Koen Poesen

Novel Role for Vascular Endothelial Growth Factor (VEGF) Receptor-1 and Its Ligand VEGF-B in Motor Neuron Degeneration

Although vascular endothelial growth factor-B (VEGF-B) is a homolog of the angiogenic factor VEGF, it has only minimal angiogenic activity, raising the question of whether this factor has other (more relevant) biological properties. Intrigued by the possibility that VEGF family members affect neuronal cells, we explored whether VEGF-B might have a role in the nervous system. Here, we document that the 60 kDa VEGF-B isoform, VEGF-B186, is a neuroprotective factor. VEGF-B186 protected cultured primary motor neurons against degeneration. Mice lacking VEGF-B also developed a more severe form of motor neuron degeneration when intercrossed with mutant SOD1 mice. The in vitro and in vivo effects of VEGF-B186 were dependent on the tyrosine kinase activities of its receptor, Flt1, in motor neurons. When delivered intracerebroventricularly, VEGF-B186 prolonged the survival of mutant SOD1 rats. Compared with a similar dose of VEGF, VEGF-B186 was safer and did not cause vessel growth or blood–brain barrier leakiness. The neuroprotective activity of VEGF-B, in combination with its negligible angiogenic/permeability activity, offers attractive opportunities for the treatment of neurodegenerative diseases.

Inhibition of tumor angiogenesis and growth by a small-molecule multi-FGF receptor blocker with allosteric properties.

Receptor tyrosine kinases (RTK) are targets for anticancer drug development. To date, only RTK inhibitors that block orthosteric binding of ligands and substrates have been developed. Here, we report the pharmacologic characterization of the chemical SSR128129E (SSR), which inhibits fibroblast growth factor receptor (FGFR) signaling by binding to the extracellular FGFR domain without affecting orthosteric FGF binding. SSR exhibits allosteric properties, including probe dependence, signaling bias, and ceiling effects. Inhibition by SSR is highly conserved throughout the animal kingdom. Oral delivery of SSR inhibits arthritis and tumors that are relatively refractory to anti-vascular endothelial growth factor receptor-2 antibodies. Thus, orally-active extracellularly acting small-molecule modulators of RTKs with allosteric properties can be developed and may offer opportunities to improve anticancer treatment.

Meta-analysis of vascular endothelial growth factor variations in amyotrophic lateral sclerosis: increased susceptibility in male carriers of the −2578AA genotype

Background: Targeted delivery of the angiogenic factor, vascular endothelial growth factor (VEGF), to motor neurons prolongs survival in rodent models of amyotrophic lateral sclerosis (ALS), while mice expressing reduced VEGF concentrations develop motor neuron degeneration reminiscent of ALS, raising the question whether VEGF contributes to the pathogenesis of ALS. An initial association study reported that VEGF haplotypes conferred increased susceptibility to ALS in humans, but later studies challenged this initial finding. Methods and findings: A meta-analysis was undertaken to critically reappraise whether any of the three common VEGF gene variations (−2578C/A, −1154G/A and −634G/C) increase the risk of ALS. Over 7000 subjects from eight European and three American populations were included in the analysis. Pooled odds ratios were calculated using fixed-effects and random-effects models, and four potential sources of heterogeneity (location of disease onset, gender, age at disease onset and disease duration) were assessed. After correction, none of the genotypes or haplotypes was significantly associated with ALS. Subgroup analysis by gender revealed, however, that the −2578AA genotype, which lowers VEGF expression, increased the risk of ALS in males (OR = 1.46 males vs females; 95% CI = 1.19 to 1.80; p = 7.8 10E-5), even after correction for publication bias and multiple testing. Conclusions: This meta-analysis does not support the original conclusion that VEGF haplotypes increase the risk of ALS in humans, but the significant association of the low-VEGF −2578AA genotype with increased susceptibility to ALS in males reappraises the link between reduced VEGF concentrations and ALS, as originally revealed by the fortuitous mouse genetic studies.

VEGF protects motor neurons against excitotoxicity by upregulation of GluR2

Influx of Ca(2+) ions through the α-amino-3-hydroxy-5-methylisoxazole propionic acid (AMPA) receptors is toxic to neurons and contributes to motor neuron degeneration observed in amyotrophic lateral sclerosis (ALS). The Ca(2+) permeability of the AMPA receptor depends on its subunit composition. If the GluR2 subunit is present in the receptor complex, the AMPA receptor is impermeable to Ca(2+). In this study, we identified vascular endothelial growth factor-A (VEGF) as a GluR2 inducing molecule. Cultured motor neurons pretreated with VEGF displayed higher GluR2 levels. This resulted in AMPA receptor currents with a low relative Ca(2+) permeability and in motor neurons that were less vulnerable to AMPA receptor-mediated excitotoxicity. This effect of VEGF was mediated through the VEGFR2 present on the motor neurons and was due to stimulation of GluR2 transcription. Intracerebroventricular treatment with VEGF similarly induced GluR2 expression in the ventral spinal cord of rats and this mechanism contributes to the protective effect of VEGF on motor neurons.

