whereas with OTA decreased production of vascular endothelial growth factor (VEGF), the angiogenic factor with well-defined functions in kidney. Moreover, the activity of transcription factors regulating VEGF expression was differentially affected by examined compounds. Activity of hypoxia inducible factors (HIFs) and SP-1 was increased by AAI but diminished by OTA. Interestingly, AP-1 activity was inhibited while NFκB was not influenced by both toxins. Mithramycin A, a SP-1 inhibitor, as well as chetomin, an inhibitor of HIFs, reversed AAI-induced up-regulation of VEGF synthesis, indicating the importance of SP-1 and HIFs in this effect. Additionally, adenoviral overexpression of HIF-2α but not HIF-1α prevented OTA-diminished VEGF production suggesting the protective effect of this isoform towards the consequences exerted by OTA.

These observations provide new insight into complex impact of AAI and OTA on angiogenic gene regulation. Additionally, it adds to our understanding of hypoxia influence on nephropathies pathology.

Genetics and genomics in human lung transplantation

Lung transplantation is the only effective treatment for many advanced lung diseases. However, long-term survival after transplantation remains relatively poor, thus limiting the application of lung transplantation to patients with end-stage disease only. Acute and chronic rejection is the main reason for allograft failure. Attempts to treat or prevent rejection have been stymied by our incomplete understanding of the mechanisms leading to this devastating complication and the lack of representative animal models. A systems-biology approach to lung transplantation with the use of genomics and gene expression profiling has led to new insights into the pathogenesis of rejection, by elucidating the mechanisms of T-cell activation and uncovering the role of B cells and innate immunity. Systems-biology approaches, such as genetics and genomics, may allow minimally invasive diagnosis of rejection and permit individually tailored immunosuppressive regimens. Herein we review the emerging application of genomics and genetics to human lung transplantation and highlight the tremendous potential for these approaches to enhance clinical practice and augment our understanding of basic transplant biology.

Biomarkers in renal transplantation

Identifying surrogate markers of renal allograft outcome and biomarkers of acute and chronic graft injury is a critical issue for the transplant community. Measurement of serum creatinine and biopsy remain the current gold standards for the evaluation of renal allografts. These tests have significant limitations in predicting which patients are destined for immune tolerance or immune-mediated graft loss, and aiding in the management of long-term immunosuppression. The goal of biomarkers is to diagnose rejection early, determine prognosis and tailor immunosuppressive therapy in a noninvasive, cost-effective manner. Biomarker research has focused on primary areas of kidney injury, the tubules and the cells that infiltrate them. This article reviews biomarkers currently under investigation in the setting of renal allograft transplantation.

Transcriptome changes of chronic tubulointerstitial damage in early kidney transplantation

BACKGROUND

Tubulointerstitial damage (TID) is a key feature of chronic kidney transplant failure; however, the associated gene expression changes are poorly defined.

METHODS

This pilot study used RNA from 59 protocol kidney transplant biopsies at implantation, 1, 3, and 12 months (n=18 patients), processed into cDNA and hybridized to 8K human cDNA microarrays. Gene expression was correlated with graft histology categorized by the Banff schema.

RESULTS

Gene and pathway expression were differentially activated according to the time after transplantation. Immune pathway activity peaked at 1 month, fibrotic expression at 3 months, wound healing-remodelling and cell proliferation-repair processes were activated between 3 and 12 months, whereas macrophage-related gene expression occurred late by 12 months. Forty percent of genes and 50% pathways initially activated persisted to 3 months. Biopsies with TID displayed 262 differentially expressed genes (P<0.001, B>2 compared with implantation), dominated by upregulated fibrogenic and immune-related genes reflecting unique immune (10% to 15% of genes) and fibrotic (15% vs. 4% in normal) pathway activation. Profibrotic genes were expressed before interstitial fibrosis was observed by sequential microscopic analysis. Kidneys progressing to TID by 3 months demonstrated 30 unique genes (B>1, P<0.05) versus nonprogressors with 95 genes (B>1, P<0.009). Fourteen of these progressor genes also occurred in the top decile from an independent validation set.

