Focal segmental glomerulosclerosis is induced by microRNA-193a and its downregulation of WT1. Nat Med. 2013;19:481-487. [PMID: 23502960 DOI: 10.1038/nm.3142]

Function and Regulation of the Wilms' Tumor Suppressor 1 (WT1) Gene in Fish

The Wilms' tumor suppressor gene Wt1 is highly conserved among vertebrates. In contrast to mammals, most fish species possess two wt1 paralogs that have been named wt1a and wt1b. Concerning wt1 in fish, most work so far has been done using zebrafish, focusing on the embryonic kidney, the pronephros. In this chapter we will describe the structure and development of the pronephros as well as the role that the wt1 genes play in the embryonic zebrafish kidney. We also discuss Wt1 target genes and describe the potential function of the Wt1 proteins in the adult kidney. Finally we will summarize data on the role of Wt1 outside of the kidney.

Live or Let Die: Is There any Cell Death in Podocytes?

Ultimately, the common final pathway of any glomerular disease is podocyte effacement, podocyte loss, and, eventually, glomerular scarring. There has been a long-standing debate on the underlying mechanisms for podocyte depletion, ranging from necrosis and apoptosis to detachment of viable cells from the glomerular basement membrane. However, this debate still continues because additional pathways of programmed cell death have been reported in recent years. Interestingly, viable podocytes can be isolated out of the urine of proteinuric patients easily, emphasizing the importance of podocyte detachment in glomerular diseases. In contrast, detection of apoptosis and other pathways of programmed cell death in podocytes is technically challenging. In fact, we still are lacking direct evidence showing, for example, the presence of apoptotic bodies in podocytes, leaving the question unanswered as to whether podocytes undergo mechanisms of programmed cell death. However, understanding the mechanisms leading to podocyte depletion is of particular interest because future therapeutic strategies might interfere with these to prevent glomerular scarring. In this review, we summarize our current knowledge on podocyte cell death, the different molecular pathways and experimental approaches to study these, and, finally, focus on the mechanisms that prevent the onset of programmed cell death.

MicroRNAs associated with the development of kidney diseases in humans and animals

Mature microRNAs (miRNAs) are single-stranded RNAs with approximately 18-25 bases, and their sequences are highly conserved among animals. miRNAs act as posttranscriptional regulators by binding mRNAs, and their main function involves the degradation of their target mRNAs. Recent studies revealed altered expression of miRNAs in the kidneys during the progression of acute kidney injury (AKI) and chronic kidney disease (CKD) in humans and experimental rodent models by using high-throughput screening techniques including microarray and small RNA sequencing. Particularly, miR-21 seems to be strongly associated with renal pathogenesis both in the glomerulus and tubulointerstitium. Furthermore, abundant evidence has been gathered showing the involvement of miRNAs in renal fibrosis. Because of the complex morphofunctional organization of the mammalian kidneys, it is crucial both to determine the exact localization of the kidney cells that express the miRNAs, which has been addressed mainly using in situ hybridization methods, and to identify precisely which mRNAs are bound and degraded by these miRNAs, which has been studied mostly through in vitro analysis. To discover novel biomarker candidates, miRNA levels in urine supernatant, sediment, and exosomal fraction were comprehensively investigated in different types of kidney disease, including drug-induced AKI, ischemia-induced AKI, diabetic nephropathy, lupus nephritis, and IgA nephropathy. Recent studies also demonstrated the therapeutic effect of miRNA and/or anti-miRNA administrations. The intent of this review is to illustrate the state-of-the-art research in the field of miRNAs associated with renal pathogenesis, especially focusing on AKI and CKD in humans and animal models.

Genetic and pharmacological inhibition of microRNA-92a maintains podocyte cell cycle quiescence and limits crescentic glomerulonephritis

Crescentic rapidly progressive glomerulonephritis (RPGN) represents the most aggressive form of acquired glomerular disease. While most therapeutic approaches involve potentially toxic immunosuppressive strategies, the pathophysiology remains incompletely understood. Podocytes are glomerular epithelial cells that are normally growth-arrested because of the expression of cyclin-dependent kinase (CDK) inhibitors. An exception is in RPGN where podocytes undergo a deregulation of their differentiated phenotype and proliferate. Here we demonstrate that microRNA-92a (miR-92a) is enriched in podocytes of patients and mice with RPGN. The CDK inhibitor p57^Kip2 is a major target of miR-92a that constitutively safeguards podocyte cell cycle quiescence. Podocyte-specific deletion of miR-92a in mice de-repressed the expression of p57^Kip2 and prevented glomerular injury in RPGN. Administration of an anti-miR-92a after disease initiation prevented albuminuria and kidney failure, indicating miR-92a inhibition as a potential therapeutic strategy for RPGN. We demonstrate that miRNA induction in epithelial cells can break glomerular tolerance to immune injury.

Crescentic rapidly progressive glomerulonephritis is a severe form of glomerula disease characterized by podocyte proliferation and migration. Here Henique et al. demonstrate that inhibition of miRNA-92a prevents kidney failure by promoting the expression of CDK inhibitor p57^Kip2 that regulates podocyte cell cycle.

An inducible mouse model of podocin-mutation-related nephrotic syndrome

Mutations in the NPHS2 gene, encoding podocin, cause hereditary nephrotic syndrome. The most common podocin mutation, R138Q, is associated with early disease onset and rapid progression to end-stage renal disease. Knock-in mice carrying a R140Q mutation, the mouse analogue of human R138Q, show developmental arrest of podocytes and lethal renal failure at neonatal age. Here we created a conditional podocin knock-in model named NPHS2^R140Q/-, using a tamoxifen-inducible Cre recombinase, which permits to study the effects of the mutation in postnatal life. Within the first week of R140Q hemizygosity induction the animals developed proteinuria, which peaked after 4–5 weeks. Subsequently the animals developed progressive renal failure, with a median survival time of 12 (95% CI: 11–13) weeks. Foot process fusion was observed within one week, progressing to severe and global effacement in the course of the disease. The number of podocytes per glomerulus gradually diminished to 18% compared to healthy controls 12–16 weeks after induction. The fraction of segmentally sclerosed glomeruli was 25%, 85% and 97% at 2, 4 and 8 weeks, respectively. Severe tubulointerstitial fibrosis was present at later disease stage and was correlated quantitatively with the level of proteinuria at early disease stages. While R140Q podocin mRNA expression was elevated, protein abundance was reduced by more than 50% within one week following induction. Whereas miRNA21 expression persistently increased during the first 4 weeks, miRNA-193a expression peaked 2 weeks after induction. In conclusion, the inducible R140Q-podocin mouse model is an auspicious model of the most common genetic cause of human nephrotic syndrome, with a spontaneous disease course strongly reminiscent of the human disorder. This model constitutes a valuable tool to test the efficacy of novel pharmacological interventions aimed to improve podocyte function and viability and attenuate proteinuria, glomerulosclerosis and progressive renal failure.

