Chapter 12 - The Role of Sex Steroids in the Effects of Immune System on Bone

Abstract

Among the hormones influencing bone modeling and remodeling, sex steroids play a crucial role. In addition to their principal role of directing sexual differentiation and reproduction, they also regulate the bone growth spurts of puberty, and they maintain bone mass throughout life. The biological importance of sex steroid hormones on bone remodeling is well demonstrated by the fact that gonadal failure and sex steroid deficiencies are major pathogenic factors in the development of bone loss. Estrogen deficiency in postmenopausal women, and androgen loss as part of the aging process in elderly men, or after therapy for prostate cancer, leads to a decline in bone mass, and markedly increases the risk of osteoporosis. Sex steroids act to regulate bone turnover, at least in part, via bone cells, through high-affinity estrogen or androgen receptors. However, it is now apparent that much of these effects, particularly those related to changes in bone resorption, are mediated by alterations in the secretion of cytokines and other mediators that are produced by bone cells, and cells of the immune system.