Planar cell polarity signaling components are a direct target of β-amyloid–associated degeneration of glutamatergic synapses

The signaling pathway directly controlling the maintenance of adult glutamatergic synapses has not been well understood. Planar cell polarity (PCP) signaling components were recently shown to play essential roles in the formation of glutamatergic synapses. Here, we show that they are localized in the adult synapses and are essential for their maintenance. Synapse loss at early stages of Alzheimer’s disease is thought to be induced by β-amyloid (Aβ) pathology. We found that oligomeric Aβ binds to Celsr3 and assists Vangl2 in disassembling synapses. Moreover, a Wnt receptor and regulator of PCP signaling, Ryk, is also required for Aβ-induced synapse loss. In the 5XFAD mouse model of Alzheimer’s disease, Ryk conditional knockout or a function-blocking monoclonal Ryk antibody protected synapses and preserved cognitive function. We propose that tipping of the fine balance of Wnt/PCP signaling components in glutamatergic synapses may cause synapse degeneration in neurodegenerative disorders with Aβ pathology.

Notch-dependent Abl signaling regulates cell motility during ommatidial rotation in Drosophila

A collective cell motility event that occurs during Drosophila eye development, ommatidial rotation (OR), serves as a paradigm for signaling pathway-regulated directed movement of cell clusters. OR is instructed by several signaling events, including the EGFR and Notch pathways, and planar cell polarity (PCP) signaling, all of which are associated with photoreceptor R3 and R4 specification and differentiation. Here, we show that Abl kinase negatively regulates ommatidial rotation through its activity in the R3/R4 pair. Interestingly in wild-type, Abl is localized to apical junctional regions in R4 but not in R3 during OR, and this apical enrichment requires Notch signaling. We further demonstrate that Abl and Notch genetically interact during OR, and Abl co-immunoprecipitates in complexes with Notch in the developing eye disc. Perturbations of Abl interfere with adherens junction dynamics of the ommatidial preclusters, which are critical for the OR process. Taken together, our data suggest a model in which Abl kinase acts directly downstream of the Notch receptor in R4 to fine-tune OR via its input into adherens junction complexes.

Glypican 4 regulates planar cell polarity of endoderm cells by controlling the localization of Cadherin 2

Non-canonical Wnt/Planar Cell Polarity (Wnt/PCP) signaling has been implicated in endoderm morphogenesis. However, the underlying cellular and molecular mechanisms of this process are unclear. We found that during convergence and extension (C&E) in zebrafish, gut endodermal cells are polarized mediolaterally, with GFP-Vangl2 enriched at the anterior edges. Endoderm cell polarity is lost, and intercalation is impaired, in the absence of glypican 4 (gpc4), a heparan-sulfate proteoglycan that promotes Wnt/PCP signaling, suggesting that this signaling is required for endodermal cell polarity. Live imaging revealed that endoderm C&E is accomplished by polarized cell protrusions and junction remodeling, which are impaired in gpc4-deficient endodermal cells. Furthermore, in the absence of gpc4, Cadherin 2 expression on the endodermal cell surface is increased due to impaired Rab5c-mediated endocytosis, which partially accounts for the endodermal defects in these mutants.These findings indicate that Gpc4 regulates endodermal planar cell polarity during endoderm C&E by influencing localization of Cadherin 2. Thus, our study uncovers a new mechanism by which Gpc4 regulates planar cell polarity and reveals the role of Wnt/PCP signaling in endoderm morphogenesis.

Regulation of Wnt/PCP signaling through p97/VCP-KBTBD7–mediated Vangl ubiquitination and endoplasmic reticulum–associated degradation

The four-pass transmembrane proteins Vangl1 and Vangl2 are dedicated core components of Wnt/planar cell polarity (Wnt/PCP) signaling that critically regulate polarized cell behaviors in many morphological and physiological processes. Here, we found that the abundance of Vangl proteins is tightly controlled by the ubiquitin-proteasome system through endoplasmic reticulum–associated degradation (ERAD). The key ERAD component p97/VCP directly binds to Vangl at a highly conserved VCP-interacting motif and recruits the E3 ligase KBTBD7 via its UBA-UBX adaptors to promote Vangl ubiquitination and ERAD. We found that Wnt5a/CK1 prevents Vangl ubiquitination and ERAD by inducing Vangl phosphorylation, which facilitates Vangl export from the ER to the plasma membrane. We also provide in vivo evidence that KBTBD7 regulates convergent extension during zebrafish gastrulation and functions as a tumor suppressor in breast cancer by promoting Vangl degradation. Our findings reveal a previously unknown regulatory mechanism of Wnt/PCP signaling through the p97/VCP-KBTBD7–mediated ERAD pathway.