The Wilms tumor protein Wt1 contributes to female fertility by regulating oviductal proteostasis

Although the zinc finger transcription factor Wt1 has been linked to female fertility, its precise role in this process has not yet been understood. We have sequenced the WT1 exons in a panel of patients with idiopathic infertility and have identified a missense mutation in WT1 in one patient out of eight. This mutation leads to an amino acid change within the zinc finger domain and results in reduced DNA binding. We utilized Wt1^+/- mice as a model to mechanistically pinpoint the consequences of reduced Wt1 levels for female fertility. Our results indicate that subfertility in Wt1^+/- female mice is a maternal effect caused by the Wt1-dependent de-regulation of Prss29, encoding a serine protease. Notably, blocking Prss29 activity was sufficient to rescue subfertility in Wt1^+/- mice indicating Prss29 as a critical factor in female fertility. Molecularly, Wt1 represses expression of Prss29. De-repression and precocious expression of Prss29 in the oviduct of Wt1^+/- mice interferes with pre-implantation development. Our study reveals a novel role for Wt1 in early mammalian development and identifies proteases as critical mediators of the maternal-embryonic interaction. Our data also suggest that the role of Wt1 in regulating fertility is conserved in mammals.

Wilms' tumour 1 (WT1) in development, homeostasis and disease

The study of genes mutated in human disease often leads to new insights into biology as well as disease mechanisms. One such gene is Wilms' tumour 1 (WT1), which plays multiple roles in development, tissue homeostasis and disease. In this Primer, I summarise how this multifaceted gene functions in various mammalian tissues and organs, including the kidney, gonads, heart and nervous system. This is followed by a discussion of our current understanding of the molecular mechanisms by which WT1 and its two major isoforms regulate these processes at the transcriptional and post-transcriptional levels.

MicroRNA-135a is involved in podocyte injury in a transient receptor potential channel 1-dependent manner

Transient receptor potential (TRP) cation channels are essential for normal cellular physiology, and their abnormal expression may lead to a number of disorders, including podocytopathy. Therefore, it is crucial to understand the mechanisms underlying the regulation of TRP channels. In the present study, microRNA (miR)-135a was found to be upregulated in patients with focal segmental glomerulosclerosis and mice treated with adriamycin (ADR). In cultured podocytes, transforming growth factor (TGF)-β and ADR were found to promote miR-135a expression. Conversely, TRP channel 1 (TRPC1) protein levels were markedly downregulated in podocytes from mice treated with ADR, as well as in cultured podocytes treated with ADR and TGF-β. Ectopic expression of miR-135a led to severe podocyte injury and disarray of the podocyte cytoskeleton, whereas podocyte-specific expression of TRPC1 was able to reverse the pathological effects of miR-135a in cultured podocytes. Moreover, using Luciferase reporter assays and western blot analysis, TRPC1 was identified as a target gene of miR-135a. To the best of our knowledge, this is the first study to demonstrate the role of TRPC1 in the development of podocyte injury and disorders of the podocyte cytoskeleton, which may contribute to the development of novel therapeutics for podocyte injury-associated kidney diseases.

Loss of mucin-type O-glycans impairs the integrity of the glomerular filtration barrier in the mouse kidney

The kidney's filtration activity is essential for removing toxins and waste products from the body. The vascular endothelial cells of the glomerulus are fenestrated, flattened, and surrounded by podocytes, specialized cells that support glomerular endothelial cells. Mucin-type core 1-derived O-glycans (O-glycans) are highly expressed on both glomerular capillary endothelial cells and their supporting podocytes, but their biological role is unclear. Biosynthesis of core 1-derived O-glycans is catalyzed by the glycosyltransferase core 1 β1,3-galactosyltransferase (C1galt1). Here we report that neonatal or adult mice with inducible deletion of C1galt1 (iC1galt1^-/-) exhibit spontaneous proteinuria and rapidly progressing glomerulosclerosis. Ultrastructural analysis of the glomerular filtration barrier components revealed that loss of O-glycans results in altered podocyte foot processes. Further analysis indicated that O-glycan is essential for the normal signaling function of podocalyxin, a podocyte foot process-associated glycoprotein. Our results reveal a new function of O-glycosylation in the integrity of the glomerular filtration barrier.

Bim gene dosage is critical in modulating nephron progenitor survival in the absence of microRNAs during kidney development

Low nephron endowment at birth has been associated with an increased risk for developing hypertension and chronic kidney disease. We demonstrated in an earlier study that conditional deletion of the microRNA (miRNA)-processing enzyme Dicer from nephron progenitors results in premature depletion of the progenitors and increased expression of the proapoptotic protein Bim (also known as Bcl-2L11). In this study, we generated a compound mouse model with conditional deletion of both Dicer and Bim, to determine the biologic significance of increased Bim expression in Dicer-deficient nephron progenitors. The loss of Bim partially restored the number of nephron progenitors and improved nephron formation. The number of progenitors undergoing apoptosis was significantly reduced in kidneys with loss of a single allele, or both alleles, of Bim compared to mutant kidneys. Furthermore, 2 miRNAs expressed in nephron progenitors (miR-17 and miR-106b) regulated Bim levels in vitro and in vivo Together, these data suggest that miRNA-mediated regulation of Bim controls nephron progenitor survival during nephrogenesis, as one potential means of regulating nephron endowment.-Cerqueira, D. M., Bodnar, A. J., Phua, Y. L., Freer, R., Hemker, S. L., Walensky, L. D., Hukriede, N. A., Ho, J. Bim gene dosage is critical in modulating nephron progenitor survival in the absence of microRNAs during kidney development.

Optimal management of primary focal segmental glomerulosclerosis in adults

Focal segmental glomerulosclerosis (FSGS) is a frequent glomerular kidney disease that is revealed by proteinuria or even nephrotic syndrome. A diagnosis can be established from a kidney biopsy that shows focal and segmental glomerulosclerosis. This histopathological lesion may be caused by a primary podocyte injury (idiopathic FSGS) but is also associated with other pathologies (secondary FSGS). The first-line treatment for idiopathic FSGS with nephrotic syndrome is a prolonged course of corticosteroids. However, steroid resistance or steroid dependence is frequent, and despite intensified immunosuppressive treatment, FSGS can lead to end-stage renal failure. In addition, in some cases, FSGS can recur on a graft after kidney transplantation: an unidentified circulating factor may be implicated. Understanding of its physiopathology is unclear, and it remains an important challenge for the scientific community to identify a specific diagnostic biomarker and to develop specific therapeutics. This study reviews the treatment of primary FSGS and the recurrence of FSGS after kidney transplantation in adults.

