Biglycan knockout mice: New models for musculoskeletal diseases
Biglycan knockout mice: New models for musculoskeletal diseases
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DOI：
10.1023/a:1025336114352
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发表时间：
2002-05-01
影响因子：
3
通讯作者：
Chen, XD
中科院分区：
文献类型：
--
作者：
Young, MF;Bi, YM;Chen, XD
Biglycan是一类富含亮氨酸的小蛋白多糖（Small Leucine Rich Proteoglycans， SLRP），定位于人类Xq28-ter染色体上。与decorin（另一类SLRP）相比，其内含子-外显子结构和蛋白质编码序列的保守性表明，这两个基因可能是由基因复制产生的。Biglycan在其NH2末端附近含有两条硫酸软骨素糖胺聚糖（GAG）链，这使得它与decorin不同，decorin只有一条GAG链。为了确定biglycan在体内的功能，我们培育了缺乏该蛋白产生的转基因小鼠（敲除）。随着年龄的增长，这些小鼠的骨量逐渐减少。双四环素-钙黄蛋白标记显示，巨多糖缺乏小鼠的骨形成能力有缺陷。基于这一观察结果，我们验证了骨质疏松样表型是由于对骨形成过程至关重要的细胞缺陷造成的假设。我们的数据显示，巨多糖缺乏的小鼠产生骨髓基质细胞（骨细胞前体）的能力减弱，而且这种缺乏随着年龄的增长而增加。与正常幼崽相比，这些细胞对转化生长因子- β (tgf - β)的反应降低，胶原合成减少，细胞凋亡相对较多。此外，通过茜素红染色判断，从biglycan缺陷小鼠分离的颅骨细胞中，骨涎蛋白和骨钙素等晚期分化标志物的表达减少，钙积累能力下降。我们认为，这些成骨细胞中的任何一种缺陷，单独或联合，都可能导致在biglycan基因敲除小鼠中观察到的骨质疏松症。其他数据表明，biglycan与骨形态发生蛋白2/4 （BMP 2/4）在控制骨细胞分化中的作用之间存在功能关系。为了验证slrp之间可能发生功能代偿的假设，我们创造了缺乏biglycan和decorin的小鼠。Decorin缺失小鼠骨量正常，而双biglycan/ Decorin敲除小鼠比单biglycan小鼠骨质减少更严重，这表明骨组织中SLRP功能冗余。为了进一步确定不同类型的SLRP之间是否会发生代偿，我们制造了缺乏biglycan（1类）和纤维调节蛋白（一种在矿化组织中高度表达的11类SLRP）的小鼠。这些双缺陷小鼠步态受损，肌腱异位钙化和过早骨关节炎。透射电镜分析显示，像decorin和biglycan基因敲除一样，它们严重扰乱了胶原纤维结构。受影响的肌腱的生物力学分析显示，与对照动物相比，它们更弱，从而得出结论，关节的不稳定可能是在纤维调素/biglycan敲除小鼠中观察到的所有骨骼缺陷的主要原因。这些研究为肌肉骨骼疾病提供了重要的新动物模型，并提供了表征通过SLRP活性控制组织完整性和功能的信号网络的机会。
Biglycan is a Class I Small Leucine Rich Proteoglycans (SLRP) that is localized on human chromosome Xq28-ter. The conserved nature of its intron-exon structure and protein coding sequence compared to decorin (another Class I SLRP) indicates the two genes may have arisen from gene duplication. Biglycan contains two chondroitin sulfate glycosaminoglycan (GAG) chains attached near its NH2 terminus making it different from decorin that has only one GAG chain. To determine the functions of biglycan in vivo, transgenic mice were developed that were deficient in the production of the protein (knockout). These mice acquire diminished bone mass progressively with age. Double tetracycline-calcein labeling revealed that the biglycan deficient mice are defective in their capacity to form bone. Based on this observation, we tested the hypothesis that the osteoporosis-like phenotype is due to defects in cells critical to the process of bone formation. Our data shows that biglycan deficient mice have diminished capacity to produce marrow stromal cells, the bone cell precursors, and that this deficiency increases with age. The cells also have reduced response to tranforming growth factor-beta (TGF-beta), reduced collagen synthesis and relatively more apoptosis than cells from normal littermates. In addition, calvaria cells isolated from biglycan deficient mice have reduced expression of late differentiation markers such as bone sialoprotein and osteocalcin and diminished ability to accumulate calcium judged by alizerin red staining. We propose that any one of these defects in osteogenic cells alone, or in combination, could contribute to the osteoporosis observed in the biglycan knockout mice. Other data suggests there is a functional relationship between biglycan and bone morphogenic protein-2/4 (BMP 2/4) action in controlling skeletal cell differentiation. In order to test the hypothesis that functional compensation can occur between SLRPs, we created mice deficient in biglycan and decorin. Decorin deficient mice have normal bone mass while the double biglycan/decorin knockout mice have more severe osteopenia than the single biglycan indicating redundancy in SLRP function in bone tissue. To further determine whether compensation could occur between different classes of SLRPs, mice were generated that are deficient in both biglycan (class 1) and fibromodulin, a class 11 SLRP highly expressed in mineralizing tissue. These doubly deficient mice had an impaired gait, ectopic calcification of tendons and premature osteoarthritis. Transmission electron microscopy analysis showed that like the decorin and biglycan knockouts, they have severely disturbed collagen fibril structures. Biomechanical analysis of the affected tendons showed they were weaker compared to control animals leading to the conclusion that instability of the joints could be the primary cause of all the skeletal defects observed in the fibromodulin/biglycan knockout mice. These studies present important new animal models for musculoskeletal diseases and provide the opportunity to characterize the network of signals that control tissue integrity and function through SLRP activity.