The CPLANE protein Fuzzy regulates ciliogenesis by suppressing actin polymerization at the base of the primary cilium via p190A RhoGAP.

The primary cilium decorates most eukaryotic cells and regulates tissue morphogenesis and maintenance. Structural or functional defects of primary cilium result in ciliopathies, congenital human disorders affecting multiple organs. Pathogenic variants in the ciliogenesis and planar cell polarity effectors (CPLANE) genes FUZZY, INTU and WDPCP disturb ciliogenesis, causing severe ciliopathies in humans and mice. Here, we show that the loss of Fuzzy in mice results in defects of primary cilia, accompanied by increased RhoA activity and excessive actin polymerization at the basal body. We discovered that, mechanistically, Fuzzy interacts with and recruits the negative actin regulator ARHGAP35 (also known as p190A RhoGAP) to the basal body. We identified genetic interactions between the two genes and found that a mutant ArhGAP35 allele increases the severity of phenotypic defects observed in Fuzzy-/- mice. Based on our findings, we propose that Fuzzy regulates ciliogenesis by recruiting ARHGAP35 to the basal body, where the latter likely restricts actin polymerization and modifies the actin network. Our study identifies a mechanism whereby CPLANE proteins control both actin polymerization and primary cilium formation.

Wilms' tumor gene 1: lessons from the interface between kidney development and cancer.

In 1990, mutations of the Wilms' tumor-1 gene (WT1), encoding a transcription factor in the embryonic kidney, were found in 10-15% of Wilms' tumors; germline WT1 mutations were associated with hereditary syndromes involving glomerular and reproductive tract dysplasia. For more than three decades, these discoveries prompted investigators to explore the embryonic role of WT1 and the mechanisms by which loss of WT1 leads to malignant transformation. Here, we discuss how alternative splicing of WT1 generates isoforms that act in a context-specific manner to activate or repress target gene transcription. WT1 also regulates posttranscriptional regulation, alters the epigenetic landscape, and activates miRNA expression. WT1 functions at multiple stages of kidney development, including the transition from resting stem cells to committed nephron progenitor, which it primes to respond to WNT9b signals from the ureteric bud. WT1 then drives nephrogenesis by activating WNT4 expression and directing the development of glomerular podocytes. We review the WT1 mutations that account for Denys-Drash syndrome, Frasier syndrome, and WAGR syndrome. Although the WT1 story began with Wilms' tumors, an understanding of the pathways that link aberrant kidney development to malignant transformation still has some important gaps. Loss of WT1 in nephrogenic rests may leave these premalignant clones with inadequate DNA repair enzymes and may disturb the epigenetic landscape. Yet none of these observations provide a complete picture of Wilms' tumor pathogenesis. It appears that the WT1 odyssey is unfinished and still holds a great deal of untilled ground to be explored.

From podocyte biology to novel cures for glomerular disease.

The podocyte is a key component of the glomerular filtration barrier. Podocyte dysfunction is central to the underlying pathophysiology of many common glomerular diseases, including diabetic nephropathy, glomerulonephritis and genetic forms of nephrotic syndrome. Collectively, these conditions affect millions of people worldwide, and account for the majority of kidney diseases requiring dialysis and transplantation. The 12th International Podocyte Conference was held in Montreal, Canada from May 30 to June 2, 2018. The primary aim of this conference was to bring together nephrologists, clinician scientists, basic scientists and their trainees from all over the world to present their research and to establish networks with the common goal of developing new therapies for glomerular diseases based on the latest advances in podocyte biology. This review briefly highlights recent advances made in understanding podocyte structure and metabolism, experimental systems in which to study podocytes and glomerular disease, disease mediators, genetic and immune origins of glomerulopathies, and the development of novel therapeutic agents to protect podocyte and glomerular injury.

Ste20-like kinase, SLK, a novel mediator of podocyte integrity.

