Changes in intragraft gene expression secondary to ischemia reperfusion after cardiac transplantation

The expression of oxidative stress genes related to myocardial ischemia reperfusion injury in patients with ST-elevation myocardial infarction

BACKGROUND

We aimed to investigate the gene expression of myocardial ischemia/reperfusion injury (MIRI) in patients with acute ST-elevation myocardial infarction (STEMI) using stress and toxicity pathway gene chip technology and try to determine the underlying mechanism.

METHODS

The mononuclear cells were separated by ficoll centrifugation, and plasma total antioxidant capacity (T-AOC) was determined by the ferric reducing ability of plasma (FRAP) assay. The expression of toxic oxidative stress genes was determined and verified by oligo gene chip and quantitative real-time polymerase chain reaction (qRT-PCR). Additionally, gene ontology (GO) enrichment analysis was performed on DAVID website to analyze the potential mechanism further.

RESULTS

The total numbers of white blood cells (WBC) and neutrophils (N) in the peripheral blood of STEMI patients (the AMI group) were significantly higher than those in the control group (WBC: 11.67±4.85 ×10⁹/L vs. 6.41±0.72 ×10⁹/L, P<0.05; N: 9.27±4.75 ×10⁹/L vs. 3.89±0.81 ×10⁹/L, P<0.05), and WBCs were significantly associated with creatine kinase-myocardial band (CK-MB) on the first day (Y=8.945+0.018X, P<0.05). In addition, the T-AOC was significantly lower in the AMI group comparing to the control group (12.80±1.79 U/mL vs. 20.48±2.55 U/mL, P<0.05). According to the gene analysis, eight up-regulated differentially expressed genes (DEGs) included GADD45A, PRDX2, HSPD1, DNAJB1, DNAJB2, RAD50, TNFSF6, and TRADD. Four down-regulated DEGs contained CCNG1, CAT, CYP1A1, and ATM. TNFSF6 and CYP1A1 were detected by polymerase chain reaction (PCR) to verify the expression at different time points, and the results showed that TNFSF6 was up-regulated and CYP1A1 was down-regulated as the total expression. GO and kyoto encyclopedia of genes and genomes (KEGG) enrichment analysis suggested that the oxidative stress genes mediate MIRI via various ways such as unfolded protein response (UPR) and apoptosis.

CONCLUSIONS

WBCs, especially neutrophils, were the critical cells that mediating reperfusion injury. MIRI was regulated by various genes, including oxidative metabolic stress, heat shock, DNA damage and repair, and apoptosis-related genes. The underlying pathway may be associated with UPR and apoptosis, which may be the novel therapeutic target.

Banff 2019 Meeting Report: Molecular diagnostics in solid organ transplantation-Consensus for the Banff Human Organ Transplant (B-HOT) gene panel and open source multicenter validation

This meeting report from the XV Banff conference describes the creation of a multiorgan transplant gene panel by the Banff Molecular Diagnostics Working Group (MDWG). This Banff Human Organ Transplant (B-HOT) panel is the culmination of previous work by the MDWG to identify a broadly useful gene panel based on whole transcriptome technology. A data-driven process distilled a gene list from peer-reviewed comprehensive microarray studies that discovered and validated their use in kidney, liver, heart, and lung transplant biopsies. These were supplemented by genes that define relevant cellular pathways and cell types plus 12 reference genes used for normalization. The 770 gene B-HOT panel includes the most pertinent genes related to rejection, tolerance, viral infections, and innate and adaptive immune responses. This commercially available panel uses the NanoString platform, which can quantitate transcripts from formalin-fixed paraffin-embedded samples. The B-HOT panel will facilitate multicenter collaborative clinical research using archival samples and permit the development of an open source large database of standardized analyses, thereby expediting clinical validation studies. The MDWG believes that a pathogenesis and pathway based molecular approach will be valuable for investigators and promote therapeutic decision-making and clinical trials.

