Features of Postpartum Hemorrhage-Associated Thrombotic Microangiopathy and Role of Short-Term Complement Inhibition.

Introduction: In pregnancy-related atypical hemolytic uremic syndrome (p-aHUS), transferring recommendations for treatment decisions from nonpregnant cohorts with thrombotic microangiopathy (TMA) is difficult. Although potential causes of p-aHUS may be unrelated to inherent complement defects, peripartal complications such as postpartum hemorrhage (PPH) or (pre)eclampsia or Hemolysis, Elevated Liver enzymes and Low Platelets (HELLP) syndrome may be unrecognized drivers of complement activation. Methods: To evaluate diagnostic and therapeutic decisions in the practical real-life setting, we conducted an analysis of a cohort of 40 patients from 3 German academic hospitals with a diagnosis of p-aHUS, stratified by the presence (n = 25) or absence (n = 15) of PPH. Results: Histological signs of TMA were observed in 84.2% of all patients (100% vs. 72.7% in patients without or with PPH, respectively). Patients without PPH had a higher likelihood (20% vs. 0%) of pathogenic genetic abnormalities in the complement system although notably less than in other published cohorts. Four of 5 patients with observed renal cortical necrosis (RCN) after PPH received complement inhibition and experienced partially recovered kidney function. Patients on complement inhibition with or without PPH had an increased need for kidney replacement therapy (KRT) and plasma exchange (PEX). Because renal recovery was comparable among all patients treated with complement inhibition, a potential beneficial effect in this group of pregnancy-associated TMAs and p-aHUS is presumed. Conclusion: Based on our findings, we suggest a pragmatic approach toward limited and short-term anticomplement therapy for patients with a clinical diagnosis of p-aHUS, which should be stopped once causes of TMA other than genetic complement abnormalities emerge.

Multiparametric Monitoring of Disease Progression in Contemporary Patients with Wild-Type Transthyretin Amyloid Cardiomyopathy Initiating Tafamidis Treatment.

BACKGROUND: Recently, a disease modifying therapy has become available for transthyretin amyloid cardiomyopathy (ATTR-CM). A validated monitoring concept of treatment is lacking, but a current expert consensus recommends three clinical domains (clinical, biomarker and ECG/imaging) assessed by several measurable features to define disease progression. METHODS: We retrospectively analyzed data of wild-type ATTR-CM patients initiating tafamidis therapy assessed within our local routine protocol at baseline and 6-months follow-up with respect to the frequency of values beyond the proposed thresholds defining disease progression. Additionally, associations of cardiac magnetic resonance (CMR) tomography with clinical domains were examined within a subgroup. RESULTS: Sixty-two ATTR-CM patients were included (88.7% male, mean age 79 years). In total, 16.1% of patients had progress in the clinical and functional domain, 33.9% in the biomarker domain and 43.5% in the imaging/electrocardiography (ECG) domain, with the latter driven by deterioration of the diastolic dysfunction grade and global longitudinal strain. In total, 35.5% of patients showed progress in none, 35.5% in one, 29.0% in two and no patient in three domains, the latter indicating overall disease progression. A subgroup analysis of twenty-two patients with available baseline and follow-up CMR data revealed an increase in CMR-based extracellular volume by more than 5% in 18.2% of patients, with no significant correlation with progress in one of the clinical domains. CONCLUSIONS: We provide first frequency estimates of the markers of disease progression according to a recent expert consensus statement, which might help refine the multiparametric monitoring concept in patients with ATTR-CM.

Stimulation of Immune Checkpoint Molecule B and T-Lymphocyte Attenuator Alleviates Experimental Crescentic Glomerulonephritis.

