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Rippling Muscle Disease (RMD) is a rare skeletal myopathy characterized by abnormal muscular excitability manifesting with wave-like muscle contractions and stretch-induced muscle mounding. Hereditary RMD is associated with caveolin-3 or cavin-1 mutations. Recently we discovered anti-cavin 4 autoantibodies as a biomarker of immune mediated Rippling Muscle Disease (iRMD), but the underlying disease-mechanisms are poorly understood. Transcriptomic studies were performed on muscle biopsies of 8 patients (5 males; 3 females; ages 26-to-80) with iRMD. Subsequent pathway analysis compared iRMD to human non-disease control and disease-control (dermatomyositis) muscle samples. Transcriptomic studies demonstrated changes in key pathways of muscle homeostasis, including muscle development, protein quality control, and autoimmunity. All iRMD samples had significantly upregulated cavin-4 expression compared to controls, likely compensatory for autoantibody-mediated protein degradation. Excitation-Contraction coupling genes (such as SERCA1, PMCA , and PLN) were significantly upregulated in iRMD compared to controls. These changes were validated by immunofluorescent staining. Comparison of iRMD to dermatomyositis transcriptomics demonstrated significant overlap in autoimmunity pathways including MHC2 antigen presentation and innate immune response. This study represents the first muscle transcriptomic analysis of iRMD patients and dissects underlying disease mechanisms. Increase of sarcolemmal and cellular calcium channels as well as PLN, an inhibitor of the SERCA pump for calcium into the sarcoplasm, likely alters the calcium dynamics in iRMD. These changes in crucial components of Excitation-Contraction coupling and muscle relaxation may underlie rippling by altering calcium flux. We propose a model in which autoantibody mediated cavin-4 destruction leads to RMD through alterations in key genes regulating Excitation-Contraction coupling. [ABSTRACT FROM AUTHOR]

Inclusion body myositis (IBM) is the most prevalent muscle disease in adults for which no current treatment exists. The pathogenesis of IBM remains poorly defined. Inflammation and mitochondrial dysfunction are the most common histopathological findings. In this study, we aimed to explore the interplay between inflammation and mitochondrial dysfunction in IBM patients. We included 38 IBM patients and 22 age- and sex-matched controls without myopathy. Bulk RNA sequencing, Meso Scale Discovery ELISA, western blotting, histochemistry and immunohistochemistry were performed on frozen muscle samples from the study participants. We demonstrated activation of the NLRP3 inflammasome in IBM muscle samples, with the NLRP3 inflammasome pathway being the most upregulated pathway. On muscle histopathology, there was increased NRLP3 immunoreactivity in both inflammatory cells and muscle fibers. Mitophagy is critical for removing damaged mitochondria and preventing the formation of a vicious cycle of mitochondrial dysfunction—NLRP3 activation. In the IBM muscle samples, we showed altered mitophagy with elevated levels of p-S65-Ubiquitin, a mitophagy marker. Furthermore, p-S65-Ubiquitin aggregates accumulated in muscle fibers that were mostly type 2 and devoid of cytochrome-c-oxidase reactivity. Type 2 muscle fibers are known to be more prone to mitochondrial dysfunction. NLRP3 RNA levels correlated with p-S65-Ubiquitin levels. NLRP3 inflammasome is activated in IBM, along with altered mitophagy, potentially forming a self-sustaining vicious cycle. These findings could have potential therapeutic significance. [ABSTRACT FROM AUTHOR]

