MicroRNAs: potential biomarker in organ transplantation

Extracellular Vesicles in Transplantation: Friend or Foe

The long-term function of transplanted organs, even under immunosuppression, is hindered by rejection, especially chronic rejection. Chronic rejection occurs more frequently after lung transplantation, termed chronic lung allograft dysfunction (CLAD), than after transplantation of other solid organs. Pulmonary infection is a known risk factor for CLAD, as transplanted lungs are constantly exposed to the external environment; however, the mechanisms by which respiratory infections lead to CLAD are poorly understood. The role of extracellular vesicles (EVs) in transplantation remains largely unknown. Current evidence suggests that EVs released from transplanted organs can serve as friend and foe. EVs carry not only major histocompatibility complex antigens but also tissue-restricted self-antigens and various transcription factors, costimulatory molecules, and microRNAs capable of regulating alloimmune responses. EVs play an important role in antigen presentation by direct, indirect, and semidirect pathways in which CD8 and CD4 cells can be activated. During viral infections, exosomes (small EVs <200 nm in diameter) can express viral antigens and regulate immune responses. Circulating exosomes may also be a viable biomarker for other diseases and rejection after organ transplantation. Bioengineering the surface of exosomes has been proposed as a tool for targeted delivery of drugs and personalized medicine. This review focuses on recent studies demonstrating the role of EVs with a focus on exosomes and their dual role (immune activation or tolerance induction) after organ transplantation, more specifically, lung transplantation.

miR-21 antagonism reprograms macrophage metabolism and abrogates chronic allograft vasculopathy

Despite much progress in improving graft outcome during cardiac transplantation, chronic allograft vasculopathy (CAV) remains an impediment to long-term graft survival. MicroRNAs (miRNAs) emerged as regulators of the immune response. Here, we aimed to examine the miRNA network involved in CAV. miRNA profiling of heart samples obtained from a murine model of CAV and from cardiac-transplanted patients with CAV demonstrated that miR-21 was most significantly expressed and was primarily localized to macrophages. Interestingly, macrophage depletion with clodronate did not significantly prolong allograft survival in mice, while conditional deletion of miR-21 in macrophages or the use of a specific miR-21 antagomir resulted in indefinite cardiac allograft survival and abrogated CAV. The immunophenotype, secretome, ability to phagocytose, migration, and antigen presentation of macrophages were unaffected by miR-21 targeting, while macrophage metabolism was reprogrammed, with a shift toward oxidative phosphorylation in naïve macrophages and with an inhibition of glycolysis in pro-inflammatory macrophages. The aforementioned effects resulted in an increase in M2-like macrophages, which could be reverted by the addition of L-arginine. RNA-seq analysis confirmed alterations in arginase-associated pathways associated with miR-21 antagonism. In conclusion, miR-21 is overexpressed in murine and human CAV, and its targeting delays CAV onset by reprogramming macrophages metabolism.

MiR-378a-3p as a putative biomarker for hepatocellular carcinoma diagnosis and prognosis: Computational screening with experimental validation

BACKGROUND

Hepatocellular carcinoma (HCC) is a malignant disease with high morbidity and mortality, and the molecular mechanism for the genesis and progression is complex and heterogeneous. Biomarker discovery is crucial for the personalized and precision treatment of HCC. The accumulation of reported microRNA biomarkers makes it possible to combine computational identification with experimental validation to accelerate the discovery of novel biomarker.

RESULTS

In the present work, we applied a rational computer-aided biomarker discovery model to screen for the HCC diagnosis biomarker. Two HCC-associated networks were constructed based on the microRNA and mRNA expression profiles, and the potential microRNA biomarkers were identified based on their unique regulatory and influential power in the network. These putative biomarkers were then experimentally validated. One prominent example among these identified biomarkers is MiR-378a-3p: It was shown to independently regulate several important transcription factors such as PLAGL2 and β-catenin, affecting the β-catenin signaling. Such mechanism may indicate a potential tumor suppressor role of MiR-378a-3p and the impact of its abnormal expression on the cell growth and invasion of HCC.

