Ligand-Selective Wnt Receptor Complexes in CNS Blood Vessels: RECK and GPR124 Plugged In

A Frizzled4-LRP5 agonist promotes blood-retina barrier function by inducing a Norrin-like transcriptional response

Norrin (NDP) and WNT7A/B induce and maintain the blood-brain and blood-retina barrier (BBB, BRB) by stimulating the Frizzled4-LDL receptor related protein 5/6 (FZD4-LRP5/6) complex to induce beta-catenin-dependent signaling in endothelial cells (ECs). Recently developed agonists for the FZD4-LRP5 complex have therapeutic potential in retinal and neurological diseases. Here, we use the tetravalent antibody modality F4L5.13 to identify agonist activities in Tspan12-/- mice, which display a complex retinal pathology due to impaired NDP-signaling. F4L5.13 administration during development alleviates BRB defects, retinal hypovascularization, and restores neural function. In mature Tspan12-/- mice F4L5.13 partially induces a BRB de novo without inducing angiogenesis. In a genetic model of impaired BRB maintenance, administration of F4L5.13 rapidly and substantially restores the BRB. scRNA-seq reveals perturbations of key mediators of barrier functions in juvenile Tspan12-/- mice, which are in large parts restored after F4L5.13 administration. This study identifies transcriptional and functional activities of FZD4-LRP5 agonists.

Therapeutic blood-brain barrier modulation and stroke treatment by a bioengineered FZD4-selective WNT surrogate in mice

Derangements of the blood-brain barrier (BBB) or blood-retinal barrier (BRB) occur in disorders ranging from stroke, cancer, diabetic retinopathy, and Alzheimer's disease. The Norrin/FZD4/TSPAN12 pathway activates WNT/β-catenin signaling, which is essential for BBB and BRB function. However, systemic pharmacologic FZD4 stimulation is hindered by obligate palmitoylation and insolubility of native WNTs and suboptimal properties of the FZD4-selective ligand Norrin. Here, we develop L6-F4-2, a non-lipidated, FZD4-specific surrogate which significantly improves subpicomolar affinity versus native Norrin. In Norrin knockout (NdpKO) mice, L6-F4-2 not only potently reverses neonatal retinal angiogenesis deficits, but also restores BRB and BBB function. In adult C57Bl/6J mice, post-stroke systemic delivery of L6-F4-2 strongly reduces BBB permeability, infarction, and edema, while improving neurologic score and capillary pericyte coverage. Our findings reveal systemic efficacy of a bioengineered FZD4-selective WNT surrogate during ischemic BBB dysfunction, with potential applicability to adult CNS disorders characterized by an aberrant blood-brain barrier.

Adhesion G protein-coupled receptors-Structure and functions

Adhesion G protein-coupled receptors (aGPCRs) are an ancient class of receptors that represent some of the largest transmembrane-integrated proteins in humans. First recognized as surface markers on immune cells, it took more than a decade to appreciate their 7-transmembrane structure, which is reminiscent of GPCRs. Roughly 30 years went by before the first functional proof of an interaction with a G protein was published. Besides classic features of GPCRs (extracellular N terminus, 7-transmembrane region, intracellular C terminus), aGPCRs display a distinct N-terminal structure, which harbors the highly conserved GPCR autoproteolysis-inducing (GAIN) domain with the GPCR proteolysis site (GPS) in addition to several functional domains. Several human diseases have been associated with variants of aGPCRs and subsequent animal models have been established to investigate these phenotypes. Much progress has been made in recent years to decipher the structure and functions of these receptors. This chapter gives an overview of our current understanding with respect to the molecular structural patterns governing aGPCR activation and the contribution of these giant molecules to the development of pathologies.

Developmental regulation of barrier- and non-barrier blood vessels in the CNS

The blood-brain barrier (BBB) is essential for creating and maintaining tissue homeostasis in the central nervous system (CNS), which is key for proper neuronal function. In most vertebrates, the BBB is localized to microvascular endothelial cells that acquire barrier properties during angiogenesis of the neuroectoderm. Complex and continuous tight junctions, and the lack of fenestrae combined with low pinocytotic activity render the BBB endothelium a tight barrier for water-soluble molecules that may only enter the CNS via specific transporters. The differentiation of these unique endothelial properties during embryonic development is initiated by endothelial-specific flavours of the Wnt/β-catenin pathway in a precise spatiotemporal manner. In this review, we summarize the currently known cellular (neural precursor and endothelial cells) and molecular (VEGF and Wnt/β-catenin) mechanisms mediating brain angiogenesis and barrier formation. Moreover, we introduce more recently discovered crosstalk with cellular and acellular elements within the developing CNS such as the extracellular matrix. We discuss recent insights into the downstream molecular mechanisms of Wnt/β-catenin in particular, the recently identified target genes like Foxf2, Foxl2, Foxq1, Lef1, Ppard, Zfp551, Zic3, Sox17, Apcdd1 and Fgfbp1 that are involved in refining and maintaining barrier characteristics in the mature BBB endothelium. Additionally, we elute to recent insight into barrier heterogeneity and differential endothelial barrier properties within the CNS, focussing on the circumventricular organs as well as on the neurogenic niches in the subventricular zone and the hippocampus. Finally, open questions and future BBB research directions are highlighted in the context of taking benefit from understanding BBB development for strategies to modulate BBB function under pathological conditions.

