1] Department of Pathology, Tokyo Women's Medical University, Tokyo, Japan [2] Department of Orthopedics, Tokyo Women's Medical University, Tokyo, Japan.
Lab Invest. 2013 Nov;93(11):1170-83. doi: 10.1038/labinvest.2013.105. Epub 2013 Aug 26.
Renal osteodystrophy (ROD) is a major problem in patients with renal insufficiency. The present study was designed to elucidate the role of bone collagen changes and osteoblast differentiation in a rat model of ROD pathogenesis induced by adenine. Typical characteristics of renal failure, including increased serum urea nitrogen, creatinine, inorganic phosphorus, and intact parathyroid hormone levels, and decreased serum calcium and 1,25(OH)2D3 levels, were observed in adenine-induced rats. Micro-computed tomography analysis of the femur in adenine-induced rats showed decreased bone mineral density and osteoporotic changes, confirmed by the three-point bending test. The cancellous bone histomorphometric parameters of the tibia showed increased osteoblast number, decreased osteoclast surface with peritrabecular fibrosis, and increased osteoid tissue, indicating a severe mineralization disorder similar to clinical ROD. Scanning and transmission electron microscopy revealed irregular alignment and increased diameter of bone collagen fibrils in adenine-induced rats. Protein expression analysis showed greater accumulation of advanced glycation end products (AGEs) in peritrabecular osteoblasts of adenine-induced rats than in the controls. In contrast, suppressed expression of runt-related transcription factor 2, alkaline phosphatase, secreted phosphoprotein 1 (Spp1), and lysyl oxidase (Lox) mRNA levels, particularly the amount of active LOX protein, were observed. In in-vitro experiments, mineralizing MC3T3-E1 osteoblastic cells stimulated with AGE-modified bovine serum albumin had attenuated the expression of Spp1 mRNA levels and active LOX protein, with a decrease in extracellular nodules of mineralization. These observations provide clues to ROD pathogenesis, as they indicate that the suppression of osteoblast differentiation and decreased active LOX protein associated with accumulation of AGEs in osteoblasts caused structural abnormalities of bone collagen fibrils and a severe mineralization disorder, leading to bone fragility.
肾性骨营养不良（ROD）是肾功能不全患者的一个主要问题。本研究旨在阐明骨胶原变化和成骨细胞分化在腺嘌呤诱导的 ROD 发病机制大鼠模型中的作用。腺嘌呤诱导的大鼠表现出典型的肾功能衰竭特征，包括血清尿素氮、肌酐、无机磷和完整甲状旁腺激素水平升高，血清钙和 1,25（OH）2D3 水平降低。腺嘌呤诱导大鼠股骨的微计算机断层扫描分析显示骨密度降低和骨质疏松变化，三点弯曲试验证实了这一点。胫骨松质骨组织形态计量学参数显示成骨细胞数量增加，骨表面破骨细胞减少，骨样组织增加，表明存在严重的矿化障碍，类似于临床 ROD。扫描和透射电子显微镜显示腺嘌呤诱导的大鼠骨胶原纤维排列不规则，直径增加。蛋白表达分析显示，与对照组相比，腺嘌呤诱导大鼠骨小梁周围成骨细胞中晚期糖基化终产物（AGEs）的积累更多。相比之下，下调了 runt 相关转录因子 2、碱性磷酸酶、分泌型磷蛋白 1（Spp1）和赖氨酰氧化酶（Lox）mRNA 水平的表达，尤其是活性 LOX 蛋白的量。在体外实验中，用 AGE 修饰的牛血清白蛋白刺激矿化 MC3T3-E1 成骨细胞后，Spp1 mRNA 水平和活性 LOX 蛋白的表达减弱，细胞外矿化结节减少。这些观察结果为 ROD 的发病机制提供了线索，表明成骨细胞中 AGEs 的积累抑制了成骨细胞的分化和活性 LOX 蛋白的表达，导致骨胶原纤维结构异常和严重的矿化障碍，从而导致骨脆弱。
