Systemic inflammation disrupts oligodendrocyte gap junctions and induces ER stress in a model of CNS manifestations of X-linked Charcot-Marie-Tooth disease

X-linked Charcot-Marie-Tooth disease (CMT1X) is a common form of inherited neuropathy resulting from different mutations affecting the gap junction (GJ) protein connexin32 (Cx32). A subset of CMT1X patients may additionally present with acute fulminant CNS dysfunction, typically triggered by conditions of systemic inflammation and metabolic stress. To clarify the underlying mechanisms of CNS phenotypes in CMT1X we studied a mouse model of systemic inflammation induced by lipopolysaccharide (LPS) injection to compare wild type (WT), connexin32 (Cx32) knockout (KO), and KO T55I mice expressing the T55I Cx32 mutation associated with CNS phenotypes. Following a single intraperitoneal LPS or saline (controls) injection at the age of 40-60 days systemic inflammatory response was documented by elevated TNF-α and IL-6 levels in peripheral blood and mice were evaluated 1 week after injection. Behavioral analysis showed graded impairment of motor performance in LPS treated mice, worse in KO T55I than in Cx32 KO and in Cx32 KO worse than WT. Iba1 immunostaining revealed widespread inflammation in LPS treated mice with diffusely activated microglia throughout the CNS. Immunostaining for the remaining major oligodendrocyte connexin Cx47 and for its astrocytic partner Cx43 revealed widely reduced expression of Cx43 and loss of Cx47 GJs in oligodendrocytes. Real-time PCR and immunoblot analysis indicated primarily a down regulation of Cx43 expression with secondary loss of Cx47 membrane localization. Inflammatory changes and connexin alterations were most severe in the KO T55I group. To examine why the presence of the T55I mutant exacerbates pathology even more than in Cx32 KO mice, we analyzed the expression of ER-stress markers BiP, Fas and CHOP by immunostaining, immunoblot and Real-time PCR. All markers were increased in LPS treated KO T55I mice more than in other genotypes. In conclusion, LPS induced neuroinflammation causes disruption of the main astrocyte-oligodendrocyte GJs, which may contribute to the increased sensitivity of Cx32 KO mice to LPS and of patients with CMT1X to various stressors. Moreover the presence of an intracellularly retained, misfolded CMT1X mutant such as T55I induces ER stress under inflammatory conditions, further exacerbating oligodendrocyte dysfunction and pathological changes in the CNS.

Targeting the colony stimulating factor 1 receptor alleviates two forms of Charcot-Marie-Tooth disease in mice

See Scherer (doi:10.1093/awv279) for a scientific commentary on this article.Charcot-Marie-Tooth type 1 neuropathies are inherited disorders of the peripheral nervous system caused by mutations in Schwann cell-related genes. Typically, no causative cure is presently available. Previous preclinical data of our group highlight the low grade, secondary inflammation common to distinct Charcot-Marie-Tooth type 1 neuropathies as a disease amplifier. In the current study, we have tested one of several available clinical agents targeting macrophages through its inhibition of the colony stimulating factor 1 receptor (CSF1R). We here show that in two distinct mouse models of Charcot-Marie-Tooth type 1 neuropathies, the systemic short- and long-term inhibition of CSF1R by oral administration leads to a robust decline in nerve macrophage numbers by ∼70% and substantial reduction of the typical histopathological and functional alterations. Interestingly, in a model for the dominant X-linked form of Charcot-Marie-Tooth type 1 neuropathy, the second most common form of the inherited neuropathies, macrophage ablation favours maintenance of axonal integrity and axonal resprouting, leading to preserved muscle innervation, increased muscle action potential amplitudes and muscle strengths in the range of wild-type mice. In another model mimicking a mild, demyelination-related Charcot-Marie-Tooth type 1 neuropathy caused by reduced P0 (MPZ) gene dosage, macrophage blockade causes an improved preservation of myelin, increased muscle action potential amplitudes, improved nerve conduction velocities and ameliorated muscle strength. These observations suggest that disease-amplifying macrophages can produce multiple adverse effects in the affected nerves which likely funnel down to common clinical features. Surprisingly, treatment of mouse models mimicking Charcot-Marie-Tooth type 1A neuropathy also caused macrophage blockade, but did not result in neuropathic or clinical improvements, most likely due to the late start of treatment of this early onset disease model. In summary, our study shows that targeting peripheral nerve macrophages by an orally administered inhibitor of CSF1R may offer a highly efficacious and safe treatment option for at least two distinct forms of the presently non-treatable Charcot-Marie-Tooth type 1 neuropathies.