SIGNIFICANCE STATEMENT: Treatment of acute, crescentic glomerulonephritis (GN) consists of unspecific and potentially toxic immunosuppression. T cells are central in the pathogenesis of GN, and various checkpoint molecules control their activation. The immune checkpoint molecule B and T-lymphocyte attenuator (BTLA) has shown potential for restraining inflammation in other T-cell-mediated disease models. To investigate its role in GN in a murine model of crescentic nephritis, the authors induced nephrotoxic nephritis in BTLA-deficient mice and wild-type mice. They found that BTLA has a renoprotective role through suppression of local Th1-driven inflammation and expansion of T regulatory cells and that administration of an agonistic anti-BTLA antibody attenuated experimental GN. These findings suggest that antibody-based modulation of BTLA may represent a treatment strategy in human glomerular disease. BACKGROUND: Modulating T-lymphocytes represents a promising targeted therapeutic option for glomerulonephritis (GN) because these cells mediate damage in various experimental and human GN types. The immune checkpoint molecule B and T-lymphocyte attenuator (BTLA) has shown its potential to restrain inflammation in other T-cell-mediated disease models. Its role in GN, however, has not been investigated. METHODS: We induced nephrotoxic nephritis (NTN), a mouse model of crescentic GN, in Btla -deficient ( BtlaKO ) mice and wild-type littermate controls and assessed disease severity using functional and histologic parameters at different time points after disease induction. Immunologic changes were comprehensively evaluated by flow cytometry, RNA sequencing, and in vitro assays for dendritic cell and T-cell function. Transfer experiments into Rag1KO mice confirmed the observed in vitro findings. In addition, we evaluated the potential of an agonistic anti-BTLA antibody to treat NTN in vivo . RESULTS: The BtlaKO mice developed aggravated NTN, driven by an increase of infiltrating renal Th1 cells. Single-cell RNA sequencing showed increased renal T-cell activation and positive regulation of the immune response. Although BTLA-deficient regulatory T cells (Tregs) exhibited preserved suppressive function in vitro and in vivo , BtlaKO T effector cells evaded Treg suppression. Administration of an agonistic anti-BTLA antibody robustly attenuated NTN by suppressing nephritogenic T effector cells and promoting Treg expansion. CONCLUSIONS: In a model of crescentic GN, BTLA signaling effectively restrained nephritogenic Th1 cells and promoted regulatory T cells. Suppression of T-cell-mediated inflammation by BTLA stimulation may prove relevant for a broad range of conditions involving acute GN.

Impact of first-line use of caplacizumab on treatment outcomes in immune thrombotic thrombocytopenic purpura.

BACKGROUND: The von Willebrand factor-directed nanobody caplacizumab has greatly changed the treatment of immune thrombotic thrombocytopenic purpura (iTTP) in recent years. Data from randomized controlled trials established efficacy and safety. OBJECTIVES: This study aims to address open questions regarding patient selection, tailoring of therapy duration, obstacles in prescribing caplacizumab in iTTP, effect on adjunct treatment, and outcomes in the real-world setting. METHODS: We report retrospective, observational cohorts of 113 iTTP episodes treated with caplacizumab and 119 historical control episodes treated without caplacizumab. We aggregated data from the caplacizumab phase II/III trials and real-world data from France, the United Kingdom, Germany, and Austria (846 episodes, 396 treated with caplacizumab, and 450 historical controls). RESULTS: Caplacizumab was efficacious in iTTP, independent of the timing of therapy initiation, but curtailed the time of active iTTP only when used in the first-line therapy within 72 hours after diagnosis and until at least partial ADAMTS13-activity remission. Aggregated data from multiple study populations showed that caplacizumab use resulted in significant absolute risk reduction of 2.87% for iTTP-related mortality (number needed to treat 35) and a relative risk reduction of 59%. CONCLUSION: Caplacizumab should be used in first line and until ADAMTS13-remission, lowers iTTP-related mortality and refractoriness, and decreases the number of daily plasma exchange and hospital stay. This trial is registered at www. CLINICALTRIALS: gov as #NCT04985318.

Alternate-day dosing of caplacizumab for immune-mediated thrombotic thrombocytopenic purpura.

