Epithelial-to-mesenchymal transition in early transplant tubulointerstitial damage

Laser capture microdissection on formalin-fixed and paraffin-embedded renal transplanted biopsies: Technical perspectives for clinical practice application

Renal biopsy (RBx) is an essential tool in the diagnostic and therapeutic process of most native kidney diseases and in the renal transplanted graft. Laser capture microdissection (LCM), combined with molecular biology, might improve the diagnostic power of RBx. However, the limited amount of available renal tissue is often an obstacle for achieving a satisfactory qualitative and quantitative analysis. In our work we present a method which allows us to obtain good quality and quantity of RNA from formalin-fixed and paraffin-embedded (FFPE) renal tissue derived from RBx performed in transplanted patients. Histology, immunohistochemistry, LCM, pre-amplify system and qRT-PCR of biomarkers related to tubular damage, inflammation and fibrosis on FFPE RBx were performed. Glomeruli, tubules and interstitium of three RBx (RB-A: no alteration; RB-B and -C: the progressive rise of creatinine) were compared. The method proposed, could well be useful in future clinical practice. It is quick, easy to perform and allows the analyses of many biomarkers. In addition, it could be extended to all types of RBx without any limitation on the sample amount. Nevertheless, the need for a higher number of well-trained technicians might represent some limitation, counterbalanced by the opportunity to elaborate more accurate diagnosis and, consequently, more targeted therapies.

Peroxiredoxin 3 deficiency accelerates chronic kidney injury in mice through interactions between macrophages and tubular epithelial cells

Chronic kidney disease (CKD) has become epidemic worldwide. Mitochondrial reactive oxygen species (ROS)-induced oxidative stress is an important mediator of CKD, and Prx3 plays a critical role in maintenance of mitochondrial ROS. The present study examined the role of Prx3 in the context of fibrosis, a common feature of CKD, using Prx3 KO mice under obstructive and diabetic stress. Prx3 deficiency accelerated fibrosis and inflammation accompanied by mitochondrial oxidative stress in obstructed and diabetic kidneys as well as in proximal tubular epithelial (mProx) cells. In addition, Prx3 deficiency induced Raw264.7 macrophages activation, leading to upregulation of proinflammatory cytokines. Conditioned media from LPS-stimulated Prx3 deficient macrophages accelerated proinflammatory and profibrotic cytokines in mProx cells. Interestingly, Prx3 deficiency induced most inflammatory and fibrotic cytokines at basal condition in both tissues and cells. Taken together, these results demonstrate that Prx3 deficiency can accelerate CKD through interactions between macrophages and tubular epithelial cells.

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.

Tubular Cytoplasmic Expression of Zinc Finger Protein SNAI1 in Renal Transplant Biopsies: A Sign of Diseased Epithelial Phenotype?

The aim of the present study was to analyze in vivo the role of zinc finger protein SNAI1 (SNAI1) on renal fibrosis. Unilateral ureteral obstruction injury was induced in Snai1 knockout mice. Snai1 gene deletion was, however, only partial and could therefore not be correlated to reduced fibrosis. Expression of SNAI1 protein and epithelial-mesenchymal transformation markers was then assessed in human chronic allograft nephropathy biopsy specimens. Significant up-regulation of SNAI1 protein was detected within cytoplasm of proximal tubules localized, for some of them, near foci of fibrosis and tubular atrophy. No concomitant epithelial-mesenchymal transformation could, however, be demonstrated analyzing the expression of the fibroblast markers vimentin, α-smooth muscle actin, and S100A4. SNAI1 cytoplasmic up-regulation was particularly evident in biopsy specimens obtained from calcineurin inhibitor-treated patients, which might be because of, as suggested by in vitro experiments, a decrease of the proteasome chimotrypsin activity. Deeper analysis on chronic allograft nephropathy biopsy specimens suggested that SNAI1 cytoplasmic up-regulation was preceded by a transient increase of phosphorylated heat shock protein 27, p38 mitogen-activated protein kinase, and glycogen synthase kinase 3β. Concomitant down-regulation of the polyubuquitinylated conjugates was detected in SNAI1⁺ tubules. Altogether, these results might suggest that calcineurin inhibitor-induced tubular SNAI1 protein cytoplasmic accumulation, possibly because of impaired SNAI1 proteasomal degradation and nuclear translocation, might be a sign of a diseased profibrotic epithelial phenotype.

Senescence in chronic allograft nephropathy

Despite increasing numbers of patients on dialysis, the numbers of renal transplants performed yearly have remained relatively static. During the last 50 years, there have been many advances in the pharmacology of prevention of organ rejection. However, most patients will suffer from a slow but steady decline in renal function leading to graft loss. The most common cause of long-term graft loss is chronic allograft nephropathy (CAN). Therefore, elucidating and understanding the mechanisms involved in CAN is crucial for achieving better posttransplant outcomes. It is thought that the development of epithelial to mesenchymal transition (EMT) in proximal tubules is one of the first steps towards CAN, and has been shown to be a result of cellular senescence. Cells undergoing senescence acquire a senescence associated secretory phenotype (SASP) leading to the production of interleukin-1 alpha (IL-1α), which has been implicated in several degenerative and inflammatory processes including renal disease. A central mediator in SASP activation is the production of reactive oxygen species (ROS), which are produced in response to numerous physiological and pathological stimuli. This review explores the connection between SASP and the development of EMT/CAN in an effort to suggest future directions for research leading to improved long-term graft outcomes.

