LMX1B is essential for the maintenance of differentiated podocytes in adult kidneys

Case report: A novel R246L mutation in the LMX1B homeodomain causes isolated nephropathy in a large Chinese family

BACKGROUND

Genetic factors contribute to chronic kidney disease (CKD) and end-stage renal disease (ESRD). Advances in genetic testing have enabled the identification of hereditary kidney diseases, including those caused by LMX1B mutations. LMX1B mutations can lead to nail-patella syndrome (NPS) or nail-patella-like renal disease (NPLRD) with only renal manifestations.

CASE PRESENTATION

The proband was a 13-year-old female who was diagnosed with nephrotic syndrome at the age of 6. Then she began intermittent hormone and drug therapy. When she was 13 years old, she was admitted to our hospital due to sudden chest tightness, which progressed to end-stage kidney disease (ESRD), requiring kidney replacement therapy. Whole-Exome Sequencing (WES) results suggest the presence of LMX1B gene mutation, c.737G > T, p.Arg246Leu. Tracing her family history, we found that her father, grandmother, uncle and 2 cousins all had hematuria, or proteinuria. In addition to the grandmother, a total of 9 members of the family performed WES. The members with kidney involved all carry the mutated gene. Healthy members did not have the mutated gene. It is characterized by co-segregation of genotype and phenotype. We followed the family for 9 year, the father developed ESRD at the age of 50 and started hemodialysis treatment. The rest patients had normal renal function. No extra-renal manifestations associated with NPS were found in any member of the family.

CONCLUSIONS

This study has successfully identified missense mutation, c.737G > T (p.Arg246Leu) in the homeodomain, which appears to be responsible for isolated nephropathy in the studied family. The arginine to leucine change at codon 246 likely disrupts the DNA-binding homeodomain of LMX1B. Previous research has documented 2 types of mutations at codon R246, namely R246Q and R246P, which are known to cause NPLRD. The newly discovered mutation, R246L, is likely to be another novel mutation associated with NPLRD, thus expanding the range of mutations at the crucial renal-critical codon 246 that contribute to the development of NPLRD. Furthermore, our findings suggest that any missense mutation occurring at the 246th amino acid position within the homeodomain of the LMX1B gene has the potential to lead to NPLRD.

Single-Cell Transcriptome Analysis Reveals Development-Specific Networks at Distinct Synchronized Antral Follicle Sizes in Sheep Oocytes

The development of the ovarian antral follicle is a complex, highly regulated process. Oocytes orchestrate and coordinate the development of mammalian ovarian follicles, and the rate of follicular development is governed by a developmental program intrinsic to the oocyte. Characterizing oocyte signatures during this dynamic process is critical for understanding oocyte maturation and follicular development. Although the transcriptional signature of sheep oocytes matured in vitro and preovulatory oocytes have been previously described, the transcriptional changes of oocytes in antral follicles have not. Here, we used single-cell transcriptomics (SmartSeq2) to characterize sheep oocytes from small, medium, and large antral follicles. We characterized the transcriptomic landscape of sheep oocytes during antral follicle development, identifying unique features in the transcriptional atlas, stage-specific molecular signatures, oocyte-secreted factors, and transcription factor networks. Notably, we identified the specific expression of 222 genes in the LO, 8 and 6 genes that were stage-specific in the MO and SO, respectively. We also elucidated signaling pathways in each antral follicle size that may reflect oocyte quality and in vitro maturation competency. Additionally, we discovered key biological processes that drive the transition from small to large antral follicles, revealing hub genes involved in follicle recruitment and selection. Thus, our work provides a comprehensive characterization of the single-oocyte transcriptome, filling a gap in the mapping of the molecular landscape of sheep oogenesis. We also provide key insights into the transcriptional regulation of the critical sizes of antral follicular development, which is essential for understanding how the oocyte orchestrates follicular development.

Single-cell transcriptomics and chromatin accessibility profiling elucidate the kidney-protective mechanism of mineralocorticoid receptor antagonists

Mineralocorticoid excess commonly leads to hypertension (HTN) and kidney disease. In our study, we used single-cell expression and chromatin accessibility tools to characterize the mineralocorticoid target genes and cell types. We demonstrated that mineralocorticoid effects were established through open chromatin and target gene expression, primarily in principal and connecting tubule cells and, to a lesser extent, in segments of the distal convoluted tubule cells. We examined the kidney-protective effects of steroidal and nonsteroidal mineralocorticoid antagonists (MRAs), as well as of amiloride, an epithelial sodium channel inhibitor, in a rat model of deoxycorticosterone acetate, unilateral nephrectomy, and high-salt consumption-induced HTN and cardiorenal damage. All antihypertensive therapies protected against cardiorenal damage. However, finerenone was particularly effective in reducing albuminuria and improving gene expression changes in podocytes and proximal tubule cells, even with an equivalent reduction in blood pressure. We noted a strong correlation between the accumulation of injured/profibrotic tubule cells expressing secreted posphoprotein 1 (Spp1), Il34, and platelet-derived growth factor subunit b (Pdgfb) and the degree of fibrosis in rat kidneys. This gene signature also showed a potential for classifying human kidney samples. Our multiomics approach provides fresh insights into the possible mechanisms underlying HTN-associated kidney disease, the target cell types, the protective effects of steroidal and nonsteroidal MRAs, and amiloride.

Quality assessment and refinement of chromatin accessibility data using a sequence-based predictive model

Chromatin accessibility assays are central to the genome-wide identification of gene regulatory elements associated with transcriptional regulation. However, the data have highly variable quality arising from several biological and technical factors. To surmount this problem, we developed a sequence-based machine learning method to evaluate and refine chromatin accessibility data. Our framework, gapped k-mer SVM quality check (gkmQC), provides the quality metrics for a sample based on the prediction accuracy of the trained models. We tested 886 DNase-seq samples from the ENCODE/Roadmap projects to demonstrate that gkmQC can effectively identify "high-quality" (HQ) samples with low conventional quality scores owing to marginal read depths. Peaks identified in HQ samples are more accurately aligned at functional regulatory elements, show greater enrichment of regulatory elements harboring functional variants, and explain greater heritability of phenotypes from their relevant tissues. Moreover, gkmQC can optimize the peak-calling threshold to identify additional peaks, especially for rare cell types in single-cell chromatin accessibility data.

