Internalization of basic fibroblast growth factor at the mouse blood-brain barrier involves perlecan, a heparan sulfate proteoglycan

Controlled growth factor delivery via a degradable poly(lactic acid) hydrogel microcarrier synthesized using degassed micromolding lithography

Controlled and targeted delivery of growth factors to biological environments is important for tissue regeneration. Polylactic acid (PLA) hydrogel microparticles are attractive carriers for the delivery of therapeutic cargoes based on their superior biocompatibility and biodegradability, uniform encapsulation of cargoes, and non-requirement of organic solvents during particle synthesis. In this study, we newly present controlled growth factor delivery utilizing PLA-based hydrogel microcarriers synthesized via degassed micromolding lithography (DML). Based on the direct gelation procedure from the single-phase aqueous precursor in DML, bovine serum albumin, a model protein of growth factor, and fibroblast growth factor were encapsulated into microparticles with uniform distribution. In addition, by tuning the monomer concentration and adding a hydrolytically stable crosslinker, the release of encapsulated cargoes was efficiently controlled and extended to 2 weeks. Finally, we demonstrated the biological activity of encapsulated FGF-2 in PLA-based microparticles using a fibroblast proliferation assay.

Quantitative Model Analysis and Simulation of Pharmacokinetics and Metastasis-Associated Lung Adenocarcinoma 1 RNA Knockdown Effect After Systemic Administration of Cholesterol-Conjugated DNA/RNA Heteroduplex Oligonucleotide Crossing Blood-Brain Barrier of Mice

The cholesterol-conjugated heteroduplex oligonucleotide (Chol-HDO) is a double-stranded complex; it comprises an antisense oligonucleotide (ASO) and its complementary strand with a cholesterol ligand. Chol-HDO is a powerful tool for achieving target RNA knockdown in the brains of mice after systemic injection. Here, a quantitative model analysis was conducted to characterize the relationship between the pharmacokinetics (PK) and pharmacodynamics (PD), non-coding RNA metastasis-associated lung adenocarcinoma 1 (Malat1) RNA, of Chol-HDO, in a time-dependent manner. The established PK model could describe regional differences in the observed brain concentration-time profiles. Incorporating the PD model enabled the unique knockdown profiles in the brain to be explained in terms of the time delay after single dosing and enhancement following repeated dosing. Moreover, sensitivity analysis of PK exposure/persistency, target RNA turnover, and knockdown potency identified key factors for the efficient and sustained target RNA knockdown in the brain. The simulation of an adequate dosing regimen quantitatively supported the benefit of Chol-HDO in terms of achieving a suitable dosing interval. This was achieved via sufficient and sustained brain exposure and subsequent strong and sustained target RNA knockdown in the brain, even after systemic injection. The present study provides new insights into drug discoveries and development strategies for HDO in patients with neurogenic disorders. SIGNIFICANCE STATEMENT: The quantitative model analysis presented here characterized the PK/PD relationship of Chol-HDO, enabled its simulation under various conditions or assumptions, and identified key factors for efficient and sustained RNA knockdown, such as PK exposure and persistency. Chol-HDO appears to be an efficient drug delivery system for the systemic administration of desired drugs to brain targets.

Perlecan Improves Blood Spinal Cord Barrier Repair Through the Integrin β1/ROCK/MLC Pathway After Spinal Cord Injury

Spinal cord injury (SCI) can lead to the destruction of the blood-spinal cord barrier (BSCB), causing various inflammatory cytokines, neutrophils, and macrophages to infiltrate the lesion area, resulting in secondary injury. Basement membranes (BMs) are maintained by all types of cells in the BSCB and contribute to BSCB maintenance. Perlecan is an important constituent of vascular BMs, maintaining vascular integrity and neuroprotection. However, it is not clear whether Perlecan is involved in BSCB repair after SCI. In this study, we found that Perlecan was specifically expressed in the BMs in the spinal cord and underwent degradation/remodeling after SCI. Subsequently, a CRISPR/Cas9-based SAM system was used to overexpress Perlecan in the injured spinal cord, resulting in significantly enhanced locomotor recovery and neural regeneration. Overexpression of Perlecan reduced BSCB permeability along with the neuroinflammatory response. Interestingly, Perlecan inhibited stress fiber formation by interacting with integrin β1 and inhibiting downstream ROCK/MLC signaling, resulting in reduced tight junctions (TJs) disassembly and improved BSCB integrity. Furthermore, the integrin receptor antagonist GRGDSP abolished the effects of Perlecan overexpression on BSCB permeability and TJs integrity. Overall, our findings suggest that Perlecan reduces BSCB permeability and the neuroinflammatory response by interacting with integrin β1 and inhibiting the downstream ROCK/MLC pathway to promote neurological recovery after SCI.

Transport of the Proinflammatory Chemokines C-C Motif Chemokine Ligand 2 (MCP-1) and C-C Motif Chemokine Ligand 5 (RANTES) across the Intact Mouse Blood-Brain Barrier Is Inhibited by Heparin and Eprodisate and Increased with Systemic Inflammation

One important function of the vascular blood-brain barrier (BBB) is to facilitate neuroimmune communication. The BBB fulfills this function, in part, through its ability to transport cytokines and chemokines. C-C motif chemokine receptor 2 (CCL2) (MCP-1) and C-C motif chemokine receptor 5 (CCL5) (RANTES) are proinflammatory chemokines that mediate neuroimmune responses to acute insults and aspects of brain injury and neurodegenerative diseases; however, a blood-to-brain transport system has not been evaluated for either chemokine in vivo. Therefore, we determined whether CCL2 and CCL5 in blood can cross the intact BBB and enter the brain. Using CD-1 mice, we found that ¹²⁵I-labeled CCL2 and CCL5 crossed the BBB and entered the brain parenchyma. We next aimed to identify the mechanisms of ¹²⁵I-CCL2 and ¹²⁵I-CCL5 transport in an in situ brain perfusion model. We found that both heparin and eprodisate inhibited brain uptake of ¹²⁵I-CCL2 and ¹²⁵I-CCL5 in situ, whereas antagonists of their receptors, CCR2 or CCR5, respectively, did not, suggesting that heparan sulfates at the endothelial surface mediate BBB transport. Finally, we showed that CCL2 and CCL5 transport across the BBB increased following a single injection of 0.3 mg/kg lipopolysaccharide. These data demonstrate that CCL2 and CCL5 in the brain can derive, in part, from the circulation, especially during systemic inflammation. Further, binding to the BBB-associated heparan sulfate is a mechanism by which both chemokines can cross the intact BBB, highlighting a novel therapeutic target for treating neuroinflammation. SIGNIFICANCE STATEMENT: Our work demonstrates that C-C motif chemokine ligand 2 (CCL2) and C-C motif chemokine ligand 5 (CCL5) can cross the intact blood-brain barrier and that transport is robustly increased during inflammation. These data suggest that circulating CCL2 and CCL5 can contribute to brain levels of each chemokine. We further show that the transport of both chemokines is inhibited by heparin and eprodisate, suggesting that CCL2/CCL5-heparan sulfate interactions could be therapeutically targeted to limit accumulation of these chemokines in the brain.