MicroRNA-130b improves renal tubulointerstitial fibrosis via repression of Snail-induced epithelial-mesenchymal transition in diabetic nephropathy

MicroRNA-130b (miR-130b) downregulation has been identified in diabetes, but the role and mechanisms for miR-130b in mediating renal tubulointerstitial fibrosis in diabetic nephropathy (DN) remain unknown. We demonstrated that plasma miR-130b downregulation exhibited clinical and biological relevance as it was linked to increased serum creatinine, β2-microglobulin and proteinuria, increased Snail expression and tubulointerstitial fibrosis in renal biopsies of DN patients. MiR-130b inhibitor caused Snail upregulation and enhanced molecular features of epithelial-to-mesenchymal transition (EMT) in high glucose (30 mM) cultured NRK-52E cells. In contrast, miR-130b mimic downregulated Snail expression and increased epithelial hallmarks. Notably, Snail was identified as an miR-130b direct target and inversely correlated with E-CADHERIN expression. Furthermore, the miR-130b-dependent effects were due to Snail suppression that in turn deregulated E-CADHERIN, VIMENTIN, COLLAGEN IV and α-smooth muscle actin (α-SMA), key mediators of EMT. These effects were reproduced in streptozotocin-induced diabetic rats. Thus, we propose a novel role of the miR-130b-SNAIL axis in fostering EMT and progression toward increased tubulointerstitial fibrosis in DN. Detection of plasma miR-130b and its association with SNAIL can be extrapolated to quantifying the severity of renal tubulointerstitial fibrosis. Targeting miR-130b could be evaluated as a potential therapeutic approach for DN.

Novel approach for the detection of tubular cell migration into the interstitium during renal fibrosis in rats

Background

The process of epithelial-mesenchymal transition (EMT), which is generally defined by phenotypic changes of injured tubules such as loss of epithelial markers or acquisition of mesenchymal markers, implies various activating steps, including proliferation, migration, and ability to produce extracellular matrix proteins. We established here a novel approach for the detection of tubular cell migration into the interstitium during renal fibrosis in vivo.

Results

Using an osmotic pump, bromodeoxyuridine (BrdU) was continuously given to 7-week-old Wistar rats for 4 weeks, and BrdU-positive cells were detected by immunostaining. BrdU-positive cells were present in aquaporin-1-positive proximal tubules, but not in the interstitium of BrdU-treated rat kidneys. After unilateral ureteral obstruction (UUO), some BrdU-positive tubular cells protruded from the basement membrane and migrated into the interstitium. Interstitial BrdU-positive cells were co-localized with alpha-smooth muscle actin, fibroblast specific protein-1, vimentin, and type I collagen, but not with CD68 or CD3. No BrdU-positive cells were observed in the interstitium of sham-operated kidneys. The number of BrdU-positive cells migrating into the interstitium significantly increased and peaked at 8 days after UUO.

Conclusions

Long-term BrdU labeling marked some of the proximal tubular cells and enabled us to detect tubular cell migration into the interstitium after UUO. This simple method might be useful to detect EMT in vivo.

The role of macrophages in the development of human renal allograft fibrosis in the first year after transplantation

The aim of this study was to investigate the role of infiltrating macrophages in renal allograft fibrosis. Forty-six protocol renal allograft biopsies obtained 1 year after transplantation were stained with Sirius red to quantify fibrosis and double stained with CD68 and CD206 to identify the proportion of alternatively activated (M2) macrophages. Biopsies were analyzed for gene expression by microarray, which was correlated with macrophage infiltration and the severity of fibrosis. The number of infiltrating CD68+ cells strongly correlated with the percentage of interstitial fibrosis (r = 0.73, p < 0.0001). Macrophage infiltration at 1 year correlated with renal dysfunction at 1, 12 and 36 months posttransplant (estimated GFR low vs. high: 1 month 78 ± 26 vs. 54 ± 19 mL/min, p < 0.01; 12 months 87 ± 29 vs. 64 ± 19 mL/min, p < 0.05; 36 months 88 ± 33 vs. 60 ± 24 mL/min, p < 0.05). Ninety-two percent of infiltrating macrophages exhibited an M2 phenotype with CD68+ CD206+ dual staining. Gene microarrays demonstrated an alloimmune response with up-regulation of interferon-γ-response genes despite the lack of rejection or inflammatory infiltrate. Consistent with this was the presence of CXCL10 in proximal tubular cells at 3 months. This suggests that M2 macrophage proliferation, or infiltration, was associated with subclinical alloimmune inflammation, tubular injury and progression of fibrosis.

Histopathology and biomarkers in prediction of renal function in children after kidney transplantation

BACKGROUND

Early detection of chronic allograft injury is a major challenge after kidney transplantation (RTx) in adults and children. We correlated the expression of four immunohistochemical biomarkers, P-selectin glycoprotein ligand-1 (PSGL-1), vimentin, α-smooth muscle actin (α-SMA) and collagen IV, to the kidney graft histology and function in pediatric RTx patients.

