Infectious risk stratification in multiple sclerosis patients receiving immunotherapy.

The increasing number of potent treatments for multiple sclerosis warrants screening for infections. To investigate the prevalence of infections in two independent German patient cohorts with multiple sclerosis/neuromyelitis optica spectrum disorders (NMOSD), we performed a retrospective chart review study of multiple sclerosis/NMOSD patients who underwent testing for infections between 2014 and 2016. We show that 6 out of 80 tested patients (Düsseldorf cohort) and 2 out of 97 tested patients (Münster cohort) had a latent tuberculosis infection; total 3.95%, 95% CI: 2-8%. Our findings suggest that latent tuberculosis infection is frequent (>1%). Screening should be performed before embarking on immunomodulatory therapies to allow treatment and mitigation of the risk of a reactivation.

Pseudomonas aeruginosa and Its Bacterial Components Influence the Cytokine Response in Thymocytes and Splenocytes.

Infections with Pseudomonas aeruginosa may cause many different diseases. The spectrum of such infections in general includes inflammation and bacterial sepsis. Hospital-acquired pneumonia, naturally resistant to a wide range of antibiotics, is associated with a particularly high mortality rate in mechanically ventilated patients. The pathogenesis of P. aeruginosa is complex and mediated by several virulence factors, as well as cell-associated factors. We have previously demonstrated that stimulation with different bacteria triggers the cytokine response of thymocytes. In this study, we investigated the effect of P. aeruginosa and its different components on the cytokine production of immature and mature immune cells. We found that the induced cytokine pattern in the thymus and the spleen after infections with P. aeruginosa is primarily mediated by lipopolysaccharide (LPS) of the outer cell membrane, but other components of the bacterium can influence the cytokine secretion as well. Stimulation with heat-killed P. aeruginosa and LPS does not influence the amount of cytokine-producing CD4(+) T cells but instead suppresses the emergence of Th17 cells. However, stimulation with P. aeruginosa or its components triggers the interleukin-17 (IL-17) response both in thymocytes and in splenocytes. We conclude that infections with P. aeruginosa affect the cytokine secretion of immature and mature cells and that IL-17 and Th17 cells play only a minor role in the development of pathological systemic inflammatory disease conditions during P. aeruginosa infections. Therefore, other inflammatory immune responses must be responsible for septic reactions of the host.

Fingolimod treatment promotes regulatory phenotype and function of B cells.

OBJECTIVE: To evaluate the influence of Fingolimod treatment on B-cell subset composition and function in multiple sclerosis patients and its potential clinical relevance. METHODS: Subset composition and cytokine production of B cells derived from peripheral blood mononuclear cells from multiple sclerosis patients under Fingolimod treatment, untreated multiple sclerosis patients and healthy controls were analyzed by flow cytometry and ELISA. Migration of lymphocyte subsets across primary human brain microvascular endothelial cells was assessed in an in vitro transmigration assay. Cell numbers and composition of B-cell subsets in cerebrospinal fluid and peripheral blood were determined by flow cytometry. Regulatory B-cell frequencies were correlated with parameters of disease stability. RESULTS: Within the peripheral B-cell compartment of Fingolimod-treated patients, the proportion of regulatory B cells (CD38(+)CD27(-)CD24(+)CD5(+)) was significantly increased as compared to treatment-naïve multiple sclerosis patients and to healthy controls, and significantly more regulatory B cells produced Interleukin-10. Fingolimod treatment enhanced the capacity of regulatory B cells to transmigrate across brain endothelial cells in an in vitro model of the blood-brain-barrier. In line with these findings, the cerebrospinal fluid/blood ratio of total B cells and regulatory B cells was strongly increased by Fingolimod treatment, and patients exhibited increased regulatory B-cell frequencies in the cerebrospinal fluid. Finally, elevated regulatory B-cell percentages in the periphery significantly correlated with clinical and paraclinical disease stability. INTERPRETATION: These data suggest a novel and as yet unrecognized role of Fingolimod in correction of the imbalance between regulatory and effector B-cell functions in multiple sclerosis both by direct effects and indirect partitioning effects on B-cell subpopulations.

