How are structural components of the BBB affected in the initiation and propagation of ischemic stroke pathology? Can we identify molecular targets to rescue barrier function and improve functional outcome?
With more than 795,000 new cases every year, stroke is the fifth leading cause of mortality and the first leading cause of long-term disability in the U.S. More than 85% of all strokes are ischemic, caused by the occlusion of one of the arteries supplying blood to the brain.
We have shown that in a murine model of ischemic stroke (transient middle cerebral artery occlusion – tMCAo), stroke-induced BBB breakdown appears as two distinct waves of increased vascular permeability: the first one, occurring between 6 and 12 hours after reperfusion, caused by increased rates of transcytosis, and the second one, starting 24 hours after reperfusion, caused by tight junction (TJ) disassembly. We have also shown that the elimination of Caveolin-1 (Cav1-/-), a protein essential for the transcellular transport through caveolae, can effectively rescue the first wave of increased BBB permeability without affecting degradation of adherens junctions (AJs) and TJs, indicating that the two processes are mechanistically independent.
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Mechanisms of blood-brain barrier dysfunction and restoration in ischemic stroke
Dysregulated BBB permeability is a key feature of the pathology of ischemic stroke. We have previously shown that BBB disruption occurs in two distinct waves: an early phase driven by an increase in transcytosis (transcellular permeability), and a later phase due to endothelial junctions dismantling (paracellular permeability). While we can successful prevent the first wave by inhibiting transcellular transport in the animal model (Caveolin-1 knock-out), we are still investigating the molecular mechanisms that regulate paracellular permeability with the ultimate goal to rescue the second wave of BBB dysruption. In particular, we are focusing and the role of Rab7, a small GTPase involved in the endocytic pathway by potentially directing endothelial junctional proteins to lysosomal degradation after stroke.
We are also interested in understanding the impact that sensory stimulation has on BBB function after ischemic stroke. Sensory stimulation in animal models of ischemic stroke has been repeatedly shown to reduce the stroke volume and to ameliorate the neurological manifestations, supposedly by providing an emergency supply of blood flow through collateral circulation. However, the translation of sensory stimulation in the human pathology has proven to be ineffective, or even deleterious. Together with a network of other European and US laboratories, we are investigating the molecular mechanisms activated by sensory stimulation, particularly at the level of the BBB, with the aim of identifying a therapeutic protocol that would be safely translatable to the clinical setting.