Blood-nerve Barrier Research Articles

Macrophage depletion alters the blood–nerve barrier without affecting Schwann cell function after neural injury

Previous work has shown that, during the early phases of chronic nerve compression (CNC) injury, axonal pathology is absent while Schwann cells undergo a dramatic process of cellular turnover with marked proliferation. It is known that macrophages may release Schwann cell mitogens, so we sought to explore the role of macrophages in CNC injury by selectively depleting the population of hematogenously derived macrophages in nerves undergoing CNC injury by injecting clodronate liposomes at days 1, 3, and 6 postinjury and evaluating both the integrity of the blood-nerve barrier (BNB) and Schwann cell function. Integrity of the BNB was evaluated by intravenously injecting Evans blue albumin (EBA), and Schwann cell number was determined via stereologic techniques. The BNB was clearly altered by 2 weeks postinjury and continued to disintegrate at later time points. Macrophage depletion attenuated this response at all observed time points. Quantification of Schwann cell nuclei in CNC nerves showed no differences between compressed sections of macrophage-depleted and nondepleted animals. Although macrophages are largely responsible for the increased vascular permeability associated with CNC injury, it is likely that the Schwann cell response to CNC injury is not influenced by macrophage-derived mitogenic signals but rather must be mediated via alternative mechanisms.

Endothelial Cells Constituting Blood-nerve Barrier Have Highly Specialized Characteristics as Barrier-forming Cells

In autoimmune disorders of the peripheral nervous system (PNS) such as Guillain-Barré syndrome and chronic inflammatory demyelinating polyradiculoneuropathy, breakdown of the blood-nerve barrier (BNB) has been considered as a key step in the disease process. Hence, it is important to know the cellular property of peripheral nerve microvascular endothelial cells (PnMECs) constituting the bulk of BNB. Although many in vitro models of the blood-brain barrier (BBB) have been established, very few in vitro BNB models have been reported so far. We isolated PnMECs from transgenic rats harboring the temperature-sensitive SV40 large T-antigen gene (tsA58 rat) and investigated the properties of these "barrier-forming cells". Isolated PnMECs (TR-BNBs) showed high transendothelial electrical resistance and expressed tight junction components and various types of influx as well as efflux transporters that have been reported to function at BBB. Furthermore, we confirmed the in vivo expression of various BBB-forming endothelial cell markers in the endoneurium of a rat sciatic nerve. These results suggest that PnMECs constituting the bulk of BNB have a highly specialized characteristic resembling the endothelial cells forming BBB.

HOW to Wrap Axons with Crooked Neck

How can RNA processing direct specific aspects of nervous system development? In this issue of Neuron, Edenfeld et al. identified a novel function for two regulators of mRNA splicing in Drosophila: peripheral glial cells require Crooked neck (Crn) and Held out wings (HOW) to mediate migration and ensheathment of peripheral axons.

