Molecular and cellular permeability control at the blood–brain barrier (original) (raw)
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Fluids and Barriers of the CNS, 2012
The Blood-brain barrier (BBB), present at the level of the endothelium of cerebral blood vessels, selectively restricts the blood-to-brain paracellular diffusion of compounds; it is mandatory for cerebral homeostasis and proper neuronal function. The barrier properties of these specialized endothelial cells notably depend on tight junctions (TJs) between adjacent cells: TJs are dynamic structures consisting of a number of transmembrane and membrane-associated cytoplasmic proteins, which are assembled in a multimolecular complex and acting as a platform for intracellular signaling. Although the structural composition of these complexes has been well described in the recent years, our knowledge about their functional regulation still remains fragmentary. Importantly, pericytes, embedded in the vascular basement membrane, and perivascular microglial cells, astrocytes and neurons contribute to the regulation of endothelial TJs and BBB function, altogether constituting the so-called neurovascular unit. The present review summarizes our current understanding of the structure and functional regulation of endothelial TJs at the BBB. Accumulating evidence points to a correlation between BBB dysfunction, alteration of TJ complexes and progression of a variety of CNS diseases, such as stroke, multiple sclerosis and brain tumors, as well as neurodegenerative diseases like Parkinson's and Alzheimer's diseases. Understanding how TJ integrity is controlled may thus help improve drug delivery across the BBB and the design of therapeutic strategies for neurological disorders.
Brain Endothelial Cell-Cell Junctions: How to “Open” the Blood Brain Barrier
Current Neuropharmacology, 2008
The blood-brain barrier (BBB) is a highly specialized structural and biochemical barrier that regulates the entry of blood-borne molecules into brain, and preserves ionic homeostasis within the brain microenvironment. BBB properties are primarily determined by junctional complexes between the cerebral endothelial cells. These complexes are comprised of tight and adherens junctions. Such restrictive angioarchitecture at the BBB reduces paracellular diffusion, while minimal vesicle transport activity in brain endothelial cells limits transcellular transport. Under normal conditions, this largely prevents the extravasation of large and small solutes (unless specific transporters are present) and prevents migration of any type of blood-borne cell. However, this is changed in many pathological conditions. There, BBB disruption ("opening") can lead to increased paracellular permeability, allowing entry of leukocytes into brain tissue, but also contributing to edema formation. In parallel, there are changes in the endothelial pinocytotic vesicular system resulting in the uptake and transfer of fluid and macromolecules into brain parenchyma. This review highlights the route and possible factors involved in BBB disruption in a variety of neuropathological disorders (e.g. CNS inflammation, Alzheimer's disease, Parkinson's disease, epilepsy). It also summarizes proposed signal transduction pathways that may be involved in BBB "opening".
Blood-Brain Barrier Permeability: From Bench to Bedside
Management of Epilepsy - Research, Results and Treatment, 2011
The concept of the blood-brain barrier (termed hematoencephalic barrier) was first introduced by Lina Stern in 1921, although the early work by Paul Ehrlich and Edwin Goldmann suggested the compartmentalization between blood and brain and a role of blood vessels in maintaining these compartments (Ehrlich, 1885; Goldmann, 1913; Vein, 2008). However, actual proof of the existence of a BBB came in the 1960s. Since then, significant progress has been made in defining the functions and properties of that barrier. The BBB is a highly specialized structural and biochemical barrier that regulates the entry of blood-borne molecules and cells into brain and preserves ionic homeostasis within the brain microenvironment (Pardridge, 2007; Rubin & Staddon, 1999; Ueno, 2007). Formed at the interface between blood and brain parenchyma, the BBB is composed of a tightly sealed monolayer of brain endothelial cells at the brain capillary surface and adjacent perivascular cells, including astrocytes and pericytes. Both astrocytic endfeet and pericyte processes wrap the abluminal capillary surface and through indirect or direct synapse-like "pegsocket" interactions provide physical support and stability to the BBB (Abbott, 2002; Armulik et al, 2010; Kim et al, 2006; Williams et al, 2001). In recent years, the concept of a BBB has been significantly extended to the concept of a neurovascular unit, which best describes the dynamic communication between brain endothelium, neurons, astrocytes, pericytes, vascular smooth muscle cells, microglia and perivascular macrophages at the interface between the blood and brain parenchyma compartments (Hawkins & Davis, 2005; Wolburg et al, 2009). A healthy brain relies on all of the cells of the neurovascular unit to function properly and communicate with each other in order for neuronal synapses and circuitries to maintain normal cognitive functions (Fig. 1). 2. Blood-brain barrier junctional complexes The structural properties of the BBB are primarily determined by the endothelial junctional complexes, consisting of tight junctions (TJ) and adherens junctions (AdJ). The interactions between brain endothelial cells provide high endothelial electrical resistance barrier, in the range of 1500-2000 Ω.cm 2 (pial vessels), as compared to 3-33 Ω.cm 2 endothelial barrier in www.intechopen.com
Blood-Brain Barrier Dysfunction in CNS Disorders and Putative Therapeutic Targets: An Overview
Pharmaceutics
The blood-brain barrier (BBB) is a fundamental component of the central nervous system (CNS). Its functional and structural integrity is vital to maintain the homeostasis of the brain microenvironment by controlling the passage of substances and regulating the trafficking of immune cells between the blood and the brain. The BBB is primarily composed of highly specialized microvascular endothelial cells. These cells’ special features and physiological properties are acquired and maintained through the concerted effort of hemodynamic and cellular cues from the surrounding environment. This complex multicellular system, comprising endothelial cells, astrocytes, pericytes, and neurons, is known as the neurovascular unit (NVU). The BBB strictly controls the transport of nutrients and metabolites into brain parenchyma through a tightly regulated transport system while limiting the access of potentially harmful substances via efflux transcytosis and metabolic mechanisms. Not surprisingly, ...