Heterotopic Abdominal Rat Heart Transplantation as a Model to Investigate Volume Dependency of Myocardial Remodeling

Heterotopic abdominal rat heart transplantation has been extensively used to investigate ischemic-reperfusion injury, immunological consequences during heart transplantations and also to study remodeling of the myocardium due to volume unloading. We provide a unique review on the latter and present a summary of the experimental studies on rat heart transplantation to illustrate changes that occur to the myocardium due to volume unloading. We divided the literature based on whether normal or failing rat heart models were used. This analysis may provide a basis to understand the physiological effects of mechanical circulatory support therapy.

Identification and association of RAC1 gene polymorphisms with mRNA and protein expression levels of Rac1 in solid organ (kidney, liver, heart) transplant recipients

The activation of Ras-related C3 botulinum toxin substrate 1 (Rac1) is critical in the renal, hepatic and cardiac diseases that lead to the requirement for transplantation, however, no investigations have been performed in Chinese populations to determine the association between RAC1 genotypes and the activation of Rac1. In the present study, 304 solid organ transplant recipients (SOTRs), consisting of 164 renal transplantations, 85 hepatic transplantations and 55 cardiac transplantations, and 332 Chinese healthy control subjects were recruited to investigate whether differences existed in the mRNA and protein expression levels of Rac1 in the different groups. Furthermore, the present study identified and investigated associations of the RAC1 (rs702482, rs10951982, rs702483 and rs6954996) genotypes with the mRNA expression levels of RAC1, and the protein expression levels of total Rac1 and active Rac1‑guanosine triphosphatase (GTP). It was identified that the healthy population had significantly higher levels of Rac1 and Rac1‑GTP, compared with the kidney, liver and heart transplantation populations (P<0.001 for all comparisons). Significant associations (P<0.05) were observed between the RAC1 genotypes and the expression levels of mRNA, Rac1 and Rac1‑GTP. However, the changes in the mRNA expression levels of RAC1 with genotypes were different from those of the proteins. The results of the present study represent the first, to the best of our knowledge, to report that Rac1 and Rac1‑GTP proteins can be downregulated in SOTRs, and that RAC1 genetic polymorphisms can potentially affect the mRNA expression of RAC1, and the protein expression of Rac1 and Rac1‑GTP. These results provide a foundation for further functional investigations to determine the biological and molecular functions of the RAC1 gene in SOTRs.

Molecular transplantation pathology: the interface between molecules and histopathology

PURPOSE OF REVIEW

In the last decade, high-throughput molecular screening methods have revolutionized the transplantation research. This article reviews the new knowledge that has emerged from transplant patient sample-derived 'omics data by examining the interface between molecular signals and allograft pathology.

RECENT FINDINGS

State-of-the-art molecular studies have shed light on the biology of organ transplant diseases and provided several potential molecular tests with diagnostic, prognostic, and theranostic applications for the implementation of personalized medicine in transplantation. By comprehensive molecular profiling of patient samples, we have learned numerous new insights into the effector mechanisms and parenchymal response during allograft diseases. It has become evident that molecular profiles are coordinated and move in patterns similar to histopathology lesions, and therefore lack qualitative specificity. However, molecular tests can empower precision diagnosis and prognostication through their objective and quantitative manner when they are integrated in a holistic approach with histopathology and clinical factors of patients.

SUMMARY

Despite clever science and large amounts of public money invested in transplant 'omics studies, multiparametric molecular testing has not yet been translated to patient care. There are serious challenges in the implementation of transplant molecular diagnostics that have increased frustration in transplant community. We appeal for a full collaboration between pathologists and researchers to accelerate transition from research to clinical practice in transplantation.

Src tyrosine kinase inhibition prevents pulmonary ischemia-reperfusion-induced acute lung injury

PURPOSE

Pulmonary ischemia-reperfusion is a pathological process seen in several clinical conditions, including lung transplantation, cardiopulmonary bypass, resuscitation for circulatory arrest, atherosclerosis, and pulmonary embolism. A better understanding of its molecular mechanisms is very important.

METHODS

Rat left lung underwent in situ ischemia for 60 min, followed by 2 h of reperfusion. The gene expression profiles and Src protein tyrosine kinase (PTK) phosphorylation were studied over time, and PP2, an Src PTK inhibitor, was intravenously administered 10 min before lung ischemia to determine the role of Src PTK in lung injury.