Background: Inclusion body myositis (IBM) is the most prevalent muscle disease in adults for which no current treatment exists. The pathogenesis of IBM remains poorly defined. In this study, we aimed to explore the interplay between inflammation and mitochondrial dysfunction in IBM., Methods: The study population consisted of 38 IBM patients and 22 age- and sex-matched controls without a myopathy. Mean age was 62.9 years (SD = 9) in IBM group and 59.7 (10) in controls. Bulk RNA sequencing, Meso Scale Discovery electrochemiluminescence (ECL), western blotting, histochemistry and immunohistochemistry were performed on frozen muscle samples from the study participants., Results: We demonstrated activation of the NLRP3 inflammasome in IBM muscle samples, with the NLRP3 inflammasome being the most upregulated pathway on RNA sequencing, along with increased expression of NLRP3 and ASC proteins in IBM group. NLRP3 RNA levels most strongly correlated with TLR7 (correlation coefficient ρ = 0.91) and complement activation-related genes, and inversely correlated with several mitochondria-related genes among others. On muscle histopathology, there was increased NRLP3 immunoreactivity in both inflammatory cells and muscle fibres. Mitophagy is critical for removing damaged mitochondria and preventing the formation of a vicious cycle of mitochondrial dysfunction-NLRP3 inflammasome activation. Herein, we showed altered mitophagy, as witnessed by the elevated levels of p-S65-Ubiquitin, a mitophagy marker, in muscle lysates from IBM patients compared to controls (median of 114.3 vs. 81.25 ECL units, p = 0.005). The p-S65-Ubiquitin levels were most significantly elevated in IBM males compared to male controls (136 vs. 83.5 ECL units; p = 0.013), whereas IBM females had milder nonsignificant elevation compared to female controls (97.25 vs. 69 ECL units, p = 0.31). On muscle histopathology, p-S65-Ubiquitin aggregates accumulated in muscle fibres that were mostly Type 2 and devoid of cytochrome-c-oxidase reactivity. NLRP3 RNA levels correlated with p-S65-Ubiquitin levels in both sexes (males: ρ = 0.48, females: ρ = 0.54) but with loss of muscle strength, as reflected by the manual motor test score, only in males (males: ρ = 0.62, females: ρ = -0.14). Lastly, we identified sex-specific molecular pathways in IBM. Females had upregulation of pathways related to response to stress, which could conceivably offset some of the pathomechanisms of IBM, while males had upregulation of pathways related to cell adhesion and migration., Conclusions: There is activation of the NLRP3 inflammasome in IBM, along with altered mitophagy, particularly in males, which is of potential therapeutic significance. These findings suggest sex-specific mechanisms in IBM that warrant further investigation., (© 2024 The Author(s). Journal of Cachexia, Sarcopenia and Muscle published by Wiley Periodicals LLC.)

Rippling Muscle Disease (RMD) is a rare skeletal myopathy characterized by abnormal muscular excitability manifesting with wave-like muscle contractions and percussion-induced muscle mounding. Hereditary RMD is associated with caveolin-3 or cavin-1 mutations. Recently, we identified cavin 4 autoantibodies as a biomarker of immune-mediated RMD (iRMD), though the underlying disease-mechanisms remain poorly understood. Transcriptomic studies were performed on muscle biopsies of 8 patients (5 males; 3 females; ages 26-to-80) with iRMD. Subsequent pathway analysis compared iRMD to human non-disease control and disease control (dermatomyositis) muscle samples. Transcriptomic studies demonstrated changes in key pathways of muscle contraction and development. All iRMD samples had significantly upregulated cavin-4 expression compared to controls, likely compensatory for autoantibody-mediated protein degradation. Proteins involved in muscle relaxation (including SERCA1, PMCA and PLN) were significantly increased in iRMD compared to controls. Comparison of iRMD to dermatomyositis transcriptomics demonstrated significant overlap in immune pathways, and the IL-6 signaling pathway was markedly increased in all iRMD patient muscle biopsies and increased in the majority of iRMD patients' serum. This study represents the first muscle transcriptomic analysis of iRMD patients and dissects underlying disease mechanisms. Increase of sarcolemmal and cellular calcium channels as well as PLN, an inhibitor of the SERCA pump for calcium into the sarcoplasm, likely alters the calcium dynamics in iRMD. These changes in crucial components of muscle relaxation may underlie rippling by altering calcium flux. Our findings provide crucial