Podocytes regulate the glomerular basement membrane protein nephronectin by means of miR-378a-3p in glomerular diseases

The pathophysiology of many proteinuric kidney diseases is poorly understood, and microRNAs (miRs) regulation of these diseases has been largely unexplored. Here, we tested whether miR-378a-3p is a novel regulator of glomerular diseases. MiR-378a-3p has two predicted targets relevant to glomerular function, the glomerular basement membrane matrix component, nephronectin (NPNT), and vascular endothelial growth factor VEGF-A. In zebrafish (Danio rerio), miR-378a-3p mimic injection or npnt knockdown by a morpholino oligomer caused an identical phenotype consisting of edema, proteinuria, podocyte effacement, and widening of the glomerular basement membrane in the lamina rara interna. Zebrafish vegf-A protein could not rescue this phenotype. However, mouse Npnt constructs containing a mutated 3'UTR region prevented the phenotype caused by miR-378a-3p mimic injection. Overexpression of miR-378a-3p in mice confirmed glomerular dysfunction in a mammalian model. Biopsies from patients with focal segmental glomerulosclerosis and membranous nephropathy had increased miR-378a-3p expression and reduced glomerular levels of NPNT. Thus, miR-378a-3p-mediated suppression of the glomerular matrix protein NPNT is a novel mechanism for proteinuria development in active glomerular diseases.

Parietal cells-new perspectives in glomerular disease

In normal glomeruli, parietal epithelial cells (PECs) line the inside of Bowman's capsule and form an inconspicuous sheet of flat epithelial cells in continuity with the proximal tubular epithelial cells (PTECs) at the urinary pole and with the podocytes at the vascular pole. PECs, PTECs and podocytes have a common mesenchymal origin and are the result of divergent differentiation during embryogenesis. Podocytes and PTECs are highly differentiated cells with well-established functions pertaining to the maintenance of the filtration barrier and transport, respectively. For PECs, no specific function other than a structural one has been known until recently. Possible important functions for PECs in the fate of the glomerulus in glomerular disease have now become apparent: (1) PECs may be involved in the replacement of lost podocytes; (2) PECs form the basis of extracapillary proliferative lesions and subsequent sclerosis in glomerular disease. In addition to the acknowledgement that PECs are crucial in glomerular disease, knowledge has been gained regarding the molecular processes driving the phenotypic changes and behavior of PECs. Understanding these molecular processes is important for the development of specific therapeutic approaches aimed at either stimulation of the regenerative function of PECs or inhibition of the pro-sclerotic action of PECs. In this review, we discuss recent advances pertaining to the role of PECs in glomerular regeneration and disease and address the major molecular processes involved.

A biomimetic gelatin-based platform elicits a pro-differentiation effect on podocytes through mechanotransduction

Using a gelatin microbial transglutaminase (gelatin-mTG) cell culture platform tuned to exhibit stiffness spanning that of healthy and diseased glomeruli, we demonstrate that kidney podocytes show marked stiffness sensitivity. Podocyte-specific markers that are critical in the formation of the renal filtration barrier are found to be regulated in association with stiffness-mediated cellular behaviors. While podocytes typically de-differentiate in culture and show diminished physiological function in nephropathies characterized by altered tissue stiffness, we show that gelatin-mTG substrates with Young’s modulus near that of healthy glomeruli elicit a pro-differentiation and maturation response in podocytes better than substrates either softer or stiffer. The pro-differentiation phenotype is characterized by upregulation of gene and protein expression associated with podocyte function, which is observed for podocytes cultured on gelatin-mTG gels of physiological stiffness independent of extracellular matrix coating type and density. Signaling pathways involved in stiffness-mediated podocyte behaviors are identified, revealing the interdependence of podocyte mechanotransduction and maintenance of their physiological function. This study also highlights the utility of the gelatin-mTG platform as an in vitro system with tunable stiffness over a range relevant for recapitulating mechanical properties of soft tissues, suggesting its potential impact on a wide range of research in cellular biophysics.

Reduced INF2 expression in nephrotic syndrome is possibly related to clinical severity of steroid resistance in children

AIM

Mutations of the inverted formin 2 gene (INF2), which encodes a member of the formin family, cause autosomal dominant focal segmental glomerulosclerosis (FSGS) and Charcot-Marie-Tooth (CMT) disease-associated FSGS. However, their role in idiopathic FSGS remains unclear. This study investigated INF2 localization in the normal adult kidney and its expression in children with idiopathic nephrotic syndrome.

METHODS

We generated a rabbit polyclonal antibody against the conjugated peptide from human INF2 and studied the glomerular expression of INF2 and synaptopodin using normal human adult kidney tissues and tissues from children with glomerular diseases such as minimal change disease (MCD), FSGS, IgA nephropathy (IgAN), non-IgA mesangial proliferative glomerulonephritis (non-IgAN), and Henoch-Schönlein purpura nephritis (HSPN).

RESULTS

The anti-INF2 antibody detected an approximately 140-kD fragment isolated from adult mature glomeruli by western blotting. Immunohistochemically, INF2 was detected in podocytes and renal arteries. Among 56 patients, INF2 in glomeruli was expressed at a similar level in patients with MCD, IgAN, non-IgAN, or HSPN and controls. In FSGS patients, INF2 expression in glomeruli was either decreased or absent. There was a relationship between decreased INF2 expression and the clinical severity of steroid resistant nephrotic syndrome (SRNS).

CONCLUSION

We propose that examination of INF2 expression may help to differentiate MCD from FSGS and evaluate the clinical severity of SRNS in children.

MicroRNAs as Master Regulators of Glomerular Function in Health and Disease

MicroRNAs (miRNAs) are important regulators of gene expression, and the dysregulation of miRNAs is a common feature of several diseases. More miRNAs are identified almost daily, revealing the complexity of these transcripts in eukaryotic cellular networks. The study of renal miRNAs, using genetically modified mice or by perturbing endogenous miRNA levels, has revealed the important biologic roles miRNAs have in the major cell lineages that compose the glomerulus. Here, we provide an overview of miRNA biogenesis and function in regulating key genes and cellular pathways in glomerular cells during development and homeostasis. Moreover, we focus on the emerging mechanisms through which miRNAs contribute to different diseases affecting the glomerulus, such as FSGS, IgA nephropathy, lupus nephritis, and diabetic nephropathy. In-depth knowledge of miRNA-based gene regulation has made it possible to unravel pathomechanisms, enabling the design of new therapeutic strategies for glomerular diseases for which available therapies are not fully efficacious.

