SEMA3A and Osteopenia: During skeletal development, nerve-derived Sema3A regulates sensory nerve development and indirectly influences bone remodeling.20 However, in aged bone, estrogen can promote osteocytes to secrete Sema3A and maintain bone homeostasis.21 And an another study suggested that deficiency of osteoblast-derived Sema3A led to osteopenia in long bones and lumbar spine.22 The determination of the specific tissue source of Sema3A during strain adaptive bone formation necessitates further investigation.