Identification of limb-specific Lmx1b auto-regulatory modules with Nail-patella syndrome pathogenicity

LMX1B haploinsufficiency causes Nail-patella syndrome (NPS; MIM 161200), characterized by nail dysplasia, absent/hypoplastic patellae, chronic kidney disease, and glaucoma. Accordingly in mice, Lmx1b has been shown to play crucial roles in the development of the limb, kidney and eye. Although one functional allele of Lmx1b appears adequate for development, Lmx1b null mice display ventral-ventral distal limbs with abnormal kidney, eye and cerebellar development, more disruptive, but fully concordant with NPS. In Lmx1b functional knockouts (KOs), Lmx1b transcription in the limb is decreased nearly 6-fold, indicating autoregulation. Herein, we report on two conserved Lmx1b-associated cis-regulatory modules (LARM1 and LARM2) that are bound by Lmx1b, amplify Lmx1b expression with unique spatial modularity in the limb, and are necessary for Lmx1b-mediated limb dorsalization. These enhancers, being conserved across vertebrates (including coelacanth, but not other fish species), and required for normal locomotion, provide a unique opportunity to study the role of dorsalization in the fin to limb transition. We also report on two NPS patient families with normal LMX1B coding sequence, but with loss-of-function variations in the LARM1/2 region, stressing the role of regulatory modules in disease pathogenesis.

Nail-patella syndrome (NPS) is characterized by nail dysplasia, absent/hypoplastic patellae, chronic kidney disease, and glaucoma and can be caused by haploinsufficiency of LMX1B; however, not all patients harbor pathogenic LMX1B mutations. Here the authors show that loss-of-function variations in upstream enhancer sequences are responsible for a limb specific form of human NPS.

A Novel LMX1B Variant Identified in a Patient Presenting with Severe Renal Involvement and Thin Glomerular Basement Membrane

We report a case of nail-patella syndrome (NPS) with unusual thinning of the glomerular basement membrane (GBM) associated with a novel heterozygous variant in the LMX1B gene. A 43-year-old female patient with a previous diagnosis of NPS, referred to our hospital for persistent proteinuria, underwent a renal biopsy, which revealed minor glomerular abnormalities. She underwent a second renal biopsy at the age of 56 owing to the presence of persistent proteinuria and decline in serum albumin, meeting the diagnostic criteria for nephrotic syndrome. Light microscopy demonstrated glomerulosclerosis and cystic dilatation of the renal tubules. Notably, electron microscopy revealed unusual thinning of the GBM, which is quite different from typical biopsy findings observed in patients with NPS, characterized by thick GBM with fibrillary material and electron-lucent structures. Comprehensive genetic screening for 168 known genes responsible for inherited kidney diseases using a next-generation sequencing panel identified a novel heterozygous in-frame deletion-insertion (c.723_729delinsCAAC: p.[Ser242_Lys243delinsAsn]) in exon 4 of the LMX1B gene, which may account for the disrupted GBM structure. Further studies are warranted to elucidate the complex genotype-phenotype relationship between LMX1B and proper GBM morphogenesis.

Zebrafish Models for Human Skeletal Disorders

In 2019, the Nosology Committee of the International Skeletal Dysplasia Society provided an updated version of the Nosology and Classification of Genetic Skeletal Disorders. This is a reference list of recognized diseases in humans and their causal genes published to help clinician diagnosis and scientific research advances. Complementary to mammalian models, zebrafish has emerged as an interesting species to evaluate chemical treatments against these human skeletal disorders. Due to its versatility and the low cost of experiments, more than 80 models are currently available. In this article, we review the state-of-art of this “aquarium to bedside” approach describing the models according to the list provided by the Nosology Committee. With this, we intend to stimulate research in the appropriate direction to efficiently meet the actual needs of clinicians under the scope of the Nosology Committee.

LMX1B-associated nephropathy that showed myelin figures on electron microscopy

The mutation of LIM homeodomain transcription factor LMX1B gene leads to nail-patella syndrome (NPS), which is characterized by dysplastic nails, hypoplastic patellae, iliac horns and nephropathy. The characteristic renal histological finding of NPS nephropathy is irregular thickening of the glomerular basement membrane with patchy lucent areas, including deposits of bundles of type III collagen fibrils revealed by electron microscopy (EM). Fabry disease is a lysosomal storage disorder caused by a deficiency of α-galactosidase A activity, and the characteristic EM finding is a lamellated membrane structure (myelin figures). We present the case of a male with LMX1B-associated nephropathy (LAN) who showed focal segmental glomerulosclerosis (FSGS) on light microscopy, and myelin figures and slight deposits of collagen fibrils on EM, without findings of glomerular basement membrane abnormality suggestive for NPS. A 21-year-old Japanese-Brazilian man was admitted to hospital for an investigation of the cause of proteinuria and decreased renal function. A renal biopsy was performed to investigate the cause of renal damage. Fabry disease was initially considered, based on the presence of myelin figures on EM, but since he had normal α-galactosidase A activity, this initial diagnosis was denied, and the patient was subsequently diagnosed with FSGS. At 22 years after that renal biopsy, the patient was incidentally diagnosed with LAN when NM_002316:3c.746G > A:p.(Arg249Gln) LMX1B variant was identified in his older brother by a pre-transplantation examination, and the same mutation was confirmed in the patient. Myelin figures revealed by EM might become one of the clues for the diagnosis of LAN.

