Nephronophthisis

SOX9-dependent fibrosis drives renal function in nephronophthisis

Fibrosis is a key feature of a broad spectrum of cystic kidney diseases, especially autosomal recessive kidney disorders such as nephronophthisis (NPHP). However, its contribution to kidney function decline and the underlying molecular mechanism(s) remains unclear. Here, we show that kidney-specific deletion of Fbxw7, the recognition receptor of the SCFFBW7 E3 ubiquitin ligase, results in a juvenile-adult NPHP-like pathology characterized by slow-progressing corticomedullary cysts, tubular degeneration, severe fibrosis, and gradual loss of kidney function. Expression levels of SOX9, a known substrate of FBW7, and WNT4, a potent pro-fibrotic factor and downstream effector of SOX9, were elevated upon loss of FBW7. Heterozygous deletion of Sox9 in compound mutant mice led to the normalization of WNT4 levels, reduced fibrosis, and preservation of kidney function without significant effects on cystic dilatation and tubular degeneration. These data suggest that FBW7-SOX9-WNT4-induced fibrosis drives kidney function decline in NPHP and, possibly, other forms of autosomal recessive kidney disorders.

The interplay between the cardiovascular system and pediatric congenital or acquired kidney diseases

Kidney diseases often have systemic effects, particularly affecting the cardiovascular system due to their shared embryological origins. The deterioration of kidney function can lead to significant cardiovascular complications. Many kidney disorders, especially congenital and cystic kidney diseases, are diagnosed in childhood, often coexisting with cardiovascular issues. This review focuses on the cardiovascular abnormalities associated with primary kidney diseases, exploring the genetic and pathophysiological connections between these dual conditions. Some primary kidney diseases with cardiovascular abnormalities include congenital abnormalities of the kidney and urinary tract (CAKUT), polycystic kidney diseases (ADPKD and ARPKD), and glomerular diseases (nephrotic syndrome, focal segmental glomerulosclerosis (FSGS), IgA nephropathy, and Alport syndrome). These conditions often lead to hypertension, left ventricular hypertrophy, and other cardiac complications. For instance, ADPKD and ARPKD are associated with early vascular stiffness and cardiac valvular disorders. Nephrotic syndrome, particularly steroid-resistant form, is linked to elevated cardiovascular risks due to hyperlipidemia, endothelial injury, and an increased propensity for thrombosis. IgA nephropathy and FSGS are also associated with cardiovascular risks, exacerbated by kidney failure and hyperlipidemia. Alport syndrome, while primarily a glomerular disorder, can also result in serious cardiovascular complications like aortic dissection.

Renal ciliopathies

Primary cilia are essential cellular organelles with pivotal roles in many signalling pathways. Here we provide an overview of the role of primary cilia within the kidney, starting with primary ciliary structure and key protein complexes. We then highlight the specialised functions of primary cilia, emphasising their role in a group of diseases known as renal ciliopathies. These conditions include forms of polycystic kidney disease, nephronophthisis, and other syndromic ciliopathies, such as Joubert syndrome and Bardet-Biedl syndrome. We explore models of renal ciliopathies, both in vitro and in vivo, shedding light on the molecular mechanisms underlying these diseases including Wnt and Hedgehog signalling pathways, inflammation, and cellular metabolism. Finally, we discuss therapeutic approaches, from current treatments to cutting-edge preclinical research and clinical trials.

Urinary Dickkopf-3 Reflects Disease Severity and Predicts Short-Term Kidney Function Decline in Renal Ciliopathies

Introduction

Phenotypic heterogeneity and unpredictability of individual disease progression present enormous challenges in ultrarare renal ciliopathies. The tubular-derived glycoprotein, Dickkopf-related protein 3 (DKK3) is a promising biomarker for kidney fibrosis and prediction of kidney function decline. Here, we measured urinary DKK3 (uDKK3) levels in 195 pediatric patients with renal ciliopathy to assess its potential as a discriminative and prediction marker.

Methods

uDKK3 concentration was measured in 357 spot urine samples from 247 individuals, including 52 healthy age-matched controls. Disease entities comprised nephronophthisis (NPH) (n = 37), autosomal recessive polycystic kidney disease (ARPKD) (n = 61), Bardet Biedl syndrome (BBS) (n = 57), and hepatocyte nuclear factor 1 beta (HNF1B)-nephropathy (n = 40). The results were correlated with chronic kidney disease (CKD) stage and annual estimated glomerular filtration rate (eGFR) decline.

Results

Median uDKK3-to-creatinine ratios (uDKK3/crea) in all disease entities were significantly higher compared with healthy controls (11pg/mg uDKK3/crea, P < 0.001): NPH, 1.219 pg/mg; HNF1B, 731 pg/mg; BBS, 541 pg/mg; and ARPKD, 437 pg/mg. A significant correlation of CKD stage with uDKK3 levels was observed for all disease entities (P < 0.0001) with no other clinical parameter having a relevant impact. In our cohort, uDKK3 values >4.700 pg/mg were associated with a significantly greater annual eGFR loss independently of diagnosis and eGFR (P = 0.0029). Although we observed a trend toward lower uDKK3 levels in glomerulopathies compared to renal ciliopathies, there was no discriminative difference between individual ciliopathy entities (P = 0.2637).

Conclusion

In renal ciliopathies, uDKK3 is a marker to assess disease severity and estimate short-term kidney function decline.

Gene therapy and kidney diseases

Chronic kidney disease (CKD) poses a significant global health challenge, projected to become one of the leading causes of death by 2040. Current treatments primarily manage complications and slow progression, highlighting the urgent need for personalized therapies targeting the disease-causing genes. Our increased understanding of the underlying genomic changes that lead to kidney diseases coupled with recent successful gene therapies targeting specific kidney cells have turned gene therapy and genome editing into a promising therapeutic approach for treating kidney disease. This review paper reflects on different delivery routes and systems that can be exploited to target specific kidney cells and the ways that gene therapy can be used to improve kidney health.

Early-onset renal dysfunction in Jeune syndrome: A case report with atypical presentation

Jeune syndrome, a rare autosomal recessive disorder, is characterized by skeletal abnormalities, particularly a narrow, bell-shaped chest, leading to severe respiratory distress in newborns. This case report details a full-term female neonate presenting with significant respiratory challenges, typical skeletal features, and early-onset renal dysfunction. Despite normal initial imaging, persistent renal abnormalities were observed, underscoring the need for early diagnosis, vigilant monitoring, and a multidisciplinary management approach to optimize outcomes for patients with Jeune syndrome.