Dysimmune polyneuropathies - new diagnostic and therapeutic insights

Polyneuropathies are systemic diseases of the nervous system that affect peripheral motor, sensory and vegetative autonomous nerve fibres. The prevalence is 2.4% in the general population and 8% in those older than 55 years. Although inflammatory polyneuropathies represent only about 10% of all polyneuropathies, they are important since they are potentially treatable. They encompass the Guillain-Barre syndrome (GBS) and its chronic sibling chronic inflammatory demyelinating polyneuropathy (CIDP), the vasculitides of the peripheral nervous system (VAS) and polyneuropathies that are associated with autoantibodies, e.g. in the context of a paraproteinaemia. Chronic inflammatory demyelinating polyradiculoneuropathy (CIDP) is an acquired immune-mediated neuropathy that causes significant neurological morbidity. Despite the resemblance to the Guillain-Barre syndrome and the observation that immunosuppressive therapies can lead to a clinical improvement the pathogenesis of CIDP is poorly understood. Since CIDP responds to plasmapheresis and intravenous immunoglobulins (IVIG), humoral mechanisms seem to be involved. But so far autoantibodies against various proteins like P0, glycoproteins and glycolipid components such as GM1, LM1, chondroitin sulfate C have only been found in a minority of patients. Most of the mononuclear inflammatory cells in nerve biopsies are macrophages and activated T-lymphocytes. But until now no specific target in human nerves for the T-cell attack could be identified. An interesting aspect is how T cells cross the blood-nerve barrier. We could show that nerve biopsies of patients with CIDP, systemic and non-systemic vasculitis expressed increased levels of the matrix metalloproteinases MMP-9 and MMP-2. Matrix metalloproteinases (MMPs) are a family of zinc-dependent endoproteinases that are effectors of the extracellular matrix remodelling. This may indicate that MMP-9 derives essentially from blood-derived immune cells where it functions as an effector molecule of extravasation and early interstitial infiltration as common pathogenetic mechanisms of inflammatory neuropathies. DNA microarray analysis is a powerful tool for simultaneous analysis and comparison of gene products expressed in normal and diseased tissues. We have undertaken gene expression analysis to identify differentially expressed genes in nerve biopsy samples of CIDP patients and compared the results to nerve biopsies of normal nerve and of vasculitic neuropathy. Of special interest were (1) tachykinin precursor 1, which may be involved in pain mediation; (2) stearoyl-CoA desaturase, which may be a marker for remyelination and (3) the allograft inflammatory factor-1, a modulator of immune response during macrophage activation and marker of blood-vessel damage. Another important aspect of dysimmune polyneuropathies is therapy. The polyneuropathy associated with antibodies to myelin-associated glycoprotein (anti-MAG) is a chronic symmetric sensorimotor demyelinating neuropathy caused by monoclonal IgM against myelin-associated glycoprotein in the context of an IgM paraproteinaemia. Rituximab is a chimeric monoclonal antibody that specifically eliminates normal and malignant B-lymphocytes and B-cell precursors. It is approved to treat B-cell lymphoma in haematology. Rituximab prevents the formation of new antibody-secreting cells and reduces titres of antibodies. We treated in a phase-II, 12-month pilot study 9 patients with anti-MAG neuropathy. There was clinical improvement in 6 of the 9 patients, and 7 had improved nerve conduction studies by at least 10%. These findings were accompanied by laboratory evidence of reduction of B cells, anti-MAG antibodies and total IgM. IgM levels fell to a median of 58% and anti-MAG antibody titres fell to a median of 38% of the initial values one year after treatment.

Permeability of Injured and Intact Peripheral Nerves and Dorsal Root Ganglia

Nerve injury that produces behavioral changes of allodynia and hyperalgesia in animals is associated with electrophysiologic changes in dorsal root ganglion (DRG) cells. The introduction of drugs into the DRG or the peripheral nerve that alter calcium, sodium, or potassium channel activity may be of therapeutic benefit after nerve injury. For this reason, the authors sought to determine whether drugs that do not ordinarily cross the blood-nerve barrier will enter the DRG after intravenous or regional injection and to determine whether nerve injury alters drug access to DRGs or peripheral nerves. Both intact and spinal nerve-ligated rats were injected with sodium fluorescein by intravenous, intrathecal, peri-DRG, perisciatic, and epidural routes. DRG, sciatic nerve, and spinal cord tissues were harvested and frozen, and histologic sections were analyzed quantitatively for tissue fluorescence. In both intact and nerve-injured animals, fluorescein accumulated in DRGs after intravenous, peri-DRG, and epidural injection. There was accumulation in the proximal portion of the ganglion after intrathecal injection. Minimal amounts of fluorescein were found in the sciatic nerve in intact animals after intravenous or perineural injection, but substantial amounts were found in some nerve fascicles in nerve-injured animals after both intravenous and perineural injection. There was almost no fluorescein found in the spinal cord except after intrathecal administration. In both intact and nerve-injured animals, fluorescein accumulates freely in the DRG after intravenous, epidural, or paravertebral injection. The sciatic nerve is relatively impermeable to fluorescein, but access by either systemic or regional injection is enhanced after nerve injury.

The structural and functional integrity of peripheral nerves depends on the glial-derived signal desert hedgehog.