Natalizumab restores aberrant miRNA expression profile in multiple sclerosis and reveals a critical role for miR-20b.

OBJECTIVE: To identify microRNAs (miRNAs) regulated by anti-α4 integrin monoclonal antibody therapy (natalizumab) in the peripheral blood of patients with relapsing-remitting (RR) multiple sclerosis (MS) and to confirm their role in experimental settings in vivo. METHODS: In a longitudinal study of 17 RR-MS patients, we investigated blood miRNA expression profiles at baseline and after 1 year of natalizumab therapy by microarray technique and quantitative PCR validation. We compared the baseline expression profiles of these patients to those of 18 age- and sex-matched healthy controls. We confirmed the contribution of resulting candidate miRNAs in an animal model of MS, experimental autoimmune encephalomyelitis (EAE) induced by adoptive transfer of proteolipid protein (PLP)139-151-activated lymphocytes in SJL/J mice or by active immunization of miR-106a∼363-deficient C57BL/6 mice (or wildtype litter mates) with myelin oligodendrocyte glycoprotein (MOG)35-55. RESULTS: Our longitudinal analysis revealed that miR-18a, miR-20b, miR-29a, and miR-103 were upregulated and predominantly expressed by CD4(+) T cells, whereas miR-326 was downregulated upon natalizumab treatment. A comparison of untreated RR-MS patients at baseline with healthy controls revealed that the four natalizumab-upregulated targets were initially downregulated in MS. All confirmed targets showed disease-dependent expression in splenocytes of mice suffering from EAE. Genetic deletion of the miRNA cluster miR-106a∼363 (containing natalizumab-regulated miR-20b) resulted in a more severe EAE course and an in vivo upregulation of the miR-20b target genes rorgt, stat3, and vegfa. INTERPRETATION: Our study indicates that natalizumab restores dysregulated miRNA patterns in MS and reveals the contribution of miR-20b in autoimmune demyelination in vivo.

Anti-JC virus antibodies in rituximab-treated patients with neuromyelitis optica spectrum disorder.

Rituximab, a chimeric monoclonal anti-CD20 antibody, has been proposed to be effective for neuromyelitis optica spectrum disorder (NMOSD). A concern for developing progressive multifocal leukoencephalopathy (PML), which is caused by John Cunningham virus (JCV), has been suggested particularly in patients treated long term with rituximab. In this study, using a modified enzyme-linked immunosorbent assay with glutathione S-transferase-tagged VP1 as the antigen, we investigated the seroprevalence of anti-JCV antibodies among 78 Korean patients with NMOSD and the change in anti-JCV antibody serostatus following long-term rituximab treatment. The overall seroprevalence of anti-JCV antibodies was 69 % prior to rituximab administration. Over a mean of 4 years of repeated treatment with rituximab, no patient developed PML. Of 24 initially seronegative patients, none converted into seropositive, whereas six (11 %) of 54 initially seropositive patients converted into seronegative. Our results might support the safety of long-term rituximab treatment in patients with NMOSD with regard to the risk of developing PML.

Natalizumab exerts a suppressive effect on surrogates of B cell function in blood and CSF.