RESULTS

Reperfusion following ischemia significantly changed the expression of 169 genes, with Mmp8, Mmp9, S100a9, and S100a8 being the most upregulated genes. Ischemia alone only affected expression of 9 genes in the lung. However, Src PTK phosphorylation (activation) was increased in the ischemic lung, mainly on the alveolar wall. Src PTK inhibitor pretreatment decreased phosphorylation of Src PTKs, total protein tyrosine phosphorylation, and STAT3 phosphorylation. It increased phosphorylation of the p85α subunit of PI3 kinase, a signal pathway that can inhibit coagulation and inflammation. PP2 reduced leukocyte infiltration in the lung, apoptotic cell death, fibrin deposition, and severity of acute lung injury after reperfusion. Src inhibition also significantly reduced CXCL1 (GRO/KI) and CCL2 (MCP-1) chemokine levels in the serum.

CONCLUSION

During pulmonary ischemia, Src PTK activation, rather than alteration in gene expression, may play a critical role in reperfusion-induced lung injury. Src PTK inhibition presents a new prophylactic treatment for pulmonary ischemia-reperfusion-induced acute lung injury.

Genome-wide transcription profile of endothelial cells after cardiac transplantation in the rat

Transcriptome analyses of organ transplants have until now usually focused on whole tissue samples containing activation profiles from different cell populations. Here, we enriched endothelial cells from rat cardiac allografts and isografts, establishing their activation profile at baseline and on days 2, 3 and 4 after transplantation. Modulated transcripts were assigned to three categories based on their regulation profile in allografts and isografts. Categories A and B contained the majority of transcripts and showed similar regulation in both graft types, appearing to represent responses to surgical trauma. By contrast, category C contained transcripts that were partly allograft-specific and to a large extent associated with interferon-gamma-responsiveness. Several transcripts were verified by immunohistochemical analysis of graft lesions, among them the matricellular protein periostin, which was one of the most highly upregulated transcripts but has not been associated with transplantation previously. In conclusion, the majority of the differentially expressed genes in graft endothelial cells are affected by the transplantation procedure whereas relatively few are associated with allograft rejection.

Molecular imaging of innate immune cell function in transplant rejection

BACKGROUND

Clinical detection of transplant rejection by repeated endomyocardial biopsy requires catheterization and entails risks. Recently developed molecular and cellular imaging techniques that visualize macrophage host responses could provide a noninvasive alternative. Yet, which macrophage functions may provide useful markers for detecting parenchymal rejection remains uncertain.

METHODS AND RESULTS

We transplanted isografts from B6 mice and allografts from Balb/c mice heterotopically into B6 recipients. In this allograft across major histocompatability barriers, the transplanted heart undergoes predictable progressive rejection, leading to graft failure after 1 week. During rejection, crucial macrophage functions, including phagocytosis and release of proteases, render these abundant innate immune cells attractive imaging targets. Two or 6 days after transplantation, we injected either a fluorescent protease sensor or a magnetofluorescent phagocytosis marker. Histological and flow cytometric analyses established that macrophages function as the major cellular signal source. In vivo, we obtained a 3-dimensional functional map of macrophages showing higher phagocytic uptake of magnetofluorescent nanoparticles during rejection using magnetic resonance imaging and higher protease activity in allografts than in isografts using tomographic fluorescence. We further assessed the sensitivity of imaging to detect the degree of rejection. In vivo imaging of macrophage response correlated closely with gradually increasing allograft rejection and attenuated rejection in recipients with a genetically impaired immune response resulting from a deficiency in recombinase-1 (RAG-1(-/-)).

CONCLUSIONS

Molecular imaging reporters of either phagocytosis or protease activity can detect cardiac allograft rejection noninvasively, promise to enhance the search for novel tolerance-inducing strategies, and have translational potential.