BACKGROUND: The anti-von Willebrand factor (VWF) nanobody caplacizumab directly prevents the fatal microthrombi formation in immune-mediated thrombotic thrombocytopenic purpura (iTTP), thereby adding a new therapeutic principle to the treatment of this disorder. However, real-world treatment modalities beyond clinical trials remain heterogeneous. METHODS: Here, we describe the risks and benefits of an alternate-day dosing regimen for caplacizumab by thoroughly analyzing the timing and outcome of this approach in a retrospective cohort of 25 iTTP patients treated with caplacizumab at seven different medical centers in Austria and Germany between 2018 and 2021. RESULTS: Alternate-day dosing of caplacizumab appeared feasible and led to persisting normal platelet counts in most patients. Five patients experienced iTTP exacerbations or relapses that led to the resumption of daily caplacizumab application. VWF activity was repeatedly measured in 16 of 25 patients and documented sufficient suppression by caplacizumab after 24 and 48 h in line with published pharmacodynamics. CONCLUSION: Extension of caplacizumab application intervals from daily to alternate-day dosing may be safely considered in selected patients after 3 to 4 weeks of daily treatment. Earlier modifications may be discussed in low-risk patients but require close monitoring for clinical and laboratory features of thrombotic microangiopathy.

Treatment of acquired thrombotic thrombocytopenic purpura without plasma exchange in selected patients under caplacizumab.

BACKGROUND: Acquired thrombotic thrombocytopenic purpura (aTTP) is a rare, life-threatening autoimmune thrombotic microangiopathy. Current standard of care is therapeutic plasma exchange, immunosuppression, and caplacizumab, an anti-von Willebrand factor nanobody, which is effective in treating aTTP episodes. PATIENTS/METHODS: Here we report on seven episodes of aTTP treated without plasma exchange in six female patients in Germany and Austria. Two episodes were initial presentations of aTTP; in five instances, patients experienced a relapse. In four episodes, moderate to severe organ dysfunction was observed; three cases presented with a mild course. All patients received caplacizumab immediately once aTTP was suspected or diagnosed, and plasma exchange was omitted based on shared decision making between patient and the treating physicians. RESULTS: We observed a rapid and robust increase of platelet counts already after the first dose of caplacizumab, leading to a doubling of platelet counts within 17 hours (median), platelet counts normalized (>150 G/L) after median 84 hours. Lactate dehydrogenase, as a surrogate parameter of organ damage, improved in parallel to the platelet counts, indicating resolving microangiopathy. CONCLUSIONS: In conclusion, in selected cases of acute bouts of aTTP, it seems feasible to delay or omit plasma exchange if platelet counts increase and organ function is stable after start of caplacizumab therapy.

Real-world data confirm the effectiveness of caplacizumab in acquired thrombotic thrombocytopenic purpura.

Acquired thrombotic thrombocytopenic purpura (aTTP) is a rare but life-threatening condition. In 2018, the nanobody caplacizumab was approved for the treatment of adults experiencing an acute episode of aTTP, in conjunction with plasma exchange (PEX) and immunosuppression for a minimum of 30 days after stopping daily PEX. We performed a retrospective, observational analysis on the use of caplacizumab in 60 patients from 29 medical centers in Germany during acute disease management. Caplacizumab led to a rapid normalization of the platelet count (median, 3 days; mean 3.78 days). One patient died after late treatment initiation due to aTTP-associated complications. In 2 patients with initial disease presentation and in 4 additional patients with laboratory signs of an exacerbation or relapse after the initial therapy, PEX-free treatment regimens could be established with overall favorable outcome. Caplacizumab is efficacious in the treatment of aTTP independent of timing and ancillary treatment modalities. Based on this real-world experience and published literature, we propose to administer caplacizumab immediately to all patients with an acute episode of aTTP. Treatment decisions regarding the use of PEX should be based on the severity of the clinical presentation and known risk factors. PEX might be dispensable in some patients.

ADAMTS13 and VWF activities guide individualized caplacizumab treatment in patients with aTTP.

