Milne M, Quail J M, Rosen C J, Baran D T
Department of Orthopedics and Physical Rehabilitation, University of Massachusetts Medical School, Worcester, Massachusetts 01655, USA.
J Cell Biochem. 2001 Mar 26;81(2):229-40. doi: 10.1002/1097-4644(20010501)81:2<229::aid-jcb1038>3.0.co;2-c.
Insulin-like growth factor (IGF)-I is an important regulator of bone metabolism. Clinical observations suggest that different anatomic sites within the adult skeleton respond differently to hormonal and therapeutic treatment, and recent studies on bone marrow stromal cells in culture show that there are skeletal site-dependent differences in the gene expression of IGF-I. The actions of IGF-I and -II on bone cells are known to be modulated by the IGF binding proteins (IGFBP)-1 through -6 and the Type I and Type II IGF receptors. Therefore, we compared the expression of IGFBP-1 through -6 in adult female rat bone marrow stromal cell cultures derived from two separate skeletal sites: vertebrae and femurs. The cultures were maintained simultaneously under conditions that support osteoblast differentiation from osteoprogenitors present in the femoral and vertebral marrow cell populations. We also addressed whether IGFBP messenger RNA levels are regulated by thyroid hormone (T(3)) and dexamethasone (dex) treatment in femoral vs. vertebral marrow stromal cells in vitro, since steroid hormones play an important role in skeletal function. Northern blot analyses revealed that there are distinct skeletal site differences in the gene expression of IGFBPs. The vertebral marrow cultures express IGFBP-2 through -6 mRNAs, with IGFBP-2, IGFBP-4, and IGFBP-6 mRNAs predominating. The femoral marrow stromal cell cultures express only IGFBP-4 and IGFBP-6. Importantly, vertebral marrow cultures have much higher IGFBP mRNA steady-state levels than femoral cultures for all the detected IGFBP transcripts. IGFBP-1 is not detected in either femoral or vertebral cultures. In addition to a skeletal site difference, we show that T(3) and dex regulate the expression of specific IGFBP mRNAs. T(3) treatment also upregulates IGF-I protein secretion by vertebral marrow stromal cell cultures. Interestingly, the type I receptor for IGF-I was expressed equivalently in cultures from the two skeletal sites. These findings have important implications for the anatomical site specificities of hormonal responses that are noted in the skeleton.
胰岛素样生长因子（IGF）-I是骨代谢的重要调节因子。临床观察表明，成年骨骼内不同解剖部位对激素和治疗的反应不同，最近对培养的骨髓基质细胞的研究表明，IGF-I的基因表达存在骨骼部位依赖性差异。已知IGF-I和-II对骨细胞的作用受IGF结合蛋白（IGFBP）-1至-6以及I型和II型IGF受体的调节。因此，我们比较了来自两个不同骨骼部位（椎骨和股骨）的成年雌性大鼠骨髓基质细胞培养物中IGFBP-1至-6的表达。这些培养物在支持成骨细胞从股骨和椎骨髓细胞群体中的骨祖细胞分化的条件下同时维持。我们还探讨了在体外，甲状腺激素（T(3)）和地塞米松（dex）处理是否会调节股骨与椎骨髓基质细胞中IGFBP信使RNA水平，因为类固醇激素在骨骼功能中起重要作用。Northern印迹分析显示，IGFBPs的基因表达存在明显的骨骼部位差异。椎骨髓培养物表达IGFBP-2至-6的mRNA，其中以IGFBP-2、IGFBP-4和IGFBP-6的mRNA为主。股骨骨髓基质细胞培养物仅表达IGFBP-4和IGFBP-6。重要的是，对于所有检测到的IGFBP转录本，椎骨髓培养物的IGFBP mRNA稳态水平远高于股骨培养物。在股骨或椎骨培养物中均未检测到IGFBP-1。除了骨骼部位差异外，我们还表明T(3)和dex调节特定IGFBP mRNA的表达。T(3)处理还上调了椎骨髓基质细胞培养物中IGF-I蛋白的分泌。有趣的是，IGF-I的I型受体在来自两个骨骼部位的培养物中表达水平相当。这些发现对骨骼中激素反应的解剖部位特异性具有重要意义。