CONCLUSIONS

Allografts display predictable immune and fibrotic gene expression profiles, with patterns of expression gradually varying by time after transplantation. The pathology reflects differential activation of intrinsic pathways. Gene expression predated histologic damage, suggesting its possible use in early diagnostic testing.

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.

Deconvoluting the 'omics' for organ transplantation

PURPOSE OF REVIEW

The desire for biomarkers for diagnosis and prognosis of diseases has never been greater. With the availability of genome data and an increased availability of proteome data, the discovery of biomarkers has become increasingly feasible. This article reviews some recent applications of the many evolving 'omic technologies to organ transplantation.

RECENT FINDINGS

With the advancement of many high-throughput 'omic techniques such as genomics, metabolomics, antibiomics, peptidomics, and proteomics, efforts have been made to understand potential mechanisms of specific graft injuries and develop novel biomarkers for acute rejection, chronic rejection, and operational tolerance.

SUMMARY

The translation of potential biomarkers from the laboratory bench to the clinical bedside is not an easy task and will require the concerted effort of the immunologists, molecular biologists, transplantation specialists, geneticists, and experts in bioinformatics. Rigorous prospective validation studies will be needed using large sets of independent patient samples. The appropriate and timely exploitation of evolving 'omic technologies will lay the cornerstone for a new age of translational research for organ transplant monitoring.

The yin and yang of B cells in graft rejection and tolerance

Various lineages of B cells are being increasingly recognized as important players in the etiology and prognosis of both acute and chronic graft rejection. The role of immature, chronically activated B cells, as efficient antigen-presenting cells, supporting recalcitrant cell-mediated graft rejection and late lineage B cells driving humoral rejections, is being increasingly recognized. This review captures the recent literature on this subject and discusses the various roles of the B cell in renal graft rejection and conversely, also in graft tolerance, both in animal and human studies. In addition, novel therapies targeting specific B-cell lineages in graft rejection are also discussed, with a view to developing more targeted therapies for graft rejection.

Thrombospondin-2 therapy ameliorates experimental glomerulonephritis via inhibition of cell proliferation, inflammation, and TGF-beta activation

We recently identified thrombospondin-2 (TSP-2) as an endogenous regulator of matrix remodelling and inflammation in experimental kidney disease by studying TSP-2-deficient mice. In this study, we asked whether systemic TSP-2 overexpression via thigh muscle transfection is able to ameliorate the time course of the anti-Thy1 glomerulonephritis model. After induction of anti-Thy1 nephritis, rats were transfected either with an overexpression plasmid for TSP-2 or lacZ as a control. Biopsies, urine, and blood samples were taken on days 1, 3, and 6 after disease induction. Muscular overexpression of TSP-2 reduced glomerular transforming growth factor (TGF)-beta activation and glomerular extracellular matrix formation as determined by collagen IV and fibronectin. In addition, activation of mesangial cells to the myofibroblast-like phenotype was also significantly decreased in TSP-2-overexpressing animals. TSP-2 overexpression inhibited both glomerular endothelial and mesangial cell proliferation, resulting in a reduced glomerular cell number and glomerular tuft area. The inflammatory response, as monitored by T cells and antigen-presenting cells, was reduced significantly by TSP-2 overexpression, but influx of macrophages was unchanged. These data demonstrate TSP-2 as a potential therapeutic agent to inhibit the glomerular proliferative and inflammatory response as well as TGF-beta activation and extracellular matrix accumulation in experimental mesangial proliferative glomerulonephritis.

Microarrays: monitoring for transplant tolerance and mechanistic insights

With recent advances in immunology and a growing understanding of transplantation biology, the development of reliable assays that may be used for identification and prediction of the current state of an immune response (rejection and tolerance) are urgently needed to allow us to predict the development of immunologic graft injury, individualize immunosuppression, rationally minimize immunosuppressive drug toxicity, promote a better understanding of the mechanisms underlying stable graft acceptance, and aid in the design of tolerance-inducing clinical transplantation trials. Microarrays can provide nonbiased, simultaneous global expression patterns for more than 40,000 human genes across different experiments. High throughput microarray technology offers a means to study disease-specific transcriptional changes in tissue biopsy, peripheral blood, and biofluids.

