This is a mechanism module, not a disease. Disorder entries reference individual nodes with conforms_to, for example "blood_brain_barrier_breakdown#Blood-Brain Barrier Permeability Increase".
What a conformer substitutes. Only the trigger node is disorder-specific: neurotrauma substitutes mechanical deformation of the neurovascular unit at the impact site; ischaemic stroke substitutes occlusion and reperfusion; sepsis-associated encephalopathy substitutes circulating bacterial products and systemic cytokines; status epilepticus and chronic epilepsy substitute seizure activity. The cell types are conserved across all of them — brain microvascular endothelial cell, brain pericyte, astrocyte — so a conformer should normally keep them rather than substituting an organ-specific cell as conformers of the fibrotic or alveolar modules do. A conformer may legitimately specialize the plasma protein it cares about: albumin where the consequence is astrocytic TGF-beta signalling and loss of potassium buffering, fibrinogen where it is perivascular microglial clustering and axonal damage.
Worked conformers to come: Traumatic_Brain_Injury (not yet created) at the permeability node, and the existing Post-Traumatic_Epilepsy node "Blood-Brain Barrier Disruption and Albumin Extravasation", which already carries the albumin/TGF-beta chain this module's effector node generalizes.
Two scope limits worth knowing before conforming. First, the module covers barrier opening after an insult to a developed barrier; it does not cover failure of barrier formation during development, which is a different mechanism with a different cell biology. Second, vasogenic oedema is the terminal node, and it is not the only oedema after CNS injury: cytotoxic (cellular) oedema arises from maladaptive ion and water transport into cells and can dominate the measured brain-water increase even while the barrier is intact or recovering. An entry whose oedema is primarily cytotoxic should not conform here on the strength of the oedema alone.
The ordering of the transcellular and paracellular steps is an open question the module does not settle. In the mouse stroke model that imaged both, the rise in endothelial caveolae and transcytosis preceded structural tight-junction defects by days, so the amplifier node names both routes and does not assert that junctional loss comes first. Whether that ordering holds in trauma or sepsis has not been shown.
Neurovascular Unit Insult
trigger
An insult reaches the neurovascular unit — the brain microvascular endothelium, its investing pericytes and basal lamina, and the astrocytic endfeet that surround the vessel. The initiating agents are heterogeneous: mechanical deformation of cerebral vessels in neurotrauma, occlusion and reperfusion in ischaemic stroke, circulating bacterial products and cytokines in sepsis, and seizure activity. Each converges on inflammatory signalling at the vessel wall and on structural disorganization of the unit — pericyte detachment from the basal lamina, loss of endfoot polarization — rather than on injury to one cell type alone. This node is the disorder-specific entry point; conforming entries substitute their own insult here.
Downstream
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Tight Junction Disassembly
The insult activates matrix metalloproteinases at the vessel wall, which proteolyse the endothelial tight-junction proteins; inhibiting the proteases prevents the junctional loss, which makes the step causal rather than coincident.
Show evidence (5 references)
"pericyte deficiency increases the permeability of the BBB to water and a range of low-molecular-mass and high-molecular-mass tracers."
Establishes that the pericyte, not the endothelium alone, is a constituent of the barrier, so loss of the pericyte compartment is itself sufficient to raise permeability.
"by inducing polarization of astrocyte end-feet surrounding CNS blood vessels."
Supports treating endothelium, pericyte and astrocytic endfoot as one coupled unit, which is why this node is written at the level of the unit rather than of a single cell type.
"LPS-treated mice exhibited a broken basal lamina and pericyte detachment from the basal lamina at 6-24 h after LPS injection."
A non-traumatic, non-ischaemic systemic inflammatory insult producing structural disorganization of the same unit, which is the module's claim that the trigger is substitutable.
+ 2 more references
Tight Junction Disassembly
amplifier
Proteases released or activated at the injured vessel wall — matrix metalloproteinase-9 and matrix metalloproteinase-2 prominently, with membrane-type MMP and furin as activators — degrade the endothelial tight-junction proteins claudin-5, occludin and ZO-1 and the perivascular extracellular matrix, and the junctional proteins are lost from or redistributed away from the cell-cell contact. In parallel the endothelium increases vesicular traffic: caveolae multiply and the transcellular transcytosis rate rises. The two routes are not alternatives but components of the same amplification step, and in the one model where both were imaged in vivo the transcellular change came first. Because claudin-5 loss alone opens the barrier only to small solutes, the magnitude of the eventual leak depends on how much of this programme runs.
Downstream
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Blood-Brain Barrier Permeability Increase
Loss of the junctional proteins and the rise in transcytosis are what the measured leak consists of. Both interventional directions support the edge: deleting the protease that degrades ZO-1 attenuates tracer leakage, and inhibiting the proteases pharmacologically prevents the barrier opening.
