RUNX2 and Osteopenia: However, Runx2 inhibits osteoblast maturation in vivo, so bone-specific Runx2 transgenic adult mice show osteopenia, with increased bone resorption and normal or suppressed bone formation.36,49 Moreover, Runx2 is a promoter of the Rankl/Opg expression ratio.37 These data support our working model that loss of Atoh8 in mice promotes Runx2 activity, leading to an increased Rankl/Opg ratio and osteoclast differentiation, with no increase in trabecular bone formation.