Electric cell-substrate impedance sensing in kidney research

Electric cell-substrate impedance sensing (ECIS) is a quantitative, label-free, non-invasive analytical method allowing continuous monitoring of the behaviour of adherent cells by online recording of transcellular impedance. ECIS offers a wide range of practical applications to study cell proliferation, migration, differentiation, toxicity and monolayer barrier integrity. All of these applications are relevant for basic kidney research, e.g. on endothelial cells, tubular and glomerular epithelial cells. This review gives an overview on the fundamental principles of the ECIS technology. We name strengths and remaining hurdles for practical applications, present an ECIS array reuse protocol, and review its past, present and potential future contributions to preclinical kidney research.

Peters Anomaly in Nail-Patella Syndrome: A Case Report and Clinico-Genetic Correlation

PURPOSE

The purpose of this study was to report the clinicopathological features of Peters anomaly in a child with nail-patella syndrome.

METHODS

Nail-patella syndrome (NPS) is a rare autosomal dominant connective tissue disorder characterized by several anomalies of the extremities, joints and nails, glomerulopathy, and rarely ocular involvement. NPS is caused by heterozygous loss-of-functional mutations in the LMX1B gene that encodes the LIM homeodomain proteins.

RESULTS

This case reports a new association of Peters anomaly in a child with NPS that also had classic skeletal/nail anomalies and protein losing nephropathy. Furthermore, DNA sequence analysis identified a novel missense heterozygous mutation in the LMX1B gene (Transcript ID: NM_001174146) resulting in the replacement of tryptophan by serine in codon 266, suggesting that the mutation (p.Trp.266Ser) affects LMX1B function by disturbing its interactions with other proteins. To the best of our knowledge, this association of Peters anomaly is novel and has not been reported earlier in the ophthalmic and systemic literature on NPS.

CONCLUSION

The corneal findings in our case with NPS are similar to those seen in congenital corneal opacification because of Peters anomaly. This novel association of Peters anomaly with NPS may be related to the effects of the LMX1B mutation on corneal development.

Case Report: Corneal Leucoma as a Novel Clinical Presentation of Nail-Patella Syndrome in a 5-Year-Old Girl

Nail-patella syndrome (NPS) is a rare autosomal-dominant disorder characterized by the classic tetrad of absent or hypoplastic finger and toe nails, absent or hypoplastic patella, skeletal deformities involving the elbow joints, and iliac horns. This disease is caused by heterozygous pathogenic variations in the LMX1B gene, which encodes the LIM homeodomain transcription factor protein (LMX1B). We report a case of corneal leucoma and dysplasia prior to overt steroid-resistant nephrotic syndrome (SRNS) in a patient with NPS. At presentation, the parents of a 5-year-old female patient reported their daughter had corneal leucoma, psychomotor delay and speech defect. We also noted the presence of bilateral edema of the lower extremities, hypertension, nail dystrophy, and the bilateral absence of patella. She developed steroid-resistant nephrotic syndrome. Lowe oculocerebrorenal syndrome and NPS were the conditions considered in differential diagnosis. Trio-based whole genome sequencing indicated a heterozygous de novo likely pathogenic variation in the LMX1B gene (c.805A>C [p.Asn269His]). Patients with NPS often develop nail, ocular, or orthopedic symptoms prior to nephrotic syndrome. Corneal leucoma may be a novel clinical presentation of NPS.

Nail-Patella syndrome with early onset end-stage renal disease in a child with a novel heterozygous missense mutation in the LMX1B homeodomain: A case report

Nail-Patella syndrome (NPS) is an inherited disease characterized by nail and skeletal anomalies, nephropathy and glaucoma. The diagnosis of NPS is based on clinical findings, including hypoplastic or absent patella, dystrophic nails, dysplasia of the elbows and iliac horns. However, the main determinant of NPS prognosis is nephropathy, which may range from asymptomatic proteinuria to end-stage renal disease. NPS is caused by heterozygous loss-of-function mutations in the LMX1B gene, which encodes the LIM homeodomain transcription factor LMX1B. LMX1B serves an essential role in the physiological development of dorsal-ventral limb structures, morphogenesis and function of podocytes, as well as in development of the anterior segments of the eyes, and in certain types of neurons. The present study aimed to identify the disease-causing mutation in a 2-year old girl with nephrotic syndrome that evolved rapidly to end-stage renal disease. The patient showed classical symptoms of NPS including dystrophic nails and an absence of the patellae. DNA sequence analysis identified a novel missense variant in exon 4 of LMX1B (c.709T>C, p.S237P); this substitution affected a conserved serine residue in the homeodomain of LMX1B and was predicted to be pathogenic. In silico modeling of the homeodomain revealed that the p.S237P mutation converted the A236-S237-F238 segment of α-helix 1 into a strand. It was hypothesized that this mutation affected binding of the transcription factor to its target DNA, thus abrogating transcription activation, which would explain the phenotype that manifested in the patient.

Myelin bodies in LMX1B-associated nephropathy: potential for misdiagnosis

BACKGROUND

Myelin figures, or zebra bodies, seen on electron microscopy were historically considered pathognomonic of Fabry disease, a rare lysosomal storage disorder caused by alpha-galactosidase A deficiency and associated with X-linked recessive mode of inheritance. More recently, iatrogenic phospholipidosis has emerged as an important alternate cause of myelin figures in the kidney.

METHODS

We report two families with autosomal dominant nephropathy presenting with proteinuria and microscopic hematuria, and the kidney biopsies were notable for the presence of myelin figures and zebra bodies.

RESULTS

Laboratory and genetic work-up for Fabry disease was negative. Genetic testing in both families revealed the same heterozygous missense mutation in LMX1B (C.737G>A, p.Arg246Gln). LMX1B mutations are known to cause nail-patella syndrome, featuring dysplastic nails and patella with or without nephropathy, as well as isolated LMX1B-associated nephropathy in the absence of extrarenal manifestations.

