Validation and characterization of a novel blood-brain barrier platform for investigating traumatic brain injury

Influence of Blood Components on Neuroinflammation, Blood-Brain Barrier Breakdown, and Functional Damage After Acute Subdural Hematoma in Rats

A central component of injury development after acute subdural hematoma (ASDH) is the increased intracranial pressure and consecutive mechanical reduction of cerebral blood flow (CBF). However, the role of different blood constituents in ASDH as additional lesioning factors remains unclear. This study examines the influence of blood components on neuroinflammation, blood-brain barrier (BBB) breakdown, and functional deficits in a rat model of ASDH. We infused corpuscular (whole blood, whole blood lysate, and red cell blood) and plasmatic (blood plasma, anticoagulated blood plasma, and aqueous isotonic solution) blood components into the subdural space while CBF was monitored. Rats then underwent behavioral testing. Lesion analysis and immunohistochemistry were performed 2 days after ASDH. Inflammatory reaction was assessed using staining for ionized calcium-binding adaptor molecule 1 and glial fibrillary acidic protein, interleukin-1ß, tumor necrosis factor-alpha, and membrane attack complex. Integrity of the BBB was evaluated with albumin and matrix metalloproteinase 9 (MMP9) staining. We observed a significant drop in CBF in the corpuscular group (75% ± 7.5% of baseline) with distinct post-operative deficits and larger lesion volume compared to the plasmatic group (13.6 ± 5.4 vs. 1.3 ± 0.4 mm3). Further, inflammation was significantly increased in the corpuscular group with stronger immunoreaction. After whole blood infusion, albumin and MMP9 immunoreaction were significantly increased, pointing toward a disrupted BBB. The interaction between corpuscular and plasmatic blood components seems to be a key factor in the detrimental impact of ASDH. This interaction results in neuroinflammation and BBB leakage. These findings underscore the importance of performing surgery as early as possible and also provide indications for potential pharmacological targets.

[Mechanobiological Mechanisms Involved in the Regualation of the Blood-Brain Barrier by Fluid Shear Force]

Objective

To explore the mechanobiological mechanism of fluid shear force (FSF) on the protection, injury, and destruction of the structure and function of the blood-brain barrier (BBB) under normal physiological conditions, ischemic hypoperfusion, and postoperative hyperperfusion conditions. BBB is mainly composed of brain microvascular endothelial cells. Rat brain microvascular endothelial cells (rBMECs) were used as model cells to conduct the investigation.

Methods

rBMECs were seeded at a density of 1×105 cells/cm2 and incubated for 48 h. FSF was applied to the rBMECs at 0.5, 2, and 20 dyn/cm2, respectively, simulating the stress BBB incurs under low perfusion, normal physiological conditions, and high FSF after bypass grafting when there is cerebral vascular stenosis. In addition, a rBMECs static culture group was set up as the control (no force was applied). Light microscope, scanning electron microscope (SEM), and laser confocal microscope (LSCM) were used to observe the changes in cell morphology and cytoskeleton. Transmission electron microscope (TEM) was used to observe the tight junctions. Immunofluorescence assay was performed to determine changes in the distribution of tight junction-associated proteins claudin-5, occludin, and ZO-1 and adherens junction-associated proteins VE-cadherin and PECAM-1. Western blot was performed to determine the expression levels of tight junction-associated proteins claudin-5, ZO-1, and JAM4, adherens junction-associated protein VE-cadherin, and key proteins in Rho GTPases signaling (Rac1, Cdc42, and RhoA) under FSF at different intensities.

Results

Microscopic observation showed that the cytoskeleton exhibited disorderly arrangement and irregular orientation under static culture and low shear force (0.5 dyn/cm2). Under normal physiological shear force (2 dyn/cm2), the cytoskeleton was rearranged in the orientation of the FSF and an effective tight junction structure was observed between cells. Under high shear force (20 dyn/cm2), the intercellular space was enlarged and no effective tight junction structure was observed. Immunofluorescence results showed that, under low shear force, the gap between the cells decreased, but there was also decreased distribution of tight junction-associated proteins and adherens junction-associated proteins at the intercellular junctions. Under normal physiological conditions, the cells were tightly connected and most of the tight junction-associated proteins were concentrated at the intercellular junctions. Under high shear force, the gap between the cells increased significantly and the tight junction and adherens junction structures were disrupted. According to the Western blot results, under low shear force, the expression levels of claudin-5, ZO-1, and VE-cadherin were significantly up-regulated compared with those of the control group (P<0.05). Under normal physiological shear force, claudin-5, ZO-1, JAM4, and VE-cadherin were highly expressed compared with those of the control group (P<0.05). Under high shear force, the expressions of claudin-5, ZO-1, JAM4, and VE-cadherin were significantly down-regulated compared with those of the normal physiological shear force group (P<0.05). Under normal physiological shear force, intercellular expressions of Rho GTPases proteins (Rac1, Cdc42, and RhoA) were up-regulated and were higher than those of the other experimental groups (P<0.05). The expressions of Rho GTPases under low and high shear forces were down-regulated compared with that of the normal physiological shear force group (P<0.05).

Conclusion

Under normal physiological conditions, FSF helps maintain the integrity of the BBB structure, while low or high shear force can damage or destroy the BBB structure. The regulation of BBB by FSF is closely related to the expression and distribution of tight junction-associated proteins and adherens junction-associated proteins.

Involvement of Astrocytes in the Formation, Maintenance, and Function of the Blood-Brain Barrier

The blood-brain barrier (BBB) is a fundamental structure that protects the composition of the brain by determining which ions, metabolites, and nutrients are allowed to enter the brain from the blood or to leave it towards the circulation. The BBB is structurally composed of a layer of brain capillary endothelial cells (BCECs) bound to each other through tight junctions (TJs). However, its development as well as maintenance and properties are controlled by the other brain cells that contact the BCECs: pericytes, glial cells, and even neurons themselves. Astrocytes seem, in particular, to have a very important role in determining and controlling most properties of the BBB. Here, we will focus on these latter cells, since the comprehension of their roles in brain physiology has been continuously expanding, even including the ability to participate in neurotransmission and in complex functions such as learning and memory. Accordingly, pathological conditions that alter astrocytic functions can alter the BBB's integrity, thus compromising many brain activities. In this review, we will also refer to different kinds of in vitro BBB models used to study the BBB's properties, evidencing its modifications under pathological conditions.