MicroRNAs in IgA nephropathy

Deciphering roles of protein post-translational modifications in IgA nephropathy progression and potential therapy

Immunoglobulin A nephropathy (IgAN), one type of glomerulonephritis, displays the accumulation of glycosylated IgA in the mesangium. Studies have demonstrated that both genetics and epigenetics play a pivotal role in the occurrence and progression of IgAN. Post-translational modification (PTM) has been revealed to critically participate in IgAN development and progression because PTM dysregulation results in impaired degradation of proteins that regulate IgAN pathogenesis. A growing number of studies identify that PTMs, including sialylation, o-glycosylation, galactosylation, phosphorylation, ubiquitination and deubiquitination, modulate the initiation and progression of IgAN. Hence, in this review, we discuss the functions and mechanisms of PTMs in regulation of IgAN. Moreover, we outline numerous compounds that govern PTMs and attenuate IgAN progression. Targeting PTMs might be a useful strategy to ameliorate IgAN.

An Update on the Genetics of IgA Nephropathy

Immunoglobulin A (IgA) nephropathy (IgAN), the most common form of glomerulonephritis, is one of the leading causes of end-stage kidney disease (ESKD). It is widely believed that genetic factors play a significant role in the development of IgAN. Previous studies of IgAN have provided important insights to unravel the genetic architecture of IgAN and its potential pathogenic mechanisms. The genome-wide association studies (GWASs) together have identified over 30 risk loci for IgAN, which emphasizes the importance of IgA production and regulation in the pathogenesis of IgAN. Follow-up fine-mapping studies help to elucidate the candidate causal variant and the potential pathogenic molecular pathway and provide new potential therapeutic targets. With the rapid development of next-generation sequencing technologies, linkage studies based on whole-genome sequencing (WGS)/whole-exome sequencing (WES) also identify rare variants associated with IgAN, accounting for some of the missing heritability. The complexity of pathogenesis and phenotypic variability may be better understood by integrating genetics, epigenetics, and environment. We have compiled a review summarizing the latest advancements in genetic studies on IgAN. We similarly summarized relevant studies examining the involvement of epigenetics in the pathogenesis of IgAN. Future directions and challenges in this field are also proposed.

Urinary exosomal miRNA signature of IgA nephropathy: a case-control study

IgA nephropathy is the most common primary glomerulonephritis worldwide and can progress to end-stage kidney disease (ESKD). The current "gold standard" for diagnosis is kidney biopsy, which is invasive and associated with morbidity. miRNAs are small, non-coding endogenous RNA that may serve as non-invasive biomarkers, and that are found in urinary exosomes. Thus far, there is a paucity of studies of the miRNA profile for the diagnosis of IgA nephropathy. Hence, we aimed to study the urinary exosomal miRNA signature of Indian patients with IgA nephropathy. Fifty biopsy-proven IgA nephropathy patients, 50 healthy controls and 25 patients with ESKD (IgA nephropathy) were recruited over 2 years (2020-2022). Urinary exosomes were isolated from which miRNA was extracted . Analysis of urinary exosomal miRNA was done using the digital multiplexed nCounter® human v3 miRNA Expression Assay which contains 799 unique miRNA barcodes. Candidate miRNAs were identified using Lasso regression and consensus clustering. The mean age of IgA nephropathy patients was 36.32 ± 3.067 years, mean creatinine was 2.26 ± 0.318 mg/dl and mean proteinuria was 2.69 ± 0.64 g/day. Compared to healthy controls, the majority (N = 150) of miRNAs were significantly downregulated. Five candidate miRNAs (hsa.miR.146b.3p, hsa.miR.599, hsa.miR.4532, hsa.miR.664b.5p and hsa.miR.221.5p) were able to differentiate between IgA nephropathy cases and controls (AUC > 0.90); the presence of all 5 was associated with 100% specificity and sensitivity for diagnosing IgA nephropathy cases. This study of Indian patients identified that there was a significant difference in the urinary exosomal miRNA profile between IgA nephropathy cases and healthy controls, suggesting that miRNAs may be valuable in the non-invasive diagnosis of IgA nephropathy.

Urinary Extracellular Vesicles in Chronic Kidney Disease: From Bench to Bedside?

Extracellular vesicles are a diverse group of particles that include exosomes, microvesicles, and apoptotic bodies and are defined by size, composition, site of origin, and density. They incorporate various bioactive molecules from their cell of origin during formation, such as soluble proteins, membrane receptors, nucleic acids (mRNAs and miRNAs), and lipids, which can then be transferred to target cells. Extracellular vesicles/exosomes have been extensively studied as a critical factor in pathophysiological processes of human diseases. Urinary extracellular vesicles could be a promising liquid biopsy for determining the pattern and/or severity of kidney histologic injury. The signature of urinary extracellular vesicles may pave the way for noninvasive methods to supplement existing testing methods for diagnosing kidney diseases. We discuss the potential role of urinary extracellular vesicles in various chronic kidney diseases in this review, highlighting open questions and discussing the potential for future research.

Blood TGF-β1 and miRNA-21-5p levels predict renal fibrosis and outcome in IgA nephropathy

BACKGROUND

IgA nephropathy (IgAN), the most common primary glomerulonephritis, often presents as advanced renal failure with end-stage renal disease at diagnosis. Tubulointerstitial injury and fibrosis on histology are the most important predictors of renal outcome. A non-invasive biomarker is required for assessment of progression in IgA nephropathy. We investigated the utility of blood profibrotic molecules, TGF-β1 and miRNA-21-5p (miR-21), to identify a non-invasive biomarker for renal fibrosis in IgAN.

MATERIALS AND METHODS

The study included 30 IgAN (mean age 31.5 ± 9 years) at the time of initial diagnosis, 25 age-sex-matched healthy controls and 10 Lupus nephritis patients as disease controls. Serum TGF-β1 was analyzed by enzyme-linked immunosorbent assay and plasma miR-21 by qRT-PCR, normalized with U6-snRNA. The levels were correlated with clinical features, laboratory parameters, histological Oxford MEST-C score and renal outcome.

RESULTS

The serum TGF-β1 and plasma miR-21 were significantly higher in patients with IgAN than in healthy controls. TGF-β1 significantly correlated with serum creatinine, eGFR, Oxford T score and miR-21. High plasma miR-21 was significantly associated with T score and interstitial inflammation. On multivariate analysis, high levels of TGF-β1 and miR-21 correlated with lower eGFR and T score, respectively. On a follow-up period of 21.5 months, high miR-21 expression at diagnosis was associated (p = 0.02) with a poor renal outcome having a shorter time to doubling of serum creatinine.

CONCLUSION

High blood TGF-β1 and miR-21 expression at diagnosis of IgAN show significant correlation with renal function and degree of chronic tubulointerstitial injury on histology.

Pathogenic Role of MicroRNA Dysregulation in Podocytopathies

MicroRNAs (miRNAs) participate in the regulation of various important biological processes by regulating the expression of various genes at the post-transcriptional level. Podocytopathies are a series of renal diseases in which direct or indirect damage of podocytes results in proteinuria or nephrotic syndrome. Despite decades of research, the exact pathogenesis of podocytopathies remains incompletely understood and effective therapies are still lacking. An increasing body of evidence has revealed a critical role of miRNAs dysregulation in the onset and progression of podocytopathies. Moreover, several lines of research aimed at improving common podocytopathies diagnostic tools and avoiding invasive kidney biopsies have also identified circulating and urine miRNAs as possible diagnostic and prognostic biomarkers for podocytopathies. The present review mainly aims to provide an updated overview of the recent achievements in research on the potential applicability of miRNAs involved in renal disorders related to podocyte dysfunction by laying particular emphasis on focal segmental glomerulosclerosis (FSGS), minimal change disease (MCD), membranous nephropathy (MN), diabetic kidney disease (DKD) and IgA nephropathy (IgAN). Further investigation into these dysregulated miRNAs will not only generate novel insights into the mechanisms of podocytopathies, but also might yield novel strategies for the diagnosis and therapy of this disease.

