Frizzled 4 Regulates Arterial Network Organization Through Noncanonical Wnt/Planar Cell Polarity Signaling

Frizzled receptors (FZDs) in Wnt signaling: potential therapeutic targets for human cancers

Frizzled receptors (FZDs) are key contributors intrinsic to the Wnt signaling pathway, activation of FZDs triggering the Wnt signaling cascade is frequently observed in human tumors and intimately associated with an aggressive carcinoma phenotype. It has been shown that the abnormal expression of FZD receptors contributes to the manifestation of malignant characteristics in human tumors such as enhanced cell proliferation, metastasis, chemotherapy resistance as well as the acquisition of cancer stemness. Given the essential roles of FZD receptors in the Wnt signaling in human tumors, this review aims to consolidate the prevailing knowledge on the specific status of FZD receptors (FZD1-10) and elucidate their respective functions in tumor progression. Furthermore, we delineate the structural basis for binding of FZD and its co-receptors to Wnt, and provide a better theoretical foundation for subsequent studies on related mechanisms. Finally, we describe the existing biological classes of small molecule-based FZD inhibitors in detail in the hope that they can provide useful assistance for design and development of novel drug candidates targeted FZDs.

Nasal polyps show decreased mucociliary transport despite vigorous ciliary beating

OBJECTIVE

Mucociliary transport function in the airway mucosa is essential for maintaining a clean mucosal surface. This function is impaired in upper and lower airway diseases. Nasal polyps are a noticeable pathological feature that develop in some of the patients with chronic rhinosinusitis. Like ordinary nasal mucosae, nasal polyps have a ciliated pseudostratified epithelium with vigorous ciliary beating. We measured ex vivo Mucociliary Transport Velocity (MCTV) and Ciliary Beat Frequency (CBF) and explored the expressions of Planar Cell Polarity (PCP) proteins in nasal polyps in comparison with turbinate mucosae.

METHODS

Inferior turbinates and nasal polyps were surgically collected from patients with chronic rhinosinusitis. Ex vivo MCTV and CBF were measured using a high-speed digital imaging system. Expressions of PCP proteins were explored by fluorescence immunohistochemistry and quantitative RT-PCR.

RESULTS

The MCTV of nasal polyps was significantly lower than that of the turbinates (7.43 ± 2.01 vs. 14.56 ± 2.09 μm/s; p = 0.0361), whereas CBF did not differ between the two tissues. The MCTV vector was pointed to the posteroinferior direction in all turbinates with an average inclination angle of 41.0 degrees. Immunohistochemical expressions of Dishevelled-1, Dishevelled-3, Frizzled3, Frizzled6, Prickle2 and Vangl2 were lower in the nasal polyps than in the turbinates. Confocal laser scanning microscopy showed that Frizzled3 was localized along the cell junction on the apical surface. The expression levels of mRNAs for Dishevelled-1, Dishevelled-3 and Frizzled3 in the nasal polyps were also decreased in comparison with the turbinates.

CONCLUSION

These results indicate that muco ciliary transport in nasal polyps is impaired although vigorous ciliary beating is maintained, and that the impairment may be caused by a decrease in Dishevelled/Frizzled proteins and resultant PCP disarrangement.

LEVEL OF EVIDENCE

Level 3.

Transcriptomic Analysis Reveals Intrinsic Abnormalities in Endometrial Polyps

Endometrial polyps (EPs) are benign overgrowths of the endometrial tissue lining the uterus, often causing abnormal bleeding or infertility. This study analyzed gene expression differences between EPs and adjacent endometrial tissue to elucidate intrinsic abnormalities promoting pathological overgrowth. RNA sequencing of 12 pairs of EPs and the surrounding endometrial tissue from infertile women revealed 322 differentially expressed genes. Protein-protein interaction network analysis revealed significant alterations in specific signaling pathways, notably Wnt signaling and vascular smooth muscle regulation, suggesting these pathways play critical roles in the pathophysiology of EPs. Wnt-related genes DKK1 and DKKL1 were upregulated, while GPC3, GREM1, RSPO3, SFRP5, and WNT10B were downregulated. Relevant genes for vascular smooth muscle contraction were nearly all downregulated in EPs, including ACTA2, ACTG2, KCNMB1, KCNMB2, MYL9, PPP1R12B, and TAGLN. Overall, the results indicate fundamental gene expression changes promote EP formation through unrestrained growth signaling and vascular defects. The intrinsic signaling abnormalities likely contribute to clinical symptoms of abnormal uterine bleeding and infertility common in EP patients. This analysis provides molecular insights into abnormal endometrial overgrowth to guide improved diagnostic and therapeutic approaches for this troublesome women's health condition. Confirmation of expanded cohorts and further investigations into implicated regulatory relationships are warranted.

The role of Wnt signaling in mesenchymal stromal cell-driven angiogenesis

Development, growth, and remodeling of blood vessels occur through an intricate process involving cell differentiation, proliferation, and rearrangement by cell migration under the direction of various signaling pathways. Recent reports highlight that resident and exogenous mesenchymal stromal cells (MSCs) have the potential to regulate the neovascularization process through paracrine secretion of proangiogenic factors. Recent research has established that the vasculogenic potential of MSCs is regulated by several signaling pathways, including the Wnt signaling pathway, and their interplay. These findings emphasize the complex nature of the vasculogenic process and underscore the importance of understanding the underlying molecular mechanisms for the development of effective cell-based therapies in regenerative medicine. This review provides an updated briefing on the canonical and non-canonical Wnt signaling pathways and summarizes the recent reports of both in vitro and in vivo studies with the involvement of MSCs of various sources in the vasculogenic process mediated by Wnt signaling pathways. Here we outline the current understanding of the plausible role of the Wnt signaling pathway, specifically in MSC-regulated angiogenesis.

Oscillatory shear stress-induced downregulation of TET1s injures vascular endothelial planar cell polarity by suppression of actin polymerization

Vascular endothelial polarity induced by blood flow plays crucial roles in the development of atherosclerosis. Loss of endothelial polarity leads to an increase in permeability and leukocyte recruitment, which are crucial hallmarks of atherosclerotic initiation. Endothelial cells exhibit a morphological adaptation to hemodynamic shear stress and possesses planar cell polarity to the direction of blood flow. However, the mechanism of how hemodynamic shear stress regulates endothelial planar cell polarity has not been firmly established. Here, we found that TET1s, a short isoform of Tet methylcytosine dioxygenase 1, was a mediator in the regulation of the planar cell polarity in endothelial cells in response to hemodynamic shear stress. In the process, low expression of TET1s induced by oscillatory shear stress led to the endothelial planar polarity damage through inhibition of F-actin polymerization. TET1s can regulate demethylation level of the sFRP-1 promoter to alter the expression of sFRP-1, which affects the interaction of sFRP-1/Fzd4 and F-actin polymerization. Our study revealed the mechanism of how TET1s mediates endothelial planar cell polarity in response to hemodynamic shear stress and provides a new insight for the prevention of atherosclerosis.