Matrix-binding vascular endothelial growth factor (VEGF) isoforms guide granule cell migration in the cerebellum via VEGF receptor Flk1

Vascular endothelial growth factor (VEGF) regulates angiogenesis, but also has important, yet poorly characterized roles in neuronal wiring. Using several genetic and in vitro approaches, we discovered a novel role for VEGF in the control of cerebellar granule cell (GC) migration from the external granule cell layer (EGL) toward the Purkinje cell layer (PCL). GCs express the VEGF receptor Flk1, and are chemoattracted by VEGF, whose levels are higher in the PCL than EGL. Lowering VEGF levels in mice in vivo or ectopic VEGF expression in the EGL ex vivo perturbs GC migration. Using GC-specific Flk1 knock-out mice, we provide for the first time in vivo evidence for a direct chemoattractive effect of VEGF on neurons via Flk1 signaling. Finally, using knock-in mice expressing single VEGF isoforms, we show that pericellular deposition of matrix-bound VEGF isoforms around PC dendrites is necessary for proper GC migration in vivo. These findings identify a previously unknown role for VEGF in neuronal migration.

Neuronal FLT1 receptor and its selective ligand VEGF-B protect against retrograde degeneration of sensory neurons

Even though VEGF‐B is a homologue of the potent angiogenic factor VEGF, its angiogenic activities have been controversial. Intrigued by findings that VEGF‐B may also affect neuronal cells, we assessed the neuroprotective and vasculoprotective effects of VEGF‐B in the skin, in which vessels and nerves are functionally intertwined. Although VEGF‐B and its FLT1 receptor were prominently expressed in dorsal root ganglion (DRG) neurons innervating the hindlimb skin, they were not essential for nerve function or vascularization of the skin. However, primary DRG cultures lacking VEGF‐B or FLT1 exhibited increased neuronal stress and were more susceptible to paclitaxel‐induced cell death. Concomitantly, mice lacking VEGF‐B or a functional FLT1 developed more retrograde degeneration of sensory neurons in a model of distal neuropathy. On the other hand, the addition of the VEGF‐B isoform, VEGF‐B186, to DRG cultures antagonized neuronal stress, maintained the mitochon‐drial membrane potential and stimulated neuronal survival. Mice overexpressing VEGF‐B186 or FLT1 selectively in neurons were protected against the distal neuropathy, whereas exogenous VEGF‐B186, either delivered by gene transfer or as a recombinant factor, was protective by directly affecting sensory neurons and not the surrounding vasculature. Overall, this indicates that VEGF‐B, instead of acting as an angiogenic factor, exerts direct neuroprotective effects through FLT1. These findings also suggest a clinically relevant role for VEGF‐B in preventing distal neuropathies.—Dhondt, J., Peeraer, E., Verheyen, A., Nuydens, R., Buysschaert, I., Poesen, K., Van Geyte, K., Beerens, M., Shibuya, M., Haigh, J. J., Meert, T., Carmeliet, P., Lambrechts, D. Neuronal FLT1 receptor and its selective ligand VEGF‐B protect against retrograde degeneration of sensory neurons. FASEB J. 25, 1461–1473 (2011). www.fasebj.org

Multicenter validation of CSF neurofilaments as diagnostic biomarkers for ALS

Abstract OBJECTIVE: Neurofilaments are leading neurochemical biomarkers for amyotrophic lateral sclerosis (ALS). Here, we investigated the effect of preanalytical factors on neurofilament concentrations in cerebrospinal fluid (CSF) in a “reverse” round-robin with 15 centers across Europe/U.S. METHODS: Samples from ALS and control patients (5/5 each center, n = 150) were analyzed for phosphorylated neurofilament heavy chain (pNfH) and neurofilament light chain (NfL) at two laboratories. RESULTS: CSF pNfH was increased (p < 0.05) in ALS in 10 out of 15 centers and NfL in 5 out of 12 centers. The coefficient of variation (CV%) of pNfH measurements between laboratories was 18.7 ± 19.1%. We calculated a diagnostic cut-off of >568.5 pg/mL for pNfH (sensitivity 78.7%, specificity 93.3%) and >1,431pg/mL for NfL (sensitivity 79.0%, specificity 86.4%). CONCLUSION: Values in ALS patients are already comparable between most centers, supporting eventual implementation into clinical routine. However, continuous quality control programs will be necessary for inclusion in the diagnostic work-up.

