ACP5 and osteoporosis: The potential therapeutic effects of elevated OPN activity on osteoporosis mainly reflected on increasing body weight gain and BMD, with the assistance effect of up-regulated level of ALP, OCN, BMP-2 and reduced tartrate-resistant acid phosphatase (TRAP) activity as well as C-terminal telopeptide of type I collagen (CTX-I) level (81, 85, 91).