Human Pluripotent Stem Cell-Derived Skeletal Muscle Organoid Model of Aging-Induced Sarcopenia.

BACKGROUND

Sarcopenia is defined by the age-related loss of muscle mass and function, with an impaired regenerative capacity of satellite cells (SCs). Despite their recognized importance in muscle regeneration, human model-based studies on SCs in sarcopenia are still lacking, limiting our understanding of their role in age-related muscle loss. Here, we aimed to develop a sarcopenia model using human pluripotent stem cells (hPSCs)-derived skeletal muscle organoids (hSkMOs) and prevent the sarcopenia progression by testosterone treatment.

METHODS

The 3D hSkMOs were generated from hPSC and exhibited structurally and functionally mature muscle fibres and spinal-derived neurons including motor neurons and interneurons. The proportion of muscle and the diameter of muscle fibres were assessed. To investigate the acute pro-inflammatory response and intrinsic regenerative capacity of hSkMOs, we induced sarcopenia-like conditions by TNF-α treatment for 2 days and analysed. To model aging-induced sarcopenia and investigate the preventive effect of testosterone, chronic TNF-α treatment was applied, followed by testosterone administration. Histological, biochemical, molecular and electrophysiological analyses were conducted in various experiments.

RESULT: We employed a stepwise differentiation protocol from 2D paraxial mesodermal induction to 3D myogenic specification, concluding with a maturation culture system. We observed that the majority of cells were T/BRA- and TBX6-positive (+) paraxial mesodermal progenitors (T/BRA+, 82.04%; TBX6+, 78.18%), whereas the neuromesodermal progenitors demonstrated a relatively low proportion (T/BRA+/SOX2+, 15.91%; TBX6+/SOX2+, 11.45%). Single-nucleus RNA-sequencing and extensive immunohistochemistry confirmed the presence of the myogenic lineage cell types (myogenic progenitors/SCs, myocytes, muscle fibres) and the neural lineage cell types (spinal-derived interneurons, motor neurons, glial cells, Schwann cells). Additionally, the growth of MyHC+ muscle fibres reached twice the thickness on Day 100 compared to that on Day 50 (p < 0.0001). We subjected them to TNF-α treatment and analysed. Western blot analysis confirmed that TNF-α/NF-κB pathway associated factors such as NF-κB p65, IκB-α and AKT were highly phosphorylated (p < 0.05, p < 0.001). The administration of testosterone increased the proportion of activated SCs (PAX7+/MYOD+, 7.97%; PAX7+/Ki67+, 7.03%) compared to the TNF-α group (PAX7+/MYOD+, 2.29%; PAX7+/Ki67+, 2.07%, p < 0.001). The administration of testosterone increased the Cross-Sectional-Area (987.1 μm2) compared to the TNF-α group (644.7 μm2, p < 0.01).

CONCLUSIONS

We successfully developed a hSkMOs to demonstrate the structural maturity of the skeletal muscle and its functional interaction with spinal-derived interneurons and motor neurons. Furthermore, we demonstrated that our hSkMOs are useful for modelling aging-induced sarcopenia and providing a valuable platform for testing therapeutic interventions.