Cytoplasmic Localization of WT1 and Decrease of miRNA-16-1 in Nephrotic Syndrome

Nephrotic syndrome (NS) is a glomerular disease that is defined by the leakage of protein into the urine and is associated with hypoalbuminemia, hyperlipidemia, and edema. Steroid-resistant NS (SRNS) patients do not respond to treatment with corticosteroids and show decreased Wilms tumor 1 (WT1) expression in podocytes. Downregulation of WT1 has been shown to be affected by certain microRNAs (miRNAs). Twenty-one patients with idiopathic NS (68.75% were SSNS and 31.25% SRNS) and 10 healthy controls were enrolled in the study. Podocyte number and WT1 location were determined by immunofluorescence, and the serum levels of miR-15a, miR-16-1, and miR-193a were quantified by RT-qPCR. Low expression and delocalization of WT1 protein from the nucleus to the cytoplasm were found in kidney biopsies of patients with SRNS and both nuclear and cytoplasmic localization were found in steroid-sensitive NS (SSNS) patients. In sera from NS patients, low expression levels of miR-15a and miR-16-1 were found compared with healthy controls, but only the miR-16-1 expression levels showed statistically significant decrease (p = 0.019). The miR-193a expression levels only slightly increased in NS patients. We concluded that low expression and delocalization from the WT1 protein in NS patients contribute to loss of podocytes while modulation from WT1 protein is not associated with the miRNAs analyzed in sera from the patients.

Hydrogen sulfide alleviates hypertensive kidney dysfunction through an epigenetic mechanism

Hypertension is a major risk factor for chronic kidney disease (CKD), and renal inflammation is an integral part in this pathology. Hydrogen sulfide (H₂S) has been shown to mitigate renal damage through reduction in blood pressure and ROS; however, the exact mechanisms are not clear. While several studies have underlined the role of epigenetics in renal inflammation and dysfunction, the mechanisms through which epigenetic regulators play a role in hypertension are not well defined. In this study, we sought to identify whether microRNAs are dysregulated in response to angiotensin II (ANG II)-induced hypertension in the kidney and whether a H₂S donor, GYY4137, could reverse the microRNA alteration and kidney function. Wild-type (C57BL/6J) mice were treated without or with ANG II and GYY4137 for 4 wk. Blood pressure, renal blood flow, and resistive index (RI) were measured. MicroRNA microarrays were conducted and subsequent target prediction revealed genes associated with a proinflammatory response. ANG II treatment significantly increased blood pressure, decreased blood flow in the renal cortex, increased RI, and reduced renal function. These effects were ameliorated in mice treated with GYY4137. Microarray analysis revealed downregulation of miR-129 in ANG II-treated mice and upregulation after GYY4137 treatment. Quantitation of proteins involved in the inflammatory response and DNA methylation revealed upregulation of IL-17A and DNA methyltransferase 3a, whereas H₂S production enzymes and anti-inflammatory IL-10 were reduced. Taken together, our data suggest that downregulation of miR-129 plays a significant role in ANG II-induced renal inflammation and functional outcomes and that GYY4137 improves renal function by reversing miR-129 expression.NEW & NOTEWORTHY We investigated epigenetic changes that occur in the hypertensive kidney and how H₂S supplementation reverses adverse effects. Inflammation, aberrant methylation, and dysfunction were observed in the hypertensive kidney, and these effects were alleviated with H₂S supplementation. We identify miR-129 as a potential regulator of blood pressure and H₂S regulation.

Regulation of hepatic microRNA expression by hepatocyte nuclear factor 4 alpha

AIM

To uncover the role of hepatocyte nuclear factor 4 alpha (HNF4α) in regulating hepatic expression of microRNAs.

METHODS

Microarray and real-time PCR were used to determine hepatic expression of microRNAs in young-adult mice lacking Hnf4α expression in liver (Hnf4α-LivKO). Integrative genomics viewer software was used to analyze the public chromatin immunoprecipitation-sequencing datasets for DNA-binding of HNF4α, RNA polymerase-II, and histone modifications to loci of microRNAs in mouse liver and human hepatoma cells. Dual-luciferase reporter assay was conducted to determine effects of HNF4α on the promoters of mouse and human microRNAs as well as effects of microRNAs on the untranslated regions (3’UTR) of two genes in human hepatoma cells.

RESULTS

Microarray data indicated that most microRNAs remained unaltered by Hnf4α deficiency in Hnf4α-LivKO mice. However, certain liver-predominant microRNAs were down-regulated similarly in young-adult male and female Hnf4α-LivKO mice. The down-regulation of miR-101, miR-192, miR-193a, miR-194, miR-215, miR-802, and miR-122 as well as induction of miR-34 and miR-29 in male Hnf4α-LivKO mice were confirmed by real-time PCR. Analysis of public chromatin immunoprecipitation-sequencing data indicates that HNF4α directly binds to the promoters of miR-101, miR-122, miR-194-2/miR-192 and miR-193, which is associated with histone marks of active transcription. Luciferase reporter assay showed that HNF4α markedly activated the promoters of mouse and human miR-101b/miR-101-2 and the miR-194/miR-192 cluster. Additionally, miR-192 and miR-194 significantly decreased activities of luciferase reporters for the 3’UTR of histone H3F3 and chromodomain helicase DNA binding protein 1 (CHD1), respectively, suggesting that miR-192 and miR-194 might be important in chromosome remodeling through directly targeting H3F3 and CHD1.

CONCLUSION

HNF4α is essential for hepatic basal expression of a group of liver-enriched microRNAs, including miR-101, miR-192, miR-193a, miR-194 and miR-802, through which HNF4α may play a major role in the post-transcriptional regulation of gene expression and maintenance of the epigenome in liver.

Urinary Exosomal miR-193a Can Be a Potential Biomarker for the Diagnosis of Primary Focal Segmental Glomerulosclerosis in Children

Background. Glomerular upregulation of miR-193a has been detected in primary focal segmental glomerulosclerosis (FSGS) but not in other glomerular diseases. We aimed to isolate exosomes from urine of children with primary FSGS and to assess the diagnostic potential of urinary exosomal miR-193a for primary FSGS. Methods. The first morning urine samples were collected from children with primary FSGS (n = 8) and minimal change disease (MCD, n = 5). Isolated urinary exosomes were confirmed by electron microscopy and Western blotting. Urinary exosomal microRNA was extracted, and the expression levels of exosomal miR-193a were quantified by real-time PCR. The diagnosis value of urinary exosomal miR-193a levels for primary FSGS was evaluated by ROC analysis. Results. The isolated vesicles were qualitatively compatible with exosomes. The levels of urinary exosomal miR-193a were significantly higher in children with primary FSGS than those in children with MCD. Moreover, the area under the ROC for the diagnosis of primary FSGS using urinary exosomal miR-193a was 0.85. Conclusions. A significant increase in the levels of urinary exosomal miR-193a in primary FSGS patients compared to those in MCD ones was observed. This study suggests that urinary exosomal miR-193a may be a new noninvasive biomarker for the diagnosis of primary FSGS.