CONCLUSIONS

LMX1B mutation-associated nephropathy should be considered in hereditary cases of proteinuria and/or hematuria, even in the absence of unique glomerular basement membrane changes indicative of nail-patella syndrome. In addition, LMX1B mutation should be included in the differential diagnosis of myelin figures and zebra bodies on kidney biopsy, so as to avoid a misdiagnosis.

Focal Segmental Glomerulosclerosis and Scheduled Pretransplant Plasmapheresis: A Timely Diagnosis of Nail-Patella Syndrome Avoided More Futile Immunosuppression

Focal and segmental glomerulosclerosis (FSGS) is a histopathological pattern of injury. As such, it encompasses a wide variety of dissimilar entities with different pathophysiologic mechanisms. Although ultrastructural morphological characteristics can specifically diagnose certain diseases and genetic mutations can also be unravelled, this ideal situation is generally not available worldwide. In this respect, when proteinuria with or without nephrotic syndrome is encountered and FSGS is the histological lesion, patients start to be prescribed different regimes of immunosuppression, which should only be indicated in cases of primary FSGS, a rare entity that is elusive to response and can hardly be precisely diagnosed. We present a 35-year-old female patient with a life-long diagnosis of FSGS and a heavy burden of immunosuppressants, which had been unable to manage the persistent proteinuria that eventually led to end-stage kidney disease. She was referred to us to organize the kidney transplant. Plasmapheresis had been previously suggested to her to prevent the relapse of primary FSGS. A genetic test disclosed that the patient was heterozygous for LMX1B, and the diagnosis of nail-patella syndrome was made. In this entity, immunosuppression is not indicated, and there is no recurrence of the disease in the transplanted allograft.

Unicompartmental Knee Arthroplasty in a Patient with Nail-Patella Syndrome: A Case Report

CASE

A 46-year-old woman with a medical history of nail-patella syndrome (NPS) presented with chronic right knee pain. Radiographic and physical examination revealed isolated medial tibiofemoral osteoarthritis and a hypoplastic laterally subluxed patella. The patient was successfully treated with a medial unicompartmental knee arthroplasty (UKA).

CONCLUSION

In patients with NPS and osteoarthritis limited to one tibiofemoral compartment, a UKA may be successfully performed.

Epigenetic transcriptional reprogramming by WT1 mediates a repair response during podocyte injury

In the context of human disease, the mechanisms whereby transcription factors reprogram gene expression in reparative responses to injury are not well understood. We have studied the mechanisms of transcriptional reprogramming in disease using murine kidney podocytes as a model for tissue injury. Podocytes are a crucial component of glomeruli, the filtration units of each nephron. Podocyte injury is the initial event in many processes that lead to end-stage kidney disease. Wilms tumor-1 (WT1) is a master regulator of gene expression in podocytes, binding nearly all genes known to be crucial for maintenance of the glomerular filtration barrier. Using murine models and human kidney organoids, we investigated WT1-mediated transcriptional reprogramming during the course of podocyte injury. Reprogramming the transcriptome involved highly dynamic changes in the binding of WT1 to target genes during a reparative injury response, affecting chromatin state and expression levels of target genes.

Foxc2 is essential for podocyte function

Foxc2 is one of the earliest podocyte markers during glomerular development. To circumvent embryonic lethal effects of global deletion of Foxc2, and to specifically investigate the role of Foxc2 in podocytes, we generated mice with a podocyte-specific Foxc2 deletion. Mice carrying the homozygous deletion developed early proteinuria which progressed rapidly into end stage kidney failure and death around postnatal day 10. Conditional loss of Foxc2 in podocytes caused typical characteristics of podocyte injury, such as podocyte foot process effacement and podocyte microvillus transformation, probably caused by disruption of the slit diaphragm. These effects were accompanied by a redistribution of several proteins known to be necessary for correct podocyte structure. One target gene that showed reduced glomerular expression was Nrp1, the gene encoding neuropilin 1, a protein that has been linked to diabetic nephropathy and proteinuria. We could show that NRP1 was regulated by Foxc2 in vitro, but podocyte-specific ablation of Nrp1 in mice did not generate any phenotype in terms of proteinuria, suggesting that the gene might have more important roles in endothelial cells than in podocytes. Taken together, this study highlights a critical role for Foxc2 as an important gene for podocyte function.

Novel missense mutation affecting the LIM-A domain of LMX1B in a family with Nail-Patella syndrome

Nail-patella syndrome (NPS) is a rare autosomal dominant disease characterized by developmental defects of dorsal limb structures, the kidney, and the eye, that manifest as dysplastic nails, hypoplastic or absent patella, elbow dysplasia, iliac horns, glomerulopathy, and adult-onset glaucoma, respectively. This disorder is inherited in an autosomal dominant mode and is caused by heterozygous loss-of-function mutations in the LMX1B gene, which encodes the LIM homeodomain transcription factor LMX1B. In this study, we report the clinical findings of a Spanish family, from the Canary Islands, with three affected members who displayed varying phenotypes. DNA sequence analysis identified a novel heterozygous missense mutation in LMX1B, c.305A>G, p.(Y102C), that segregated with the disease. The tyrosine residue affected by the mutation is highly conserved in evolution, and is located in the LIM-A domain, next to one of the cysteine residues involved in zinc binding, suggesting that p.(Y102C) affects LMX1B function by disturbing its interactions with other proteins. Our results expand the mutation spectrum of LMX1B and provide insight into the molecular mechanisms of NPS pathology.

Total knee arthroplasty in a patient with nail-patella syndrome (NPS)

Nail-patella syndrome (NPS) or hereditary onycho-osteodyaplasia is a rare genetic condition involving a mutation in the LMX1B gene affecting nails, elbows, knees, and pelvis. Due to the regulatory functions of the gene in many developmental processes through the body, patients with NPS experience wide-ranging musculoskeletal problems including patellar instability, fingernail anomalies, iliac exostoses/horns, and elbow abnormalities. The patellar changes often involve aplasia, hypoplasia, and chronic dislocation. Due to these musculoskeletal involvement, arthritis of joints can occur in patients with NPS causing severe pain and disability. This is a case report of a patient with NPS who underwent a total knee arthroplasty for symptomatic knee arthritis.

