Exacerbation of experimental autoimmune encephalomyelitis in P2X7R-/- mice: evidence for loss of apoptotic activity in lymphocytes

The purinergic receptor P2X7R is a nucleotide-gated ion channel that has been proposed to function as a major regulator of inflammation. In this study we examined the role of this receptor in regulating inflammation in the CNS by determining the effects of the loss of this receptor (P2X7R-/-) on experimental autoimmune encephalomyelitis (EAE), an animal model for multiple sclerosis. We show here that P2X7R-/- mice developed more severe clinical and pathological expression of EAE than wild type (WT) controls and that spleen and lymph node cells from P2X7R-/- mice proliferated more vigorously to Ag in vitro. Bone marrow (BM) radiation chimeras revealed that enhanced susceptibility to EAE was detected in chimeric mice of WT host engrafted with P2X7R-/- BM cells, indicating that the genotype of the BM cells regulated disease susceptibility. Coculture of P2X7R-/- macrophages with WT lymphocytes and vice versa showed that enhanced proliferative activity resided within the P2X7R-/- lymphocyte population and correlated with reduced levels of IFN-gamma and NO and apoptosis of lymphocytes. mRNA and protein for IFN-gamma were also significantly reduced in the CNS of P2X7R-/- mice with EAE. FACS analysis of cells isolated from the CNS showed significantly fewer annexin V/propidium iodide-positive lymphocytes in the CNS of P2X7R-/- mice early in the disease, and TUNEL staining of inflamed CNS tissues supported this result. From these data we conclude that enhanced susceptibility of P2X7R-/- mice to EAE reflects a loss of apoptotic activity in lymphocytes, supporting an important role for this receptor in lymphocyte homeostasis.     

Annexin A1 restores Aβ1‐42‐induced blood–brain barrier disruption through the inhibition of RhoA‐ROCK signaling pathway

The blood–brain barrier (BBB) is composed of brain capillary endothelial cells and has an important role in maintaining homeostasis of the brain separating the blood from the parenchyma of the central nervous system (CNS). It is widely known that disruption of the BBB occurs in various neurodegenerative diseases, including Alzheimer's disease (AD). Annexin A1 (ANXA1), an anti‐inflammatory messenger, is expressed in brain endothelial cells and regulates the BBB integrity. However, its role and mechanism for protecting BBB in AD have not been identified. We found that β‐Amyloid 1‐42 (Aβ42)‐induced BBB disruption was rescued by human recombinant ANXA1 (hrANXA1) in the murine brain endothelial cell line bEnd.3. Also, ANXA1 was decreased in the bEnd.3 cells, the capillaries of 5XFAD mice, and the human serum of patients with AD. To find out the mechanism by which ANXA1 recovers the BBB integrity in AD, the RhoA‐ROCK signaling pathway was examined in both Aβ42‐treated bEnd.3 cells and the capillaries of 5XFAD mice as RhoA was activated in both cases. RhoA inhibitors alleviated Aβ42‐induced BBB disruption and constitutively overexpressed RhoA‐GTP (active form of RhoA) attenuated the protective effect of ANXA1. When pericytes were cocultured with bEnd.3 cells, Aβ42‐induced RhoA activation of bEnd.3 cells was inhibited by the secretion of ANXA1 from pericytes. Taken together, our results suggest that ANXA1 restores Aβ42‐induced BBB disruption through inhibition of RhoA‐ROCK signaling pathway and we propose ANXA1 as a therapeutic reagent, protecting against the breakdown of the BBB in AD.     

