Bone adapts to external loads to maintain healthy mass through a process known as mechanoadaptation. The specific mechanical stimuli triggering adaptation remain unclear, making it challenging to design therapy regimens to induce bone formation when and where needed. In aging individuals, the ability to adapt to mechanical loading diminishes, increasing fracture risk. Understanding mechanoadaptation is crucial, especially regarding the relationship between the mechanical three-dimensional environment and the bone's responses at the molecular, cellular, and tissue levels. This thesis aims to characterize bone mechanoadaptation through innovative tools that offer new perspectives on this phenomenon.

We first employed a poroelastic three-dimensional finite element model to predict the distribution and magnitude of mechanical stimuli in mouse bone and to design in vivo loading profiles. Our findings revealed that load-induced high fluid flow velocity can effectively promote bone adaptation even at low strain magnitudes, while loading profiles that generate high strain, but low fluid flow velocity, do not induce adaptation. This suggests a new strategy for stimulating bone adaptation. Next, we examined the effects of two weeks of tibia loading combined with a Piezo1 agonist, which chemically activates the mechanosensitive ion channels, on bone adaptation in aged mice. Our results show that this combination enhances cortical bone parameters in 22-month-old mice, offering a promising approach to promote bone formation in age-related bone loss. Finally, we introduced WISH-BONE, a novel method for labeling osteocyte mRNA and protein in threedimensional mouse bones, addressing spatial limitations of commonly used methods. We demonstrated WISH-BONE’s efficacy by investigating the three-dimensional spatial regulation of a mechanosensitive gene and its protein in whole mouse bones in response to mechanical loading, revealing region-specific regulation in the loaded legs compared to controls.

Together, these findings provide new insights into the mechanoadaptation process in adult mouse bones and strategies to restore it in aging mice. They also offer novel promising approaches and methods to explore how the three-dimensional environment influences bone cell activity and inform the design of new treatment strategies to maintain bone mass.