VEGF-C prophylaxis favors lymphatic drainage and modulates neuroinflammation in a stroke model

Meningeal lymphatic vessels (MLVs) promote tissue clearance and immune surveillance in the central nervous system (CNS). Vascular endothelial growth factor-C (VEGF-C) regulates MLV development and maintenance and has therapeutic potential for treating neurological disorders. Herein, we investigated the effects of VEGF-C overexpression on brain fluid drainage and ischemic stroke outcomes in mice. Intracerebrospinal administration of an adeno-associated virus expressing mouse full-length VEGF-C (AAV-mVEGF-C) increased CSF drainage to the deep cervical lymph nodes (dCLNs) by enhancing lymphatic growth and upregulated neuroprotective signaling pathways identified by single nuclei RNA sequencing of brain cells. In a mouse model of ischemic stroke, AAV-mVEGF-C pretreatment reduced stroke injury and ameliorated motor performances in the subacute stage, associated with mitigated microglia-mediated inflammation and increased BDNF signaling in brain cells. Neuroprotective effects of VEGF-C were lost upon cauterization of the dCLN afferent lymphatics and not mimicked by acute post-stroke VEGF-C injection. We conclude that VEGF-C prophylaxis promotes multiple vascular, immune, and neural responses that culminate in a protection against neurological damage in acute ischemic stroke.

Compartmentalized ocular lymphatic system mediates eye-brain immunity

The eye, an anatomical extension of the central nervous system (CNS), exhibits many molecular and cellular parallels to the brain. Emerging research demonstrates that changes in the brain are often reflected in the eye, particularly in the retina1. Still, the possibility of an immunological nexus between the posterior eye and the rest of the CNS tissues remains unexplored. Here, studying immune responses to herpes simplex virus in the brain, we observed that intravitreal immunization protects mice against intracranial viral challenge. This protection extended to bacteria and even tumours, allowing therapeutic immune responses against glioblastoma through intravitreal immunization. We further show that the anterior and posterior compartments of the eye have distinct lymphatic drainage systems, with the latter draining to the deep cervical lymph nodes through lymphatic vasculature in the optic nerve sheath. This posterior lymphatic drainage, like that of meningeal lymphatics, could be modulated by the lymphatic stimulator VEGFC. Conversely, we show that inhibition of lymphatic signalling on the optic nerve could overcome a major limitation in gene therapy by diminishing the immune response to adeno-associated virus and ensuring continued efficacy after multiple doses. These results reveal a shared lymphatic circuit able to mount a unified immune response between the posterior eye and the brain, highlighting an understudied immunological feature of the eye and opening up the potential for new therapeutic strategies in ocular and CNS diseases.

VEGF-C promotes brain-derived fluid drainage, confers neuroprotection, and improves stroke outcomes

Meningeal lymphatic vessels promote tissue clearance and immune surveillance in the central nervous system (CNS). Vascular endothelium growth factor-C (VEGF-C) is essential for meningeal lymphatic development and maintenance and has therapeutic potential for treating neurological disorders, including ischemic stroke. We have investigated the effects of VEGF-C overexpression on brain fluid drainage, single cell transcriptome in the brain, and stroke outcomes in adult mice. Intra-cerebrospinal fluid administration of an adeno-associated virus expressing VEGF-C (AAV-VEGF-C) increases the CNS lymphatic network. Post-contrast T1 mapping of the head and neck showed that deep cervical lymph node size and drainage of CNS-derived fluids were increased. Single nuclei RNA sequencing revealed a neuro-supportive role of VEGF-C via upregulation of calcium and brain-derived neurotrophic factor (BDNF) signaling pathways in brain cells. In a mouse model of ischemic stroke, AAV-VEGF-C pretreatment reduced stroke injury and ameliorated motor performances in the subacute stage. AAV-VEGF-C thus promotes CNS-derived fluid and solute drainage, confers neuroprotection, and reduces ischemic stroke damage.

Short abstract

Intrathecal delivery of VEGF-C increases the lymphatic drainage of brain-derived fluids confers neuroprotection, and improves neurological outcomes after ischemic stroke.

Netrin-1 binding to Unc5B regulates Blood-Retina Barrier integrity

Background

The blood brain barrier (BBB) preserves neuronal function in the central nervous system (CNS) by tightly controlling metabolite exchanges with the blood. In the eye, the retina is likewise protected by the blood-retina barrier (BRB) to maintain phototransduction. We showed that the secreted guidance cue Netrin-1 regulated BBB integrity, by binding to endothelial Unc5B and regulating canonical β-catenin dependent expression of BBB gene expression.

Objective

Here, we investigated if Netrin-1-binding to endothelial Unc5B also controlled BRB integrity, and if this process involved Norrin/β-catenin signaling, which is the major known driver of BRB development and maintenance.

Methods

We analyzed Tamoxifen-inducible loss- and gain- of-function alleles of Unc5B, Ntn1 and Ctnnb1 in conjunction with tracer injections and biochemical signaling studies.

Results

Inducible endothelial Unc5B deletion, and inducible global Ntn1 deletion in postnatal mice reduced phosphorylation of the Norrin receptor LRP5, leading to reduced β-catenin and LEF1 expression, conversion of retina endothelial cells from a barrier-competent Claudin-5+/PLVAP- state to a Claudin-5-/PLVAP+ leaky phenotype, and extravasation of injected low molecular weight tracers. Inducible Ctnnb1 gain of function rescued vascular leak in Unc5B mutants, and Ntn1 overexpression induced BRB tightening. Unc5B expression in pericytes contributed to BRB permeability, via regulation of endothelial Unc5B. Mechanistically, Netrin-1-Unc5B signaling promoted β-catenin dependent BRB signaling by enhancing phosphorylation of the Norrin receptor LRP5 via the Discs large homologue 1 (Dlg1) intracellular scaffolding protein.