Blockade of K(ATP) channels reduces endothelial hyperpolarization and leukocyte recruitment upon reperfusion after hypoxia

Ischemia/reperfusion injury in renal transplantation leads to slow or initial nonfunction, and predisposes to acute and chronic rejection. In fact, severe ischemia reperfusion injury can significantly reduce graft survival, even with modern immunosuppressive agents. One of the mechanisms by which ischemia/reperfusion causes injury is activation of endothelial cells resulting in inflammation. Although several therapies can be used to prevent leukocyte recruitment to ischemic vessels (e.g. antiadhesion molecule antibodies), there have been no clinical treatments reported that can prevent initial immediate neutrophil recruitment upon reperfusion. Using intravital microscopy, we describe abrogation of immediate neutrophil recruitment to ischemic microvessels by the K(ATP) antagonist glibenclamide (Glyburide). Further, we show that glibenclamide can reduce leukocyte recruitment in vitro under physiologic flow conditions. ATP-regulated potassium channels (K(ATP)) are important in the control of cell membrane polarization. Here we describe profound hyperpolarization of endothelial cells during hypoxia, and the reduction of this hyperpolarization using glibenclamide. These findings suggest that control of endothelial membrane potential during ischemia may be an important therapeutic tool in avoiding ischemia/reperfusion injury, and therefore, enhancing transplant long-term function.

Heterotopic rat heart transplantation (Lewis to F344): early ICAM-1 expression after 8 hours of cold ischemia

BACKGROUND

Primary graft dysfunction is a still poorly understood complication after cardiac transplantation. Ischemia/reperfusion injury contributes to different disorders resulting in impaired graft function.

METHODS

In a heterotopic rat heart transplantation model we extended graft ischemic time up to 8 hours.

RESULTS

Using immunohistochemistry we detected an up to 4-fold increase in intracellular adhesion molecule-1 (ICAM-1) expression during 4 hours of reperfusion, independent of ischemic time (30-minute ischemia: 7.65 +/- 2.15 without reperfusion, 19.46 +/- 4.6 after 4-hour reperfusion; 240-minute ischemia: 5.6 +/- 1.99 and 22.3 +/- 3.77; 480-minute ischemia: 3.7 +/- 1.56 and 13.1 +/- 2.2). Eight-hour ischemic allografts had an increase in CD8-positive cells (1.37 +/- 0.5 and 2.3 +/- 0.77) and a significant increase in MHC II expression (11.48 +/- 2.1 and 18.27 +/- 1.34) during 4 hours of reperfusion.

CONCLUSIONS

We hypothesize that these findings reflect an early inflammatory reaction in the allograft possibly triggered by oxidative stress. During therapeutic interventions, both of these pathways must be considered.

Heme oxygenase-1 ameliorates ischemia/reperfusion injury by targeting dendritic cell maturation and migration

Ischemia/reperfusion injury (IRI) has a major impact on short- and long-term renal allograft survival by increasing graft immunogenicity. Donor preconditioning by inducing heme oxygenase 1 (HO-1) has been proven to exert cytoprotective and antiinflammatory effects on the graft, thus resulting in reduced graft immunogenicity. The study analyzed the effects and mechanisms of HO-1-mediated cytoprotection in rat kidney transplants exposed to cold preservation. We studied the differential gene-expression patterns of allografts after either short or long cold ischemia using a customized cDNA microarray. Prolonged cold ischemia led, 12 h after engraftment, to enhanced levels of adhesion molecules, heat-shock proteins, chemokines (CXCL10), and a remarkable upregulation of immunoproteasomes. Next we addressed the question whether induction of HO-1 or its byproduct carbon monoxide (CO) in organ donors targets these candidate markers related to enhanced immunogenicity. Induction of HO-1 or CO in organ donors 24 h before organ harvesting resulted in reduced mRNA levels of immunoproteasomes, MHC class II expression, and co-stimulatory molecules in the recipient's spleen, suggesting diminished migration and activation of donor dendritic cells. This observation suggests that HO-1/CO induction protects marginal allografts by inhibiting the immunogenicity of donor-derived dendritic cells.