METHODS

We analyzed the histopathology and immunohistochemical stainings of 165 biopsies from 56 patients. Histopathology was scored according to Banff '05 classification and biomarker expression semiquantitatively. Glomerular filtration rate (GFR) was measured annually by (51)Cr-EDTA clearance.

RESULTS

In protocol biopsies, the expression of all four biomarkers correlated with the interstitial fibrosis and tubular atrophy (IF/TA) changes, which increased during the first 36months after RTx. At the time of 18month biopsy, we observed the deterioration of GFR in patients with high (≥2) IF/TA score (50 vs. 68ml/min/1.73m(2), p=0.004) or collagen IV expression (45 vs. 65ml/min/1.73m(2), p=0.016). Intense stainings of IF/TA, collagen IV and vimentin are also associated with poor GFR at 36 and 48months, however, the biomarker scores revealed no additional predictive value for concomitant or late GFR compared to IF/TA score. Patients with high and low biomarker expressions showed no significant differences in annual deterioration of GFR, which declined on average 2.2ml/min/1.73m(2)/year over the 7years follow-up.

CONCLUSIONS

Overall, the results suggest that traditional histopathology is a sufficient predictor for graft function, and the routine use of these histochemical markers as surrogates for graft function deterioration is questioned.

Progression of pulse pressure in kidney recipients durably exposed to CsA is a risk factor for epithelial phenotypic changes: an ancillary study of the CONCEPT trial

In this ancillary study of the CONCEPT trial, we studied the role of CsA withdrawal at 3 months (3M) post-transplant on the intensity of epithelial phenotypic changes (EPC, an early marker for kidney fibrogenesis) on the 12 M surveillance biopsy. Although conversion from CsA to sirolimus (SRL) at 3M was reported to have improved mean graft function at 12 M, it did not reduce the score of EPC (1.73 ± 1.15 in the SRL group vs. 1.87 ± 1 in the CsA group, P = 0.61). Acute rejection, which had occurred twice more frequently in SRL-converted patients included here, was associated with 12 M EPC. Interestingly, we observed that the patients durably exposed to CsA and who developed 12 M EPC had a significant progression of blood pulse pressure (pp) from 1 to 6M post-transplantation (Δpp = +12.3 mmHg, P = 0.0035). Pulse pressure at 4, 6, and 9 M and pp progression from 1 to 6M were significantly associated with the development of EPC at 12 M in renal grafts. Logistic regression analysis revealed that a high 6M pp (≥ 60 mmHg) was an independent risk factor for 12 M EPC with an odds ratio of 2.25 per additional 10 mmHg pp (95%CI: 1.14-4.4, P = 0.02) after adjustment with recipient's and donor's age, acute rejection incidence and immunosuppressive regimen. A post hoc analysis of the data collected in the whole population CONCEPT study revealed that pp was significantly higher at 6 months in patients maintained on CsA and that at this time point pp correlated negatively with GFR at 1 year.

Pathophysiology of the diabetic kidney

Diabetes mellitus contributes greatly to morbidity, mortality, and overall health care costs. In major part, these outcomes derive from the high incidence of progressive kidney dysfunction in patients with diabetes making diabetic nephropathy a leading cause of end-stage renal disease. A better understanding of the molecular mechanism involved and of the early dysfunctions observed in the diabetic kidney may permit the development of new strategies to prevent diabetic nephropathy. Here we review the pathophysiological changes that occur in the kidney in response to hyperglycemia, including the cellular responses to high glucose and the responses in vascular, glomerular, podocyte, and tubular function. The molecular basis, characteristics, and consequences of the unique growth phenotypes observed in the diabetic kidney, including glomerular structures and tubular segments, are outlined. We delineate mechanisms of early diabetic glomerular hyperfiltration including primary vascular events as well as the primary role of tubular growth, hyperreabsorption, and tubuloglomerular communication as part of a "tubulocentric" concept of early diabetic kidney function. The latter also explains the "salt paradox" of the early diabetic kidney, that is, a unique and inverse relationship between glomerular filtration rate and dietary salt intake. The mechanisms and consequences of the intrarenal activation of the renin-angiotensin system and of diabetes-induced tubular glycogen accumulation are discussed. Moreover, we aim to link the changes that occur early in the diabetic kidney including the growth phenotype, oxidative stress, hypoxia, and formation of advanced glycation end products to mechanisms involved in progressive kidney disease.

Dexamethasone prevents monocyte-induced tubular epithelial-mesenchymal transition in HK-2 cells

Epithelial-mesenchymal transition (EMT) is a key cellular event in the early stage of tubulointerstitial fibrosis (TIF). Monocyte infiltration plays an important role in the progression of TIF. We have previously demonstrated that monocytes can directly induce HK-2 cell transition by direct contact. Dexamethasone, an important anti-inflammatory and immunosuppressant agent, has been widely used in renal disease for decades. Whether it could influence the monocyte and HK-2 cell interaction and prevent EMT is still uncertain. In this study, we found that the typical epithelial cell morphology of HK-2 cells disappeared 24 h after co-culture with monocytes, and dexamethasone significantly prevented this change in a dose-dependent manner. In addition, we found that dexamethasone prevented monocytes from binding to HK-2 cells by inhibiting ICAM-1 expression on HK-2 cells. Further analysis demonstrated that there was increased E-cadherin expression and decreased α-SMA and fibronectin expression after co-culture with dexamethasone, suggesting that dexamethasone prevents monocyte-induced HK-2 cell transition. The nuclear transcription factor κB (NF-κB) pathway played an important role in this process. These findings suggest a novel mechanism by which corticosteroids may delay the progression of TIF via preventing EMT.