SLK is essential for embryonic development and may play a key role in wound healing, tumor growth, and metastasis. Expression and activation of SLK are increased in kidney development and during recovery from ischemic acute kidney injury. Overexpression of SLK in glomerular epithelial cells/podocytes in vivo induces injury and proteinuria. Conversely, reduced SLK expression leads to abnormalities in cell adhesion, spreading, and motility. Tight regulation of SLK expression thus may be critical for normal renal structure and function. We produced podocyte-specific SLK-knockout mice to address the functional role of SLK in podocytes. Mice with podocyte-specific deletion of SLK showed reduced glomerular SLK expression and activity compared with control. Podocyte-specific deletion of SLK resulted in albuminuria at 4-5 mo of age in male mice and 8-9 mo in female mice, which persisted for up to 13 mo. At 11-12 mo, knockout mice showed ultrastructural changes, including focal foot process effacement and microvillous transformation of podocyte plasma membranes. Mean foot process width was approximately twofold greater in knockout mice compared with control. Podocyte number was reduced by 35% in knockout mice compared with control, and expression of nephrin, synaptopodin, and podocalyxin was reduced in knockout mice by 20-30%. In summary, podocyte-specific deletion of SLK leads to albuminuria, loss of podocytes, and morphological evidence of podocyte injury. Thus, SLK is essential to the maintenance of podocyte integrity as mice age.

Use of genomic and functional analysis to characterize patients with steroid-resistant nephrotic syndrome.

BACKGROUND: Children with genetic causes of steroid-resistant nephrotic syndrome (SRNS) usually do well after renal transplantation, while some with idiopathic SRNS show recurrence due to a putative podocyte-toxic factor. Distinguishing different forms of SRNS based on clinical criteria has been difficult. The aim of our study was to test a novel approach that allows categorization of patients into clinically useful subgroups. METHODS: Seventeen patients with clinically confirmed SRNS were analyzed by next-generation sequencing (NGS) of 37 known SRNS genes and a functional assay of cultured human podocytes, which indirectly tests for toxicity of patients' sera by evidenced loss of podocyte focal adhesion complex (FAC) number. RESULTS: We identified a pathogenic mutation in seven patients (41%). Sera from patients with monogenic SRNS caused mild loss of FAC number down to 73% compared to untreated controls, while sera from seven of the remaining ten patients with idiopathic SRNS caused significant FAC number loss to 43% (non-overlapping difference 30%, 95% CI 26-36%, P < 0.001). All patients with recurrent SRNS (n = 4) in the graft showed absence of podocyte gene mutations but significant FAC loss. Three patients had no mutation nor serum podocyte toxicity. CONCLUSIONS: Our approach allowed categorization of patients into three subgroups: (1) patients with monogenic SRNS; (2) patients with idiopathic SRNS and marked serum podocyte toxicity; and (3) patients without identifiable genetic cause nor evidence of serum podocyte toxicity. Post-transplant SRNS recurrence risk appears to be low in groups 1 and 3, but high in group 2.

Wilms Tumor Suppressor, WT1, Cooperates with MicroRNA-26a and MicroRNA-101 to Suppress Translation of the Polycomb Protein, EZH2, in Mesenchymal Stem Cells.

Hereditary forms of Wilms arise from developmentally arrested clones of renal progenitor cells with biallelic mutations of WT1; recently, it has been found that Wilms tumors may also be associated with biallelic mutations in DICER1 or DROSHA, crucial for miRNA biogenesis. We have previously shown that a critical role for WT1 during normal nephrogenesis is to suppress transcription of the Polycomb group protein, EZH2, thereby de-repressing genes in the differentiation cascade. Here we show that WT1 also suppresses translation of EZH2. All major WT1 isoforms induce an array of miRNAs, which target the 3' UTR of EZH2 and other Polycomb-associated transcripts. We show that the WT1(+KTS) isoform binds to the 5' UTR of EZH2 and interacts directly with the miRNA-containing RISC to enhance post-transcriptional inhibition. These observations suggest a novel mechanism through which WT1 regulates the transition from resting stem cell to activated progenitor cell during nephrogenesis. Our findings also offer a plausible explanation for the fact that Wilms tumors can arise either from loss of WT1 or loss of miRNA processing enzymes.