Introduction of the nanobody caplacizumab was shown to be effective in the treatment of acquired thrombotic thrombocytopenic purpura (aTTP) in the acute setting. The official recommendations include plasma exchange (PEX), immunosuppression, and the use of caplacizumab for a minimum of 30 days after stopping daily PEX. This study was a retrospective, observational analysis of the use of caplacizumab in 60 patients from 29 medical centers in Germany. Immunosuppressive treatment led to a rapid normalization of ADAMTS13 activities (calculated median, 21 days). In 35 of 60 patients, ADAMTS13 activities started to normalize before day 30 after PEX; in 11 of 60 patients, the treatment was extended beyond day 30; and in 5 patients, it was extended even beyond day 58 due to persistent autoimmune activity. In 34 of 60 instances, caplacizumab was stopped before day 30 with a favorable outcome whenever ADAMTS13 activities were >10%. In contrast, 11 of 34 patients with ADAMTS13 activities <10% at the time of stopping caplacizumab treatment developed a nonfavorable outcome (disease exacerbation or relapse). In some cases, prolongation of the treatment interval to every other day was feasible and resulted in a sustained reduction of von Willebrand factor activity. ADAMTS13 activity measurements are central for a rapid diagnosis in the acute setting but also to tailor disease management. An ADAMTS13 activity-guided approach seems safe for identifying the individual time point when to stop caplacizumab to prevent overtreatment and undertreatment; this approach will result in significant cost savings without jeopardizing the well-being of patients. In addition, von Willebrand factor activity may serve as a biomarker for drug monitoring.

A case report of recurrent membranoproliferative glomerulonephritis after kidney transplantation due to ventriculoatrial shunt infection.

BACKGROUND: Transplant failure requires the consideration of numerous potential causes including rejection, acute tubular necrosis, infection, and recurrence of the original kidney disease. Kidney biopsy is generally required to approach these differential diagnoses. However, the histopathological findings on their own do not always lead to a definite diagnosis. Consequently, it is crucial to integrate them with clinical findings and patient history when discussing histopathological patterns of injury. The histopathologic finding of a membranoproliferative glomerulonephritis (MPGN) is one of the most challenging constellations since it does not refer to a specific disease entity but rather reflects a pattern of injury that is the result of many different causes. Whilst MPGN is occasionally classified as immune complex mediated, careful evaluation usually reveals an underlying disorder such as chronic infection, plasma cell dyscrasia, complement disorders, and autoimmune disease. CASE PRESENTATION: We describe the case of a 43-year-old woman who was referred to us because of a slowly rising serum creatinine 4 years after kidney transplantation. As in the native kidney, the biopsy revealed an MPGN pattern of injury. The cause of this finding had not been established prior to transplantation leading to a classification as idiopathic MPGN in the past. Further workup at the time of presentation and allograft failure revealed chronic infection of a ventriculoatrial shunt as the most probable cause. CONCLUSION: This case underlines the fact that MPGN is not a disease but a histopathological description. Consequently, the causative disorder needs to be identified to avoid kidney failure and recurrence after transplantation.

Neph2/Kirrel3 regulates sensory input, motor coordination, and home-cage activity in rodents.

Adhesion molecules of the immunoglobulin superfamily (IgSF) are essential for neuronal synapse development across evolution and control various aspects of synapse formation and maturation. Neph2, also known as Kirrel3, is an IgSF adhesion molecule implicated in synapse formation, synaptic transmission and ultrastructure. In humans, defects in the NEPH2 gene have been associated with neurodevelopmental disorders such as Jacobsen syndrome, intellectual disability, and autism-spectrum disorders. However, the precise role in development and function of the nervous system is still unclear. Here, we present the histomorphological and phenotypical analysis of a constitutive Neph2-knockout mouse line. Knockout mice display defects in auditory sensory processing, motor skills, and hyperactivity in the home-cage analysis. Olfactory, memory and metabolic testing did not differ from controls. Despite the wide-spread expression of Neph2 in various brain areas, no gross anatomic defects could be observed. Neph2 protein could be located at the cerebellar pinceaux. It interacted with the pinceau core component neurofascin and other synaptic proteins thus suggesting a possible role in cerebellar synapse formation and circuit assembly. Our results suggest that Neph2/Kirrel3 acts on the synaptic ultrastructural level and neuronal wiring rather than on ontogenetic events affecting macroscopic structure. Neph2-knockout mice may provide a valuable rodent model for research on autism spectrum diseases and neurodevelopmental disorders.