Renal allografts with IF/TA display distinct expression profiles of metzincins and related genes

Chronic renal allograft injury is often reflected by interstitial fibrosis (IF) and tubular atrophy (TA) without evidence of specific etiology. In most instances, IF/TA remains an irreversible disorder, representing a major cause of long-term allograft loss. As members of the protease family metzincins and functionally related genes are involved in fibrotic and sclerotic processes of the extracellular matrix (ECM), we hypothesized their deregulation in IF/TA. Gene expression and protein level analyses using allograft biopsies with and without Banff'05 classified IF/TA illustrated their deregulation. Expression profiles of these genes differentiated IF/TA from Banff'05 classified Normal biopsies in three independent microarray studies and demonstrated histological progression of IF/TA I to III. Significant upregulation of matrix metalloprotease-7 (MMP-7) and thrombospondin-2 (THBS-2) in IF/TA biopsies and sera was revealed in two independent patient sets. Furthermore, elevated THBS-2, osteopontin (SPP1) and beta-catenin may play regulatory roles on MMP. Our findings further suggest that deregulated ECM remodeling and possibly epithelial to mesenchymal transition (EMT) are implicated in IF/TA of kidney transplants, and that metzincins and related genes play an important role in these processes. Profiling of these genes may be used to complement IF/TA diagnosis and to disclose IF/TA progression in kidney transplant recipients.

In praise of arrays

Microarray technologies have both fascinated and frustrated the transplant community since their introduction roughly a decade ago. Fascination arose from the possibility offered by the technology to gain a profound insight into the cellular response to immunogenic injury and the potential that this genomic signature would be indicative of the biological mechanism by which that stress was induced. Frustrations have arisen primarily from technical factors such as data variance, the requirement for the application of advanced statistical and mathematical analyses, and difficulties associated with actually recognizing signature gene-expression patterns and discerning mechanisms. To aid the understanding of this powerful tool, its versatility, and how it is dramatically changing the molecular approach to biomedical and clinical research, this teaching review describes the technology and its applications, as well as the limitations and evolution of microarrays, in the field of organ transplantation. Finally, it calls upon the attention of the transplant community to integrate into multidisciplinary teams, to take advantage of this technology and its expanding applications in unraveling the complex injury circuits that currently limit transplant survival.

Hyperuricemia is associated with the development of the composite outcomes of new cardiovascular events and chronic allograft nephropathy

BACKGROUND

To investigate the prevalence and the predictors for the development of hyperuricemia at 6 months after kidney transplantation, and its association with clinical outcomes including patient and graft survival, the development of new cardiovascular events and chronic allograft nephropathy (CAN).

MATERIALS AND METHODS

Adult patients who underwent kidney transplantation at Mount Sinai Medical Center between January 1, 2001 and December 30, 2004 were included in the study. New cardiovascular events and biopsy-proven CAN were investigated.

RESULTS

Of the 307 patients, 163 patients (53%) had normal uric acid levels and 144 patients (47%) had hyperuricemia. After adjustment for age, race, and sex, receiving a cadaveric kidney, having an estimated glomerular filtration rate (eGFR) less than 50 mL/min, and taking diuretics or cyclosporine were associated with hyperuricemia at 6 months after transplantation. Over a mean 4.3 years of follow-up, 83 patients had one, or more, of the events, 4 died, 20 had graft failure, 40 had new cardiovascular events, and 41 developed CAN. Kaplan-Meier survival curves showed that these events occurred more frequently in patients with hyperuricemia (P<0.001). Among transplant recipients with an eGFR less than 50 mL/min, 45% of hyperuricemic and 21% of normouricemic patients had an event (P=0.038). For patients with an eGFR more than 50 mL/min, event rates were similar for patients with and without hyperuricemia, 25.0% vs. 19.4%, respectively.

CONCLUSIONS

These results suggest an important association between hyperuricemia at 6 months after kidney transplantation and new cardiovascular events and CAN in patients with decreased allograft function.