We show that desert hedgehog (dhh), a signaling molecule expressed by Schwann cells, is essential for the structural and functional integrity of the peripheral nerve. Dhh-null nerves display multiple abnormalities that affect myelinating and nonmyelinating Schwann cells, axons, and vasculature and immune cells. Myelinated fibers of these mice have a significantly increased (more than two times) number of Schmidt-Lanterman incisures (SLIs), and connexin 29, a molecular component of SLIs, is strongly upregulated. Crossing Dhh-null mice with myelin basic protein (MBP)-deficient shiverer mice, which also have increased SLI numbers, results in further increased SLIs, suggesting that Dhh and MBP control SLIs by different mechanisms. Unmyelinated fibers are also affected, containing many fewer axons per Schwann cell in transverse profiles, whereas the total number of unmyelinated axons is reduced by approximately one-third. In Dhh-null mice, the blood-nerve barrier is permeable and neutrophils and macrophage numbers are elevated, even in uninjured nerves. Dhh-null nerves also lack the largest-diameter myelinated fibers, have elevated numbers of degenerating myelinated axons, and contain regenerating fibers. Transected dhh nerves degenerate faster than wild-type controls. This demonstrates that a single identified glial signal, Dhh, plays a critical role in controlling the integrity of peripheral nervous tissue, in line with its critical role in nerve sheath development (Parmantier et al., 1999). The complexity of the defects raises a number of important questions about the Dhh-dependent cell-cell signaling network in peripheral nerves.

Axonal Ensheathment and Septate Junction Formation in the Peripheral Nervous System ofDrosophila

Axonal insulation is critical for efficient action potential propagation and normal functioning of the nervous system. In Drosophila, the underlying basis of nerve ensheathment is the axonal insulation by glial cells and the establishment of septate junctions (SJs) between glial cell membranes. However, the details of the cellular and molecular mechanisms underlying axonal insulation and SJ formation are still obscure. Here, we report the characterization of axonal insulation in the Drosophila peripheral nervous system (PNS). Targeted expression of tau-green fluorescent protein in the glial cells and ultrastructural analysis of the peripheral nerves allowed us to visualize the glial ensheathment of axons. We show that individual or a group of axons are ensheathed by inner glial processes, which in turn are ensheathed by the outer perineurial glial cells. SJs are formed between the inner and outer glial membranes. We also show that Neurexin IV, Contactin, and Neuroglian are coexpressed in the peripheral glial membranes and that these proteins exist as a complex in the Drosophila nervous system. Mutations in neurexin IV, contactin, and neuroglian result in the disruption of blood-nerve barrier function in the PNS, and ultrastructural analyses of the mutant embryonic peripheral nerves show loss of glial SJs. Interestingly, the murine homologs of Neurexin IV, Contactin, and Neuroglian are expressed at the paranodal SJs and play a key role in axon-glial interactions of myelinated axons. Together, our data suggest that the molecular machinery underlying axonal insulation and axon-glial interactions may be conserved across species.