Endothelial-specific loss of IKKβ disrupts pulmonary endothelial angiogenesis and impairs postnatal lung growth

Pulmonary angiogenesis drives alveolarization, but the transcriptional regulators directing pulmonary angiogenesis remain poorly defined. Global, pharmacological inhibition of nuclear factor-kappa B (NF-κB) impairs pulmonary angiogenesis and alveolarization. However, establishing a definitive role for NF-κB in pulmonary vascular development has been hindered by embryonic lethality induced by constitutive deletion of NF-κB family members. We created a mouse model allowing inducible deletion of the NF-κB activator, IKKβ, in endothelial cells (ECs) and assessed the effect on lung structure, endothelial angiogenic function, and the lung transcriptome. Embryonic deletion of IKKβ permitted lung vascular development but resulted in a disorganized vascular plexus, while postnatal deletion significantly decreased radial alveolar counts, vascular density, and proliferation of both endothelial and nonendothelial lung cells. Loss of IKKβ impaired survival, proliferation, migration, and angiogenesis in primary lung ECs in vitro, in association with decreased expression of VEGFR2 and activation of downstream effectors. Loss of endothelial IKKβ in vivo induced broad changes in the lung transcriptome with downregulation of genes related to mitotic cell cycle, extracellular matrix (ECM)-receptor interaction, and vascular development, and the upregulation of genes related to inflammation. Computational deconvolution suggested that loss of endothelial IKKβ decreased general capillary, aerocyte capillary, and alveolar type I cell abundance. Taken together, these data definitively establish an essential role for endogenous endothelial IKKβ signaling during alveolarization. A deeper understanding of the mechanisms directing this developmental, physiological activation of IKKβ in the lung vasculature may provide novel targets for the development of strategies to enhance beneficial proangiogenic signaling in lung development and disease.NEW & NOTEWORTHY This study highlights the cell-specific complexity of nuclear factor kappa B signaling in the developing lung by demonstrating that inducible loss of IKKβ in endothelial cells impairs alveolarization, disrupts EC angiogenic function, and broadly represses genes important for vascular development.

Spatial and temporal regulation of Wnt signaling pathway members in the development of butterfly wing patterns

Wnt signaling members are involved in the differentiation of cells associated with eyespot and band color patterns on the wings of butterflies, but the identity and spatio-temporal regulation of specific Wnt pathway members remains unclear. Here, we explore the localization and function of Armadillo/β-catenin dependent (canonical) and Armadillo/β-catenin independent (noncanonical) Wnt signaling in eyespot and band development in Bicyclus anynana by localizing Armadillo (Arm), the expression of all eight Wnt ligand and four frizzled receptor transcripts present in the genome of this species and testing the function of some of the ligands and receptors using CRISPR-Cas9. We show that distinct Wnt signaling pathways are essential for eyespot and band patterning in butterflies and are likely interacting to control their active domains.

Planar cell polarity regulators in asymmetric organogenesis during development and disease

The phenomenon of planar cell polarity is critically required for a myriad of morphogenetic processes in metazoan and is accurately controlled by several conserved modules. Six "core" proteins, including Frizzled, Flamingo (Celsr), Van Gogh (Vangl), Dishevelled, Prickle, and Diego (Ankrd6), are major components of the Wnt/planar cell polarity pathway. The Fat/Dchs protocadherins and the Scrib polarity complex also function to instruct cellular polarization. In vertebrates, all these pathways are essential for tissue and organ morphogenesis, such as neural tube closure, left-right symmetry breaking, heart and gut morphogenesis, lung and kidney branching, stereociliary bundle orientation, and proximal-distal limb elongation. Mutations in planar polarity genes are closely linked to various congenital diseases. Striking advances have been made in deciphering their contribution to the establishment of spatially oriented pattern in developing organs and the maintenance of tissue homeostasis. The challenge remains to clarify the complex interplay of different polarity pathways in organogenesis and the link of cell polarity to cell fate specification. Interdisciplinary approaches are also important to understand the roles of mechanical forces in coupling cellular polarization and differentiation. This review outlines current advances on planar polarity regulators in asymmetric organ formation, with the aim to identify questions that deserve further investigation.

A single-cell comparison of adult and fetal human epicardium defines the age-associated changes in epicardial activity

Re-activating quiescent adult epicardium represents a potential therapeutic approach for human cardiac regeneration. However, the exact molecular differences between inactive adult and active fetal epicardium are not known. In this study, we combined fetal and adult human hearts using single-cell and single-nuclei RNA sequencing and compared epicardial cells from both stages. We found that a migratory fibroblast-like epicardial population only in the fetal heart and fetal epicardium expressed angiogenic gene programs, whereas the adult epicardium was solely mesothelial and immune responsive. Furthermore, we predicted that adult hearts may still receive fetal epicardial paracrine communication, including WNT signaling with endocardium, reinforcing the validity of regenerative strategies that administer or reactivate epicardial cells in situ. Finally, we explained graft efficacy of our human embryonic stem-cell-derived epicardium model by noting its similarity to human fetal epicardium. Overall, our study defines epicardial programs of regenerative angiogenesis absent in adult hearts, contextualizes animal studies and defines epicardial states required for effective human heart regeneration.

Morphological Characteristics and Transcriptome Landscapes of Chicken Follicles during Selective Development

Ovarian follicle selection largely depends on the transition of granulosa cells from an undifferentiated to a fully differentiated state, which is accompanied by morphological and functional changes in follicles. The processes and transcriptional regulation of follicles during follicle selection are unclear; we thus used follicles from the prehierarchal to the hierarchal stage to investigate histology, reproductive endocrinology, and transcription. The morphology of follicles changed markedly during follicle selection. The numbers of large white, small yellow, and large yellow follicles (LWF, SYF, and LYF, respectively) were 11.83 ± 2.79, 6.83 ± 2.23, and 1.00, respectively, per ovary. LYF showed thicker granulosa cell layers than those of other prehierarchal follicles. Progesterone concentrations were significantly higher in LYF than that in LWF and SYF. In total, 16,823 genes were positively expressed in LWF, SYF, and LYF. Among follicle types, 1,290 differentially expressed genes were enriched regarding cell differentiation, blood vessel morphogenesis, and response to steroid hormones. Candidate genes associated with follicle selection participated in the Wnt signaling pathway, steroid hormone biosynthesis, and the TGF-β signaling pathway. We produced insights into crucial morphological characteristics of transcriptional regulation in follicle development. Our results provide an important basis for revealing the mechanism of follicle selection and potential impact on the poultry industry.

KIF26B Silencing Prevents Osseous Transdifferentiation of Progenitor/Stem Cells and Attenuates Ectopic Calcification in a Murine Model

Ectopic calcification is an osteogenic process that leads to the formation of inappropriate bone within intra-articular soft tissues, often in response to injury or surgery. The molecular mechanisms governing this phenotype have yet to be determined. Using a population genetics approach, we identified an association of the kinesin superfamily member 26b (Kif26b) with injury-induced ectopic calcification through quantitative trait locus analysis of recombinant inbred mouse strains, consistent with a genomewide association study that identified KIF26B as a severity locus for ectopic calcification in patients with hip osteoarthritis. Despite these associations of KIF26B with ectopic calcification, its mechanistic role and functional implications have not yet been fully elucidated. Here, we aim to decipher the functional role of KIF26B in osseous and chondrogenic transdifferentiation of human and murine progenitor/stem cells and in a murine model of non-invasive injury-induced intra-articular ectopic calcification. We found that KIF26B ablation via lentivirus-mediated shRNA significantly arrested osteogenesis of progenitor/stem cells and suppressed the expression of typical osteogenic marker genes. Conversely, KIF26B loss-of-function increased chondrogenesis as demonstrated by enhanced Safranin-O staining and by the elevated expression of chondrogenic marker genes. Furthermore, cell function analysis revealed that KIF26B knockdown significantly decreased cell viability and proliferation and induced cellular apoptosis. Mechanistically, loss of osteogenesis was reverted by the addition of a Wnt agonist, SKL2001, demonstrating a role of KIF26B in canonical Wnt/β-catenin signaling. Finally, intra-articular delivery of Kif26b shRNA in B6-129SF2/J mice significantly hampered the development of intra-articular ectopic calcification at 8 weeks after injury compared with mice treated with non-target scrambled shRNA. In summary, these observations highlight that KIF26B plays a crucial role in ectopic bone formation by repressing osteogenesis, but not chondrogenesis, potentially via modulating Wnt/β-catenin signaling. These findings establish KIF26B as a critical determinant of the osteogenic process in pathologic endochondral bone formation and an actionable target for pharmacotherapy to mitigate ectopic calcification (and heterotopic ossification). © 2021 American Society for Bone and Mineral Research (ASBMR).

