MicroRNAs in Kidney Transplantation: Living up to Their Expectations?

Extracellular Vesicles Mediate Immune Responses to Tissue-Associated Self-Antigens: Role in Solid Organ Transplantations

Transplantation is a treatment option for patients diagnosed with end-stage organ diseases; however, long-term graft survival is affected by rejection of the transplanted organ by immune and nonimmune responses. Several studies have demonstrated that both acute and chronic rejection can occur after transplantation of kidney, heart, and lungs. A strong correlation has been reported between de novo synthesis of donor-specific antibodies (HLA-DSAs) and development of both acute and chronic rejection; however, some transplant recipients with chronic rejection do not have detectable HLA-DSAs. Studies of sera from such patients demonstrate that immune responses to tissue-associated antigens (TaAgs) may also play an important role in the development of chronic rejection, either alone or in combination with HLA-DSAs. The synergistic effect between HLA-DSAs and antibodies to TaAgs is being established, but the underlying mechanism is yet to be defined. We hypothesize that HLA-DSAs damage the transplanted donor organ resulting in stress and leading to the release of extracellular vesicles, which contribute to chronic rejection. These vesicles express both donor human leukocyte antigen (HLA) and non-HLA TaAgs, which can activate antigen-presenting cells and lead to immune responses and development of antibodies to both donor HLA and non-HLA tissue-associated Ags. Extracellular vesicles (EVs) are released by cells under many circumstances due to both physiological and pathological conditions. Primarily employing clinical specimens obtained from human lung transplant recipients undergoing acute or chronic rejection, our group has demonstrated that circulating extracellular vesicles display both mismatched donor HLA molecules and lung-associated Ags (collagen-V and K-alpha 1 tubulin). This review focuses on recent studies demonstrating an important role of antibodies to tissue-associated Ags in the rejection of transplanted organs, particularly chronic rejection. We will also discuss the important role of extracellular vesicles released from transplanted organs in cross-talk between alloimmunity and autoimmunity to tissue-associated Ags after solid organ transplantation.

Role of miR-139-5p in ectopic endometrial stromal cells and the underlying molecular mechanism

Endometriosis is an estrogen-dependent disease. Studies have shown that miR-139-5p is significantly upregulated in endometriosis lesions, but its specific role and molecule mechanism in endometriosis has not yet been reported. The malignant biological behavior of ectopic endometrial stromal cells (ESCs) is similar to that of malignant cancer cells. BBC3 (BCL2 binding component 3) is a known apoptosis inducer and it serves key roles in the regulation of cell behavior. However, the role of BBC3 in ectopic ESCs remains unknown. The present study aimed to investigate the role of miR-139-5p in the progression of endometriosis and to determine its underlying molecular mechanism of action. Ectopic, non-ectopic and normal endometrial stromal cells (ESCs) were extracted from endometrial samples, and reverse transcription-quantitative PCR was performed to determine microRNA (miR)-139-5p and Bcl-2 binding component 3 (BBC3) mRNA expression levels in endometrial tissue samples and ESCs. The target gene of miR-139-5p was predicted using TargetScan software and verified using a dual luciferase reporter assay. Western blotting was performed to determine BBC3 protein expression levels. Flow cytometry analysis, and MTT and Transwell assays were performed to assess cell apoptosis, viability, and migration and invasion of the cells transfected with inhibitor control, miR-139-5p inhibitor, miR-139-5p inhibitor + control-small interfering (si)RNA or miR-139-5p inhibitor + BBC3-siRNA, respectively. The results demonstrated that miR-139-5p expression levels were upregulated in ectopic endometrial samples and ESCs compared with the respective control groups. Furthermore, it was verified that BBC3 was a direct target of miR-139-5p, and both BBC3 mRNA and protein expression levels were downregulated in ectopic endometrial samples and ESCs. Both transfection with the miR-139-5p inhibitor and BBC3-small interfering (si)RNA markedly downregulated miR-139-5p and BBC3 expression levels in ectopic ESCs, respectively. miR-139-5p inhibitor-induced upregulated BBC3 expression was reversed following transfection with BBC3-siRNA. Furthermore, the miR-139-5p inhibitor significantly decreased viability, migration and invasion, while inducing apoptosis in ectopic ESCs compared with the inhibitor control group. Notably, the aforementioned effects were reversed by knocking down BBC3 expression. In conclusion, the results of the present study suggested that miR-139-5p may play a key role in the progression of endometriosis by regulating the viability of ESCs and directly targeting BBC3.

Surgically induced ischemia has no impact on protein expression levels of HIF-1α and related biomarkers in renal cell carcinoma

The increasing demands for personalized targeted therapy directed against renal cell carcinoma have driven a search for predictive markers. Novel therapies targeting HIF-1α in renal cell carcinoma have been developed, and HIF-1α has been suggested as a novel predictive marker of response to therapy. The surgical resection of a kidney tumor induces tissue ischemia, and HIF-1α is an oxygen-sensitive transcription factor, which is known to be upregulated during hypoxia. This study investigated the impact of intra-surgical and post-surgical ischemia on protein expression levels of HIF-1α and three related biomarkers (VEGF, GLUT-1, and CAIX) in 20 patients with renal cell carcinoma with immunohistochemistry and Western blotting. Surgical ischemia did not have a significant impact on protein expression levels of any of the investigated markers. Long-post-surgical ischemia resulted in reduced expression levels of HIF-1α, probably due to autolysis. Our results suggest that HIF-1α is a stable protein, with expression levels not affected by intra-surgical ischemia, and hence, HIF-1α is suited for marker analysis.