Show evidence (5 references)
"Our results provide direct evidence that MMPs open the BBB by degrading TJPs and that an MMP inhibitor prevents degradation of the TJPs by MMPs."
The authors' own statement of the mechanism this node asserts — protease degradation of tight-junction proteins as the route by which the barrier opens.
"zonae occludens-1 was degraded after ischemia, but this was reduced in knock-out mice."
Identifies ZO-1 as a protease substrate degraded after the insult, naming one of the specific junctional proteins lost at this node. Note the same study found no detectable change in occludin, so the substrate set is protease-specific rather than uniform.
"the BBB against small molecules (<800 D), but not larger molecules, was selectively affected."
Loss of claudin-5 alone is sufficient to open the barrier, but only to small solutes, which is why this node treats the magnitude of the leak as depending on how much of the junctional and transcellular programme runs rather than on claudin-5 loss alone.
+ 2 more references
Blood-Brain Barrier Permeability Increase
central effector
The cerebrovascular barrier now passes solutes and proteins it normally excludes. This is the module's rate-limiting, disorder-agnostic state and the node conforming entries should target. It is a state rather than an event: after neurotrauma it is detectable within hours, persists for months in animal models and is still present in a substantial proportion of human late survivors, so an entry modelling a chronic post-injury process can place its mechanism downstream of this node rather than treating barrier opening as a transient acute phenomenon. It is also the step the available readouts measure directly — gadolinium or tracer leakage in vivo, parenchymal fibrinogen, immunoglobulin or albumin immunostaining in tissue — which is what makes the module auditable across diseases whose triggers have nothing in common.
Downstream
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Extravasation of Plasma Proteins into the Brain Parenchyma
A barrier that passes macromolecules admits the abundant plasma proteins first, so the permeability state is read out in tissue as perivascular and parenchymal fibrinogen, immunoglobulin and albumin.
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Vasogenic Cerebral Edema
Raised permeability lets protein-rich plasma filtrate follow its osmotic and hydrostatic gradients into the extracellular space; that accumulation is what vasogenic oedema is, so the definitional link runs from this node to the oedema node.
Show evidence (4 references)
"These preliminary data demonstrate evidence of widespread BBB disruption in a proportion of TBI patients emerging in the acute phase and, intriguingly, persisting in a high proportion of late survivors."
Human evidence for both properties this node asserts — early onset and persistence — in an autopsy series spanning acute to decades-long survival. The authors call the data preliminary, and the proportions are of a selected autopsy cohort rather than of injured people generally.
"MRI indicated persistent Gd leakage in the impacted cortex and thalamus of variable severity in all rats with TBI which correlated with fluorescein extravasation."
Longitudinal in vivo measurement of the permeability state after trauma, with two independent tracers agreeing, supporting the node as a persistent measurable state rather than an acute event.
"These changes were attenuated in Mmp9(-/-) mice and were associated with lesser loss of short-term memory in these mice than in WT mice."
Removing the upstream protease reduces the permeability state and its parenchymal protein deposition after trauma, which supports this node sitting downstream of the junctional step in a second insult type.
+ 1 more reference
Vasogenic Cerebral Edema
consequence
Protein-rich fluid accumulating in the extracellular space expands brain volume. Because the skull is closed, this raises intracranial pressure, impairs cerebral perfusion and oxygenation, and so causes further ischaemic injury — the step at which a local barrier failure becomes a whole-organism problem and the clinical target of osmotherapy. Clearance runs partly through astrocytic aquaporin-4, so the oedema's severity reflects the balance between the rate of entry across the failed barrier and the rate of transcellular removal, not the entry rate alone. In focal ischaemia the same capillary dysfunction can progress beyond vasogenic oedema to frank haemorrhagic conversion.
Show evidence (3 references)
"Brain edema leading to an expansion of brain volume has a crucial impact on morbidity and mortality following traumatic brain injury (TBI) as it increases intracranial pressure, impairs cerebral perfusion and oxygenation, and contributes to additional ischemic injuries."
States the organism-level consequence chain this node asserts — volume expansion, raised intracranial pressure, impaired perfusion, secondary ischaemia.
"We organise the progressive changes in osmotic and hydrostatic conductivity of abnormal capillaries into three phases: formation of ionic oedema, formation of vasogenic oedema, and catastrophic failure with haemorrhagic conversion."
Places vasogenic oedema in a graded sequence of capillary dysfunction that can progress to haemorrhagic conversion, which is the severity statement in this node's description.
"Thus, AQP4-mediated transcellular water movement is crucial for fluid clearance in vasogenic brain edema, suggesting AQP4 activation and/or up-regulation as a novel therapeutic option in vasogenic brain edema."
Supports the clearance arm of this node — that severity depends on astrocytic transcellular water removal as well as on entry across the failed barrier.