Biology of the blood-nerve barrier and its alteration in immune mediated neuropathies
The blood-nerve barrier (BNB) is a dynamic and competent interface between the endoneurial microenvironment and the surrounding extracellular space or blood. It is localised at the innermost layer of the multilayered ensheathing perineurium and endoneurial microvessels, and is the key structure that controls the internal milieu of the peripheral nerve parenchyma. Since the endoneurial BNB is the point of entry for pathogenic T cells and various soluble factors, including cytokines, chemokines and immunoglobulins, understanding this structure is important to prevent and treat human immune mediated neuropathies such as Guillain-Barré syndrome, chronic inflammatory demyelinating polyneuropathy, POEMS (polyneuropathy, organomegaly, endocrinopathy, monoclonal protein and skin changes) syndrome and a subset of diabetic neuropathy. However, compared with the blood-brain barrier, only limited knowledge has been accumulated regarding the function, cell biology and clinical significance of the BNB. This review describes the basic structure and functions of the endoneurial BNB, provides an update of the biology of the cells comprising the BNB, and highlights the pathology and pathomechanisms of BNB breakdown in immune mediated neuropathies. The human immortalised cell lines of BNB origin established in our laboratory will facilitate the future development of BNB research. Potential therapeutic strategies for immune mediated neuropathies manipulating the BNB are also discussed.
Available from: Michael Polydefkis
- "These findings confirm these soluble factors in plasma are associated with monocyte activation and traffic during SIV-PN. Because the blood-nerve barrier is more promiscuous (or leakier) than the blood-brain barrier, we assumed that neurons were exposed to all proteins found in plasma. Several inflammatory cytokines have been found to be neurotoxic in vitro[61,62], but this direct causation is difficult to prove in vivo. "
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Peripheral neuropathy (PN) continues to be a major complication of human immunodeficiency virus (HIV) infection despite successful anti-retroviral therapy. Human HIV-PN can be recapitulated in a CD8-depleted, simian immunodeficiency virus (SIV)-infected rhesus macaque animal model, characterized by a loss of intraepidermal nerve fiber density (IENFD) and damage to the dorsal root ganglia (DRG). Increased monocyte traffic to the DRG has previously been associated with severe DRG pathology, as well as a loss in IENFD. Here, we sought to characterize the molecular signals associated with monocyte activation and trafficking to the DRGs.
Eleven SIV-infected CD8-depleted rhesus macaques were compared to four uninfected control animals. sCD14, sCD163, sCD137, regulated on activation normal T cell expressed and secreted (RANTES), and monocyte chemoattractant protein 1 (MCP-1) were measured in plasma and the latter three proteins were also quantified in DRG tissue lysates. All SIV-infected animals received serial skin biopsies to measure IENFD loss as well as BrdU inoculations to measure monocyte turnover during the course of infection. The number of BrdU+ and CD14+ CD16+ peripheral blood monocytes was determined by flow cytometry. The number of MAC387+, CCR2+, CCR5+, and CD137+ cells in DRG tissue was quantified by immunohistochemistry.
sCD14, sCD163, MCP-1, and sCD137 increased significantly in plasma from pre-infection to necropsy. Plasma sCD163 and RANTES inversely correlated with IENFD. Additionally, sCD137 in DRG tissue lysate was elevated with severe DRG pathology and associated with the recruitment of MAC387+ cells to DRG. Elevated numbers of CCR5+ and CCR2+ satellite cells in the DRG were found, suggesting a chemotactic role of their ligands, RANTES, and MCP-1 in recruiting monocytes to the tissue.
We characterized the role of systemic (plasma) and tissue-specific (DRG) monocyte activation and associated cytokines in the pathogenesis of SIV-PN. We identified sCD163 and RANTES as potential biomarkers for HIV-PN, as these were associated with a loss of IENFD. Additionally, we identified CD137 signaling to play a role in MAC387+ cell traffic to DRG and possibly contribute to severe pathology. These studies highlight the role of monocyte activation and traffic in the pathogenesis of SIV-PN, while identifying specific signaling proteins for future pharmacological blockade.
