Strain-conditioned spatial gene expression in female mouse bone under physiological and non-physiological strain distribution.

Osteoporosis, the most common bone metabolic disease, impairs the ability of bone to sense and adapt to mechanical stimuli. Mechanical strain distribution plays a crucial role in bone adaptation, yet the molecular mechanisms underlying differential remodeling responses to distinct strain conditions remain unclear. To address this, we compared mouse tibiae subjected to axial compressive (physiological strain distribution) or medial-lateral (non-physiological strain distribution) loading. Strain distributions were calculated by finite element analysis and validated by strain gauge measurements, identifying the posterior-lateral (PL) site as a key region of differential strain between the 2 loading conditions. Loading was optimized to induce equivalent strain magnitude by opposite mode at this site and applied daily for 3 d to 16-wk-old female C57Bl/6J mice. Tibial cross-sections at 37% of the tibial length measured from the tibial plateau were analyzed using the GeoMX Digital Spatial Profiler to assess strain-dependent spatial transcriptomic changes. Medial-lateral loading elicited spatially distinct gene expression patterns at the PL site, with significant downregulation of genes involved in bone remodeling, cellular stress responses, and vasculature. These effects were not observed in axial compressive loading. Notably, the non-physiological tensile strain induced by medial-lateral loading exhibited unique transcriptomic profiles compared to physiological tensile strain, suggesting strain conditioning-dependent activation of bone homeostasis pathways. Our findings highlight the role of strain distribution in spatially regulating upstream signaling pathways driving bone adaptation. This study advances our understanding of how non-physiological strain condition influences bone remodeling and provides a foundation for developing therapeutic strategies for osteoporosis.