Immunosuppressive drug-free operational immune tolerance in human kidney transplant recipients: Part I. Blood gene expression statistical analysis

Survival of solid organ grafts depends on life-long immunosuppression, which results in increased rates of infection and malignancy. Induction of tolerance to allografts would represent the optimal solution for controlling both chronic rejection (CR) and side effects of immunosuppression. Although spontaneous "operational tolerance" can occur in human kidney transplantation, the lack of noninvasive peripheral blood biological markers of this rare phenomenon precludes the identification of potentially tolerant patients in whom immunosuppression could be tapered as well as the development of new tolerance inducing strategies. Here, the potential of high throughput microarray technology to decipher complex pathologies allowed us to study the peripheral blood specific gene expression profile and corresponding EASE molecular pathways associated to operational tolerance in a cohort of human kidney graft recipients. In comparison with patients with CR, tolerant patients displayed a set of 343 differentially expressed genes, mainly immune and defense genes, in their peripheral blood mononuclear cells (PBMC), of which 223 were also different from healthy volunteers. Using the expression pattern of these 343 genes, we were able to classify correctly >80% of the patients in a cross-validation experiment and classified correctly all of the samples over time. Collectively, this study identifies a unique PBMC gene signature associated with human operational tolerance in kidney transplantation by a classical statistical microarray analysis and, in the second part, by a nonstatistical analysis.

Molecular pathways involved in loss of kidney graft function with tubular atrophy and interstitial fibrosis

Loss of kidney graft function with tubular atrophy (TA) and interstitial fibrosis (IF) causes most kidney allograft losses. We aimed to identify the molecular pathways involved in IF/TA progression. Kidney biopsies from normal kidneys (n = 24), normal allografts (n = 6), and allografts with IF/TA (n = 17) were analyzed using high-density oligonucleotide microarray. Probe set level tests of hypotheses tests were conducted to identify genes with a significant trend in gene expression across the three groups using Jonckheere-Terpstra test for trend. Interaction networks and functional analysis were used. An unsupervised hierarchical clustering analysis showed that all the IF/TA samples were associated with high correlation. Gene ontology classified the differentially expressed genes as related to immune response, inflammation, and matrix deposition. Chemokines (CX), CX receptor (for example, CCL5 and CXCR4), interleukin, and interleukin receptor (for example, IL-8 and IL10RA) genes were overexpressed in IF/TA samples compared with normal allografts and normal kidneys. Genes involved in apoptosis (for example, CASP4 and CASP5) were importantly overexpressed in IF/TA. Genes related to angiogenesis (for example, ANGPTL3, ANGPT2, and VEGF) were downregulated in IF/TA. Genes related to matrix production-deposition were upregulated in IF/TA. A distinctive gene expression pattern was observed in IF/TA samples compared with normal allografts and normal kidneys. We were able to establish a trend in gene expression for genes involved in different pathways among the studied groups. The top-scored networks were related to immune response, inflammation, and cell-to-cell interaction, showing the importance of chronic inflammation in progressive graft deterioration.

Reduction of chronic allograft nephropathy by inhibition of extracellular signal-regulated kinase 1 and 2 signaling

Chronic allograft nephropathy (CAN), the most common cause of late kidney allograft failure, is not effectively prevented by immunosuppressive regimens. Activation of extracellular signal-regulated kinases 1 and 2 (ERK1/2) via MEK mediates actions of various growth factors, including transforming growth factor (TGF)-beta1, which plays a key role in CAN. Hence, we tested the therapeutic potential of MEK-ERK1/2 signaling disruption to prevent CAN. Kidneys from C57BL/6J (H-2(b)) mice were transplanted to bilaterally nephrectomized BALB/c (H-2(d)) mice. At 14 days after transplantation, the recipients were subjected to 28 days of treatment with the MEK inhibitor CI-1040. All six CI-1040-treated allografts survived, while two of seven grafts in the vehicle-treated group were lost. At the end of the experiment, the function and structure of grafts in the CI-1040-treated group were significantly preserved, as indicated by lower levels of serum creatinine or blood urea nitrogen than in the vehicle-treated group [30 +/- 6 vs. 94 +/- 39 microM creatinine (P = 0.0015) and 22 +/- 8 vs. 56 +/- 25 mM BUN (P = 0.0054)] and reduced CAN in the CI-1040-treated group compared with vehicle controls (CAN score = 4.2 vs. 10.3, P = 0.0119). The beneficial effects induced by CI-1040 were associated with reduction of ERK1/2 phosphorylation and TGFbeta1 levels in grafts. Also, CI-1040 potently suppressed not only TGFbeta biosynthesis in kidney cell cultures but also antiallograft immune responses in vitro and in vivo. Our data suggest that interference of MEK-ERK1/2 signaling with a pharmacological agent (e.g., CI-1040) has therapeutic potential to prevent CAN in kidney transplantation.