CONCLUSIONS

A bioinformatics model with network topological and functional characterization was successfully applied to the identification of HCC biomarkers. The predicted microRNA biomarkers were than validated with experiments using human HCC cell lines, model animal, and clinical specimens. The results confirmed the prediction by our proposed model that miR-378a-3p was a putative biomarker for diagnosis and prognosis of HCC.

Advances of miRNAs in kidney graft injury

Kidney transplantation is the preferred treatment for patients with end-stage renal disease. However, various types of kidney graft injury after transplantation are still key factors that affect the survival of the kidney graft. Therefore, exploring the underlying mechanisms involved is very important. Current diagnostic measures for kidney graft injury (including needle biopsy, blood creatinine, eGFR, etc.) have many limiting factors such as invasiveness, insufficient sensitivity and specificity, so they cannot provide timely and effective information to clinicians. As for kidney grafts that have occurred injury, the traditional treatment has a little efficacy and many side effects. Therefore, there is an urgent need for developing new biomarkers and targeted treatment for kidney graft injury. Recently, studies have found that miRNAs are involved in the regulation of the progression of kidney graft injury. At the same time, it has high stability in blood, urine, and other body fluids, so it is suggested to have the potential as a biomarker and therapeutic target for kidney graft injury. Here, we reviewed the miRNAs involved in the pathophysiology of kidney graft injury such as ischemia/reperfusion injury, acute rejection, drug-induced nephrotoxicity, chronic allograft dysfunction, BK virus infection, and the latest advances of miRNAs as biomarkers and therapeutic targets of kidney graft injury, then summarized the specific data of miRNAs expression level in kidney graft injury, which aims to provide a reference for subsequent basic research and clinical transformation.

MicroRNA expression levels in lung recipients: correlations with clinical and laboratory data

Objective: to evaluate the expression levels of miRNA (miR-27, miR-101, miR-142, miR-339 and miR-424) and its relationship with clinical and laboratory parameters in lung transplant recipients. Materials and methods. The study included 57 lung recipients aged 10 to 74 years (35 ± 15), including six children (9%) – four boys 10, 12, 13 and 17 years and girls 13 and 14 years old – and 51 adult recipients, including 30 men (62.5%). The control group was made up of 14 healthy individuals that were not significantly different by gender and age. Expression levels of the microRNAs studied in blood plasma were determined via quantitative polymerase chain reaction (PCR). Correlations of miRNA expression levels with complete blood count and biochemical blood test indicators were analyzed. Results. Patients with end-stage chronic respiratory failure (potential lung recipients) were found to have significantly higher expression levels of miR-27, miR-101 and miR-339 in plasma than the healthy individuals (p = 0.02, p = 0.03 and p = 0.01, respectively). The expression level of miR-339 correlated with the age of potential lung recipients (p = 0.04). It was a negative correlation (r = –0.46). The expression levels of the other four miRNAs were age independent. The average expression level of miR-424 in lung recipients in the long-term period after lung transplant was higher than in waitlisted patients (p = 0.03). Analysis of the relationship between miRNA expression levels and external respiration function in the long-term post-transplant period showed that miR-142 expression level (r = 0.61; p = 0.04) positively correlates with the Tiffeneau-Pinelli index. This strong correlation, which exceeds 85%, indicates the presence of restrictive lung diseases. A year and more after transplantation, it was found that in the recipients, there were close positive correlations between miR-27, miR-142, miR-424 expression levels and blood leukocyte concentration, as well as between the miR-142 expression level and the sCD40L concentration during this period. Conclusion. A comparative study of the expression level of miRNAs (miR-27, miR-101, miR-142, miR-339 and miR-424) in the blood plasma of patients suffering from end-stage chronic lung diseases of various origin and in lung recipients enables us to conclude that further studies of the miRNA panels are needed in order to assess their effectiveness as potential molecular and genetic markers of post-transplant complications.