Molecular triggers of neuroinflammation in mouse models of demyelinating diseases

Myelinating cells wrap axons with multi-layered myelin sheaths for rapid impulse propagation. Dysfunctions of oligodendrocytes or Schwann cells are often associated with neuroinflammation, as observed in animal models of leukodystrophies and peripheral neuropathies, respectively. The neuroinflammatory response modulates the pathological changes, including demyelination and axonal injury, but also remyelination and repair. Here we discuss different immune mechanisms as well as factors released or exposed by myelinating glia in disease conditions. The spectrum of inflammatory mediators varies with different myelin disorders and has a major impact on the beneficial or detrimental role of immune cells in keeping nervous system integrity.

Thrombotic thrombocytopenic purpura with severe ADAMTS-13 deficiency in a patient with antiphospholipid antibodies and Charcot-Marie-Tooth disease

A 26-year-old woman with a history of mild mental retardation, Charcot-Marie-Tooth disease (CMT) and idiopathic thrombocytopenic purpura developed severe thrombocytopenia with Coombs-negative hemolytic anemia. Magnetic resonance imaging revealed a fresh cerebral infarction in the left precentral gyrus. ADAMTS-13 deficiency caused by an inhibitor and anti-cardiolipin antibodies were detected in the blood. After treatment with prednisolone and fresh frozen plasma, ADAMTS-13 activity was normalized, the ADAMTS-13 inhibitor had disappeared and the thrombocytopenia with a bleeding tendency was improved. To our knowledge, this is the first case of thrombotic thrombocytopenic purpura caused by ADAMTS-13 deficiency associated with antiphospholipid antibodies and CMT.

Aggravation aiguë régressive d’une maladie de Charcot-Marie-Tooth de type 1B : la Protéine P0 peut-elle agir comme un auto-antigène ?

INTRODUCTION

The natural history of Charcot-Marie-Tooth neuropathy is marked by accentuated motor and sensitive deficits suggestive of acute polyradiculoneuritis or, more generally, chronic inflammatory demyelinizing polyneuropathy.

OBSERVATION

A 41-year-old woman, with Charcot-Marie-Tooth (CMT) 1B neuropathy associated with a P0 gene mutation, developed several episodes of ataxia which resolved after intravenous administration of IgG or corticosteroids.

CONCLUSION

The sudden increase of a motor or sensitive deficit in this patient with CMT type I led to two hypotheses: chance association between an inherited and an inflammatory neuropathy, or a dysimmune inflammatory reaction, the mutated protein acting like an autoantigen. These two hypotheses are discussed.

Immune-mediated components of hereditary demyelinating neuropathies: lessons from animal models and patients

Most demyelinating forms of Charcot-Marie-Tooth type 1 (CMT1) neuropathy are slowly progressive and do not respond to anti-inflammatory treatment. In nerve biopsy samples, overt lymphocytic infiltration is absent, but pathological features typical of macrophage-related demyelination have been reported. In mouse models of CMT1, demyelination was substantially reduced when the mutants were backcrossed into an immunodeficient genetic background. A few individual patients with CMT1 respond to anti-inflammatory treatment; however, unlike most patients with CMT1, these patients show accelerated worsening of symptoms, inflammatory infiltrates in nerve biopsies, and clinical features resembling chronic inflammatory demyelinating polyneuropathy as well as CMT1. We conclude that in patients with typical CMT1 and in animal models, a cryptic and mild inflammatory process not responsive to standard anti-inflammatory treatment fosters genetically mediated demyelination.