Chronic allograft nephropathy

PURPOSE OF REVIEW

Despite dramatic declines in acute rejection and early graft failure, long-term outcomes after kidney transplantation have improved little during the past 25 years. Most late allograft failure is attributed to chronic allograft nephropathy, but this is a clinicopathological description and not a diagnosis, and its pathogenesis and treatment are largely unknown.

RECENT FINDINGS

Recent studies suggest that acute rejection during the first few months, and calcineurin inhibitor toxicity thereafter, may both contribute to chronic allograft nephropathy. There is also accumulating evidence that injury from antibody-mediated rejection may play an important pathogenic role in at least some patients with chronic allograft nephropathy, particularly those with transplant glomerulopathy. Therapeutic measures, including protocols to reduce calcineurin inhibitor exposure, remain largely unproven.

SUMMARY

Understanding why so many kidney allografts fail, despite effective preventive measures for early acute rejection, is one of the most important areas of research in kidney transplantation today.

Tribbles-1 as a novel biomarker of chronic antibody-mediated rejection

Diagnosis of the specific cause of late allograft injury is necessary if more personalized and efficient immunosuppressive regimens are to be introduced. This study sought previously unrecognized biomarkers for specific histologic diagnoses of late graft scarring by comparison of gene sets from published microarray studies. Tribbles-1 (TRIB1), a human homolog of Drosophila tribbles, was identified to be a potentially informative biomarker. For testing this, mRNA expression in 76 graft biopsies, 71 blood samples, and 11 urine samples were profiled from independent cohorts of renal transplant patients with different histologic diagnoses recruited at two European centers. TRIB1 but not TRIB2 or TRIB3 was found to be a potential blood and tissue biomarker of chronic antibody-mediated rejection, an active immune-mediated form of chronic allograft failure associated with a poor prognosis. TRIB1 mRNA levels in peripheral blood mononuclear cells discriminated patients with chronic antibody-mediated rejection from those with other types of late allograft injury with high sensitivity and specificity. TRIB1 was also upregulated in a rodent model of chronic cardiac vasculopathy, suggesting that this biomarker may be useful in other solid-organ transplants and across species. It was determined that TRIB1 is expressed primarily by antigen-presenting cells and activated endothelial cells. Overall, these data support the potential use of TRIB1 as a biomarker of chronic antibody-mediated allograft failure.

A non-parametric meta-analysis approach for combining independent microarray datasets: application using two microarray datasets pertaining to chronic allograft nephropathy

Background

With the popularity of DNA microarray technology, multiple groups of researchers have studied the gene expression of similar biological conditions. Different methods have been developed to integrate the results from various microarray studies, though most of them rely on distributional assumptions, such as the t-statistic based, mixed-effects model, or Bayesian model methods. However, often the sample size for each individual microarray experiment is small. Therefore, in this paper we present a non-parametric meta-analysis approach for combining data from independent microarray studies, and illustrate its application on two independent Affymetrix GeneChip studies that compared the gene expression of biopsies from kidney transplant recipients with chronic allograft nephropathy (CAN) to those with normal functioning allograft.