MiR-27a-3p downregulation contributes to the development of occlusive bronchiolitis

The only effective clinical treatment for many end-stage lung diseases is lung transplantation. However, chronic rejection of transplanted lung affects the long-term efficacy of lung transplantation to a large extent, thereby limiting the clinical application of lung transplantation. Occlusive bronchiolitis (OB) is a major cause of chronic functional loss of the transplanted lung. However, the OB pathogenesis remains unclear. Therefore, studying the OB pathogenesis and finding effective intervention methods are highly important. This study analyzed changes in the expression profile of microRNAs and transcription factors in mice with OB after orthotopic tracheal transplantation. miR-27a-3p was upregulated in lung tissue 20 days after transplantation. Transcription factor microarray analysis revealed that Smad3 was significantly downregulated. A miRNA-mRNA interaction network was constructed, and specific regulatory effects of miR-27a-3p on Smad3 were found. Smad3 was strongly associated with tumorigenesis and organ fibrosis. Compared with the control group, miR-27a-3p inhibited the epithelial-mesenchymal transformation (EMT) of lung epithelial cells. In addition, miR-27a-3p inhibition promoted the invasion and migration of lung epithelial cells. Dual luciferase reporter gene assay showed that miR-27a-3p can regulate the promoter activity of Smad3. MiR-27a-3p also inhibited the expression of inflammatory cytokines. Western blot results showed that miR-27a-3p can upregulate the E-cadherin expression and downregulate the expression of vimentin, fibronectin, and α-SMA. By studying the OB pathogenesis, we found that inhibition or alteration of the occurrence of EMT may reduce the proportion of chronic rejection of lung transplantation. MiR-27a-3p may also be developed as a new drug for the OB therapy. This finding will provide many possibilities for OB treatment and improve the prognosis of patients with OB.

Expression and Regulation Profile of Mature MicroRNA in the Pig: Relevance to Xenotransplantation

The pig is an important source of meat production and provides a valuable model for certain human diseases. MicroRNA (miRNA), which is noncoding RNA and regulates gene expression at the posttranscriptional level, plays a critical role in various biological processes. Studies on identification and function of mature miRNAs in multiple pig tissues are increasing, yet the literature is limited. Therefore, we reviewed current research to determine the miRNAs expressed in specific pig tissues that are involved in carcass values (including muscle and adipocytes), reproduction (including pituitary, testis, and ovary), and development of some solid organs (e.g., brain, lung, kidney, and liver). We also discuss the possible regulating mechanisms of miRNA. Finally, as pig organs are suitable candidates for xenotransplantation, biomarkers of their miRNA in xenotransplantation were evaluated.

Effects of MicroRNA on Regulatory T Cells and Implications for Adoptive Cellular Therapy to Ameliorate Graft-versus-Host Disease

Regulatory T cells (Tregs) are key mediators of the immune system. MicroRNAs (miRNAs) are a family of ~22 nucleotide non-coding RNAs that are processed from longer precursors by the RNases Drosha and Dicer. miRNA regulates protein expression posttranscriptionally through mRNA destabilization or translational silencing. A critical role for miRNA in Treg function was initially discovered when both Dicer and Drosha knockout (KO) mice were found to develop a fatal autoimmune disease phenotypically similar to Foxp3 KO mice.

Role of Circulating MicroRNAs in the Immunopathogenesis of Rejection After Pediatric Lung Transplantation

BACKGROUND

Acute rejection (AR) and development of chronic rejection, bronchiolitis obliterans syndrome (BOS) remain major limiting factors for lung transplantation (LTx). This retrospective study is to identify differentially expressed circulating microRNAs (miRNAs) that associate with development of AR and BOS in pediatric lung transplant recipients (LTxR).

METHODS

We determined the circulating levels of 7 selected candidate miRNAs in 14 LTxR with AR, 7 with BOS, and compared them against 13 stable pediatric LTxR at 1, 6, and 12 months after LTx. In addition, 6 AR, 7 BOS, and 8 stable pediatric LTxR, 16 AR, 17 BOS, and 16 stable adult LTxR were included for validation.