Therapeutic miR-21 Silencing Ameliorates Diabetic Kidney Disease in Mice

Diabetic nephropathy is the main cause of end-stage renal disease. MicroRNAs are powerful regulators of the genome, and global expression profiling revealed miR-21 to be among the most highly regulated microRNAs in kidneys of mice with diabetic nephropathy. In kidney biopsies of diabetic patients, miR-21 correlated with tubulointerstitial injury. In situ PCR analysis showed a specific enrichment of miR-21 in glomerular cells. We identified cell division cycle 25a (Cdc25a) and cyclin-dependent kinase 6 (Cdk6) as novel miR-21 targets in mesangial cells. miR-21-mediated repression of Cdc25a and Cdk6 resulted in impaired cell cycle progression and subsequent mesangial cell hypertrophy. miR-21 increased podocyte motility by regulating phosphatase and tensin homolog (Pten). miR-21 antagonism in vitro and in vivo in streptozotocin-induced diabetic mice decreased mesangial expansion, interstitial fibrosis, macrophage infiltration, podocyte loss, albuminuria, and fibrotic- and inflammatory gene expression. In conclusion, miR-21 antagonism rescued various functional and structural parameters in mice with diabetic nephropathy and, thus, might be a viable option in the treatment of patients with diabetic kidney disease.

MicroRNAs Involvement in Renal Pathophysiology: A Bird's Eye View

MicroRNAs (miRNAs) are known to suppress gene expression by binding to messenger RNAs and in turn regulate different pathophysiological processes. Transforming growth factor-β, mitogen-activated protein kinase signaling, and Wnt signaling-like major pathways associated with miRNAs are involved with kidney diseases. The discovery of miRNAs has provided new insights into kidney pathologies and may provide effective therapeutic strategies. Research has demonstrated the role of miRNAs in a variety of kidney diseases including diabetic nephropathy, lupus nephritis, hypertension, nephritic syndrome, acute kidney injury, renal cell carcinoma, and renal fibrosis. miRNAs are implicated as playing a role in these diseases due to their role in apoptosis, cell proliferation, differentiation, and development. As miRNAs have been detected in a stable condition in different biological fluids, they have the potential to be tools to study the pathogenesis of human diseases with a great potential to be used in disease diagnosis and prognosis. The purpose of this review is to examine the role of miRNA in kidney disease.

Absence of miR-146a in Podocytes Increases Risk of Diabetic Glomerulopathy via Up-regulation of ErbB4 and Notch-1

Podocyte injury is an early event in diabetic kidney disease and is a hallmark of glomerulopathy. MicroRNA-146a (miR-146a) is highly expressed in many cell types under homeostatic conditions, and plays an important anti-inflammatory role in myeloid cells. However, its role in podocytes is unclear. Here, we show that miR-146a expression levels decrease in the glomeruli of patients with type 2 diabetes (T2D), which correlates with increased albuminuria and glomerular damage. miR-146a levels are also significantly reduced in the glomeruli of albuminuric BTBR ob/ob mice, indicating its significant role in maintaining podocyte health. miR-146a-deficient mice (miR-146a^-/-) showed accelerated development of glomerulopathy and albuminuria upon streptozotocin (STZ)-induced hyperglycemia. The miR-146a targets, Notch-1 and ErbB4, were also significantly up-regulated in the glomeruli of diabetic patients and mice, suggesting induction of the downstream TGFβ signaling. Treatment with a pan-ErbB kinase inhibitor erlotinib with nanomolar activity against ErbB4 significantly suppressed diabetic glomerular injury and albuminuria in both WT and miR-146a^-/- animals. Treatment of podocytes in vitro with TGF-β1 resulted in increased expression of Notch-1, ErbB4, pErbB4, and pEGFR, the heterodimerization partner of ErbB4, suggesting increased ErbB4/EGFR signaling. TGF-β1 also increased levels of inflammatory cytokine monocyte chemoattractant protein-1 (MCP-1) and MCP-1 induced protein-1 (MCPIP1), a suppressor of miR-146a, suggesting an autocrine loop. Inhibition of ErbB4/EGFR with erlotinib co-treatment of podocytes suppressed this signaling. Our findings suggest a novel role for miR-146a in protecting against diabetic glomerulopathy and podocyte injury. They also point to ErbB4/EGFR as a novel, druggable target for therapeutic intervention, especially because several pan-ErbB inhibitors are clinically available.

Primary focal segmental glomerulosclerosis: miRNAs and targeted therapies

BACKGROUND

Primary focal segmental glomerulosclerosis (FSGS) is a common cause of nephrotic syndrome.

AIMS

The pathogenic steps leading to primary FSGS are still obscure, although evidence suggests that circulatory factor(s) are involved in the onset of disease.

RESULTS

Recent technical advances allow the analysis of miRNA expression in tissues and body fluids, leading to reports of miRNAs involved in the molecular mechanisms of FSGS-aetiopathogenesis. Moreover, investigations have also highlighted miRNAs that might serve as biomarkers for primary FSGS.

DISCUSSION/CONCLUSIONS

The aim of this review was to summarize reports showing a direct relation between miRNAs and primary FSGS. In addition, the impact of identified miRNAs on treatment response, prediction of the disease onset as well as the regulation in different disease activities is summarized.

miR-93 regulates Msk2-mediated chromatin remodelling in diabetic nephropathy

How the kidney responds to the metabolic cues from the environment remains a central question in kidney research. This question is particularly relevant to the pathogenesis of diabetic nephropathy (DN) in which evidence suggests that metabolic events in podocytes regulate chromatin structure. Here, we show that miR-93 is a critical metabolic/epigenetic switch in the diabetic milieu linking the metabolic state to chromatin remodelling. Mice with inducible overexpression of a miR-93 transgene exclusively in podocytes exhibit significant improvements in key features of DN. We identify miR-93 as a regulator of nucleosomal dynamics in podocytes. miR-93 has a critical role in chromatin reorganization and progression of DN by modulating its target Msk2, a histone kinase, and its substrate H3S10. These findings implicate a central role for miR-93 in high glucose-induced chromatin remodelling in the kidney, and provide evidence for a previously unrecognized role for Msk2 as a target for DN therapy.

Podocyte injury is central to kidney dysfunction in diabetic nephropathy. Here the authors show that Msk2 is a target of miR-93 and this interaction mediates pathogenic chromatin remodelling in diabetic nephropathy.

2015 Homer W. Smith Award: The Podocyte from Periphery to Center Stage

This overview summarizes selected major developments over the last 40 years in understanding podocyte biology and its involvement in glomerular disease subjectively from my perspective. Serendipity has played a major role in my contributions to investigative nephrology that range from basic mechanisms of immune deposit formation in experimental membranous nephropathy to the role of a microRNA in FSGS. This review emphasizes the importance of continuous reality checks of experimental results obtained in vitro or with genetically modified animals with human disease.

