Androgens and bone.
OBJECTIVE
The present review will focus on the most important recent findings with respect to skeletal androgen action. Many studies have indicated that part of the androgen action may be related to the conversion of androgens into estrogens. Therefore, some of the most recent findings of skeletal estrogen action relevant for male skeletal physiology will also be discussed.


RESULTS
Androgens and estrogens stimulate bone formation and inhibit bone resorption. Sex steroids may interact with different receptors, target cells and other bone anabolic pathways. Androgen receptor and estrogen receptor signalling appear to be important for male bone formation during growth. Sex steroid signalling may involve genomic and nongenomic pathways, interaction with mechanical loading, the growth hormone/insulin-like growth factor-I axis and/or other bone anabolic pathways. Estrogen receptor alpha in osteoclasts appears to regulate bone resorption in women but not men, whereas androgen receptor signalling in osteoblasts may only partly regulate bone resorption in males.


CONCLUSIONS
The latest developments indicate that androgens and estrogens are important for male bone metabolism and homeostasis and therefore selective estrogen receptor alpha and androgen receptor signalling remain interesting drug targets for the stimulation of bone formation and male skeletal integrity.
Vanderschueren
Dirk
D
Bone Research Unit, Laboratory for Experimental Medicine and Endocrinology, Department of Experimental Medicine, Katholieke Universiteit Leuven, Leuven, Belgium. dirk.vanderschueren@uz.kuleuven.ac.be
Gaytant
Jemima
J
Boonen
Steven
S
Venken
Katrien
K
D000728:Androgens / Q000235:genetics / Q000378:metabolism*; D016723:Bone Remodeling; D001842:Bone and Bones / Q000502:physiology*; D047628:Estrogen Receptor alpha / Q000235:genetics / Q000378:metabolism*; D004967:Estrogens / Q000378:metabolism; D005260:Female; D006801:Humans; D008297:Male; D010012:Osteogenesis; D011944:Receptors, Androgen / Q000235:genetics / Q000378:metabolism*; D012737:Sex Factors; D015398:Signal Transduction
D000728:Androgens; D047628:Estrogen Receptor alpha; D004967:Estrogens; D011944:Receptors, Androgen