RESULTS

MiR-10a, -195, -133b were significantly lower in AR and miR-144, -142-5p, -155 were higher in AR compared to stable (P < 0.05). In addition, circulating levels of miR-134, -10a, -195, -133b were significantly lower and miR-144, -142-5p, -155 were higher (P < 0.05) with development of BOS. The receiver-operating characteristic demonstrated that miR-142-5p, miR-155, and miR-195 strongly discriminated patients with AR from stable LTxR (P < 0.001 for all comparisons): miR-142-5p (area under the curve [AUC], 0.854), miR-155 (AUC, 0.876), and miR-195 (AUC, 0.872). Further, miR-10a, miR-142-5p, miR-144, and miR-155 strongly discriminated BOS from stable LTxR (P < 0.001 for all comparisons).

CONCLUSIONS

We demonstrated that differential expression of circulating miRNAs occurs in LTxR with AR and BOS, suggesting that they can provide not only important clues to pathogenesis but also may serve as potential noninvasive biomarkers for AR and BOS after pediatric LTx.

Urinary miR-155-5p and CXCL10 as prognostic and predictive biomarkers of rejection, graft outcome and treatment response in kidney transplantation

AIMS

MicroRNAs (miRNAs) may be useful biomarkers of rejection and allograft outcome in kidney transplantation. Elevated urinary CXCL10 levels have been associated with acute rejection (AR) and may predict allograft failure. We examined the correlation of miRNA, CXCL10 levels and immunosuppressive drug exposure with AR and graft function in kidney transplant recipients.

METHODS

Eighty de novo kidney transplant recipients were recruited from four European centres. All patients received tacrolimus, mycophenolate mofetil, and methylprednisolone. Urinary pellet expression of miR-142-3p, miR-210-3p and miR-155-5p was assessed by quantitative real-time polymerase chain reaction and urinary CXCL10 levels by enzyme-linked immunosorbent assay at the 1^st week and the 1^st , 2^nd , 3^rd and 6^th months post-transplantation.

RESULTS

Eight patients experienced AR. Before and during AR, patients showed a significant increase of urinary miR-142-3p, miR-155-5p and CXCL10 levels and a decrease of miR-210-3p levels. Receiver operating characteristic curve analysis showed that miR-155-5p (area under the curve = 0.875; P = 0.046) and CXCL10 (area under the curve = 0.865; P = 0.029) had excellent capacity to discriminate between rejectors and nonrejectors. The optimal cut-off values for the prognosis of AR were 0.51, with 85% sensitivity and 86% specificity for miR-155-5p and 84.73 pg ml^-1 , with 84% sensitivity and 80% specificity for CXCL10. miR-155-5p and CXCL10 levels correlated with glomerular filtration rate. Levels of both biomarkers normalized after recovery of graft function.

CONCLUSIONS

The regular early post-transplantation monitoring of urinary miR-155-5p and CXCL10 can help in the prognosis of AR and graft dysfunction. Large prospective randomized multicentre trials are warranted to refine our cut-off values and validate the clinical usefulness of these biomarkers.

Regulatory RNAs and cardiovascular disease - with a special focus on circulating microRNAs

MicroRNAs (miRNAs) are a class of short non-coding regulatory RNA molecules which play an important role in intracellular communication and cell signaling and which influence cellular processes such as proliferation, differentiation, and cellular death. Over the past two decades, the crucial role of microRNAs in controlling tissue homeostasis and disease in cardiovascular systems has become widely recognized. By controlling the expression levels of their targets, several miRNAs have been shown to modulate the function of endothelial cells (miR-221/222 and -126), vascular smooth muscle cells (miR-143/145) and macrophages (miR-33, -758, and -26), thereby regulating the development and progression of atherosclerosis. The stability of miRNAs within the blood suggests that circulating miRNAs may function as important biomarkers of disease development and progression. Numerous circulating miRNAs have been found to be dysregulated in a wide variety of different disease states, including diabetes, cancer, and cardiovascular disease.

