Naddaf Elie, Nguyen Thi Kim Oanh, Watzlawik Jens O, Gao Huanyao, Hou Xu, Fiesel Fabienne C, Mandrekar Jay, Kokesh Eileen, Harmsen William S, Lanza Ian R, Springer Wolfdieter, Trushina Eugenia
Department of Neurology, Mayo Clinic, Rochester, Minnesota, USA.
Department of Neuroscience, Mayo Clinic, Jacksonville, Florida, USA.
J Cachexia Sarcopenia Muscle. 2025 Feb;16(1):e13672. doi: 10.1002/jcsm.13672.
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.
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.
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.
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.
包涵体肌炎（IBM）是成人中最常见的肌肉疾病，目前尚无有效治疗方法。IBM的发病机制仍不清楚。在本研究中，我们旨在探讨IBM中炎症与线粒体功能障碍之间的相互作用。
研究人群包括38例IBM患者和22例年龄及性别匹配的无肌病对照者。IBM组的平均年龄为62.9岁（标准差=9），对照组为59.7岁（10）。对研究参与者的冷冻肌肉样本进行了批量RNA测序、Meso Scale Discovery电化学发光（ECL）、蛋白质印迹、组织化学和免疫组织化学分析。
我们证实在IBM肌肉样本中NLRP3炎性小体被激活，NLRP3炎性小体是RNA测序中上调最明显的途径，同时IBM组中NLRP3和ASC蛋白的表达增加。NLRP3 RNA水平与TLR7（相关系数ρ=0.91）和补体激活相关基因的相关性最强，与其他几个线粒体相关基因呈负相关。在肌肉组织病理学上，炎症细胞和肌纤维中的NRLP3免疫反应性均增加。线粒体自噬对于清除受损线粒体和防止线粒体功能障碍-NLRP3炎性小体激活的恶性循环形成至关重要。在此，我们发现线粒体自噬发生改变，与对照组相比，IBM患者肌肉裂解物中自噬标记物p-S65-泛素水平升高（中位数为114.3 vs. 81.25 ECL单位，p=0.005）。与男性对照组相比，IBM男性患者的p-S65-泛素水平显著升高（136 vs. 83.5 ECL单位；p=0.013），而与女性对照组相比，IBM女性患者虽有轻度升高但无统计学意义（97.25 vs. 69 ECL单位，p=0.31）。在肌肉组织病理学上，p-S65-泛素聚集物积聚在主要为2型且缺乏细胞色素c氧化酶反应性的肌纤维中。NLRP3 RNA水平在男女两性中均与p-S65-泛素水平相关（男性：ρ=0.48，女性：ρ=0.54），但仅在男性中与肌肉力量丧失相关，如手动运动测试评分所示（男性：ρ=0.62，女性：ρ=-0.14）。最后，我们在IBM中鉴定出了性别特异性分子途径。女性上调了与应激反应相关的途径，这可能在一定程度上抵消了IBM的一些病理机制，而男性上调了与细胞黏附和迁移相关的途径。
IBM中存在NLRP3炎性小体激活以及线粒体自噬改变，尤其是在男性中，这具有潜在的治疗意义。这些发现提示了IBM中存在性别特异性机制，值得进一步研究。