Transcriptome analysis reveals heterogeneity in the injury response of kidney transplants

We studied the transcripts that are increased by stress and injury in mouse kidney transplants, focusing on transcripts increased in parenchymal cells-injury and repair-induced transcripts (IRITs). We compared four types of stressed kidneys: isografts, allografts, host kidneys of mice with isografts and nontransplant kidneys with ischemic acute tubular necrosis (ATN). After excluding transcripts associated with infiltrating cells and interferon-gamma-induced transcripts, we defined 790 IRITs in isografts. IRITs were remarkably heterogeneous in timing and mechanisms. Some were increased in host as well as donor kidneys, reflecting systemic influences (wounding, anesthetic). Most reflected local stress, resembling changes in ATN despite the lack of ATN histopathology. Mathematical decomposition of IRIT expression patterns confirmed heterogeneity, separating IRIT changes into component subsets, with an early peak (day 1) showing systemic effects and late peaks that resembled ATN, manifested Tgf-ss1 effects and recapitulated embryonic development. In allografts IRITs were initially similar to isografts but diverged due to allogeneic injury. The allospecific induction of IRITs was T-cell-dependent but perforin-granzyme-independent, compatible with delayed type hypersensitivity. The alloresponse strikingly and selectively increased the late IRITs but not the IRITs that peak early, indicating that rejection triggers parenchymal responses similar to those in ATN.

Thrombus organization and healing in the swine experimental aneurysm model. Part I. A histological and molecular analysis

Object

The authors describe the process of thrombus organization in the swine surgical aneurysm model.

Methods

Lateral carotid artery aneurysms with immediately induced thrombosis were created in 31 swine for a time-course study. Aneurysms were evaluated at 1, 3, 7, 14, 30, and 90 days after they were created. Histological analyses included quantitative immunohistochemical studies and evaluation of collagen deposition. Complementary DNA microarray analysis was performed for gene expression profiling. The lists of up- and downregulated genes were cross-matched with lists of genes known to be associated with cytokines or the extracellular matrix. The expression of selected genes was quantified using real-time polymerase chain reaction. Functional clustering was performed with the Expression Analysis Systematic Explorer (EASE) bioinformatics package.

Results

Histological analysis demonstrated leukocyte and macrophage infiltration in the thrombus at Day 3, myofibroblast infiltration at Days 7 to 14, and progressive collagen deposition and contraction thereafter. Tissue organization occurred in a centripetal fashion. A previously undescribed reticular network of connective tissue was observed at the periphery of the aneurysm at Day 3. Macrophages appeared critical to this thrombus organization. A total of 1109 genes were significantly changed from reference time zero during the time course: CXCL14, which produces a monocyte-specific chemokine, was upregulated over 100-fold throughout the time course; IGF1 was upregulated fourfold at Day 7, whereas IGFBP2 was downregulated approximately 50% at Days 7 and 14. Osteopontin (SPP1) upregulation increased from 30-fold at Day 30 to 45-fold at Day 14. The EASE analysis yielded eight functional classes of gene expression.

Conclusions

This investigation provides a detailed histological and molecular analysis of thrombus organization in the swine aneurysm model. The companion study will describe the effect of embolic bioabsorbable polymers on this process.

Expression changes in tolerant murine cardiac allografts after gene therapy with a lentiviral vector expressing alpha1,3 galactosyltransferase

Comparison of intragraft gene expression changes in tolerant cardiac allograft models may provide the basis for identifying pathways involved in graft survival. Our laboratory has previously demonstrated that tolerance to the gal alpha1,3 gal epitope, the major target of rejection of wild-type pig hearts in human cardiac transplantation, can be achieved after transplantation with bone marrow transduced with a lentiviral vector expressing alpha1,3 galactosyltransferase. We now present intracardiac gene expression changes associated with long-term tolerance in this model. Biotin-labeled cRNA was hybridized to Affymetrix GeneChip 430 2.0 Mouse Genome Arrays. Data were subjected to functional annotation analysis to identify genes of known function in which expression was increased or decreased by at least 2-fold (t-test, P < .05) in tolerant gal+/+ wild-type hearts as compared to transplanted syngeneic controls. Tolerant hearts demonstrated increased expression of genes associated with the stress response, modulation of immune function and cell survival (HSPa9a, CD56, and Akt1s1), and decreased expression of several immunoregulatory genes (CD209, CD26, and PDE4b). These data suggest that tolerance may be associated with activation of immunomodulatory and survival pathways.