Essential Role of X-Box Binding Protein-1 during Endoplasmic Reticulum Stress in Podocytes

Podocytes are terminally differentiated epithelial cells that reside along the glomerular filtration barrier. Evidence suggests that after podocyte injury, endoplasmic reticulum stress response is activated, but the molecular mechanisms involved are incompletely defined. In a mouse model, we confirmed that podocyte injury induces endoplasmic reticulum stress response and upregulated unfolded protein response pathways, which have been shown to mitigate damage by preventing the accumulation of misfolded proteins in the endoplasmic reticulum. Furthermore, simultaneous podocyte-specific genetic inactivation of X-box binding protein-1 (Xbp1), a transcription factor activated during endoplasmic reticulum stress and critically involved in the untranslated protein response, and Sec63, a heat shock protein-40 chaperone required for protein folding in the endoplasmic reticulum, resulted in progressive albuminuria, foot process effacement, and histology consistent with ESRD. Finally, loss of both Sec63 and Xbp1 induced apoptosis in podocytes, which associated with activation of the JNK pathway. Collectively, our results indicate that an intact Xbp1 pathway operating to mitigate stress in the endoplasmic reticulum is essential for the maintenance of a normal glomerular filtration barrier.

Update on the treatment of focal segmental glomerulosclerosis in renal transplantation

Focal segmental glomerulosclerosis (FSGS) represents one of the most severe glomerular diseases, with frequent progression to end-stage renal disease and a high rate of recurrence in renal allografts (30%-50%). Recurrent FSGS portends a negative outcome, with the hazard ratio of graft failure being two-fold higher then that of other glomerulonephritis. Two patterns of clinical presentations are observed: Early recurrence, which is characterized by massive proteinuria within hours to days after implantation of the renal graft, and late recurrence, which occurs several months or years after the transplantation. Many clinical conditions have been recognized as risk factors for recurrence, including younger age, rapid progression of the disease to end-stage renal disease on native kidneys, and loss of previous renal allografts due to recurrence. However, much less is known about the incidence and risk factors of the so-called “de novo” type of FSGS, for which sufferers are transplanted patients without disease on native kidneys; but, rapid development of allograft failure is frequently observed. Management of both forms is challenging, and none of the approaches proposed to date have been demonstrated as consistently beneficial or effective. In the present review we report an update on the available therapeutic strategies for FSGS in renal transplantation within the context of a critical overview of the current literature.

Podocyte injury and its consequences

Podocytes maintain the glomerular filtration barrier, and the stability of this barrier depends on their highly differentiated postmitotic phenotype, which also defines the particular vulnerability of the glomerulus. Recent podocyte biology and gene disruption studies in vivo indicate a causal relationship between abnormalities of single podocyte molecules and proteinuria and glomerulosclerosis. Podocytes live under various stresses and pathological stimuli. They adapt to maintain homeostasis, but excessive stress leads to maladaptation with complex biological changes including loss of integrity and dysregulation of cellular metabolism. Podocyte injury causes proteinuria and detachment from the glomerular basement membrane. In addition to "sick" podocytes and their detachment, our understanding of glomerular responses following podocyte loss needs to address the pathways from podocyte injury to sclerosis. Studies have found a variety of glomerular responses to podocyte dysfunction in vivo, such as disruption of podocyte-endothelial cross talk and activation of podocyte-parietal cell interactions, all of which help us to understand the complex scenario of podocyte injury and its consequences. This review focuses on the cellular aspects of podocyte dysfunction and the adaptive or maladaptive glomerular responses to podocyte injury that lead to its major consequence, glomerulosclerosis.

Renal microRNA- and RNA-profiles in progressive chronic kidney disease

BACKGROUND

MicroRNAs (miRNAs) contribute to chronic kidney disease (CKD) progression via regulating mRNAs involved in renal homeostasis. However, their association with clinical outcome remains poorly understood.

MATERIALS AND METHODS

We performed miRNA and mRNA expression profiling on renal biopsy sections by qPCR (miRNA) and microarrays (mRNA) in a discovery (n = 43) and in a validation (n = 29) cohort. miRNAs differentiating stable and progressive cases were inversely correlated with putative target mRNAs, which were further characterized by pathway analysis using KEGG pathways.

RESULTS

miR-30d, miR-140-3p, miR-532-3p, miR-194, miR-190, miR-204 and miR-206 were downregulated in progressive cases. These seven miRNAs correlated with upregulated 29 target mRNAs involved in inflammatory response, cell-cell interaction, apoptosis and intra-cellular signalling. In particular, miR-206 and miR-532-3p were associated with distinct biological processes via the expression of their target mRNAs: Reduced expression of miR-206 in progressive disease correlated with the upregulation of target mRNAs participating in inflammatory pathways (CCL19, CXCL1, IFNAR2, NCK2, PTK2B, PTPRC, RASGRP1 and TNFRSF25). Progressive cases also showed a lower expression of miR-532-3p and an increased expression of target transcripts involved in apoptosis pathways (MAP3K14, TNFRSF10B/TRAIL-R2, TRADD and TRAF2). In the validation cohort, we confirmed the decreased expression of miR-206 and miR-532-3p, and the inverse correlation of these miRNAs with the expression of nine of the 12 target genes. The levels of the identified miRNAs and the target mRNAs correlated with clinical parameters and histological damage indices.

CONCLUSIONS

These results suggest the involvement of specific miRNAs and mRNAs in biological pathways associated with the progression of CKD.

DNA methylation transcriptionally regulates the putative tumor cell growth suppressor ZNF677 in non-small cell lung cancers

In our study, we investigated the role of ZNF677 in non-small cell lung cancers (NSCLC). By comparing ZNF677 expression in primary tumor (TU) and in the majority of cases also of corresponding non-malignant lung tissue (NL) samples from > 1,000 NSCLC patients, we found tumor-specific downregulation of ZNF677 expression (adjusted p-values < 0.001). We identified methylation as main mechanism for ZNF677 downregulation in NSCLC cells and we observed tumor-specific ZNF677 methylation in NSCLC patients (p < 0.0001). In the majority of TUs, ZNF677 methylation was associated with loss of ZNF677 expression. Moreover, ZNF677 overexpression in NSCLC cells was associated with reduced cell proliferation and cell migration. ZNF677 was identified to regulate expression of many genes mainly involved in growth hormone regulation and interferon signalling. Finally, patients with ZNF677 methylated TUs had a shorter overall survival compared to patients with ZNF677 not methylated TUs (p = 0.013). Overall, our results demonstrate that ZNF677 is trancriptionally regulated by methylation in NSCLCs, suggest that ZNF677 has tumor cell growth suppressing properties in NSCLCs and that ZNF677 methylation might serve as prognostic parameter in these patients.