Inflammatory demyelination in a patient with CMT1A

We report a case of Charcot-Marie-Tooth disease (CMT), with identified PMP22 gene duplication (CMT type 1A), and with evidence of an inflammatory demyelinating process superimposed on the course of the chronic genetic disease. Macrophage-associated demyelination was observed on the peripheral nerve biopsy. This observation supports some experimental data from the literature and shows that there may be a genetic susceptibility to inflammatory demyelinating processes in certain CMT kindreds.

Preserved myelin integrity and reduced axonopathy in connexin32-deficient mice lacking the recombination activating gene-1

Mice heterozygously deficient for myelin protein zero (P0) mimicking human Charcot-Marie-Tooth (CMT) disease 1B show T-lymphocyte and macrophage upregulation in peripheral nerves, which aggravates and modulates the genetically mediated demyelinating neuropathy. In connexin32 (cx32)-deficient (cx32(def)) mice, which mimic the X-linked dominant form of CMT (CMTX), T-lymphocyte and macrophage numbers are also significantly elevated in peripheral nerves. To test the hypothesis that immune cells are indeed pathogenic in this model, we cross-bred cx32(def) mice with recombination activating gene-1 (RAG-1)-deficient mice, which lack mature T- and B-lymphocytes. In these immunoincompetent double mutants, the number of endoneurial macrophages was reduced. Furthermore, features indicative of myelin degeneration and axonopathic changes were mitigated in the RAG-1-deficient double mutants, whereas enlarged periaxonal Schwann cell collars, a hallmark specific for cx32-mutants, were not reduced. Since both cx32- and P0 deficiency lead to similar immunopathogenic processes, we conclude that immune-mediated demyelination may be a feature common to many CMT-like neuropathies independent of the genetic origin.

Role of immune cells in animal models for inherited neuropathies: facts and visions

Mice heterozygously deficient in the peripheral myelin adhesion molecule P0 (P0+/- mice) are models for some forms of Charcot-Marie-Tooth (CMT) neuropathies. In addition to the characteristic hallmarks of demyelination, elevated numbers of CD8-positive T-lymphocytes and F4/80-positive macrophages are striking features in the nerves of these mice. These immune cells increase in number with age and progress of demyelination, suggesting that they might be functionally related to myelin damage. In order to investigate the pathogenetic role of lymphocytes, the myelin mutants were cross-bred with recombination activating gene 1 (RAG-1)-deficient mice, which lack mature T- and B-lymphocytes. The immunodeficient myelin mutants showed a less severe myelin degeneration. The beneficial effect of lymphocyte-deficiency was reversible, since demyelination worsened in immunodeficient myelin-mutants when reconstituted with bone marrow from wild-type mice. Ultrastructural analysis revealed macrophages in close apposition to myelin and demyelinated axons. We therefore cross-bred the P0+/- mice with spontaneous osteopetrotic (op) mutants deficient in the macrophage colony-stimulating factor (M-CSF), hence displaying impaired macrophage activation. In the corresponding double mutants the numbers of macrophages were not elevated in the peripheral nerves, and the demyelinating phenotype was less severe than in the genuine P0+/- mice, demonstrating that macrophages are also functionally involved in the pathogenesis of genetically mediated demyelination. We also examined other models for inherited neuropathies for a possible involvement of immune cells. We chose mice deficient in the gap junction component connexin 32, a model for the X-linked form of CMT. Similar to P0-deficient mice, T-lymphocytes and macrophages were elevated and macrophages showed a close apposition to degenerating myelin. We conclude that the involvement of T-lymphocytes and macrophages is a common pathogenetic feature in various forms of slowly progressive inherited neuropathies.

Expression of IL-17B in neurons and evaluation of its possible role in the chromosome 5q-linked form of Charcot-Marie-Tooth disease

IL-17B is a recently identified homolog of IL-17. Northern analysis revealed that IL-17B mRNA is expressed at very high levels in spinal cord and at much lower and more variable levels in trachea, prostate, lung, small intestine, testes, adrenal, and pancreas. In developing mouse embryos IL-17B expression was first detected at day 11 and appeared to peak at day 15. In situ analysis of mouse spinal cord, dorsal root ganglia, and brain demonstrated that IL-17B mRNA is primarily expressed by the neurons. Immunohistochemical analysis of human spinal cord, dorsal root ganglia, cerebral cortex, cerebellum, and hippocampus demonstrated that IL-17B protein is primarily localized to the neuronal cell bodies and axons. Radiation hybrid mapping localized the IL-17B gene to a region on human chromosome 5q that is associated with a rare autosomal recessive form of Charcot-Marie-Tooth demyelinating disease. However, no changes were found in the coding regions, splice junctions, intron 1, or the 5' and 3' untranslated regions of IL-17B genes of patients affected with this disease.

