Reduced cortical bone strength and altered osteocyte canaliculi despite preserved bone mass in male Becn 1^+/- mice

Bone strength depends on tissue quality as well as bone mass and geometry. Osteocytes help maintain bone material quality by remodeling the matrix surrounding their lacunae and canaliculi. How reduced expression of Beclin-1, a protein implicated in skeletal homeostasis, affects this microenvironment and bone mechanics remains unclear. We characterized cortical bone mechanics and the osteocyte lacunar-canalicular environment in 14-week-old male mice with heterozygous Beclin-1 deficiency (Becn1^+/-) and age-matched wild-type controls. Bone architecture was assessed by microcomputed tomography; whole-bone properties by three-point bending; cortical tissue hardness by microindentation; and osteocyte canalicular and pericellular features by silver staining, transmission electron microscopy, elemental analysis, acridine orange imaging, and molecular assays. No statistically significant differences were observed in trabecular bone mass and microarchitecture, cortical geometry, or cortical tissue mineral density across genotypes. In contrast, whole-bone mechanical properties, apparent bending modulus, ultimate bending stress, and cortical Vickers hardness were lower in Becn1^+/- mice. Osteocyte canaliculi were shorter and wider, and pericanalicular thickness was greater. The calcium-to‑phosphorus atomic ratio was lower at the lacunar wall but did not differ significantly in the interstitial cortical matrix. Osteocyte lacunae showed a higher acidic-to-neutral fluorescence ratio, accompanied by increased cortical bone expression of Atp6v0b, Ctsk, and Acp5, whereas Mmp13 expression did not differ significantly. Together, these findings show impaired bone mechanical properties despite largely preserved bone mass and geometry in young adult male Becn1^+/- mice. The accompanying canalicular and perilacunar changes suggest that the osteocyte microenvironment may contribute to reduced bone quality in this model.