Lipid modification in Wnt structure and function

Advances in Regenerative Dentistry: A Systematic Review of Harnessing Wnt/β-Catenin in Dentin-Pulp Regeneration

Dentin pulp has a complex function as a major unit in maintaining the vitality of teeth. In this sense, the Wnt/β-Catenin pathway has a vital part in tooth development, maintenance, repair, and regeneration by controlling physiological activities such as growth, differentiation, and migration. This pathway consists of a network of proteins, such as Wnt signaling molecules, which interact with receptors of targeted cells and play a role in development and adult tissue homeostasis. The Wnt signals are specific spatiotemporally, suggesting its intricate mechanism in development, regulation, repair, and regeneration by the formation of tertiary dentin. This review provides an overview of the recent advances in the Wnt/β-Catenin signaling pathway in dentin and pulp regeneration, how different proteins, molecules, and ligands influence this pathway, either upregulating or silencing it, and how it may be used in the future for clinical dentistry, in vital pulp therapy as an effective treatment for dental caries, as an alternative approach for root canal therapy, and to provide a path for therapeutic and regenerative dentistry.

Wnt/β-catenin signaling pathway in carcinogenesis and cancer therapy

The Wnt/β-catenin signaling pathway plays a crucial role in various physiological processes, encompassing development, tissue homeostasis, and cell proliferation. Under normal physiological conditions, the Wnt/β-catenin signaling pathway is meticulously regulated. However, aberrant activation of this pathway and downstream target genes can occur due to mutations in key components of the Wnt/β-catenin pathway, epigenetic modifications, and crosstalk with other signaling pathways. Consequently, these dysregulations contribute significantly to tumor initiation and progression. Therapies targeting the Wnt/β-catenin signaling transduction have exhibited promising prospects and potential for tumor treatment. An increasing number of medications targeting this pathway are continuously being developed and validated. This comprehensive review aims to summarize the latest advances in our understanding of the role played by the Wnt/β-catenin signaling pathway in carcinogenesis and targeted therapy, providing valuable insights into acknowledging current opportunities and challenges associated with targeting this signaling pathway in cancer research and treatment.

Got WNTS? Insight into bone health from a WNT perspective

WNT signaling, essential for many aspects of development, is among the most commonly altered pathways associated with human disease. While initially studied in cancer, dysregulation of WNT signaling has been determined to be essential for skeletal development and the maintenance of bone health throughout life. In this review, we discuss the role of Wnt signaling in bone development and disease with a particular focus on two areas. First, we discuss the roles of WNT signaling pathways in skeletal development, with an emphasis on congenital and idiopathic skeletal syndromes and diseases that are associated with genetic variations in WNT signaling components. Next, we cover a topic that has long been an interest of our laboratory, how high and low levels of WNT signaling affects the establishment and maintenance of healthy bone mass. We conclude with a discussion of the status of WNT-based therapeutics in the treatment of skeletal disease.

miR-26b-5p/TCF-4 Controls the Adipogenic Differentiation of Human Adipose-derived Mesenchymal Stem Cells

In this study, we assessed the ability of miR-26b-5p to regulate T cell factor 4 (TCF-4) expression and thereby control human adipose-derived mesenchymal stem cell (hADMSC) adipogenic differentiation. Adipogenic medium was used to induce hADMSC differentiation over a 6-d period. The ability of miR-26b-5p to interact with the TCF-4 mRNA was confirmed through both predictive bioinformatics analyses and luciferase reporter assays. Immunofluorescent staining was used to visualize the impact of miR-26b-5p inhibition or overexpression on TCF-4 and β-catenin levels in hADMSCs. Further functional analyses were conducted by transfecting these cells with siRNAs specific for TCF-4 and β-catenin. Adipogenic marker and Wnt/β-catenin pathway gene expression levels were assessed via real-time polymerase chain reaction and western blotting. β-catenin localization was assessed via immunofluorescent staining. As expected, our adipogenic media induced the adipocytic differentiation of hADMSCs. In addition, we confirmed that TCF-4 is an miR-26b-5p target gene in these cells, and that protein levels of both TCF-4 and β-catenin were reduced when these cells were transfected with miR-26b-5p mimics. Overexpression of this microRNA also enhanced hADMSC adipogenesis, whereas TCF-4 and β-catenin overexpression inhibited this process. The enhanced hADMSC adipogenic differentiation that was observed following TCF-4 or β-catenin knockdown was partially reversed when miR-26b-5p expression was inhibited. We found that miR-26b-5p serves as a direct negative regulator of TCF-4 expression within hADMSCs, leading to inactivation of the Wnt/β-catenin pathway and thereby promoting the adipogenic differentiation of these cells in vitro.