Proteinuric Kidney Diseases: A Podocyte's Slit Diaphragm and Cytoskeleton Approach

Proteinuric kidney diseases are a group of disorders with diverse pathological mechanisms associated with significant losses of protein in the urine. The glomerular filtration barrier (GFB), comprised of the three important layers, the fenestrated glomerular endothelium, the glomerular basement membrane (GBM), and the podocyte, dictates that disruption of any one of these structures should lead to proteinuric disease. Podocytes, in particular, have long been considered as the final gatekeeper of the GFB. This specialized visceral epithelial cell contains a complex framework of cytoskeletons forming foot processes and mediate important cell signaling to maintain podocyte health. In this review, we will focus on slit diaphragm proteins such as nephrin, podocin, TRPC6/5, as well as cytoskeletal proteins Rho/small GTPases and synaptopodin and their respective roles in participating in the pathogenesis of proteinuric kidney diseases. Furthermore, we will summarize the potential therapeutic options targeting the podocyte to treat this group of kidney diseases.

Myocardin-related transcription factor A (MRTF-A) contributes to acute kidney injury by regulating macrophage ROS production

A host of pathogenic factors induce acute kidney injury (AKI) leading to insufficiencies of renal function. In the present study we evaluated the role of myocardin-related transcription factor A (MRTF-A) in the pathogenesis of AKI. We report that systemic deletion of MRTF-A or inhibition of MRTF-A activity with CCG-1423 significantly attenuated AKI in mice induced by either ischemia-reperfusion or LPS injection. Of note, MRTF-A deficiency or suppression resulted in diminished renal ROS production in AKI models with down-regulation of NAPDH oxdiase 1 (NOX1) and NOX4 expression. In cultured macrophages, MRTF-A promoted NOX1 transcription in response to either hypoxia-reoxygenation or LPS treatment. Interestingly, macrophage-specific MRTF-A deletion ameliorated AKI in mice. Mechanistic analyses revealed that MRTF-A played a role in regulating histone H4K16 acetylation surrounding the NOX gene promoters by interacting with the acetyltransferase MYST1. MYST1 depletion repressed NOX transcription in macrophages. Finally, administration of a MYST1 inhibitor MG149 alleviated AKI in mice. Therefore, we data illustrate a novel epigenetic pathway that controls ROS production in macrophages contributing to AKI. Targeting the MRTF-A-MYST1-NOX axis may yield novel therapeutic strategies to combat AKI.

Lmx1a is required for the development of the ovarian stem cell niche in Drosophila

The Drosophila ovary serves as a model for pioneering studies of stem cell niches, with defined cell types and signaling pathways supporting both germline and somatic stem cells. The establishment of the niche units begins during larval stages with the formation of terminal filament-cap structures; however, the genetics underlying their development remains largely unknown. Here, we show that the transcription factor Lmx1a is required for ovary morphogenesis. We found that Lmx1a is expressed in early ovarian somatic lineages and becomes progressively restricted to terminal filaments and cap cells. We show that Lmx1a is required for the formation of terminal filaments, during the larval-pupal transition. Finally, our data demonstrate that Lmx1a functions genetically downstream of Bric-à-Brac, and is crucial for the expression of key components of several conserved pathways essential to ovarian stem cell niche development. Importantly, expression of chicken Lmx1b is sufficient to rescue the null Lmx1a phenotype, indicating functional conservation across the animal kingdom. These results significantly expand our understanding of the mechanisms controlling stem cell niche development in the fly ovary.

Do you know this syndrome? Nail patela syndrome: a pathognomonic dermatologic finding

The nail-patella syndrome involves a clinical tetrad of changes in the nails, knees, elbows and the presence of iliac horns. Nail changes are the most constant feature: absent, hypoplastic, or dystrophic. A pathognomonic finding is the presence of the triangular lunula. The diagnosis of nail-patella syndrome is based on clinical findings. In this paper we will discuss a case report of this syndrome and its relation with a dermatological finding.

Spectrum of LMX1B mutations: from nail-patella syndrome to isolated nephropathy

Nail-patella syndrome (NPS) is an autosomal-dominant disease caused by LMX1B mutations and is characterized by dysplastic nails, absent or hypoplastic patellae, elbow dysplasia, and iliac horns. Renal involvement is the major determinant of the prognosis for NPS. Patients often present with varying degrees of proteinuria or hematuria, and can occasionally progress to chronic renal failure. Recent genetic analysis has found that some mutations in the homeodomain of LMX1B cause isolated nephropathy without nail, patellar or skeletal abnormality (LMX1B-associated nephropathy). The classic term "nail-patella syndrome" would not represent disease conditions in these cases. This review provides an overview of NPS, and highlights the molecular genetics of NPS nephropathy and LMX1B-associated nephropathy. Our current understanding of LMX1B function in the pathogenesis of NPS and LMX1B-associated nephropathy is also presented, and its downstream regulatory networks discussed. This recent progress provides insights that help to define potential targeted therapeutic strategies for LMX1B-associated diseases.