Recent findings on the role of microRNAs in genetic kidney diseases

BACKGROUND

MicroRNAs (miRNAs) are non-coding, endogenous, single-stranded, small (21-25 nucleotides) RNAs. Various target genes at the post-transcriptional stage are modulated by miRNAs that are involved in the regulation of a variety of biological processes such as embryonic development, differentiation, proliferation, apoptosis, inflammation, and metabolic homeostasis. Abnormal miRNA expression is strongly associated with the pathogenesis of multiple common human diseases including cardiovascular diseases, cancer, hepatitis, and metabolic diseases.

METHODS AND RESULTS

Various signaling pathways including transforming growth factor-β, apoptosis, and Wnt signaling pathways have also been characterized to play an essential role in kidney diseases. Most importantly, miRNA-targeted pharmaceutical manipulation has represented a promising new therapeutic approach against kidney diseases. Furthermore, miRNAs such as miR-30e-5p, miR-98-5p, miR-30d-5p, miR-30a-5p, miR-194-5p, and miR-192-5p may be potentially employed as biomarkers for various human kidney diseases.

CONCLUSIONS

A significant correlation has also been found between some miRNAs and the clinical markers of renal function like baseline estimated glomerular filtration rate (eGFR). Classification of miRNAs in different genetic renal disorders may promote discoveries in developing innovative therapeutic interventions and treatment tools. Herein, the recent advances in miRNAs associated with renal pathogenesis, emphasizing genetic kidney diseases and development, have been summarized.

ICAM-1 related long noncoding RNA is associated with progression of IgA nephropathy and fibrotic changes in proximal tubular cells

Intercellular adhesion molecule 1 (ICAM-1) related long noncoding RNA (ICR) is on the antisense strand of ICAM-1 and regulates ICAM-1 expression. ICAM-1 is involved in renal tubulointerstitial injury; however, the expression and clinical implication of ICR are not determined in IgA nephropathy (IgAN). We compared renal ICR levels in 337 IgAN patients with those of 89 biopsy controls, and a markedly increased ICR level was observed in IgAN patients. By Cox proportional hazards models, higher levels of renal ICR were independently associated with disease progression event defined as end-stage renal disease or ≥ 40% decline in estimated glomerular filtration rate. Patients in the highest tertile of renal ICR had a 3.5-fold higher risk for disease progression compared with those in the lowest tertile. The addition of renal ICR to a model with traditional risk factors improved risk prediction of disease progression (net reclassification index: 0.31 [95% CI 0.01–0.50]; integrated discrimination index: 0.10 [95% CI 0.04–0.16]). Inhibition of ICR by transfection with plasmids containing ICR shRNA significantly reduced expression of collagen I and α-SMA, and phosphorylation of Akt and mTOR in TGF-β1- treated HK-2 cells. Our findings suggest that renal ICR might be an independent predictor of IgAN progression and contribute to renal fibrosis.

Renal Megalin mRNA Downregulation Is Associated with CKD Progression in IgA Nephropathy

INTRODUCTION

Megalin plays an important role in proximal tubule uptake of filtered proteins. Downregulation and dysfunction of megalin were previously demonstrated in IgA nephropathy (IgAN); however, its relationship to IgAN progression remains unclear.

METHODS

We measured renal megalin mRNA and miR-148b, previously identified as a regulator of megalin, in a retrospective cohort of 417 IgAN patients at the time of biopsy, and evaluated their associations with chronic kidney disease (CKD) progression event, defined as end-stage renal disease or ≥40% decline in estimated glomerular filtration rate, using Cox proportional hazard models. Risk classification statistics were calculated for CKD progression.

RESULTS

During a median follow-up of 43 months, 121 (29.0%) patients reached the CKD progression event. Patients in the highest tertile of renal megalin mRNA had a lower risk for CKD progression than in the lowest tertile (hazard ratio (HR): 0.407, 95% confidence interval (CI) 0.231-0.719; p = 0.002). Log megalin mRNA was independent and negatively associated with CKD progression in IgAN (HR: 0.529, 95% CI 0.377-0.742; p < 0.001). The addition of renal megalin mRNA to a model with traditional risk factors improved risk prediction of disease progression (C statistic from 0.76 to 0.80; integrated discrimination index: 0.04 [95% CI: 0.02-0.07]). Moreover, patients in the highest tertile of renal miR-148b had a 2.3-fold higher risk for CKD progression compared with those in the lowest tertile.

CONCLUSIONS

Lower renal megalin mRNA levels were associated with a greater risk of CKD progression in IgAN independent of clinical and pathological characteristics, suggesting that renal megalin could be an important prognostic factor for IgAN.

The Diagnostic and Predictive Significance of Immune-Related Genes and Immune Characteristics in the Occurrence and Progression of IgA Nephropathy

Objective

To investigate the potential diagnostic and predictive significance of immune-related genes in IgA nephropathy (IgAN) and discover the abnormal glomerular inflammation in IgAN.

Methods

GSE116626 was used as a training set to identify different immune-related genes (DIRGs) and establish machine learning models for the diagnosis of IgAN; then, a nomogram model was generated based on GSE116626, and GSE115857 was used as a test set to evaluate its clinical value. Short Time-Series Expression Miner (STEM) analysis was also performed to explore the changing trend of DIRGs with the progression of IgAN lesions. GSE141344 was used with DIRGs to establish the ceRNA network associated with IgAN progression. Finally, ssGSEA analysis was performed on the GSE141295 dataset to discover the abnormal inflammation in IgAN.

Results

Machine learning (ML) performed excellently in diagnosing IgAN using six DIRGs. A nomogram model was constructed to predict IgAN based on the six DIRGs. Three trends related to IgAN lesions were identified using STEM analysis. A ceRNA network associated with IgAN progression which contained 8 miRNAs, 14 lncRNAs, and 3 mRNAs was established. A higher macrophage ratio and lower CD4+ T cell ratio in IgAN compared to controls were observed, and the correlation between macrophages and monocytes in the glomeruli of IgAN patients was inverse compared to controls.

Conclusion

This study reveals the diagnostic and predictive significance of DIRGs in IgAN and finds that the imbalance between macrophages and CD4+ immune cells may be an important pathomechanism of IgAN. These results provide potential directions for the treatment and prevention of IgAN.

Elevated Serum Chloride Levels Contribute to a Poor Prognosis in Patients with IgA Nephropathy

Introduction

The identification of reliable prognostic factors is a crucial requirement for patients with IgA nephropathy (IgAN). Here, we explored the relationship between serum chloride levels and prognosis in patients with IgAN.

Methods

We recruited all patients with primary IgAN, as diagnosed by renal biopsy, between 1^st January 2015 and 1^st April 2019. Patients were divided two groups (high chloride group and low chloride group) based on the best cut-off values from survival receiver operating characteristic (ROC) curves. The baseline clinicopathological characteristics of two groups were then compared. Cox proportional hazard models were used to determine the prognostic value of serum chloride levels in patients with IgAN. Finally, we screened reliable prognostic indicators and built a clinical prediction model and validated the performance of the model.

Results

Compared with patients in the high chloride group, patients in the low chloride group had significantly lower levels of 24-hour urinary total protein (24 h-UTP), serum creatinine (sCr), and higher levels of hemoglobin (Hb), albumin (all p < 0.05), and less proportion of Oxford classification grade E1 (endothelial cell proliferation) and T2 (renal tubule atrophy or renal interstitial fibrosis). Cox analysis revealed that serum chloride level ≥ 105.4 mmol/L was a significant and independent risk factor for prognosis in patients with IgAN (p < 0.05). Serum chloride, sCr, T, hypertension, and Hb were used to generate a predictive model for prognosis. Thec-indices of our predictive model were 0.80, 0.86, and 0.78, for 1, 2, and 3 years, respectively; Brier scores were 0.06, 0.09, and 0.16, respectively.

Conclusions

A serum chloride level ≥ 105.4 mmol/l was identified as a significant and independent risk factor for the prognosis of patients with IgAN. A predictive prognosis model was generated using serum chloride, sCr, T, hypertension, and Hb; this model exhibited a good predictive effect.