The release of microRNA-122 during liver preservation is associated with early allograft dysfunction and graft survival after transplantation

Early allograft dysfunction (EAD) after liver transplantation (LT) is associated with inferior graft survival. EAD is more prevalent in grafts from donation after circulatory death (DCD). However, accurate prediction of liver function remains difficult because of the lack of specific biomarkers. Recent experimental and clinical studies highlight the potential of hepatocyte-derived microRNAs (miRNAs) as sensitive, stable, and specific biomarkers of liver injury. The aim of this study was to determine whether miRNAs in graft preservation fluid are predictive for EAD after clinical LT and in an experimental DCD model. Graft preservation solutions of 83 liver grafts at the end of cold ischemia were analyzed for miRNAs by reverse transcription polymerase chain reaction. Of these grafts, 42% developed EAD after transplantation. Results were verified in pig livers (n = 36) exposed to different lengths of warm ischemia time (WIT). The absolute miR-122 levels and miR-122/miR-222 ratios in preservation fluids were significantly higher in DCD grafts (P = 0.001) and grafts developing EAD (P = 0.004). In concordance, the miR-122/miR-222 ratios in perfusion fluid correlate with serum transaminase levels within the first 24 hours after transplantation. Longterm graft survival was significantly diminished in grafts with high miR-122/miR-222 ratios (P = 0.02). In the porcine DCD model, increased WIT lead to higher absolute miR-122 levels and relative miR-122/miR-222 ratios in graft perfusion fluid (P = 0.01 and P = 0.02, respectively). High miR-122/miR-222 ratios in pig livers were also associated with high aspartate aminotransferase levels after warm oxygenated reperfusion. In conclusion, both absolute and relative miR-122 levels in graft preservation solution are associated with DCD, EAD, and early graft loss after LT. As shown in a porcine DCD model, miRNA release correlated with the length of WITs. Liver Transplantation 23 946-956 2017 AASLD.

Analysis of circulating miRNAs in patients with familial hypercholesterolaemia treated by LDL/Lp(a) apheresis

BACKGROUND

LDL/Lp(a) apheresis therapy is a well-established method of aggressively lowering LDL and Lp(a). Recently, miRNAs have been discussed as markers of vascular status including atherosclerosis. MiRNAs inhibit post-transcriptional processes through RNA duplex formation resulting in gene silencing or regulation of gene expression.

MATERIALS AND METHODS

We measured a profile of 175 plasma-circulating miRNAs using pre-defined Serum/Plasma Focus Human microRNA PCR Panels in pooled samples of 11 subjects with familial hypercholesterolaemia under long-term apheresis treatment. Subsequently we analysed expressions of ten pre-selected miRNAs potentially involved in lipid homeostasis in the same group of subjects. We compared plasma-circulating miRNA levels isolated from peripheral blood collected immediately before and after apheresis.

RESULTS

The greatest differences in plasma levels were found in miR-451a, miR-16, miR-19a/b, miR-223 and miR-185. In subsequent individual miRNA assay we detected a significant increase in miR-33b levels after apheresis (P < 0.05). Additionally, correlations between plasma lipids and miR-33a (P < 0.04) and miR-122 (P < 0.01) have been determined. Moreover, miR-122 levels in LDLR homozygotes were higher compared to heterozygotes after, but not before, apheresis treatment (P < 0.04).

CONCLUSIONS

LDL/Lp(a) apheresis has an impact on miRNAs associated with lipid homeostasis and vascular status.

Tissue-specific exosome biomarkers for noninvasively monitoring immunologic rejection of transplanted tissue

In transplantation, there is a critical need for noninvasive biomarker platforms for monitoring immunologic rejection. We hypothesized that transplanted tissues release donor-specific exosomes into recipient circulation and that the quantitation and profiling of donor intra-exosomal cargoes may constitute a biomarker platform for monitoring rejection. Here, we have tested this hypothesis in a human-into-mouse xenogeneic islet transplant model and validated the concept in clinical settings of islet and renal transplantation. In the xenogeneic model, we quantified islet transplant exosomes in recipient blood over long-term follow-up using anti-HLA antibody, which was detectable only in xenoislet recipients of human islets. Transplant islet exosomes were purified using anti-HLA antibody-conjugated beads, and their cargoes contained the islet endocrine hormone markers insulin, glucagon, and somatostatin. Rejection led to a marked decrease in transplant islet exosome signal along with distinct changes in exosomal microRNA and proteomic profiles prior to appearance of hyperglycemia. In the clinical settings of islet and renal transplantation, donor exosomes with respective tissue specificity for islet β cells and renal epithelial cells were reliably characterized in recipient plasma over follow-up periods of up to 5 years. Collectively, these findings demonstrate the biomarker potential of transplant exosome characterization for providing a noninvasive window into the conditional state of transplant tissue.