Novel insights into lung transplant rejection by microarray analysis

Gene expression microarrays can estimate the prevalence of mRNA for thousands of genes in a small sample of cells or tissue. Organ transplant researchers are increasingly using microarrays to identify specific patterns of gene expression that predict and characterize acute and chronic rejection, and to improve our understanding of the mechanisms underlying organ allograft dysfunction. We used microarrays to assess gene expression in bronchoalveolar lavage cell samples from lung transplant recipients with and without acute rejection on simultaneous lung biopsies. These studies showed increased expression during acute rejection of genes involved in inflammation, apoptosis, and T-cell activation and proliferation. We also studied gene expression during the evolution of airway obliteration in a murine heterotopic tracheal transplant model of chronic rejection. These studies demonstrated specific patterns of gene expression at defined time points after transplantation in allografts, whereas gene expression in isografts reverted back to that of native tracheas within 2 wk after transplantation. These studies demonstrate the potential power of microarrays to identify biomarkers of acute and chronic lung rejection. The application of new genetic, genomic, and proteomic technologies is in its infancy, and the microarray-based studies described here are clearly only the beginning of their application to lung transplantation. The massive amount of data generated per tissue or cell sample has spawned an outpouring of invention in the bioinformatics field, which is developing methodologies to turn data into meaningful and reproducible clinical and mechanistic inferences.

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.

Changes in the transcriptome in allograft rejection: IFN-gamma-induced transcripts in mouse kidney allografts

We used Affymetrix Microarrays to define interferon-gamma (IFN-gamma)-dependent, rejection-induced transcripts (GRITs) in mouse kidney allografts. The algorithm included inducibility by recombinant IFN-gamma in kidneys of three normal mouse strains, increase in kidney allografts in three strain combinations and less induction in IFN-gamma-deficient allografts. We identified 40 transcripts, which were highly IFN-gamma inducible (e.g. Cxcl9, ubiquitin D, MHC), and 168 less sensitive to IFN-gamma in normal kidney. In allografts, expression of GRITs was intense and consistent at all time points (day 3 through 42). These transcripts were partially dependent on donor IFN-gamma receptors (IFN-gammars): receptor-deficient allografts manifested up to 76% less expression, but some transcripts were highly dependent (ubiquitin D) and others relatively independent (Cxcl9). Kidneys of hosts rejecting allografts showed expression similar to that observed with IFN-gamma injections. Many GRITs showed transient IFN-gamma-dependent increase in isografts, peaking at day 4-5. GRITs were increased in heart allografts, indicating them as generalized feature of alloresponse. Thus, expression of rejection-induced transcripts is robust and consistent in allografts, reflecting the IFN-gamma produced by the alloresponse locally and systemically, acting via host and donor IFN-gammar, as well as local IFN-gamma production induced by post-operative stress.

Expression of CTL associated transcripts precedes the development of tubulitis in T-cell mediated kidney graft rejection

The usual phenotype of clinical kidney allograft rejection is infiltration by lymphocytes and macrophages and evolution of histologic Banff lesions, particularly tubulitis, which indicate parenchymal injury. Using Affymetrix microarrays, we evaluated the relationship between the evolution of pathologic lesions and the transcriptome. We studied CBA/J into C57Bl/6 mouse kidney allografts in which one host kidney is left in place to permit observation of lesion development. Histology was dominated by early infiltration by mononuclear cells from day 3 and slower evolution of tubulitis after day 7. We defined a set of cytotoxic T lymphocyte-associated transcripts (CATs) on the basis of expression in purified cytotoxic T lymphocytes (CTL) and in a mixed lymphocyte culture, and absence in normal kidney. CATs were detectable by day 3 and highly expressed by day 5 in rejecting kidneys, with a median signal 14% of that in CTL, compared to 4% in isografts and normal kidneys, and persisted through day 42. Lack of mature B cells had little effect on CAT expression, confirming that CATs reflect T-cell-mediated rejection. Expression of CATs was established before diagnostic lesions and remained remarkably consistent through day 42 despite massive alterations in the pathology, and probably reflects T cells recruited to the graft.