Prediction methods for microRNA targets in bilaterian animals: Toward a better understanding by biologists

MicroRNAs (miRNAs) are small noncoding RNAs that regulate gene expression at the posttranscriptional level. Because of their wide network of interactions, miRNAs have become the focus of many studies over the past decade, particularly in animal species. To streamline the number of potential wet lab experiments, the use of miRNA target prediction tools is currently the first step undertaken. However, the predictions made may vary considerably depending on the tool used, which is mostly due to the complex and still not fully understood mechanism of action of miRNAs. The discrepancies complicate the choice of the tool for miRNA target prediction. To provide a comprehensive view of this issue, we highlight in this review the main characteristics of miRNA-target interactions in bilaterian animals, describe the prediction models currently used, and provide some insights for the evaluation of predictor performance.

The increased miRNA-150-5p expression of the tonsil tissue in patients with IgA nephropathy may be related to the pathogenesis of disease

BACKGROUND

The microRNA (miRNA) expression of the tonsil tissues in patients with immunoglobulin A (IgA) nephropathy (IgAN) has not been reported in the literature.

METHODS

In this study, the expression of nine miRNAs was measured in the tonsil tissues of patients with IgAN, including miRNA-21-5p, miRNA-29a-3p, miRNA-34a-5p, miRNA-146a-5p, miRNA-146b-5p, miRNA-148b-3p, miRNA-150-5p, miRNA-155-5p, and miRNA-181a-5p. Forty patients with proved primary IgA nephropathy were enrolled in our study, 20 IgAN patients with gross hematuria, which induced by tonsillitis (GH-IgAN group) and 20 IgAN patients without gross hematuria in the history (non-GH-IgAN group). Another 20 patients recruited as the control group (CT group) were chronic tonsillitis without kidney disease.

RESULTS

Compared to the CT group, the expression level of miRNA-150-5p in the tonsils was significantly upregulated in the GH-IgAN group, but not in the non-GH-IgAN group (P = 0.031 and P = 0.122, respectively). A correlation analysis was performed between the expression of miRNAs in the tonsils and the clinical data of IgAN patients. The results showed that in the GH-IgAN group, the miRNA-150 expression was positively correlated with systolic blood pressure (β = 2.36, 95% CI 1.11-3.61, P = 0.0016), diastolic blood pressure (β = 1.02, 95% CI 0.22-1.82, P = 0.0224), uric acid (β = 7.43, 95% CI 1.81-13.04, P = 0.0184), leukocyte count (β = 0.22, 95% CI 0.09-0.35, P = 0039), neutrophil count (β = 0.19, 95% CI 0.06-0.32, P = 0.0096), cholesterol (β = 0.09, 95% CI 0.02-0.16, P = 0.0207) and triglyceride level (β = 0.16, 95% CI 0.10-0.22, P < 0.000). Besides, it was negatively correlated with the estimated glomerular filtration rate (eGFR) (β = -2.06, 95% CI: -3.90 - -0.21, P = 0.0421) in the GH-IgAN group; however, no significant correlation was found in the non-GH-IgAN group.

CONCLUSION

The present findings suggest that miRNA-150-5p may be important in the pathogenesis of IgAN, especially in mucosal immunity against the disease.

MicroRNAs in IgA nephropathy

IgA nephropathy (IgAN) is the most common primary glomerulonephritis worldwide. It is considered that the pathogenesis of IgAN involves the ‘multiple hit theory’ and the immune-inflammatory mechanism; however, these theories have certain limitations. The gold standard for diagnosing IgAN is still renal biopsy. Although renal biopsy is accurate, it is traumatic and is associated with some risks and limitations, so there is a need for non-invasive diagnostic methods. According to recent studies, microRNAs (miRNAs) play important roles in the occurrence and development of IgAN; thus, they provide the possibility of the noninvasive diagnosis of IgAN and also have some value in predicting prognosis. This review summarizes the current research status of miRNAs in the occurrence, development, diagnosis, and prognosis of IgAN. We also highlight some interesting and challenging points that require further study.

Downregulation of miR‑214-3p attenuates mesangial hypercellularity by targeting PTEN‑mediated JNK/c-Jun signaling in IgA nephropathy

Mesangial cell (MC) proliferation and matrix expansion are basic pathological characteristics of IgA nephropathy (IgAN). However, the stepwise mechanism of MC proliferation and the exact set of related signaling molecules remain largely unclear. In this study, we found a significant upregulation of miR-214-3p in the renal cortex of IgAN mice by miRNA sequencing. In situ hybridization analysis showed that miR-214-3p expression was obviously elevated in MCs in the renal cortex in IgAN. Functionally, knockdown of miR-214-3p alleviated mesangial hypercellularity and renal lesions in IgAN mice. In vitro, the inhibition of miR-214-3p suppressed MC proliferation and arrested G1-S cell cycle pSrogression in IgAN. Mechanistically, a luciferase reporter assay verified PTEN as a direct target of miR-214-3p. Downregulation of miR-214-3p increased PTEN expression and reduced p-JNK and p-c-Jun levels, thereby inhibiting MC proliferation and ameliorating renal lesions in IgAN. Moreover, these changes could be attenuated by co-transfection with PTEN siRNA. Collectively, these results illustrated that miR-214-3p accelerated MC proliferation in IgAN by directly targeting PTEN to modulate JNK/c-Jun signaling. Therefore, miR-214-3p may represent a novel therapeutic target for IgAN.

Podocyte-derived microparticles in IgA nephropathy

Microparticles are a general term for different types of cell plasma membrane-originated vesicles that are released into the extracellular environment. The paracrine action of these nano-sized vesicles is crucial for intercellular communications through the transfer of diverse lipids, cytosolic proteins, RNA as well as microRNAs. The progression of different diseases influences the composition, occurrence, and functions of these cell-derived particles. Podocyte injury has been shown to have an important role in the pathophysiology of many glomerular diseases including IgA nephropathy (IgAN). This review would focus on the possible potential of podocyte-derived microparticles detected in urine to be used as a diagnostic tool in IgAN.

Detection of microRNA-33a-5p in serum, urine and renal tissue of patients with IgA nephropathy

The present study aimed to detect the levels of microRNA (miR)-33a-5p in the renal tissue, serum and urine of patients with primary IgA nephropathy (IgAN), thereby preliminarily exploring the association between the levels of miR-33a-5p and the condition of primary IgAN to provide evidence for the expression of miR-33a-5p in the serum and urine of IgAN patients as a clinical marker. Reverse-transcription quantitative PCR was performed to evaluate the level of miR-33a-5p in IgAN patients according to severity and pathological classification. The results suggested that the levels of miR-33a-5p in the serum, urine and kidney tissues of patients with IgAN were lower than those of the control tissues obtained from cancer patients (0.28±0.25 vs. 1.00±0.45, P<0.05; 0.34±0.28 vs. 1.00±0.53, P<0.05; 0.47±0.27 vs. 1.00±0.38, P<0.05, respectively). Receiver operating characteristic curve analysis suggested that the serum and urine levels of miR-33a-5p may be used as a marker to differentiate renal injury in IgAN patients from healthy individuals. At the same time, according to the estimated glomerular filtration rate (eGFR) and Lee classification of nephropathy, it was determined that with the progression of renal failure and the increase of the pathological grade of kidney tissue, the relative level of miR-33a-5p in kidney tissue also decreased (eGFR <50 ml/min vs. eGFR ≥50 ml/min/1.73 m² group: 0.38±0.27 vs. 1.00±0.34, P<0.001; Lee grade ≤3 group vs. Lee grade >3: 1.00±0.48 vs. 0.38±0.45, P<0.05). This result suggested that the levels of miR-33a-5p in serum, urine and kidney tissues decreased with the severity of renal injury and the progression of renal failure in patients with IgAN. Hence, miR-33a-5p detected in the serum and urine may be used as a non-invasive biomarker to reflect the progression of renal injury and renal failure in patients with IgAN.

Kidney microRNA-21 Expression and Kidney Function in IgA Nephropathy

Rationale & Objective

Previous studies have suggested that microRNA-21 (miR-21) plays an important role in kidney fibrosis. We examined the relationship between intrarenal miR-21 level and rate of kidney function loss in immunoglobulin A nephropathy (IgAN).

Study Design

Prospective cohort study.

Setting & Participants

40 patients with IgAN and 10 with hypertensive nephrosclerosis as controls.

