Podocyte-selective deletion of dicer induces proteinuria and glomerulosclerosis

Circulating and urinary microRNA profile in focal segmental glomerulosclerosis: a pilot study

BACKGROUND

MicroRNAs (miRNAs) are noncoding RNA molecules that play important roles in the pathogenesis of various kidney diseases. We investigated whether patients with minimal change disease (MCD) and focal segmental glomerulosclerosis (FSGS) have distinct circulating and urinary miRNA expression profiles that could lead to potential development of noninvasive biomarkers of the disease.

MATERIALS AND METHODS

Exosome miRNAs were extracted from plasma and urine samples of patients with primary FSGS (n = 16) or MCD (n = 5) and healthy controls (n = 5). Differences in miRNA abundance were examined using Affymetrix GeneChip miRNA 3.0 arrays. QRT-PCR was used to validate the findings from the array.

RESULTS

Comparison analysis of FSGS versus MCD revealed 126 and 155 differentially expressed miRNAs in plasma and in urine, respectively. Only 38 of these miRNAs were previously cited, whereas the remaining miRNAs have not been described. Comparison analysis showed that a significant number of miRNAs were downregulated in both plasma and urine samples of patients with FSGS compared to those with MCD. Plasma levels of miR-30b, miR-30c, miR-34b, miR-34c and miR-342 and urine levels of mir-1225-5p were upregulated in patients with MCD compared to patients with FSGS and controls (P < 0.001). Urinary levels of mir-1915 and miR-663 were downregulated in patients with FSGS compared to MCD and controls (P < 0.001), whereas the urinary levels of miR-155 were upregulated in patients with FSGS when compared to patients with MCD and controls (P < 0.005).

CONCLUSIONS

Patients with FSGS and MCD have a unique circulating and urinary miRNA profile. The diagnostic and prognostic potential of miRNAs in FSGS and MCD warrants further studies.

Genetic variants of MicroRNA-related genes in susceptibility and prognosis of end-stage renal disease and renal allograft outcome among north Indians

BACKGROUND AND AIM

MicroRNAs are important molecules of the innate and adaptive immune system, which may play an important role in maintaining normal immune homeostasis. The aim of this study was to investigate the impact of MIR146A C>G (rs2910164), MIR149 T>C (rs2292832), MIR196A2 T>C (rs11614913), and MIR499A A>G (rs3746444) single nucleotide polymorphisms (SNPs) among end-stage renal disease (ESRD) and acute allograft rejection (AR) cases.

MATERIALS AND METHODS

Genotyping of MicroRNA SNPs was performed using a PCR, followed by restriction fragment length polymorphism in 350 ESRD patients and 350 age-matched, sex-matched, and ethnically matched controls.

RESULTS

We observed an increased risk of almost two-fold for ESRD and three-fold for AR cases under univariate and multivariate models for mutant genotypes of rs2910164, rs11614913, and rs3746444 SNPs. Subsequently, no susceptible/protective effect was observed for rs2292832 SNP with ESRD and AR cases. Interestingly, all the SNPs that were significant after multiple comparisons in ESRD and AR cases remained significant in the bootstrap analysis, providing internal validation to our initial observations. Survival analysis showed that the mutant genotypes of rs2910164, rs11614913, and rs3746444 SNPs were associated with the lowest overall survival compared with heterozygous and wild genotypes among renal allograft recipients. The crude and adjusted hazard ratios in univariate and multivariate Cox regression models showed an almost two-fold increased risk for overall survival against mutant genotypes of rs2910164, rs11614913, and rs3746444 SNPs in renal allograft recipients.

CONCLUSION

These results suggest that the variants of MicroRNA SNPs, namely, rs2910164, rs11614913, and rs3746444, might be involved in susceptibility to ESRD and AR.

Translational value of animal models of kidney failure

Acute kidney injury (AKI) and chronic kidney disease (CKD) are associated with decreased renal function and increased mortality risk, while the therapeutic armamentarium is unsatisfactory. The availability of adequate animal models may speed up the discovery of biomarkers for disease staging and therapy individualization as well as design and testing of novel therapeutic strategies. Some longstanding animal models have failed to result in therapeutic advances in the clinical setting, such as kidney ischemia-reperfusion injury and diabetic nephropathy models. In this regard, most models for diabetic nephropathy are unsatisfactory in that they do not evolve to renal failure. Satisfactory models for additional nephropathies are needed. These include anti-neutrophil cytoplasmic antibody (ANCA)-associated vasculitis, IgA nephropathy, anti-phospholipase-A2-receptor (PLA2R) membranous nephropathy and Fabry nephropathy. However, recent novel models hold promise for clinical translation. Thus, the AKI to CKD translation has been modeled, in some cases with toxins of interest for human CKD such as aristolochic acid. Genetically modified mice provide models for Alport syndrome evolving to renal failure that have resulted in clinical recommendations, polycystic kidney disease models that have provided clues for the development of tolvaptan, that was recently approved for the human disease in Japan; and animal models also contributed to target C5 with eculizumab in hemolytic uremic syndrome. Some ongoing trials explore novel concepts derived from models, such TWEAK targeting as tissue protection for lupus nephritis. We now review animal models reproducing diverse, genetic and acquired, causes of AKI and CKD evolving to kidney failure and discuss the contribution to clinical translation and prospects for the future.

Selective dicer suppression in the kidney alters GSK3β/β-catenin pathways promoting a glomerulocystic disease

Dicer is a crucial enzyme for the maturation of miRNAs. Mutations in the Dicer gene are highly associated with Pleuro Pulmonary Blastoma-Family Dysplasia Syndrome (PPB-FDS, OMIM 601200), recently proposed to be renamed Dicer syndrome. Aside from the pulmonary phenotype (blastoma), renal nephroma and thyroid goiter are frequently part of Dicer syndrome. To investigate the renal phenotype, conditional knockout (cKO) mice for Dicer in Pax8 expressing cells were generated. Dicer cKO mice progressively develop a glomerulocystic phenotype coupled with urinary concentration impairment, proteinuria and severe renal failure. Higher cellular turnover of the parietal cells of Bowman's capsule precedes the development of the cysts and the primary cilium progressively disappears with cyst-enlargement. Upregulation of GSK3β precedes the development of the glomerulocystic phenotype. Downregulation of β-catenin in the renal cortex and its cytosolic removal in the cells lining the cysts may be associated with observed accumulation of GSK3β. Alterations of β-catenin regulating pathways could promote cystic degeneration as in other models. Thus, miRNAs are fundamental in preserving renal morphology and function. Alteration of the GSK3β/β-catenin pathway could be a crucial mechanism linking miRNA dysregulation and the development of a glomerulocystic disease.

