Chapter 11 - From Gonads to Bone, and Back

Abstract

The sex steroid hormones are essential for skeletal development and the maintenance of bone health throughout adult life. The biological importance of this regulation is best exemplified by the fact that estrogen and androgen deficiencies are major pathogenic factors in the development of osteoporosis in postmenopausal women and elderly men. Bone physiology is traditionally studied with the view that the skeleton is only a recipient for the hormonal input. However, it is clear nowadays that in most of the hormonal regulation there are crosstalks between the different organs. Based on this notion, the skeleton has recently emerged as an endocrine organ of major importance. This is particularly relevant to the interplay between bone and gonads. It was shown that bone, via the osteoblast-derived hormone osteocalcin, promotes testosterone biosynthesis. In addition, several observations also suggest that defects in production of osteocalcin or in its receptor signaling may have ramifications not only for male fertility, but also for susceptibility to prostate cancer. This chapter will review the mutual dependence between gonads and bone, mechanisms of action of osteocalcin, and the implication of this novel regulation in humans.