Predictors

miR-21 levels in kidney biopsy specimen and urinary sediment, quantified as ratio to the housekeeping gene.

Outcomes

Kidney event–free survival and rate of kidney function decline.

Analytic Approach

Time-to-event and correlation analysis.

Results

The IgAN group had significantly higher intrarenal miR-21 expression compared with the hypertensive nephrosclerosis group (1.71 [IQR, 0.99-2.77] vs 0.31 [IQR, 0.25-1.32]; P < 0.0001), but urinary miR-21 levels were similar. Intrarenal miR-21 expression had significant but modest correlation with severity of glomerulosclerosis (r = 0.293; P = 0.05) and tubulointerstitial fibrosis (r = 0.341; P = 0.03). Patients with high intrarenal miR-21 expression had significantly higher risk for developing kidney end points compared with those with low expression (log-rank test, P = 0.017). Univariate Cox analysis showed that intrarenal miR-21 expression significantly predicted the development of kidney end points (unadjusted HR, 1.586; 95% CI, 1.179-2.134; P = 0.002). However, the result was just short of statistical significance after adjusting for the severity of histologic damage (P = 0.06). There was also a significant correlation between intrarenal miR-21 expression and the slope of kidney function decline by univariate analysis (r = −0.399; P = 0.02).

Limitations

Small sample size; uncertain cellular origin of miR-21.

Conclusions

We found that intrarenal miR-21 expression is increased in patients with IgAN, modestly correlated with the severity of histologic damage, and predictive of subsequent kidney function loss.

microRNA-630 Regulates Underglycosylated IgA1 Production in the Tonsils by Targeting TLR4 in IgA Nephropathy

IgA nephropathy (IgAN) is the most common primary glomerular disease. The characteristic pathology involves immune complexes formed by the deposition of IgA1 and underglycosylated IgA1 aggregates in the mesangial area, which may be accompanied by the deposition of IgG and/or IgM and complement components. However, the molecular mechanisms of IgAN remain unclear. In the present study, microarray analysis showed that the expression of microRNA-630 (miR-630) was significantly reduced in palatal tonsils from IgAN patients compared with chronic tonsillitis. Additionally, bioinformatic analysis showed that Toll-like receptor 4 (TLR4) was the predicted target gene of miR-630 and was regulated by miR-630. When miR-630 was overexpressed in palatal tonsil mononuclear cells from IgAN patients, the expression of TLR4 was reduced and the content of IgA1 in the cell culture supernatant was decreased, and the level of galactosylation in the IgA1 hinge region was increased. Moreover, immunohistochemical analysis showed that the expression of TLR4 in IgAN patients was significantly increased. After knocking down the expression of TLR4, both the concentration of IgA1 and the binding force of IgA1 with broad bean lectin were significantly reduced in IgAN. Furthermore, the mechanism study demonstrated that TLR4 might regulate the expression of IL-1β and IL-8 through NF-κB signaling pathway to modulate the concentration of IgA1 and the glycosylation level of IgA1. This interesting finding may offer new insight into the molecular mechanism of IgAN.

MicroRNAs in Chronic Kidney Disease: Four Candidates for Clinical Application

There are still major challenges regarding the early diagnosis and treatment of chronic kidney disease (CKD), which is in part due to the fact that its pathophysiology is very complex and not clarified in detail. The diagnosis of CKD commonly is made after kidney damage has occurred. This highlights the need for better mechanistic insight into CKD as well as improved clinical tools for both diagnosis and treatment. In the last decade, many studies have focused on microRNAs (miRs) as novel diagnostic tools or clinical targets. MiRs are small non-coding RNA molecules that are involved in post-transcriptional gene regulation and many have been studied in CKD. A wide array of pre-clinical and clinical studies have highlighted the potential role for miRs in the pathogenesis of hypertensive nephropathy, diabetic nephropathy, glomerulonephritis, kidney tubulointerstitial fibrosis, and some of the associated cardiovascular complications. In this review, we will provide an overview of the miRs studied in CKD, especially highlighting miR-103a-3p, miR-192-5p, the miR-29 family and miR-21-5p as these have the greatest potential to result in novel therapeutic and diagnostic strategies.

Small RNA deep sequencing reveals novel miRNAs in peripheral blood mononuclear cells from patients with IgA nephropathy

Peripheral blood mononuclear cells (PBMCs) contribute to the deposition of immunoglobulin A (IgA) and progression of IgA nephropathy (IgAN). This study was performed to identify novel microRNAs (miRNAs/miRs) associated with IgAN. Small RNAs were isolated from PBMCs collected from 10 healthy participants and 10 patients with IgAN; the RNAs were then subjected to high‑throughput small RNA sequencing. The results showed that miRNAs constituted 70.33 and 69.83% of small RNAs in PBMCs from healthy participants and patients with IgAN, respectively. In total, 44 differentially expressed miRNAs were identified, of which 34 were upregulated and 10 were downregulated. Among these differentially expressed miRNAs, most showed novel associations with IgAN, except miR‑148a‑3p, miR‑184 and miR‑200a. Furthermore, Kyoto Encyclopedia of Genes and Genomes pathway analysis revealed that the target genes of the differentially expressed miRNAs were primarily enriched in cancer pathways, the PI3K‑Akt signaling pathway and MAPK pathways, all of which control cell proliferation and gene expression. Moreover, miR‑3121‑3p, miR‑203a‑3p and miR‑200a‑3p may regulate core 1 synthase, glycoprotein‑N‑acetylgalactosamine 3‑β‑galactosyltransferase 1 (C1GALT1) expression by binding to its 3' untranslated region. In conclusion, 44 differentially expressed miRNAs were discovered, 41 of which were newly found to be associated with IgAN. The differentially expressed miRNAs may regulate the progression of IgAN by controlling the behavior of PBMCs or deposition of IgA via targeting of signaling pathways or expression of C1GALT1. These findings may provide a basis for further research regarding IgAN diagnosis and therapy.

MicroRNA-27a-3p directly targets FosB to regulate cell proliferation, apoptosis, and inflammation responses in immunoglobulin a nephropathy

Immunoglobulin A nephropathy (IgAN) constitutes the most common primary glomerulonephritis worldwide; however, the exact pathogenesis of IgAN is unknown. Previous genome-wide analysis of microRNA (miRNA) expression in the kidney has confirmed that miRNAs are closely related to the pathological changes of IgAN. Accordingly, in this study we found that miR-27a-3p is upregulated in IgAN kidney tissues in addition to human podocytes and tubule epithelial HK2 but not mesangial cells. Methylthiazolyldiphenyl-tetrazolium bromide (MTT), flow cytometry, real-time polymerase chain reaction, western blot, and enzyme-linked immunosorbent assays were used to verify the regulatory effects of miR-27a-3p and its inhibition on cell proliferation, apoptosis, and release of inflammatory factors in podocytes and HK2 cells. The target genes of miR-27a-3p were predicted using bioinformatics software; the identity of FosB as a target gene of miR-27a-3p was confirmed by luciferase report assay and western blot. Overall, our findings demonstrated that miR-27a-3p regulates cell apoptosis, cell proliferation, and the release of inflammatory cytokines of human podocytes and HK2 cells by directly targeting FosB. Our results therefore suggested that miR-27a-3p might be associated with the pathophysiology of IgAN and may represent a potential target for further studies related to IgAN mechanism or therapeutics.

The upregulation of miR-98-5p affects the glycosylation of IgA1 through cytokines in IgA nephropathy

OBJECTIVE

Increases in galactose-deficient IgA1 (Gd-IgA1) play a crucial role in the pathogenesis of IgA nephropathy (IgAN), and several recent experiments have shown that microRNAs (miRNAs) are involved in regulating the development and physiological function of the kidney. The aims of this study were to identify miRNAs that can affect the pathogenesis of IgAN and reveal the underlying regulatory mechanism of IgA1 glycosylation in peripheral blood.

METHODS

The differentially expressed miRNAs in peripheral blood mononuclear cells (PBMCs) between IgAN patients and healthy controls were screened by high-throughput sequencing, and the targets of these miRNAs were predicted and verified by dual-luciferase reporter assays. We also explored the miRNA regulation of Gd-IgA1 through the transfection of miRNA mimics and related plasmids.