Podocalyxin influences malignant potential by controlling epithelial-mesenchymal transition in lung adenocarcinoma

Epithelial-mesenchymal transition (EMT) plays an important role in the progression of lung carcinoma. Podocalyxin (PODXL), which belongs to the CD34 family and regulates cell morphology, has been linked to EMT in lung cancer, and PODXL overexpression is associated with poor prognosis in several different classes of cancers. The aim of this study was to clarify the role of PODXL overexpression in EMT in lung cancer, and to determine the prognostic value of PODXL overexpression in tumors from lung cancer patients. The morphology, EMT marker expression, and migration and invasion abilities of engineered A549 PODXL-knockdown (KD) or PODXL-overexpression (OE) lung adenocarcinoma cells were examined. PODXL expression levels were assessed by immunohistochemistry in 114 human clinical lung adenocarcinoma specimens and correlated with clinical outcomes. PODXL-KD cells were epithelial in shape, whereas PODXL-OE cells displayed mesenchymal morphology. Epithelial markers were upregulated in PODXL-KD cells and downregulated in PODXL-OE cells, whereas mesenchymal markers were downregulated in the former and upregulated in the latter. A highly selective inhibitor of phosphatidylinositol 3-kinase-Akt signaling attenuated EMT of PODXL-OE cells, while a transforming growth factor inhibitor did not, suggesting that PODXL induces EMT of lung adenocarcinoma cells via the phosphatidylinositol 3-kinase pathway. In lung adenocarcinoma clinical specimens, PODXL expression was detected in minimally invasive and invasive adenocarcinoma, but not in non-invasive adenocarcinoma. Disease free survival and cancer-specific survival were significantly worse for patients whose tumors overexpressed PODXL. PODXL overexpression induces EMT in lung adenocarcinoma and contributes to tumor progression.

Clinical and histological findings of autosomal dominant renal-limited disease with LMX1B mutation

AIM

Mutations of LMX1B cause nail-patella syndrome, a rare autosomal dominant disorder. Recently, LMX1B R246Q heterozygous mutations were recognised in nephropathy without extrarenal manifestation. The aim of this study was to clarify characteristics of nephropathy caused by R246Q mutation.

METHODS

Whole exome sequencing was performed on a large family with nonsyndromic autosomal dominant nephropathy without extrarenal manifestation. Clinical and histological findings of patients with LMX1B mutation were investigated.

RESULTS

LMX1B R246Q heterozygous mutation was identified in five patients over three generations. Proteinuria or haematoproteinuria was recognized by urinary screening from all patients in childhood. Proteinuria gradually increased to nephrotic levels and renal function decreased in adolescence. Two patients progressed to end-stage renal disease in adulthood. Renal histology demonstrated minimal change in childhood and focal segmental glomerulosclerosis in adulthood. Using electron microscopy, focal collagen deposition could be detected in glomeruli even when a "moth-eaten appearance" was not apparent in the glomerular basement membrane. In addition, podocin expression in glomerular podocytes was significantly decreased, even in the early stages of disease progression.

CONCLUSION

Comprehensive genetic analyses and collagen or tannic acid staining may be useful for diagnosis of LMX1B-associated nephropathy. While renal prognosis of R246Q may be worse than that of typical NPS nephropathy, signs of podocytopathy can be detected during the infantile period; thus, childhood urinary screening may facilitate early detection.

Podocyte-actin dynamics in health and disease

Genetic studies of hereditary forms of nephrotic syndrome have identified several proteins that are involved in regulating the permselective properties of the glomerular filtration system. Further extensive research has elucidated the complex molecular basis of the glomerular filtration barrier and clearly established the pivotal role of podocytes in the pathophysiology of glomerular diseases. Podocyte architecture is centred on focal adhesions and slit diaphragms - multiprotein signalling hubs that regulate cell morphology and function. A highly interconnected actin cytoskeleton enables podocytes to adapt in order to accommodate environmental changes and maintain an intact glomerular filtration barrier. Actin-based endocytosis has now emerged as a regulator of podocyte integrity, providing an impetus for understanding the precise mechanisms that underlie the steady-state control of focal adhesion and slit diaphragm components. This Review outlines the role of actin dynamics and endocytosis in podocyte biology, and discusses how molecular heterogeneity in glomerular disorders could be exploited to deliver more rational therapeutic interventions, paving the way for targeted medicine in nephrology.

Natriuretic Peptide Receptor Guanylyl Cyclase-A in Podocytes is Renoprotective but Dispensable for Physiologic Renal Function

The cardiac natriuretic peptides (NPs), atrial NP and B-type NP, regulate fluid homeostasis and arterial BP through renal actions involving increased GFR and vascular and tubular effects. Guanylyl cyclase-A (GC-A), the transmembrane cGMP-producing receptor shared by these peptides, is expressed in different renal cell types, including podocytes, where its function is unclear. To study the effects of NPs on podocytes, we generated mice with a podocyte-specific knockout of GC-A (Podo-GC-A KO). Despite the marked reduction of GC-A mRNA in GC-A KO podocytes to 1% of the control level, Podo-GC-A KO mice and control littermates did not differ in BP, GFR, or natriuresis under baseline conditions. Moreover, infusion of synthetic NPs similarly increased the GFR and renal perfusion in both genotypes. Administration of the mineralocorticoid deoxycorticosterone-acetate (DOCA) in combination with high salt intake induced arterial hypertension of similar magnitude in Podo-GC-A KO mice and controls. However, only Podo-GC-A KO mice developed massive albuminuria (controls: 35-fold; KO: 5400-fold versus baseline), hypoalbuminemia, reduced GFR, and marked glomerular damage. Furthermore, DOCA treatment led to decreased expression of the slit diaphragm-associated proteins podocin, nephrin, and synaptopodin and to enhanced transient receptor potential canonical 6 (TRPC6) channel expression and ATP-induced calcium influx in podocytes of Podo-GC-A KO mice. Concomitant treatment of Podo-GC-A KO mice with the TRPC channel blocker SKF96365 markedly ameliorated albuminuria and glomerular damage in response to DOCA. In conclusion, the physiologic effects of NPs on GFR and natriuresis do not involve podocytes. However, NP/GC-A/cGMP signaling protects podocyte integrity under pathologic conditions, most likely by suppression of TRPC channels.

Zebrafish kidney development

The kidney of the zebrafish shares many features with other vertebrate kidneys including the human kidney. Similar cell types and shared developmental and patterning mechanisms make the zebrafish pronephros a valuable model for kidney organogenesis. Here we review recent advances in studies of zebrafish pronephric development and provide experimental protocols to analyze kidney cell types and structures, measure nephron function, live image kidney cells in vivo, and probe mechanisms of kidney regeneration after injury.