Beyond barrier functions: Roles of pericytes in homeostasis and regulation of neuroinflammation

Pericytes are contractile cells that extend along the vasculature to mediate key homeostatic functions of endothelial barriers within the body. In the central nervous system (CNS), pericytes are important contributors to the structure and function of the neurovascular unit, which includes endothelial cells, astrocytes and neurons. The understanding of pericytes has been marred by an inability to accurately distinguish pericytes from other stromal cells with similar expression of identifying markers. Evidence is now growing in favor of pericytes being actively involved in both CNS homeostasis and pathology of neurological diseases, including multiple sclerosis, spinal cord injury, and Alzheimer's disease among others. In this review, we discuss the current understanding on the characterization of pericytes, their roles in maintaining the integrity of the blood-brain barrier, and their contributions to neuroinflammation and neurorepair. Owing to its plethora of surface receptors, pericytes respond to inflammatory mediators such as CCL2 (monocyte chemoattractant protein-1) and tumor necrosis factor-α, in turn secreting CCL2, nitric oxide, and several cytokines. Pericytes can therefore act as promoters of both the innate and adaptive arms of the immune system. Much like professional phagocytes, pericytes also have the ability to clear up cellular debris and macromolecular plaques. Moreover, pericytes promote the activities of CNS glia, including in maturation of oligodendrocyte lineage cells for myelination. Conversely, pericytes can impair regenerative processes by contributing to scar formation. A better characterization of CNS pericytes and their functions would bode well for therapeutics aimed at alleviating their undesirable properties and enhancing their benefits.

Low Serum Levels of Fibroblast Growth Factor 2 in Gunn Rats: A Hyperbilirubinemia Animal Model of Schizophrenic Symptoms

BACKGROUND

Fibroblast Growth Factor (FGF) 2 (also referred to as basic FGF) is a multifunctional growth factor that plays a pivotal role in the pro-survival, pro-migration and prodifferentiation of neurons.

METHOD

Because alterations in FGF2 levels are suggested to contribute to the pathogenesis of schizophrenia, we investigated serum levels of FGF2 in the Gunn rat, a hyperbilirubinemia animal model of schizophrenic symptoms.

RESULTS

The enzyme-linked immunosorbent assay showed that the serum levels of FGF2 in Gunn rats were 5.09 ± 0.236 pg/mL, while those in the normal strain Wistar rats, serum levels were 11.90 ± 2.142 pg/mL. The serum FGF2 levels in Gunn rats were significantly lower than those in Wistar rats. We also measured serum levels of Unconjugated Bilirubin (UCB) and found a significant negative correlation between UCB and FGF2 in terms of serum levels in all the rats studied.

CONCLUSION

Since it is known that FGF2 regulates dopaminergic neurons and have antineuroinflammatory effects, our finding suggests that low FGF2 levels may contribute to the pathogenesis of schizophrenia, in which imbalanced dopamin-ergic signaling and neuroinflammation are supposed to play certain roles.

Sulfated syndecan 1 is critical to preventing cellular senescence by modulating fibroblast growth factor receptor endocytosis

Cellular senescence can be triggered by various intrinsic and extrinsic stimuli. We previously reported that silencing of 3'-phosphoadenosine 5'-phosphosulfate synthetase 2 (PAPSS2) induces cellular senescence through augmented fibroblast growth factor receptor 1 (FGFR1) signaling. However, the exact molecular mechanism connecting heparan sulfation and cellular senescence remains unclear. Here, we investigated the potential involvement of heparan sulfate proteoglycans (HSPGs) in augmented FGFR1 signaling and cellular senescence. Depletion of several types of HSPGs revealed that cells depleted of syndecan 1 (SDC1) exhibited typical senescence phenotypes, and those depleted of PAPSS2-, SDC1-, or heparan sulfate 2-O sulfotransferase 1 (HS2ST1) showed decreased FGFR1 internalization along with hyperresponsiveness to and prolonged activation of fibroblast growth factor 2 (FGF2)-stimulated FGFR1- v-akt murine thymoma viral oncogene homolog (AKT) signaling. Clathrin- and caveolin-mediated FGFR1 endocytosis contributed to cellular senescence through the FGFR1-AKT-p53-p21 signaling pathway. Dynasore treatment triggered senescence phenotypes, augmented FGFR1-AKT-p53-p21 signaling, and decreased SDC1 expression. Finally, the replicatively and prematurely senescent cells were characterized by decreases of SDC1 expression and FGFR1 internalization, and an increase in FGFR1-AKT-p53-p21 signaling. Together, our results demonstrate that properly sulfated SDC1 plays a critical role in preventing cellular senescence through the regulation of FGFR1 endocytosis.

Decreased levels of serum fibroblast growth factor-2 in children with autism spectrum disorder

The neurodevelopment and functioning of the central nervous system, and especially the cerebral cortex, have basic importance to understand neuropsychiatric disorders like autism. Fibroblast growth factor-2 (FGF-2) plays a very important role in the development and functioning of the cortex. FGF-2 is related to developmental processes in the central nervous system such as neurogenesis, migration, differentiation and survival. This study researched the serum FGF-2 levels in children with autism spectrum disorder (ASD). With this aim, 60 ASD children and 40 healthy controls were compared. We applied a sociodemographic form and the Childhood Autism Rating Scale (CARS) to each subject with their family to assess the severity of autism. Additionally, all subjects had routine laboratory tests performed. Serum samples were studied with ELISA. The results found that serum FGF-2 levels were statistically significantly low in the patient group compared to the healthy control group (p value 0.003). Additionally there was a statistically significant negative correlation identified between serum FGF-2 levels and CARS score for all subjects (r = -0.300; p = 0.02). In conclusion, FGF-2 may contribute to the etiopathogenesis of ASD.

An astrocyte derived extracellular matrix coating reduces astrogliosis surrounding chronically implanted microelectrode arrays in rat cortex

Available evidence suggests that the magnitude of the foreign body response (FBR) to implants placed in cortical brain tissue is affected by the extent of vasculature damage following device insertion and the magnitude of the ensuing macrophage response. Since the extracellular matrix (ECM) serves as a natural hemostatic and immunomodulatory agent, we examined the ability of an FDA-approved neurosurgical hemostatic coating and an ECM coating derived from primary rat astrocytes to reduce the FBR surrounding a penetrating microelectrode array chronically implanted in rat cortex. Using quantitative methods, we examined various components of the FBR in vitro and after implantation. In vitro assays showed that both coatings accelerated coagulation in a similar fashion but only the astrocyte-derived material suppressed macrophage activation. In addition, the ECM coating derived from astrocytes, also decreased the astrogliotic response 8 weeks after implantation. Neither coating had a significant influence on the intensity or spatial distribution of FBR biomarkers 1 week after implantation or on degree of macrophage activation or neuronal survival at the later time point. The results show that microelectrode coatings with similar hemostatic properties but different immunomodulatory characteristics differentially affect the FBR to an anchored, single-shank, silicon microelectrode array. The results also support the concept that divergent biological pathways affect the various components of the FBR in the CNS and suggests that decreasing its impact will require a multifaceted approach.

The vascular basement membrane in the healthy and pathological brain

The vascular basement membrane contributes to the integrity of the blood-brain barrier (BBB), which is formed by brain capillary endothelial cells (BCECs). The BCECs receive support from pericytes embedded in the vascular basement membrane and from astrocyte endfeet. The vascular basement membrane forms a three-dimensional protein network predominantly composed of laminin, collagen IV, nidogen, and heparan sulfate proteoglycans that mutually support interactions between BCECs, pericytes, and astrocytes. Major changes in the molecular composition of the vascular basement membrane are observed in acute and chronic neuropathological settings. In the present review, we cover the significance of the vascular basement membrane in the healthy and pathological brain. In stroke, loss of BBB integrity is accompanied by upregulation of proteolytic enzymes and degradation of vascular basement membrane proteins. There is yet no causal relationship between expression or activity of matrix proteases and the degradation of vascular matrix proteins in vivo. In Alzheimer's disease, changes in the vascular basement membrane include accumulation of Aβ, composite changes, and thickening. The physical properties of the vascular basement membrane carry the potential of obstructing drug delivery to the brain, e.g. thickening of the basement membrane can affect drug delivery to the brain, especially the delivery of nanoparticles.