Novel mutation in XPNPEP3 in a patient with heart failure without nephronophthisis-like nephropathy (NPHPL1): case report and literature review

BACKGROUND X-PROLYL AMINOPEPTIDASE 3: (XPNPEP3) mutations are known to cause nephronophthisis-like nephropathy-1 (NPHPL1), a rare autosomal-recessive kidney disease characterized by progressive kidney failure and cystic kidney disease in childhood. The full phenotypic spectrum associated with mutations in XPNPEP3 is not fully elucidated. CASE PRESENTATION: A 13-year-old Chinese female patient with intellectual disability presented with a 2-year history of convulsions and fatigue, with a recent episode of swelling, breathlessness, and nocturnal dyspnea lasting 10 days. The patient was diagnosed with heart failure and kidney failure. Whole exome sequencing revealed a homozygous c.970-2 A > G mutation in XPNPEP3 associated with severe cardiac dysfunction and neurological symptoms, including epilepsy and intellectual disability. Notably, kidney ultrasound did not reveal the typical changes of NPHPL1, and kidney failure was hypothesized to be secondary to cardiac dysfunction rather than primary kidney pathology. CONCLUSIONS: This case suggests the possible association of additional phenotypic features associated with XPNPEP3 mutations, emphasizing the need for further investigation into the heterogeneous clinical presentations associated with XPNPEP3 mutations. The findings highlight the importance of considering alternative phenotypes in patients with genetic mutations traditionally associated with specific diseases. Segregation and functional analyses are necessary to determine causality between the c.970-2 A > G XPNPEP3 mutation and disease.

IQCB1 (NPHP5)-Retinopathy: Clinical and Genetic Characterization and Natural History

PURPOSE

To describe the clinical and genetic features, and explore the natural history of retinopathy associated with IQCB1 variants in children and adults with retinopathy.

DESIGN

Retrospective cohort study at a single tertiary care referral center.

METHODS

The study recruited 19 patients with retinopathy, harboring likely disease-causing variants in IQCB1. Demographic data and clinical presentation, best corrected visual acuity (BCVA), fundus appearance, optical coherence tomography (OCT) and autofluorescence features, electroretinography (ERG) and molecular genetics are reported.

RESULTS

Ten patients had best corrected visual acuity better than 1.0 LogMAR, and BCVA remained stable till the last review. Seven patients had a vision of hand movements or worse in at least one eye at presentation. There was no correlation found between age of onset and severity of vision loss. Nine patients (47.4%) had a diagnosis of end-stage renal failure at presentation. The other 10 patients (52.6%) had a diagnosis of non-syndromic IQCB1-retinopathy and maintained normal renal function until the last follow-up. The mean age at diagnosis of renal failure was 26.3 ±19.8 years. OCT showed ellipsoid zone (EZ) disruption with foveal sparing in 8/13 patients. All patients had stable OCT findings. Full-field ERGs in four adults revealed a severe cone-rod dystrophy and three children had extinguished ERGs. We identified 17 IQCB1 variants, all predicted to cause loss of function.

CONCLUSION

IQCB1-retinopathy is a severe early-onset cone-rod dystrophy. The dissociation between severely decreased retinal function and relative preservation of retinal structure over a wide age window makes the disease a candidate for gene therapy.

Retinal primary cilia and their dysfunction in retinal neurodegenerative diseases: beyond ciliopathies

Primary cilia are sensory organelles that extend from the cellular membrane and are found in a wide range of cell types. Cilia possess a plethora of vital components that enable the detection and transmission of several signaling pathways, including Wnt and Shh. In turn, the regulation of ciliogenesis and cilium length is influenced by various factors, including autophagy, organization of the actin cytoskeleton, and signaling inside the cilium. Irregularities in the development, maintenance, and function of this cellular component lead to a range of clinical manifestations known as ciliopathies. The majority of people with ciliopathies have a high prevalence of retinal degeneration. The most common theory is that retinal degeneration is primarily caused by functional and developmental problems within retinal photoreceptors. The contribution of other ciliated retinal cell types to retinal degeneration has not been explored to date. In this review, we examine the occurrence of primary cilia in various retinal cell types and their significance in pathology. Additionally, we explore potential therapeutic approaches targeting ciliopathies. By engaging in this endeavor, we present new ideas that elucidate innovative concepts for the future investigation and treatment of retinal ciliopathies.

The dominant findings of a recessive man: from Mendel's kid pea to kidney

The research of Mendel, born two centuries ago, still has many direct implications for our everyday clinical work. He introduced the terms "dominant" and "recessive" characters and determined their 3:1 ratio in the offspring of heterozygous "hybrid" plants. This distribution allowed calculation of the number of the phenotype-determining "elements," i.e., the alleles, and has been used ever since to prove the monogenic origin of a disorder. The Mendelian inheritance of monogenic kidney disorders is still of great help in distinguishing them from those with multifactorial origin in clinical practice. Inheritance of most monogenic kidney disorders fits to Mendel's observations: the equal contribution of the two parents and the complete penetrance or the direct correlation between the frequency of the recessive character and the degree of inbreeding. Nevertheless, beyond the truth of these basic concepts, several observations have expanded their genetic characteristics. The extreme genetic heterogeneity, the pleiotropy of the causal genes and the role of modifiers in ciliopathies, the digenic inheritance and parental imprinting in some tubulopathies, and the incomplete penetrance and eventual interallelic interactions in podocytopathies, reflect this expansion. For all these reasons, the transmission pattern in a natural setting may depend not only on the "character" but also on the causal gene and the variant. Mendel's passion for research combined with his modest personality and meticulous approach can still serve as an example in the work required to understand the non-Mendelian universe of genetics.

1H, 13C, and 15N resonance assignments and solution structure of the N-terminal divergent calponin homology (NN-CH) domain of human intraflagellar transport protein 54

The intraflagellar transport (IFT) machinery plays a crucial role in the bidirectional trafficking of components necessary for ciliary signaling, such as the Hedgehog, Wnt/PCR, and cAMP/PKA systems. Defects in some components of the IFT machinery cause dysfunction, leading to a wide range of human diseases and developmental disorders termed ciliopathies, such as nephronophthisis. The IFT machinery comprises three sub-complexes: BBsome, IFT-A, and IFT-B. The IFT protein 54 (IFT54) is an important component of the IFT-B sub-complex. In anterograde movement, IFT54 binds to active kinesin-II, walking along the cilia microtubule axoneme and carrying the dynein-2 complex in an inactive state, which works for retrograde movement. Several mutations in IFT54 are known to cause Senior-Loken syndrome, a ciliopathy. IFT54 possesses a divergent Calponin Homology (CH) domain termed as NN-CH domain at its N-terminus. However, several aspects of the function of the NN-CH domain of IFT54 are still obscure. Here, we report the 1H, 15N, and 13C resonance assignments of the NN-CH domain of human IFT54 and its solution structure. The NN-CH domain of human IFT54 adopts essentially the α1-α2-α3-α4-α5 topology as that of mouse IFT54, whose structure was determined by X-ray crystallographic study. The structural information and assignments obtained in this study shed light on the molecular function of the NN-CH domain in IFT54.