RESULTS

The high-throughput sequencing results showed that miR-98-5p was more highly expressed in the PBMCs of IgAN patients compared with healthy controls, and the luciferase reporter gene system confirmed that miR-98-5p might target chemokine ligand 3 (CCL3). The transfection of si-CCL3 confirmed that a decrease in CCL3 can affect the expression of interleukin-6 (IL-6) and C1GALT1. The overexpression of miR-98-5p in PBMCs through the transfection of miR-98-5p mimic reduced the CCL3 and C1GALT1 levels and increased the IL-6 levels, and these changes in PBMCs were attenuated by cotransfection with the CCL3 plasmid.

CONCLUSION

The results showed that in PBMCs, miR-98-5p can target CCL3 to decrease its expression and thereby increase the IL-6 levels, and the resulting increase in IL-6 can decrease C1GALT1 expression. Therefore, miR-98-5p might be involved in the development of IgAN.

MicroRNA profiling in kidney in pigs fed ochratoxin A contaminated diet

OTA is a toxic metabolite produced by fungus belonging to Aspergillus and Penicillium genera. Kidney is the main target of this toxin; OTA is considered as one of the etiological factors at the origin of the human Balkan endemic nephropathy. microRNA are short non-coding transcrips (18-22 nucleotides in length) regulating key cellular processes. Various miRNAs have been established to play important roles in development of renal carcinoma and urothelial cancer. The objective of this study is to analyse the miRNA profiling in the kidney of piglets experimentally intoxicated with feed contaminated with OTA. Fifteen piglets (five pigs/group) were randomly distributed into 3 groups, fed normal diet (Group 1: control), or diets contaminated with OTA in two concentrations: 50 μg OTA/kg feed (Group 2: 50 μg OTA/kg feed) or 200 μg OTA/kg feed (Group 3: 200 μg OTA/kg feed) for 28 days. At the end of the experiment blood samples were taken for serological analyses. Animals from control group and 200 μg OTA/kg feed were sacrificed and kidney samples were taken for histological and molecular analyses. As resulted from molecular profiling study there are 8 miRNA differentially expressed in OTA kidney vs control kidney, in which five miRNA were overexpressed in the kidney of OTA intoxicated animals: miR-497 (FC = 6.34), miR-133a-3p (FC = 5.75), miR-423-3p (FC = 5.48), miR-34a (FC = 1.68), miR-542-3p (1.65) while three miRNA were downregulated: miR-421-3p (FC = -3.96); miR-490 (FC = -3.87); miR-9840-3p (FC = -2.13). The altered miRNAs as effect of OTA are strongly connected to the engine of cancer, disturbing nodal points in different pathways, as TP53 signalling. This proof-of-concept study proves the actual utility of miRNAs as biomarkers of mycotoxin exposure, including OTA.

MicroRNA-146a-deficient mice develop immune complex glomerulonephritis

MicroRNAs (miRNAs) play an important role in the kidneys under physiological and pathological conditions, but their role in immune glomerulonephritis is unclear. miR-146a has been identified as a key player in innate immunity and inflammatory responses, and in the kidney, this miRNA is involved in the response of injured tubular cells. We studied the renal and immune phenotypes of miR-146a^+/+ and miR-146a^−/− mice at 12 months of age, and the results showed that miR-146a^−/− mice developed autoimmunity during aging, as demonstrated by circulating antibodies targeting double-stranded DNA and an immune complex-mediated glomerulonephritis associated with a mild renal immune infiltrate. In addition, miR-146a^−/− mice showed reduced expression of the transmembrane protein Kim1/Tim1, a key regulator of regulatory B cell (Breg) homeostasis, in the kidney and the immune cells. The numbers of memory B cells and plasmablasts were increased in miR-146a^−/− mice compared with the numbers in wild-type mice, whereas Bregs were decreased in number and displayed an altered capacity to produce IL-10. Finally, we showed that miR-146a^−/− mice develop an autoimmune syndrome with increasing age, and this syndrome includes immune complex glomerulonephritis, which might be due to altered B cell responses associated with Kim1/Tim1 deficiency. This study unravels a link between miR-146a and Kim1 and identifies miR-146a as a significant player in immune-mediated glomerulonephritis pathogenesis.

Urinary miRNA profile for the diagnosis of IgA nephropathy

Background

IgA nephropathy (IgAN) is the most common primary glomerulonephritis worldwide. Urinary micro-RNA (miRNA) level is increasingly reported to as non-invasive markers of various kidney diseases. We aim to identify urinary miRNA targets for the diagnosis of IgAN.

Methods

In the development cohort, we performed complete miRNA profiling of urinary sediment in 22 patients with IgAN and 11 healthy controls (CTL). Potential miRNA targets were quantified by a separate validation cohort of 33 IgAN patients and 9 healthy controls.

Results

In the development cohort, we identified 39 miRNA targets that have significantly different expression between IgAN and CTL (14 up-regulated, and 25 down-regulated). Among the 8 miRNA targets chosen for validation study, urinary miR-204, miR-431 and miR-555 remained significantly reduced, and urinary miR-150 level was significantly increased in the IgAN as compared to CTL. The area-under-curve of the receiver operating characteristic (ROC) curve for urinary mi-204 level for the diagnosis of IgAN was 0.976, and the diagnostic performance of combining additional miRNA targets was not further improved. At the cut-off 1.70 unit, the sensitivity and specificity of urinary miR-204 was 100 and 55.5%, respectively, for diagnosing IgAN.

Conclusions

Urinary miR-150, miR-204, miR-431 and miR-555 levels are significantly different between IgAN and healthy controls; urinary miR-204 level alone has the best diagnostic accuracy.

Electronic supplementary material

The online version of this article (10.1186/s12882-019-1267-4) contains supplementary material, which is available to authorized users.

Renal miR-148b is associated with megalin down-regulation in IgA nephropathy

Megalin is essential for proximal tubule reabsorption of filtered proteins, hormones, and vitamins, and its dysfunction has been reported in IgA nephropathy (IgAN). miR-148b has been shown to regulate renal megalin expression in vitro and in animal models of kidney disease. We examined a potential role of miR-148b and other miRNAs in regulating megalin expression in IgAN by analyzing the association between megalin and miR-148b, miR-21, miR-146a, and miR-192 expression. Quantitative PCR (qPCR) analysis identified a marked increase in renal levels of several miRNAs, including miR-148b, miR-21, miR-146a, and a significant decrease in megalin mRNA levels in IgAN patients when compared with normal controls. By multiple linear regression analysis, however, only renal miR-148b was independently associated with megalin mRNA levels in IgAN. Proximal tubule megalin expression was further evaluated by immunofluorescence labeling of biopsies from the patients. The megalin expression was significantly lower in patients with highest levels of renal miR-148b compared with patients with lowest levels. To examine the direct effects of the miRNAs on megalin and other membrane proteins expression, proximal tubule LLC-PK1 cells were transfected with miR-148b, miR-21, miR-146a, or miR-192 mimics. Transfection with miR-148b mimic, but not the other three miRNA mimics inhibited endogenous megalin mRNA expression. No significant effect of any of the four miRNA mimics was observed on cubilin or aquaporin 1 (AQP1) mRNA expression. The findings suggest that miR-148b negatively regulates megalin expression in IgAN, which may affect renal uptake and metabolism of essential substances.