BACKGROUND: Natalizumab for multiple sclerosis (MS) increases the risk of progressive multifocal leukoencephalopathy (PML). OBJECTIVE: We aimed to assess the effect of natalizumab on cellular composition and functional B cell parameters including patients with natalizumab-associated PML (n=37). METHODS: Cellular composition by flow cytometry, levels of immunoglobulin (Ig)G/IgM by immunonephelometry, and oligoclonal bands by isoelectric focusing were studied in blood and cerebrospinal fluid. RESULTS: In MS patients treated with natalizumab without PML (n=59) the proportion of CD19+ B cells was higher in blood, but lower in cerebrospinal fluid compared with MS patients not treated with natalizumab (n=17). The CD4/CD8-ratio in cerebrospinal fluid was lower, and IgG and IgM levels as well as the IgG index dropped in longitudinal samples during natalizumab therapy. Oligoclonal bands persisted, but the total amount of the intrathecally produced IgG fraction, and the polyclonal intrathecal IgG reactivity to measles, rubella, and zoster declined. At the time of diagnosis of PML patients with natalizumab-associated PML had low total IgG levels in blood and cerebrospinal fluid. CONCLUSIONS: Natalizumab impacts B and T cell distribution and exerts an inhibitory effect on surrogates of B cell function in periphery and in cerebrospinal fluid, potentially contributing to the increased risk of developing PML.

Initial lymphocyte count and low BMI may affect fingolimod-induced lymphopenia.

OBJECTIVE: To assess whether pretreatment-lymphocyte counts, treatment before fingolimod, age, sex, or body mass index (BMI) affects the risk of fingolimod-induced lymphopenia in patients with relapsing-remitting multiple sclerosis (RRMS). METHODS: Data were obtained from a German multicenter, single-arm, open-label study of patients with RRMS treated with fingolimod, and findings were validated in an independent Swedish national pharmacovigilance study. RESULTS: Four hundred eighteen patients with RRMS from Germany and 438 patients from Sweden were included. A nadir ≤0.2 × 10(9) lymphocytes/L was reached in 15% (95% confidence interval [CI] 12%-17%) of all 856 patients. Patients with lower starting lymphocyte counts (below 1.6 × 10(9)/L) and patients with BMI lower than 18.5 kg/m(2) (women only) were at higher risk of developing lymphopenia with values ≤0.2 × 10(9)/L in the combined analysis, increasing the risk in these subgroups to 26% (95% CI 20%-31%) or 46% (95% CI 23%-71%), respectively. In the German cohort, infection rates were similar in patients who developed severe lymphopenia and those who did not. CONCLUSIONS: Our findings suggest that patients with low baseline lymphocyte counts and underweight women in which fingolimod treatment will be initiated should possibly be monitored more closely.

Interleukin-17 impedes Schwann cell-mediated myelination.

BACKGROUND: Pro-inflammatory cytokines are known to have deleterious effects on Schwann cells (SCs). Interleukin 17 (IL-17) is a potent pro-inflammatory cytokine that exhibits relevant effects during inflammation in the peripheral nervous system (PNS), and IL-17-secreting cells have been reported within the endoneurium in proximity to the SCs. METHODS: Here, we analyzed the effects of IL-17 on myelination and the immunological properties of SCs. Dorsal root ganglia (DRG) co-cultures containing neurons and SCs from BL6 mice were used to define the impact of IL-17 on myelination and on SC differentiation; primary SCs were analyzed for RNA and protein expression to define the putative immunological alignment of the SCs. RESULTS: SCs were found to functionally express the IL-17 receptors A and B. In DRG cultures, stimulation with IL-17 resulted in reduced myelin synthesis, while pro-myelin gene expression was suppressed at the mRNA level. Neuronal outgrowth and SC viability, as well as structural myelin formation, remained unaffected. Co-cultures exhibited SC-relevant pro-inflammatory markers, such as matrix metalloproteinase 9 and SCs significantly increased the expression of the major histocompatibility complex (MHC) I and exhibited a slight, nonsignificant increase in expression of MHCII, and a transporter associated with antigen presentation (TAP) II molecules relevant for antigen processing and presentation. CONCLUSIONS: IL-17 may act as a myelin-suppressive mediator in the peripheral nerve, directly propagating SC-mediated demyelination, paralleled by an inflammatory alignment of the SCs. Further analyses are warranted to elucidate the role of IL-17 during inflammation in the PNS in vivo, which could be useful in the development of target therapies.