EMT-MET in renal disease: should we curb our enthusiasm?

Renal epithelial cells arise during embryogenesis by mesenchymal to epithelial transition (MET). In the context of renal diseases, these cells can switch back to a mesenchymal phenotype, in a process thus reminiscent of an epithelial-to-mesenchymal transition (EMT) in which we referred to as "Epithelial Phenotypic Changes" (EPC). The pathophysiological consequence of EPC is controversial: in particular, to what extent EPC contribute to the pool of disease-associated renal fibroblasts is very uncertain. However, there is strong evidence that EPC correlate with a poor renal outcome. EPC indeed reflect an exposure to a profibrotic environment, at an early and potentially reversible stage. Detecting EPC has potential therapeutic implications for patients prone to renal fibrosis, both as a marker of efficacy or more directly as a target. In opposition to the EMT occurring during embryogenesis, EMT in fibrosis as well as in cancer is an anarchic cellular process actually developing at the expense of the whole organ(ism).

Expression of hypoxia-inducible factor-1α (HIF-1α) in infiltrating inflammatory cells is associated with chronic allograft dysfunction and predicts long-term graft survival

BACKGROUND

In chronic kidney failure, a hypoxic state, infiltrating inflammatory cells play a crucial role in the progression to end-stage renal disease. No studies have evaluated the influence of hypoxia and infiltrating inflammatory cells on chronic allograft dysfunction.

METHODS

Renal transplant recipients who underwent renal allograft biopsy with interstitial fibrosis/tubular atrophy (IF/TA) were enrolled and renal allograft tissue sections were processed for immunohistochemical staining including hypoxia-inducible factor-1α (HIF-1α), nitrotyrosine, α-smooth muscle actin and e-cadherin. Patients with total renal tissue HIF score ≥1 were defined as positive for HIF-1α. To assess the phenotype of the infiltrating cells, dual staining of HIF-1α with CD45, CD68 and CD3 was performed. The correlation between HIF-1α score and Banff's score was analysed. Clinical parameters including renal survival among patients with or without an expression of HIF-1α were compared.

RESULTS

Out of 55 patients enrolled, 23 patients (41.8%) had an HIF-1α score ≥1 (Group B). Compared with Group A (total renal HIF score <1), Group B had a significantly higher Banff score of interstitial infiltrates (i) (P = 0.029), vascular fibrous intimal thickening (cv) (P = 0.007) and arteriolar hyaline thickening (ah) (P = 0.026). Clinically, patients with an HIF-1α score were associated with a poor graft survival. Significantly inferior allograft survival was noted in Group B. HIF scores had an adjusted hazard ratio of 3.25 (95% confidence inteval: 1.71-6.16, P = 0.0003) in allograft failure.

CONCLUSIONS

We first demonstrated the expression of HIF-1α protein among infiltrating inflammatory cells in areas with IF/TA in patients with chronic allograft dysfunction.

Epithelial-mesenchymal crosstalk alteration in kidney fibrosis

The incidence of chronic kidney diseases (CKD) is constantly rising, reaching epidemic proportions in the western world and leading to an enormous threat, even to modern health-care systems, in industrialized countries. Therapies of CKD have greatly improved following the introduction of drugs targeting the renin-angiotensin system (RAAS) but even this refined pharmacological approach has failed to stop progression to end-stage renal disease (ESRD) in many individuals. In vitro historical data and recent new findings have suggested that progression of renal fibrosis might occur as a result of an altered tubulo-interstitial microenvironment and, more specifically, as a result of an altered epithelial-mesenchymal crosstalk. Here we the review biological findings that support the hypothesis of an altered cellular crosstalk in an injured local tubulo-interstitial microenvironment leading to renal disease progression. Copyright © 2012 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.

Monocytes induce proximal tubular epithelial-mesenchymal transition through NF-kappa B dependent upregulation of ICAM-1

Inflammatory cell infiltration plays a key role in the pathogenesis of tubulointerstitial damage in chronic renal diseases. In addition to secreting the profibrotic cytokines, monocytes themselves have been demonstrated to be directly associated with renal fibrogenesis. However, how infiltrating monocytes interact with resident cells and the underlying mechanisms remain elusive. In this study we investigated the effects of monocytes on phenotypic changes of human proximal tubular HK-2 cells. The typical epithelial cell morphology of HK-2 cells disappeared after co-culture with monocytes, accompanied by decreased E-cadherin expression, and increased α-SMA and fibronectin expression, suggesting that HK-2 cells undergo epithelial-mesenchymal transition (EMT). Further analysis revealed that the effects were dependent on direct contact of the two types of cells as conditioned medium had no effects. Interestingly, administration of CD18 antibody directly inhibited this process. Furthermore, by microarray and RT-PCR we found that NF-kB signaling may play a role in this process and blockade of this signaling pathway in HK-2 cells could inhibit ICAM-1 expression and EMT phenotypes. Taken together, these findings suggest that monocytes infiltration could directly induce EMT of HK-2 cells via upregulation ICAM-1 through NF-kB signaling pathway.