Exogenous expression of claudin-5 induces barrier properties in cultured rat brain capillary endothelial cells

Claudins are thought to be major components of tight junctions (TJs), and claudin-5 and -12 are localized at TJs of the blood-brain barrier (BBB). Claudin-5-deficient mice exhibit size-selective (<800 Da) opening of the BBB. The purpose of this study was to clarify the expression levels of claudin-5 and -12 in rat brain capillary endothelial cells, and to examine the ability of claudin-5 to form TJs in cultured rat brain capillary endothelial cells (TR-BBB). Expression of claudin-5 mRNA in rat brain capillary fraction was 751-fold greater than that of claudin-12. The level of claudin-5 mRNA in the rat brain capillary fraction (per total mRNA) was 35.6-fold greater than that in whole brain, while the level of claudin-12 mRNA was only 13.9% of that in whole brain, suggesting that expression of claudin-12 mRNA is not restricted to brain capillaries. Transfection of TR-BBB cells with the claudin-5 gene afforded TR-BBB/CLD5 cells, which showed no change in expression of claudin-12 or ZO-1, while the expressed claudin-5 was detected at the cell-cell boundaries. The permeability surface product of [(14)C]inulin at a TR-BBB/CLD5 cell monolayer was significantly smaller (P < 0.01) than that for the parental TR-BBB cells, and the values of the permeability coefficient (Pe) were 1.14 x 10(-3) and 11.6 x 10(-3) cm/min, respectively. These results indicate that claudin-5, but not claudin-12, is predominantly expressed in brain capillaries, and plays a key role in the appearance of barrier properties of brain capillary endothelial cells.     

Pericyte-derived Glial Cell Line-derived Neurotrophic Factor Increase the Expression of Claudin-5 in the Blood–brain Barrier and the Blood-nerve Barrier

The destruction of blood–brain barrier (BBB) and blood-nerve barrier (BNB) has been considered to be a key step in the disease process of a number of neurological disorders including cerebral ischemia, Alzheimer’s disease, multiple sclerosis, and diabetic neuropathy. Although glial cell line-derived neurotrophic factor (GDNF) and brain-derived neurotrophic factor (BDNF) facilitate neuronal or axonal regeneration in the brain or peripheral nerves, their action in the BBB and BNB remains unclear. The purpose of the present study was to elucidate whether these neurotrophic factors secreted from the brain or peripheral nerve pericytes increase the barrier function of the BBB or BNB, using our newly established human brain microvascular endothelial cell (BMEC) line or peripheral nerve microvascular endothelial cell (PnMEC) line. GDNF increased the expression of claudin-5 and the transendothelial electrical resistance (TEER) of BMECs and PnMECs, whereas BDNF did not have this effect. Furthermore, we herein demonstrate that the GDNF secreted from the brain and peripheral nerve pericytes was one of the key molecules responsible for the up-regulation of claudin-5 expression and the TEER value in the BBB and BNB. These results indicate that the regulation of GDNF secreted from pericytes may therefore be a novel therapeutic strategy to modify the BBB or BNB functions and promote brain or peripheral nerve regeneration.     

Normobaric hyperoxia attenuates early blood–brain barrier disruption by inhibiting MMP-9-mediated occludin degradation in focal cerebral ischemia

Early blood–brain barrier (BBB) disruption resulting from excessive neurovascular proteolysis by matrix metalloproteinases (MMPs) is closely associated with hemorrhagic transformation events in ischemic stroke. We have shown that normobaric hyperoxia (NBO) treatment reduces MMP-9 increase in the ischemic brain. The aim of this study was to determine whether NBO could attenuate MMP-9-mediated early BBB disruption following ischemic stroke. Rats were exposed to NBO (95% O₂) or normoxia (30% O₂) during 90-min middle cerebral artery occlusion, followed by 3-hour reperfusion. NBO-treated rats showed a significant reduction in Evan's blue extravasation in the ischemic hemisphere compared with normoxic rats. Topographically, Evan's blue leakage was mainly seen in the subcortical regions including the striatum, which was accompanied by increased gelatinolytic activity and reduced immunostaining for tight-junction protein, occludin. Increased gelatinolytic activities and occludin protein loss were also observed in isolated ischemic microvessels. Gel gelatin zymography identified that MMP-9 was the main enzymatic source in the cerebral microvessels. Incubation of brain slices or isolated microvessels with purified MMP-9 revealed specific degradation of occludin. Inhibition of MMP-9 by NBO or MMP-inhibitor, BB1101, significantly reduced occludin protein loss in ischemic microvessels. These results suggest that NBO attenuates early BBB disruption, and inhibition of MMP-9-mediated occludin degradation is an important mechanism for this protection.     

