Department of Molecular Medicine, Section of Biochemistry, University of Pavia, Via Taramelli 3/B, Pavia, Italy.
Stem Cells. 2012 Jul;30(7):1465-76. doi: 10.1002/stem.1107.
The molecular basis underlying the clinical phenotype in bone diseases is customarily associated with abnormal extracellular matrix structure and/or properties. More recently, cellular malfunction has been identified as a concomitant causative factor and increased attention has focused on stem cells differentiation. Classic osteogenesis imperfecta (OI) is a prototype for heritable bone dysplasias: it has dominant genetic transmission and is caused by mutations in the genes coding for collagen I, the most abundant protein in bone. Using the Brtl mouse, a well-characterized knockin model for moderately severe dominant OI, we demonstrated an impairment in the differentiation of bone marrow progenitor cells toward osteoblasts. In mutant mesenchymal stem cells (MSCs), the expression of early (Runx2 and Sp7) and late (Col1a1 and Ibsp) osteoblastic markers was significantly reduced with respect to wild type (WT). Conversely, mutant MSCs generated more colony-forming unit-adipocytes compared to WT, with more adipocytes per colony, and increased number and size of triglyceride drops per cell. Autophagy upregulation was also demonstrated in mutant adult MSCs differentiating toward osteogenic lineage as consequence of endoplasmic reticulum stress due to mutant collagen retention. Treatment of the Brtl mice with the proteasome inhibitor Bortezomib ameliorated both osteoblast differentiation in vitro and bone properties in vivo as demonstrated by colony-forming unit-osteoblasts assay and peripheral quantitative computed tomography analysis on long bones, respectively. This is the first report of impaired MSC differentiation to osteoblasts in OI, and it identifies a new potential target for the pharmacological treatment of the disorder.
骨骼疾病的临床表型的根本分子基础通常与细胞外基质结构和/或特性的异常有关。最近，细胞功能障碍已被确定为伴随的致病因素，并且越来越多的注意力集中在干细胞分化上。经典的成骨不全症（OI）是遗传性骨发育不良的原型：它具有显性遗传，是由编码 I 型胶原的基因突变引起的，I 型胶原是骨骼中最丰富的蛋白质。我们使用 Brtl 小鼠，一种特征明确的中度严重显性 OI 的基因敲入模型，证明了骨髓祖细胞向成骨细胞分化的功能障碍。在突变的间充质干细胞（MSCs）中，早期（Runx2 和 Sp7）和晚期（Col1a1 和 Ibsp）成骨细胞标志物的表达相对于野生型（WT）显著降低。相反，与 WT 相比，突变的 MSCs 产生了更多的集落形成单位脂肪细胞，每个集落的脂肪细胞更多，并且每个细胞的甘油三酯滴的数量和大小增加。自噬的上调也在突变的成年 MSC 中被证明，这是由于突变型胶原蛋白的保留导致内质网应激而向成骨谱系分化的结果。用蛋白酶体抑制剂硼替佐米治疗 Brtl 小鼠，分别通过集落形成单位-成骨细胞测定法和长骨的外周定量计算机断层扫描分析，改善了体外成骨细胞分化和体内骨特性。这是 OI 中 MSC 向成骨细胞分化受损的第一个报告，并确定了该疾病药物治疗的一个新的潜在靶点。