N-Degradomic Analysis Reveals a Proteolytic Network Processing the Podocyte Cytoskeleton.

Regulated intracellular proteostasis, controlled in part by proteolysis, is essential in maintaining the integrity of podocytes and the glomerular filtration barrier of the kidney. We applied a novel proteomics technology that enables proteome-wide identification, mapping, and quantification of protein N-termini to comprehensively characterize cleaved podocyte proteins in the glomerulus in vivo We found evidence that defined proteolytic cleavage results in various proteoforms of important podocyte proteins, including those of podocin, nephrin, neph1, α-actinin-4, and vimentin. Quantitative mapping of N-termini demonstrated perturbation of protease action during podocyte injury in vitro, including diminished proteolysis of α-actinin-4. Differentially regulated protease substrates comprised cytoskeletal proteins as well as intermediate filaments. Determination of preferential protease motifs during podocyte damage indicated activation of caspase proteases and inhibition of arginine-specific proteases. Several proteolytic processes were clearly site-specific, were conserved across species, and could be confirmed by differential migration behavior of protein fragments in gel electrophoresis. Some of the proteolytic changes discovered in vitro also occurred in two in vivo models of podocyte damage (WT1 heterozygous knockout mice and puromycin aminonucleoside-treated rats). Thus, we provide direct and systems-level evidence that the slit diaphragm and podocyte cytoskeleton are regulated targets of proteolytic modification, which is altered upon podocyte damage.

A functional variant in NEPH3 gene confers high risk of renal failure in primary hematuric glomerulopathies. Evidence for predisposition to microalbuminuria in the general population.

BACKGROUND: Recent data emphasize that thin basement membrane nephropathy (TBMN) should not be viewed as a form of benign familial hematuria since chronic renal failure (CRF) and even end-stage renal disease (ESRD), is a possible development for a subset of patients on long-term follow-up, through the onset of focal and segmental glomerulosclerosis (FSGS). We hypothesize that genetic modifiers may explain this variability of symptoms. METHODS: We looked in silico for potentially deleterious functional SNPs, using very strict criteria, in all the genes significantly expressed in the slit diaphragm (SD). Two variants were genotyped in a cohort of well-studied adult TBMN patients from 19 Greek-Cypriot families, with a homogeneous genetic background. Patients were categorized as "Severe" or "Mild", based on the presence or not of proteinuria, CRF and ESRD. A larger pooled cohort (HEMATURIA) of 524 patients, including IgA nephropathy patients, was used for verification. Additionally, three large general population cohorts [Framingham Heart Study (FHS), KORAF4 and SAPHIR] were used to investigate if the NEPH3-V353M variant has any renal effect in the general population. RESULTS AND CONCLUSIONS: Genotyping for two high-scored variants in 103 TBMN adult patients with founder mutations who were classified as mildly or severely affected, pointed to an association with variant NEPH3-V353M (filtrin). This promising result prompted testing in the larger pooled cohort (HEMATURIA), indicating an association of the 353M variant with disease severity under the dominant model (p = 3.0x10-3, OR = 6.64 adjusting for gender/age; allelic association: p = 4.2x10-3 adjusting for patients' kinships). Subsequently, genotyping 6,531 subjects of the Framingham Heart Study (FHS) revealed an association of the homozygous 353M/M genotype with microalbuminuria (p = 1.0x10-3). Two further general population cohorts, KORAF4 and SAPHIR confirmed the association, and a meta-analysis of all three cohorts (11,258 individuals) was highly significant (p = 1.3x10-5, OR = 7.46). Functional studies showed that Neph3 homodimerization and Neph3-Nephrin heterodimerization are disturbed by variant 353M. Additionally, 353M was associated with differential activation of the unfolded protein response pathway, when overexpressed in stressed cultured undifferentiated podocyte cells, thus attesting to its functional significance. Genetics and functional studies support a "rare variant-strong effect" role for NEPH3-V353M, by exerting a negative modifier effect on primary glomerular hematuria. Additionally, genetics studies provide evidence for a role in predisposing homozygous subjects of the general population to micro-albuminuria.