Unlocking the Wnt pathway: Therapeutic potential of selective targeting FZD7 in cancer

The Wnt signaling is of paramount pathophysiological importance. Despite showing promising anticancer activities in pre-clinical studies, current Wnt pathway inhibitors face complications in clinical trials resulting from on-target toxicity. Hence, the targeting of pathway component(s) that are essential for cancer but dispensable for normal physiology is key to the development of a safe Wnt signaling inhibitor. Frizzled₇ (FZD₇) is a Wnt pathway receptor that is redundant in healthy tissues but crucial in various cancers. FZD₇ modulates diverse aspects of carcinogenesis, including cancer growth, metastasis, maintenance of cancer stem cells, and chemoresistance. In this review, we describe state-of-the-art knowledge of the functions of FZD₇ in carcinogenesis and adult tissue homeostasis. Next, we overview the development of small molecules and biomolecules that target FZD₇. Finally, we discuss challenges and possibilities in developing FZD₇-selective antagonists.

Activation of Frizzled-7 attenuates blood-brain barrier disruption through Dvl/β-catenin/WISP1 signaling pathway after intracerebral hemorrhage in mice

BACKGROUND

Destruction of blood-brain barrier (BBB) ​​is one of the main mechanisms of secondary brain injury following intracerebral hemorrhage (ICH). Frizzled-7 is a key protein expressed on the surface of endothelial cells that controls vascular permeability through the Wnt-canonical pathway involving WNT1-inducible signaling pathway protein 1 (WISPI). This study aimed to investigate the role of Frizzled-7 signaling in BBB preservation after ICH in mice.

METHODS

Adult CD1 mice were subjected to sham surgery or collagenase-induced ICH. Frizzled-7 activation or knockdown was performed by administration of Clustered Regularly Interspaced Palindromic Repeats (CRISPR) by intracerebroventricular injection at 48 h before ICH induction. WISP1 activation or WISP1 knockdown was performed to evaluate the underlying signaling pathway. Post-ICH assessments included neurobehavior, brain edema, BBB permeability, hemoglobin level, western blot and immunofluorescence.

RESULTS

The brain expressions of Frizzled-7 and WISP1 significantly increased post-ICH. Frizzled-7 was expressed in endothelial cells, astrocytes, and neurons after ICH. Activation of Frizzled-7 significantly improved neurological function, reduced brain water content and attenuated BBB permeability to large molecular weight substances after ICH. Whereas, knockdown of Frizzled-7 worsened neurological function and brain edema after ICH. Activation of Frizzled-7 significantly increased the expressions of Dvl, β-Catenin, WISP1, VE-Cadherin, Claudin-5, ZO-1 and reduced the expression of phospho-β-Catenin. WISP1 knockdown abolished the effects of Frizzled-7 activation on the expressions of VE-Cadherin, Claudin-5 and ZO-1 at 24 h after ICH.

CONCLUSIONS

Frizzled-7 activation potentially attenuated BBB permeability and improved neurological deficits after ICH through Dvl​​/β-Catenin/WISP1 pathway. Frizzled-7 may be a potential target for the development of ICH therapeutic drugs.

Therapies targeting Frizzled-7/β-catenin pathway prevent the development of pathological angiogenesis in an ischemic retinopathy model

Retinopathies remain major causes of visual impairment in diabetic patients and premature infants. Introduction of anti-angiogenic drugs targeting vascular endothelial growth factor (VEGF) has transformed therapy for these proliferative retinopathies. However, limitations associated with anti-VEGF medications require to unravel new pathways of vessel growth to identify potential drug targets. Here, we investigated the role of Wnt/Frizzled-7 (Fzd7) pathway in a mouse model of oxygen-induced retinopathy (OIR). Using transgenic mice, which enabled endothelium-specific and time-specific Fzd7 deletion, we demonstrated that Fzd7 controls both vaso-obliteration and neovascular phases (NV). Deletion of Fzd7 at P12, after the ischemic phase of OIR, prevented formation of aberrant neovessels into the vitreous by suppressing proliferation of endothelial cells (EC) in tufts. Next we validated in vitro two Frd7 blocking strategies: a monoclonal antibody (mAbFzd7) against Fzd7 and a soluble Fzd7 receptor (CRD). In vivo a single intravitreal microinjection of mAbFzd7 or CRD significantly attenuated retinal neovascularization (NV) in mice with OIR. Molecular analysis revealed that Fzd7 may act through the activation of Wnt/β-catenin and Jagged1 expression to control EC proliferation in extra-retinal neovessels. We identified Fzd7/β-catenin signaling as new regulator of pathological retinal NV. Fzd7 appears to be a potent pharmacological target to prevent or treat aberrant angiogenesis of ischemic retinopathies.

Comparison of endothelial promoter efficiency and specificity in mice reveals a subset of Pdgfb-positive hematopoietic cells

Essentials To reliably study the respective roles of blood and endothelial cells in hemostasis, mouse models with a strong and specific endothelial expression of the Cre recombinase are needed. Using mT/mG reporter mice and conditional JAK2V617F/WT mice, we compared Pdgfb-iCreERT2 and Cdh5(PAC)-CreERT2 with well-characterized Tie2-Cre mice. Comparison of recombination efficiency and specificity towards blood lineage reveals major differences between endothelial transgenic mice. Cre-mediated recombination occurs in a small number of adult hematopoietic stem cells in Pdgfb-iCreERT2;JAK2V617F/WT transgenic mice. SUMMARY: Background The vessel wall, and particularly blood endothelial cells (BECs), are intensively studied to better understand hemostasis and target thrombosis. To understand the specific role of BECs, it is important to have mouse models that allow specific and homogeneous expression of genes of interest in all BEC beds without concomitant expression in blood cells. Inducible Pdgfb-iCreERT2 and Cdh5(PAC)-CreERT2 transgenic mice are widely used for BEC targeting. However, issues remain in terms of recombination efficiency and specificity regarding hematopoietic cells. Objectives To determine which mouse model to choose when strong expression of a transgene is required in adult BECs from various organs, without concomitant expression in hematopoietic cells. Methods Using mT/mG reporter mice to measure recombination efficiency and conditional JAK2V617F/WT mice to assess specificity regarding hematopoietic cells, we compared Pdgfb-iCreERT2 and Cdh5(PAC)-CreERT2 with well-characterized Tie2-Cre mice. Results Adult Cdh5(PAC)-CreERT2 mice are endothelial specific but require a dose of 10 mg of tamoxifen to allow constant Cre expression. Pdgfb-iCreERT2 mice injected with 5 mg of tamoxifen are appropriate for most endothelial research fields except liver studies, as hepatic sinusoid ECs are not recombined. Surprisingly, 2 months after induction of Cre-mediated recombination, all Pdgfb-iCreERT2;JAK2V617F/WT mice developed a myeloproliferative neoplasm that is related to the presence of JAK2V617F in hematopoietic cells, showing for the first time that Cre-mediated recombination occurs in a small number of adult hematopoietic stem cells in Pdgfb-iCreERT2 transgenic mice. Conclusion This study provides useful guidelines for choosing the best mouse line to study the role of BECs in hemostasis and thrombosis.