Peripheral nerve pericytes originating from the blood-nerve barrier expresses tight junctional molecules and transporters as barrier-forming cells

The objective of this study was to establish pure blood-nerve barrier (BNB)-derived peripheral nerve pericyte cell lines and to investigate their unique properties as barrier-forming cells. We isolated peripheral nerve, brain, and lung pericytes from transgenic rats harboring the temperature-sensitive simian virus 40 large T-antigen gene. These cell lines expressed several pericyte markers such as alpha-smooth muscle actin, NG2, osteopontin, and desmin, whereas they did not express endothelial cell markers such as vWF and PECAM. In addition, these cell lines expressed several tight junction molecules such as occludin, claudin-12, ZO-1, and ZO-2. In particular, the expression of occludin was detected in peripheral nerve and brain pericytes, although it was not detected in lung pericytes by a Western blot analysis. An immunocytochemical analysis confirmed that occludin and ZO-1 were localized at the cell-cell boundaries among the pericytes. Brain and peripheral nerve pericytes also showed significantly higher trans-pericyte electrical resistance values and lower inulin clearances than lung pericytes. We considered that occludin localized at the cell-cell boundaries among the pericytes might mechanically stabilize the microvessels of the BNB and the blood-brain barrier. Furthermore, we also showed that these cell lines expressed many barrier-related transporters. ABCG2, p-gp, MRP-1, and Glut-1 were detected by a Western blot analysis and were observed in the cytoplasm and outer membrane by an immunocytochemical analysis. These transporters on pericytes might facilitate the peripheral nerve-to-blood efflux and blood-to-peripheral nerve influx transport of substrates in cooperation with those on endothelial cells in order to maintain peripheral nerve homeostasis.     

Blood-brain barrier-associated pericytes internalize and clear aggregated amyloid-β42 by LRP1-dependent apolipoprotein E isoform-specific mechanism

Background

Clearance at the blood-brain barrier (BBB) plays an important role in removal of Alzheimer’s amyloid-β (Aβ) toxin from brain both in humans and animal models. Apolipoprotein E (apoE), the major genetic risk factor for AD, disrupts Aβ clearance at the BBB. The cellular and molecular mechanisms, however, still remain unclear, particularly whether the BBB-associated brain capillary pericytes can contribute to removal of aggregated Aβ from brain capillaries, and whether removal of Aβ aggregates by pericytes requires apoE, and if so, is Aβ clearance on pericytes apoE isoform-specific.

Methods

We performed immunostaining for Aβ and pericyte biomarkers on brain capillaries (<?6 μm in diameter) on tissue sections derived from AD patients and age-matched controls, and APP^Swe/0 mice and littermate controls. Human Cy3-Aβ42 uptake by pericytes was studied on freshly isolated brain slices from control mice, pericyte LRP1-deficient mice (Lrp^lox/lox;Cspg4-Cre) and littermate controls. Clearance of aggregated Aβ42 by mouse pericytes was studied on multi-spot glass slides under different experimental conditions including pharmacologic and/or genetic inhibition of the low density lipoprotein receptor related protein 1 (LRP1), an apoE receptor, and/or silencing mouse endogenous Apoe in the presence and absence of human astrocyte-derived lipidated apoE3 or apoE4. Student’s t-test and one-way ANOVA followed by Bonferroni's post-hoc test were used for statistical analysis.