Corticosteroid therapy in IgA nephropathy with minimal proteinuria and high renal pathological score: A single‑center cohort study

Currently, there is no clear evidence that advocates the widespread use of corticosteroids for the treatment of immunoglobulin A nephropathy (IgAN) with minimal proteinuria (<1 g/day). The recent Kidney Disease: Improving Global Outcomes Clinical Practice Guideline recommends supportive corticosteroid treatment. In the present study, 45 IgAN patients with high renal pathological scores and minimal proteinuria were enrolled. The patients were randomly divided into two groups. The treatment group received methylprednisolone tablets in addition to angiotensin‑converting‑enzyme inhibitor (ACE‑I) and/or angiotensin‑receptor blocker (ARB) treatment. The control group only received ACE‑I and/or ARB treatment. In the treatment group, a single dose of 1 mg/kg (maximum 60 mg/day) methylprednisolone tablets was given daily followed by gradually decreasing dosage. The follow‑up time of the patients was 3 years. In addition, the underlying mechanisms were investigated. The results indicated that there was a significant reduction in the amount of urinary proteins in the treatment group compared with the control group. At the end of the follow‑up, the endpoint event rate of moderate or severe proteinuria and decrease in estimated glomerular filtration rate (eGFR) in the treatment group was significantly lower than the control group. Furthermore, higher levels of serum cytokines, interleukin (IL)‑4, IL‑17, transforming growth factor‑β1 and IL‑21, were detected in patients with IgAN compared with a group of healthy controls. There was no significant difference in IFN‑γ expression between the IgAN and healthy control groups. Furthermore, the expression of Janus kinase (Jak)1, Jak3, signal transducer and activator of transcription (STAT)3 and STAT6 was significantly upregulated in patients with IgAN compared with healthy controls. However, the expression levels of STAT5 and chaperone protein, C1GALT1 specific chaperone 1, in IgAN patients were significantly reduced compared with healthy controls. In addition, there was no significant difference in the expression of Jak2, tyrosine kinase 2, STAT1 and STAT4 between the two groups. In conclusion, for IgAN patients with minimal proteinuria and high renal pathological score corticosteroid therapy is likely to be effective. The dysregulation of serum cytokine levels in these patients with IgAN may have a role in the pathogenesis and progression of disease, which is associated with the activation of the JAK/STAT signaling pathway.

The Emerging Role of Pathogenesis of IgA Nephropathy

IgA nephropathy is an autoimmune disease induced by fthe ormation of galactose-deficient IgA1 and anti-glycans autoantibody. A multi-hit hypothesis was promoted to explain full expression of IgA nephropathy. The deposition of immune complex resulted in activation of the complement, increasing oxidative stress, promoting inflammatory cascade, and inducing cell apoptosis via mesangio-podocytic-tubular crosstalk. The interlinked signaling pathways of immune-complex-mediated inflammation can offer a novel target for therapeutic approaches. Treatments of IgA nephropathy are also summarized in our review article. In this article, we provide an overview of the recent basic and clinical studies in cell molecular regulation of IgAN for further treatment interventions.

U6 can be used as a housekeeping gene for urinary sediment miRNA studies of IgA nephropathy

Recent studies have indicated that urinary sediment miRNAs not only are able to serve as non-invasive diagnostic biomarkers for IgA nephropathy (IgAN) but may also be closely related to several clinical and pathological indicators. However, the lack of a suitable internal reference miRNA has hampered research into urinary sediment miRNAs. To date, U6 has been used as a reference gene in urinary sediment miRNA studies mostly based on the results from studies using tissue samples and cell lines. In a total of 330 IgAN patients, 164 disease control patients and 130 normal control patients, there was no significant difference in U6 levels. We also compared the U6 levels in different types of primary glomerular disease groups (IgA nephropathy, membranous nephropathy, minimal change nephrosis and focal segmental glomerular sclerosis). The results confirmed that there was no significant difference in the expression of U6 in different primary glomerular disease groups. Moreover, treatment had no significant effect on the expression levels of U6 in IgA nephropathy. Therefore, U6 is an excellent housekeeping gene for urinary sediment miRNA studies of IgA nephropathy.

Plasma microRNA panel is a novel biomarker for focal segmental glomerulosclerosis and associated with podocyte apoptosis

Focal segmental glomerulosclerosis (FSGS) is a frequent glomerular disease, and is the common cause of nephrotic syndrome. However, there is no validated diagnostic blood biomarker for FSGS. Here, we performed a real-time PCR-based high-throughput miRNA profiling to identify the plasma signature for FSGS. We found four miRNAs (miR-17, miR-451, miR-106a, and miR-19b) were significantly downregulated in the plasma of FSGS patients (n = 97) compared with healthy controls (n = 124) in the training, validation, and blinded-test phases. The miRNA panel produced an AUC value of 0.82, and was associated with FSGS severity and histologic classification. A three-miRNA panel, including miR-17, miR-451, and miR-106a was related to FSGS remission. Furthermore, the downregulation of plasma-miRNA signature was not detected in disease controls (n = 119) such as IgA nephropathy (IgAN), mesangial proliferative glomerulonephritis (MSPGN), and membranous nephropathy (MN), and the miRNA panel discriminated between FSGS and disease controls. Pathway analysis showed that the four-miRNA panel may cooperatively regulate the pathways involved in the development of FSGS, such as apoptosis. We identified that phosphatase and tensin homolog (PTEN), Bcl-2-like protein 11 (BCL2L11), and chemokine (C-X-C motif) ligand 14 (CXCL14) were targets of miR-106a in human podocyte. Additionally, miR-106a overexpression suppressed podocyte apoptosis in vitro and the downregulation of four-miRNA panel probably resulted in the enhanced apoptosis in podocyte during FSGS development. Taken together, our data show that the plasma-miRNA panel is a potential independent diagnostic and prognostic factor for FSGS. Above miRNAs are involved in FSGS pathogenesis through regulating podocyte apoptosis.

Plasma microRNA signature of patients with IgA nephropathy

We looked for differentially expressed MicroRNAs (miRNAs) in Immunoglobulin A nephropathy (IgAN). Forty-eight miRNAs were identified through the initial screening phase (2 IgAN pools vs. 1 normal control (NC) pool) using quantitative reverse transcription polymerase chain reaction (qRT-PCR) based Exiqon panel (miRCURY-Ready-to-Use-PCR-Human-panel-I + II-V₁.M). By qRT-PCR, these miRNAs were further assessed in the training (32 IgAN VS. 31 NCs) and testing stages (51 IgAN VS. 51 NCs). The renal pathological lesions of patients with IgAN were evaluated according to Lee's grading system. We discovered a plasma miRNA signature including four up-regulated miRNAs (miR-148a-3p, miR-150-5p, miR-20a-5p and miR-425-3p) and the areas under the receiver operating characteristic (ROC) curve (AUC) were 0.80 and 0.76 for the training and testing stage, respectively. The expression of the four miRNAs in IgAN grade I-II subgroups (according to Lee's grading system) was obviously higher than that in IgAN grade III-V (P < .05). In summary, the plasma expression of miR-148a-3p, miR-150-5p, miR-20a-5p and miR-425-3p were up-regulated in patients with IgAN, especially the early-stage disease. Further studies are needed to explore the roles of the four miRNAs in the pathogenesis and progression of IgAN.

Differentially expressed long non‑coding RNAs and mRNAs in patients with IgA nephropathy

Long non‑coding RNAs (lncRNAs) have been reported to serve a crucial role in renal diseases; however, their role in immunoglobulin A nephropathy (IgAN) remains unclear. In the present study, peripheral blood mononuclear cells (PBMCs) were collected from both patients with IgAN and healthy controls. A microarray analysis was then performed to identify differentially expressed lncRNAs and mRNAs in PBMCs, which were confirmed by quantitative polymerase chain reaction. In addition, Gene Ontology (GO), Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway and lncRNA‑mRNA co‑expression network analyses were conducted. The present study identified 167 differentially expressed lncRNAs and 94 differentially expressed mRNAs. Numerous GO terms, including innate immune response, inflammatory response, IPAF inflammasome complex and UDP‑galactose:β‑N‑acetylglucosamine β‑1, and 3‑galactosyltransferase activity, were significantly enriched in the differentially expressed mRNAs. The top five KEGG signaling pathways included nucleotide‑binding oligomerization domain‑like receptor signaling pathway, hematopoietic cell lineage, inflammatory bowel disease, tumor necrosis factor signaling pathway and other types of O‑glycan biosynthesis. In addition, a total of 149 lncRNAs were shown to interact with 7 mRNAs that were associated with the 'innate immune response' GO term. The results of the present study demonstrated that differentially expressed lncRNAs and mRNAs may have a role in the development of IgAN. These results may aid in the elucidation of a basic pathogenic mechanism, the identification of possible biomarkers and the generation of potential novel treatment strategies for IgAN.

