The effects of prednisone and steroid-sparing agents on decay accelerating factor (CD55) expression: implications in myasthenia gravis

Mitochondrial bioenergetics in ocular fibroblasts of two myasthenia gravis cases

Myasthenia gravis (MG) is a rare, treatable, antibody-mediated disease characterized by fatigable muscle weakness of extraocular muscles (EOMs) and non-ocular skeletal muscles. The antibodies are directed against muscle-endplate proteins, most frequently the acetylcholine receptor (AChR) alpha-subunit. Although most MG patients respond to immunosuppressive treatment, some individuals, frequently with African-genetic ancestry, develop treatment-resistant ophthalmoplegia (OP-MG). Although the underlying pathogenetic mechanisms of OP-MG remain unknown, experimental rodent models of MG showed upregulation of genes involved in oxidative metabolism in muscles. EOMs are highly dependent on oxidative metabolism. We opportunistically sampled EOM-tendons of two rare OP-MG patients (and non-MG controls) undergoing re-alignment surgery, and established ocular fibroblast cultures. Metabolic assays were performed on these live cells to assess real-time differences in energy metabolism. To study the cellular bioenergetic profiles in the context of MG, we exposed the cultures to homologous 5% MG sera for 24 h, vs. growth media, from two independent MG patients (with circulating AChR-antibodies) and five controls without MG, and estimated the fold change in oxygen consumption rates in response to three compounds which inhibit different mitochondrial chain complexes. Quantitative PCR (qPCR) was performed in cells before and after MG sera exposure, to assess transcript levels of mitochondrial genes, PDK4, ANGPTL4 and UCP3, which were altered in experimental MG. In response to the mitochondrial stressors, basal oxidative metabolism parameters were similar between OP-MG and control fibroblasts (p = 0.81). However, after exposure to MG sera, bioenergetic parameters (oxygen consumption rate as an indicator of oxidative phosphorylation; extracellular acidification rate as an indicator of glycolysis), were induced to higher levels in OP-MG fibroblasts compared to controls (2.6-fold vs 1.5-fold; p = 0.031) without evidence of mitochondrial insufficiency in the OP-MG ocular fibroblasts. In support of the bioenergetic responses to the same MG sera, gene transcripts of PDK4 and ANGPLT4 in ocular fibroblasts also showed significant upregulation (p ≤ 0.041), but similarly in OP-MG and control cases. Taken together we showed similar basal and metabolic adaptive responses after exposure to mitochondrial inhibitors in ocular fibroblasts derived from OP-MG cases and controls, although the OP-MG cells showed greater activation in response to MG conditions. These pilot results in orbital-derived tissues provide support for myasthenic-induced changes in cellular metabolism and evidence that orbital fibroblasts may be useful for dynamic bioenergetic assessments.

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Orbital fibroblasts may be useful for dynamic bioenergetic assays.

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Orbital-fibroblast cultures showed shifts in oxidative metabolism induced by homologous myasthenic sera.

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Altered bioenergetic adaptation was induced by MG sera in orbital fibroblasts from ophthalmoplegic MG patients compared to controls.

A Randomized Open-Labeled Trial of Methotrexate as a Steroid-Sparing Agent for Patients With Generalized Myasthenia Gravis

Background and Purpose

Two clinical trials assessing the steroid-sparing effect of methotrexate (MTX) yielded conflicting results. Our objective was to investigate whether MTX would show a steroid-sparing effect in the treatment of generalized myasthenia gravis (MG) patients who fitted Myasthenia Gravis Foundation of America (MGFA) Class II and Class III.

Methods

We performed an 18-month prospective, randomized, open-labeled trial of prednisone combined with MTX 10 mg orally every week versus prednisone alone in 40 recently diagnosed MG patients of MGFA Class II and Class III between July 2014 and July 2018. The primary endpoint was the prednisone area under the dose–time curve (AUDTC) from months 3 to 18. Secondary endpoints included changes of the Quantitative Myasthenia Gravis Score (QMG), the Myasthenia Gravis Activity of Daily Living Score (MG-ADL), initial time of prednisone reduction, the median prednisone daily dose in each month, adverse events, and treatment failures in each group.