Results

First, we found that 35% and 60% of brain capillary pericytes accumulate Aβ in AD patients and 8.5-month-old APP^Sw/0 mice, respectively, compared to negligible uptake in controls. Cy3-Aβ42 species were abundantly taken up by pericytes on cultured mouse brain slices via LRP1, as shown by both pharmacologic and genetic inhibition of LRP1 in pericytes. Mouse pericytes vigorously cleared aggregated Cy3-Aβ42 from multi-spot glass slides via LRP1, which was inhibited by pharmacologic and/or genetic knockdown of mouse endogenous apoE. Human astrocyte-derived lipidated apoE3, but not apoE4, normalized Aβ42 clearance by mouse pericytes with silenced mouse apoE.

Conclusions

Our data suggest that BBB-associated pericytes clear Aβ aggregates via an LRP1/apoE isoform-specific mechanism. These data support the role of LRP1/apoE interactions on pericytes as a potential therapeutic target for controlling Aβ clearance in AD.

     

Comparative changes in the blood-brain barrier and cerebral infarction of SHR and WKY rats

Hypertension is involved in the exacerbation of stroke. It is unclear how blood-brain barrier (BBB) tight-junction (TJ) and ion transporter proteins critical for maintaining brain homeostasis contribute to cerebral infarction during hypertension development. In the present study, we investigated cerebral infarct volume following permanent 4-h middle cerebral artery occlusion (MCAO) and characterized the expression of BBB TJ and ion transporter proteins in brain microvessels of spontaneously hypertensive rats (SHR) compared with age-matched Wistar-Kyoto (WKY) rats at 5 wk (prehypertension), 10 wk (early-stage hypertension), and 15 wk (later-stage hypertension) of age. Hypertensive SHR show increased infarct volume following MCAO compared with WKY control rats. BBB TJ and ion transporter proteins, known to contribute to edema and fluid volume changes in the brain, show differential protein expression patterns during hypertension development. Western blot analysis of TJ protein zonula occludens-2 (ZO-2) showed decreased expression, while ion transporter, Na(+)/H(+) exchanger 1 (NHE-1), was markedly increased in hypertensive SHR. Expression of TJ proteins ZO-1, occludin, actin, claudin-5, and Na(+)-K(+)-2Cl(-) cotransporter remain unaffected in SHR compared with control. Selective inhibition of NHE-1 using dimethylamiloride significantly attenuated ischemia-induced infarct volume in hypertensive SHR following MCAO, suggesting a novel role for NHE-1 in the brain in the regulation of ischemia-induced infarct volume in SHR.     

A new blood–brain barrier model using primary rat brain endothelial cells,pericytes and astrocytes

Blood–brain barrier (BBB) characteristics are induced and maintained by cross-talk between brain microvessel endothelial cells and neighbouring elements of the neurovascular unit. While pericytes are the cells situated closest to brain endothelial cells morphologically and share a common basement membrane, they have not been used in co-culture BBB models for testing drug permeability. We have developed and characterized a new syngeneic BBB model using primary cultures of the three main cell types of cerebral microvessels. The co-culture of endothelial cells, pericytes and astrocytes mimick the anatomical situation in vivo. In the presence of both pericytes and astrocytes rat brain endothelial cells expressed enhanced levels of tight junction (TJ) proteins occludin, claudin-5 and ZO-1 with a typical localization at the cell borders. Further morphological evidence of the presence of interendothelial TJs was provided by electron microscopy. The transendothelial electrical resistance (TEER) of brain endothelial monolayers in triple co-culture, indicating the tightness of TJs reached 400 Ω cm² on average, while the endothelial permeability coefficients (P_e) for fluorescein was in the range of 3 × 10^?6 cm/s. Brain endothelial cells in the new model expressed glucose transporter-1, efflux transporters P-glycoprotein and multidrug resistance protein-1, and showed a polarized transport of rhodamine 123, a ligand for P-glycoprotein. To further characterize the model, drug permeability assays were performed using a set of 19 compounds with known in vivo BBB permeability. Good correlation (R² = 0.89) was found between in vitro P_e values obtained from measurements on the BBB model and in vivo BBB permeability data. The new BBB model, which is the first model to incorporate pericytes in a triple co-culture setting, can be a useful tool for research on BBB physiology and pathology and to test candidate compounds for centrally acting drugs.     