insights into the differential expression of genes regulating muscle relaxation and highlight potential disease pathomechanisms., Competing Interests: Declarations. Ethics approval and consent to participate: This study was approved by the Mayo Clinic Institutional Review Board (IRB#18-010637). Consent for publication: All authors have reviewed and approved the final version of the manuscript and consent to its publication in Acta Neuropathologica Communications. The study was approved by the Mayo Clinic Institutional Review Board (IRB#18-010637). Competing interests: MM has received personal compensation for serving on a Scientific Advisory or Data Safety Monitoring board for Argenx on an unrelated topic and for serving as an Associate Editor for Neurology Genetics, AAN. SP has received personal compensation for consulting roles with Genentech, Sage Therapeutics, Prime Therapeutics, UCB, Roche/Genentech, and Arialys Therapeutics, as well as for serving on a Scientific Advisory or Data Safety Monitoring board for UCB, Inc., Genentech, and F. Hoffman/LaRoche, for advisory work with Hoffman/LaRoche AG and Alexion, for consulting roles with Astellas, Alexion, MedImmune/Viela Bio, and Roche/Genentech. His institution has received research support from Grifols, NIH, Viela Bio/MedImmune/Horizon, Alexion Pharmaceuticals, F. Hoffman/LaRoche/Genentech, NovelMed, and AstraZeneca. SP holds intellectual property interests in healthcare-related discoveries and technologies. D.D. has consulted for UCB, Immunovant, Argenx, Arialys and Astellas pharmaceuticals. All compensation for consulting activities is paid directly to Mayo Clinic. He is a named inventor on filed patent that relates to KLHL11 as marker of autoimmunity and germ cell tumor. He has patents pending for LUZP4-IgG, cavin-4-IgG and SKOR2 IgG as markers of neurological autoimmunity. He has received funding from the DOD (CA210208 & PR220430), David J. Tomassoni ALS Research Grant Program and UCB., (© 2025. The Author(s).)

Background: Inclusion body myositis (IBM) is the most prevalent muscle disease in adults for which no current treatment exists. The pathogenesis of IBM remains poorly defined. Inflammation and mitochondrial dysfunction are the most common histopathological findings. In this study, we aimed to explore the interplay between inflammation and mitochondrial dysfunction in IBM patients, highlighting sex differences., Methods: We included 38 IBM patients and 22 age- and sex-matched controls without myopathy. Bulk RNA sequencing, Meso Scale Discovery ELISA, western blotting, histochemistry and immunohistochemistry were performed on frozen muscle samples from the study participants., Results: We demonstrated activation of the NLRP3 inflammasome in IBM muscle samples, with the NLRP3 inflammasome pathway being the most upregulated. On muscle histopathology, there is increased NRLP3 immunoreactivity in both inflammatory cells and muscle fibers. Mitophagy is critical for removing damaged mitochondria and preventing the formation of a vicious cycle of mitochondrial dysfunction-NLRP3 activation. In the IBM muscle samples, we showed altered mitophagy, most significantly in males, with elevated levels of p-S65-Ubiquitin, a mitophagy marker. Furthermore, p-S65-Ubiquitin aggregates accumulated in muscle fibers that were mostly type 2 and devoid of cytochrome-c-oxidase reactivity. Type 2 muscle fibers are known to be more prone to mitochondrial dysfunction. NLRP3 RNA levels correlated with p-S65-Ubiquitin levels in both sexes but with loss of in muscle strength only in males. Finally, we identified sex-specific molecular pathways in IBM, with females having activation of pathways that could offset some of the pathomechanisms of IBM., Conclusions: NLRP3 inflammasome is activated in IBM, along with altered mitophagy particularly in males, which is of potential therapeutic significance. These findings suggest sex-specific mechanisms in IBM that warrant further investigation., Competing Interests: Competing interests: Mayo Clinic, F.C.F. and W.S. have filed a patent related to PRKN mitophagy activators. All other authors report no conflicts of interest.