MicroRNA-10b downregulation mediates acute rejection of renal allografts by derepressing BCL2L11

Kidney transplantation is the major therapeutic option for end-stage kidney diseases. However, acute rejection could cause allograft loss in some of these patients. Emerging evidence supports that microRNA (miRNA) dysregulation is implicated in acute allograft rejection. In this study, we used next-generation sequencing to profile miRNA expression in normal and acutely rejected kidney allografts. Among 75 identified dysregulated miRNAs, miR-10b was the most significantly downregulated miRNAs in rejected allografts. Transfecting miR-10b inhibitor into human renal glomerular endothelial cells recapitulated key features of acute allograft rejection, including endothelial cell apoptosis, release of pro-inflammatory cytokines (interleukin-6, tumor necrosis factor α, interferon-γ, and chemokine (C-C motif) ligand 2) and chemotaxis of macrophages whereas transfection of miR-10b mimics had opposite effects. Downregulation of miR-10b directly derepressed the expression of BCL2L11 (an apoptosis inducer) as revealed by luciferase reporter assay. Taken together, miR-10b downregulation mediates many aspects of disease pathogenicity of acute kidney allograft rejection. Restoring miR-10b expression in glomerular endothelial cells could be a novel therapeutic approach to reduce acute renal allograft loss.

Age and sex differences in kidney microRNA expression during the life span of F344 rats

Background

Growing evidence suggests that epigenetic mechanisms of gene regulation may play a role in susceptibilities to specific toxicities and adverse drug reactions. MiRNAs in particular have been shown to be important regulators in cancer and other diseases and show promise as predictive biomarkers for diagnosis and prognosis. In this study, we characterized the global kidney miRNA expression profile in untreated male and female F344 rats throughout the life span. These findings were correlated with sex-specific susceptibilities to adverse renal events, such as male-biased renal fibrosis and inflammation in old age.

Methods

Kidney miRNA expression was examined in F344 rats at 2, 5, 6, 8, 15, 21, 78, and 104 weeks of age in both sexes using Agilent miRNA microarrays. Differential expression was determined using filtering criteria of ≥1.5 fold change and ANOVA or pairwise t-test (FDR <5%) to determine significant age and sex effects, respectively. Pathway analysis software was used to investigate the possible roles of these target genes in age- and sex-specific differences.

Results

Three hundred eleven miRNAs were found to be expressed in at least one age and sex. Filtering criteria revealed 174 differentially expressed miRNAs in the kidney; 173 and 34 miRNAs exhibiting age and sex effects, respectively. Principal component analysis revealed age effects predominated over sex effects, with 2-week miRNA expression being much different from other ages. No significant sexually dimorphic miRNA expression was observed from 5 to 8 weeks, while the most differential expression (13 miRNAs) was observed at 21 weeks. Potential target genes of these differentially expressed miRNAs were identified.

Conclusions

The expression of 56% of detected renal miRNAs was found to vary significantly with age and/or sex during the life span of F344 rats. Pathway analysis suggested that 2-week-expressed miRNAs may be related to organ and cellular development and proliferation pathways. Male-biased miRNA expression at older ages correlated with male-biased renal fibrosis and mononuclear cell infiltration. These miRNAs showed high representation in renal inflammation and nephritis pathways, and included miR-214, miR-130b, miR-150, miR-223, miR-142-5p, miR-185, and miR-296*. Analysis of kidney miRNA expression throughout the rat life span will improve the use of current and future renal biomarkers and inform our assessments of kidney injury and disease.

Electronic supplementary material

The online version of this article (doi:10.1186/s13293-014-0019-1) contains supplementary material, which is available to authorized users.

Cell- and developmental stage-specific Dicer1 ablation in the lung epithelium models cystic pleuropulmonary blastoma

Inherited syndromes provide unique opportunities to identify key regulatory mechanisms governing human disease. We previously identified germline loss-of-function DICER1 mutations in a human syndrome defined by the childhood lung neoplasm pleuropulmonary blastoma (PPB), which arises during lung development. DICER1 regulates many biological processes critical in development and disease pathogenesis. Significant challenges in defining the role of DICER1 in human disease are identifying cause-effect relationships and generating manipulatable systems that model the complexity of organ development and disease pathogenesis. Here we report the generation of a murine model for PPB and demonstrate that precise temporal and cell type-specific Dicer1 ablation is necessary and sufficient for the development of cystic lungs that histologically and phenotypically model PPB. Dicer1 ablation in the distal airway epithelium during early stages of lung development resulted in a cystic lung phenotype indistinguishable from PPB, whereas DICER1 function was not required for development of the proximal airway epithelium or during later stages of organogenesis. Mechanistic studies demonstrate that Dicer1 loss results in epithelial cell death, followed by cystic airway dilatation accompanied by epithelial and mesenchymal proliferation. These studies define precise temporal and epithelial cell type-specific DICER1 functions in the developing lung and demonstrate that loss of these DICER1 functions is sufficient for the development of cystic PPB. These results also provide evidence that PPB arise through a novel mechanism of non-cell-autonomous tumour initiation, in which the genetic abnormality initiating the neoplasm does not occur in the cells that ultimately transform, but rather occurs in a benign-appearing epithelial cell component that predisposes underlying mesenchymal cells to malignant transformation.

MicroRNA-687 Induced by Hypoxia-Inducible Factor-1 Targets Phosphatase and Tensin Homolog in Renal Ischemia-Reperfusion Injury

Ischemia-reperfusion injury contributes to tissue damage and organ failure in clinical settings, but the underlying mechanism remains elusive and effective therapies are still lacking. Here, we identified microRNA 687 (miR-687) as a key regulator and therapeutic target in renal ischemia-reperfusion injury. We show that miR-687 is markedly upregulated in the kidney during renal ischemia-reperfusion in mice and in cultured kidney cells during hypoxia. MiR-687 induction under these conditions was mediated by hypoxia-inducible factor-1 (HIF-1). Upon induction in vitro, miR-687 repressed the expression of phosphatase and tensin homolog (PTEN) and facilitated cell cycle progression and apoptosis. Blockade of miR-687 preserved PTEN expression and attenuated cell cycle activation and renal apoptosis, resulting in protection against kidney injury in mice. Collectively, these results unveil a novel HIF-1/miR-687/PTEN signaling pathway in ischemia-reperfusion injury that may be targeted for therapy.