Results

Forty participants were included; among those, 5 individuals withdrew. A total of 35 participants completed 18 months of follow-up (18 in prednisone+MTX, 17 in prednisone group). Combined use of MTX reduced the month 3–18 prednisone AUDTC (prednisone+MTX 5,663.44 ± 1,678.08 mg, prednisone 6,683.94 ± 678.08 mg, p = 0.03, 95% confidence interval -1916.01 to -124.98). The initial times of prednisone reduction were 4.34 ± 1.44 months in the prednisone+MTX group and 5.56 ± 2.05 months in the prednisone group (p = 0.04, 95% CI -2.41 to -0.03). The median daily prednisone dose was significantly lower in the prednisone+MTX group at month 6 and months 9–18. No significant differences were found in QMG and MG-ADL scores between the two groups. No serious drug-related adverse events were observed in both groups.

Conclusions

This study provides evidence that MTX has the steroid-sparing ability in generalized MG patients of MGFA Class II and Class III.

Clinical Trial Registration

http://www.chictr.org.cn/showproj.aspx?proj=10563 identifier ChiCTR-IPR-15006081.

Gene expression profiling of orbital muscles in treatment-resistant ophthalmoplegic myasthenia gravis

Background

Unbiased in silico approaches applied to genome-wide data prioritized putative functional gene variants associating with treatment-resistant ophthalmoplegic myasthenia gravis (OP-MG). Although altered expression of genes harbouring these variants, or associated pathways, were shown in patient-derived transdifferentiated-myocyte models, gene expression in orbital-derived muscle was required to test the validity of the predictions.

Methods

We sampled orbicularis oculi muscle (OOM) and one paralysed extraocular muscle (EOM) from six individuals with OP-MG during blepharoptosis and re-alignment surgeries, respectively. For controls, the OOMs were sampled from four individuals without myasthenia undergoing surgery for non-muscle causes of ptosis, and one non-paralysed EOM. Using a qPCR array, expression of 120 genes was compared between OP-MG and control OOMs, profiling putative “OP-MG” genes, genes in related biological pathways and genes reported to be dysregulated in MG cases or experimental MG models, and in EOMs of cases with strabismus. Normalization was performed with two stable reference genes. Differential gene expression was compared between OP-MG and control samples using the ΔΔCT method. Co-expression was analysed by pairwise correlation of gene transcripts to infer expression networks.

Results

Overall, transcript levels were similar in OOMs and EOMs (p = 0.72). In OOMs, significant downregulated expression of eight genes was observed in OP-MG cases compared with controls (> twofold; p ≤ 0.016), including TFAM, a mitochondrial transcription factor, and genes related to the following pathways: atrophy signalling; muscle regeneration and contraction; glycogen synthesis; and extracellular matrix remodelling. Several microRNAs, known to be highly expressed in EOMs, are predicted to regulate some of these genes. Co-expression analyses of gene-pairs suggested high interconnectedness of gene expression networks in OP-MG muscle, but not controls (r > 0.96, p < 0.01). Significant inverse directions of gene-pair correlations were noted in OP-MG versus controls OOM networks (r ≥ 0.92, p < 0.001) involving most OP-MG genes overlapping prominently with muscle atrophy/contractility and oxidative metabolism genes.

Conclusions

The gene expression in orbital muscles derived from OP-MG individuals compared with normal controls, support the pathogenic hypothesis previously generated from whole genome sequence analyses. Repression of gene transcripts in OP-MG orbital muscle implicate tissue-specific regulatory mechanisms, which may inform future biomarker discovery approaches.

Exome sequencing identifies targets in the treatment-resistant ophthalmoplegic subphenotype of myasthenia gravis

Treatment-resistant ophthalmoplegia (OP-MG) is not uncommon in individuals with African genetic ancestry and myasthenia gravis (MG). To identify OP-MG susceptibility genes, extended whole exome sequencing was performed using extreme phenotype sampling (11 OP-MG vs 4 control-MG) all with acetylcholine receptor-antibody positive MG. This approach identified 356 variants that were twice as frequent in OP-MG compared to control-MG individuals. After performing probability test estimates and filtering variants according to those 'suggestive' of association with OP-MG (p < 0.05), only three variants remained which were expressed in extraocular muscles. Validation in 25 OP-MG and 50 control-MG cases supported the association of DDX17_delG (p = 0.014) and SPTLC3_insACAC (p = 0.055) with OP-MG, but ST8SIA1_delCCC could not be verified by Sanger sequencing. A parallel approach, using a semantic model informed by current knowledge of MG-pathways, identified an African-specific interleukin-6 receptor (IL6R) variant, IL6R c.*3043 T>C, that was more frequent in OP-MG compared to control-MG cases (p = 0.069) and population controls (p = 0.043). A weighted genetic risk score, derived from the odds ratios of association of these variants with OP-MG, correlated with the OP-MG phenotype as opposed to control MG. This unbiased approach implicates several potentially functional gene variants in the gangliosphingolipid and myogenesis pathways in the development of the OP-MG subphenotype.