A disease-causing mutation illuminates the protein membrane topology of the kidney-expressed prohibitin homology (PHB) domain protein podocin.

Mutations in the NPHS2 gene are a major cause of steroid-resistant nephrotic syndrome, a severe human kidney disorder. The NPHS2 gene product podocin is a key component of the slit diaphragm cell junction at the kidney filtration barrier and part of a multiprotein-lipid supercomplex. A similar complex with the podocin ortholog MEC-2 is required for touch sensation in Caenorhabditis elegans. Although podocin and MEC-2 are membrane-associated proteins with a predicted hairpin-like structure and amino and carboxyl termini facing the cytoplasm, this membrane topology has not been convincingly confirmed. One particular mutation that causes kidney disease in humans (podocin(P118L)) has also been identified in C. elegans in genetic screens for touch insensitivity (MEC-2(P134S)). Here we show that both mutant proteins, in contrast to the wild-type variants, are N-glycosylated because of the fact that the mutant C termini project extracellularly. Podocin(P118L) and MEC-2(P134S) did not fractionate in detergent-resistant membrane domains. Moreover, mutant podocin failed to activate the ion channel TRPC6, which is part of the multiprotein-lipid supercomplex, indicative of the fact that cholesterol recruitment to the ion channels, an intrinsic function of both proteins, requires C termini facing the cytoplasmic leaflet of the plasma membrane. Taken together, this study demonstrates that the carboxyl terminus of podocin/MEC-2 has to be placed at the inner leaflet of the plasma membrane to mediate cholesterol binding and contribute to ion channel activity, a prerequisite for mechanosensation and the integrity of the kidney filtration barrier.

Characterization of a short isoform of the kidney protein podocin in human kidney.

BACKGROUND: Steroid resistant nephrotic syndrome is a severe hereditary disease often caused by mutations in the NPHS2 gene. This gene encodes the lipid binding protein podocin which localizes to the slit diaphragm of podocytes and is essential for the maintenance of an intact glomerular filtration barrier. Podocin is a hairpin-like membrane-associated protein that multimerizes to recruit lipids of the plasma membrane. Recent evidence suggested that podocin may exist in a canonical, well-studied large isoform and an ill-defined short isoform. Conclusive proof of the presence of this new podocin protein in the human system is still lacking. METHODS: We used database analyses to identify organisms for which an alternative splice variant has been annotated. Mass spectrometry was employed to prove the presence of the shorter isoform of podocin in human kidney lysates. Immunofluorescence, sucrose density gradient fractionation and PNGase-F assays were used to characterize this short isoform of human podocin. RESULTS: Mass spectrometry revealed the existence of the short isoform of human podocin on protein level. We cloned the coding sequence from a human kidney cDNA library and showed that the expressed short variant was retained in the endoplasmic reticulum while still associating with detergent-resistant membrane fractions in sucrose gradient density centrifugation. The protein is partially N-glycosylated which implies the presence of a transmembranous form of the short isoform. CONCLUSIONS: A second isoform of human podocin is expressed in the kidney. This isoform lacks part of the PHB domain. It can be detected on protein level. Distinct subcellular localization suggests a physiological role for this isoform which may be different from the well-studied canonical variant. Possibly, the short isoform influences lipid and protein composition of the slit diaphragm complex by sequestration of lipid and protein interactors into the endoplasmic reticulum.

Mutations in NEK8 link multiple organ dysplasia with altered Hippo signalling and increased c-MYC expression.

