Deletion of Filamin A in Monocytes Protects Cortical and Trabecular Bone from Post-menopausal Changes in Bone Microarchitecture

The objective of the study was to determine the in vivo role of Filamin A (FLNA) in osteoclast generation and function, through the assessment of trabecular bone morphology, bone turnover, and the resulting changes in mechanical properties of the skeleton in mice with targeted deletion of FLNA in pre-osteoclasts. Using a conditional targeted knockdown of FLNA in osteoclasts, we assessed bone characteristics in vivo including micro-computed tomography (micro-ct), histomorphometric analyses, and bone mechanical properties. These parameters were assessed in female mice at 5 months of age, in an aging protocol (comparing 5-month-old and 11-month-old mice) and an osteoporosis protocol [ovariectomized (OVX) at 5 months of age and then sacrificed at 6 and 11 months of age]. In vivo bone densitometry, mechanical and histomorphometric analyses revealed a mild osteoporotic phenotype in the FLNA-null 5-month and aging groups. The WT and FLNA-KO bones did not appear to age differently. However, the volumetric bone mineral density decrease associated with OVX in WT is absent in FLNA-KO-OVX groups. The skeleton in the FLNA-KO-OVX group does not differ from the FLNA-KO group both in mechanical and structural properties as shown by mechanical testing of femora and vertebrae and histomorphometry of vertebrae. Additionally, FLNA-KO femora are tougher and more ductile than WT femora. The result of this study indicates that while FLNA-KO bones are weaker than WT bones, they do not age differently and are protected from estrogen-mediated post-menopausal osteoporosis.