Characteristics Of acetylcholine-receptor-antibody-negative myasthenia gravis in a South African cohort

INTRODUCTION

In this study we determined the frequencies of antibodies (Abs) directed against muscle-specific kinase (MuSK) and lipoprotein receptor-related protein 4 (LRP4) in the sera of a South African cohort with acetylcholine receptor (AChR)-antibody-negative generalized MG and determined outcomes to therapies.

METHODS

Sera negative by commercial AChR radioimmunoassay (RIA) were tested by MuSK RIA (n = 30; 2006-2012) and AChR, MuSK, and LRP4 RIA with or without cell-based assays (CBA) (n = 53; 2012-2015).

RESULTS

AChR-Abs were detected in 4 of 53 and MuSK-Abs in 20 of 83 (24%) cases. Thirty-six of 53 (68%) were triple seronegative (triple-SNMG) for MuSK, AChR, and LRP4-Abs. When compared with triple-SNMG, individuals with MuSK-MG had a younger onset age (P = 0.008), a greater likelihood of African genetic ancestry (P = 0.008), and 4-fold higher odds of reaching MGFA grade IVB/V (P = 0.018), but were also 9-fold more likely to reach at least minimal manifestations status after ≥12 months of therapy (P = 0.003).

CONCLUSIONS

Individuals with African genetic ancestry and severe bulbar/respiratory AChR-Ab-negative MG are likely to have MuSK-MG, but most respond favorably to maintenance immunotherapies. Muscle Nerve 54: 1023-1029, 2016.

The African-387 C>T TGFB1 variant is functional and associates with the ophthalmoplegic complication in juvenile myasthenia gravis

Although extraocular muscles are commonly affected by myasthenia gravis (MG) at presentation, a treatment-resistant ophthalmoplegic complication of MG (OP-MG) occurs in younger patients with African-genetic ancestry. In MG, pathogenic antibodies activate complement-mediated muscle damage and this may be potentiated in some OP-MG cases because of relative deficiency of decay-accelerating factor/CD55. Extending this argument, we hypothesized that OP-MG individuals may harbor African-specific polymorphisms in key genes influencing extraocular muscle remodeling. We screened the regulatory region of the transforming growth factor beta-1 (TGFB1) gene encoding the cytokine pivotal in muscle healing responses. We show the frequency of an African-specific polymorphism TGFB1 c.-387 T (rs11466316) among South Africans with African-genetic ancestry is higher than 1000 Genomes African controls (17.2% vs 4.8%; P<1 × 10(-7)), and associates with juvenile OP-MG (28%; P=0.043). Further, TGFB1 -387 C>T is functional because it represses the TGFB1 promoter construct basal activity by fivefold, and OP-MG fibroblasts (-387 C/T or T/T) have lower basal TGFB1 mRNA transcripts compared with controls (-387 C/C)(P=0.001). Co-transfections with Sp1 show less responsiveness of the -387 T promoter compared with wild-type -387 C (P=0.015). Our findings suggest that population-specific alleles may lower TGFB1 expression, thereby influencing OP-MG susceptibility by inhibiting extraocular muscle CD55 upregulation and/or altered endplate remodeling.

Detecting key genes regulated by miRNAs in dysfunctional crosstalk pathway of myasthenia gravis

Myasthenia gravis (MG) is a neuromuscular autoimmune disorder resulting from autoantibodies attacking components of the neuromuscular junction. Recent studies have implicated the aberrant expression of microRNAs (miRNAs) in the pathogenesis of MG; however, the underlying mechanisms remain largely unknown. This study aimed to identify key genes regulated by miRNAs in MG. Six dysregulated pathways were identified through differentially expressed miRNAs and mRNAs in MG, and significant crosstalk was detected between five of these. Notably, crosstalk between the "synaptic long-term potentiation" pathway and four others was mediated by five genes involved in the MAPK signaling pathway. Furthermore, 14 key genes regulated by miRNAs were detected, of which six-MAPK1, RAF1, PGF, PDGFRA, EP300, and PPP1CC-mediated interactions between the dysregulated pathways. MAPK1 and RAF1 were responsible for most of this crosstalk (80%), likely reflecting their central roles in MG pathogenesis. In addition, most key genes were enriched in immune-related local areas that were strongly disordered in MG. These results provide new insight into the pathogenesis of MG and offer new potential targets for therapeutic intervention.