Delayed graft function in kidney transplantation

Delayed graft function is a form of acute renal failure resulting in post-transplantation oliguria, increased allograft immunogenicity and risk of acute rejection episodes, and decreased long-term survival. Factors related to the donor and prerenal, renal, or postrenal transplant factors related to the recipient can contribute to this condition. From experimental studies, we have learnt that both ischaemia and reinstitution of blood flow in ischaemically damaged kidneys after hypothermic preservation activate a complex sequence of events that sustain renal injury and play a pivotal part in the development of delayed graft function. Elucidation of the pathophysiology of renal ischaemia and reperfusion injury has contributed to the development of strategies to decrease the rate of delayed graft function, focusing on donor management, organ procurement and preservation techniques, recipient fluid management, and pharmacological agents (vasodilators, antioxidants, anti-inflammatory agents). Several new drugs show promise in animal studies in preventing or ameliorating ischaemia-reperfusion injury and possibly delayed graft function, but definitive clinical trials are lacking. The goal of monotherapy for the prevention or treatment of is perhaps unattainable, and multidrug approaches or single drug targeting multiple signals will be the next step to reduce post-transplantation injury and delayed graft function.

Kidney transplant rejection and tissue injury by gene profiling of biopsies and peripheral blood lymphocytes

A major challenge for kidney transplantation is balancing the need for immunosuppression to prevent rejection, while minimizing drug-induced toxicities. We used DNA microarrays (HG-U95Av2 GeneChips, Affymetrix) to determine gene expression profiles for kidney biopsies and peripheral blood lymphocytes (PBLs) in transplant patients including normal donor kidneys, well-functioning transplants without rejection, kidneys undergoing acute rejection, and transplants with renal dysfunction without rejection. We developed a data analysis schema based on expression signal determination, class comparison and prediction, hierarchical clustering, statistical power analysis and real-time quantitative PCR validation. We identified distinct gene expression signatures for both biopsies and PBLs that correlated significantly with each of the different classes of transplant patients. This is the most complete report to date using commercial arrays to identify unique expression signatures in transplant biopsies distinguishing acute rejection, acute dysfunction without rejection and well-functioning transplants with no rejection history. We demonstrate for the first time the successful application of high density DNA chip analysis of PBL as a diagnostic tool for transplantation. The significance of these results, if validated in a multicenter prospective trial, would be the establishment of a metric based on gene expression signatures for monitoring the immune status and immunosuppression of transplanted patients.

Acute Nephrotoxicity of Tacrolimus and Sirolimus in Renal Isografts: Differential Intragraft Expression of Transforming Growth Factor-??1 and ??-Smooth Muscle Actin

BACKGROUND

Renal dysfunction early after kidney transplantation has multiple causes including ischemia-reperfusion (I/R) injury and drug-induced nephrotoxicity. This study assesses the acute nephrotoxicity of tacrolimus (Tac) and sirolimus (Sir) in a rat renal isograft model.

METHODS

Lewis renal isografts and uninephrectomized rats that did not undergo transplantation were treated with various doses of Tac (0.5-5.0 mg/kg/d) or Sir (0.5-6.5 mg/kg/d). Kidneys were examined on day 14 by routine histology and immunohistochemistry for transforming growth factor (TGF)-beta1 and alpha-smooth muscle actin (SMA).

RESULTS

Both Tac and Sir demonstrated evidence of nephrotoxicity in the early posttransplant period including increased serum creatinine and morphologic changes in the graft including interstitial inflammation, fibrosis, and tubular vacuolization. Nephrotoxicity was most prominent in the high-dose treatment groups for both drugs and was more severe in transplanted kidneys than in uninephrectomized animals that did not undergo transplantation, suggesting an additive effect of I/R injury and drug nephrotoxicity. Both Tac and Sir increased intragraft TGF-beta1 and alpha-SMA, but there were distinct differences in the patterns of TGF-beta1 expression. Both demonstrated TGF-beta1 in tubular epithelial cells, but Sir was associated with proximal tubular TGF-beta1 localization in a bright granular pattern, whereas Tac was associated with diffuse distal tubular staining.