Pericytes from Brain Microvessels Strengthen the Barrier Integrity in Primary Cultures of Rat Brain Endothelial Cells

(1) The blood–brain barrier (BBB) characteristics of cerebral endothelial cells are induced by organ-specific local signals. Brain endothelial cells lose their phenotype in cultures without cross-talk with neighboring cells. (2) In contrast to astrocytes, pericytes, another neighboring cell of endothelial cells in brain capillaries, are rarely used in BBB co-culture systems. (3) Seven different types of BBB models, mono-culture, double and triple co-cultures, were constructed from primary rat brain endothelial cells, astrocytes and pericytes on culture inserts. The barrier integrity of the models were compared by measurement of transendothelial electrical resistance and permeability for the small molecular weight marker fluorescein. (4) We could confirm that brain endothelial monolayers in mono-culture do not form tight barrier. Pericytes induced higher electrical resistance and lower permeability for fluorescein than type I astrocytes in co-culture conditions. In triple co-culture models the tightest barrier was observed when endothelial cells and pericytes were positioned on the two sides of the porous filter membrane of the inserts and astrocytes at the bottom of the culture dish. (5) For the first time a rat primary culture based syngeneic triple co-culture BBB model has been constructed using brain pericytes beside brain endothelial cells and astrocytes. This model, mimicking closely the anatomical position of the cells at the BBB in vivo, was superior to the other BBB models tested. (6) The influence of pericytes on the BBB properties of brain endothelial cells may be as important as that of astrocytes and could be exploited in the construction of better BBB models.     

2-(2-Benzofuranyl)-2-Imidazoline Attenuates the Disruption of the Blood–Brain Barrier in EAE via NMDAR

Blood–brain barrier (BBB) disruption has been recognized as an early hallmark of multiple sclerosis (MS) pathology. Our previous studies have shown that 2-(2-Benzofuranyl)-2-imidazoline (2-BFI) protected against experimental autoimmune encephalomyelitis (EAE), a classic animal model of MS. However, the potential effects of 2-BFI on BBB permeability have not yet been evaluated in the context of EAE. Herein, we aimed to investigate the effect of 2-BFI on BBB permeability in both an animal model and an in vitro BBB model using TNF-α to imitate the inflammatory damage to the BBB in MS. In the animal model, 2-BFI reduced neurological deficits and BBB permeability in EAE mice compared with saline treatment. The Western blot results indicated that 2-BFI not only alleviated the loss of the tight junction protein occludin caused by EAE but also inhibited the activation of the NR1-ERK signaling pathway. In an in vitro BBB model, 2-BFI (100 μM) alleviated the TNF-α-induced increase in permeability and reduction in expression of occludin in monolayer bEnd.3 cells. Similar protective effects were also observed after treatment with the NMDAR antagonist MK801. The Western blot results showed that the TNF-α-induced BBB breakdown and increase in NMDAR subunit 1 (NR1) levels and ERK phosphorylation could be blocked by pretreatment with 2-BFI or MK801. However, no additional effect was observed on BBB permeability or the expression of occludin and p-ERK after pretreatment with both 2-BFI and MK801. Our study indicates that 2-BFI alleviates the disruption of BBB in the context of inflammatory injury similar to that of MS by targeting NMDAR1, as well as by likely activating the subsequent ERK signaling pathway. These results provide further evidence for 2-BFI as a potential drug for the treatment of MS.