Structure-guided design fine-tunes pharmacokinetics, tolerability, and antitumor profile of multispecific frizzled antibodies

Aberrant activation of Wnt/β-catenin signaling occurs frequently in cancer. However, therapeutic targeting of this pathway is complicated by the role of Wnt in stem cell maintenance and tissue homeostasis. Here, we evaluated antibodies blocking 6 of the 10 human Wnt/Frizzled (FZD) receptors as potential therapeutics. Crystal structures revealed a common binding site for these monoclonal antibodies (mAbs) on FZD, blocking the interaction with the Wnt palmitoleic acid moiety. However, these mAbs displayed gastrointestinal toxicity or poor plasma exposure in vivo. Structure-guided engineering was used to refine the binding of each mAb for FZD receptors, resulting in antibody variants with improved in vivo tolerability and developability. Importantly, the lead variant mAb significantly inhibited tumor growth in the HPAF-II pancreatic tumor xenograft model. Taken together, our data demonstrate that anti-FZD cancer therapeutic antibodies with broad specificity can be fine-tuned to navigate in vivo exposure and tolerability while driving therapeutic efficacy.

Planar cell polarity protein Dishevelled 3 (Dvl3) regulates ectoplasmic specialization (ES) dynamics in the testis through changes in cytoskeletal organization

In the mammalian testes, such as in rats, the directional alignment of polarized elongating/elongated spermatids, in particular step 17–19 spermatids, across the plane of seminiferous epithelium resembles planar cell polarity (PCP) found in hair cells of the cochlea. It is obvious that spermatid PCP is necessary to support the simultaneous development of maximal number of elongating/elongated spermatids to sustain the daily production of > 50 million sperm per adult rat. Studies have shown that the testis indeed expresses multiple PCP proteins necessary to support spermatid PCP. Herein, using physiological and biochemical assays, and morphological analysis, and with the technique of RNA interference (RNAi) to knockdown PCP protein Dishevelled (Dvl) 1 (Dvl1), Dvl2, Dvl3, or Dvl1/2/3, Dvl proteins, in particular Dvl3, it was shown that Dvl3 played a crucial role of support Sertoli cell tight junction (TJ)-permeability barrier function through changes in the organization of actin- and microtubule (MT)-based cytoskeletons. More important, an in vivo knockdown of Dvl1/2/3 in the testis, defects of spermatid polarity were remarkably noted across the seminiferous epithelium, concomitant with defects of spermatid adhesion and spermatid transport, leading to considerably defects in spermatogenesis. More important, Dvl1/2/3 triple knockdown in the testis also impeded the organization of actin- and MT-based cytoskeletons owing to disruptive spatial expression of actin- and MT-regulatory proteins. In summary, PCP Dishevelled proteins, in particular, Dvl3 is a regulator of Sertoli cell blood–testis barrier (BTB)  and also spermatid PCP function through its effects on the actin- and MT-based cytoskeletons in Sertoli cells.

WNT Signaling in Cardiac and Vascular Disease

WNT signaling is an elaborate and complex collection of signal transduction pathways mediated by multiple signaling molecules. WNT signaling is critically important for developmental processes, including cell proliferation, differentiation and tissue patterning. Little WNT signaling activity is present in the cardiovascular system of healthy adults, but reactivation of the pathway is observed in many pathologies of heart and blood vessels. The high prevalence of these pathologies and their significant contribution to human disease burden has raised interest in WNT signaling as a potential target for therapeutic intervention. In this review, we first will focus on the constituents of the pathway and their regulation and the different signaling routes. Subsequently, the role of WNT signaling in cardiovascular development is addressed, followed by a detailed discussion of its involvement in vascular and cardiac disease. After highlighting the crosstalk between WNT, transforming growth factor-β and angiotensin II signaling, and the emerging role of WNT signaling in the regulation of stem cells, we provide an overview of drugs targeting the pathway at different levels. From the combined studies we conclude that, despite the sometimes conflicting experimental data, a general picture is emerging that excessive stimulation of WNT signaling adversely affects cardiovascular pathology. The rapidly increasing collection of drugs interfering at different levels of WNT signaling will allow the evaluation of therapeutic interventions in the pathway in relevant animal models of cardiovascular diseases and eventually in patients in the near future, translating the outcomes of the many preclinical studies into a clinically relevant context.

Collagen triple helix repeat containing 1 promotes tumor angiogenesis in gastrointestinal stromal tumors

Collagen triple helix repeat containing 1 (Cthrc1) is a secreted protein that has been observed to lead to poorer prognosis by inducing the invasion and metastasis in different tumors; however, it has not been demonstrated that Cthrc1 is involved in tumor angiogenesis. Immunohistochemical staining of Cthrc1 and CD31 in gastrointestinal stromal tumor tissue demonstrated that Cthrc1 is associated with microvascular density. Overexpression of Cthrc1 protein may alter the properties of human umbilical vein endothelial cells (HUVECs), including migration, invasion, tubule formation and aortic ring sprouting. Small interfering RNA-mediated knockdown of Cthrc1 was performed to verify the opposite effects. Migration and tubule formation induced by Cthrc1 overexpression in HUVECs was attenuated by inhibition of phosphorylation in extracellular-signal-regulated protein kinase (ERK) and c-Jun N-terminal kinase (JNK) signaling pathways. The pro-angiogenic effect of Cthcr1 is associated with increased phosphorylation of ERK and JNK in HUVECs. Silencing the expression of Cthrc1 protein may be a promising strategy to inhibit tumor angiogenesis.

WNT signaling - lung cancer is no exception

Since the initial discovery of the oncogenic activity of WNT ligands our understanding of the complex roles for WNT signaling pathways in lung cancers has increased substantially. In the current review, the various effects of activation and inhibition of the WNT signaling pathways are summarized in the context of lung carcinogenesis. Recent evidence regarding WNT ligand transport mechanisms, the role of WNT signaling in lung cancer angiogenesis and drug transporter regulation and the importance of microRNA and posttranscriptional regulation of WNT signaling are also reviewed.

Earliest phases of chondrogenesis are dependent upon angiogenesis during ectopic bone formation in mice

Endochondral ossification is the process where cartilage forms prior to ossification and in which new bone forms during both fracture healing and ectopic bone formation. Transitioning to ossification is a highly coordinated process between hypertrophic chondrocytes, vascular endothelial cells, osteoblasts and osteoclasts. A critical biological process that is central to the interactions of these various cell types is angiogenesis. Although it is well established that angiogenesis is crucial for fracture repair, less is known pertaining to the role of angiogenesis in ectopic bone formation. Furthermore, fracture repair models are complicated by extensive trauma, subsequent inflammatory responses and concurrent repair processes in multiple tissues. In order to more definitively characterize the relationship between angiogenesis and postnatal endochondral ossification, a model of ectopic bone formation was used. Human demineralized bone matrix (DBM) was implanted in immune-deficient mice (rag null (B6.129S7-Rag1^tm1/MOM/J)) to induce ectopic bone. Inhibition of angiogenesis with either a small molecule (TNP-470) or a targeted biological (Vascular Endothelial Growth Factor Receptor type 2 [VEGFR2] blocking antibody) prevented ectopic bone formation by 83% and 77%, respectively. Most striking was that the progression of chondrogenesis was halted during very early phases of chondrocyte differentiation between condensation and prehypertrophy (TNP-470) or the proliferative phase (VEGFR2 blockade) prior to hypertrophy, while osteoclast recruitment and resorption were almost completely inhibited. Our results demonstrate angiogenesis plays a developmental role in endochondral bone formation at a much earlier phase of chondrogenesis than suggested by prior findings.