Bickerstaff brainstem encephalitis after heat stroke

Sirs: Bickerstaff brainstem encephalitis (BBE) is characterized by acute onset of ophthalmoplegia and ataxia with symptoms and signs indicative of involvement of the central nervous system such as consciousness disturbance [1]. It has been proposed that BBE, Miller Fisher syndrome, and Guillain-Barre syndrome (GBS) are related disorders [8–10]. In fact, a considerable number of patients with BBE have overlapping GBS [8, 15]. A number of factors have been described as triggers of GBS [13]. Heat stroke produces a wide variety of neurological complications [6], but only one case of GBS after heat stroke has been reported [11]. We present a patient with overlapping BBE and GBS after heat stroke. To our knowledge, this is the first report of such a patient. A previously healthy 43-year-old man experienced generalized tonic seizure with loss of consciousness during hard physical work on a hot summer day. He was transferred to our intensive care unit. The core temperature was 42.8°C, heart rate 173 bpm, and blood pressure 66/36 mmHg. Deep coma and bilateral miotic pupils were observed. Laboratory tests showed a platelet count of 113.000/mm3, creatinine 2.73 mg/dL, creatine kinase 2833 U/L, and serum interleukin-6 8594 pg/ml (normal < 4). He was treated with surface cooling (35 °C), mechanical ventilation, intravenous dopamine, and continuous hemodiafiltration. His general status gradually improved. On day 8, he was weaned from mechanical ventilation. On day 9, he was fully conscious with no weakness in the limbs, normal external ocular movements, and normal tendon reflexes. The next day, he again showed consciousness disturbance and weakness in all four limbs. On day 11, he was drowsy, but he was able to respond to commands. His pupils were equal (3.0 mm) and pupillary light reflexes absent. There were complete external ophthalmoplegia, bilateral facial palsy, aphonia, tetraparesis (MRC grade 3 for the upper extremities, grade 2 for the lower ones), limb ataxia, and areflexia. Laboratory examinations on day 12 revealed near-normal blood cell count (white blood cell, 9.900/mm3), and normal serum electrolytes and vitamin B1 levels. Brain MRI found no obvious abnormalities responsible for his consciousness disturbance and muscle weakness. Serum antibodies against ganglioside GM1, GD1a, GT1a, or GQ1b were negative. Cerebrospinal fluid (CSF) contents on day 12 were normal (cell count, 0/mm3; protein level, 21 mg/dl), and a follow-up CSF examination on day 30 revealed the slightly increased protein level (43 mg/dl; normal < 40 mg/dl). Nerve conduction studies (NCS) showed slightly decreased compound muscle action potential (CMAP) amplitudes, normal nerve conduction velocities and distal latencies, and absent F-waves in all the nerves tested (the median, ulnar, peroneal, and tibial nerves). He underwent plasmapheresis 4 times, every other day from day 15. After this treatment, his neurological symptoms were gradually improved. On day 24, he could talk, but his speech was slurred and ataxic. On day 35, when his muscle strength was near-normal, NCS revealed restored F-waves and increased CMAP amplitudes. On day 60, he was discharged to a rehabilitation facility because he was still unable to stand independently due to ataxia. This patient was characterized by acute consciousness disturbance, ophthalmoplegia, facial palsy, tetraparesis, and ataxia, 7 days after heat stroke. After treatment with plasmapheresis, the signs gradually lessened, resulting in a monophasic course. Although several diseases including Wernicke’s encephalopathy, infectious brainstem encephalitis, and GBSlike syndrome by severe exertion [16] should be considered in the differential diagnosis, his clinical features met the criteria for BBE and overlapping GBS [8, 15], suggesting that the disorders may have been triggered by heat stroke. The absence of F-waves during tetraparesis and their restitution in the recovery phase are consistent with proximal conduction block [7]. Pfeiffer reported the only case of GBS after heat stroke, and speculated that heat stroke activates the immune system by cytokine release which opens the blood-nerve barrier and exposes peripheral nerve antigens, thereby inducing GBS [11]. In fact, various cytokines including tumor necrosis factoralpha and interleukin (IL)–6 are conjectured to function in the pathogenesis of heat stroke [2, 4], and also of GBS and related diseases [3, 5, 12, 14]. Elevated serum IL-6 was detected in our patient. Hypercytokinemia may be the key to the association of GBS and related diseases with heat stroke. LETTER TO THE EDITORS

Enhancement of Perineurial Repair and Inhibition of Nerve Adhesion by Viscous Injectable Pure Alginate Sol