Novel Anti-fibrotic Therapies

Fibrosis is a major player in cardiovascular disease, both as a contributor to the development of disease, as well as a post-injury response that drives progression. Despite the identification of many mechanisms responsible for cardiovascular fibrosis, to date no treatments have emerged that have effectively reduced the excess deposition of extracellular matrix associated with fibrotic conditions. Novel treatments have recently been identified that hold promise as potential therapeutic agents for cardiovascular diseases associated with fibrosis, as well as other fibrotic conditions. The purpose of this review is to provide an overview of emerging antifibrotic agents that have shown encouraging results in preclinical or early clinical studies, but have not yet been approved for use in human disease. One of these agents is bone morphogenetic protein-7 (BMP7), which has beneficial effects in multiple models of fibrotic disease. Another approach discussed involves altering the levels of micro-RNA (miR) species, including miR-29 and miR-101, which regulate the expression of fibrosis-related gene targets. Further, the antifibrotic potential of agonists of the peroxisome proliferator-activated receptors will be discussed. Finally, evidence will be reviewed in support of the polypeptide hormone relaxin. Relaxin is long known for its extracellular remodeling properties in pregnancy, and is rapidly emerging as an effective antifibrotic agent in a number of organ systems. Moreover, relaxin has potent vascular and renal effects that make it a particularly attractive approach for the treatment of cardiovascular diseases. In each case, the mechanism of action and the applicability to various fibrotic diseases will be discussed.

Noncoding RNA and epigenetic gene regulation in renal diseases

Kidneys have a major role in normal physiology and metabolic homeostasis. Loss or impairment of kidney function is a common occurrence in several metabolic disorders, including hypertension and diabetes. Chronic kidney disease (CKD) affect nearly 10% of the population worldwide; ranks 18th in the list of causes of death; and contributes to a significant proportion of healthcare costs. The tissue repair and regenerative potential of kidneys are limited and they decline during aging. Recent studies have demonstrated a key role for epigenetic processes and players, such as DNA methylation, histone modifications, noncoding (nc)RNA, and so on, in both kidney development and disease. In this review, we highlight these recent findings with an emphasis on aberrant epigenetic changes that accompany renal diseases, key targets, and their therapeutic value.

Differential expression of urinary exosomal microRNAs in IgA nephropathy

BACKGROUND

Immunoglobulin A nephropathy (IgAN) is the most common type of primary glomerulonephritis in the world. Reliable biomarkers are required for the non-invasive diagnosis and monitoring of IgAN. This study aims to investigate the difference in urinary exosomal microRNA (miRNA) expression profiles between patients with IgA nephropathy (IgAN) and healthy controls, which may provide clues to identify novel potential non-invasive miRNA biomarkers for renal diseases.

METHODS

Urine samples were collected from eighteen healthy controls and eighteen patients with IgAN. Differential centrifugation was performed to isolate exosomes from urine samples. High-throughput sequencing and real-time quantitative polymerase chain reaction (RT-qPCR) were sequentially used to screen and further validate miRNA expression profiles in urinary exosomes of patients with IgAN in two independent cohorts.

RESULTS

Urinary exosomes were successfully isolated to obtain exosomal miRNAs. MiR-215-5p and miR-378i were significantly upregulated in urinary exosomes of patients with IgAN compared with healthy controls (P<.01), while miR-29c and miR-205-5p were significantly downregulated (P<.05). MiR-215-5p, miR-378i, miR-365b-3p and miR-135b-5p were found to have altered expression in patients with IgAN from validation cohorts, which was consistent with the high-throughput sequencing analysis.

CONCLUSION

This study suggests that there is a significant difference in urinary exosomal miRNA profiles between patients with IgAN and healthy controls. These exosomal miRNAs, such as miR-29c, miR-146a and miR-205 may potentially serve as novel non-invasive biomarkers for IgAN.

MicroRNA-148b regulates megalin expression and is associated with receptor downregulation in mice with unilateral ureteral obstruction

Megalin is a multiligand, endocytic receptor that is important for the normal, proximal tubule reabsorption of filtered proteins, hormones, enzymes, essential nutrients, and nephrotoxins. Megalin dysfunction has been associated with acute, as well as chronic kidney diseases. Tubular proteinuria has been observed following unilateral ureteral obstruction (UUO), suggesting megalin dysfunction; however, the pathophysiological mechanism has not been determined. To identify potential regulators of megalin expression, we examined renal microRNAs (miRNAs) expression and observed an upregulation of microRNA-148b (miR-148b) in obstructed mouse kidneys 7 days after UUO, which was associated with a significant reduction in proximal tubule megalin expression and accumulation of megalin ligands. By in silico miRNA target prediction analysis, we identified megalin messenger RNA (mRNA) as a potential target of miR-148b and confirmed using a dual-luciferase reporter assay that miR-148b targeted the 3'-untranslated region of the megalin gene. Transfection of LLC-PK1 cells with miR-148b mimic reduced endogenous megalin mRNA and protein levels in a concentration-dependent manner, while transfection with miR-148b inhibitor resulted in an increase. Our findings suggest that miR-148b directly downregulates megalin expression and that miR-148b negatively regulates megalin expression in UUO-induced kidney injury. Furthermore, the identification of a miRNA regulating megalin expression may allow for targeted interventions to modulate megalin function and proximal tubule uptake of proteins, as well as other ligands.

Comparison of different normalization strategies for the analysis of glomerular microRNAs in IgA nephropathy

Small nucleolar RNAs (snoRNAs) have been used for normalization in glomerular microRNA (miRNA) quantification without confirmation of validity. Our aim was to identify glomerular reference miRNAs in IgA nephropathy. We compared miRNAs in human paraffin-embedded renal biopsies from patients with cellular-crescentic IgA-GN (n = 5; crescentic IgA-GN) and non-crescentic IgA-GN (n = 5; IgA-GN) to mild interstitial nephritis without glomerular abnormalities (controls, n = 5). Laser-microdissected glomeruli were used for expression profiling of 762 miRNAs by low-density TaqMan arrays (cards A and B). The comparison of different normalization methods (GeNormPlus, NormFinder, global mean and snoRNAs) in crescentic IgA-GN, IgA-GN and controls yielded similar results. However, levels of significance and the range of relative expression differed. In median, two normalization methods demonstrated similar results. GeNormPlus and NormFinder gave different top ranked reference miRNAs. Stability ranking for snoRNAs varied between cards A and B. In conclusion, we suggest the geometric mean of the most stable reference miRNAs found in GeNormPlus (miR-26b-5p), NormFinder (miR-28-5p) and snoRNAs (RNU44) as reference. It should be considered that significant differences could be missed using one particular normalization method. As a starting point for glomerular miRNA studies in IgA nephropathy we provide a library of miRNAs.

MicroRNA-146a in Human and Experimental Ischemic AKI: CXCL8-Dependent Mechanism of Action

AKI leads to tubular injury and interstitial inflammation that must be controlled to avoid the development of fibrosis. We hypothesized that microRNAs are involved in the regulation of the balance between lesion formation and adaptive repair. We found that, under proinflammatory conditions, microRNA-146a (miR-146a) is transcriptionally upregulated by ligands of IL-1 receptor/Toll-like receptor family members via the activation of NF-κB in cultured renal proximal tubular cells. In vivo, more severe renal ischemia-reperfusion injury (IRI) associated with increased expression of miR-146a in both allografts and urine of human kidney transplant recipients, and unilateral IRI in mice induced miR-146a expression in injured kidneys. After unilateral IRI, miR-146a^-/- mice exhibited more extensive tubular injury, inflammatory infiltrates, and fibrosis than wild-type mice. In vitro, overexpression or downregulation of miR-146a diminished or enhanced, respectively, IL-1 receptor-associated kinase 1 expression and induced similar effects on C-X-C motif ligand 8 (CXCL8)/CXCL1 expression by injured tubular cells. Moreover, inhibition of CXCL8/CXCL1 signaling prevented the development of inflammation and fibrosis after IRI in miR-146a^-/- mice. In conclusion, these results indicate that miR-146a is a key mediator of the renal tubular response to IRI that limits the consequences of inflammation, a key process in the development of AKI and CKD.

miR-21-5p renal expression is associated with fibrosis and renal survival in patients with IgA nephropathy