The Role of MicroRNAs in Kidney Disease

MicroRNAs (miRNAs) are short noncoding RNAs that regulate pathophysiological processes that suppress gene expression by binding to messenger RNAs. These biomolecules can be used to study gene regulation and protein expression, which will allow better understanding of many biological processes such as cell cycle progression and apoptosis that control the fate of cells. Several pathways have also been implicated to be involved in kidney diseases such as Transforming Growth Factor-β, Mitogen-Activated Protein Kinase signaling, and Wnt signaling pathways. The discovery of miRNAs has provided new insights into kidney pathologies and may provide new innovative and effective therapeutic strategies. Research has demonstrated the role of miRNAs in a variety of kidney diseases including renal cell carcinoma, diabetic nephropathy, nephritic syndrome, renal fibrosis, lupus nephritis and acute pyelonephritis. MiRNAs are implicated as playing a role in these diseases due to their role in apoptosis, cell proliferation, differentiation and development. As miRNAs have been detected in a stable condition in different biological fluids, they have the potential to be tools to study the pathogenesis of human diseases with a great potential to be used in disease prognosis and diagnosis. The purpose of this review is to examine the role of miRNA in kidney disease.

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.

Analysis of the genes responsible for steroid-resistant nephrotic syndrome and/or focal segmental glomerulosclerosis in Japanese patients by whole-exome sequencing analysis

Steroid-resistant nephrotic syndrome (SRNS) represents glomerular disease resulting from a number of different etiologies leading to focal segmental glomerulosclerosis (FSGS). Recently, many genes causing SRNS/FSGS have been identified. These genes encode the proteins associated with the formation and/or maintenance of glomerular filtration barrier. Next-generation sequencing is used to analyze large numbers of genes at lower costs. To identify the genetic background of Japanese patients, we studied 26 disease-causing genes using whole-exome sequencing analysis in 24 patients with SRNS and/or FSGS from 22 different Japanese families. We finally found eight causative gene mutations, four recessive and four dominant gene mutations, including three novel mutations, in six patients from five different families, and one novel predisposing mutation in two patients from two different families. Causative gene mutations have only been identified in ~20% of families and further analysis is necessary to identify the unknown disease-causing gene. Identification of the disease-causing gene would support clinical practices, including the diagnosis, understanding of pathogenesis and treatment.

MicroRNA-30 family members regulate calcium/calcineurin signaling in podocytes

Calcium/calcineurin signaling is critical for normal cellular physiology. Abnormalities in this pathway cause many diseases, including podocytopathy; therefore, understanding the mechanisms that underlie the regulation of calcium/calcineurin signaling is essential. Here, we showed that critical components of calcium/calcineurin signaling, including TRPC6, PPP3CA, PPP3CB, PPP3R1, and NFATC3, are the targets of the microRNA-30 family (miR-30s). We found that these 5 genes are highly expressed as mRNA, but the level of the proteins is low in normal podocytes. Conversely, protein levels were markedly elevated in podocytes from rats treated with puromycin aminonucleoside (PAN) and from patients with focal segmental glomerulosclerosis (FSGS). In both FSGS patients and PAN-treated rats, miR-30s were downregulated in podocytes. In cultured podocytes, PAN or a miR-30 sponge increased TRPC6, PPP3CA, PPP3CB, PPP3R1, and NFATC3 expression; calcium influx; intracellular Ca2+ concentration; and calcineurin activity. Moreover, NFATC3 nuclear translocation, synaptopodin degradation, integrin β3 (ITGB3) activation, and actin fiber loss, which are downstream of calcium/calcineurin signaling, were induced by miR-30 reduction but blocked by the calcineurin inhibitor FK506. Podocyte-specific expression of the miR-30 sponge in mice increased calcium/calcineurin pathway component protein expression and calcineurin activity. The mice developed podocyte foot process effacement and proteinuria, which were prevented by FK506. miR-30s also regulated calcium/calcineurin signaling in cardiomyocytes. Together, our results identify miR-30s as essential regulators of calcium/calcineurin signaling.

Role of Asxl1 in kidney podocyte development via its interaction with Wtip

Additional sex comb-like (ASXL) family proteins are chromatin factors that function in transcriptional activation and repression. However, the underlying mechanisms and biological implications have not been well established. Here, we identified a LIM domain-containing protein, Wilms tumor 1-interacting protein (WTIP), as an ASXL1-binding partner. Biochemical assays confirmed an interaction between the murine homologs Asxl1 and Wtip. The suppressive role of Wtip in WT1 function and the expression of Wtip in kidney podocytes prompted us to investigate the role of Asxl1 in the kidney using Asxl1-null mice. In homozygous Asxl1(-/-) embryos, defects in kidney size and glomerular podocyte morphology were observed. Furthermore, up-regulation of Wt1/Wtip target genes was observed in the kidneys of Asxl1-null embryos. Overall, these findings implicate Asxl1 in the maintenance of podocyte structure via its association with Wtip and in the regulation of WT1 signaling during early kidney development.

Wnt/β-catenin signalling and podocyte dysfunction in proteinuric kidney disease

Podocytes are unique, highly specialized, terminally differentiated cells that are integral components of the kidney glomerular filtration barrier. Podocytes are vulnerable to a variety of injuries and in response they undergo a series of changes ranging from hypertrophy, autophagy, dedifferentiation, mesenchymal transition and detachment to apoptosis, depending on the nature and extent of the insult. Emerging evidence indicates that Wnt/β-catenin signalling has a central role in mediating podocyte dysfunction and proteinuria. Wnts are induced and β-catenin is activated in podocytes in various proteinuric kidney diseases. Genetic or pharmacologic activation of β-catenin is sufficient to impair podocyte integrity and causes proteinuria in healthy mice, whereas podocyte-specific ablation of β-catenin protects against proteinuria after kidney injury. Mechanistically, Wnt/β-catenin controls the expression of several key mediators implicated in podocytopathies, including Snail1, the renin-angiotensin system and matrix metalloproteinase 7. Wnt/β-catenin also negatively regulates Wilms tumour protein, a crucial transcription factor that safeguards podocyte integrity. Targeted inhibition of Wnt/β-catenin signalling preserves podocyte integrity and ameliorates proteinuria in animal models. This Review highlights advances in our understanding of the pathomechanisms of Wnt/β-catenin signalling in mediating podocyte injury, and describes the therapeutic potential of targeting this pathway for the treatment of proteinuric kidney disease.