Defining nephrotic syndrome from an integrative genomics perspective

Nephrotic syndrome (NS) is a clinical condition with a high degree of morbidity and mortality, caused by failure of the glomerular filtration barrier, resulting in massive proteinuria. Our current diagnostic, prognostic and therapeutic decisions in NS are largely based upon clinical or histological patterns such as "focal segmental glomerulosclerosis" or "steroid sensitive". Yet these descriptive classifications lack the precision to explain the physiologic origins and clinical heterogeneity observed in this syndrome. A more precise definition of NS is required to identify mechanisms of disease and capture various clinical trajectories. An integrative genomics approach to NS applies bioinformatics and computational methods to comprehensive experimental, molecular and clinical data for holistic disease definition. A unique aspect is analysis of data together to discover NS-associated molecules, pathways, and networks. Integrating multidimensional datasets from the outset highlights how molecular lesions impact the entire individual. Data sets integrated range from genetic variation to gene expression, to histologic changes, to progression of chronic kidney disease (CKD). This review will introduce the tenets of integrative genomics and suggest how it can increase our understanding of NS from molecular and pathophysiological perspectives. A diverse group of genome-scale experiments are presented that have sought to define molecular signatures of NS. Finally, the Nephrotic Syndrome Study Network (NEPTUNE) will be introduced as an international, prospective cohort study of patients with NS that utilizes an integrated systems genomics approach from the outset. A major NEPTUNE goal is to achieve comprehensive disease definition from a genomics perspective and identify shared molecular drivers of disease.

The sclerosing glomerulus in mice and man: novel insights

PURPOSE OF REVIEW

Segmental glomerulosclerosis is the end-point of a series of processes with have podocyte damage as a common denominator. This review summarizes the important advances that have been made in the past 2 years leading to the comprehension of several molecular mechanisms of regulation of podocyte physiology and pathology.

RECENT FINDINGS

From recent studies it has become clear that the dynamic cytoskeleton of podocyte foot processes has to be highly regulated to maintain cell shape and function. The importance of intracellular calcium in this process has started to be revealed, together with the channels and the organelles appointed to calcium entry and buffering.Novel data highlight the centrality and the complexity of the mammalian target of rapamycin pathways, which are implicated in the regulation of autophagy. Similarities between podocytes and neuronal cells have been extended to the process of dynamin-regulated endocytosis, and further data in mice and humans provide support to the idea that podocytes can be directly targeted by old and new drugs.

SUMMARY

Research is bringing numerous advances regarding the role of podocytes in the development of glomerulosclerosis, which can lead to novel and specific therapeutic approaches, as well as to a more rational use of drugs already in use. Consequently, renal biopsy becomes the indispensable instrument not only for diagnosis but also to precisely detect molecular therapeutic targets and guide personalized therapy.

MiRNA expression profile and miRNA-mRNA integrated analysis (MMIA) during podocyte differentiation

The podocyte is a prominent cell type, which encases the capillaries of glomerulus. Podocyte-selective deletion of Dicer or Drosha was reported to induce proteinuria and glomerulosclerosis, suggesting the essential role of microRNA (miRNA) in podocytes for renal function. However, no comprehensive miRNA expression or miRNA-mRNA integrated analysis (MMIA) can be found during podocyte differentiation. Herein, miRNA and mRNA microarrays are presented, which were carried out in differentiated and undifferentiated mouse podocyte cell lines (MPC5). A total of 50 abnormal miRNAs (26 down-regulated and 24 up-regulated) were identified in differentiated and undifferentiated podocytes. Using MMIA, 80 of the 743 mRNAs (>twofold change) were predicted for potential crosstalk with 30 miRNAs of the 50 abnormal miRNAs. In addition, the gene ontology of mRNAs and the pathway analysis of miRNAs revealed a new potential-regulated network during podocyte differentiation. The expressions of three remarkably changed miRNAs (miR-34c, miR-200a and miR-467e) and four mRNAs (Runx1t1, Atp2a2, Glrp1, and Mmp15), were randomly chosen for further validation by the quantitative real-time polymerase chain reaction, and their expression trends were consistent with the microarray data. Reference searching was also conducted to confirm our data and to find potential new molecules and miRNA-target pairs involved in the podocyte differentiation. The dual luciferase reporter assay for miR-200a/GLRX and let-7b/ARL4D confirmed the prediction of MMIA. The results of this study provide a detailed integration of mRNA and miRNA during podocyte differentiation. The molecular integration mode will open up new perspectives for a better understanding of the mechanism during podocyte differentiation.

Genetic and epigenetic factors influencing chronic kidney disease

Chronic kidney disease (CKD) has become a serious public health problem because of its associated morbidity, premature mortality, and attendant healthcare costs. The rising number of persons with CKD is linked with the aging population structure and an increased prevalence of diabetes, hypertension, and obesity. There is an inherited risk associated with developing CKD, as evidenced by familial clustering and differing prevalence rates across ethnic groups. Previous studies to determine the inherited risk factors for CKD rarely identified genetic variants that were robustly replicated. However, improvements in genotyping technologies and analytic methods are now helping to identify promising genetic loci aided by international collaboration and multiconsortia efforts. More recently, epigenetic modifications have been proposed to play a role in both the inherited susceptibility to CKD and, importantly, to explain how the environment dynamically interacts with the genome to alter an individual's disease risk. Genome-wide, epigenome-wide, and whole transcriptome studies have been performed, and optimal approaches for integrative analysis are being developed. This review summarizes recent research and the current status of genetic and epigenetic risk factors influencing CKD using population-based information.

Developments in renal pharmacogenomics and applications in chronic kidney disease

Chronic kidney disease (CKD) has shown an increasing prevalence in the last century. CKD encompasses a poor prognosis related to a remarkable number of comorbidities, and many patients suffer from this disease progression. Once the factors linked with CKD evolution are distinguished, it will be possible to provide and enhance a more intensive treatment to high-risk patients. In this review, we focus on the emerging markers that might be predictive or related to CKD progression physiopathology as well as those related to a different pattern of response to treatment, such as inhibitors of the renin–angiotensin system (including angiotensin-converting enzyme inhibitors and angiotensin II receptor blockers; the vitamin D receptor agonist; salt sensitivity hypertension; and progressive kidney-disease markers with identified genetic polymorphisms). Candidate-gene association studies and genome-wide association studies have analyzed the genetic basis for common renal diseases, including CKD and related factors such as diabetes and hypertension. This review will, in brief, consider genotype-based pharmacotherapy, risk prediction, drug target recognition, and personalized treatments, and will mainly focus on findings in CKD patients. An improved understanding will smooth the progress of switching from classical clinical medicine to gene-based medicine.

Evaluation of microRNAs miR-196a, miR-30a-5P, and miR-490 as biomarkers of disease activity among patients with FSGS

BACKGROUND AND OBJECTIVES

This study aimed to identify urinary microRNAs (miRNAs) as biomarkers for FSGS disease activity.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

Candidate urinary miRNAs were identified in pooled urine samples from patients with active FSGS (FSGS-A) and FSGS in remission (FSGS-CR), and were then validated using individual samples. Their levels were compared both under different treatment responses in a prospective study of FSGS and in patients with different membranous nephropathy (MN) and diabetic nephropathy (DN) disease activity. The prediction of these miRNAs for treatment responses was further analyzed in both retrospective and prospective cohorts of patients with FSGS.