Wnt-controlled sphingolipids modulate Anthrax Toxin Receptor palmitoylation to regulate oriented mitosis in zebrafish

Oriented cell division is a fundamental mechanism to control asymmetric stem cell division, neural tube elongation and body axis extension, among other processes. During zebrafish gastrulation, when the body axis extends, dorsal epiblast cells display divisions that are robustly oriented along the animal-vegetal embryonic axis. Here, we use a combination of lipidomics, metabolic tracer analysis and quantitative image analysis to show that sphingolipids mediate spindle positioning during oriented division of epiblast cells. We identify the Wnt signaling as a regulator of sphingolipid synthesis that mediates the activity of serine palmitoyltransferase (SPT), the first and rate-limiting enzyme in sphingolipid production. Sphingolipids determine the palmitoylation state of the Anthrax receptor, which then positions the mitotic spindle of dividing epiblast cells. Our data show how Wnt signaling mediates sphingolipid-dependent oriented division and how sphingolipids determine Anthrax receptor palmitoylation, which ultimately controls the activation of Diaphanous to mediate spindle rotation and oriented mitosis.

During development, oriented cell division is important to proper body axis extension. Here, the authors show that sphingolipids are required to direct spindle rotation and oriented mitosis via Anthrax receptor palmitoylation in zebrafish gastrulation.

Regulation of Wnt Signaling through Ubiquitination and Deubiquitination in Cancers

The Wnt signaling pathway plays important roles in embryonic development, homeostatic processes, cell differentiation, cell polarity, cell proliferation, and cell migration via the β-catenin binding of Wnt target genes. Dysregulation of Wnt signaling is associated with various diseases such as cancer, aging, Alzheimer’s disease, metabolic disease, and pigmentation disorders. Numerous studies entailing the Wnt signaling pathway have been conducted for various cancers. Diverse signaling factors mediate the up- or down-regulation of Wnt signaling through post-translational modifications (PTMs), and aberrant regulation is associated with several different malignancies in humans. Of the numerous PTMs involved, most Wnt signaling factors are regulated by ubiquitination and deubiquitination. Ubiquitination by E3 ligase attaches ubiquitins to target proteins and usually induces proteasomal degradation of Wnt signaling factors such as β-catenin, Axin, GSK3, and Dvl. Conversely, deubiquitination induced by the deubiquitinating enzymes (DUBs) detaches the ubiquitins and modulates the stability of signaling factors. In this review, we discuss the effects of ubiquitination and deubiquitination on the Wnt signaling pathway, and the inhibitors of DUBs that can be applied for cancer therapeutic strategies.

The Regulation of Bone Metabolism and Disorders by Wnt Signaling

Wnt, a secreted glycoprotein, has an approximate molecular weight of 40 kDa, and it is a cytokine involved in various biological phenomena including ontogeny, morphogenesis, carcinogenesis, and maintenance of stem cells. The Wnt signaling pathway can be classified into two main pathways: canonical and non-canonical. Of these, the canonical Wnt signaling pathway promotes osteogenesis. Sclerostin produced by osteocytes is an inhibitor of this pathway, thereby inhibiting osteogenesis. Recently, osteoporosis treatment using an anti-sclerostin therapy has been introduced. In this review, the basics of Wnt signaling, its role in bone metabolism and its involvement in skeletal disorders have been covered. Furthermore, the clinical significance and future scopes of Wnt signaling in osteoporosis, osteoarthritis, rheumatoid arthritis and neoplasia are discussed.

Wnt Signaling in Neural Crest Ontogenesis and Oncogenesis

Neural crest (NC) cells are a temporary population of multipotent stem cells that generate a diverse array of cell types, including craniofacial bone and cartilage, smooth muscle cells, melanocytes, and peripheral neurons and glia during embryonic development. Defective neural crest development can cause severe and common structural birth defects, such as craniofacial anomalies and congenital heart disease. In the early vertebrate embryos, NC cells emerge from the dorsal edge of the neural tube during neurulation and then migrate extensively throughout the anterior-posterior body axis to generate numerous derivatives. Wnt signaling plays essential roles in embryonic development and cancer. This review summarizes current understanding of Wnt signaling in NC cell induction, delamination, migration, multipotency, and fate determination, as well as in NC-derived cancers.