Clinical treatment of recurrent symptoms following peripheral nerve decompression is problematic. Removal of scar tissue can produce an inappropriately pronounced healing response and thereby lead to more serious tethering or compression of the nerve. The goal of the present study was to test the ability of viscous injectable pure alginate sol to prevent perineurial adhesion using a rat neurolysis model. The antiadhesive effect of viscous injectable pure alginate sol after neurolysis was evaluated histologically and biomechanically. A total of 40 rats were used in this study. The viscous injectable pure alginate sol was applied topically on the right side after external (six rats) or extensive internal (six rats) neurolysis, whereas the left side received no treatment. The nerves were harvested over 6 weeks, and histologic analysis was performed with hematoxylin and eosin staining and Masson trichrome staining. Functional analysis of the blood and perineurial barriers was also evaluated with Evans blue albumin (four rats). Sixteen rats were used for biomechanical analysis, and eight rats were used as a control group. The results were analyzed statistically using a post hoc test. Histologic examination showed that the use of viscous injectable pure alginate sol was associated with excellent biocompatibility and strong inhibition of perineurial granulation. Viscous injectable pure alginate sol was absorbed completely within 6 weeks without inducing inflammation. In addition, viscous injectable pure alginate sol enhanced repair of the perineurium associated with regeneration of epithelial-like cell layers, a key structure necessary for barrier function of the inner layer of the perineurium. Functional analysis with Evans blue albumin clearly demonstrated that, although blood nerve barrier function recovered by 6 weeks postoperatively in all nerves, the perineurial barrier function recovered only in the sol-treated nerves. Biomechanical study showed a significant antiadhesive effect of viscous injectable pure alginate sol. Viscous injectable pure alginate sol inhibited adhesion formation around nerves and enhanced regeneration of the perineurium with barrier function. Because excessive perineurial fibrosis and tethering at the neurolysis or neurorrhaphy site is a common postoperative problem in peripheral nerve surgery, viscous injectable pure alginate sol appears to have potentially broad clinical applications.

Human Antiganglioside Autoantibodies: Validation of ELISA

Gangliosides have a hydrophilic sugar chain that contains antigenic determinants and a hydrophobic ceramide. In humans, gangliosides elicit a T-cell independent IgM response; antiganglioside IgM autoantibodies may be pentameric or polymeric. A correlation between specific neuropathies and antiganglioside autoantibodies has been confirmed. Although many neurologists attempt to lower titers of antiganglioside autoantibodies, oncologists are developing strategies to augment production of IgM antibodies that will remove immunosuppressive gangliosides from the circulation of patients and target gangliosides and kill tumor cells. Antiganglioside IgM antibodies can cause leakage of the blood-nerve barrier in a concentration-dependent and complement-independent manner, bind to neuronal gangliosides to create a neuromuscular block and serve as a marker of axonal damage in neuropathies such as multiple sclerosis. They are also a promising biomarker of early prostate cancer. There is a need to validate the protocol for enzyme-linked immunosorbent assay (ELISA) of antiganglioside IgM autoantibodies. This validation must consider the purity of gangliosides from different commercial sources, the coating of gangliosides onto a solid matrix in a manner that maximizes exposure of oligosaccharide epitopes to IgM paratopes, techniques to minimize background noise and eliminate nonspecific antibody binding, and carefully defined positive and negative controls. The validated protocol also must include a simple formula to estimate titers for several replicas. Finally, antibody titers must be converted to natural logs for statistical appraisal.

The Histologic Effects of Pulsed and Continuous Radiofrequency Lesions at 42°C to Rat Dorsal Root Ganglion and Sciatic Nerve

Experimental histologic study of the effects of radiofrequency (RF) or convective heating of the rat dorsal root ganglion or sciatic nerve to 42 degrees C. To determine whether treatment causes neuropathologic changes in an effort to explore the mechanisms and safety of pulsed RF pain therapy. Clinical data suggest that low temperature pulsed RF energy delivered to the DRG is a safe and effective form of therapy for low back pain. However, the mechanism by which this treatment modifies pain is unclear. A total of 118 Sprague-Dawley rats were divided into five groups for different RF and thermal treatments. All treatments increased tissue temperature to 42 degrees C. Treatments of the DRG included pulsed RF, continuous RF, and conductive heat. The generator output was increased until 42 degrees C was obtained in the tissue and was then maintained for 120 seconds. As a positive control, some rat sciatic nerves were treated with continuous RF lesions at 80 degrees C. Animals were killed for histologic study at 2, 7, or 21 days after treatment. Tissue was fixed in gluteraldehyde and embedded in plastic resin for detailed light microscopic neuropathologic evaluation. The methods used to heat the tissue to 42 degrees C caused no significant difference in pathology. However, subclinical changes included endoneurial edema caused by alterations in the function of the blood-nerve barrier, fibroblast activation, and collagen deposition. Tissue returned to normal conditions by 7 days in nerve and 21 days in the DRG. These minor structural changes observed at the light microscopic level in normal animals do not exclude the possibility that there would be nonstructural changes in gene expression or cytokine upregulation in injured tissue. Lesions at 80 degrees C caused consistent thermal injury characterized by Wallerian degeneration of nerve fibers. The data support the hypothesis that pulsed RF treatment does not rely on thermal injury of neurologic tissue to achieve its effect.

