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Les myopathies inflammatoires (MI) sont des maladies auto-immunes rares caractérisées par une faiblesse musculaire proximale, une baisse de la qualité de vie et une surmortalité. Le traitement de première ligne chez les patients atteints de MI repose sur l'utilisation empirique des glucocorticoïdes (GC) dont l'efficacité est partielle et les évènements indésirables nombreux. Des études mécanistiques menées par notre équipe ont montré que la prednisone induit la production d'épinéphrine par la fibre musculaire squelettique dans des modèles précliniques de MI (in vitro et in vivo). L'effet de l'épinéphrine sur le système immunitaire ainsi que sur le muscle squelettique passe par la stimulation du récepteur bêta2-adrénergique. Dans une vaste cohorte de patients atteints de polyarthrite rhumatoïde, l'utilisation de bêtabloquants a été associée de manière indépendante à une rémission moins fréquente [1]. Le but de ce projet était d'étudier si le blocage de la voie bêta-adrénergique empêche l'effet thérapeutique de la prednisone dans un modèle murin de MI. Une myopathie inflammatoire expérimentale (ME) a été induite par l'immunisation contre la protéine-C musculaire au jour 0 (J0) chez des souris femelles C57BL/6 de 8 à 10 semaines d'âge. À J14 jusqu'à J20, les souris ont été traitées par prednisone (PDN) par voie orale à la dose de 1 mg/kg/jour pendant 7 jours associée ou pas à la même dose de propanolol, ou par véhicule. La force musculaire a été mesurée par grip test à J0, J14 et avant le sacrifice (J20). Les valeurs de créatine-kinase (CK) dans le sang ont été évaluées au sacrifice (J21). Une diminution de force du 20 % a été constatée à J14 de l'induction de la ME (p = 0,0001), qui se maintenait jusqu'à J20 sous traitement par véhicule (p = 0,0001) par rapport à J0. Les souris ME traitées par PDN recouvraient leur force à J20 qui était comparable à celle de J0 (p = 0,008, vs J14). Cet effet de la PDN sur la faiblesse musculaire était aboli alors qu'un co-traitement PDN-propanolol était administré (p = 0,0001, vs J0). Au moment du sacrifice, les taux sériques de CK étaient deux fois plus élevés chez les souris EM traitées par véhicule par rapport aux souris témoins (p = 0,004), et ils étaient normalisés chez les souris EM traitées avec la PDN. Cet effet de la PDN sur la myolyse était aboli alors que le co-traitement PDN-propanolol était administré (p = 0,008 vs souris témoins). Ces résultats montrent que la PDN normalise les fonctions musculaires et la myolyse dans la ME, et que le co-traitement PDN-propanolol supprime cet effet thérapeutique de la PDN. L'inhibition de la voie bêta-adrénergique abolit l'effet thérapeutique de la PDN au cours des MI, alors que la stimulation de cette voie pourrait représenter une nouvelle stratégie pour le traitement des MI. [ABSTRACT FROM AUTHOR]

Objectives: To assess the ability of dual-energy X-ray absorptiometry (DXA) and hand-grip dynamometer to measure damage in inflammatory myopathies (IM)., Methods: Forty adult IM patients with a disease duration ≥12 months, low or no disease activity for ≥6 months, were prospectively enrolled. Thirty healthy age and sex-matched volunteers were enrolled as controls. Whole-body DXA and hand-grip dynamometer were used to measure muscle mass, grip strength and diagnose sarcopenia (EWGSOP2 criteria). Relationships between the results of strength in 12 muscles, functional tests, patient-reported disability, IMACS damage score, and history of the disease were assessed. The serum levels of potential molecular actors in the damage were measured., Results: DXA and grip strength measurements took ≤20 min. Both muscle mass and grip strength were decreased in IM patients vs volunteers (-10% and -30%, respectively) with a dispersion that varied widely (interquartile range -24.3% to +7.8% and -51.3% to -18.9%, respectively). Muscle mass and grip strength were non-redundantly correlated (r up to 0.6, P = 0.0001) with strength in 14 muscles (manual muscle test and hand-held dynamometer), functions (of limbs, respiratory and deglutition muscles), patient-reported disability, damage (extension and severity in muscular and extra-muscular domains) and blood levels of several myokines. Seven IM patients (17.5%) were sarcopenic. They had the worst damage, impaired functions, disability and history of severe myopathy. Decreased irisin and osteonectin levels were associated with sarcopenia (area under the curve 0.71 and 0.80, respectively)., Conclusion: DXA and hand-grip dynamometer are useful tools to assess damage in IM. Irisin and osteonectin may play a role in IM damage pathogenesis., (© The Author(s) 2024. Published by Oxford University Press on behalf of the British Society for Rheumatology. All rights reserved. For permissions, please email: journals.permissions@oup.com.)