RESULTS

All 54 miRNAs were included as candidate biomarkers, including those with high levels in patients with FSGS-A (n=9) under the TaqMan Low Density Array as well as those with conserved expression in kidneys and involved in immune response. TaqMan probe-based quantitative RT-PCR confirmed the higher levels of four miRNAs in patients with FSGS-A in two independent cohorts (n=18 and n=80). Urinary miR-196a, miR-30a-5p, and miR-490 discriminated FSGS-A from FSGS-CR, with an area under the curve of ≥ 0.80. After steroid treatment, their levels were lower in steroid-responsive patients with FSGS (all P<0.001), but were unchanged in steroid-resistant patients. The levels of miRNAs were similar between active MN and MN in remission as well as active DN and incipient DN (all P>0.05). Urinary miR-30a-5p marginally predicted the response to steroid treatment in patients with FSGS-A, with an area under the curve of 0.63 (P=0.03).

CONCLUSIONS

The levels of urinary miR-196a, miR-30a-5p, and miR-490 are associated with FSGS disease activity.

Diabetic nephropathy--emerging epigenetic mechanisms

Diabetic nephropathy (DN), a severe microvascular complication frequently associated with both type 1 and type 2 diabetes mellitus, is a leading cause of renal failure. The condition can also lead to accelerated cardiovascular disease and macrovascular complications. Currently available therapies have not been fully efficacious in the treatment of DN, suggesting that further understanding of the molecular mechanisms underlying the pathogenesis of DN is necessary for the improved management of this disease. Although key signal transduction and gene regulation mechanisms have been identified, especially those related to the effects of hyperglycaemia, transforming growth factor β1 and angiotensin II, progress in functional genomics, high-throughput sequencing technology, epigenetics and systems biology approaches have greatly expanded our knowledge and uncovered new molecular mechanisms and factors involved in DN. These mechanisms include DNA methylation, chromatin histone modifications, novel transcripts and functional noncoding RNAs, such as microRNAs and long noncoding RNAs. In this Review, we discuss the significance of these emerging mechanisms, how they mediate the actions of growth factors to augment the expression of extracellular matrix and inflammatory genes associated with DN and their potential usefulness as diagnostic biomarkers or novel therapeutic targets for DN.

Epigenetics of progression of chronic kidney disease: fact or fantasy?

Epigenetic modifications are important in the normal functioning of the cell, from regulating dynamic expression of essential genes and associated proteins to repressing those that are unneeded. Epigenetic changes are essential for development and functioning of the kidney, and aberrant methylation, histone modifications, and expression of microRNA could lead to chronic kidney disease (CKD). Here, epigenetic modifications modulate transforming growth factor β signaling, inflammation, profibrotic genes, and the epithelial-to-mesenchymal transition, promoting renal fibrosis and progression of CKD. Identification of these epigenetic changes is important because they are potentially reversible and may serve as therapeutic targets in the future to prevent subsequent renal fibrosis and CKD. In this review we discuss the different types of epigenetic control, methods to study epigenetic modifications, and how epigenetics promotes progression of CKD.

Recurrent somatic mutation in DROSHA induces microRNA profile changes in Wilms tumour

Wilms tumour (WT) is an embryonal kidney neoplasia for which very few driver genes have been identified. Here we identify DROSHA mutations in 12% of WT samples (26/222) using whole-exome sequencing and targeted sequencing of 10 microRNA (miRNA)-processing genes. A recurrent mutation (E1147K) affecting a metal-binding residue of the RNase IIIb domain is detected in 81% of the DROSHA-mutated tumours. In addition, we identify non-recurrent mutations in other genes of this pathway (DGCR8, DICER1, XPO5 and TARBP2). By assessing the miRNA expression pattern of the DROSHA-E1147K-mutated tumours and cell lines expressing this mutation, we determine that this variant leads to a predominant downregulation of a subset of miRNAs. We confirm that the downregulation occurs exclusively in mature miRNAs and not in primary miRNA transcripts, suggesting that the DROSHA E1147K mutation affects processing of primary miRNAs. Our data underscore the pivotal role of the miRNA biogenesis pathway in WT tumorigenesis, particularly the major miRNA-processing gene DROSHA.

Wilms tumour (WT) is the most common paediatric kidney cancer and few driver genes related to its development have been identified. Here, the authors identify DROSHA mutations that may contribute to WT tumorigenesis through their effect on primary microRNA processing.

Dipping your feet in the water: podocytes in urine

Podocyte injury and loss plays an important role in the pathogenesis and progression of many kidney diseases. Studies have shown that podocyte-related markers and products can be detected in the urine of patients with glomerular diseases such as focal segmental glomerulosclerosis, IgA nephropathy, lupus nephritis, diabetic nephropathy and pre-eclampsia. Therefore, detecting the loss of podocytes in the urine provides a useful noninvasive technique of gathering information about the disease type and/or activity of glomerular diseases. Currently, urine podocyte-related protein markers, mRNA, microRNA and exosomes have been used with varying degrees of success to study glomerular diseases. The determination of urinary podocyte loss may become an important noninvasive tool in the evaluation of glomerular diseases.

miRNAs in mammalian ureteric bud development

The collecting duct network and the urothelium of the ureter of the metanephric kidney are derived from the ureteric bud epithelium, initially an outgrowth from the caudal end of the Wolffian duct at the onset of the metanephric kidney development. The tips of the ureteric bud epithelium undergo reiterative branching morphogenesis, which generates more tips and trunks, whereas the ureteric trunks grow and differentiate into principal cells and intercalated cells of the collecting ducts that regulate body water and acid-base homeostasis. microRNAs (miRNAs) are a family of small non-coding RNAs that regulate a diversity of biological processes including organogenesis, mostly by negatively regulating their target gene expression. In this review, I will summarize the current knowledge on the critical roles of miRNAs expressed in the ureteric bud epithelium in ureteric bud morphogenesis and differentiation, including ureteric bud branching morphogenesis, collecting duct terminal differentiation, cystogenesis of the collecting ducts, and ureter development.

New insights into molecular mechanisms of diabetic kidney disease

Diabetic kidney disease remains a major microvascular complication of diabetes and the most common cause of chronic kidney failure requiring dialysis in the United States. Medical advances over the past century have substantially improved the management of diabetes mellitus and thereby have increased patient survival. However, current standards of care reduce but do not eliminate the risk of diabetic kidney disease, and further studies are warranted to define new strategies for reducing the risk of diabetic kidney disease. In this review, we highlight some of the novel and established molecular mechanisms that contribute to the development of the disease and its outcomes. In particular, we discuss recent advances in our understanding of the molecular mechanisms implicated in the pathogenesis and progression of diabetic kidney disease, with special emphasis on the mitochondrial oxidative stress and microRNA targets. Additionally, candidate genes associated with susceptibility to diabetic kidney disease and alterations in various cytokines, chemokines, and growth factors are addressed briefly.