Immunological study of hereditary motor and sensory neuropathy type 1a (HMSN1a)

OBJECTIVES

Fifty three patients were studied to investigate whether autoimmune or inflammatory mechanisms could explain the phenotypic heterogeneity of patients with hereditary motor and sensory neuropathy type 1a (HMSN1a).

METHODS

Serum samples were examined for antibodies to peripheral nerve myelin protein 22 (PMP22), ganglioside GM1 and cauda equina homogenate, and interleukin-6 (IL-6) and soluble tumour necrosis factor receptor 1 (sTNF R1) concentrations. Serological results were compared with those from patients with other neuropathies (ONPs, n=30) and with normal subjects (n=51).

RESULTS

In the group as a whole, no relation emerged between clinical severity and any immune parameters. Immunohistochemical examination of four sural nerve biopsies did not show significant inflammatory infiltration. In a subset of 12 patients who experienced stepwise progression of disease, there was a trend towards a higher proportion having anti-PMP22 antibodies (33% v 15% of those with gradual disease progression, 3% ONPs, and no normal controls) and complement fixing antibodies to human cauda equina (25% v 5% with gradual progression, 8.6% ONPs, 3.9% normal controls, p=0.07).

CONCLUSIONS

Patients with HMSN1a and a stepwise disease progression may have an inflammatory, autoimmune component superimposed on the genetic condition.

Characterisation of autoantibodies to peripheral myelin protein 22 in patients with hereditary and acquired neuropathies

To investigate the possibility that an autoimmune mechanism may play a role in the hereditary neuropathy Charcot-Marie-Tooth type 1A (CMT1A), sera were analysed by Western blot for anti-peripheral myelin protein 22 (PMP22) autoantibodies. These sera were compared with sera from patients with CMT type 2 (CMT2), acquired peripheral neuropathies such as chronic inflammatory demyelinating neuropathy (CIDP), anti-MAG IgM neuropathy, Miller-Fisher syndrome (MFS), diabetic neuropathy and with control blood donors. Anti-PMP22 positive sera were detected in 70% of patients with CMT1 and unexpectedly in 60% of patients with CMT2. Interestingly, 44% of the patients with other peripheral neuropathies and 23% of the apparently healthy controls showed also anti-PMP22 antibody reactivity. Immunohistochemical analysis of the human anti-PMP22 antisera on healthy sural nerve sections and on PMP22-expressing COS cells revealed that these sera did not recognise endogenous PMP22. Our results indicate that anti-PMP22 autoantibodies are found in sera of patients with different types of peripheral neuropathies, but their role in the pathogenesis of these diseases remains to be determined.

Expression of glial cell line-derived neurotrophic factor and GDNFR-alpha mRNAs in human peripheral neuropathies

The steady-state mRNA levels of glial cell line-derived neurotrophic factor (GDNF), GDNFR-alpha and RET were examined in various human peripheral neuropathies to determine the relationship with myelinated fiber pathology, and T cell and macrophage invasions in the diseased nerves. GDNF and GDNFR-alpha mRNA levels were elevated to variable extent in the diseased nerves, although they were not specific to the type of diseases. The increase of GDNFR-alpha mRNA levels was correlated with the extent of the nerves with axonal pathology, and was proportional to the extent of invasion of the nerves by T cells and macrophages. The GDNF mRNA levels were not related to axonal, demyelinating pathology, or inflammatory cell invasions. RET mRNA expression was not detected in normal nor diseased nerves. The GDNF and GDNFR-alpha expression in the diseased human nerves is regulated by an underlying pathology-related process, and could play a role in peripheral nerve repair.