Cerebrospinal fluid JC virus antibody index for diagnosis of natalizumab-associated progressive multifocal leukoencephalopathy.

OBJECTIVE: Progressive multifocal leukoencephalopathy (PML), caused by JC virus (JCV), can occur in patients receiving natalizumab for multiple sclerosis (MS). JCV detection by quantitative polymerase chain reaction (qPCR) in cerebrospinal fluid (CSF), or brain biopsy, is required for probable or definite diagnosis of PML. However, in some patients only low levels of JCV DNA (<100 copies/ml) are present in CSF, making the diagnosis challenging. Our objective was to assess the complementary value of a CSF JCV antibody index (AIJCV ) in the diagnosis of natalizumab-associated PML. METHODS: AIJCV was assessed in 37 cases of natalizumab-associated PML and 89 MS-patients treated with natalizumab without PML. Sera and CSF were tested in a capture enzyme-linked immunosorbent assay, using JCV-VP1 fused to glutathione S-transferase as antigen. Albumin levels and total immunoglobulin G concentration were determined by immunonephelometry, and the AIJCV was calculated as published. RESULTS: Twenty-six of 37 (70%) patients with natalizumab-associated PML exhibited an AIJCV > 1.5, whereas this was seen in none of the controls (p < 0.0001). At time of the first positive qPCR for JCV DNA, 11 of 20 (55%) patients with natalizumab-associated PML had an AIJCV > 1.5. JCV DNA levels of <100 copies/ml were seen in 14 (70%) of these 20 patients, of whom 8 (57%) demonstrated an AIJCV > 1.5. INTERPRETATION: Determination of the AIJCV could be an added tool in the diagnostic workup for PML and should be included in the case definition of natalizumab-associated PML.

Natalizumab affects the T-cell receptor repertoire in patients with multiple sclerosis.

OBJECTIVE: To assess changes in the T-cell receptor (TCR) repertoire in peripheral venous blood and CSF of patients with multiple sclerosis (MS) treated with natalizumab and the potential implication for developing progressive multifocal leukoencephalopathy (PML) and PML-immune reconstitution inflammatory syndrome (IRIS). METHODS: The TCR repertoire in blood and CSF was assessed by complementarity determining region 3 spectratyping in 59 patients with MS treated with natalizumab for at least 18 months, 5 cases of natalizumab-associated PML, 17 age- and sex-matched patients with MS not treated with natalizumab, and 12 healthy controls. RESULTS: Patients with MS presented with peripheral TCR repertoire expansions in blood, which appeared less prominent during therapy with natalizumab. TCR repertoire restrictions observed in CSF were most pronounced in patients with MS treated with natalizumab. In patients who developed PML with longitudinal samples available, new identical TCR receptor length expansions in blood and CSF were observed following plasma exchange, and preceded the development of IRIS. CONCLUSIONS: Profound TCR repertoire restrictions in CSF of patients treated with natalizumab reflect an altered immune surveillance of the CNS, which may contribute to an increased risk of developing PML. Natalizumab seems to prompt an impaired or delayed peripheral expansion of antigen-specific T cells, whereas increased reconstitution of peripheral T-cell expansion following plasma exchange may trigger PML-IRIS. Our data suggest that treatment with natalizumab results in broader changes in the T-cell immune repertoire beyond lymphocyte migration.

Citalopram suppresses thymocyte cytokine production.