Results

The simulation study comparing the non-parametric meta-analysis approach to a commonly used t-statistic based approach shows that the non-parametric approach has better sensitivity and specificity. For the application on the two CAN studies, we identified 309 distinct genes that expressed differently in CAN. By applying Fisher's exact test to identify enriched KEGG pathways among those genes called differentially expressed, we found 6 KEGG pathways to be over-represented among the identified genes. We used the expression measurements of the identified genes as predictors to predict the class labels for 6 additional biopsy samples, and the predicted results all conformed to their pathologist diagnosed class labels.

Conclusion

We present a new approach for combining data from multiple independent microarray studies. This approach is non-parametric and does not rely on any distributional assumptions. The rationale behind the approach is logically intuitive and can be easily understood by researchers not having advanced training in statistics. Some of the identified genes and pathways have been reported to be relevant to renal diseases. Further study on the identified genes and pathways may lead to better understanding of CAN at the molecular level.

Evaluation of gene panel mRNAs in urine samples of kidney transplant recipients as a non-invasive tool of graft function

Non-invasive monitoring may be useful after kidney transplantation (KT), particularly for predicting acute rejection (AR). It is less clear whether chronic allograft nephropathy (CAN) is also associated with changes in urine cells. To identify non-invasive markers of allograft function in kidney transplant patients (KTP), mRNA levels of AGT, TGF-beta1, EGFR, IFN-gamma, TSP-1, and IL-10 in urine (Ur) samples were studied using QRT-PCR. Ninety-five KTP and 111 Ur samples were evaluated. Patients (Pts) were divided as, within six months (N = 31), and with more than six months post-KT (N = 64). KTP with more than six months post-KT were classified as KTP with stable kidney function (SKF) (N = 32), KTP with SKF (creatinine < 2 mg/dL) and proteinuria > 500 mg/24 h (N = 18), and KTP with biopsy proven CAN (N = 14). F-test was used to test for equality of variances between groups. IL-10 mRNA was decreased in Ur samples from KTP with less than six months post-KT (P = 0.005). For KTR groups with more than six months post-KT, AGT and EGFR mRNA were statistically different among KTP with SKF, KTP with SKF and proteinuria, and CAN Pts (P = 0.003, and P = 0.01), with KTP with SKF having higher mean expression. TSP-1 mRNA levels also were significantly different among these three groups (P = 0.04), with higher expression observed in CAN Pts. Using the random forest algorithm, AGT, EGFR, and TGF-beta1 were identified as predictors of CAN, SKF, SKF with proteinuria. A characteristic pattern of mRNA levels in the different KTP groups was observed indicating that the mRNA levels in Ur cells might reflect allograft function.

Applying genomics to organ transplantation medicine in both discovery and validation of biomarkers

The field of biomarker discovery made a significant leap over the past few decades. As we enter the Era of the Human Genome, thousands of biomarkers can be identified in a relatively high-throughput fashion. While such magnitude and diversity of biomarkers can be seen as a challenge by itself, the field is being moved forward by new advances in bioinformatics and Systems Biology. Because of the life and death nature of end stage organ failure that transplantation treats, the severe donor organ shortage, and the powerful and toxic drug therapies required for the lifetimes of transplant patients, we envision a future for biomarkers as tools to diagnose disease in its early stages, predict prognosis, suggest treatment options and then assist in the implementation of therapies. By harnessing the power of multiple technologies in parallel makes it possible to discover and then validate the next generation of biomarkers for transplantation. We see the road ahead diverge into two paths: one from biomarkers to diagnosis and therapy and the other to a new level of insight into the complex molecular networks that determine when a healthy state becomes diseased and dysfunctional.

Molecular evidence of injury and inflammation in normal and fibrotic renal allografts one year posttransplant

INTRODUCTION

Factors contributing to kidney transplant fibrosis remain incompletely understood, particularly in the absence of acute complications.

METHODS

Baseline and 1-year surveillance biopsies from 15 uncomplicated living donor kidney transplants were subjected to microarray and quantitative reverse transcription polymerase chain reaction (qRT-PCR) analyses to examine changes in gene expression patterns over time. Biopsy pairs were purposefully selected from allografts with no history of acute complications and were divided into those that were histologically normal (n=7) and those that had developed subclinical interstitial fibrosis (n=8) at 1 year.