Urinary MicroRNA-21-5p as Potential Biomarker of Interstitial Fibrosis and Tubular Atrophy (IFTA) in Kidney Transplant Recipients

Chronic renal allograft dysfunction (CAD) is a major limiting factor of long-term graft survival. The hallmarks of progressive CAD are interstitial fibrosis and tubular atrophy (IFTA). MicroRNAs are small, regulatory RNAs involved in many immunological processes. In particular, microRNA-21-5p (miR-21) is considered to be strongly associated with pathogenesis regarding tubulointerstitium. The aim of this study was to assess urinary miR-21 expression levels in the kidney transplant recipients and determine their application in the evaluation of IFTA and kidney allograft function. The expression levels of miR-21 were quantified in the urine of 31 kidney transplant recipients with biopsy-assessed IFTA (IFTA 0 + I: n = 17; IFTA II + III: n = 14) by real-time quantitative PCR. Urine samples were collected at the time of protocolar biopsies performed 1 or 2 years after kidney transplantation. MicroRNA-191-5p was used as reference gene. MiR-21 was significantly up-regulated in IFTA II + III group compared to IFTA 0 + I group (p = 0.003). MiR-21 correlated significantly with serum concentration of creatinine (r = 0.52, p = 0.003) and eGFR (r = -0.45; p = 0.01). ROC analysis determined the diagnostic value of miR-21 with an area under curve (AUC) of 0.80 (p = 0.0002), sensitivity of 0.86 and specificity of 0.71. miR-21 is associated with renal allograft dysfunction and IFTA. Therefore, it could be considered as a potential diagnostic, non-invasive biomarker for monitoring renal graft function.

Ischaemia reperfusion injury: mechanisms of progression to chronic graft dysfunction

The increasing use of extended criteria organs to meet the demand for kidney transplantation raises an important question of how the severity of early ischaemic injury influences long-term outcomes. Significant acute ischaemic kidney injury is associated with delayed graft function, increased immune-associated events and, ultimately, earlier deterioration of graft function. A comprehensive understanding of immediate molecular events that ensue post-ischaemia and their potential long-term consequences are key to the discovery of novel therapeutic targets. Acute ischaemic injury primarily affects tubular structure and function. Depending on the severity and persistence of the insult, this may resolve completely, leading to restoration of normal function, or be sustained, resulting in persistent renal impairment and progressive functional loss. Long-term effects of acute renal ischaemia are mediated by several mechanisms including hypoxia, HIF-1 activation, endothelial dysfunction leading to vascular rarefaction, sustained pro-inflammatory stimuli involving innate and adaptive immune responses, failure of tubular cells to recover and epigenetic changes. This review describes the biological relevance and interaction of these mechanisms based on currently available evidence.

Preconditioning against renal ischaemia reperfusion injury: the failure to translate to the clinic

Acute kidney injury (AKI) as a result of ischaemia-reperfusion represents a major healthcare burden worldwide. Mortality rates from AKI in hospitalized patients are extremely high and have changed little despite decades of research and medical advances. In 1986, Murry et al. demonstrated for the first time the phenomenon of ischaemic preconditioning to protect against ischaemia-reperfusion injury (IRI). This seminal finding paved the way for a broad body of research, which attempted to understand and ultimately harness this phenomenon for human application. The ability of preconditioning to limit renal IRI has now been demonstrated in multiple different animal models. However, more than 30 years later, a safe and consistent method of protecting human organs, including the kidneys, against IRI is still not available. This review highlights agents which, despite strong preclinical data, have recently failed to reduce AKI in human trials. The multiple reasons which may have contributed to the failure to translate some of the promising findings to clinical therapies are discussed. Agents which hold promise in the clinic because of their recent efficacy in preclinical large animal models are also reviewed.

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.

MicroRNA mediated regulation of immunity against gram-negative bacteria

Evidence over the last couple decades has comprehensively established that short, highly conserved, non-coding RNA species called microRNA (miRNA) exhibit the ability to regulate expression and function of host genes at the messenger RNA (mRNA) level. MicroRNAs play key regulatory roles in immune cell development, differentiation, and protective function. Intrinsic host immune response to invading pathogens rely on intricate orchestrated events in the development of innate and adaptive arms of immunity. We discuss the involvement of miRNAs in regulating these processes against gram negative pathogens in this review.