Reduced Frizzled Receptor 4 Expression Prevents WNT/β-Catenin-driven Alveolar Lung Repair in Chronic Obstructive Pulmonary Disease

RATIONALE

Chronic obstructive pulmonary disease (COPD), in particular emphysema, is characterized by loss of parenchymal alveolar tissue and impaired tissue repair. Wingless and INT-1 (WNT)/β-catenin signaling is reduced in COPD; however, the mechanisms thereof, specifically the role of the frizzled (FZD) family of WNT receptors, remain unexplored.

OBJECTIVES

To identify and functionally characterize specific FZD receptors that control downstream WNT signaling in impaired lung repair in COPD.

METHODS

FZD expression was analyzed in lung homogenates and alveolar epithelial type II (ATII) cells of never-smokers, smokers, patients with COPD, and two experimental COPD models by quantitative reverse transcriptase-polymerase chain reaction, immunoblotting, and immunofluorescence. The functional effects of cigarette smoke on FZD4, WNT/β-catenin signaling, and elastogenic components were investigated in primary ATII cells in vitro and in three-dimensional lung tissue cultures ex vivo. Gain- and loss-of-function approaches were applied to determine the effects of FZD4 signaling on alveolar epithelial cell wound healing and repair, as well as on expression of elastogenic components.

MEASUREMENTS AND MAIN RESULTS

FZD4 expression was reduced in human and experimental COPD lung tissues as well as in primary human ATII cells from patients with COPD. Cigarette smoke exposure down-regulated FZD4 expression in vitro and in vivo, along with reduced WNT/β-catenin activity. Inhibition of FZD4 decreased WNT/β-catenin-driven epithelial cell proliferation and wound closure, and it interfered with ATII-to-ATI cell transdifferentiation and organoid formation, which were augmented by FZD4 overexpression. Moreover, FZD4 restoration by overexpression or pharmacological induction led to induction of WNT/β-catenin signaling and expression of elastogenic components in three-dimensional lung tissue cultures ex vivo.

CONCLUSIONS

Reduced FZD4 expression in COPD contributes to impaired alveolar repair capacity.

The many postures of noncanonical Wnt signaling in development and diseases

Wnt signaling regulates many aspects of vertebrate development. Its dysregulation causes developmental defects and diseases including cancer. The signaling can be categorized in two pathways: canonical and noncanonical. Canonical pathway plays a key role in regulating proliferation and differentiation of cells whilst noncanonical Wnt signaling mainly controls cellular polarity and motility. During development, noncanonical Wnt signaling is required for tissue formation. Recent studies have shown that noncanonical Wnt signaling is involved in adult tissue development and cancer progression. In this review, we try to describe and discuss the mechanisms behind the biological effects of noncanonical Wnt signaling, diseases caused by its dysregulation, and implications in adult tissue development biology.

Planar cell polarity genes frizzled4 and frizzled6 exert patterning influence on arterial vessel morphogenesis

Quantitative analysis of the vascular network anatomy is critical for the understanding of the vasculature structure and function. In this study, we have combined microcomputed tomography (microCT) and computational analysis to provide quantitative three-dimensional geometrical and topological characterization of the normal kidney vasculature, and to investigate how 2 core genes of the Wnt/planar cell polarity, Frizzled4 and Frizzled6, affect vascular network morphogenesis. Experiments were performed on frizzled4 (Fzd4^-/-) and frizzled6 (Fzd6^-/-) deleted mice and littermate controls (WT) perfused with a contrast medium after euthanasia and exsanguination. The kidneys were scanned with a high-resolution (16 μm) microCT imaging system, followed by 3D reconstruction of the arterial vasculature. Computational treatment includes decomposition of 3D networks based on Diameter-Defined Strahler Order (DDSO). We have calculated quantitative (i) Global scale parameters, such as the volume of the vasculature and its fractal dimension (ii) Structural parameters depending on the DDSO hierarchical levels such as hierarchical ordering, diameter, length and branching angles of the vessel segments, and (iii) Functional parameters such as estimated resistance to blood flow alongside the vascular tree and average density of terminal arterioles. In normal kidneys, fractal dimension was 2.07±0.11 (n = 7), and was significantly lower in Fzd4^-/- (1.71±0.04; n = 4), and Fzd6^-/- (1.54±0.09; n = 3) kidneys. The DDSO number was 5 in WT and Fzd4^-/-, and only 4 in Fzd6^-/-. Scaling characteristics such as diameter and length of vessel segments were altered in mutants, whereas bifurcation angles were not different from WT. Fzd4 and Fzd6 deletion increased vessel resistance, calculated using the Hagen-Poiseuille equation, for each DDSO, and decreased the density and the homogeneity of the distal vessel segments. Our results show that our methodology is suitable for 3D quantitative characterization of vascular networks, and that Fzd4 and Fzd6 genes have a deep patterning effect on arterial vessel morphogenesis that may determine its functional efficiency.

Planar cell polarity (PCP) proteins and spermatogenesis

In adult mammalian testes, spermatogenesis is comprised of several discrete cellular events that work in tandem to support the transformation and differentiation of diploid spermatogonia to haploid spermatids in the seminiferous epithelium during the seminiferous epithelial cycle. These include: self-renewal of spermatogonial stem cells via mitosis and their transformation into differentiated spermatogonia, meiosis I/II, spermiogenesis and the release of sperms at spermiation. Studies have shown that these cellular events are under precise and coordinated controls of multiple proteins and signaling pathways. These events are also regulated by polarity proteins that are known to confer classical apico-basal (A/B) polarity in other epithelia. Furthermore, spermatid development is likely supported by planar cell polarity (PCP) proteins since polarized spermatids are aligned across the plane of seminiferous epithelium in an orderly fashion, analogous to hair cells in the cochlea of the inner ear. Thus, the maximal number of spermatids can be packed and supported by a fixed population of differentiated Sertoli cells in the limited space of the seminiferous epithelium in adult testes. In this review, we briefly summarize recent findings regarding the role of PCP proteins in the testis. This information should be helpful in future studies to better understand the role of PCP proteins in spermatogenesis.

Fzd7 (Frizzled-7) Expressed by Endothelial Cells Controls Blood Vessel Formation Through Wnt/β-Catenin Canonical Signaling

OBJECTIVE

Vessel formation requires precise orchestration of a series of morphometric and molecular events controlled by a multitude of angiogenic factors and morphogens. Wnt/frizzled signaling is required for proper vascular formation. In this study, we investigated the role of the Fzd7 (frizzled-7) receptor in retinal vascular development and its relationship with the Wnt/β-catenin canonical pathway and Notch signaling.