Novel unbiased assay for circulating podocyte-toxic factors associated with recurrent focal segmental glomerulosclerosis.

Focal segmental glomerular sclerosis (FSGS) is an irreversible renal pathology characterized by podocyte detachment from the glomerular basement membrane, hyalinosis, and sclerosis. Clinically, it manifests with proteinuria and progressive loss of glomerular filtration. Primary idiopathic FSGS can occur in isolation and frequently progresses to end-stage renal disease, requiring dialysis or kidney transplantation. In 30-50% of these patients, proteinuria and FSGS recur in the renal allograft, suggesting the presence of a podocyte-toxic factor(s) in the recipient's serum. Currently, there is no reliable way to quantify the serum activity or predict the subset of FSGS patients at risk for recurrence after transplantation. We describe a novel in vitro method that measures the podocyte-toxic activity of sera from FSGS patients using cultured human podocytes; we compare this with the effect of compounds such as adriamycin. Using immunofluorescence microscopy followed by computerized image-processing analysis, we show that incubation of human podocytes with adriamycin leads to a dose-dependent disassembly of focal adhesion complexes (FACs). We then demonstrate that sera from patients with posttransplant recurrent or idiopathic FSGS cause a similar FAC disturbance. In contrast, sera from nonrecurrent FSGS patients do not affect FACs. In some FSGS patients, toxic effects of serum can be prevented by blockade of the tumor necrosis factor-α pathway. We propose that this method may be useful as a diagnostic tool to identify FSGS patients with serum podocyte-toxic activity that presumably places them at increased risk for recurrence in the renal allograft.

New insights into precursors of renal endothelium.

The kidney vasculature is extremely complex, yet, despite recent progress, our understanding of how the renal vascular system develops is limited. By using advanced tissue engineering techniques and in vivo and in vitro depletion of specific populations of endothelial cell precursors, Halt et al. have identified a CD146-expressing precursor as an important player in the development of the renal vasculature.

Deficiency of the planar cell polarity protein Vangl2 in podocytes affects glomerular morphogenesis and increases susceptibility to injury.

The planar cell polarity (PCP) signaling pathway is crucial for tissue morphogenesis. Van Gogh-like protein 2 (Vangl2) is central in the PCP pathway; in mice, Vangl2 loss is embryonically lethal because of neural tube defects, and mutations in Vangl2 are associated with human neural tube defects. In the kidney, PCP signaling may be important for tubular morphogenesis and organization of glomerular epithelial cells (podocytes) along the glomerular basement membrane. Podocyte cell protrusions (foot processes) are critical for glomerular permselectivity; loss of foot process architecture results in proteinuria and FSGS. Previously, we showed a profound effect of PCP signaling on podocyte shape, actin rearrangement, cell motility, and nephrin endocytosis. To test our hypothesis that the PCP pathway is involved in glomerular development and function and circumvent lethality of the ubiquitous Vangl2 mutation in the Looptail mouse, we generated a mouse model with a podocyte-specific ablation of the Vangl2 gene. We report here that podocyte-specific deletion of Vangl2 leads to glomerular maturation defects in fetal kidneys. In adult mice, we detected significantly smaller glomeruli, but it did not affect glomerular permselectivity in aging animals. However, in the context of glomerular injury induced by injection of antiglomerular basement membrane antibody, deletion of Vangl2 resulted in exacerbation of injury and accelerated progression to chronic segmental and global glomerular sclerosis. Our results indicate that Vangl2 function in podocytes is important for glomerular development and protects against glomerular injury in adult animals.

Planar cell polarity pathway regulates nephrin endocytosis in developing podocytes.