Looking at the blood–brain barrier: Molecular anatomy and possible investigation approaches
Brain Research Reviews, 2010
The blood-brain barrier (BBB) is a dynamic and complex interface between blood and the central nervous system that strictly controls the exchanges between the blood and brain compartments, therefore playing a key role in brain homeostasis and providing protection against many toxic compounds and pathogens. In this review, the unique properties of brain microvascular endothelial cells and intercellular junctions are examined. The specific interactions between endothelial cells and basement membrane as well as neighboring perivascular pericytes, glial cells and neurons, which altogether constitute the neurovascular unit and play an essential role in both health and function of the central nervous system, are also explored. Some relevant pathways across the endothelium, as well as mechanisms involved in the regulation of BBB permeability, and the emerging role of the BBB as a signaling interface are addressed as well. Furthermore, we summarize some of the experimental approaches that can be used to monitor BBB properties and function in a variety of conditions and have allowed recent advances in BBB knowledge. Elucidation of the molecular anatomy and dynamics of the BBB is an essential step for the development of new strategies directed to maintain or restore BBB integrity and barrier function and ultimately preserve the delicate interstitial brain environment.
Blood-brain barrier transport machineries and targeted therapy of brain diseases
BioImpacts, 2016
Introduction Microcirculation of nutrients and drugs into the brain is selectively controlled by a unique biological barrier called blood-brain barrier (BBB). Such biological barrier is formed by the brain capillary endothelial cells (BCECs) whose maturation and functions is largely dependent upon intercellular interaction with brain astrocytes and pericytes. 1-3 Of the BBB cooperating cells, the astrocytes are members of the glial family, which are able to interact with neurons and other brain cells (e.g., microglia and endothelial cells) directly and/or indirectly through the exchange of soluble materials. At the BBB, the astrocytic foot process covers 99% of the abluminal surface of the capillary basement membrane, while the brain capillary pericytes share the basement membrane with BCECs (Fig. 1). The BCECs form a cooperating complex with astrocytes and pericytes (the "Neurovascular Unit") to: (a) maintain brain homeostasis, (b) selectively control the delivery of nutrients and blood-borne solutes to the brain parenchyma. 1 In addition to other modulation roles of astrocytes and pericytes on BCECs (e.g., restrictive tight junction (TJ) regulation and differentiation), they are also involved in modulating the functional expression of transport machineries required for the selective inward/ outward transportation of nutrients and drugs. 4 It is now well-documented that the capability of a
Frontiers in Psychiatry, 2012
Interendothelial cell tight junctions (TJs) proteins contribute to maintain the structural and functional integrity of the blood-brain barrier (BBB) and several efflux transporters regulate transport of compounds across BBB. A unique double compartment-model of the BBB, consisting of cerebral endothelial cells isolated from cryopreserved human glial tumors, alone and in the presence of human astroglial cells derived from the same tissue preparation was established. Endothelial cell viability and transendothelial electrical resistance (TEER) were measured in this model and three representative TJ proteins-occludin (OCLN), zonula occludens-1 (ZO-1) and claudin-5 (CLN-5)-as well as several drug efflux transporters-P-glycoprotein (P-gp), multidrug resistance protein-1 and 2 (MRP-1 and MRP-2), organic anion-transporting polypeptide-1 and 3 (oatp1 and oatp3) were analyzed at both the protein and gene transcript level. Functional activity of P-gp and MRP-1 was also assessed. Endothelial cell viability as well asTEER significantly increased in the presence of glial cells. A significant increase of expression of OCLN, ZO-1, and CLN-5 proteins as well as of several drug transporter proteins except oatp3 and MRP-1, was also found in the presence of glial cells. All the gene transcripts protein analyzed were found to be significantly increased in the presence of glial cells. A suitable functional activity of P-gp and MRP-1 was also found. These results demonstrate that this brain endothelium culture system mimics a physiologically relevant situation and may therefore provide a new tool for studying the effects of biological fluids such as serum and cerebrospinal fluid from patients with neurological disorders underlying a BBB alteration in disease pathogenesis.