Endothelial mitochondrial oxidative stress determines podocyte depletion in segmental glomerulosclerosis

Focal segmental glomerular sclerosis (FSGS) is a primary kidney disease that is commonly associated with proteinuria and progressive loss of glomerular function, leading to development of chronic kidney disease (CKD). FSGS is characterized by podocyte injury and depletion and collapse of glomerular capillary segments. Progression of FSGS is associated with TGF-β activation in podocytes; however, it is not clear how TGF-β signaling promotes disease. Here, we determined that podocyte-specific activation of TGF-β signaling in transgenic mice and BALB/c mice with Adriamycin-induced glomerulosclerosis is associated with endothelin-1 (EDN1) release by podocytes, which mediates mitochondrial oxidative stress and dysfunction in adjacent endothelial cells via paracrine EDN1 receptor type A (EDNRA) activation. Endothelial dysfunction promoted podocyte apoptosis, and inhibition of EDNRA or scavenging of mitochondrial-targeted ROS prevented podocyte loss, albuminuria, glomerulosclerosis, and renal failure. We confirmed reciprocal crosstalk between podocytes and endothelial cells in a coculture system. Biopsies from patients with FSGS exhibited increased mitochondrial DNA damage, consistent with EDNRA-mediated glomerular endothelial mitochondrial oxidative stress. Our studies indicate that segmental glomerulosclerosis develops as a result of podocyte-endothelial crosstalk mediated by EDN1/EDNRA-dependent mitochondrial dysfunction and suggest that targeting the reciprocal interaction between podocytes and endothelia may provide opportunities for therapeutic intervention in FSGS.

The regulation and function of microRNAs in kidney diseases

MicroRNAs (miRNA) are endogenous short noncoding RNAs, which regulate virtually all major cellular processes by inhibiting target gene expression. In kidneys, miRNAs have been implicated in renal development, homeostasis, and physiological functions. In addition, miRNAs play important roles in the pathogenesis of various renal diseases, including renal carcinoma, diabetic nephropathy, acute kidney injury, hypertensive nephropathy, polycystic kidney disease, and others. Furthermore, miRNAs may have great values as biomarkers in different kidney diseases.

MicroRNA-17~92 is required for nephrogenesis and renal function

Deletion of all microRNAs (miRNAs) in nephron progenitors leads to premature loss of these cells, but the roles of specific miRNAs in progenitors have not been identified. Deletions in the MIR17HG cluster (miR-17~92 in mice), detected in a subset of patients with Feingold syndrome, represent the first miRNA mutations to be associated with a developmental defect in humans. Although MIR17HG is expressed in the developing kidney, and patients with Feingold syndrome caused by MYCN mutations have renal anomalies, it remains unclear to what extent MIR17HG contributes to renal development and function. To define the role of miR-17~92, we generated mice with a conditional deletion of miR-17~92 in nephron progenitors and their derivatives. The nephron progenitor population was preserved in these mice; however, this deletion impaired progenitor cell proliferation and reduced the number of developing nephrons. Postnatally, mutant mice developed signs of renal disease, including albuminuria by 6 weeks and focal podocyte foot process effacement and glomerulosclerosis at 3 months. Taken together, these data support a role for this miRNA cluster in renal development, specifically in the regulation of nephron development, with subsequent consequences for renal function in adult mice.

Dicer function is required in the metanephric mesenchyme for early kidney development

MicroRNAs (miRNAs) are small, noncoding regulatory RNAs that act as posttranscriptional repressors by binding to the 3'-untranslated region (3'-UTR) of target genes. They require processing by Dicer, an RNase III enzyme, to become mature regulatory RNAs. Previous work from our laboratory revealed critical roles for miRNAs in nephron progenitors at midgestation (Ho J, Pandey P, Schatton T, Sims-Lucas S, Khalid M, Frank MH, Hartwig S, Kreidberg JA. J Am Soc Nephrol 22: 1053-1063, 2011). To interrogate roles for miRNAs in the early metanephric mesenchyme, which gives rise to nephron progenitors as well as the renal stroma during kidney development, we conditionally ablated Dicer function in this lineage. Despite normal ureteric bud outgrowth and condensation of the metanephric mesenchyme to form nephron progenitors, early loss of miRNAs in the metanephric mesenchyme resulted in severe renal dysgenesis. Nephron progenitors are initially correctly specified in the mutant kidneys, with normal expression of several transcription factors known to be critical in progenitors, including Six2, Pax2, Sall1, and Wt1. However, there is premature loss of the nephron progenitor marker Cited1, marked apoptosis, and increased expression of the proapoptotic protein Bim shortly after the initial inductive events in early kidney development. Subsequently, there is a failure in ureteric bud branching and nephron progenitor differentiation. Taken together, our data demonstrate a previously undetermined requirement for miRNAs during early kidney organogenesis and indicate a crucial role for miRNAs in regulating the survival of this lineage.

miRWalk database for miRNA-target interactions

miRWalk (http://mirwalk.uni-hd.de/) is a publicly available comprehensive resource, hosting the predicted as well as the experimentally validated microRNA (miRNA)-target interaction pairs. This database allows obtaining the possible miRNA-binding site predictions within the complete sequence of all known genes of three genomes (human, mouse, and rat). Moreover, it also integrates many novel features such as a comparative platform of miRNA-binding sites resulting from ten different prediction datasets, a holistic view of genetic networks of miRNA-gene pathway, and miRNA-gene-Online Mendelian Inheritance in Man disorder interactions, and unique experimentally validated information (e.g., cell lines, diseases, miRNA processing proteins). In this chapter, we describe a schematic workflow on how one can access the stored information from miRWalk and subsequently summarize its applications.

MicroRNAs in Diabetic Kidney Disease

Rapid growth of diabetes and diabetic kidney disease exerts a great burden on society. Owing to the lack of effective treatments for diabetic kidney disease, treatment relies on drugs that either reduces its progression or involve renal replacement therapies, such as dialysis and kidney transplantation. It is urgent to search for biomarkers for early diagnosis and effective therapy. The discovery of microRNAs had lead to a new era of post-transcriptional regulators of gene expression. Studies from cells, experimental animal models and patients under diabetic conditions demonstrate that expression patterns of microRNAs are altered during the progression of diabetic kidney disease. Functional studies indicate that the ability of microRNAs to bind 3' untranslated region of messenger RNA not only shows their capability to regulate expression of target genes, but also their therapeutic potential to diabetic kidney disease. The presence of microRNAs in plasma, serum, and urine has been shown to be possible biomarkers in diabetic kidney disease. Therefore, identification of the pathogenic role of microRNAs possesses an important clinical impact in terms of prevention and treatment of progression in diabetic kidney disease because it allows us to design novel and specific therapies and diagnostic tools for diabetic kidney disease.