Real-time acquisition of transendothelial electrical resistance in an all-human, in vitro, 3-dimensional, blood-brain barrier model exemplifies tight-junction integrity

The blood–brain barrier (BBB) consists of endothelial cells, astrocytes, and pericytes embedded in basal lamina (BL). Most in vitro models use nonhuman, monolayer cultures for therapeutic-delivery studies, relying on transendothelial electrical resistance (TEER) measurements without other tight-junction (TJ) formation parameters. We aimed to develop reliable, reproducible, in vitro 3-dimensional (3D) models incorporating relevant human, in vivo cell types and BL proteins. The 3D BBB models were constructed with human brain endothelial cells, human astrocytes, and human brain pericytes in mono-, co-, and tricultures. TEER was measured in 3D models using a volt/ohmmeter and cellZscope. Influence of BL proteins—laminin, fibronectin, collagen type IV, agrin, and perlecan—on adhesion and TEER was assessed using an electric cell-substrate impedance–sensing system. TJ protein expression was assessed by Western blotting (WB) and immunocytochemistry (ICC). Perlecan (10 µg/ml) evoked unreportedly high, in vitro TEER values (1200 Ω) and the strongest adhesion. Coculturing endothelial cells with astrocytes yielded the greatest resistance over time. ICC and WB results correlated with resistance levels, with evidence of prominent occludin expression in cocultures. BL proteins exerted differential effects on TEER, whereas astrocytes in contact yielded higher TEER values and TJ expression.—Maherally, Z., Fillmore, H. L., Tan, S. L., Tan, S. F., Jassam, S. A., Quack, F. I., Hatherell, K. E., Pilkington, G. J. Real-time acquisition of transendothelial electrical resistance in an all-human, in vitro, 3-dimensional, blood–brain barrier model exemplifies tight-junction integrity.

Apo E-Functionalization of Solid Lipid Nanoparticles Enhances Brain Drug Delivery: Uptake Mechanism and Transport Pathways

Several strategies have been implemented to enhance brain drug delivery, and herein solid lipid nanoparticles functionalized with apolipoprotein E were tested in hCMEC/D3 cell monolayers. The mean diameter of 160 nm, negative charge of -12 mV, and their lipophilic characteristics make these nanosystems suitable for brain delivery. Confocal images and flow cytometry data showed a cellular uptake increase of 1.8-fold for SLN-Palmitate-ApoE and 1.9-fold for SLN-DSPE-ApoE when compared with the non-functionalized SLNs. Clathrin-mediated endocytosis was distinguished as the preferential internalization pathway involved in cellular uptake and nanoparticles could cross the blood-brain barrier predominantly by a transcellular pathway. The understanding of the mechanisms involved in the transport of these nanosystems through the blood-brain barrier may potentiate their application on brain drug delivery.

Synthesis and deposition of basement membrane proteins by primary brain capillary endothelial cells in a murine model of the blood-brain barrier

The brain vascular basement membrane is important for both blood-brain barrier (BBB) development, stability, and barrier integrity and the contribution hereto from brain capillary endothelial cells (BCECs), pericytes, and astrocytes of the BBB is probably significant. The aim of this study was to analyse four different in vitro models of the murine BBB for expression and possible secretion of major basement membrane proteins from murine BCECs (mBCECs). mBCECs, pericytes and glial cells (mainly astrocytes and microglia) were prepared from brains of C57BL/6 mice. The mBCECs were grown as monoculture, in co-culture with pericytes or mixed glial cells, or as a triple-culture with both pericytes and mixed glial cells. The integrity of the BBB models was validated by measures of transendothelial electrical resistance (TEER) and passive permeability to mannitol. The expression of basement membrane proteins was analysed using RT-qPCR, mass spectrometry and immunocytochemistry. Co-culturing mBCECs with pericytes, mixed glial cells, or both significantly increased the TEER compared to the monoculture, and a low passive permeability was correlated with high TEER. The mBCECs expressed all major basement membrane proteins such as laminin-411, laminin-511, collagen [α1(IV)]₂ α2(IV), agrin, perlecan, and nidogen 1 and 2 in vitro. Increased expression of the laminin α5 subunit correlated with the addition of BBB-inducing factors (hydrocortisone, Ro 20-1724, and pCPT-cAMP), whereas increased expression of collagen IV α1 primarily correlated with increased levels of cAMP. In conclusion, BCECs cultured in vitro coherently form a BBB and express basement membrane proteins as a feature of maturation. Cover Image for this issue: doi: 10.1111/jnc.13789.

Apicobasal polarity of brain endothelial cells

Normal brain homeostasis depends on the integrity of the blood-brain barrier that controls the access of nutrients, humoral factors, and immune cells to the CNS. The blood-brain barrier is composed mainly of brain endothelial cells. Forming the interface between two compartments, they are highly polarized. Apical/luminal and basolateral/abluminal membranes differ in their lipid and (glyco-)protein composition, allowing brain endothelial cells to secrete or transport soluble factors in a polarized manner and to maintain blood flow. Here, we summarize the basic concepts of apicobasal cell polarity in brain endothelial cells. To address potential molecular mechanisms underlying apicobasal polarity in brain endothelial cells, we draw on investigations in epithelial cells and discuss how polarity may go awry in neurological diseases.

Hippocampal Proteomic and Metabonomic Abnormalities in Neurotransmission, Oxidative Stress, and Apoptotic Pathways in a Chronic Phencyclidine Rat Model

Schizophrenia is a neuropsychiatric disorder affecting 1% of the world's population. Due to both a broad range of symptoms and disease heterogeneity, current therapeutic approaches to treat schizophrenia fail to address all symptomatic manifestations of the disease. Therefore, disease models that reproduce core pathological features of schizophrenia are needed for the elucidation of pathological disease mechanisms. Here, we employ a comprehensive global label-free liquid chromatography-mass spectrometry proteomic (LC-MS(E)) and metabonomic (LC-MS) profiling analysis combined with the targeted proteomics (selected reaction monitoring and multiplex immunoassay) of serum and brain tissues to investigate a chronic phencyclidine (PCP) rat model in which glutamatergic hypofunction is induced through noncompetitive NMDAR-receptor antagonism. Using a multiplex immunoassay, we identified alterations in the levels of several cytokines (IL-5, IL-2, and IL-1β) and fibroblast growth factor-2. Extensive proteomic and metabonomic brain tissue profiling revealed a more prominent effect of chronic PCP treatment on both the hippocampal proteome and metabonome compared to the effect on the frontal cortex. Bioinformatic pathway analysis confirmed prominent abnormalities in NMDA-receptor-associated pathways in both brain regions, as well as alterations in other neurotransmitter systems such as kainate, AMPA, and GABAergic signaling in the hippocampus and in proteins associated with neurodegeneration. We further identified abundance changes in the level of the superoxide dismutase enzyme (SODC) in both the frontal cortex and hippocampus, which indicates alterations in oxidative stress and substantiates the apoptotic pathway alterations. The present study could lead to an increased understanding of how perturbed glutamate receptor signaling affects other relevant biological pathways in schizophrenia and, therefore, support drug discovery efforts for the improved treatment of patients suffering from this debilitating psychiatric disorder.