Genetic and radiological aspects of pediatric renal cystic disease: A case series

Renal cystic diseases are common conditions whose etiology can be highly heterogeneous. They require a correct approach for adequate diagnosis and management. We aimed to illustrate part of the spectrum of renal cystic diseases through some clinical cases managed in our service. We describe 11 clinical cases including clinical entities such as renal multicystic dysplasia, and autosomal dominant and autosomal recessive polycystic renal disease, among other pathologies. Renal cystic diseases are heterogeneous in their clinical presentation, natural history, radiological findings, and genetic and pathophysiological basis. An integral clinical approach is needed to get a clear etiological diagnosis and offer adequate individualized care and follow-up for patients.

Nephronophthisis-associated FBW7 mediates cyst-dependent decline of renal function in ADPKD

Nephronophthisis (NPHP) and autosomal dominant Polycystic Kidney Disease (ADPKD) are two genetically distinct forms of Polycystic Kidney Disease (PKD), yet both diseases present with kidney cysts and a gradual decline in renal function. Prevailing dogma in PKD is that changes in kidney architecture account for the decline in kidney function, but the molecular/cellular basis of such coupling is unknown. To address this question, we induced a form of proteome reprogramming by deleting Fbxw7 encoding FBW7, the recognition receptor of the SCF FBW7 E3 ubiquitin ligase in different segments of the kidney tubular system. Deletion of Fbxw7 in the medulla led to a juvenile-adult NPHP-like phenotype, where the decline in renal function was due to SOX9-mediated interstitial fibrosis rather than cystogenesis. In contrast, the decline of renal function in ADPKD is coupled to cystic expansion via the abnormal accumulation of FBW7 in the proximal tubules and other cell types in the renal cortex. We propose that FBW7 functions at the apex of a protein network that determines renal function in ADPKD by sensing architectural changes induced by cystic expansion.

Primary cilia and actin regulatory pathways in renal ciliopathies

Ciliopathies are a group of rare genetic disorders caused by defects to the structure or function of the primary cilium. They often affect multiple organs, leading to brain malformations, congenital heart defects, and anomalies of the retina or skeletal system. Kidney abnormalities are among the most frequent ciliopathic phenotypes manifesting as smaller, dysplastic, and cystic kidneys that are often accompanied by renal fibrosis. Many renal ciliopathies cause chronic kidney disease and often progress to end-stage renal disease, necessitating replacing therapies. There are more than 35 known ciliopathies; each is a rare hereditary condition, yet collectively they account for a significant proportion of chronic kidney disease worldwide. The primary cilium is a tiny microtubule-based organelle at the apex of almost all vertebrate cells. It serves as a "cellular antenna" surveying environment outside the cell and transducing this information inside the cell to trigger multiple signaling responses crucial for tissue morphogenesis and homeostasis. Hundreds of proteins and unique cellular mechanisms are involved in cilia formation. Recent evidence suggests that actin remodeling and regulation at the base of the primary cilium strongly impacts ciliogenesis. In this review, we provide an overview of the structure and function of the primary cilium, focusing on the role of actin cytoskeleton and its regulators in ciliogenesis. We then describe the key clinical, genetic, and molecular aspects of renal ciliopathies. We highlight what is known about actin regulation in the pathogenesis of these diseases with the aim to consider these recent molecular findings as potential therapeutic targets for renal ciliopathies.

Cleavage of periostin by MMP9 protects mice from kidney cystic disease

The matrix metalloproteinase MMP9 influences cellular morphology and function, and plays important roles in organogenesis and disease. It exerts both protective and deleterious effects in renal pathology, depending upon its specific substrates. To explore new functions for MMP9 in kidney cysts formation and disease progression, we generated a mouse model by breeding juvenile cystic kidney (jck) mice with MMP9 deficient mice. Specifically, we provide evidence that MMP9 is overexpressed in cystic tissue where its enzymatic activity is increased 7-fold. MMP9 deficiency in cystic kidney worsen cystic kidney diseases by decreasing renal function, favoring cyst expansion and fibrosis. In addition, we find that periostin is a new critical substrate for MMP9 and in its absence periostin accumulates in cystic lining cells. As periostin promotes renal cyst growth and interstitial fibrosis in polycystic kidney diseases, we propose that the control of periostin by MMP9 and its associated intracellular signaling pathways including integrins, integrin-linked kinase and focal adhesion kinase confers to MMP9 a protective effect on the severity of the disease.

Cystic Kidney Diseases in Children and Adults: Differences and Gaps in Clinical Management

Cystic kidney diseases, when broadly defined, have a wide differential diagnosis extending from recessive diseases with a prenatal or pediatric diagnosis, to the most common autosomal-dominant polycystic kidney disease primarily affecting adults, and several other genetic or acquired etiologies that can manifest with kidney cysts. The most likely diagnoses to consider when assessing a patient with cystic kidney disease differ depending on family history, age stratum, radiologic characteristics, and extrarenal features. Accurate identification of the underlying condition is crucial to estimate the prognosis and initiate the appropriate management, identification of extrarenal manifestations, and counseling on recurrence risk in future pregnancies. There are significant differences in the clinical approach to investigating and managing kidney cysts in children compared with adults. Next-generation sequencing has revolutionized the diagnosis of inherited disorders of the kidney, despite limitations in access and challenges in interpreting the data. Disease-modifying treatments are lacking in the majority of kidney cystic diseases. For adults with rapid progressive autosomal-dominant polycystic kidney disease, tolvaptan (V2-receptor antagonist) has been approved to slow the rate of decline in kidney function. In this article, we examine the differences in the differential diagnosis and clinical management of cystic kidney disease in children versus adults, and we highlight the progress in molecular diagnostics and therapeutics, as well as some of the gaps meriting further attention.

Cystic kidney diseases in children

Cystic kidney disease comprises a broad group of heterogeneous diseases, which differ greatly in age at onset, disease manifestation, systemic involvement, disease progression, and long-term prognosis. As our understanding of these diseases continues to evolve and new treatment strategies continue to emerge, correctly differentiating and diagnosing these diseases becomes increasingly important. In this review, we aim to highlight the key features of the most relevant cystic kidney diseases, underscore important diagnostic characteristics of each disease, and present specific management options if applicable.

Renal ciliopathies: promising drug targets and prospects for clinical trials

INTRODUCTION

Renal ciliopathies represent a collection of genetic disorders characterized by deficiencies in the biogenesis, maintenance, or functioning of the ciliary complex. These disorders, which encompass autosomal dominant polycystic kidney disease (ADPKD), autosomal recessive polycystic kidney disease (ARPKD), and nephronophthisis (NPHP), typically result in cystic kidney disease, renal fibrosis, and a gradual deterioration of kidney function, culminating in kidney failure.

AREAS COVERED

Here we review the advances in basic science and clinical research into renal ciliopathies which have yielded promising small compounds and drug targets, within both preclinical studies and clinical trials.

