Peptides Derived from Vascular Endothelial Growth Factor B Show Potent Binding to Neuropilin-1.

Vascular endothelial growth factors (VEGFs) regulate significant pathways in angiogenesis, myocardial and neuronal protection, metabolism, and cancer progression. The VEGF-B growth factor is involved in cell survival, anti-apoptotic and antioxidant mechanisms, through binding to VEGF receptor 1 and neuropilin-1 (NRP1). We employed surface plasmon resonance technology and X-ray crystallography to analyse the molecular basis of the interaction between VEGF-B and the b1 domain of NRP1, and developed VEGF-B C-terminus derived peptides to be used as chemical tools for studying VEGF-B - NRP1 related pathways. Peptide lipidation was used as a means to stabilise the peptides. VEGF-B-derived peptides containing a C-terminal arginine show potent binding to NRP1-b1. Peptide lipidation increased binding residence time and improved plasma stability. A crystal structure of a peptide with NRP1 demonstrated that VEGF-B peptides bind at the canonical C-terminal arginine binding site. VEGF-B C-terminus imparts higher affinity for NRP1 than the corresponding VEGF-A165 region. This tight binding may impact on the activity and selectivity of the full-length protein. The VEGF-B167 derived peptides were more effective than VEGF-A165 peptides in blocking functional phosphorylation events. Blockers of VEGF-B function have potential applications in diabetes and non-alcoholic fatty liver disease.

Diaphragm Muscle Weakness Following Acute Sustained Hypoxic Stress in the Mouse Is Prevented by Pretreatment with N-Acetyl Cysteine.

Oxygen deficit (hypoxia) is a major feature of cardiorespiratory diseases characterized by diaphragm dysfunction, yet the putative role of hypoxic stress as a driver of diaphragm dysfunction is understudied. We explored the cellular and functional consequences of sustained hypoxic stress in a mouse model. Adult male mice were exposed to 8 hours of normoxia, or hypoxia (FiO2 = 0.10) with or without antioxidant pretreatment (N-acetyl cysteine, 200 mg/kg i.p.). Ventilation and metabolism were measured. Diaphragm muscle contractile function, myofibre size and distribution, gene expression, protein signalling cascades, and oxidative stress (TBARS) were determined. Hypoxia caused pronounced diaphragm muscle weakness, unrelated to increased respiratory muscle work. Hypoxia increased diaphragm HIF-1α protein content and activated MAPK, mTOR, Akt, and FoxO3a signalling pathways, largely favouring protein synthesis. Hypoxia increased diaphragm lipid peroxidation, indicative of oxidative stress. FoxO3 and MuRF-1 gene expression were increased. Diaphragm 20S proteasome activity and muscle fibre size and distribution were unaffected by acute hypoxia. Pretreatment with N-acetyl cysteine substantially enhanced cell survival signalling, prevented hypoxia-induced diaphragm oxidative stress, and prevented hypoxia-induced diaphragm dysfunction. Hypoxia is a potent driver of diaphragm weakness, causing myofibre dysfunction without attendant atrophy. N-acetyl cysteine protects the hypoxic diaphragm and may have application as a potential adjunctive therapy.

Small Molecule Neuropilin-1 Antagonists Combine Antiangiogenic and Antitumor Activity with Immune Modulation through Reduction of Transforming Growth Factor Beta (TGFß) Production in Regulatory T-Cells.

We report the design, synthesis, and biological evaluation of some potent small-molecule neuropilin-1 (NRP1) antagonists. NRP1 is implicated in the immune response to tumors, particularly in Treg cell fragility, required for PD1 checkpoint blockade. The design of these compounds was based on a previously identified compound EG00229. The design of these molecules was informed and supported by X-ray crystal structures. Compound 1 (EG01377) was identified as having properties suitable for further investigation. Compound 1 was then tested in several in vitro assays and was shown to have antiangiogenic, antimigratory, and antitumor effects. Remarkably, 1 was shown to be selective for NRP1 over the closely related protein NRP2. In purified Nrp1+, FoxP3+, and CD25+ populations of Tregs from mice, 1 was able to block a glioma-conditioned medium-induced increase in TGFß production. This comprehensive characterization of a small-molecule NRP1 antagonist provides the basis for future in vivo studies.

Architecture and hydration of the arginine-binding site of neuropilin-1.

Neuropilin-1 (NRP1) is a transmembrane co-receptor involved in binding interactions with variety of ligands and receptors, including receptor tyrosine kinases. Expression of NRP1 in several cancers correlates with cancer stages and poor prognosis. Thus, NRP1 has been considered a therapeutic target and is the focus of multiple drug discovery initiatives. Vascular endothelial growth factor (VEGF) binds to the b1 domain of NRP1 through interactions between the C-terminal arginine of VEGF and residues in the NRP1-binding site including Tyr297, Tyr353, Asp320, Ser346 and Thr349. We obtained several complexes of the synthetic ligands and the NRP1-b1 domain and used X-ray crystallography and computational methods to analyse atomic details and hydration profile of this binding site. We observed side chain flexibility for Tyr297 and Asp320 in the six new high-resolution crystal structures of arginine analogues bound to NRP1. In addition, we identified conserved water molecules in binding site regions which can be targeted for drug design. The computational prediction of the VEGF ligand-binding site hydration map of NRP1 was in agreement with the experimentally derived, conserved hydration structure. Displacement of certain conserved water molecules by a ligand's functional groups may contribute to binding affinity, whilst other water molecules perform as protein-ligand bridges. Our report provides a comprehensive description of the binding site for the peptidic ligands' C-terminal arginines in the b1 domain of NRP1, highlights the importance of conserved structural waters in drug design and validates the utility of the computational hydration map prediction method in the context of neuropilin. DATABASE: The structures were deposited to the PDB with accession numbers PDB ID: 5IJR, 5IYY, 5JHK, 5J1X, 5JGQ, 5JGI.

