Intranasal VEGFD Treatment Reduces Brain Damage Following Stroke
Post by Cody Walters
What’s the science?
Ischemic stroke occurs when an artery supplying the brain is obstructed. The resulting loss of blood flow causes dendrite loss and cell death in the surrounding brain tissue. Stroke is also known to result in an increase in extracellular glutamate which triggers toxic NMDAR signaling. Currently, there are no pharmacological treatments designed to preserve the structural integrity of dendrites post-stroke despite the promise of such a therapy to mitigate stroke-associated motor and cognitive impairment. This week in PNAS, Mauceri et al. report that administering either vascular endothelial growth factor D (VEGFD, a protein implicated in dendritic maintenance) or VEGFD peptide mimetics reduced dendrite loss, brain damage, and behavioral impairment in a mouse model of ischemic stroke.
How did they do it?
The authors studied the effects of stroke on VEGFD expression levels, dendrite morphology, and behavior both in vitro and in vivo. They studied the effects of oxygen-glucose deprivation on cultured mouse hippocampal neurons in vitro (by incubating their cultures in a deoxygenated, glucose-free medium to mimic stroke) and the effects of middle cerebral artery occlusion (a mouse model of ischemic stroke) in vivo. The authors then used qRT-PCR to quantify mRNA levels, Golgi staining to assess dendrite length, and the corner test to investigate behavioral impairment following middle cerebral artery occlusion. They also tested the effects of administering VEGFD and VEGFD peptide mimetics on dendrite length, cell death, and behavioral impairment using their stroke injury models.
What did they find?
In vitro, the authors found that bath application of NMDA (therefore stimulating NMDA receptors) to cultured hippocampal neurons dramatically reduced VEGFD mRNA levels relative to control levels. To determine whether this effect was driven by synaptic NMDARs or extrasynaptic NMDARs, they selectively blocked synaptic NMDARs (using bicuculline, a GABAA receptor antagonist, and MK-801, an open-channel NMDAR blocker) to isolate extrasynaptic NMDARs. Then, they applied NMDA and discovered that VEGFD mRNA levels were still reduced relative to controls, suggesting that this effect is mediated by extrasynaptic NMDARs.
In vivo, the authors injected recombinant VEGFD directly into the ventricles (fluid-filled cavities in the brain) and found that there was a reduction in the volume of infarct tissue (i.e. dead tissue) and behavioral impairment following middle cerebral artery occlusion relative to controls. Furthermore, the cell cultures of animals that were treated with intraventricular recombinant VEGFD had less dendrite loss but no reduction in hippocampal cell death (relative to untreated controls) following oxygen-glucose deprivation. These data suggest that VEGFD is not directly neuroprotective, but rather that its ability to preserve neuronal structure might indirectly attenuate stroke-related cell death. Finally, the authors demonstrated that intranasal delivery of either recombinant VEGFD or VEGFD peptide mimetics (they synthesized a library of VEGFD-derived peptides and screened for variants that had the highest binding affinity for the VEGFD receptor VEGFR3) had similar effects to injecting recombinant VEGFD into the ventricles – both of these methods also resulted in reduced dendrite loss, neuronal cell death, and behavioral impairment relative to controls.
What’s the impact?
This study outlines a model of stroke-associated dendrite loss as well as a novel, non-invasive therapeutic to alleviate structural and functional impairment following ischemic stroke. Interestingly, a variety of neurodegenerative disorders such as Huntington’s, Alzheimer’s, and Lou Gehrig’s disease are, like stroke, characterized by elevated levels of extrasynaptic NMDAR activity. Thus, these findings suggest that future research should consider investigating VEGFD supplementation as a treatment option not only for stroke but for a range of neurodegenerative diseases.
Mauceri et al. Nasally delivered VEGFD mimetics mitigate stroke-induced dendrite loss and brain damage. PNAS (2020). Access the original scientific publication here.