EXPERT OPINION

Tolvaptan is currently the sole approved treatment option available for ADPKD patients, while no approved treatment alternatives exist for ARPKD or NPHP patients. Clinical trials are presently underway to evaluate additional medications in ADPKD and ARPKD patients. Based on preclinical models, other potential therapeutic targets for ADPKD, ARPKD, and NPHP look promising. These include molecules targeting fluid transport, cellular metabolism, ciliary signaling and cell-cycle regulation. There is a real and urgent clinical need for translational research to bring novel treatments to clinical use for all forms of renal ciliopathies to reduce kidney disease progression and prevent kidney failure.

Reducing GEF-H1 Expression Inhibits Renal Cyst Formation, Inflammation, and Fibrosis via RhoA Signaling in Nephronophthisis

Nephronophthisis (NPHP) is the most prevalent monogenic disease leading to end-stage renal failure in childhood. RhoA activation is involved in NPHP pathogenesis. This study explored the role of the RhoA activator guanine nucleotide exchange factor (GEF)-H1 in NPHP pathogenesis. We analyzed the expression and distribution of GEF-H1 in NPHP1 knockout (NPHP1^KO) mice using Western blotting and immunofluorescence, followed by GEF-H1 knockdown. Immunofluorescence and renal histology were used to examine the cysts, inflammation, and fibrosis. A RhoA GTPase activation assay and Western blotting were used to detect the expression of downstream GTP-RhoA and p-MLC2, respectively. In NPHP1 knockdown (NPHP1^KD) human kidney proximal tubular cells (HK2 cells), we detected the expressions of E-cadherin and α-smooth muscle actin (α-SMA). In vivo, increased expression and redistribution of GEF-H1, and higher levels of GTP-RhoA and p-MLC2 in renal tissue of NPHP1^KO mice were observed, together with renal cysts, fibrosis, and inflammation. These changes were alleviated by GEF-H1 knockdown. In vitro, the expression of GEF-H1 and activation of RhoA were also increased, with increased expression of α-SMA and decreased E-cadherin. GEF-H1 knockdown reversed these changes in NPHP1^KD HK2 cells. Thus, the GEF-H1/RhoA/MLC2 axis is activated in NPHP1 defects and may play a pivotal role in NPHP pathogenesis.

A Brief Focus on Joubert Syndrome and Related Acute Complications

Joubert syndrome (JS) and related disorders are a group of congenital anomalies syndromes in which the obligatory hallmark is the molar tooth sign, a complex midbrain–hindbrain malformation. Moreover, JS may be associated with multiorgan involvement, mainly nephronophthisis, hepatic fibrosis, retinal dystrophy, and other abnormalities with both inter- and intra-familial variability. Therefore, these patients should be followed by both diagnostic protocol and multidisciplinary approach to assess multiorgan involvement. Here, we briefly summarize the possible complications in patients with JS.

Joubert Syndrome: Diagnostic Evaluation and Follow-up

The follow-up of a child with genetic syndrome is necessarily multidisciplinary because of the multiplicity of problems and calls for close collaboration between different specialists. The primary objective is the total care of the child and his family, regardless of the rarity and complexity of the disease, to obtain the highest possible degree of mental and physical health and autonomy.

Baseline characteristics of participants in the NAVKIDS2 trial: a patient navigator program in children with chronic kidney disease

BACKGROUND

Children with chronic kidney disease (CKD) require multidisciplinary care to meet their complex healthcare needs. Patient navigators are trained non-medical personnel who assist patients and caregivers to overcome barriers to accessing health services through care coordination. This trial aims to determine the effectiveness of a patient navigator program in children with CKD.

METHODS

The NAVKIDS² trial is a multi-center, waitlisted, randomized controlled trial of patient navigators in children with CKD conducted at five sites across Australia. Children (0-16 years) with CKD from low socioeconomic status rural or remote areas were randomized to an intervention group or a waitlisted control group (to receive intervention after 6 months). The study primary and secondary endpoints include the self-rated health (SRH) (primary), and utility-based quality of life, progression of kidney dysfunction of the child, SRH, and satisfaction with healthcare of the caregiver at 6 months post-randomization.

RESULTS

The trial completed recruitment in October 2021 with expected completion of follow-up by October 2022. There were 162 patients enrolled with 80 and 82 patients randomized to the immediate intervention and waitlisted groups, respectively. Fifty-eight (36%) participants were from regional/remote areas, with a median (IQR) age of 9.5 (5.0, 13.0) years, 46% were of European Australian ethnicity, and 65% were male. A total of 109 children (67%) had CKD stages 1-5, 42 (26%) were transplant recipients, and 11 (7%) were receiving dialysis.

CONCLUSION

The NAVKIDS² trial is designed to evaluate the effectiveness of patient navigation in children with CKD from families experiencing socioeconomic disadvantage. A higher resolution version of the Graphical abstract is available as Supplementary information.

NPHP3 splice acceptor site variant is associated with infantile nephronophthisis and asphyxiating thoracic dystrophy; A rare combination

Nephronophthisis (NPHP) is a group of rare inherited ciliopathy disorders characterized by the multicystic dysplastic kidney, oligohydramnios, and tubulointerstitial nephritis that progresses to end-stage renal disease (ESRD). NPHP is a clinically and genetically heterogeneous disorder with extrarenal symptoms including skeletal deformities, nervous system anomalies, and ophthalmologic features. Three clinical subtypes, infantile, juvenile, and adolescent, have been recognized based on age of onset of ESRD. Infantile nephronophthisis with asphyxiating thoracic dystrophy is a very rare association. Here, we investigated a consanguineous family having two neonates with a clinical phenotype of lethal infantile NPHP associated with asphyxiating thoracic dystrophy. Whole exome sequence data analysis identified a splice acceptor site variant (Chr3-132408107-CCT-C; NM_153240.4: c.2694-2_2694-1del) in the NPHP3 gene. The segregation of a variant in the family was confirmed by Sanger sequencing. The lethal phenotype in our case might be due to respiratory insufficiency secondary to a severely restricted thoracic cage. Present work is an exclusive depiction of lethal infantile NPHP phenotype in association with asphyxiating thoracic dystrophy that has not been reported before in families segregating NPHP3 mutations. Moreover, this work expands the phenotypic spectrum of NPHP3 variants. Overall, our findings add to the increasing body of evidence that mutations in ciliary genes/proteins show pleiotropic effects with phenotypic overlap between related disorders and apparently unrelated clinical entities.

Refining Kidney Survival in 383 Genetically Characterized Patients With Nephronophthisis

Introduction

Nephronophthisis (NPH) comprises a group of rare disorders accounting for up to 10% of end-stage kidney disease (ESKD) in children. Prediction of kidney prognosis poses a major challenge. We assessed differences in kidney survival, impact of variant type, and the association of clinical characteristics with declining kidney function.

Methods

Data was obtained from 3 independent sources, namely the network for early onset cystic kidney diseases clinical registry (n = 105), an online survey sent out to the European Reference Network for Rare Kidney Diseases (n = 60), and a literature search (n = 218).

