Project description:Skeletal muscle accounts for the largest proportion of human body mass, on average, and is a key tissue in complex diseases and mobility. It is composed of several different cell and muscle fiber types. Here, we optimize single-nucleus ATAC-seq (snATAC-seq) to map skeletal muscle cell-specific chromatin accessibility landscapes in frozen human and rat samples, and single-nucleus RNA-seq (snRNA-seq) to map cell-specific transcriptomes in human. We additionally perform multi-omics profiling (gene expression and chromatin accessibility) on human and rat muscle samples.
Project description:Age-related sarcopenia is associated with a variety of changes in skeletal muscle. These changes are interrelated with each other and associated with systemic metabolism, the details of which, however, are largely unknown. Eicosapentaenoic acid (EPA) is a promising nutrient against sarcopenia and has multifaceted effects on systemic metabolism. Although several human studies have suggested that EPA supplementation protects against sarcopenia, the causal relationship of EPA supplementation and an increase of muscle strength has poor evidence in vivo. We demonstrated that aging skeletal muscle in male mice shows lower grip strength and fiber type changes, both of which can be inhibited by EPA supplementation irrespective of muscle mass alteration. We hypothesized that the aging process in skeletal muscle can be intervened by the administration of EPA, via transcriptomic changes in skeletal muscle. This analysis revealed fast-to-slow fiber type transition in aging muscle, which was partially inhibited by EPA.
Project description:Skeletal muscle aging is a major causative factor for disability and frailty in the elderly. Recent theories about the origins of the progressive impairment of skeletal muscle with aging emphasize a disequilibrium between damage and repair. Macrophages participate in muscle tissue repair first as pro-inflammatory M1 subtype and then as M2 anti-inflammatory subtype. However, information on macrophage presence in skeletal muscle is still sporadic and the effect of aging on different phenotypes remains unknown. In this study, we sought to characterize the polarization status of macrophages human skeletal muscle at different ages. We found that most macrophages in human skeletal muscle are M2, and that this number increased with advancing age. On the contrary, M1 macrophages decline with aging, making the total number of macrophages invariant with older age. Notably, M2 macrophages co-localized with increasing intermuscular adipose tissue (IMAT) in aging skeletal muscle. The mouse strain BALB/c, intrinsically M2-prone, showed increased IMAT and regenerating myofibers in skeletal muscle, accompanied by elevated expression of adipocyte markers and M2 cytokines. Collectively, we report that polarization of macrophages to the major M2 subtype is associated with IMAT, and propose that increased M2 in aged skeletal muscle may reflect active repair of aging-associated muscle damage.
Project description:Mitochondrial fusion and fission proteins regulate mitochondrial quality control and mitochondrial metabolism. In turn, mitochondrial dysfunction is associated with aging, although its causes are still under debate. Here, we show that aging is characterized by a progressive reduction of Mitofusin 2 (Mfn2) in mouse skeletal muscle and that skeletal muscle Mfn2 ablation in mice generates a gene signature linked to aging. Furthermore, muscle Mfn2-deficient mice show unhealthy aging characterized by altered metabolic homeostasis and sarcopenia. Mfn2 deficiency impairs mitochondrial quality control, which contributes to an exacerbated age-related mitochondrial dysfunction. Surprisingly, aging-induced Mfn2 deficiency triggers a ROS-dependent retrograde signaling pathway through induction of HIF1 transcription factor and BNIP3. This pathway ameliorates mitochondrial autophagy and minimizes mitochondrial damage. Our findings reveal that repression of Mfn2 in skeletal muscle during aging is determinant for the loss of mitochondrial quality, contributing to age-associated metabolic alterations and loss of muscle fitness. Quadriceps muscle from four mice per genotype were used (Control young (6 month-old), Mfn2KO young (6-month-old), control old (22-month-old) and Mfn2KO old (22-month-old)