Tokuda Haruhiko, Takai Shinji, Matsushima-Nishiwaki Rie, Akamatsu Shigeru, Hanai Yoshiteru, Hosoi Takayuki, Harada Atsushi, Ohta Toshiki, Kozawa Osamu
Department of Clinical Laboratory, National Hospital for Geriatric Medicine, National Center for Geriatrics and Gerontology, Obu, Aichi 474-8511, Japan.
J Cell Biochem. 2007 Apr 1;100(5):1146-53. doi: 10.1002/jcb.21104.
Catechin, one of the major flavonoids presented in plants such as tea, reportedly suppresses bone resorption. We previously reported that prostaglandin F(2alpha) (PGF(2alpha)) stimulates the synthesis of vascular endothelial growth factor (VEGF) via p44/p42 mitogen-activated protein (MAP) kinase in osteoblast-like MC3T3-E1 cells. To clarify the mechanism of catechin effect on osteoblasts, we investigated the effect of (--)-epigallocatechin gallate (EGCG), one of the major green tea flavonoids, on the VEGF synthesis by PGF(2alpha) in MC3T3-E1 cells. The PGF(2alpha)-induced VEGF synthesis was significantly enhanced by EGCG. The amplifying effect of EGCG was dose dependent between 10 and 100 microM. EGCG did not affect the PGF(2alpha)-induced phosphorylation of p44/p42 MAP kinase. SB203580, a specific inhibitor of p38 MAP kinase, and SP600125, a specific inhibitor of stress-activated protein kinase/c-Jun N-terminal kinase (SAPK/JNK), reduced the PGF(2alpha)-induced VEGF synthesis. EGCG markedly enhanced the phosphorylation of SAPK/JNK induced by PGF(2alpha) without affecting the PGF(2alpha)-induced phosphorylation of p38 MAP kinase. SP600125 markedly reduced the amplification by EGCG of the SAPK/JNK phosphorylation. In addition, the PGF(2alpha)-induced phosphorylation of c-Jun was amplified by EGCG. These results strongly suggest that EGCG upregulate PGF(2alpha)-stimulated VEGF synthesis resulting from amplifying activation of SAPK/JNK in osteoblasts.
儿茶素是茶等植物中主要的黄酮类化合物之一，据报道它能抑制骨吸收。我们之前报道过，前列腺素F(2α)（PGF(2α)）通过p44/p42丝裂原活化蛋白（MAP）激酶刺激成骨样MC3T3-E1细胞中血管内皮生长因子（VEGF）的合成。为了阐明儿茶素对成骨细胞作用的机制，我们研究了主要的绿茶黄酮类化合物之一（-）-表没食子儿茶素没食子酸酯（EGCG）对MC3T3-E1细胞中PGF(2α)诱导的VEGF合成的影响。EGCG显著增强了PGF(2α)诱导的VEGF合成。EGCG的放大作用在10至100微摩尔之间呈剂量依赖性。EGCG不影响PGF(2α)诱导的p44/p42 MAP激酶磷酸化。p38 MAP激酶的特异性抑制剂SB203580和应激激活蛋白激酶/c-Jun N端激酶（SAPK/JNK）的特异性抑制剂SP600125降低了PGF(2α)诱导的VEGF合成。EGCG显著增强了PGF(2α)诱导的SAPK/JNK磷酸化，而不影响PGF(2α)诱导的p38 MAP激酶磷酸化。SP600125显著降低了EGCG对SAPK/JNK磷酸化的放大作用。此外，EGCG放大了PGF(2α)诱导的c-Jun磷酸化。这些结果强烈表明，EGCG通过增强成骨细胞中SAPK/JNK的激活上调PGF(2α)刺激的VEGF合成。