Results

A total of 383 individuals were available for analysis: 116 NPHP1, 101 NPHP3, 81 NPHP4 and 85 NPHP11/TMEM67 patients. Kidney survival differed between the 4 cohorts with a highly variable median age at onset of ESKD as follows: NPHP3, 4.0 years (interquartile range 0.3–12.0); NPHP1, 13.5 years (interquartile range 10.5–16.5); NPHP4, 16.0 years (interquartile range 11.0–25.0); and NPHP11/TMEM67, 19.0 years (interquartile range 8.7–28.0). Kidney survival was significantly associated with the underlying variant type for NPHP1, NPHP3, and NPHP4. Multivariate analysis for the NPHP1 cohort revealed growth retardation (hazard ratio 3.5) and angiotensin-converting enzyme inhibitor (ACEI) treatment (hazard ratio 2.8) as 2 independent factors associated with an earlier onset of ESKD, whereas arterial hypertension was linked to an accelerated glomerular filtration rate (GFR) decline.

Conclusion

The presented data will enable clinicians to better estimate kidney prognosis of distinct patients with NPH and thereby allow personalized counseling.

Long-Term Outcomes of Kidney Transplant Recipients With Juvenile Nephronophthisis

OBJECTIVES

Nephronophthisis is the most common genetic cause of kidney failure in childhood. Treatment for nephronophthisis is symptomatic, and kidney transplant is a good treatment option when kidney failure has developed. We reported the outcomes of kidney transplant recipients with primary diagnosis of juvenile nephronophthisis who were followed-up in our center.

MATERIALS AND METHODS

We retrospectively examined medical records of 17 kidney transplant patients with a primary diagnosis of juvenile nephronophthisis. We compared this group of 17 patients with kidney transplant recipients who had other etiologies of kidney failure in terms of transplant age, donor type, immunosuppressive treatment, acute rejection, graft loss rates, and glomerular filtration rates at 1 and 5 years posttransplant (N = 180 total analyzed).

RESULTS

Among 180 kidney transplant recipients, the 17 patients (9.4%) with nephronophthisis had a mean age of 12.6 ± 4.3 years and mean follow-up time posttransplant of 79.5 ± 41.9 months. Five of 17 patients received a kidney transplant from a deceased donor (29.4%), and the remaining 12 patients (70.6%) received transplants from living related donors. Preemptive kidney transplant was performed in 4 patients (23.5%). There was a statistically significant difference (P < .05) in terms of acute rejection between patients with nephronophthisis (17.6%) versus patients with other primary diagnoses (34%). However, the patients with nephronophthisis versus those with other primary diagnoses were similar (P > .05) in terms of transplant age (12.6 ± 4.3 vs 13.8 ± 6.7 years, respectively) and follow-up time (79.5 ± 41.9 vs 59.1 ± 38.8 months, respectively). Donor type, immunosuppressive treatment, and 1-year (96.7 ± 23.2 vs 97.6 ± 28.4 mL/min/1.73 m2) and 5-year (84.7 ± 31.1 vs 86.7 ± 21.7 mL/min/1.73 m2) glomerular filtration rates were also similar (P > .05) between groups.

CONCLUSIONS

Posttransplant prognosis was good among kidney transplant recipients with juvenile nephronophthisis.

Agonists of prostaglandin E2 receptors as potential first in class treatment for nephronophthisis and related ciliopathies

SignificanceJuvenile nephronophthisis (NPH) is a renal ciliopathy due to a dysfunction of primary cilia for which no curative treatment is available. This paper describes the identification of agonists of prostaglandin E₂ receptors as a potential therapeutic approach for the most common NPHP1-associated ciliopathies. We demonstrated that prostaglandin E₁ rescues defective ciliogenesis and ciliary composition in NPHP1 patient urine-derived renal tubular cells and improves ciliary and kidney phenotypes in our NPH zebrafish and Nphp1^-/- mouse models. In addition, Taprenepag alleviates the severe retinopathy observed in Nphp1^-/- mice. Finally, transcriptomic analyses pointed out several pathways downstream the prostaglandin receptors as cell cycle progression, extracellular matrix, or actin cytoskeleton organization. Altogether, our findings provide an alternative for treatment of NPH.

[Genetic screening is essential in polycystic kidney disease: It is never too late!]

In France, numerous patients suffered from chronic kidney disease on polycystic kidney disorder. If PKD1 and PKD2 inactivating mutations are the most prevalent, several other genetic polycystic kidney diseases are responsible for similar kidney features and may be associated with severe extrarenal phenotypes. Genetic analysis in front of a polycystic disorder is not systematic, but is essential to assess the genetic diagnosis, discuss the intensity of treatment (vaptan) and precise the prognostic and the transmission of the phenotype. We detailed the case of a patient with end stage renal disease due to a polycystic kidney disease. Genetic analysis at 70 year of age revealed an oral-facial-digital syndrome type 1. The diagnosis had an important impact in the familial history and to attach the extrarenal phenotype to the syndrome. Our case illustrates that, in front of a polycystic kidney disease (even in aged patients with end stage renal disease) genetic screening is essential, for the propositus and their family and to take care of the extrarenal manifestations.

Genetic Etiologies, Diagnosis, and Management of Neonatal Cystic Kidney Disease

Fetal kidney development is a complex and carefully orchestrated process. The proper formation of kidney tissue involves many transcription factors and signaling pathways. Pathogenic variants in the genes that encodethese factors and proteins can result in neonatal cystic kidney disease. Advancements in genomic sequencing have allowed us to identify many of these variants and better understand the genetic underpinnings for an increasing number of presentations of childhood kidney disorders. This review discusses the genes essential in kidney development, particularly those involved in the structure and function of primary cilia, and implications of gene identification for prognostication and management of cystic kidney disorders.

The Role of Centrosome Distal Appendage Proteins (DAPs) in Nephronophthisis and Ciliogenesis

The primary cilium is found in most mammalian cells and plays a functional role in tissue homeostasis and organ development by modulating key signaling pathways. Ciliopathies are a group of genetically heterogeneous disorders resulting from defects in cilia development and function. Patients with ciliopathic disorders exhibit a range of phenotypes that include nephronophthisis (NPHP), a progressive tubulointerstitial kidney disease that commonly results in end-stage renal disease (ESRD). In recent years, distal appendages (DAPs), which radially project from the distal end of the mother centriole, have been shown to play a vital role in primary ciliary vesicle docking and the initiation of ciliogenesis. Mutations in the genes encoding these proteins can result in either a complete loss of the primary cilium, abnormal ciliary formation, or defective ciliary signaling. DAPs deficiency in humans or mice commonly results in NPHP. In this review, we outline recent advances in our understanding of the molecular functions of DAPs and how they participate in nephronophthisis development.

