Androgens and Bone: Basic Aspects

The specific mechanisms by which androgens affect skeletal homeostasis, and whether these effects are directly mediated in bone, are areas of intensified research. As a classic steroid hormone, the biological cellular signaling responses to androgen are mediated through the androgen receptor (AR), a ligand-inducible transcription factor. ARs have been identified in a variety of cells found in bone and the characterization of AR expression in these cells thus clearly identifies bone as a target tissue for androgen action. The direct effects of androgen that influence the complex processes of proliferation, differentiation, mineralization and gene expression in the osteoblast are being characterized, but much remains to be established. Androgen effects on bone may also be indirectly modulated and/or mediated by other autocrine and paracrine factors in the bone microenvironment. This chapter reviews recent progress on the characterization of androgen action in bone.