Antidepressant drugs, in particular those targeting the serotonin (5-HT)-reuptake system via the serotonin transporter (5-HTT), are known to exhibit antiinflammatory properties and have demonstrated therapeutic efficacy in rodent models of autoimmune disease like experimental autoimmune encephalomyelitis or experimental rheumatoid arthritis. A crucial difference between animal models and the actual human autoimmune disease is the fact that in animals predominantly induced T cells are studied after sensitization with autoantigen. In humans, however, naturally occurring cytokine-producing T cells might play a significant role as well. For this reason, we investigated the effect of the selective serotonin reuptake inhibitor citalopram on cytokine-producing cells in the thymus of C57BL/6 mice, focusing on the (predominantly) T-cell-produced cytokines IL-2, IL-4 and IL-17. Citalopram was able to strongly reduce the frequency of IL-4- and IL-2-producing cells triggered by CD3 stimulation, but exhibited a less pronounced effect on IL-17-producing cells. 5-HTT expression was found to be very low in thymocytes in comparison with splenocytes, and the effect of free extracellular serotonin on CD3-induced thymocyte cytokine production did not mimic the effect of citalopram. We conclude that citalopram has a potent suppressive effect on cytokine production in the thymus, and that this effect is unlikely to be mediated by elevation of extracellular serotonin levels via the 5-HTT.

Promoting myelination in an in vitro mouse model of the peripheral nervous system: the effect of wine ingredients [corrected].

Protective properties of moderate wine consumption against cancers, cardiovascular, metabolic and degenerative diseases have been reported in various clinical studies. Here, we analysed the effect of red wine (RW) and white wine (WW) on myelination using an in vitro embryonic co-culture mouse model. The total amount of myelin was found to be significantly increased after RW and WW treatment, while only RW significantly increased the number of internodes. Both types of wine increased rat Schwann cell- (rSC) expression of the NAD+-dependent deacetylase sirtuin-two-homolog 2 (Sirt2), a protein known to be involved in myelination. Detailed chemical analysis of RW revealed a broad spectrum of anthocyanins, piceids, and phenolics, including resveratrol (RSV). In our assay system RSV in low concentrations induced myelination. Furthermore RSV raised intracellular glutathione concentrations in rSCs and in co-cultures and therefore augmented antioxidant capacity. We conclude that wine promotes myelination in a rodent in vitro model by controlling intracellular metabolism and SC plasticity. During this process, RSV exhibits protective properties; however, the fostering effect on myelinaton during exposure to wine appears to be a complex interaction of various compounds.

Disease amelioration with tocilizumab in a treatment-resistant patient with neuromyelitis optica: implication for cellular immune responses.

BACKGROUND: Neuromyelitis optica (NMO) is an autoimmune disease of the central nervous system in which aberrant antibody responses to the astrocytic water channel aquaporin 4 have been described. Experimental evidence is emerging that NMO is partly driven by the proinflammatory cytokine interleukin 6 (IL-6), which propagates the survival of disease-specific B cell subclasses, and deviates CD4+ T helper cell differentiation toward IL-17-producing T helper 17 cells. Tocilizumab is a recombinant humanized monoclonal antibody against the IL-6 receptor approved for treatment of rheumatoid arthritis. OBJECTIVES: To study clinical and paraclinical effects of tocilizumab in a patient with NMO. DESIGN: Case report. SETTING: Academic neurology department. PATIENT: A patient with highly active aquaporin 4­seropositive NMO who failed numerous immunosuppressive interventions, including high-dose corticosteroids, mitoxantrone, plasma exchange (PE), rituximab (anti-CD20), and alemtuzumab (anti-CD52), before receiving tocilizumab. MAIN OUTCOME MEASURES: Clinical disability, magnetic resonance imaging, cytokines and transcription factors levels in the cerebrospinal fluid, and peripheral blood mononuclear cells. RESULTS: A patient who continued to accumulate neurological disability and magnetic resonance imaging activity while receiving numerous immunoactive therapies stabilized, and eventually improved clinically and on magnetic resonance metrics after treatment initiation with tocilizumab. Treatment and clinical response correlated with a significant reduction of IL-6 levels in the CSF as well as a diminished expression of signal transducer and activator of transcription 3. CONCLUSIONS: Tocilizumab might be effective in NMO, here in a patient not responding to leukocyte depletion. Our findings further support data that implicate IL-6 as a critical molecule in the immunopathogenesis of NMO, and a critical role for T cells in the pathogenesis of this disorder.