Nephronophthisis-Pathobiology and Molecular Pathogenesis of a Rare Kidney Genetic Disease

The exponential rise in our understanding of the aetiology and pathophysiology of genetic cystic kidney diseases can be attributed to the identification of cystogenic genes over the last three decades. The foundation of this was laid by positional cloning strategies which gradually shifted towards next-generation sequencing (NGS) based screenings. This shift has enabled the discovery of novel cystogenic genes at an accelerated pace unlike ever before and, most notably, the past decade has seen the largest increase in identification of the genes which cause nephronophthisis (NPHP). NPHP is a monogenic autosomal recessive cystic kidney disease caused by mutations in a diverse clade of over 26 identified genes and is the most common genetic cause of renal failure in children. NPHP gene types present with some common pathophysiological features alongside a diverse range of extra-renal phenotypes associated with specific syndromic presentations. This review provides a timely update on our knowledge of this disease, including epidemiology, pathophysiology, anatomical and molecular features. We delve into the diversity of the NPHP causing genes and discuss known molecular mechanisms and biochemical pathways that may have possible points of intersection with polycystic kidney disease (the most studied renal cystic pathology). We delineate the pathologies arising from extra-renal complications and co-morbidities and their impact on quality of life. Finally, we discuss the current diagnostic and therapeutic modalities available for disease management, outlining possible avenues of research to improve the prognosis for NPHP patients.

SENIOR-LØKEN SYNDROME: A Case Series and Review of the Renoretinal Phenotype and Advances of Molecular Diagnosis

PURPOSE

To report genetic and clinical findings in a case series of 10 patients from eight unrelated families diagnosed with Senior-Løken syndrome.

METHODS

A retrospective study of patients with Senior-Løken syndrome. Data collected included clinical findings electroretinography and ocular imaging. Genetic analysis was based on molecular inversion probes, whole-exome sequencing (WES), and Sanger sequencing.

RESULTS

All patients who underwent electrophysiology (8/10) had widespread photoreceptor degeneration. Genetic analysis revealed two mutations in NPHP1, two mutations in NPHP4, and two mutations in IQCB1 (NPHP5). Five of the six mutations identified in the current study were found in a single family each in our cohort. The IQCB1-p.R461* mutation has been identified in 3 families. Patients harboring mutations in IQCB1 were diagnosed with Leber congenital amaurosis, while patients with NPHP4 and NPHP1 mutations showed early and sector retinitis pigmentosa, respectively. Full-field electroretinography was extinct for 6 of 10 patients, moderately decreased for two, and unavailable for another 2 subjects. Renal involvement was evident in 7/10 patients at the time of diagnosis. Kidney function was normal (based on serum creatinine) in patients younger than 10 years. Mutations in IQCB1 were associated with high hypermetropia, whereas mutations in NPHP4 were associated with high myopia.

CONCLUSION

Patients presenting with infantile inherited retinal degeneration are not universally screened for renal dysfunction. Modern genetic tests can provide molecular diagnosis at an early age and therefore facilitate early diagnosis of renal disease with recommended periodic screening beyond childhood and family planning.

Paraneoplastic focal segmental glomerulosclerosis associated with gastrointestinal stromal tumor with cutaneous metastasis: A case report

BACKGROUND

Gastrointestinal stromal tumor (GIST) with cutaneous metastasis is very rare. As a result, cutaneous GISTs have not been well characterized. Focal segmental glomerulosclerosis (FSGS) is also a rare symptom among paraneoplastic nephritic syndromes (PNS).

CASE SUMMARY

In this case report, we describe a patient with cutaneous metastatic GIST accompanied by nephrotic syndrome occurring as a malignancy-associated PNS, for whom symptomatic treatment was ineffective, but clinical remission was achieved after surgery. Moreover, the patient has a missense mutation in NPHP4, which can explain the occurrences of GIST and FSGS in this patient and indicates that the association is not random.

CONCLUSION

This is the first reported case of a GIST with cutaneous metastasis accompanied by nephrotic syndrome manifesting as a PNS.

Clinical and genetic heterogeneity of primary ciliopathies (Review)

Ciliopathies comprise a group of complex disorders, with involvement of the majority of organs and systems. In total, >180 causal genes have been identified and, in addition to Mendelian inheritance, oligogenicity, genetic modifications, epistatic interactions and retrotransposon insertions have all been described when defining the ciliopathic phenotype. It is remarkable how the structural and functional impairment of a single, minuscule organelle may lead to the pathogenesis of highly pleiotropic diseases. Thus, combined efforts have been made to identify the genetic substratum and to determine the pathophysiological mechanism underlying the clinical presentation, in order to diagnose and classify ciliopathies. Yet, predicting the phenotype, given the intricacy of the genetic cause and overlapping clinical characteristics, represents a major challenge. In the future, advances in proteomics, cell biology and model organisms may provide new insights that could remodel the field of ciliopathies.

Urinary proteomics for kidney dysfunction: insights and trends

Introduction: Kidney dysfunction poses a high burden on patients and health care systems. Early detection and accurate prediction of kidney disease progression remains a major challenge. Compared to existing clinical parameters, urinary proteomics has the potential to reveal molecular alterations within the kidney that may alter its function before the onset of clinical symptoms. Thus, urinary proteomics has greater prognostic potential for assessment of kidney dysfunction progression.Areas covered: Advances in urinary proteomics for major causes of kidney dysfunction are discussed. The application of urinary extracellular vesicles for studying kidney dysfunction are discussed. Technological advances in urinary proteomics are discussed. The literature was identified using a database search for titles containing 'proteom*' and 'urin*' and published within the past 5 years. Retrieved literature was manually filtered to retain kidney dysfunctions-related studies.Expert opinion: Despite major advances, diagnosis by urinary proteomics has not been fully applied in any clinical settings. This could be attributed to the complex nature of kidney diseases, in addition to the constraints on study power and feasibility of incorporating mass spectrometry techniques in daily routine analysis. Nevertheless, we are confident that advances in urinary proteomics will soon provide superior insights into kidney disease beyond existing clinical parameters.

NPHP1 gene-associated nephronophthisis is associated with an occult retinopathy

Biallelic deletions in the NPHP1 gene are the most frequent molecular defect of nephronophthisis, a kidney ciliopathy and leading cause of hereditary end-stage kidney disease. Nephrocystin 1, the gene product of NPHP1, is also expressed in photoreceptors where it plays an important role in intra-flagellar transport between the inner and outer segments. However, the human retinal phenotype has never been investigated in detail. Here, we characterized retinal features of 16 patients with homozygous deletions of the entire NPHP1 gene. Retinal assessment included multimodal imaging (optical coherence tomography, fundus autofluorescence) and visual function testing (visual acuity, full-field electroretinography, color vision, visual field). Fifteen patients had a mild retinal phenotype that predominantly affected cones, but with relative sparing of the fovea. Despite a predominant cone dysfunction, night vision problems were an early symptom in some cases. The consistent retinal phenotype on optical coherence tomography images included reduced reflectivity and often a granular appearance of the ellipsoid zone, fading or loss of the interdigitation zone, and mild outer retinal thinning. However, there were usually no obvious structural changes visible upon clinical examination and fundus autofluorescence imaging (occult retinopathy). More advanced retinal degeneration might occur with ageing. An identified additional CEP290 variant in one patient with a more severe retinal degeneration may indicate a potential role for genetic modifiers, although this requires further investigation. Thus, diagnostic awareness about this distinct retinal phenotype has implications for the differential diagnosis of nephronophthisis and for individual prognosis of visual function.