The role of microRNAs in diabetic nephropathy

Diabetic nephropathy (DN), as one of the chronic complications of diabetes, is the major cause of end-stage renal disease. However, the pathogenesis of this disease is not fully understood. In recent years, research on microRNAs (miRNAs) has become a hotspot because of their critical role in regulating posttranscriptional levels of protein-coding genes that may serve as key pathogenic factors in diseases. Several miRNAs were found to participate in the pathogenesis of DN, while others showed renal protective effects. Therefore, targeting miRNAs that are involved in DN may have a good prospect in the treatment of the disease. The aim of this review is to summarize DN-related miRNAs and provide potential targets for diagnostic strategies and therapeutic intervention.

Stem cells: potential and challenges for kidney repair

Renal damage resulting from acute and chronic kidney injury poses an important problem to public health. Currently, patients with end-stage renal disease rely solely on kidney transplantation or dialysis for survival. Emerging therapies aiming to prevent and reverse kidney damage are thus in urgent need. Although the kidney was initially thought to lack the capacity for self-repair, several studies have indicated that this might not be the case; progenitor and stem cells appear to play important roles in kidney repair under various pathological conditions. In this review, we summarize recent findings on the role of progenitor/stem cells on kidney repair as well as discuss their potential as a therapeutic approach for kidney diseases.

Smad2-dependent downregulation of miR-30 is required for TGF-β-induced apoptosis in podocytes

Transforming growth factors beta (TGF-β) are multi-functional cytokines capable of inducing apoptosis in epithelial cells, including glomerular podocytes. We and others have previously shown that podocyte-selective genetic deletion of the microRNA (miR)-processing enzyme, Dicer, caused glomerulosclerosis that was associated with podocyte apoptosis, and the miR-30 family was implicated in the process. Here, we report that apoptosis-associated genes were highly enriched among the predicted targets of miR-30 when compared with randomly selected miRs (26% vs. 4.5 ± 2.1%) or with the known TGF-β-regulated miR-192 (6%), miR-216a (5.1%), and miR-217 (0%). miR-30 family members were abundantly expressed in podocytes in normal mice but were downregulated in albumin/TGF-β transgenic mice with podocyte apoptosis and glomerulosclerosis. In vitro, TGF-β downregulated miR-30s in wildtype and Smad3-deficient, but not Smad2- or Smad2/Smad3-deficient, podocytes. The TGF-β-induced activation of caspase 3 and an increase in TUNEL-positive nuclei were significantly inhibited by the lentivirus-mediated overexpression of miR-30d, but not by a scrambled control miR, in podocytes. TGF-β stimulated the phosphorylation of pro-apoptotic p53 in podocytes with lentiviral expression of a scrambled miR, but not in podocytes expressing miR-30d. In contrast, miR-30d had no effect on the phosphorylation of pro-apoptotic p38 MAP kinase induced by TGF-β. Thus, we report that Smad2-dependent inhibition of miR-30s in podocytes is required for the activation of p53 and the induction of apoptosis by TGF-β. These results demonstrate a novel functional role for miR-30 in podocyte survival and indicate that the loss of miR-30 survival signaling is a novel and specific mechanism of TGF-β-induced podocyte apoptosis during glomerulosclerosis. We propose the therapeutic replacement of miR-30 as a novel strategy to prevent the podocyte apoptosis that is characteristic of progressive glomerular diseases.

MiR-181b targets Six2 and inhibits the proliferation of metanephric mesenchymal cells in vitro

MicroRNAs (miRNAs) are small non-coding RNAs that down-regulate gene expression by binding to target mRNA for cleavage or translational repression, and play important regulatory roles in renal development. Despite increasing genes have been predicted to be miRNA targets by bioinformatic analysis during kidney development, few of them have been verified by experiment. The objective of our study is to identify the miRNAs targeting Six2, a critical transcription factor that maintains the mesenchymal progenitor pool via self-renewal (proliferation) during renal development. We initially analyzed the 3'UTR of Six2 and found 37 binding sites targeted by 50 putative miRNAs in the 3'UTR of Six2. Among the 50 miRNAs, miR-181b is the miRNAs predicted by the three used websites. In our study, the results of luciferase reporter assay, realtime-PCR and Western blot demonstrated that miR-181b directly targeted on the 3'UTR of Six2 and down-regulate the expression of Six2 at mRNA and protein levels. Furthermore, EdU proliferation assay along with the Six2 rescue strategy showed that miR-181b suppresses the proliferation of metanephric mesenchymal by targeting Six2 in part. In our research, we concluded that by targeting the transcription factor gene Six2, miR-181b inhibits the proliferation of metanephric mesenchymal cells in vitro and might play an important role in the formation of nephrons.

Downregulation of microRNA-30 facilitates podocyte injury and is prevented by glucocorticoids

MicroRNAs (miRNAs) are essential for podocyte homeostasis, and the miR-30 family may be responsible for this action. However, the exact roles and clinical relevance of miR-30s remain unknown. In this study, we examined the expression of the miR-30 family in the podocytes of patients with FSGS and found that all members are downregulated. Treating cultured human podocytes with TGF-β, LPS, or puromycin aminonucleoside (PAN) also downregulated the miR-30 family. Podocyte cytoskeletal damage and apoptosis caused by treatment with TGF-β or PAN were ameliorated by exogenous miR-30 expression and aggravated by miR-30 knockdown. Moreover, we found that miR-30s exert their protective roles by direct inhibition of Notch1 and p53, which mediate podocyte injury. In rats, treatment with PAN substantially downregulated podocyte miR-30s and induced proteinuria and podocyte injury; however, transfer of exogenous miR-30a to podocytes of PAN-treated rats ameliorated proteinuria and podocyte injury and reduced Notch1 activation. Finally, we demonstrated that glucocorticoid treatment maintains miR-30 expression in cultured podocytes treated with TGF-β, LPS, or PAN and in the podocytes of PAN-treated rats. Glucocorticoid-sustained miR-30 expression associated with reduced Notch1 activation and alleviated podocyte damage. Taken together, these findings demonstrate that miR-30s protect podocytes by targeting Notch1 and p53 and that the loss of miR-30s facilitates podocyte injury. In addition, sustained miR-30 expression may be a novel mechanism underlying the therapeutic effectiveness of glucocorticoids in treating podocytopathy.

