Polymyositis And Dermatomyositis - Inflammation, Muscle Structure & Immunosuppressive Treatment

Polymyositis and dermatomyositis are chronic, inflammatory disorders characterized by muscle weakness, low muscle endurance and by inflammation in skeletal muscle tissues. The pathogenesis is not completely understood and several mechanisms are believed to be involved. Conventional immunosuppressive treatment for patients is primarily with glucocorticoids in combination with another immune-modulating drug. Although most patients respond to the treatment to some degree, persisting muscle weakness as well as continued presence of muscle tissue inflammation is often evident. The main aim was to investigate different pathways that may play a role in the disease pathogenesis and contribute to the muscle weakness in patients with polymyositis and dermatomyositis. We wanted to determine whether these mechanisms were associated with clinical outcome and if immunosuppressive treatment could alter the processes. Studies were thus performed by characterizing muscle tissue samples from patients before and after immunosuppressive treatment, and through comparison with samples from healthy individuals. We also collected in vivo samples from quadriceps muscles by microdialysis before and after exercise in both patients and healthy individuals. Some novel observations were made. Firstly, we determined that the pro-inflammatory cytokine interleukin (IL) 15 and the IL-15 receptor alpha (IL-15Rα) were over-expressed in muscle tissues from the patients compared to in healthy individuals. Immunosuppressive treatment had no effect on IL-15 expression in 1/3 of the patients along with a poorer functional outcome. Secondly, we investigated the prostaglandin (PG) E2 and leukotriene (LT) B4 pathways. Here we found that PGE2 pathway is up-regulated in muscle tissue from patients with polymyositis or dermatomyositis compared to healthy individuals. A higher expression of cyclooxygenase (COX) 1, COX-2 and microsomal PGE synthase (mPGES)-1 in the patients was apparent and while COX-2 was down-regulated by treatment, COX-1 and mPGES-1 levels remained high. LTB4 pathway was also found to be active in patients and the expression of both 5-lipoxygenase (5-LO) and the LTB4 receptor 1 (BLT1) were higher compared to in healthy individuals. 5-LO activating protein (FLAP), was highly expressed in a subgroup of patients who did not respond to immunosuppressive treatment. These results may suggest an involvement of PGE2 and LTB4 in vascular permeability and chemotaxis for infiltrating immune cells, but perhaps also to serve a purpose in skeletal muscle regeneration in patients with polymyositis and dermatomyositis. Lastly, we could report that patients with newly diagnosed polymyositis or dermatomyositis did not display a low proportion of oxidative type I muscle fibers typically seen in muscle tissue of patients in a chronic state of disease. This finding implies that the proportion of oxidative fibers does not contribute to the low muscle endurance, at least not in early polymyositis and dermatomyositis. The conclusions drawn from this thesis are that several mechanisms may contribute to the muscle weakness in different subgroups of polymyositis and dermatomyositis patients. New pathways discovered in this thesis include IL-15 and the eicosanoids PGE2 and LTB4, but the fiber type composition in the muscle tissue might play a lesser role, at least in early disease. The mechanisms identified could provide a basis for further studies and possibly new therapies

Effects on muscle tissue remodeling and lipid metabolism in muscle tissue from adult patients with polymyositis or dermatomyositis treated with immunosuppressive agents.

BACKGROUND: Polymyositis (PM) and dermatomyositis (DM) are autoimmune muscle diseases, conventionally treated with high doses of glucocorticoids in combination with immunosuppressive drugs. Treatment is often dissatisfying, with persisting muscle impairment. We aimed to investigate molecular mechanisms that might contribute to the persisting muscle impairment despite immunosuppressive treatment in adult patients with PM or DM using gene expression profiling of repeated muscle biopsies. METHODS: Paired skeletal muscle biopsies from six newly diagnosed adult patients with DM or PM taken before and after conventional immunosuppressive treatment were examined by gene expression microarray analysis. Selected genes that displayed changes in expression were analyzed by Western blot. Muscle biopsy sections were evaluated for inflammation, T lymphocytes (CD3), macrophages (CD68), major histocompatibility complex (MHC) class I expression and fiber type composition. RESULTS: After treatment, genes related to immune response and inflammation, including inflammasome pathways and interferon, were downregulated. This was confirmed at the protein level for AIM-2 and caspase-1 in the inflammasome pathway. Changes in genes involved in muscle tissue remodeling suggested a negative effect on muscle regeneration and growth. Gene markers for fast type II fibers were upregulated and fiber composition was switched towards type II fibers in response to treatment. The expression of genes involved in lipid metabolism was altered, suggesting a potential lipotoxic effect on muscles of the immunosuppressive treatment. CONCLUSION: The anti-inflammatory effect of immunosuppressive treatment was combined with negative effects on genes involved in muscle tissue remodeling and lipid metabolism, suggesting a negative effect on recovery of muscle performance which may contribute to persisting muscle impairment in adult patients with DM and PM

Expression of interleukin-18 in muscle tissue of patients with polymyositis or dermatomyositis and effects of conventional immunosuppressive treatment