Renal Ciliopathies: Sorting Out Therapeutic Approaches for Nephronophthisis

Nephronophthisis (NPH) is an autosomal recessive ciliopathy and a major cause of end-stage renal disease in children. The main forms, juvenile and adult NPH, are characterized by tubulointerstitial fibrosis whereas the infantile form is more severe and characterized by cysts. NPH is caused by mutations in over 20 different genes, most of which encode components of the primary cilium, an organelle in which important cellular signaling pathways converge. Ciliary signal transduction plays a critical role in kidney development and tissue homeostasis, and disruption of ciliary signaling has been associated with cyst formation, epithelial cell dedifferentiation and kidney function decline. Drugs have been identified that target specific signaling pathways (for example cAMP/PKA, Hedgehog, and mTOR pathways) and rescue NPH phenotypes in in vitro and/or in vivo models. Despite identification of numerous candidate drugs in rodent models, there has been a lack of clinical trials and there is currently no therapy that halts disease progression in NPH patients. This review covers the most important findings of therapeutic approaches in NPH model systems to date, including hypothesis-driven therapies and untargeted drug screens, approached from the pathophysiology of NPH. Importantly, most animal models used in these studies represent the cystic infantile form of NPH, which is less prevalent than the juvenile form. It appears therefore important to develop new models relevant for juvenile/adult NPH. Alternative non-orthologous animal models and developments in patient-based in vitro model systems are discussed, as well as future directions in personalized therapy for NPH.

Nephronophthisis and central veins abnormalities: A case report

Patients with genetic disorders are potentially more susceptible to present vascular abnormalities compared to the general population. For these patients, unusual difficulties could appear during a CVC placement procedure that could lead to major complications if venous abnormalities are undiagnosed. Ultrasound and fluoroscopy guidance should be used routinely for all patients in order to avoid complications and catheter misplacement.

Ultrasound Imaging of Renal Cysts in Children

Renal cysts can be focal or diffuse and unilateral or bilateral. In childhood, most renal cysts are due to hereditary diseases rather than simple cysts or acquired cystic diseases, unlike adults. Inherited cystic diseases can be ciliopathies due to a primary ciliary defect (as in polycystic kidney diseases and nephronophthisis). Acquired causes include obstructive cystic dysplasia, dyselectrolytemia, and acquired cysts in renal replacement therapy. The final diagnosis requires a multispecialty approach, including radiology, pathology, and genetics. Imaging is a very important component in treating patients with cystic renal diseases. This article discusses the ultrasound findings of cystic renal diseases in children, along with a brief discussion of other imaging modalities and a suggested ultrasound reporting format.

Integration of genetic and histopathology data in interpretation of kidney disease

For many years renal biopsy has been the gold standard for diagnosis in many forms of kidney disease. It provides rapid, accurate and clinically useful information in most individuals with kidney disease. However, in recent years, other diagnostic modalities have become available that may provide more detailed and specific diagnostic information in addition to, or instead of, renal biopsy. Genomics is one of these modalities. Previously prohibitively expensive and time consuming, it is now increasingly available and practical in a clinical setting for the diagnosis of inherited kidney disease. Inherited kidney disease is a significant cause of kidney disease, in both the adult and paediatric populations. While individual inherited kidney diseases are rare, together they represent a significant burden of disease. Because of the heterogenicity of inherited kidney disease, diagnosis and management can be a challenge and often multiple diagnostic modalities are needed to arrive at a diagnosis. We present updates in genomic medicine for renal disease, how genetic testing integrates with our knowledge of renal histopathology and how the two modalities may interact to enhance patient care.

Ciliopathies and the Kidney: A Review

Primary cilia are specialized sensory organelles that protrude from the apical surface of most cell types. During the past 2 decades, they have been found to play important roles in tissue development and signal transduction, with mutations in ciliary-associated proteins resulting in a group of diseases collectively known as ciliopathies. Many of these mutations manifest as renal ciliopathies, characterized by kidney dysfunction resulting from aberrant cilia or ciliary functions. This group of overlapping and genetically heterogeneous diseases includes polycystic kidney disease, nephronophthisis, and Bardet-Biedl syndrome as the main focus of this review. Renal ciliopathies are characterized by the presence of kidney cysts that develop due to uncontrolled epithelial cell proliferation, growth, and polarity, downstream of dysregulated ciliary-dependent signaling. Due to cystic-associated kidney injury and systemic inflammation, cases result in kidney failure requiring dialysis and transplantation. Of the handful of pharmacologic treatments available, none are curative. It is important to determine the molecular mechanisms that underlie the involvement of the primary cilium in cyst initiation, expansion, and progression for the development of novel and efficacious treatments. This review updates research progress in defining key genes and molecules central to ciliogenesis and renal ciliopathies.

Living-Related Kidney Transplantation in a Patient with Juvenile Nephronophthisis

Nephronophthisis (NPHP) is an autosomal recessive disease manifesting as tubulointerstitial nephritis uniformly progressing to ESRD in approximately 5-10% patients in childhood. Living donor transplantation is the most beneficial mean of renal replacement therapy compared to other methods. However, living kidney donation is contraindicated in potential donor with diseases of autosomal dominant mode of inheritance potentially leading to kidney failure in future. On the other hand, autosomal recessive genetic kidney diseases, such as NPHP, are not usually contraindication to living kidney donation. Herein, we are reporting related living kidney transplantation with a family history of NPHP form 46-year-old mother (heterozygote) to 17-year-old daughter with (autosomal recessive homozygote) with focus on donor follow-up after nephrectomy.

Medullary Cystic Kidney Disease and Focal Segmental Glomerulosclerosis Caused by a Compound Heterozygous Mutation in TTC21B

Mutations in the TTC21B gene have been identified in patients with nephronophthisis and were recently found in some patients with focal segmental glomerulosclerosis. We herein report a Japanese boy with end-stage renal disease due to medullary polycystic kidney disease and primary focal segmental glomerulosclerosis. Next-generation sequencing detected a new compound heterozygous missense mutation in the TTC21B gene. His renal pathological findings and gene mutations have not been previously reported in patients with ciliopathy. For children with severe renal dysfunction, mutations in the TTC21B gene cause both ciliopathy characterized by bilateral polycystic kidney disease and primary focal segmental glomerulosclerosis.

Whole Exome Sequencing Reveals a XPNPEP3 Novel Mutation Causing Nephronophthisis in a Pediatric Patient

Background

Nephronophthisis (NPHP) is a progressive tubulointestinal kidney condition that demonstrates an AR inheritance pattern. Up to now, more than 20 various genes have been detected for NPHP, with NPHP1 as the first one detected. X-prolyl aminopeptidase 3 (XPNPEP3) mutation is related to NPHP-like 1 nephropathy and late onset NPHP.

