Neuropathy is a debilitating condition that affects Diabetic patients. The development of neuropathy is associated with a loss of VEGF-A signaling in the central nervous system and, as a result, dysfunction within the neurovascular interactions. Here, we investigate the loss of spinal cord vasculature and the development of neuropathy in an endothelial cell specific inducible VEGF receptor 2 (VEGFR2) knockdown model in mice. Procedures were carried out in accordance with the UK Home Office Animals Scientific Procedures Act 1986. 24 transgenic mice (C57bl6 30g; both genders) were used. All mice used were vegfr2fl/fl and either Tie2CreERT2 positive (n=12) or Tie2CreERT2 negative (n=12), dosed once daily intraperitoneally (i.p) with 1mg tamoxifen or vehicle (10% ethanol in autoclaved sunflower oil), for 5 consecutive days. Nociceptive behavior was tested using Hargreaves test. After 8 days, hypoxyprobe (60mg/kg) i.p or tritc-dextan intravenously (1mg/20g body weight under sodium pentobarbital 60mg/kg i.p anaesthesia) was injected 30 minutes before euthanasia, then transcardially perfused with 4% paraformaldehyde under terminal anaesthesia (sodium pentobarbital 60mg/kg i.p). Spinal cord tissue was collected and frozen. Cryosections (40μM) were stained using Isolectin B4 (IB4), and Anti-hypoxyprobe. Confocal imaging was performed followed by Imaris 8.1 3D rendering. Values are mean ± S.E.M. One-way ANOVA unless otherwise stated. VegfR2ko (Tie2CreERT2 VEGFR2flfl + tamoxifen; cKO) mice showed a pronounced response to heat as compared to mice treated with vehicle (Tie2CreERT2 VEGFR2flfl+vehicle; Veh) or negative for Tie2CreERT2 (VEGFR2flfl+tamoxifen; WT) (6±2 vs. 8±1s, Veh and 8±1s, WT, p<0.001,n=5). Confocal images of IB4 stained vessels followed by 3D rendering revealed a significant reduction in vessel volume (cKO=400±100 vs Veh=800±100μm3/fieldview, p<0.001 and WT=600±100μm3/fieldview, p<0.05, n=6) and diameter (cKO=2±0.5μm vs. Veh=3.2±0.5, p<0.05, and WT=3.2±0.5, p<0.05, n=6) in the cKO as compared to controls. Confocal images showed an increase in the intensity of hypoxyprobe staining in the cKO versus WT (cKO=1.6±0.2 vs. WT=1.0 ±0.1 x 106 pixels, p<0.05, Unpaired T-test). Mapping of the dorsal horn of the spinal cord showed an increase in hypoxic cells per lamina (lx) in the cKO against WT (l2= cKO=33±6.5 vs. WT=2.5±0.8 p<0.001, l4 = cKO=12±2.2 vs. WT=1±0.4, p<0.05, Two way ANOVA, n=4). A reduction in perfusion was seen in cKO (cKO=3.7±0.5 vs. WT=4.7±0.6 % fluorescence area fraction, p<0.01 Mann-Whitney, n=4) as to WTs. Thus our data suggests a loss of VEGFR2 signaling in the endothelium leads to spinal cord vascular degeneration and hypoxia, which is associated with neuropathic pain development.
Future Physiology (Leeds, UK) (2017) Proc Physiol Soc 39, PC15
Poster Communications: The role of VEGF signaling in spinal cord vasculopathy and hypoxia; contributing factors in neuropathic pain development
M. Da Vitoria Lobo1, R. Madden1, D. O. Bates1, R. P. Hulse1
1. Cancer Biology, Univerisity of Nottingham, Nottingham, Nottinghamshire, United Kingdom.
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Where applicable, experiments conform with Society ethical requirements.