| The relationship among estrogen, cytokines, and the metabolism of bone tissue is close but complex. Estrogen can not only produce biological effect through binding the estrogen receptors both on osteoblasts and osteoclasts, but also affect the role of the osteoblasts, osteoclasts, and fibroblasts on the production of cytokines, such as activating the OPG/RANK/RANKL system, improving the secretion of TGF-β and IGF-1, reducing the expression of IL-1, IL-6, and TNF-α. All the cytokines are closely correlated, forming a complicated network. Together with the extracellular matrix, the cytokines provide a particular bone microenvironment in the development of the bone. The cytokines can promote the differentiation and maturity of bone cells, and regulate the bone metabolism. Because of the loss of estrogen in postmenopausal period, the expression of these cytokines has also changed, which plays an important role in the bone metabolism and the pathogenesis of metabolic bone disease. |