WNT5A is transported via lipoprotein particles in the cerebrospinal fluid to regulate hindbrain morphogenesis

WNTs are lipid-modified proteins that control multiple functions in development and disease via short- and long-range signaling. However, it is unclear how these hydrophobic molecules spread over long distances in the mammalian brain. Here we show that WNT5A is produced by the choroid plexus (ChP) of the developing hindbrain, but not the telencephalon, in both mouse and human. Since the ChP produces and secretes the cerebrospinal fluid (CSF), we examine the presence of WNT5A in the CSF and find that it is associated with lipoprotein particles rather than exosomes. Moreover, since the CSF flows along the apical surface of hindbrain progenitors not expressing Wnt5a, we examined whether deletion of Wnt5a in the ChP controls their function and find that cerebellar morphogenesis is impaired. Our study thus identifies the CSF as a route and lipoprotein particles as a vehicle for long-range transport of biologically active WNT in the central nervous system.

Wnt Signaling in Ewing Sarcoma, Osteosarcoma, and Malignant Peripheral Nerve Sheath Tumors

PURPOSE OF REVIEW

Wnt signaling plays a central role in development and homeostasis, and its dysregulation is a common event in many types of human cancer. Here we explore in detail the contributions of Wnt signaling to the initiation and maintenance of three types of saroma: Ewing sarcoma, osteosarcoma, and malignant peripheral nerve sheath tumors. This review provides an overview of the Wnt signaling pathway and explores in detail the current knowledge about its role in the initiation or maintenance of three tumor types: Ewing sarcoma, osteosarcoma, and malignant peripheral nerve sheath tumors.

RECENT FINDINGS

Recent work has assessed the role(s) of Wnt signaling within these cell types. This review provides an overview of the mechanistic insights that have been gained from a number of recent studies to set the foundation for potential therapeutic applications. Wnt signaling has emerged as a potentially critical pathway in maintaining the growth of these types of tumors. Given the fact that many new inhibitors of the pathway have recently or will soon enter Phase 1 clinical trials, it is likely that assessment of their activity in these tumor types will occur in human patients.

Role of the Wnt signaling molecules in the tooth

Wnt signaling plays a central role in many processes during embryonic development and adult homeostasis. At least 19 types of Wnt ligands, receptors, transducers, transcription factors, and antagonists have been identified in mammals. Two distinct Wnt signaling pathways, the canonical signaling pathway and the noncanonical signaling pathway, have been described. Some Wnt signaling pathway components are expressed in the dental epithelium and mesenchyme during tooth development in humans and mice. Functional studies and experimental analysis of relevant animal models confirm the effects of Wnt signaling pathway on the regulation of developing tooth formation and adult tooth homeostasis. Mutations in some Wnt signaling pathway components have been identified in syndromic and non-syndromic tooth agenesis. This review provides an overview of progress in elucidating the role of Wnt signaling pathway components in the tooth and the resulting possibilities for therapeutic development.

Genetically engineered mouse models to evaluate the role of Wnt secretion in bone development and homeostasis

Alterations in components of the Wnt signaling pathway are associated with altered bone development and homeostasis in several human diseases. We created genetically engineered mouse models (GEMMs) that mimic the cellular defect associated with the Porcupine mutations in patients with Goltz Syndrome/Focal Dermal Hypoplasia. These GEMMs were established by utilizing mice containing a conditionally inactivatable allele of Wntless/GPR177 (a gene encoding a protein required for the transport of Porcupine-modified ligand to the plasma membrane for secretion). We crossed this strain to another which drives cre-mediated gene deletion in mature osteoblasts (Osteocalcin-cre) resulted in mice lacking the ability to secrete Wnt ligands in this cell type. These mice displayed severely reduced bone mass and provide a model to understand the effects of disrupting the ability to secrete Wnt ligands on the skeletal system.