The noncanonical Wnt/planar cell polarity (PCP) pathway controls a variety of cell behaviors such as polarized protrusive cell activity, directional cell movement, and oriented cell division and is crucial for the normal development of many tissues. Mutations in the PCP genes cause malformation in multiple organs. Recently, the PCP pathway was shown to control endocytosis of PCP and non-PCP proteins necessary for cell shape remodeling and formation of specific junctional protein complexes. During formation of the renal glomerulus, the glomerular capillary becomes enveloped by highly specialized epithelial cells, podocytes, that display unique architecture and are connected via specialized cell-cell junctions (slit diaphragms) that restrict passage of protein into the urine; podocyte differentiation requires active remodeling of cytoskeleton and junctional protein complexes. We report here that in cultured human podocytes, activation of the PCP pathway significantly stimulates endocytosis of the core slit diaphragm protein, nephrin, via a clathrin/ß-arrestin-dependent endocytic route. In contrast, depletion of the PCP protein Vangl2 leads to an increase of nephrin at the cell surface; loss of Vangl2 functions in Looptail mice results in disturbed glomerular maturation. We propose that the PCP pathway contributes to podocyte development by regulating nephrin turnover during junctional remodeling as the cells differentiate.

Mutations in the planar cell polarity gene, Fuzzy, are associated with neural tube defects in humans.

Neural tube defects (NTDs) are a heterogeneous group of common severe congenital anomalies which affect 1-2 infants per 1000 births. Most genetic and/or environmental factors that contribute to the pathogenesis of human NTDs are unknown. Recently, however, pathogenic mutations of VANGL1 and VANGL2 genes have been associated with some cases of human NTDs. Vangl genes encode proteins of the planar cell polarity (PCP) pathway that regulates cell behavior during early stages of neural tube formation. Homozygous disruption of PCP genes in mice results in a spectrum of NTDs, including defects that affect the entire neural axis (craniorachischisis), cranial NTDs (exencephaly) and spina bifida. In this paper, we report the dynamic expression of another PCP gene, Fuzzy, during neural tube formation in mice. We also identify non-synonymous Fuzzy amino acid substitutions in some patients with NTDs and demonstrate that several of these Fuzzy mutations affect formation of primary cilia and ciliary length or affect directional cell movement. Since Fuzzy knockout mice exhibit both NTDs and defective primary cilia and Fuzzy is expressed in the emerging neural tube, we propose that mutations in Fuzzy may account for a subset of NTDs in humans.

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.

TNFα pathway blockade ameliorates toxic effects of FSGS plasma on podocyte cytoskeleton and ß3 integrin activation.

BACKGROUND: In the absence of mutant genes encoding components of the podocyte slit diaphragm, about 30-50 % of children with primary glucocorticoid-resistant focal segmental glomerulosclerosis (FSGS) develop recurrent proteinuria and slowly progressive FSGS lesions following renal transplantation. Recurrence of FSGS in the allograft strongly suggests a circulating factor that disturbs normal podocyte biology. To date, the nature of the circulating factor is unclear, and there is no cure for the recurrent form of FSGS (R-FSGS). METHODS: Cultured differentiated human podocytes were exposed to the plasmapheresis effluent or blood plasma samples from pediatric patients with recurrent or primary FSGS; in some cases, podocytes were pre-incubated with specific antibodies to block the tumor necrosis factor-alpha (TNFα) signaling pathway. Integrity of focal adhesion complexes and actin cytoskeleton were investigated by immunofluorescent microscopy. RESULTS: Plasmapheresis effluent from an R-FSGS child or fresh plasma from two children with primary FSGS rapidly disturbed the cytoskeleton of normal human podocytes in vitro. Plasma from a child with R-FSGS also activated ß3 integrin and dispersed focal adhesion complexes. The effects were reversed by pre-incubation with antibodies against TNFα or either of the two TNFα receptors. When our patient with R-FSGS became resistant to plasmapheresis, we initiated treatment with twice weekly etanercept injections and then infliximab. Within 3 weeks of regular anti-TNFα therapy, the patient achieved sustained partial remission of proteinuria, allowing us to wean her off plasmapheresis completely. CONCLUSIONS: We suggest that in some FSGS patients, disruption of the podocyte cytoskeleton and ß3 integrin-mediated podocyte attachment are driven by the TNFα pathway.