Methods

The proband (index patient) had polyuria, polydipsia and chronic kidney disease and was clinically suspected of NPHP. After the collection of blood sample from proband and her parents, whole exome sequencing (WES) was performed to identify the possible variants in the proband from a consanguineous marriage. The functional importance of variants was estimated by bioinformatic analysis. In the affected proband and her parents, Sanger sequencing was conducted for variants’ confirmation and segregation analysis.

Results

Clinical and paraclinical investigations of the patient was not informative. Using WES, we could detect a novel homozygous frameshift mutation in XPNPEP3 (NM_022098.2: c.719_720insA; p. Q241Tfs*13), and by Sanger sequencing, we demonstrated an insertion in XPNPEP3.

Conclusion

The homozygous genotype of the novel p.Q241Tfs*31 variant in XPNPEP3 may cause NPHP in the early childhood age.

Auxiliary genetic analysis in a Chinese adolescent NPH family by single nucleotide polymorphism screening

Hereditary nephropathy is a progressive fatal renal disease caused by genetic changes. In this study, genetic screening was used to reveal mutations in a family in Southern China, in which there are two patients with confirmed hereditary nephropathy, who are alive at the time of publication. Imaging tests, including color Doppler ultrasonography and magnetic resonance imaging (MRI), as well as pathological examinations, including hematoxylin-eosin staining, electron microscopy and immunohistochemistry were performed. Target sequencing of nephrosis 2 (NPHS2), wilms tumor 1 (WT1), phospholipase C ε 1 (PLCE1), actinin α 4 (ACTN4), angiotensin I converting enzyme (ACE), uromodulin (UMOD) and nephrocystin 1 (NPHP1) was also carried out. This study indicated that heterozygous genetic variants of NPHS2, WT1, ACTN4, PLCE1 and UMOD found in the patients were gene polymorphisms. A renal biopsy showed sclerosing glomerulonephritis, dilated tubules and lymphocyte/monocyte infiltration in the interstitium of the index patients. Genetic analysis showed vertical transmission of the disease-causing mutations, including a homozygous deletion in NPHP1 and a nonsense mutation in ACE found via PCR-based single nucleotide polymorphism screening. Further network analysis identified direct and indirect co-location genes between NPHP1 and ACE. To conclude, familial adolescent nephronophthisis was diagnosed in two index patients in this study. It is recommended that comprehensive gene mutation screening is used in the diagnosis of complex hereditary diseases.

Metabolic perturbations caused by depletion of nephronophthisis factor Anks6 in mIMCD3 cells

INTRODUCTION

Nephronophthisis (NPH) is an inherited form of cystic kidney disease with various extrarenal manifestations accounting for the largest amount of endstage renal disease in childhood. Patient mutations of Anks6 have also been found to cause NPH like phenotypes in animal models. However, little is known about functionality of Anks6.

OBJECTIVES/METHODS

We investigated the impact of Anks6 depletion on cellular metabolism of inner medullary collecting duct cells by GC-MS profiling and targeted LC-MS/MS analysis using two different shRNA cell lines for tetracycline-inducible Anks6 downregulation, namely mIMCD3 krab shANKS6 i5² and mIMCD3 krab shANKS6 i1².

RESULTS

In combination, we could successfully identify 158 metabolites of which 20 compounds showed similar alterations in both knockdown systems. Especially, large neutral amino acids, such as phenylalanine, where found to be significantly downregulated indicating disturbances in amino acid metabolism. Arginine, lysine and spermidine, which play an important role in cell survival and proliferation, were found to be downregulated. Accordingly, cell growth was diminished in tet treated mIMCD3 krab shANKS6 i5² knockdown cells. Deoxynucleosides were significantly downregulated in both knockdown systems. Hence, PARP1 levels were increased in tet treated mIMCD3 krab shANKS6 i5² cells, but not in tet treated mIMCD3 krab shANKS6 i1² cells. However, yH2AX was found to be increased in the latter.

CONCLUSION

In combination, we hypothesise that Anks6 affects DNA damage responses and proliferation and plays a crucial role in physiological amino acid and purine/pyrimidine metabolism.

Cystic Kidney Diseases From the Adult Nephrologist's Point of View

Cystic kidney diseases affect patients of all age groups with the onset spanning from prenatal disease to late adulthood. Autosomal-dominant polycystic kidney disease (ADPKD) is by far the most common renal cystic disease. However, there are various cystic kidney diseases, the onset of which occurs at different times in life and depends on the type of the disease and the causative genes involved. When genetic kidney diseases are discussed in the adult setting this view is usually limited on autosomal-dominant kidney disease, the most frequent genetic disorder causing adult onset ESRD. Other diseases-such as autosomal-recessive polycystic kidney disease-are often being viewed as a disorder only important in pediatric nephrology. However, more recent data has revealed that, despite clear age peaks of onset for each disorder, all of them can also show highly variable phenotypes with classical adult onset genetic diseases being of importance in pediatrics and vice versa. Furthermore, the affected children need to be seen by adult nephrologists in the long term after transition, requiring knowledge on the underlying pediatric disease, potential extrarenal manifestations, and genetic counseling. Consequently, the view on these diseases should be widened on both ends. Close interaction between pediatric and adult nephrology is key to appropriate care of patients suffering from genetic kidney disease to profit from each other's experience.

Engineering small tubes with changes in diameter for the study of kidney cell organization

Multicellular tubes are structures ubiquitously found during development and in adult organisms. Their topologies (diameter, direction or branching), together with their mechanical characteristics, play fundamental roles in organ function and in the emergence of pathologies. In tubes of micrometric range diameters, typically found in the vascular system, renal tubules or excretory ducts, cells are submitted to a strong curvature and confinement effects in addition to flow. Then, small tubes with change in diameter are submitted to a local gradient of shear stress and curvature, which may lead to complex mechanotransduction responses along tubes, and may be involved in the onset or propagation of cystic or obstructive pathologies. We describe here a simple method to build a microfluidic device that integrates cylindrical channels with changes in diameter that mimic in vivo tube geometries. This microfabrication approach is based on molding of etched tungsten wires, which can achieve on a flexible way any change in diameter in a polydimethylsiloxane (PDMS) microdevice. The interest of this biomimetic multitube system has been evidenced by reproducing renal tubules on chip. In particular, renal cell lines were successfully seeded and grown in PDMS circular tubes with a transition between 80 μm and 50 μm diameters. Thanks to this biomimetic platform, the effect of the tube curvature has been investigated especially regarding cell morphology and orientation. The effect of shear stress on confluent cells has also been assessed simultaneously in both parts of tubes. It is thus possible to study interconnected cell response to differential constraints which is of central importance when mimicking tubes present in the organism.