When Barriers Break: Tight Junction Regulation and Dynamic Alterations of Barrier Integrity in Neurological Injury.

The blood-brain barrier and blood-spinal cord barrier (BBB/BSCB) are essential protective components for the healthy functioning of the central nervous system (CNS). While these barriers protect the CNS from peripheral factors, such as immune cells and blood products, they can become disrupted in pathological conditions and injury. The neurovascular unit (NVU) is composed of endothelial cells (ECs), pericytes, astrocytes, microglia, and neurons, all of which contribute to proper function and the maintenance of the BBB/BSCB. Tight junctions (TJs) unite cellular components and are modulated by both intrinsic and extrinsic factors. Systemic processes, such as pain (nociceptive activity), inflammation, and blood hemostasis, can impact BBB/BSCB function, often leading to a disrupted barrier and increased peripheral infiltration. This, in turn, can increase neuroinflammation and drive microglia activation, progressive hemorrhagic necrosis (PHN), and matrix metalloproteinase (MMP) activity. Targeting these processes and mitigating the deleterious effects of BBB/BSCB breakdown represents a key therapeutic target after neural injury and other pathological conditions.