MicroRNA-150 negatively regulates the function of CD4(+) T cells through AKT3/Bim signaling pathway

Donor-derived CD4(+) T lymphocytes are the major effector cells directly involved in the development of graft-versus-host disease (GVHD). As a negative regulator of immune cell differentiation and development, microRNA-150 (miR-150) induces immunological tolerance in CD4(+) T cells after transplantation. However, the specific mechanisms have not been fully elucidated. In this study, we demonstrated that miR-150 is capable of not only inhibiting proliferation and activation of CD4(+) T cells but also promoting apoptosis. Mechanistically, miR-150 targets v-akt murine thymoma viral oncogene homolog 3 (AKT3), and subsequently downregulates B-cell lymphoma 2 (Bcl-2) interacting mediator of cell death (BIM). We have also demonstrated that re-expression of AKT3 reversed miR-150-mediated inhibition of CD4(+) T lymphocyte development. Therefore, we conclude that miR-150 negatively regulates CD4(+) T cell function by inhibiting the AKT3/BIM signaling pathway. These findings also suggest that manipulating the levels of miRNA-150 could be a valuable strategy in prevention and/or treatment of acute graft-versus-host disease.

In vitro application of ribonucleases: comparison of the effects on mRNA and miRNA stability

Background

MicroRNA has become important in a wide range of research interests. Due to the increasing number of known microRNAs, these molecules are likely to be increasingly seen as a new class of biomarkers. This is driven by the fact that microRNAs are relatively stable when circulating in the plasma. Despite extensive analysis of mechanisms involved in microRNA processing, relatively little is known about the in vitro decay of microRNAs under defined conditions or about the relative stabilities of mRNAs and microRNAs.

Methods

In this in vitro study, equal amounts of total RNA of identical RNA pools were treated with different ribonucleases under defined conditions. Degradation of total RNA was assessed using microfluidic analysis mainly based on ribosomal RNA. To evaluate the influence of the specific RNases on the different classes of RNA (ribosomal RNA, mRNA, miRNA) ribosomal RNA as well as a pattern of specific mRNAs and miRNAs was quantified using RT-qPCR assays. By comparison to the untreated control sample the ribonuclease-specific degradation grade depending on the RNA class was determined.

Results

In the present in vitro study we have investigated the stabilities of mRNA and microRNA with respect to the influence of ribonucleases used in laboratory practice. Total RNA was treated with specific ribonucleases and the decay of different kinds of RNA was analysed by RT-qPCR and miniaturized gel electrophoresis. In addition, we have examined whether the integrity observed for ribosomal RNA is applicable to microRNA and mRNA. Depending on the kind of ribonuclease used, our results demonstrated a higher stability of microRNA relative to mRNA and a limitation of the relevance of ribosomal RNA integrity to the integrity of other RNA groups.

Conclusion

Our results suggest that the degradation status of ribosomal RNA is not always applicable to mRNA and microRNA. In fact, the stabilities of these RNA classes to exposure to ribonucleases are independent from each other, with microRNA being more stable than mRNA. The relative stability of microRNAs supports their potential and further development as biomarkers in a range of applications.

Differential expression and functions of microRNAs in liver transplantation and potential use as non-invasive biomarkers

MicroRNAs (miRNAs) are important regulators in many biologic processes and have been implicated in the control of genes relevant to acute rejection and liver functions. Here we review the miRNAs specifically expressed in allografts during acute rejection and discuss potential roles for these miRNAs in liver dysfunction. We focus on miRNAs dysregulated both in the liver and in peripheral blood mononuclear cells and include a discussion of the potential for these miRNAs as non-invasive biomarkers to reflect liver status posttransplant.