Abstract 12540: Neural Crest Cell-derived Wnt5a Regulates Planar Cell Polarity in Cranial Second Heart Field Progenitor Cells

Introduction: Wnt5a is a known regulator of planar cell polarity (PCP) signaling in second heart field (SHF) progenitor cells. It is generally believed that Wnt5a ligands are secreted by the SHF; however, SHF-specific conditional deletion of Wnt5a does not recapitulate outflow tract (OFT) defects observed in global Wnt5a mutants. Hypothesis: Given the proximity and interaction between neural crest cells (NCC) and cranial SHF that contributes to the developing OFT, we hypothesize that NCC may serve as an additional source of Wnt5a for SHF progenitors. Methods: Wnt5a was conditionally deleted in the neural crest using transgenic Wnt1-cre mice. Embryos were harvested from control and mutant litter mates and immunofluoresence, in situ hybridization, and hematoxylin-eosin stains were performed on histologic sections using standard techniques. India ink injections were performed to evaluate pharyngeal arch artery and outflow tract morphology in whole mount embryos. Results: Wnt1-cre driven conditional deletion of Wnt5a in NCC did not impact NCC survival or migration into the developing OFT. However, SHF cells in mutant E10.5 embryos showed altered PCP signaling with reduced phalloidin and laminin expression. The resulting loss in polarized directional movement of the SHF led to reduced incorporation into and elongation of the developing OFT. The shortened OFT was mal-aligned resulting in fully penetrant double outlet right ventricle (DORV) at E14.5. In addition, maturation of pharyngeal arch arteries was also impaired such that all mutants express pharyngeal arch artery defects, including aortic arch abnormalities and aberrant right subclavian artery. In contrast, there was no observed effect on PCP in the more caudal SHF cells, and none of the mutant embryos had inflow tract or venous pole defects. Conclusions: Our results demonstrate that NCC are a novel source of Wnt5a. NCC-derived Wnt5a is critically required to regulate PCP signals in the most cranial SHF regulating the development of the OFT and pharyngeal arch arteries.

Protecting synapses from amyloid β-associated degeneration by manipulations of Wnt/planar cell polarity signaling

ABSTRACTSynapse loss is an early event in Alzheimer’s disease and is thought to be associated with amyloid pathology and caused by Amyloid β (Aβ) oligomers. Whether and how Aβ oligomers directly target signaling pathways for glutamatergic synapse maintenance is unknown. Glutamatergic synapse development is controlled by the opposing functions of Celsr3 and Vangl2, core components of the Wnt/planar cell polarity (PCP) signaling pathway, functioning directly in the synapses. Celsr3 promotes synapse formation, whereas Vangl2 inhibits synapse formation. Here we show that oligomeric Aβ binds to Celsr3 and assists Vangl2 in disassembling synapses by disrupting the intercellular Celsr3/Frizzled3-Celsr3 complex, essential for PCP signaling. Together with Vangl2, a Wnt receptor, Ryk, is also required for Aβ oligomer-induced synapse loss in a mouse model of Alzheimer’s disease, 5XFAD, where conditional Ryk knockout protected synapses and preserved cognitive function. Our study reveals a fine balance of Wnt/PCP signaling components in glutamatergic synapse maintenance and suggests that overproduced Aβ oligomers may lead to excessive synapse loss by tipping this balance. Together with previous reports that an inhibitor of Wnt/Ryk signaling, WIF1, is found reduced in Alzheimer’s disease patients, our results suggest that the imbalance of PCP signaling in these patients may contribute to synapse loss in Alzheimer’s disease and manipulating Wnt/PCP signaling may preserve synapses and cognitive function.

Par protein localization during the early development of Mnemiopsis leidyi suggests different modes of epithelial organization in the metazoa

In bilaterians and cnidarians, epithelial cell-polarity is regulated by the interactions between Par proteins, Wnt/PCP signaling pathway, and cell-cell adhesion. Par proteins are highly conserved across Metazoa, including ctenophores. But strikingly, ctenophore genomes lack components of the Wnt/PCP pathway and cell-cell adhesion complexes raising the question if ctenophore cells are polarized by mechanisms involving Par proteins. Here, by using immunohistochemistry and live-cell imaging of specific mRNAs, we describe for the first time the subcellular localization of selected Par proteins in blastomeres and epithelial cells during the embryogenesis of the ctenophore Mnemiopsis leidyi. We show that these proteins distribute differently compared to what has been described for other animals, even though they segregate in a host-specific fashion when expressed in cnidarian embryos. This differential localization might be related to the emergence of different junctional complexes during metazoan evolution.