CLOCK and osteoporosis: Physiological glucocorticoids signaling in osteoblast progenitors is essential for maintaining the normal bone density, whereas endogenous glucocorticoid excess and high dose therapeutic glucocorticoids result in osteoporosis by suppressing osteoblast activity and bone formation [55, 60]. In vitro study demonstrated that a glucocorticoid rather than a β-agonist synchronized circadian expression of clock and osteoclast-related genes in osteoclasts [61].