MicroRNAs in kidney fibrosis and diabetic nephropathy: roles on EMT and EndMT

MicroRNAs (miRNAs) are a family of small, noncoding RNAs that regulate gene expression in diverse biological and pathological processes, including cell proliferation, differentiation, apoptosis, and carcinogenesis. As a result, miRNAs emerged as major area of biomedical research with relevance to kidney fibrosis. Fibrosis is characterized by the excess deposition of extracellular matrix (ECM) components, which is the end result of an imbalance of metabolism of the ECM molecule. Recent evidence suggests that miRNAs participate in the fibrotic process in a number of organs including the heart, kidney, liver, and lung. Epithelial mesenchymal transition (EMT) and endothelial mesenchymal transition (EndMT) programs play vital roles in the development of fibrosis in the kidney. A growing number of the extracellular and intracellular molecules that control EMT and EndMT have been identified and could be exploited in developing therapeutics for fibrosis. This review highlights recent advances on the role of miRNAs in the kidney diseases; diabetic nephropathy especially focused on EMT and EndMT program responsible for the development of kidney fibrosis. These miRNAs can be utilized as a potential novel drug target for the studying of underlying mechanism and treatment of kidney fibrosis.

MicroRNAs: potential mediators and biomarkers of diabetic complications

The incidence of diabetes is escalating worldwide and, consequently, this has become a major health care problem. Moreover, both type 1 and type 2 diabetes are associated with significantly accelerated rates of microvascular complications, including retinopathy, nephropathy, and neuropathy, as well as macrovascular complications such as atherosclerotic cardiovascular and hypertensive diseases. Key factors have been implicated in leading to these complications, including hyperglycemia, insulin resistance, dyslipidemia, advanced glycation end products, growth factors, inflammatory cytokines/chemokines, and related increases in cellular oxidant stress (including mitochondrial) and endoplasmic reticulum stress. However, the molecular mechanisms underlying the high incidence of diabetic complications, which often progress despite glycemic control, are still not fully understood. MicroRNAs (miRNAs) are short noncoding RNAs that have elicited immense interest in recent years. They repress target gene expression via posttranscriptional mechanisms and have diverse cellular and biological functions. Herein, we discuss the role of miRNAs in the pathobiology of various diabetic complications, their involvement in oxidant stress, and also the potential use of differentially expressed miRNAs as novel diagnostic biomarkers and therapeutic targets.

MicroRNA regulation in renal pathophysiology

MicroRNAs are small, noncoding RNA molecules that regulate a considerable amount of human genes on the post-transcriptional level, and participate in many key biological processes. MicroRNA deregulation has been found associated with major kidney diseases. Here, we summarize current knowledge on the role of microRNAs in renal glomerular and tubular pathologies, with emphasis on the mesangial cell and podocyte dysfunction in diabetic nephropathy, the proximal tubular cell survival in acute kidney injury, the transport function of the thick ascending limb in Ca⁺⁺ imbalance diseases, and the regulation of salt, K⁺ and blood pressure in the distal tubules. Identification of microRNAs and their target genes provides novel therapeutic candidates for treating these diseases. Manipulation of microRNA function with its sense or antisense oligonucleotide enables coordinated regulation of the entire downstream gene network, which has effectively ameliorated several renal disease phenotypes. The therapeutic potentials of microRNA based treatments, though promising, are confounded by major safety issues related to its target specificity, which remain to be fully elucidated.

MicroRNAs in kidney diseases: new promising biomarkers for diagnosis and monitoring

A series of microRNAs (miRNAs) have a critical role in many cellular and physiological activities such as cell cycle, growth, proliferation, apoptosis and metabolism. miRNAs are also important in the maintenance of renal homeostasis and kidney diseases. In vitro and in vivo animal models have shown a critical role of miRNAs in the development of diabetic nephropathy (DN) and in the progression of renal fibrosis. Specific miRNAs in renal tissue and peripheral blood mononuclear cells (PBMCs) are up and downregulated in different kidney diseases. They represent new potential biomarkers for diagnosis and targeted therapy. In addition, urinary miRNAs may be considered non-invasive biomarkers for monitoring the progression of renal damage. The activity of miRNAs can be modified by different approaches such as the use of antisense oligonucleotide inhibitors (antagomirs), tandem miRNA-binding site repeats manufactured by Decoy or Sponge technologies and miRNA mimics. The use of miRNA blockers or antagonists as therapeutic agents is very attractive but new information will be necessary considering their role in other systems.

RAGE-mediated cell signaling

RAGE (receptor for advanced glycation end products) is a multi-ligand receptor that belongs to the immunoglobulin superfamily of transmembrane proteins. RAGE binds AGEs (advanced glycation end products), HMGB1 (high-mobility group box-1; also designated as amphoterin), members of the S100 protein family, glycosaminoglycans and amyloid β peptides. Recent studies using tools of structural biology have started to unravel common molecular patterns in the diverse set of ligands recognized by RAGE. The distal Ig domain (V1 domain) of RAGE has a positively charged patch, the geometry of which fits to anionic surfaces displayed at least in a proportion of RAGE ligands. Association of RAGE to itself, to HSPGs (heparan sulfate proteoglycans), and to Toll-like receptors in the cell membrane plays a key role in cell signaling initiated by RAGE ligation. Ligation of RAGE activates cell signaling pathways that regulate migration of several cell types. Furthermore, RAGE ligation has profound effects on the transcriptional profile of cells. RAGE signaling has been mainly studied as a pathogenetic factor of several diseases, where acute or chronic inflammation plays a role. Recent studies have suggested a physiological role for RAGE in normal lung function and in neuronal signaling.

Novel DICER1 mutation as cause of multinodular goiter in children

BACKGROUND

The aim of this report was to present a rare case of an adolescent with multinodular goiter (MNG) found to have a DICER1 mutation.

METHODS AND RESULTS

The methodology includes a presentation and discussion of a chart review including endocrine hormone tests, thyroid ultrasound, and genetic testing for DICER1. A 12-year-old girl presented with a diffusely enlarged thyroid gland. Family history revealed an older sister with a history of bilateral ovarian Sertoli-Leydig cell tumors and MNG. Thyroid function tests were normal. Serial thyroid ultrasounds showed enlarging multiple bilateral nodules. Fine-needle aspiration suggested MNG. Genetic testing revealed a novel heterozygous premature termination mutation (c.1525C>T p.R509X) in the DICER1 gene.

CONCLUSIONS

Thyroid nodules are rare in children but carry a higher risk for malignancy. It is essential to inquire about family history and refer for genetic evaluation with a family history of MNG. In patients with DICER1 mutations, tumor surveillance is critical due to the increased risk of multiple tumors, including ovarian tumors and pleuropulmonary blastoma.