HIV-1 Tat Interactions with p300 and PCAF Transcriptional Coactivators Inhibit Histone Acetylation and Neurotrophin Signaling through CREB

The human immunodeficiency virus type-1 (HIV-1) infects microglia, macrophages, and astrocytes in the central nervous system (CNS) and may cause severe neurological diseases, such as AIDS-related dementias or progressive encephalopathies, as a result of CNS inflammation and neurotrophin signaling defects associated with expression of viral antigens and HIV-1 replication in the brain. The HIV Tat protein can be endocytosed by surrounding uninfected cells; interacts with transcriptional coactivators/acetyltransferases, p300/CREB-binding protein, and p300/CREB-binding protein-associated factor (PCAF); and induces neuronal apoptosis. Since nerve growth factor (NGF) receptor and brain-derived neurotrophic factor receptor signaling through CREB requires p300 and PCAF histone acetyltransferases, we sought to determine whether HIV-1 Tat coactivator interactions interfere with neurotrophin receptor signaling in neuronal cells. Here, we demonstrate that Tat-coactivator interactions inhibit NGF- and brain-derived neurotrophic factor-responsive CRE trans-activation and neurotrophin protection against apoptosis in PC12 and IMR-32 neuroblastoma cells. Purified recombinant Tat or Tat-derived synthetic peptides, spanning p300- and PCAF-binding sequences, inhibit histone H3/H4 acetylation in vitro. A Tat mutant, TatK28A/K50A, defective for binding p300 and PCAF, neither repressed NGF-responsive CRE transactivation nor inhibited histone acetylation. HIV-1 Tat interacts in PCAF complexes in post-mortem CNS tissues from donor neuro-AIDS patients, as determined by fluorescence resonance energy transfer immunoconfocal microscopy. Importantly, these findings suggest that HIV-1 Tat-coactivator interactions may contribute to neurotrophin signaling impairments and neuronal apoptosis associated with HIV-1 infections of the CNS.

Antiglycolipid antibodies in Guillain-Barré syndrome and related diseases: Review of clinical features and antibody specificities

Guillain-Barré syndrome (GBS) is an acute inflammatory polyradiculoneuropathy that usually develops following a respiratory or intestinal infection. Although the pathogenic mechanisms of GBS have not been fully established, both humoral and cell-mediated immune factors have been shown to contribute to the disease process. Several antiglycosphingolipid (anti-GSL) antibodies have been found in the sera of patients with GBS or related diseases. Measurements of these antibody titers are very important in the diagnosis of GBS and in evaluating the effectiveness of treatments in clinical trials. The most common treatment strategies for these disorders involve plasmapheresis and the use of steroids for reducing anti-GSL antibody titers to ameliorate patients' clinical symptoms. Administration of intravenous immunoglobulin may also be beneficial in the treatment of neuropathies by suppressing the immune-mediated processes that are directed against antigenic targets in myelin and axons. In certain demyelinating neuropathies, the destruction or malfunctioning of the blood-nerve barrier, which results in the leakage of circulating antibodies into the peripheral nerve parenchyma, has been considered to be an initial step in development of the disease process. In addition, anti-GSL antibodies, such as anti-GM1, may cause nerve dysfunction and injury by interfering with the ion channel function at the nodes of Ranvier, where carbohydrate epitopes of glycoconjugates are located. These malfunctions thus contribute to the pathogenic mechanisms of certain demyelinating neuropathies.