Journal of Visualized Experiments, 2014
The blood brain barrier (BBB) specifically regulates molecular and cellular flux between the blood and the nervous tissue. Our aim was to develop and characterize a highly reproducible rat syngeneic in vitro model of the BBB using co-cultures of primary rat brain endothelial cells (RBEC) and astrocytes to study receptors involved in transcytosis across the endothelial cell monolayer. Astrocytes were isolated by mechanical dissection following trypsin digestion and were frozen for later co-culture. RBEC were isolated from 5-week-old rat cortices. The brains were cleaned of meninges and white matter, and mechanically dissociated following enzymatic digestion. Thereafter, the tissue homogenate was centrifuged in bovine serum albumin to separate vessel fragments from nervous tissue. The vessel fragments underwent a second enzymatic digestion to free endothelial cells from their extracellular matrix. The remaining contaminating cells such as pericytes were further eliminated by plating the microvessel fragments in puromycin-containing medium. They were then passaged onto filters for co-culture with astrocytes grown on the bottom of the wells. RBEC expressed high levels of tight junction (TJ) proteins such as occludin, claudin-5 and ZO-1 with a typical localization at the cell borders. The transendothelial electrical resistance (TEER) of brain endothelial monolayers, indicating the tightness of TJs reached 300 ohm•cm 2 on average. The endothelial permeability coefficients (Pe) for lucifer yellow (LY) was highly reproducible with an average of 0.26 ± 0.11 x 10-3 cm/min. Brain endothelial cells organized in monolayers expressed the efflux transporter P-glycoprotein (P-gp), showed a polarized transport of rhodamine 123, a ligand for P-gp, and showed specific transport of transferrin-Cy3 and DiILDL across the endothelial cell monolayer. In conclusion, we provide a protocol for setting up an in vitro BBB model that is highly reproducible due to the quality assurance methods, and that is suitable for research on BBB transporters and receptors.
Journal of Visualized Experiments, 2014
The blood brain barrier (BBB) specifically regulates molecular and cellular flux between the blood and the nervous tissue. Our aim was to develop and characterize a highly reproducible rat syngeneic in vitro model of the BBB using co-cultures of primary rat brain endothelial cells (RBEC) and astrocytes to study receptors involved in transcytosis across the endothelial cell monolayer. Astrocytes were isolated by mechanical dissection following trypsin digestion and were frozen for later co-culture. RBEC were isolated from 5-week-old rat cortices. The brains were cleaned of meninges and white matter, and mechanically dissociated following enzymatic digestion. Thereafter, the tissue homogenate was centrifuged in bovine serum albumin to separate vessel fragments from nervous tissue. The vessel fragments underwent a second enzymatic digestion to free endothelial cells from their extracellular matrix. The remaining contaminating cells such as pericytes were further eliminated by plating the microvessel fragments in puromycin-containing medium. They were then passaged onto filters for co-culture with astrocytes grown on the bottom of the wells. RBEC expressed high levels of tight junction (TJ) proteins such as occludin, claudin-5 and ZO-1 with a typical localization at the cell borders. The transendothelial electrical resistance (TEER) of brain endothelial monolayers, indicating the tightness of TJs reached 300 ohm•cm 2 on average. The endothelial permeability coefficients (Pe) for lucifer yellow (LY) was highly reproducible with an average of 0.26 ± 0.11 x 10-3 cm/min. Brain endothelial cells organized in monolayers expressed the efflux transporter P-glycoprotein (P-gp), showed a polarized transport of rhodamine 123, a ligand for P-gp, and showed specific transport of transferrin-Cy3 and DiILDL across the endothelial cell monolayer. In conclusion, we provide a protocol for setting up an in vitro BBB model that is highly reproducible due to the quality assurance methods, and that is suitable for research on BBB transporters and receptors.
Structure and function of the blood-brain barrier
Frontiers in Pharmacology, 2010
Neural signalling within the central nervous system (CNS) requires a highly controlled microenvironment. Cells at three key interfaces form barriers between the blood and the CNS: the blood-brain barrier (BBB), blood-CSF barrier and the arachnoid barrier. The BBB at the level of brain microvessel endothelium is the major site of blood-CNS exchange. The structure and function of the BBB is summarised, the physical barrier formed by the endothelial tight junctions, and the transport barrier resulting from membrane transporters and vesicular mechanisms. The roles of associated cells are outlined, especially the endfeet of astrocytic glial cells, and pericytes and microglia. The embryonic development of the BBB, and changes in pathology are described. The BBB is subject to short and long-term regulation, which may be disturbed in pathology. Any programme for drug discovery or delivery, to target or avoid the CNS, needs to consider the special features of the BBB.