Selective stimulation of VEGFR2 accelerates progressive renal disease

Vascular endothelial growth factor A (VEGF-A) can play both beneficial and deleterious roles in renal diseases, where its specific function might be determined by nitric oxide bioavailability. The complexity of VEGF-A in renal disease could in part be accounted for by the distinct roles of its two receptors; VEGFR1 is involved in the inflammatory responses, whereas VEGFR2 predominantly mediates angiogenesis. Because nondiabetic chronic renal disease is associated with capillary loss, we hypothesized that selective stimulation of VEGFR2 could be beneficial in this setting. However, VEGFR2 activation may be deleterious in the presence of nitric oxide deficiency. We systematically overexpressed a mutant form of VEGF-A binding only VEGFR2 (Flk-sel) using an adeno-associated virus-1 vector in wild-type and eNOS knockout mice and then induced renal injury by uninephrectomy. Flk-sel treatment increased angiogenesis and lowered blood pressure in both mouse types. Flk-sel overexpression caused mesangial injury with increased proliferation associated with elevated expression of PDGF, PDGF-β receptor, and VEGFR2; this effect was greater in eNOS knockout than in wild-type mice. Flk-sel also induced tubulointerstitial injury, with some tubular epithelial cells expressing α-smooth muscle actin, indicating a phenotypic evolution toward myofibroblasts. In conclusion, prestimulation of VEGFR2 can potentiate subsequent renal injury in mice, an effect enhanced in the setting of nitric oxide deficiency.

Epithelial to mesenchymal transition as a biomarker in renal fibrosis: are we ready for the bedside?

Over the past two decades, the concept of the epithelial to mesenchymal transition (EMT) has been imported from embryology and oncology to fibrosis, particularly in the kidney. This interest in EMT in the context of renal fibrosis stems from observations of epithelial cells undergoing phenotypic changes reminiscent of fibroblasts. Whether EMT is actually a source of interstitial fibroblasts has been the subject of heated debate, and this controversy has caused physicians to neglect the value of EMT as a biomarker in renal fibrosis. In this review, we describe the evolution of the techniques used to detect EMT during fibrosing renal diseases, and what information they provide in the diagnosis of various renal diseases. Highlighting the great heterogeneity of these techniques and the need to standardize them, we warn against some misleading uses of EMT markers. We suggest using the association of vimentin and β-catenin for the diagnosis of EMT in renal pathology because it is both sensitive and prognostic, thus satisfying the properties required for a screening test. Finally, we discuss the potential interests to diagnose EMT for the comprehension of renal fibrosis and for clinical practice.

The molecular phenotype of 6-week protocol biopsies from human renal allografts: reflections of prior injury but not future course

We assessed the molecular phenotype of 107 6-week protocol biopsies from human renal allografts, using Affymetrix microarrays. Transcript changes were summarized as nonoverlapping pathogenesis-based transcript sets (PBTs) reflecting inflammation (T cells, macrophages, IFNG effects) and the injury-repair response of the parenchyma, stroma and microcirculation-increased ('injury-up') and decreased ('injury-down') transcripts. The molecular changes were highly correlated with each other, even when all rejection and borderline cases were excluded. Inflammation and injury-down PBTs correlated with histologic inflammation and tubulitis, and the inflammation transcripts were greater in kidneys diagnosed as T cell-mediated or borderline rejection. Injury-up PBTs did not correlate with histopathology but did correlate with kidney function: thus functional disturbances are represented in transcript changes but not in histopathology. PBT changes correlated with prior delayed graft function. However, there was little difference between live donor kidneys and deceased donor kidneys that had not shown delayed graft function. Molecular changes did not predict future biopsies for clinical indications, rejection episodes, functional deterioration or allograft loss. Thus while detecting T cell-mediated inflammation, the molecular phenotype of early protocol biopsies mostly reflects the injury-repair response to implantation stresses, and has little relationship to future events and outcomes.

Contribution of epithelial plasticity to renal transplantation-associated fibrosis

Every year in the United States, 5000 renal transplant recipients start or restart dialysis because of the unusual propensity of these allografts to develop interstitial fibrosis and tubular atrophy (IF/TA). Although IF/TA often follows one or more identifiable events, our capacity to specifically treat, prevent, or even detect IF/TA at an early stage is poor. These limitations are largely related to our lack of adequate tools to assess graft failure over time. Data accumulated over the past 5 years have demonstrated that tubular epithelial cells may react to certain fibrogenic stimuli to engage in the process of epithelial-to-mesenchymal transition (EMT). In this review, we highlight the current view of EMT with a focus on both its role in the context of renal transplantation and the potential for utilizing markers of EMT to identify patients undergoing early IF/TA.

Intragraft tubular vimentin and CD44 expression correlate with long-term renal allograft function and interstitial fibrosis and tubular atrophy

BACKGROUND

Development of interstitial fibrosis and tubular atrophy (IF/TA) is the main histologic feature involved in renal allograft deterioration. The aim of this study was to validate whether de novo tubular expression of CD44 (transmembrane glycoprotein) and vimentin (mesenchymal cell marker), both involved in renal fibrosis, can operate as surrogate markers for late IF/TA and renal function. Furthermore, we wanted to establish the interrater reproducibility for the scoring system, which can be a problem in histologic assessments.

