Clinical, cellular and molecular phenotypes of aging bone.

Our understanding of gerontological bone loss and osteoporosis has grown substantially in the recent past. Clinical as well as basic and translational studies have been pivotal in providing us with the pathophysiology of this condition. They have also informed us of the various cellular and molecular mechanisms underlying age related bone loss. This chapter focuses on the current concepts and paradigms of age related bone loss in humans and how various animal and cellular models have broadened our understanding in this fascinating but complex area. Changes in hormonal, neuronal and biochemical cues with age and their effect on bone have been discussed. This chapter also outlines recent studies on the relationship between bone and fat in the marrow, and the fate of the marrow mesenchymal stromal cell population which can give rise to either bone forming osteoblasts or fat-forming adipocytic cells as a function of age.