What is it about?
When someone has an ischemic stroke, a clot blocks blood flow to part of the brain. Doctors can now remove the main clot in nearly all eligible patients using a procedure called thrombectomy. Yet up to half of these patients still don't recover well, because blood flow fails to fully return to the smallest vessels. This problem is known as "no reflow." We studied why this happens. Using live imaging of the brain in mice, computer modeling of blood flow, and blood samples from stroke patients, we found that two forces combine to clog these tiny vessels. First, after the clot is removed, blood begins flowing in new, converging directions that physically stretch and switch on a sticky blood protein called von Willebrand factor (VWF), which then traps platelets. Second, an inflammatory signal called IL-6, released during the acute phase of stroke, blocks the body's natural enzyme (ADAMTS13) that normally cuts VWF back down to size. Together these create ideal conditions for new microscopic clots. In patients, higher IL-6 tracked with higher VWF activity, and the highest VWF activity appeared in those with the worst outcomes. Blocking VWF, blocking IL-6, or restoring the cutting enzyme in mice all improved blood flow.
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Why is it important?
Removing the clot is only half the battle in stroke care. Restoring blood flow in the large vessel doesn't guarantee that the brain's tiny vessels reopen, which is why many patients remain disabled despite a successful procedure. This work identifies the specific mechanical and inflammatory triggers behind that failure and points to von Willebrand factor as a promising, targetable culprit. Because VWF only becomes active where blood flow is abnormal, drugs aimed at it may reduce clotting in the injured brain without raising bleeding risk as much as standard blood thinners do. Our findings suggest add-on therapies, targeting VWF could be given alongside thrombectomy to help more patients recover.
Perspectives
Stroke care has been transformed by our ability to physically remove clots, and it would be easy to treat reopening the blocked artery as the finish line. Our work suggests it is closer to a midpoint. It is worth being precise about scope here: this is about large-vessel occlusion (LVO) stroke, the subset severe enough to be treated with endovascular thrombectomy, not stroke in general. Most strokes are not LVOs and are not treated this way. But for the patients who do undergo thrombectomy, watching microclots form in real time in the living brain showed us that reperfusion also sets off a second battle in the smallest vessels, one that a successful procedure does not settle on its own. We are cautious about overstating this. No reflow is not caused by any single failure, and von Willebrand factor is one contributor among several, alongside neutrophils, pericytes, and endothelial changes. What drew our attention is that VWF sits where two different triggers meet: a physical one from the altered, converging blood flow after reperfusion, and a chemical one from acute IL-6 that blunts the enzyme normally keeping VWF in check. That convergence is what makes it an appealing target, though not necessarily a sufficient one. The therapeutic picture is also more complicated than a clean cause and effect. Blocking IL-6 improved early blood flow but did not improve outcomes the next day, most likely because IL-6 also has protective roles in the injured brain. Restoring the ADAMTS13 enzyme did improve outcomes, which points us toward VWF-directed strategies rather than broadly suppressing inflammation. Our patient data are correlative, and the mouse model captures only part of human stroke, so we see this as a strong hypothesis to test rather than a settled answer. Mostly, we hope it shifts attention to the vulnerable period right after clot removal in LVO stroke, and encourages careful trials of add-on therapies that protect the smallest vessels for the patients receiving thrombectomy.
Frederik Denorme
Universiteit Antwerpen
Read the Original
This page is a summary of: Mechanisms of von Willebrand factor activation driving no reflow in ischemic stroke, Proceedings of the National Academy of Sciences, July 2026, Proceedings of the National Academy of Sciences,
DOI: 10.1073/pnas.2610397123.
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