     

Activation of P2X7R and downstream effects in bleomycin treated lung epithelial cells

Changes in intracellular calcium concentration [Ca(2+)](i) are believed to influence the proliferation and differentiation of airway epithelial cells both in vivo and in vitro. In the present study, using mouse alveolar epithelial E10 cells, we demonstrated that the treatment of lung epithelial cells with BLM resulted in elevated intracellular Ca(2+) levels. BLM further increased P2rx7 mRNA expression and P2X7R protein levels, paralleled by increased PKC-β1 levels. BLM treatment or stimulation of the P2X7R with the P2X7R agonist BzATP induced translocation of PKC-β1 from the cytoplasm to the membrane. The expression of PKC-β1 was repressed by the P2X7R inhibitor oxATP, suggesting that PKC-β1 is downstream of P2X7R activation. Furthermore, cells exposed to BLM contained increased amounts of P2X7R and PKC-β1 in Cav-1 containing lipid raft fractions. The comparison of lung tissues from wild-type and P2rx7(-/-) mice revealed decreased protein and mRNA levels of PKC-β1 and CaM as well as decreased immunoreactivity for PKC-β1. The knockdown of P2X7R in alveolar epithelial cells resulted also in a loss of PKC-β1. These data suggest that the effect of P2X7R on expression of PKC-β1 detected in alveolar epithelial cells is also functioning in the animal model. Immunohistochemical evaluation of fibrotic lungs derived from a BLM-induced mouse model revealed a strong increase in PKC-β1 immunoreactivity. The present experiments demonstrated that the increased expression of P2X7R influences PKC-β1. We predict that increased Ca(2+) concentration stimulates PKC-β1, whereas the prerequisite for activating PKC-β1 after P2X7R increase remained to be determined. Our findings suggest that PKC-β1 is important in the pathogenesis of pulmonary fibrosis.     

Demonstration and structural comparison of receptors for insulin-like growth factor-I and -II (IGF-I and -II) in brain and blood-brain barrier

Specific receptors for insulin-like growth factors (IGF) I and II on microvessel-free rat brain cell membranes (RBCM) and in the microvessels that constitute the blood-brain barrier (BBB) were identified and characterized by means of affinity cross-linking techniques and specific anti-receptor antibodies. Two different models of BBB were examined: isolated rat brain capillaries and cultured bovine brain microvessel endothelial cells. Cross-linking with 125-I-IGF-I, followed by sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE), revealed an alpha subunit of apparent Mr = 138,000 in both BBB preparations, compared to 120,000 in RBCM. Cross-linking was inhibited by unlabeled IGF and insulin, but not by antibody directed against the IGF-II receptor. When 125-I-IGF-II was cross-linked, followed by SDS-PAGE under reducing conditions, a major band of apparent Mr = 250,000 was identified in RBCM and both BBB preparations. This band, which migrated with an approximately equivalent Mr in both brain and BBB membranes, was inhibited by unlabeled IGF and by antibody specific for the IGF-II receptor. Thus, both rat and bovine brain microvessels possess classical Type I and II IGF receptors. While the alpha subunit of the Type I receptor of brain is smaller than that of the BBB, the Type II receptor of brain and BBB appear to be structurally and immunologically identical.     

A Triple Culture Model of the Blood-Brain Barrier Using Porcine Brain Endothelial cells,Astrocytes and Pericytes

In vitro blood-brain barrier (BBB) models based on primary brain endothelial cells (BECs) cultured as monoculture or in co-culture with primary astrocytes and pericytes are useful for studying many properties of the BBB. The BECs retain their expression of tight junction proteins and efflux transporters leading to high trans-endothelial electric resistance (TEER) and low passive paracellular permeability. The BECs, astrocytes and pericytes are often isolated from small rodents. Larger species as cows and pigs however, reveal a higher yield, are readily available and have a closer resemblance to humans, which make them favorable high-throughput sources for cellular isolation. The aim of the present study has been to determine if the preferable combination of purely porcine cells isolated from the 6 months old domestic pigs, i.e. porcine brain endothelial cells (PBECs) in co-culture with porcine astrocytes and pericytes, would compare with PBECs co-cultured with astrocytes and pericytes isolated from newborn rats with respect to TEER value and low passive permeability. The astrocytes and pericytes were grown both as contact and non-contact co-cultures as well as in triple culture to examine their effects on the PBECs for barrier formation as revealed by TEER, passive permeability, and expression patterns of tight junction proteins, efflux transporters and the transferrin receptor. This syngenic porcine in vitro BBB model is comparable to triple cultures using PBECs, rat astrocytes and rat pericytes with respect to TEER formation, low passive permeability, and expression of hallmark proteins signifying the brain endothelium (tight junction proteins claudin 5 and occludin, the efflux transporters P-glycoprotein (PgP) and breast cancer related protein (BCRP), and the transferrin receptor).     

