Gentile Michael A, Soung Do Y, Horrell Carlyle, Samadfam Rana, Drissi Hicham, Duong Le T
Bone Biology Group, Merck Research Laboratories, West Point, PA, USA.
New England Musculoskeletal Institute, University of Connecticut Health Center, Farmington, CT, USA.
Bone. 2014 Sep;66:72-81. doi: 10.1016/j.bone.2014.04.032. Epub 2014 Jun 10.
Cathepsin K (CatK) is a cysteine protease, expressed predominantly in osteoclasts (OC) which degrades demineralized bone matrix. Novel selective inhibitors of CatK are currently being developed for the treatment of postmenopausal osteoporosis. Pharmacological inhibition of CatK reduces OC resorption activity while preserving bone formation in preclinical models. Disruption of the CatK gene in mice also results in high bone mass due to impaired bone resorption and elevated formation. Here, we assessed mid-shaft femoral fracture healing in 8-10week old CatK knock-out (KO) versus wild type (WT) mice. Fracture healing and callus formation were determined in vivo weekly via X-ray, and ex vivo at days 14, 18, 28 and 42 post-fracture by radiographic scoring, micro-computed tomography (μCT), histomorphometry and terminal mechanical four point bend strength testing. Radiological evaluation indicated accelerated bone healing and remodeling for CatK KO animals based on increased total radiographic scores that included callus opacity and bridging at days 28 and 42 post-fracture. Micro-CT based total callus volume was similar in CatK KO and WT mice at day 14. Callus size in CatK KO mice was 25% smaller than that in WT mice at day 18, statistically significant by day 28 and exhibited significantly higher mineralized tissue volume and volumetric BMD as compared to WT by day 18 onward. Osteoclast surface and osteoid surface trended higher in CatK KO calluses at all time-points and osteoblast number was also significantly increased at day 28. Increased CatK KO callus mineral density was reflected in significant increases in peak load and stiffness over WT at day 42 post-fracture. Regression analysis indicated a positive correlation (r=0.8671; p<0.001) between callus BMC and peak load indicating normal mineral properties in CatK KO calluses. Taken together, gene deletion of cathepsin K in mice accelerated callus size resolution, significantly increased callus mineralized mass, and improved mechanical strength as compared to wild type mice.
组织蛋白酶K（CatK）是一种半胱氨酸蛋白酶，主要在破骨细胞（OC）中表达，可降解脱矿质骨基质。目前正在开发新型CatK选择性抑制剂用于治疗绝经后骨质疏松症。在临床前模型中，CatK的药理学抑制可降低OC的吸收活性，同时保留骨形成。小鼠CatK基因的破坏也会由于骨吸收受损和骨形成增加而导致骨量增加。在此，我们评估了8至10周龄CatK基因敲除（KO）小鼠与野生型（WT）小鼠股骨干中段骨折的愈合情况。通过X射线每周在体内测定骨折愈合和骨痂形成，并在骨折后第14、18、28和42天通过放射学评分、微型计算机断层扫描（μCT）、组织形态计量学和终端机械四点弯曲强度测试在体外进行测定。放射学评估表明，基于骨折后第28天和第42天包括骨痂不透明度和骨痂桥接在内的总放射学评分增加，CatK KO动物的骨愈合和重塑加速。在第14天，基于μCT的CatK KO小鼠和WT小鼠的总骨痂体积相似。在第18天，CatK KO小鼠的骨痂大小比WT小鼠小25%，到第28天具有统计学意义，并且从第18天起，与WT相比，其矿化组织体积和体积骨密度显著更高。在所有时间点，CatK KO骨痂中的破骨细胞表面和类骨质表面均呈上升趋势，并且在第28天成骨细胞数量也显著增加。骨折后第42天，CatK KO骨痂矿物质密度的增加反映在峰值负荷和刚度比WT显著增加上。回归分析表明，骨痂骨矿含量与峰值负荷之间呈正相关（r=0.8671；p<0.001），表明CatK KO骨痂具有正常的矿物质特性。综上所述，与野生型小鼠相比，小鼠组织蛋白酶K基因缺失加速了骨痂大小的消退，显著增加了骨痂矿化质量，并提高了机械强度。