Telmisartan inhibits AGE-induced podocyte damage and detachment

Advanced glycation end products (AGE) formed at an accelerated rate under diabetes, could cause podocyte apoptosis, thereby being involved in the development and progression of diabetic nephropathy. Renin-angiotensin system (RAS) plays a role in diabetic nephropathy as well. However, it remains unknown whether there exists a pathophysiological crosstalk between the RAS and AGE in podocyte damage in diabetic nephropathy. Therefore, this study investigated the effects of telmisartan, an angiotensin II (Ang II) type 1 receptor (AT1R) blocker on AGE or Ang II-induced podocyte damage in vitro. We further examined here the effects of AGE on AT1R expression levels in podocytes. AGE or Ang II not only increased DNA damage of podocytes which was evaluated by comet assay, but also induced cell detachment, both of which were significantly blocked by the treatment with telmisartan. AGE significantly increased AT1R levels in podocytes, whereas podocyte Ang II production was modestly stimulated by AGE. Telmisartan alone did not affect the release of lactate dehydrogenase from podocytes. Our present study suggests that AGE could induce podocyte DNA damage and detachment partly via stimulation of the Ang II-AT1R axis, thus providing a novel beneficial aspect of telmisartan in diabetic nephropathy.

The baboon kidney transcriptome: analysis of transcript sequence, splice variants, and abundance

The baboon is an invaluable model for the study of human health and disease, including many complex diseases of the kidney. Although scientists have made great progress in developing this animal as a model for numerous areas of biomedical research, genomic resources for the baboon, such as a quality annotated genome, are still lacking. To this end, we characterized the baboon kidney transcriptome using high-throughput cDNA sequencing (RNA-Seq) to identify genes, gene variants, single nucleotide polymorphisms (SNPs), insertion-deletion polymorphisms (InDels), cellular functions, and key pathways in the baboon kidney to provide a genomic resource for the baboon. Analysis of our sequencing data revealed 45,499 high-confidence SNPs and 29,813 InDels comparing baboon cDNA sequences with the human hg18 reference assembly and identified 35,900 cDNAs in the baboon kidney, including 35,150 transcripts representing 15,369 genic genes that are novel for the baboon. Gene ontology analysis of our sequencing dataset also identified numerous biological functions and canonical pathways that were significant in the baboon kidney, including a large number of metabolic pathways that support known functions of the kidney. The results presented in this study catalogues the transcribed mRNAs, noncoding RNAs, and hypothetical proteins in the baboon kidney and establishes a genomic resource for scientists using the baboon as an experimental model.

The next level of complexity: post-transcriptional regulation by microRNAs

MicroRNAs (miRNAs) are endogenous, small, noncoding RNAs that regulate expression of about half of human genes. Canonical miRNA biosynthesis involves two RNase III-type proteins, Drosha and Dicer. A podocyte-specific knockout of Dicer resulted in foot process effacement. In this issue, Zhdanova et al. report on targeting Drosha in a podocyte-specific fashion. Their study demonstrates an essential role of canonical miRNAs in maintaining the fully differentiated podocyte phenotype.

A microRNA-30e/mitochondrial uncoupling protein 2 axis mediates TGF-β1-induced tubular epithelial cell extracellular matrix production and kidney fibrosis

Mitochondria dysfunction has been reported in various kidney diseases but how it leads to kidney fibrosis and how this is regulated is unknown. Here we found that mitochondrial uncoupling protein 2 (UCP2) was induced in kidney tubular epithelial cells after unilateral ureteral obstruction in mice and that mice with ablated UCP2 resisted obstruction-induced kidney fibrosis. We tested this association further in cultured NRK-52E cells and found that TGF-β1 remarkably induced UCP2 expression. Knockdown of UCP2 largely abolished the effect of TGF-β1, whereas overexpression of UCP2 promoted tubular cell phenotype changes. Analysis using a UCP2 mRNA-3′-untranslated region luciferase construct showed that UCP2 mRNA is a direct target of miR-30e. MiR-30e was downregulated in tubular cells from fibrotic kidneys and TGF-β1-treated NRK-52E cells. A miR-30e mimic significantly inhibited TGF-β1-induced tubular-cell epithelial–mesenchymal transition, whereas a miR-30e inhibitor imitated TGF-β1 effects. Finally, genipin, an aglycone UCP2 inhibitor, significantly ameliorated kidney fibrosis in mice. Thus, the miR-30e/UCP2 axis has an important role in mediating TGF-β1-induced epithelial–mesenchymal transition and kidney fibrosis. Targeting this pathway may shed new light for the future of fibrotic kidney disease therapy.

Focal segmental glomerulosclerosis is induced by microRNA-193a and its downregulation of WT1

Focal segmental glomerulosclerosis (FSGS) is a frequent and severe glomerular disease characterized by destabilization of podocyte foot processes. We report that transgenic expression of the microRNA miR-193a in mice rapidly induces FSGS with extensive podocyte foot process effacement. Mechanistically, miR-193a inhibits the expression of the Wilms' tumor protein (WT1), a transcription factor and master regulator of podocyte differentiation and homeostasis. Decreased expression levels of WT1 lead to downregulation of its target genes PODXL (podocalyxin) and NPHS1 (nephrin), as well as several other genes crucial for the architecture of podocytes, initiating a catastrophic collapse of the entire podocyte-stabilizing system. We found upregulation of miR-193a in isolated glomeruli from individuals with FSGS compared to normal kidneys or individuals with other glomerular diseases. Thus, upregulation of miR-193a provides a new pathogenic mechanism for FSGS and is a potential therapeutic target.

Towards microRNA-based therapeutics for diabetic nephropathy

There is no cure for diabetic nephropathy and the molecular mechanisms underlying disease aetiology remain poorly understood. While current paradigms for clinical management of diabetic nephropathy are useful in delaying disease onset and preventing its progression, they do not do so for a significant proportion of diabetic individuals, who eventually end up developing renal failure. Thus, novel therapeutic targets are needed for the treatment and prevention of the disease. MicroRNAs (miRNAs), a class of non-coding RNAs that negatively regulate gene expression, have recently been identified as attractive targets for therapeutic intervention. It is widely recognised that dysregulation of miRNA expression or action contributes to the development of a number of different human diseases, and evidence of a role for miRNAs in the aetiology of diabetic nephropathy is emerging. The discovery that modulation of miRNA expression in vivo is feasible, combined with recent results from successful clinical trials using this technology, opens the way for future novel therapeutic applications. For instance, inhibition of miRNAs that are commonly upregulated in diabetic nephropathy decreases albuminuria and mesangial matrix accumulation in animal models, suggesting that a therapeutic agent against these molecules may help to prevent the development of diabetic nephropathy. Certain challenges, including the development of safe and reliable delivery systems, remain to be overcome before miRNA-based therapeutics become a reality. However, the findings accumulated to date, in conjunction with newly emerging results, are expected to yield novel insights into the complex pathogenesis of diabetic nephropathy, and may eventually lead to the identification of improved therapeutic targets for treatment of this disease.