The Sanofi-Genzyme R&D Center, Genzyme, A Sanofi Company, Framingham, MA 01701, USA.
J Bone Miner Res. 2012 Aug;27(8):1757-72. doi: 10.1002/jbmr.1630.
Chronic kidney disease-mineral bone disorder (CKD-MBD) is defined by abnormalities in mineral and hormone metabolism, bone histomorphometric changes, and/or the presence of soft-tissue calcification. Emerging evidence suggests that features of CKD-MBD may occur early in disease progression and are associated with changes in osteocyte function. To identify early changes in bone, we utilized the jck mouse, a genetic model of polycystic kidney disease that exhibits progressive renal disease. At 6 weeks of age, jck mice have normal renal function and no evidence of bone disease but exhibit continual decline in renal function and death by 20 weeks of age, when approximately 40% to 60% of them have vascular calcification. Temporal changes in serum parameters were identified in jck relative to wild-type mice from 6 through 18 weeks of age and were subsequently shown to largely mirror serum changes commonly associated with clinical CKD-MBD. Bone histomorphometry revealed progressive changes associated with increased osteoclast activity and elevated bone formation relative to wild-type mice. To capture the early molecular and cellular events in the progression of CKD-MBD we examined cell-specific pathways associated with bone remodeling at the protein and/or gene expression level. Importantly, a steady increase in the number of cells expressing phosphor-Ser33/37-β-catenin was observed both in mouse and human bones. Overall repression of Wnt/β-catenin signaling within osteocytes occurred in conjunction with increased expression of Wnt antagonists (SOST and sFRP4) and genes associated with osteoclast activity, including receptor activator of NF-κB ligand (RANKL). The resulting increase in the RANKL/osteoprotegerin (OPG) ratio correlated with increased osteoclast activity. In late-stage disease, an apparent repression of genes associated with osteoblast function was observed. These data confirm that jck mice develop progressive biochemical changes in CKD-MBD and suggest that repression of the Wnt/β-catenin pathway is involved in the pathogenesis of renal osteodystrophy.
慢性肾脏病-矿物质和骨异常（CKD-MBD）的定义是矿物质和激素代谢异常、骨组织形态计量学改变和/或软组织钙化。新出现的证据表明，CKD-MBD 的特征可能在疾病进展的早期发生，并与破骨细胞功能的变化有关。为了识别骨的早期变化，我们利用 jck 小鼠，一种多囊肾病的遗传模型，其表现为进行性肾病。在 6 周龄时，jck 小鼠的肾功能正常，没有骨病的证据，但在 20 周龄时肾功能持续下降，约 40%至 60%的小鼠发生血管钙化。在 jck 相对于野生型小鼠的 6 至 18 周龄之间，确定了血清参数的时间变化，随后显示这些变化在很大程度上反映了与临床 CKD-MBD 相关的血清变化。骨组织形态计量学显示，与野生型小鼠相比，jck 小鼠的破骨细胞活性增加和骨形成率升高。为了捕获 CKD-MBD 进展中的早期分子和细胞事件，我们在蛋白和/或基因表达水平上研究了与骨重塑相关的细胞特异性途径。重要的是，在人和鼠骨中均观察到表达磷酸化 Ser33/37-β-连环蛋白的细胞数量稳步增加。骨细胞中 Wnt/β-连环蛋白信号的总体抑制与 Wnt 拮抗剂（SOST 和 sFRP4）的表达增加以及与破骨细胞活性相关的基因（包括核因子-κB 受体激活剂配体（RANKL））的表达增加有关。RANKL/骨保护素（OPG）比值的增加与破骨细胞活性的增加相关。在疾病晚期，观察到与成骨细胞功能相关的基因明显受到抑制。这些数据证实 jck 小鼠在 CKD-MBD 中发生进行性生化变化，并表明 Wnt/β-连环蛋白途径的抑制参与了肾性骨营养不良的发病机制。