METHODS

Six-month protocol renal allograft biopsies (n=30 for matching 12 months estimated glomerular filtration rate (eGFR) from which 20 matched the 12-month protocol biopsy) were immunostained for CD44 and vimentin, semiquantitatively scored by three observers of two centers, and correlated with IF/TA and eGFR at 12 months.

RESULTS

The interobserver agreement was excellent for CD44 (Kendall's W-coefficient: 0.69; P<0.001) and vimentin (Kendall's W-coefficient: 0.79; P<0.001). CD44 and vimentin expression at 6 months were significantly correlated with IF/TA (rho=0.481 for CD44 and rho=0.619 for vimentin) and eGFR (rho=-0.569 for CD44 and rho=-0.376 for vimentin) at 12 months.

CONCLUSIONS

Summarizing, de novo tubular expression of CD44 and vimentin can function as surrogate marker for IF/TA and eGFR at 12 months. Further area under receiver operator characteristic curve analysis has to establish the predictive value for both biomarkers.

miR-200b precursor can ameliorate renal tubulointerstitial fibrosis

Members of the miR-200 family of micro RNAs (miRNAs) have been shown to inhibit epithelial-mesenchymal transition (EMT). EMT of tubular epithelial cells is the mechanism by which renal fibroblasts are generated. Here we show that miR-200 family members inhibit transforming growth factor-beta (TGF-beta)-induced EMT of tubular cells. Unilateral ureter obstruction (UUO) is a common model of EMT of tubular cells and subsequent tubulointerstitial fibrosis. In order to examine the role of miR-200 family members in tubulointerstitial fibrosis, their expression was investigated in the kidneys of UUO mice. The expression of miR-200 family miRNAs was increased in a time-dependent manner, with induction of miR-200b most pronounced. To clarify the effect of miR-200b on tubulointerstitial fibrosis, we injected miR-200b precursor intravenously. A single injection of 0.5 nM miR-200b precursor was sufficient to inhibit the increase of collagen types I, III and fibronectin in obstructed kidneys, and amelioration of fibrosis was confirmed by observation of the kidneys with Azan staining. miR-200 family members have been previously shown to inhibit EMT by reducing the expression of ZEB-1 and ZEB-2 which are known repressors of E-cadherin. We demonstrated that expression of ZEB-1 and ZEB-2 was increased after ureter obstruction and that administration of the miR-200b precursor reversed this effect. In summary, these results indicate that miR-200 family is up-regulated after ureter obstruction, miR-200b being strongly induced, and that miR-200b ameliorates tubulointerstitial fibrosis in obstructed kidneys. We suggest that members of the miR-200 family, and miR-200b specifically, might constitute novel therapeutic targets in kidney disease.

Mechanisms of tubulointerstitial fibrosis

The pathologic paradigm for renal progression is advancing tubulointerstitial fibrosis. Whereas mechanisms underlying fibrogenesis have grown in scope and understanding in recent decades, effective human treatment to directly halt or even reverse fibrosis remains elusive. Here, we examine key features mediating the molecular and cellular basis of tubulointerstitial fibrosis and highlight new insights that may lead to novel therapies. How to prevent chronic kidney disease from progressing to renal failure awaits even deeper biochemical understanding.

Resolved: EMT produces fibroblasts in the kidney

Epithelial-mesenchymal transition (EMT) is a mechanism for generating primitive mesenchymal cells during gastrulation or mobile tumor cells during cancer metastasis. For 15 years, EMT has also been viewed as a principal source of fibroblasts in tissue fibrosis. Because several recent studies question its role in fibrogenesis, it seems like a good time for debate.

[Interstitial fibrosis in renal grafts: On the way to a better detection]

In renal grafts, the progression of interstitial fibrosis and tubular atrophy (IF/TA) is exponential during the first months post-transplant. Consequently, roughly 40% of the cadaveric grafts will function less than ten years. There is, however, no specific strategy to halt fibrogenesis, i.e. the progression of fibrosis with time, in kidney recipients. Epithelial to mesenchymal transition (EMT) is a biological process used to disperse cells during embryogenesis. In the setting of injury, it is also a mechanism to escape cellular death. The last five years, several studies demonstrated that EMT does occur in tubular epithelial cells, which have been shown to loose the expression of epithelial markers, and acquire the expression of mesenchymal proteins, like vimentin. The aim of this review is triple: 1) discuss the connections between EMT and the context of transplantation; 2) explain how EMT markers may be useful in clinical practice, as promising surrogate markers for fibrogenesis; 3) discuss some therapeutic perspectives.

[Replacing calcineurin inhibitors with proliferation signal inhibitors after kidney transplantation: indications, results, and disadvantages]

In the kidney transplant patient, calcineurin inhibitor (CNI) treatment is a major risk factor for chronic allograft nephropathy (CAN). Immunosuppressive strategies based on non-nephrotoxic drugs such as proliferation signal inhibitors (PSIs) have been conceived to reduce or even interrupt CNIs. CNI conversion, with progressive cessation over 3 months with a PSI can significantly improve renal function, notably if the patient presents proteinuria less than 0.8 g/day and if conversion is undertaken early, when the glomerular filtration rate (GFR) is 40 ml/min or greater. In these conditions GRF improvement is associated with a histological CADI score and chronic lesion markers. Nevertheless, replacing CNIs with a PSI can occasionally induce proteinuria that is potentially related to direct toxicity of the PSI on the podocytes, which must be monitored to prevent recurrence of nephrotoxicity lesions.