Urine of Preterm Neonates as a Novel Source of Kidney Progenitor Cells

In humans, nephrogenesis is completed prenatally, with nephrons formed until 34 weeks of gestational age. We hypothesized that urine of preterm neonates born before the completion of nephrogenesis is a noninvasive source of highly potent stem/progenitor cells. To test this hypothesis, we collected freshly voided urine at day 1 after birth from neonates born at 31-36 weeks of gestational age and characterized isolated cells using a single-cell RT-PCR strategy for gene expression analysis and flow cytometry and immunofluorescence for protein expression analysis. Neonatal stem/progenitor cells expressed markers of nephron progenitors but also, stromal progenitors, with many single cells coexpressing these markers. Furthermore, these cells presented mesenchymal stem cell features and protected cocultured tubule cells from cisplatin-induced apoptosis. Podocytes differentiated from the neonatal stem/progenitor cells showed upregulation of podocyte-specific genes and proteins, albumin endocytosis, and calcium influx via podocyte-specific transient receptor potential cation channel, subfamily C, member 6. Differentiated proximal tubule cells showed upregulation of specific genes and significantly elevated p-glycoprotein activity. We conclude that urine of preterm neonates is a novel noninvasive source of kidney progenitors that are capable of differentiation into mature kidney cells and have high potential for regenerative kidney repair.

Podocytes

Podocytes are highly specialized cells of the kidney glomerulus that wrap around capillaries and that neighbor cells of the Bowman’s capsule. When it comes to glomerular filtration, podocytes play an active role in preventing plasma proteins from entering the urinary ultrafiltrate by providing a barrier comprising filtration slits between foot processes, which in aggregate represent a dynamic network of cellular extensions. Foot processes interdigitate with foot processes from adjacent podocytes and form a network of narrow and rather uniform gaps. The fenestrated endothelial cells retain blood cells but permit passage of small solutes and an overlying basement membrane less permeable to macromolecules, in particular to albumin. The cytoskeletal dynamics and structural plasticity of podocytes as well as the signaling between each of these distinct layers are essential for an efficient glomerular filtration and thus for proper renal function. The genetic or acquired impairment of podocytes may lead to foot process effacement (podocyte fusion or retraction), a morphological hallmark of proteinuric renal diseases. Here, we briefly discuss aspects of a contemporary view of podocytes in glomerular filtration, the patterns of structural changes in podocytes associated with common glomerular diseases, and the current state of basic and clinical research.

Cell fate determination, neuronal maintenance and disease state: The emerging role of transcription factors Lmx1a and Lmx1b

LIM-homeodomain (LIM-HD) proteins are evolutionary conserved developmental transcription factors. LIM-HD Lmx1a and Lmx1b orchestrate complex temporal and spatial gene expression of the dopaminergic pathway, and evidence shows they are also involved in adult neuronal homeostasis. In this review, the multiple roles played by Lmx1a and Lmx1b will be discussed. Controlled Lmx1a and Lmx1b expression and activities ensure the proper formation of critical signaling centers, including the embryonic ventral mesencephalon floor plate and sharp boundaries between lineage-specific cells. Lmx1a and Lmx1b expression persists in mature dopaminergic neurons of the substantia nigra pars compacta and the ventral tegmental area, and their role in the adult brain is beginning to be revealed. Notably, LMX1B expression was lower in brain tissue affected by Parkinson's disease. Actual and future applications of Lmx1a and Lmx1b transcription factors in stem cell production as well as in direct conversion of fibroblast into dopaminergic neurons are also discussed. A thorough understanding of the role of LMX1A and LMX1B in a number of disease states, including developmental diseases, cancer and neurodegenerative diseases, could lead to significant benefits for human healthcare.

The Genetics of Nephrotic Syndrome

Nephrotic syndrome (NS) is a common pediatric kidney disease and is defined as massive proteinuria, hypoalbuminemia, and edema. Dysfunction of the glomerular filtration barrier, which is made up of endothelial cells, glomerular basement membrane, and visceral epithelial cells known as podocytes, is evident in children with NS. While most children have steroid-responsive nephrotic syndrome (SSNS), approximately 20% have steroid-resistant nephrotic syndrome (SRNS) and are at risk for progressive kidney dysfunction. While the cause of SSNS is still not well understood, there has been an explosion of research into the genetic causes of SRNS in the past 15 years. More than 30 proteins regulating the function of the glomerular filtration barrier have been associated with SRNS including podocyte slit diaphragm proteins, podocyte actin cytoskeletal proteins, mitochondrial proteins, adhesion and glomerular basement membrane proteins, transcription factors, and others. A genetic cause of SRNS can be found in approximately 70% of infants presenting in the first 3 months of life and 50% of infants presenting between 4 and 12 months, with much lower likelihood for older patients. Identification of the underlying genetic etiology of SRNS is important in children because it allows for counseling of other family members who may be at risk, predicts risk of recurrent disease after kidney transplant, and predicts response to immunosuppressive therapy. Correlations between genetic mutation and clinical phenotype as well as genetic risk factors for SSNS and SRNS are reviewed in this article.

Genetic causes of proteinuria and nephrotic syndrome: impact on podocyte pathobiology

In the past 20 years, multiple genetic mutations have been identified in patients with congenital nephrotic syndrome (CNS) and both familial and sporadic focal segmental glomerulosclerosis (FSGS). Characterization of the genetic basis of CNS and FSGS has led to the recognition of the importance of podocyte injury to the development of glomerulosclerosis. Genetic mutations induce injury due to effects on the podocyte's structure, actin cytoskeleton, calcium signaling, and lysosomal and mitochondrial function. Transgenic animal studies have contributed to our understanding of podocyte pathobiology. Podocyte endoplasmic reticulum stress response, cell polarity, and autophagy play a role in maintenance of podocyte health. Further investigations related to the effects of genetic mutations on podocytes may identify new pathways for targeting therapeutics for nephrotic syndrome.