Idiopathic inflammatory myopathies (IIMs) are severe autoimmune diseases with poorly understood pathogenesis and unmet medical needs. Here, we examine the role of interferon γ (IFNγ) using NOD female mice deficient in the inducible T cell co-stimulator (Icos), which have previously been shown to develop spontaneous IFNγ-driven myositis mimicking human disease. Using muscle proteomic and spatial transcriptomic analyses we reveal profound myofiber metabolic dysregulation in these mice. In addition, we report muscle mitochondrial abnormalities and oxidative stress in diseased mice. Supporting a pathogenic role for oxidative stress, treatment with a reactive oxygen species (ROS) buffer compound alleviated myositis, preserved muscle mitochondrial ultrastructure and respiration, and reduced inflammation. Mitochondrial anomalies and oxidative stress were diminished following anti-IFNγ treatment. Further transcriptomic analysis in IIMs patients and human myoblast in vitro studies supported the link between IFNγ and mitochondrial dysfunction observed in mice. These results suggest that mitochondrial dysfunction, ROS and inflammation are interconnected in a self-maintenance loop, opening perspectives for mitochondria therapy and/or ROS targeting drugs in myositis., (© 2024. The Author(s).)

Weight cycling is a major challenge in obesity management. Caloric restriction is known to promote this phenomenon, but the impact of macronutrient changes during dieting remains unclear. This study aimed to determine the role of macronutrient changes in weight maintenance without caloric restriction by alternating between two hypercaloric diets: a high-carbohydrate, high-fat Western diet (WD) and a low-carbohydrate, high-fat diet (LCHDF). Obesity was induced in 8-week-old C57BL/6 male mice by 10 weeks of WD feeding. Then, the mice were subjected to 12 weeks of LCHFD interspersed with WD (I-WD), 3 periods of 2-week LCHFD followed by 2 periods of 3-week WD, or 12 weeks of continuous WD (C-WD). C-WD and I-WD mice were compared to standard diet (SD) mice. In the I-WD group, each LCHFD period decreased weight gain, but mice regained weight after WD resumption. I-WD mice exhibited obesity, dyslipidemia, and glucose intolerance, similarly to the C-WD mice. I-WD mice also developed nonalcoholic steatohepatitis, associated with an increase in type-III collagen gene expression and a decrease in FGF21 protein levels, in comparison with SD. I-WD mice developed weight cycling despite maintaining a high caloric consumption, suggesting that changes in macronutrients during dieting are also a trigger of weight regain.