Bone marrow mononuclear cells attenuate fibrosis development after severe acute kidney injury

One of the early phases that lead to fibrosis progression is inflammation. Once this stage is resolved, fibrosis might be prevented. Bone marrow mononuclear cells (BMMCs) are emerging as a new therapy for several pathologies, including autoimmune diseases, because they enact immunosuppression. In this study we aimed to evaluate the role of BMMC administration in a model of kidney fibrosis induced by an acute injury. C57Bl6 mice were subjected to unilateral severe ischemia by clamping the left renal pedicle for 1h. BMMCs were isolated from femurs and tibia, and after 6h of reperfusion, 1 x 10(6) cells were administrated intraperitoneally. At 24h after surgery, treated animals showed a significant decrease in creatinine and urea levels when compared with untreated animals. Different administration routes were tested. Moreover, interferon (IFN) receptor knockout BMMCs were used, as this receptor is necessary for BMMC activation. Labeled BMMCs were found in ischemic kidney on FACS analysis. This improved outcome was associated with modulation of inflammation in the kidney and systemic modulation, as determined by cytokine expression profiling. Despite non-amelioration of functional parameters, kidney mRNA expression of interleukin (IL)-6 at 6 weeks was lower in BMMC-treated animals, as were levels of collagen 1, connective tissue growth factor (CTGF), transforming growth factor-beta (TGF-beta) and vimentin. Protective molecules, such as IL-10, heme oxygenase 1 (HO-1) and bone morphogenetic 7 (BMP-7), were increased in treated animals after 6 weeks. Moreover, Masson and Picrosirius red staining analyses showed less fibrotic areas in the kidneys of treated animals. Thus, early modulation of inflammation by BMMCs after an ischemic injury leads to reduced fibrosis through modulation of early inflammation.

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.

Characterization of connective tissue growth factor expression in primary cultures of human tubular epithelial cells: modulation by hypoxia

Tubular epithelial cells secrete connective tissue growth factor (CTGF, CCN2), which contributes to tubulointerstitial fibrosis. However, the molecular regulation of CTGF in human primary tubular epithelial cells (hPTECs) is not well defined. Therefore, CTGF expression was characterized in hPTECs isolated from healthy parts of tumor nephrectomies, with special emphasis on the regulation by transforming growth factor-β (TGF-β) and hypoxia, essential factors in the development of fibrosis. CTGF synthesis was strongly dependent on cell density. High CTGF levels were detected in sparse cells, whereas CTGF expression was reduced in confluent cells. Concomitantly, stimulation of CTGF by TGF-β or the histone deacetylase inhibitor trichostatin was prevented in dense cells. Exposure of hPTECs to low oxygen tension (1% O2) or the hypoxia mimetic dimethyl-oxalylglycine for 24 h reduced CTGF gene expression in most of the 17 preparations analyzed. Preincubation of the cells under hypoxic conditions significantly reduced TGF-β-mediated upregulation of CTGF. In line with these data, CTGF mRNA was only induced in interstitial cells, but not in tubular cells in kidneys of mice exposed to hypoxia. Longer exposure to hypoxia or TGF-β (up to 72 h) did not induce hPTECs to adopt a mesenchymal phenotype characterized by upregulation of α-smooth muscle actin, downregulation of E-cadherin, or increased sensitivity of the cells in terms of CTGF expression. Sensitivity was restored by inhibition of DNA methylation. Taken together, our data provide evidence that exposure to hypoxia decreased CTGF gene expression. Furthermore, hypoxia per se was not sufficient to induce a mesenchymal phenotype in primary tubular epithelial cells.

New insights into epithelial-mesenchymal transition in kidney fibrosis

Epithelial-mesenchymal transition (EMT), a process by which differentiated epithelial cells undergo a phenotypic conversion that gives rise to the matrix-producing fibroblasts and myofibroblasts, is increasingly recognized as an integral part of tissue fibrogenesis after injury. However, the degree to which this process contributes to kidney fibrosis remains a matter of intense debate and is likely to be context-dependent. EMT is often preceded by and closely associated with chronic interstitial inflammation and could be an adaptive response of epithelial cells to a hostile or changing microenvironment. In addition to tubular epithelial cells, recent studies indicate that endothelial cells and glomerular podocytes may also undergo transition after injury. Phenotypic alteration of podocytes sets them in motion to functional impairment, resulting in proteinuria and glomerulosclerosis. Several intracellular signal transduction pathways such as TGFbeta/Smad, integrin-linked kinase (ILK) and Wnt/beta-catenin signaling are essential in controlling the process of EMT and presently are potential targets of antifibrotic therapy. This review highlights the current understanding of EMT and its underlying mechanisms to stimulate further discussion on its role, not only in the pathogenesis of renal interstitial fibrosis but also in the onset of podocyte dysfunction, proteinuria, and glomerulosclerosis.