Peripheral neuropathy in systemic vasculitides

Peripheral nervous system (PNS) involvement is of great diagnostic value in systemic vasculitides, because it occurs frequently and often early during the course of these diseases, despite the supposed blood-nerve barrier that should prevent or at least minimize PNS damage. However, it carries no poor prognostic value in vasculitides. Recent advances have been made in understanding the pathogenetic mechanisms of PNS involvement. Vasculitic neuropathy may result from primary or secondary systemic vasculitides, or may be restricted to the PNS, in a form that is now also considered to be a systemic vasculitis. The blood-nerve barrier is not as efficient as the blood-brain barrier. Inflammatory cell infiltration into the vasa nervorum and epineurial arteries leads to ischemic axonal nerve injury and is facilitated by additional breaches in the blood-nerve barrier, induced by proinflammatory cytokines, oxidative stress-derived molecules, and matrix metalloproteinases. Although animal models of myeloperoxidase or, now, proteinase 3-antineutrophil cytoplasmic autoantibody-inducing vasculitis have been developed, they do not support a role for antineutrophil cytoplasmic autoantibodies in PNS involvement. Treatment should be chosen based on the other organ involvement and the patient's general condition. When PNS involvement is isolated, corticosteroids alone should be used as first-line treatment. Apart from the so-called nonsystemic nerve vasculitis, PNS involvement is rarely the sole clinical sign of systemic necrotizing vasculitis, and its association with other typical manifestations is often suggestive of the diagnosis of vasculitis. Herein are summarized recent advances that have clarified but not yet fully elucidated the pathogenesis of peripheral neuropathy in systemic vasculitides, together with the latest clinical findings and therapeutic strategies.

Water Channel Aquaporin 1 (AQP1) Is Present in the Perineurium and Perichondrium

Aquaporin 1 (AQP1) is an isoform of membrane water channels. We examined the distribution of AQP1 in peripheral nerves. Immunofluorescence microscopy with specific antibodies to AQP1 was performed in the tissue sections of the rat tongue, esophagus, trachea, and sciatic nerve. AQP1 was present in the perineurium of nerve fiber bundles in the sciatic nerve and nerve fiber bundles in the tongue, esophagus, and trachea. Laser confocal microscopy of the double-labeled specimens for AQP1 and sugar transporter GLUT1 revealed that AQP1 was localized in the outer layer(s) of the perineurial cell layers, whereas GLUT1 was present throughout the entire perineurial cell layers. AQP1 and GLUT1 were also present in blood vessels inside the nerve fiber bundle. They were rarely found in the same blood vessels, namely, AQP1 was hardly detectable in GLUT1-positive blood vessels and GLUT1 was hardly detectable in AQP1-positive vessels. AQP1 in these sites of the blood-nerve barrier may participate in the water transfer across the barrier and contribute to the maintenance of the milieu of the nerve. In addition, we showed the presence of AQP1 in the perichondrium of the tracheal cartilage suggesting a possible role in water transfer between the cartilage and surrounding connective tissues.

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-β2 (TGF-β2) passes through the blood–brain barrier and blood–nerve barriers, after intravenous, intraperitoneal or intramuscular injections. The entry of the [ 125I]-TGF-β2 to the brain was rapid, saturable and inhibited by co-injection of unlabelled TGF-β2. In contrast, co-injection of unlabelled TGF-β2 increased the retention of [ 125I]-TGF-β2 in the blood. The [ 125I]-TGF-β2 transported into the brain was localised by autoradiography to the extracellular space, and was intact as judged by SDS-PAGE. The [ 125I]-TGF-β2 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-β2 had a half-life of 4 h in the brain. These results indicate that therapeutically relevant levels of TGF-β2 reach the brain after peripheral administration of TGF-β2.

Developmental actions of natriuretic peptides in the brain and skeleton.

The concept that atrial natriuretic peptide (ANP) and the closely related peptides BNP and CNP might be involved in the ontogeny of several organ systems emerged in the late 1980s. While many of the reported in vitro actions have not been examined in the context of organ development in vivo, recent studies demonstrate that mice which lack or overexpress natriuretic peptides or receptors exhibit pronounced skeletal growth defects. This article discusses how natriuretic peptides and other factors appear to regulate bone growth as an example of how natriuretic peptides might participate in the ontogeny of other organ systems. Evidence indicating that natriuretic peptides regulate neural development is then reviewed. Natriuretic peptides and receptors exhibit complex expression patterns in the developing nervous system, where they have been shown to act on neural cells as early as at the embryonic neural tube stage. Interestingly, both bone and brain growth appear to utilize primarily CNP and the CNP-specific type B receptor, and perhaps the type C receptor. In vitro data indicate that CNP may act on developing neurons, astrocytes and Schwann cells like a classical growth factor, regulating proliferation, patterning, phenotypic specification, survival and axonal pathfinding. Natriuretic peptides might also have roles in the vascularization of the embryonic brain, establishment of the blood-brain and blood-nerve barriers, and perhaps in nerve regeneration.