An assay to quantify species-specific anti-JC virus antibody levels in MS patients.

BACKGROUND: The StratifyJCV® test is a qualitative assay to classify MS patients as anti-JC virus (JCV) antibody positive or negative. Quantification of anti-JCV antibody levels in serum and cerebrospinal fluid (CSF) of multiple sclerosis (MS) patients might add to the progressive multifocal leukoencephalopathy (PML) risk assessment. OBJECTIVE: The objective of this study is to test sera of patients in a quantitative anti-JCV antibody assay, and to compare the results with preexisting data from the StratifyJCV® test. METHODS: Sera of a total of 175 MS patients and matched non-MS-controls were tested for anti-JCV antibodies using glutathione S-transferase-tagged-VP1 as antigen. Antibody reactivity was quantified in arbitrary units using human immunoglobulin as standard. RESULTS: The comparison of our assay with StratifyJCV® showed good inter-assay agreement (kappa 0.6), and strong correlation for antibody reactivity (r (2) = 0.94). Discordant samples had low-reactive positivity, and a higher proportion (13% vs. 4%) tested positive in the StratifyJCV® test only. CONCLUSIONS: The method presented is a tool for the reliable quantification of anti-JCV antibodies, which demonstrates good agreement with results from StratifyJCV®. In contrast to StratifyJCV®, we pre-adsorbed all of the sera with BK virus (BKV) VP1 protein to reduce cross-reactivity. This step may account for a higher species-specificity of our assay. As such, our assay might be a promising additional tool for PML risk assessment.

A reliable in vitro model for studying peripheral nerve myelination in mouse.

The rat dorsal root ganglia (DRG) model is a long-standing in vitro model for analysis of myelination in the peripheral nervous system. For performing systematic, high throughput analysis with transgenic animals, a simplified BL6 mouse protocol is indispensable. Here we present a stable and reliable protocol for myelinating co-cultures producing a high myelin ratio using cells from C57BL/6 mice. As an easy accessible and operable method, Sudan staining proved to be efficient in myelin detection for fixed cultures. Green fatty acid stain turned out to be highly reliable for analysis of the dynamic biological processes of myelination in vital cultures. Once myelinated we were able to induce demyelination by the addition of forskolin into the model system. In addition, we provide an optimised rat DRG protocol with significantly improved myelin ratio and a comparison of the protocols presented. Our results strengthen the value of ex vivo myelination models in neurobiology.

Recovery of the T-cell repertoire in CIDP by IV immunoglobulins.

OBJECTIVE: To investigate changes in the T-cell repertoire in patients with chronic inflammatory demyelinating polyneuropathy (CIDP) without and with treatment of IV immunoglobulins (IVIg). METHODS: The T-cell receptor (TCR) repertoire of CD4+ and CD8+ T cells in the peripheral blood was analyzed using CDR3 spectratyping. Patients with CIDP were included without (n = 14) and with IVIg treatment (n = 11) cross-sectionally and longitudinally (n = 2). RESULTS: While the TCR length distribution of patients with CIDP was only moderately altered for most of the Vß elements of CD4+ T cells, the CD8+ population displayed extensive oligoclonal expansions in all analyzed 24 Vß elements. A public expansion of a distinct TCR length in one Vß element within a majority of affected patients was not detectable. Treatment with IVIg reduced the oligoclonal expansions within both the CD4+ and CD8+ population. CONCLUSIONS: Our data demonstrate that cytotoxic CD8+ T cells exhibit a much broader activation than CD4+ T cells, indicating a potentially crucial role of CD8+ T cells in the immunopathogenesis of CIDP. The profound oligoclonal response in T-cell activation suggests that multiple peptides may induce and propagate this autoimmune-driven disease. The observed reduction of highly activated T cells may contribute to the therapeutic effects of IVIg.

Fingolimod impedes Schwann cell-mediated myelination: implications for the treatment of immune neuropathies?