Brain dead donor kidneys are immunologically active: is intervention justified?

The improvement in the field of kidney transplantation, during the last decades, has brought kindey transplantation to the top of patient preference as the best kidney replacement therapy. The use of marginal kidney grafts, which are highly immunogenic has become common practice because of lack of kidney donors. Inflammatory activity in the kidneys after brain death is an ongoing phenomenon. The inappropriate treatment of brain dead donor may result to primary non function (PNF) of the graft, delayed graft function (DGF) or to long term graft dysfunction and shortened graft survival. Therefore correct handling of the brain dead donor is of paramount importance. The impact of various pharmacologic agents (catecholamines, glucocorticoids, carbamylated recombinant human erythropoietin, recombinant soluble P-selectin glycoprotein ligant, heme oxygenase-1, carbon monoxide, and mycophenolate mofetil) on the immunogenicity of brain dead donor kidneys is discussed.

Using gene arrays in diagnosis of rejection

PURPOSE OF REVIEW

In the last decade, microarray technology has revolutionized biological research by allowing the screening of tens of thousands of genes simultaneously. This article reviews recent studies in organ transplantation using microarrays and highlights the issues that should be addressed in order to use microarrays in diagnosis of rejection.

RECENT FINDINGS

Microarrays have been useful in identifying potential biomarkers for chronic rejection in peripheral blood mononuclear cells, novel pathways for induction of tolerance, and genes involved in protecting the graft from the host immune system. Microarray analysis of peripheral blood mononuclear cells from chronic antibody-mediated rejection has identified potential noninvasive biomarkers. In a recent study, correlation of pathogenesis-based transcripts with histopathologic lesions is a promising step towards inclusion of microarrays in clinics for organ transplants.

SUMMARY

Despite promising results in diagnosis of histopathologic lesions using microarrays, the low dynamic range of microarrays and large measured expression changes within the probes for the same gene continue to cast doubts on their readiness for diagnosis of rejection. More studies must be performed to resolve these issues. Dominating expression of globin genes in whole blood poses another challenge for identification of noninvasive biomarkers. In addition, studies are also needed to demonstrate effects of different immunosuppression therapies and their outcomes.

Oncostatin M pathway plays a major role in the renal acute phase response

The acute phase response is traditionally characterized by hepatic synthesis of proteins as an inflammatory response to injury, with interleukin-6 (IL-6) being the key mediator. In contrast, microarray studies in human renal transplant implantation biopsies indicate a strong acute phase response in the deceased donor kidney, associated with a significant upregulation of oncostatin M receptor β (OSMR). The aim of this study was to determine whether the kidney can generate a strong acute phase response, mediated by the OSM/OSMR gateway. Genes associated with the IL-6 cytokine family and acute phase reactants were analyzed by real-time RT-PCR in four groups of human biopsies spanning a spectrum of renal injury. OSM, OSMR, and fibrinogen β (FGB) were progressively more highly expressed from prenephrectomy, living donor, deceased donor, to discarded donor kidneys, suggesting correlation with severity of injury and local renal synthesis. Acute phase response gene expression was analyzed in human proximal tubular cells in culture in response to OSM. OSM induced a significant increase in expression of FGB, OSMR, serpin peptidase inhibitor A1, IL-6, and lipopolysaccharide binding protein, and a decrease in IL-6R. These changes were largely attenuated by coincubation with an OSMR blocking antibody, indicating the OSM effect was mediated through OSMR. OSM also resulted in a significantly altered expression of acute phase genes compared with IL-6 or leukemia inhibitory factor, suggesting that OSM is the predominant cytokine mediating the renal tubular acute phase response. In conclusion, the renal parenchyma is capable of generating a strong acute phase response, likely mediated via OSM/OSMR.

Chronic allograft dysfunction: can we use mammalian target of rapamycin inhibitors to replace calcineurin inhibitors to preserve graft function?

PURPOSE OF REVIEW

Graft loss after first year of transplantation can be due to composite of factors that may include immunological and nonimmunological factors. Among the nonimmunological factors, toxicity of immunosuppression drugs, especially calcineurin inhibitor (CNI) toxicity is perhaps the leading cause of graft dysfunction. The most common phenotype associated with progressive graft dysfunction is the development of interstitial fibrosis and tubular atrophy not otherwise specified, a hallmark finding of chronic allograft nephropathy as well as CNI toxicity. Protocol biopsies have demonstrated that histological lesions of CNI toxicity can develop as early as 3 months posttransplantation.

RECENT FINDINGS

Early detection of interstitial fibrosis and tubular atrophy offers the opportunity for replacement of the CNI with mammalian target of rapamycin inhibitors. Early detection of CNI-associated graft damage even before the onset of graft dysfunction is critical to prevent progressive nephron loss. Furthermore, the conversion to sirolimus in patients with advanced graft dysfunction may not be beneficial.

SUMMARY

Until the day transcriptomic assays and high-density microarrays are available routinely to detect the incipient graft injury, early allograft biopsy, preferably during the first 3-6 months of transplantation can detect the presence of interstitial fibrosis and tubular atrophy not otherwise specified before the onset of graft dysfunction and replacement of CNI with sirolimus could prevent the progressive nephron loss.