Mutations affecting the integrity and function of cilia have been identified in various genes over the last decade accounting for a group of diseases called ciliopathies. Ciliopathies display a broad spectrum of phenotypes ranging from mild manifestations to lethal combinations of multiple severe symptoms and most of them share cystic kidneys as a common feature. Our starting point was a consanguineous pedigree with three affected fetuses showing an early embryonic phenotype with enlarged cystic kidneys, liver and pancreas and developmental heart disease. By genome-wide linkage analysis, we mapped the disease locus to chromosome 17q11 and identified a homozygous nonsense mutation in NEK8/NPHP9 that encodes a kinase involved in ciliary dynamics and cell cycle progression. Missense mutations in NEK8/NPHP9 have been identified in juvenile cystic kidney jck mice and in patients suffering from nephronophthisis (NPH), an autosomal-recessive cystic kidney disease. This work confirmed a complete loss of NEK8 expression in the affected fetuses due to nonsense-mediated decay. In cultured fibroblasts derived from these fetuses, the expression of prominent polycystic kidney disease genes (PKD1 and PKD2) was decreased, whereas the oncogene c-MYC was upregulated, providing potential explanations for the observed renal phenotype. We furthermore linked NEK8 with NPHP3, another NPH protein known to cause a very similar phenotype in case of null mutations. Both proteins interact and activate the Hippo effector TAZ. Taken together, our study demonstrates that NEK8 is essential for organ development and that the complete loss of NEK8 perturbs multiple signalling pathways resulting in a severe early embryonic phenotype.

Conditional loss of kidney microRNAs results in congenital anomalies of the kidney and urinary tract (CAKUT).

MicroRNAs have emerged as essential regulators of gene expression and may play important roles in a variety of human disorders. To understand the role of microRNA-mediated gene regulation in the kidney, we deleted the microRNA-processing enzyme Dicer in developing renal tubules and parts of the ureteric bud in mice. Genetic deletion of Dicer resulted in renal failure and death of the animals at 4-6 weeks of age. Interestingly, the kidneys of microRNA-deficient animals were small due to a reduced number of nephrons and showed massive hydronephrosis due to ureteropelvic junction obstruction. This phenotype is reminiscent of congenital anomalies of the kidney and urinary tract (CAKUT), an important group of human disorders characterized by a combination of renal hypoplasia with congenital abnormalities of the urinary tract. We used metanephric kidney cultures to examine the developmental defects underlying these pathologies. Dicer knockout kidneys showed a significant reduction of tubular branching explaining renal hypoplasia. Moreover, the ureters of these kidneys showed an altered morphology and impaired motility. These functional changes went along with altered expression of smooth muscle actin implying a defect in the differentiation of ureteric smooth muscle cells. In addition, we show the polycystic kidney disease gene Pkd1 to be a target of miR-20 implying that this interaction may contribute to the molecular basis for the cystogenesis in our model. In conclusion, these data demonstrate an essential role for microRNA-dependent gene regulation in mammalian kidney development and suggest that deregulation of microRNAs may underlie CAKUT, the most important group of renal disorders in humans.

Survival and distribution of injected haematopoietic stem cells in acute kidney injury.

BACKGROUND: Endogenous bone marrow-derived cells are known to incorporate into renal epithelium at a low rate. Haematopoietic stem cells (HSCs) rather than mesenchymal stem cells (MSC) are responsible for this phenomenon. MSCs have the potential to ameliorate kidney function after acute kidney injury (AKI) without directly repopulating the tubules. However, little is known about the short-term effect of HSCs. METHODS: In this article, we analysed the survival rate and organ distribution of isolated rat HSCs injected into the renal artery after ischaemic renal injury, using quantitative real-time PCR, as well as their impact on renal function and histomorphology. RESULTS: Intra-arterially injected Lin(-)CD90(+) HSCs were detected in the kidney at significant amounts only within the first 24 h after injection and were virtually absent by Day 2. Compared with control animals, no differences were seen after HSC administration with respect to kidney function or histomorphologic changes of AKI. At Day 7 HSCs were again readily detectable in the kidney suggesting a redistribution of cells at later time points. Of note, HSCs did not seem to have an exclusive tropism for the injured kidney but were detectable in the lungs, liver, spleen, heart and brain at all time points. CONCLUSIONS: Injected HSCs do not appear to significantly contribute to tubular repair or ameliorate renal damage in ischaemic AKI although they may show considerable engraftment in various organs. These data further challenge the concept that injection of HSCs may be used as a therapeutic approach in treating AKI.