Neurovascular unit senescence as a driver of blood-brain barrier dysfunction in Alzheimer's disease：Mechanisms, consequences, and therapeutic implications.

Alzheimer's disease (AD) is a common age-related neurodegenerative disorder (NDD), with ageing as its primary risk factor. Cellular senescence, characterized by permanent cell-cycle arrest, apoptosis resistance and acquisition of the senescence-associated secretory phenotype (SASP), is the cellular hallmark of ageing. Recent evidence indicates that blood-brain barrier (BBB) dysfunction precedes cognitive decline and pathological protein deposition, representing an early event in AD, with the neurovascular unit (NVU) providing the structural and functional basis of the BBB. Mounting evidence shows that the core NVU cells-brain microvascular endothelial cells (BMECs), pericytes and astrocytes-enter senescence under AD-related conditions. SASP factors released by these cells disrupt BBB junction proteins and trans-BBB transport systems, and propagate senescence within the NVU via paracrine signaling. Peripheral inflammatory mediators and immune cells then traverse the compromised BBB, aggravating AD pathology, while accumulating Aβ, tau and reactive oxygen species (ROS) reciprocally accelerate NVU senescence, constituting a proposed vicious cycle. At the molecular level, the cGAS-STING pathway concurrently drives senescence maintenance, SASP induction and type I interferon (IFN-I)-mediated downregulation of BBB junction proteins, serving as a key convergence point linking NVU senescence to BBB injury. From the NVU perspective, this review systematically examines how cellular senescence drives BBB dysfunction and AD progression, clarifies the role of cGAS-STING as a molecular node, and discusses therapeutic strategies targeting NVU senescence to preserve BBB integrity, aiming to offer new insights into AD mechanisms and treatment.