Objective: Inflammatory myopathies (IM), characterized by muscle inflammation and weakness, are rare systemic diseases. Our previous study estimated an IM incidence rate of 7.98 cases per million people per year (95% confidence interval 7.38-8.66) and highlighted important variations that were likely because of methodologic issues rather than true epidemiologic differences. In this study, we aimed to refine the incidence of IM, using the 2017 European League Against Rheumatism (EULAR)/American College of Rheumatology (ACR) classification criteria for IM and a quadruple-source capture-recapture method during a 6-year period in Alsace, France, a region with a population of 2 million having benefits of good access to health care and accredited IM referral centers., Methods: Clinical data of potential IM patients were obtained from 4 sources (general practitioners and community specialists, public and private hospital records, public and private laboratories, and archives from the pathology department). Patients residing in Alsace and who fulfilled the 2017 EULAR/ACR criteria for IM between January 1, 2006, and January 1, 2013, were included. We corrected potentially incomplete ascertainment of cases with capture-recapture analyses. We studied both spatial and temporal distributions of incidence of IM. We also assessed systemic manifestations of the disease., Results: Our review of 1,742 potential cases identified 106 patients with IM. No spatial or temporal heterogeneity was observed. Use of log-linear models showed an estimated 14.9 additional missed cases. Thus, the incidence rate of IM was 8.22 new cases per million inhabitants per year (95% confidence interval 6.76-9.69). Extramuscular manifestations other than dermatomyositis rash were frequently recorded., Conclusion: The stringent methodology used in our study provides an accurate estimation of the incidence of IM. This study also demonstrates, in a population-based cohort, the systemic nature of IM., (© 2023 The Authors. Arthritis & Rheumatology published by Wiley Periodicals LLC on behalf of American College of Rheumatology.)

Chemotherapy is a common therapy to treat patients with breast cancer but also leads to skeletal muscle deconditioning. Skeletal muscle deconditioning is multifactorial and intermuscular adipose tissue (IMAT) accumulation is closely linked to muscle dysfunction. To date, there is no clinical study available investigating IMAT development through a longitudinal protocol and the underlying mechanisms remain unknown. Our study was dedicated to investigating IMAT content in patients with early breast cancer who were treated with chemotherapy and exploring the subsequent cellular mechanisms involved in its development. We included 13 women undergoing chemotherapy. Muscle biopsies and ultrasonography assessment were performed before and after chemotherapy completion. Histological and Western blotting analyses were conducted. We found a substantial increase in protein levels of three mature adipocyte markers (perilipin, +901%; adiponectin, +135%; FABP4, +321%; P < 0.05). These results were supported by an increase in oil red O-positive staining (+358%; P < 0.05). A substantial increase in PDGFRα protein levels was observed (+476%; P < 0.05) highlighting an increase in fibro-adipogenic progenitors (FAPs) content. The cross-sectional area of the vastus lateralis muscle fibers substantially decreased (-21%; P < 0.01), and muscle architecture was altered, as shown by a decrease in fascicle length (-15%; P < 0.05) and a decreasing trend in muscle thickness (-8%; P = 0.08). We demonstrated both IMAT development and muscle atrophy in patients with breast cancer who were treated with chemotherapy. FAPs, critical stem cells inducing both IMAT development and skeletal muscle atrophy, also increased, suggesting that FAPs likely play a critical role in the skeletal muscle deconditioning observed in patients with breast cancer who were treated with chemotherapy.

Background: The post-COVID-19 condition, defined as COVID-19-related signs and symptoms lasting at least 2 months and persisting more than 3 months after infection, appears now as a public health issue in terms of frequency and quality of life alterations. Nevertheless, few data are available concerning long term evolution of malnutrition and sarcopenia, which deserve further attention., Method: Sarcopenia was investigated prospectively, together with weight evolution, at admission and at 3 and 6 months after hospital discharge in 139 COVID-19 patients, using the European Working Group on Sarcopenia in Older People (EWGSOP2) criteria, associating both decreased muscle strength and muscle mass, assessed, respectively, with hand dynamometer and dual-energy X-ray absorptiometry., Results: Of the 139 patients, 22 presented with sarcopenia at 3 months; intensive care units (ICU) length of stay was the sole factor associated with sarcopenia after multivariate analysis. Although the entire group did not demonstrate significant weight change, weight decreased significantly in the sarcopenia group (Five and eight patients, showing, respectively, >5 or >10% weight decrease). Interestingly, at 6 months, 16 of the 22 patients recovered from sarcopenia and their weight returned toward baseline values., Conclusions: Sarcopenia and malnutrition are frequently observed in patients hospitalized for COVID-19, even 3 months after infection occurrence, but can largely be reversed at 6 months after discharge. Enhanced patient care is needed in sarcopenic patients, particularly during long stays in an ICU.