Mechanical and material properties of cortical and trabecular bone from cannabinoid receptor-1-null (Cnr1-/-) mice

The endocannabinoid system is known for its regulatory effects on bone metabolism through the cannabinoid receptors, Cnr1 and Cnr2. In this study we analysed the mechanical and material properties of long bones from Cnr1-/- mice on a C57BL/6 background. Tibiae and femora from 5- and 12-week-old mice were subjected to threepoint bending to measure bending stiffness and yield strength. Elastic modulus, density and mineral content were measured in the diaphyses. Second moment of area (MOA2), inner and outer perimeters of the cortical shaft and trabecular fractional bone volume (BV/TV) were measured using micro-CT. In Cnr1-/- males and females at both ages the bending stiffness was reduced due to a smaller MOA2. Bone from Cnr1-/- females had a greater modulus than wild-type controls, although no differences were observed in males. BV/TV of 12-week-old Cnr1-/- females was greater than controls, although no difference was seen at 5-weeks. On the contrary, Cnr1-/- males had the same BV/TV as controls at 12-weeks while they had significantly lower values at 5-weeks. This study shows that deleting Cnr1 decreases the amount of cortical bone in both males and females at 12- weeks, but increases the amount of trabecular bone only in females.