Identification of a novel variant of the ciliopathic gene FUZZY associated with craniosynostosis.

Craniosynostosis is a birth defect occurring in approximately one in 2000 live births, where premature fusion of the cranial bones inhibits growth of the skull during critical periods of brain development. The resulting changes in skull shape can lead to compression of the brain, causing severe complications. While we have some understanding of the molecular pathology of craniosynostosis, a large proportion of cases are of unknown genetic aetiology. Based on studies in mouse, we previously proposed that the ciliopathy gene Fuz should be considered a candidate craniosynostosis gene. Here, we report a novel variant of FUZ (c.851 G > C, p.(Arg284Pro)) found in monozygotic twins presenting with craniosynostosis. To investigate whether Fuz has a direct role in regulating osteogenic fate and mineralisation, we cultured primary osteoblasts and mouse embryonic fibroblasts (MEFs) from Fuz mutant mice. Loss of Fuz resulted in increased osteoblastic mineralisation. This suggests that FUZ protein normally acts as a negative regulator of osteogenesis. We then used Fuz mutant MEFs, which lose functional primary cilia, to test whether the FUZ p.(Arg284Pro) variant could restore FUZ function during ciliogenesis. We found that expression of the FUZ p.(Arg284Pro) variant was sufficient to partially restore cilia numbers, but did not mediate a comparable response to Hedgehog pathway activation. Together, this suggests the osteogenic effects of FUZ p.(Arg284Pro) do not depend upon initiation of ciliogenesis.

Advancing Discovery Research in Nephrology in Canada: A Conference Report From the 2021 Molecules and Mechanisms Mediating Kidney Health and Disease (M3K) Scientific Meeting and Investigator Summit.

Purpose of conference: New discoveries arising from investigations into fundamental aspects of kidney development and function in health and disease are critical to advancing kidney care. Scientific meetings focused specifically on fundamental biology of the kidney can facilitate interactions, support the development of collaborative groups, and accelerate translation of key findings. The Canadian fundamental kidney researcher community has lacked such a forum. On December 3 to 4, 2021, the first Molecules and Mechanisms Mediating Kidney Health and Disease (M3K) Scientific Meeting and Investigator Summit was held to address this gap with the goal of advancing fundamental kidney research nationally. The meeting was held virtually and was supported by a planning and dissemination grant from the Canadian Institutes of Health Research. Attendees included PhD scientists, nephrology clinician scientists, engineers, industry representatives, graduate students, medical residents, and fellows. Sources of information: This report was prepared from the scientific program, registration numbers, and details obtained from the online platform WHOVA, and summaries written by organizers and participants of the 2021 meeting. Methods: A 21-person team, consisting of the organizing committee members and participants from the meeting, was assembled. Key highlights of the meeting and future directions were identified and the team jointly assembled this report. Key findings: Participation in the meeting was strong, with more than 140 attendees across a range of disciplines. The program featured state-of-the-art presentations on diabetic nephropathy, the immune system, kidney development, and fibrosis, and was heavily focused on trainee presentations. The moderated "Investigator Summit" identified key barriers to research advancement and discussed strategies for overcoming them. These included establishment of a pan-Canadian fundamental kidney research network, development of key resources, cross-pollination with clinical nephrology, better reintegration into the Canadian Society of Nephrology, and further establishment of identity and knowledge translation. Limitations and implications: The 2021 M3K meeting represented a key first step in uniting fundamental kidney researchers in Canada. However, it was universally agreed that regular meetings were necessary to sustain this momentum. The proceedings of this meeting and future actions to sustain the M3K Scientific Meeting and Investigator Summit are presented in this article.

