Table_2_Characterizing the skeletal muscle immune microenvironment for sarcopenia: insights from transcriptome analysis and histological validation.xlsx

BackgroundSarcopenia is a condition characterized by the age-related loss of skeletal muscle mass and function. The pathogenesis of the disease is influenced by chronic low-grade inflammation. However, the specific changes in the immune landscape changes of sarcopenic muscle are not yet fully understood.
MethodsTo gain insights into the immune cell composition and interactions, we combined single-nucleus RNA sequencing data, bulk RNA sequencing dataset, and comprehensive bioinformatic analyses on the skeletal muscle samples from young, aged, and sarcopenic individuals. Histological staining was then performed on skeletal muscles to validate the distribution of immune cells in clinical samples.
ResultsWe analyzed the transcriptomes of 101,862 single nuclei, revealing a total of 10 major cell types and 6 subclusters of immune cell types within the human skeletal muscle tissues. Notable variations were identified in the immune microenvironment between young and aged skeletal muscle. Among the immune cells from skeletal muscle microenvironment, macrophages constituted the largest fraction. A specific marker gene LYVE1 for skeletal muscle resident macrophages was further identified. Cellular subclasses included four distinct groups of resident macrophages, which play different roles in physiological or non-physiological conditions. Utilizing bulk RNA sequencing data, we observed a significant enrichment of macrophage-rich inflammation in sarcopenia.
ConclusionsOur findings demonstrate age-related changes in the composition and cross-talk of immune cells in human skeletal muscle microenvironment, which contribute to chronic inflammation in aged or sarcopenia muscle. Furthermore, macrophages emerge as a potential therapeutic target, thus advancing our understanding of the pathogenesis of sarcopenia.

【背景】肌少症（Sarcopenia）是一种以年龄相关性骨骼肌质量与功能丧失为特征的疾病。该病的发病机制受慢性低度炎症的影响，但目前对于肌少症骨骼肌的免疫图谱特征的具体变化仍未完全阐明。
【方法】为深入解析免疫细胞的组成与相互作用，我们对来自青年、老年及肌少症个体的骨骼肌样本，整合了单细胞核RNA测序（single-nucleus RNA sequencing）数据、批量RNA测序（bulk RNA sequencing）数据集，并开展了全面的生物信息学分析。随后我们对骨骼肌组织进行组织学染色，以验证临床样本中免疫细胞的分布情况。
【结果】我们对101,862个单细胞核的转录组进行了分析，共鉴定出人类骨骼肌组织中的10种主要细胞类型及6种免疫细胞亚簇。研究发现青年与老年骨骼肌的免疫微环境存在显著差异。在骨骼肌微环境的免疫细胞中，巨噬细胞占比最高。我们进一步鉴定出骨骼肌驻留巨噬细胞的特异性标记基因LYVE1。细胞亚类包含4种不同的驻留巨噬细胞群，它们在生理与非生理状态下发挥不同功能。通过整合批量RNA测序数据，我们观察到肌少症患者体内存在显著的巨噬细胞富集性炎症反应。
【结论】本研究揭示了人类骨骼肌微环境中免疫细胞的组成及细胞互作随年龄发生的变化，这些变化是老年及肌少症骨骼肌慢性炎症的诱因之一。此外，巨噬细胞有望成为潜在的治疗靶点，从而加深我们对肌少症发病机制的理解。