CONCLUSIONS

Both Tac and Sir may be nephrotoxic in the early posttransplant period, especially at high doses and when combined with I/R injury. Immunohistochemical localization of TGF-beta1 in the tubular cells was distinctly different with each drug, suggesting possible differences in the mechanism(s) of nephrotoxicity requiring further study.

Age-related changes of cardiac gene expression following myocardial ischemia/reperfusion

Young and old (4 and 25 months of age, respectively) Fisher 344/Brown Norway hybrid female rats were subjected to four 3 min episodes of ischemia separated by 5 min of reperfusion. Corresponding open-chest sham-operated groups received 32 min of no intervention. All rats were allowed to recover, and 24h later hearts were removed and frozen in liquid nitrogen. Global gene profiling in the ischemic and the non-ischemic areas and in the sham-operated hearts as well was carried out by using Affymetrix Gene Chips. Young ischemic hearts demonstrated down-regulation of gene expression associated with early-remodeling including down-regulation of tissue inhibitor of metalloproteinase 1, decorin, collagen, tropoelastin, and fibulin, as well as decreases in hypertrophy-related transcripts. In contrast, old hearts showed a unique injury-related response, which included up-regulation of mRNAs for proteins associated with hypertrophy or apoptosis (including H36-alpha7 integrin, alpha-actin, tubulin, filamin, connective tissue growth factor, calcineurin, serine protease, and apoptosis inducing factor). These injury-related changes in gene expression could in part explain increased gravity of outcomes of ischemia and myocardial infarction in elderly hearts.

Accommodation in ABO-incompatible kidney allografts, a novel mechanism of self-protection against antibody-mediated injury

To elucidate the mechanism of self-protection against anti-donor blood-group antibody known as accommodation, we studied 16 human ABO-incompatible living-donor kidney transplant recipients at 3 and 12 months post transplantation. Both circulating anti-blood-group antibody and the target blood-group antigen in the graft were demonstrable in all patients after transplantation. Thirteen of 16 grafts had normal renal function and histology, while three grafts with prior humoral rejection demonstrated significant glomerulopathy and thus did not meet the criterion for accommodation. Using microarrays, we compared five 1-year protocol ABO-compatible renal graft biopsies to four accommodated ABO-incompatible graft biopsies. Significant alterations in gene expression in 440 probe sets, including SMADs, protein tyrosine kinases, TNF-alpha and Mucin 1 were identified. We verified these changes in gene expression using RT-PCR and immunohistochemistry. Heme oxygenase-1, Bcl-2 and Bcl-xl were not increased in ABO-incompatible grafts at any time-point. We conclude that accommodation is always present in well-functioning, long-surviving ABO-incompatible kidney transplants. This self-protection against antibody-mediated damage may involve several novel mechanisms including the disruption of normal signal transduction, attenuation of cellular adhesion and the prevention of apoptosis.

Microarray analysis: a novel research tool for cardiovascular scientists and physicians

The massive increase in information on the human DNA sequence and the development of new technologies will have a profound impact on the diagnosis and treatment of cardiovascular diseases. The microarray is a micro-hybridisation based assay. The filter, called microchip or chip, is a special kind of membrane in which are spotted several thousands of oligonucleotides of cDNA fragments coding for known genes or expressed sequence tags. The resulting hybridisation signal on the chip is analysed by a fluorescent scanner and processed with a software package utilising the information on the oligonucleotide or cDNA map of the chip to generate a list of relative gene expression. Microarray technology can be used for many different purposes, most prominently to measure differential gene expression, variations in gene sequence (by analysing the genome of mutant phenotypes), or more recently, the entire binding site for transcription factors. Measurements of gene expression have the advantage of providing all available sequence information for any given experimental design and data interpretation in pursuit of biological understanding. This research tool will contribute to radically changing our understanding of cardiovascular diseases.