Systemic administration of fibroblast growth factor-2 (FGF2) reduces BACE1 expression and amyloid pathology in APP23 mice

There is an emerging evidence that growth factors may have a potential beneficial use in the treatment of Alzheimer's disease (AD) because of their neuroprotective properties and effects on neuronal proliferation. Basic fibroblast growth factor or fibroblast growth factor-2 (FGF2) is an anti-inflammatory, angiogenic, and neurotrophic factor that is expressed in many cell types, including neurons and glial cells. Here, we explored whether subcutaneous administration of FGF2 could have therapeutic effects in the APP 23 transgenic mouse, a model of amyloid pathology. FGF2 treatment attenuated spatial memory deficits, reduced amyloid-β (Aβ) and tau pathologies, decreased inducible nitric oxide synthase expression, and increased the number of astrocytes in the dentate gyrus in APP 23 mice compared with the vehicle-treated controls. The decrease in Aβ deposition was associated with a reduction in the expression of BACE1, the main enzyme responsible for Aβ generation. These results were confirmed in a neuroblastoma cell line, which demonstrated that incubation with FGF2 regulates BACE1 transcription. In addition, and in contrast with what has been previously published, the levels of FGF2 were reduced in postmortem brains from AD patients compared with controls. These data, therefore, suggest that systemic administration of FGF2 could have a potential therapeutic application in AD.

Targeted discovery and validation of plasma biomarkers of Parkinson's disease

Despite extensive research, an unmet need remains for protein biomarkers of Parkinson's disease (PD) in peripheral body fluids, especially blood, which is easily accessible clinically. The discovery of such biomarkers is challenging, however, due to the enormous complexity and huge dynamic range of human blood proteins, which are derived from nearly all organ systems, with those originating specifically from the central nervous system (CNS) being exceptionally low in abundance. In this investigation of a relatively large cohort (∼300 subjects), selected reaction monitoring (SRM) assays (a targeted approach) were used to probe plasma peptides derived from glycoproteins previously found to be altered in the CNS based on PD diagnosis or severity. Next, the detected peptides were interrogated for their diagnostic sensitivity and specificity as well as the correlation with PD severity, as determined by the Unified Parkinson's Disease Rating Scale (UPDRS). The results revealed that 12 of the 50 candidate glycopeptides were reliably and consistently identified in plasma samples, with three of them displaying significant differences among diagnostic groups. A combination of four peptides (derived from PRNP, HSPG2, MEGF8, and NCAM1) provided an overall area under curve (AUC) of 0.753 (sensitivity: 90.4%; specificity: 50.0%). Additionally, combining two peptides (derived from MEGF8 and ICAM1) yielded significant correlation with PD severity, that is, UPDRS (r = 0.293, p = 0.004). The significance of these results is at least two-fold: (1) it is possible to use a targeted approach to identify otherwise very difficult to detect CNS related biomarkers in peripheral blood and (2) the novel biomarkers, if validated in independent cohorts, can be employed to assist with clinical diagnosis of PD as well as monitoring disease progression.

Investigating the role of perlecan domain V in post-ischemic cerebral angiogenesis

Cerebral angiogenesis is an important process for physiological events such as brain development, but it also occurs in pathological conditions such as stroke. Defined as the generation of new blood vessels from preexisting vasculature, angiogenesis after ischemic stroke is important to limit the subsequent neuronal injury and death, as well as contribute to neurorepair. However, current therapies for ischemic stroke are largely focused on reestablishing uninterrupted blood flow, an important but inherently risky proposition. Furthermore, these therapies can have limited efficacy due to narrow therapeutic windows, and in the case of mechanical clot removal, are invasive procedures. Therefore, better stroke therapies are needed. Since the brain possesses mechanisms, including angiogenesis, to attempt self-repair after injury, it may prove beneficial to look at how such mechanisms are regulated to identify potential targets for new and improved stroke therapies. Perlecan domain V (DV), an endogenous extracellular matrix protein fragment, may represent one such therapeutic target. Key to its appeal is that perlecan DV is endogenously and persistently generated in the brain after stroke and has significant angio-modulatory properties. These, and other properties, have been therapeutically manipulated to improve experimental stroke outcomes, suggesting that DV could represent a promising new stroke therapy. Here we discuss a novel approach to studying DV-mediated angiogenesis in vitro using a coculture model.

Perlecan regulates bidirectional Wnt signaling at the Drosophila neuromuscular junction

Perlecan/Trol at the neuromuscular junction suppresses presynaptic canonical Wg signaling but enhances the postsynaptic Frizzled nuclear import pathway.

Heparan sulfate proteoglycans (HSPGs) play pivotal roles in the regulation of Wnt signaling activity in several tissues. At the Drosophila melanogaster neuromuscular junction (NMJ), Wnt/Wingless (Wg) regulates the formation of both pre- and postsynaptic structures; however, the mechanism balancing such bidirectional signaling remains elusive. In this paper, we demonstrate that mutations in the gene of a secreted HSPG, perlecan/trol, resulted in diverse postsynaptic defects and overproduction of synaptic boutons at NMJ. The postsynaptic defects, such as reduction in subsynaptic reticulum (SSR), were rescued by the postsynaptic activation of the Frizzled nuclear import Wg pathway. In contrast, overproduction of synaptic boutons was suppressed by the presynaptic down-regulation of the canonical Wg pathway. We also show that Trol was localized in the SSR and promoted postsynaptic accumulation of extracellular Wg proteins. These results suggest that Trol bidirectionally regulates both pre- and postsynaptic activities of Wg by precisely distributing Wg at the NMJ.

Perlecan and the blood-brain barrier: beneficial proteolysis?

The cerebral microvasculature is important for maintaining brain homeostasis. This is achieved via the blood-brain barrier (BBB), composed of endothelial cells with specialized tight junctions, astrocytes, and a basement membrane (BM). Prominent components of the BM extracellular matrix (ECM) include fibronectin, laminin, collagen IV, and perlecan, all of which regulate cellular processes via signal transduction through various cell membrane bound ECM receptors. Expression and proteolysis of these ECM components can be rapidly altered during pathological states of the central nervous system. In particular, proteolysis of perlecan, a heparan sulfate proteoglycan, occurs within hours following ischemia induced by experimental stroke. Proteolysis of ECM components following stroke results in the degradation of the BM and further disruption of the BBB. While it is clear that such proteolysis has negative consequences for the BBB, we propose that it also may lead to generation of ECM protein fragments, including the C-terminal domain V (DV) of perlecan, that potentially have a positive influence on other aspects of CNS health. Indeed, perlecan DV has been shown to be persistently generated after stroke and beneficial as a neuroprotective molecule and promoter of post-stroke brain repair. This mini-review will discuss beneficial roles of perlecan protein fragment generation within the brain during stroke.

