CD44 mediates shear stress mechanotransduction in an in vitro blood-brain barrier model through small GTPases RhoA and Rac1.

Fluid shear stress is an important mediator of vascular permeability, yet the molecular mechanisms underlying the effect of shear on the blood-brain barrier (BBB) have yet to be clarified in cerebral vasculature despite its importance for brain homeostasis. The goal of this study is to probe components of shear mechanotransduction within the BBB to gain a better understanding of pathologies associated with changes in cerebral perfusion including ischemic stroke. Interrogating the effects of shear stress in vivo is complicated by the complexity of factors in the brain parenchyma and the difficulty associated with modulating blood flow regimes. The in vitro model used in this study is compatible with real-time measurement of barrier function using a transendothelial electrical resistance as well as immunocytochemistry and dextran permeability assays. These experiments reveal that there is a threshold level of shear stress required for barrier formation and that the composition of the extracellular matrix, specifically the presence of high molecular weight hyaluronan, dictates the flow response. Gene editing to modulate the expression of CD44, a mechanosensitive receptor for hyaluronan, demonstrates that the receptor is required for the endothelial response to shear stress. Manipulation of small GTPase activity reveals CD44 activates Rac1 while inhibiting RhoA activation. Additionally, adducin-γ localizes to tight junctions in response to shear stress and RhoA inhibition and is required to maintain the barrier. This study identifies specific components of the mechanosensing complex associated with the BBB response to fluid shear stress and, therefore, illuminates potential targets for barrier manipulation in vivo.

How accurate is the neurosurgery literature? A review of references.

BACKGROUND: The reference list is an important part of academic manuscripts. The goal of this study is to evaluate the reference accuracy in the field of neurosurgery. METHODS: This study examines four major peer-reviewed neurosurgery journals, chosen based on their clinical impact factor: Neurosurgery, J Neurosurg, World Neurosurg, and Acta Neurochir. For each of the four journals, five articles from each of the journal's 12 issues published in 2019 were randomly selected using an online generator. This resulted in a total of 240 articles, 60 from each journal. Additionally, from each article's list of references, one reference was again randomly selected and checked for a citation or quotation error. The chi-square test was used to analyze the association between the occurrence of citation and quotation errors and the presence of hypothesized risk factors that could impact reference accuracy. RESULTS: 62.1% of articles had a minor citation error, 8.33% had a major citation error, 12.1% had a minor quotation error, and 5.8% of articles had a major quotation error. Overall, Acta Neurochir presented with the fewest quotation errors compared with the other journals evaluated. The only association between the frequency of errors and potential markers of reference mistakes was with the length of the bibliography. Surprisingly, this correlation indicated that the articles with longer reference lists had fewer citation errors (p < 0.01). Statistical significance was found between the occurrence of citation errors and the journals of publication (p < 0.01). CONCLUSIONS: In order to advance medical treatment and patient care in neurosurgery, detailed documentation and attention to detail are necessary. The results from this analysis illustrate that improved reference accuracy is required.

Reference accuracy in spine surgery.

OBJECTIVE: The references list is an important part of a scientific article that serves to confirm the accuracy of the authors' statements. The goal of this study was to evaluate the reference accuracy in the field of spine surgery. METHODS: Four major peer-reviewed spine surgery journals were chosen for this study based on their subspecialty clinical impact factors. Sixty articles per journal were selected from 12 issues each of The Spine Journal, Spine, and Journal of Neurosurgery: Spine, and 40 articles were selected from 8 issues of Global Spine Journal, for a total of 220 articles. All the articles were published in 2019 and were selected using computer-generated numbers. From the references list of each article, one reference was again selected by using a computer-generated number and then checked for citation or quotation errors. RESULTS: The results indicate that 84.1% of articles have a minor citation error, 4.5% of articles have a major citation error, 9.5% of articles have a minor quotation error, and 9.1% of articles have a major quotation error. Journal of Neurosurgery: Spine had the fewest citation errors compared with the other journals evaluated in this study. Using chi-square analysis, no association was determined between the occurrence of errors and potential markers of reference mistakes. Still, statistical significance was found between the occurrence of citation errors and the spine journals tested. CONCLUSIONS: In order to advance medical treatment and patient care in spine surgery, detailed documentation and attention to detail are necessary. The results from this study illustrate that improved reference accuracy is required.