Major histocompatibility complex class II expression and macrophage responses in genetically proven Charcot-Marie-Tooth type 1 and hereditary neuropathy with liability to pressure palsies

This study examined major histocompatibility complex (MHC) class II expression and macrophage infiltration in sural nerve biopsies from patients with genetically proven Charcot-Marie-Tooth (CMT) 1A and 1B and hereditary neuropathy with liability to pressure palsies (HNPP) by immunocytochemistry. In both young and older patients with duplication of the PMP22 gene, MHC class II expression was consistently up-regulated and not closely related to the extent of macrophage infiltration. On the other hand, MHC class II expression was more variable in CMT1A and CMT1B caused by point mutations and in HNPP. The extent of nerve pathology as assessed by teased fiber preparations or electron microscopy was not predictive for the degree of MHC class II expression in CMT1/HNPP. We conclude that MHC class II up-regulation is a common feature in hereditary neuropathies. As shown for the animal model of globoid cell dystrophy, it is conceivable that increased expression of MHC class II molecules in CMT1 and HNPP accelerates nerve pathology.

Motor conduction parameters in neuropathies associated with anti-MAG antibodies and other types of demyelinating and axonal neuropathies

We measured residual latency (RL), motor conduction velocity (MCV), and terminal latency index (TLI) in 15 patients with neuropathy and anti-MAG or SGPG antibodies and compared these to values obtained in 103 patients with other types of polyneuropathy (PN) and to 57 normal subjects. Ten patients had anti-MAG antibody titers of 25,600 or higher, and 5 had titers between 800 and 12,600. Patients with the highest titers had longer RL, slower MCV and shorter TLI than those with lower titers, acute or chronic inflammatory demyelinating PN, hereditary neuropathy, and metabolic or axonal neuropathy. In contrast F-wave latencies did not contribute to the differentiation between the groups of demyelinating neuropathies. RL and TLI correlated best with anti-MAG antibody titers, whereas there was a poor correlation with anti-SGPG titers suggesting that MAG more than SGPG may be the antigen in PN, and that the distal nerves are affected more than their proximal segments. The RL rather than TLI turned out to be the best variable to classify the demyelinating type of anti-MAG neuropathy. Sural nerve biopsy in 5 of the patients with the highest titer of anti-MAG antibodies showed deposits of IgM and C3 on the myelin sheaths, pronounced demyelination and widening of the myelin lamellae. In 4 of the patients with lower titers demyelination was absent or less pronounced.

Circulating cytotoxic immune components in dominant Charcot-Marie-Tooth syndrome

Activated T cells, measured repeatedly in the demyelinating peripheral neuropathy, Charcot-Marie-Tooth syndrome (CMT; hereditary motor sensory neuropathy), might participate in myelin loss by a destructive inflammatory autoimmune process. To explore this possibility, plasma proportions of hydroxyleukotrienes, their fatty acid precursor, arachidonic acid, and lymphocyte epitopes associated with immune cell activation expression were measured in 18 adults with dominant, Type I CMT. Compared to age-matched normal controls, CMT I patients showed eicosanoid-linked immunoactivation by an elevated content of 12-hydroxy-eicosatetraenoic acid (12-HETE) in parallel with a decreased plasma percentage of its fatty acid precursor, arachidonic acid. CMT patients also had increased numbers of peripheral lymphocytes expressing activation-related epitopes, CD25+, CD26+, CD4+, and CD4/CD45RO+ primed memory cells, with enhanced CD8+ cytotoxic cells and soluble CD8 protein content. Therefore, endogenously stimulated CMT I lymphocytes include functional cytotoxic cells which appear to deplete the plasma fatty acid precursor of prostenoid agents during the secretion of potentially destructive cytokines.

Expression of Schwann cell and peripheral T-cell activation epitopes in hereditary motor and sensory neuropathy

To evaluate possible immune-mediated mechanisms in hereditary motor and sensory neuropathy (HMSN-I, Charcot-Marie-Tooth syndrome), we examined class II major histocompatibility complex antigen expression (MHC-II, HLA-DR) in Schwann cells and peripheral lymphocyte T-cell (Ta1, CD26) activation in five unrelated adults with HMSN-I. Evidence of increased activation expression was found in both compartments but the pattern did not suggest a general state of hyperimmunity or appear related to clinical characteristics of HMSN. Significantly increased CD26+ T-cell activation and greater than normal fluctuation of values occurred intermittently in sequential tests of eight HMSN patients and at single time points in 24 others. The combined data, consistent with repeated stimulations of an immune reaction under normal feedback control, suggest that HMSN-I expresses some characteristics also found in autoimmune polyneuropathies.

