Lab-Grown Muscle Organoids Model Sarcopenia and Test Testosterone as a Fix
Scientists built 3D human muscle organoids from stem cells, recreated age-related sarcopenia with TNF-α, and showed testosterone can partially reverse muscle loss.
Summary
Researchers developed human pluripotent stem cell-derived skeletal muscle organoids (hSkMOs) that contain mature muscle fibers, satellite cells, motor neurons, and interneurons. By repeatedly exposing these organoids to TNF-α—a chronic inflammation marker elevated in aging—they recreated the hallmarks of sarcopenia: muscle fiber atrophy, impaired satellite cell activation, and NF-κB pathway hyperactivation. Testosterone treatment significantly reversed these effects, increasing satellite cell proliferation and restoring muscle fiber cross-sectional area. Single-nucleus RNA sequencing and immunohistochemistry confirmed the organoids replicate the full myogenic and neural lineage diversity found in native muscle, offering a powerful human-specific platform for studying age-related muscle loss and screening therapies.
Detailed Summary
Sarcopenia—the progressive loss of muscle mass and strength with aging—affects hundreds of millions globally and lacks effective treatments. A core obstacle has been the absence of human-specific models; animal models are slow, expensive, and poorly recapitulate human muscle biology, particularly the role of satellite cells (SCs), the resident stem cells responsible for muscle repair.
This study from Korean and Singaporean institutions developed an advanced 3D human skeletal muscle organoid (hSkMO) system derived from human pluripotent stem cells (hPSCs). The protocol proceeds in stages: a 2D paraxial mesodermal induction phase (Days 1–3) using CHIR99021 and LDN193189, followed by 3D myogenic specification in ultra-low-binding plates with HGF, IGF-1, and bFGF, then a long-term maturation phase extending to Day 100. By Day 3, over 80% of cells were confirmed paraxial mesodermal progenitors (T/BRA+ ~82%; TBX6+ ~78%), with only ~16% neuromesodermal progenitors. The resulting organoids, growing to ~2 mm by Day 100, were validated by single-nucleus RNA sequencing and extensive immunohistochemistry, confirming the presence of myogenic progenitors and satellite cells (PAX7+), myocytes, mature MyHC+ muscle fibers with sarcomere structures, motor neurons, spinal interneurons, glial cells, and Schwann cells. Muscle fiber diameter doubled between Day 50 and Day 100 (p < 0.0001), demonstrating robust maturation.
To model sarcopenia, the team applied TNF-α—a key pro-inflammatory cytokine chronically elevated in aging muscle—either acutely (2 days) or chronically (repeated dosing). Acute TNF-α exposure triggered significant phosphorylation of NF-κB p65, IκB-α, and AKT (p < 0.05 to p < 0.001), confirming activation of the canonical inflammatory/atrophy pathway. Chronic TNF-α treatment produced sustained muscle atrophy, reducing fiber cross-sectional area to 644.7 μm² and dramatically suppressing satellite cell activation (PAX7+/MYOD+ cells fell to 2.29%; PAX7+/Ki67+ to 2.07%).
Testosterone was then applied as a candidate therapeutic. It significantly increased activated satellite cell populations (PAX7+/MYOD+: 7.97%; PAX7+/Ki67+: 7.03%, p < 0.001 vs. TNF-α group) and restored muscle fiber cross-sectional area to 987.1 μm² (p < 0.01 vs. TNF-α). Electrophysiological analyses further confirmed functional neuromuscular connectivity in the organoids, strengthening their validity as a disease model.
This work establishes hSkMOs as a tractable, human-specific platform for sarcopenia research, capable of modeling chronic inflammatory muscle degeneration and evaluating therapeutic candidates. Testosterone's anabolic rescue effect in this system aligns with clinical observations and supports the organoid's translational relevance. Future work should explore additional interventions—exercise mimetics, anti-inflammatory agents, myostatin inhibitors—using this platform.
Key Findings
- hSkMOs grown to Day 100 contained mature muscle fibers, satellite cells, motor neurons, and interneurons confirmed by snRNA-seq.
- Chronic TNF-α treatment reduced muscle fiber cross-sectional area to 644.7 μm² and suppressed satellite cell activation to ~2%.
- Testosterone restored fiber cross-sectional area to 987.1 μm² and boosted activated satellite cells ~3.5-fold versus TNF-α alone.
- NF-κB p65, IκB-α, and AKT were significantly phosphorylated under TNF-α, confirming inflammatory atrophy pathway activation.
- Muscle fiber diameter doubled from Day 50 to Day 100, demonstrating progressive maturation of the organoid system.
Methodology
3D hSkMOs were derived from hPSCs via stepwise 2D paraxial mesodermal induction followed by 3D myogenic specification and long-term maturation to Day 100. Sarcopenia was modeled using acute and chronic TNF-α treatment; outcomes were assessed by immunohistochemistry, Western blot, single-nucleus RNA sequencing, and electrophysiology. Testosterone was tested as a therapeutic intervention in the chronic TNF-α sarcopenia model.
Study Limitations
The model uses hPSC-derived cells that may not fully replicate the epigenetic aging state of elderly human muscle; true aging hallmarks like telomere shortening or accumulated senescent cells are not yet incorporated. The sarcopenia was induced chemically (TNF-α) rather than through natural aging, which may not capture the full complexity of in vivo sarcopenic processes. Vascularization and systemic hormonal or metabolic crosstalk present in aging humans are absent from this in vitro system.
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