Diaphragm muscle weakness and increased UCP-3 gene expression following acute hypoxic stress in the mouse.

The effects of acute hypoxia on the diaphragm are largely unknown despite the clinical relevance to respiratory conditions such as acute respiratory distress syndrome and ventilator-induced lung injury. Adult male C57BL6/J mice were exposed to 1, 4 or 8h of hypoxia (FiO2=0.10) or normoxia. Ventilation was assessed by whole-body plethysmography during gas exposures. Diaphragm isotonic contractile parameters were assessed ex vivo. Diaphragm gene expression was determined using qRT-PCR. Acute hypoxic stress resulted in significant diaphragm muscle weakness. Gene expression data revealed that hypoxia results in temporal changes in various transcriptional genes regulating mitochondrial function and a time-dependent progressive increase in the expression of the mitochondrial uncoupling protein 3 (UCP-3) with concomitant changes in genes encoding sarcoplasmic reticulum calcium release proteins. Altered gene expression and muscle weakness are likely due to direct effects of hypoxic stress per se, and not related to increased diaphragm muscle activity, as there was no persistent change in ventilation during hypoxic exposure. These findings suggest a potentially critical role for hypoxia in diaphragm muscle remodeling in acute respiratory-related disorders.

Beta-Adrenoceptor Activation Reduces Both Dermal Microvascular Endothelial Cell Migration via a cAMP-Dependent Mechanism and Wound Angiogenesis.

Angiogenesis is an essential process during tissue regeneration; however, the amount of angiogenesis directly correlates with the level of wound scarring. Angiogenesis is lower in scar-free foetal wounds while angiogenesis is raised and abnormal in pathophysiological scarring such as hypertrophic scars and keloids. Delineating the mechanisms that modulate angiogenesis and could reduce scarring would be clinically useful. Beta-adrenoceptors (ß-AR) are G protein-coupled receptors (GPCRs) expressed on all skin cell-types. They play a role in wound repair but their specific role in angiogenesis is unknown. In this study, a range of in vitro assays (single cell migration, scratch wound healing, ELISAs for angiogenic growth factors and tubule formation) were performed with human dermal microvascular endothelial cells (HDMEC) to investigate and dissect mechanisms underpinning ß-AR-mediated modulation of angiogenesis in chick chorioallantoic membranes (CAM) and murine excisional skin wounds. ß-AR activation reduced HDMEC migration via cyclic adenosine monophosphate (cAMP)-dependent and protein kinase A (PKA)-independent mechanisms as demonstrated through use of an EPAC agonist that auto-inhibited the cAMP-mediated ß-AR transduced reduction in HDMEC motility; a PKA inhibitor was, conversely, ineffective. ELISA studies demonstrated that ß-AR activation reduced pro-angiogenic growth factor secretion from HDMECs (fibroblast growth factor 2) and keratinocytes (vascular endothelial growth factor A) revealing possible ß-AR-mediated autocrine and paracrine anti-angiogenic mechanisms. In more complex environments, ß-AR activation delayed HDMEC tubule formation and decreased angiogenesis both in the CAM assay and in murine excisional skin wounds in vivo. ß-AR activation reduced HDMEC function in vitro and angiogenesis in vivo; therefore, ß-AR agonists could be promising anti-angiogenic modulators in skin.

ß2AR antagonists and ß2AR gene deletion both promote skin wound repair processes.

Skin wound healing is a complex process requiring the coordinated, temporal orchestration of numerous cell types and biological processes to regenerate damaged tissue. Previous work has demonstrated that a functional ß-adrenergic receptor autocrine/paracrine network exists in skin, but the role of ß2-adrenergic receptor (ß2AR) in wound healing is unknown. A range of in vitro (single-cell migration, immunoblotting, ELISA, enzyme immunoassay), ex vivo (rat aortic ring assay), and in vivo (chick chorioallantoic membrane assay, zebrafish, murine wild-type, and ß2AR knockout excisional skin wound models) models were used to demonstrate that blockade or loss of ß2AR gene deletion promoted wound repair, a finding that is, to our knowledge, previously unreported. Compared with vehicle-only controls, ß2AR antagonism increased angiogenesis, dermal fibroblast function, and re-epithelialization, but had no effect on wound inflammation in vivo. Skin wounds in ß2AR knockout mice contracted and re-epithelialized faster in the first few days of wound repair in vivo. ß2AR antagonism enhanced cell motility through distinct intracellular signalling mechanisms and increased vascular endothelial growth factor secretion from keratinocytes. ß2AR antagonism promoted wound repair processes in the early stages of wound repair, revealing a possible new avenue for therapeutic intervention.