Class II antigen expression on human cultured Schwann cells from patients with Charcot-Marie-Tooth disease

T lymphocytes control the extent of the immune reaction by recognizing the antigen in connection with class II histocompatibility surface molecules, coded by genes located on the HLA-D locus. The expression of HLA-DR antigens is confined to a few antigen presenting cells, like lymphocytes and macrophages, which can therefore induce the initial phase of the immune reaction. We report that also Schwann cells (SC) from patients with Charcot-Marie-Tooth disease (CMT), an hereditary disorder of the peripheral nervous system, are able to express HLA-DR antigens. Human SC cultures were carried out from sural nerve biopsies of CMT and normal control cases. Cultures were tested on day 7, 14, 21 and 28, with double immunofluorescence technique using rabbit antiserum anti-S-100 and mouse anti-HLA-DR monoclonal antibody. SC from CMT were HLA-DR positive since the first few days, continuing to express class II antigens for all the duration of the culture. The presence of class II antigens on cultured SC from CMT disease suggests that immune-mediated mechanisms may be relevant in the pathogenesis of this degenerative disorder of the peripheral nervous system.

[Hereditary sensory motor neuropathy: degenerative disease or a disease with an immune-mediated pathogenesis?]

The clinical data proving that some hereditary motor-sensory neuropathies (HMSN type 1) are steroid sensitive may indicate inflammatory or immunomediated mechanisms as cofactors contributing to the clinical course of these disorders. The finding of HLA-DR positivity of Schwann cells in HMSN type I along with the presence in some cases of inflammatory infiltrates in nerve sections provides further evidence for this hypothesis.

Activated T cells in type I Charcot-Marie-Tooth disease: evidence for immunologic heterogeneity

Common recognized variability in the familial peripheral neuropathy, type I Charcot-Marie-Tooth disease (CMT I), led to an examination of cell-mediated immune responses in 23 CMT I patients. Increased numbers of activated T cells were found in the peripheral blood of 14 (61%) patients using fluorescent monoclonal Ta1 antibody as quantitated by flow cytometry. Altered immunoregulation was also suggested by increased levels of prostaglandin-mediated lymphocyte suppression. In the other nine CMT I patients, immune responses were normal. Lack of a relationship between Ta1 expression and CMT clinical symptoms, but with consistency within six CMT families, support the concept of immunologic heterogeneity in type I CMT with a possible genetic component.

Gm and Km allotypes in Charcot-Marie-Tooth disease

Gm and Km immunoglobulin allotypes were studied in 46 Caucasian patients with Charcot-Marie-Tooth disease (CMT). No significant association of Gm and Km phenotypes with CMT was found. Family studies revealed that Gm haplotypes and CMT were not inherited together, thus arguing against the involvement of immunoglobulin allotypes in CMT.

Hereditary neurologic disorders, characterized by ataxia. Immunological in vitro parameters and HLA

Nineteen untreated patients with hereditary ataxia, hereditary spastic paraplegia and Charcot-Marie-Tooth's syndrome were investigated for immunological in vitro parameters (lymphocyte transformation with PHA, con A, PWM, antigens, determination of T- and B-lymphocytes and HLA-typing). When compared with normal controls, no significant deviation was found.

Selective IgA deviciency in Charcot-Marie-Tooth disease

A selective IgA deficiency was found in five of 15 random patients with Charcot-Marie-Tooth disease. Immunologic studies of 32 members of the five families showed low IgA in 17 of the members, associated with elevated IgM in 20, without other significant immune abnormalities. The immunoglobulin pattern and the variability of symptoms in this familial peripheral neuropathy suggest that a thymic or gut-associated immune deficiency or both, may be causally related to the disease process.