IgA nephropathy (IgAN) is the most prevalent primary glomerulonephritis, whose prognosis is highly variable. Interstitial fibrosis is a strong independent prognosis factor. Among microRNA involved in renal fibrogenesis, only few have been investigated in IgAN. In the context of IgAN, we aimed to analyze the role of miR-21-5p, miR-214-3p and miR-199a-5p, three established "fibromiRs" involved in renal fibrosis. Fifty-six IgAN biopsy specimens were retrospectively scored according to Oxford classification. Renal expression of miR-21-5p, miR-214-3p and miR-199a-5p were significantly associated with T score (miR-21-5p T0 RQ median = 1.23, T1 RQ = 3.01, T2 RQ = 3.90; miR-214-5p T0 RQ = 1.39, T1 RQ = 2.20, T2 RQ = 2.48; miR-199a-5p T0 RQ = 0.76, T1 RQ = 1.41, T2 RQ = 1.87). miR-21-5p expression was associated with S score (S0 RQ median = 1.31, S1 RQ = 2.65), but not miR-214-3p nor miR-199a-5p. In our cohort, poor renal survival was associated with high blood pressure, proteinuria and elevated creatininemia, as well as T and S scores. Moreover, renal expression of miR-21-5p, miR-214-3p were associated with renal survival. In conclusion, miR-21-5p, miR-214-3p and miR-199a-5p are three "fibromiRs" involved in renal fibrosis in the course of IgAN and miR-21-5p and miR-214-3p are associated with renal survival.

MicroRNA in rectal cancer

In rectal cancer, one of the most common cancers worldwide, the proper staging of the disease determines the subsequent therapy. For those with locally advanced rectal cancer, a neoadjuvant chemoradiotherapy (CRT) is recommended before any surgery. However, response to CRT ranges from complete response (responders) to complete resistance (non-responders). To date we are not able to separate in advance the first group from the second, due to the absence of a valid biomarker. Therefore all patients receive the same therapy regardless of whether they reap benefits. On the other hand almost all patients receive a surgical resection after the CRT, although a watch-and-wait procedure or an endoscopic resection might be sufficient for those who responded well to the CRT. Being highly conserved regulators of gene expression, microRNAs (miRNAs) seem to be promising candidates for biomarkers. Many studies have been analyzing the miRNAs expressed in rectal cancer tissue to determine a specific miRNA profile for the ailment. Unfortunately, there is only a small overlap of identified miRNAs between different studies, posing the question as to whether different methods or differences in tissue storage may contribute to that fact or if the results simply are not reproducible, due to unknown factors with undetected influences on miRNA expression. Other studies sought to find miRNAs which correlate to clinical parameters (tumor grade, nodal stage, metastasis, survival) and therapy response. Although several miRNAs seem to have an impact on the response to CRT or might predict nodal stage, there is still only little overlap between different studies. We here aimed to summarize the current literature on rectal cancer and miRNA expression with respect to the different relevant clinical parameters.

Markers for the progression of IgA nephropathy

We have summarized the latest findings on markers for progression of immunoglobulin A (IgA) nephropathy (IgAN), the most common primary glomerulonephritis with a high prevalence among end-stage renal disease (ESRD) patients. The clinical predictors of renal outcome in IgAN nephropathy, such as proteinuria, hypertension, and decreased estimated glomerular filtration rate (eGFR) at the time of the diagnosis, are well known. The Oxford classification of IgAN identified four types of histological lesions (known as the MEST score) associated with the development of ESRD and/or a 50 % reduction in eGFR. In addition, the role of genetic risk factors associated with IgAN is being elucidated by genome-wide association studies, with multiple risk alleles described. Recently, biomarkers in serum (galactose-deficient IgA1, IgA/IgG autoantibodies against galactose-deficient IgA1, and soluble CD 89-IgA complexes) and urine (soluble transferrin receptor, interleukin-6/epidermal growth factor ratio, fractalkine, laminin G-like 3 peptide, κ light chains, and mannan-binding lectin) have been identified. Some of these biomarkers may represent candidates for the development of noninvasive diagnostic tests, that would be useful for detection of subclinical disease activity, monitoring disease progression, assessment of treatment, and at the same time circumventing the complications associated with renal biopsies. These advances, along with future disease-specific therapy, will be helpful in improving the treatment effectiveness, prognosis, and the quality of life in connection with IgAN.

Selection of urinary sediment miRNAs as specific biomarkers of IgA nephropathy

The miRNAs in urinary sediment are easy to obtain, which provides a new approach to searching for non-invasive biomarkers of IgA nephropathy (IgAN). Compared with normal controls (n = 3), 214 different miRNAs in the urinary sediment of IgAN (n = 9) were found by miRNA chip assay. By quantitative PCR analysis, miR-25-3p, miR-144-3p and miR-486-5p were confirmed to be significantly higher in IgAN (n = 93) than in the normal group (n = 82) or disease control (n = 40). These three miRNAs had good specificity and sensitivity for the diagnosis of IgAN by receiver operating characteristic curve analysis, in which the AUC value of miR-486-5p was the largest at 0.935. Urinary sediment miR-25-3p, miR-144-3p and miR-486-5p were demonstrated to be mainly derived from urinary erythrocytes, which were separated by CD235a magnetic beads. The increased expression of urinary erythrocyte miRNAs in IgAN patients was not associated with those in the blood erythrocytes. In addition, urinary supernatant microvesicles of miR-144-3p and miR-486-5p in the IgAN group were also significantly increased. This study showed that the miR-25-3p, miR-144-3p and miR-486-5p in urinary sediment were mainly derived from urinary erythrocytes, which could be non-invasive candidate biomarkers for IgA nephropathy.

IgA nephropathy

Globally, IgA nephropathy (IgAN) is the most common primary glomerulonephritis that can progress to renal failure. The exact pathogenesis of IgAN is not well defined, but current biochemical and genetic data implicate overproduction of aberrantly glycosylated IgA1. These aberrant immunoglobulins are characterized by galactose deficiency of some hinge-region O-linked glycans. However, aberrant glycosylation alone is insufficient to induce renal injury: the participation of glycan-specific IgA and IgG autoantibodies that recognize the undergalactosylated IgA1 molecule is required. Glomerular deposits of immune complexes containing undergalactosylated IgA1 activate mesangial cells, leading to the local overproduction of cytokines, chemokines and complement. Emerging data indicate that mesangial-derived mediators that are released following mesangial deposition of IgA1 lead to podocyte and tubulointerstitial injury via humoral crosstalk. Patients can present with a range of signs and symptoms, from asymptomatic microscopic haematuria to macroscopic haematuria. The clinical progression varies, with 30-40% of patients reaching end-stage renal disease 20-30 years after the first clinical presentation. Currently, no IgAN-specific therapies are available and patients are managed with the aim of controlling blood pressure and maintaining renal function. However, new therapeutic approaches are being developed, building upon our ever-improving understanding of disease pathogenesis.

Update on immunoglobulin a nephropathy. Part II: Clinical, diagnostic and therapeutical aspects

Immunoglobulin A nephropathy (IgAN) is characterized by different clinical manifestations and by long-term different outcomes. Major problem for the physicians is to understanding which patients are at risk of a disease evolution and to prescribe the right therapy to the right patients. Indeed, in addition to patients with a stable disease with no trend to evolution or even with a spontaneous recovery, patients with an active disease and patients with a rapidly evolving glomerulonephritis are described. Several histopathological, biological and clinical markers have been described and are currently used to a better understanding of patients at risk, to suggest the right therapy and to monitor the therapy effect and the IgAN evolution over time. The clinical markers are the most reliable and allow to divide the IgAN patients into three categories: The low risk patients, the intermediate risk patients and the high risk patients. Accordingly, the therapeutic measures range from no therapy with the only need of repeated controls, to supportive therapy eventually associated with low dose immunosuppression, to immunosuppressive treatment in the attempt to avoid the evolution to end stage renal disease. However the current evidence about the different therapies is still matter of discussion. New drugs are in the pipeline and are described. They are object of randomized controlled trials, but studies with a number of patients adequately powered and with a long follow up are needed to evaluate efficacy and safety of these new drugs.

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.