APPROACH AND RESULTS

Using transgenic mice, we demonstrated that Fzd7 is required for postnatal vascular formation. Endothelial cell (EC) deletion of fzd7 (fzd7^ECKO) delayed retinal plexus formation because of an impairment in tip cell phenotype and a decrease in stalk cell proliferation. Dvl (dishevelled) proteins are a main component of Wnt signaling and play a functionally redundant role. We found that Dvl3 depletion in dvl1^-/- mice mimicked the fzd7^ECKO vascular phenotype and demonstrated that Fzd7 acted via β-catenin activation by showing that LiCl treatment rescued impairment in tip and stalk cell phenotypes induced in fzd7 mutants. Deletion of fzd7 or Dvl1/3 induced a strong decrease in Wnt canonical genes and Notch partners' expression. Genetic and pharmacological rescue strategies demonstrated that Fzd7 acted via β-catenin activation, upstream of Notch signaling to control Dll4 and Jagged1 EC expression.

CONCLUSIONS

Fzd7 expressed by EC drives postnatal angiogenesis via activation of Dvl/β-catenin signaling and can control the integrative interaction of Wnt and Notch signaling during postnatal angiogenesis.

Distinctive Roles of Canonical and Noncanonical Wnt Signaling in Human Embryonic Cardiomyocyte Development

Wnt signaling is a key regulator of vertebrate heart development; however, specific roles for human cardiomyocyte development remain uncertain. Here we use human embryonic stem cells (hESCs) to analyze systematically in human cardiomyocyte development the expression of endogenous Wnt signaling components, monitor pathway activity, and dissect stage-specific requirements for canonical and noncanonical Wnt signaling mechanisms using small-molecule inhibitors. Our analysis suggests that WNT3 and WNT8A, via FZD7 and canonical signaling, regulate BRACHYURY expression and mesoderm induction; that WNT5A/5B, via ROR2 and noncanonical signaling, regulate MESP1 expression and cardiovascular development; and that later in development WNT2, WNT5A/5B, and WNT11, via FZD4 and FZD6, regulate functional cardiomyocyte differentiation via noncanonical Wnt signaling. Our findings confirm in human development previously proposed roles for canonical Wnt signaling in sequential stages of vertebrate cardiomyogenesis, and identify more precise roles for noncanonical signaling and for individual Wnt signal and Wnt receptor genes in human cardiomyocyte development.

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hESCs were used to study Wnt signaling during human cardiomyocyte development

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Previously proposed roles for canonical Wnt signaling were confirmed in human

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Specific roles for noncanonical Wnt signaling were identified in cardiomyogenesis

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Individual Wnt signal and receptor genes were identified in human cardiomyogenesis

Wnt signaling pathway in retinal vascularization

Wnt-signaling, a ubiquitous pathway that directs differentiation, cell polarity, and tissue specificity, has been implicated as an important gene-expression pathway in retinal development. An increasing body of evidence supports the importance of Wnt-signaling, and specifically, norrin-mediated Wnt-signaling in retinal development and retinal maintenance. Gene mutations affecting the Wnt-signaling pathways result in a variety of inherited vitreoretinopathies. Additionally, there is growing evidence that prematurity and associated retinopathy are associated with alterations in the Wnt-signaling pathways. Further investigations may allow for improved diagnoses, management, and therapies in the future.

"Decoding" Angiogenesis: New Facets Controlling Endothelial Cell Behavior

Angiogenesis, the formation of new blood vessels, is a unique and crucial biological process occurring during both development and adulthood. A better understanding of the mechanisms that regulates such process is mandatory to intervene in pathophysiological conditions. Here we highlight some recent argument on new players that are critical in endothelial cells, by summarizing novel discoveries that regulate notorious vascular pathways such as Vascular Endothelial Growth Factor (VEGF), Notch and Planar Cell Polarity (PCP), and by discussing more recent findings that put metabolism, redox signaling and hemodynamic forces as novel unforeseen facets in angiogenesis. These new aspects, that critically regulate angiogenesis and vascular homeostasis in health and diseased, represent unforeseen new ground to develop anti-angiogenic therapies.

Endothelial RSPO3 Controls Vascular Stability and Pruning through Non-canonical WNT/Ca(2+)/NFAT Signaling

The WNT signaling enhancer R-spondin3 (RSPO3) is prominently expressed in the vasculature. Correspondingly, embryonic lethality of Rspo3-deficient mice is caused by vessel remodeling defects. Yet the mechanisms underlying vascular RSPO3 function remain elusive. Inducible endothelial Rspo3 deletion (Rspo3-iECKO) resulted in perturbed developmental and tumor vascular remodeling. Endothelial cell apoptosis and vascular pruning led to reduced microvessel density in Rspo3-iECKO mice. Rspo3-iECKO mice strikingly phenocopied the non-canonical WNT signaling-induced vascular defects of mice deleted for the WNT secretion factor Evi/Wls. An endothelial screen for RSPO3 and EVI/WLS co-regulated genes identified Rnf213, Usp18, and Trim30α. RNF213 targets filamin A and NFAT1 for proteasomal degradation attenuating non-canonical WNT/Ca(2+) signaling. Likewise, USP18 and TRIM5α inhibited NFAT1 activation. Consequently, NFAT protein levels were decreased in endothelial cells of Rspo3-iECKO mice and pharmacological NFAT inhibition phenocopied Rspo3-iECKO mice. The data identify endothelial RSPO3-driven non-canonical WNT/Ca(2+)/NFAT signaling as a critical maintenance pathway of the remodeling vasculature.

Kif26b controls endothelial cell polarity through the Dishevelled/Daam1-dependent planar cell polarity-signaling pathway

Angiogenesis involves the coordinated growth and migration of endothelial cells (ECs) toward a proangiogenic signal. The Wnt planar cell polarity (PCP) pathway, through the recruitment of Dishevelled (Dvl) and Dvl-associated activator of morphogenesis (Daam1), has been proposed to regulate cell actin cytoskeleton and microtubule (MT) reorganization for oriented cell migration. Here we report that Kif26b--a kinesin--and Daam1 cooperatively regulate initiation of EC sprouting and directional migration via MT reorganization. First, we find that Kif26b is recruited within the Dvl3/Daam1 complex. Using a three-dimensional in vitro angiogenesis assay, we show that Kif26b and Daam1 depletion impairs tip cell polarization and destabilizes extended vascular processes. Kif26b depletion specifically alters EC directional migration and mislocalized MT organizing center (MTOC)/Golgi and myosin IIB cell rear enrichment. Therefore the cell fails to establish a proper front-rear polarity. Of interest, Kif26b ectopic expression rescues the siDaam1 polarization defect phenotype. Finally, we show that Kif26b functions in MT stabilization, which is indispensable for asymmetrical cell structure reorganization. These data demonstrate that Kif26b, together with Dvl3/Daam1, initiates cell polarity through the control of PCP signaling pathway-dependent activation.

A comprehensive gene expression analysis at sequential stages of in vitro cardiac differentiation from isolated MESP1-expressing-mesoderm progenitors

In vitro cardiac differentiation of human pluripotent stem cells (hPSCs) closely recapitulates in vivo embryonic heart development, and therefore, provides an excellent model to study human cardiac development. We recently generated the dual cardiac fluorescent reporter MESP1^mCherry/wNKX2-5^eGFP/w line in human embryonic stem cells (hESCs), allowing the visualization of pre-cardiac MESP1+ mesoderm and their further commitment towards the cardiac lineage, marked by activation of the cardiac transcription factor NKX2-5. Here, we performed a comprehensive whole genome based transcriptome analysis of MESP1-mCherry derived cardiac-committed cells. In addition to previously described cardiac-inducing signalling pathways, we identified novel transcriptional and signalling networks indicated by transient activation and interactive network analysis. Furthermore, we found a highly dynamic regulation of extracellular matrix components, suggesting the importance to create a versatile niche, adjusting to various stages of cardiac differentiation. Finally, we identified cell surface markers for cardiac progenitors, such as the Leucine-rich repeat-containing G-protein coupled receptor 4 (LGR4), belonging to the same subfamily of LGR5, and LGR6, established tissue/cancer stem cells markers. We provide a comprehensive gene expression analysis of cardiac derivatives from pre-cardiac MESP1-progenitors that will contribute to a better understanding of the key regulators, pathways and markers involved in human cardiac differentiation and development.