Podocytes: recent biomolecular developments

Podocytes are postmitotic renal glomerular cells with multiple ramifications that extend from the cell body. Processes departing from a podocyte interdigitate with corresponding projections from neighboring cells and form an intricate web that enwraps the glomerular capillary completely. Podocyte processes are interconnected by the slit diaphragm, an adhesion junction mostly formed by Ig-like molecules, cadherins/protocadherins, ephrin/eph, and neurexin molecules organized in an assembly that resembles synaptic junctions. Podocyte failure is primarily or secondarily implicated in all forms of proteinuric glomerular diseases, as confirmed by the morphological changes of their elaborate cell architecture detectable by electron microscopy. Importantly, mutations of podocyte proteins are responsible for the most severe forms of congenital nephrotic syndrome. In the last 15 years, progressive technological advances have aided the study of podocyte biology and pathology, confirming the relevance of podocyte molecules and signaling pathways for the function of the glomerular filter. This review will examine the most important and newest discoveries in the field, which is rapidly evolving, hopefully leading to a detailed knowledge of this fascinating cell and to the development of specific therapeutic options for proteinuric diseases.

Towards an understanding of kidney diseases associated with WT1 mutations

Mutations in Wilms' tumor 1 (WT1) cause a wide spectrum of renal manifestations, eventually leading to end-stage kidney failure. Insufficient understanding of WT1's molecular functions in kidney development has hampered efficient therapeutic applications for WT1-associated diseases. Recently, the generation and characterization of mouse models and application of multiple state-of-the-art approaches have significantly expanded our understanding of the molecular mechanisms of how WT1 mutations lead to kidney failure. Here, we discuss the WT1 binding consensus and illustrate the major roles of WT1 in different cell populations in kidney biology. WT1 controls metanephric mesenchyme (MM) self-renewal and proliferation mainly by regulating FGF and BMP-pSMAD signaling pathways as well as Sall1 and Pax2, encoding key transcription factors; WT1 drives MM differentiation and mesenchyme–epithelial transition by targeting Fgf8 and Wnt4; WT1 defines podocyte identity by activation of other podocyte-specific transcription factors, including Mafb, Lmx1b, FoxC2, and Tcf21. These factors potentially cooperate with WT1 regulating the expression of components and regulators of the cytoskeleton for establishing podocyte polarity, slit diaphragm structure, and focal adhesion to the glomerular basement membrane. Understanding of WT1's function in kidney biology including WT1-regulated pathways will give insights that will eventually help therapeutic applications.

microRNAs in glomerular diseases from pathophysiology to potential treatment target

miRNAs are regulators of gene expression in diverse biological and pathological courses in life. Their discovery may be considered one of the most important steps in the story of modern biology. miRNAs are packed within exosomes and released by cells for cellular communications; they are present in bodily fluids. Their study opens the way for understanding the pathogenetic mechanisms of many diseases; furthermore, as potential candidate biomarkers, they can be measured in bodily fluids for non-invasive monitoring of disease outcomes. The present review highlights recent advances in the role of miRNAs in the pathogenesis of primary and secondary glomerulonephritides such as IgA nephropathy, focal segmental glomerular sclerosis, lupus nephritis and diabetic nephropathy. The identification of reciprocal expression of miRNAs and their target genes provides the molecular basis for additional information on the pathogenetic mechanisms of kidney diseases. Finally, recent findings demonstrate that miRNAs can be considered as potential targets for novel drugs.

Deficiency in WT1-targeting microRNA-125a leads to myeloid malignancies and urogenital abnormalities

The Wilms' tumor gene WT1 is overexpressed in leukemia and solid tumors and has an oncogenic role in leukemogenesis and tumorigenesis. However, precise regulatory mechanisms of WT1 overexpression remain undetermined. In the present study, microRNA-125a (miR-125a) was identified as a miRNA that suppressed WT1 expression via binding to the WT1-3'UTR. MiR-125a knockout mice overexpressed WT1, developed myeloproliferative disorder (MPD) characterized by expansion of myeloid cells in bone marrow (BM), spleen and peripheral blood, and displayed urogenital abnormalities. Silencing of WT1 expression in hematopoietic stem/progenitor cells of miR-125a knockout MPD mice by short-hairpin RNA inhibited myeloid colony formation in vitro. Furthermore, the incidence and severity of MPD were lower in miR-125a (-/-) mice than in miR-125a (+/-) mice, indicating the operation of compensatory mechanisms for the complete loss of miR-125a. To elucidate the compensatory mechanisms, miRNA array was performed. MiR-486 was occasionally induced in compete loss of miR-125a and inhibited WT1 expression instead of miR-125a, resulting in the cancellation of MPD occurrence. These results showed for the first time the post-transcriptional regulatory mechanisms of WT1 by both miR-125a and miR-486 and should contribute to the elucidation of mechanisms of normal hematopoiesis and kidney development.

MicroRNAs and their applications in kidney diseases

MicroRNAs (miRNAs) are short, non-coding RNAs that employ classic Watson-Crick base-pairing to identify their target genes, ultimately resulting in destabilization of their target mRNAs and/or inhibition of their translation. The role of miRNAs in a wide range of human diseases, including those afflicting the kidney, has been intensely investigated. However, there is still a vast dearth of knowledge regarding their specific mode of action and therapeutic effects in various kidney diseases. This review discusses the latest efforts to further our understanding of the basic biology of miRNAs, their impact on various kidney diseases and their potential as novel biomarkers and therapeutic agents. We initially provide an overview of miRNA biology and the canonical pathway implicated in their biogenesis. We then discuss commonly employed experimental strategies for miRNA research and highlight some of the newly described state-of-the-art technologies to identify miRNAs and their target genes. Finally, we carefully examine the emerging role of miRNAs in the pathogenesis of various kidney diseases.

Renal allograft fibrosis: biology and therapeutic targets

Renal tubulointerstitial fibrosis is the final common pathway of progressive renal diseases. In allografts, it is assessed with tubular atrophy as interstitial fibrosis/tubular atrophy (IF/TA). IF/TA occurs in about 40% of kidney allografts at 3-6 months after transplantation, increasing to 65% at 2 years. The origin of renal fibrosis in the allograft is complex and includes donor-related factors, in particular in case of expanded criteria donors, ischemia-reperfusion injury, immune-mediated damage, recurrence of underlying diseases, hypertensive damage, nephrotoxicity of immunosuppressants, recurrent graft infections, postrenal obstruction, etc. Based largely on studies in the non-transplant setting, there is a large body of literature on the role of different cell types, be it intrinsic to the kidney or bone marrow derived, in mediating renal fibrosis, and the number of mediator systems contributing to fibrotic changes is growing steadily. Here we review the most important cellular processes and mediators involved in the progress of renal fibrosis, with a focus on the allograft situation, and discuss some of the challenges in translating experimental insights into clinical trials, in particular fibrosis biomarkers or imaging modalities.

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.