Mechanical Stimulation Reverses Bone Aging by Unlocking Key Longevity Gene

Bone aging is driven in large part by the functional decline of bone marrow mesenchymal stem cells (BMSCs), which lose their capacity to generate new bone tissue while accumulating hallmarks of cellular senescence. While biochemical and genetic contributors to this process are increasingly understood, the role of mechanical signaling had remained largely unexplored — a gap this study directly addresses.

The researchers isolated BMSCs from 21 elderly donors (ages 50–80) and 17 young donors (ages 18–35) and subjected them to a battery of mechanical assessments. Using traction force microscopy, FRET-based actin tension sensors, and nanoindentation, they showed that aged BMSCs generated roughly half the traction force of young cells (122 vs. 227 Pa), were significantly softer (Young's modulus ~470 vs. ~790 Pa), and displayed disorganized actin stress fibers. Accompanying these changes were reductions in myosin IIa activity, Lamin A/C expression, and nuclear YAP localization — collectively indicating a broad collapse of the cytoskeletal-to-nuclear mechanotransduction axis.

To test whether restoring mechanical force could reverse senescence, the team employed two approaches: cyclic mechanical stretching (5% strain, 0.02 Hz) and pharmacological activation of myosin II with calyculin A. Both methods successfully increased cellular traction forces and produced consistent reductions in canonical senescence markers including p16INK4a, p53, p21WAF1/Cip1, and SA-β-gal activity. These effects were validated in both 2D cultures and 3D bone marrow-mimicking hydrogel and fiber network environments. Conversely, reducing traction force in young BMSCs using soft hydrogels or blebbistatin (a myosin II inhibitor) induced senescence markers, establishing a causal bidirectional relationship between cellular mechanics and senescent state.

Mechanistically, ATAC-seq chromatin accessibility profiling revealed that mechanical stimulation selectively opened chromatin at the FOXO1 locus in aged cells, driving upregulation of this key transcription factor. FOXO1 is known to promote antioxidant defense, DNA repair, and cell survival. Genetic knockdown of FOXO1 completely abolished the rejuvenating effects of mechanical stimulation, confirming its role as a critical mediator. In aged mice, low-magnitude whole-body vibration or voluntary treadmill exercise restored bone microarchitecture (improved trabecular number, thickness, and bone volume fraction by microCT), enhanced physical performance in grip strength and rotarod tests, and showed a tendency — though not statistically significant in all measures — to reduce circulating SASP-associated inflammatory cytokines. Importantly, excessive mechanical loading caused chromatin overextension and DNA double-strand breaks (evidenced by γH2AX foci), establishing an inverted-U dose-response relationship that underscores the necessity of precise force calibration.

The study presents a compelling mechanobiological model in which aging-associated loss of intracellular tension leads to chromatin compaction, silencing of pro-longevity genes like FOXO1, and self-reinforcing senescence. Restoring that tension through mechanical means remodels chromatin accessibility and reverses the trajectory. These findings open a new conceptual avenue — mechanical epigenetics — for understanding and potentially treating age-related tissue decline.