Genome-Wide Analysis of Wilms' Tumor 1-Controlled Gene Expression in Podocytes Reveals Key Regulatory Mechanisms

The transcription factor Wilms' tumor suppressor 1 (WT1) is key to podocyte development and viability; however, WT1 transcriptional networks in podocytes remain elusive. We provide a comprehensive analysis of the genome-wide WT1 transcriptional network in podocytes in vivo using chromatin immunoprecipitation followed by sequencing (ChIPseq) and RNA sequencing techniques. Our data show a specific role for WT1 in regulating the podocyte-specific transcriptome through binding to both promoters and enhancers of target genes. Furthermore, we inferred a podocyte transcription factor network consisting of WT1, LMX1B, TCF21, Fox-class and TEAD family transcription factors, and MAFB that uses tissue-specific enhancers to control podocyte gene expression. In addition to previously described WT1-dependent target genes, ChIPseq identified novel WT1-dependent signaling systems. These targets included components of the Hippo signaling system, underscoring the power of genome-wide transcriptional-network analyses. Together, our data elucidate a comprehensive gene regulatory network in podocytes suggesting that WT1 gene regulatory function and podocyte cell-type specification can best be understood in the context of transcription factor-regulatory element network interplay.

Human Urine-Derived Renal Progenitors for Personalized Modeling of Genetic Kidney Disorders

The critical role of genetic and epigenetic factors in the pathogenesis of kidney disorders is gradually becoming clear, and the need for disease models that recapitulate human kidney disorders in a personalized manner is paramount. In this study, we describe a method to select and amplify renal progenitor cultures from the urine of patients with kidney disorders. Urine-derived human renal progenitors exhibited phenotype and functional properties identical to those purified from kidney tissue, including the capacity to differentiate into tubular cells and podocytes, as demonstrated by confocal microscopy, Western blot analysis of podocyte-specific proteins, and scanning electron microscopy. Lineage tracing studies performed with conditional transgenic mice, in which podocytes are irreversibly tagged upon tamoxifen treatment (NPHS2.iCreER;mT/mG), that were subjected to doxorubicin nephropathy demonstrated that renal progenitors are the only urinary cell population that can be amplified in long-term culture. To validate the use of these cells for personalized modeling of kidney disorders, renal progenitors were obtained from (1) the urine of children with nephrotic syndrome and carrying potentially pathogenic mutations in genes encoding for podocyte proteins and (2) the urine of children without genetic alterations, as validated by next-generation sequencing. Renal progenitors obtained from patients carrying pathogenic mutations generated podocytes that exhibited an abnormal cytoskeleton structure and functional abnormalities compared with those obtained from patients with proteinuria but without genetic mutations. The results of this study demonstrate that urine-derived patient-specific renal progenitor cultures may be an innovative research tool for modeling of genetic kidney disorders.

Glomerular development--shaping the multi-cellular filtration unit

The glomerulus represents a highly structured filtration unit, composed of glomerular endothelial cells, mesangial cells, podocytes and parietal epithelial cells. During glomerulogenesis an intricate network of signaling pathways involving transcription factors, secreted factors and cell-cell communication is required to guarantee accurate evolvement of a functional, complex 3-dimensional glomerular architecture. Here, we want to provide an overview on the critical steps and relevant signaling cascades of glomerular development.

Quantitative trait Loci for resistance to the congenital nephropathy in tensin 2-deficient mice

The ICR-derived glomerulonephritis (ICGN) mouse is a chronic kidney disease (CKD) model that is characterized histologically by glomerulosclerosis, vascular sclerosis and tubulointerstitial fibrosis, and clinically by proteinuria and anemia, which are common symptoms and pathological changes associated with a variety of kidney diseases. Previously, we performed a quantitative trait locus (QTL) analysis to identify the causative genes for proteinuria in ICGN mice, and found a deletion mutation of the tensin 2 gene (Tns2^nph, MGI no: 2447990). Interestingly, the congenic strain carrying the Tns2^nph mutation on a C57BL/6J (B6) genetic background exhibited milder phenotypes than did ICGN mice, indicating the presence of several modifier genes controlling the disease phenotype. In this study, to identify the modifier/resistant loci for CKD progression in Tns2-deficient mice, we performed QTL analysis using backcross progenies from susceptible ICGN and resistant B6 mice. We identified a significant locus on chromosome (Chr) 2 (LOD = 5.36; 31 cM) and two suggestive loci on Chrs 10 (LOD = 2.27; 64 cM) and X (LOD = 2.65; 67 cM) with linkage to the severity of tubulointerstitial injury. One significant locus on Chr 13 (LOD = 3.49; approximately 14 cM) and one suggestive locus on Chr 2 (LOD = 2.41; 51 cM) were identified as QTLs for the severity of glomerulosclerosis. Suggestive locus in BUN was also detected in the same Chr 2 region (LOD = 2.34; 51 cM). A locus on Chr 2 (36 cM) was significantly linked with HGB (LOD = 4.47) and HCT (LOD = 3.58). Four novel epistatic loci controlling either HGB or tubulointerstitial injury were discovered. Further genetic analysis should lead to identification of CKD modifier gene(s), aiding early diagnosis and providing novel approaches to the discovery of drugs for the treatment and possible prevention of kidney disease.

The Ebf1 knockout mouse and glomerular maturation

Mice deficient in the transcription factor early B-cell factor 1 (Ebf1) lack mature B lymphocytes but have additional phenotypes suggesting functions outside the hematopoietic system. Fretz et al. report that these mice also exhibit quantitative and qualitative developmental renal defects and develop progressive podocyte foot process effacement. The findings not only suggest that Ebf1 may be pivotal to the transcriptional podocyte network, but also illustrate the importance of distinguishing cell-autonomous and non-autonomous inputs to podocyte maturation and integrity.