Available from: Satoshi Kuwabara
- "These findings might not reflect the direct effects of VEGF alone, because multiple inflammatory cytokines such as interleukin-12, and tumor necrosis-a are simultaneously and markedly upregulated in the active phase of POEMS syndrome (Kanai et al., 2012), and it is possible such cytokines other than VEGF affect ion channel function, although this should be investigated in further studies. Nevertheless, increased vascular permeability mediated by VEGF presumably responsible for nerve edema, frequently found on pathological examination (Kanda, 2013). We initially expected membrane depolarization due to edema-induced compression ischemia in POEMS syndrome, and nerve edema detected by ultrasound partly correlated with axonal excitability. "
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ABSTRACT: POEMS (polyneuropathy, organomegaly, endocrinopathy, M-protein, and skin changes) syndrome is a rare cause of demyelinating neuropathy with upregulation of vascular endothelial growth factor (VEGF). This study aimed to elucidate axonal excitability properties and their relation to VEGF levels and nerve edema in POEMS neuropathy.
Axonal excitability measurement and nerve ultrasound were performed in the median nerve of 33 patients with POEMS syndrome. Serum VEGF levels were measured by ELISA.
Compared with normal subjects (n=87), POEMS patients showed longer strength-duration time constant, fanning-out of threshold electrotonus curves, and greater threshold changes in a hyperpolarizing current-threshold relationship. Nerve ultrasound showed significant enlargement in POEMS patients. Serum VEGF levels and the extent of nerve edema partly correlated with nerve conduction slowing, as well as persistent sodium currents and inward rectification.
In POEMS syndrome, patterns of changes in excitability properties could suggest increased persistent sodium currents, and impaired potassium and inward rectifying channels. The findings were not consistent with depolarization due to nerve edema and compression ischemia.
In addition to demyelination, nerve edema induced by upregulated VEGF, and upregulated inflammatory cytokines could modulate profiles of POEMS neuropathy.
Copyright © 2015 International Federation of Clinical Neurophysiology. Published by Elsevier Ireland Ltd. All rights reserved.
Available from: Stepan Capek
- ", 1995 ) or hematogenous ( Yoshizawa et al . , 1991 ) spread , but the absence of lymphatic vessels within endoneurium and the existence of blood – nerve barrier ( Kanda , 2013 ) make these theories unlikely . More recent studies have suggested that more complex reciprocal signaling interactions between cancer cells and nerves may be involved ( Liebig et al . "
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ABSTRACT: Several groups have reported cases of rectal cancer with carcinomatous involvement of the lumbosacral plexus and sciatic, obturator, pudendal, or spinal nerves. To our best knowledge, clear examples of perineural tumor spread in rectal carcinoma have not yet been described. We retrospectively reviewed clinical data and imaging studies of three patients with primary or recurrent rectal cancer involving the lumbosacral plexus. Imaging studies included MRI and 18FDG PET/CT scans in all (n = 3) patients, histological samples were available in two (n = 2). Imaging studies demonstrated distinct features of tumor spread from the organ to the plexus and beyond in all cases (n = 3), histological specimens demonstrated perineural involvement thus supporting our theory (n = 2). We present these three cases of perineural tumor spread in rectal cancer as a proof of concept. We hypothesize that not only our cases, but other similar reported cases can be explained anatomically by extension of the rectal cancer to the inferior hypogastric plexus with perineural tumor spread to the lumbosacral plexus using the pelvic and sacral splanchnic nerves as conduits. Once the tumor reaches the lumbosacral plexus, it can continue to spread proximally or distally. We believe that perineural spread of colon cancer represents an important, under-recognized mechanism of recurrence to neighboring major nerves in the pelvis. Clin. Anat., 2014. © 2014 Wiley Periodicals, Inc.
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