E- and P-selectin are not required for the development of experimental autoimmune encephalomyelitis in C57BL/6 and SJL mice

In multiple sclerosis and in its animal model experimental autoimmune encephalomyelitis (EAE), inflammatory cells migrate across the endothelial blood-brain barrier (BBB) and gain access to the CNS. It is well-established that alpha4 integrins are actively involved in leukocyte recruitment across the BBB during EAE. In contrast, the role of endothelial E- and P-selectin in this process has been a controversial issue. In this study, we demonstrate that P-selectin protein can be detected in meningeal blood vessel endothelial cells in healthy SJL and C57BL/6 mice and on rare parenchymal CNS blood vessels in C57BL/6, but not SJL, mice. During EAE, expression of P-selectin but not E-selectin was found up-regulated on inflamed CNS microvessels surrounded by inflammatory infiltrates irrespective of their meningeal or parenchymal localization with a more prominent immunostaining detected in C57BL/6 as compared with SJL mice. P-selectin immunostaining could be localized to CNS endothelial cells and to CD41-positive platelets adhering to the vessel wall. Despite the presence of P-selectin in wild-type mice, E/P-selectin-deficient SJL and C57BL/6 mice developed clinical EAE indistinguishable from wild-type mice. Absence of E- and P-selectin did neither influence the activation of myelin-specific T cells nor the composition of the cellular infiltrates in the CNS during EAE. Finally, endothelial-specific tetracycline-inducible expression of E-selectin at the BBB in transgenic C57BL/6 mice did not alter the development of EAE. Thus, E- and P-selectin are not required for leukocyte recruitment across the BBB and the development of EAE in C57BL/6 and in SJL mice.     

Chronic inflammatory pain leads to increased blood-brain barrier permeability and tight junction protein alterations

The blood-brain barrier (BBB) maintains brain homeostasis by limiting entry of substances to the central nervous system through interaction of transmembrane and intracellular proteins that make up endothelial cell tight junctions (TJs). Recently it was shown that the BBB can be modulated by disease pathologies including inflammatory pain. This study examined the effects of chronic inflammatory pain on the functional and molecular integrity of the BBB. Inflammatory pain was induced by injection of complete Freund's adjuvant (CFA) into the right plantar hindpaw in female Sprague-Dawley rats under halothane anesthesia; control animals were injected with saline. Edema and hyperalgesia were assessed by plethysmography and infrared paw-withdrawal latency. At 72 h postinjection, significant edema formation and hyperalgesia were noted in the CFA-treated rats. Examination of permeability of the BBB by in situ perfusion of [14C]sucrose while rats were under pentobarbital anesthesia demonstrated that CFA treatment significantly increased brain sucrose uptake. Western blot analysis of BBB TJ proteins showed no change in expression of zonula occludens-1 (an accessory protein) or actin (a cytoskeletal protein) with CFA treatment. Expression of the transmembrane TJ proteins occludin and claudin-3 and -5 significantly changed with CFA treatment with a 60% decrease in occludin, a 450% increase in claudin-3, and a 615% increase in claudin-5 expression. This study demonstrates that during chronic inflammatory pain, alterations in BBB function are associated with changes in specific transmembrane TJ proteins.