BACKGROUND: Fingolimod (FTY720), a first-in-class sphingosine-1-phosphate (S1P) receptor agonist, is a recently approved drug for treating relapsing multiple sclerosis. Experimental evidence suggests that FTY720 not only exhibits anti-inflammatory properties but also promotes myelination in the central nervous system by direct interaction with oligodendrocytes. OBJECTIVE: To assess the effects of FTY720 on Schwann cells (SCs) and peripheral nerve myelination. DESIGN: Receptor expression studies and myelination were investigated in primary rat SCs and rat neuronal/SC cocultures. Cells were treated with physiologically relevant concentrations of the active phosphorylated form of FTY720 (FTY720P). In addition, S1P receptor expression was corroborated in human and rat peripheral nerve tissue sections. RESULTS: Schwann cells express all known S1P receptors on the RNA level, not altered by FTY720P. In the myelination model, treatment with FTY720P resulted in a significant reduction of quantitative myelin formation. FTY720P induced reactive oxygen species in SCs associated with apoptosis of these cells, as demonstrated by the detection of cysteine aspartic acid­specific protease 3 and 7, as well as terminal deoxynucleotidyl transferase dUTP nick-end labeling. This effect was dependent of S1P signaling because the blocking of S1P receptors ameliorated reactive oxygen species production, SC apoptosis, and myelin loss. CONCLUSIONS: FTY720P at greater concentrations induces apoptosis in SCs and may interfere with peripheral nerve myelination.

Ex vivo activation of naturally occurring IL-17-producing T cells does not require IL-6.

Interleukin (IL-)17 is a potent proinflammatory cytokine for which an important role in the immune response against infections and in autoimmune diseases has been demonstrated. Recently, it has been shown that - in addition to mature T cells which are primed in the immune periphery - this cytokine can also be produced by T cells in the thymus, so-called naturally occurring IL-17-producing T cells (nT17 cells). In this study we demonstrate that the generation and activation of nT17 cells in the thymus do not depend on the cytokine IL-6. In addition, nT17 cells are not regulated by IL-2. These properties of nT17 cells significantly differ from induced IL-17-producing T cells primed in the immune periphery (iT17 cells). Given the strong association of IL-17-producing T cells with immune responses against infections and human autoimmune diseases, closer characterization of nT17 cells is warranted.

Charcot-Marie-Tooth disease CMT4A: GDAP1 increases cellular glutathione and the mitochondrial membrane potential.

Mutations in GDAP1 lead to recessively or dominantly inherited peripheral neuropathies (Charcot-Marie-Tooth disease, CMT), indicating that GDAP1 is essential for the viability of cells in the peripheral nervous system. GDAP1 contains domains characteristic of glutathione-S-transferases (GSTs), is located in the outer mitochondrial membrane and induces fragmentation of mitochondria. We found GDAP1 upregulated in neuronal HT22 cells selected for resistance against oxidative stress. GDAP1 over-expression protected against oxidative stress caused by depletion of the intracellular antioxidant glutathione (GHS) and against effectors of GHS depletion that affect the mitochondrial membrane integrity like truncated BH3-interacting domain death agonist and 12/15-lipoxygenase. Gdap1 knockdown, in contrast, increased the susceptibility of motor neuron-like NSC34 cells against GHS depletion. Over-expression of wild-type GDAP1, but not of GDAP1 with recessively inherited mutations that cause disease and reduce fission activity, increased the total cellular GHS content and the mitochondrial membrane potential up to a level where it apparently limits mitochondrial respiration, leading to reduced mitochondrial Ca(2+) uptake and superoxide production. Fibroblasts from autosomal-recessive CMT4A patients had reduced GDAP1 levels, reduced GHS concentration and a reduced mitochondrial membrane potential. Thus, our results suggest that the potential GST GDAP1 is implicated in the control of the cellular GHS content and mitochondrial activity, suggesting an involvement of oxidative stress in the pathogenesis of CMT4A.