MicroRNA sequence profiles of human kidney allografts with or without tubulointerstitial fibrosis

BACKGROUND

MicroRNA (miRNA) alterations accompanying interstitial fibrosis and tubular atrophy (IFTA) in kidney allografts may point toward pathologic mechanisms. Small-RNA sequencing provides information on total miRNA abundance and specific miRNA expression and allows analysis of differential expression based on read counts.

METHODS

MiRNA expression profiles of 8 human kidney allograft biopsies (4 IFTA and 4 normal biopsies, discovery set) were characterized using barcoded deep-sequencing of a cDNA library prepared from multiplexed RNA. Statistical analysis of the sequence data guided selection of miRNAs for validation and the levels of selected miRNAs were quantified in 18 biopsies (10 IFTA and 8 normal) using real-time quantitative PCR assays (RT-QPCR).

RESULTS

Total miRNA content was 50% lower in RNA from IFTA compared with normal biopsies. Global miRNA profiles clustered in partial agreement with diagnosis. Several miRNAs, including miR-21, 142-3p, and 5p and the cluster comprising miR-506 on chromosome X had twofold to sevenfold higher expression in IFTA compared with normal biopsies, whereas miRNA miR-30b and 30c were lower in IFTA biopsies (miR-30a, -30d, -30e, and all respective star sequences showed similar trends). IFTA and normal biopsy distinction was also noted in the pattern of miRNA nucleotide sequence variations. Differentially expressed miRNAs were confirmed on the larger set of allograft biopsies using RT-QPCR, and the levels of miRNAs were found to be associated with allograft function and survival.

CONCLUSION

Differentially expressed miRNAs and their predicted targets identified by deep sequencing are candidates for further investigation to decipher the mechanism and management of kidney allograft fibrosis.

MicroRNAs as biomarkers in solid organ transplantation

Important progress has been made in improving short-term outcomes in solid organ transplantation. However, long-term outcomes have not improved during the last decades. There is a critical need for biomarkers of donor quality, early diagnosis of graft injury and treatment response. MicroRNAs (miRNAs) are a class of small single-stranded noncoding RNAs that function through translational repression of specific target mRNAs. MiRNA expression has been associated with different diseases and physiological conditions. Moreover, miRNAs have been detected in different biological fluids and these circulating miRNAs can distinguish diseased individuals from healthy controls. The noninvasive nature of circulating miRNA detection, their disease specificity and the availability of accurate techniques for detecting and monitoring these molecules has encouraged a pursuit of miRNA biomarker research and the evaluation of specific applications in the transplant field. miRNA expression might develop as excellent biomarkers of allograft injury and function. In this minireview, we summarize the main accomplishments of recently published reports focused on the identification of miRNAs as biomarkers in organ quality, ischemia-reperfusion injury, acute rejection, tolerance and chronic allograft dysfunction emphasizing their mechanistic and clinical potential applications and describing their methodological limitations.

Circulating microRNAs as biomarkers, therapeutic targets, and signaling molecules

Small noncoding microRNAs (miRNAs) are important regulators of post-transcriptional gene regulation and have altered the prevailing view of a linear relationship between gene and protein expression. Aberrant miRNA expression is an emerging theme for a wide variety of diseases, highlighting the fundamental role played by miRNAs in both physiological and pathological states. The identification of stable miRNAs in bodily fluids paved the way for their use as novel biomarkers amenable to clinical diagnosis in translational medicine. Identification of miRNAs in exosomes that are functional upon delivery to the recipient cells has highlighted a novel method of intercellular communication. Delivery of miRNAs to recipient cells via blood, with functional gene regulatory consequences, opens up novel avenues for target intervention. Exosomes thus offer a novel strategy for delivering drugs or RNA therapeutic agents. Though much work lies ahead, circulating miRNAs are unequivocally ushering in a new era of novel biomarker discovery, intercellular communication mechanisms, and therapeutic intervention strategies.