Wnt signaling in bone and muscle

Wnt signaling plays key roles in many aspects of development. In this review, we will briefly describe the components of signaling pathways induced by Wnt ligands and then describe the current state of research as this applies to aspects of development and disease as it relates to skeletal muscle and bone. We will conclude with a discussion of the parallels and differences in Wnt signaling in these two contexts and how these pathways are being (or could potentially be) targeted for therapeutic treatment of musculoskeletal diseases. This article is part of a Special Issue entitled "Muscle Bone Interactions".

Distinct requirements for Wntless in habenular development

Secreted Wnt proteins play pivotal roles in development, including regulation of cell proliferation, differentiation, progenitor maintenance and tissue patterning. The transmembrane protein Wntless (Wls) is necessary for secretion of most Wnts and essential for effective Wnt signaling. During a mutagenesis screen to identify genes important for development of the habenular nuclei in the dorsal forebrain, we isolated a mutation in the sole wls gene of zebrafish and confirmed its identity with a second, independent allele. Early embryonic development appears normal in homozygous wls mutants, but they later lack the ventral habenular nuclei, form smaller dorsal habenulae and otic vesicles, have truncated jaw and fin cartilages and lack swim bladders. Activation of a reporter for β-catenin-dependent transcription is decreased in wls mutants, indicative of impaired signaling by the canonical Wnt pathway, and expression of Wnt-responsive genes is reduced in the dorsal diencephalon. Wnt signaling was previously implicated in patterning of the zebrafish brain and in the generation of left-right (L-R) differences between the bilaterally paired dorsal habenular nuclei. Outside of the epithalamic region, development of the brain is largely normal in wls mutants and, despite their reduced size, the dorsal habenulae retain L-R asymmetry. We find that homozygous wls mutants show a reduction in two cell populations that contribute to the presumptive dorsal habenulae. The results support distinct temporal requirements for Wls in habenular development and reveal a new role for Wnt signaling in the regulation of dorsal habenular progenitors.

Isolation and characterization of recombinant murine Wnt3a

Wnt proteins are a family of morphogens that possess potent biological activity. Structure-function studies have been impeded by poor yield of biologically active recombinant Wnt as well as a propensity of isolated Wnt to self-associate in the absence of detergent. Using stably transfected Drosophila S2 cells, studies have been conducted to improve recovery of recombinant murine Wnt3a, establish conditions for a detergent-free Wnt preparation and examine the effects of limited proteolysis. S2 cell culture conditioned media was subjected to a 3-step protocol including dye-ligand chromatography, immobilized metal affinity chromatography and gel filtration chromatography. Through selective pooling of column fractions, homogeneous and purified Wnt3a preparations were obtained. Limited proteolysis of Wnt3a with thrombin resulted in site-specific cleavage within the N-terminal saposin-like motif. To generate detergent-free protein, Wnt3a was immobilized on Cu(2+)-charged, iminodiacetic acid-derivatized Sepharose beads, detergent-free buffer was applied and Wnt3a eluted from the beads with buffer containing imidazole plus 30mM methyl-ß-cyclodextrin (MßCD). Wnt3a recovered in MßCD-containing buffer was soluble and biologically active. Insofar as MßCD is a member of a family of non-toxic, low molecular weight compounds capable of binding and solubilizing small hydrophobic ligands, Wnt-cyclodextrin complexes may facilitate structure-activity studies in the absence of adverse detergent effects.

Regulation of Wnt/β-catenin signaling by posttranslational modifications

The canonical Wnt signaling pathway (or Wnt/β-catenin pathway) plays a pivotal role in embryonic development and adult homeostasis; deregulation of the Wnt pathway contributes to the initiation and progression of human diseases including cancer. Despite its importance in human biology and disease, how regulation of the Wnt/β-catenin pathway is achieved remains largely undefined. Increasing evidence suggests that post-translational modifications (PTMs) of Wnt pathway components are essential for the activation of the Wnt/β-catenin pathway. PTMs create a highly dynamic relay system that responds to Wnt stimulation without requiring de novo protein synthesis and offer a platform for non-Wnt pathway components to be involved in the regulation of Wnt signaling, hence providing alternative opportunities for targeting the Wnt pathway. This review highlights the current status of PTM-mediated regulation of the Wnt/β-catenin pathway with a focus on factors involved in Wnt-mediated stabilization of β-catenin.