SMAD2 and osteoporosis: In this study, we identified a novel circRNA known as circZfp644-205 and investigated its effect on osteogenic differentiation and apoptosis in osteoporosis.<h4>Methods</h4>CircZfp644-205, miR-445-3p, and SMAD2 levels were measured using quantitative real-time polymerase chain reaction (qRT-PCR).