Short-term metformin ingestion by healthy older adults improves myoblast function

Abstract

Muscle progenitor cells (MPCs) in aged muscle exhibit impaired activation into proliferating myoblasts, thereby impairing fusion and changes in secreted factors. The antihyperglycemic drug metformin, currently studied as a candidate antiaging therapy, may have potential to promote function of aged MPCs. We evaluated the impact of 2 wk of metformin ingestion on primary myoblast function measured in vitro after being extracted from muscle biopsies of older adult participants. MPCs were isolated from muscle biopsies of community-dwelling older (4 male/4 female, ∼69 yr) adult participants before (pre) and after (post) the metformin ingestion period and studied in vitro. Cells were extracted from Young participants (4 male/4 female, ∼27 yr) to serve as a "youthful" comparator. MPCs from Old subjects had lower fusion index and myoblast-endothelial cell homing compared with Young, while Old MPCs, extracted after short-term metformin ingestion, performed better at both tasks. Transcriptomic analyses of Old MPCs (vs. Young) revealed decreased histone expression and increased myogenic pathway activity, yet this phenotype was partially restored by metformin. However, metformin ingestion exacerbated pathways related to inflammation signaling. Together, this study demonstrated that 2 wk of metformin ingestion induced persistent effects on Old MPCs that improved function in vitro and altered their transcriptional signature including histone and chromatin remodeling.

Keywords: aging; diabetes; satellite cells; senescence; skeletal muscle.

Figure 1.

Metformin increases fusion index in vitro. A: study design. B: images of proliferating myoblasts, myoblasts 8 days post induction to differentiate, and myotubes. C and D: quantification of fusion index with myosin heavy chain 4 antibody (MF20) (Cy5: purple) and nuclei (DAPI: blue): fusion index (C) and myonuclear area (D). Sample size Young: 4 f/4 m; Old: 4 f/4 m. MPC, muscle progenitor cell; P3 and P4, passage 3 and 4. #Different than Young, post hoc.

Figure 2.

Metformin increases muscle progenitor cell (MPC)-endothelial cell homing in vitro. A: images of cocultures at 0, 10, and 24 h postremoval of well insert. B: schematic of coculture assay design. C: distance traveled by myoblasts and endothelial cells within a coculture. Endothelial cell only (EC Only) control consists of endothelial cells seeded in both chambers. D: quantification of the length of the gap closed after 24 h. Sample size Young: 4 f/4 m; Old: 4 f/4 m.

Figure 3.

Two weeks of metformin ingestion has lingering transcriptional implications for Old muscle progenitor cells (MPCs). A: significantly altered genes by age and metformin using the raw P value and 5% false discovery rate adjusted (adj.) P value. B: gene expression for markers of myogenic cells. C: heat map of the top 10 genes up or down by age organized by magnitude of fold change. D: table of the top 20 genes up or down by metformin organized by magnitude of fold change. Gene set sample size Young: 4 f/4 m; Old: 2 f/4 m. F.C., fold change; RPKM, reads per kilobase per million mapped reads.

Figure 4.

Metformin may reverse aspects of muscle progenitor cell aging at the expense of increasing inflammation signaling. A: gene set enrichment analysis (GSEA) for pathways altered by age or metformin. FDR, false discovery rate. B: individual gene changes within Myogenesis, Apical Junction, Interferon Responses, and Vascular Remodeling pathways. C: Upstream Regulators [ingenuity pathway analysis (IPA)] impacted by age but reversed by metformin. Gene set sample size Young: 4 f/4 m; Old: 2 f/4 m.

Figure 5.

Short-term metformin treatment induces chromatin remodeling in Old muscle progenitor cells. A: gene expression of histones significantly altered by age or metformin [adjusted (adj.) P ≤ 0.05]. B: Upstream Regulators involved in chromatin remodeling predicted to be significantly altered by metformin treatment. Sample size Young: 4 f/4 m; Old: 4 f/4 m.