Targeting Oncogenic Pathways in the Era of Personalized Oncology: A Systemic Analysis Reveals Highly Mutated Signaling Pathways in Cancer Patients and Potential Therapeutic Targets

Cancer is the second leading cause of death globally. One of the main hallmarks in cancer is the functional deregulation of crucial molecular pathways via driver genetic events that lead to abnormal gene expression, giving cells a selective growth advantage. Driver events are defined as mutations, fusions and copy number alterations that are causally implicated in oncogenesis. Molecular analysis on tissues that have originated from a wide range of anatomical areas has shown that mutations in different members of several pathways are implicated in different cancer types. In recent decades, significant efforts have been made to incorporate this knowledge into daily medical practice, providing substantial insight towards clinical diagnosis and personalized therapies. However, since there is still a strong need for more effective drug development, a deep understanding of the involved signaling mechanisms and the interconnections between these pathways is highly anticipated. Here, we perform a systemic analysis on cancer patients included in the Pan-Cancer Atlas project, with the aim to select the ten most highly mutated signaling pathways (p53, RTK-RAS, lipids metabolism, PI-3-Kinase/Akt, ubiquitination, b-catenin/Wnt, Notch, cell cycle, homology directed repair (HDR) and splicing) and to provide a detailed description of each pathway, along with the corresponding therapeutic applications currently being developed or applied. The ultimate scope is to review the current knowledge on highly mutated pathways and to address the attractive perspectives arising from ongoing experimental studies for the clinical implementation of personalized medicine.

Retinitis Pigmentosa and Retinal Degenerations: Deciphering Pathways and Targets for Drug Discovery and Development

Inherited retinal diseases (IRDs) are a group of retinopathies generally caused by genetic mutations. Retinitis pigmentosa (RP) represents one of the most studied IRDs. RP leads to intense vision loss or blindness resulting from the degeneration of photoreceptor cells. To date, RP is mainly treated with palliative supplementation of vitamin A and retinoids, gene therapies, or surgical interventions. Therefore, a pharmacologically based therapy is an urgent need requiring a medicinal chemistry approach, to validate molecular targets able to deal with retinal degeneration. This Review aims at outlining the recent research efforts in identifying new drug targets for RP, especially focusing on the neuroprotective role of the Wnt/β-catenin/GSK3β pathway and apoptosis modulators (in particular PARP-1) but also on growth factors such as VEGF and BDNF. Furthermore, the role of spatiotemporally expressed G protein-coupled receptors (GPR124) in the retina and the emerging function of histone deacetylase inhibitors in promoting retinal neuroprotection will be discussed.

Effect of Wnt signaling pathway on neurogenesis after cerebral ischemia and its therapeutic potential

Neurogenesis process in the chronic phase of ischemic stroke has become the focus of research on stroke treatment recently, mainly through the activation of related pathways to increase the differentiation of neural stem cells (NSCs) in the brain sub-ventricular zone (SVZ) and subgranular zone (SGZ) of hippocampal dentate gyrus (DG) areas into neurons, promoting neurogenesis. While there is still debate about the longevity of active adult neurogenesis in humans, the SVZ and SGZ have the capacity to upregulate neurogenesis in response to cerebral ischemia, which opens discussion about potential treatment strategies to harness this neuronal regenerative response. Wnt signaling pathway is one of the most important approaches potentially targeting on neurogenesis after cerebral ischemia, appropriate activation of which in NSCs may help to improve the sequelae of cerebral ischemia. Various therapeutic approaches are explored on preclinical stage to target endogenous neurogenesis induced by Wnt signaling after stroke onset. This article describes the composition of Wnt signaling pathway and the process of neurogenesis after cerebral ischemia, and emphatically introduces the recent studies on the mechanisms of this pathway for post-stroke neurogenesis and the therapeutic possibility of activating the pathway to improve neurogenesis after stroke.

Adhesion G protein-coupled receptors: opportunities for drug discovery

Adhesion G protein-coupled receptors (aGPCRs) - one of the five main families in the GPCR superfamily - have several atypical characteristics, including large, multi-domain N termini and a highly conserved region that can be autoproteolytically cleaved. Although GPCRs overall have well-established pharmacological tractability, currently no therapies that target any of the 33 members of the aGPCR family are either approved or in clinical trials. However, human genetics and preclinical research have strengthened the links between aGPCRs and disease in recent years. This, together with a greater understanding of their functional complexity, has led to growing interest in aGPCRs as drug targets. A framework for prioritizing aGPCR targets and supporting approaches to develop aGPCR modulators could therefore be valuable in harnessing the untapped therapeutic potential of this family. With this in mind, here we discuss the unique opportunities and challenges for drug discovery in modulating aGPCR functions, including target identification, target validation, assay development and safety considerations, using ADGRG1 as an illustrative example.

Expression of the adhesion G protein-coupled receptor A2 (adgra2) during Xenopus laevis development

The adhesion G protein-coupled receptor A2 (Adgra2) is a seven transmembrane receptor that has been described to be a regulator for angiogenesis in mice. Furthermore, the zebrafish ouchless mutant is unable to develop dorsal root ganglia through a disrupted trafficking of Adgra2. Besides RNA sequencing data, nothing is reported about Adgra2 in the south African crawled frog Xenopus laevis. In this study, we investigated for the first time the spatio-temporal expression of adgra2 during early Xenopus embryogenesis in detail. In silico approaches showed that the genomic adgra2 region as well as the Adgra2 protein sequence is highly conserved among different species including Xenopus. RT-PCR experiments confirmed that embryonic adgra2 expression is primarily detected at the beginning of neurulation and is then present throughout the whole Xenopus embryogenesis until stage 42. Whole mount in situ hybridization approaches visualized adgra2 expression in many tissues during Xenopus embryogenesis such as the cardiovascular system including the heart, the migrating neural crest cells and the developing eye including the periocular mesenchyme. Our results indicate a role of Adgra2 for embryogenesis and are a good starting point for further functional studies during early vertebrate development.