Collagen (I) homotrimer potentiates the osteogenesis imperfecta (oim) mutant allele and reduces survival in male mice
Collagen (I) homotrimer potentiates the osteogenesis imperfecta (oim) mutant allele and reduces survival in male mice
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DOI：
10.1101/2020.07.13.198283
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发表时间：
2020-07
影响因子：
4.3
通讯作者：
K. Lee;Lisa Rambault;George Bou-Gharios;P. Clegg;R. Akhtar;G. Czanner;R. J. van ‘t Hof;E. Canty-Laird
中科院分区：
文献类型：
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作者：
K. Lee;Lisa Rambault;George Bou-Gharios;P. Clegg;R. Akhtar;G. Czanner;R. J. van ‘t Hof;E. Canty-Laird
I型胶原蛋白是骨的主要结构成分，在所有脊椎动物中以（α1）2（α2）1异源三聚体形式存在。由于功能失调的α2链，仅包含同源三聚体（α1）3 I型胶原的成骨诱导（oim）小鼠模型具有脆性骨表型，这意味着生理骨功能需要异源三聚体形式。然而，具有阻止α2链合成的罕见无效等位基因的人具有结缔组织和心血管异常（心脏瓣膜Ehlers Danlos综合征），没有明显的骨脆性。相反，导致同源三聚体合成增加的普遍的人类单核苷酸多态性与骨质疏松症相关。虽然对oim系进行了充分研究，但尚未证明同源三聚体I型胶原蛋白在骨中是否与异源三聚体形式功能等同。在本研究中使用Col 1a 2 null和oim小鼠系，并通过microCT和3点弯曲分析骨骼。还从杂合子组织中提取RNA，并使用qRT-PCR进行等位基因区分分析。在这里，我们首次全面地表明，与oim纯合子小鼠不同，缺乏α2（I）链的小鼠没有受损的骨生物力学或结构特性。然而，孟德尔遗传在两个品系的雄性小鼠中均受到影响，α2链缺失的雄性小鼠表现出年龄相关的状况丧失。oim纯合子的脆骨表型可能是由oim突变等位基因的有害影响引起的，然而，已知oim杂合子的表型不太严重。我们使用等位基因辨别来显示oim突变等位基因在杂合子中没有下调。然后，我们通过产生复合杂合子来测试基因剂量是否对oim杂合子的不太严重的表型负责。数据显示，复合杂合子与oim杂合子相比，骨结构特性受损，尽管程度低于oim纯合子。因此，我们得出结论，在oim杂合子中存在异源三聚体胶原蛋白-1会影响oim突变等位基因的作用，但同源三聚体胶原蛋白-1和oim突变等位基因之间的遗传相互作用会导致骨脆性。
Type I collagen is the major structural component of bone where it exists as an (α1)2(α2)1 heterotrimer in all vertebrates. The osteogenesis imperfecta (oim) mouse model comprising solely homotrimeric (α1)3 type I collagen, due to a dysfunctional α2 chain, has a brittle bone phenotype implying that the heterotrimeric form is required for physiological bone function. However, humans with rare null alleles preventing synthesis of the α2 chain have connective tissue and cardiovascular abnormalities (cardiac valvular Ehlers Danlos Syndrome), without evident bone fragility. Conversely a prevalent human single nucleotide polymorphism leading to increased homotrimer synthesis is associated with osteoporosis. Whilst the oim line is well-studied, whether homotrimeric type I collagen is functionally equivalent to the heterotrimeric form in bone has not been demonstrated. Col1a2 null and oim mouse lines were used in this study and bones analysed by microCT and 3-point bending. RNA was also extracted from heterozygote tissues and allelic discrimination analyses performed using qRT-PCR. Here we comprehensively show for the first time that mice lacking the α2(I) chain do not have impaired bone biomechanical or structural properties, unlike oim homozygous mice. However Mendelian inheritance was affected in male mice of both lines and male mice null for the α2 chain exhibited age-related loss of condition. The brittle bone phenotype of oim homozygotes could result from detrimental effects of the oim mutant allele, however, the phenotype of oim heterozygotes is known to be less severe. We used allelic discrimination to show that the oim mutant allele is not downregulated in heterozygotes. We then tested whether gene dosage was responsible for the less severe phenotype of oim heterozygotes by generating compound heterozygotes. Data showed that compound heterozygotes had impaired bone structural properties as compared to oim heterozygotes, albeit to a lesser extent than oim homozygotes. Hence, we concluded that the presence of heterotrimeric collagen-1 in oim heterozygotes alleviates the effect of the oim mutant allele but a genetic interaction between homotrimeric collagen-1 and the oim mutant allele leads to bone fragility.