Perlecan/Hspg2 deficiency alters the pericellular space of the lacunocanalicular system surrounding osteocytic processes in cortical bone

Osteocytes project long, slender processes throughout the mineralized matrix of bone, where they connect and communicate with effector cells. The interconnected cellular projections form the functional lacunocanalicular system, allowing fluid to pass for cell-to-cell communication and nutrient and waste exchange. Prevention of mineralization in the pericellular space of the lacunocanalicular pericellular space is crucial for uninhibited interstitial fluid movement. Factors contributing to the ability of the pericellular space of the lacunocanalicular system to remain open and unmineralized are unclear. Immunofluorescence and immunogold localization by transmission electron microscopy demonstrated perlecan/Hspg2 signal localized to the osteocyte lacunocanalicular system of cortical bone, and this proteoglycan was found in the pericellular space of the lacunocanalicular system. In this study we examined osteocyte lacunocanalicular morphology in mice deficient in the large heparan sulfate proteoglycan perlecan/Hspg2 in this tissue. Ultrastructural measurements with electron microscopy of perlecan/Hspg2-deficient mice demonstrated diminished osteocyte canalicular pericellular area, resulting from a reduction in the total canalicular area. Additionally, perlecan/Hspg2-deficient mice showed decreased canalicular density and a reduced number of transverse tethering elements per canaliculus. These data indicated that perlecan/Hspg2 contributed to the integrity of the osteocyte lacunocanalicular system by maintaining the size of the pericellular space, an essential task to promote uninhibited interstitial fluid movement in this mechanosensitive environment. This work thus identified a new barrier function for perlecan/Hspg2 in murine cortical bone.

The CNS microvascular pericyte: pericyte-astrocyte crosstalk in the regulation of tissue survival

The French scientist Charles Benjamin Rouget identified the pericyte nearly 140 years ago. Since that time the role of the pericyte in vascular function has been difficult to elucidate. It was not until the development of techniques to isolate and culture pericytes that scientists have begun to understand the true impact of this unique cell in the maintenance of tissue homeostasis. In the brain the pericyte is an integral cellular component of the blood-brain barrier and, together with other cells of the neurovascular unit (endothelial cells, astrocytes and neurons) the pericyte makes fine-tuned regulatory adjustments and adaptations to promote tissue survival. These regulatory changes involve trans-cellular communication networks between cells. In this review we consider evidence for cell-to-cell crosstalk between pericytes and astrocytes during development and in adult brain.

Association of the HSPG2 gene with neuroleptic-induced tardive dyskinesia

Tardive dyskinesia (TD) is characterized by repetitive, involuntary, and purposeless movements that develop in patients treated with long-term dopaminergic antagonists, usually antipsychotics. By a genome-wide association screening of TD in 50 Japanese schizophrenia patients with treatment-resistant TD and 50 Japanese schizophrenia patients without TD (non-TD group) and subsequent confirmation in independent samples of 36 treatment-resistant TD and 136 non-TD subjects, we identified association of a single nucleotide polymorphism, rs2445142, (allelic p=2 x 10(-5)) in the HSPG2 (heparan sulfate proteoglycan 2, perlecan) gene with TD. The risk allele was significantly associated with higher expression of HSPG2 in postmortem human prefrontal brain (p<0.01). Administration of daily injection of haloperidol (HDL) for 50 weeks significantly reduced Hspg2 expression in mouse brains (p<0.001). Vacuous chewing movements (VCMs) induced by 7-week injection of haloperidol-reserpine were significantly infrequent in adult Hspg2 hetero-knockout mice compared with wild-type littermates (p<0.001). Treatment by the acetylcholinesterase inhibitor, physostigmine, was significantly effective for reduction of VCMs in wild-type mice but not in Hspg2 hetero-knockout mice. These findings suggest that the HSPG2 gene is involved in neuroleptic-induced TD and higher expression of HSPG2, probably even after antipsychotic treatment, and may be associated with TD susceptibility.

Multifunctional Nanocarriers for diagnostics, drug delivery and targeted treatment across blood-brain barrier: perspectives on tracking and neuroimaging

Nanotechnology has brought a variety of new possibilities into biological discovery and clinical practice. In particular, nano-scaled carriers have revolutionalized drug delivery, allowing for therapeutic agents to be selectively targeted on an organ, tissue and cell specific level, also minimizing exposure of healthy tissue to drugs. In this review we discuss and analyze three issues, which are considered to be at the core of nano-scaled drug delivery systems, namely functionalization of nanocarriers, delivery to target organs and in vivo imaging. The latest developments on highly specific conjugation strategies that are used to attach biomolecules to the surface of nanoparticles (NP) are first reviewed. Besides drug carrying capabilities, the functionalization of nanocarriers also facilitate their transport to primary target organs. We highlight the leading advantage of nanocarriers, i.e. their ability to cross the blood-brain barrier (BBB), a tightly packed layer of endothelial cells surrounding the brain that prevents high-molecular weight molecules from entering the brain. The BBB has several transport molecules such as growth factors, insulin and transferrin that can potentially increase the efficiency and kinetics of brain-targeting nanocarriers. Potential treatments for common neurological disorders, such as stroke, tumours and Alzheimer's, are therefore a much sought-after application of nanomedicine. Likewise any other drug delivery system, a number of parameters need to be registered once functionalized NPs are administered, for instance their efficiency in organ-selective targeting, bioaccumulation and excretion. Finally, direct in vivo imaging of nanomaterials is an exciting recent field that can provide real-time tracking of those nanocarriers. We review a range of systems suitable for in vivo imaging and monitoring of drug delivery, with an emphasis on most recently introduced molecular imaging modalities based on optical and hybrid contrast, such as fluorescent protein tomography and multispectral optoacoustic tomography. Overall, great potential is foreseen for nanocarriers in medical diagnostics, therapeutics and molecular targeting. A proposed roadmap for ongoing and future research directions is therefore discussed in detail with emphasis on the development of novel approaches for functionalization, targeting and imaging of nano-based drug delivery systems, a cutting-edge technology poised to change the ways medicine is administered.

ATP-binding cassette transporter A1 (ABCA1) deficiency does not attenuate the brain-to-blood efflux transport of human amyloid-beta peptide (1-40) at the blood-brain barrier

ATP-binding cassette transporter A1 (ABCA1) mediates apolipoprotein-dependent cholesterol release from cellular membranes. Recent studies using ABCA1 knockout mice have demonstrated that ABCA1 affects amyloid-beta peptide (A beta) levels in the brain and the production of senile plaque. Cerebral A beta(1-40) was eliminated from the brain to the circulating blood via the blood-brain barrier (BBB), which expresses ABCA1. Therefore, in the present study, we examined whether ABCA1 affects the brain-to-blood efflux transport of human A beta(1-40)(hA beta(1-40)) at the BBB. The apparent uptake of [125I]hA beta(1-40) into ABCA1-expressing HEK293 cells was not significantly different from that into parental HEK293 cells. In addition, the apparent uptake was not significantly affected even in the presence of apolipoprotein A-I as a cholesterol release acceptor. Moreover, [125I]hA beta(1-40) elimination from mouse brain across the BBB was not significantly different between ABCA1-deficient and wild-type mice 60 min after its administration into the cerebrum. These results suggest that ABCA1 does not directly transport hA beta(1-40) and a deficiency of ABCA1 does not attenuate the brain-to-blood efflux transport of hA beta(1-40) across the BBB.

Heparan and chondroitin sulfate on growth plate perlecan mediate binding and delivery of FGF-2 to FGF receptors

Fibroblast growth factor (FGF)-2 regulates chondrocyte proliferation in the growth plate. Heparan sulfate (HS) proteoglycans bind FGF-2. Perlecan, a heparan sulfate proteoglycan (HSPG) in the developing growth plate, however, contains both HS and chondroitin sulfate (CS) chains. The binding of FGF-2 to perlecan isolated from the growth plate was evaluated using cationic filtration (CAF) and immunoprecipitation (IP) assays. FGF-2 bound to perlecan in both the CAF and IP assays primarily via the HS chains on perlecan. A maximum of 123 molecules of FGF-2 was calculated to bind per molecule of perlecan. When digested with chondroitinase ABC to remove its CS chains, perlecan augmented binding of FGF-2 to the FGFR-1 and FGFR-3 receptors and also increased FGF-2 stimulation of [(3)H]-thymidine incorporation in BaF3 cells expressing these FGF receptors. These data show that growth plate perlecan binds to FGF-2 by its HS chains but can only deliver FGF-2 to FGF receptors when its CS chains are removed.