Objectif de la conférence: De nouvelles découvertes découlant des enquêtes sur les aspects fondamentaux du développement et de la fonction des reins en santé ou malades sont essentielles pour faire progresser les soins rénaux. Les réunions scientifiques axées spécifiquement sur la biologie fondamentale du rein peuvent faciliter les interactions, appuyer le développement de groupes de collaboration et accélérer l'application des principaux résultats. La communauté canadienne des chercheurs fondamentaux en néphrologie a manqué d'un tel forum. Les 3 et 4 décembre 2021, le premier Sommet des chercheurs et la réunion scientifique M3K (Molecules and Mechanisms Mediating Kidney Health and Disease) sur les molécules et les médiateurs de la santé et des maladies rénales ont eu lieu pour combler cette lacune; l'objectif était de faire progresser la recherche fondamentale en néphrologie à l'échelle nationale. La réunion s'est tenue virtuellement et était financée par une subvention de planification et de diffusion des Instituts de recherche en santé du Canada. Des doctorants, cliniciens-chercheurs en néphrologie, ingénieurs, représentants de l'industrie, étudiants diplômés, résidents en médecine et en surspécialisation figuraient parmi les participants. Sources: Ce rapport a été préparé à partir du program scientifique, des informations et des numéros d'inscription tirés de la plateforme en ligne WHOVA, et des résumés rédigés par les organisateurs et les participants à la réunion de 2021. Méthodologie: Une équipe de 20 personnes composée de membres du comité organisateur et de participants à la réunion a été formée. Les principaux points saillants de la réunion et les orientations futures ont été déterminés, puis l'équipe a rédigé conjointement le présent rapport. Principaux résultats: La réunion s'est avérée un succès; plus de 140 personnes provenant d'un large éventail de disciplines y ont participé. Le program comprenait des présentations de pointe sur la néphropathie diabétique, le système immunitaire, le développement des reins et la fibrose, et était fortement axé sur des présentations par des stagiaires. Le « Sommet des chercheurs ¼, animé par un modérateur, a permis de déterminer les principaux obstacles à l'avancement de la recherche et de discuter des stratégies pour les surmonter. Ces dernières incluent notamment la création d'un réseau pancanadien de recherche fondamentale en néphrologie, le développement de ressources clés, la pollinisation croisée avec la néphrologie clinique, une « meilleure réintégration dans la Société canadienne de néphrologie ¼ et la poursuite de l'établissement de l'identité et de l'application des connaissances. Limites et implications: La réunion M3K de 2021 a constitué une première étape clé dans l'unification des chercheurs fondamentaux en néphrologie au Canada. On a cependant universellement convenu que des réunions régulières étaient nécessaires pour maintenir cet élan. Le compte rendu de cette réunion ainsi que les actions futures pour soutenir la réunion scientifique M3K et le Sommet des chercheurs sont présentés dans le présent article.

Can Peer Review Be Kinder? Supportive Peer Review: A Re-Commitment to Kindness and a Call to Action.

Peer review aims to select articles for publication and to improve articles before publication. We believe that this process can be infused by kindness without losing rigor. In 2014, the founding editorial team of the Canadian Journal of Kidney Health and Disease (CJKHD) made an explicit commitment to treat authors as we would wish to be treated ourselves. This broader group of authors reaffirms this principle, for which we suggest the terminology "supportive review."

L'évaluation par les pairs vise à sélectionner les articles à publier et à en améliorer le contenu avant publication. Nous sommes d'avis que ce processus peut être fait avec bienveillance sans perdre en rigueur. En 2014, l'équipe de rédaction fondatrice du Canadian Journal of Kidney Health and Disease (CJKHD) a pris l'engagement ferme de traiter les auteurs comme ses membres souhaiteraient eux-mêmes être traités. Aujourd'hui, notre groupe élargi d'auteur(e)s réaffirme ce principe pour lequel nous proposons la terminologie « évaluation constructive ¼.

