Effects Of Cathepsin K On Bone Formation And Resorption In Metaphysis Of Long Bone In Young Mice

Background:Skeletal system consists of bone matrix and cellular components. Type Ⅰ collagen is the most important organic content in bone matrix. Osteoblast and osteoclast mediate the bone formation and resorption, respectively. Their coordination plays a major role in bone modeling and remodeling. Cathepsin K (CatK) locates in osteoclast and can catalyze type Ⅰ collagen very efficiently. Osteoporosis is among the most common skeletal diseases, and happens in postmenopausal women mostly. Most of the medicines available for adult osteoporosis have relatively good therapeutic effects. However, children osteoporosis is a really big problem that has been overlooked. Actually, osteoporosis is a disorder that is involved in almost all the pediatric subspecialties. What’s more, children osteoporosis can lead to a low peak bone mass and increase the chance of osteoporosis and bone fracture when people get older. Unfortunately, no medicine for adult osteoporosis has been approved for children, except for supplements like calcium and vitamin D. So the development of a medicine for children osteoporosis is quite urgent. Odanacatib, a CatK inhibitor, a new drug for osteoporosis in postmenopausal women has passed the phase Ⅱ clinical trial, and shows positive effects in the improvement of bone mineral density, a much less affected bone formation and less adverse effects compared with other anti-resorptive medicines. These features make CatK inhibitor a possible candidate for children osteoporosis. There is no clinical trial researching the effects of CatK inhibitor in children now. In this thesis, I compared the CatK wild type (WT) mice, CatK knockout (KO) mice and CatK WT mice treated with CatK inhibitor to reveal the effects of CatK on long bone metaphysis in young mice and provided evidences for whether CatK inhibitor can be used it in children osteoporosis.Methods:In this research, I used2,4and8week-old mice, stained the long bone with H&E staining, TRAP staining and osterix immunohistochemical staining to compare the cancellous bone area, number of osteoclast and number of preosteoblasts qualitatively and quantitatively in metaphysis of long bone in CatK WT and KO mice. Using micro-CT to analysis the secondary spongiosa of long bone in8week-old CatK WT, CatK KO mice. I also used the CatK WT mice treated with CatK inhibitor, L-006235, from4to8week-old, and analysis the cancellous bone with micro-CT to confirm the effect of CatK. Results:the effects of CatK on cancellous bone area, osteoclast number and preosteoblasts number change with age and location of cancellous bone. In secondary spongiosa of all ages and primary spongiosa of8week-old mice, CatK deficiency can increase cancellous bone area, number of osteoclast and preosteoblasts. In primary spongiosa of2and4week-old mice, CatK deficiency can decrease the number of osteoclast, but maintain the preosteoblasts and bone area the same as the level in CatK WT mice.Conclusion:in spongy bone where bone modeling is dominant, the primary spongiosa of2to4week-old mice in this experiment, CatK deficiency doesn’t significantly affect the bone formation and spongy bone area, though it causes the decreasing of osteoclast number. However, in spongy bone where bone remodeling is dominant, the primary spongiosa of8week-old and secondary spongiosa, CatK deficiency can increase osteoclast and preosteoblasts simultaneously and spongy bone area as well, which indicates that CatK deficiency increases bone mineral density while maintains the normal coupling of bone formation and resorption. These features of CatK make CatK inhibitor possible to increase bone mineral density while maintain the normal bone modeling in children with osteoporosis.