Receptor-mediated transport of LIF across blood-spinal cord barrier is upregulated after spinal cord injury

Leukemia inhibitory factor (LIF) crosses the normal blood-brain and blood-spinal cord barrier (BBB) by a saturable transport system [Pan, W., Kastin, A.J., Brennan, J.M., 2000. Saturable entry of leukemia inhibitory factor from blood to the central nervous system. J. Neuroimmunol. 106, 172-180]. Since LIF is a cytokine beneficial to spinal cord regeneration, understanding the regulation of its transport across the injured BBB may help in the design of strategies for the treatment of spinal cord injury (SCI). In this study, we initially showed that transport of LIF is mediated by its specific receptor LIFRalpha (gp190), using both adult mice and monolayers of mouse brain microvessel endothelial cells. Permeation of radioactively labeled LIF was inhibited not only by excess unlabeled LIF, but also by a blocking antibody to the extracellular domain of gp190 LIFRalpha receptor. This showed that the saturable transport of LIF across the BBB involves LIFRalpha. We then tested the hypothesis that this transport system can be upregulated after SCI. SCI was generated by an established compression method at the upper lumbar level. Transport was studied 1 week after SCI, a time of tissue repair following ischemia and inflammation. Spinal cord uptake of 99mTc-albumin 10 min after intravenous injection was used as an indicator of paracellular permeability of the BBB, its small but significant increase at the injury site indicating the level of persistent BBB disruption. The uptake of 125I-LIF by the injured lumbar spinal cord was significantly greater than that in the uninjured controls as well as that of 99mTc-albumin. Both excess unlabeled LIF and the blocking antibody against LIFRalpha significantly suppressed the increased entry of 125I-LIF without affecting that of 99mTc-albumin. Thus, the increased blood-to-spinal cord permeation of LIF was not solely explained by barrier disruption but involved LIFRalpha. This enhanced transport correlated with increased expression of LIFRalpha shown by immunofluorescent staining and Western blot. Therefore, LIFR at the BBB provides an important target for therapeutic intervention.

Intracellular trafficking in neurones and glia of fibroblast growth factor-2, fibroblast growth factor receptor 1 and heparan sulphate proteoglycans in the injured adult rat cerebral cortex

The potent gliogenic and neurotrophic fibroblast growth factor (FGF)-2 signals through a receptor complex comprising high-affinity FGF receptor (FGFR)1 with heparan sulphate proteoglycans (HSPGs) as co-receptors. We examined the intracellular dynamics of FGF-2, FGFR1 and the HSPGs syndecan-2 and -3, glypican-1 and -2, and perlecan in neurones and glia in and around adult rat cerebral wounds. In the intact cerebral cortex, FGF-2 and FGFR1 mRNA and protein were constitutively expressed in astrocytes and neurones respectively. FGF-2 protein was localized exclusively to astrocyte nuclei. After injury, expression of FGF-2 mRNA was up-regulated only in astrocytes, whereas FGFR1 mRNA expression was increased in both glia and neurones, a disparity indicating that FGF-2 may act as a paracrine and autocrine factor for neurones and glia respectively. FGF-2 protein localized to both cytoplasm and nuclei of injury-responsive neurones and glia. There was weak or no staining of HSPGs in the normal cerebral neuropil and glia nuclei, with a few immunopositive neurones. Specific HSPGs responded to injury by differentially co-localizing with trafficked intracellular FGF-2 and FGFR1. The spatiotemporal dynamics of FGF-2-FGFR1-HSPG complex formation implies a role for individual HSPGs in regulating FGF-2 storage, nuclear trafficking and cell-specific injury responses in CNS wounds.

Basic fibroblast growth factor suppresses p53 activation in the neoplastic cells of a proportion of patients with chronic lymphocytic leukaemia

p53 is the most frequently inactivated gene in human cancers, reflecting its pivotal role in maintaining genomic integrity. The present study was conducted to explore the possibility that tumour cells with no intrinsic defects of the p53 pathway might nevertheless acquire p53 dysfunction through extrinsic suppression of the pathway by microenvironmental factors. Neoplastic cells from patients with chronic lymphocytic leukaemia (CLL) were cultured in the presence or absence of basic fibroblast growth factor (bFGF) and exposed to ionizing radiation (IR) to induce p53 accumulation. bFGF is greatly increased in the plasma of CLL patients and can suppress p53 activation in some experimental models. IR induced a marked increase in p53 levels in 28 samples from 24 patients. bFGF inhibited IR-induced p53 accumulation to some extent in most of these samples and by more than 50% in seven samples from seven patients. Suppression of p53 activation by bFGF was frequently but not always accompanied by upregulation of the p53-inhibitory protein MDM2 and/or phosphorylation of MDM2 at serine 166, and was associated with impaired transcriptional activation of the p53 target gene p21. These observations provide the first demonstration in human cancer cells that the p53 pathway can be suppressed by factors in the tumour-cell microenvironment.

Permeation of growth hormone across the blood-brain barrier

Exogenous GH can affect central nervous system function when given peripherally to animals and as a supplemental therapy to humans. This study tested whether GH crosses the blood-brain barrier (BBB) by a specific transport system and found that both mice and rats have small but significant uptake of GH into the brain without a species difference. Determined by multiple-time regression analysis, the blood-to-brain influx transfer constants of 125I-labeled rat GH in mice (0.23+/-0.07 microl/g.min) and rats (0.32+/-0.04 microl/g.min) were comparable to those of some cytokines of similar size, with a half-time disappearance of 125I-GH of 3.8-7.6 min in blood. Intact 125I-GH was present in both serum and brain homogenate 20 min after iv injection. At this time, about 26.8% of GH in brain entered the parenchyma, whereas 10% was entrapped in endothelial cells. Neither excess GH nor insulin showed acute modulation of the influx, indicating lack of a saturable transport system for GH at the BBB. Binding and cellular uptake studies in cultured cerebral microvessel endothelial cells (RBE4) further ruled out the presence of high-capacity adsorptive endocytosis. The brain influx of GH by simple diffusion adds definitive value to the long-disputed question of whether and how GH crosses the BBB. The central nervous system effects of peripheral GH can be attributed to permeation of the BBB despite the absence of a specific transport system.

Computational analysis of EGFR inhibition by Argos

Argos, a secreted inhibitor of the Drosophila epidermal growth factor receptor, and the only known secreted receptor tyrosine kinase inhibitor, acts by sequestering the EGFR ligand Spitz. We use computational modeling to show that this biochemically-determined mechanism of Argos action can explain available genetic data for EGFR/Spitz/Argos interactions in vivo. We find that efficient Spitz sequestration by Argos is key for explaining the existing data and for providing a robust feedback loop that modulates the Spitz gradient in embryonic ventral ectoderm patterning. Computational analysis of the EGFR/Spitz/Argos module in the ventral ectoderm shows that Argos need not be long-ranged to account for genetic data, and can actually have very short range. In our models, Argos with long or short length scale functions to limit the range and action of secreted Spitz. Thus, the spatial range of Argos does not have to be tightly regulated or may act at different ranges in distinct developmental contexts.