Vascularization of self-assembled peptide scaffolds for spinal cord injury repair.

The disruption of the blood-spinal cord barrier (BSCB) following spinal cord injury contributes to inflammation and glial scarring that inhibits axon growth and diminishes the effectiveness of conduits transplanted to the injury site to promote this growth. The purpose of this study is to evaluate whether scaffolds containing microvessels that exhibit BSCB integrity reduce inflammation and scar formation at the injury site and lead to increased axon growth. For these studies, a self-assembling peptide scaffold, RADA-16I, is used due to its established permissiveness to axon growth and ability to support vascularization. Immunocytochemistry and permeability transport assays verify the formation of tight-junction containing microvessels within the scaffold. Peptide scaffolds seeded with different concentrations of microvascular cells are then injected into a spinal contusion injury in rats to evaluate how microvessels affect axon growth and neurovascular interaction. The effect of the vascularized scaffold on inflammation and scar formation is evaluated by quantifying histological sections stained with ED-1 and GFAP, respectively. Our results indicate that the peptide scaffolds containing microvessels reduce inflammation and glial scar formation and increase the density of axons growing into the injury/transplant site. These results demonstrate the potential benefit of scaffold vascularization to treat spinal cord injury. STATEMENT OF SIGNIFICANCE: This study evaluates the benefit of transplanting microvascular cells within a self-assembling peptide scaffold, RADA-16I, that has shown promise for facilitating regeneration in the central nervous system in previous studies. Our results indicate that vasculature featuring tight junctions that give rise to the blood-spinal cord barrier can be formed within the peptide scaffold both in vitro and in a rat model of a subacute contusion spinal cord injury. Histological analysis indicates that the presence of the microvessels encourages axon infiltration into the site of injury and reduces the area of astrocyte activation and inflammation. Overall, these results demonstrate the potential of vascularizing scaffolds for the repair of spinal cord injury.

Harnessing neurovascular interaction to guide axon growth.

Regulating the intrinsic interactions between blood vessels and nerve cells has the potential to enhance repair and regeneration of the central nervous system. Here, we evaluate the efficacy of aligned microvessels to induce and control directional axon growth from neural progenitor cells in vitro and host axons in a rat spinal cord injury model. Interstitial fluid flow aligned microvessels generated from co-cultures of cerebral-derived endothelial cells and pericytes in a three-dimensional scaffold. The endothelial barrier function was evaluated by immunostaining for tight junction proteins and quantifying the permeability coefficient (~10-7 cm/s). Addition of neural progenitor cells to the co-culture resulted in the extension of Tuj-positive axons in the direction of the microvessels. To validate these findings in vivo, scaffolds were transplanted into an acute spinal cord hemisection injury with microvessels aligned with the rostral-caudal direction. At three weeks post-surgery, sagittal sections indicated close alignment between the host axons and the transplanted microvessels. Overall, this work demonstrates the efficacy of exploiting neurovascular interaction to direct axon growth in the injured spinal cord and the potential to use this strategy to facilitate central nervous system regeneration.

Mechanical stress regulates transport in a compliant 3D model of the blood-brain barrier.

Transport of fluid and solutes is tightly controlled within the brain, where vasculature exhibits a blood-brain barrier and there is no organized lymphatic network facilitating waste transport from the interstitial space. Here, using a compliant, three-dimensional co-culture model of the blood-brain barrier, we show that mechanical stimuli exerted by blood flow mediate both the permeability of the endothelial barrier and waste transport along the basement membrane. Application of both shear stress and cyclic strain facilitates tight junction formation in the endothelial monolayer, with and without the presence of astrocyte endfeet in the surrounding matrix. We use both dextran perfusion and TEER measurements to assess the initiation and maintenance of the endothelial barrier, and microparticle image velocimetry to characterize the fluid dynamics within the in vitro vessels. Application of pulsatile flow to the in vitro vessels induces pulsatile strain to the vascular wall, providing an opportunity to investigate stretch-induced transport along the basement membrane. We find that a pulsatile wave speed of approximately 1 mm/s with Womersley number of 0.004 facilitates retrograde transport of high molecular weight dextran along the basement membrane between the basal endothelium and surrounding astrocytes. Together, these findings indicate that the mechanical stress exerted by blood flow is an important regulator of transport both across and along the walls of cerebral microvasculature.