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.

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.

Background:The PCP pathway controls many cell processes during development. Results: The PCP pathway induces nephrin endocytosis when cultured podocytes are treated with Wnt5a. Loss of PCP protein Vangl2 decreases nephrin endocytosis. Conclusion: During glomerular development, endocytosis of nephrin is regulated by the PCP pathway. Significance: Implicating the PCP pathway in nephrin endocytosis is important for understanding the complexity of PCP signaling during mammalian development.

During vertebrate development, the PCP pathway controls multiple cellular processes. Loss of the gene for the PCP effector Fuzzy affects formation of primary cilia via mostly unknown mechanisms. We report that Fuzzy localizes to the primary cilia and orchestrates delivery of Rab8 and Dishevelled to the primary cilium; loss of Fuzzy affects cilia-dependent signaling.

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. 26: 576-586, 201526: 576-586, . doi: 10.1681 Renal glomerular visceral epithelial cells (podocytes) are highly polarized cells with complex threedimensional architecture characterized by the presence of unique actin-based projections (foot processes [FPs]). 1 The FPs from neighboring podocytes form intercellular bridges, slit diaphragms, that are the only points of contact between adjacent cells and the base for the permselective filtration barrier, allowing small solutes to pass into the urinary space while retaining large proteins in the blood. 1 Slit diaphragm protein complexes are connected with the podocyte cytoskeleton by various adaptor proteins and serve as a signaling nexus to relay information from the FP surface to control podocyte structure. 2 The characteristic shape of podocytes is directly related to glomerular filtration. Mutations in proteins that link slit diaphragms and the cytoskeleton (e.g., a-actinin-4 and CD2-associated protein) 3,4 or regulators of actin polymerization and organization (e.g., Inverted Formin-2, Myosin 1e, Rho GDP-Dissociation Inhibitor 1, and Cdc42) 5-9 give rise to glomerular dysfunction, such as proteinuria, J Am Soc Nephrol