Post by Kasey Hemington
What's the science?
Ischemia (lack of oxygen) after stroke can cause severe disability, in part because there is limited blood vessel regeneration (angiogenesis) and repair in damaged brain tissue around the stroke (periinfarct zone). An axonal guidance molecule called Nogo-A is an angiogenesis inhibitor, so blocking this pathway after stroke could result in improved recovery via increased vascular restoration. This week in PNAS, Rust and colleagues assessed the effect of a genetic deletion or antibody-mediated neutralization of Nogo-A on mice after cerebral (brain) ischemia.
How did they do it?
The authors included 13 control mice, nine mice deficient for Nogo-A, and five mice deficient for S1PR2, (Nogo-A’s receptor) in the study. They also applied an anti-Nogo-A antibody to control mice, as an alternative to genetic deletion of Nogo-A. The mice’s motor skills were assessed at several time points between three and 21 days after ischemic brain injury. The authors also characterized gene expression using mRNA extracted from the periinfarct zone, in order to understand what genes were upregulated after stroke. Three weeks post-stroke, histological analysis was performed on the mice’s brains, and vascular function and regeneration, synapse and neurotransmitter function, and cell survival were evaluated. The authors also evaluated the relationship between any functional improvement in mice deficient of Nogo-A and angiogenesis, by applying an anti-VEGF antibody, in order to directly link vascular repair with functional improvement. VEGF is a growth factor critical for angiogenesis.
What did they find?
The authors found that several genes were upregulated post-stroke, including increased expression of Nogo-A and S1PR2 and other inhibitory vascular and neural factors, indicating these genes may be involved in post-stroke brain tissue damage or poor recovery. In control mice three weeks post-stroke, the authors observed low vascular branching and low overall vascular area in the periinfarct region, compared to the uninjured hemisphere of the brain. In Nogo-A and S1PR2 deficient mice, the vascular area was 179% and 53% improved and vascular branching was 179% improved and 85% improved respectively. In the uninjured hemisphere of the brain, vasculature and blood perfusion were not altered in Noga-A or S1PR2 mice compared to control mice. Similar results were found when the vasculature of mice was treated with an anti-Nogo-A antibody. The results suggest inhibiting Nogo-A improved the re-vascularization post-stroke, but didn’t alter vascularization in healthy brain tissue. In functional tests, three weeks post-stroke, Nogo-A and S1PR2 deficient mice experienced less paw dragging, and less error touches in a horizontal ladder test. Paw dragging was negatively correlated with vascular branching, indicating the functional improvement was related to the degree of vascular repair. When VEGF-mediated angiogenesis was blocked using an anti-VEGF antibody in Nogo-A deficient mice, vascular branching and other metrics were decreased compared to Nogo-A deficient mice (that received a control-antibody). These results suggest that the anti-VEGF antibody counteracts the beneficial effects of Nogo-A deletion.
What's the impact?
This study demonstrated that blocking Nogo-A, which can inhibit angiogenesis, results in improved both vascular and functional (behavioural) recovery post-stroke. This study, performed in mice, points to Nogo-A and other neurite outgrowth inhibitors as promising areas for future research, with the potential to improve vascular repair and functional recovery for stroke patients.
Rust et al. Nogo-A targeted therapy promotes vascular repair and functional recovery following stroke. PNAS (2019). Access the original scientific publication here.