HDAC1 and osteoporosis: Specifically, mechanical loading directly induced a downregulation of HDAC1 expression, which was involved in the promotion of osteogenic differentiation and bone formation through the targeting of JAG1, a master inducer of osteogenic differentiation.21, 22, 23 Our findings also demonstrate that the therapeutic inhibition of HDAC1 may partly rescue osteoporosis caused by mechanical unloading.