Conclusions

The data identify Netrin1-Unc5B as novel regulators of BRB integrity, with implications for diseases associated with BRB disruption.

Endothelial cell cycle state determines propensity for arterial-venous fate

During blood vessel development, endothelial cells become specified toward arterial or venous fates to generate a circulatory network that provides nutrients and oxygen to, and removes metabolic waste from, all tissues. Arterial-venous specification occurs in conjunction with suppression of endothelial cell cycle progression; however, the mechanistic role of cell cycle state is unknown. Herein, using Cdh5-CreER^T2;R26FUCCI2aR reporter mice, we find that venous endothelial cells are enriched for the FUCCI-Negative state (early G1) and BMP signaling, while arterial endothelial cells are enriched for the FUCCI-Red state (late G1) and TGF-β signaling. Furthermore, early G1 state is essential for BMP4-induced venous gene expression, whereas late G1 state is essential for TGF-β1-induced arterial gene expression. Pharmacologically induced cell cycle arrest prevents arterial-venous specification defects in mice with endothelial hyperproliferation. Collectively, our results show that distinct endothelial cell cycle states provide distinct windows of opportunity for the molecular induction of arterial vs. venous fate.

Defective Flow-Migration Coupling Causes Arteriovenous Malformations in Hereditary Hemorrhagic Telangiectasia

BACKGROUND

Activin receptor-like kinase 1 (ALK1) is an endothelial transmembrane serine threonine kinase receptor for BMP family ligands that plays a critical role in cardiovascular development and pathology. Loss-of-function mutations in the ALK1 gene cause type 2 hereditary hemorrhagic telangiectasia, a devastating disorder that leads to arteriovenous malformations. Here, we show that ALK1 controls endothelial cell polarization against the direction of blood flow and flow-induced endothelial migration from veins through capillaries into arterioles.

METHODS

Using Cre lines that recombine in different subsets of arterial, capillary-venous, or endothelial tip cells, we show that capillary-venous Alk1 deletion was sufficient to induce arteriovenous malformation formation in the postnatal retina.

RESULTS

ALK1 deletion impaired capillary-venous endothelial cell polarization against the direction of blood flow in vivo and in vitro. Mechanistically, ALK1-deficient cells exhibited increased integrin signaling interaction with vascular endothelial growth factor receptor 2, which enhanced downstream YAP/TAZ nuclear translocation. Pharmacologic inhibition of integrin or YAP/TAZ signaling rescued flow migration coupling and prevented vascular malformations in Alk1-deficient mice.

CONCLUSIONS

Our study reveals ALK1 as an essential driver of flow-induced endothelial cell migration and identifies loss of flow-migration coupling as a driver of arteriovenous malformation formation in hereditary hemorrhagic telangiectasia disease. Integrin-YAP/TAZ signaling blockers are new potential targets to prevent vascular malformations in patients with hereditary hemorrhagic telangiectasia.

Abstract 4413: Thrombospondin-1 is a master regulator of glioblastoma vascularization and infiltration

Glioblastoma are heterogeneous tumours composed of different subpopulations of cells with different behavioral characteristics. Areas of highly angiogenic cells co-exist with populations of non-angiogenic but highly invasive and infiltrative cells. This heterogeneity is a key clinical challenge in glioma treatment.

We used a large scale RNA sequencing approach to investigate the molecular components which differentiate infiltrative from angiogenic cells, in a Patient Derived Xenograft (PDX) mouse model. Our bioinformatic analysis revealed TGFβ1 to be a master regulator of tumor development, and Thrombospondin-1 (Tsp1) to be up regulated in infiltrative areas as compared to angiogenic area. Thrombospondins are known as anti-angiogenic factors, however the full roles of these multi domain proteins in tumor development remain to be elucidated.

We found Tsp1 expression to be upregulated in grade IV-GBM and in silico in the GBM mesenchymal subclass. It is expressed not only in tumor cells, but also in tumor blood vessel endothelial cells (ECs). TGFβ1 transcriptionally regulated Tsp1 via Smad1 and Smad3. However, contrary to previous results, we found that Tsp1 was not involved in TGFβ1-activation in tumor cells. We showed that Tsp1 regulates cell migration and invasion both in vitro and in vivo. Inhibition of Tsp1 expression in vivo correlated with increased tumor vascularization in both the chick CAM assay and the PDX mouse model.

Anti-angiogenic treatments in the PDX mouse model leads to increased tumor hypoxia and invasive tumor cell behavior, as described in our previous work. In this context, both TGFβ1 and Tsp1 were upregulated in tumor cells. Downregulation of tumor-derived Tsp1 by shRNA in the presence of anti-angiogenic therapy led to reduced tumor growth and invasion in vivo. Finally, peptide-mediated inhibition of Tsp1 activity demonstrated that Tsp1/CD47 interaction is involved in the invasive capacity of GBM cells.

Taken together, our data suggest that Tsp1 inhibition may be a promising therapeutic approach to limit tumor infiltration induced by treatment with anti-angiogenic agents.

Citation Format: Thomas Daubon, Celine Leon, Kim Clarke, Mathilde Poulet, Hrvoje Miletic, Francesco Falciani, Rolf Bjerkvig, Andreas Bikfalvi. Thrombospondin-1 is a master regulator of glioblastoma vascularization and infiltration. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 4413.