RESULTS

Compared with the paired baseline specimens, expression levels of 3578 probesets were found altered in all the 1-year biopsies studied. A large proportion of the up-regulated genes in this transplant-associated profile were functionally linked with inflammation, immunity, or response to injury. These included components of inflammation-related signaling pathways (integrin, interferon, and Toll-like receptor) as well as individual mediators of inflammatory and immune responses. An additional 2884 probesets demonstrated altered expression in fibrotic grafts only at 1 year. The gene products in this fibrosis-associated profile also were predominantly linked with inflammation and immune function, suggesting exaggerated inflammatory activity within the fibrotic grafts. qRT-PCR analyses confirmed the predicted expression patterns for selected transcripts from the microarray profiles.

CONCLUSIONS

Transcriptional profiles of histologically normal living donor renal allografts indicate that there is ongoing injury response and inflammation at 1 year compared to the immediate posttransplant period. Subclinical development of interstitial fibrosis during the first posttransplant year is associated with additional up-regulation of inflammation-related genes.

Diagnostic Tools for Monitoring Kidney Transplant Recipients

Recent advancements in immunobiology have introduced several new diagnostic tools for monitoring kidney transplant recipients. These have been added to more established tests that, although imperfect, remain important benchmarks of diagnostic utility. Both new and old tests can be characterized with regard to their practicality, and as to whether they detect aberrant function or define the cause of dysfunction. Unfortunately, no current test is both practical and specific to a particular disease entity. Accordingly, the diagnosis of graft dysfunction remains dependent on the proper use and interpretation of many studies. This article reviews the current assays that have been evaluated in the clinic for the diagnosis of renal allograft-related diseases. These are limited to assays based on routinely obtainable samples such as blood, biopsy tissue, and urine. Newer studies are presented, along with more mundane assays, to highlight the practical use of studies regardless of their degree of mechanistic sophistication.

Evaluation of gene panel mRNAs in urine samples of kidney transplant recipients as a non-invasive tool of graft function

Non-invasive monitoring may be useful after kidney transplantation (KT), particularly for predicting acute rejection (AR). It is less clear whether chronic allograft nephropathy (CAN) is also associated with changes in urine cells. To identify non-invasive markers of allograft function in kidney transplant patients (KTP), mRNA levels of AGT, TGF-beta1, EGFR, IFN-gamma, TSP-1, and IL-10 in urine (Ur) samples were studied using QRT-PCR. Ninety-five KTP and 111 Ur samples were evaluated. Patients (Pts) were divided as, within six months (N = 31), and with more than six months post-KT (N = 64). KTP with more than six months post-KT were classified as KTP with stable kidney function (SKF) (N = 32), KTP with SKF (creatinine < 2 mg/dL) and proteinuria > 500 mg/24 h (N = 18), and KTP with biopsy proven CAN (N = 14). F-test was used to test for equality of variances between groups. IL-10 mRNA was decreased in Ur samples from KTP with less than six months post-KT (P = 0.005). For KTR groups with more than six months post-KT, AGT and EGFR mRNA were statistically different among KTP with SKF, KTP with SKF and proteinuria, and CAN Pts (P = 0.003, and P = 0.01), with KTP with SKF having higher mean expression. TSP-1 mRNA levels also were significantly different among these three groups (P = 0.04), with higher expression observed in CAN Pts. Using the random forest algorithm, AGT, EGFR, and TGF-beta1 were identified as predictors of CAN, SKF, SKF with proteinuria. A characteristic pattern of mRNA levels in the different KTP groups was observed indicating that the mRNA levels in Ur cells might reflect allograft function.

Establishing the molecular pathways involved in chronic allograft nephropathy for testing new noninvasive diagnostic markers

BACKGROUND

Chronic allograft nephropathy (CAN) is a cause of graft loss. The multistage processes that result in CAN are poorly understood. Noninvasive assays for detecting allograft dysfunction and predicting long-term outcomes are a priority in transplantation (Tx).

