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Updated: Aug 25, 2025
Preparation and Culture of Myogenic Precursor Cells/Primary Myoblasts from Skeletal Muscle of Adult and Aged Humans
Published on: February 16, 2017
Single-cell analysis of skeletal muscle macrophages reveals age-associated functional subpopulations
Linda K Krasniewski1, Papiya Chakraborty1, Chang-Yi Cui1
1Laboratory of Genetics and Genomics, National Institute on Aging Intramural Research Program, National Institutes of Health, Baltimore, United States.
Abstract:
Tissue-resident macrophages represent a group of highly responsive innate immune cells that acquire diverse functions by polarizing toward distinct subpopulations. The subpopulations of macrophages that reside in skeletal muscle (SKM) and their changes during aging are poorly characterized. By single-cell transcriptomic analysis with unsupervised clustering, we found 11 distinct macrophage clusters in male mouse SKM with enriched gene expression programs linked to reparative, proinflammatory, phagocytic, proliferative, and senescence-associated functions. Using a complementary classification, membrane markers LYVE1 and MHCII identified four macrophage subgroups: LYVE1-/MHCIIhi (M1-like, classically activated), LYVE1+/MHCIIlo (M2-like, alternatively activated), and two new subgroups, LYVE1+/MHCIIhi and LYVE1-/MHCIIlo. Notably, one new subgroup, LYVE1+/MHCIIhi, had traits of both M2 and M1 macrophages, while the other new subgroup, LYVE1-/MHCIIlo, displayed strong phagocytic capacity. Flow cytometric analysis validated the presence of the four macrophage subgroups in SKM and found that LYVE1- macrophages were more abundant than LYVE1+ macrophages in old SKM. A striking increase in proinflammatory markers (S100a8 and S100a9 mRNAs) and senescence-related markers (Gpnmb and Spp1 mRNAs) was evident in macrophage clusters from older mice. In sum, we have identified dynamically polarized SKM macrophages and propose that specific macrophage subpopulations contribute to the proinflammatory and senescent traits of old SKM.
Insights
Skeletal muscle macrophages exhibit diverse functions. Aging increases proinflammatory and senescence markers in specific macrophage subsets, contributing to age-related muscle changes.
Area of Science:
- Immunology
- Cell Biology
- Skeletal Muscle Physiology
Background:
- Tissue-resident macrophages are key innate immune cells with diverse, plastic functions.
- Skeletal muscle macrophages (SKM) and their aging-related changes are not well understood.
Purpose of the Study:
- To characterize macrophage subpopulations in male mouse skeletal muscle.
- To investigate how these macrophage populations change with aging.
Main Methods:
- Single-cell transcriptomic analysis and unsupervised clustering identified 11 macrophage clusters.
- Flow cytometry and membrane markers (LYVE1, MHCII) classified four subgroups.
- Gene expression analysis focused on reparative, inflammatory, phagocytic, proliferative, and senescence markers.
Main Results:
- Eleven distinct macrophage clusters were found in mouse SKM, displaying varied functional gene expression.
- Four subgroups were identified: LYVE1-/MHCIIhi (M1-like), LYVE1+/MHCIIlo (M2-like), and two novel subgroups (LYVE1+/MHCIIhi and LYVE1-/MHCIIlo).
- Older mice showed increased proinflammatory (S100a8, S100a9) and senescence (Gpnmb, Spp1) markers in SKM macrophages, with LYVE1- macrophages being more abundant.
Conclusions:
- Distinct, dynamically polarized macrophage subpopulations exist in skeletal muscle.
- Specific macrophage subsets, particularly LYVE1- macrophages, are associated with the proinflammatory and senescent characteristics of aged skeletal muscle.