Deposition and passage of transthyretin through the blood-nerve barrier in recipients of familial amyloid polyneuropathy livers

Familial amyloid polyneuropathy (FAP) is characterized by deposition of mutated transthyretin (TTR) in the peripheral nervous system. Prior to amyloid fibrils, nonfibrillar TTR aggregates are deposited inducing oxidative stress with increased nitration (3-NT). As the major source of TTR is the liver, liver transplantation (LT) is used to halt FAP. Given the shortage of liver donors, domino LT (DLT) using FAP livers is performed. The correlation between TTR deposition in the skin and nerve was tested in biopsies from normal individuals, asymptomatic carriers (FAP 0) and FAP patients; in FAP 0, nonfibrillar TTR was observed both in the skin and nerve in the same individuals; in patients, amyloid was detected in both tissues. The occurrence of amyloidosis in recipients of FAP livers was evaluated 1–7 years after DLT: TTR deposition occurred in the skin 3 years after transplantation either as amyloid or aggregates; in one of the recipients, fibrillar TTR was present in the epineurium 6 years after DLT. Deposits were scarce and 3-NT immunostaining was irrelevant. Nerve biopsies from DLT recipients had no FAP-related neuropathy. Our findings suggest that TTR amyloid formation occurs faster than predicted and that TTR of liver origin can cross the blood-nerve barrier. Recipients of FAP livers should be under surveillance for TTR deposition and tissue damage.

Treatment of inflammatory and paraproteinemic neuropathies.

Acquired demyelinating and inflammatory neuropathies encompass a number of acute and chronic autoimmune conditions characterized by variable degrees of clinical involvement. These disorders, including Guillain-Barre syndrome (GBS), chronic inflammatory demyelinating polyradiculoneuropathy (CIDP), multifocal motor neuropathy (MMN), and paraprotein-associated neuropathy, have an overall annual incidence of 2-4/100,000 worldwide and are potentially treatable. Over the last few years, several investigations have helped clarify the pathogenesis of immune neuropathies and the definition of molecular targets involved in these diseases, thus providing firmer grounds for treatment with classical immunosuppressive drugs and new biological agents. In GBS and related variants, which are characterized by cellular inflammation and alterations of the blood-nerve barrier, randomized clinical trials show that plasma exchange (PE) and intravenous immunoglobulin (IVIg) are equally effective as disease-modifying treatments, although IVIg has been adopted as the favourite treatment in most centres. In CIDP, controlled clinical trials have established the efficacy of oral prednisone, PE and IVIg, with intermittent IVIg treatment or corticosteroids being usually preferred. Adding azathioprine can help keep lower the required dose of prednisone, while other immunosuppressive agents, such as cyclophosphamide and cyclosporin A may have side effects, limiting their use to selected cases. Currently, the efficacy of interferon beta and alfa is under evaluation. Controlled trials support the view that IVIg is the treatment of choice in MMN. Patients resistant to IVIg administration may benefit of treatments which deplete B cells, such as cyclophosphamide and rituximab. Demyelinating neuropathies associated with circulating paraproteins are clinically heterogeneous, depending on the reactivity and type of the monoclonal (M) protein. In many cases, neuropathies associated with IgM M proteins are not treated because of their slow progression. In patients with a disabling or rapid progression, small trials have shown short-term benefits from IVIg or PE. Recently, fludarabine and rituximab have been reported as beneficial in selected cases.

Chronic inflammatory demyelinating polyneuropathy: decreased claudin-5 and relocated ZO-1

Objectives: To clarify the dynamics of molecules composing the blood–nerve barrier (BNB) in inflammatory neuropathies. Methods: The expression of four tight junction (TJ) proteins—claudin-1, claudin-5, occludin, and ZO-1—was analysed immunohistochemically...