Planar cell polarity pathway regulates actin rearrangement, cell shape, motility, and nephrin distribution in podocytes.

Glomerular podocytes are highly polarized cells characterized by dynamic actin-based foot processes (FPs). Neighboring FPs form specialized junctions, slit diaphragms (SDs), which prevent passage of proteins into the ultrafiltrate. The SD protein complex is linked to cytoskeletal actin filaments and mutations in SD proteins lead to a dramatic change in cell morphology; proteinuria is accompanied by FP retraction and loss of SD structure. Thus, organization of the podocyte cytoskeleton is tightly linked to filtration barrier function. In a variety of cell systems, cytoskeleton arrangement is regulated by the planar cell polarity (PCP) pathway. PCP signals lead to the appearance of highly organized cellular structures that support directional cell movement and oriented cell division. Derangement of the PCP pathway causes neural tube defects and cystic kidney disease in mice. Here, we establish that the PCP pathway regulates the cytoskeleton of podocytes. We identify expression of core PCP proteins in mouse kidney sections and of PCP transcripts in murine and human cultured podocytes. The pathway is functional since Wnt5a causes redistribution of PCP proteins Dishevelled and Daam1. We also show that Wnt5a treatment changes podocyte morphology, alters nephrin distribution, increases the number of stress fibers, and increases cell motility. In reciprocal experiments, siRNA depletion of the core PCP gene Vangl2 reduced the number of cell projections and decreased stress fibers and cell motility. Finally, we demonstrate direct interactions between Vangl2 and the SD protein, MAGI-2. This suggests that the PCP pathway may be directly linked to organization of the SD as well as to regulation of podocyte cytoskeleton. Our observations indicate that PCP signaling may play an important role both in podocyte development and FP cytoskeleton dynamics.

The kidney and ear: emerging parallel functions.

The association between renal dysplasia and minor malformations of the external ear is weak. However, there is a remarkable list of syndromes that link the kidney to the inner ear. To organize these seemingly disparate syndromes, we cluster representative examples into three groups: (a) syndromes that share pathways regulating development; (b) syndromes involving dysfunction of the primary cilium, which normally provides critical information to epithelial cells about the fluid in which they are bathed; (c) syndromes arising from dysfunction of specialized proteins that transport ions and drugs in and out of the extracellular fluid or provide structural support.

Plasma from a case of recurrent idiopathic FSGS perturbs non-muscle myosin IIA (MYH9 protein) in human podocytes.

The MYH9 gene encodes a non-muscle myosin IIA heavy chain (NMMHC-IIA) expressed in podocytes. Heterozygous MYH9 mutations cause a set of overlapping syndromes characterized by variable degrees of deafness, morphologic abnormalities of platelets and focal segmental glomerulosclerosis (FSGS) with progressive renal dysfunction. Similar glomerular lesions are seen in a variety of nephropathies, including an idiopathic form of FSGS in children which recurs in renal allografts, implying a circulating factor that affects glomerular podocyte biology. It is unknown whether NMMHC-IIA is perturbed in the idiopathic form of FSGS. We describe a pediatric patient with typical idiopathic FSGS, in whom proteinuria recurred within hours of deceased donor renal transplantation but who responded to plasmapheresis. We demonstrate in vitro that plasmapheresis effluent from our patient rapidly decreased cultured podocyte levels of the phosphorylated myosin light chain (MLC) that mediates NMMHC-IIA binding to actin and induced dispersion of NMMHC-IIA from its usual position along actin stress fibers. FSGS plasma also caused dispersion of slit diaphragm proteins (nephrin and podocin) and vinculin-positive focal adhesion complexes. Our observations suggest that the putative circulating factor in idiopathic FSGS disrupts normal NMMHC-IIA function in podocytes and might contribute to the pathogenesis of recurrent FSGS in other children.