Parker E A, Hegde A, Buckley M, Barnes K M, Baron J, Nilsson O
Developmental Endocrinology Branch, National Institutes of Health, National Institute of Child Health and Human Development, Building 10/CRC, Rm 1-3330, MSC 1103, 10 Center drive, Bethesda, Maryland 20892, USA.
J Endocrinol. 2007 Jul;194(1):31-40. doi: 10.1677/JOE-07-0012.
Previous studies of the GH-IGF system gene expression in growth plate using immunohistochemistry and in situ hybridization have yielded conflicting results. We therefore studied the spatial and temporal patterns of mRNA expression of the GH-IGF system in the rat proximal tibial growth plate quantitatively. Growth plates were microdissected into individual zones. RNA was extracted, reverse transcribed and analyzed by real-time PCR. In 1-week-old animals, IGF-I mRNA expression was minimal in growth plate compared with perichondrium, metaphyseal bone, muscle, and liver (70-, 130-, 215-, and 400-fold less). In contrast, IGF-II mRNA was expressed at higher levels than in bone and liver (65- and 2-fold). IGF-II expression was higher in the proliferative and resting zones compared with the hypertrophic zone (P < 0.001). GH receptor and type 1 and 2 IGF receptors were expressed throughout the growth plate. Expression of IGF-binding proteins (IGFBPs)-1 through -6 mRNA was low throughout the growth plate compared with perichondrium and bone. With increasing age (3-, 6-, 9-, and 12-week castrated rats), IGF-I mRNA levels increased in the proliferative zone (PZ) but remained at least tenfold lower than levels in perichondrium and bone. IGF-II mRNA decreased dramatically in PZ (780-fold; P < 0.001) whereas, type 2 IGF receptor and IGFBP-1, IGFBP-2, IGFBP-3, and IGFBP-4 increased significantly with age in growth plate and/or surrounding perichondrium and bone. These data suggest that IGF-I protein in the growth plate is not produced primarily by the chondrocytes themselves. Instead, it derives from surrounding perichondrium and bone. In addition, the decrease in growth velocity that occurs with age may be caused, in part, by decreasing expression of IGF-II and increasing expression of type 2 IGF receptor and multiple IGFBPs.
以往利用免疫组织化学和原位杂交技术对生长板中生长激素-胰岛素样生长因子（GH-IGF）系统基因表达的研究结果相互矛盾。因此，我们定量研究了大鼠胫骨近端生长板中GH-IGF系统mRNA表达的时空模式。将生长板显微切割成各个区域。提取RNA，进行逆转录并通过实时PCR分析。在1周龄的动物中，与骨膜、干骺端骨、肌肉和肝脏相比，生长板中IGF-I mRNA表达极低（分别低70倍、130倍、215倍和400倍）。相比之下，IGF-II mRNA的表达水平高于骨骼和肝脏（分别高65倍和2倍）。与肥大区相比，增殖区和静止区的IGF-II表达更高（P < 0.001）。生长激素受体以及1型和2型胰岛素样生长因子受体在整个生长板中均有表达。与骨膜和骨骼相比，整个生长板中胰岛素样生长因子结合蛋白（IGFBPs）-1至-6 mRNA的表达较低。随着年龄增长（3周、6周、9周和12周去势大鼠），增殖区（PZ）的IGF-I mRNA水平升高（P < 0.001），但仍比骨膜和骨骼中的水平低至少10倍。增殖区的IGF-II mRNA显著下降（780倍；P < 0.001），而2型胰岛素样生长因子受体以及IGFBP-1、IGFBP-2、IGFBP-3和IGFBP-4在生长板和/或周围骨膜及骨骼中随年龄显著增加。这些数据表明，生长板中的IGF-I蛋白并非主要由软骨细胞自身产生。相反，它来源于周围的骨膜和骨骼。此外，随着年龄增长出现的生长速度下降可能部分是由于IGF-II表达降低以及2型胰岛素样生长因子受体和多种IGFBPs表达增加所致。