Objectives: To investigate the expression of IL-18 in symptomatic and asymptomatic muscle tissues of patients with PM and DM and the effects of conventional immunosuppressive treatment on such expression. Methods: Two cohorts of patients were included in this study. The first cohort consisted of 10 new-onset myositis patients. IL-18 expression was compared between symptomatic and asymptomatic muscle biopsies that were taken prior to treatment. The second cohort consisted of another 10 patients with repeated muscle biopsies before and after 8 months with conventional immunosuppressive treatment. Using immunohistochemistry, IL-18 expression in muscle tissues was compared before and after treatment. Biopsies from seven healthy individuals were included as controls. Results: IL-18 expression was predominantly localized to inflammatory cells and capillaries in patients and mostly to capillaries in healthy controls. Total IL-18 expression in muscle tissues from the new-onset patients, at both symptomatic and asymptomatic sites, was significantly higher compared with healthy controls (P = 0.007 and P = 0.002) with no statistical difference in appearances between symptomatic and asymptomatic sites. The number of IL-18 positive capillaries was not different among symptomatic, asymptomatic and healthy muscles. Total IL-18 expression appeared lower in biopsies from patients receiving and improving with immunosuppressive treatment, particularly the number of IL-18 positive inflammatory cells but not the number of IL-18 positive capillaries, which was consistent with significantly decreased expression of CD68+ macrophages (P = 0.04). Conclusion: IL-18 is highly expressed in muscle tissue in the context of inflammatory myopathies and based on its plausible effector functions could provide a novel therapeutic target in future

Improved exercise performance and increased aerobic capacity after endurance training of patients with stable polymyositis and dermatomyositis

Introduction: This randomized, controlled study on patients with polymyositis or dermatomyositis was based on three hypotheses: patients display impaired endurance due to reduced aerobic capacity and muscle weakness, endurance training improves their exercise performance by increasing the aerobic capacity, and endurance training has general beneficial effects on their health status. Methods: In the first part of this study, we compared 23 patients with polymyositis or dermatomyositis with 12 age-and gender-matched healthy controls. A subgroup of patients were randomized to perform a 12-week endurance training program (exercise group, n = 9) or to a non-exercising control group (n = 6). We measured maximal oxygen uptake (VO2 max) and the associated power output during a progressive cycling test. Endurance was assessed as the cycling time to exhaustion at 65% of VO2 max. Lactate levels in the vastus lateralis muscle were measured with microdialysis. Mitochondrial function was assessed by measuring citrate synthase (CS) and beta-hydroxyacyl-CoA dehydrogenase (beta-HAD) activities in muscle biopsies. Clinical improvement was assessed according to the International Myositis Assessment and Clinical Studies Group (IMACS) improvement criteria. All assessors were blinded to the type of intervention (that is, training or control). Results: Exercise performance and aerobic capacity were lower in patients than in healthy controls, whereas lactate levels at exhaustion were similar. Patients in the exercise group increased their cycling time, aerobic capacity and CS and beta-HAD activities, whereas lactate levels at exhaustion decreased. Six of nine patients in the exercise group met the IMACS improvement criteria. Patients in the control group did not show any consistent changes during the 12-week study. Conclusions: Polymyositis and dermatomyositis patients have impaired endurance, which could be improved by 12 weeks of endurance training. The clinical improvement corresponds to increases in aerobic capacity and muscle mitochondrial enzyme activities. The results emphasize the importance of endurance exercise in addition to immunosuppressive treatment of patients with polymyositis or dermatomyositis

Effect of endurance exercise on microRNAs in myositis skeletal muscle-A randomized controlled study.

Objective To identify changes in skeletal muscle microRNA expression after endurance exercise and associate the identified microRNAs with mRNA and protein expression to disease-specific pathways in polymyositis (PM) and dermatomyositis (DM) patients. Methods Following a parallel clinical trial design, patients with probable PM or DM, exercising less than once a week, and on stable medication for at least one month were randomized into two groups at Karolinska University Hospital: a 12-week endurance exercise group (n = 12) or a non-exercised control group (n = 11). Using an Affymetrix microarray, microRNA expression was determined in paired muscle biopsies taken before and after the exercise intervention from 3 patients in each group. Ingenuity pathway analysis with a microRNA target filter was used to identify microRNA transcript targets. These targets were investigated at the mRNA (microarray) and protein (mass spectrometry) levels in patients. Results Endurance exercise altered 39 microRNAs. The microRNAs with increased expression were predicted to target transcripts involved in inflammatory processes, metabolism, and muscle atrophy. Further, these target transcripts had an associated decrease in mRNA expression in exercised patients. In particular, a decrease in the NF-κB regulator IKBKB was associated with an increase in its target microRNA (miR-196b). At the protein level, there was an increase in mitochondrial proteins (AK3, HIBADH), which were associated with a decrease in microRNAs that were predicted to regulate their expression. Conclusion Improvement in disease phenotype after exercise is associated with increasing microRNAs that target and downregulate immune processes at the transcript level, as well as decreasing microRNAs that target and upregulate mitochondrial content at the protein level. Therefore, microRNAs may improve disease by decreasing immune responses and increasing mitochondrial biogenesis. Trial registration ClinicalTrials.gov NCT0118462

Validation of miR-196b expression after exercise and its associated effect on classical NF-κB signaling.

<p>(A) RT-qPCR validated that miR-196b was increased after exercise. For normalization, pre Ct values were first subtracted from post Ct values from both miR-196b and the housekeeper, U47. Double delta Ct method was then used to calculate the average fold change (2^-((Normalized Target-Housekeeper)-(Average(Normalized Control-Housekeeper)). (B) Western blot in pre-and post exercised skeletal muscle shows an average increase of 42% in total IκBα protein after exercise.</p

Pathway analysis of expression-paired microRNA-protein alterations in exercised patients.

<p>Pathway analysis of expression-paired microRNA-protein alterations in exercised patients.</p

Overview of microRNA expression pairing with mRNA and proteomic data sets.

<p>Overview of microRNA expression pairing with mRNA and proteomic data sets.</p