METHODS

Renal tissue from kidney transplant patients (KTP) with CAN (n=11) and normal kidneys (NK; n=7) were studied using microarrays. Markers resulting from the microarray analysis (transforming growth factor [TGF]-beta, epidermal growth factor receptor [EGFR], angiotensinogen [AGT]) were tested in urine (Ur) and peripheral blood (PB) samples from the CAN patients (collected at the biopsy time) using reverse-transcriptase real-time polymerase chain reaction. Ur and PB samples from long-term KTP with stable renal function (SRF; n=20) were used as control.

RESULTS

Assuming unequal variances between CAN and NK, using a false discovery rate of 0.005, and running 1,000 of all possible permutations, 728 probe sets were differentially expressed. Genes related to fibrosis and extracellular matrix deposition (i.e., TGF-beta, laminin, gamma 2, metalloproteinases-9, and collagen type IX alpha 3) were up-regulated. Genes related to immunoglobulins, B cells, T-cell receptor, nuclear factor of activated T cells, and cytokine and chemokines receptors were also upregulated. EGFR and growth factor receptor activity (FGFR)2 were downregulated in CAN samples. AGT, EGFR, and TGF-beta levels were statistical different in urine but not in blood samples of CAN patients when compared to KTP with SRF (P<0.001, P=0.04, and P<0.001, respectively).

CONCLUSIONS

Genes related to fibrosis, extracellular matrix deposition, and immune response were found up-regulated in CAN. Markers resulting from the microarray analysis were differentially expressed in Ur samples of the CAN patients and in concordance with the microarray profiles.

Microarrays: a monitoring tool for transplant patients?

Microarray technology holds a distinct advantage over traditional genomic methods, with the unique capability to rapidly generate multiple global gene expression profiles in parallel. This technology is quickly gaining widespread use in many areas of science and medicine because it can be easily adapted to study many experimental questions, particularly relating to disease heterogeneity. Microarray experiments have begun to advance our understanding of the underlying molecular processes in solid organ transplantation; however, several obstacles must be overcome before this technology is ready for application in the clinical setting. This article will review the current applications of microarray technology in the field of transplantation, and discuss the potential impact of this technology on monitoring of solid organ transplant recipients.

IL-1beta induces VEGF, independently of PGE2 induction, mainly through the PI3-K/mTOR pathway in renal mesangial cells

Vascular endothelial growth factor (VEGF) could play a relevant role in angiogenesis associated with chronic allograft nephropathy. Interleukin-1beta (IL-1beta) has a key role in inflammatory response. It induces prostaglandin (PG) E2, which is involved in VEGF release by some normal and tumor cells. In the present work, we studied the effect of IL-1beta on VEGF release by rat mesangial cells, the transduction signal, and whether or not PGE2 is involved in this effect. IL-1beta induced a time-dependent formation of VEGF (analyzed by enzyme-linked immunosorbent assay) and PGE2 (analyzed by enzyme immunoassay). The latter correlated with microsomal-PGE-synthase (mPGES)-1 expression rather than with cyclooxygenase (COX)-2 in terms of protein, determined by Western blotting. No effect of IL-1beta on COX-1, cytosolic PGES, or mPGES-2 expression was observed. Indomethacin exerted a nonsignificant effect on IL-1beta-induced VEGF, and exogenously added PGE2 exhibited a nonsignificant stimulatory effect on VEGF formation. SB 203580, a p38 mitogen-activated protein kinase inhibitor, weakly inhibited the induction of VEGF by IL-1beta in a concentration-dependent manner, whereas LY 294002, a phosphoinoside 3-kinase (PI3-K) inhibitor, and rapamycin, a mammalian target of rapamycin (mTOR) inhibitor, strongly inhibited both IL-1beta- and tumor necrosis factor-alpha-induced VEGF formation in a concentration-dependent manner. Rapamycin also decreased glomerular VEGF levels in the anti-Thy1.1 model of experimental glomerulonephritis. In conclusion, the PI3-K-mTOR pathway seems to be essential in cytokine-induced release of VEGF in mesangial cells.