The Intracellular Loop 2 F328S Frizzled-4 Mutation Implicated in Familial Exudative Vitreoretinopathy Impairs Dishevelled Recruitment

Familial exudative vitreoretinopathy (FEVR) is a disease state characterized by aberrant retinal angiogenesis. Norrin-induced activation of Frizzled-4 (Fz4) has a major role in regulating beta-catenin levels in the eye that, in turn, modulate the blood retina barrier (BRB). Here we gain insight on the basis of the pathology of a FEVR implicated F328S Fz4 mutant by study. The receptor exhibits a substantially reduced ability to activate Lef/Tcf-dependent transcription. This impaired activation correlates with a decreased ability to stabilize and recruit Dishevelled-2 (Dvl2) to the cell surface. Aromaticity at position 328 of the intracellular loop 2 (iloop2) is revealed similarly as a prerequisite for Dvl2 recruitment to the Fz4. This aromaticity at 328 enables normal Norrin-induced canonical activation. The corresponding position in iloop2 of other Frizzleds likely functions in Dvl recruitment.

Endothelial miR-17∼92 cluster negatively regulates arteriogenesis via miRNA-19 repression of WNT signaling

The contribution of endothelial-derived miR-17∼92 to ischemia-induced arteriogenesis has not been investigated in an in vivo model. In the present study, we demonstrate a critical role for the endothelial-derived miR-17∼92 cluster in shaping physiological and ischemia-triggered arteriogenesis. Endothelial-specific deletion of miR-17∼92 results in an increase in collateral density limbs and hearts and in ischemic limbs compared with control mice, and consequently improves blood flow recovery. Individual cluster components positively or negatively regulate endothelial cell (EC) functions in vitro, and, remarkably, ECs lacking the cluster spontaneously form cords in a manner rescued by miR-17a, -18a, and -19a. Using both in vitro and in vivo analyses, we identified FZD4 and LRP6 as targets of miR-19a/b. Both of these targets were up-regulated in 17∼92 KO ECs compared with control ECs, and both were shown to be targeted by miR-19 using luciferase assays. We demonstrate that miR-19a negatively regulates FZD4, its coreceptor LRP6, and WNT signaling, and that antagonism of miR-19a/b in aged mice improves blood flow recovery after ischemia and reduces repression of these targets. Collectively, these data provide insights into miRNA regulation of arterialization and highlight the importance of vascular WNT signaling in maintaining arterial blood flow.

Mechanisms of Vessel Pruning and Regression

The field of angiogenesis research has primarily focused on the mechanisms of sprouting angiogenesis. Yet vascular networks formed by vessel sprouting subsequently undergo extensive vascular remodeling to form a functional and mature vasculature. This "trimming" includes distinct processes of vascular pruning, the regression of selected vascular branches. In some situations complete vascular networks may undergo physiological regression. Vessel regression is an understudied yet emerging field of research. This review summarizes the state-of-the-art of vessel pruning and regression with a focus on the cellular processes and the molecular regulators of vessel maintenance and regression.

Mapping the dynamic expression of Wnt11 and the lineage contribution of Wnt11-expressing cells during early mouse development

Planar cell polarity (PCP) signaling is an evolutionarily conserved mechanism that coordinates polarized cell behavior to regulate tissue morphogenesis during vertebrate gastrulation, neurulation and organogenesis. In Xenopus and zebrafish, PCP signaling is activated by non-canonical Wnts such as Wnt11, and detailed understanding of Wnt11 expression has provided important clues on when, where and how PCP may be activated to regulate tissue morphogenesis. To explore the role of Wnt11 in mammalian development, we established a Wnt11 expression and lineage map with high spatial and temporal resolution by creating and analyzing a tamoxifen-inducible Wnt11-CreER BAC (bacterial artificial chromosome) transgenic mouse line. Our short- and long-term lineage tracing experiments indicated that Wnt11-CreER could faithfully recapitulate endogenous Wnt11 expression, and revealed for the first time that cells transiently expressing Wnt11 at early gastrulation were fated to become specifically the progenitors of the entire endoderm. During mid-gastrulation, Wnt11-CreER expressing cells also contribute extensively to the endothelium in both embryonic and extraembryonic compartments, and the endocardium in all chambers of the developing heart. In contrast, Wnt11-CreER expression in the myocardium starts from late-gastrulation, and occurs in three transient, sequential waves: first in the precursors of the left ventricular (LV) myocardium from E7.0 to 8.0; subsequently in the right ventricular (RV) myocardium from E8.0 to 9.0; and finally in the superior wall of the outflow tract (OFT) myocardium from E8.5 to 10.5. These results provide formal genetic proof that the majority of the endocardium and myocardium diverge by mid-gastrulation in the mouse, and suggest a tight spatial and temporal control of Wnt11 expression in the myocardial lineage to coordinate with myocardial differentiation in the first and second heart field progenitors to form the LV, RV and OFT. The insights gained from this study will also guide future investigations to decipher the role of non-canonical Wnt/PCP signaling in endoderm development, vasculogenesis and heart formation.

The ubiquitin ligase PDZRN3 is required for vascular morphogenesis through Wnt/planar cell polarity signalling

Development and stabilization of a vascular plexus requires the coordination of multiple signalling processes. Wnt planar cell polarity (PCP) signalling is critical in vertebrates for diverse morphogenesis events, which coordinate cell orientation within a tissue-specific plane. However, its functional role in vascular morphogenesis is not well understood. Here we identify PDZRN3, an ubiquitin ligase, and report that Pdzrn3 deficiency impairs embryonic angiogenic remodelling and postnatal retinal vascular patterning, with a loss of two-dimensional polarized orientation of the intermediate retinal plexus. Using in vitro and ex vivo Pdzrn3 loss-of-function and gain-of-function experiments, we demonstrate a key role of PDZRN3 in endothelial cell directional and coordinated extension. PDZRN3 ubiquitinates Dishevelled 3 (Dvl3), to promote endocytosis of the Frizzled/Dvl3 complex, for PCP signal transduction. These results highlight the role of PDZRN3 to direct Wnt PCP signalling, and broadly implicate this pathway in the planar orientation and highly branched organization of vascular plexuses.

Canonical WNT signaling components in vascular development and barrier formation

Canonical WNT signaling is required for proper vascularization of the CNS during embryonic development. Here, we used mice with targeted mutations in genes encoding canonical WNT pathway members to evaluate the exact contribution of these components in CNS vascular development and in specification of the blood-brain barrier (BBB) and blood-retina barrier (BRB). We determined that vasculature in various CNS regions is differentially sensitive to perturbations in canonical WNT signaling. The closely related WNT signaling coreceptors LDL receptor-related protein 5 (LRP5) and LRP6 had redundant functions in brain vascular development and barrier maintenance; however, loss of LRP5 alone dramatically altered development of the retinal vasculature. The BBB in the cerebellum and pons/interpeduncular nuclei was highly sensitive to decrements in canonical WNT signaling, and WNT signaling was required to maintain plasticity of barrier properties in mature CNS vasculature. Brain and retinal vascular defects resulting from ablation of Norrin/Frizzled4 signaling were ameliorated by stabilizing β-catenin, while inhibition of β-catenin-dependent transcription recapitulated the vascular development and barrier defects associated with loss of receptor, coreceptor, or ligand, indicating that Norrin/Frizzled4 signaling acts predominantly through β-catenin-dependent transcriptional regulation. Together, these data strongly support a model in which identical or nearly identical canonical WNT signaling mechanisms mediate neural tube and retinal vascularization and maintain the BBB and BRB.