Transport of transforming growth factor-β2 across the blood–brain barrier

The blood-brain barrier acts as an interface between the brain and body through a combination of restrictive mechanisms and transport processes. Substances essential for brain function pass through the barrier either by passive diffusion or by active transport. We report here that [125I]-transforming growth factor-beta2 (TGF-beta2) passes through the blood-brain barrier and blood-nerve barriers, after intravenous, intraperitoneal or intramuscular injections. The entry of the [125I]-TGF-beta2 to the brain was rapid, saturable and inhibited by co-injection of unlabelled TGF-beta2. In contrast, co-injection of unlabelled TGF-beta2 increased the retention of [125I]-TGF-beta2 in the blood. The [125I]-TGF-beta2 transported into the brain was localised by autoradiography to the extracellular space, and was intact as judged by SDS-PAGE. The [125I]-TGF-beta2 was widely distributed throughout the brain, with the highest concentrations in the hypothalamus and nerves and the lowest in the cerebral hemispheres. The [125I]-TGF-beta2 had a half-life of 4 h in the brain. These results indicate that therapeutically relevant levels of TGF-beta2 reach the brain after peripheral administration of TGF-beta2.

An Apolipoprotein E-Derived Peptide Mediates Uptake of Sterically Stabilized Liposomes into Brain Capillary Endothelial Cells

A promising strategy to solve the problems of insufficient membrane penetration of drugs and low target specificity is the localization of targeting and uptake-facilitating ligands on the surface of drug-carrier systems. This study investigated the role of a peptide derived from the LDL receptor (LDLr)-binding domain of apolipoprotein E (apoE) in initiating endocytosis in brain capillary endothelial cells. The highly cationic tandem dimer of apoE residues (141-150) was coupled covalently onto poly(ethylene glycol)-derivatized liposomes. Membrane binding and cellular uptake was monitored qualitatively by confocal-laser-scanning microscopy as well as quantitatively using a fluorescence assay. The peptide mediated an efficient, energy-dependent translocation of liposomes across the membrane of brain capillary endothelial cells. Liposomes without surface-located peptides displayed neither membrane accumulation nor cellular uptake. Low peptide affinity to LDLr and internalization of the complex into fibroblasts with up- and down-regulated receptor expression levels, as well as complex translocation into cells incubated with an antibody against the LDLr, pointed to a dominating role of an LDLr-independent transport route. Enzymatic digestion of heparan sulfate proteoglycan (HSPG) with heparinase I and addition of heparin and poly-l-lysin as competitors of HSPG and HSPG ligands, respectively, resulted in a significant loss in liposome internalization. The results suggested that HSPG played a major role in the apoE-peptide-mediated uptake of liposomes into endothelial cells of brain microvessels.

Localization of brain endothelial luminal and abluminal transporters with immunogold electron microscopy

Immunogold electron microscopy has identified a variety of blood-brain barrier (BBB) proteins with transporter and regulatory functions. For example, isoforms of the glucose transporter, protein kinase C (PKC), and caveolin-1 are BBB specific. Isoform 1 of the facilitative glucose transporter family (GLUT1) is expressed solely in endothelial (and pericyte) domains, and approximately 75% of the protein is membrane-localized in humans. Evidence is presented for a water cotransport function of BBB GLUT1. A shift in transporter polarity characterized by increased luminal membrane GLUT1 is seen when BBB glucose transport is upregulated; but a greater abluminal membrane density is seen in the human BBB when GLUT1 is downregulated. PKC colocalizes with GLUT1 within these endothelial domains during up- and downregulation, suggesting that a PKC-mediated mechanism regulates human BBB glucose transporter expression. Occludin and claudin-5 (like other tight-junctional proteins) exhibit a restricted distribution, and are expressed solely within interendothelial clefts of the BBB. GFAP (glial fibrillary acidic protein) is uniformly expressed throughout the foot-processes and the entire astrocyte. But the microvascular-facing membranes of the glial processes that contact the basal laminae are also polarized, and their transporters may also redistribute within the astrocyte. Monocarboxylic acid transporter and water channel (Aquaporin-4) expression are enriched at the glial foot-process, and both undergo physiological modulation. We suggest that as transcytosis and efflux mechanisms generate interest as potential neurotherapeutic targets, electron microscopic confirmation of their site-specific expression patterns will continue to support the CNS drug discovery process.

Poly(beta-amino ester)s promote cellular uptake of heparin and cancer cell death

Heparin/heparan sulfate-like glycosaminoglycans (HSGAGs) are involved in diverse cellular processes in the extracellular matrix (ECM). The biological effect of HSGAGs depends on disaccharide content and physiological location within the ECM. HSGAGs are also brought into cells during membrane transcytosis and growth factor signaling while protein bound. We sought to probe the impact of free HSGAGs within the cell by using heparin as a model HSGAG. A library of poly(beta-amino ester)s, which internalize DNA, was examined for the capacity of its members to internalize heparin. Fourteen polymers enabled heparin internalization. The most efficacious polymer reduced murine melanoma cell growth by 73%. No glycosaminoglycan was as efficacious as highly sulfated, full-length heparin. Internalized heparin likely interferes with transcription factor function and subsequently induces apoptotic cell death. Therefore, internalized heparin is a novel mechanism for inducing apoptosis of cancer cells.

Specific structural features of heparan sulfate proteoglycans potentiate neuregulin-1 signaling

Neuregulins are a family of growth and differentiation factors that act through activation of cell-surface erbB receptor tyrosine kinases and have essential functions both during development and on the growth of cancer cells. One alternatively spliced neuregulin-1 form has a distinct heparin-binding immunoglobulin-like domain that enables it to adhere to heparan sulfate proteoglycans at key locations during development and substantially potentiates its activity. We examined the structural specificity needed for neuregulin-1-heparin interactions using a gel mobility shift assay together with an assay that measures the ability of specific oligosaccharides to block erbB receptor phosphorylation in L6 muscle cells. Whereas the N-sulfate group of heparin was most important, the 2-O-sulfate and 6-O-sulfate groups also contributed to neuregulin-1 binding in these two assays. Optimal binding to neuregulin-1 required eight or more heparin disaccharides; however, as few as two disaccharides were still able to bind neuregulin-1 to a lesser extent. The physiological importance of this specificity was shown both by chemical and siRNA treatment of cultured muscle cells. Pretreatment of muscle cells with chlorate that blocks all sulfation or with an siRNA that selectively blocks N-sulfation significantly reduced erbB receptor activation by neuregulin-1 but had no effect on the activity of neuregulin-1 that lacks the heparin-binding domain. These results suggest that the regulation of glycosaminoglycan sulfation is an important biological mechanism that can modulate both the localization and potentiation of neuregulin-1 signaling.

Why study transport of peptides and proteins at the neurovascular interface

The blood-brain barrier (BBB) is an immense neurovascular interface. In neurodegenerative, ischemic, and traumatic disorders of the central nervous system (CNS), the BBB may hinder the delivery of many therapeutic peptides and proteins to the brain and spinal cord. Fortunately, the mistaken dogma that peptides and proteins do not cross the BBB has been corrected during the past two decades by the accumulating evidence that peptides and proteins in the periphery exert potent effects in the CNS. Not only can peptides and proteins serve as carriers for selective therapeutic agents, but they themselves may directly cross the BBB after delivery into the bloodstream. Their passage may be mediated by simple diffusion or specific transport, both of which can be affected by interactions in the blood compartment (outside the BBB) and within the endothelial cells (at the BBB level). Although the majority of current delivery strategies focuses on modification of the molecule to be delivered, understanding the mechanisms of transport will eventually facilitate regulation of the BBB directly. We review the different aspects of interactions and discuss recent advances in the cell biology of peptide/protein transport across the BBB. Better understanding of the nature and regulation of the transport systems at the BBB will provide a new direction to enhance the interactions of peripheral peptides and proteins with the CNS.

