Han V K, Smith A, Myint W, Nygard K, Bradshaw S
Medical Research Council Group in Fetal and Neonatal Health, University of Western Ontario, London, Canada.
Endocrinology. 1992 Sep;131(3):1134-42. doi: 10.1210/endo.131.3.1380434.
Newborn rat astroglia cells possess epidermal growth factor (EGF) and insulin-like growth factor (IGF) receptors, which suggests that these growth factors regulate their growth and development. To determine the relative roles and interactions between the two growth factors on astroglial growth, primary cultures of astroglial cells from newborn rats (1 day postnatal) were treated with pure peptides, singly or in combination in various concentrations, and the growth response was determined by DNA synthesis ([3H]thymidine incorporation). EGF, IGF-I, and IGF-II, as single peptides, stimulated DNA synthesis, with half-maximal stimulatory concentrations of 0.25 ng/ml for EGF, 2.0 ng/ml for IGF-I, and 25 ng/ml for IGF-II, respectively. These findings indicate that astroglial cells are responsive to these growth factors in physiological concentrations, with the relative sensitivity of EGF greater than IGF greater than IGF-II. When EGF and IGF-I were added in combination, the growth stimulatory effect was greater than the additive effects of each growth factor added alone, indicating that the two growth factors act in synergism with each other. In particular, addition of increasing concentrations of EGF from 0.25-10 ng/ml to a constant concentration of 50 ng/ml IGF-I resulted in significant potentiation of [3H]thymidine incorporation of astroglial cells. To determine if the synergistic effect was due to a local synthesis of IGF-I by astroglia, a specific monoclonal antibody against IGF-I (Sm 1.2) was added to the peptides. Sm 1.2 decreased not only IGF-I-stimulated DNA synthesis, but also EGF-stimulated DNA synthesis, suggesting that the effects of EGF were contributed to in part by the local synthesis of IGF-I by astroglial cells. Analysis of conditioned medium from cells treated with EGF revealed a significant increase (approximately 2-fold) in IGF-I (from 4.5 to 8.8 ng/ml), but not IGF-II. To determine if the EGF effect on IGF synthesis was at the level of IGF-I mRNA transcription, stable IGF-I mRNA levels were determined in the astroglial cells before and after stimulation with EGF, using Northern analysis and quantification by densitometry. Astroglia expressed four IGF-I mRNA transcripts as in the adult and fetal liver, but only one (3.6 kilobases) IGF-II mRNA.(ABSTRACT TRUNCATED AT 400 WORDS)
新生大鼠星形胶质细胞具有表皮生长因子（EGF）和胰岛素样生长因子（IGF）受体，这表明这些生长因子调节其生长和发育。为了确定这两种生长因子在星形胶质细胞生长上的相对作用及相互作用，用不同浓度的纯肽单独或联合处理新生大鼠（出生后1天）的星形胶质细胞原代培养物，并通过DNA合成（[3H]胸苷掺入）来测定生长反应。作为单一肽，EGF、IGF-I和IGF-II均刺激DNA合成，其半最大刺激浓度分别为：EGF为0.25 ng/ml，IGF-I为2.0 ng/ml，IGF-II为25 ng/ml。这些发现表明星形胶质细胞对这些生理浓度的生长因子有反应，其相对敏感性为EGF大于IGF大于IGF-II。当联合添加EGF和IGF-I时，生长刺激作用大于单独添加每种生长因子的累加效应，表明这两种生长因子相互协同作用。特别是，将EGF浓度从0.25 - 10 ng/ml增加到恒定的50 ng/ml IGF-I时，星形胶质细胞的[3H]胸苷掺入显著增强。为了确定协同效应是否是由于星形胶质细胞局部合成IGF-I所致，将一种针对IGF-I的特异性单克隆抗体（Sm 1.2）添加到肽中。Sm 1.2不仅降低了IGF-I刺激的DNA合成，也降低了EGF刺激的DNA合成，这表明EGF的作用部分是由星形胶质细胞局部合成IGF-I所致。对用EGF处理的细胞的条件培养基进行分析发现，IGF-I显著增加（约2倍）（从4.5 ng/ml增至8.8 ng/ml），但IGF-II没有增加。为了确定EGF对IGF合成的影响是否在IGF-I mRNA转录水平，在用EGF刺激前后，使用Northern分析和光密度定量法测定星形胶质细胞中稳定的IGF-I mRNA水平。星形胶质细胞表达四种与成年和胎儿肝脏中相同的IGF-I mRNA转录本，但仅表达一种（3.6千碱基）IGF-II mRNA。（摘要截短于400字）
