Endothelial-to-mesenchymal Transition at the Blood-brain Barrier: Molecular Mechanisms and Pathological Roles Across...

Endothelial-to-Mesenchymal Transition (EndMT) is a significant contributor to Blood- Brain Barrier (BBB) dysfunction in various brain diseases. The majority of current therapies, aimed at reducing BBB dysfunction, focus on preventing inflammation or stabilizing tight junctions. In most cases, these therapies do not provide adequate or long-lasting vascular protection. Endothelial cells undergo phenotypic programming, losing their barrier-forming capacity and developing features of mesenchymal and extracellular matrix-producing cells as the disease progresses. The change leads to chronic vascular leakage, neuroinflammation, microvascular fibrosis, and dysfunctional neurovascular coupling. Several upstream stimuli, including inflammatory cytokines, TGF-β/BMP-Smad signaling, and oxidative damage, converge to drive EndMT within the distinctive, specialized environment of the brain endothelium. Ischemic stroke, multiple sclerosis, cerebral cavernous malformations, arteriovenous malformations, glioblastoma, brain metastasis, and Alzheimer's disease indicate that EndMT is not a rare or unique process but a shared and common pathologic process that may result in disease progression and eventual resistance to treatment. Recent single-cell and spatial transcriptomic data have shown that partial EndMT states exist and may be precursors to irreversible microvascular remodeling. It is necessary to identify therapeutic approaches that go beyond short-term stabilization of the BBB and target the molecular programs underlying the loss of endothelial identity. This review synthesizes mechanistic, disease-related, and therapeutic evidence indicating that EndMT is a leading cause of BBB failure and highlights therapeutic opportunities for targeting this endothelial plasticity in brain diseases.