Urinary MicroRNA as Biomarker in Renal Transplantation

Urine represents a noninvasive source in which proteins and nucleic acids can be assessed. Such analytes may function as biomarkers to monitor kidney graft pathology at every desired frequency, thereby providing a time window to prevent graft damage by therapeutic intervention. Recently, several proteins have been measured in urine as markers of graft injury. However, the specificity is limited, and measuring urinary proteins generally lacks the potential to predict early kidney graft damage. Currently, urinary mRNA and microRNA are being investigated to evaluate the prognostic value of changes in gene expression during the initial stages of graft damage. At such time point, a change in treatment regimen and dosage is expected to have maximum potency to minimize future decline in graft function. Both mRNA and microRNAs have shown promising results in both detection and prediction of graft injury. An advantage of microRNAs compared to mRNA molecules is their stability, a characteristic that is beneficial when working with urine samples. In this review, we provide the current state of urinary biomarkers in renal transplantation, with a focus on urinary microRNA. In addition, we discuss the methods used to study urinary microRNA expression.

Upregulation of microRNA 142-3p in the peripheral blood and urinary cells of kidney transplant recipients with post-transplant graft dysfunction

We analyzed microRNA (miR)-142-3p expression in leucocytes of the peripheral blood and urinary sediment cell samples obtained from kidney transplant recipients who developed graft dysfunction. Forty-one kidney transplant recipients with kidney graft dysfunction and 8 stable patients were included in the study. The groups were divided according to histological analysis into acute rejection group (n=23), acute tubular necrosis group (n=18) and stable patients group used as a control for gene expression (n=8). Percutaneous biopsies were performed and peripheral blood samples and urine samples were obtained. miR-142-3p was analyzed by real-time polymerase chain reaction. The group of patients with acute tubular necrosis presented significantly higher expressions in peripheral blood (P<0.05) and urine (P<0.001) compared to the stable patients group. Also, in the peripheral blood, miR-142-3p expression was significantly higher in the acute tubular necrosis group compared to the acute rejection group (P<0.05). Urine samples of the acute rejection group presented higher expression compared to the stable patients group (P<0.001) but the difference between acute tubular necrosis and acute rejection groups was not significant in the urinary analyzes (P=0.079). miR-142-3p expression has a distinct pattern of expression in the setting of post-operative acute tubular necrosis after kidney transplantation and may potentially be used as a non-invasive biomarker for renal graft dysfunction.

Improving the outcome of kidney transplantation by ameliorating renal ischemia reperfusion injury: lost in translation?

Kidney transplantation is the treatment of choice in patients with end stage renal disease. During kidney transplantation ischemia reperfusion injury (IRI) occurs, which is a risk factor for acute kidney injury, delayed graft function and acute and chronic rejection. Kidneys from living donors show a superior short- and long-term graft survival compared with deceased donors. However, the shortage of donor kidneys has resulted in expansion of the donor pool by using not only living- and brain death donors but also kidneys from donation after circulatory death and from extended criteria donors. These grafts are associated with an increased sensitivity to IRI and decreased graft outcome due to prolonged ischemia and donor comorbidity. Therefore, preventing or ameliorating IRI may improve graft survival. Animal experiments focus on understanding the mechanism behind IRI and try to find methods to minimize IRI either before, during or after ischemia. This review evaluates the different experimental strategies that have been investigated to prevent or ameliorate renal IRI. In addition, we review the current state of translation to the clinical setting. Experimental research has contributed to the development of strategies to prevent or ameliorate IRI, but promising results in animal studies have not yet been successfully translated to clinical use.

MicroRNA profiling identifies miR-129-5p as a regulator of EMT in tubular epithelial cells

The importance of microRNAs in various diseases has been demonstrated, but their potential role in the pathogenesis of renal fibrosis needs to further research. We have profiled changes in microRNA levels in human kidney proximal tubular cell line HK-2 with TGF-β treatment and identified significantly altered miRNAs. miR-129-5p, was one of the significant down-regulated miRNAs in experimental models. PDPK1 was a potential target gene of miR-129-5p and luciferase assay analysis identified PDPK1 as a new direct target gene of miR-129-5p. Further research indicated that miR-129-5p suppressed PDPK1 mRNA and protein levels in HK-2 cells. miR-129-5p inhibited EMT via PDPK1 in HK-2 cells. In a conclusion, our findings suggested that miR-129-5p may function as a suppressor in renal fibrosis by targeting PDPK1.

Mini-review: emerging roles of microRNAs in the pathophysiology of renal diseases

MicroRNAs (miRNA) are endogenously produced short noncoding regulatory RNAs that can repress gene expression by posttranscriptional mechanisms. They can therefore influence both normal and pathological conditions in diverse biological systems. Several miRNAs have been detected in kidneys, where they have been found to be crucial for renal development and normal physiological functions as well as significant contributors to the pathogenesis of renal disorders such as diabetic nephropathy, acute kidney injury, lupus nephritis, polycystic kidney disease, and others, due to their effects on key genes involved in these disease processes. miRNAs have also emerged as novel biomarkers in these renal disorders. Due to increasing evidence of their actions in various kidney segments, in this mini-review we discuss the functional significance of altered miRNA expression during the development of renal pathologies and highlight emerging miRNA-based therapeutics and diagnostic strategies for early detection and treatment of kidney diseases.