Impaired Autonomic Regulation of Resistance Arteries in Mice With Low Vascular Endothelial Growth Factor or Upon Vascular Endothelial Growth Factor Trap Delivery

Background— Control of peripheral resistance arteries by autonomic nerves is essential for the regulation of blood flow. The signals responsible for the maintenance of vascular neuroeffector mechanisms in the adult, however, remain largely unknown. Methods and Results— Here, we report that VEGF∂/∂ mice with low vascular endothelial growth factor (VEGF) levels suffer defects in the regulation of resistance arteries. These defects are due to dysfunction and structural remodeling of the neuroeffector junction, the equivalent of a synapse between autonomic nerve endings and vascular smooth muscle cells, and to an impaired contractile smooth muscle cell phenotype. Notably, short-term delivery of a VEGF inhibitor to healthy mice also resulted in functional and structural defects of neuroeffector junctions. Conclusions— These findings uncover a novel role for VEGF in the maintenance of arterial neuroeffector function and may help us better understand how VEGF inhibitors cause vascular regulation defects in cancer patients.

Therapeutic potential of VEGF and VEGF - derived peptide in peripheral neuropathies

Besides its prominent role in angiogenesis, the vascular endothelial growth factor (VEGF) also exerts important protective effects on neurons. In particular, mice expressing reduced levels of VEGF suffer from late-onset motor neuron degeneration, whereas VEGF delivery significantly delays motor neuron death in ALS mouse models, at least partly through neuroprotective effects. Additionally, VEGF protects dorsal root ganglion (DRG) neurons against paclitaxel-induced neurotoxicity. Here, we demonstrate that VEGF also protects DRG neurons against hyperglycemia-induced neuronal stress as a model of diabetes-induced peripheral neuropathy. Specifically, VEGF decreased expression of the stress-related gene activating transcription factor 3 (ATF3) in DRG neurons isolated from streptozotocin-induced diabetic mice (ex vivo) and in isolated DRG neurons exposed to high glucose concentrations (in vitro). In vivo, local VEGF application also protected against paclitaxel- and diabetes-induced neuropathies without causing side effects. A small synthetic VEGF mimicking pentadecapeptide (QK) exerted similar effects on DRG cultures: the peptide reduced ATF3 expression in vitro and ex vivo in paclitaxel- and hyperglycemia-induced models of neuropathy to a similar extent as the full-length recombinant VEGF protein. By using transgenic mice selectively overexpressing the VEGF receptor 2 in postnatal neurons, these neuroprotective effects were shown to be mediated through VEGF receptor 2. Overall, these results underscore the potential of VEGF and VEGF-derived peptides for the treatment of peripheral neuropathies.

Systemic anti-vascular endothelial growth factor therapies induce a painful sensory neuropathy

Systemic vascular endothelial growth factor inhibition, in combination with chemotherapy, improves the outcome of patients with metastatic cancer. Peripheral sensory neuropathies occurring in patients receiving both drugs are attributed to the chemotherapy. Here, we provide unprecedented evidence that vascular endothelial growth factor receptor inhibitors trigger a painful neuropathy and aggravate paclitaxel-induced neuropathies in mice. By using transgenic mice with altered neuronal vascular endothelial growth factor receptor expression, systemic inhibition of vascular endothelial growth factor receptors was shown to interfere with the endogenous neuroprotective activities of vascular endothelial growth factor on sensory neurons. In vitro, vascular endothelial growth factor prevented primary dorsal root ganglion cultures from paclitaxel-induced neuronal stress and cell death by counteracting mitochondrial membrane potential decreases and normalizing hyperacetylation of α-tubulin. In contrast, vascular endothelial growth factor receptor inhibitors exerted opposite effects. Intriguingly, vascular endothelial growth factor or vascular endothelial growth factor receptor inhibitors exerted their effects through a mechanism whereby Hdac6, through Hsp90, controls vascular endothelial growth factor receptor-2-mediated expression of the anti-apoptotic Bcl2. Our observations that systemic anti-vascular endothelial growth factor therapies interfere with the neuroprotective activities of vascular endothelial growth factor may have important implications for the application of anti-vascular endothelial growth factor therapies in cancer patients.