Contribution of proteoglycans to human immunodeficiency virus type 1 brain invasion

As a neurotropic virus, human immunodeficiency virus type 1 (HIV-1) invades the brain and causes severe neuronal, astrocyte, and myelin damage in AIDS patients. To gain access to the brain, HIV-1 must migrate through brain microvascular endothelial cells (BMECs), which compose the blood-brain barrier (BBB). Given that BMECs lack the entry receptor CD4, HIV-1 must use receptors distinct from CD4 to enter these cells. We previously reported that cell surface proteoglycans serve as major HIV-1 receptors on primary human endothelial cells. In this study, we examined whether proteoglycans also impact cell-free HIV-1 invasion of the brain. Using an artificial BBB transmigration assay, we found that both heparan and chondroitin sulfate proteoglycans (HSPGs and CSPGs, respectively) are abundantly expressed on primary BMECs and promote HIV-1 attachment and entry. In contrast, the classical entry receptors, CXCR4 and CCR5, only moderately enhanced these processes. HSPGs and CSPGs captured HIV-1 in a gp120-dependent manner. However, no correlation between coreceptor usage and transmigration was identified. Furthermore, brain-derived viruses did not transmigrate more efficiently than lymphoid-derived viruses, suggesting that the ability of HIV-1 to replicate in the brain does not correlate with its capacity to migrate through the BBB as cell-free virus. Given that HIV-1-proteoglycan interactions are based on electrostatic contacts between basic residues in gp120 and sulfate groups in proteoglycans, HIV-1 may exploit these interactions to rapidly enter and migrate through the BBB to invade the brain.

Thrombin- and Factor Xa–Induced DNA Synthesis Is Mediated by Transactivation of Fibroblast Growth Factor Receptor-1 in Human Vascular Smooth Muscle Cells

Thrombin and factor Xa (FXa) are agonists for G protein–coupled receptors (GPRCs) and may contribute to vascular lesion formation by stimulating proliferation of vascular smooth muscle cells (SMCs). Mitogenic signaling of GPCRs requires transactivation of receptor tyrosine kinases (RTKs). In rat SMCs, thrombin transactivates the epidermal growth factor receptor (EGFR) via a pathway that involves heparin-binding EGF-like growth factor (HB-EGF) as ligand for EGFR. The purpose of this study was to investigate in human SMCs the role of receptor transactivation in the mitogenic response to thrombin and FXa. Thrombin (10 nmol/L) and FXa (100 nmol/L) cause a 3.3- and 2.6-fold increase in DNA synthesis, respectively. In human SMCs, neither thrombin nor FXa causes EGFR phosphorylation, and blockade of EGFR kinase does not inhibit DNA synthesis. However, DNA synthesis and phosphorylation of fibroblast growth factor receptor-1 (FGFR-1) induced by thrombin or FXa are inhibited by antibodies neutralizing basic fibroblast growth factor (bFGF) or by heparin. Hirudin inhibits thrombin-, but not FXa-induced mitogenesis, indicating that FXa acts independently of thrombin. We further demonstrate by ELISA that upon thrombin and FXa stimulation, bFGF is released and binds to the extracellular matrix. Our data suggest that in human vascular SMCs, both thrombin and FXa rapidly release bFGF into the pericellular matrix. This is followed by transactivation of the FGFR-1 and increased proliferation. Heparin may inhibit the mitogenic effects of thrombin and FXa in human SMCs by preventing bFGF binding to FGFR-1.

Increased levels of serum basic fibroblast growth factor in schizophrenia

Basic fibroblast growth factor (bFGF) is a multifunctional growth factor that has been implicated in a variety of neurodevelopmental processes. The aim of the present study was to examine whether bFGF contributes to the pathophysiology of schizophrenia. Serum bFGF levels in 40 patients with schizophrenia (15 drug-naive and 25 medicated patients) and in 40 age- and sex-matched healthy normal controls were measured. Serum bFGF levels were significantly higher in the medicated patients than in the normal controls. Analysis of partial correlation coefficients showed that the increased bFGF levels might not be attributable to antipsychotic medication. Although there was no significant overall difference in bFGF levels between drug-naive patients and normal controls, the bFGF levels in these patients significantly correlated with the severity of negative symptoms. Furthermore, we found a significant negative correlation between serum bFGF levels and the age of onset in the entire patient group. Our finding of elevated bFGF levels in the serum of patients with schizophrenia, especially in earlier age-of-onset cases considered to have more neurodevelopmental insults, suggests that bFGF abnormalities may be involved in the pathophysiology of schizophrenia.

Blood-brain barrier transport of a novel micro 1-specific opioid peptide, H-Tyr-D-Arg-Phe-beta-Ala-OH (TAPA)

The purpose of this study was to clarify the mechanism of the blood-brain barrier (BBB) transport of H-Tyr-D-Arg-Phe-beta-Ala-OH (TAPA), which is a novel dermorphin analog with high affinity for the micro 1-opioid receptor. The in vivo BBB permeation influx rate of [125I]TAPA after an i.v. bolus injection (7.3 pmol/g body weight) into mice was estimated to be 0.265 +/- 0.025 microL/(min.g of brain). The influx rate of [125I]TAPA was reduced 70% by the coadministration of unlabeled TAPA (33 nmol/g of brain), suggesting the existence of a specific transport system for TAPA at the BBB. In order to elucidate the BBB transport mechanism of TAPA, a conditionally immortalized mouse brain capillary endothelial cell line (TM-BBB4) was used as an in vitro model of the BBB. The acid-resistant binding of [125I]TAPA, which represents the internalization of the peptide into cells, was temperature- and concentration-dependent with a half-saturation constant of 10.0 +/- 1.7 microm. The acid-resistant binding of TAPA was significantly inhibited by 2,4-dinitrophenol, dansylcadaverine (an endocytosis inhibitor) and poly-l-lysine and protamine (polycations). These results suggest that TAPA is transported through the BBB by adsorptive-mediated endocytosis, which is triggered by binding of the peptide to negatively charged sites on the surface of brain capillary endothelial cells. Blood-brain barrier transport via adsorptive-mediated endocytosis plays a key role in the expression of the potent opioid activity of TAPA in the CNS.

Application of In Vivo Brain Microdialysis to the Study of Blood-brain Barrier Transport of Drugs

Recent advances in blood-brain barrier (BBB) research have led to a new understanding of drug transport processes at the BBB. The BBB acts as a dynamic regulatory interface at which nutrients necessary for neural activity are actively taken up into the brain from the blood circulation, and actively excludes metabolites that might interfere with the maintenance of brain homeostasis. Such influx and efflux transport functions at the BBB would also control the concentrations of various drugs in the brain interstitial fluid (ISF), which are an important determinant of the central nervous system (CNS) effects. Thus, direct measurement of the brain ISF concentration of drugs can provide significant information for clarifying the influx and efflux transport functions of drugs across the BBB. Although several experimental techniques have been developed to investigate transport functions across the BBB, in vivo brain microdialysis seems to be one of the most suitable techniques for characterizing the influx and efflux transport functions across the BBB under physiological and pathological conditions. This review covers studies during the past decade, in which the influx and efflux transport of drugs across the BBB was kinetically and mechanistically evaluated by means of the brain microdialysis technique. Some applications of brain microdialysis to studies on neuronal function and neurotherapeutics are also included.