Is Alzheimer's disease related to metabolic syndrome? A Wnt signaling conundrum

Alzheimer's disease (AD) is the most common cause of dementia, affecting more than 36 million people worldwide. AD is characterized by a progressive loss of cognitive functions. For years, it has been thought that age is the main risk factor for AD. Recent studies suggest that life style factors, including nutritional behaviors, play a critical role in the onset of dementia. Evidence about the relationship between nutritional behavior and AD includes the role of conditions such as obesity, hypertension, dyslipidemia and elevated glucose levels. The coexistence of some of these cardio-metabolic risk factors is generally known as metabolic syndrome (MS). Some clinical studies support the role of MS in the onset of AD. However, the cross-talk between the molecular signaling implicated in these disorders is unknown. In the present review, we focus on the molecular correlates that support the relationship between MS and the onset of AD. We also discuss relevant issues such as the role of leptin, insulin and renin-angiotensin signaling in the brain and the possible role of Wnt signaling in both MS and AD. We discuss the evidence supporting the use of ob/ob mice, high-fructose diets, aortic coarctation-induced hypertension and Octodon degus, which spontaneously develops β-amyloid deposits and metabolic derangements, as suitable animal models to address the relationships between MS and AD. Finally, we examine emergent data supporting the role of Wnt signaling in the modulation of AD and MS, implicating this pathway as a therapeutic target in both conditions.

Wnt5a uses CD146 as a receptor to regulate cell motility and convergent extension

Dysregulation of Wnt signalling leads to developmental defects and diseases. Non-canonical Wnt signalling via planar cell polarity proteins regulates cell migration and convergent extension; however, the underlying mechanisms are poorly understood. Here we report that Wnt5a uses CD146 as a receptor to regulate cell migration and zebrafish embryonic convergent extension. CD146 binds to Wnt5a with the high affinity required for Wnt5a-induced activation of Dishevelled (Dvl) and c-jun amino-terminal kinase (JNK). The interaction between CD146 and Dvl2 is enhanced on Wnt5a treatment. Mutation of the Dvl2-binding region impairs its ability to activate JNK, promote cell migration and facilitate the formation of cell protrusions. Knockdown of Dvls impairs CD146-induced cell migration. Interestingly, CD146 inhibits canonical Wnt signalling by promoting β-catenin degradation. Our results suggest a model in which CD146 acts as a functional Wnt5a receptor in regulating cell migration and convergent extension, turning off the canonical Wnt signalling branch.

Endothelial cell-derived non-canonical Wnt ligands control vascular pruning in angiogenesis

Multiple cell types involved in the regulation of angiogenesis express Wnt ligands. Although β-catenin dependent and independent Wnt signaling pathways have been shown to control angiogenesis, the contribution of individual cell types to activate these downstream pathways in endothelial cells (ECs) during blood vessel formation is still elusive. To investigate the role of ECs in contributing Wnt ligands for regulation of blood vessel formation, we conditionally deleted the Wnt secretion factor Evi in mouse ECs (Evi-ECKO). Evi-ECKO mice showed decreased microvessel density during physiological and pathological angiogenesis in the postnatal retina and in tumors, respectively. The reduced microvessel density resulted from increased vessel regression accompanied by decreased EC survival and proliferation. Concomitantly, survival-related genes were downregulated and cell cycle arrest- and apoptosis-inducing genes were upregulated. EVI silencing in cultured HUVECs showed similar target gene regulation, supporting a mechanism of EC-derived Wnt ligands in controlling EC function. ECs preferentially expressed non-canonical Wnt ligands and canonical target gene expression was unaffected in Evi-ECKO mice. Furthermore, the reduced vascularization of Matrigel plugs in Evi-ECKO mice could be rescued by introduction of non-canonical Wnt5a. Treatment of mouse pups with the non-canonical Wnt inhibitor TNP470 resulted in increased vessel regression accompanied by decreased EC proliferation, thus mimicking the proliferation-dependent Evi-ECKO remodeling phenotype. Taken together, this study identified EC-derived non-canonical Wnt ligands as regulators of EC survival, proliferation and subsequent vascular pruning during developmental and pathological angiogenesis.

Frizzled7 controls vascular permeability through the Wnt-canonical pathway and cross-talk with endothelial cell junction complexes

AIMS

Vascular permeability is essential for the health of normal tissues and is an important characteristic of many disease states. The role of the Wnt/frizzled pathway in vascular biology has recently been reported. The objectives of this study are to analyse the role of Frizzled7 (Fzd7) receptor in the control of vascular integrity.

METHODS AND RESULTS

Fzd7 is expressed in endothelial cells and accumulates at the points of cell-cell contact in association with VE-cadherin and β-catenin, two major adherens junction molecules. To selectively delete fzd7 in the vasculature, we developed gene targeting approaches using CreLox strategy in mice. Genetic fzd7 inhibition in the endothelium increases vascular permeability in basal and factor-induced conditions. On the cellular level, fzd7 knockdown or depletion leads to an increase in paracellular permeability with a loss of adherens junction organization. These impairments are associated with a decrease in both VE-Cadherin and β-catenin expression, a decrease in their association and an increase of tyrosine phosphorylation of VE-cadherin/β-catenin. Fzd7 transduces a Wnt/β-catenin signalling cascade that is required to regulate β-catenin and canonical target gene expression. Finally, LiCl, a GSK3 inhibitor, and β-catenin overexpression rescued endothelial integrity and adherens junction organization, induced by fzd7 deletion.

CONCLUSION

These findings establish that Fzd7 is a new partner of adherens junctional complex and represents a novel molecular switch for the control of vascular permeability via activation of the Wnt-canonical pathway.

Planar cell polarity and the kidney

Planar cell polarity (PCP) is the uniform orientation and alignment of a group of cells orthogonal to the apical–basal axis within a tissue. Originally described in insects, it is now known that PCP is required for many processes in vertebrates, including directional cell movement, polarized cell division, ciliary orientation, neural tube closure, heart development and lung branching. In this review, we outline the evidence implicating PCP in kidney development and disease focusing initially on the function of PCP in ureteric bud branching and elongation. We then describe how defects in PCP may lead to polycystic kidney disease and discuss a newly identified role for PCP in the kidney filtration barrier.

Macrophages and angiogenesis: a role for Wnt signaling

Macrophages regulate many developmental and pathological processes in both embryonic and adult tissues, and recent studies have shown a significant role in angiogenesis. Similarly, Wnt signaling is fundamental to tissue morphogenesis and also has a role in vascular development. In this review, we summarize recent advances in the field of macrophage-regulated angiogenesis, with a focus on the role of macrophage-derived Wnt ligands. We review data that provide both direct and indirect evidence for macrophage-derived Wnt regulation of physiologic and pathologic angiogenesis. Finally, we propose that Wnt signaling plays a central role in differentiation of tumor associated and wound infiltrating macrophages to a proangiogenic phenotype.